Coupling factor 6 attenuates CXCR4 expression through the HIF-1α and c-Src pathways and promotes endothelial apoptosis and inflammation.

Vascular endothelial cells are exposed to an acidic pH, and CXC chemokine receptor type 4 (CXCR4) is a key protective molecule against acidosis. We investigated the effect of coupling factor 6 (CF6), a novel proton import activator, on CXCR4 signaling and its molecular mechanism. CF6 decreased CXCR4 expression in human umbilical vein endothelial cells (HUVECs) in a time- and dose-dependent manner. Pretreatment with small interfering RNA (siRNA) for hypoxia-inducible factor (HIF)-1α or PP1, a specific c-Src inhibitor, attenuated the CF6-induced decrease in CXCR4 without affecting CF6-induced intracellular acidosis. Chromatin immunoprecipitation revealed that CF6 enhanced the interaction between HIF-1α and the CXCR4 promoter at the hypoxia response element. CF6 also enhanced protein-protein interactions between phospho-c-Src and histone deacetylase 3 (HDAC3), but did not affect the binding of HDAC3 to the CXCR4 promoter at the hypoxia response element. Apoptotic cells, as measured by an Annexin-V-FITC Propidium Iodide Kit, were increased by CF6 in normoxia and hypoxia at 24 h; however, this increase was abolished by pretreatment with either siRNA for HIF-1α or the CXCR4 ligand. The coronary arteries and perivascular tissues obtained from CF6-overexpressing transgenic mice showed a lower expression of CXCR4 in the heart, increased wall thickness and infiltration of CD16-positive, CD206-positive or apoptotic cells. CF6 decreases CXCR4 expression through both HIF-1α- and c-Src-mediated mechanisms in vascular endothelial cells. Because CXCR4 has an important role in survival function, CF6 may have a role in the progression of arteriosclerosis via these complex mechanisms.

Coupling factor 6 enhances the spontaneous microaggregation of platelets by decreasing cytosolic cAMP irrespective of antiplatelet therapy.

The spontaneous microaggregation of platelets (SMAPs) is a marker for the prognosis of patients with cardiovascular diseases. Coupling factor 6 (CF6) binds to the plasma membrane ATP synthase and functions as a pro-atherogenic molecule in the cardiovascular system. However, the role of CF6 in SMAPs and stroke remains unknown. In 650 consecutive patients, including those with acute-onset stroke, and 20 control subjects, platelet-rich plasma (PRP) was obtained, and SMAP was measured using a laser light-scattering aggregometer. The cytosolic cyclic adenosine monophosphate (cAMP) concentration in platelets was measured using an enzyme-linked immunosorbent assay. CF6 increased SMAPs in patients and control subjects to a similar degree by binding to the α- and ß-subunits of ATP synthase and inducing intracellular acidosis. It was abolished by PRP pretreatment with antibodies against CF6, and the α- or ß-subunit of the plasma membrane ATP synthase, and the ATP synthase inhibitor efrapeptin. CF6 increased SMAPs in patient groups with and without antiplatelet therapy to a similar degree, and no difference was found among the subgroups taking aspirin, thienopyridine or cilostazol. The cytosolic cAMP concentration in platelets was decreased by CF6 in the presence of the direct adenylate cyclase activator forskolin. Pretreatment of PRP with the Gs activator cholera toxin blocked the decrease, whereas the Gi inactivator pertussis toxin and cilostazol had no influence. The CF6-induced acceleration of SMAPs was suppressed by cholera toxin but not by cilostazol or pertussis toxin. CF6 enhanced SMAPs by decreasing cytosolic cAMP. Because it was observed irrespective of antiplatelet agents, CF6 appears to be a novel target for antiplatelet therapy.

Upregulation of soluble vascular endothelial growth factor receptor type 1 by endogenous prostacyclin inhibitor coupling factor 6 in vascular endothelial cells: a role of acidosis-induced c-Src activation.

