Nitric oxide regulates mitochondrial oxidative stress protection via the transcriptional coactivator PGC-1alpha

AMP-activated protein kinase attenuates nitric oxide-induced beta-cell death

During the initial autoimmune response in type 1 diabetes, islets are exposed to a damaging mix of pro-inflammatory molecules that stimulate the production of nitric oxide by beta-cells. Nitric oxide causes extensive but reversible cellular damage. In response to nitric oxide, the cell activates pathways for functional recovery and adaptation as well as pathways that direct beta-cell death. The molecular events that dictate cellular fate following nitric oxide-induced damage are currently unknown. In this study, we provide evidence that AMPK plays a primary role controlling the response of beta-cells to nitric oxide-induced damage. AMPK is transiently activated by nitric oxide in insulinoma cells and rat islets following IL-1 treatment or by the exogenous addition of nitric oxide. Active AMPK promotes the functional recovery of beta-cell oxidative metabolism and abrogates the induction of pathways that mediate cell death such as caspase-3 activation following exposure to nitric oxide. Overall, these data show that nitric oxide activates AMPK and that active AMPK suppresses apoptotic signaling allowing the beta-cell to recover from nitric oxide-mediated cellular stress.

Effect of melatonin and vitamin C on expression of endothelial NOS in heart of chronic alcoholic rats

The aim of this study was to investigate the effects of melatonin and vitamin C on expression of endothelial nitric oxide synthase (NOS) in heart tissue of chronic alcoholic rats. Twenty-four adult male Wistar rats weighing 200-250 g were used in this study. Rats were divided into four groups. The first group served as control (n = 6). The second group was treated with ethanol (%7.2) for 28 days (n = 6), which was administered in artificial isocaloric diets. The third group was given ethanol and supplemented with 40 mg/kg vitamin C [intraperitoneally (i.p.)] (n = 6). The fourth group was given ethanol and supplemented with 4 mg/kg melatonin (i.p.) (n = 6). At the end of the experiment, rats were sacrificed and heart tissues were processed for immunohistochemistry analysis to endothelial NOS (eNOS). eNOS immunoreactivity showed heterogeneous distribution in control group. eNOS immunoreactivity was (+) in some myocytes and (++) in some others. Expression of eNOS in alcohol group was heterogeneous like control group but also stronger than that. Immunoreactivity was (+++) in myocytes near the epicardial zone and (++) in myocytes near the endocardium border. In melatonin and vitamin C-treated groups, eNOS immunoreactivity was diffuse and the intensity of reaction was (+++) in subepicardial region. However, eNOS immunoreactivity scores were weaker in these groups when compared with the alcohol group. Our results indicate that alleviation of oxidative stress by antioxidant therapy reduces reactive oxygen species-mediated nitric oxide inactivation.

Pyrroloquinoline quinone stimulates mitochondrial biogenesis through cAMP response element-binding protein phosphorylation and increased PGC-1alpha expression

Bioactive compounds reported to stimulate mitochondrial biogenesis are linked to many health benefits such increased longevity, improved energy utilization, and protection from reactive oxygen species. Previously studies have shown that mice and rats fed diets lacking in pyrroloquinoline quinone (PQQ) have reduced mitochondrial content. Therefore, we hypothesized that PQQ can induce mitochondrial biogenesis in mouse hepatocytes. Exposure of mouse Hepa1-6 cells to 10-30 microm PQQ for 24-48 h resulted in increased citrate synthase and cytochrome c oxidase activity, Mitotracker staining, mitochondrial DNA content, and cellular oxygen respiration. The induction of this process occurred through the activation of cAMP response element-binding protein (CREB) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), a pathway known to regulate mitochondrial biogenesis. PQQ exposure stimulated phosphorylation of CREB at serine 133, activated the promoter of PGC-1alpha, and increased PGC-1alpha mRNA and protein expression. PQQ did not stimulate mitochondrial biogenesis after small interfering RNA-mediated reduction in either PGC-1alpha or CREB expression. Consistent with activation of the PGC-1alpha pathway, PQQ increased nuclear respiratory factor activation (NRF-1 and NRF-2) and Tfam, TFB1M, and TFB2M mRNA expression. Moreover, PQQ protected cells from mitochondrial inhibition by rotenone, 3-nitropropionic acid, antimycin A, and sodium azide. The ability of PQQ to stimulate mitochondrial biogenesis accounts in part for action of this compound and suggests that PQQ may be beneficial in diseases associated with mitochondrial dysfunction.

