Development of a pericyte-based strategy to recover aged skeletal muscle after disuse

Skeletal muscle disuse atrophy is the decline of muscle mass that occurs after periods of extended bed rest or immobilization. Recovery via physical rehabilitation is often incomplete in special populations such as older adults, due to injury and pain, functional limitations, and anabolic resistance. Prolonged loss of muscle can lead to metabolic disorders, physical disability, loss of independence and premature death. Therefore, it is necessary to develop novel approaches to facilitate recovery of muscle mass and function after periods of disuse. Our laboratory previously demonstrated that muscle-resident perivascular stem cells (NG2+ and CD146+ pericytes), also considered the primary mesenchymal stem cell (MSC) in muscle, can effectively recover muscle mass in young adult mice following a period of immobilization. However, several questions remained after the completion of this study. What cell surface marker provided the best means to isolate therapeutic pericytes? What was the mechanistic basis by which pericyte transplantation assisted in the recovery of muscle after disuse? And could pericytes provide similar benefits in aged mice? This study was conducted to address these important questions. In Chapter 2, pericytes were isolated based on two cell surface markers (NG2 and CD146) and then transplanted into tibialis anterior muscle (TA) in young adult mice after two weeks of immobilization. Muscle recovery was improved by CD146+ but not NG2+ pericytes, as assessed by muscle fiber size, capillary density and collagen degradation. In Chapter 3, single-cell RNA sequencing was conducted on hindlimb muscle two weeks after immobilization to evaluate differential gene expression in pericytes and other mononuclear cells. The upregulation of the long non-coding RNA metastasis associated lung adenocarcinoma transcript 1 (Malat1, also known as Neat2) specifically in pericytes suggested disruption to antioxidant production. To test this hypothesis, pericytes were obtained from healthy or immobilized skeletal muscle and exposed to a hydrogen peroxide load in vitro. Only the healthy pericytes were able to mount an antioxidant response to oxidative stress. On a similar note, only healthy pericytes were able to decrease ROS and fully recover muscle after immobilization. Interestingly, extracellular vesicles derived from pericytes in culture were able to significantly improve myofiber size and collagen degradation in both adult and aged mice after immobilization. Overall, the findings presented in this dissertation demonstrate that CD146+ pericytes and CD146+ pericyte-derived extracellular vesicles possess high capacity to stimulate muscle regrowth after immobilization, which may in part be due to resolution of oxidative stress. These results represent an important step in the design of a cell-free therapy to recover muscle health in older adults after periods of disuse.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste