Cyclophilin D, a component of the permeability transition-pore, is an apoptosis repressor

Context-dependent roles for ubiquitous mitochondrial creatine kinase CKMT1 in breast cancer progression

Metabolic reprogramming is a hallmark of cancer, enabling cancer cells to rapidly proliferate, invade, and metastasize. We show that creatine levels in metastatic breast cancer cell lines and secondary metastatic tumors are driven by the ubiquitous mitochondrial creatine kinase (CKMT1). We discover that, while CKMT1 is highly expressed in primary tumors and promotes cell viability, it is downregulated in metastasis. We further show that CKMT1 downregulation, as seen in breast cancer metastasis, drives up mitochondrial reactive oxygen species (ROS) levels. CKMT1 downregulation contributes to the migratory and invasive potential of cells by ROS-induced upregulation of adhesion and degradative factors, which can be reversed by antioxidant treatment. Our study thus reconciles conflicting evidence about the roles of metabolites in the creatine metabolic pathway in breast cancer progression and reveals that tight, context-dependent regulation of CKMT1 expression facilitates cell viability, cell migration, and cell invasion, which are hallmarks of metastatic spread.

Cyclophilin D knockout significantly prevents HCC development in a streptozotocin-induced mouse model of diabetes-linked NASH

A family of Peptidyl-prolyl isomerases (PPIases), called Cyclophilins, localize to numerous intracellular and extracellular locations where they contribute to a variety of essential functions. We previously reported that non-immunosuppressive pan-cyclophilin inhibitor drugs like reconfilstat (CRV431) or NV556 decreased multiple aspects of non-alcoholic fatty liver disease (NAFLD) in mice under two different non-alcoholic steatohepatitis (NASH) mouse models. Both CRV431 and NV556 inhibit several cyclophilin isoforms, among which cyclophilin D (CypD) has not been previously investigated in this context. It is unknown whether it is necessary to simultaneously inhibit multiple cyclophilin family members to achieve therapeutic benefits or if loss-of-function of one is sufficient. Furthermore, narrowing down the isoform most responsible for a particular aspect of NAFLD/NASH, such as hepatocellular carcinoma (HCC), would allow for more precise future therapies. Features of human diabetes-linked NAFLD/NASH can be reliably replicated in mice by administering a single high dose of streptozotocin to disrupt pancreatic beta cells, in conjunction with a high sugar, high fat, high cholesterol western diet over the course of 30 weeks. Here we show that while both wild-type (WT) and Ppif-/- CypD KO mice develop multipe severe NASH disease features under this model, the formation of HCC nodules was significantly blunted only in the CypD KO mice. Furthermore, of differentially expressed transcripts in a qPCR panel of select HCC-related genes, nearly all were downregulated in the CypD KO background. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NAFLD/NASH. This study highlights the impact of CypD loss-of-function on the development of HCC, one of the most severe disease outcomes.

Promising Strategy of mPTP Modulation in Cancer Therapy: An Emerging Progress and Future Insight

Cancer has been progressively a major global health concern. With this developing global concern, cancer determent is one of the most significant public health challenges of this era. To date, the scientific community undoubtedly highlights mitochondrial dysfunction as a hallmark of cancer cells. Permeabilization of the mitochondrial membranes has been implicated as the most considerable footprint in apoptosis-mediated cancer cell death. Under the condition of mitochondrial calcium overload, exclusively mediated by oxidative stress, an opening of a nonspecific channel with a well-defined diameter in mitochondrial membrane allows free exchange between the mitochondrial matrix and the extra mitochondrial cytosol of solutes and proteins up to 1.5 kDa. Such a channel/nonspecific pore is recognized as the mitochondrial permeability transition pore (mPTP). mPTP has been established for regulating apoptosis-mediated cancer cell death. It has been evident that mPTP is critically linked with the glycolytic enzyme hexokinase II to defend cellular death and reduce cytochrome c release. However, elevated mitochondrial Ca2+ loading, oxidative stress, and mitochondrial depolarization are critical factors leading to mPTP opening/activation. Although the exact mechanism underlying mPTP-mediated cell death remains elusive, mPTP-mediated apoptosis machinery has been considered as an important clamp and plays a critical role in the pathogenesis of several types of cancers. In this review, we focus on structure and regulation of the mPTP complex-mediated apoptosis mechanisms and follow with a comprehensive discussion addressing the development of novel mPTP-targeting drugs/molecules in cancer treatment.

Cyclophilin D: Guardian or Executioner for Tumor Cells?

Cyclophilin D (CypD) is a peptide-proline cis-trans isomerase (PPIase) distributed in the mitochondrial matrix. CypD regulates the opening of the mitochondrial permeability conversion pore (mPTP) and mitochondrial bioenergetics through PPIase activity or interaction with multiple binding partners in mitochondria. CypD initially attracted attention due to its regulation of mPTP overopening-mediated cell death. However, recent studies on the effects of CypD on tumors have shown conflicting results. Although CypD has been proven to promote the aerobic glycolysis in tumor cells, its regulation of malignant characteristics such as the survival, invasion and drug resistance of tumor cells remains controversial. Here, we elaborate the main biological functions of CypD and its relationships with tumor progression identified in recent years, focusing on the dual role of CypD in tumors.

Targeting the mitochondrial permeability transition pore for drug discovery: Challenges and opportunities

Several drug targets have been amenable to drug discovery pursuit not until the characterization of the mitochondrial permeability transition pore (MPTP), a pore with an undefined molecular identity that forms on the inner mitochondrial membrane upon mitochondrial permeability transition (MPT) under the influence of calcium overload and oxidative stress. The opening of the pore which is presumed to cause cell death in certain human diseases also has implications under physiological parlance. Different models for this pore have been postulated following its first identification in the last six decades. The mitochondrial community has witnessed many protein candidates such as; voltage-dependent anion channel (VDAC), adenine nucleotide translocase (ANT), Mitochondrial phosphate carrier (PiC), Spastic Paralegin (SPG7), disordered proteins, and F1Fo ATPase. However, genetic studies have cast out most of these candidates with only F1Fo ATPase currently under intense argument. Cyclophilin D (CyPD) remains the widely accepted positive regulator of the MPTP known to date, but no drug candidate has emerged as its inhibitor, raising concern issues for therapeutics. Thus, in this review, we discuss various models of MPTP reported with the hope of stimulating further research in this field. We went beyond the classical description of the MPTP to ascribe a 'two-edged sword property' to the pore for therapeutic function in human disease because its inhibition and activation have pharmacological relevance. We suggested putative proteins upstream to CyPD that can regulate its activity and prevent cell deaths in neurodegenerative disease and ischemia-reperfusion injury.

