Panglial Gap Junctional Communication is Essential for Maintenance of Myelin in the CNS

Abstract

In this study, we have investigated the contribution of oligodendrocytic connexin47 (Cx47) and astrocytic Cx30 to panglial gap junctional networks as well as myelin maintenance and function by deletion of both connexin coding DNAs in mice. Biocytin injections revealed complete disruption of oligodendrocyte-to-astrocyte coupling in the white matter of 10-to 15-d-old Cx30/Cx47 double-deficient mice, while oligodendrocyte-to-oligodendrocyte coupling was maintained. There were no quantitative differences regarding cellular networks in acute brain slices obtained from Cx30/Cx47 double-null mice and control littermates, probably caused by the upregulation of oligodendrocytic Cx32 in Cx30/Cx47 double-deficient mice. We observed early onset myelin pathology, and ϳ40% of Cx30/Cx47 doubledeficient animals died within 42 to 90 d after birth, accompanied by severe motor impairments. Histological and ultrastructural analyses revealed severe vacuolization and myelination defects in all white matter tracts of the CNS. Furthermore, Cx30/Cx47 double-deficient mice exhibited a decreased number of oligodendrocytes, severe astrogliosis, and microglial activation in white matter tracts. Although less affected concerning motor impairment, surviving double-knock-out (KO) mice showed behavioral alterations in the open field and in the rotarod task. Vacuole formation and thinner myelin sheaths were evident also with adult surviving double-KO mice. Since interastrocytic coupling due to Cx43 expression and interoligodendrocytic coupling because of Cx32 expression are still maintained, Cx30/Cx47 double-deficient mice demonstrate the functional role of both connexins for interastrocytic, interoligodendrocytic, and panglial coupling, and show that both connexins are required for maintenance of myelin.

Oligodendroglia: metabolic supporters of neurons

“…In addition, double knockouts for the astrocyte hemichannels Cx43 and Cx30 develop widespread white matter pathology with impairment of oligodendrocyte maturation and myelin vacuolation, whereas mice with astrocyte-targeted loss of Cx43 or Cx30-null mice do not show signs of abnormal myelination (85)(86)(87). Double knockouts affecting both oligodendrocyte and astrocyte hemichannels (Cx47/ Cx30) develop a progressive phenotype with early vacuolization of myelin with microgliosis, astrogliosis, motor impairment, and early death (88). Glial fibrillary acidic protein (Gfap)-Cre-mediated depletion of astrocyte Cx43 in oligodendrocyte Cx32-null mice revealed a similar phenotype characterized by severe myelin vacuolization, astrocyte loss, and early death (89).…”

Disrupting MLC1 and GlialCAM and ClC-2 interactions in leukodystrophy entails glial chloride channel dysfunction

“…To examine whether these changes occur in vivo, we performed whole-cell patch clamp experiments in brain slices (Figs 6 and 7). Patch pipette solutions contained CsCl to suppress K þ currents and the gap junction blocker carbenoxolone to electrically isolate the patched cell from the panglial network 21 . Control experiments with transfected HEK cells confirmed that carbenoxolone did not affect ClC-2 currents ( Supplementary Fig.…”

Connexin-based channels contribute to metabolic pathways in the oligodendroglial lineage

“…However, the mechanisms underlying their energy metabolism, in particular the pathways involved in energy metabolite uptake and trafficking remain unidentified. Functional tests have shown that astrocytes and oligodendrocytes are connected by gap junctions to form panglial networks (Griemsmann et al, 2014;Ransom and Giaume, 2013;Tress et al, 2012). Moreover, astroglial connexin channels (gap junction channels and hemichannels) are permeable to glucose derivatives (2-NBDG) in both in vitro and ex vivo models (Blomstrand and Giaume, 2006;Retamal et al, 2007a), thus they provide the basis to form metabolic intercellular networks (Rouach et al, 2008).…”

“…This dependence might partly explain why OPCs are more vulnerable to oxygen-glucose deprivation than oligodendrocytes (Fern and Moller, 2000;Ziabreva et al, 2010). Moreover, likely due to deficient Cx47-based hemichannel properties, Cx47-null mice exhibit decreased oligodendroglial lineage cell numbers at P14, but gene knockdown does not influence myelination in adult mice (Tress et al, 2012). Finally, abnormal connexin expression is involved in limiting OPC recruitment and consequent remyelination failure in multiple sclerosis patients and in autoimmune encephalomyelitis mice (a model of multiple sclerosis) (Markoullis et al, 2012a(Markoullis et al, ,b, 2014.…”

“…However, it is not clear whether this gapjunction-mediated energy substrate pathway also exists between OPCs and astrocytes. Given that connexin-based channel functions are related to the development of astrocytes and oligodendrocytes (Tress et al, 2012;Venance et al, 1995;Von Blankenfeld et al, 1993), it is worthwhile exploring whether connexin-based channels also contribute to energy uptake in OPCs.…”