Inhibiting Myozenin 1 Attenuated Muscular Dystrophy Pathology in mdx Mice by Enhancing Calcineurin Activity.

Myozenin 1 (MYOZ1) is expressed in fast-twitch muscle fibers and functions as a calcineurin (CaN)-interacting protein. The deletion of MYOZ1 was reported to enhance the exercise capacity of mice. It would be prospective to explore the exact role of MYOZ1 in Duchenne muscular dystrophy pathology. The transfection of an adenoviral MYOZ1 shRNA in mdx mice was used to knock down MYOZ1 expression. Forelimb grip strength test, hanging wire test, and run-to-exhaustion test were conducted for assessing muscle strength and exercise ability of mice. Muscle tissue pathology was detected by HE and Masson staining. In addition, the myofiber composition of tibialis anterior muscle relied on detecting the markers of slow- fast-twitch muscle fibers. Then, the indicators of mitochondrial function, autophagy, and fission were also investigated. According to the results, in the tibialis anterior muscle of mdx mice, MYOZ1 inhibition facilitated CaN signal transduction and ameliorated muscle atrophy, also upregulated slow-twitch muscle fiber markers and downregulated fast-twitch muscle fiber markers. Besides, mitochondrial DNA and ATP content and mitochondrial membrane potential were increased in the MYOZ1 silenced group. The inhibition of MYOZ1 also promoted the expressions of mitochondrial autophagy and fission-associated proteins, including LC3I, LC3II, and p-DRP1 (Ser637). Cyclosporin A, a CaN signaling inhibitor, reversed the effect of MYOZ1 inhibition described above. In conclusion, MYOZ1 inhibition mitigated the pathological progression of tibialis anterior muscle in mdx mice, presenting as the improved mitochondrial function and increased slow-twitch muscle fibers.