Cyclophilin D deficiency protects against the development of mitochondrial ROS and cellular inflammation in aorta

INTRODUCTION

Inflammation and oxidative stress are closely correlated in the pathology of cardiovascular disease. Mitochondrial cyclophilin D (CypD), the important modulator for mPTP opening, is increasingly recognized as a key regulator of cellular ROS generation. Besides, its association with cell inflammation is also being discovered. However, the effects of CypD in modulating vascular inflammatory response is unknown. We sought to investigate whether CypD deficiency attenutes vascular inflammation under physical conditions.

METHODS AND RESULTS

We adopted CypD KO mouse and their littermate controls to observe the effects of CypD deficiency on aortic mitochondrial functions and vascular inflammation. As we found in our study, we confirmed that under physical conditions, CypD deficiency enhanced mouse whole body metabolic status, increased aortic mitochondrial complex III activity and decreased mitochondrial ROS generation. Functionally, CypD deficiency also attenuated inflammatory molecules expression, including VCAM-1, IL-6 and TNF-α in mouse aorta.

CONCLUSIONS

Our results review that mitochondrial CypD is involved in the regulation of inflammation in aorta and provide insights that blocking mitochondrial CypD enhances vascular resistance to inflammatory injuries.

Cyclophilin D deficiency attenuates mitochondrial F1Fo ATP synthase dysfunction via OSCP in Alzheimer's disease

Mitochondrial dysfunction is pivotal in inducing synaptic injury and neuronal stress in Alzheimer's disease (AD). Mitochondrial F1Fo ATP synthase deregulation is a hallmark mitochondrial defect leading to oxidative phosphorylation (OXPHOS) failure in this neurological disorder. Oligomycin sensitivity conferring protein (OSCP) is a crucial F1Fo ATP synthase subunit. Decreased OSCP levels and OSCP interaction with amyloid β (Aβ) constitute key aspects of F1Fo ATP synthase pathology in AD-related conditions. However, the detailed mechanisms promoting such AD-related OSCP changes have not been fully resolved. Here, we have found increased physical interaction of OSCP with Cyclophilin D (CypD) in AD cases as well as in an AD animal model (5xFAD mice). Genetic depletion of CypD mitigates OSCP loss via ubiquitin-dependent OSCP degradation in 5xFAD mice. Moreover, the ablation of CypD also attenuates OSCP/Aβ interaction in AD mice. The relieved OSCP changes by CypD depletion in 5xFAD mice are along with preserved F1Fo ATP synthase function, restored mitochondrial bioenergetics as well as improved mouse cognition. The simplest interpretation of our results is that CypD is a critical mediator that promotes OSCP deficits in AD-related conditions. Therefore, to block the deleterious impact of CypD on OSCP has the potential to be a promising therapeutic strategy to correct mitochondrial dysfunction for AD therapy.

Estrogen receptor beta modulates permeability transition in brain mitochondria

Recent evidence highlights a role for sex and hormonal status in regulating cellular responses to ischemic brain injury and neurodegeneration. A key pathological event in ischemic brain injury is the opening of a mitochondrial permeability transition pore (MPT) induced by excitotoxic calcium levels, which can trigger irreversible damage to mitochondria accompanied by the release of pro-apoptotic factors. However, sex differences in brain MPT modulation have not yet been explored. Here, we show that mitochondria isolated from female mouse forebrain have a lower calcium threshold for MPT than male mitochondria, and that this sex difference depends on the MPT regulator cyclophilin D (CypD). We also demonstrate that an estrogen receptor beta (ERβ) antagonist inhibits MPT and knockout of ERβ decreases the sensitivity of mitochondria to the CypD inhibitor, cyclosporine A. These results suggest a functional relationship between ERβ and CypD in modulating brain MPT. Moreover, co-immunoprecipitation studies identify several ERβ binding partners in mitochondria. Among these, we investigate the mitochondrial ATPase as a putative site of MPT regulation by ERβ. We find that previously described interaction between the oligomycin sensitivity-conferring subunit of ATPase (OSCP) and CypD is decreased by ERβ knockout, suggesting that ERβ modulates MPT by regulating CypD interaction with OSCP. Functionally, in primary neurons and hippocampal slice cultures, modulation of ERβ has protective effects against glutamate toxicity and oxygen glucose deprivation, respectively. Taken together, these results reveal a novel pathway of brain MPT regulation by ERβ that could contribute to sex differences in ischemic brain injury and neurodegeneration.

Mitochondrial Dysfunction, Through Impaired Autophagy, Leads to Endoplasmic Reticulum Stress, Deregulated Lipid Metabolism, and Pancreatitis in Animal Models

BACKGROUND & AIMS

Little is known about the signaling pathways that initiate and promote acute pancreatitis (AP). The pathogenesis of AP has been associated with abnormal increases in cytosolic Ca2+, mitochondrial dysfunction, impaired autophagy, and endoplasmic reticulum (ER) stress. We analyzed the mechanisms of these dysfunctions and their relationships, and how these contribute to development of AP in mice and rats.

METHODS

Pancreatitis was induced in C57BL/6J mice (control) and mice deficient in peptidylprolyl isomerase D (cyclophilin D, encoded by Ppid) by administration of L-arginine (also in rats), caerulein, bile acid, or an AP-inducing diet. Parameters of pancreatitis, mitochondrial function, autophagy, ER stress, and lipid metabolism were measured in pancreatic tissue, acinar cells, and isolated mitochondria. Some mice with AP were given trehalose to enhance autophagic efficiency. Human pancreatitis tissues were analyzed by immunofluorescence.

RESULTS

Mitochondrial dysfunction in pancreas of mice with AP was induced by either mitochondrial Ca2+ overload or through a Ca2+ overload-independent pathway that involved reduced activity of ATP synthase (80% inhibition in pancreatic mitochondria isolated from rats or mice given L-arginine). Both pathways were mediated by cyclophilin D and led to mitochondrial depolarization and fragmentation. Mitochondrial dysfunction caused pancreatic ER stress, impaired autophagy, and deregulation of lipid metabolism. These pathologic responses were abrogated in cyclophilin D-knockout mice. Administration of trehalose largely prevented trypsinogen activation, necrosis, and other parameters of pancreatic injury in mice with L-arginine AP. Tissues from patients with pancreatitis had markers of mitochondrial damage and impaired autophagy, compared with normal pancreas.

CONCLUSIONS

In different animal models, we find a central role for mitochondrial dysfunction, and for impaired autophagy as its principal downstream effector, in development of AP. In particular, the pathway involving enhanced interaction of cyclophilin D with ATP synthase mediates L-arginine-induced pancreatitis, a model of severe AP the pathogenesis of which has remained unknown. Strategies to restore mitochondrial and/or autophagic function might be developed for treatment of AP.

Molecular analysis of axonal-intrinsic and glial-associated co-regulation of axon degeneration

Wallerian degeneration is an active program tightly associated with axonal degeneration, required for axonal regeneration and functional recovery after nerve damage. Here we provide a functional molecular foundation for our undertstanding of the complex non-cell autonomous role of glial cells in the regulation of axonal degeneration. To shed light on the complexity of the molecular machinery governing axonal degeneration we employ a multi-model, unbiased, in vivo approach combining morphological assesment and quantitative proteomics with in silico-based higher order functional clustering to genetically uncouple the intrinsic and extrinsic processes governing Wallerian degeneration. Highlighting a pivotal role for glial cells in the early stages fragmenting the axon by a cytokinesis-like process and a cell autonomous stage of axonal disintegration associated to mitochondrial dysfunction.

Cyclophilin inhibitor NIM811 ameliorates experimental allergic encephalomyelitis

Cyclophilins have diverse functions that may affect the course of central nervous system (CNS) inflammatory disorders. Anti-inflammatory and neuroprotective mechanisms may be targeted by inhibition of cyclophilin A-dependent and cyclophilin D-dependent functions, respectively. We tested the effect of cyclophilin inhibition on CNS inflammation by administering N-methyl-4-isoleucine-cyclosporin (NIM811) to mice undergoing experimental allergic encephalomyelitis (EAE). Treatment with NIM811 resulted in significant reduction of EAE clinical severity. Analysis of mitochondrial calcium retention capacity and the course of EAE in cyclophilin D knockout mice indicated that the effect of NIM811 on EAE was not entirely cyclophilin D-dependent. NIM811-treated EAE animals showed reduction in interleukin-2 expression and reduction in CNS inflammatory infiltrates. These results indicate that anti-inflammatory rather than neuroprotective mechanisms associated with cyclophilins are likely involved in the mechanism of NIM811 in EAE.

Neutrophil macroaggregates promote widespread pulmonary thrombosis after gut ischemia

Gut ischemia is common in critically ill patients, promoting thrombosis and inflammation in distant organs. The mechanisms linking hemodynamic changes in the gut to remote organ thrombosis remain ill-defined. We demonstrate that gut ischemia in the mouse induces a distinct pulmonary thrombotic disorder triggered by neutrophil macroaggregates. These neutrophil aggregates lead to widespread occlusion of pulmonary arteries, veins, and the microvasculature. A similar pulmonary neutrophil-rich thrombotic response occurred in humans with the acute respiratory distress syndrome. Intravital microscopy during gut ischemia-reperfusion injury revealed that rolling neutrophils extract large membrane fragments from remnant dying platelets in multiple organs. These platelet fragments bridge adjacent neutrophils to facilitate macroaggregation. Platelet-specific deletion of cyclophilin D, a mitochondrial regulator of cell necrosis, prevented neutrophil macroaggregation and pulmonary thrombosis. Our studies demonstrate the existence of a distinct pulmonary thrombotic disorder triggered by dying platelets and neutrophil macroaggregates. Therapeutic targeting of platelet death pathways may reduce pulmonary thrombosis in critically ill patients.