Vascular endothelial growth factor (VEGF) is a well-known promoter of angiogenesis, but its receptor VEGFR-1 and a soluble short form of VEGFR-1 (sFlt-1) play a negative role in the VEGF signal pathway by trapping VEGF. We recently showed that endogenous prostacyclin inhibitor coupling factor 6 (CF6) forces the clockwise rotation of F(1) motor of plasma membrane adenosine triphosphate synthase and induces intracellular acidosis and c-Src activation. We investigated the role of CF6 in regulation of sFlt-1, and its mechanism in human umbilical vein endothelial cells. The ratio of sFlt-1 to glyceraldehyde 3-phosphate dehydrogenase mRNA was increased at 24 h by 1.59+/-0.29-fold by 10(-7) M CF6 (P<0.05), concomitantly with the increases in intercellular adhesion molecule-1 and lectin-like oxidized low-density lipoprotein receptor-1 and no change in VEGF-A. When the dose of CF6 was increased to 10(-6) M, no further increase in sFlt-1 mRNA was observed. The release of sFlt-1 protein was increased by 1.72+/-0.24-fold (P<0.05) at 48 h after exposure to CF6 at 10(-7) M, and it was blocked by pretreatment with anti-CF6 antibody. The immunoreactive bands for sFlt-1 and VEGFR-1 were both increased by CF6 to similar degrees. Pretreatment with PP1, an inhibitor of c-Src, and 10(-5) Mefrapeptin, an inhibitor of F(1) motor, inhibited CF6-induced increases in expression and release of sFlt-1 (P<0.05). In mice overexpressing CF6, the plasma level of sFlt-1 was increased by 1.36+/-0.29-fold compared with that in wild-type mice (P<0.05). These indicate that CF6 might increase the expression and release of sFlt-1 in the vessels through acidosis-induced c-Src activation.

Long-term hypothermia reduces infarct volume in aged rats after focal ischemia.

UNLABELLED: In aged humans, stroke is a major cause of disability for which no neuroprotective measures are available. A viable alternative to conventional drug-based neuroprotective therapies is brain/body cooling, or hypothermia. In animal studies of focal ischemia, short-term hypothermia consistently reduces infarct size. Nevertheless, efficient neuroprotection requires long-term, regulated lowering of whole body temperature. Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 17-month-old male Sprague-Dawley rats. After stroke, the aged rats were exposed for 2 days to a mixture of air and a mild inhibitor of oxidative phosphorylation, hydrogen sulfide (H(2)S), which resulted in sustained, deep hypothermia (30.8+/-0.7 degrees C). Long-term hypothermia led to a 50% reduction in infarct size with a concomitant reduction in the number of phagocytic cells. At the transcription level, hypothermia caused a reduction in the mRNA coding for caspase 12, NF-kappa B and grp78 in the peri-infarcted region, suggesting an overall decrease in the transcriptional activity related to inflammation and apoptosis. Behaviorally, hypothermia was associated with better performance on tests that require complex sensorimotor skills, in the absence of obvious neurological deficits or physiological side effects, in aged rats. CONCLUSIONS: Prolonged, H(2)S-induced hypothermia is a simple and efficacious method to limit the damage inflicted by stroke in aged rats.

Effect of vasoconstrictor coupling factor 6 on gene expression profile in human vascular endothelial cells: enhanced release of asymmetric dimethylarginine.

BACKGROUND: Coupling factor 6 (CF6), a component of ATP synthase, inhibits phospholipase A2 and induces vasoconstriction. However, because arachidonic acid acts in the widespread fields of vascular biology, CF6 might exert profound effects in addition to vasoconstriction. We investigated the effect of CF6 on the gene expression profile in human umbilical vein endothelial cells. METHODS AND RESULTS: The increased gene expression after 24-h exposure to CF6 at 10 mol/l, assessed by cDNA microarray (n = 3), included neuregulin-1 (1.84 +/- 0.07 fold compared with control, P < 0.05) and relaxin-1 (1.74 +/- 0.20, P < 0.05), both relating to congestive heart failure, urokinase type plasminogen activator receptor (1.77 +/- 0.24, P = 0.06) and estrogen receptor beta (1.74 +/- 0.36, P = 0.08), both relating to vascular inflammation and cell infiltration, and protein arginine methyltransferase (PRMT-1; 1.73 +/- 0.20, P < 0.05). Out of these genes, the enzyme relating to the synthesis (PRMT-1) of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), was further examined concomitantly with the degradation enzyme, dimethylarginine dimethylaminohydrolase 2 (DDAH-2). The ratio of PRMT-1 to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA, measured by real-time quantitative reverse transcription-polymerase chain reaction, was increased by 9 +/- 2% (n = 10, P < 0.01) at 48 h after CF6 at 10 mol/l, whereas the ratio of DDAH-2 to GAPDH was decreased by 12 +/- 2% (n = 8, P < 0.01). DDAH-2 protein and activity were decreased by 28 +/- 5% (n = 5, P < 0.01) and 19 +/- 2% (n = 6, P < 0.01) by CF6, respectively. ADMA release was enhanced by 20 +/- 8% and NOS activity was decreased by 13 +/- 1% (both n = 8, P < 0.05) by CF6. CONCLUSIONS: CF6 changes the gene expression profile to be proatherogenic and functions as a novel stimulator for ADMA release by enhancing its synthesis and suppressing its degradation.

