MicroRNA-33 inhibition ameliorates muscular dystrophy by enhancing skeletal muscle regeneration

Background Muscular dystrophies are inherited disorders characterized by progressive skeletal muscle weakness and tissue degeneration. Duchenne muscular dystrophy (DMD), caused by a mutation in the dystrophin gene, results in a severe clinical course. Dystrophin deficiency renders muscle fibers vulnerable to contraction-induced damage, triggering inflammation and fibrosis. Although treatments like exon skipping and stop codon read-through can partially restore dystrophin in some DMD patients, no definitive cure exists. Supportive therapies (e.g., nutritional management, rehabilitation, and respiratory support) offer limited relief. Recent evidence suggests that manipulating certain microRNAs (miRNAs) may represent a novel therapeutic avenue. Purpose This study aimed to determine the role of miR-33a/b in muscle repair and fibrosis in DMD and to evaluate whether inhibiting miR-33 might offer therapeutic benefits. Methods Genetically modified mouse models were employed to dissect miR-33 function. miR-33a-knockout (KO) mice were analyzed in both a cardiotoxin (CTX)-induced injury model and in mdx mice (a standard DMD model). Humanized miR-33b knock-in (miR-33b-KI) mdx mice were generated to reflect the human-specific miR-33b variant. Expression levels of key miR-33 target genes (including Cdk6, Fst, and Abca1) were measured to link molecular alterations with histopathological changes. Additionally, anti-miRNA oligonucleotides (AMOs) targeting miR-33 were administered to mdx mice—locally and systemically—to gauge therapeutic efficacy. Lastly, miR-33b inhibition was tested in myotubes derived from DMD patient iPS cells to validate potential translational impact. Results In both the CTX-injury and mdx models, miR-33a-KO mice displayed enhanced muscle regeneration and reduced fibrosis, suggesting that removing miR-33a confers protective effects. In contrast, miR-33b-KI mdx mice showed exacerbated muscle pathology, characterized by weaker regenerative capacity and increased fibrotic tissue. These phenotypic outcomes correlated with changes in Cdk6, Fst, and Abca1 expression. AMO-mediated inhibition of miR-33a/b improved skeletal muscle pathology and exercise performance in mdx mice. Moreover, human DMD iPS cell–derived myotubes treated with miR-33b inhibitors exhibited upregulation of the same target genes, supporting the clinical relevance of these findings. Conclusions These results indicate that miR-33a/b are key regulators of muscle regeneration and fibrosis in DMD. Genetic deletion or pharmacological blockade of miR-33 yields marked improvements in skeletal muscle integrity. Moreover, because DMD frequently involves cardiac complications, the beneficial impact of miR-33 inhibition on muscle repair could also extend to mitigating cardiomyopathy. Further investigation is warranted to validate miR-33–targeted therapies as a comprehensive approach to managing both skeletal and cardiac manifestations of DMD.