Mitochondria signaling pathways in allergic asthma

Mitochondria, as the powerhouse organelle of cells, are greatly involved in regulating cell signaling pathways, including those related to the innate and acquired immune systems, cellular differentiation, growth, death, apoptosis, and autophagy as well as hypoxic stress responses in various diseases. Asthma is a chronic complicated airway disease characterized by airway hyperresponsiveness, eosinophilic inflammation, mucus hypersecretion, and remodeling of airway. The asthma mortality and morbidity rates have increased worldwide, so understanding the molecular mechanisms underlying asthma progression is necessary for new anti-asthma drug development. The lung is an oxygen-rich organ, and mitochondria, by sensing and processing O₂, contribute to the generation of ROS and activation of pro-inflammatory signaling pathways. Asthma pathophysiology has been tightly associated with mitochondrial dysfunction leading to reduced ATP synthase activity, increased oxidative stress, apoptosis induction, and abnormal calcium homeostasis. Defects of the mitochondrial play an essential role in the pro-remodeling mechanisms of lung fibrosis and airway cells’ apoptosis. Identification of mitochondrial therapeutic targets can help repair mitochondrial biogenesis and dysfunction and reverse related pathological changes and lung structural remodeling in asthma. Therefore, we here overviewed the relationship between mitochondrial signaling pathways and asthma pathogenic mechanisms.

Role of mitochondrial dysfunction, oxidative stress and autophagy in progression of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. The pathological hallmarks of AD are amyloid plaques [aggregates of amyloid beta (A)] and neurofibrillary tangles (aggregates of tau protein). Growing evidence suggests that tau accumulation is pathologically more relevant to the development of neurodegeneration and cognitive decline in AD patients than A plaques. Mitochondrial damage plays an important role in AD. Mitochondrial damage has been related to amyloid-beta or tau pathology or to the presence of specific presenilin-1 mutations. Elevate reactive oxygen species/reactive nitrogen species production and defective mitochondrial dynamic balance has been suggested to be the reason as well as the consequence of AD related pathology. Oxidative stress is a prominent early event in the pathogenesis of AD and is therefore believed to contribute to tau hyperphosphorylation. Several studies have shown that the autophagy pathway in neurons is important under physiological and pathological conditions. Therefore, this pathway plays a crucial role for the degradation of endogenous soluble tau. However, the relationship between mitochondrial dysfunctioning, oxidative stress, autophagy dysregulation, and neuronal cell death in AD remains unclear. Here, we review the latest progress in AD, with a special emphasis on mitochondrial dysfunctioning, oxidative stress, and autophagy. We also discuss the interlink mechanism of these three factors in AD.

Plant Cyclophilins: Multifaceted Proteins With Versatile Roles

Cyclophilins constitute a family of ubiquitous proteins that bind cyclosporin A (CsA), an immunosuppressant drug. Several of these proteins possess peptidyl-prolyl cis-trans isomerase (PPIase) activity that catalyzes the cis-trans isomerization of the peptide bond preceding a proline residue, essential for correct folding of the proteins. Compared to prokaryotes and other eukaryotes studied until now, the cyclophilin gene families in plants exhibit considerable expansion. With few exceptions, the role of the majority of these proteins in plants is still a matter of conjecture. However, recent studies suggest that cyclophilins are highly versatile proteins with multiple functionalities, and regulate a plethora of growth and development processes in plants, ranging from hormone signaling to the stress response. The present review discusses the implications of cyclophilins in different facets of cellular processes, particularly in the context of plants, and provides a glimpse into the molecular mechanisms by which these proteins fine-tune the diverse physiological pathways.

Novel insights into molecular mechanisms of Pseudourostyla cristata encystment using comparative transcriptomics

The encystment of many ciliates is an advanced survival strategy against adversity and the most important reason for ciliates existence worldwide. However, the molecular mechanism for the encystment of free-living ciliates is poorly understood. Here, we performed comparative transcriptomic analysis of dormant cysts and trophonts from Pseudourostyla cristata using transcriptomics, qRT-PCR and bioinformatic techniques. We identified 2565 differentially expressed unigenes between the dormant cysts and the trophonts. The total number of differentially expressed genes in GO database was 1752. The differential unigenes noted to the GO terms were 1993. These differential categories were mainly related to polyamine transport, pectin decomposition, cytoplasmic translation, ribosome, respiratory chain, ribosome structure, ion channel activity, and RNA ligation. A total of 224 different pathways were mapped. Among them, 184 pathways were upregulated, while 162 were downregulated. Further investigation showed that the calcium and AMPK signaling pathway had important induction effects on the encystment. In addition, FOXO and ubiquitin-mediated proteolysis signaling pathway jointly regulated the encystment. Based on these findings, we propose a hypothetical signaling network that regulates Pseudourostyla cristata encystment. Overall, these results provide deeper insights into the molecular mechanisms of ciliates encystment and adaptation to adverse environments.

Parkin Regulates Programmed Necrosis and Myocardial Ischemia/Reperfusion Injury by Targeting Cyclophilin-D

Aims: Cardiomyocyte death critically contributes to the pathogenesis of cardiac disorders, such as myocardial infarction, heart failure, and cardiac ischemia/reperfusion (I/R) injury. As one of the main forms of cardiac cell death, necrosis plays a critical role in heart diseases. Multiple signaling pathways of necrosis have been demonstrated, in which death receptors, receptor-interacting serine/threonine-protein 1 and 3 kinases, and cyclophilin-D (CypD) have been deeply implicated. However, the fundamental mechanism underlying myocardial necroptosis, especially the mitochondrial permeability transition pore (mPTP)-CypD-dependent death pathway, is poorly understood. Parkin functions as an E3 ubiquitin protein ligase that mainly mediates mitophagy cascades. As yet, it is not clear whether Parkin participates in regulating necrosis and myocardial I/R injury. Results: Here, our results showed that Parkin mediated mitophagy and inhibited necrosis under oxidative stress. In further exploring the underlying mechanisms, we found that Parkin suppressed mPTP opening by catalyzing the ubiquitination of CypD in necrotic cascades, which were not involved in Parkin-regulated mitophagy. Parkin inhibited necrosis, reduced myocardial I/R injury, and improved cardiac function. Innovation: Our present work reveals a highlighted connection between the mitochondrial matrix-localized Parkin and the mPTP-CypD-dependent necrotic signaling pathway in cardiac injury. Conclusion: Our results revealed a novel myocardial necrotic regulating model composed of Parkin, CypD, and mPTP, which may provide potential therapeutic targets and strategies to modulate the levels of these molecules.

Down-regulation of miRNA-27b-3p suppresses keratinocytes apoptosis in oral lichen planus

Oral lichen planus (OLP) is considered a precancerous lesion with no known cure. Recent studies reported that abnormal regulation of apoptosis was involved in the pathogenesis of OLP. Next generation sequencing was used to screen the candidate microRNAs and genes in biopsies from patients with OLP and healthy mucosa. Human oral keratinocytes were transfected into the related oligonucleotides of miR‐27b‐3p/cyclophilin D and their control groups. Apoptosis was detected by TdT‐mediated dUTP nick end labelling and flow cytometry. The levels of mRNA and protein were detected by quantitative PCR, Western blots, and enzyme‐linked immunosorbent assays, respectively. Luciferase assays were performed to detect the luciferase activities of miR‐27b‐3p and cyclophilin D. Here, we showed that basal epithelium apoptosis was reduced and the miR‐27b‐3p levels were decreased in clinical OLP samples. We also found that down‐regulation of miR‐27b‐3p inhibited epithelial keratinocyte apoptosis by up‐regulating cyclophilin D expression. Moreover, cyclophilin D increased the protein stability of Bcl2 through direct binding, and Bcl2 suppressed caspase9/3 activation and cytochrome C release. Taken together, these data showed that miR‐27b‐3p regulated keratinocyte apoptosis through cyclophilin D/Bcl2 signalling, suggesting the miR‐27b‐3p regulated the pathogenesis of OLP.

