PKC downregulation upon rapamycin treatment attenuates mitochondrial disease.

Leigh syndrome is a fatal neurometabolic disorder caused by defects in mitochondrial function. Mechanistic target of rapamycin (mTOR) inhibition with rapamycin attenuates disease progression in a mouse model of Leigh syndrome (Ndufs4 knock-out (KO) mouse); however, the mechanism of rescue is unknown. Here we identify protein kinase C (PKC) downregulation as a key event mediating the beneficial effects of rapamycin treatment of Ndufs4 KO mice. Assessing the impact of rapamycin on the brain proteome and phosphoproteome of Ndufs4 KO mice, we find that rapamycin restores mitochondrial protein levels, inhibits signalling through both mTOR complexes and reduces the abundance and activity of multiple PKC isoforms. Administration of PKC inhibitors increases survival, delays neurological deficits, prevents hair loss and decreases inflammation in Ndufs4 KO mice. Thus, PKC may be a viable therapeutic target for treating severe mitochondrial disease.

Intellectual disability-associated factor Zbtb11 cooperates with NRF-2/GABP to control mitochondrial function.

Zbtb11 is a conserved transcription factor mutated in families with hereditary intellectual disability. Its precise molecular and cellular functions are currently unknown, precluding our understanding of the aetiology of this disease. Using a combination of functional genomics, genetic and biochemical approaches, here we show that Zbtb11 plays essential roles in maintaining the homeostasis of mitochondrial function. Mechanistically, we find Zbtb11 facilitates the recruitment of nuclear respiratory factor 2 (NRF-2) to its target promoters, activating a subset of nuclear genes with roles in the biogenesis of respiratory complex I and the mitoribosome. Genetic inactivation of Zbtb11 resulted in a severe complex I assembly defect, impaired mitochondrial respiration, mitochondrial depolarisation, and ultimately proliferation arrest and cell death. Experimental modelling of the pathogenic human mutations showed these have a destabilising effect on the protein, resulting in reduced Zbtb11 dosage, downregulation of its target genes, and impaired complex I biogenesis. Our study establishes Zbtb11 as an essential mitochondrial regulator, improves our understanding of the transcriptional mechanisms of nuclear control over mitochondria, and may help to understand the aetiology of Zbtb11-associated intellectual disability.

The reduction of NDUFC2 expression is associated with mitochondrial impairment in circulating mononuclear cells of patients with acute coronary syndrome.

BACKGROUND: Deficiency of NADH dehydrogenase [ubiquinone], the mitochondrial complex I, represents an emerging mechanism of cardiovascular diseases. Ndufc2, a subunit of mitochondrial complex I, is involved in stroke development. We aimed to gain some insights on the role of Ndufc2 into acute coronary syndrome (ACS) through the assessment of its gene expression, along with that of anti-oxidant proteins and of mitochondrial function parameters, in circulating mononuclear cells (PBMCs) of ACS versus stable angina (SA) patients. The impact of NDUFC2 silencing in human endothelial and vascular smooth muscle cells was assessed in vitro. METHODS AND RESULTS: One hundred twenty-three patients presenting with SA (n = 41) or ACS (n = 82) were enrolled. PBMCs were used to assess the gene expression level of: NDUFC2, uncoupling protein 2 (UCP2), superoxide dysmutases 1 and 2 (SOD1, SOD2), levels of ROS and ATP. The mitochondrial dysfunction was assessed by cytofluorimetry; the structural damage by transmission electron microscopy. Cell viability, angiogenesis, markers of atherogenesis were evaluated in NDUFC2-silenced vascular cells. NDUFC2 mRNA level was significantly downregulated, along with UCP2, SOD1, SOD2 expression, in ACS patients. We found significant increases of ROS levels, reduced ATP levels, higher degree of mitochondrial structural damage and dysfunction in ACS patients. In vitro, NDUFC2 silencing favored mechanisms involved in atherogenesis and plaque vulnerability. CONCLUSIONS: A significant reduction of NDUFC2 expression is detected in ACS. In vitro, NDUFC2 silencing affects vascular cell viability and angiogenesis while stimulating the expression of markers of plaque rupture. Our observations suggest that these mechanisms may contribute to ACS development.

The Mitochondrial Isoform of FASTK Modulates Nonopsonic Phagocytosis of Bacteria by Macrophages via Regulation of Respiratory Complex I.

