Sarcopenia is the age-related progressive loss of skeletal muscle (SkM) mass, function, and strength. It has been well elucidated that resistance exercise can attenuate the development of sarcopenia. A population of extracellular vesicles, termed ‘exosomes’ (EXO), can contain microRNA and facilitates intercellular communication, including within SkM, though the response to prolonged training is not well understood. Given the potential role of SkM-derived exosomes in the response to exercise, we examined older adults (n = 30, OLD) before (PRE) and after a 12-week (POST), resistance training program. Healthy, young controls (n = 12, YNG) were used for comparison of baseline measures. Exosomes were isolated from platelet-free plasma using size exclusion chromatography in combination with ultracentrifugation (SEC-UC) and characterized via western blotting, nanoparticle tracking analysis and electron microscopy. To assess exosome biogenesis and miRNA synthesis in skeletal muscle, biopsies were taken from the vastus lateralis. Circulating EXO-enclosed and SkM miRNA expression was measured using RT-PCR. In SEC-UC isolates, EXO-markers CD81 and CD9 were significantly lower in PRE compared to YNG (p<0.05) but did not change with training. At baseline, ALIX, TSG101 and CD63 (markers of exosomes) were not altered with aging as compared to YNG; however, their expression significantly increased with training (p<0.05) Circulating EXO-derived mir-1, -133, -23 and -27a were significantly lower in expression of OLD participants as compared to YNG. Following resistance training, their expression significantly increased (p<0.05), returning to a YNG phenotype. Next, we aimed to investigate the contribution of skeletal muscle in the exosome responses. Our data indicate that a small fraction of circulatory exosomes may originate from skeletal muscle. In addition, in biopsy-derived SkM tissue, expression of proteins involved in EXO and miRNA biogenesis (Alix, XPO-5, DICER) were significantly higher in PRE compared to YNG (p<0.05), and further increased with resistance training (POST, p<0.05). Expression of Rab27a, a marker of exosome trafficking, was significantly higher in PRE (p<0.05) but did not respond to training. In conclusion, here we show alterations in circulating EXO content and cargo with age and resistance training partially restores the values to a younger phenotype. / Thesis / Master of Science in Medical Sciences (MSMS) / Aging is the slow and time-dependent process that our organs, down to the cellular level, deteriorate in function reducing the biological fitness of our bodies. Aging specific to skeletal muscle, or sarcopenia, is especially important because skeletal muscle makes up 40% of our weight, is essential for posture, balance, locomotion and breathing. Sarcopenic individuals have low muscle mass, strength, and function and as a result are associated with low independence in activities of daily living and increased risks of falls and fractures. Exercise, and in particular resistance training, has been shown to be beneficial and cost-effective in treating sarcopenia and delaying aging throughout the body. Part of the underlying mechanism regarding how exercise affects us in a multi-systemic manner is not well understood. We know that skeletal muscle releases a multitude of molecular factors during exercise. Amongst them, extracellular vesicles and specifically exosomes are worth investigating because they have been shown to function in intercellular communication by delivering molecular signals, called microRNAs, from origin cells to recipient cells throughout the body. In this thesis project, we investigate exosomes in circulation of older individuals before and after a 12-week resistance training program. We found that aging alters the exosome pool in circulation as well as their miRNA content. After resistance training, many of miRNAs altered with age, return to levels comparable to young. In addition, we showed that at the skeletal muscle level, aging and resistance training affect exosome biogenesis and miRNA expressions. In conclusion, we provide evidence that aging significantly alters circulatory exosomes and miRNA and show that resistance training normalizes the miRNA profile to levels seen in exosomes derived from young plasma. How exosomes and their molecular signals change with aging and how exercise affects them gives us an insight on how exercise elicits multi-systemic benefits against aging and sarcopenia.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/27036 |
| Date | January 2021 |
| Creators | Xhuti, Donald |
| Contributors | Tarnopolsky, Mark, Medical Sciences (Cell Biology and Metabolism) |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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