Mitochondrial Precursor Overaccumulation Stress

Damage to mitochondria imparts multifaceted cellular stress that extends beyond bioenergetic deficit. One newly emerged example is mitochondrial precursor overaccumulation stress (mPOS). mPOS is marked by impaired mitochondrial protein import, causing the toxic accumulation and aggregation of unimported mitochondrial precursor proteins in the cytosol. Analogous to the well-studied endoplasmic reticulum stress, which blocks proteins from leaving the cell, mPOS can impose a drastic proteostatic burden in the cytosol and closely interconnects with cell signaling pathways. Here, we review how researchers discovered mPOS and discuss its central importance in several major mitochondria-induced stress signaling pathways. We then focus on the emerging field of mPOS in cell demise and human disease, and we present recent evidence that mPOS can affect cell fitness and survival independent of bioenergetics. Looking forward, mPOS may provide a complementary or alternative pathogenic mechanism to bioenergetic deficit for classic mitochondriopathy and many aging-associated degenerative diseases involving mitochondrial stress.