Phagocytosis is a pivotal process by which innate immune cells eliminate bacteria. In this study, we explore novel regulatory mechanisms of phagocytosis driven by the mitochondria. Fas-activated serine/threonine kinase (FASTK) is an RNA-binding protein with two isoforms, one localized to the mitochondria (mitoFASTK) and the other isoform to cytosol and nucleus. The mitoFASTK isoform has been reported to be necessary for the biogenesis of the mitochondrial ND6 mRNA, which encodes an essential subunit of mitochondrial respiratory complex I (CI, NADH:ubiquinone oxidoreductase). This study investigates the role and the mechanisms of action of FASTK in phagocytosis. Macrophages from FASTK─/─ mice exhibited a marked increase in nonopsonic phagocytosis of bacteria. As expected, CI activity was specifically reduced by almost 50% in those cells. To explore if decreased CI activity could underlie the phagocytic phenotype, we tested the effect of CI inhibition on phagocytosis. Indeed, treatment with CI inhibitor rotenone or short hairpin RNAs against two CI subunits (NDUFS3 and NDUFS4) resulted in a marked increase in nonopsonic phagocytosis of bacteria. Importantly, re-expression of mitoFASTK in FASTK-depleted macrophages was sufficient to rescue the phagocytic phenotype. In addition, we also report that the decrease in CI activity in FASTK─/─ macrophages is associated with an increase in phosphorylation of the energy sensor AMP-activated protein kinase (AMPK) and that its inhibition using Compound C reverted the phagocytosis phenotype. Taken together, our results clearly demonstrate for the first time, to our knowledge, that mitoFASTK plays a negative regulatory role on nonopsonic phagocytosis of bacteria in macrophages through its action on CI activity.

The m1A landscape on cytosolic and mitochondrial mRNA at single-base resolution.

Modifications on mRNA offer the potential of regulating mRNA fate post-transcriptionally. Recent studies suggested the widespread presence of N1-methyladenosine (m1A), which disrupts Watson-Crick base pairing, at internal sites of mRNAs. These studies lacked the resolution of identifying individual modified bases, and did not identify specific sequence motifs undergoing the modification or an enzymatic machinery catalysing them, rendering it challenging to validate and functionally characterize putative sites. Here we develop an approach that allows the transcriptome-wide mapping of m1A at single-nucleotide resolution. Within the cytosol, m1A is present in a low number of mRNAs, typically at low stoichiometries, and almost invariably in tRNA T-loop-like structures, where it is introduced by the TRMT6/TRMT61A complex. We identify a single m1A site in the mitochondrial ND5 mRNA, catalysed by TRMT10C, with methylation levels that are highly tissue specific and tightly developmentally controlled. m1A leads to translational repression, probably through a mechanism involving ribosomal scanning or translation. Our findings suggest that m1A on mRNA, probably because of its disruptive impact on base pairing, leads to translational repression, and is generally avoided by cells, while revealing one case in mitochondria where tight spatiotemporal control over m1A levels was adopted as a potential means of post-transcriptional regulation.

Oxidative Phosphorylation System in Gastric Carcinomas and Gastritis.

Switching of cellular energy production from oxidative phosphorylation (OXPHOS) by mitochondria to aerobic glycolysis occurs in many types of tumors. However, the significance of this switching for the development of gastric carcinoma and what connection it may have to Helicobacter pylori infection of the gut, a primary cause of gastric cancer, are poorly understood. Therefore, we investigated the expression of OXPHOS complexes in two types of human gastric carcinomas ("intestinal" and "diffuse"), bacterial gastritis with and without metaplasia, and chemically induced gastritis by using immunohistochemistry. Furthermore, we analyzed the effect of HP infection on several key mitochondrial proteins. Complex I expression was significantly reduced in intestinal type (but not diffuse) gastric carcinomas compared to adjacent control tissue, and the reduction was independent of HP infection. Significantly, higher complex I and complex II expression was present in large tumors. Furthermore, higher complex II and complex III protein levels were also obvious in grade 3 versus grade 2. No differences of OXPHOS complexes and markers of mitochondrial biogenesis were found between bacterially caused and chemically induced gastritis. Thus, intestinal gastric carcinomas, but not precancerous stages, are frequently characterized by loss of complex I, and this pathophysiology occurs independently of HP infection.

5-HT2 Receptor Regulation of Mitochondrial Genes: Unexpected Pharmacological Effects of Agonists and Antagonists.

