Defense Date

2019

Document Type

Thesis

Degree Name

Master of Science

Department

Physiology and Biophysics

First Advisor

Murthy S. Karnum

Second Advisor

John Grider

Abstract

Deficiency of dystrophin, a cytoskeletal protein localized in the inner face of the plasma membrane in skeletal, cardiac and smooth muscle, results in Duchenne Muscular Dystrophy (DMD). Through its interactions with extracellular matrix and plasma membrane proteins, dystrophin plays a role in contraction and signal transduction. In DMD, gastrointestinal disorders such as gastric dilation and intestinal pseudo-obstruction resulting from altered motility have been reported. The role of dystrophin in the regulation of contractile protein expression and smooth muscle function, per se, is not known. Studies have suggested that inflammation contributes to the pathophysiology of DMD. Exogenous H2S had been shown to exert beneficial cardiovascular and gastrointestinal functions, probably via exerting anti-inflammatory actions. Aim. To test the hypothesis that a lack of dystrophin causes a decrease in contractile protein expression and smooth muscle function and that treatment with H2S restores the effects of dystrophin deficiency. Methods. The role of dystrophin was examined using mice deficient in dystrophin alone (mdx) and mice deficient in dystrophin plus telomerase RNA (mdx/mTR), which exhibit increased disease severity. The effect of an orally-active, slow releasing H2S agent (SG1002) was tested in mdx/mTRmice (40 mg/kg body weight in chow/every 3 days starting from 3 weeks to 9 months). Contraction in response to acetylcholine (ACh) was measured in gastric muscle strips isolated from mdx, mdx/mTRand SG1002-treated mdx/mTRmice. Age-matched control mice were used for each group. Contraction was also measured in muscle cells isolated from the stomach of control and mdxmice by scanning micrometry and expressed as the percent decrease in muscle cell length. Expression of mRNA and contractile proteins such as smoothelin, caldesmon, calponin and tropomyosin was measured by qRT- PCR and western blot. Results. Acetylcholine-induced contraction was reduced in muscle strips from mdx/mTRmice (18±4 mN/100 mg tissue) compared to age-matched 9-month old control mice (33±7 mN/100 mg tissue). Treatment of mdx/mTRmice with SG1002 restored contraction to above normal levels (56 ± 8 mN/100 mg tissue). Contraction was also decreased in gastric muscle strips from mdxmice (24±5 mN/100 mg tissue) compared to age-matched 3- month old control mice (45±4 mN/100 mg tissue). Both Ca2+-dependent initial contraction and Ca2+-independent sustained contraction was also decreased in isolated gastric muscle cells from mdxmice compared to control mice. Conclusion. The results support our hypothesis that dystrophin deficiency reduces smooth muscle contraction. Furthermore, treatment with H2S restores gastric smooth muscle function and contractile mRNA expression suggesting therapeutic potential of H2S in the treatment of motility disorders in DMD.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

5-6-2019

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