Effect of ganoderic acid D on colon cancer Warburg effect: Role of SIRT3/cyclophilin D

Ganoderic acid D (GAD) is a highly oxygenated tetracyclic triterpenoid. This study aims to assess the effects of GAD on the energy metabolism of colon cancer through the regulation of SIRT3 expression and whether this effect is related to acetylated cyclophilin D. The results demonstrated that GAD inhibits the energy reprogramming of colon cancer cells including glucose uptake, lactate production, pyruvate and acetyl-coenzyme production in colon cancer cells. Meanwhile, GAD upregulated the protein expression of SIRT3. Furthermore, the interruption of SIRT3 expression significantly reversed all the effects of SIRT3 on the energy reprogramming of colon cancer. In addition, GAD induced the deacetylated cyclophilin D (CypD) by SIRT3, whereas SIRT3-shRNA inhibited its combining effect on CypD. The energy reprogramming effects of GAD on colon cancer seem to be mediated by SIRT3 upregulation via acetylated CypD inhibition.

Overexpression of aryl hydrocarbon receptor (AHR) signalling pathway in human meningioma

Aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor and involved in tumorigenesis of many cancers. However there are no reports on AHR in human meningioma. Therefore we examined the status of the AHR and its signalling molecules in human meningioma by using tumor biopsy samples and autopsy control meninges. We report the up regulation of AHR pathway genes like aryl hydrocarbon receptor nuclear translocator (ARNT), aldehyde dehydrogenase1family memberA3 (ALDH1A3), cytochrome P450, family1, subfamily A polypeptide1 (CYP1A1) and TCCD induced poly ADP ribose polymerase (TIPARP) gene expression in human meningioma. Further, AHR protein expression was found to be up regulated in all grades of human meningioma. We found that AHR localized in the nucleus for high grade anaplastic meningioma through immunohistochemical analysis. Since AHR signalling pathway was known to involve in inhibition of apoptosis in cancer cells, we evaluated the cyclophilin D levels which maintains mitochondrial permeability transition pore a critical event during apoptosis. We report that cyclophilin D levels were upregulated in all grades of human meningioma compared to control meninges. Finally we also evaluated c-Fos protein levels as its levels were regulated by AHR. Here we report that c-Fos protein levels were down regulated in all grades of human meningioma compared to control meninges. To sum-up we found that AHR signalling pathway components were upregulated, as the grade of the meningioma progresses from low to high grade, suggesting an important role of AHR signalling pathway in human meningioma.

Mitochondrial permeability transition in cardiac ischemia-reperfusion: whether cyclophilin D is a viable target for cardioprotection?

Growing number of studies provide strong evidence that the mitochondrial permeability transition pore (PTP), a non-selective channel in the inner mitochondrial membrane, is involved in the pathogenesis of cardiac ischemia-reperfusion and can be targeted to attenuate reperfusion-induced damage to the myocardium. The molecular identity of the PTP remains unknown and cyclophilin D is the only protein commonly accepted as a major regulator of the PTP opening. Therefore, cyclophilin D is an attractive target for pharmacological or genetic therapies to reduce ischemia-reperfusion injury in various animal models and humans. Most animal studies demonstrated cardioprotective effects of PTP inhibition; however, a recent large clinical trial conducted by international groups demonstrated that cyclosporine A, a cyclophilin D inhibitor, failed to protect the heart in patients with myocardial infarction. These studies, among others, raise the question of whether cyclophilin D, which plays an important physiological role in the regulation of cell metabolism and mitochondrial bioenergetics, is a viable target for cardioprotection. This review discusses previous studies to provide comprehensive information on the physiological role of cyclophilin D as well as PTP opening in the cell that can be taken into consideration for the development of new PTP inhibitors.

Characterization of cyclophilin D in freshwater pearl mussel (Hyriopsis schlegelii)

Cyclophilin D (referred to as HsCypD) was obtained from the freshwater pearl mussel (Hyriopsis schlegelii). The full-length cDNA was 2 671 bp, encoding a protein consisting of 367 amino acids. HsCypD was determined to be a hydrophilic intracellular protein with 10 phosphorylation sites and four tetratricopeptide repeat (TPR) domains, but no signal peptide. The core sequence region YKGCIFHRIIKDFMVQGG is highly conserved in vertebrates and invertebrates. Phylogenetic tree analysis indicated that CypD from all species had a common origin, and HsCypD had the closest phylogenetic relationship with CypD from Lottia gigantea. The constitutive mRNA expression levels of HsCypD exhibited tissue-specific patterns, with the highest level detected in the intestines, followed by the gonads, and the lowest expression found in the hemocytes.

Cyclophilin D counteracts P53-mediated growth arrest and promotes Ras tumorigenesis

Mitochondrial alterations induced by oncogenes are known to be crucial for tumorigenesis. Ras oncogene leads to proliferative signals through a Raf-1/MEK/ERK kinase cascade, whose components have been found to be also associated with mitochondria. The mitochondrial pepdidyl-prolyl isomerase cyclophilin D (CypD) is an important regulator of the mitochondrial permeability transition and a key player in mitochondria physiology; however, its role in cancer is still unclear. Using cellular and in vivo mouse models, we demonstrated that CypD protein upregulation induced by oncogenic Ras through the Raf-1/MEK/ERK pathway has a deterministic role in tumor progression. In fact, targeting CypD gene expression clearly affected RasV12-induced transformation, as showed by in vitro data on murine NIH3T3 and human MCF10A mammary epithelial cells. In addition, studies in xenograft and K-Ras lung cancer mouse models demonstrated that genetic deletion or pharmacological suppression of CypD efficiently prevented Ras-dependent tumor formation. Furthermore, Erbb2-mediated breast tumorigenesis was similarly prevented by targeting CypD. From a mechanistic point of view, CypD expression was associated with a reduced induction of p21(WAF1/CIP1) and p53 functions, unraveling an antagonistic function of CypD on p21-p53-mediated growth suppression. CypD activity is p53 dependent. Interestingly, a physical association between p53 and CypD was detected in mitochondria of MCF10A cells; furthermore, both in vitro and in vivo studies proved that CypD inhibitor-based treatment was able to efficiently impair this interaction, leading to a tumor formation reduction. All together, these findings indicate that the countering effect of CypD on the p53-p21 pathway participates in oncogene-dependent transformation.