Intracellular signaling for vasoconstrictor coupling factor 6: novel function of beta-subunit of ATP synthase as receptor.

Coupling factor 6 (CF6), a component of adenosine triphosphate (ATP) synthase, is circulating and functions as an endogenous vasoconstrictor by inhibiting cytosolic phospholipase A2. We showed a high plasma level of CF6 in human hypertension. The present study focused on the identification and characterization of a receptor for CF6 and its post-receptor signaling pathway. Incubation of human umbilical vein endothelial cells (HUVECs) with an excess of free CF6 reduced by 50% the immunoreactivity for the antibody to beta-subunit of ATP synthase at the cell surface, but unaffected that for the alpha-subunit antibody. A significant displacement of radioligand was observed at 3x10(-9) through 10(-7) M unlabeled CF6, and the Kd was 7.6 nM. Adenosine diphosphate (ADP) at 10(-7) M and beta-subunit antibody suppressed the binding of (125)I-CF6 by 81.3+/-9.7% and 32.0+/-2.0%, respectively, whereas the alpha-subunit antibody unaffected it. The hydrolysis activity of ATP to ADP was increased by 1.6-fold by CF6 at 10(-7) M, and efrapeptin at 10(-5) M, an inhibitor of ATP synthase, blocked it. CF6 at 10(-7) M decreased intracellular pH in 2',7'-bis(carboxyethyl-5 (6))-carboxyfluorescein-loaded HUVEC. Amyloride at 10(-4) M augmented the pH decrease in response to CF6, whereas efrapeptin at 10(-5) M blocked it. Arachidonic acid release was suppressed by CF6, and it was reversed by efrapeptin at 10(-5) M or beta-subunit antibody or ADP at 10(-7) M. The beta-subunit antibody suppressed coupling factor 6-induced increase in blood pressure. These indicate that membrane-bound ATP synthase functions as a receptor for CF6 and may have a previously unsuspected role in the genesis of hypertension by modulating the concentration of intracellular hydrogen.

Total synthesis of human and rat coupling factor-6 amide and pressor effects in the rat.

Mitochondrial coupling factor-6 (CF-6) is a component of the ATP synthase complex essential for energy transduction. CF-6, which is localized to the surface of endothelial cells (ECs) and released by shear stress, has been implicated as an endogenous vasoconstrictor. Previous methods of obtaining CF-6 through purification and recombinant methods were laborious and inefficient. Here, we describe the chemical synthesis of human CF-6, (33-108)-NH(2), its C-terminal fragment (55-108)-NH(2), which is termed pCF-6; the rat CF-6, (33-108)-NH(2), its C-terminal fragment pCF-6, (55-108)-NH(2); and two N-terminal fragments of the rat pro-coupling factor-6, (24-52)-NH(2) and (33-52)-NH(2). Biological activities of each peptide were initially screened with bioassays and verified by in vivo studies. Accordingly, intravenous administration of CF-6, pCF-6, rat CF-6, and rat pCF-6 produced a modest but statistically significant increase in blood pressure and heart rate in urethane anesthetized rats, whereas the N-terminal rat pro-coupling factor-6, (24-52)-NH(2) and (33-52)-NH(2) caused no significant pressor response. Thus, the biologically active site probably resides at the C-terminal portion of CF-6 peptides.

