Exploring the role of the unfolded protein response in C. elegans neurons
The nervous system of C. elegans plays a role in the orchestration of systemic stress responses. One of these stress responses, the unfolded protein response of the endoplasmic reticulum (UPRER), is activated to re-establish protein homeostasis (proteostasis) upon the detection of ER stress. Overexpression of active, spliced XBP-1 (XBP-1s), a transcription factor that acts downstream of the UPRER kinase/endoribonuclease IRE-1, in the nervous system of C. elegans increases the lifespan and healthspan of worms through UPRER induction in the intestine cell non-autonomously. To investigate XBP-1s-dependent changes in the nervous system of these animals, we conducted tissue-specific RNA-Seq in neurons. This approach allowed us to characterise differentially regulated neuronal and synaptic components, which may mediate changes to the nervous system that cause the release of inter-tissue UPRER-activating signals. Furthermore, we extended our tissue-specific RNA-Seq analyses to the intestine, using intestinal cells from neuronal xbp-1s- or intestinal xbp-1s-overexpressing worms. We identified lysosomal gene upregulation in the intestine, which leads to activation of intestinal lysosomes downstream of neuronal xbp-1s. Moreover, comparison of cell autonomous and cell non-autonomous targets of XBP-1s within the intestine showed that XBP-1s has different but overlapping sets of target genes via different activation mechanisms. We also employed a candidate screening approach based on our previous finding that neurotransmitter secretion is required for intestinal UPRER activation upon neuronal xbp-1s overexpression, and identified positive and negative regulators of intestinal UPRER activation. This showed that distal UPRER activation relies on tyramine/octopamine production, and is modulated by the worm TGF-β homologue DAF-7. We then asked whether neuronal xbp-1s can affect other systemic outputs requiring neuron-specific functions, such as the regulation of behaviour. We found that a branch of the neuronal circuitry required to activate UPRER in the intestine following neuronal XBP-1s overexpression is also required to generate neuronal xbp-1s-dependent behavioural phenotypes in food-leaving and reproduction. These findings suggest that inter-tissue UPRER activation, increased longevity and healthspan can be coordinately regulated with stress-responsive behaviour by the activation of XBP-1s in the nervous system.