SRSF2 is upregulated in Duchenne muscular dystrophy and impairs myoblast autophagy by alternatively splicing HUWE1.

This study aimed to investigate the effect of serine and arginine rich splicing factor 2 (SRSF2) on myoblast autophagy in Duchenne muscular dystrophy (DMD). Protein expressions of SRSF2 and HUWE1, and mRNA expressions of SRSF2, HUWE1 isoform 1/2/3 (HUWE1-S1/S2/S3) were detected in mdx mice (DMD model). SRSF2, HUWE1-S1 and HUWE1-S2 overexpression plasmids, and SRSF2, HUWE1-S1 and HUWE1-S2 siRNAs were transfected into mouse myoblast C2C12 cells alone or in combination. SRSF2, HUWE1-S1, and HUWE1-S2, but not HUWE1-S3, were upregulated in mdx mice compared with control mice. In myoblasts, SRSF2 positively regulated HUWE1-S1 and HUWE1-S2 but less affected HUWE1-S3. RNA immunoprecipitation confirmed that SRSF2 protein directly bound to HUWE1-S1 and HUWE1-S2, but not HUWE1-S3. SRSF2 overexpression reduced myoblast autophagy reflected by lower LC3B(II/I) expression and autophagic flux, while higher p62 expression; however, SRSF2 siRNA revealed opposite effects. Moreover, SRSF2 overexpression decreased while siRNA increased autophagy in dystrophin-deficient myoblasts. HUWE1-S1 overexpression or siRNA did not alter autophagy or attenuated SRSF2's effect on autophagy in myoblasts. Notably, HUWE1-S2 siRNA improved autophagy in myoblasts, and attenuated SRSF2 overexpression-mediated myoblast autophagy impairment; meanwhile, HUWE1-S2 overexpression revealed opposite effects. Conclusively, SRSF2 is upregulated in DMD mouse model and impairs myoblast autophagy through alterative splicing HUWE1.