In acute organ injuries, mitochondria are often dysfunctional, and recent research has revealed that recovery of mitochondrial and renal functions is accelerated by induction of mitochondrial biogenesis (MB). We previously reported that the nonselective 5-HT2 receptor agonist DOI [1-(4-iodo-2,5-dimethoxyphenyl)propan-2-amine] induced MB in renal proximal tubular cells (RPTCs). The goal of this study was to determine the role of 5-HT2 receptors in the regulation of mitochondrial genes and oxidative metabolism in the kidney. The 5-HT2C receptor agonist CP-809,101 [2-[(3-chlorophenyl)methoxy]-6-(1-piperazinyl)pyrazine] and antagonist SB-242,084 [6-chloro-2,3-dihydro-5-methyl-N-[6-[(2-methyl-3-pyridinyl)oxy]-3-pyridinyl]-1H-indole-1-carboxyamide dihydrochloride] were used to examine the induction of renal mitochondrial genes and oxidative metabolism in RPTCs and in mouse kidneys in the presence and absence of the 5-HT2C receptor. Unexpectedly, both CP-809,101 and SB-242,084 increased RPTC respiration and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) mRNA expression in RPTCs at 1-10 nM. In addition, CP-809,101 and SB-242,084 increased mRNA expression of PGC-1α and the mitochondrial proteins NADH dehydrogenase subunit 1 and NADH dehydrogenase (ubiquinone) ß subcomplex 8 in mice. These compounds increased mitochondrial genes in RPTCs in which the 5-HT2C receptor was downregulated with small interfering RNA and in the renal cortex of mice lacking the 5-HT2C receptor. By contrast, the ability of these compounds to increase PGC-1α mRNA and respiration was blocked in RPTCs treated with 5-HT2A receptor small interfering RNA or the 5-HT2A receptor antagonist eplivanserin. In addition, the 5-HT2A receptor agonist NBOH-2C-CN [4-[2-[[(2-hydroxyphenyl)methyl]amino]ethyl]-2,5-dimethoxybenzonitrile] increased RPTC respiration at 1-100 nM. These results suggest that agonism of the 5-HT2A receptor induces MB and that the classic 5-HT2C receptor agonist CP-809,101 and antagonist SB-242,084 increase mitochondrial genes and oxidative metabolism through the 5-HT2A receptor. To our knowledge, this is the first report that links 5-HT2A receptor agonism to mitochondrial function.

Low-dose ionizing radiation induces mitochondrial fusion and increases expression of mitochondrial complexes I and III in hippocampal neurons.

High energy ionizing radiation can cause DNA damage and cell death. During clinical radiation therapy, the radiation dose could range from 15 to 60 Gy depending on targets. While 2 Gy radiation has been shown to cause cancer cell death, studies also suggest a protective potential by low dose radiation. In this study, we examined the effect of 0.2-2 Gy radiation on hippocampal neurons. Low dose 0.2 Gy radiation treatment increased the levels of MTT. Since hippocampal neurons are post-mitotic, this result reveals a possibility that 0.2 Gy irradiation may increase mitochondrial activity to cope with stimuli. Maintaining neural plasticity is an energy-demanding process that requires high efficient mitochondrial function. We thus hypothesized that low dose radiation may regulate mitochondrial dynamics and function to ensure survival of neurons. Our results showed that five days after 0.2 Gy irradiation, no obvious changes on neuronal survival, neuronal synapses, membrane potential of mitochondria, reactive oxygen species levels, and mitochondrial DNA copy numbers. Interestingly, 0.2 Gy irradiation promoted the mitochondria fusion, resulting in part from the increased level of a mitochondrial fusion protein, Mfn2, and inhibition of Drp1 fission protein trafficking to the mitochondria. Accompanying with the increased mitochondrial fusion, the expressions of complexes I and III of the electron transport chain were also increased. These findings suggest that, hippocampal neurons undergo increased mitochondrial fusion to modulate cellular activity as an adaptive mechanism in response to low dose radiation.

Eukaryotic translation initiation factor 6 is a novel regulator of reactive oxygen species-dependent megakaryocyte maturation.