Transcriptional control of mitochondrial biogenesis and function

Mitochondria play central roles in energy homeostasis, metabolism, signaling, and apoptosis. Accordingly, the abundance, morphology, and functional properties of mitochondria are finely tuned to meet cell-specific energetic, metabolic, and signaling demands. This tuning is largely achieved at the level of transcriptional regulation. A highly interconnected network of transcription factors regulates a broad set of nuclear genes encoding mitochondrial proteins, including those that control replication and transcription of the mitochondrial genome. The same transcriptional network senses cues relaying cellular energy status, nutrient availability, and the physiological state of the organism and enables short- and long-term adaptive responses, resulting in adjustments to mitochondrial function and mitochondrial biogenesis. Mitochondrial dysfunction is associated with many human diseases. Characterization of the transcriptional mechanisms that regulate mitochondrial biogenesis and function can offer insights into possible therapeutic interventions aimed at modulating mitochondrial function.

Oxidative stress induced lung cancer and COPD: opportunities for epigenetic therapy

Reactive oxygen species (ROS) form as a natural by-product of the normal metabolism of oxygen and play important roles within the cell. Under normal circumstances the cell is able to maintain an adequate homeostasis between the formation of ROS and its removal through particular enzymatic pathways or via antioxidants. If however, this balance is disturbed a situation called oxidative stress occurs. Critically, oxidative stress plays important roles in the pathogenesis of many diseases, including cancer. Epigenetics is a process where gene expression is regulated by heritable mechanisms that do not cause any direct changes to the DNA sequence itself, and disruption of epigenetic mechanisms has important implications in disease. Evidence is emerging that histone deacetylases (HDACs) play decisive roles in regulating important cellular oxidative stress pathways including those involved with sensing oxidative stress and those involved with regulating the cellular response to oxidative stress. In particular aberrant regulation of these pathways by HDACs may play critical roles in cancer progression. In this review we discuss the current evidence linking epigenetics and oxidative stress and cancer, using chronic obstructive pulmonary disease and non-small cell lung cancer to illustrate the importance of epigenetics on these pathways within these disease settings.

Nitric oxide production by endothelial cells derived from blood progenitors cultured on NaOH-treated polycaprolactone films: A biofunctionality study

Poly(epsilon-caprolactone) (PCL) is a biodegradable polyester whose biocompatibility has been widely demonstrated both in vivo and in vitro. In the last few years, our group has confirmed that NaOH-treated PCL films can serve as a suitable biomaterial for vascular tissue engineering by supporting the culture of primary vascular cells and, more recently, endothelial-like EC(2) cells derived from endothelial progenitor cells (EPC). In the present study, NO production in basal conditions and after stimulation with different agents has been evaluated and related to the reactive oxygen species (ROS) content and the intracellular calcium levels on EC(2) cells cultured on NaOH-treated PCL films. The results obtained demonstrate that EC(2) seeded on NaOH-treated PCL films enhance the basal NO levels and show a faster, more intense response to physiological stimuli such as VEGF, bradykinin and thrombin than vein endothelial cells (ECv). This result could be indicative of a better capacity of EC(2) cells to maintain their endothelial functionality when seeded on polymers. On the other hand, the culture of both EC(2) and ECv cells on NaOH-treated PCL films induces a significant increase in both ROS content and intracellular calcium that is balanced out through the stimulation of NO production in these cells. In conclusion, these results demonstrate the ability of NaOH-treated PCL films to support endothelial cell production of nitric oxide and reinforce the idea of considering the endothelial-like EC(2) cells derived from blood progenitors as an adequate source of endothelial cells to functionalize vascular grafts. Furthermore, NaOH-treated PCL films could be considered as a promising cellular NO production-inducing biomaterial for vascular tissue engineering applications.

