No abstract

Uncoupling protein mediates electrophoretic transport of protons and anions across the inner membrane of brown adipose tissue mitochondria. The mechanism and site of proton transport, the mechanism by which fatty acids activate proton transport, and the relationship between fatty acids and anion transport are unknown. We used fluorescent probes to measure H (ii) Lauric acid was rapidly transported across the bilayer by nonionic diffusion, whereas undecanesulfonic was not. We infer that the role of uncoupling protein in H ؉ transport is to transport fatty acid anions and that fatty acids induce H ؉ transport because they can diffuse electroneutrally across the membrane. According to this hypothesis, uncoupling protein is a pure anion porter and does not transport protons; rather it is designed to enable fatty acids to behave as cycling protonophores.

Uncoupling protein 1 (UCP1) dissipates energy and generates heat by catalyzing back-flux of protons into the mitochondrial matrix, probably by a fatty acid cycling mechanism. If the newly discovered UCP2 and UCP3 function similarly, they will enhance peripheral energy expenditure and are potential molecular targets for the treatment of obesity. We expressed UCP2 and UCP3 in Escherichia coli and reconstituted the detergent-extracted proteins into liposomes. Ion flux studies show that purified UCP2 and UCP3 behave identically to UCP1. They catalyze electrophoretic flux of protons and alkylsulfonates, and proton flux exhibits an obligatory requirement for fatty acids. Proton flux is inhibited by purine nucleotides but with much lower affinity than observed with UCP1. These findings are consistent with the hypothesis that UCP2 and UCP3 behave as uncoupling proteins in the cell.Uncoupling protein 1 (UCP1) 1 of brown adipose tissue mitochondria occupies a special place in bioenergetics, because it is the exception that proves the rule of Mitchell's elegant chemiosmotic theory (1), a protein designed to short circuit the redox proton pumps in order to generate heat and dissipate energy. UCP1 was identified from functional studies on brown adipose tissue mitochondria (2) and was one of the first membrane proteins to be sequenced (3).For many years it was thought that UCP was expressed solely in mammalian brown adipose tissue; however, it now turns out that Nature has engineered at least five uncoupling proteins. In 1995, a plant uncoupling protein was discovered and later sequenced (4, 5), and 2 years later, UCP2 and UCP3 were identified (6 -9). UCP4 was recently described as a brainspecific UCP (10). UCP2 maps to regions of human chromosome 11 and mouse chromosome 7 that have been linked to hyperinsulinemia and obesity, and it is hypothesized that UCP2 is the peripheral target for energy dissipation in the regulation of body weight. UCP2 is ubiquitously expressed in mammalian tissues, whereas UCP3 is expressed primarily in glycolytic skeletal muscle in humans and may account for the thermogenic effect of thyroid hormone (11). These aspects of this rapidly emerging area of research have been nicely reviewed by Boss et al. (12).Virtually nothing is known about the transport functions of UCP2 and UCP3, and their putative physiological functions have been deduced primarily from their striking sequence identities with UCP1 (12). To address this problem, we expressed human UCP2 and UCP3 in Escherichia coli, where they accumulated in inclusion bodies. Following detergent extraction, we reconstituted the proteins into liposomes and measured H ϩ and K ϩ fluxes. Purified UCP2 and UCP3 both catalyzed electrophoretic flux of protons and alkylsulfonates, and proton flux exhibited an obligatory requirement for fatty acids. We also found that FA-dependent proton transport by UCP2 and UCP3 was inhibited by purine nucleotides, albeit with lower apparent affinities for nucleotides than those observed with UCP1. From these results, we co...

In PH, miR-124, through the alternative splicing factor PTBP1, regulates the PKM2/PKM1 ratio, the overall metabolic, proliferative, and inflammatory state of cells. This PH phenotype can be rescued with interventions at various levels of the metabolic cascade. These findings suggest a more integrated view of vascular cell metabolism, which may open unique therapeutic prospects in targeting the dynamic glycolytic and mitochondrial interactions and between mesenchymal inflammatory cells in PH.

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We hypothesize that fatty acid-induced uncoupling serves in bioenergetic systems to set the optimum efficiency and tune the degree of coupling of oxidative phosphorylation. Uncoupling results from fatty acid cycling, enabled by several phylogenetically specialized proteins and, to a lesser extent, by other mitochondrial carriers. It is suggested that the regulated uncoupling in mammalian mitochondria is provided by uncoupling proteins UCP-1, UCP-2 and UCP-3, whereas in plant mitochondria by PUMP and StUCP, all belonging to the gene family of mitochondrial carriers. UCP-1, and hypothetically UCP-3, serve mostly to provide nonshivering thermogenesis in brown adipose tissue and skeletal muscle, respectively. Fatty acid cycling was documented for UCP-1, PUMP and ADP/ATP carrier, and is predicted also for UCP-2 and UCP-3. UCP-1 mediates a purine nucleotide-sensitive uniport of monovalent unipolar anions, including anionic fatty acids. The return of protonated fatty acid leads to H+ uniport and uncoupling. UCP-2 is probably involved in the regulation of body weight and energy balance, in fever, and defense against generation of reactive oxygen species. PUMP has been discovered in potato tubers and immunologically detected in fruits and corn, whereas StUCP has been cloned and sequenced froma a potato gene library. PUMP is supposed to act in the termination of synthetic processes in mature fruits and during the climacteric respiratory rise.

We propose that the ETC is a suitable therapeutic target in Her2 disease. Antioxid. Redox Signal. 26, 84-103.

Aims: Pancreatic β-cell chronic lipotoxicity evolves from acute free fatty acid (FA)–mediated oxidative stress, unprotected by antioxidant mechanisms. Since mitochondrial uncoupling protein-2 (UCP2) plays antioxidant and insulin-regulating roles in pancreatic β-cells, we tested our hypothesis, that UCP2-mediated uncoupling attenuating mitochondrial superoxide production is initiated by FA release due to a direct H2O2-induced activation of mitochondrial phospholipase iPLA2γ. Results: Pro-oxidant tert-butylhydroperoxide increased respiration, decreased membrane potential and mitochondrial matrix superoxide release rates of control but not UCP2- or iPLA2γ-silenced INS-1E cells. iPLA2γ/UCP2-mediated uncoupling was alternatively activated by an H2O2 burst, resulting from palmitic acid (PA) β-oxidation, and it was prevented by antioxidants or catalase overexpression. Exclusively, nascent FAs that cleaved off phospholipids by iPLA2γ were capable of activating UCP2, indicating that the previously reported direct redox UCP2 activation is actually indirect. Glucose-stimulated insulin release was not affected by UCP2 or iPLA2γ silencing, unless pro-oxidant activation had taken place. PA augmented insulin secretion via G-protein–coupled receptor 40 (GPR40), stimulated by iPLA2γ-cleaved FAs (absent after GPR40 silencing). Innovation and Conclusion: The iPLA2γ/UCP2 synergy provides a feedback antioxidant mechanism preventing oxidative stress by physiological FA intake in pancreatic β-cells, regulating glucose-, FA-, and redox-stimulated insulin secretion. iPLA2γ is regulated by exogenous FA via β-oxidation causing H2O2 signaling, while FAs are cleaved off phospholipids, subsequently acting as amplifying messengers for GPR40. Hence, iPLA2γ acts in eminent physiological redox signaling, the impairment of which results in the lack of antilipotoxic defense and contributes to chronic lipotoxicity. Antioxid. Redox Signal. 23, 958–972.