Abstract

Mitochondrial fission, regulated by dynamin-related protein-1 (Drp1), is a newly recognized determinant of mitochondrial function, but its contribution to left ventricular (LV) impairment following ischemia-reperfusion (IR) injury is unknown. We report that Drp1 activation during IR results in LV dysfunction and that Drp1 inhibition is beneficial. In both isolated neonatal murine cardiomyocytes and adult rat hearts (Langendorff preparation) mitochondrial fragmentation and swelling occurred within 30 min of IR. Drp1-S637 (serine 637) dephosphorylation resulted in Drp1 mitochondrial translocation and increased mitochondrial fission. The Drp1 inhibitor Mdivi-1 preserved mitochondrial morphology, reduced cytosolic calcium, and prevented cell death. Drp1 siRNA similarly preserved mitochondrial morphology. In Langendorff hearts, Mdivi-1 reduced mitochondrial reactive oxygen species, improved LV developed pressure (92±5 vs. 28±10 mmHg, P<0.001), and lowered LV end diastolic pressure (10±1 vs. 86±13 mmHg, P<0.001) following IR. Mdivi-1 was protective if administered prior to or following ischemia. Because Drp1-S637 dephosphorylation is calcineurin sensitive, we assessed the effects of a calcineurin inhibitor, FK506. FK506 treatment prior to IR prevented Drp1-S637 dephosphorylation and preserved cardiac function. Likewise, therapeutic hypothermia (30°C) inhibited Drp1-S637 dephosphorylation and preserved mitochondrial morphology and myocardial function. Drp1 inhibition is a novel strategy to improve myocardial function following IR.