NMDA receptor dependent PGC-1alpha up-regulation protects the cortical neuron against oxygen-glucose deprivation/reperfusion injury

The peroxisome proliferator activated receptor coactivator 1 alpha (PGC-1alpha) is a nuclear transcriptional coactivator that is widely expressed in the brain areas. Over-expression of PGC-1alpha can protect neuronal cells from oxidant-induced injury. The purpose of the current study is to investigate the role of PGC-1alpha in the oxygen (anoxia) deprivation (OGD) neurons. The PGC-1alpha mRNA and protein level between control and OGD neurons were examined by real-time PCR and Western blot. More PGC-1alpha expression was found in the OGD neurons compared with the normal group. Over-expression of PGC-1alpha suppressed cell apoptosis while inhibition of the PGC-1alpha expression induced cell apoptosis in OGD neurons. Furthermore, increase of PGC-1alpha resulted in activation of N-methyl-D-aspartate (NMDA) receptor, p38, and ERK mitogen-activated protein kinase (MAPK) pathway. The blocking of the NMDA receptor by its antagonists MK-801 reduced PGC-1alpha mRNA expression in OGD neurons, while NMDA itself can directly induce the expression of PGC-1alpha in neuronal cells. At the same time, PD98059 (ERK MAPK inhibitor) and SB203580 (P38 MAPK inhibitor) also prevented the up-regulation of PGC-1alpha in OGD neurons and MK801 can inhibit the expression of P38 and ERK MAPK. These data suggested that the expression of PGC-1alpha was up-regulated in OGD mice cortical neurons, which protected the neurons against OGD injury. Moreover, this effect was correlated to the NMDA receptor and the ERK and P38 MAPK pathway. The protective effect of PGC-1alpha on OGD cortical neurons may be useful for stroke therapy.

Mutual dependence of Foxo3a and PGC-1alpha in the induction of oxidative stress genes

Oxidative stress is a hallmark of metabolism-related diseases and a risk factor for atherosclerosis. FoxO factors have been shown to play a key role in vascular endothelial development and homeostasis. Foxo3a can protect quiescent cells from oxidative stress through the regulation of detoxification genes such as sod2 and catalase. Here we show that Foxo3a is a direct transcriptional regulator of a group of oxidative stress protection genes in vascular endothelial cells. Importantly, Foxo3a activity requires the transcriptional co-activator PGC-1alpha, because it is severely curtailed in PGC-1alpha-deficient endothelial cells. Foxo3a and PGC-1alpha appear to interact directly, as shown by co-immunoprecipitation and in vitro interaction assays, and are recruited to the same promoter regions. The notion that Foxo3a and PGC-1alpha interact directly to regulate oxidative stress protection genes in the vascular endothelium is supported by the observation that PGC-1alpha transcriptional activity at the sod2 (manganese superoxide dismutase) promoter requires a functional FoxO site. We also demonstrate that Foxo3a is a direct transcriptional regulator of PGC-1alpha, suggesting that an auto-regulatory cycle regulates Foxo3a/PGC-1alpha control of the oxidative stress response.

TZDs reduce mitochondrial ROS production and enhance mitochondrial biogenesis

Although it has been reported that thiazolidinediones (TZDs) may reduce cardiovascular events in type 2 diabetic patients, its precise mechanism is unclear. We previously demonstrated that hyperglycemia-induced production of reactive oxygen species from mitochondria (mtROS) contributed to the development of diabetic complications, and metformin normalized mt ROS production by induction of MnSOD and promotion of mitochondrial biogenesis by activating the PGC-1alpha pathway. In this study, we examined whether TZDs could inhibit hyperglycemia-induced mtROS production by activating the PGC-1alpha pathway. We revealed that pioglitazone and ciglitazone attenuated hyperglycemia-induced ROS production in human umbilical vein endothelial cells (HUVECs). Both TZDs increased the expression of NRF-1, TFAM and MnSOD mRNA. Moreover, pioglitazone increased mtDNA and mitochondrial density. These results suggest that TZDs normalize hyperglycemia-induced mtROS production by induction of MnSOD and promotion of mitochondrial biogenesis by activating PGC-1alpha. This phenomenon could contribute to the prevention of diabetic vascular complications.