BACKGROUND: Ribosomopathies constitute a class of inherited disorders characterized by defects in ribosome biogenesis and function. Classically, bone marrow (BM) failure is a clinical symptom shared between these syndromes, including Shwachman-Bodian-Diamond syndrome (SBDS). Eukaryotic translation initiation factor 6 (eIF6) is a critical translation factor that rescues the quasilethal effect of the loss of the SBDS protein. OBJECTIVES: To determine whether eIF6 activity is necessary for BM development. METHODS: We used eIF6(+/-) mice and primary BM megakaryocytes to investigate the involvement of eIF6 in the regulation of hematopoiesis. RESULTS: We provide evidence that reduced eIF6 expression negatively impacts on megakaryopoiesis. We show that inhibition of eIF6 leads to a reduction in cell size and mean ploidy level of megakaryocytes and a delay in megakaryocyte maturation by blocking the G1 /S transition. Consistent with this phenotype, only few megakaryocyte-forming proplatelets were found in eIF6(+/-) cells. We also discovered that, in eIF6(+/-) cells, the steady-state abundance of mitochondrial respiratory chain complex I-encoding mRNAs is decreased, resulting in decreased reactive oxygen species (ROS) production. Intriguingly, connectivity map analysis showed that eIF6-mediated changes overlap with specific translational inhibitors. eIF6 is a translation factor acting downstream of insulin/phorbol 12-myristate 13-acetate (PMA) stimulation. PMA treatment significantly restored eIF6(+/-) megakaryocyte maturation, indicating that activation of eIF6 is essential for the rescue of the phenotype. CONCLUSIONS: Taken together, our results show a role for eIF6-driven translation in megakaryocyte development, and unveil the novel connection between translational control and ROS production in this cell subset.

Mitochondrial complex I and III mRNA levels in bipolar disorder.

BACKGROUND: Studies that have focused on the mitochondrial electron transport chain indicate that bipolar disorder (BD) is associated with pathology in mitochondrial function. These pathological processes occur in the brain circuits that regulate affective functions, emotions, and motor behaviors. The present study aimed to determine the relationship between mitochondrial complex dysfunction and BD. METHODS: The BD group included 32 male patients diagnosed with first-episode manic BD. The control group included 35 sociodemographically matched healthy males. Messenger ribonucleic acid (mRNA) was isolated from peripheral blood samples obtained from the patients and control group, and the mRNA levels of the NDUFV1, NDUFV2, and NDUFS1 genes of mitochondrial complex I and the UQCR10 gene of mitochondrial complex III were investigated. RESULTS: Significant differences were identified in complex I gene mRNA levels between the BD group (n = 32) and the control group (n = 35) for the following genes: NDUFV1 (P = 0.01), NDUFV2 (P < 0.01), and NDUFS1 (P = 0.02). The UQCR10 gene (complex III) mRNA level did not differ between the groups (P = 0.1). The mRNA levels of the four genes studied were lower at the 3-month follow-up; however, these differences were not significant (P > 0.05). LIMITATIONS: All of the BD patients were in manic episodes; thus, we were unable to separately compare these levels with those during depressive and euthymic episodes. CONCLUSIONS: The mRNA levels of all of the genes representing the subunits of mitochondrial complex I (NDUFV1, NDUFV2, and NDUFS1) were significantly higher in the present study's BD patients during manic episodes than in the controls. With the data obtained from further research, biomarkers that could be used for the diagnosis and follow-up of neuropsychiatric disorders may be discovered.

Frataxin silencing inactivates mitochondrial Complex I in NSC34 motoneuronal cells and alters glutathione homeostasis.

Friedreich's ataxia (FRDA) is a hereditary neurodegenerative disease characterized by a reduced synthesis of the mitochondrial iron chaperon protein frataxin as a result of a large GAA triplet-repeat expansion within the first intron of the frataxin gene. Despite neurodegeneration being the prominent feature of this pathology involving both the central and the peripheral nervous system, information on the impact of frataxin deficiency in neurons is scant. Here, we describe a neuronal model displaying some major biochemical and morphological features of FRDA. By silencing the mouse NSC34 motor neurons for the frataxin gene with shRNA lentiviral vectors, we generated two cell lines with 40% and 70% residual amounts of frataxin, respectively. Frataxin-deficient cells showed a specific inhibition of mitochondrial Complex I (CI) activity already at 70% residual frataxin levels, whereas the glutathione imbalance progressively increased after silencing. These biochemical defects were associated with the inhibition of cell proliferation and morphological changes at the axonal compartment, both depending on the frataxin amount. Interestingly, at 70% residual frataxin levels, the in vivo treatment with the reduced glutathione revealed a partial rescue of cell proliferation. Thus, NSC34 frataxin silenced cells could be a suitable model to study the effect of frataxin deficiency in neurons and highlight glutathione as a potential beneficial therapeutic target for FRDA.

