BS05 Nrf3-mediated mitochondrial superoxide promotes cardiomyocyte apoptosis and impairs cardiac functions by suppressing pitx2

Background Myocardial infarction (MI) elicits mitochondria reactive oxygen species (ROS) production and cardiomyocyte apoptosis. Nrf3 (Nuclear factor erythroid 2-related factor 3) has an established role in regulating redox signaling and tissue homeostasis. Herein, we aimed to uncover the exact role and potential mechanism of Nrf3 in injury-induced cardiac remodeling. Methods Global (Nrf3-KO) and cardiomyocyte-specific (NRF3△CM) Nrf3 knockout mice were subjected to MI or ischemia/reperfusion (I/R) injury, followed by functional and histopathological analysis. Primary neonatal mice (NMCMs) and rat (NRCMs) cardiomyocytes as well as cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) were used to detect cardiomyocyte apoptosis and mitochondria ROS production. Chromatin immunoprecipitation sequencing and immunoprecipitation–mass spectrometry analysis were used to uncover potential targets of Nrf3. MitoPQ administration and cardiomyocyte-specific AAV vector were used to further confirm the in vivo relevance of the identified signal pathways. Results Increased level of Nrf3 was observed in cardiomyocytes within border zone of infarcted human heart and murine cardiac tissues post-MI. Both global and cardiomyocyte-specific Nrf3 knockout significantly decreased injury-induced mitochondria ROS production and cardiomyocyte apoptosis, consequently improving cardiac functions. Additionally, cardiac-specific Nrf3 overexpression reverses the cardiac phenotypes observed in Nrf3-KO mice. Functional studies showed that Nrf3 promotes NMCM, NRCM and hiPSC-CM apoptosis by increasing mitochondria ROS production. Critically, restoring mitochondrial ROS using MitoParaquat blunts the beneficial effects of Nrf3 deletion on cardiac functions and remodeling. Mechanistically, the cardiac redox regulator Pitx2 was identified as one of the main target genes of Nrf3. Specifically, Nrf3 binds to Pitx2 gene promoter where it recruits hnRNPK and DNMT1 to increase DNA methylation and inhibit Pitx2 expression. Importantly, cardiac-specific knockdown of Pitx2 blunts the beneficial effects of Nrf3 deletion on cardiac functions and remodeling. Conclusions Nrf3 promotes injury-induced cardiomyocyte apoptosis and deteriorates cardiac functions by increasing mitochondria ROS production via suppressing Pitx2 expression. Conflict of Interest None