Exosomes and microRNAs as mediators of the exercise

Abstract

MicroRNAs (miRNAs), also known as microribonucleic acids, are small molecules found in specific tissues that are essential for maintaining proper control of genes and cellular processes. Environmental factors, such as physical exercise, can modulate miRNA expression and induce targeted changes in gene transcription. This article presents an overview of the present knowledge on the principal miRNAs influenced by physical activity in different tissues and bodily fluids. Numerous research projects have emphasized the significant impact of miRNAs on controlling biological changes brought about by physical activity. These molecules play main roles in important processes such as the growth of skeletal muscle and heart muscle cells, the creation of mitochondria, the development of the vascular system, and the regulation of metabolism. Studies have shown that physical exertion utilizes the contributions of miR-1, miR-133, miR-206, miR-208, and miR-486 to revitalize and restore skeletal muscle tissue. Moreover, detecting alterations in miRNA levels and connecting them to the specific outcomes of various exercise routines and intensities can act as indicators for physical adaptation and the reaction to physical activity in long-term diseases. Numerous studies have confirmed that extracellular vesicles (EVs) which composed of different members such as exosomes have the ability to reduce inflammation through the activation of the nuclear factor kappa B (NF-κB pathway. Furthermore, physical activity greatly affects the levels of specific miRNAs present in exosomes derived from skeletal muscle. Therefore, exosomal miRNAs target some pathways that are related to growth and development, such asWnt/β-catenin, PI3K/AKT, and insulin-like growth factor 1 (IGF1). Exercise-induced exosomes have also been identified as important mediators in promoting beneficial effects throughout the body. The aim of this review is to summarize the effect of exercise on the function of miRNAs and exosomes.

Introduction

Physical activities are characterized as any physical movement that involves using the muscles in our body and results in the use of energy throughout the day. It can be grouped into various categories, such as sports, work-related, domestic, fitness, or other types of activities [1]. Physical exercise is a structured and planned form of physical activity that is regularly carried out with the purpose of enhancing or preserving physical well-being and overall wellness [2]. Regular physical activity and exercise are vital for keeping our metabolism in check and increasing our daily calorie expenditure. In other words, exercise is not only important for our overall well-being, but also plays a fundamental role in preserving our cellular makeup.

Engaging in physical activity on a regular basis has a positive impact on protecting against long-term metabolic conditions [3]. Scientists have established that physical activity has overall impacts on the body; notwithstanding, there remain undisclosed particulars about altered molecular processes and the advantages it provides for overall wellness [4]. The enhancement of knowledge in biological processes will result in targeted and imitative interventions being created. miRNAs play a vital role as facilitators of the actions related to physical activity [5]. Many miRNAs have been identified as controllers of signaling pathways related to the adaptation of exercise, and researchers have investigated their biological roles using methods that eliminate individual miRNAs [5, 6]. Physical activity involves exerting physical energy and can enhance one's well-being and physical condition, potentially mitigating the negative effects of age-related diseases [6, 7].

Exosomes are small circular structures, ranging from 30 to 150 nm, made up of a mixture of proteins, lipids, mRNA, miRNA, and DNA. Produced by different cells, they are carried through the bloodstream to reach distant organs [8,9,10]. As a result, it is immensely important in enabling the transfer of substances and communication of data among various body parts [11, 12]. Due to the lipid bilayer that forms a protective shield around exosomes, the biologically active substances they contain are not easily broken down, making them highly influential in various bodily functions [13,14,15]. Over recent times, the impact of exosomes on the muscle structure has been exposed. In other words, the study conducted by Miao and colleagues found evidence that exosomes released by cancer cells could contribute to the deterioration of muscle in individuals with colon cancer cachexia [16]. Engaging in physical exercise causes a multitude of alterations in the body, which collaborate to enhance one's general health and serve as a safeguard against numerous chronic diseases brought about by poor lifestyle habits. Recent studies suggest that miRNAs transfer through circulating exosomes may contribute to the positive outcomes of physical activity. However, the exact mechanisms responsible for these changes induced by physical activity are not yet fully understood. Identifying the specific miRNAs in the bloodstream affected by exercise could lead to a better understanding of how the body adapts to physical activity. Intensive resistance training causes an increase in hormone levels in tissues, which plays a crucial role in muscle adaptation compared to prolonged exercise. Studying the impact of acute exercise on circulating miRNAs will provide valuable insight into identifying unique markers of exercise physiology and immediate adaptation to physical activity [17]. The aim of this review is to summarize the effect of exercise on the function of miRNAs and exosomes.

Methodology

We decided to utilize a narrative review instead of a systematic review in order to encompass diverse study designs and research inquiries, tackle developing areas without sufficient evidence for a systematic review, and link concepts across various domains. We examine the topic of physical activity and thoroughly cover all the changes in miRNAs and exosomes caused by it, bringing attention to areas of knowledge that still require further exploration. In order to gather pertinent materials pertaining to the subject, electronic databases were utilized to conduct a search. A comprehensive search was performed on several databases including PubMed, MEDLINE, ScienceDirect, Scopus, and Google Scholar, using filters such as publication date. To expand the scope of the search, older publications were also considered as long as they were deemed relevant. To avoid potential bias in narrative reviews, a comprehensive search was carried out to ensure the inclusion of both research studies and reviews. An in-depth examination of relevant index terms and content in the retrieved papers was employed to conduct this search. The search criteria consisted of keywords like microRNA, exosome, exercise, physical activity, and extracellular vesicle.