Ablation of Cyclophilin D Results in an Activation of FAK, Akt, and ERK Pathways in the Mouse Heart

Cyclophilin D (CypD) is a mitochondrial chaperone that regulates the mitochondrial permeability transition pore. Metabolically, deletion of Ppif (the gene encoding CypD) in mice is associated with elevated levels of mitochondrial matrix Ca2+ that leads to increased glucose as relative to fatty acid oxidation. Here, we characterized the adaptive mechanisms involved in the regulation of glucose metabolism including the regulation of Akt and ERK kinases that we evaluated by Western blot analysis of Ppif-/- in comparison to wild type (WT) mouse hearts. CypD loss led to adaptive mechanisms in the heart resulting in an upregulation of focal adhesion kinase (phosphorylated at Tyr925) and increased phosphorylation of Akt at S473. The increased activity of this pathway (pAktS473 increased to 170% and 145% in Ppif-/- versus WT males and females, respectively) could be responsible for the observed metabolic switch towards glycolysis. Furthermore, the phosphorylation of ERK1/2 proteins was elevated following CypD ablation. In addition, we observed differences in protein expression and activity in male versus female hearts that were independent of CypD expression. This included an upregulation of pAktS473 (to 273% and 269% in Ppif-/- and WT females as compared to their corresponding males, respectively). Furthermore, decreased levels of endothelial nitric oxide synthase (eNOS) inhibitor asymmetric dimethylarginine were accompanied by an upregulation of eNOS in female mice. The higher extent of kinases phosphorylation may be responsible for the reported lowered tolerance of CypD animals to stress. Moreover, the higher nitric oxide production could be responsible for the cardioprotective properties observed only in female hearts. J. Cell. Biochem. 118: 2933-2940, 2017. © 2017 Wiley Periodicals, Inc.

Cyclophilin D Modulates the Cardiac Mitochondrial Target of Isoflurane, Sevoflurane, and Desflurane

BACKGROUND

Volatile anesthetics are known to limit myocardial ischemia-reperfusion injuries. Mitochondria were shown to be major contributors to cardioprotection. Cyclophilin D (CypD) is one of the main regulators of mitochondria-induced cell death. We compared the effect of isoflurane, sevoflurane, and desflurane in the presence or absence of CypD, to clarify its role in the mechanism of cardioprotection induced by these anesthetics.

METHODS

Oxidative phosphorylation, mitochondrial membrane potential, and H2O2 production were measured in isolated mitochondria from wild-type (WT) or CypD knockout mice in basal conditions and after hypoxia-reoxygenation in the presence or absence of volatile anesthetics.

RESULTS

All volatile anesthetics inhibited mitochondrial state 3 of complex I, decreased membrane potential, and increased adenosine diphosphate consumption duration in both WT and CypD knockout mice. However, they differently modified H2O2 production after stimulation by succinate: CypD ablation reduced H2O2 production, isoflurane decreased H2O2 level in WT but not in CypD knockout mice, sevoflurane affected both lines whereas desflurane increased H2O2 production in CypD knockout and had no effect on WT mice.

CONCLUSIONS

This study showed different effects of isoflurane, sevoflurane, and desflurane on mitochondrial functions and highlighted the implication of CypD in the regulation of adenosine diphosphate consumption and complex I-induced radical oxygen species production.

Cyclophilin D Promotes Brain Mitochondrial F1FO ATP Synthase Dysfunction in Aging Mice

Brain aging is the known strongest risk factor for Alzheimer's disease (AD). In recent years, mitochondrial deficits have been proposed to be a common mechanism linking brain aging to AD. Therefore, to elucidate the causative mechanisms of mitochondrial dysfunction in aging brains is of paramount importance for our understanding of the pathogenesis of AD, in particular its sporadic form. Cyclophilin D (CypD) is a specific mitochondrial protein. Recent studies have shown that F1FO ATP synthase oligomycin sensitivity conferring protein (OSCP) is a binding partner of CypD. The interaction of CypD with OSCP modulates F1FO ATP synthase function and mediates mitochondrial permeability transition pore (mPTP) opening. Here, we have found that increased CypD expression, enhanced CypD/OSCP interaction, and selective loss of OSCP are prominent brain mitochondrial changes in aging mice. Along with these changes, brain mitochondria from the aging mice demonstrated decreased F1FO ATP synthase activity and defective F1FO complex coupling. In contrast, CypD deficient mice exhibited substantially mitigated brain mitochondrial F1FO ATP synthase dysfunction with relatively preserved mitochondrial function during aging. Interestingly, the aging-related OSCP loss was also dramatically attenuated by CypD depletion. Therefore, the simplest interpretation of this study is that CypD promotes F1FO ATP synthase dysfunction and the resultant mitochondrial deficits in aging brains. In addition, in view of CypD and F1FO ATP synthase alterations seen in AD brains, the results further suggest that CypD-mediated F1FO ATP synthase deregulation is a shared mechanism linking mitochondrial deficits in brain aging and AD.

Anesthesia/Surgery Induces Cognitive Impairment in Female Alzheimer's Disease Transgenic Mice

Anesthesia and/or surgery may promote Alzheimer's disease (AD) by accelerating its neuropathogenesis. Other studies showed different findings. However, the potential sex difference among these studies has not been well considered, and it is unknown whether male or female AD patients are more vulnerable to develop postoperative cognitive dysfunction. We therefore set out to perform a proof of concept study to determine whether anesthesia and surgery can have different effects in male and female AD transgenic (Tg) mice, and in female AD Tg plus Cyclophilin D knockout (CypD KO) mice. The mice received an abdominal surgery under sevoflurane anesthesia (anesthesia/surgery). Fear Conditioning System (FCS) was used to assess the cognitive function. Hippocampal levels of synaptic marker postsynaptic density 95 (PSD-95) and synaptophysin (SVP) were measured using western blot analysis. Here we showed that the anesthesia/surgery decreased the freezing time in context test of FCS at 7 days after the anesthesia/surgery in female, but not male, mice. The anesthesia/surgery reduced hippocampus levels of synaptic marker PSD-95 and SVP in female, but not male, mice. The anesthesia/surgery induced neither reduction in freezing time in FCS nor decreased hippocampus levels of PSD-95 and SVP in the AD Tg plus CypD KO mice. These data suggest that the anesthesia/surgery induced a sex-dependent cognitive impairment and reduction in hippocampus levels of synaptic markers in AD Tg mice, potentially via a mitochondria-associated mechanism. These findings could promote clinical investigations to determine whether female AD patients are more vulnerable to the development of postoperative cognitive dysfunction.

Involvement of mitochondrial permeability transition pore (mPTP) in cardiac arrhythmias: Evidence from cyclophilin D knockout mice

In the present study, we have used a genetic mouse model that lacks cyclophilin D (CypD KO) to assess the cardioprotective effect of mitochondrial permeability transition pore (mPTP) inhibition on Ca2+ waves and Ca2+ alternans at the single cell level, and cardiac arrhythmias in whole-heart preparations. The protonophore carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) caused mitochondrial membrane potential depolarization to the same extent in cardiomyocytes from both WT and CypD KO mice, however, cardiomyocytes from CypD KO mice exhibited significantly less mPTP opening than cardiomyocytes from WT mice (p<0.05). Consistent with these results, FCCP caused significant increases in CaW rate in WT cardiomyocytes (p<0.05) but not in CypD KO cardiomyocytes. Furthermore, the incidence of Ca2+ alternans after treatment with FCCP and programmed stimulation was significantly higher in WT cardiomyocytes (11 of 13), than in WT cardiomyocytes treated with CsA (2 of 8; p<0.05) or CypD KO cardiomyocytes (2 of 10; p<0.01). (Pseudo-)Lead II ECGs were recorded from ex vivo hearts. We observed ST-T-wave alternans (a precursor of lethal arrhythmias) in 5 of 7 WT hearts. ST-T-wave alternans was not seen in CypD KO hearts (n=5) and in only 1 of 6 WT hearts treated with CsA. Consistent with these results, WT hearts exhibited a significantly higher average arrhythmia score than CypD KO (p<0.01) hearts subjected to FCCP treatment or chemical ischemia-reperfusion (p<0.01). In conclusion, CypD deficiency- induced mPTP inhibition attenuates CaWs and Ca2+ alternans during mitochondrial depolarization, and thereby protects against arrhythmogenesis in the heart.

Phenotypic Characterization of a Leishmania donovani Cyclophilin 40 Null Mutant

Protozoan parasites of the genus Leishmania adapt to their arthropod and vertebrate hosts through the development of defined life cycle stages. Stage differentiation is triggered by environmental stress factors and has been linked to parasite chaperone activities. Using a null mutant approach we previously revealed important, nonredundant functions of the cochaperone cyclophilin 40 in L. donovani-infected macrophages. Here, we characterized in more detail the virulence defect of cyp40-/- null mutants. In vitro viability assays, infection tests using macrophages, and mixed infection experiments ruled out a defect of cyp40-/- parasites in resistance to oxidative and hydrolytic stresses encountered inside the host cell phagolysosome. Investigation of the CyP40-dependent proteome by quantitative 2D-DiGE analysis revealed up regulation of various stress proteins in the null mutant, presumably a response to compensate for the lack of CyP40. Applying transmission electron microscopy we showed accumulation of vesicular structures in the flagellar pocket of cyp40-/- parasites that we related to a significant increase in exosome production, a phenomenon previously linked to the parasite stress response. Together these data suggest that cyp40-/- parasites experience important intrinsic homeostatic stress that likely abrogates parasite viability during intracellular infection.

