Pelizaeus–Merzbacher-like disease is caused not only by a loss of connexin47 function but also by a hemichannel dysfunction

Abstract

Autosomal recessive mutations in the GJA12/GJC2 gene encoding the gap junction protein connexin47 (CÂ47) cause a form of Pelizaeus-Merzbacher-like disease (PMLD) with hypomyelination, nystagmus, impaired psychomotor development and progressive spasticity. We investigated the functional consequences of four CÂ47 missense mutations (G149S, G236R, T265A, and T398I) and one CÂ47 complex mutation (A98G_V99insT) by immunoblot analysis and immunocytochemistry in transfected communication-incompetent HeLa cells and in OLI-neu cells. All studied CÂ47 mutants, except G236R, generated stable proteins in transfected HeLa cells and OLI-neu cells. The mutants T265A and A98G_V99insT were retained in the ER, T398I formed gap junctional plaques at the plasma membrane, and G149S showed both, structures at the plasma membrane and ER localization. Two-microelectrode voltage clamp analyses in Xenopus laevis oocytes injected with wild-type and mutant CÂ47 cRNA revealed reduced hemichannel currents for G236R, T265A, and A98G_V99insT. In contrast, T398I revealed hemichannel currents comparable to wild-type. For CÂ47 mutant T398I, our results indicate a defect in hemichannel function, whereas CÂ47 mutants G149S, G236R, T265A, and A98G_V99insT are predicted to result in a loss of CÂ47 hemichannel function. Thus, PMLD is likely to be caused by two different disease mechanisms: a loss of function and a dysfunction.

Rapid identification of mutations in GJC2 in primary lymphoedema using whole exome sequencing combined with linkage analysis with delineation of the phenotype

“…It is of interest that there appear to be at least two mechanisms for the effect of mutations in PMLD—namely, a loss of hemichannel function, or in some cases a dysfunction 32 33. To complicate the picture further, a mutation identified by Ferrell et al as causative in lymphoedema, p.Gly149Ser, is also reported as being causative for PMLD 33. A mechanism to explain this is currently difficult, especially as this mutation is one of those proposed to be loss of function of hemichannels in PMLD rather than dysfunction 33…”

Gap junctions in inherited human disorders of the central nervous system

“…[80] However, recent work suggests that at least in cultured astrocytes, pannexin 1 and not Cx43 is responsible for the membrane conductances and permeabilities ascribed to astrocytic hemichannels. [81] Hemichannel activities ascribed to Cx30, [82, 83] Cx47, [84] Cx32, [85-87] and Cx31.3 [21] have all been identified in cultured cells.…”

A novelGJA3mutation associated with congenital nuclear pulverulent and posterior polar cataract in a chinese family

“…On the other hand, it is reported that the altered Cx hemichannel function may lead to cell death and thus causes cataracts [Minogue et al, 2009]. The Cx46G2D significantly inhibited the hemichannel permeability, may therefore lead to ionic and biochemical changes, disrupted the cells' ability to maintain homeostasis [Diekmann et al, 2010;Matos et al, 2008], and ultimately resulted in apoptosis.…”