Cyclophilin J is a novel peptidyl-prolyl isomerase and target for repressing the growth of hepatocellular carcinoma

Cyclophilin J (CYPJ) is a new member of the peptidyl-prolyl cis/trans-isomerase (PPIase) identified with upregulated expression in human glioma. However, the biological function of CYPJ remained unclear. We aimed to study the role of CYPJ in hepatocellular carcinoma (HCC) carcinogenesis and its therapeutic potential. We determined the expression of CYPJ in HCC/adjacent normal tissues using Western blot, Northern blot and semi-quantitative RT-PCR, analyzed the biochemical characteristics of CYPJ, and resolved the 3D-structure of CYPJ/Cyclosporin A (CsA) complex. We also studied the roles of CYPJ in cell cycle, cyclin D1 regulation, in vitro and in vivo tumor growth. We found that CYPJ expression was upregulated in over 60% HCC tissues. The PPIase activity of CYPJ could be inhibited by the widely used immunosuppressive drug CsA. CYPJ was found expressed in the whole cell of HCC with preferential location at the cell nucleus. CYPJ promoted the transition of cells from G1 phase to S phase in a PPIase-dependent manner by activating cyclin D1 promoter. CYPJ overexpression accelerated liver cell growth in vitro (cell growth assay, colony formation) and in vivo (xenograft tumor formation). Inhibition of CYPJ by its inhibitor CsA or CYPJ-specific RNAi diminished the growth of liver cancer cells in vitro and in vivo. In conclusion, CYPJ could facilitate HCC growth by promoting cell cycle transition from G1 to S phase through the upregulation of cyclin D1. Suppression of CYPJ could repress the growth of HCC, which makes CYPJ a potential target for the development of new strategies to treat this malignancy.

ERRγ target genes are poor prognostic factors in Tamoxifen-treated breast cancer

BACKGROUND

One-third of estrogen (ER+) and/or progesterone receptor-positive (PGR+) breast tumors treated with Tamoxifen (TAM) do not respond to initial treatment, and the remaining 70% are at risk to relapse in the future. Estrogen-related receptor gamma (ESRRG, ERRγ) is an orphan nuclear receptor with broad, structural similarities to classical ER that is widely implicated in the transcriptional regulation of energy homeostasis. We have previously demonstrated that ERRγ induces resistance to TAM in ER+ breast cancer models, and that the receptor's transcriptional activity is modified by activation of the ERK/MAPK pathway. We hypothesize that hyper-activation or over-expression of ERRγ induces a pro-survival transcriptional program that impairs the ability of TAM to inhibit the growth of ER+ breast cancer. The goal of the present study is to determine whether ERRγ target genes are associated with reduced distant metastasis-free survival (DMFS) in ER+ breast cancer treated with TAM.

METHODS

Raw gene expression data was obtained from 3 publicly available breast cancer clinical studies of women with ER+ breast cancer who received TAM as their sole endocrine therapy. ERRγ target genes were selected from 2 studies that published validated chromatin immunoprecipitation (ChIP) analyses of ERRγ promoter occupancy. Kaplan-Meier estimation was used to determine the association of ERRγ target genes with DMFS, and selected genes were validated in ER+, MCF7 breast cancer cells that express exogenous ERRγ.

RESULTS

Thirty-seven validated receptor target genes were statistically significantly altered in women who experienced a DM within 5 years, and could classify several independent studies into poor vs. good DMFS. Two genes (EEF1A2 and PPIF) could similarly separate ER+, TAM-treated breast tumors by DMFS, and their protein levels were measured in an ER+ breast cancer cell line model with exogenous ERRγ. Finally, expression of ERRγ and these two target genes are elevated in models of ER+ breast cancer with hyperactivation of ERK/MAPK.

CONCLUSIONS

ERRγ signaling is associated with poor DMFS in ER+, TAM-treated breast cancer, and ESRRG, EEF1A2, and PPIF comprise a 3-gene signaling node that may contribute to TAM resistance in the context of an active ERK/MAPK pathway.

Overexpression of 17β-hydroxysteroid dehydrogenase type 10 increases pheochromocytoma cell growth and resistance to cell death

BACKGROUND

17β-hydroxysteroid dehydrogenase type 10 (HSD10) has been shown to play a protective role in cells undergoing stress. Upregulation of HSD10 under nutrient-limiting conditions leads to recovery of a homeostatic state. Across disease states, increased HSD10 levels can have a profound and varied impact, such as beneficial in Parkinson's disease and harmful in Alzheimer's disease. Recently, HSD10 overexpression has been observed in some prostate and bone cancers, consistently correlating with poor patient prognosis. As the role of HSD10 in cancer remains underexplored, we propose that cancer cells utilize this enzyme to promote cancer cell survival under cell death conditions.

METHODS

The proliferative effect of HSD10 was examined in transfected pheochromocytoma cells by growth curve analysis and a xenograft model. Fluctuations in mitochondrial bioenergetics were evaluated by electron transport chain complex enzyme activity assays and energy production. Additionally, the effect of HSD10 on pheochromocytoma resistance to cell death was investigated using TUNEL staining, MTT, and complex IV enzyme activity assays.

RESULTS

In this study, we examined the tumor-promoting effect of HSD10 in pheochromocytoma cells. Overexpression of HSD10 increased pheochromocytoma cell growth in both in vitro cell culture and an in vivo xenograft mouse model. The increases in respiratory enzymes and energy generation observed in HSD10-overexpressing cells likely supported the accelerated growth rate observed. Furthermore, cells overexpressing HSD10 were more resistant to oxidative stress-induced perturbation.

CONCLUSIONS

Our findings demonstrate that overexpression of HSD10 accelerates pheochromocytoma cell growth, enhances cell respiration, and increases cellular resistance to cell death induction. This suggests that blockade of HSD10 may halt and/or prevent cancer growth, thus providing a promising novel target for cancer patients as a screening or therapeutic option.

Mitochondrial Ca(2+) influx targets cardiolipin to disintegrate respiratory chain complex II for cell death induction

Massive Ca(2+) influx into mitochondria is critically involved in cell death induction but it is unknown how this activates the organelle for cell destruction. Using multiple approaches including subcellular fractionation, FRET in intact cells, and in vitro reconstitutions, we show that mitochondrial Ca(2+) influx prompts complex II of the respiratory chain to disintegrate, thereby releasing an enzymatically competent sub-complex that generates excessive reactive oxygen species (ROS) for cell death induction. This Ca(2+)-dependent dissociation of complex II is also observed in model membrane systems, but not when cardiolipin is replaced with a lipid devoid of Ca(2+) binding. Cardiolipin is known to associate with complex II and upon Ca(2+) binding coalesces into separate homotypic clusters. When complex II is deprived of this lipid, it disintegrates for ROS formation and cell death. Our results reveal Ca(2+) binding to cardiolipin for complex II disintegration as a pivotal step for oxidative stress and cell death induction.