MicroRNA and exercise

MiRNAs are a type of small RNA molecules that have the ability to inhibit mRNA messages after they have been transcribed. They achieve this through their interaction with a cellular structure known as RNA-induced silencing complex [18]. MiRNAs play a crucial role in controlling cellular functions related to the production, elimination, or repair of harm caused by reactive oxygen species [19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36]. Additionally, they play a significant role in maintaining the balance of redox levels in the cell. Regular physical activity leads to an increase in the growth and functioning of mitochondria in skeletal muscle, which helps the muscle adapt to exercise over time (Fig. 1) [18]. MiRNAs play a main and effective role in controlling the expression of genes in diverse cellular activities, including growth, development, replication, and metabolic processes [37,38,39,40,41,42,43,44,45,46,47,48]. As of now, there have been more than 2200 genes discovered that contain instructions for producing miRNAs in the genomes of mammals [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63]. Multiple myomiRs are a group of miRNAs that can be found in large amounts in both the heart and skeletal muscle. These include miR-1, miR-133a, miR-133b, miR-206, miR-208, miR-208b, miR-486, and miR-499, as shown in Fig. 2 [64,65,66,67].

Fig. 1

Crosstalk between miRNAs and exercise

Fig. 2

The role of miRNAs in the mechanism of restoring and renewing skeletal muscle tissue. miRNAs including miR-27, miR-133,miR-1, miR-378, miR-181, miR206, miR-140 and miR-486 have critical roles in various parts of skeletal muscle. Pax3 paired box gene 3, Msc mesenchymal stem cell, SRFs serum response factors, Myo D myogenic differentiation, FOXO Forkhead box O, PTEN phosphatase and tensin homolog

The study demonstrated that engaging in rigorous resistance training causes a decrease in miR-1 concentrations in skeletal muscles, ultimately leading to an improved IGF1/AKT signaling pathway and a boost in protein production. Resistance training has a significant impact on muscle growth, as it triggers the IGF-1/AKT pathway and inhibits miR-1. This is crucial because the IGF and aromatase pathways play a vital role in the development of cancer through physical activity. The activation of IGFs promotes glucose uptake in peripheral tissues, which is necessary for cellular growth. However, with time, this process can become a potent catalyst for cancer. The connection between miR-1 and the IGF1 pathway is widely acknowledged, as this miRNA works to suppress the expression of IGF-1 mRNA in both heart and skeletal muscles. Moreover, there is a negative correlation between miR-1 levels and IGF proteins [68].

Research has confirmed the significant impact that physical activity has on skeletal muscles, as it has been shown to alter the expression of miRNAs within these muscles [69]. A group of males, ranging from youths to adults, took part in a 12-week program focused on resistance exercise. The individuals' changes in lean body mass were used to divide them into two groups: "low-responders" and "high-responders" [70]. The objective of this research was to compare the levels of highly expressed miRNAs between the two groups and determine any differences. In the vastus lateralis muscle, the levels of 21 miRNAs were analyzed and it was concluded that the high-responder group did not exhibit any changes in miRNA quantities. Conversely, subjects with a low response had a significant decrease in the levels of miR-451 and miR-378, as well as a continuous decrease in miR-26a and miR-29a in the same muscle group. The researchers discovered that an elevation in miR-378 levels was closely associated with a rise in lean body mass, indicating the importance of maintaining proper levels of miR-378 to attain a greater lean body mass [70, 71]. Based on experimental evidence, it is thought that miR-378 influences driving the maturation of myoblast cells by specifically targeting Myogenic Repressor (MyoR), a protein that restrains the function of myogenic differentiation 1 (MyoD), a critical controller in the process of muscle formation. Furthermore, research has demonstrated that miR-378 can manage the operation and generation of energy in mitochondria through its regulation of peroxisome proliferator-activated receptor gamma coactivator 1 beta (PGC1-β) expression. This increase in miR-378 levels appears to be a typical response to engaging in endurance exercise [70, 72]. According to research by Ceccarelli and colleagues, the most effective method of increasing levels of miR-23a-3p (90%), miR-23b-3p (39%), miR-133b (80%), miR-181-5p (50%), and miR-378-5p (41%) after exercise is through a combination of weightlifting and cycling, which combines both anaerobic and aerobic components. This increase was observed four hours after the exercise session. A recent review also highlights the impact of exercise-specific miRNAs on controlling gene expression [73]. Numerous studies have demonstrated that miRNA targets play a wide range of roles, including: (1) regulating main pathways connected to calcium and AMP kinase; (2) controlling class IIa histone deacetylase activity; (3) influencing various transcription factors involved in muscle function, such as MyoD and MyoG; (4) targeting mitochondrial factors including mtTFA and FoxJ-3/MEF-2; (5) modulating mitogen-activated protein kinases (MAPKs); (6) affecting the genes Run 1, Sox9, and Pax3; and (7) managing the expression of growth factors VEGF and IGF-1 [73]. Overall, these discoveries demonstrate that miRNAs play a significant role in regulating muscle metabolism through participation in physical exercise [73, 74].

Exercise, miRNA, and immune system

Physical activity has been proven to improve the body's ability to fight off disease. Many experts agree that physical activity has a significant impact on both the inborn and acquired defenses of the body, resulting in a lower risk of infections, the inhibition of cancer development, and a greater ability to fight against the growth of tumors [75,76,77,78,79]. Taking part in physical activity can greatly impact the immune response of the body, and this can be influenced by numerous aspects such as the kind of exercise, the length of time it is done, and the level of intensity. Additionally, an individual's level of training and nutrition, as well as environmental variables like temperature and altitude, can also play a role in the extent of this impact. Research has demonstrated that a brief timeframe of physical activity can result in noteworthy changes in genetic pathways and inflammation markers in diverse immune cells. Moreover, studies have placed importance on the function of miRNAs in controlling the body's immune reaction to physical activity [80,81,82,83]. Adom-Aizik and colleagues [81] looked at how a single instance of physical exercise (ten 2-min bouts of cycling at 76% of maximum oxygen intake) affected the transcription of mRNA and miRNA in neutrophils in the bloodstream. Neutrophils, comprising a substantial portion (40–75%) of the overall white blood cells in mammals, have a critical function in the innate immune system. The research uncovered that physical activity has the dual effect of elevating neutrophil count in the bloodstream and inducing significant alterations in gene activity [84]. The findings of the pathway analysis indicated a strong association between the genetic factor and various significant mechanisms related to inflammation, namely the ubiquitin-mediated proteolysis pathway, the JAK/STAT signaling pathway, and the Hedgehog signaling pathway [81].

