Inter-tissue communication of mitochondrial stress in aging.

The protein homeostasis in mitochondria is critical for the normal physiological function of cells. To cope with mitochondrial stress, cells elicit specific stress response named mitochondrial unfolded protein response (UPR), to maintain mitochondrial homeostasis and repair mitochondrial function. Although severe damage to mitochondria is detrimental, studies in worms, flies, and mice have shown that mild mitochondrial damage promotes longevity by activating UPR. Interestingly, UPR can also be induced in a cell non-autonomous manner in cells or tissues which are not directly experiencing mitochondrial stress. The secreted molecules called "mitokine" are responsible for the mitochondrial stress communication between different tissues. This inter-tissue regulation of mitochondrial stress response systematically coordinates the adaptation ability which is closely associated with aging and a variety of diseases such as neurodegeneration and cancer. In this review, we summarize recent advances about inter-tissue mitochondrial stress communications, and introduce the current knowledge about the "mitokine" and its regulation on aging for further studies.