The mitochondrial unfolded protein response: A multitasking giant in the fight against human diseases.

Mitochondria, which serve as the energy factories of cells, are involved in cell differentiation, calcium homeostasis, amino acid and fatty acid metabolism and apoptosis. In response to environmental stresses, mitochondrial homeostasis is regulated at both the organelle and molecular levels to effectively maintain the number and function of mitochondria. The mitochondrial unfolded protein response (UPR) is an adaptive intracellular stress mechanism that responds to stress signals by promoting the transcription of genes encoding mitochondrial chaperones and proteases. The mechanism of the UPR in Caenorhabditis elegans (C. elegans) has been clarified over time, and the main regulatory factors include ATFS-1, UBL-5 and DVE-1. In mammals, the activation of the UPR involves eIF2α phosphorylation and the uORF-regulated expression of CHOP, ATF4 and ATF5. Several additional factors, such as SIRT3 and HSF1, are also involved in regulating the UPR. A deep and comprehensive exploration of the UPR can provide new directions and strategies for the treatment of human diseases, including aging, neurodegenerative diseases, cardiovascular diseases and diabetes. In this review, we mainly discuss the function of UPR, describe the regulatory mechanisms of UPR in C. elegans and mammals, and summarize the relationship between UPR and various human diseases.