miRNAs, endurance exercise, and cardiovascular system

Swimming training programs produce distinct effects on blood flow, both in the short and long term, in contrast to running regimens [85]. In addition, rats who swim regularly have been observed to experience significant growth in their heart muscles and an increase in the size of their left ventricle at the end of their relaxation phase [86]. It has been definitively established by Ma and his team that participating in swimming as a means of exercise leads to a notable increase and strength in the heart, known as physiological cardiac hypertrophy [87]. The rise is linked to a limited number of miRNAs (rno-miR-21, rno-miR-124, rno-miR-144, and rno-miR-145) that regulate the PI3K/AKT/mTOR signaling pathway (Pik3a, Pten, and Tsc2). These particular miRNAs have been confirmed as targets within this pathway. The findings demonstrate that both swimming and running have an effect on the levels of cardiac miRNAs that specifically target elements of the renin–angiotensin–aldosterone system, which is closely tied to the development of left ventricular hypertrophy. Participation in swimming resulted in a rise in the levels of rno-miR-27a and rno-miR-27b, two specific miRNAs that target the angiotensin-converting enzyme (Ace) gene. This activity also caused a decrease in rno-miR-143, which regulates the expression of Ace type 2 (Ace2) in the heart [88]. Da Silva Jr and his team demonstrated that participating in swimming as exercise therapy resulted in a significant increase in rno-miR-126 levels, which is a recognized substance that specifically acts on Spred-1 and aids in the development of new blood vessels [89]. After a duration of 10 weeks, the levels of rno-miR-126 experienced a significant decrease in rats following endurance training. Despite the fact that rno-miR-126 has been known to target Pi3kr2, there was no change in the expression of this gene in rats after a swimming exercise. However, with prolonged physical activity, it was noticed that the levels of miR-1 and miR-133 increased in the vastus lateralis muscle, but this effect was only evident prior to starting a 12-week endurance training program [90]. Additionally, there was a decline in the amounts of miR-1, miR-133a, miR-133b, and miR-206 during the first phase of the 12-week training period. However, within 2 weeks after completing the training program, these levels returned to their original state. The study by Keller et al. demonstrated that engaging in a 6-week cycling regimen resulted in a significant decrease in the levels of miR-1 and miR-133 upon finishing the training [91].

Russell and his team carried out a research project involving untrained individuals, where they were subjected to a 10-day training program of either moderate or high-velocity endurance cycling. However, their findings contradict the results of Nielsen et al.'s study as they saw a significant rise in miR-1 and miR-29b levels, along with a decrease in miR-31 levels after the training period [90, 92]. Following a round of comprehensive physical activity prior to the training session, experts observed a significant increase in the levels of various miRNAs (miR-1, miR-133a, miR-133b, and miR-181a), while levels of others (miR-9, miR-23a, miR-23b, and miR-31) decreased. Furthermore, they uncovered an inverse relationship between the levels of miR-31 and those of HDAC4 and NFR1, both of which are known to suppress the expression of muscle function-related genes and may be influenced by miR-31 [92].

miRNAs and resistance exercise

Resistance exercise is an activity that requires the body to exert a significant amount of effort, causing the muscles to undergo various transformations, with the most prominent being an increase in muscle size. Through their research, McCarthy and Esser, along with Drummond et al., were among the first to discover evidence supporting the involvement of miRNAs in the adaptation of muscles during this process [64, 93]. Research has shown that subjecting mice to functional overload and humans to resistance exercise leads to a decrease in miR-1 and miR-133 levels. This leads to an increase in IGF/AKT signaling, resulting in improved protein production. One study by Davidsen and his colleagues aimed to examine the relationship between miRNA levels and an individual's response to 12 weeks of resistance training [71]. After completing the prescribed training, the participants were categorized into two cohorts based on the changes observed in their lean body mass. These groups were referred to as "low-responders" and "high-responders". The high-responders did not show any significant variations in their miRNA expression levels in the vastus lateralis muscle. On the other hand, the low-responders exhibited notable modifications, with a decrease in miR-378 and an increase in miR-451. The authors of the study concluded that this decrease in miR-378 production is directly linked to a reduction in lean body mass. They proposed that this decline may be the cause of impaired muscle growth. This notion is further supported by the findings of a laboratory study conducted by Gagan and colleagues, which demonstrated that miR-378 actively hinders the MyoR, thereby promoting the differentiation of muscle cells, as pointed out by Kirby and McCarthy [70, 94, 95]. Studies have shown that elevating the levels of miR-378 triggers a rise in the MyoD protein's ability to transcribe, promoting the development of muscle tissue, while simultaneously reducing the inhibitory impact of MyoR. This mechanism helps facilitate the proliferation of muscle cells and the integration of satellite cells into existing muscle fibers, potentially resulting in muscular growth in human beings [90].

Physical activity can alter the effects on cardiac tissue and this process can be influenced by miRNAs and their target genes, particularly cardiac hypertrophy (listed in Table 1 and depicted in Fig. 3A). Multiple studies have recognized that in rats undergoing a variety of physical training protocols, including treadmill, swimming, and voluntary exercise, certain miRNAs (such as miR-17-3p, miR-124, miR-21, miR-144, miR-145, miR-133, miR-199a, miR-26-5p, miR-204-5p, miR-497-3p, miR-208a, and miR-208b) are present in the heart [87, 96]. Overexpression of miRNAs (miR-21 and miR-144) causes a decrease in phosphatase and tensin homolog (PTEN) levels, indirectly controlling PI3K/AKT/mTOR signaling [87, 97]. Several other miRNAs have an indirect effect on PTEN expression. Specifically, miR-17-3p directly adjusts TIMP3 levels, leading to enhanced cardiomyocyte growth, while also indirectly influencing PTEN and causing an increase in cardiomyocyte size [98].

