Development of a cell‐free strategy to recover aged skeletal muscle after disuse

Abstract

Extended periods of bed rest and limb immobilization are required for healing post‐injury or disease, yet disuse can result in significant muscle atrophy and decreased quality of life in older adults. Physical rehabilitation is commonly prescribed to recover these deficits, yet accumulation of reactive oxygen species and sustained rates of protein degradation persist during the rehabilitation period that can significantly delay or prevent recovery. Pericytes, considered the primary mesenchymal and vascular stromal cell in skeletal muscle, secrete beneficial factors that maintain baseline muscle mass, yet minimal information exists regarding the pericyte response to disuse and recovery. In the current study, single‐cell RNA sequencing and functional assays were performed to demonstrate that pericytes in mouse skeletal muscle lose the capacity to synthesize antioxidants during disuse and recovery. This information was used to guide the design of a strategy in which healthy donor pericytes were stimulated with hydrogen peroxide (H2O2) to produce small extracellular vesicles (sEVs) that effectively restored myofibre size in adult and aged muscle after disuse. Proteomic assessment detected 11 differentially regulated proteins in primed sEVs that may account for recovery of muscle, including proteins associated with extracellular matrix composition and anti‐inflammatory and antioxidant processes. This study demonstrates that healthy H2O2‐primed pericyte‐derived sEVs effectively improve skeletal muscle recovery after immobilization, presenting a novel acellular approach to rebuild muscle mass in older adults after a period of disuse.Key points Previous studies suggest that prolonged oxidative stress is a barrier to skeletal muscle recovery after a period of immobilization. In this study we demonstrate that muscle‐resident perivascular stromal cells (pericytes) become dysfunctional and lack the capacity to mount an antioxidant defence after disuse in mice. Hydrogen peroxide treatment of healthy pericytes in vitro simulates the release of small extracellular vesicles (sEVs) that effectively recover skeletal muscle fibre size and extracellular matrix remodelling in young adult and aged mice after disuse. Pericyte‐derived sEVs present a novel acellular strategy to recover skeletal muscle after disuse.

A novel acellular approach to treat muscles after disuse

“…Indeed, pericytes secrete beneficial immunomodulatory, anti‐fibrotic and pro‐angiogenic factors in response to contraction that promote skeletal muscle remodelling (Dvoretskiy et al., 2019). The presented study further emphasizes the underappreciated role of pericytes in muscle recovery (Wu et al., 2022).…”

“…As such, they induced an antioxidative response in both groups by exposing their respective pericytes to H 2 O 2 in vitro for 3 h. As expected, the control/mobile group demonstrated a compensatory increase in antioxidant gene expression in response to H 2 O 2 (Wu et al, 2022). In contrast, a significant decrease in the expression of antioxidant genes was observed in the immobile cluster, demonstrating the inability of endogenous pericytes to respond to oxidative stress after limb immobilization (Wu et al, 2022). As mentioned above, one of the main functions of pericytes is their role in muscle recovery.…”

“…Healthy versus disused muscle Wu et al conducted various experiments to demonstrate the differences between disused and healthy muscles upon exposure to oxidative stress (Wu et al, 2022). In their study, they modelled disused muscle by unilaterally immobilizing tibialis anterior (TA) muscles for 2 weeks and compared them with another group mobilizing normally (control).…”

“…After 3 days of remobilization following the 2 weeks of immobilization, Wu et al analysed the differentially expressed genes through single-cell RNA sequencing (sc-RNA) in both groups. From the obtained clusters, they demonstrated that, in nearly all clusters obtained from immobilized cells, numerous genes important for muscle contractility and those associated with mitochondrial complex proteins were significantly decreased (Wu et al, 2022).…”

“…In 2019, the same lab demonstrated that treatment of pericytes after immobilization improved muscle recovery as they secrete small extracellular vesicles (sEVs) which encapsulate antioxidants and therefore contribute to the antioxidative response (Munroe et al, 2019). Altogether, their results demonstrated that endogenous immobilized pericytes will have reduced capacity to generate an antioxidative response, but pericyte transplantation following immobilization improves muscle recovery (Munroe et al, 2019;Wu et al, 2022). With this in mind, and the fact that stimulation by H 2 O 2 will increase antioxidative response, they hypothesized that transplanting immobilized muscle with pericytes already primed with H 2 O 2 would be an effective approach in improving muscle recovery.…”