Regulation of ageing by electrical synapses in the Nematode Caenorhabditis elegans

Abstract

Electrical synapses formed by gap junctions are abundant in nervous systems and critical for brain function. They allow not only the exchange of ions, but also of metabolites and second messengers and have been implicated in the transmission of damage or death signals between cells. However, it was not known if they play a role in the processes that regulate neural ageing and lifespan. In my PhD project, I sought to explore if gap junctions affect ageing and lifespan using the roundworm Caenorhabditis elegans. Gap junctions are present in virtually all cells and tissues of C. elegans and are formed by twenty-five innexin genes encoding gap junction subunits. I assayed lifespan of loss-of-function mutants of most C. elegans innexins and discovered that innexins have a significant impact on lifespan, some leading to an extension of lifespan while others accelerate the ageing process and shorten lifespan. Specifically, null mutations in unc-9, the most widely expressed innexin in the nervous system, extended lifespan by up to thirty-five percent compared to wild-type. Its effect on longevity is likely due to the intercellular coupling provided by UNC-9, as loss of the UNC-9-regulating stomatin unc-1 extends lifespan in the same manner. In follow-up experiments, I used RNA interference to ask if UNC-9 acts in specific sets of cells to modulate longevity. Its removal from glutamatergic neurons led to an increase in lifespan, whereas I found no effects of unc-9 knock-down in GABAergic, dopaminergic or cholinergic neurons or muscle. Interestingly, my RNAi results point to a potential neural circuit mostly consisting of mechanosensory and interneurons where coupling via UNC-9 limits lifespan. Subsequently, I exposed unc-9 mutants to a battery of tests which examined the animals’ healthspan and resistance to oxidative stress. These assays revealed that unc-9 mutants stay motile and responsive for longer. Furthermore, our results of experiments with pro- and anti- oxidative agents suggest that direct coupling through UNC-9 could facilitate the transmission of oxidative stress-linked signals that negatively impact longevity. We are only beginning to appreciate the diverse and complex roles of gap junctions in brain functioning and their roles in development and neuronal injury. My work for the first time reveals that gap junction coupling also regulates ageing and longevity.