A Noncanonical Role of Delta Protein Kinase C (δPKC) Phosphorylation of Troponin I in Cardiac Reperfusion Injury

Injury of the myocardium due to reperfusion following an ischemic period (ischemia/reperfusion injury; IR) is the consequence of an imbalance between the production of oxidants and the availability of endogenous antioxidants. Depriving the heart of oxygen and nutrients (ischemia) leads to impaired mitochondrial function, elevated mitochondrial fission, cardiac damage, and death. Paradoxically, restoring blood flow (reperfusion) to the heart following an ischemic event poses another type of insult in the form of increased mitochondrial dysfunction, apoptosis, and necrosis, resulting in cardiac failure. Our laboratory has found that δPKC mediates reperfusion injury; treatment with a selective inhibitor of δPKC, δV1‐1, at reperfusion reduces infarct size by 60% in a variety of animal models. One of several substrates of δPKC, cardiac troponin I (cTnI), undergoes partial proteolysis upon phosphorylation by δPKC during IR. Interestingly, using western blot and microscopy studies, we found that the N‐terminal fragment of cTnI co‐localizes with mitochondria following IR and that inhibition of δPKC by δV1‐1 inhibits this cleavage. To determine the role of phosphorylated cTnI, we rationally designed a highly selective inhibitor of cTnI phosphorylation by δPKC, ψTnI. ψTnI inhibits only cTnI phosphorylation and not the phosphorylation of pyruvate dehydrogenase kinase (PDK), myristoylated alanine rich C kinase substrate (MARCKS), signal transducers and activators of transcription (STAT), and glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) – substrates of δPKC that are elevated during reperfusion injury to the myocardium. ψTnI also diminishes cTnI association with mitochondria following reperfusion. Importantly, ψTnI treatment alone was sufficient to obviate acute IR injury in a whole heart ischemic model, reducing infarct size by over 70% and improving mitochondrial respiration when given at reperfusion. Additionally, ψTnI treatment at reperfusion of H9c2 cardiomyocytes restored mitochondrial oxygen consumption, preserved mitochondrial morphology, and rescued mitochondrial membrane potential in a dose‐dependent manner. We will determine the effects of cTnI phosphorylation and fragment association with mitochondria using loss‐ and gain‐of‐function mutations, live‐imaging, and functional assays. Together, our study identified a non‐contractile role for cTnI; in addition to regulating cardiac contractility, we find that cTnI regulates mitochondrial function following reperfusion injury to the heart. Support or Funding Information NIH grant R01‐HL052141 to DM‐R and AHA Postdoctoral Fellowship 19POST34380299 to AJL This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .