Depolarization causes the formation of a ternary complex between GlialCAM, MLC1 and ClC-2 in astrocytes: implications in megalencephalic leukoencephalopathy

Hum Mol Genet. 2017 Jul 1;26(13):2436-2450. doi: 10.1093/hmg/ddx134.

Abstract

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare type of leukodystrophy caused by mutations in either MLC1 or GLIALCAM. GlialCAM is necessary for the correct targeting of MLC1, but also for the targeting of the Cl- channel ClC-2. Furthermore, GlialCAM modifies ClC-2 functional properties in vitro. However, in vivo studies in GlialCAM-/- mice have shown that the modification of ClC-2 activity only occurs in oligodendrocytes, despite GlialCAM and ClC-2 being expressed in astrocytes. Thus, the relationship between GlialCAM, MLC1 and ClC-2 in astrocytes is unknown. Here, we show that GlialCAM, ClC-2 and MLC1 can form a ternary complex in cultured astrocytes, but only under depolarizing conditions. We also provide biochemical evidences that this ternary complex exists in vivo. The formation of this complex changes ClC-2 localization in the membrane and its functional properties. ClC-2 association with GlialCAM/MLC1 depends on calcium flux through L-type calcium channels and activation of calcium-dependent calpain proteases. Based on these studies, we propose that the chloride influx mediated by GlialCAM/MLC1/ClC-2 in astrocytes may be needed to compensate an excess of potassium, as occurs in conditions of high neuronal activity. We suggest that a defect in this compensation may contribute to the pathogenesis of MLC disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Astrocytes / metabolism
  • Brain / metabolism
  • Brain Diseases / pathology
  • Calcium Channels, L-Type / genetics
  • Cell Adhesion Molecules, Neuron-Glia / metabolism*
  • Chloride Channels
  • Cysts / genetics
  • Cysts / metabolism*
  • HEK293 Cells
  • HeLa Cells
  • Hereditary Central Nervous System Demyelinating Diseases / genetics
  • Hereditary Central Nervous System Demyelinating Diseases / metabolism*
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Nerve Tissue Proteins / metabolism*
  • Protein Transport / genetics

Substances

  • Calcium Channels, L-Type
  • Cell Adhesion Molecules, Neuron-Glia
  • Chloride Channels
  • ClC-2 chloride channels
  • GlialCAM protein, mouse
  • MLC1 protein, human
  • Membrane Proteins
  • Mlc1 protein, mouse
  • Nerve Tissue Proteins

Supplementary concepts

  • Megalencephalic leukoencephalopathy with subcortical cysts