Papel de las proteínas desacoplantes en la obesidad / Role of uncoupling proteins in obesity

El descubrimiento de una proteína de la membrana mitocondrial interna de adipocitos marrones, la UCP1, supuso un importante avance en el conocimiento del proceso termogénico, así como del funcionamiento del tejido adiposo marrón. Esta proteína es sólo importante en neonatos y animales pequeños, no obstante el posterior hallazgo de proteínas análogas a la UCP1 (UCP2, ampliamente distribuida, y UCP3, presente principalmente en músculo) con un funcionamiento similar y presentes también en tejido humano, creó nuevas perspectivas y objetivos científicos. Estas proteínas desacoplan la cadena respiratoria de la fosforilación oxidativa, disipando así energía en forma de calor sin que se produzca ATP, mediante un mecanismo aún debatido. De los estudios de regulación realizados trasciende que su actividad se ve modificada ante distintos estímulos fisiológicos y nutricionales, observándose una mayor actividad de las mismas en situaciones en las que se requiere un aumento del gasto energético. Los estudios realizados en humanos parecen corroborar los resultados obtenidos en la experimentación con animales, por lo que podría plantearse la actuación sobre la actividad o la cantidad de estas proteínas en humanos como medio para combatir el sobrepeso y la obesidad. Sin embargo, existe aún una evidente necesidad de completar y mejorar la información existente acerca de la importancia de estas proteínas transportadoras de protones en humanos. (AU)

Mitochondrial coupling factor 6 as a potent endogenous vasoconstrictor.

We demonstrated recently that coupling factor 6, an essential component of the energy-transducing stalk of mitochondrial ATP synthase, suppresses the synthesis of prostacyclin in vascular endothelial cells. Here, we tested the hypothesis that coupling factor 6 is present on the cell surface and is involved in the regulation of systemic circulation. This peptide is present on the surface of CRL-2222 vascular endothelial cells and is released by these cells into the medium. In vivo, the peptide circulates in the vascular system of the rat, and its gene expression and plasma concentration are higher in spontaneously hypertensive rats (SHRs) than in normotensive controls. Elevation of blood pressure with norepinephrine did not affect the plasma concentration of coupling factor 6. Intravenous injection of recombinant peptide increased blood pressure, apparently by suppressing prostacyclin synthesis, whereas a specific Ab to coupling factor 6 decreased systemic blood pressure concomitantly with an increase in plasma prostacyclin. Interestingly, the antibody's hypotensive effect could be abolished by treating with the cyclooxygenase inhibitor indomethacin. These findings indicate that mitochondrial coupling factor 6 functions as a potent endogenous vasoconstrictor in the fashion of a circulating hormone and may suggest a new mechanism for hypertension.

Uncoupling of intestinal mitochondrial oxidative phosphorylation and inhibition of cyclooxygenase are required for the development of NSAID-enteropathy in the rat.

BACKGROUND: The pathogenesis of NSAID-induced gastrointestinal damage is believed to involve a nonprostaglandin dependent effect as well as prostaglandin dependent effects. One suggestion is that the nonprostaglandin mechanism involves uncoupling of mitochondrial oxidative phosphorylation. AIMS: To assess the role of uncoupling of mitochondrial oxidative phosphorylation in the pathogenesis of small intestinal damage in the rat. METHODS: We compared key pathophysiologic events in the small bowel following (i) dinitrophenol, an uncoupling agent (ii) parenteral aspirin, to inhibit cyclooxygenase without causing a 'topical' effect and (iii) the two together, using (iv) indomethacin as a positive control. RESULTS: Dinitrophenol altered intestinal mitochondrial morphology, increased intestinal permeability and caused inflammation without affecting gastric permeability or intestinal prostanoid levels. Parenteral aspirin decreased mucosal prostanoids without affecting intestinal mitochondria in vivo, gastric or intestinal permeability. Aspirin caused no inflammation or ulcers. When dinitrophenol and aspirin were given together the changes in intestinal mitochondrial morphology, permeability, inflammation and prostanoid levels and the macro- and microscopic appearances of intestinal ulcers were similar to indomethacin. CONCLUSIONS: These studies allow dissociation of the contribution and consequences of uncoupling of mitochondrial oxidative phosphorylation and cyclooxygenase inhibition in the pathophysiology of NSAID enteropathy. While uncoupling of enterocyte mitochondrial oxidative phosphorylation leads to increased intestinal permeability and low grade inflammation, concurrent decreases in mucosal prostanoids appear to be important in the development of ulcers.

