PMP2+ Schwann cells maintain the survival of large-caliber motor axons.

Abstract

Neurodegenerative diseases of both the central and peripheral nervous system are characterized by selective neuronal vulnerability, i.e., pathology that affects particular types of neurons. While much of this cell type selectivity may be driven by intrinsic differences among the neuron subpopulations, neuron-extrinsic mechanisms such as the selective malfunction of glial support cells may also play a role. Recently, we identified a population of Schwann cells (SCs) expressing Adamtsl1, Cldn14, and Pmp2 (a.k.a. PMP2+ SCs) that preferentially myelinate large-caliber motor axons. PMP2+ SCs are decreased in both ALS model mice and ALS patient nerves. Thus, PMP2+ SC dysfunction could contribute to motor-selective neuropathies. We engineered a tamoxifen-inducible Pmp2-CreERT2 mouse and expressed diphtheria toxin in PMP2+ SCs to assess the consequences of ablating this SC subtype in male and female mice. Loss of PMP2+ SCs led to significant loss of large-caliber motor axons with concomitant behavioral, electrophysiological, and ultrastructural defects. Subsequent withdrawal of tamoxifen restored both PMP2+ SCs and large-caliber motor axons and improved behavioral and electrophysiological readouts. Together, our findings highlight that the survival of large-caliber motor axons relies on PMP2+ SCs, demonstrating that malfunction of a specific SC subtype can lead to selective neuronal vulnerability.Significance Statement A hallmark of neurodegenerative disease is the differential vulnerability of neuron subtypes. While differences between neurons explain some differential sensitivity of neuronal subtypes, neuron-extrinsic mechanisms likely also contribute to selective neuronal vulnerability. Building on the recent identification of genetically distinct subtypes of myelinating Schwann cells, we test the hypothesis that Schwann cell subtypes support distinct classes of peripheral axons. To examine this, we ablated the PMP2+ subclass of myelinating Schwann cells and found preferential loss of large-caliber motor axons. These findings demonstrate that disrupting a specific SC subtype results in selective axonal vulnerability, highlighting the importance of considering neuron-extrinsic mechanisms when dissecting selective neuronal vulnerability in neurodegenerative disorders.