In vivo evidence that TRAF4 is required for central nervous system myelin homeostasis

PLoS One. 2012;7(2):e30917. doi: 10.1371/journal.pone.0030917. Epub 2012 Feb 17.

Abstract

Tumor Necrosis Factor Receptor-Associated Factors (TRAFs) are major signal transducers for the TNF and interleukin-1/Toll-like receptor superfamilies. However, TRAF4 does not fit the paradigm of TRAF function in immune and inflammatory responses. Its physiological and molecular functions remain poorly understood. Behavorial analyses show that TRAF4-deficient mice (TRAF4-KO) exhibit altered locomotion coordination typical of ataxia. TRAF4-KO central nervous system (CNS) ultrastructure shows strong myelin perturbation including disorganized layers and disturbances in paranode organization. TRAF4 was previously reported to be expressed by CNS neurons. Using primary cell culture, we now show that TRAF4 is also expressed by oligodendrocytes, at all stages of their differentiation. Moreover, histology and electron microscopy show degeneration of a high number of Purkinje cells in TRAF4-KO mice, that was confirmed by increased expression of the Bax pro-apoptotic marker (immunofluorescence), TUNEL analysis, and caspase-3 activation and PARP1 cleavage (western blotting). Consistent with this phenotype, MAG and NogoA, two myelin-induced neurite outgrowth inhibitors, and their neuron partners, NgR and p75NTR were overexpressed (Q-RT-PCR and western blotting). The strong increased phosphorylation of Rock2, a RhoA downstream target, indicated that the NgR/p75NTR/RhoA signaling pathway, known to induce actin cytoskeleton rearrangement that favors axon regeneration inhibition and neuron apoptosis, is activated in the absence of TRAF4 (western blotting). Altogether, these results provide conclusive evidence for the pivotal contribution of TRAF4 to myelination and to cerebellar homeostasis, and link the loss of TRAF4 function to demyelinating or neurodegenerative diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging / pathology
  • Animals
  • Behavior, Animal / physiology
  • Blotting, Western
  • Body Weight / physiology
  • Cells, Cultured
  • Central Nervous System / metabolism*
  • Central Nervous System / pathology
  • Central Nervous System / physiopathology
  • Fluorescent Antibody Technique
  • GPI-Linked Proteins / metabolism
  • Homeostasis*
  • Locomotion / physiology
  • Mice
  • Mice, Knockout
  • Myelin Proteins / metabolism
  • Myelin Sheath / metabolism*
  • Myelin Sheath / pathology
  • Myelin-Associated Glycoprotein / metabolism
  • Nerve Degeneration / metabolism
  • Nerve Degeneration / pathology
  • Nerve Degeneration / physiopathology
  • Neurites / metabolism
  • Neurons / metabolism
  • Neurons / pathology
  • Nogo Proteins
  • Oligodendroglia / metabolism
  • Oligodendroglia / pathology
  • Purkinje Cells / metabolism
  • Purkinje Cells / pathology
  • Receptors, Nerve Growth Factor / metabolism
  • Signal Transduction
  • TNF Receptor-Associated Factor 4 / deficiency
  • TNF Receptor-Associated Factor 4 / metabolism*
  • rhoA GTP-Binding Protein / metabolism

Substances

  • GPI-Linked Proteins
  • Myelin Proteins
  • Myelin-Associated Glycoprotein
  • Nogo Proteins
  • Omg protein, mouse
  • Receptors, Nerve Growth Factor
  • Rtn4 protein, mouse
  • TNF Receptor-Associated Factor 4
  • TNFRSF16 protein, mouse
  • rhoA GTP-Binding Protein