Septin 7 interacts with Numb to preserve sarcomere structural organization and muscle contractile function

• Published in: eLife 2024-05, Vol.12
• Main Authors: De Gasperi, Rita, Csernoch, Laszlo, Dienes, Beatrix, Gonczi, Monika, Chakrabarty, Jayanta K, Goeta, Shahar, Aslan, Abdurrahman, Toro, Carlos A, Karasik, David, Brown, Lewis M, Brotto, Marco, Cardozo, Christopher P
• Format: Article
• Language: English
• Subjects: Adaptor proteins; Animals; Cell Biology; Cell division; Cytoskeleton; excitation–contraction coupling; Filaments; GTP-binding protein; Immunofluorescence; Immunoprecipitation; Intracellular Signaling Peptides and Proteins; Intracellular signalling; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Mice, Knockout; Morphology; Muscle contraction; Muscle Contraction - physiology; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - physiology; Muscle strength; Musculoskeletal system; Myotubes; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Numb; Numbl protein; Physiology; Protein Binding; Proteins; Proteomics; sarcomere structure; Sarcomeres; Sarcomeres - metabolism; Sarcopenia; Septin; Septins - genetics; Septins - metabolism; Skeletal muscle; Statistical analysis
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.89424

Here, we investigated the mechanisms by which aging-related reductions of the levels of in skeletal muscle fibers contribute to loss of muscle strength and power, two critical features of sarcopenia. Numb is an adaptor protein best known for its critical roles in development, including asymmetric cell division, cell-type specification, and termination of intracellular signaling. expression is reduced in old humans and mice. We previously showed that, in mouse skeletal muscle fibers, Numb is localized to sarcomeres where it is concentrated near triads; conditional inactivation of and a closely related protein -like ( ) in mouse myofibers caused weakness, disorganization of sarcomeres, and smaller mitochondria with impaired function. Here, we found that a single knockout of in myofibers causes reduction in tetanic force comparable to a double , knockout. We found by proteomics analysis of protein complexes isolated from C2C12 myotubes by immunoprecipitation using antibodies against Numb that Septin 7 is a potential Numb-binding partner. Septin 7 is a member of the family of GTP-binding proteins that organize into filaments, sheets, and rings, and is considered part of the cytoskeleton. Immunofluorescence evaluation revealed a partial overlap of staining for Numb and Septin 7 in myofibers. Conditional, inducible knockouts of led to disorganization of Septin 7 staining in myofibers. These findings indicate that Septin 7 is a Numb-binding partner and suggest that interactions between Numb and Septin 7 are critical for structural organization of the sarcomere and muscle contractile function.