Figure 3.

As the major signaling pathway driving AChRs clustering, Agrin diffusion, reduced MuSk activation and increased LRP4 degradation may contribute to AChRs morphological degeneration during aging, which is consistent with reduced TrkB. Then as a kind of compensatory mechanism, the expression of Sarcoglycan-α and Syntrophin was increased. MRFs could regulate AChRs gene expression and reduced MRF4 may be closely related to decreased AChR-δ and -ε in type IIa muscle fibers and increased AChRs-α, -γ, and -δ in type IIb muscle fibers at mRNA level. AChR, acetylcholine receptor; LRP4, low-density lipoprotein receptor-related protein 4; MuSk, muscle-specific kinase; Dok7, docking protein 7; Rapsyn, receptor-associated protein of the synapse; TrkB, tyrosine kinase B; MRF4, myogenic regulator factors 4.