Mitochondrial nitric oxide synthase drives redox signals for proliferation and quiescence in rat liver development

TRPM8 contributes to liver regeneration via mitochondrial energy metabolism mediated by PGC1α

Impairment of liver regeneration leads to severe morbidity in acute and chronic severe liver disease. Transient receptor potential melastain 8 (TRPM8) is involved in a variety of processes, including temperature sensing, ion homeostasis, and cell proliferation. However, whether TRPM8 contributes to liver regeneration is still unclear. We assessed the effect and mechanism of TRPM8 in liver regeneration and hepatocyte proliferation in vivo and in vitro. In this study, we found that TRPM8 deficiency impairs liver regeneration in mice. Mechanistically, the results revealed that mitochondrial energy metabolism was attenuated in livers from TRPM8 knockout (KO) mice. Furthermore, we found that TRPM8 contributes to the proliferation of hepatocytes via PGC1α. Taken together, this study shows that TRPM8 contributes to liver regeneration in mice after hepatectomy. Genetic approaches and pharmacological approaches to regulate TRPM8 activity may be beneficial to the promotion of liver regeneration.

Reactive Oxygen Species Bridge the Gap between Chronic Inflammation and Tumor Development

According to numerous animal studies, adverse environmental stimuli, including physical, chemical, and biological factors, can cause low-grade chronic inflammation and subsequent tumor development. Human epidemiological evidence has confirmed the close relationship between chronic inflammation and tumorigenesis. However, the mechanisms driving the development of persistent inflammation toward tumorigenesis remain unclear. In this study, we assess the potential role of reactive oxygen species (ROS) and associated mechanisms in modulating inflammation-induced tumorigenesis. Recent reports have emphasized the cross-talk between oxidative stress and inflammation in many pathological processes. Exposure to carcinogenic environmental hazards may lead to oxidative damage, which further stimulates the infiltration of various types of inflammatory cells. In turn, increased cytokine and chemokine release from inflammatory cells promotes ROS production in chronic lesions, even in the absence of hazardous stimuli. Moreover, ROS not only cause DNA damage but also participate in cell proliferation, differentiation, and apoptosis by modulating several transcription factors and signaling pathways. We summarize how changes in the redox state can trigger the development of chronic inflammatory lesions into tumors. Generally, cancer cells require an appropriate inflammatory microenvironment to support their growth, spread, and metastasis, and ROS may provide the necessary catalyst for inflammation-driven cancer. In conclusion, ROS bridge the gap between chronic inflammation and tumor development; therefore, targeting ROS and inflammation represents a new avenue for the prevention and treatment of cancer.

Bnip3 regulates airway smooth muscle cell focal adhesion and proliferation

Increased airway smooth muscle (ASM) mass is a key contributor to airway narrowing and airway hyperresponsiveness in asthma. Besides conventional pathways and regulators of ASM proliferation, recent studies suggest that changes in mitochondrial morphology and function play a role in airway remodeling in asthma. In this study, we aimed at determining the role of mitochondrial Bcl-2 adenovirus E1B 19 kDa-interacting protein, Bnip3, in the regulation of ASM proliferation. Bnip3 is a member of the Bcl-2 family of proteins critical for mitochondrial health, mitophagy, and cell survival/death. We found that Bnip3 expression is upregulated in ASM cells from asthmatic donors compared with that in ASM cells from healthy donors and transient downregulation of Bnip3 expression in primary human ASM cells using an siRNA approach decreased cell adhesion, migration, and proliferation. Furthermore, Bnip3 downregulation altered the structure (electron density) and function (cellular ATP levels, membrane potential, and reacitve oxygen species generation) of mitochondria and decreased expression of cytoskeleton proteins vinculin, paxillin, and actinin. These findings suggest that Bnip3 via regulation of mitochondria functions and expression of adhesion proteins regulates ASM adhesion, migration, and proliferation. This study reveals a novel role for Bnip3 in ASM functions and establishes Bnip3 as a potential target in mitigating ASM remodeling in asthma.

SPARC gene deletion protects against toxic liver injury and is associated to an enhanced proliferative capacity and reduced oxidative stress response

SPARC, also known as osteonectin and BM-40, is a matricellular protein with a number of biological functions. Hepatic SPARC expression is induced in response to thioacetamide, bile-duct ligation, and acute injuries such as concanavalin A and lipopolysacharide (LPS)/D-galactosamine. We have previously demonstrated that the therapeutic inhibition of SPARC or SPARC gene deletion protected mice against liver injury. We investigated the mechanisms involved in the protective effect of SPARC inhibition in mice. We performed a proteome analysis of livers from SPARC+/+ and SPARC-/- mice chronically treated with thioacetamide. Catalase activity, carbonylation levels, oxidative stress response, and mitochondrial function were studied. Genomic analysis revealed that SPARC-/- mice had an increased expression of cell proliferation genes. Proteins involved in detoxification of reactive oxygen species such as catalase, peroxirredoxine-1, and glutathione-S-transferase P1 and Mu1 were highly expressed as evidenced by proteome analysis; hepatic catalase activity was increased in SPARC-/- mice. Oxidative stress response and carbonylation levels were lower in livers from SPARC-/- mice. Hepatic mitochondria showed lower levels of nitrogen reactive species in the SPARC-/- concanavalin A-treated mice. Mitochondrial morphology was preserved, and its complex activity reduced in SPARC-/- mice. In conclusion, our data suggest that the protection associated with SPARC gene deletion may be partially due to a higher proliferative capacity of hepatocytes and an enhanced oxidative stress defense in SPARC-/- mice after liver injury.

Mitochondrial regulation of airway smooth muscle functions in health and pulmonary diseases

Mitochondria are important for airway smooth muscle physiology due to their diverse yet interconnected roles in calcium handling, redox regulation, and cellular bioenergetics. Increasing evidence indicates that mitochondria dysfunction is intimately associated with airway diseases such as asthma, IPF and COPD. In these pathological conditions, increased mitochondrial ROS, altered bioenergetics profiles, and calcium mishandling contribute collectively to changes in cellular signaling, gene expression, and ultimately changes in airway smooth muscle contractile/proliferative properties. Therefore, understanding the basic features of airway smooth muscle mitochondria and their functional contribution to airway biology and pathology are key to developing novel therapeutics for airway diseases. This review summarizes the recent findings of airway smooth muscle mitochondria focusing on calcium homeostasis and redox regulation, two key determinants of physiological and pathological functions of airway smooth muscle.

Overexpression of miR-142-3p improves mitochondrial function in cardiac hypertrophy

BACKGROUND AND PURPOSE

Our previous studies have shown that Src homology 2 (SH2) B adaptor protein 1 (SH2B1) plays an important role in cardiac hypertrophy, but the specific mechanism remains to be studied. Through bioinformatics and related research, it is found that miR-14 2-3 p is closely related to SH2B1. Exploring the relationship between miR-14 2-3 p and gene SH2B1 expression is beneficial for the treatment of cardiac hypertrophy. SH2B1 is a key factor regulating energy metabolism, mitochondria are the main organelles of energy metabolism and cardiac hypertrophy are closely related to mitochondrial dysfunction. So it is particularly important to explore the relationship between miR-14 2-3 p and SH2B1 and myocardial mitochondrial function. In this study, we investigated whether overexpression of miR-14 2-3 p can inhibit the expression of gene SH2B1, ameliorate cardiac mitochondrial dysfunction and cardiac hypertrophy.