A novel inhibitory effect on prostacyclin synthesis of coupling factor 6 extracted from the heart of spontaneously hypertensive rats.

The possible presence of an unknown prostacyclin synthesis inhibitory substance has been reported in some strains of rats. We purified the inhibitory substance from the heart of spontaneously hypertensive rats by collecting active fractions after gel-filtration column chromatography and two steps of reverse-phase high performance liquid chromatography. The amino acid composition and automated gas-phase sequencing of the full-length substance and fragments cleaved by AspN indicated that the prostacyclin-inhibitory peptide was identical to coupling factor 6. Recombinant rat coupling factor 6, which was synthesized using a cleavable fusion protein strategy, attenuated base-line and bradykinin (10(-6) M)-induced prostacyclin synthesis and [3H]arachidonic acid (AA) release in human umbilical vein endothelial cells in a dose-dependent manner (10(-9)-10(-7) M). Exogenous AA- and prostaglandin H2-induced prostacyclin synthesis were unchanged even after treatment with 10(-7) M recombinant coupling factor 6. Base-line and bradykinin-induced [3H]AA release were suppressed by arachidonyltrifluoromethyl ketone, a relatively specific inhibitor of cytosolic phospholipase A2 at 40 microM, and simultaneous administration of coupling factor 6 showed no further effect. Neither oleyloxyethyl phosphorylcholine at 1 microM nor bromoenol lactone at 1 microM affected AA release. Preincubation (1 min) with 10(-7) M recombinant coupling factor 6 had no influence on adenosine diphosphate- and collagen-induced platelet aggregations. We conclude that coupling factor 6 possesses a novel function of prostacyclin synthesis inhibition in endothelial cells via suppression of Ca2+-dependent cytosolic phospholipase A2, although it is unclear whether coupling factor 6 functions in normal conditions or only in pathophysiological states.

Uncoupling of oxidative phosphorylation does not induce thermotolerance in cultured Chinese hamster cells.

Two uncouplers of oxidative phosphorylation, 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP), were tested for their ability to modify the survival of cultured Chinese hamster ovary (CHO) and Chinese hamster V79 cells treated with hyperthermia. The uncouplers were used under conditions that inhibit oxidative ATP synthesis, as judged from measurements of cellular ATP levels. Incubation of CHO cells in glucose-free Hanks' balanced salt solution (HBSS) containing 1 mM DNP for 1 h at 37 degrees C followed by reincubation at 37 degrees C in complete growth medium for 3 or 16 h, showed no substantial changes in the 45 degrees C heat survival curve as compared to heated cells not exposed to DNP. Thus, DNP treatment of CHO cells did not induce thermotolerance. Carbonyl cyanide m-chlorophenylhydrazone (CCCP), tested under similar experimental conditions, did alter cellular heat resistance. The major change in the 45 degrees C survival curve of CHO cells pretreated with CCCP was an increase in the width of the shoulder: the Dq value increased from 14 min to 24 min, for the control and CCCP-treated cells respectively. The D0 value did not change appreciably. In contrast, heat-induced thermotolerance (10 min, 45 degrees C + 16 h, 37 degrees C) was characterized primarily by an increase in the D0 parameter from 4 min (unheated cells) to 17 min. Similar results were observed with CCCP-treated V79 cells. The data demonstrate that heat resistance induced by 1.2 microM CCCP was manifest as an increased cellular capacity to accumulate and/or repair hyperthermia damage, rather than an induction of thermotolerance, and that this effect probably was not related to the action of CCCP as an uncoupler of oxidative phosphorylation.

[Redox regulation in ATP synthesis]. / Okislitel'no-vosstanovitel'naia reguliatsiia v sinteze ATF.

