Loss of MEGF10 Decreases the Number of Perisynaptic Schwann Cells and Innervation of Neuromuscular Junctions in Aging Mice

Abstract

Background and Aims

At the neuromuscular junction (NMJ), the synapse between motor neurons and muscle fibers, reside perisynaptic Schwann cells (PSCs) which are specialized glia that regulate the maintenance and repair of this synapse. While we know how PSC morphology and numbers change in aging and various neuromuscular disorders that adversely affect the NMJ, the molecular mechanisms that alter PSC functions remain unknown. In this study, we investigated whether MEGF10 in PSCs modulates NMJ stability in developing, healthy young adult, middle-aged, and axotomized mice. MEGF10 is a glial phagocytic receptor that is enriched in PSCs compared to other Schwann cells (SCs).

Methods

We isolated PSCs from a transgenic reporter mouse line to assess Megf10 expression at different ages and following nerve injury using qPCR. We then used a conditional mouse lacking Megf10 in all SCs, including PSCs (Megf10 SC-KO mice). We examined NMJs and axonal debris clearance in Megf10 SC-KO mice using confocal microscopy.

Results

We found that Megf10 expression in PSCs peaks during development and decreases during aging and following denervation of NMJs. NMJs were morphologically normal in developing and young adult Megf10 SC-KO mice. This was not the case in middle-aged Megf10 SC-KO mice, in which NMJs presented with fewer PSCs, decreased PSC coverage of the endplate, and decreased innervation in comparison to control mice. Following nerve injury-induced damage, axonal debris at the NMJ was cleared faster in Megf10 SC-KO mice; yet, the rate of reinnervation was unchanged compared to control mice.

Interpretation

The data in this study suggest that MEGF10 in PSCs functions to maintain PSC number and NMJ innervation during aging. This study also suggests important roles for MEGF10 in mediating the clearance of axonal debris at NMJs following nerve injury.