Table 1 Effect of aerobic exercise on miRNA expression and its function in target location

Fig. 3

A Heart tissue—a summary of how miRNAs function and stimulate pathways in response to physical activity, and their effects on cardiac muscle cells. B Muscular tissue—the role of miRNAs in causing various modifications in skeletal muscle cells. C Bone—how miRNAs contribute to changes in bone tissue

Recent studies have demonstrated that performing aerobic exercise with a group of runners training for a half-marathon resulted in an elevation of miRNA-21-5P, which stimulated the production of osteoblasts through the stimulation of RUNX2 using the Smad7-Smad1/5/8 signaling pathways. Additionally, the presence of miR-129-5P increased RUNX2 levels by targeting the transcriptional repressor STAT1. Furthermore, miR-378-5P initiated the activation of the PI3K/Akt pathway by targeting CASP3, leading to the promotion of osteogenesis. Meanwhile, the levels of miRNA-188-5P were lowered, leading to the deactivation of PPARγ and preventing the progression of adipogenesis [99,100,101] (Table 1 and Fig. 3C).

Boehler et al. showed that one way physical activity triggers an anti-inflammatory response is through the action of miRNAs [102]. Following a period of 12 weeks of physical activity among people with myositis, a rise in miR-196b levels coincided with a decrease in IKBKB mRNA. This proposed that miRNA-196b functions as an upstream regulator of NF-κB by controlling IKBKB (Fig. 3B). The trained group showed a significant increase in miR-196b levels, leading to an enhanced production of IκB. As a result, the activation of the NF-κB cascade was prevented. Aerobic exercise serves as an anti-inflammatory agent by facilitating the decrease of the NF-κB cascade. As a result, engaging in aerobic exercise leads to a rise in miR-196b levels and has the ability to control inflammation in muscles through the reduction of the NF-κB pathway [103].

Researchers have demonstrated that miRNAs play a significant role in a multitude of crucial biological processes during physical activity. As we continue to gain a better understanding of how miRNAs regulate various bodily functions, our comprehension of exercise adaptation and regeneration is poised to significantly advance in the future. This creates opportunities for innovative methods to track and enhance athletic performance, resilience and recovery. Due to their involvement in numerous pathological states, miRNAs have the potential to serve as important indicators in the diagnosis and prediction of a variety of illnesses. Moreover, this potential positions them as valuable new options for treating individuals with various illnesses. However, the examination of miRNAs is still a relatively new area and further research is necessary to confirm many of the findings.

MicroRNAs as biomarkers for exercise

Currently, there is proof that miRNAs can be detected in bodily liquids such as serum, plasma, urine, saliva, and cerebrospinal fluid [122]. Small molecules called circulating miRNAs are known for their remarkable stability, high detectability, and potential ability to control gene expression in specific cells and tissues. This unique characteristic makes them a revolutionary method of communication between cells 123(123). At present, a significant amount of research has demonstrated that miRNAs found in the bloodstream could potentially be used as reliable markers for specific illnesses and the effectiveness of medicinal therapies [124,125,126,127]. Numerous scientific studies have thoroughly examined the effects of physical activity on the levels of circulating miRNAs in both individuals with and without medical conditions. This suggests that these tiny molecules may play a significant role in the body's reaction to exercise. The composition of miRNAs present in the blood appears to differ depending on the type, duration, and intensity of physical exertion [128,129,130,131,132]. Currently, our understanding of the changes in circulating miRNAs during the process of adapting to cardiopulmonary exercise testing (CPET) and the impact of acute exercise training (AET) is limited. However, by participating in physical activities aimed at improving both endurance and strength, there can be a notable shift in the overall miRNA profiles [133]. An increase in physical activity has been linked to changes in the levels of circulating ci-miRNAs [134]. Numerous research has shown that engaging in resistance training can greatly affect the cellular expression of a variety of miRNAs. Changes in the levels of miRNAs can be immediately observed after a single session of resistance training and can persist for up to 24 h, with miR-206 and miR-181a showing changes at 1 h, miR-133a at 4 h, and miR-133b at 24 h after the training [135,136,137]. Participating in a single session of prolonged physical activities resulted in a significant increase in the levels of miR-1 and miR-133a expression [138]. Following a 3-h session of endurance training, the levels of miR-1, miR-133a, miR-133b, and miR-181a were observed to increase, while the levels of miR-9, miR-23a, miR-23b, and miR-31 decreased [133]. In addition, following the completion of a marathon, there was a notable rise in the quantities of miR-1, -30a, and -133a observed in the bloodstream of both highly skilled and less experienced runners [139]. Furthermore, the levels of ci-miRNAs largely reverted to their initial point after 24 h, except for a slight rise in ci-miR-133a noted among non-elite athletes [139]. After an extended duration, participating in a 12-week program of endurance training leads to diminished amounts of diverse miRNAs specifically tied to muscle cells [138]. It is of utmost importance to emphasize that there are miRNAs that are distinctively present in particular tissues [140]. Different cells not only exhibit different amounts of miRNA production but the specific kind and degree of training can lead to unique miRNA patterns [137]. In previous studies, the main emphasis has been on examining the impact of strength training on miRNA patterns, while there is limited data available about their reaction to endurance training. There have been multiple scientific investigations that have clearly established a notable link between the levels of miRNAs and the indicators of physical exercise. Furthermore, these studies have uncovered a strong connection between three specific miRNAs (miR-29a, miR-1, and miR-486) and the maximum capacity for oxygen consumption, known as VO2max. Due to this evidence, further studies are necessary in order to gain a comprehensive understanding of the relationship between miRNA patterns and endurance training [141, 142]. Additionally, there are notable connections between different factors related to bodily movement, such as the highest level of physical fitness, the level of serum creatine kinase (which indicates muscle injury), fluctuations in high-sensitivity C-reactive protein (a marker of acute inflammation), and the existence of miR-221 and miR-146a [130]. Furthermore, it seems that numerous miRNAs can adjust according to a particular type of training. As an example, the way these particular miRNAs function in the pathways of important tissues can have a potential effect on physical abilities such as heart and muscle strength, endothelial function, and the use of oxygen. An outstanding example of miR-206's importance in myogenesis can be seen through its predominant expression in skeletal muscle myoblasts and during embryonic development, along with its involvement in the differentiation of muscle cells [143]. Moreover, skeletal muscle-specific miRNAs, specifically miR-1 and miR-133a/b, have the ability to impact a variety of physiological functions such as growth, size, degradation, and enlargement [144]. The process of myogenesis results in a notable rise in the concentrations of previously identified miRNAs, and a larger skeletal muscle can be linked to decreased levels of miR-1 and miR-133a/b [145]. Previous studies have indicated that the lack of miR-1 and miR-133a can promote muscle growth by alleviating their inhibitory effects on growth factors during the transcription of genes [146]. The development and recovery of myogenesis and skeletal muscle heavily rely on the genetic makeup of myoblasts, which are the progenitors of muscle cells. Similarly, miR-21 has a specific presence in vascular endothelial cells and contributes to the process of altering vascular structure [147, 148]. The role of training and its specific forms, including endurance and strength training, in moderating the specific effects of miRNA is a subject of discussion. A study conducted by Wardle et al. included a control group of individuals who did not receive any prior training [149]. To establish the precise discrepancies in c-miRNA levels between elite male athletes who prioritize endurance training and those who focus on strength training, a scientific investigation was initiated. The findings indicate that individuals with exceptional abilities in endurance-oriented activities have significantly elevated levels of miR-21, miR-221, miR-222, and miR-146a in their blood plasma in comparison to those who excel in strength-related tasks. Following a combination of brief and extended aerobic workouts, researchers examined the fluctuations in c-miRNA levels in the bloodstream of subjects with chronic kidney illness. According to the research, patients with chronic kidney disease experienced an increase in levels of miR-125b after a single cycling session, while both healthy individuals and patients saw a rise in miR-150. Furthermore, there was a noticeable decline in miR-146a levels among kidney disease patients following acute exercise, while no such change was observed in healthy individuals. After 12 weeks of doing aerobic exercises at home, patients with chronic kidney disease had decreased levels of miR-210 after their workout, in contrast to healthy individuals who did not encounter a similar alteration [150].

