Nejvíce citovaný článek - PubMed ID 25925080
H₂O₂-Activated Mitochondrial Phospholipase iPLA₂γ Prevents Lipotoxic Oxidative Stress in Synergy with UCP2, Amplifies Signaling via G-Protein-Coupled Receptor GPR40, and Regulates Insulin Secretion in Pancreatic β-Cells
We asked whether acute redox signaling from mitochondria exists concomitantly to fatty acid- (FA-) stimulated insulin secretion (FASIS) at low glucose by pancreatic β-cells. We show that FA β-oxidation produces superoxide/H2O2, providing: i) mitochondria-to-plasma-membrane redox signaling, closing KATP-channels synergically with elevated ATP (substituting NADPH-oxidase-4-mediated H2O2-signaling upon glucose-stimulated insulin secretion); ii) activation of redox-sensitive phospholipase iPLA2γ/PNPLA8, cleaving mitochondrial FAs, enabling metabotropic GPR40 receptors to amplify insulin secretion (IS). At fasting glucose, palmitic acid stimulated IS in wt mice; palmitic, stearic, lauric, oleic, linoleic, and hexanoic acids also in perifused pancreatic islets (PIs), with suppressed 1st phases in iPLA2γ/PNPLA8-knockout mice/PIs. Extracellular/cytosolic H2O2-monitoring indicated knockout-independent redox signals, blocked by mitochondrial antioxidant SkQ1, etomoxir, CPT1 silencing, and catalase overexpression, all inhibiting FASIS, keeping ATP-sensitive K+-channels open, and diminishing cytosolic [Ca2+]-oscillations. FASIS in mice was a postprandially delayed physiological event. Redox signals of FA β-oxidation are thus documented, reaching the plasma membrane, essentially co-stimulating IS.
- Klíčová slova
- Fatty acid-stimulated insulin secretion, GPR40, Mitochondrial fatty acids, Pancreatic β-cells, Redox signaling, Redox-activated phospholipase iPLA2γ,
- MeSH
- beta-buňky * metabolismus MeSH
- buněčná membrána * metabolismus MeSH
- fosfolipasy A2, skupina VI metabolismus genetika MeSH
- glukosa metabolismus MeSH
- inzulin metabolismus MeSH
- mastné kyseliny * metabolismus MeSH
- mitochondrie * metabolismus MeSH
- myši knockoutované MeSH
- myši MeSH
- oxidace-redukce * MeSH
- peroxid vodíku metabolismus MeSH
- receptory spřažené s G-proteiny MeSH
- sekrece inzulinu * MeSH
- signální transdukce * MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- Ffar1 protein, mouse MeSH Prohlížeč
- fosfolipasy A2, skupina VI MeSH
- glukosa MeSH
- inzulin MeSH
- mastné kyseliny * MeSH
- peroxid vodíku MeSH
- Pla2g6 protein, mouse MeSH Prohlížeč
- receptory spřažené s G-proteiny MeSH
Mitochondria (mt) represent the vital hub of the molecular physiology of the cell, being decision-makers in cell life/death and information signaling, including major redox regulations and redox signaling. Now we review recent advances in understanding mitochondrial redox homeostasis, including superoxide sources and H2O2 consumers, i.e., antioxidant mechanisms, as well as exemplar situations of physiological redox signaling, including the intramitochondrial one and mt-to-cytosol redox signals, which may be classified as acute and long-term signals. This review exemplifies the acute redox signals in hypoxic cell adaptation and upon insulin secretion in pancreatic beta-cells. We also show how metabolic changes under these circumstances are linked to mitochondrial cristae narrowing at higher intensity of ATP synthesis. Also, we will discuss major redox buffers, namely the peroxiredoxin system, which may also promote redox signaling. We will point out that pathological thresholds exist, specific for each cell type, above which the superoxide sources exceed regular antioxidant capacity and the concomitant harmful processes of oxidative stress subsequently initiate etiology of numerous diseases. The redox signaling may be impaired when sunk in such excessive pro-oxidative state.