CKMT1 regulates the mitochondrial permeability transition pore in a process that provides evidence for alternative forms of the complex

The permeability transition pore (PT-pore) mediates cell death through the dissipation of the mitochondrial membrane potential (ΔΨm). Because the exact composition of the PT-pore is controversial, it is crucial to investigate the actual molecular constituents and regulators of this complex. We found that mitochondrial creatine kinase-1 (CKMT1) is a universal and functionally necessary gatekeeper of the PT-pore, as its depletion induces mitochondrial depolarization and apoptotic cell death. This can be inhibited efficiently by bongkrekic acid, a compound that is widely used to inhibit the PT-pore. However, when the 'classical' PT-pore subunits cyclophilin D and VDAC1 are pharmacologically inhibited or their expression levels reduced, mitochondrial depolarization by CKMT1 depletion remains unaffected. At later stages of drug-induced apoptosis, CKMT1 levels are reduced, suggesting that CKMT1 downregulation acts to reinforce the commitment of cells to apoptosis. A novel high-molecular-mass CKMT1 complex that is distinct from the known CKMT1 octamer disintegrates upon treatment with cytotoxic drugs, concomitant with mitochondrial depolarization. Our study provides evidence that CKMT1 is a key regulator of the PT-pore through a complex that is distinct from the classical PT-pore.

Thyroid hormone, thyromimetics, and metabolic efficiency

Thyroid hormone (TH) has long been recognized as a major modulator of metabolic efficiency, energy expenditure, and thermogenesis. TH effects in regulating metabolic efficiency are transduced by controlling the coupling of mitochondrial oxidative phosphorylation and the cycling of extramitochondrial substrate/futile cycles. However, despite our present understanding of the genomic and nongenomic modes of action of TH, its control of mitochondrial coupling still remains elusive. This review summarizes historical and up-to-date findings concerned with TH regulation of metabolic energetics, while integrating its genomic and mitochondrial activities. It underscores the role played by TH-induced gating of the mitochondrial permeability transition pore (PTP) in controlling metabolic efficiency. PTP gating may offer a unified target for some TH pleiotropic activities and may serve as a novel target for synthetic functional thyromimetics designed to modulate metabolic efficiency. PTP gating by long-chain fatty acid analogs may serve as a model for such strategy.

Cyclophilin B supports Myc and mutant p53-dependent survival of glioblastoma multiforme cells

Glioblastoma multiforme is an aggressive, treatment-refractory type of brain tumor for which effective therapeutic targets remain important to identify. Here, we report that cyclophilin B (CypB), a prolyl isomerase residing in the endoplasmic reticulum (ER), provides an essential survival signal in glioblastoma multiforme cells. Analysis of gene expression databases revealed that CypB is upregulated in many cases of malignant glioma. We found that suppression of CypB reduced cell proliferation and survival in human glioblastoma multiforme cells in vitro and in vivo. We also found that treatment with small molecule inhibitors of cyclophilins, including the approved drug cyclosporine, greatly reduced the viability of glioblastoma multiforme cells. Mechanistically, depletion or pharmacologic inhibition of CypB caused hyperactivation of the oncogenic RAS-mitogen-activated protein kinase pathway, induction of cellular senescence signals, and death resulting from loss of MYC, mutant p53, Chk1, and Janus-activated kinase/STAT3 signaling. Elevated reactive oxygen species, ER expansion, and abnormal unfolded protein responses in CypB-depleted glioblastoma multiforme cells indicated that CypB alleviates oxidative and ER stresses and coordinates stress adaptation responses. Enhanced cell survival and sustained expression of multiple oncogenic proteins downstream of CypB may thus contribute to the poor outcome of glioblastoma multiforme tumors. Our findings link chaperone-mediated protein folding in the ER to mechanisms underlying oncogenic transformation, and they make CypB an attractive and immediately targetable molecule for glioblastoma multiforme therapy.

The role of cyclophilin D in interspecies differences in susceptibility to hepatotoxic drug-induced mitochondrial injury

Test compound A ((5Z)-6-[(2R,3S)-3-({[(4-Chloro-2-methylphenyl)sulfonyl]amino}methyl) bicyclo[2.2.2]oct-2-yl]hex-5-enoic acid) was withdrawn from premarketing clinical trials due to severe liver injury. Intracellular accumulation of lipids (steatosis) has been observed in human-derived cells and may account for the severe hepatotoxicity. Mitochondrial β-oxidation and ketogenesis play a fundamental role in energy homeostasis. Mitochondrial dysfunction can therefore cause severe deficiency in fatty acid oxidation and apoptosis which finally triggers the hepatocellular injury. Some of hepatotoxic drugs (e.g., salicylic acid, diclofenac and troglitazone) are known to induce mitochondrial dysfunction. This study therefore examined the effect of compound A on the mitochondrial permeability transition (MPT) and membrane potential in mitochondria isolated from mouse, rat and monkey livers. The incubation of rat and monkey mitochondria energized by succinate in the presence of Ca(2+) (20μM) and compound A (2.5-10μM) resulted in cyclosporin A (CsA)-sensitive MPT pore opening and a decline in mitochondrial membrane potential in a concentration-dependent manner. However, mouse mitochondria showed low susceptibility to compound A-induced dysfunction. Rat mitochondrial expression of cyclophilin D (CyPD) was about twice that of mouse mitochondria, but the expression levels of other MPT pore proteins (adenine nucleotide translocator and voltage-dependent anion channel) were comparable in both species. An assessment of the effect of compound A on CyPD knockdown cells demonstrated that mitochondrial susceptibility to compound A was attenuated in CyPD knockdown cells. These results suggest that an interspecies difference in the susceptibility to mitochondrial dysfunction induced by compound A exists as a result of species-specific discrepancies in CyPD expression.

Mitochondrial dysfunction and permeability transition in osteosarcoma cells showing the Warburg effect

Metabolic reprogramming in cancer is manifested by persistent aerobic glycolysis and suppression of mitochondrial function and is known as the Warburg effect. The Warburg effect contributes to cancer progression and is considered to be a promising therapeutic target. Understanding the mechanisms used by cancer cells to suppress their mitochondria may lead to development of new approaches to reverse metabolic reprogramming. We have evaluated mitochondrial function and morphology in poorly respiring LM7 and 143B osteosarcoma (OS) cell lines showing the Warburg effect in comparison with actively respiring Saos2 and HOS OS cells and noncancerous osteoblastic hFOB cells. In LM7 and 143B cells, we detected markers of the mitochondrial permeability transition (MPT), such as mitochondrial swelling, depolarization, and membrane permeabilization. In addition, we detected mitochondrial swelling in human OS xenografts in mice and archival human OS specimens using electron microscopy. The MPT inhibitor sanglifehrin A reversed MPT markers and increased respiration in LM7 and 143B cells. Our data suggest that the MPT may play a role in suppression of mitochondrial function, contributing to the Warburg effect in cancer.

