The targeting of cyclophilin D by RNAi as a novel cardioprotective therapy: evidence from two-photon imaging

An opening of the mitochondrial permeability transition pore (MPTP), which leads to the loss of mitochondrial membrane potential (delta Psi(m)), is the earliest event that commits cells to death, and this process is potentially a prime target for therapeutic intervention against myocardial ischaemia/reperfusion. We aimed to investigate the protective effects of RNA interference (RNAi)-mediated gene silencing of cyclophilin D (CypD), one of the putative components of the MPTP, against myocardial ischaemia/reperfusion using two-photon laser scanning microscopy. We created an adenovirus carrying short-interfering RNA (siRNA) that inactivates CypD. Transduction of CypD-siRNA in rat cardiomyocytes achieved a 61% reduction in CypD mRNA and a 63% reduction in protein levels as well as protection against oxidant-induced delta Psi(m) loss and cytotoxicity. To further investigate the effects in vivo, we monitored the spatio-temporal changes of delta Psi(m) in perfused rat hearts subjected to ischaemia/reperfusion using two-photon imaging. Adult rats received direct intramyocardial injections of the adenovirus. Two to three days after injection, rat hearts were perfused by the Langendorff method and delta Psi(m) levels of individual cells were monitored. The progressive loss of delta Psi(m) during ischaemia/reperfusion was significantly suppressed in CypD-siRNA-transduced cells compared with non-transduced cells. Furthermore, the protective effect of CypD-siRNA was dose-dependent. Therapeutic interventions designed to inactivate CypD may be a promising strategy for reducing cardiac injury against myocardial ischaemia/reperfusion. The two-photon imaging technique provides deeper insight into cardioprotective therapy that targets mitochondria.