Calcium Regulation of the Mitochondrial Permeability Transition Pore during Ischemia Reperfusion Injury of the Heart
The objective of this work was to elucidate the molecular mechanisms and functional consequences of non-canonical regulation of Glycogen Synthase Kinase 3 (GSK-3) in the process of Ischemia/Reperfusion (I/R) injury. The current primary treatment for myocardial infarction (MI) is to open the occluded vessel. However, this leads to a second wave of tissue damage known as I/R injury. A major event leading to the secondary cell death during I/R is the sensitization and opening of the mitochondrial permeability transition pore (mPTP). It has been shown that GSK-3 plays a regulatory role in this process, but the exact mechanism remains unknown. GSK-3 was first discovered as negative regulators of glycogen synthase and has two isoforms, α and β. The two isoforms are ubiquitously expressed at equivalent levels and have 98% structural homology but differ in the N and C terminus; GSK-3α has an extended poly-glycine rich N-terminus relative to GSK-3β. GSK-3β activity is protective during the ischemic phase, but detrimental during the reperfusion phase of I/R injury. Additionally, inhibition of GSK-3β activity measured by canonical S9 phosphorylation or by addition of GSK-3 inhibitor SB216763, has been implicated as a necessary component to both Pre- and Post-conditioning mediated cardioprotection. Canonical regulation of GSK-3β is mediated through the protein kinase B (PKB/AKT) phosphorylation site at S9, where most of the research attention is focused. Indeed, little attention is paid to the subcellular location of GSK-3β and whether the pools have varying levels of activity or substrate affinity. In addition, non-canonical regulation of GSK-3β has been identified; an Inhibitory P38 MAPK phosphorylation at T390 and an activating proline-rich tyrosine kinase 2 (Pyk-2) phosphorylation at Y216, Finally, It was recently shown that calpain 1, can cleave GSK-3β in vitro at T39 and I384 removing the inhibitory sites, including the canonical S9 site. Both Calpain and Pyk-2 can be activated by Ca2+ and oxidative stress, present during I/R injury. Our data indicate that GSK-3β is truncated during mitochondrial Ca2+ overload by calpain, and this event leads to phosphorylation of mitochondrial Cyclophilin D (CypD) and susceptibility to cell death. Additionally, we found that phosphorylation of CypD was closely correlated with its binding affinity for the oligomycin sensitivity conferring protein of the ATP Synthase, a proposed component of the mPTP.
Hurst, Stephen J, "Calcium Regulation of the Mitochondrial Permeability Transition Pore during Ischemia Reperfusion Injury of the Heart" (2019). ETD Collection for Thomas Jefferson University. AAI27547941.