METHODS

We first constructed a pressure overload myocardial hypertrophy model by ligation of the abdominal aorta(AB) of rats. After 4 weeks of modeling, echocardiographic examination showed that the heart volume of the model group became larger, and Hematoxylin and Eosin Staining Kit (HE) staining showed that the cross-sectional area of the heart tissue became larger. The expression of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), β-Myosin Heavy Chain (β-MHC) messenger RNA (mRNA) increased by real‑time polymerase chain reaction (PCR), which proved that the model of cardiac hypertrophy was successfully constructed. Then, miR-14 2-3 p agomir was injected into the tail vein of rats 2 weeks and 4 weeks respectively. The expression of miR-4 2-3 p mRNA was increased by PCR, suggesting that the miR-14 2-3 p plasmid was successfully transfected. At 4 weeks of pressure overload myocardial hypertrophy model, echocardiography was used to detect cardiac function. HE staining of heart tissue and the expression of ANP, BNP, β-MHC mRNA were used to detect cardiac hypertrophy. Flow cytometry was used to detect changes in mitochondrial membrane potential. Secondly, we observed the effect of miR-14 2-3 p on cardiomyocyte hypertrophy and mitochondrial function in vitro by culture neonatal rat cardiomyocytes. Afterwards, using angiotensin (Ang)II-, miRNA mimic- and miRNA mimic nc- treated cardiomyocytes for a given time. α-actin staining found that the myocardial cells became larger, The expression of ANP, BNP, β-MHC mRNA increased by PCR, which proved that AngII-induced cardiac hypertrophy was successfully constructed. Then, the mitochondrial density was measured using mitochondrial Mito-Red staining by Confocal microscope, the mitochondrial membrane potential was evaluated using flow cytometry, Mitochondrial respiration oxygen consumption rate (OCR) was measured by a Seahorse Extracellular Flux Analyzer XF96, and the expression levels of miR-14 2-3 p, ANP, BNP, β-MHC mRNA, SH2B1 in the cardiomyocytes of different groups were measured by RT-PCR and Western blotting. Finally, we used luciferase assay and transfected miR-14 2-3 p agomir in rats, transfected miR-14 2-3 p mimic in Cardiomyocytes, it is found that myocardial SH2B1 mRNA and protein expression both were reduced.

RESULTS

When the pressure overload myocardial hypertrophy model was constructed for four weeks, echocardiography revealed that the heart volume, Left ventricular end diastolic diameter(LVIDd), Left ventricular end systolic diameter (LVIDs), Left ventricular posterior wall thickness (LVPWd), Systolic left ventricular posterior wall (LVPWs), Left ventricle (LV) Mass increased, Ejection fraction (EF) % decreased of AB group increased, but transfected with miR-14 2-3 p agomir of AB, these increase was not significant, EF% reduction was not obvious. HE staining showed that the myocardial cross-sectional area of AB group increased significantly, but the miR-14 2-3 p agomir treatment of AB group did not increase significantly. PCR analysis showed that the expression of ANP, BNP,β-MHC mRNA was significantly increased in AB group, but the miR-14 2-3 p agomir treatment of AB group was not significantly increased. Flow cytometry showed that the mitochondrial membrane potential of AB group was significantly reduced, and the miR-14 2-3 p agomir treatment of AB group was not significantly decreased. During AngII-induced cardiomyocyte hypertrophy, ANP, BNP,β-MHC mRNA expression was increased, while these factors was not significantly increased in miR-14 2-3 p mimic treatment group; mitochondrial membrane potential, mitochondrial density and OCR was significantly decreased in AngII treated group, and these were not significantly reduced in miR-14 2-3 p mimic treatment group; CONCLUSIONS: miR-14 2-3 p not only mitigate cardiac hypertrophy by directly inhibit the expression of gene SH2B1, but also can protect mitochondrial function in cardiac hypertrophy of vitro and vivo.

Nicotinamide mononucleotide preserves mitochondrial function and increases survival in hemorrhagic shock

Hemorrhagic shock depletes nicotinamide adenine dinucleotide (NAD) and causes metabolic derangements that, in severe cases, cannot be overcome, even after restoration of blood volume and pressure. However, current strategies to treat acute blood loss do not target cellular metabolism. We hypothesized that supplemental nicotinamide mononucleotide (NMN), the immediate biosynthetic precursor to NAD, would support cellular energetics and enhance physiologic resilience to hemorrhagic shock. In a rodent model of decompensated hemorrhagic shock, rats receiving NMN displayed significantly reduced lactic acidosis and serum IL-6 levels, two strong predictors of mortality in human patients. In both livers and kidneys, NMN increased NAD levels and prevented mitochondrial dysfunction. Moreover, NMN preserved mitochondrial function in isolated hepatocytes cocultured with proinflammatory cytokines, indicating a cell-autonomous protective effect that is independent from the reduction in circulating IL-6. In kidneys, but not in livers, NMN was sufficient to prevent ATP loss following shock and resuscitation. Overall, NMN increased the time animals could sustain severe shock before requiring resuscitation by nearly 25% and significantly improved survival after resuscitation (P = 0.018), whether NMN was given as a pretreatment or only as an adjunct during resuscitation. Thus, we demonstrate that NMN substantially mitigates inflammation, improves cellular metabolism, and promotes survival following hemorrhagic shock.

p66Shc Inactivation Modifies RNS Production, Regulates Sirt3 Activity, and Improves Mitochondrial Homeostasis, Delaying the Aging Process in Mouse Brain

Programmed and damage aging theories have traditionally been conceived as stand-alone schools of thought. However, the p66Shc adaptor protein has demonstrated that aging-regulating genes and reactive oxygen species (ROS) are closely interconnected, since its absence modifies metabolic homeostasis by providing oxidative stress resistance and promoting longevity. p66Shc(-/-) mice are a unique opportunity to further comprehend the bidirectional relationship between redox homeostasis and the imbalance of mitochondrial biogenesis and dynamics during aging. This study shows that brain mitochondria of p66Shc(-/-) aged mice exhibit a reduced alteration of redox balance with a decrease in both ROS generation and its detoxification activity. We also demonstrate a strong link between reactive nitrogen species (RNS) and mitochondrial function, morphology, and biogenesis, where low levels of ONOO- formation present in aged p66Shc(-/-) mouse brain prevent protein nitration, delaying the loss of biological functions characteristic of the aging process. Sirt3 modulates age-associated mitochondrial biology and function via lysine deacetylation of target proteins, and we show that its regulation depends on its nitration status and is benefited by the improved NAD+/NADH ratio in aged p66Shc(-/-) brain mitochondria. Low levels of protein nitration and acetylation could cause the metabolic homeostasis maintenance observed during aging in this group, thus increasing its lifespan.

