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Title:Development of a pericyte-derived extracellular vesicle therapy for the recovery of skeletal muscle mass following immobilization
Author(s):Dvoretskiy, Svyatoslav
Director of Research:Boppart, Marni D
Doctoral Committee Chair(s):Boppart, Marni D
Doctoral Committee Member(s):Boppart, Stephen A; Woods, Jeffrey; Dobrucki, Wawrzyniec
Department / Program:Kinesiology & Community Health
Discipline:Kinesiology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Pericytes
Extracellular Vesicles
Disuse Atrophy
Abstract:Extended bed rest and single limb immobilization (casting) are necessary for tissue healing during periods of illness, disease and/or injury. Unfortunately, prolonged inactivity can result in significant declines in protein synthesis and skeletal muscle mass, a condition known as disuse atrophy. Physical therapy is standard practice following disuse atrophy and may be sufficient for complete recovery of muscle mass and function in young individuals. However, the majority of older adults are not able to fully engage in a rehabilitation program due to limitations in mobility and/or pain associated with movement, making this population highly susceptible to long-term disabilities. Pharmacological or nutritional interventions do not exist to effectively promote recovery of muscle mass following disuse, thus alternative strategies must be explored to prevent disability and prevent early mortality in our rapidly growing population of older adults. The molecular mechanisms responsible for exercise-induced beneficial gains in muscle mass and strength are not completely understood. Mechanical strain associated with contraction can initiate the mammalian target of rapamycin (mTOR) signaling pathway in the myofiber, a manner that is critical for increased rates of myofibrillar protein synthesis and gains in mass in response to exercise. However, stem and stromal cells residing in the microenvironment (extrinsic to the myofiber) may also contribute. Studies have demonstrated that myogenic stem cells, or satellite cells (SCs), communicate with fibroblasts to prevent excess deposition of connective tissue, suggesting an indirect role for SCs in muscle growth. While intriguing, a recent study confirmed that SCs, while important for exercise-induced myofiber hypertrophy, do not impact recovery of muscle mass following disuse. Several other mononuclear cells with stem and/or stromal capacity reside in skeletal muscle, including pericytes and fibroblasts, yet minimal information exists regarding their response to exercise and their subsequent contribution to muscle growth. Thus, the purpose of this study was to characterize the perivascular stem/stromal cell response to acute contraction, determine the contribution of these cells to exercise-induced muscle growth, and examine the capacity for pericyte-derived materials to improve skeletal muscle recovery following disuse. The mouse model was chosen to complete this work due to the unique localization of pericytes in the vascular niche, which is typically avoided when obtaining muscle biopsies in humans. An in vivo electrical stimulation model was developed to ensure equal application of mechanical load between mice. Pericyte (CD146+Lin-, NG2+Lin-) and fibroblast (PDGFα+Lin-) relative quantity was assessed 24 hours post-stimulation using multiplex flow cytometry, and the perivascular cell response to contraction was determined using targeted qPCR and/or RNA sequencing 3 and 24 hours following electrical stimulation. CD146+Lin- pericytes were collected using fluorescence-activated cell sorting (FACS) and intramuscularly transplanted prior to 2x/week electrical stimulation for 4 weeks to determine contribution to skeletal muscle growth. Finally, based on the results obtained here and separately in the lab demonstrating an important role for pericytes in recovery of muscle mass following disuse, pericyte-derived EVs (CD146+ EVs) were collected from the plasma of electrically stimulated mice and assessed for their ability to recover atrophied tibialis anterior muscles using a unilateral hindlimb immobilization model. The results from this dissertation demonstrate that perivascular stem/stromal cell quantity is not significantly altered following an acute bout of electrical stimulation. However, pericyte gene expression is highly upregulated 3 hours following stimulation in a manner that suggests a critical role in processes such as angiogenesis, myogenesis and extracellular matrix (ECM) remodeling. Pericyte intramuscular transplantation concurrent with 4 weeks of electrical stimulation significantly increased collagen remodeling and muscle capillarization. Lastly, intramuscular transplantation of plasma-derived CD146+ EVs significantly increased collagen remodeling and restored muscle capillarization following disuse atrophy. The data from these experiments suggest that pericytes are highly responsive to mechanical stimuli and positively contribute to muscle growth through increased ECM remodeling and capillarization. These beneficial effects may be packaged within pericyte-derived EVs, as pericyte-derived EV transplantation improved skeletal muscle recovery when introduced immediately prior to remobilization. These novel findings justify further development of a pericyte-derived EV therapy for the treatment of disuse atrophy.
Issue Date:2020-05-01
Type:Thesis
URI:http://hdl.handle.net/2142/108297
Rights Information:Copyright 2020 Svyatoslav Dvoretskiy
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05


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