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

Abstract

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.

Transgenic Expression of HumanConnexin32in Myelinating Schwann Cells Prevents Demyelination inConnexin32-Null Mice

“…Using a rat Mpz promoter, we were able to show that mouse myelinating Schwann cells express human Cx32, that human Cx32 is properly localized to incisures and paranodes, and that human Cx32 "rescues" the demyelinating phenotype in cx32 Ϫ/Y Schwann cells. That the selective expression of human Cx32 in myelinating Schwann cells is sufficient to rescue the phenotype of cx32 Ϫ/Y mice indicates that demyelination initiates the complex events of neuropathy, which includes immune-mediated damage and axonal loss (Kobsar et al, 2002(Kobsar et al, , 2003. Cell autonomy and the pathogenesis of demyelinating neuropathies Dominant mutations in PMP22, MPZ, EGR2, LITAF/SIMPLE, and GJB1, as well as recessive mutations in GDAP1, MTMR2, MTMR13, KIAA1985, NDRG1, PRX, and EGR2 cause demyelinating neuropathies http://www.molgen.ua.ac.be/CMTMutations/DataSource/MutByGene.cfm).…”

Intrathecal gene therapy rescues a model of demyelinating peripheral neuropathy

“…Macrophages were identified in semithin sections at 400× magnification as cells laden with myelin debris, devoid of a basement membrane, and extending small, microvilli-like processes, as described previously (16,46). The macrophage count was calculated as the ratio per 1,000 myelinated fibers, to account for size differences between different roots and nerves.…”

“…To further examine the effect of treatment on inflammation, a well-characterized feature of Cx32 KO mice (16,17), we also immunostained cryosections of lumbar roots and sciatic nerves from 8-mo-old mock-treated (n = 4) and fully treated (n = 4) mice with inflammatory cell markers. This analysis revealed lower numbers of CD68 + macrophages, CD3 + T lymphocytes, and CD45 + leukocytes in anterior spinal roots (Fig.…”

The Role of Gap Junctions in Charcot-Marie-Tooth Disease

“…Finally, a number of studies support the role of secondary immune mechanisms in the pathological changes observed in CMT1X mouse models (Kobsar et al, 2003;Groh et al, 2010). This appears to be a more general phenomenon shared by other inherited demyelinating neuropathies (Ip et al, 2006).…”