The pan-caspase inhibitor Emricasan (IDN-6556) decreases liver injury and fibrosis in a murine model of non-alcoholic steatohepatitis

BACKGROUND & AIMS

Hepatocyte apoptosis, the hallmark of non-alcoholic steatohepatitis (NASH) contributes to liver injury and fibrosis. Although, both the intrinsic and extrinsic apoptotic pathways are involved in the pathogenesis of NASH, the final common step of apoptosis is executed by a family of cysteine-proteases termed caspases. Thus, our aim was to ascertain if administration of Emricasan, a pan-caspase inhibitor, ameliorates liver injury and fibrosis in a murine model of NASH.

METHODS

C57/BL6J-mice were fed regular chow or high fat diet (HFD) for 20 weeks. All mice were treated with vehicle or Emricasan.

RESULTS

Mice fed a HFD diet demonstrate a five-fold increase in hepatocyte apoptosis by the TUNEL assay and a 1.5-fold and 1.3-fold increase in caspase-3 and-8 activities respectively; this increase in apoptosis was substantially attenuated in mice fed a HFD treated with Emricasan (HFD-Em). Likewise, liver injury and inflammation were reduced in mice fed HFD-Em as compare to HFD by measuring serum aspartate aminotransferase and alanine aminotransferase levels, NAS histological score and IL 1-β, TNF-α, monocyte chemoattractant protein (MCP-1) and C-X-C chemokine ligand-2 (CXCL2) quantitative reverse-transcription polymerase chain reaction (qPCR). These differences could not be attributed to differences in hepatic steatosis as liver triglycerides content were similar in both HFD groups. Hepatic fibrosis was reduced by Emricasan in HFD animals by decreasing αSMA (a marker for hepatic stellate cell activation), fibrosis score, Sirius red staining, hydroxyproline liver content and profibrogenic cytokines by qPCR.

CONCLUSION

In conclusion, these data demonstrate that in a murine model of NASH, liver injury and fibrosis are suppressed by inhibiting hepatocytes apoptosis and suggests that Emricasan may be an attractive antifibrotic therapy in NASH.

Pathogenic role of oxidative and nitrosative stress in primary biliary cirrhosis

Primary biliary cirrhosis is a multifactor autoimmune disease characterized by hepatic and systemic manifestations, with immune system dysregulation and abnormalities in the hepatic metabolism of bile salts, lipids, and nutrients, as well as destruction of membrane lipids and mitochondrial dysfunction. Both oxidative and nitrosative stress are associated with ongoing manifestations of the disease. In particular, abnormalities in nitric oxide metabolism and thiol oxidation already occur at early stages, thus leading to the hypothesis that these biochemical events play a pathogenic role in primary biliary cirrhosis. Moreover, the association of these metabolic abnormalities with the progression of the disease may indicate some biochemical parameters as early diagnostic markers of disease evolution, and may open up the potential for pharmacological intervention to inhibit intra- and extra-cellular stress events for resuming hepatocellular functions. The following paragraphs summarize the current knowledge by outlining molecular mechanisms of the disease related to these stress events.

p38 MAPK: a dual role in hepatocyte proliferation through reactive oxygen species

p38 MAPKs are important mediators of signal transduction that respond to a wide range of extracellular stressors such as UV radiation, osmotic shock, hypoxia, pro-inflammatory cytokines, and oxidative stress. The most abundant family member is p38α, which helps to couple cell proliferation and growth in response to certain damaging stimuli. In fact, increased proliferation and impaired differentiation are hallmarks of p38α-deficient cells. It has been reported that reactive oxygen species (ROS) play a critical role in cytokine-induced p38α activation. Under physiological conditions, p38α can function as a mediator of ROS signaling and either activate or suppress cell cycle progression depending on the activation stimulus. The interplay between cell proliferation, p38 MAPK activation, and ROS production plays an important role in hepatocytes. In fact, low levels of ROS seem to be needed to activate several signaling pathways in response to hepatectomy and to orchestrate liver regeneration. p38 MAPK works as a sensor of oxidative stress and cells that have developed mechanisms to uncouple p38 MAPK activation from oxidative stress are more likely to become tumorigenic. So far, p38α influences the redox balance, determining cell survival, terminal differentiation, proliferation, and senescence. Further studies would be necessary in order to clarify the precise role of p38 MAPK signaling as a redox therapeutical target.

Impact of exercise training on redox signaling in cardiovascular diseases

Reactive oxygen and nitrogen species regulate a wide array of signaling pathways that governs cardiovascular physiology. However, oxidant stress resulting from disrupted redox signaling has an adverse impact on the pathogenesis and progression of cardiovascular diseases. In this review, we address how redox signaling and oxidant stress affect the pathophysiology of cardiovascular diseases such as ischemia-reperfusion injury, hypertension and heart failure. We also summarize the benefits of exercise training in tackling the hyperactivation of cellular oxidases and mitochondrial dysfunction seen in cardiovascular diseases.

Simvastatin enhances human osteoblast proliferation involved in mitochondrial energy generation

Simvastatin has been shown to stimulate osteogenic cell differentiation. Our previous study showed osteoblasts on trabecular surface are increased by simvastatin treatment in animal study. However, whether simvastatin stimulates osteoblast proliferation and by what molecular mechanism have not been adequately investigated. Because the mitochondrial function is crucial for cell survival and proliferation, we hypothesize that simvastatin may promote human osteoblast (hOBs) proliferation and it may be related to mitochondrial function. Our results showed that simvastatin significantly enhanced proliferation and increased both mRNA and protein levels of cyclin D2, Bcl-2 and the ratio of Bcl-2 to Bax (Bcl-2/Bax). Furthermore, simvastatin increased mitochondrial activity and ATP content of hOBs. Most importantly, treatment with ATP synthase blocker, oligomycin, significantly decreased both simvastatin-stimulated ATP content and cell proliferation, and completely reversed the simvastatin-induced up-regulation of cyclin D2 and Bcl-2 expression in hOBs. On the other hand, rotenone, the complex I blocker, also partially blocked simvastatin-stimulated ATP content and cell proliferation, but the blocker did not suppress the effect of simvastatin on cyclin D2 and Bcl-2 expression. These results indicate that the up-regulation of cyclin D2 and Bcl-2/Bax by simvastatin depends on the intact function of ATP synthase in the mitochondria of hOBs. It suggests that simvastatin may promote hOB proliferation, at least partly, via up-regulating mitochondrial function and subsequently cyclin D2 and Bcl-2/Bax expression. The findings provide new information for the basic medical science in bone physiology and for new therapy strategy of simvastatin on bone formation in future.

