Cataract-causing mutation of human connexin 46 impairs gap junction, but increases hemichannel function and cell death.

Qian Ren,Manuel A Riquelme,Ji Xu,Bruce J Nicholson,Jean X Jiang,Xiang Yan,Sumin Gu

doi:10.1371/journal.pone.0074732

Abstract

Connexin channels play a critical role in maintaining metabolic homeostasis and transparency of the lens. Mutations in connexin genes are linked to congenital cataracts in humans. The G143R missense mutation on connexin (Cx) 46 was recently reported to be associated with congenital Coppock cataracts. Here, we showed that the G143R mutation decreased Cx46 gap junctional coupling in a dominant negative manner; however, it significantly increased gap junctional plaques. The G143R mutant also increased hemichannel activity, inversely correlated with the level of Cx46 protein on the cell surface. The interaction between cytoplasmic loop domain and C-terminus has been shown to be involved in gating of connexin channels. Interestingly, the G143R mutation enhanced the interaction between intracellular loop and Cx46. Furthermore, this mutation decreased cell viability and the resistance of the cells to oxidative stress, primarily due to the increased hemichannel function. Together, these results suggest that mutation of this highly conserved residue on the cytoplasmic loop domain of Cx46 enhances its interaction with the C-terminus, resulting in a reduction of gap junction channel function, but increased hemichannel function. This combination leads to the development of human congenital cataracts.

Highlights

The crystalline lens is a transparent, avascular, biconvex structure in the anterior part of eye, which helps to refract and focus light on the retina
This mutation decreased cell viability and the resistance of the cells to oxidative stress, primarily due to the increased hemichannel function. These results suggest that mutation of this highly conserved residue on the cytoplasmic loop domain of Cx46 enhances its interaction with the C-terminus, resulting in a reduction of gap junction channel function, but increased hemichannel function
We focused on a human mutation of a highly conserved residue in the Cx46 protein, the gene (GJA3) linked to human congenital Coppock cataracts in a four-generation Chinese family

Summary

Introduction

The crystalline lens is a transparent, avascular, biconvex structure in the anterior part of eye, which helps to refract and focus light on the retina. The lens consists of three parts, the outermost lens capsule, the interior lens fiber that forms the bulk of lens, and the lens epithelium, which is located between other two structures and only present on anterior side [1]. The fiber cells are linked to each other and connected with cells at the lens surface via gap junction channels, forming a large intercellular communication network. Each connexon consists of six connexins, a family of membrane proteins containing 21 members in humans [5]. Connexins have four conserved transmembrane domains, two extracellular loop domains, one intracellular loop domain, and cytoplasmic NH2- and COOHterminal domains. Compared with conserved transmembrane domains, extracellular loop and cytoplasmic NH2-terminal, the intracellular loop and COOH-terminal domains are highly variable between family members

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