Reduction of infarct size by the therapeutic protein TAT-Ndi1 in vivo.

Lethal myocardial ischemia-reperfusion (I/R) injury has been attributed in part to mitochondrial respiratory dysfunction (including damage to complex I) and the resultant excessive production of reactive oxygen species. Recent evidence has shown that reduced nicotinamide adenine dinucleotide-quinone internal oxidoreductase (Ndi1; the single-subunit protein that in yeast serves the analogous function as complex I), transduced by addition of the TAT-conjugated protein to culture media and perfusion buffer, can preserve mitochondrial function and attenuate I/R injury in neonatal rat cardiomyocytes and Langendorff-perfused rat hearts. However, this novel metabolic strategy to salvage ischemic-reperfused myocardium has not been tested in vivo. In this study, TAT-conjugated Ndi1 and placebo-control protein were synthesized using a cell-free system. Mitochondrial uptake and functionality of TAT-Ndi1 were demonstrated in mitochondrial preparations from rat hearts after intraperitoneal administration of the protein. Rats were randomized to receive either TAT-Ndi1 or placebo protein, and 2 hours later all animals underwent 45-minute coronary artery occlusion followed by 2 hours of reperfusion. Infarct size was delineated by tetrazolium staining and normalized to the volume of at-risk myocardium, with all analysis conducted in a blinded manner. Risk region was comparable in the 2 cohorts. Preischemic administration of TAT-Ndi1 was profoundly cardioprotective. These results demonstrate that it is possible to target therapeutic proteins to the mitochondrial matrix and that yeast Ndi1 can substitute for complex I to ameliorate I/R injury in the heart. Moreover, these data suggest that cell-permeable delivery of mitochondrial proteins may provide a novel molecular strategy to treat mitochondrial dysfunction in patients.

Mitochondrial complex I activity and NAD+/NADH balance regulate breast cancer progression.

Despite advances in clinical therapy, metastasis remains the leading cause of death in breast cancer patients. Mutations in mitochondrial DNA, including those affecting complex I and oxidative phosphorylation, are found in breast tumors and could facilitate metastasis. This study identifies mitochondrial complex I as critical for defining an aggressive phenotype in breast cancer cells. Specific enhancement of mitochondrial complex I activity inhibited tumor growth and metastasis through regulation of the tumor cell NAD+/NADH redox balance, mTORC1 activity, and autophagy. Conversely, nonlethal reduction of NAD+ levels by interfering with nicotinamide phosphoribosyltransferase expression rendered tumor cells more aggressive and increased metastasis. The results translate into a new therapeutic strategy: enhancement of the NAD+/NADH balance through treatment with NAD+ precursors inhibited metastasis in xenograft models, increased animal survival, and strongly interfered with oncogene-driven breast cancer progression in the MMTV-PyMT mouse model. Thus, aberration in mitochondrial complex I NADH dehydrogenase activity can profoundly enhance the aggressiveness of human breast cancer cells, while therapeutic normalization of the NAD+/NADH balance can inhibit metastasis and prevent disease progression.

Quercetin up-regulates mitochondrial complex-I activity to protect against programmed cell death in rotenone model of Parkinson's disease in rats.

