Dysregulation of myelin synthesis and actomyosin function underlies aberrant myelin in CMT4B1 neuropathy

Proc Natl Acad Sci U S A. 2021 Mar 9;118(10):e2009469118. doi: 10.1073/pnas.2009469118.

Abstract

Charcot-Marie-Tooth type 4B1 (CMT4B1) is a severe autosomal recessive demyelinating neuropathy with childhood onset, caused by loss-of-function mutations in the myotubularin-related 2 (MTMR2) gene. MTMR2 is a ubiquitously expressed catalytically active 3-phosphatase, which in vitro dephosphorylates the 3-phosphoinositides PtdIns3P and PtdIns(3,5)P2, with a preference for PtdIns(3,5)P2 A hallmark of CMT4B1 neuropathy are redundant loops of myelin in the nerve termed myelin outfoldings, which can be considered the consequence of altered growth of myelinated fibers during postnatal development. How MTMR2 loss and the resulting imbalance of 3'-phosphoinositides cause CMT4B1 is unknown. Here we show that MTMR2 by regulating PtdIns(3,5)P2 levels coordinates mTORC1-dependent myelin synthesis and RhoA/myosin II-dependent cytoskeletal dynamics to promote myelin membrane expansion and longitudinal myelin growth. Consistent with this, pharmacological inhibition of PtdIns(3,5)P2 synthesis or mTORC1/RhoA signaling ameliorates CMT4B1 phenotypes. Our data reveal a crucial role for MTMR2-regulated lipid turnover to titrate mTORC1 and RhoA signaling thereby controlling myelin growth.

Keywords: Charcot-Marie-Tooth neuropathies; Schwann cells; myelin; myotubularin; phosphoinositides.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Charcot-Marie-Tooth Disease / genetics
  • Charcot-Marie-Tooth Disease / metabolism*
  • Mechanistic Target of Rapamycin Complex 1 / genetics
  • Mechanistic Target of Rapamycin Complex 1 / metabolism
  • Mice
  • Mice, Knockout
  • Myelin Sheath / genetics
  • Myelin Sheath / metabolism*
  • Myosin Type II / genetics
  • Myosin Type II / metabolism
  • Phosphatidylinositol Phosphates / biosynthesis*
  • Phosphatidylinositol Phosphates / genetics
  • Protein Tyrosine Phosphatases, Non-Receptor / genetics
  • Protein Tyrosine Phosphatases, Non-Receptor / metabolism*
  • Signal Transduction*
  • rhoA GTP-Binding Protein / genetics
  • rhoA GTP-Binding Protein / metabolism

Substances

  • Phosphatidylinositol Phosphates
  • phosphatidylinositol 3,5-diphosphate
  • Mechanistic Target of Rapamycin Complex 1
  • Mtmr2 protein, mouse
  • Protein Tyrosine Phosphatases, Non-Receptor
  • Myosin Type II
  • RhoA protein, mouse
  • rhoA GTP-Binding Protein

Supplementary concepts

  • Charcot-Marie-Tooth disease, Type 4B1