Association Between L‐OPA1 Cleavage/OMA1 Activity and Cardiac Function During Ischemia‐Reperfusion Injury in the Rat

Abstract

Cardiac ischemia‐reperfusion (IR) injury is a complex process associated with high ROS production, intracellular Ca2+ overload and ATP depletion that together lead to cell death. Structural and functional changes in mitochondria, particularly, the inner mitochondrial membrane (IMM) permeability play a critical role in IR‐induced cell death. Two potential intra‐mitochondrial factors can diminish the structural and functional integrity of the IMM: i) mitochondrial (matrix) swelling due to increased permeability transition (PT) that triggers the opening of PT pores (PTP), and ii) proteolytic cleavage of optic atrophy type 1 (OPA1), a dynamin‐like GTPase localized in the IMM that, in addition to the role in mitochondrial fusion, maintains the structural organization/integrity of the cristae. OPA1 is present in a long IMM‐bound (L‐OPA1) and a short‐soluble (S‐OPA1) forms. The latter results from L‐OPA1 proteolytic cleavage by one of its peptidases, OMA1, which is activated during the conditions that occur in response to oxidative stress such as IR. However, the relationship between cardiac/mitochondria function and L‐OPA1/cleavage/OMA1 activity in response to oxidative stress remains unclear. Here, we elucidated the effects of cardiac IR injury on L‐OPA1 cleavage and OMA1 activity in rats. Isolated and Langendorff‐mode perfused Sprague‐Dawley rat hearts were subjected to 25‐min of global ischemia followed by 90‐min reperfusion in the following groups: i) control (no IR), ii) IR, iii) IR+XJB (XJB‐5‐131, a mitochondria‐targeting electron and ROS scavenger), iv) IR+SfA (sanglifehrin A, a PTP inhibitor), and v) IR+XJB+SfA. Hearts were perfused with Krebs‐Henseleit solution supplemented with XJB, SfA or XJB+SfA. Isolated mitochondria were analyzed for respiratory control index (RCI), calcium‐induced swelling (a marker of PTP opening), ROS production, L‐OPA/S‐OPA1 protein levels, and OMA1 activity/protein levels. Our results show that IR hearts recovered 45% of the control (no IR) group. However, XJB and XJB+SfA increased the post‐ischemic recovery to 70% and 74%, respectively, compared to IR alone. XJB+SfA group was able to reduce mitochondrial ROS production with calcium addition in comparison to IR. Both basal and calcium‐induced swelling was affected in XJB and SfA treated hearts. L‐OPA1 levels reduced by 30% in IR hearts compared to control hearts. Neither XJB, SfA nor their combination prevented IR‐induced reduction of L‐OPA cleavage. Likewise, IR increased the OMA1 enzymatic activity that was remained unchanged in the presence of XJB and/or SfA. In conclusion, our data show that although IR stimulates OMA1 activity/L‐OPA1 cleavage, beneficial effects on cardiac function and mitochondrial swelling are not associated with prevention of OMA1 activation/L‐OPA1 proteolytic cleavage. This study suggests that in addition to mitochondrial swelling other mechanisms can be involved in OMA1 activation.Support or Funding InformationThis study was supported by the NIH NIGMS (Grants SC1GM128210 and R25GM061838).