Reconstitution of CKMT1 expression fails to rescue cells from mitochondrial membrane potential dissipation: implications for controlling RNAi experiments

RNA interference (RNAi) is an essential method in molecular biology to reduce the expression of target genes and thereby determine their function. Since this tool is known to also have unspecific effects, control experiments are needed, chiefly among them the exclusion of off-target effects and the reconstitution of the genes' expression for the rescue of the cellular RNAi effects. We show here that the knock-down of the mitochondrial creatine kinase-1 (CKMT1) by RNA interference causes the dissipation of the mitochondrial membrane potential ΔΨm. This was accomplished with 11 different RNAi constructs designed to target 7 distinct exons as well as exon/intron junctions making unspecific off-target effects unlikely. However, all our attempts failed to rescue human cells from ΔΨm dissipation by the expression of CKMT1 alleles not targeted by RNAi. This included the transient and stable expression of the murine CKMT1 homologue, the expression of human codon usage-modified alleles, the transfection of a novel splice-isoform of CKMT1, and even the introduction of a human genomic clone for CKMT1 with codon usage changes. Our results indicate that while off-target effects of RNA interference can easily be addressed, the rescue of the knock-down phenotype is not necessarily achievable.

Trauma-associated human neutrophil alterations revealed by comparative proteomics profiling

PURPOSE

Polymorphonuclear neutrophils (PMNs) play an important role in mediating the innate immune response after severe traumatic injury; however, the cellular proteome response to traumatic condition is still largely unknown.

EXPERIMENTAL DESIGN

We applied 2D-LC-MS/MS-based shotgun proteomics to perform comparative proteome profiling of human PMNs from severe trauma patients and healthy controls.

RESULTS

A total of 197 out of ~2500 proteins (being identified with at least two peptides) were observed with significant abundance changes following the injury. The proteomics data were further compared with transcriptomics data for the same genes obtained from an independent patient cohort. The comparison showed that the protein abundance changes for the majority of proteins were consistent with the mRNA abundance changes in terms of directions of changes. Moreover, increased protein secretion was suggested as one of the mechanisms contributing to the observed discrepancy between protein and mRNA abundance changes. Functional analyses of the altered proteins showed that many of these proteins were involved in immune response, protein biosynthesis, protein transport, NRF2-mediated oxidative stress response, the ubiquitin-proteasome system, and apoptosis pathways.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data suggest increased neutrophil activation and inhibited neutrophil apoptosis in response to trauma. The study not only reveals an overall picture of functional neutrophil response to trauma at the proteome level, but also provides a rich proteomics data resource of trauma-associated changes in the neutrophil that will be valuable for further studies of the functions of individual proteins in PMNs.

Cyclophilin D modulates cell death transition from early apoptosis to programmed necrosis induced by honokiol

Honokiol is a pharmacologically active small molecule with multifunctional antitumor effects. Although plenty of literature is available on honokiol-triggered apoptosis and programmed necrosis, few studies have investigated the potential existence of death mode transition from apoptosis to programmed necrosis. In the current study, we demonstrated that the necrotic cell population (PI-positive) gradually increased and the early-stage apoptotic cell population (PI-negative and AV-positive) decreased in a dose- and time-dependent manner following honokiol treatment. Furthermore, we demonstrated that these PI-positive cells were under necrotic cell death, since no late-apoptosis characteristics including conspicuous chromatin condensation or DNA ladder patterns were detected. These results demonstrated that cells suffered death mode transition from early-stage apoptosis to programmed necrosis with the increase of honokiol dose or treatment time. The protein expression of RIP3 markedly increased in parallel with HNK-triggered death mode transition, while the expression of RIP1 decreased. Cyclophilin D expression increased during cell death mode transition, and inhibition of cyclophilin D by cyclosporin A clearly blocked HNK-triggered programmed necrosis. These data indicated that honokiol-induced programmed necrosis and death mode transition are potentially RIP3‑dependent, cyclophilin D-regulated. Further results showed that blocked cyclophilin D by cyclosporin A inhibited HNK-induced necrosis, but did not affect HNK-induced RIP3 overexpression. This indicated that cyclophilin D was a potential modulator at downstream of RIP3. In conclusion, honokiol triggers a potential RIP3-dependent cell death mode transition from early-stage apoptosis to programmed necrosis, which is highly regulated by cyclophilin D.

Mitochondrial permeability transition pore as a selective target for anti-cancer therapy

Mitochondrial outer membrane permeabilization (MOMP) is the ultimate step in dozens of lethal apoptotic signal transduction pathways which converge on mitochondria. One of the representative systems proposed to be responsible for the MOMP is the mitochondrial permeability transition pore (MPTP). Although the molecular composition of the MPTP is not clearly understood, the MPTP attracts much interest as a promising target for resolving two conundrums regarding cancer treatment: tumor selectivity and resistance to treatment. The regulation of the MPTP is closely related to metabolic reprogramming in cancer cells including mitochondrial alterations. Restoration of deregulated apoptotic machinery in cancer cells by tumor-specific modulation of the MPTP could therefore be a promising anti-cancer strategy. Currently, a number of MPTP-targeting agents are under pre-clinical and clinical studies. Here, we reviewed the structure and regulation of the MPTP as well as the current status of the development of promising MPTP-targeting drugs.

Physiological roles of the permeability transition pore

Mitochondria are implicated in many important cellular functions covering the whole life cycle from mitochondrial biogenesis to cell death. Mitochondrial homeostasis is tightly regulated, and mitochondrial dysfunction is frequently associated with severe human pathologies (eg, cardiovascular diseases, cancer, and neurodegeneration). The permeability transition pore (PTP) is an unselective voltage-dependent mitochondrial channel. Despite the extensive use of electrophysiology, biochemistry, pharmacology, and genetic invalidation in mice, the molecular identity of PTP is still unknown. Nevertheless, PTP is central to mitochondrial vital functions and can play a lethal role in many pathophysiological conditions. This review recapitulates the current knowledge of the various modes of conductance of the PTP channel and discusses their implication in the physiological roles of PTP and their regulation. Based on its involvement in normal physiology and human pathology, a better understanding of this channel and its roles remains a major goal for basic scientists and clinicians.

Sirtuin-3 modulates Bak- and Bax-dependent apoptosis

Sirtuin-3 exhibits properties of a tumor suppressor partly emanating from its ability to control the state of mitochondrial metabolism, with depletion of sirt-3 increasing tumor cell survival. In the present study we demonstrate that depletion of sirtuin-3 brings about an anti-apoptotic phenotype via stimulating cyclophilin-D activity, which promotes the binding of hexokinase II to the mitochondria, thereby preventing Bak/Bax dependent mitochondrial injury and cell death. By contrast, increased expression of sirtuin-3 decreases cyclophilin-D activity, resulting in detachment of hexokinase II from the mitochondria and potentiation of Bak- and Bax-induced mitochondrial injury and loss of cell viability.

Mitochondrial Markers for Cancer: Relevance to Diagnosis, Therapy, and Prognosis and General Understanding of Malignant Disease Mechanisms

Cancer cells display changes that aid them to escape from cell death, sustain their proliferative powers, and shift their metabolism toward glycolytic energy production. Mitochondria are key organelles in many metabolic and biosynthetic pathways, and the adaptation of mitochondrial function has been recognized as crucial to the changes that occur in cancer cells. This paper zooms in on the pathologic evaluation of mitochondrial markers for diagnosing and staging of human cancer and determining the patients’ prognoses.

