Rapamycin improves peripheral nerve myelination while it fails to benefit neuromuscular performance in neuropathic mice

Abstract

Charcot–-Marie–Tooth disease type 1A (CMT1A) is a hereditary peripheral neuropathy characterized by progressive demyelination and distal muscle weakness. Abnormal expression of peripheral myelin protein 22 (PMP22) has been linked to CMT1A and is modeled by Trembler J (TrJ) mice, which carry the same leucine to proline substitution in PMP22 as affected pedigrees. Pharmacologic modulation of autophagy by rapamycin in neuron-Schwann cell explant cultures from neuropathic mice reduced PMP22 aggregate formation and improved myelination. Here we asked whether rapamycin administration by food supplementation, or intraperitoneal injection, could alleviate the neuropathic phenotype of affected mice and improve neuromuscular performance. Cohorts of male and female wild type (Wt) and TrJ mice were assigned to placebo or rapamycin treatment starting at 2 or 4months of age and tested monthly on the rotarod. While neither long-term feeding (8 or 10months) on rapamycin-enriched diet, or short-term injection (2months) of rapamycin improved locomotor performance of the neuropathic mice, both regimen benefited peripheral nerve myelination. Together, these results indicate that while treatment with rapamycin benefits the myelination capacity of neuropathic Schwann cells, this intervention does not improve neuromuscular function. The observed outcome might be the result of the differential response of nerve and skeletal muscle tissue to rapamycin.