Phosphorylation and subcellular localization of p27Kip1 regulated by hydrogen peroxide modulation in cancer cells

The Cyclin-dependent kinase inhibitor 1B (p27Kip1) is a key protein in the decision between proliferation and cell cycle exit. Quiescent cells show nuclear p27Kip1, but this protein is exported to the cytoplasm in response to proliferating signals. We recently reported that catalase treatment increases the levels of p27Kip1 in vitro and in vivo in a murine model. In order to characterize and broaden these findings, we evaluated the regulation of p27Kip1 by hydrogen peroxide (H(2)O(2)) in human melanoma cells and melanocytes. We observed a high percentage of p27Kip1 positive nuclei in melanoma cells overexpressing or treated with exogenous catalase, while non-treated controls showed a cytoplasmic localization of p27Kip1. Then we studied the levels of p27Kip1 phosphorylated (p27p) at serine 10 (S10) and at threonine 198 (T198) because phosphorylation at these sites enables nuclear exportation of this protein, leading to accumulation and stabilization of p27pT198 in the cytoplasm. We demonstrated by western blot a decrease in p27pS10 and p27pT198 levels in response to H(2)O(2) removal in melanoma cells, associated with nuclear p27Kip1. Melanocytes also exhibited nuclear p27Kip1 and lower levels of p27pS10 and p27pT198 than melanoma cells, which showed cytoplasmic p27Kip1. We also showed that the addition of H(2)O(2) (0.1 µM) to melanoma cells arrested in G1 by serum starvation induces proliferation and increases the levels of p27pS10 and p27pT198 leading to cytoplasmic localization of p27Kip1. Nuclear localization and post-translational modifications of p27Kip1 were also demonstrated by catalase treatment of colorectal carcinoma and neuroblastoma cells, extending our findings to these other human cancer types. In conclusion, we showed in the present work that H(2)O(2) scavenging prevents nuclear exportation of p27Kip1, allowing cell cycle arrest, suggesting that cancer cells take advantage of their intrinsic pro-oxidant state to favor cytoplasmic localization of p27Kip1.

Effects of analogues of hydra peptide morphogen on DNA synthesis in the myocardium of newborn albino rats

DNA-synthetic activity of myocardial cells was studied by (3)H-thymidine autoradiography in newborn albino rats after intraperitoneal injection of hydra peptide morphogen and its analogues. Administration of hydra peptide morphogen stimulated proliferative activity in the myocardium. Short analogues of hydra peptide morphogen, 6C and 3C peptides, produced a similar effect. Administration of arginine-containing analogue of hydra peptide morphogen significantly reduced the number of DNA-synthesizing nuclei in the ventricular myocardium of newborn albino rats. The role of the structure of the peptide molecule in the realization of the morphogenetic effects of hydra peptide morphogen is discussed.

Mitochondrial regulation of cell cycle and proliferation

Eukaryotic mitochondria resulted from symbiotic incorporation of α-proteobacteria into ancient archaea species. During evolution, mitochondria lost most of the prokaryotic bacterial genes and only conserved a small fraction including those encoding 13 proteins of the respiratory chain. In this process, many functions were transferred to the host cells, but mitochondria gained a central role in the regulation of cell proliferation and apoptosis, and in the modulation of metabolism; accordingly, defective organelles contribute to cell transformation and cancer, diabetes, and neurodegenerative diseases. Most cell and transcriptional effects of mitochondria depend on the modulation of respiratory rate and on the production of hydrogen peroxide released into the cytosol. The mitochondrial oxidative rate has to remain depressed for cell proliferation; even in the presence of O₂, energy is preferentially obtained from increased glycolysis (Warburg effect). In response to stress signals, traffic of pro- and antiapoptotic mitochondrial proteins in the intermembrane space (B-cell lymphoma-extra large, Bcl-2-associated death promoter, Bcl-2 associated X-protein and cytochrome c) is modulated by the redox condition determined by mitochondrial O₂ utilization and mitochondrial nitric oxide metabolism. In this article, we highlight the traffic of the different canonical signaling pathways to mitochondria and the contributions of organelles to redox regulation of kinases. Finally, we analyze the dynamics of the mitochondrial population in cell cycle and apoptosis.

Pathological alteration in the choroid plexus of Alzheimer's disease: implication for new therapy approaches

Morphological alterations of choroid plexus in Alzheimer’s disease (AD) have been extensively investigated. These changes include epithelial atrophy, thickening of the basement membrane, and stroma fibrosis. As a result, synthesis, secretory, and transportation functions are significantly altered resulting in decreased cerebrospinal fluid (CSF) turnover. Recent studies discuss the potential impacts of these changes, including the possibility of reduced resistance to stress insults and slow clearance of toxic compounds from CSF with specific reference to the amyloid peptide. Here, we review new evidences for AD-related changes in the choroid plexus. The data suggest that the significantly altered functions of the choroid plexus contribute to the multiparametric pathogenesis of late-onset AD.

Impact of age at administration, lysosomal storage, and transgene regulatory elements on AAV2/8-mediated rat liver transduction

Liver-directed gene transfer is being investigated for the treatment of systemic or liver-specific diseases. Recombinant vectors based on adeno-associated virus serotype 8 (AAV2/8) efficiently transduce liver cells allowing long term transgene expression after a single administration in animal models and in patients.We evaluated the impact on AAV2/8-mediated rat liver transduction of the following variables: i) age at vector administration, ii) presence of lysosomal storage in liver cells, and iii) regulatory elements included in the transgene expression cassette. We found that systemic administration of AAV2/8 to newborn rats results in vector genome dilution and reduced transduction efficacy when compared to adult injected animals, presumably due to hepatocyte proliferation. Accumulation of glycosaminoglycans in lysosomes does not impact on levels and distribution of AAV2/8-mediated liver transduction. Transgene expression occurs in hepatocytes but not in Kupffer or liver endothelial cells when the liver-specific thyroxine-binding-globulin promoter is used. However, extra-hepatic transduction is observed in the spleen and kidney of animals injected at birth. The use of target sequences for the hematopoietic-specific microRNA miR142-3p does not improve liver transduction efficacy neither reduce immune responses to the lysosomal enzyme arylsulfatase B. The inclusion of a variant of the Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE-m) decreases AAV2/8-mediated liver transduction levels.As AAV2/8-mediated liver gene transfer is entering in the clinical arena, these data will provide relevant information to the design of efficient AAV2/8-based therapeutic strategies.

Defective leptin-AMP-dependent kinase pathway induces nitric oxide release and contributes to mitochondrial dysfunction and obesity in ob/ob mice

AIMS

Obesity arises on defective neuroendocrine pathways that increase energy intake and reduce mitochondrial metabolism. In the metabolic syndrome, mitochondrial dysfunction accomplishes defects in fatty acid oxidation and reciprocal increase in triglyceride content with insulin resistance and hyperglycemia. Mitochondrial inhibition is attributed to reduced biogenesis, excessive fission, and low adipokine-AMP-activated protein kinase (AMPK) level, but lateness of the respiratory chain contributes to perturbations. Considering that nitric oxide (NO) binds cytochrome oxidase and inhibits respiration, we explored NO as a direct effector of mitochondrial dysfunction in the leptin-deficient ob/ob mice.

RESULTS

A remarkable three- to fourfold increase in neuronal nitric oxide synthase (nNOS) expression and activity was detected by western blot, citrulline assay, electronic and confocal microscopy, flow cytometry, and NO electrode sensor in mitochondria from ob/ob mice. High NO reduced oxygen uptake in ob/ob mitochondria by inhibition of complex IV and nitration of complex I. Low metabolic status restricted β-oxidation in obese mitochondria and displaced acetyl-CoA to fat synthesis; instead, small interference RNA nNOS caused a phenotype change with fat reduction in ob/ob adipocytes.

