Date of Graduation

5-2016

Document Type

Thesis

Degree Name

Bachelor of Science

Degree Level

Undergraduate

Department

Health, Human Performance and Recreation

Advisor/Mentor

Washington, Tyrone

Committee Member/Reader

Ganio, Matthew S.

Committee Member/Second Reader

Greene, Nicholas

Abstract

Skeletal muscle has the ability to regenerate from damage; however, recent studies have reported a negative effect of obesity on skeletal muscle regenerative capacity. The extracellular matrix (ECM) contributes to skeletal muscle structure acting as a scaffold for skeletal muscle. Additionally, skeletal muscle serves as a reservoir for proteins and growth factors that promote regeneration. Optimal skeletal muscle regeneration includes inflammation, ECM remodeling, and myofiber growth. Disruption to any of these processes can negatively affect skeletal muscle regeneration. PURPOSE: The purpose of this study was to determine how diet-induced obesity (DIO) affects ECM remodeling during skeletal muscle regeneration. METHODS: Fifty-six male C57BL/6J mice were randomly assigned to two groups; lean diet (10% fat) and high fat diet (HFD) (60% fat). Within those two groups, mice were randomly assigned to either a PBS (uninjured) group or a bupivacaine (injured) group. Bupivacaine is a myotoxin which induces injury to skeletal muscle. Both groups received injections into the tibialis anterior (TA). Three or 28 days post-bupivacaine injection, the TAs were extracted and PCR reaction was done to quantify ECM-related gene expression (i.e. Collagen-I, Collagen-III, Fibronectin, TGF-β, MMP2, MMP-9, and TIMP-I). RESULTS: There was no difference in Collagen III:I gene expression 3 days post-injection in the lean group (p>0.05). However, there was a 3 fold increase (p<0.05) in Collagen III:I gene expression in the obese group 3 days post-injection. Twenty-eight days post-injection there was an increase in Collagen III:I ratio gene expression in the lean group due to injury as compared to the uninjured lean group (p<0.05). Three days post injection there was a main effect of injury to increase TGF-β gene expression (p<0.05). Twenty-eight days post injection there were no significant differences in TGF-β gene expression between groups (p>0.05). Three and 28 days post injection there was a main effect of injury to increase MMP-2 gene expression (p<0.05). Three days post injury there was a main effect of injury to increase MMP-9 gene expression (p<0.05). Twenty-eight days post injection there was a main effect of HFD to decrease MMP-9 gene expression (p<0.05). Three days post injection there was a main effect of injury to increase TIMP-I gene expression (p<0.05). Twenty-eight days post injection there was a main effect of HFD to decrease TIMP-I gene expression regardless of diet (p<0.05). CONCLUSION: Obesity altered ECM composition during skeletal muscle regeneration. This could negatively impact the ability of obese muscle to recovery form injury. These findings suggest that an altered composition could lead to a change in exercise prescription for this specific population.

Skeletal muscle has the ability to regenerate from damage; however, recent studies have reported a negative effect of obesity on skeletal muscle regenerative capacity. The extracellular matrix (ECM) contributes to skeletal muscle structure acting as a scaffold for skeletal muscle. Additionally, skeletal muscle serves as a reservoir for proteins and growth factors that promote regeneration. Optimal skeletal muscle regeneration includes inflammation, ECM remodeling, and myofiber growth. Disruption to any of these processes can negatively affect skeletal muscle regeneration. PURPOSE: The purpose of this study was to determine how diet-induced obesity (DIO) affects ECM remodeling during skeletal muscle regeneration. METHODS: Fifty-six male C57BL/6J mice were randomly assigned to two groups; lean diet (10% fat) and high fat diet (HFD) (60% fat). Within those two groups, mice were randomly assigned to either a PBS (uninjured) group or a bupivacaine (injured) group. Bupivacaine is a myotoxin which induces injury to skeletal muscle. Both groups received injections into the tibialis anterior (TA). Three or 28 days post-bupivacaine injection, the TAs were extracted and PCR reaction was done to quantify ECM-related gene expression (i.e. Collagen-I, Collagen-III, Fibronectin, TGF-β, MMP-2, MMP-9, and TIMP-I). RESULTS: There was no difference in Collagen III:I gene expression 3 days post-injection in the lean group (p>0.05). However, there was a 3 fold increase (p0.05). Three and 28 days post injection there was a main effect of injury to increase MMP-2 gene expression (pCONCLUSION: Obesity altered ECM composition during skeletal muscle regeneration. This could negatively impact the ability of obese muscle to recovery form injury. These findings suggest that an altered composition could lead to a change in exercise prescription for this specific population.

This work was supported by a grant from the American Biosciences Institute and a Student Undergraduate Research Fellowship Grant.

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