- MeSH
- antioxidancia metabolismus MeSH
- beta-buňky metabolismus MeSH
- lidé MeSH
- mitochondrie * metabolismus MeSH
- oxidace-redukce * MeSH
- oxidační stres fyziologie MeSH
- signální transdukce fyziologie MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Názvy látek
- antioxidancia MeSH
Significance: Mitochondrial (mt) reticulum network in the cell possesses amazing ultramorphology of parallel lamellar cristae, formed by the invaginated inner mitochondrial membrane. Its non-invaginated part, the inner boundary membrane (IBM) forms a cylindrical sandwich with the outer mitochondrial membrane (OMM). Crista membranes (CMs) meet IBM at crista junctions (CJs) of mt cristae organizing system (MICOS) complexes connected to OMM sorting and assembly machinery (SAM). Cristae dimensions, shape, and CJs have characteristic patterns for different metabolic regimes, physiological and pathological situations. Recent Advances: Cristae-shaping proteins were characterized, namely rows of ATP-synthase dimers forming the crista lamella edges, MICOS subunits, optic atrophy 1 (OPA1) isoforms and mitochondrial genome maintenance 1 (MGM1) filaments, prohibitins, and others. Detailed cristae ultramorphology changes were imaged by focused-ion beam/scanning electron microscopy. Dynamics of crista lamellae and mobile CJs were demonstrated by nanoscopy in living cells. With tBID-induced apoptosis a single entirely fused cristae reticulum was observed in a mitochondrial spheroid. Critical Issues: The mobility and composition of MICOS, OPA1, and ATP-synthase dimeric rows regulated by post-translational modifications might be exclusively responsible for cristae morphology changes, but ion fluxes across CM and resulting osmotic forces might be also involved. Inevitably, cristae ultramorphology should reflect also mitochondrial redox homeostasis, but details are unknown. Disordered cristae typically reflect higher superoxide formation. Future Directions: To link redox homeostasis to cristae ultramorphology and define markers, recent progress will help in uncovering mechanisms involved in proton-coupled electron transfer via the respiratory chain and in regulation of cristae architecture, leading to structural determination of superoxide formation sites and cristae ultramorphology changes in diseases. Antioxid. Redox Signal. 39, 635-683.
- Klíčová slova
- ATP-synthase dimeric rows, MICOS, OPA1, mitochondrial cristae, mitochondrial superoxide formation, respiratory chain supercomplexes,
- MeSH
- adenosintrifosfát metabolismus MeSH
- homeostáza MeSH
- mitochondriální membrány * metabolismus MeSH
- mitochondriální proteiny metabolismus MeSH
- oxidace-redukce MeSH
- superoxidy * metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
- Názvy látek
- adenosintrifosfát MeSH
- mitochondriální proteiny MeSH
- superoxidy * MeSH
Redox signaling from mitochondria (mt) to the cytosol and plasma membrane (PM) has been scarcely reported, such as in the case of hypoxic cell adaptation or (2-oxo-) 2-keto-isocaproate (KIC) β-like-oxidation stimulating insulin secretion in pancreatic β-cells. Mutual redox state influence between mitochondrial major compartments, the matrix and the intracristal space, and the cytosol is therefore derived theoretically in this article to predict possible conditions, when mt-to-cytosol and mt-to-PM signals may occur, as well as conditions in which the cytosolic redox signaling is not overwhelmed by the mitochondrial antioxidant capacity. Possible peroxiredoxin 3 participation in mt-to-cytosol redox signaling is discussed, as well as another specific case, whereby mitochondrial superoxide release is diminished, whereas the matrix MnSOD is activated. As a result, the enhanced conversion to H2O2 allows H2O2 diffusion into the cytosol, where it could be a predominant component of the H2O2 release. In both of these ways, mt-to-cytosol and mt-to-PM signals may be realized. Finally, the use of redox-sensitive probes is discussed, which disturb redox equilibria, and hence add a surplus redox-buffering to the compartment, where they are localized. Specifically, when attempts to quantify net H2O2 fluxes are to be made, this should be taken into account.
Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca2+ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca2+ influx was found to enhance GSIS, reflecting cytosolic Ca2+ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca2+ and K+ channels) or the superimposed Ca2+ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca2+ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.
- Klíčová slova
- ATP-sensitive K+ channel, GLP-1, TRPM channels, branched-chain ketoacid oxidation, fatty acid-stimulated insulin secretion, insulin secretion, mitochondrial Ca2+ transport, pancreatic β-cell metabolism, redox signaling,
- MeSH
- adenosintrifosfát metabolismus MeSH
- beta-buňky * metabolismus MeSH
- glukosa metabolismus MeSH
- inzulin metabolismus MeSH
- Langerhansovy ostrůvky * metabolismus MeSH
- mitochondrie metabolismus MeSH
- NAD metabolismus MeSH
- NADP metabolismus MeSH
- sekrece inzulinu MeSH
- sekretagoga metabolismus MeSH
- vápník metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
- Názvy látek
- adenosintrifosfát MeSH
- glukosa MeSH
- inzulin MeSH
- NAD MeSH
- NADP MeSH
- sekretagoga MeSH
- vápník MeSH
Mitochondrial Ca2+-independent phospholipase A2γ (iPLA2γ/PNPLA8) was previously shown to be directly activated by H2O2 and release free fatty acids (FAs) for FA-dependent H+ transport mediated by the adenine nucleotide translocase (ANT) or uncoupling protein 2 (UCP2). The resulting mild mitochondrial uncoupling and consequent partial attenuation of mitochondrial superoxide production lead to an antioxidant effect. However, the antioxidant role of iPLA2γ in the brain is not completely understood. Here, using wild-type and iPLA2γ-KO mice, we demonstrate the ability of tert-butylhydroperoxide (TBHP) to activate iPLA2γ in isolated brain mitochondria, with consequent liberation of FAs and lysophospholipids. The liberated FA caused an increase in respiratory rate, which was fully inhibited by carboxyatractyloside (CATR), a specific inhibitor of ANT. Employing detailed lipidomic analysis, we also demonstrate a typical cleavage pattern for TBHP-activated iPLA2γ, reflecting cleavage of glycerophospholipids from both sn-1 and sn-2 positions releasing saturated FAs, monoenoic FAs, and predominant polyunsaturated FAs. The acute antioxidant role of iPLA2γ-released FAs is supported by monitoring both intramitochondrial superoxide and extramitochondrial H2O2 release. We also show that iPLA2γ-KO mice were more sensitive to stimulation by pro-inflammatory lipopolysaccharide, as reflected by the concomitant increase in protein carbonyls in the brain and pro-inflammatory IL-6 release in the serum. These data support the antioxidant and anti-inflammatory role of iPLA2γ in vivo. Our data also reveal a substantial decrease of several high molecular weight cardiolipin (CL) species and accumulation of low molecular weight CL species in brain mitochondria of iPLA2γ-KO mice. Collectively, our results support a key role of iPLA2γ in the remodeling of lower molecular weight immature cardiolipins with predominantly saturated acyl chains to high molecular weight mature cardiolipins with highly unsaturated PUFA acyl chains, typical for the brain.