INNOVATION

We evidenced that leptin increases mitochondrial respiration and fat utilization by potentially inhibiting NO release. Accordingly, leptin administration to ob/ob mice prevented nNOS overexpression and mitochondrial dysfunction in vivo and rescued leptin-dependent effects by matrix NO reduction, whereas leptin-Ob-Rb disruption increased the formation of mitochondrial NO in control adipocytes. We demonstrated that in ob/ob, hypoleptinemia is associated with critically low mitochondrial p-AMPK and that, oppositely to p-Akt2, p-AMPK is a negative modulator of nNOS.

CONCLUSION

Thereby, defective leptin-AMPK pathway links mitochondrial NO to obesity with complex I syndrome and dysfunctional mitochondria.

p38α Signaling Induces Anoikis and Lumen Formation During Mammary Morphogenesis

The stress-activated protein kinase (SAPK) p38 can induce apoptosis, and its inhibition facilitates mammary tumorigenesis. We found that during mammary acinar morphogenesis in MCF-10A cells grown in three-dimensional culture, detachment of luminal cells from the basement membrane stimulated mitogen-activated protein kinase (MAPK) kinases 3 and 6 (MKK3/6) and p38α signaling to promote anoikis. p38α signaling increased transcription of the death-promoting protein BimEL by phosphorylating the activating transcription factor 2 (ATF-2) and increasing c-Jun protein abundance, leading to cell death by anoikis and acinar lumen formation. Inhibition of p38α or ATF-2 caused luminal filling reminiscent of that observed in ductal carcinoma in situ (DCIS). The mammary glands of MKK3/6 knockout mice (MKK3(-/-)/MKK6(+/- )) showed accelerated branching morphogenesis relative to those of wild-type mice, as well as ductal lumen occlusion due to reduced anoikis. This phenotype was recapitulated by systemic pharmacological inhibition of p38α and β (p38α/β) in wild-type mice. Moreover, the development of DCIS-like lesions showing marked ductal occlusion was accelerated in MMTV-Neu transgenic mice treated with inhibitors of p38α and p38β. We conclude that p38α is crucial for the development of hollow ducts during mammary gland development, a function that may be crucial to its ability to suppress breast cancer.

A novel CARD containing splice-isoform of CIITA regulates nitric oxide synthesis in dendritic cells

MHC class II expression is controlled mainly at transcriptional level by class II transactivator (CIITA), which is a non-DNA binding coactivator and serves as a master control factor for MHC class II genes expression. Here, we describe the function of a novel splice-isoform of CIITA, DC-expressed caspase inhibitory isoform of CIITA (or DC-CASPIC), and we show that the expression of DCCASPIC in DC is upregulated upon lipopolysaccharides (LPS) induction. DC-CASPIC localizes to mitochondria, and protein-protein interaction study demonstrates that DC-CASPIC interacts with caspases and inhibits its activity in DC. Consistently, DC-CASPIC suppresses caspases-induced degradation of nitric oxide synthase-2 (NOS2) and subsequently promotes the synthesis of nitric oxide (NO). NO is an essential regulatory molecule that modulates the capability of DC in stimulating T cell proliferation/activation in vitro; hence, overexpression of DC-CASPIC in DC enhances this stimulation. Collectively, our findings reveal that DC-CASPIC is a key molecule that regulates caspases activity and NO synthesis in DC.

High doses of vitamin E improve mitochondrial dysfunction in rat hippocampus and frontal cortex upon aging

Rat aging from 4 to 12 mo was accompanied by hippocampus and frontal cortex mitochondrial dysfunction, with decreases of 23 to 53% in tissue and mitochondrial respiration and in the activities of complexes I and IV and of mitochondrial nitric oxide synthase (mtNOS) (P < 0.02). In aged rats, the two brain areas showed mitochondria with higher content (35-78%) of oxidation products of phospholipids and proteins and with higher (59-95%) rates of O(2)(-) and H(2)O(2) production (P < 0.02). Dietary supplementation with vitamin E (2.0 or 5.0 g/kg of food) from 9 to 12 mo of rat age, restored in a dose-dependent manner, the decreases in tissue and mitochondrial respiration (to 90-96%) and complexes I and IV and mtNOS activities (to 86-88%) of the values of 4-mo-old rats (P < 0.02). Vitamin E prevented, by 73-80%, the increases in oxidation products, and by 62-68%, the increases in O(2)(-) and H(2)O(2) production (P < 0.05). High resolution histochemistry of cytochrome oxidase in the hippocampal CA1 region showed higher staining in vitamin E-treated rats than in control animals. Aging decreased (19%) hippocampus mitochondrial mass, an effect that was restored by vitamin E. High doses of vitamin E seem to sustain mitochondrial biogenesis in synaptic areas.

Redox control of liver function in health and disease

Reactive oxygen species (ROS), a heterogeneous population of biologically active intermediates, are generated as by-products of the aerobic metabolism and exhibit a dual role in biology. When produced in controlled conditions and in limited quantities, ROS may function as signaling intermediates, contributing to critical cellular functions such as proliferation, differentiation, and cell survival. However, ROS overgeneration and, particularly, the formation of specific reactive species, inflicts cell death and tissue damage by targeting vital cellular components such as DNA, lipids, and proteins, thus arising as key players in disease pathogenesis. Given the predominant role of hepatocytes in biotransformation and metabolism of xenobiotics, ROS production constitutes an important burden in liver physiology and pathophysiology and hence in the progression of liver diseases. Despite the recognized role of ROS in disease pathogenesis, the efficacy of antioxidants as therapeutics has been limited. A better understanding of the mechanisms, nature, and location of ROS generation, as well as the optimization of cellular defense strategies, may pave the way for a brighter future for antioxidants and ROS scavengers in the therapy of liver diseases.

A new paradigm for MAPK: structural interactions of hERK1 with mitochondria in HeLa cells

Extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) are members of the MAPK family and participate in the transduction of stimuli in cellular responses. Their long-term actions are accomplished by promoting the expression of specific genes whereas faster responses are achieved by direct phosphorylation of downstream effectors located throughout the cell. In this study we determined that hERK1 translocates to the mitochondria of HeLa cells upon a proliferative stimulus. In the mitochondrial environment, hERK1 physically associates with (i) at least 5 mitochondrial proteins with functions related to transport (i.e. VDAC1), signalling, and metabolism; (ii) histones H2A and H4; and (iii) other cytosolic proteins. This work indicates for the first time the presence of diverse ERK-complexes in mitochondria and thus provides a new perspective for assessing the functions of ERK1 in the regulation of cellular signalling and trafficking in HeLa cells.

Mitochondrial nitric oxide synthase: a masterpiece of metabolic adaptation, cell growth, transformation, and death

Mitochondria are specialized organelles that control energy metabolism and also activate a multiplicity of pathways that modulate cell proliferation and mitochondrial biogenesis or, conversely, promote cell arrest and programmed cell death by a limited number of oxidative or nitrative reactions. Nitric oxide (NO) regulates oxygen uptake by reversible inhibition of cytochrome oxidase and the production of superoxide anion from the mitochondrial electron transfer chain. In this sense, NO produced by mtNOS will set the oxygen uptake level and contribute to oxidation-reduction reaction (redox)-dependent cell signaling. Modulation of translocation and activation of neuronal nitric oxide synthase (mtNOS activity) under different physiologic or pathologic conditions represents an adaptive response properly modulated to adjust mitochondria to different cell challenges.