Several miRNAs have been discovered to have control over different signaling pathways, including the IGF1/PI3K/AKT/mTOR pathway, which is important in adapting to exercise. Depending on the type of training and the individual's physical characteristics such as VO2 max, the levels of miRNAs can differ. These muscle-specific miRNAs are thought to influence the connection between skeletal muscle and the heart during physical activity, promoting adaptation. The altering levels of miRNAs may also be linked to molecular communication patterns activated during exercise, aiding in recovery and adaptation to training. Both short-term exercise and regular training have been found to impact the amounts of specific miRNAs in both healthy and unhealthy individuals (Table 2). However, the accuracy of these findings has been limited due to inconsistencies in methods, experimental designs, and participant characteristics. Multiple studies indicate that miRNAs have a significant impact on various processes, including cell differentiation, proliferation, and apoptosis. Moreover, they also play a crucial role in regulating extracellular matrix composition and ensuring homeostasis. Many research studies have demonstrated alterations in the distribution patterns of circulating miRNAs (c-miRNAs) in connection with different illnesses and disorders, and also in samples collected during states of physical well-being like pregnancy or exercise.

Table 2 Effect of exercise/training on circulating miRNA concentration

Exosome and exercise

Exosomes, a type of extracellular vesicle (EV), exhibit a range of features, including size, origin, composition, and density. By utilizing ultracentrifugation, it is feasible to differentiate EVs into three separate sizes: big, medium, and small [162]. Moreover, EVs are differentiated into two types, "ectosomes" or "exosomes", based on their mechanism of creation, which involves either the merging of multivesicular bodies with the cell membrane or the protrusion of micro-vesicles from the cell membrane [162,163,164]. Exosomes and the process of their formation serve as a means of maintaining protein quality, as their release leads to a restructuring of the surrounding extracellular matrix and facilitates cellular communication [165, 166]. New studies examining exosomes have concentrated on how they can effectively transmit intricate messages by binding and forming clusters with particular receptors on the surface of cells [167, 168].

Exosomes are substances that are created by both intact and unhealthy cells and can be found in various bodily fluids. These particles originate from the endosomal region and are formed through a two-part process [169,170,171]. In the beginning, the formation of early endosomes (depicted in Fig. 4) occurs due to the internal absorption of the cell membrane. Following this, the emergence of multiple intraluminal vesicles (ILVs) takes place through a mechanism known as inward invagination of endosomal membranes. Ultimately, this results in the development of multivesicular bodies (MVBs) [172]. The production and release of exosomes require the use of a tool that can bring opposing membranes together and then sever the link between them, ultimately releasing intraluminal vesicles into the external environment [173]. Proteins called soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) may assist in joining together MVBs and the outer layer of a cell, known as the cellular membrane [174].

