HSF-1 promotes longevity through ubiquilin-1 dependent mitochondrial remodelling

Impaired protein homeostasis promotes age-associated tissue dysregulation, presenting a need for therapeutic approaches that can restore proteome integrity. The heat shock factor HSF-1 is the master transcriptional regulator of proteostasis and regulates the expression of heat shock proteins (HSPs), which facilitate proper protein folding, localisation, and degradation. Increased HSF-1 activity can suppress proteotoxicity and enhance longevity across species. Studies into the mechanisms behind these beneficial effects have mostly focused on HSPs; however, the precise mechanisms by which increased HSF-1 activity extends lifespan are not known. To address this, we conducted an RNAi screen for genes that promote longevity, in C. elegans over expressing HSF-1 (hsf-1 OE). We found that ubiquilin-1 (ubql-1), a multifaceted shuttle protein that functions in protein degradation pathways is necessary for full lifespan extension in hsf-1OE worms. Surprisingly, we find that lack of ubql-1 does not impact proteostasis capacity, but does alter mitochondrial dynamics, in hsf-1 OE worms. These effects are independent of mitophagy or the mitochondrial unfolded protein response (mitoUPR) suggesting enhanced turnover of mitochondrial outer membrane proteins may be important for increased longevity via the HSF-1-ubiquilin-1 axis. Additionally, we reveal a role for ubql-1, a protein quality control regulator in regulating lipid homeostasis in hsf-1 OE animals. Lack of ubql-1 in hsf-1 OE animals supresses the expression of a key mitochondrial β-oxidation and lipid mobilization gene regulated by NHR-49 - acyl-CoA synthetase-2, ACS-2 amongst other genes. We propose that ubql-1 is required for mito-fusion and metabolic modulations that promote longevity in hsf-1 OE by interacting with NHR-49.