Semester

Spring

Date of Graduation

2013

Document Type

Thesis

Degree Type

MS

College

College of Physical Activity and Sport Sciences

Department

Exercise Physiology

Committee Chair

Stephen E Alway

Committee Co-Chair

Randall W Bryner

Committee Member

Paul D Chantler

Abstract

The main objective of this master's thesis project was to elucidate the role of the deacetylase Sirtuin 1 (Sirt1) in skeletal muscle regeneration. We developed two specific aims to accomplish this task, which involved separate studies in order to study the effects of Sirt1 in multiple models of regeneration. The results from these studies may potentially lead to the development of novel therapies to treat various clinical conditions which require muscle regeneration.;Specific aim 1 utilized resveratrol, a Sirt1 activator, as a supplement to improve muscle regeneration following a period of disuse in aged animals. Aged Fisher 344 x Brown Norway rats were hindlimb suspended for a total of fourteen days (HS), whereupon one-half of the animals were sacrificed and the remainder were unloaded and allowed a fourteen day recovery period of normal ambulation (R), at which point they were sacrificed. During the experimental period, each rat received either 1ml of resveratrol (125 mg/kg) or 1ml of carboxymethylcellulose dissolved in distilled water (vehicle) via oral gavage at approximately the same time each morning. Additionally, a group of vehicle treated animals maintained normal ambulation throughout the protocol and served as cage controls for the suspended animals.;Resveratrol was not able to attenuate losses in either body or muscle wet weights following HS and did not provide any additional benefits to these measures during the R period. Surprisingly, resveratrol treated animals did not fare as well on a fatigue protocol and few differences were observed upon examination of a force-frequency curve. However, fiber type analyses revealed a shift towards increased type IIA myosin heavy chain (MyHC) fibers following HS. Resveratrol also attenuated decreases in fiber area in type IIA MyHC fibers following HS and in both type IIA and IIB MyHC fibers following the R period.;Our results from this study indicate a potential for the use of resveratrol in benefitting skeletal muscle regeneration in aged populations following periods of disuse such as extended hospitalizations. Although resveratrol was unable to maintain muscle function as determined by the force characteristics, it clearly benefitted muscle fiber size which is important in this population as the elderly have diminished regenerative abilities. Future research should be aimed at determining the optimal dosage to fully maximize the benefits of this supplement in skeletal muscle regeneration.;Specific aim 2 attempted to establish the role of Sirt1 in muscle regeneration using transgenic mice which either overexpressed (Sirt1+/+) or had diminished Sirt1 expression (Sirt1-/-) in the skeletal muscles. Tibialis anterior (TA) muscles were examined either 3 or 7 days following a cardiotoxin (CTX) injection in the animals left TA muscles. The right TA muscles were injected with sterile PBS and were used as intranimal controls for the CTX administration.;Increasing Sirt1 expression did not have an effect on muscle mass or fiber area at either 3 or 7 days. However, increasing its expression attenuated decreases in maximal tetanic force production at both 3 and 7 days post-injury while there were no differences observed in these forces in the Sirt1 -/- animals. There were no differences observed between any of the groups in BrdU incorporation and furthermore, in apoptosis as determined via TUNEL staining.;Results from this study indicate that Sirt1 may not play a significant role in muscle mass or fiber area during the early stages of muscle regeneration. However, increasing Sirt1 expression was beneficial in that it improved muscle force characteristics which would suggest improved functional recovery in these animals. Therefore, although inconclusive, increasing Sirt1 expression may be beneficial at improving skeletal muscle regeneration in that it may reduce functional impairments in muscle viability. Future research may thus be directed at developing therapies to exploit these benefits and be applied toward clinical populations which require skeletal muscle regeneration.

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