Mst1 regulates post-infarction cardiac injury through the JNK-Drp1-mitochondrial fission pathway

BACKGROUND: Post-infarction cardiac injury is closely associated with cardiac remodeling and heart dysfunction. Mammalian STE20-like kinase 1 (Mst1), a regulator of cellular apoptosis, is involved in cardiac remodeling in post-infarction heart, but the mechanisms remain poorly defined. We aimed to explore the role of Mst1 in regulating chronic post-infarction cardiac injury, with a focus on mitochondrial homoeostasis. METHODS: Wild-type (WT) and Mst1-knockout mice were as the cardiac myocardial infarction model. Cardiac fibrosis, myocardial inflammation response, heart dysfunction and cardiomyocyte death were measured in vivo using immunohistochemistry, immunofluorescence, western blot, qPCR and TUNEL assays. Cardiomyocytes were isolated from WT and Mst1-knockout mice, and a chronic hypoxia model was used to induce damage. Mitochondrial function was determined via JC1 staining, ROS measurement, cyt-c leakage detection and mitochondrial apoptotic pathways analysis. Mitochondrial fission was observed using immunofluorescence. A pathway activator and inhibitor were applied to establish the signaling pathways involved in regulating mitochondrial homeostasis. RESULTS: Our study demonstrated that Mst1 expression was significantly upregulated in the heart post-infarction. Activated Mst1 induced cardiac fibrosis, an excessive inflammatory response, and cardiomyocyte death, whereas the genetic ablation of Mst1 protected the myocardium against chronic post-infarction injury. Function assays showed that upregulation of Mst1 activity contributed to JNK pathway activation, which led to Drp1 migration from the cytoplasm onto the surface of the mitochondria, indicative of mitochondrial fission activation. Excessive mitochondrial fission caused mitochondrial fragmentation, resulting in mitochondrial potential collapse, ROS overproduction, mitochondrial pro-apoptotic leakage into the cytoplasm, and the initiation of caspase-9-mediated mitochondrial apoptosis. By contrast, Mst1 deletion helped to maintain mitochondrial structure and function, sending pro-survival signals to the cardiomyocytes. CONCLUSIONS: Our results identify Mst1 as a malefactor in the development of post-infarction cardiac injury and that it acts through the JNK-Drp1-mitochondrial fission pathway.