The SR/ER-mitochondria calcium crosstalk is regulated by GSK3β during reperfusion injury

Glycogen synthase kinase-3 beta (GSK3 beta) is a multifunctional kinase whose inhibition is known to limit myocardial ischemia-reperfusion injury. However, the mechanism mediating this beneficial effect still remains unclear. Mitochondria and sarco/endoplasmic reticulum (SR/ER) are key players in cell death signaling. Their involvement in myocardial ischemia-reperfusion injury has gained recognition recently, but the underlying mechanisms are not yet well understood. We questioned here whether GSK3 beta might have a role in the Ca2+ transfer from SR/ER to mitochondria at reperfusion. We showed that a fraction of GSK3 beta protein is localized to the SR/ER and mitochondria-associated ER membranes (MAMs) in the heart, and that GSK3 beta specifically interacted with the inositol 1,4,5-trisphosphate receptors (IP(3)Rs) Ca2+ channeling complex in MAMs. We demonstrated that both pharmacological and genetic inhibition of GSK3 beta decreased protein interaction of IP3R with the Ca2+ channeling complex, impaired SR/ER Ca2+ release and reduced the histamine-stimulated Ca2+ exchange between SR/ER and mitochondria in cardiomyocytes. During hypoxia reoxygenation, cell death is associated with an increase of GSK3 beta activity and IP3R phosphorylation, which leads to enhanced transfer of Ca2+ from SR/ER to mitochondria. Inhibition of GSK3 beta at reperfusion reduced both IP3R phosphorylation and SR/ER Ca2+ release, which consequently diminished both cytosolic and mitochondrial Ca2+ concentrations, as well as sensitivity to apoptosis. We conclude that inhibition of GSK3 beta at reperfusion diminishes Ca2+ leak from IP3R at MAMs in the heart, which limits both cytosolic and mitochondrial Ca2+ overload and subsequent cell death.