Dissecting mitochondrial apoptosis pathways by gain-of-function cell culture screens

While more primitive organism such as Caenorhabditis elegans and Drosophila melanogaster feature a limited, and by now probably mostly known, array of basic cell death factors, the mammalian cell is replete with additional regulators of the cell's demise. This abundance of apoptosis mediators has made it imperative to set up a systematic inventory of mammalian cell death genes. Genetic screens in this biological system have recently uncovered the rich diversity of cell death signalling and have in particular highlighted mitochondria as an organelle loaded with apoptosis regulators. Many of the screens that have addressed this utilised the novel technique of RNA interference but some also looked at gain-of-functions with transfected cDNAs. Here we give an overview of the rationale for the latter approach, present the genes discovered by this strategy and in particular describe the involvement of mitochondria and their signalling pathways defined by those genes.

SIRT3 protects from hypoxia and staurosporine-mediated cell death by maintaining mitochondrial membrane potential and intracellular pH

Mitochondrial sirtuin 3 (SIRT3) mediates cellular resistance toward various forms of stress. Here, we show that in mammalian cells subjected to hypoxia and staurosporine treatment SIRT3 prevents loss of mitochondrial membrane potential (ΔΨ(mt)), intracellular acidification and reactive oxygen species accumulation. Our results indicate that: (i) SIRT3 inhibits mitochondrial permeability transition and loss of membrane potential by preventing HKII binding to the mitochondria, (ii) SIRT3 increases catalytic activity of the mitochondrial carbonic anhydrase VB, thereby preventing intracellular acidification, Bax activation and apoptotic cell death. In conclusion we propose that, in mammalian cells, SIRT3 has a central role in connecting changes in ΔΨ(mt), intracellular pH and mitochondrial-regulated apoptotic pathways.

Necroptosis: an emerging form of programmed cell death

Necrosis plays an important role in multiple physiological and pathological processes. Recently, a relatively new form of necrosis has been characterized as "necroptosis". Morphologically, necroptosis exhibits the features of necrosis; however, necroptosis exhibits a unique signaling pathway that requires the involvement of receptor interaction protein kinase 1 and 3 (RIP1 and RIP3) and can be specifically inhibited by necrostatins. Necroptosis has been found to contribute to the regulation of immune system, cancer development as well as cellular responses to multiple stresses. In this review, we will summarize the signaling pathway, biological effects and pathological significance of this specific form of programmed cell death.

Determining signalling nodes for apoptosis by a genetic high-throughput screen

BACKGROUND

With the ever-increasing information emerging from the various sequencing and gene annotation projects, there is an urgent need to elucidate the cellular functions of the newly discovered genes. The genetically regulated cell suicide of apoptosis is especially suitable for such endeavours as it is governed by a vast number of factors.

METHODOLOGY/PRINCIPAL FINDINGS

We have set up a high-throughput screen in 96-well microtiter plates for genes that induce apoptosis upon their individual transfection into human cells. Upon screening approximately 100,000 cDNA clones we determined 74 genes that initiate this cellular suicide programme. A thorough bioinformatics analysis of these genes revealed that 91% are novel apoptosis regulators. Careful sequence analysis and functional annotation showed that the apoptosis factors exhibit a distinct functional distribution that distinguishes the cell death process from other signalling pathways. While only a minority of classic signal transducers were determined, a substantial number of the genes fall into the transporter- and enzyme-category. The apoptosis factors are distributed throughout all cellular organelles and many signalling circuits, but one distinct signalling pathway connects at least some of the isolated genes. Comparisons with microarray data suggest that several genes are dysregulated in specific types of cancers and degenerative diseases.

CONCLUSIONS/SIGNIFICANCE

Many unknown genes for cell death were revealed through our screen, supporting the enormous complexity of cell death regulation. Our results will serve as a repository for other researchers working with genomics data related to apoptosis or for those seeking to reveal novel signalling pathways for cell suicide.

Amyloid-β as a modulator of synaptic plasticity

Alzheimer's disease is associated with synapse loss, memory dysfunction, and pathological accumulation of amyloid-β (Aβ) in plaques. However, an exclusively pathological role for Aβ is being challenged by new evidence for an essential function of Aβ at the synapse. Aβ protein exists in different assembly states in the central nervous system and plays distinct roles ranging from synapse and memory formation to memory loss and neuronal cell death. Aβ is present in the brain of symptom-free people where it likely performs important physiological roles. New evidence indicates that synaptic activity directly evokes the release of Aβ at the synapse. At physiological levels, Aβ is a normal, soluble product of neuronal metabolism that regulates synaptic function beginning early in life. Monomeric Aβ40 and Aβ42 are the predominant forms required for synaptic plasticity and neuronal survival. With age, some assemblies of Aβ are associated with synaptic failure and Alzheimer's disease pathology, possibly targeting the N-methyl-D-aspartic acid receptor through the nicotinic acetylcholine receptor, mitochondrial Aβ alcohol dehydrogenase, and cyclophilin D. But emerging data suggests a distinction between age effects on the target response in contrast to the assembly state or the accumulation of the peptide. Both aging and Aβ independently decrease neuronal plasticity. Our laboratory has reported that Aβ, glutamate, and lactic acid are each increasingly toxic with neuron age. The basis of the age-related toxicity partly resides in age-related mitochondrial dysfunction and an oxidative shift in mitochondrial and cytoplasmic redox potential. In turn, signaling through phosphorylated extracellular signal-regulated protein kinases is affected along with an age-independent increase in phosphorylated cAMP response element-binding protein. This review examines the long-awaited functional impact of Aβ on synaptic plasticity.

Targeting the mitochondrial permeability transition: cardiac ischemia-reperfusion versus carcinogenesis

Cardiovascular diseases and cancer continue to be major causes of death worldwide, and despite intensive research only modest progress has been reached in reducing the morbidity and mortality of these awful diseases. Mitochondria are broadly accepted as the key organelles that play a crucial role in cell life and death. They provide cells with ATP produced via oxidative phosphorylation under physiological conditions, and initiate cell death through both apoptosis and necrosis in response to severe stress. Oxidative stress accompanied by calcium overload and ATP depletion induces the mitochondrial permeability transition (mPT) with formation of pathological, non-specific mPT pores (mPTP) in the mitochondrial inner membrane. Opening of the mPTP with a high conductance results in matrix swelling ultimately inducing rupture of the mitochondrial outer membrane and releasing pro-apoptotic proteins into the cytoplasm. The ATP level is the determining factor in deciding whether cells die through apoptosis or necrosis. Cardiac cells undergoing ischemia followed by reperfusion (IR) possess exactly the same conditions mentioned above to induce mPTP opening. Due to its critical role in cell death, inhibition of mPTP opening has been accepted as a major therapeutic approach to protect the heart against IR. In contrast to cardiac IR, cancer cells exhibit less sensitivity to pore opening which can be in part explained by increased expression of mPTP compounds/modulators and metabolic remodeling. Since the main goal of chemotherapy is to provoke apoptosis, mPT induction may represent an attractive approach for the development of new cancer therapeutics to induce mitochondria-mediated cell death and prevent cell differentiation in carcinogenesis. This review focuses on the role of the mPTP in cardiac IR and cancer, and pharmacological agents to prevent or initiate mPT-mediated cell death, respectively in these diseases.