Interactions between ROS and AMP kinase activity in the regulation of PGC-1alpha transcription in skeletal muscle cells

Reactive oxygen species (ROS) play an important role in cellular function via the activation of signaling cascades. ROS have been shown to affect mitochondrial biogenesis, morphology, and function. Their beneficial effects are likely mediated via the upregulation of transcriptional regulators such as peroxisome proliferator-activated receptor-gamma coactivator-1 protein-alpha (PGC-1alpha). However, the ROS signals that regulate PGC-1alpha transcription in skeletal muscle are not understood. Here we examined the effect of H2O2 on the regulation of PGC-1alpha expression, and its relationship to AMPK activation. We demonstrate that 24 h of exogenous H2O2 treatment increased PGC-1alpha promoter activity and mRNA expression. Both effects were blocked with the addition of N-acetylcysteine, a ROS scavenger. These effects were mediated, in part, via upstream stimulatory factor-1/Ebox DNA binding and involved 1) interactions with downstream sequences and 2) the activation of AMPK. Elevated ROS led to the activation of AMPK, likely via a decline in ATP levels. The activation of AMPK using 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside increased PGC-1alpha promoter activity and mRNA levels but reduced ROS production. Thus the net effect of AMPK activation on PGC-1alpha expression was a result of increased transcriptional activation, counterbalanced by reduced ROS production. The effects of H2O2 on PGC-1alpha expression differed depending on the level of ROS within the cell. Low levels of ROS result in reduced PGC-1alpha mRNA in the absence of an effect on PGC-1alpha promoter activation. In contrast, elevated levels of H2O2 induce PGC-1alpha transcription indirectly, via AMPK activation. These data identify unique interactions between ROS and AMPK activation on the expression of PGC-1alpha in muscle cells.

Suppression of the JNK pathway by induction of a metabolic stress response prevents vascular injury and dysfunction

BACKGROUND

Oxidative injury and dysfunction of the vascular endothelium are early and causal features of many vascular diseases. Single antioxidant strategies to prevent vascular injury have met with mixed results.

METHODS AND RESULTS

Here, we report that induction of a metabolic stress response with adenosine monophosphate kinase (AMPK) prevents oxidative endothelial cell injury. This response is characterized by stabilization of the mitochondrion and increased mitochondrial biogenesis, resulting in attenuation of oxidative c-Jun N-terminal kinase (JNK) activation. We report that peroxisome proliferator coactivator 1alpha is a key downstream target of AMPK that is both necessary and sufficient for the metabolic stress response and JNK attenuation. Moreover, induction of the metabolic stress response in vivo attenuates reactive oxygen species-mediated JNK activation and endothelial dysfunction in response to angiotensin II in wild-type mice but not in animals lacking either the endothelial isoform of AMPK or peroxisome proliferator coactivator 1alpha.

CONCLUSIONS

These data highlight AMPK and peroxisome proliferator coactivator 1alpha as potential therapeutic targets for the amelioration of endothelial dysfunction and, as a consequence, vascular disease.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

The transcriptional coactivator PGC-1alpha is essential for maximal and efficient cardiac mitochondrial fatty acid oxidation and lipid homeostasis

High-capacity mitochondrial ATP production is essential for normal function of the adult heart, and evidence is emerging that mitochondrial derangements occur in common myocardial diseases. Previous overexpression studies have shown that the inducible transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1alpha is capable of activating postnatal cardiac myocyte mitochondrial biogenesis. Recently, we generated mice deficient in PGC-1alpha (PGC-1alpha(-/-) mice), which survive with modestly blunted postnatal cardiac growth. To determine if PGC-1alpha is essential for normal cardiac energy metabolic capacity, mitochondrial function experiments were performed on saponin-permeabilized myocardial fibers from PGC-1alpha(-/-) mice. These experiments demonstrated reduced maximal (state 3) palmitoyl-l-carnitine respiration and increased maximal (state 3) pyruvate respiration in PGC-1alpha(-/-) mice compared with PGC-1alpha(+/+) controls. ATP synthesis rates obtained during maximal (state 3) respiration in permeabilized myocardial fibers were reduced for PGC-1alpha(-/-) mice, whereas ATP produced per oxygen consumed (ATP/O), a measure of metabolic efficiency, was decreased by 58% for PGC-1alpha(-/-) fibers. Ex vivo isolated working heart experiments demonstrated that PGC-1alpha(-/-) mice exhibited lower cardiac power, reduced palmitate oxidation, and increased reliance on glucose oxidation, with the latter likely a compensatory response. (13)C NMR revealed that hearts from PGC-1alpha(-/-) mice exhibited a limited capacity to recruit triglyceride as a source for lipid oxidation during beta-adrenergic challenge. Consistent with reduced mitochondrial fatty acid oxidative enzyme gene expression, the total triglyceride content was greater in hearts of PGC-1alpha(-/-) mice relative to PGC-1alpha(+/+) following a fast. Overall, these results demonstrate that PGC-1alpha is essential for the maintenance of maximal, efficient cardiac mitochondrial fatty acid oxidation, ATP synthesis, and myocardial lipid homeostasis.

