A Noncanonical Role for Troponin I In Cardiac Reperfusion Injury Following Delta Protein Kinase C (δPKC) Phosphorylation

Ischemia reperfusion (IR) injury, which is characterized by the paradoxical acceleration of damage associated with reoxygenation following ischemia, is a hallmark of myocardial infarction (MI) and is responsible for many post-MI complications, such as heart failure. IR injury is primarily mediated through signaling cascades that converge at mitochondria. However, developing therapeutics that target the specific mitochondrial factors that mediate IR damage has been challenging. Previous work in the Mochly- Rosen Lab has shown that inhibition of cTnI phosphorylation by delta PKC (δPKC) using a rationally designed peptide inhibitor protects against IR injury, suggesting that phosphorylated cTnI, a canonically cytoskeletal protein, plays a damaging role at the level of mitochondria. However, the underlying mechanism that precipitates the inhibitor’s protection is not well understood.

To further investigate, the rational design methodology of this inhibitor we called ѰTnI was validated using computational tools. Then live microscopy and high throughput image analysis was performed to investigated the localization of cTnI following IR. The C-terminal domain of cTnI co-localized with mitochondria in response to IR. Parameters such as mitochondrial morphology, mitochondrial membrane potential, mitochondrial ROS production all improved in the presence of ѰTnI. Lastly, in silico modeling demonstrated plausible mechanisms behind cTnI-mediated mitochondrial dysfunction.

Further work will attempt to identify the order of IR cellular events induced by δPKC phosphorylation of cTnI, including where the phosphorylation takes place and how ѰTnI prevents this phosphorylation. Additionally, investigation into cTnI’s mitochondrial interaction partners may reveal how cTnI-mediated mitochondrial dysfunction takes place, potentially leading to new rational design targets for more specific therapeutics.