The mitochondrial permeability transition pore regulates nitric oxide-mediated apoptosis of neurons induced by target deprivation

Ablation of mouse occipital cortex induces precisely timed and uniform p53-modulated and Bax-dependent apoptosis of thalamocortical projection neurons in the dorsal lateral geniculate nucleus (LGN) by 7 d after lesion. We tested the hypothesis that this neuronal apoptosis is initiated by oxidative stress and the mitochondrial permeability transition pore (mPTP). Preapoptotic LGN neurons accumulate mitochondria, Zn(2+) and Ca(2+), and generate higher levels of reactive oxygen species (ROS), including superoxide, nitric oxide (NO), and peroxynitrite, than LGN neurons with an intact cortical target. Preapoptosis of LGN neurons is associated with increased formation of protein carbonyls, protein nitration, and protein S-nitrosylation. Genetic deletion of nitric oxide synthase 1 (nos1) and inhibition of NOS1 with nitroindazole protected LGN neurons from apoptosis, revealing NO as a mediator. Putative components of the mPTP are expressed in mouse LGN, including the voltage-dependent anion channel (VDAC), adenine nucleotide translocator (ANT), and cyclophilin D (CyPD). Nitration of CyPD and ANT in LGN mitochondria occurs by 2 d after cortical injury. Chemical cross-linking showed that LGN neuron preapoptosis is associated with formation of CyPD and VDAC oligomers, consistent with mPTP formation. Mice without CyPD are rescued from neuron apoptosis as are mice treated with the mPTP inhibitors TRO-19622 (cholest-4-en-3-one oxime) and TAT-Bcl-X(L)-BH4. Manipulation of the mPTP markedly attenuated the early preapoptotic production of reactive oxygen/nitrogen species in target-deprived neurons. Our results demonstrate in adult mouse brain neurons that the mPTP functions to enhance ROS production and the mPTP and NO trigger apoptosis; thus, the mPTP is a target for neuroprotection in vivo.

Mitochondrial sirtuins in the regulation of mitochondrial activity and metabolic adaptation

In eukaryotes, mitochondria carry out numerous functions that are central to cellular and organismal health. How mitochondrial activities are regulated in response to differing environmental conditions, such as variations in diet, remains an important unsolved question in biology. Here, we review emerging evidence suggesting that reversible acetylation of mitochondrial proteins on lysine residues represents a key mechanism by which mitochondrial functions are adjusted to meet environmental demands. In mammals, three members of the sirtuin class of NAD(+)-dependent deacetylases - SIRT3, SIRT4, and SIRT5 - localize to mitochondria and regulate targets involved in a diverse array of biochemical pathways. The importance of this activity is highlighted by recent studies of SIRT3 indicating that this protein suppresses the emergence of diverse age-related pathologies: hearing loss, cardiac fibrosis, and malignancy. Together, these findings argue that mitochondrial protein acetylation represents a central means by which mammals regulate mitochondrial functions to maintain cellular and organismal homeostasis.

Ethanol sensitizes mitochondria to the permeability transition by inhibiting deacetylation of cyclophilin-D mediated by sirtuin-3

Ethanol increases the vulnerability of mitochondria to induction of the mitochondrial permeability transition (MPT). Cyclophilin-D activity enhances the potential for the permeability transition pore (PTP) to open. In the present study, we demonstrate that ethanol and its metabolism sensitize the PTP to opening, in part by increasing the acetylation and activity of cyclophilin-D. This effect of ethanol is mediated by inhibiting the activity of sirtuin-3, an NAD(+) dependent deacetylase that is localized to the mitochondrial matrix. The ethanol-enhanced acetylation of cyclophilin-D also increases the interaction of cyclophilin-D with the adenine nucleotide translocator-1 (ANT-1) and is dependent on ethanol metabolism. Moreover, activation of AMPK, a known positive modulator of sirtuin activity, prevented the ethanol-induced suppression of sirtuin-3 activity and the attendant increase of cyclophilin-D acetylation, activity and association with ANT-1. Additionally, AMPK reactivation of sirtuin-3 prevented the sensitization to the MPT and the enhancement of cell killing by TNF in cells exposed to ethanol.

An Overview of Cyclophilins in Human Cancers

Cyclophilins (Cyps) belong to a group of proteins that have peptidyl-prolyl cis–trans isomerase (PPIase) and molecular chaperone activities. Originally, Cyps were identified as the intracellular receptors for the immunosuppressive drug cyclosporin A. Cyps are found in all prokaryotes and eukaryotes, and have been structurally conserved throughout evolution, implying their importance in cellular function. There are seven major Cyp isoforms in humans. CypA is up-regulated in many human cancers, and there is a strong correlation between over-expression of the CYPA gene and malignant transformation in some cancers. Moreover, CypA is directly under the transcriptional control of two critical transcription factors for cancer development: p53 and hypoxia inducible factor-1α. This review discusses the general biological functions of Cyps under a variety of stress conditions, and the importance and diverse roles of over-expression of CYP genes in human cancers, with a particular emphasis on CYPA. These oncogenic properties suggest that CypA is a promising target for cancer therapy.

Sirtuin-3 deacetylation of cyclophilin D induces dissociation of hexokinase II from the mitochondria

We demonstrate that the transition from a reliance on glycolysis to oxidative phosphorylation in a transformed cell line is dependent on an increase in the levels and activity of sirtuin-3. Sirtuin-3 deacetylates cyclophilin D, diminishing its peptidyl-prolyl cis-trans isomerase activity and inducing its dissociation from the adenine nucleotide translocator. Moreover, the sirtuin-3-induced inactivation of cyclophilin D causes a detachment of hexokinase II from the mitochondria that is necessary for stimulation of oxidative phosphorylation. These results might have important implications for the role of sirtuin-3 in the metabolism of some cancer cells and their susceptibility to mitochondrial injury and cytotoxicity.

The Warburg effect and mitochondrial stability in cancer cells

The last decade has witnessed a renaissance of Otto Warburg's fundamental hypothesis, which he put forward more than 80 years ago, that mitochondrial malfunction and subsequent stimulation of cellular glucose utilization lead to the development of cancer. Since most tumor cells demonstrate a remarkable resistance to drugs that kill non-malignant cells, the question has arisen whether such resistance might be a consequence of the abnormalities in tumor mitochondria predicted by Warburg. The present review discusses potential mechanisms underlying the upregulation of glycolysis and silencing of mitochondrial activity in cancer cells, and how pharmaceutical intervention in cellular energy metabolism might make tumor cells more susceptible to anti-cancer treatment.