Fig. 4

A diagram illustrating the formation and release of exosomes reveals that they originate as ILVs and are filled with cargoes such as nucleic acids, proteins, and lipids. ALIX Apoptosis-Linked Gene 2-Interacting Protein X, ESCRT endosomal sorting complex required for transport, RAB27 Ras-related protein Rab-27, MVB multivesicular body, SNARE soluble NSF attachment protein receptor, ILV intraluminal vesicle

The pioneering discovery made by Guescini et al. was a major breakthrough, as it was the first demonstration of skeletal muscle cells producing extracellular vesicles, including exosomes [175]. In addition to proteins, myokines, and cytokines, physical activity can also activate other substances such as miRNAs (see Fig. 5). Research suggests that engaging in physical activity can lead to an increase in the production of various miRNAs found in exosomes, such as miR-1 during short cycling routines or miR-1, miR-133a and b, miR-206, miR-208a, and miR-499 after longer periods of exercise [176,177,178]. Like other research, it also showed that various types of exercise lead to the rise of exosomes containing miRNAs in the bloodstream [179, 180].

Fig. 5

A representation showing the emanation of exercise-triggered exosomes from actively moving skeletal muscle. These exosomes contains various substance such as DNA, lipids, proteins, and miRNAs

Despite being relatively new, there have been a handful of carefully conducted research studies delving into the impact of acute physical activity on a specific type of "exosome-like EVs” through meticulous observation of their particles and gene expression. The available research on the subject suggests that acute exercise has a clear impact on the body, as indicated by a notable rise in EVs in the body during and directly after working out (as shown in Table 3). In another study [181], even though it is a relatively recent field of study, a few carefully planned experiments have delved into examining the effects of immediate physical activity on particular 'exosome-like EVs’ through extensive examination of their particles and expression patterns. The small yet reliable collection of in vivo research strongly suggests that acute physical activity does indeed have an impact, as there is a clear increase in systemic EVs during and after exercise (as displayed in Table 3). In a subsequent research project led by the same group, they investigated the reaction of EVs to gradual cycling physical activity. This investigation utilized more sophisticated methods for collecting blood and purifying EVs and focused on male athletes trained in aerobic exercise (with an average maximum oxygen consumption of approximately 50 mm per kg of body weight per minute). After abstaining from food overnight and having no recent exercise for 24 h, the participants completed a cycling test that gradually increased in intensity, starting at 40 watts and increasing by 40 watts every 3 min. They were unable to continue until exhaustion. During a period of inactivity, venous blood was collected and placed into tubes containing tripotassium EDTA. The collection process was repeated at a respiratory quotient of 0.9, while the subject was engaged in physical activity, and immediately following the conclusion of the exercise. The platelet-free plasma (PFP) was acquired through the application of conventional techniques during the processing stage. EVs were extracted from the platelet-free plasma (PFP) through size exclusion chromatography (SEC) and immunobead pull-down methods, utilizing isolation kits specific for CD9 + , CD63 + , and CD81 + markers. These EVs were then subjected to analysis using nanoparticle tracking analysis (NTA) and immunoblotting to study their response to exercise. According to their prior investigation into samples taken from patients with UC, the examination of SEC-EVs using the immunoblotting technique indicated an increase in recognizable exosomal indicators during and immediately following physical activity, such as CD9, CD63, and CD81. It should be highlighted that there has been an observed rise in the identification of EVs in the body during submaximal physical activity (with an RQ of 0.9), which is consistent with previous research done on EVs derived from UC and demonstrated a rapid surge immediately after exercise. Despite this, it was noticed that NTA methods were insufficient in revealing the increase in SEC-EVs induced by physical activity. As a result, the authors concluded that semi-quantitative approaches are better suited for this purpose since they are less susceptible to disruption from external influences [182]. In a study [181] a wealth of proof has been presented which shows that the exercise-generated EVs have a diverse range of constituents, primarily consisting of lymphocytes (specifically CD4 + and CD8 +), monocytes (specifically CD14 +), endothelial cells (specifically CD105 + and CD146 +), and platelets (specifically CD41 + , CD41 + and CD62 +). Unexpectedly, the involvement of skeletal muscle, specifically α-sarcoglycan + EVs (SCGA +), was minimal in this process. This implies that even when physical activity is at a lower level (before the rise of systemic lactate levels and spike of catecholamines), it can still stimulate the secretion of EVs, but as the exercise persists or becomes more intense, the secretion of EVs can become even more powerful. EVs may rapidly appear due to exercise cues in the beginning, such as shear stress, mechanical signaling, muscle contraction, or calcium-mediated events. Later on, signals like hormones (like cortisol), metabolic stress, and reactive oxygen species may heighten the EV response [183,184,185]. It is essential to emphasize that the discharge of EVs is heavily influenced by the existence of Ca2 + ions, and when the synaptotagmin-7 gene (a protein responsible for detecting Ca2 +) is suppressed, the production of EVs is diminished as well [183, 186]. After an action potential travels through the motor neuron, the sarcoplasmic reticulum releases Ca2 + into the surrounding area. This Ca2 + then binds to Troponin C, allowing for the movement of crossbridges. In skeletal muscle, intense contractions during physical activity can lead to a significant increase in Ca2 + released, potentially causing a faster release of EVs compared to other tissues. The precise function of skeletal muscle in generating EVs during physical activity remains unclear. Although previous research has demonstrated the release of various exercise-related substances from skeletal muscle, it has yet to be determined if it plays a significant role in the creation of the observed EV pool following a single session of exercise. Conversely, it is feasible that the liberation of EVs amid physical activity is a combined endeavor powered by a multitude of cellular varieties (refer to Fig. 6) [187].

