Abstract 16892: Cold Exposure Induces Drp1-Mediated Mitochondrial Elongation in Cardiomyocytes and is Associated With Sustained Respiratory Suppression

Abstract

Introduction: The effects of cold exposure on the heart are poorly understood. Cardiac hypothermia arises exclusively in the context of coincident ischemia, either in out-of-hospital cardiac arrest, or in the setting of cardiac surgery. Our lab has recently described an intraoperative increase in mitochondrial protein expression in atria of patients undergoing coronary artery bypass graft surgery. We have been exploring the role of cold stimulus as a potential trigger for mitochondrial remodeling. Methods: The effects of cold exposure on mitochondrial morphology, fusion/fission protein expression and respiration were assessed in H9C2 cardiomyocytes and the Langendorff-perfused rat heart. Results: H9C2 cardiomyocytes were exposed to a range of hypothermic temperatures (25-32°C) under normoxic conditions for up to 24 hrs. Immunofluorescence imaging revealed elongated mitochondria under hypothermic conditions, which was associated with decreased levels of active pDrp1 (Ser616) and its receptor mitochondrial fission factor (MFF). Seahorse respirometry (conducted at 37°C) revealed depression of oxygen consumption in cells previously exposed to hypothermic temperatures. Both morphological and respiratory phenomena persisted when cells were rewarmed to 37°C for 2 hours. In Drp1 siRNA-treated H9C2 cardiomyocytes, mitochondria exhibited elongated morphology as well as depression of oxygen consumption. In Langendorff perfused rat hearts, 1 hour normoxic perfusion at 28 or 32°C gave rise to a reduction in pDrp1(Ser616). Furthermore, reductions in pDrp1 levels persisted following a subsequent 1 hour rewarming at 37°C. Conclusions: Hypothermia promoted elongation of cardiac mitochondria via reduced fission activity of Drp1, which was also associated with suppression of cellular oxygen consumption. The presence of mitochondrial elongation and suppressed oxygen consumption in Drp1 siRNA-treated cells suggests a link between Drp1 activity and respiratory function. In cardiomyocytes and Langendorff-perfused hearts, cold-induced Drp1 inhibition persisted following rewarming, suggesting that hypothermia may sustainably inhibit Drp1 activity.