SYNJ2BP is associated with mitochondrial abnormalities and skeletal muscle atrophy in experimental models

Skeletal muscle atrophy is associated with mitochondrial dysfunction, but the contribution of synaptojanin 2 binding protein (SYNJ2BP) remains unclear. Proteomic profiling of human supraspinatus muscle identified increased SYNJ2BP abundance in atrophied tissue, together with changes in mitochondrial and calcium-related protein sets. Increased SYNJ2BP abundance was also observed in mouse supraspinatus muscle after tendon transection. In C2C12 cells, SYNJ2BP overexpression was accompanied by altered myogenic and atrophy-associated proteins, abnormal mitochondrial ultrastructure, lower ATP content, and increased Rhod-2 fluorescence. VBIT-4 attenuated several of these changes but also reduced SYNJ2BP abundance, limiting interpretation as a selective downstream rescue. SYNJ2BP, IP3R1, and GRP75 were recovered in VDAC1 immunoprecipitates. Increased VDAC1 bait recovery and differences in input abundance preclude interpreting greater protein recovery as stronger relative association. In a separate mouse hindlimb immobilization model, local SYNJ2BP knockdown was associated with preserved mitochondrial morphology, less muscle wasting, and improved physical performance. These complementary observations implicate SYNJ2BP in muscle wasting and motivate investigation of IP3R1/GRP75/VDAC1-associated calcium regulation. They do not establish a shared causal mechanism across models. The GFP-containing expression vector also necessitates independent validation of the reactive oxygen species and membrane-potential measurements. Further work should establish physiological expression relevance, cell differentiation status, and the direction and specificity of calcium transfer.