Table 3 The effects of acute exercise on exosome-like vesicles

Fig. 6

Diagram illustrating the suggested source, discharge, content, and load of exosome-like vesicles in response to physical exertion. After undergoing multiple training sessions or a single occurrence of physical activity, EVs may be released from individual muscles or other cell clusters and enter the general circulation of the body. Modifications in the number of exosomes found in the bloodstream, coupled with the presence and abundance of specific markers (such as ALIX, TSG101, tetraspanins, flotillin, and heat shock proteins), as well as their contents (such as miRNA and 'myomiR'), have been observed as a result of physical activity

Witham and his colleagues utilized specific numerical methods in protein analysis to describe the release of proteins contained within extracellular vesicles after exercise [188]. After a one-hour session of cycling, they noticed a rise in the movement of more than 300 proteins in healthy individuals. This was most significant in the abundance of certain groups of proteins that make up exosomes and small vesicles. Based on pulse-chase and intravital imaging studies, it has been indicated that physical activity releases EVs that tend to accumulate in the liver and are capable of transferring their load of proteins. Furthermore, through the use of arteriovenous balance studies on a contracting human limb, they discovered several new potential myokines that are released into the bloodstream without following the traditional secretion process. This information reveals a novel model in which tissue communication during physical activity can produce widespread physiological outcomes [188].

Overall, the data indicate that when muscles undergo stress or normal functioning, they release multiple peptides. However, there is limited understanding of how exosomes are released and their role in promoting benefits across various systems in response to intense endurance exercise. To date, there has been only one assessment examining the impact of immediate physical activity on the concentration of extracellular vesicles in the blood of human subjects [182]. Small EVs and MVs were measured using ultracentrifugation and filtration after subjects participated in acute endurance exercises, including cycling and treadmill running. The results showed a significant increase in small EVs/exosomes, depending on the intensity of the exercise, while MVs did not change. However, both levels returned to resting levels after 90 min (cycling) and 180 min (running) [182]. The exact ratio of exosomes within the small EV fraction is uncertain as the average diameter of the vesicles in the treadmill images was over 140 nm. As this represents the largest possible dimension of exosomes, a significant proportion of these vesicles were likely smaller MVs. Additionally, the investigation on acute exercise noted a slight increase in HSP70 levels in EVs after exercise [182, 189]. According to the same organization, they have also stated that the rise in cell-free DNA (cfDNA) due to acute endurance exercise was not connected to MVs [190]. Despite not being derived from skeletal muscle, a single research study revealed that a short period of endurance exercise resulted in a proangiogenic genetic profile in CD62E + and CD34 + blood cells [191]. The later research found that males had a significant rise in CD62E + ve cell microparticles after exercising, while females had a greater abundance of CD34 + ve cell microparticles [191]. A study involving the db/db mouse model of type 2 diabetes revealed that the heart generates exosomes containing various miRNAs (miR-455, miR-29b, miR-323-5p, and miR-466) when exposed to brief periods of endurance exercise [145]. According to the researchers, there is potential for a decline in MMP9 gene expression and subsequent reduction in cardiac fibrosis, a frequently encountered complication in aging individuals with type 2 diabetes, through the increase of these specific miRNAs [112]. At present, there is a dearth of studies investigating the discharge of MVs and EVs during alternative modalities of physical exertion. Nonetheless, based on the notable increase in CD34 + cell circulation following participation in sprint interval training, and the existing evidence, it is reasonable to assume that other forms of exercise may also induce the release of exosomes and/or MVs into the bloodstream [192].

Extensive research has conclusively proven that EVs have the capability to significantly decrease inflammation [193,194,195,196]. In addition, the researchers thoroughly examined the role of EVs in the amplification of overall inflammation triggered by physical exertion, which can be seen in Fig. 7. Recent studies have indicated that EVs produced by muscle tissue can heighten inflammatory signaling and facilitate cellular growth and proliferation, as well as induce the formation of tubes by activating the NF-κB signaling pathway. A study conducted by Sullivan and colleagues showed that obesity can greatly affect the amount of specific miRNAs found in EVs derived from skeletal muscle. This can then influence the expression of genes involved in growth, such as those related to cardiac hypertrophy, Wnt/β-catenin, PI3K/RAC-alpha serine/threonine-protein kinase, PI3K/AKT, IGF-1, and PTEN, as well as those related to inflammation signaling, such as pigment endothelium-derived factor (PEDF), death receptor, and Gαi. After 7 days of engaging in aerobic and resistance exercises, there was a noticeable change in the levels of miRNAs found in small EVs from skeletal muscle. These miRNAs specifically targeted various mRNA molecules involved in inflammation (e.g., interleukin-10, IL-6, macrophage function, Toll-like receptor, HMGB1, and NF-κB), growth (e.g., cardiac hypertrophy and Gβγ), and metabolism (e.g., PPAR), leading to a reduction in inflammation levels. One of the ways that PPAR signaling is activated is through the conversion of lipids, which has been linked to improved physical endurance and the production of new mitochondria through the activation of PGC1-α. Studies have demonstrated that levels of Wnt3a, Wnt5a, and Wnt7a, as well as IGF-1 mRNA, are decreased in individuals who are overweight. However, after one week of engaging in a combination of physical activities, there was a 25% decrease in Jun levels, a 65% decrease in Fos levels, and a 50% decrease in IL-8 mRNA levels in skeletal muscle cells among both lean and overweight individuals [197]. Given that participating in physical activity results in the creation of EVs within the skeletal muscle, which have qualities that effectively decrease inflammation. Additionally, the contraction of muscles releases IL-6, further aiding in reducing inflammation.

Fig. 7

Engaging in physical exercise can have a positive impact on reducing inflammation through the release of EVs. These EVs, coming from various sources, are known to carry molecules such as miRNAs and cytokines that have anti-inflammatory effects. Whether they originate from leukocytes, muscle cells, or platelets, the EVs work both locally and throughout the body via the bloodstream to target specific tissues. Ultimately, EVs produced during exercise act as a powerful anti-inflammatory force

Therefore, an acute bout of endurance exercise increases circulating exosomes that are hypothesized to mediate organ cross-talk to promote systemic adaptation to endurance exercise.