We tested quercetin, a dietary bioflavonoid with potent free radical scavenging action and antioxidant activity, for its neuroprotective effects in rotenone-induced hemi-parkinsonian rats. Rats were infused unilaterally with rotenone into the substantia nigra, and quercetin (25-75mg/kg, i.p.) was administered at 12-h intervals for 4days, and analyzed on the 5th day. Amphetamine- or apomorphine-induced unilateral rotations were significantly reduced in quercetin-treated rats, when analyzed on 14th or 16th day post-surgery, respectively. Quercetin possessed potent hydroxyl radical scavenging action in a cells-free, Fenton-like reaction in test tubes, and in isolated mitochondria when measured by salicylate hydroxylation method. We observed dose-dependent attenuation of the rotenone-induced loss in striatal dopamine, and nigral oxidized and reduced glutathione, as well as the increases in endogenous antioxidant enzymes (catalase and superoxide dismutase) activities supporting the notion that quercetin-effect is mediated via its powerful hydroxyl radicals-scavenging and antioxidant actions. Quercetin's dose-dependent ability to up-regulate mitochondrial complex-I activity, as evidenced by NADH-oxidation, and as seen in blue native-polyacrylamide gel electrophoresis (PAGE) staining in both the contra- and ipsi-lateral nigra suggests the containment of reactive oxygen production at the mitochondrial level. Rotenone-induced induction of NADH-diaphorase activity in the nigral neurons, and its attenuation by quercetin pointed to the possible involvement of nitric oxide too. Reversal of neuronal death induced by rotenone as observed by increased tyrosine hydroxylase-positive cells and decreased TdT-mediated dUTP nick end-labeling (TUNEL) staining in the substantia nigra confirmed the potential of quercetin to revamp dopaminergic cells following oxidative stress mediated programmed cell death and neuronal demise. The present study strongly implicates quercetin's potential ability to repair mitochondrial electron transport defects and to up-regulate its function as the basis of neuroprotection observed in a mitochondrial neurotoxin-induced Parkinsonism.

Low-intensity laser irradiation at 660 nm stimulates transcription of genes involved in the electron transport chain.

BACKGROUND DATA: Low-intensity laser irradiation (LILI) has been shown to stimulate cellular functions leading to increased adenosine triphosphate (ATP) synthesis. This study was undertaken to evaluate the effect of LILI on genes involved in the mitochondrial electron transport chain (ETC, complexes I-IV) and oxidative phosphorylation (ATP synthase). METHODS: Four human skin fibroblast cell models were used in this study: normal non-irradiated cells were used as controls while wounded, diabetic wounded, and ischemic cells were irradiated. Cells were irradiated with a 660 nm diode laser with a fluence of 5 J/cm(2) and gene expression determined by quantitative real-time reverse transcription (RT) polymerase chain reaction (PCR). RESULTS: LILI upregulated cytochrome c oxidase subunit VIb polypeptide 2 (COX6B2), cytochrome c oxidase subunit VIc (COX6C), and pyrophosphatase (inorganic) 1 (PPA1) in diabetic wounded cells; COX6C, ATP synthase, H+transporting, mitochondrial Fo complex, subunit B1 (ATP5F1), nicotinamide adenine dinucleotide (NADH) dehydrogenase (ubiquinone) 1 alpha subcomplex, 11 (NDUFA11), and NADH dehydrogenase (ubiquinone) Fe-S protein 7 (NDUFS7) in wounded cells; and ATPase, H+/K+ exchanging, beta polypeptide (ATP4B), and ATP synthase, H+ transporting, mitochondrial Fo complex, subunit C2 (subunit 9) (ATP5G2) in ischemic cells. CONCLUSIONS: LILI at 660 nm stimulates the upregulation of genes coding for subunits of enzymes involved in complexes I and IV and ATP synthase.

MicroRNA-155 inhibits proliferation and migration of human extravillous trophoblast derived HTR-8/SVneo cells via down-regulating cyclin D1.

MiR-155 is known to participate in various cellular processes by targeting gene expression. We previously revealed a link between miR-155 and perturbation of trophoblast invasion and differentiation. This study aimed to investigate the target molecule(s) of miR-155 on the influence on the proliferation and migration of trophoblast cells. Bioinformatics analysis showed that, at the 3' untranslated region (UTR) of cyclin D1, six bases are complementary to the seed region of miR-155. Luciferase assays and cyclin D1 3'UTR transfection assays validated that cyclin D1 3'UTR was the target of miR-155 in HTR-8/SVneo cells. Overexpression of miR-155 in HTR-8/SVneo cells reduced the level of cyclin D1 protein, decreased cell proliferation and invasion, and increased cell number at the G1 stage. Furthermore, the increased expression of miR-155 also regulated the protein levels of kinase inhibitory protein p27 and phosphorylated cytoskeletal protein filamin A. In conclusion, we found that cyclin D1 may be a target of miR-155 in HTR-8/SVneo cells, and demonstrated a negative regulatory role of miR-155 involved in cyclin D1/p27 pathway in proliferation and migration of the cells.

Rat embryo exposure to all-trans retinoic acid results in postnatal oxidative damage of respiratory complex I in the cerebellum.