Evidence is considered which points to changes of redox potential of the redox-centres in mitochondria during energization, to high sensitivity of ATP-synthetase to redox agents. Examples of ATP-syntheses in model systems stimulated with an electron are discussed. This stimulation is so efficient that it permits weakening of the bond between phosphorus atom and extremely bad leaving group O- in inorganic phosphate-phosphorylating agent in ATP synthesis during oxidative phosphorylation. The sum of these data suggests that function of the redox-centres found in the coupling site may be the accumulation of the intermediate inducing ADP and Phinorg interactions. The electron pool may serve as an intermediate. Thus the redoxcentre function in the coupling site accepting and accumulating the electrons during energization may be compared with chlorophyll function in photosynthesis. Change of redox potential of redox-centres at energization (by protonation, for example) initiates electron transfer in ATP-synthetase, which by the formation of highly reactive-free radical of ADP provides the occurrence of endergonic reaction of ATP synthesis, i.e. storage of energy as a chemical bond.

Indirect immunofluorescence studies on the steroid-producing activity of hamster ova.

Steroidogenesis in the unfertilized hamster ova was investigated by indirect immunofluorescence study. delta 5-3 beta-Hydroxysteroid dehydrogenase (delta 5-3 beta-HSD) activity was found in hamster follicular and ovulatory ova with pregnenolone used as the substrate. A significant quantity of 17 beta-estradiol was detected in the ooplasm of follicular and ovulatory ova. No progesterone was found. The activity of delta 5-3 beta-HSD in follicular and ovulatory ova was inhibited by preincubation with 10 IU of human chorionic gonadotropin (hCG) in 1 ml of phosphate buffer solution. Trilostane, a potent new inhibitor of the delta 5-3 beta-HSD system, was found to inhibit the activity of delta 5-3 beta-HSD in ovulatory ova in 1 ml of phosphate buffer solution at a concentration of 10(-7)M. After these results were obtained, steroidogenesis of hamster ova was suggested in an indirect immunofluorescence study, and the implications of steroidogenesis for oocyte maturation and subsequent fertilization are discussed.

Uncoupler-reversible inhibition of mitochondrial ATPase by metal chelates of bathophenanthroline. I. General features.

(1) Certain metal chelates of 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline, BPh) are potent inhibitors of soluble mitochondrial F1-ATPase. (2) The BPh-metal chelate inhibition of soluble mitochondrial F1-ATPase is relieved by uncouplers of oxidative phosphorylation. (3) The uncouplers appear to interact directly with the inhibitory chelates, forming stoichiometric adducts. (4) A complex between F1 and bPh3Fe2+, containing 3 mol BPh3Fe2+/mol F1, has been isolated. The enzymically inactive F1-BPh3Fe2+ complex binds uncouplers, yielding an enzymically active F1-BPh3Fe2+-uncoupler complex.

Inhibition of E coli ATPase activity by a troponin component, TN-I, and by mitochondrial ATPase inhibitor.

The enzymic activity of Mg2+- or Ca2+-stimulated ATPase from Escherichia coli was inhibited by one of the troponin components, TN-I, and by mitochondrial ATPase inhibitor (F1-inhibitor). The inhibitory ability of component TN-I against Mg2+-stimulated AtPase activity was lost after digestion of component TN-I with trypsin. The Mg2+-stimulated ATPase activity inhibited by component TN-I was completely restored by the addition of another troponin component TN-C.

Energization of mitochondrial inner membranes caused by L-malate.

It was found that 0.06 mug antimycin A/mg mitochondrial protein, an amount sufficient to inhibit electron transfer between cytochromes b and c1 completely, fully reversed the oxidation of cytochrome a caused by L-malate in anaerobic mitochondria. The effect of L-malate on cytochrome a was insensitive to oligomycin, but all the uncouplers and detergents tested reversed the oxidation of cytochrome a caused by L-malate in anaerobic mitochondria. It was also found that addition of L-malate to anaerobic mitochondria, like addition of ATP, decreased the fluorescence of 1-anilinonaphthalene-8-sulphonate, and that subsequent addition of uncouplers reversed this effect. The effect of L-malate on the fluorescence of the dye was insensitive to oligomycin. The present findings suggest that addition of L-malate may cause energization of the mitochondrial inner membranes and that the oxidation of cytochrome a caused by L-malate in anaerobic mitochondria may result from an L-malate-induced, energy-linked reversal of electron transfer in site II.