Progressive axonopathy when oligodendrocytes lack the myelin protein CMTM5

Abstract

Oligodendrocytes facilitate rapid impulse propagation along the axons they myelinate and support their long-term integrity. However, the functional relevance of many myelin proteins has remained unknown. Here we find that expression of the tetraspan-transmembrane protein CMTM5 (Chemokine-like factor-like MARVEL-transmembrane domain containing protein 5) is highly enriched in oligodendrocytes and CNS myelin. Genetic disruption of the Cmtm5-gene in oligodendrocytes of mice does not impair the development or ultrastructure of CNS myelin. However, oligodendroglial Cmtm5-deficiency causes an early-onset progressive axonopathy, which we also observe in global and in tamoxifen-induced oligodendroglial Cmtm5-mutants. Presence of the Wlds mutation ameliorates the axonopathy, implying a Wallerian degeneration-like pathomechanism. These results indicate that CMTM5 is involved in the function of oligodendrocytes to maintain axonal integrity rather than myelin biogenesis.

CMTM5 - a novel CNS myelin protein involved in preserving axonal integrity

“…Myelin samples for proteome analysis were prepared by Ramona Jung (Neurogenetics group, MPI-EM, Göttingen). The whole procedure for proteome experiments was described in (Buscham et al, 2021) as follows: The Insolution digestion of myelin proteins according to an automated filter-aided sample preparation (FASP)…”

“…Preparation of cryosections was performed as described in (Buscham et al, 2021) Slides were dried for 30 minutes at room temperature and stored at -20°C until further use.…”

“…Protocol for the preparation of retinae and quantification of RGC number was described in (Buscham et al, 2021): To assess retinal ganglion cell numbers (RGC), eyes of 1 year old Cmtm5 -/mice and respective controls were dissected and fixed for one hour with 4% PFA/Phosphate Buffer (PB). Eyes were then rinsed in PB and retinae were dissected as follows.…”

“…TEM sections were prepared as described in (Buscham et al, 2021): Ultrathin (50nm) sections were prepared using a PTPC Powertome Ultramicrotome (RMC, Tuscon Arizona, USA) and a diamond knife (Diatome AG, Biel, Switzerland). Sections were cut and collected on formwar coated cooper grids (AGAR scientific, Essex, UK).…”

“…Samples were prepared according to (Buscham et al, 2021;Steyer et al, 2020). In short, the dissected samples were immersed in primary fixative and processed with a modified OTO-protocol (Deerinck et al, 2010), as described previously (Weil et al, 2018).…”