Restoration of Contractile Protein Expression and Colonic Smooth Muscle Function by H2S in Duchenne Muscular Dystrophy Mice

Duchenne Muscular Dystrophy (DMD), characterized by the lack of dystrophin, results from a mutation in the Xp21 gene which encodes for the protein dystrophin that links the extracellular matrix to the actin cytoskeleton in skeletal, cardiac and smooth muscle. Slow colonic transit and chronic constipation are common in DMD patients due to the weakening of the abdominal wall muscles and gut smooth muscle. However, the cause of this hypocontractility in DMD patients and the expression of contractile proteins in smooth muscle are unknown. Expression of contractile proteins is regulated by the signaling pathways activated by excitatory (e.g., acetylcholine, ACh) and inhibitory transmitters (e.g., nitric oxide and hydrogen sulfide (H 2 S)). H 2 S is a well‐known gasotransmitter in the gut which promotes gut motility; however, its effect on colonic contractility in DMD is unknown. AIM To investigate the expression of contractile proteins and smooth muscle function in the colon of wild type mice and models of DMD ( mdx and mdx/mTR mice) and the effect of H 2 S on these in mdx mice. METHODS Contraction of colonic segments was measured in the longitudinal orientation from 3‐month old control and mdx mice, and 9‐month old control and mdx/mTR mice, (mdx/ mTR exhibit increased disease severity). The effect of SG1002, an orally active slow releasing H 2 S agent, was tested in mdx/mTR mice (40 mg/kg body weight in chow/every 3 days starting from 3 weeks to 9 months). Expression of contractile proteins was measured by qRT‐PCR and western blot. RESULTS Expression of smoothelin, caldesmon, calponin and tropomyosin was decreased in colonic smooth muscle of mdx mice compared to control. This decrease was associated with a decrease in ACh‐induced contraction in colonic segments (21 ± 3 mN/100 mg tissue in control and 3 ± 1 mN/100 mg tissue in mdx mice). To identify the specific involvement of smooth muscle dysfunction in the decrease in contraction, colonic muscle cells were isolated and contraction in response to ACh was measured by scanning micrometry and expressed as the percent decrease in cell length from control cell length. ACh‐induced contraction was also inhibited in muscle cells isolated from mdx mice compared to control (43 ± 5% in control and 27 ± 3 % in mdx mice). ACh‐induced contraction were decreased in colonic segments from mdx/mTR mice (12 ± 2 mN/100 mg tissue in control versus 4 ± 1 mN/100 mg tissue in mdx/mTR ) and the decrease was partly reversed by SG1002 treatment (9 ± 1 mN/100 mg tissue). Expression of contractile proteins was also decreased in colonic smooth muscle from mdx/mTR mice and the decrease was reversed by SG1002. These results suggest that H 2 S restores contractile protein expression and contraction in mdx/mTR mice. Conclusion The data indicate that the lack of dystrophin in mdx mice adversely affects colonic smooth muscle contractility through the down regulation of contractile protein expression. Treatment of mdx/mTR mice with H 2 S restores contractile phenotype. Thus, H 2 S treatment would be an area of study in therapeutic control of DMD‐induced gastrointestinal motility disorders. Support or Funding Information Supported by DK15564, DK28300, DK34153 and HL133167. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .