Functional Insights into Novel Roles for Gap Junction Protein-Protein Interaction Networks in Liver and Brain

Abstract

Gap junctions are highly-conserved communicating junctions composed of the connexin family of proteins. In addition to this channel function, gap junctions mediate adhesive contacts at extracellular domains, and are host to a variety of signalling metabolites at intracellular surfaces. In this thesis, I explore the emerging theme of the connexin interactome. Starting with a non-biased proteomic approach, I identified endogenous protein interactions with the predominant liver and oligodendrocyte connexin, connexin32 (Cx32). Here, I identified novel mitochondrial protein interactions suggesting that Cx32 might localize to mitochondrial membranes, as has been reported for cardiac Cx43. Following proteomic quantitation of WT and Cx32 KO membranes, I determined that loss of Cx32 specifically induces mitochondrial protein expression. Bioenergetic analysis of isolated mitochondria then confirmed that oxygen consumption and rates of reactive oxygen species (ROS) generation were elevated in Cx32 KO mitochondria. In addition to novel intracellular connexin protein interactions, we hypothesized that connexin-mediated glial cell:cell interactions were responsible for mediating fate decisions in the complex hippocampal neurogenic niche environment. We identified that Cx32-mediated glial cell:cell interactions exert significant proliferative and fate specifying pressures on hippocampal progenitor cell types, wherein the loss of Cx32 enables improved histological and functional regeneration following excitotoxic injury. Together, this thesis identifies novel connexin-mediated signalling pathways that provide mechanistic insight into both intracellular and extracellular interactomedependent functions for Cx32, and outlines a potentially transformative avenue for brain repair.