Preserved myelin integrity and reduced axonopathy in connexin32-deficient mice lacking the recombination activating gene-1.

Mice heterozygously deficient for myelin protein zero (P0) mimicking human Charcot-Marie-Tooth (CMT) disease 1B show T-lymphocyte and macrophage upregulation in peripheral nerves, which aggravates and modulates the genetically mediated demyelinating neuropathy. In connexin32 (cx32)-deficient (cx32(def)) mice, which mimic the X-linked dominant form of CMT (CMTX), T-lymphocyte and macrophage numbers are also significantly elevated in peripheral nerves. To test the hypothesis that immune cells are indeed pathogenic in this model, we cross-bred cx32(def) mice with recombination activating gene-1 (RAG-1)-deficient mice, which lack mature T- and B-lymphocytes. In these immunoincompetent double mutants, the number of endoneurial macrophages was reduced. Furthermore, features indicative of myelin degeneration and axonopathic changes were mitigated in the RAG-1-deficient double mutants, whereas enlarged periaxonal Schwann cell collars, a hallmark specific for cx32-mutants, were not reduced. Since both cx32- and P0 deficiency lead to similar immunopathogenic processes, we conclude that immune-mediated demyelination may be a feature common to many CMT-like neuropathies independent of the genetic origin.