Fiber type-specific nitric oxide protects oxidative myofibers against cachectic stimuli

Oxidative skeletal muscles are more resistant than glycolytic muscles to cachexia caused by chronic heart failure and other chronic diseases. The molecular mechanism for the protection associated with oxidative phenotype remains elusive. We hypothesized that differences in reactive oxygen species (ROS) and nitric oxide (NO) determine the fiber type susceptibility. Here, we show that intraperitoneal injection of endotoxin (lipopolysaccharide, LPS) in mice resulted in higher level of ROS and greater expression of muscle-specific E3 ubiqitin ligases, muscle atrophy F-box (MAFbx)/atrogin-1 and muscle RING finger-1 (MuRF1), in glycolytic white vastus lateralis muscle than in oxidative soleus muscle. By contrast, NO production, inducible NO synthase (iNos) and antioxidant gene expression were greatly enhanced in oxidative, but not in glycolytic muscles, suggesting that NO mediates protection against muscle wasting. NO donors enhanced iNos and antioxidant gene expression and blocked cytokine/endotoxin-induced MAFbx/atrogin-1 expression in cultured myoblasts and in skeletal muscle in vivo. Our studies reveal a novel protective mechanism in oxidative myofibers mediated by enhanced iNos and antioxidant gene expression and suggest a significant value of enhanced NO signaling as a new therapeutic strategy for cachexia.

Abnormal glucose homeostasis in skeletal muscle-specific PGC-1alpha knockout mice reveals skeletal muscle-pancreatic beta cell crosstalk

The transcriptional coactivator PPARgamma coactivator 1alpha (PGC-1alpha) is a strong activator of mitochondrial biogenesis and oxidative metabolism. While expression of PGC-1alpha and many of its mitochondrial target genes are decreased in the skeletal muscle of patients with type 2 diabetes, no causal relationship between decreased PGC-1alpha expression and abnormal glucose metabolism has been established. To address this question, we generated skeletal muscle-specific PGC-1alpha knockout mice (MKOs), which developed significantly impaired glucose tolerance but showed normal peripheral insulin sensitivity. Surprisingly, MKOs had expanded pancreatic beta cell mass, but markedly reduced plasma insulin levels, in both fed and fasted conditions. Muscle tissue from MKOs showed increased expression of several proinflammatory genes, and these mice also had elevated levels of the circulating IL-6. We further demonstrated that IL-6 treatment of isolated mouse islets suppressed glucose-stimulated insulin secretion. These data clearly illustrate a causal role for muscle PGC-1alpha in maintenance of glucose homeostasis and highlight an unexpected cytokine-mediated crosstalk between skeletal muscle and pancreatic islets.