Mitochondrial nitric oxide metabolism during rat heart adaptation to high altitude: effect of sildenafil, L-NAME, and L-arginine treatments

Rats submitted to high altitude (Cerro de Pasco, Perú, 4,340 m, Po(2) = 12.2 kPa) for up to 84 days showed a physiological adaptive response with decreased body weight gain (15%), increased right ventricle weight (100%), and increased hematocrit (40%) compared with sea level animals. These classical parameters of adaptation to high altitude were accompanied by an increase in heart mitochondrial enzymes: complexes I-III activity by 34% and mitochondrial nitric oxide synthase (mtNOS) activity and expression by >75%. The hyperbolic increase for mtNOS activity during adaptation to high altitude was similar to the observed pattern for hematocrit. Hematocrit and mtNOS activity mean values correlated linearly (r(2) = 0.75, P <or= 0.05). Chronic treatment for 28 days with sildenafil (50 mg*kg(-1).day(-1)) decreased the response of mtNOS to high altitude by 25%. Conversely, N(G)-nitro-l-arginine methyl ester treatment (8.3 mg*kg(-1)*day(-1)) increased such response by 40%, whereas l-arginine treatment (106 mg*kg(-1)*day(-1)) had no effect. Nitric oxide (NO) production by mtNOS accounts for approximately 49% of total cellular NO production in sea level rats and for approximately 54% in rats exposed to high altitude for 84 days. It is concluded that mtNOS is a substantial source of cardiac NO, a factor in the adaptive response to sustained heart hypoxia that is susceptible to be modified by pharmacological treatments.

The formation of peroxynitrite in the applied physiology of mitochondrial nitric oxide

Mitochondria require nitric oxide ((.)NO) to exert a delicate control of metabolic rate as well as to regulate life functions, cell cycle activation and arrest, and apoptosis. All activities depend on the matrical (.)NO steady state concentration as provided by mitochondrial (mtNOS) and cytosolic sources (eNOS) and reduced by forming superoxide anion and H2O2 and a low peroxynirite (ONOO(-)) yield. We review herein the biochemical pathways involved in the control of (.)NO mitochondrial level and its biological and physiological significance in hormone effects and aging. At high ()NO, the cost of this physiological regulation is that ONOO(-) excess will lead to nitrosation/nitration and oxidization of mitochondrial and cell proteins and lipids. The disruption of (.)NO modulation of mitochondrial respiration supports then, a platform for prevalent neurodegenerative and metabolic diseases.

Tumor cell phenotype is sustained by selective MAPK oxidation in mitochondria

Mitochondria are major cellular sources of hydrogen peroxide (H₂O₂), the production of which is modulated by oxygen availability and the mitochondrial energy state. An increase of steady-state cell H₂O₂ concentration is able to control the transition from proliferating to quiescent phenotypes and to signal the end of proliferation; in tumor cells thereby, low H₂O₂ due to defective mitochondrial metabolism can contribute to sustain proliferation. Mitogen-activated protein kinases (MAPKs) orchestrate signal transduction and recent data indicate that are present in mitochondria and regulated by the redox state. On these bases, we investigated the mechanistic connection of tumor mitochondrial dysfunction, H₂O₂ yield, and activation of MAPKs in LP07 murine tumor cells with confocal microscopy, in vivo imaging and directed mutagenesis. Two redox conditions were examined: low 1 µM H₂O₂ increased cell proliferation in ERK1/2-dependent manner whereas high 50 µM H₂O₂ arrested cell cycle by p38 and JNK1/2 activation. Regarding the experimental conditions as a three-compartment model (mitochondria, cytosol, and nuclei), the different responses depended on MAPKs preferential traffic to mitochondria, where a selective activation of either ERK1/2 or p38-JNK1/2 by co-localized upstream kinases (MAPKKs) facilitated their further passage to nuclei. As assessed by mass spectra, MAPKs activation and efficient binding to cognate MAPKKs resulted from oxidation of conserved ERK1/2 or p38-JNK1/2 cysteine domains to sulfinic and sulfonic acids at a definite H₂O₂ level. Like this, high H₂O₂ or directed mutation of redox-sensitive ERK2 Cys²¹⁴ impeded binding to MEK1/2, caused ERK2 retention in mitochondria and restricted shuttle to nuclei. It is surmised that selective cysteine oxidations adjust the electrostatic forces that participate in a particular MAPK-MAPKK interaction. Considering that tumor mitochondria are dysfunctional, their inability to increase H₂O₂ yield should disrupt synchronized MAPK oxidations and the regulation of cell cycle leading cells to remain in a proliferating phenotype.

Control of muscle mitochondria by insulin entails activation of Akt2-mtNOS pathway: implications for the metabolic syndrome

Background

In the metabolic syndrome with hyperinsulinemia, mitochondrial inhibition facilitates muscle fat and glycogen accumulation and accelerates its progression. In the last decade, nitric oxide (NO) emerged as a typical mitochondrial modulator by reversibly inhibiting citochrome oxidase and oxygen utilization. We wondered whether insulin-operated signaling pathways modulate mitochondrial respiration via NO, to alternatively release complete glucose oxidation to CO₂ and H₂O or to drive glucose storage to glycogen.

Methodology/Principal Findings

We illustrate here that NO produced by translocated nNOS (mtNOS) is the insulin-signaling molecule that controls mitochondrial oxygen utilization. We evoke a hyperinsulinemic-normoglycemic non-invasive clamp by subcutaneously injecting adult male rats with long-lasting human insulin glargine that remains stable in plasma by several hours. At a precise concentration, insulin increased phospho-Akt2 that translocates to mitochondria and determines in situ phosphorylation and substantial cooperative mtNOS activation (+4–8 fold, P<.05), high NO, and a lowering of mitochondrial oxygen uptake and resting metabolic rate (−25 to −60%, P<.05). Comparing in vivo insulin metabolic effects on gastrocnemius muscles by direct electroporation of siRNA nNOS or empty vector in the two legs of the same animal, confirmed that in the silenced muscles disrupted mtNOS allows higher oxygen uptake and complete (U-¹⁴C)-glucose utilization respect to normal mtNOS in the vector-treated ones (respectively 37±3 vs 10±1 µmolO₂/h.g tissue and 13±1 vs 7.2±1 µmol ³H₂O/h.g tissue, P<.05), which reciprocally restricted glycogen-synthesis by a half.

Conclusions/Significance

These evidences show that after energy replenishment, insulin depresses mitochondrial respiration in skeletal muscle via NO which permits substrates to be deposited as macromolecules; at discrete hyperinsulinemia, persistent mtNOS activation could contribute to mitochondrial dysfunction with insulin resistance and obesity and therefore, to the progression of the metabolic syndrome.

