Inhibition of complex I regulates the mitochondrial permeability transition through a phosphate-sensitive inhibitory site masked by cyclophilin D
ABSTRACT Inhibition of the mitochondrial permeability transition pore (PTP) has proved to be an effective strategy for preventing oxidative stress-induced cell death, and the pore represents a viable cellular target for drugs. Here, we report that inhibition of complex I by rotenone is more effective at PTP inhibition than cyclosporin A in tissues that express low levels of the cyclosporin A mitochondrial target, cyclophilin D; and, conversely, that tissues in which rotenone does not affect the PTP are characterized by high levels of expression of cyclophilin D and sensitivity to cyclosporin A. Consistent with a regulatory role of complex I in the PTP-inhibiting effects of rotenone, the concentrations of the latter required for PTP inhibition precisely match those required to inhibit respiration; and a similar effect is seen with the antidiabetic drug metformin, which partially inhibits complex I. Remarkably (i) genetic ablation of cyclophilin D or its displacement with cyclosporin A restored PTP inhibition by rotenone in tissues that are otherwise resistant to its effects; and (ii) rotenone did not inhibit the PTP unless phosphate was present, in striking analogy with the phosphate requirement for the inhibitory effects of cyclosporin A [Basso et al. (2008) J. Biol. Chem. 283, 26307-26311]. These results indicate that inhibition of complex I by rotenone or metformin and displacement of cyclophilin D by cyclosporin A affect the PTP through a common mechanism; and that cells can modulate their PTP response to complex I inhibition by modifying the expression of cyclophilin D, a finding that has major implications for pore modulation in vivo.
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- "While this is a widely accepted and effective strategy in the heart, Li et al. have shown tissue-specific differences in CyP-D expression and therefore sensitivity to CsA (Li et al., 2012). In particular, they reported that mPTP inhibition in tissues exhibiting low expression of CyP-D, is achieved more effectively using Rotenone than CsA (Li et al., 2012). "
ABSTRACT: Permeability transition pore (mPTP) opening leads to mitochondrial dysfunction & cell death during oxidative stress (OS). However mPTP desensitization with cyclosporine A (CsA) has shown variable efficacy in limiting post-ischemic arrhythmias. We hypothesized that feedback between energy dissipating (mPTP) and cardioprotective (mKATP) channels determine vulnerability to OS. Methods & Results: Guinea pig hearts (N=61) were perfused with H2O2 to elicit mitochondrial membrane potential (MMP) depolarization. Optical mapping was used to measure MMP or action potentials (AP). Hearts were treated with CsA under conditions that altered mKATP activity directly or indirectly via its regulation by PKC. CsA blunted OS-induced MMP depolarization and delayed loss of contractility but did not affect arrhythmia propensity. Surprisingly, prevention of mKATP activation with the phosphatase BDM reversed the protective effect of CsA, paradoxically exacerbating OS-induced MMP depolarization and accelerating arrhythmia onset in CsA treated hearts. To elucidate the putative molecular mechanisms, mPTP inhibition by CsA was tested under conditions of selective PKC inhibition, mKATP activation or blockade. Similar to BDM, CHE did not alter OS-induced MMP depolarization. However, it completely abrogated CsA-mediated protection against OS. Pharmacological block of mKATP, a target of PKC signaling, equally abolished the protective effect of CsA on MMP depolarization, whereas channel activation with DZX protected against MMP depolarization. Conditions that prevented mKATP activation led to accelerated MMP depolarization and early onset of VF in response to OS. Investigation of the electrophysiological substrate revealed accelerated APD shortening in response to OS in arrhythmia-prone hearts. Conclusions: Cardioprotection by CsA requires mKATP activation through a PKC-dependent pathway. Increasing mKATP activity during CsA administration is required for limiting OS-induced electrical dysfunction.Frontiers in Physiology 07/2014; 5:264. DOI:10.3389/fphys.2014.00264 · 3.50 Impact Factor
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- "Inhibition of the PT by rotenone is maximal in mitochondria from tissues that express low levels of CyPD, where CsA has little inhibitory effect; while inhibition by CsA is maximal in mitochondria from tissues with high levels of expression of CyPD, where rotenone does not affect the PTP. Finally, tissues with mitochondria expressing intermediate levels of CyPD are sensitive to both rotenone and CsA, with additive effects of the two inhibitors (Li et al., 2012). "
ABSTRACT: The permeability transition (PT) denotes an increase of the mitochondrial inner membrane permeability to solutes with molecular masses up to about 1500 Da. It is presumed to be mediated by opening of a channel, the permeability transition pore (PTP), whose molecular nature remains a mystery. Here I briefly review the history of the PTP, discuss existing models, and present our new results indicating that reconstituted dimers of the FOF1 ATP synthase form a channel with properties identical to those of the mitochondrial megachannel (MMC), the electrophysiological equivalent of the PTP. Open questions remain, but there is now promise that the PTP can be studied by genetic methods to solve the large number of outstanding problems.Frontiers in Physiology 05/2013; 4(1):95. DOI:10.3389/fphys.2013.00095 · 3.50 Impact Factor
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- "Recent in vitro studies demonstrated that CyP-D association to the lateral stalk of F0F1-ATP synthase modulates the activity of the complex, and the ATP synthase-CyP-D interactions were modulated by Pi and CsA, respectively, increasing and decreasing CyP-D binding to the enzyme (Giorgio et al., 2009). Interestingly, Pi was specifically required for PTP desensitization by CsA or by CyP-D ablation (Basso et al., 2008) as well as for inhibition of mPTP by blocking the complex I (Li et al., 2012). "
ABSTRACT: Mitochondria serve as a "powerhouse" which provides near 90% of ATP necessary for cell life. However, recent studies provide strong evidence that mitochondria also play a central role in cell death. Mitochondrial permeability transition (mPT) at high conductance in response to oxidative or other cellular stresses is accompanied by pathological and non-specific mPT pore (mPTP) opening in the inner membrane of mitochondria. Mitochondrial PTP can serve as a target to prevent cell death under pathological conditions such as cardiac and brain ischemia/reperfusion injury and diabetes. On the other hand, mPTP can be used as an executioner to specifically induce cell death thus blocking tumorigenesis in cancer diseases. Despite many studies, the molecular identity of the mPTP remains unclear. Cyclophilin D (CyP-D) plays an essential regulatory role in pore opening. This review will discuss direct and indirect mechanisms underlying CyP-D interaction with a target protein of the mPTP complex. Understanding of the mechanisms of mPTP opening will be helpful to further develop new pharmacological agents targeting mitochondria-mediated cell death.Frontiers in Physiology 04/2013; 4:76. DOI:10.3389/fphys.2013.00076 · 3.50 Impact Factor