Isoflavones promote mitochondrial biogenesis

Mitochondrial damage is often both the cause and outcome of cell injury resulting from a variety of toxic insults, hypoxia, or trauma. Increasing mitochondrial biogenesis after renal proximal tubular cell (RPTC) injury accelerated the recovery of mitochondrial and cellular functions (Biochem Biophys Res Commun 355:734-739, 2007). However, few pharmacological agents are known to increase mitochondrial biogenesis. We report that daidzein, genistein, biochanin A, formononetin, 3-(2',4'-dichlorophenyl)-7-hydroxy-4H-chromen-4-one (DCHC), 7-hydroxy-4H-chromen-4-one (7-C), 4'7-dimethoxyisoflavone (4',7-D), and 5,7,4'-trimethoxyisoflavone (5,7,4'-T) increased peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha expression and resulted in mitochondrial biogenesis as indicated by increased expression of ATP synthase beta and ND6, and 1.5-fold increases in respiration and ATP in RPTC. Inhibition of estrogen receptors with ICI182780 (fulvestrant) had no effect on daidzein-induced mitochondrial biogenesis. The isoflavone derivatives showed differential effects on the activation and expression of sirtuin (SIRT)1, a deacetylase and activator of PGC-1alpha. Daidzein and formononetin induced the expression of SIRT1 in RPTC and the activation of recombinant SIRT1, whereas DCHC and 7-C only induced the activation of recombinant SIRT1. In contrast, genistein, biochanin A, 4',7-D, and 5,7,4'-T only increased SIRT1 expression in RPTC. We have identified a series of substituted isoflavones that produce mitochondrial biogenesis through PGC1alpha and increased SIRT1 activity and/or expression, independently of the estrogen receptor. Furthermore, different structural components are responsible for the activities of isoflavones: the hydroxyl group at position 7 is required SIRT1 activation, a hydroxyl group at position 5 blocks SIRT1 activation, and the loss of the phenyl ring at position 3 or the 4'-hydroxy or -methoxy substituent blocks increased SIRT1 expression.

Activated macrophages inhibit enterocyte gap junctions via the release of nitric oxide

Enterocytes exist in close association with tissue macrophages, whose activation during inflammatory processes leads to the release of nitric oxide (NO). Repair from mucosal injury requires the migration of enterocytes into the mucosal defect, a process that requires connexin43 (Cx43)-mediated gap junction communication between adjacent enterocytes. Enterocyte migration is inhibited during inflammatory conditions including necrotizing enterocolitis, in part, through impaired gap junction communication. We now hypothesize that activated macrophages inhibit gap junctions of adjacent enterocytes and seek to determine whether NO release from macrophages was involved. Using a coculture system of enterocytes and macrophages, we now demonstrate that "activation" of macrophages with lipopolysaccharide and interferon reduces the phosphorylation of Cx43 in adjacent enterocytes, an event known to inhibit gap junction communication. The effects of macrophages on enterocyte gap junctions could be reversed by treatment of macrophages with the inducible nitric oxide synthase (iNOS) inhibitor l-Lysine omega-acetamidine hydrochloride (l-NIL) and by incubation with macrophages from iNOS(-/-) mice, implicating NO in the process. Activated macrophages also caused a NO-dependent redistribution of connexin43 in adjacent enterocytes from the cell surface to an intracellular location, further suggesting NO release may inhibit gap junction function. Treatment of enterocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) markedly inhibited gap junction communication as determined using single cell microinjection of the gap junction tracer Lucifer yellow. Strikingly, activated macrophages inhibited enterocyte migration into a scraped wound, which was reversed by l-NIL pretreatment. These results implicate enterocyte gap junctions as a target of the NO-mediated effects of macrophages during intestinal inflammation, particularly where enterocyte migration is impaired.

Mitochondria are an essential mediator of nitric oxide/cyclic guanosine 3',5'-monophosphate blocking of glucose depletion induced cytotoxicity in human HepG2 cells

It is well known that glucose is a major energy source in tumors and that mitochondria are specialized organelles required for energy metabolism. Previous studies have revealed that nitric oxide (NO) protects against glucose depletion-induced cytotoxicity in mouse liver cells and in rat hepatocytes, but the detailed mechanism is not well understood. Therefore, we investigated the involvement of mitochondria in the NO protective effect in human hepatoma HepG2 cells. In this study, we showed that glucose depletion resulted in a time-dependent decrease in intracellular NO and in the protein expression of NO synthases. This glucose depletion-induced decrease in NO was blocked by NO donors. Next, we showed that the cytoprotective effect of NO is via a cyclic guanosine 3',5'-monophosphate-dependent pathway. Additionally, SNP blocked a glucose depletion-induced decrease in mitochondrial mass, mitochondrial DNA copies, and ATP level in HepG2 cells. Moreover, glucose depletion decreased the expression of various mitochondrial proteins, including cytochrome c, complex I (NADH dehydrogenase), complex III (cytochrome c reductase), and heat shock protein 60; these glucose depletion-induced effects were blocked by SNP. Furthermore, we found that rotenone and antimycin A (mitochondria complex I and III inhibitors, respectively) blocked SNP cytoprotection against glucose depletion-induced cytotoxicity. Taken together, our results indicated that the mitochondria serve as an important cellular mediator of NO during protection against glucose deprivation-induced damage.

