Regulation of MiR-206 in denervated and dystrophic muscles and its effect on AChR clustering.

Muscle-specific microRNA miR-206 has recently emerged as a potential regulator of genes involved in the formation and regeneration of the neuromuscular junction (NMJ). This study investigated miR-206-3p (miR-206) expression in synaptic and non-synaptic regions of denervated and in alpha-dystrobrevin (Dtnb) knockout mice, as well as its impact on the formation and/or maintenance of agrin-induced acetylcholine receptor (AChR) clusters. In denervated, Dtnb-deficient, and crushed muscles, miR-206 expression significantly increased compared to innervated muscles. While miR-206 expression is slightly elevated in the synaptic regions of innervated muscles, it dramatically rises in non-synaptic areas of denervated muscles. miR-206 targets transcripts of essential NMJ proteins such as Dtnb, alpha-syntrophin (Snta1), and rapsyn, but not AchRα subunit or Lrp4 in innervated muscles. However, in denervated muscles, AChRα transcripts, which increase significantly, become a target of miR-206. Co-expression of miR-206 with rapsyn, Dtnb, and Snta1 in C2C12 myoblasts significantly reduced their protein levels, and overexpression of miR-206 in myotubes disrupted agrin-induced AChR clustering. These results indicate that miR-206 fine-tunes NMJ signaling proteins by regulating transcripts of various proteins with different localizations under normal and pathological conditions.