Myopalladin promotes muscle growth through modulation of the serum response factor pathway

Myopalladin (MYPN) is a striated muscle-specific protein located in the Z-line and I-band of the sarcomere as well as the nucleus. Analysis of MYPN knockout (MKO) mice showed a 48% reduction in myofiber cross-sectional area in MKO mice and a consequent reduction in isometric force generation and power output. Similarly, reduced myotube width was observed in MKO primary myoblast cultures. RNA-Seq studies revealed downregulation of serum response factor (SRF)-target genes in MKO mice, important for muscle growth and differentiation, and further studies revealed that MYPN, like its homologue PALLD, can bind and bundle filamentous actin as well as interact with MRTF-A, both major players in the regulation of the SRF pathway. Consistently, MYPN increased MRTF-A-mediated activation of SRF signaling in myogenic cells, and transduction of MKO myoblasts with constitutive active SRF rescued the reduced myotube width, demonstrating that MYPN promotes skeletal muscle growth through activation of the SRF pathway. Profiling of the transcriptome of tibialis anterior muscle from 2- and 4-week-old MYPN knockout and control mice. Two biological replicates were profiled for each condition and time point.