F1F0 ATP Synthase-Cyclophilin D Interaction Contributes to Diabetes-Induced Synaptic Dysfunction and Cognitive Decline

Mitochondrial abnormalities are well known to cause cognitive decline. However, the underlying molecular basis of mitochondria-associated neuronal and synaptic dysfunction in the diabetic brain remains unclear. Here, using a mitochondrial single-channel patch clamp and cyclophilin D (CypD)-deficient mice (Ppif -/-) with streptozotocin-induced diabetes, we observed an increase in the probability of Ca2+-induced mitochondrial permeability transition pore (mPTP) opening in brain mitochondria of diabetic mice, which was further confirmed by mitochondrial swelling and cytochrome c release induced by Ca2+ overload. Diabetes-induced elevation of CypD triggers enhancement of F1F0 ATP synthase-CypD interaction, which in turn leads to mPTP opening. Indeed, in patients with diabetes, brain cypD protein levels were increased. Notably, blockade of the F1F0 ATP synthase-CypD interaction by CypD ablation protected against diabetes-induced mPTP opening, ATP synthesis deficits, oxidative stress, and mitochondria dysfunction. Furthermore, the absence of CypD alleviated deficits in synaptic plasticity, learning, and memory in diabetic mice. Thus, blockade of ATP synthase interaction with CypD provides a promising new target for therapeutic intervention in diabetic encephalopathy.

Cyclophilin D Knock-Out Mice Show Enhanced Resistance to Osteoporosis and to Metabolic Changes Observed in Aging Bone

Pathogenic factors associated with aging, such as oxidative stress and hormone depletion converge on mitochondria and impair their function via opening of the mitochondrial permeability transition pore (MPTP). The MPTP is a large non-selective pore regulated by cyclophilin D (CypD) that disrupts mitochondrial membrane integrity. MPTP involvement has been firmly established in degenerative processes in heart, brain, and muscle. Bone has high energy demands and is therefore expected to be highly sensitive to mitochondrial dysfunction. Despite this, the role of mitochondria and the MPTP in bone maintenance and bone pathology has not been elucidated. Our goal was to determine whether mitochondria are impaired in aging bone and to see if protecting mitochondria from MPTP opening via CypD deletion protects against bone loss. We found that bone mass, strength, and formation progressively decline over the course of 18 months in C57BL/6J mice. Using metabolomics and electron microscopy, we determined that oxidative metabolism is impaired in aging bone leading to a glycolytic shift, imbalance in nucleotides, and decreased NAD+/NADH ratio. Mitochondria in osteocytes appear swollen which is a major marker of MPTP opening. CypD deletion by CypD knockout mouse model (CypD KO) protects against bone loss in 13- and 18-month-old mice and prevents decline in bone formation and mitochondrial changes observed in wild type C57BL/6J mice. Together, these data demonstrate that mitochondria are impaired in aging bone and that CypD deletion protects against this impairment to prevent bone loss. This implicates CypD-regulated MPTP and mitochondrial dysfunction in the impairment of bone cells and in aging-related bone loss. Our findings suggest mitochondrial metabolism as a new target for bone therapeutics and inhibition of CypD as a novel strategy against bone loss.

Deletion of Cyclophilin D Impairs β-Oxidation and Promotes Glucose Metabolism

Cyclophilin D (CypD) is a mitochondrial matrix protein implicated in cell death, but a potential role in bioenergetics is not understood. Here, we show that loss or depletion of CypD in cell lines and mice induces defects in mitochondrial bioenergetics due to impaired fatty acid β-oxidation. In turn, CypD loss triggers a global compensatory shift towards glycolysis, with transcriptional upregulation of effectors of glucose metabolism, increased glucose consumption and higher ATP production. In vivo, the glycolytic shift secondary to CypD deletion is associated with expansion of insulin-producing β-cells, mild hyperinsulinemia, improved glucose tolerance, and resistance to high fat diet-induced liver damage and weight gain. Therefore, CypD is a novel regulator of mitochondrial bioenergetics, and unexpectedly controls glucose homeostasis, in vivo.

The mitochondrial permeability transition pore regulates endothelial bioenergetics and angiogenesis

RATIONALE

The mitochondrial permeability transition pore is a well-known initiator of cell death that is increasingly recognized as a physiological modulator of cellular metabolism.

OBJECTIVE

We sought to identify how the genetic deletion of a key regulatory subunit of the mitochondrial permeability transition pore, cyclophilin D (CypD), influenced endothelial metabolism and intracellular signaling.

METHODS AND RESULTS

In cultured primary human endothelial cells, genetic targeting of CypD using siRNA or shRNA resulted in a constitutive increase in mitochondrial matrix Ca(2+) and reduced nicotinamide adenine dinucleotide (NADH). Elevated matrix NADH, in turn, diminished the cytosolic NAD(+)/NADH ratio and triggered a subsequent downregulation of the NAD(+)-dependent deacetylase sirtuin 1 (SIRT1). Downstream of SIRT1, CypD-deficient endothelial cells exhibited reduced phosphatase and tensin homolog expression and a constitutive rise in the phosphorylation of angiogenic Akt. Similar changes in SIRT1, phosphatase and tensin homolog, and Akt were also noted in the aorta and lungs of CypD knockout mice. Functionally, CypD-deficient endothelial cells and aortic tissue from CypD knockout mice exhibited a dramatic increase in angiogenesis at baseline and when exposed to vascular endothelial growth factor. The NAD(+) precursor nicotinamide mononucleotide restored the cellular NAD(+)/NADH ratio and normalized the CypD-deficient phenotype. CypD knockout mice also presented accelerated wound healing and increased neovascularization on tissue injury as monitored by optical microangiography.

CONCLUSIONS

Our study reveals the importance of the mitochondrial permeability transition pore in the regulation of endothelial mitochondrial metabolism and vascular function. The mitochondrial regulation of SIRT1 has broad implications in the epigenetic regulation of endothelial phenotype.

Traumatic brain injury-induced axonal phenotypes react differently to treatment

Injured axons with distinct morphologies have been found following mild traumatic brain injury (mTBI), although it is currently unclear whether they reflect varied responses to the injury or represent different stages of progressing pathology. This complicates evaluation of therapeutic interventions targeting axonal injury. To address this issue, we assessed axonal injury over time within a well-defined axonal population, while also evaluating mitochondrial permeability transition as a therapeutic target. We utilized mice expressing yellow fluorescent protein (YFP) in cortical neurons which were crossed with mice which lacked Cyclophilin D (CypD), a positive regulator of mitochondrial permeability transition pore opening. Their offspring were subjected to mTBI and the ensuing axonal injury was assessed using YFP expression and amyloid precursor protein (APP) immunohistochemistry, visualized by confocal and electron microscopy. YFP(+) axons initially developed a single, APP(+), focal swelling (proximal bulb) which progressed to axotomy. Disconnected axonal segments developed either a single bulb (distal bulb) or multiple bulbs (varicosities), which were APP(-) and whose ultrastructure was consistent with ongoing Wallerian degeneration. CypD knock-out failed to reduce proximal bulb formation but decreased the number of distal bulbs and varicosities, as well as a population of small, APP(+), callosal bulbs not associated with YFP(+) axons. The observation that YFP(+) axons contain several pathological morphologies points to the complexity of traumatic axonal injury. The fact that CypD knock-out reduced some, but not all, subtypes highlights the need to appropriately characterize injured axons when evaluating potential neuroprotective strategies.

β3 adrenergic receptor selective stimulation during ischemia/reperfusion improves cardiac function in translational models through inhibition of mPTP opening in cardiomyocytes

Selective stimulation of β3 adrenergic-receptor (β3AR) has been shown to reduce infarct size in a mouse model of myocardial ischemia/reperfusion. However, its functional long-term effect and the cardioprotective mechanisms at the level of cardiomyocytes have not been elucidated, and the impact of β3AR stimulation has not been evaluated in a more translational large animal model. This study aimed at evaluating pre-perfusion administration of BRL37344 both in small and large animal models of myocardial ischemia/reperfusion. Pre-reperfusion administration of the β3AR agonist BRL37344 (5 μg/kg) reduced infarct size at 2-and 24-h reperfusion in wild-type mice. Long-term (12-weeks) left ventricular (LV) function assessed by echocardiography and cardiac magnetic resonance (CMR) was significantly improved in β3AR agonist-treated mice. Incubation with β3AR agonist (BRL37344, 7 μmol/L) significantly reduced cell death in isolated adult mouse cardiomyocytes during hypoxia/reoxygenation and decreased susceptibility to deleterious opening of the mitochondrial permeability transition pore (mPTP), via a mechanism dependent on the Akt-NO signaling pathway. Pre-reperfusion BRL37344 administration had no effect on infarct size in cyclophilin-D KO mice, further implicating mPTP in the mechanism of protection. Large-white pigs underwent percutaneous coronary ischemia/reperfusion and 3-T CMR at 7 and 45 days post-infarction. Pre-perfusion administration of BRL37344 (5 μg/kg) decreased infarct size and improved long-term LV contractile function. A single-dose administration of β3AR agonist before reperfusion decreased infarct size and resulted in a consistent and long-term improvement in cardiac function, both in small and large animal models of myocardial ischemia/reperfusion. This protection appears to be executed through inhibition of mPTP opening in cardiomyocytes.

