Abstract 14: Pim-1 Preserves Mitochondrial Morphology by Inhibiting Drp1 Translocation

Abstract

Rationale: Mitochondrial morphological dynamics affect the outcome of ischemic heart damage. Mitochondrial fission protein Dynamin Related Protein 1 (Drp1) is a mediator of mitochondrial morphological changes and cell death during ischemic injury. Mitochondrial integrity is maintained by cardioprotective kinase Pim1, which enhances resistance to apoptotic challenge and ischemia reperfusion injury. In this study we examine the relationship between Pim1 activity and Drp1 regulation of mitochondrial morphology in cardiomyocytes challenged by ischemia. Objective: To demonstrate that Pim1 inhibits Drp1 translocation to the mitochondria in response to ischemic injury. Methods and Results: Simulated ischemia and simulated ischemia reperfusion (sI & sI/R) induced mitochondrial fragmentation and cell death in neonatal rat cardiac myocytes (NRCM), respectively. Mitochondrial fragmentation accompanied Drp1 translocation to the mitochondria in NRCM. Inhibition of Drp1 by mdivi1 preserved mitochondrial reticular morphology and inhibited apoptotic cell death. Mice subjected to sI/R injury displayed Drp1 mitochondrial localization, while exposure to mdivi1 led to reduced infarct size. Interestingly, transgenic hearts overexpressing Pim1 decreased total Drp1 levels, increased phosphorylation of Drp1 at serine 637, and inhibited Drp1 localization to mitochondria while preserving reticular morphology after sI. In contrast, Pim1 dominant negative (PDN) transgenic hearts and NRCM exhibit increased Drp1 translocation to mitochondria and fragmented mitochondria. PDN hearts exhibit decreased phosphorylation of serine 637 and upregulation of BH3 protein PUMA, inducing Drp1 accumulation at mitochondria and increased sensitivity to apoptotic stimuli. In PDN NRCMs, overexpression of Puma dominant negative (PumaDN) attenuated localization of Drp1 to mitochondria and inhibited cell death during sI. Conclusion: Pim1 activity prevents Drp1 compartmentalization to the mitochondria and preserves reticular mitochondrial morphology in response to simulated ischemia. Therefore, selective manipulation of Pim1 should be pursued as a therapeutic target to maintain mitochondrial morphology for cardioprotection.