Glycogen synthase kinase-3β mediates convergence of protection signaling to inhibit the mitochondrial permeability transition pore

TLDR

Environmental stresses converge on mitochondria to trigger or inhibit cell death, and excitable postmitotic cells activate protective mechanisms after sublethal stress. Protective memory arises from mitochondrial swelling that boosts ROS and activates PKC to inhibit GSK‑3β, while receptor‑mediated pathways also inhibit GSK‑3β via Akt/mTOR, PKC, or PKA, all converging on the permeability transition pore. Reoxygenation after prolonged hypoxia lowers the ROS threshold for MPT and cell survival is inversely related to depolarized mitochondria, and inhibition of GSK‑3β limits MPT induction, constituting the general cardiomyocyte protection mechanism.

Abstract

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, postmitotic cells, in response to sublethal noxious stress, engage mechanisms that afford protection from subsequent insults. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species (ROS) threshold for the mitochondrial permeability transition (MPT) in cardiomyocytes and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. Cell protection that exhibits a memory (preconditioning) results from triggered mitochondrial swelling that causes enhanced substrate oxidation and ROS production, leading to redox activation of PKC, which inhibits glycogen synthase kinase-3β (GSK-3β). Alternatively, receptor tyrosine kinase or certain G protein–coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3β, via protein kinase B/Akt and mTOR/p70s6k pathways, PKC pathways, or protein kinase A pathways. The convergence of these pathways via inhibition of GSK-3β on the end effector, the permeability transition pore complex, to limit MPT induction is the general mechanism of cardiomyocyte protection.