Involvement of the mitochondrial permeability transition pore in chronic ethanol-mediated liver injury in mice

Chronic ethanol consumption increases sensitivity of the mitochondrial permeability transition (MPT) pore induction in liver. Ca(2+) promotes MPT pore opening, and genetic ablation of cyclophilin D (CypD) increases the Ca(2+) threshold for the MPT. We used wild-type (WT) and CypD-null (CypD(-/-)) mice fed a control or an ethanol-containing diet to investigate the role of the MPT in ethanol-mediated liver injury. Ca(2+)-mediated induction of the MPT and mitochondrial respiration were measured in isolated liver mitochondria. Steatosis was present in WT and CypD(-/-) mice fed ethanol and accompanied by increased terminal deoxynucleotidyl transferase dUTP-mediated nick-end label-positive nuclei. Autophagy was increased in ethanol-fed WT mice compared with ethanol-fed CypD(-/-) mice, as reflected by an increase in the ratio of microtubule protein 1 light chain 3B II to microtubule protein 1 light chain 3B I. Higher levels of p62 were measured in CypD(-/-) than WT mice. Ethanol decreased mitochondrial respiratory control ratios and select complex activities in WT and CypD(-/-) mice. Ethanol also increased CypD protein in liver of WT mice. Mitochondria from control- and ethanol-fed WT mice were more sensitive to Ca(2+)-mediated MPT pore induction than mitochondria from their CypD(-/-) counterparts. Mitochondria from ethanol-fed CypD(-/-) mice were also more sensitive to Ca(2+)-induced swelling than mitochondria from control-fed CypD(-/-) mice but were less sensitive than mitochondria from ethanol-fed WT mice. In summary, CypD deficiency was associated with impaired autophagy and did not prevent ethanol-mediated steatosis. Furthermore, increased MPT sensitivity was observed in mitochondria from ethanol-fed WT and CypD(-/-) mice. We conclude that chronic ethanol consumption likely lowers the threshold for CypD-regulated and -independent characteristics of the ethanol-mediated MPT pore in liver mitochondria.

Molecular mechanisms of the crosstalk between mitochondria and NADPH oxidase through reactive oxygen species-studies in white blood cells and in animal models

AIMS

Oxidative stress is involved in the development of cardiovascular disease. There is a growing body of evidence for a crosstalk between different enzymatic sources of oxidative stress. With the present study, we sought to determine the underlying crosstalk mechanisms, the role of the mitochondrial permeability transition pore (mPTP), and its link to endothelial dysfunction.

RESULTS

NADPH oxidase (Nox) activation (oxidative burst and translocation of cytosolic Nox subunits) was observed in response to mitochondrial reactive oxygen species (mtROS) formation in human leukocytes. In vitro, mtROS-induced Nox activation was prevented by inhibitors of the mPTP, protein kinase C, tyrosine kinase cSrc, Nox itself, or an intracellular calcium chelator and was absent in leukocytes with p47phox deficiency (regulates Nox2) or with cyclophilin D deficiency (regulates mPTP). In contrast, the crosstalk in leukocytes was amplified by mitochondrial superoxide dismutase (type 2) (MnSOD(+/-)) deficiency. In vivo, increases in blood pressure, degree of endothelial dysfunction, endothelial nitric oxide synthase (eNOS) dysregulation/uncoupling (e.g., eNOS S-glutathionylation) or Nox activity, p47phox phosphorylation in response to angiotensin-II (AT-II) in vivo treatment, or the aging process were more pronounced in MnSOD(+/-) mice as compared with untreated controls and improved by mPTP inhibition by cyclophilin D deficiency or sanglifehrin A therapy.

INNOVATION

These results provide new mechanistic insights into what extent mtROS trigger Nox activation in phagocytes and cardiovascular tissue, leading to endothelial dysfunction.

CONCLUSIONS

Our data show that mtROS trigger the activation of phagocytic and cardiovascular NADPH oxidases, which may have fundamental implications for immune cell activation and development of AT-II-induced hypertension.

Cyclophilin D modulates mitochondrial acetylome

RATIONALE

Mice lacking cyclophilin D (CypD(-/-)), a mitochondrial chaperone protein, have altered cardiac metabolism. As acetylation has been shown to regulate metabolism, we tested whether changes in protein acetylation might play a role in these metabolic changes in CypD(-/-) hearts.

OBJECTIVE

Our aim was to test the hypothesis that loss of CypD alters the cardiac mitochondrial acetylome.

METHODS AND RESULTS

To identify changes in lysine-acetylated proteins and to map acetylation sites after ablation of CypD, we subjected tryptic digests of isolated cardiac mitochondria from wild-type and CypD(-/-) mice to immunoprecipitation using agarose beads coupled to antiacetyl lysine antibodies followed by mass spectrometry. We used label-free analysis for the relative quantification of the 875 common peptides that were acetylated in wild-type and CypD(-/-) samples and found 11 peptides (10 proteins) decreased and 96 peptides (48 proteins) increased in CypD(-/-) samples. We found increased acetylation of proteins in fatty acid oxidation and branched-chain amino acid metabolism. To evaluate whether this increase in acetylation might play a role in the inhibition of fatty acid oxidation that was previously reported in CypD(-/-) hearts, we measured the activity of l-3-hydroxyacyl-CoA dehydrogenase, which was acetylated in the CypD(-/-) hearts. Consistent with the hypothesis, l-3-hydroxyacyl-CoA dehydrogenase activity was inhibited by ≈50% compared with the wild-type mitochondria.

CONCLUSIONS

These results implicate a role for CypD in modulating protein acetylation. Taken together, these results suggest that ablation of CypD leads to changes in the mitochondrial acetylome, which may contribute to altered mitochondrial metabolism in CypD(-/-) mice.

Depressing mitochondria-reticulum interactions protects cardiomyocytes from lethal hypoxia-reoxygenation injury

BACKGROUND

Under physiological conditions, Ca(2+) transfer from the endoplasmic reticulum (ER) to mitochondria might occur at least in part at contact points between the 2 organelles and involves the VDAC1/Grp75/IP3R1 complex. Accumulation of Ca(2+) into the mitochondrial matrix may activate the mitochondrial chaperone cyclophilin D (CypD) and trigger permeability transition pore opening, whose role in ischemia/reperfusion injury is well recognized. We questioned here whether the transfer of Ca(2+) from ER to mitochondria might play a role in cardiomyocyte death after hypoxia-reoxygenation.

METHODS AND RESULTS

We report that CypD interacts with the VDAC1/Grp75/IP3R1 complex in cardiomyocytes. Genetic or pharmacological inhibition of CypD in both H9c2 cardiomyoblasts and adult cardiomyocytes decreased the Ca(2+) transfer from ER to mitochondria through IP3R under normoxic conditions. During hypoxia-reoxygenation, the interaction between CypD and the IP3R1 Ca(2+) channeling complex increased concomitantly with mitochondrial Ca(2+) content. Inhibition of either CypD, IP3R1, or Grp75 decreased protein interaction within the complex, attenuated mitochondrial Ca(2+) overload, and protected cells from hypoxia-reoxygenation. Genetic or pharmacological inhibition of CypD provided a similar effect in adult mice cardiomyocytes. Disruption of ER-mitochondria interaction via the downregulation of Mfn2 similarly reduced the interaction between CypD and the IP3R1 complex and protected against hypoxia-reoxygenation injury.

CONCLUSIONS

Our data (1) point to a new role of CypD at the ER-mitochondria interface and (2) suggest that decreasing ER-mitochondria interaction at reperfusion can protect cardiomyocytes against lethal reperfusion injury through the reduction of mitochondrial Ca(2+) overload via the CypD/VDAC1/Grp75/IP3R1 complex.

Endoplasmic reticulum stress contributes to heart protection induced by cyclophilin D inhibition

Preventing cyclophilin D (cypD) translocation to the inner mitochondrial membrane can limit lethal reperfusion injury through the inhibition of the opening of the mitochondrial permeability transition pore. Inhibition or loss of function of cypD may also result into an endoplasmic reticulum (ER) stress that has been shown to alter cell survival. We therefore questioned whether ER stress might play a role in the protection induced by CypD deficiency or inhibition. CypD-KO and NIM811 (a CypD inhibitor)-treated mice were subjected to a prolonged ischemia-reperfusion (I/R). Area at risk and infarct size was measured using blue dye and triphenyltetrazolium chloride staining. ER stress markers were measured in the hearts during the reperfusion phase. As expected, cypD-KO mice exhibited a decreased infarct size when compared to wild-type mice (8 ± 1 vs. 20 ± 4% of left ventricular weight; p < 0.01). CypD-deficient mice displayed an increased expression of ER stress proteins such as eukaryotic initiation factor 2α (eIF2α) or glucose regulated protein 78 (Grp78 or Bip). The ER stress inhibitor TUDCA prevented the infarct size reduction afforded by the loss of cypD function (mean infarct size averaged 21 ± 4% of LV weight, p < 0.01 vs. cypD-KO). Similar results were obtained when NIM811, an analog of cyclosporine A, was used to pharmacologically (instead of genetically) inhibit cypD function. This study suggests that the ER stress induced by the inhibition of cypD function plays a key role in protecting the heart against lethal ischemia-reperfusion injury.

The P66Shc/mitochondrial permeability transition pore pathway determines neurodegeneration

Mitochondrial-mediated oxidative stress and apoptosis play a crucial role in neurodegenerative disease and aging. Both mitochondrial permeability transition (PT) and swelling of mitochondria have been involved in neurodegeneration. Indeed, knockout mice for cyclophilin-D (Cyc-D), a key regulatory component of the PT pore (PTP) that triggers mitochondrial swelling, resulted to be protected in preclinical models of multiple sclerosis (MS), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). However, how neuronal stress is transduced into mitochondrial oxidative stress and swelling is unclear. Recently, the aging determinant p66Shc that generates H2O2 reacting with cytochrome c and induces oxidation of PTP and mitochondrial swelling was found to be involved in MS and ALS. To investigate the role of p66Shc/PTP pathway in neurodegeneration, we performed experimental autoimmune encephalomyelitis (EAE) experiments in p66Shc knockout mice (p66Shc-/-), knock out mice for cyclophilin-D (Cyc-D-/-), and p66Shc Cyc-D double knock out (p66Shc/Cyc-D-/-) mice. Results confirm that deletion of p66Shc protects from EAE without affecting immune response, whereas it is not epistatic to the Cyc-D mutation. These findings demonstrate that p66Shc contributes to EAE induced neuronal damage most likely through the opening of PTP suggesting that p66Shc/PTP pathway transduces neurodegenerative stresses.