The results of the present work show that the exposure of pregnant rats to low doses of all-trans-retinoic acid (ATRA) (2.5 mg/kg body weight) results in postnatal dysfunction of complex I of the respiratory chain in the cerebellum of the offspring. ATRA had no effect on the postnatal expression of complex I and did not exert any direct inhibitory effect on the enzymatic activity of the complex. The ATRA embryonic exposure resulted, however, in a marked increase in the level of carbonylated proteins in the mitochondrial fraction of the cerebellum, in particular of complex I subunits. The postnatal increase of the carbonylated proteins correlated directly with the inhibition of the activity of complex I. ATRA had, on the other hand, no effect on oxygen free-radical scavengers. It is proposed that embryonic exposure to ATRA results in impairment of protein surveillance in the cerebellum, which persists after birth and results in accumulation of oxidatively damaged complex I.

[Involvement of hydrogen peroxide in the regulation of coexpression of alternative oxidase and rotenone-insensitive NADH dehydrogenase in tomato leaves and calluses].

The involvement of active oxygen forms in the regulation of the expression of mitochondrial respiratory chain components, which are not related to energy storing, has been in vitro and in vivo studied in Lycopersicum esculentum L. The highest level of transcription of genes encoding alternative oxidase and NADH dehydrogenase has been observed in green tomato leaves. It has been shown that even low H2O2 concentrations activate both aoxlalpha and ndb1 genes, encoding alternative oxidase and external mitochondrial rotenone-insensitive NADH dehydrogenase, respectively. According to our results, in the case of an oxidative stress, alternative oxidase and NADH dehydrogenase are coexpressed in tomato plant tissues, and active oxygen forms serve as the secondary messengers of their coexpression.

Gamma oscillations in the hippocampus require high complex I gene expression and strong functional performance of mitochondria.

Fast neuronal network oscillations in the gamma range (~30-90 Hz) have been implicated in complex brain functions such as sensory processing, memory formation and, perhaps, consciousness, and appear to be exceptionally vulnerable to various pathologies. However, both energy demand and mitochondrial performance underlying gamma oscillations are unknown. We investigated the fundamental relationship between acetylcholine-induced gamma oscillations, mitochondrial gene expression and oxidative metabolism in hippocampal slice preparations of mouse and rat by applying electrophysiology, in situ hybridization, quantitative polymerase chain reaction, oxygen sensor microelectrode (interstitial partial oxygen pressure) and imaging of mitochondrial redox state [nicotinamide adenine dinucleotide (phosphate) and flavin adenine dinucleotide fluorescence]. We show that (i) gamma oscillation power, oxygen consumption and expression of complex I (nicotinamide adenine dinucleotide:ubiquinone oxidoreductase) subunits are higher in hippocampal subfield CA3 than in CA1 and dentate gyrus; (ii) the amount of oxygen consumption of gamma oscillations reaches that of seizure-like events; (iii) gamma oscillations are exquisitely sensitive to pharmacological complex I inhibition; and (iv) gamma oscillations utilize mitochondrial oxidative capacity near limit. These data suggest that gamma oscillations are especially energy demanding and require both high complex I expression and strong functional performance of mitochondria. Our study helps to explain the exceptional vulnerability of complex brain functions in ischaemia as well as in neurodegenerative and psychiatric disorders that are associated with mitochondrial dysfunction.

Acyl-CoA dehydrogenase 9 is required for the biogenesis of oxidative phosphorylation complex I.

Acyl-CoA dehydrogenase 9 (ACAD9) is a recently identified member of the acyl-CoA dehydrogenase family. It closely resembles very long-chain acyl-CoA dehydrogenase (VLCAD), involved in mitochondrial beta oxidation of long-chain fatty acids. Contrary to its previously proposed involvement in fatty acid oxidation, we describe a role for ACAD9 in oxidative phosphorylation. ACAD9 binds complex I assembly factors NDUFAF1 and Ecsit and is specifically required for the assembly of complex I. Furthermore, ACAD9 mutations result in complex I deficiency and not in disturbed long-chain fatty acid oxidation. This strongly contrasts with its evolutionary ancestor VLCAD, which we show is not required for complex I assembly and clearly plays a role in fatty acid oxidation. Our results demonstrate that two closely related metabolic enzymes have diverged at the root of the vertebrate lineage to function in two separate mitochondrial metabolic pathways and have clinical implications for the diagnosis of complex I deficiency.