Ablation of Sam50 is associated with fragmentation and alterations in metabolism in human myotubes.

The Sorting and Assembly Machinery (SAM) Complex functions in the assembly of β-barrel in the mitochondrial membrane. The SAM complex is made up of three subunits, Sam35, Sam37, and Sam50. While both Sam35 and Sam37 are peripheral membrane proteins that are not required for survival, Sam50 interacts with the MICOS complex to connect the inner and outer mitochondrial membranes and forms the mitochondrial intermembrane space bridging (MIB) complex. Specifically, Sam50 stabilizes the MIB complex for protein transport, respiratory chain complex assembly, and cristae integrity regulation. To structurally form and sustain the cristae, the MICOS complex assembles at the cristae junction and binds directly to Sam50. However, the role of Sam50 in overall mitochondrial structure and metabolism in skeletal muscle remains unclear. Here, we use SBF-SEM and Amira software perform 3D renderings of mitochondria and autophagosomes in human myotubes. Beyond this, Gas Chromatography-Mass Spectrometry-based metabolomics was utilized to interrogate differential changes of the metabolites in wild-type (WT) and Sam50 deficient myotubes. Ablation of Sam50 , revealed increases in ß-Alanine, propanoate, and phenylalanine, and tyrosine metabolism. Additionally, we observed that mitochondrial fragmentation and autophagosome formation was increased in Sam50 -deficient myotubes compared to control myotubes. Beyond this, the metabolomic analysis revealed an increase in amino acid metabolism and fatty acid metabolism. XF24 Seahorse Analyzer shows that oxidative capacity is further impaired upon ablation of Sam50 in both murine and human myotubes. Together, these data suggest Sam50 is critical for establishing and maintaining mitochondria, mitochondrial cristae structure, and mitochondrial metabolism.