Enhancing mitochondrial calcium buffering capacity reduces aggregation of misfolded SOD1 and motor neuron cell death without extending survival in mouse models of inherited amyotrophic lateral sclerosis

Mitochondria have been proposed as targets for toxicity in amyotrophic lateral sclerosis (ALS), a progressive, fatal adult-onset neurodegenerative disorder characterized by the selective loss of motor neurons. A decrease in the capacity of spinal cord mitochondria to buffer calcium (Ca(2+)) has been observed in mice expressing ALS-linked mutants of SOD1 that develop motor neuron disease with many of the key pathological hallmarks seen in ALS patients. In mice expressing three different ALS-causing SOD1 mutants, we now test the contribution of the loss of mitochondrial Ca(2+)-buffering capacity to disease mechanism(s) by eliminating ubiquitous expression of cyclophilin D, a critical regulator of Ca(2+)-mediated opening of the mitochondrial permeability transition pore that determines mitochondrial Ca(2+) content. A chronic increase in mitochondrial buffering of Ca(2+) in the absence of cyclophilin D was maintained throughout disease course and was associated with improved mitochondrial ATP synthesis, reduced mitochondrial swelling, and retention of normal morphology. This was accompanied by an attenuation of glial activation, reduction in levels of misfolded SOD1 aggregates in the spinal cord, and a significant suppression of motor neuron death throughout disease. Despite this, muscle denervation, motor axon degeneration, and disease progression and survival were unaffected, thereby eliminating mutant SOD1-mediated loss of mitochondrial Ca(2+) buffering capacity, altered mitochondrial morphology, motor neuron death, and misfolded SOD1 aggregates, as primary contributors to disease mechanism for fatal paralysis in these models of familial ALS.

CypD(-/-) hearts have altered levels of proteins involved in Krebs cycle, branch chain amino acid degradation and pyruvate metabolism

Cyclophilin D (CypD) is a mitochondrial chaperone that has been shown to regulate the mitochondrial permeability transition pore (MPTP). MPTP opening is a major determinant of mitochondrial dysfunction and cardiomyocyte death during ischemia/reperfusion (I/R) injury. Mice lacking CypD have been widely used to study regulation of the MPTP, and it has been shown recently that genetic depletion of CypD correlates with elevated levels of mitochondrial Ca(2+). The present study aimed to characterize the metabolic changes in CypD(-/-) hearts. Initially, we used a proteomics approach to examine protein changes in CypD(-/-) mice. Using pathway analysis, we found that CypD(-/-) hearts have alterations in branched chain amino acid metabolism, pyruvate metabolism and the Krebs cycle. We tested whether these metabolic changes were due to inhibition of electron transfer from these metabolic pathways into the electron transport chain. As we found decreased levels of succinate dehydrogenase and electron transfer flavoprotein in the proteomics analysis, we examined whether activities of these enzymes might be altered. However, we found no alterations in their activities. The proteomics study also showed a 23% decrease in carnitine-palmitoyltransferase 1 (CPT1), which prompted us to perform a metabolomics analysis. Consistent with the decrease in CPT1, we found a significant decrease in C4/Ci4, C5-OH/C3-DC, C12:1, C14:1, C16:1, and C20:3 acyl carnitines in hearts from CypD(-/-) mice. In summary, CypD(-/-) hearts exhibit changes in many metabolic pathways and caution should be used when interpreting results from these mice as due solely to inhibition of the MPTP.

Cyclophilin D deficiency rescues axonal mitochondrial transport in Alzheimer's neurons

Normal axonal mitochondrial transport and function is essential for the maintenance of synaptic function. Abnormal mitochondrial motility and mitochondrial dysfunction within axons are critical for amyloid β (Aβ)-induced synaptic stress and the loss of synapses relevant to the pathogenesis of Alzheimer's disease (AD). However, the mechanisms controlling axonal mitochondrial function and transport alterations in AD remain elusive. Here, we report an unexplored role of cyclophilin D (CypD)-dependent mitochondrial permeability transition pore (mPTP) in Aβ-impaired axonal mitochondrial trafficking. Depletion of CypD significantly protects axonal mitochondrial motility and dynamics from Aβ toxicity as shown by increased axonal mitochondrial density and distribution and improved bidirectional transport of axonal mitochondria. Notably, blockade of mPTP by genetic deletion of CypD suppresses Aβ-mediated activation of the p38 mitogen-activated protein kinase signaling pathway, reverses axonal mitochondrial abnormalities, improves synaptic function, and attenuates loss of synapse, suggesting a role of CypD-dependent signaling in Aβ-induced alterations in axonal mitochondrial trafficking. The potential mechanisms of the protective effects of lacking CypD on Aβ-induced abnormal mitochondrial transport in axon are increased axonal calcium buffer capability, diminished reactive oxygen species (ROS), and suppressing downstream signal transduction P38 activation. These findings provide new insights into CypD-dependent mitochondrial mPTP and signaling on mitochondrial trafficking in axons and synaptic degeneration in an environment enriched for Aβ.

Absence of FKBP10 in recessive type XI osteogenesis imperfecta leads to diminished collagen cross-linking and reduced collagen deposition in extracellular matrix

Recessive osteogenesis imperfecta (OI) is caused by defects in genes whose products interact with type I collagen for modification and/or folding. We identified a Palestinian pedigree with moderate and lethal forms of recessive OI caused by mutations in FKBP10 or PPIB, which encode endoplasmic reticulum resident chaperone/isomerases FKBP65 and CyPB, respectively. In one pedigree branch, both parents carry a deletion in PPIB (c.563_566delACAG), causing lethal type IX OI in their two children. In another branch, a child with moderate type XI OI has a homozygous FKBP10 mutation (c.1271_1272delCCinsA). Proband FKBP10 transcripts are 4% of control and FKBP65 protein is absent from proband cells. Proband collagen electrophoresis reveals slight band broadening, compatible with ≈10% over-modification. Normal chain incorporation, helix folding, and collagen T(m) support a minimal general collagen chaperone role for FKBP65. However, there is a dramatic decrease in collagen deposited in culture despite normal collagen secretion. Mass spectrometry reveals absence of hydroxylation of the collagen telopeptide lysine involved in cross-linking, suggesting that FKBP65 is required for lysyl hydroxylase activity or access to type I collagen telopeptide lysines, perhaps through its function as a peptidylprolyl isomerase. Proband collagen to organics ratio in matrix is approximately 30% of normal in Raman spectra. Immunofluorescence shows sparse, disorganized collagen fibrils in proband matrix.

Chaperoning the chaperone: a role for the co-chaperone Cpr7 in modulating Hsp90 function in Saccharomyces cerevisiae

Heat-shock protein 90 (Hsp90) of Saccharomyces cerevisiae is an abundant essential eukaryotic molecular chaperone involved in the activation and stabilization of client proteins, including several transcription factors and oncogenic kinases. Hsp90 undergoes a complex series of conformational changes and interacts with partner co-chaperones such as Sba1, Cpr6, Cpr7, and Cns1 as it binds and hydrolyzes ATP. In the absence of nucleotide, Hsp90 is dimerized only at the carboxy-terminus. In the presence of ATP, Hsp90 also dimerizes at the amino-terminus, creating a binding site for Sba1. Truncation of a charged linker region of yeast Hsp90 (Hsp82Δlinker) was known to disrupt the ability of Hsp82 to undergo amino-terminal dimerization and bind Sba1. We found that yeast expressing Hsp82Δlinker constructs exhibited a specific synthetic lethal phenotype in cells lacking CPR7. The isolated tetratricopeptide repeat domain of Cpr7 was both necessary and sufficient for growth in those strains. Cpr6 and Cpr7 stably bound the carboxy-terminus of wild-type Hsp82 only in the presence of nonhydrolyzable ATP and formed an Hsp82-Cpr6-Cpr7 ternary complex. However, in cells expressing Hsp82Δlinker or lacking CPR7, Cpr6 was able to bind Hsp82 in the presence or absence of nucleotide. Overexpression of CNS1, but not of other co-chaperones, in cpr7 cells restored nucleotide-dependent Hsp82-Cpr6 interaction. Together, our results suggest that the in vivo functions of Cpr7 include modulating Hsp90 conformational changes, mediating proper signaling of the nucleotide-bound state to the carboxy-terminus of Hsp82, or regulating Hsp82-Cpr6 interaction.

Genetic inactivation of the p66 isoform of ShcA is neuroprotective in a murine model of multiple sclerosis

Although multiple sclerosis (MS) has traditionally been considered to be an inflammatory disease, recent evidence has brought neurodegeneration into the spotlight, suggesting that accumulated damage and loss of axons is critical to disease progression and the associated irreversible disability. Proposed mechanisms of axonal degeneration in MS posit cytosolic and subsequent mitochondrial Ca(2+) overload, accumulation of pathologic reactive oxygen species (ROS), and mitochondrial dysfunction leading to cell death. In this context, the role of the p66 isoform of ShcA protein (p66) may be significant. The ShcA isoform is uniquely targeted to the mitochondrial intermembrane space in response to elevated oxidative stress, and serves as a redox enzyme amplifying ROS generation in a positive feedforward loop that eventually mediates cell death by activation of the mitochondrial permeability transition pore. Consequently, we tested the hypothesis that genetic inactivation of p66 would reduce axonal injury in a murine model of MS, experimental autoimmune encephalomyelitis (EAE). As predicted, the p66-knockout (p66-KO) mice developed typical signs of EAE, but had less severe clinical impairment and paralysis than wild-type (WT) mice. Histologic examination of spinal cords and optic nerves showed significant axonal protection in the p66-KO tissue, despite similar levels of inflammation. Furthermore, cultured p66-KO neurons treated with agents implicated in MS neurodegenerative pathways showed greater viability than WT neurons. These results confirm the critical role of ROS-mediated mitochondrial dysfunction in the axonal loss that accompanies EAE, and identify p66 as a new pharmacologic target for MS neuroprotective therapeutics.

