An intestinal Sir2-HSF1-ATGL1 pathway regulates lipolysis in C. elegans

Proteostasis maintenance and lipid metabolism are critical for survival and promote longevity, however, their coordination is largely unclear. Here we show that the heat shock factor HSF-1 and the proteostasis state regulates lipolysis in C. elegans. We find that in response to starvation, the sirtuin 1 ortholog SIR-2.1 activates lipolysis by upregulation of the adipose triglyceride lipase ATGL-1. In feeding worms, intestinal HSF-1 represses ATGL-1 expression and lipolysis via the microRNA system. In starving worms, SIR-2.1 suspends a miR-53- mediated suppression of lipolysis by inhibiting its HSF-1-dependent expression. The apparent antagonism of SIR-2.1 and HSF-1, distinct from their synergism at heat shock promoters suggests a context-specific regulation of HSF-1 by SIR-2.1. We demonstrate that the SIR-2.1 and protein kinase A pathways are both indispensable, and independently converge on ATGL- 1 for lipolysis. HSF-1 activation by proteostasis disturbances inhibits starvation-induced lipid mobilization, whereas its age-related decline limits fat deposition through atgl-1. Our findings reveal a crosstalk between proteostasis and lipid/energy metabolism, which may modulate stress resilience and aging.