Mitochondrial and cellular heme-dependent proteins as targets for the bioactive function of the heme oxygenase/carbon monoxide system

The toxic effect of high concentrations of CO gas in living organisms is coherently typified at biochemical levels by the high affinity of CO for hemoglobin and cytochromes, heme-dependent proteins that are indispensable for oxygen transport and mitochondrial respiration. However, the basal production of CO during heme degradation and the ability of heme oxygenase-1 (HO-1) to increase CO availability pose the question of how this gaseous molecule interacts with metal centers within the intracellular milieu to serve as one of the most unconventional signaling mediators. Emerging evidence indicates that the diverse and multifaceted beneficial effects exerted by "low concentrations" of CO cannot be explained solely by the activation of classic prototypic targets (i.e., guanylate cyclase/potassium channels) but entails the dynamic and concerted activation/inhibition of a group of CO-responsive proteins. As the complexity of the temporal and spatial action of CO is progressively being appreciated, this review aims to (a) highlight the current knowledge on certain metal-containing proteins that interact directly with CO; (b) analyze the latest notions on their functional role in response to CO; and finally (c) propose a rational view on the mode these CO targets may interrelate with and be regulated by the HO/CO pathway.

Mitochondrial nitric oxide in the signaling of cell integrated responses

Mitochondria are the specialized organelles for energy metabolism, but, as a typical example of system biology, they also activate a multiplicity of pathways that modulate cell proliferation and mitochondrial biogenesis or oppositely promote cell arrest and programmed cell death by a limited number of oxidative or nitrosative reactions. These reactions are influenced by matrix nitric oxide (NO) steady-state concentration, either from local production or by gas diffusion to mitochondria from the canonical sources. Likewise, in a range of ∼30–200 nM, NO turns mitochondrial O2utilization down by binding to cytochrome oxidase and elicits a burst of superoxide anion and hydrogen peroxide that diffuses outside mitochondria. Depending on NO levels and antioxidant defenses, more or less H2O2accumulates in cytosol and nucleus, and the resulting redox grading contributes to dual activation of proliferating and proapoptotic cascades, like ERK1/2 or p38 MAPK. Moreover, these sequential activating pathways participate in rat liver and brain development and in thyroid modulation of mitochondrial metabolism and contribute to hypothyroid phenotype through complex I nitration. On the contrary, lack of NO disrupts pathways like S-nitrosylation or H2O2production and likewise is a gateway to disease in amyotrophic lateral sclerosis with superoxide dismutase 1 mutations or to cancer proliferation.

Mutual changes of thioredoxin and nitrosothiols during biliary cirrhosis: results from humans and cholestatic rats

Cholestasis is associated with changes in NO metabolism and thiol oxidation. Thioredoxin contributes to regulate vascular tone and intracellular redox status by cleaving nitrosothiols and maintaining -SH groups. This study investigated the changes in circulating thioredoxin and nitrosothiols and the relationship with protein sulfhydryls (PSH), hepatic concentrations, hyaluronate, and histology in patients with primary biliary cirrhosis (PBC) and in rats with bile duct ligation (BDL). PSH in erythrocytes were significantly decreased in stage III and IV PBC and at day 10 after BDL. Compared with controls, erythrocyte thioredoxin levels were higher in stage I through III PBC and lower in stage IV patients. Serum thioredoxin levels were significantly higher in PBC stages I and II and lower in stages III and IV. Serum nitrosothiols were higher in all PBC patients and inversely related to thioredoxin and hyaluronate. In rats, serum, hepatic, and mitochondrial thioredoxin had initially increased after BDL (day 1-3) and then decreased. After day 7 BDL, nitrosothiols were 10-fold increased in serum and liver, and even higher in mitochondria. In the liver, thioredoxin was inversely related to both nitrosothiols and PSH. In rats, the difference in time average changes from baseline among serum, hepatic, and erythrocyte thioredoxin suggests that most of circulating thioredoxin originates from the liver.

CONCLUSION

Our findings indicate that cholestasis is associated with significant mutual and interrelated changes between circulating and hepatic thioredoxin and nitrosothiols. The increase of hepatic, mitochondrial, and circulating nitrosothiols with ongoing cholestasis suggests an active participation of NO in both liver injury and extrahepatic changes.

CO–metal interaction: vital signaling from a lethal gas

The past few years have witnessed intense research into the biological significance of carbon monoxide (CO) as an essential signaling mediator in cells and tissues. To transduce the signal properly, CO must react selectively with functional and structural proteins containing moieties that show preferred reactivity towards this gaseous molecule. This selectivity is exemplified by the interaction of CO with iron- and heme-dependent proteins, although systems containing other transition metals can potentially become a preferential target for CO. Notably, transition metal carbonyls, which carry and liberate CO, are also emerging as a pharmacological tool to mimic the bioactivity of endogenously generated CO. Thus, exploring how CO binding to metal complexes is translated into a cytoprotective function is a challenging task and might open up opportunities for therapeutic applications based on CO delivery.

Interactions between nitric oxide, oxygen, reactive oxygen species and reactive nitrogen species

ROS (reactive oxygen species) and RNS (reactive nitrogen species) are central to the innate immunity that protects us from infection, but also contribute to degenerative diseases and possibly aging. However, ROS and RNS are increasingly recognized to contribute to physiological signalling. This review briefly describes the main interactions between ROS and RNS and shows how their origins, chemistry, metabolism and biological actions are intimately linked.

HO‐1 is located in liver mitochondria and modulates mitochondrial heme content and metabolism

This study investigated whether inducible heme oxygenase-1[corrected] (HO-1) [corrected] is targeted to mitochondria and its putative effects on oxidative metabolism in rat liver. Western blot and immune-electron microscopy in whole purified and fractionated organelles showed basal expression of HO-1 protein in both microsomes and mitochondria (inner membrane), accompanied by a parallel HO activity. Inducers of HO-1 increased HO-1 targeting to the inner mitochondrial membrane, which also contained biliverdin reductase, supporting that both enzymes are in the same compartmentalization. Induction of mitochondrial HO-1 was associated with a decrease of mitochondrial heme content and selective reduction of protein expression of cytochrome oxidase (COX) subunit I, which is coded by the mitochondrial genome and synthesized in the mitochondria depending on heme availability; these changes resulted in decreased COX spectrum and activity. Mitochondrial HO-1 induction was also associated with down-regulation of mitochondrial-targeted NO synthase expression and activity, resulting in a reduction of NO-dependent mitochondrial oxidant yield; inhibition of HO-1 activity reverted these effects. In conclusion, we demonstrated for the first time localization of HO-1 protein in mitochondria. It is surmised that mitochondrial HO-1 has important biological roles in regulating mitochondrial heme protein turnover and in protecting against conditions such as hypoxia, neurodegenerative diseases, or sepsis, in which substantially increased mitochondrial NO and oxidant production have been implicated.