The role of mitochondrial permeability transition in reperfusion-induced cardiomyocyte death depends on the duration of ischemia

Mitochondrial permeability transition (MPT) is critical in cardiomyocyte death during reperfusion but it is not the only mechanism responsible for cell injury. The objectives of the study is to investigate the role of the duration of myocardial ischemia on mitochondrial integrity and cardiomyocyte death. Mitochondrial membrane potential (ΔΨm, JC-1) and MPT (calcein) were studied in cardiomyocytes from wild-type and cyclophilin D (CyD) KO mice refractory to MPT, submitted to simulated ischemia and 10 min reperfusion. Reperfusion after 15 min simulated ischemia induced a rapid recovery of ΔΨm, extreme cell shortening (contracture) and mitochondrial calcein release, and CyD ablation did not affect these changes or cell death. However, when reperfusion was performed after 25 min simulated ischemia, CyD ablation improved ΔΨm recovery and reduced calcein release and cell death (57.8 ± 4.9% vs. 77.3 ± 4.8%, P < 0.01). In a Langendorff system, CyD ablation increased infarct size after 30 min of ischemia (61.3 ± 6.4% vs. 45.3 ± 4.0%, P = 0.02) but reduced it when ischemia was prolonged to 60 min (52.8 ± 8.1% vs. 87.6 ± 3.7%, P < 0.01). NMR spectroscopy in rat hearts showed a rapid recovery of phosphocreatine after 30 min ischemia followed by a marked decay associated with contracture and LDH release, that were preventable with contractile blockade but not with cyclosporine A. In contrast, after 50 min ischemia, phosphocreatine recovery was impaired even with contractile blockade (65.2 ± 4% at 2 min), and cyclosporine A reduced contracture, LDH release and infarct size (52.1 ± 4.2% vs. 82.8 ± 3.6%, P < 0.01). In conclusion, the duration of ischemia critically determines the importance of MPT on reperfusion injury. Mechanisms other than MPT may play an important role in cell death after less severe ischemia.

High-fat diet-induced adipocyte cell death occurs through a cyclophilin D intrinsic signaling pathway independent of adipose tissue inflammation

OBJECTIVE

Previous studies have demonstrated that mice fed a high-fat diet (HFD) develop insulin resistance with proinflammatory macrophage infiltration into white adipose tissue. Concomitantly, adipocytes undergo programmed cell death with the loss of the adipocyte-specific lipid droplet protein perilipin, and the dead/dying adipocytes are surrounded by macrophages that are organized into crown-like structures. This study investigated whether adipocyte cell death provides the driving signal for macrophage inflammation or if inflammation induces adipocyte cell death.

RESEARCH DESIGN AND METHODS

Two knockout mouse models were used: granulocyte/monocyte-colony stimulating factor (GM-CSF)-null mice that are protected against HFD-induced adipose tissue inflammation and cyclophilin D (CyP-D)-null mice that are protected against adipocyte cell death. Mice were fed for 4-14 weeks with a 60% HFD, and different markers of cell death and inflammation were analyzed.

RESULTS

HFD induced a normal extent of adipocyte cell death in GM-CSF-null mice, despite a marked reduction in adipose tissue inflammation. Similarly, depletion of macrophages by clodronate treatment prevented HFD-induced adipose tissue inflammation without any affect on adipocyte cell death. However, CyP-D deficiency strongly protected adipocytes from HFD-induced cell death, without affecting adipose tissue inflammation.

CONCLUSIONS

These data demonstrate that HFD-induced adipocyte cell death is an intrinsic cellular response that is CyP-D dependent but is independent of macrophage infiltration/activation.

Cyclophilin D deficiency improves mitochondrial function and learning/memory in aging Alzheimer disease mouse model

Mitochondrial stress is one of the early features of Alzheimer disease (AD). Mitochondrial Aβ has been linked to mitochondrial toxicity. Our recent study demonstrated that cyclophilin D (CypD) mediated mitochondrial permeability transition pore (mPTP) is an important mechanism for neuronal and synaptic stress induced by both Aβ and oxidative stress. In transgenic AD-type mice overexpressing mutant amyloid precursor protein (APP) and Aβ (mAPP), CypD deficiency improves mitochondrial and synaptic function and learning/memory up to 12 months old. Here we provide evidence of the protective effects of CypD deficiency in aged AD mice (22-24 months). Cyp D deficient mAPP mice demonstrate less calcium-induced mitochondrial swelling, increased mitochondrial calcium uptake capacity, preserved mitochondrial respiratory function and improved spatial learning/memory even in old age (known to be the age for late stage AD pathology and synaptic dysfunction). These data demonstrate that abrogation of CypD results in persistent life-long protection against Aβ toxicity in an Alzheimer's disease mouse model, thereby suggesting that blockade of CypD may be of benefit for Alzheimer disease treatment.

Cyclophilin-D is dispensable for atrophy and mitochondrial apoptotic signalling in denervated muscle

In the present study, we specifically determined whether the regulatory protein cyclophilin-D (CypD), and by extension opening of the permeability transition pore (PTP), is involved in the activation of mitochondria-derived apoptotic signalling previously described in skeletal muscle following loss of innervation. For this purpose, CypD-defficient (CypD-KO) mice and their littermate controls were submitted to unilateral sciatic nerve transection, and mitochondrial resistance to Ca2+-induced opening of the PTP, and muscle apoptotic signalling were investigated 14 days post-surgery. Denervation caused atrophy, facilitated Ca2+-induced opening of the PTP in vitro in permeabilized muscle fibres, and activation of the apoptotic proteolytic cascade in the whole muscle of both mouse strains. In CypD-KO mice, mitochondrial resistance to Ca2+-induced PTP opening was greater than in WT mice, in both the normal and the denervated state, indicating that lack of CypD desensitized to PTP opening. However, denervation in CypD-KO mice still resulted in a facilitation of PTP opening compared to normally innervated contralateral muscle, indicating that in vitro additional factors could poise mitochondria from denervated muscle toward PTP opening. At the whole muscle level, lack of CypD, despite conferring greater resistance to PTP opening, did not protect against atrophy, release of mitochondrial pro-apoptotic factors and activation of caspases following denervation. Altogether, these results provide direct evidence that CypD-dependent PTP opening is dispensable for atrophy and apoptotic signalling in skeletal muscle following denervation.

Cyclophilin D deficiency protects against acetaminophen-induced oxidant stress and liver injury

Acetaminophen (APAP) hepatotoxicity is the main cause of acute liver failure in humans. Although mitochondrial oxidant stress and induction of the mitochondrial permeability transition (MPT) have been implicated in APAP-induced hepatotoxicity, the link between these events is unclear. To investigate this, this study evaluated APAP hepatotoxicity in mice deficient of cyclophilin D, a protein component of the MPT. Treatment of wild type mice with APAP resulted in focal centrilobular necrosis, nuclear DNA fragmentation and formation of reactive oxygen (elevated glutathione disulphide levels) and peroxynitrite (nitrotyrosine immunostaining) in the liver. CypD-deficient (Ppif(-/-)) mice were completely protected against APAP-induced liver injury and DNA fragmentation. Oxidant stress and peroxynitrite formation were blunted but not eliminated in CypD-deficient mice. Thus, mitochondrial oxidative stress and induction of the MPT are critical events in APAP hepatotoxicity in vivo and at least part of the APAP-induced oxidant stress and peroxynitrite formation occurs downstream of the MPT.

Immunophilin deficiency augments Ca2+-dependent glutamate release from mouse cortical astrocytes

Immunophilins are receptors for immunosuppressive drugs such as the macrolides cyclosporin A (CsA) and FK506; correspondingly these immunophilins are referred to as cyclophilins and FK506-binding proteins (FKBPs). In particular, CsA targets cyclophilin D (CypD), which can modulate mitochondrial Ca(2+) dynamics. Since mitochondria have been implicated in the regulation of astrocytic cytosolic Ca(2+) (Ca(cyt)(2+)) dynamics and consequential Ca(2+)-dependent exocytotic release of glutamate, we investigated the role of CypD in this process. Cortical astrocytes isolated from CypD deficient mice Ppif(-/-) displayed reduced mechanically induced Ca(cyt)(2+) increases, even though these cells showed augmented exocytotic release of glutamate, when compared to responses obtained from astrocytes isolated from wild-type mice. Furthermore, acute treatment with CsA to inhibit CypD modulation of mitochondrial Ca(2+) buffering, or with FK506 to inhibit FKBP12 interaction with inositol-trisphosphate receptor of the endoplasmic reticulum, led to similar reductive effects on astrocytic Ca(cyt)(2+) dynamics, but also to an enhanced Ca(2+)-dependent exocytotic release of glutamate in wild-type astrocytes. These findings point to a possible role of immunophilin signal transduction pathways in astrocytic modulation of neuronal activity at the tripartite synapse.

