The Mitochondrial UPR in Ischemic Protection

Mitochondria are central to ischemia-reperfusion (IR) injury and protection. The mitochondrial unfolded protein response (UPRmt) is a signaling pathway that responds to mitochondrial dysfunction and proteotoxic stress. Our preliminary data suggests that the UPRmt protects against IR injury, consistent with up-regulation of mitochondrial chaperone genes, ROS detoxification machinery, and glycolytic capacity. In the genetic model organism C. elegans, the UPRmt’s central mechanism of action has recently been described: mitochondrial proteotoxic stress regulates the matrix import and subsequent degradation of ATFS-1, a bZip transcription factor with dual targeting motifs. Under conditions of mild proteotoxic stress, matrix import is prevented through an ABC transport protein, HAF-1, acting in an undefined manner to suppress TIM/TOM activity. ATFS-1 instead traffics to the nucleus and activates a pro-survival repertoire of genes. Nuclear trafficking is both necessary and sufficient for protection, suggesting that the import of ATFS-1 into mitochondria provides a uniquely specific focal point for eliciting adaptation. This proposal aims to identify mechanisms through which the UPRmt protects C. elegans and to translate these findings to a mammalian cardiac model. Our approach will include defining mechanistic crosstalk with other signaling pathways that are also protective and will result in the identification of functional orthologs that perform similarly in mammals as ATFS-1 and HAF-1.