Mitochondrial metabolic states regulate nitric oxide and hydrogen peroxide diffusion to the cytosol

Mitochondria isolated from rat heart, liver, kidney and brain (respiratory control 4.0-6.5) release NO and H2O2 at rates that depend on the mitochondrial metabolic state: releases are higher in state 4, about 1.7-2.0 times for NO and 4-16 times for H2O2, than in state 3. NO release in rat liver mitochondria showed an exponential dependence on membrane potential in the range 55 to 180 mV, as determined by Rh-123 fluorescence. A similar behavior was reported for mitochondrial H2O2 production by [S.S. Korshunov, V.P. Skulachev, A.A. Starkov, High protonic potential actuates a mechanism of production of reactive oxygen species in mitochondria. FEBS Lett. 416 (1997) 15_18.]. Transition from state 4 to state 3 of brain cortex mitochondria was associated to a decrease in NO release (50%) and in membrane potential (24-53%), this latter determined by flow cytometry and DiOC6 and JC-1 fluorescence. The fraction of cytosolic NO provided by diffusion from mitochondria was 61% in heart, 47% in liver, 30% in kidney, and 18% in brain. The data supports the speculation that NO and H2O2 report a high mitochondrial energy charge to the cytosol. Regulation of mtNOS activity by membrane potential makes mtNOS a regulable enzyme that in turn regulates mitochondrial O2 uptake and H2O2 production.

Hypothyroid phenotype is contributed by mitochondrial complex I inactivation due to translocated neuronal nitric-oxide synthase

Although transcriptional effects of thyroid hormones have substantial influence on oxidative metabolism, how thyroid sets basal metabolic rate remains obscure. Compartmental localization of nitric-oxide synthases is important for nitric oxide signaling. We therefore examined liver neuronal nitric-oxide synthase-alpha (nNOS) subcellular distribution as a putative mechanism for thyroid effects on rat metabolic rate. At low 3,3',5-triiodo-L-thyronine levels, nNOS mRNA increased by 3-fold, protein expression by one-fold, and nNOS was selectively translocated to mitochondria without changes in other isoforms. In contrast, under thyroid hormone administration, mRNA level did not change and nNOS remained predominantly localized in cytosol. In hypothyroidism, nNOS translocation resulted in enhanced mitochondrial nitric-oxide synthase activity with low O2 uptake. In this context, NO utilization increased active O2 species and peroxynitrite yields and tyrosine nitration of complex I proteins that reduced complex activity. Hypothyroidism was also associated to high phospho-p38 mitogen-activated protein kinase and decreased phospho-extracellular signal-regulated kinase 1/2 and cyclin D1 levels. Similarly to thyroid hormones, but without changing thyroid status, nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester increased basal metabolic rate, prevented mitochondrial nitration and complex I derangement, and turned mitogen-activated protein kinase signaling and cyclin D1 expression back to control pattern. We surmise that nNOS spatial confinement in mitochondria is a significant downstream effector of thyroid hormone and hypothyroid phenotype.

Neuronal nitric oxide synthase controls enzyme activity pattern of mitochondria and lipid metabolism

Mitochondria are affected by endogenous nitric oxide (NO). Besides effects of NO on mitochondrial enzymes and the stimulation of mitochondrial H2O2 production, a NO-dependent increase in mitochondrial biogenesis in several tissues has been reported. It is still obscure whether NO generated by one specific or different NO synthase (NOS) isoenzymes determine such effects. Therefore, we analyzed the amount of mitochondria, respiratory chain enzyme complexes, and citrate synthase in the brain, muscle, heart, kidney, and liver by comparing wild-type (WT) mice and mice lacking the neuronal nitric oxide synthase isoform (nNOS-KO). Our results show that the activities of NADH:cytochrome c oxidoreductase and succinate cytochrome c oxidoreductase differ between WT and nNOS-KO mice. However, similar quantities of mitochondria were found in the homogenates of tissues in WT and nNOS-KO animals. Most impressive, higher activities and protein of citrate synthase were found in the brain, muscle, heart, kidney, and liver of nNOS-KO mice. Additionally, higher contents of fatty acid synthase and lipids were determined in the livers of nNOS-KO mice but not in the heart and brain. Furthermore, liver mitochondria from nNOS-KO mice consumed pyruvate at a higher rate and released more citric acid. Our data document a previously unrecognized role of endogenous NO in the regulation of lipid metabolism.

Bilirubin decreases nos2 expression via inhibition of NAD(P)H oxidase: implications for protection against endotoxic shock in rats

We investigated a possible beneficial role for bilirubin, one of the products of heme degradation by the cytoprotective enzyme heme oxygenase-1 in counteracting Escherichia coli endotoxin-mediated toxicity. Homozygous jaundice Gunn rats, which display high plasma bilirubin levels due to deficiency of glucuronyl transferase activity, and Sprague-Dawley rats subjected to sustained exogenous bilirubin administration were more resistant to endotoxin (LPS)-induced hypotension and death compared with nonhyperbilirubinemic rats. LPS-stimulated production of nitric oxide (NO) was significantly decreased in hyperbilirubinemic rats compared with normal animals; this effect was associated with reduction of inducible NO synthase (NOS2) expression in renal, myocardial, and aortic tissues. Furthermore, NOS2 protein expression and activity were reduced in murine macrophages stimulated with LPS and preincubated with bilirubin at concentrations similar to that found in the serum of hyperbilirubinemic animals. This effect was secondary to inhibition of NAD(P)H oxidase since 1) inhibition of NAD(P)H oxidase attenuated NOS2 induction by LPS, 2) bilirubin decreased NAD(P)H oxidase activity in vivo and in vitro, and 3) down-regulation of NOS2 by bilirubin was reversed by addition of NAD(P)H. These findings indicate that bilirubin can act as an effective agent to reduce mortality and counteract hypotension elicited by endotoxin through mechanisms involving a decreased NOS2 induction secondary to inhibition of NAD(P)H oxidase.

Cell H2O2 steady-state concentration and mitochondrial nitric oxide

For many years, mitochondrial respiration was thought to follow an "all or nothing" paradigm supporting the notion that in the normal O2 concentration range, respiration is mainly controlled by tissue demands. However, nitric oxide produced by cytosol or mitochondrial nitric oxide synthases adapts respiration to different physiologic conditions and increases the mitochondrial production of O2 active species that contributes to NO clearance. Because mitochondrial NO utilization is sensitive to environmental or hormonal modulation, and because diffusible active species, like H2O2, are able to regulate genes related to proliferation, quiescence, and death, we surmised that the two mechanisms converge to elicit the different responses in cell physiology.

Increased mitochondrial biogenesis in primary leukemia cells: the role of endogenous nitric oxide and impact on sensitivity to fludarabine

B cell chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia in the Western hemisphere, yet many biological and molecular features of the disease remain undefined. CLL cells generate increased levels of radical species such as superoxide and nitric oxide (NO), which is associated with mitochondrial DNA mutations. Considering that NO levels can affect mitochondrial biogenesis, we hypothesized that the inherent nitrosative stress in CLL cells may lead to hyperactive mitochondrial biogenesis. Here we report that primary CLL cells contained significantly more mitochondria than normal lymphocytes and that their mitochondrial mass was significantly related to endogenous NO levels. Expression of the mitochondrial biogenesis factors nuclear respiratory factor-1 and mitochondrial transcription factor A was elevated in most CLL specimens examined and appeared to be related to cellular NO levels. Treatment of B cells with exogenous NO caused a substantial increase in mitochondrial mass. In vitro sensitivity of CLL cells to fludarabine was highly related to mitochondrial mass in that cells with greater mitochondrial mass were less sensitive to the drug. Taken together, our results suggest that NO is a key mediator of mitochondrial biogenesis in CLL and that modulation of mitochondrial biogenesis by NO may alter cellular sensitivity to fludarabine.