Pharmacologic targeting or genetic deletion of mitochondrial cyclophilin D protects from NSAID-induced small intestinal ulceration in mice

Small intestinal ulceration is a frequent and potentially serious condition associated with nonselective cyclooxygenase 1/2 inhibitors (nonsteroidal anti-inflammatory drugs, NSAIDs) including diclofenac (DCF). An initial topical effect involving mitochondria has been implicated in the pathogenesis, but the exact mechanisms of NSAID-induced enteropathy are unknown. We aimed at investigating whether DCF caused enterocyte demise via the mitochondrial permeability transition (mPT) and whether inhibition of critical mPT regulators might protect the mucosa from DCF injury. Cultured enterocytes (IEC-6) exposed to DCF readily underwent mPT-mediated cell death. We then targeted mitochondrial cyclophilin D (CypD), a key regulator of the mPT, in a mouse model of NSAID enteropathy. C57BL/6J mice were treated with an ulcerogenic dose of DCF (60 mg/kg, ip), followed (+ 1 h) by a non-cholestatic dose (10 mg/kg, ip) of the CypD inhibitor, cyclosporin A (CsA). CsA greatly reduced the extent of small intestinal ulceration. To avoid potential calcineurin-mediated effects, we used the non-immunosuppressive cyclosporin analog, D-MeAla(3)-EtVal(4)-cyclosporin (Debio 025). Debio 025 similarly protected the mucosa from DCF injury. To exclude drug-drug interactions, we exposed mice genetically deficient in mitochondrial CypD (peptidyl-prolyl cis-trans isomerase F [Ppif(-/-)]) to DCF. Ppif-null mice were largely protected from the ulcerogenic effects of DCF, whereas their wild-type littermates developed typical enteropathy. Enterocyte injury was preceded by upregulation of the proapoptotic transcription factor C/EBP homologous protein (Chop). Chop-null mice were refractory to DCF enteropathy, suggesting a critical role of endoplasmic reticulum stress induced by DCF. In conclusion, mitochondrial CypD plays a key role in NSAID-induced enteropathy, lending itself as a potentially new therapeutic target for cytoprotective intervention.

Mitochondrial cyclophilin-D as a critical mediator of ischaemic preconditioning

AIMS

It has been suggested that mitochondrial reactive oxygen species (ROS), Akt and Erk1/2 and more recently the mitochondrial permeability transition pore (mPTP) may act as mediators of ischaemic preconditioning (IPC), although the actual interplay between these mediators is unclear. The aim of the present study is to determine whether the cyclophilin-D (CYPD) component of the mPTP is required by IPC to generate mitochondrial ROS and subsequently activate Akt and Erk1/2.

METHODS AND RESULTS

Mice lacking CYPD (CYPD-/-) and B6Sv129 wild-type (WT) mice were used throughout. We have demonstrated that under basal conditions, non-pathological mPTP opening occurs (indicated by the percent reduction in mitochondrial calcein fluorescence). This effect was greater in WT cardiomyocytes compared with CYPD-/- ones (53 ± 2% WT vs. 17 ± 3% CYPD-/-; P < 0.01) and was augmented by hypoxic preconditioning (HPC) (70 ± 9% WT vs. 56 ± 1% CYPD-/-; P < 0.01). HPC reduced cell death following simulated ischaemia-reperfusion injury in WT (23.2 ± 3.5% HPC vs. 43.7 ± 3.2% WT; P < 0.05) but not CYPD-/- cardiomyocytes (19.6 ± 1.4% HPC vs. 24.4 ± 2.6% control; P > 0.05). HPC generated mitochondrial ROS in WT (four-fold increase; P < 0.05) but not CYPD-/- cardiomyocytes. HPC induced significant Akt phosphorylation in WT cardiomyocytes (two-fold increase; P < 0.05), an effect which was abrogated by ciclosporin-A (a CYPD inhibitor) and N-2-mercaptopropionyl glycine (a ROS scavenger). Finally, in vivo IPC of adult murine hearts resulted in significant phosphorylation of Akt and Erk1/2 in WT but not CYPD-/- hearts.

CONCLUSION

The CYPD component of the mPTP is required by IPC to generate mitochondrial ROS and phosphorylate Akt and Erk1/2, major steps in the IPC signalling pathway.

Knockdown of Cyclophilin D Gene by RNAi Protects Rat from Ischemia/ Reperfusion-Induced Renal Injury

BACKGROUND/AIMS

Mitochondrial permeability transition has a critical role in ischemia/reperfusion (I/R)-induced kidney injury. It is thought that mitochondrial permeability transition occurs after the opening of the permeability transition pore, a channel which putatively consists of a voltage-dependent anion channel, adenine nucleotide translocator and cyclophilin D (CypD). Much evidence shows that CypD plays an important role in I/R-induced injury.

METHODS

To evaluate the role of CypD following I/R renal injury, we tested the hypothesis that knockdown of CypD gene by RNA interference (RNAi) protects rat from I/R-induced renal injury.

RESULTS

Our data show that knockdown of CypD by RNAi protects normal rat kidney cell line from hypoxia-induced necrotic death. Infection of lentivirus expressing CypD RNAi sequence produces a significant reduction of CypD at both mRNA and protein levels. Both pathologic and biochemical analyses show that knockdown of CypD by RNAi protects rat kidney from I/R-induced renal injury.

CONCLUSION

Our study provides the evidence that CypD may be a potential target for protecting I/R-induced renal injury.

Cyclophilin D in mitochondrial pathophysiology

Cyclophilins are a family of peptidyl-prolyl cis-trans isomerases whose enzymatic activity can be inhibited by cyclosporin A. Sixteen cyclophilins have been identified in humans, and cyclophilin D is a unique isoform that is imported into the mitochondrial matrix. Here we shall (i) review the best characterized functions of cyclophilin D in mitochondria, i.e. regulation of the permeability transition pore, an inner membrane channel that plays an important role in the execution of cell death; (ii) highlight new regulatory interactions that are emerging in the literature, including the modulation of the mitochondrial F1FO ATP synthase through an interaction with the lateral stalk of the enzyme complex; and (iii) discuss diseases where cyclophilin D plays a pathogenetic role that makes it a suitable target for pharmacologic intervention.

Lack of cyclophilin B in osteogenesis imperfecta with normal collagen folding

Osteogenesis imperfecta is a heritable disorder that causes bone fragility. Mutations in type I collagen result in autosomal dominant osteogenesis imperfecta, whereas mutations in either of two components of the collagen prolyl 3-hydroxylation complex (cartilage-associated protein [CRTAP] and prolyl 3-hydroxylase 1 [P3H1]) cause autosomal recessive osteogenesis imperfecta with rhizomelia (shortening of proximal segments of upper and lower limbs) and delayed collagen folding. We identified two siblings who had recessive osteogenesis imperfecta without rhizomelia. They had a homozygous start-codon mutation in the peptidyl-prolyl isomerase B gene (PPIB), which results in a lack of cyclophilin B (CyPB), the third component of the complex. The proband's collagen had normal collagen folding and normal prolyl 3-hydroxylation, suggesting that CyPB is not the exclusive peptidyl-prolyl cis-trans isomerase that catalyzes the rate-limiting step in collagen folding, as is currently thought.

The role of cyclophilin D in learning and memory

Cyclophilin D (Cyp D) is implicated in cell death pathway and blockade of Cyp D could be a potent therapeutic strategy for degenerative disorders such as Alzheimer's disease, ischemia, and multiple sclerosis, but physiological role of Cyp D remains elusive. Here, we investigated the ability of learning and memory in several behavioral tasks in mice that lacked Cyp D (Cyp D(-/-)) and the relationship between ability of learning and memory and hippocampal architecture or neuronal transmission in Cyp D(-/-) mice. Cyp D(-/-) mice showed impairments of short-term memory in the Y-maze, object recognition memory in the novel-object recognition test, reference memory in the water maze test, and associative learning in the conditioned fear learning test. Hippocampal infusion of Cyclosporine A, which binds to Cyp D, replicated the defect in hippocampus-dependent cognition observed in Cyp D(-/-) mice. The Cyp D(-/-) mice did not show histopathological abnormalities upon Nissl staining and GFAP immunostaining or irregular expression of neuronal and glial marker proteins on Western blotting. However, release of glutamate and acetylcholine was decreased from the hippocampus in response to high-potassium treatment in the Cyp D(-/-) mice than in the wild-type mice. These results suggest a physiological role for Cyp D in learning and memory via the regulation of neurotransmission.

Severe osteogenesis imperfecta in cyclophilin B-deficient mice

Osteogenesis Imperfecta (OI) is a human syndrome characterized by exquisitely fragile bones due to osteoporosis. The majority of autosomal dominant OI cases result from point or splice site mutations in the type I collagen genes, which are thought to lead to aberrant osteoid within developing bones. OI also occurs in humans with homozygous mutations in Prolyl-3-Hydroxylase-1 (LEPRE1). Although P3H1 is known to hydroxylate a single residue (pro-986) in type I collagen chains, it is unclear how this modification acts to facilitate collagen fibril formation. P3H1 exists in a complex with CRTAP and the peptidyl-prolyl isomerase cyclophilin B (CypB), encoded by the Ppib gene. Mutations in CRTAP cause OI in mice and humans, through an unknown mechanism, while the role of CypB in this complex has been a complete mystery. To study the role of mammalian CypB, we generated mice lacking this protein. Early in life, Ppib-/- mice developed kyphosis and severe osteoporosis. Collagen fibrils in Ppib-/- mice had abnormal morphology, further consistent with an OI phenotype. In vitro studies revealed that in CypB–deficient fibroblasts, procollagen did not localize properly to the golgi. We found that levels of P3H1 were substantially reduced in Ppib-/- cells, while CRTAP was unaffected by loss of CypB. Conversely, knockdown of either P3H1 or CRTAP did not affect cellular levels of CypB, but prevented its interaction with collagen in vitro. Furthermore, knockdown of CRTAP also caused depletion of cellular P3H1. Consistent with these changes, post translational prolyl-3-hydroxylation of type I collagen by P3H1 was essentially absent in CypB–deficient cells and tissues from CypB–knockout mice. These data provide significant new mechanistic insight into the pathophysiology of OI and reveal how the members of the P3H1/CRTAP/CypB complex interact to direct proper formation of collagen and bone.