PGC-1alpha-induced mitochondrial alterations in 3T3 fibroblast cells

Peroxisome proliferation activator receptor (PPAR) gamma-coactivator 1alpha (PGC-1alpha), a transcription coactivator, functions as a master regulator of a wide array of metabolic and physiological processes and is an essential factor in the process of mitochondrial biogenesis. Transfection of NIH 3T3 fibroblasts with a mouse cDNA for PGC-1alpha led to the induction of markers of mitochondrial biogenesis, that is, mitochondrial transcription factor A (mtTFA), cytochrome c, and mitochondrial DNA (mtDNA). Mitochondrial biogenesis-associated net protein synthesis appears to be accomplished by a reduction in the rate of mitochondrial protein degradation with little or no change in the rate of protein synthesis. Overexpression of PGC-1alpha did not adversely affect cellular proliferation. Cellular ATP levels were increased in the transfected cells and they were more resistant to oxidative stress than the control nontransfected 3T3 cells. This resistance to oxidative stress was manifested by both an improved viability and the maintenance of mitochondrial membrane potential in the transfected cells when exposed to t-butyl hydroperoxide (t-BOOH). It therefore appears that PGC-1alpha overexpression stimulates mitochondrial biogenesis in 3T3 cells making them more resistant to oxidative stressors.

Potential targets of FOXL2, a transcription factor involved in craniofacial and follicular development, identified by transcriptomics

FOXL2 is a gene encoding a forkhead transcription factor, whose mutations are responsible for the blepharophimosis-ptosis-epicanthus inversus syndrome that often involves premature ovarian failure. FOXL2 is one of the earliest ovarian markers and it offers, along with its targets, an excellent model to study ovarian development and function in normal and pathological conditions. We have recently shown that the aromatase gene is a target of FOXL2, and only three other targets have been reported so far. To detect potential transcriptional targets of FOXL2, we used DNA chips and quantitative PCR to compare the transcriptomes of granulosa-like cells overexpressing, or not, FOXL2. This analysis showed that mediators of inflammation, apoptotic and transcriptional regulators, genes involved in cholesterol metabolism, and genes encoding enzymes and transcription factors involved in reactive oxygen species detoxification were up-regulated. On the other hand, FOXL2 down-regulated the transcription of several genes involved in proteolysis and signal transduction and in transcription regulation. A bioinformatic analysis was conducted to discriminate between potential target promoters activated and repressed by FOXL2. In addition, the promoters of strongly activated genes were enriched in forkhead recognition sites, suggesting that these genes might be direct FOXL2 targets. Altogether, these results provide insight into the activity of FOXL2 and may help in understanding the mechanisms of pathogenesis of FOXL2 mutations if the targets prove to be the same in the ovary.

PGC-1alpha over-expression promotes recovery from mitochondrial dysfunction and cell injury

Cell death from mitochondrial dysfunction and compromised bioenergetics is common after ischemia-reperfusion injury and toxicant exposure. Thus, promoting mitochondrial biogenesis is therapeutically attractive for sustaining oxidative phosphorylation and maintaining ATP-dependent cellular functions. Here, we evaluated increased mitochondrial biogenesis prior to or after oxidant exposure in primary cultures of renal proximal tubular cells (RPTC). Over-expression of the mitochondrial biogenesis regulator PPAR-gamma cofactor-1 alpha (PGC-1alpha) in control RTPC increased basal and uncoupled cellular respiration, ATP, and mitochondria. Increasing mitochondrial number/function prior to oxidant exposure did not preserve mitochondrial function, but potentiated dysfunction and cell death. However, increased mitochondrial biogenesis after oxidant injury accelerated recovery of mitochondrial function. In oxidant treated RPTC, mitochondrial protein expression was reduced by 50%. Also, ATP and cellular respiration decreased 48 h after oxidant exposure, whereas mitochondrial function in injured RPTC over-expressing PGC-1alpha returned to control values. Thus, up-regulation of mitochondrial biogenesis after oxidant exposure accelerates recovery of mitochondrial and cellular functions.