Uncoupling protein 3 mediates H2O2 preconditioning-afforded cardioprotection through the inhibition of MPTP opening

Aims Uncoupling protein 3 (UCP3), located in the mitochondrial inner membrane, is cardioprotective, but its mechanisms of preserving mitochondrial function during ischaemia/reperfusion (I/R) are not fully understood. This study investigated whether UCP3 mediates/mimics the cardioprotection of H2O2 preconditioning (H2O2PC) against I/R injury and the downstream pathway that mediates H2O2PC- and UCP3-afforded cardioprotection. Methods and results H2O2PC at 20 µM for 5 min significantly improved post-ischaemic functional recovery and reduced lactate dehydrogenase (LDH) release and infarct size with concurrently up-regulated UCP3 expressions in perfused rat hearts subjected to global no-flow I/R. These protections were blocked by UCP3 knockdown with short hairpin RNA but mimicked by UCP3 overexpression. Consistently, H2O2PC-attenuated I/R-induced cytosolic and mitochondrial Ca2+ overload, Ca2+ transient suppression, mitochondrial reactive oxygen species burst, and loss of mitochondrial inner membrane potential were reversed by UCP3 knockdown but mimicked by UCP3 overexpression. Moreover, co-immunoprecipitation assay revealed an interaction of UCP3 with the mitochondrial permeability transition pore (mPTP) component, adenine nucleotide translocator (ANT), while the cardioprotection induced by H2O2PC- and UCP3 overexpression in mitochondria, cardiac function, and cell survival was abolished by atractyloside, a mPTP opener binding to ANT, and partially inhibited by a PI3K/Akt inhibitor wortmannin. Furthermore, H2O2PC up-regulated the phosphorylation of Akt, and glycogen synthase kinase 3β was blocked by UCP3 knockdown but mimicked by UCP3 overexpression. Conclusion UCP3 mediates the cardioprotection of H2O2PC against I/R injury by preserving the mitochondrial function through inhibiting mPTP opening via the interaction with ANT and the PI3K/Akt pathway. Our findings reveal novel mechanisms of UCP3 in the cardioprotection.