Osteogenesis Imperfecta (OI), also known as “brittle bone disease,” is an inherited condition with multiple defects in collagen-containing structures, including the bones, skin, and other connective tissues. Patients with OI suffer from short stature, scoliosis, thin skin, hearing loss, and, most notably, fragile bones that break with little or no trauma. Although many cases are due to dominantly inherited point mutations in the collagen genes, autosomal recessive forms have been described due to defects in the genes for Prolyl-3-Hydroxylase-1 (LEPRE1) and Cartilage-Associated Protein (CRTAP), proteins that modify newly synthesized procollagen. Some patients with OI do not have mutations in any of the known disease-related genes. Here, through the use of newly generated knockout mice, we identify the endoplasmic-reticulum resident prolyl-isomerase cyclophilin B (CypB) as a new autosomal recessive OI gene in mice. CypB, P3H1, and CRTAP were shown to have interrelated effects in maintaining their respective protein levels and ability to bind to collagen. These studies enhance our understanding about how collagen, the most abundant protein in the body, becomes properly assembled to form bones with adequate strength.

Cyclophilin D gene ablation protects mice from ischemic renal injury

Increased oxidative stress and intracellular calcium levels and mitochondrial overloading of calcium during ischemic renal injury (IRI) favor mitochondrial membrane permeability transition pore (MPTP) opening and subsequent necrotic cell death. Cyclophilin D (CypD) is an essential component of MPTP, and recent findings implicate its role in necrotic, but not apoptotic, cell death. To evaluate the role of CypD following IRI, we tested the hypothesis that CypD gene ablation protects mice from IRI. Renal function as assessed by plasma levels of both creatinine and blood urea nitrogen was significantly reduced in CypD knockout (CypD(-/-)) mice compared with wild-type mice during the 5-day post-ischemia period. Erythrocyte trapping, tubular cell necrosis, tubular dilatation, and neutrophil infiltration were significantly decreased in CypD(-/-) mice. To define the mechanisms by which CypD deficiency protect the kidneys, an in vitro model of IRI was employed. Inhibition of CypD using cyclosporin A in oxidant-injured cultured proximal tubular cells (PTC) prevented mitochondrial membrane depolarization, reduced LDH release, ATP depletion and necrotic cell death. Similarly, oxidant-injured CypD(-/-) PTC primary cultures were protected from cytotoxicity and necrosis. To conclude, CypD gene ablation offers both functional and morphological protection in mice following IRI by decreasing necrotic cell death possibly via inhibition of MPTP and ATP depletion.

Developmental shift of cyclophilin D contribution to hypoxic-ischemic brain injury

Cyclophilin D (CypD), a regulator of the mitochondrial membrane permeability transition pore (PTP), enhances Ca(2+)-induced mitochondrial permeabilization and cell death in the brain. However, the role of CypD in hypoxic-ischemic (HI) brain injury at different developmental ages is unknown. At postnatal day (P) 9 or P60, littermates of CypD-deficient [knock-out (KO)], wild-type (WT), and heterozygous mice were subjected to HI, and brain injury was evaluated 7 d after HI. CypD deficiency resulted in a significant reduction of HI brain injury at P60 but worsened injury at P9. After HI, caspase-dependent and -independent cell death pathways were more induced in P9 CypD KO mice than in WT controls, and apoptotic activation was minimal at P60. The PTP had a considerably higher induction threshold and lower sensitivity to cyclosporin A in neonatal versus adult mice. On the contrary, Bax inhibition markedly reduced caspase activation and brain injury in immature mice but was ineffective in the adult brain. Our findings suggest that CypD/PTP is critical for the development of brain injury in the adult, whereas Bax-dependent mechanisms prevail in the immature brain. The role of CypD in HI shifts from a predominantly prosurvival protein in the immature to a cell death mediator in the adult brain.

Enhancement of anxiety, facilitation of avoidance behavior, and occurrence of adult-onset obesity in mice lacking mitochondrial cyclophilin D

In this report, we have assessed the behavioral responses of mice missing the Ppif gene (CyPD-KO), encoding mitochondrial cyclophilin D (CyPD). Mitochondrial CyPD is a key modulator of the mitochondrial permeability transition which is involved in the regulation of calcium- and oxidative damage-induced cell death. Behavioral screening of CyPD-KO mice (ranging between 4 and 15 months of age) was accomplished using a battery of behavioral paradigms which included testing of motor functions, exploratory activity, and anxiety/emotionality, as well as learning and memory skills. We found that, compared with wild-type mice, CyPD-KO mice were (i) more anxious and less explorative in open field and elevated plus maze and (ii) performed better in learning and memory of avoidance tasks, such as active and passive avoidance. However, the absence of CyPD did not alter the nociceptive threshold for thermal stimuli. Finally, deletion of CyPD caused also an abnormal accumulation of white adipose tissue resulting in adult-onset obesity, which was not dependent on increased food and/or water intake. Taken together, our results suggest a new fundamental role of mitochondrial CyPD in basal brain functions and body weight homeostasis.

AtCYP38 ensures early biogenesis, correct assembly and sustenance of photosystem II

AtCYP38 is a thylakoid lumen protein comprising the immunophilin domain and the phosphatase inhibitor module. Here we show the association of AtCYP38 with the photosystem II (PSII) monomer complex and address its functional role using AtCYP38-deficient mutants. The dynamic greening process of etiolated leaves failed in the absence of AtCYP38, due to specific problems in the biogenesis of PSII complexes. Also the development of leaves under short-day conditions was severely disturbed. Detailed biophysical and biochemical analysis of mature AtCYP38-deficient plants from favorable growth conditions (long photoperiod) revealed: (i) intrinsic malfunction of PSII, which (ii) occurred on the donor side of PSII and (iii) was dependent on growing light intensity. AtCYP38 mutant plants also showed decreased accumulation of PSII, which was shown not to originate from impaired D1 synthesis or assembly of PSII monomers, dimers and supercomplexes as such but rather from the incorrect fine-tuning of the oxygen-evolving side of PSII. This, in turn, rendered PSII centers extremely susceptible to photoinhibition. AtCYP38 deficiency also drastically decreased the in vivo phosphorylation of PSII core proteins, probably related to the absence of the AtCYP38 phosphatase inhibitor domain. It is proposed that during PSII assembly AtCYP38 protein guides the proper folding of D1 (and CP43) into PSII, thereby enabling the correct assembly of the water-splitting Mn(4)-Ca cluster even with high turnover of PSII.

Genetic and pharmacologic inhibition of mitochondrial-dependent necrosis attenuates muscular dystrophy

Muscular dystrophies comprise a diverse group of genetic disorders that lead to muscle wasting and, in many instances, premature death. Many mutations that cause muscular dystrophy compromise the support network that connects myofilament proteins within the cell to the basal lamina outside the cell, rendering the sarcolemma more permeable or leaky. Here we show that deletion of the gene encoding cyclophilin D (Ppif) rendered mitochondria largely insensitive to the calcium overload-induced swelling associated with a defective sarcolemma, thus reducing myofiber necrosis in two distinct models of muscular dystrophy. Mice lacking delta-sarcoglycan (Scgd(-/-) mice) showed markedly less dystrophic disease in both skeletal muscle and heart in the absence of Ppif. Moreover, the premature lethality associated with deletion of Lama2, encoding the alpha-2 chain of laminin-2, was rescued, as were other indices of dystrophic disease. Treatment with the cyclophilin inhibitor Debio-025 similarly reduced mitochondrial swelling and necrotic disease manifestations in mdx mice, a model of Duchenne muscular dystrophy, and in Scgd(-/-) mice. Thus, mitochondrial-dependent necrosis represents a prominent disease mechanism in muscular dystrophy, suggesting that inhibition of cyclophilin D could provide a new pharmacologic treatment strategy for these diseases.

Critical role for the mitochondrial permeability transition pore and cyclophilin D in platelet activation and thrombosis

Many of the cellular responses that occur in activated platelets resemble events that take place following activation of cell-death pathways in nucleated cells. We tested the hypothesis that formation of the mitochondrial permeability transition pore (MPTP), a key signaling event during cell death, also plays a critical role in platelet activation. Stimulation of murine platelets with thrombin plus the glycoprotein VI agonist convulxin resulted in a rapid loss of mitochondrial transmembrane potential (Deltapsi(m)) in a subpopulation of activated platelets. In the absence of cyclophilin D (CypD), an essential regulator of MPTP formation, murine platelet activation responses were altered. CypD-deficient platelets exhibited defects in phosphatidylserine externalization, high-level surface fibrinogen retention, membrane vesiculation, and procoagulant activity. Also, in CypD-deficient platelet-rich plasma, clot retraction was altered. Stimulation with thrombin plus H(2)O(2), a known activator of MPTP formation, also increased high-level surface fibrinogen retention, phosphatidylserine externalization, and platelet procoagulant activity in a CypD-dependent manner. In a model of carotid artery photochemical injury, thrombosis was markedly accelerated in CypD-deficient mice. These results implicate CypD and the MPTP as critical regulators of platelet activation and suggest a novel CypD-dependent negative-feedback mechanism regulating arterial thrombosis.