The positive impacts of regular endurance exercise on various organs and tissues and overall risk of death have been widely recognized, particularly in regard to obesity, type 2 diabetes, cancer, and heart disease. The research strongly supports the idea that intense physical activity triggers the release of substances known as myokines and exerkines from muscles and other tissues, which play a crucial role in coordinating the numerous positive effects of exercise on the body. The function of exosomes and possibly MVs as messengers between cells is firmly supported by existing research. It has been theorized by scientists that exosomes (and potentially MVs) play a role in transmitting endocrine-like substances (such as myokines and exerkines) between organs, thus truly acting as the "exercise factors". Based on limited data, it appears that exosomes and small MVs are released into the blood in response to exercise, with the level of release correlating with the intensity of the exercise.

Strengths, limitations and future prospective

Regarding the miRNAs found in circulation, they serve as biomarkers for physical activity and are known for their durability in bodily fluids. They can also be retrieved easily using non-invasive techniques. Notwithstanding the potential of miRNAs as biomarkers, it is crucial to note that while writing this review, we came across a number of methodological shortcomings in the studies we examined. A significant factor leading to this issue can be identified as the absence of a consistent technical approach for collecting samples (such as the specific anticoagulant utilized), storing them, extracting miRNA, and determining the housekeeping method during miRNA evaluation. Therefore, it is difficult to make a direct comparison between miRNAs extracted from serum and those from plasma because of the varying protocols used. An additional crucial aspect is that there is no research that has clearly outlined or identified if the samples being examined also had other technical issues, such as hemolysis or coagulation (which are common occurrences during blood collection and can impact the accuracy of miRNA measurements in plasma/serum). Furthermore, certain articles that were referenced lacked sufficient detail about the protocol being utilized. Ultimately, accurately contextualizing the impact of physical activity and exercise on the presence of miRNAs in plasma, serum, and cancer tissues proved challenging due to the wide variation in subject recruitment (such as age, therapy, and comorbidity descriptions) and the diversity in the type and intensity of exercise (including long or short term, recommended only, and supervised or unsupervised). Truly, although alterations in the levels of miRNAs following physical activity may indicate the specific type and level of exercise, the disruption of miRNA functioning could also be attributed to the influence of other lifestyle factors, such as diet and smoking, and the varying methods of selecting participants for the control and experimental groups. As a result, there is still uncertainty regarding the specific types and methods of exercise that can affect the expression of miRNAs. As a result, it is imperative to conduct additional research in order to surpass these limitations. Going forward, there should be a greater expansion of our understanding of exercise-induced miRNA expression, particularly through larger scale studies involving a greater number of subjects. Additionally, it is important to optimize and standardize protocols (such as exercise and miRNA evaluation) in order to ensure accuracy and consistency. This would involve conducting additional research using omics technologies to examine the impact of physical activity/exercise on cancer patients. It would also involve enhancing methods for distinguishing the effects of both short-term and long-term exercise. While the potential of this field of research is promising, there are a few constraints that need to be addressed when designing studies. One obstacle is the challenge of examining various subgroups of EVs; accurately determining which biogenesis pathway an EV belongs to is extremely arduous, unless it is observed during its release through real-time imaging methods. The reason for this is that there is currently no agreed-upon set of indicators that can clearly distinguish between different EV subtypes, such as "exosomes" originating from endosomes and "ectosomes" originating from the plasma membrane. In addition, while it may indicate the beginning and development of certain illnesses, difficulties and restrictions are arising in comprehending the functional significance of miRNAs found in EVs and how they affect the cells they are received by. It is important to note that numerous research studies evaluate immediate post-exercise evaluations, which mainly emphasize the short-term effects of exercise. However, the fluctuations in the quantity and makeup of EVs in serum may be impacted by stress-related elements, and only a limited number of studies delve into the lasting impacts. Future research should prioritize using a larger number of participants who have been affected by or are at risk for different diseases. This will allow for a more comprehensive evaluation of the impact of exercise on the modulation of extracellular lipid vesicles (ELVs) and their contents in the long term. Particular emphasis should be placed on examining the miRNAs contained within ELVs, as evidence suggests their potential for integration into target tissue cells and regulation of gene expression, unlike free miRNAs. Furthermore, careful consideration should be given to controlling the FITT-VP parameters of the intervention protocol, as they can significantly influence the results of the study.

Conclusion

Research has consistently revealed that exercise triggers the release of a variety of miRNAs that are distinctive to certain tissues, giving us a better understanding of how the body responds to physical strain [17]. Traditional biochemical markers only provide a general indication of tissue damage and stress caused by exercise, without revealing the specific cellular mechanism of adaptation. In contrast, miRNAs present as promising biomarkers as they can easily be obtained through minimally invasive methods and are known to remain stable in bodily fluids [17]. Conducting a thorough investigation into the process and regulation of skeletal muscle miRNAs during all stages of muscle repair in individuals with and without health issues will significantly improve our comprehension of skeletal muscle capabilities and potentially result in groundbreaking treatments for disorders that affect muscle development, recovery, and performance during the aging process and disease [202]. Despite difficulties in precisely measuring and identifying the origin and function of circulating miRNAs, they demonstrate promising capabilities as indicators for tracking the effects of physical activity. Identifying the distinct miRNA patterns linked to a particular type of exercise could greatly impact the enhancement of training techniques, injury prevention, and thorough monitoring of overall health [152]. Small fluid-filled structures, similar to exosomes, that travel throughout the body have the potential to assist in communication between cells, possibly offering a new explanation for the beneficial outcomes of physical activity. In recent years, the influence of exosomes on muscle composition has been uncovered. For instance, a study by Miao et al. revealed that exosomes produced by cancer cells could lead to the deterioration of muscle tissue, particularly in individuals with colon cancer and cachexia [16]. Despite the challenges involved in isolating exosome-like vesicles and identifying their precise origin and response to exercise, the opportunity to gain a more comprehensive understanding of the beneficial effects of physical activity on skeletal muscles is a greatly promising potential.