Age‐dependent heat shock hormesis to HSF‐1 deficiency suggests a compensatory mechanism mediated by the unfolded protein response and innate immunity in young Caenorhabditis elegans.

The transcription factor HSF‐1 (heat shock factor 1) acts as a master regulator of heat shock response in eukaryotic cells to maintain cellular proteostasis. The protein has a protective role in preventing cells from undergoing ageing, and neurodegeneration, and also mediates tumorigenesis. Thus, modulating HSF‐1 activity in humans has a promising therapeutic potential for treating these pathologies. Loss of HSF‐1 function is usually associated with impaired stress tolerance. Contrary to this conventional knowledge, we show here that inactivation of HSF‐1 in the nematode Caenorhabditis elegans results in increased thermotolerance at young adult stages, whereas HSF‐1 deficiency in animals passing early adult stages indeed leads to decreased thermotolerance, as compared to wild‐type. Furthermore, a gene expression analysis supports that in young adults, distinct cellular stress response and immunity‐related signaling pathways become induced upon HSF‐1 deficiency. We also demonstrate that increased tolerance to proteotoxic stress in HSF‐1‐depleted young worms requires the activity of the unfolded protein response of the endoplasmic reticulum and the SKN‐1/Nrf2‐mediated oxidative stress response pathway, as well as an innate immunity‐related pathway, suggesting a mutual compensatory interaction between HSF‐1 and these conserved stress response systems. A similar compensatory molecular network is likely to also operate in higher animal taxa, raising the possibility of an unexpected outcome when HSF‐1 activity is manipulated in humans. [ABSTRACT FROM AUTHOR]