- Klíčová slova
- adenine nucleotide translocase, cardiolipin remodeling, mitochondria, phospholipase iPLA2γ/PNPLA8, redox homeostasis,
- Publikační typ
- časopisecké články MeSH
Patatin-like phospholipase domain-containing protein PNPLA8, also termed Ca2+-independent phospholipase A2γ (iPLA2γ), is addressed to the mitochondrial matrix (or peroxisomes), where it may manifest its unique activity to cleave phospholipid side-chains from both sn-1 and sn-2 positions, consequently releasing either saturated or unsaturated fatty acids (FAs), including oxidized FAs. Moreover, iPLA2γ is directly stimulated by H2O2 and, hence, is activated by redox signaling or oxidative stress. This redox activation permits the antioxidant synergy with mitochondrial uncoupling proteins (UCPs) or other SLC25 mitochondrial carrier family members by FA-mediated protonophoretic activity, termed mild uncoupling, that leads to diminishing of mitochondrial superoxide formation. This mechanism allows for the maintenance of the steady-state redox status of the cell. Besides the antioxidant role, we review the relations of iPLA2γ to lipid peroxidation since iPLA2γ is alternatively activated by cardiolipin hydroperoxides and hypothetically by structural alterations of lipid bilayer due to lipid peroxidation. Other iPLA2γ roles include the remodeling of mitochondrial (or peroxisomal) membranes and the generation of specific lipid second messengers. Thus, for example, during FA β-oxidation in pancreatic β-cells, H2O2-activated iPLA2γ supplies the GPR40 metabotropic FA receptor to amplify FA-stimulated insulin secretion. Cytoprotective roles of iPLA2γ in the heart and brain are also discussed.
Redox status is a key determinant in the fate of β-cell. These cells are not primarily detoxifying and thus do not possess extensive antioxidant defense machinery. However, they show a wide range of redox regulating proteins, such as peroxiredoxins, thioredoxins or thioredoxin reductases, etc., being functionally compartmentalized within the cells. They keep fragile redox homeostasis and serve as messengers and amplifiers of redox signaling. β-cells require proper redox signaling already in cell ontogenesis during the development of mature β-cells from their progenitors. We bring details about redox-regulated signaling pathways and transcription factors being essential for proper differentiation and maturation of functional β-cells and their proliferation and insulin expression/maturation. We briefly highlight the targets of redox signaling in the insulin secretory pathway and focus more on possible targets of extracellular redox signaling through secreted thioredoxin1 and thioredoxin reductase1. Tuned redox homeostasis can switch upon chronic pathological insults towards the dysfunction of β-cells and to glucose intolerance. These are characteristics of type 2 diabetes, which is often linked to chronic nutritional overload being nowadays a pandemic feature of lifestyle. Overcharged β-cell metabolism causes pressure on proteostasis in the endoplasmic reticulum, mainly due to increased demand on insulin synthesis, which establishes unfolded protein response and insulin misfolding along with excessive hydrogen peroxide production. This together with redox dysbalance in cytoplasm and mitochondria due to enhanced nutritional pressure impact β-cell redox homeostasis and establish prooxidative metabolism. This can further affect β-cell communication in pancreatic islets through gap junctions. In parallel, peripheral tissues losing insulin sensitivity and overall impairment of glucose tolerance and gut microbiota establish local proinflammatory signaling and later systemic metainflammation, i.e., low chronic inflammation prooxidative properties, which target β-cells leading to their dedifferentiation, dysfunction and eventually cell death.
- Klíčová slova
- de/differentiation, inflammation, oxidative stress, pancreatic β-cells, redox homeostasis, redox signaling,
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H2O2 production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K+ channel (KATP) can only be closed when both ATP and H2O2 are elevated. Otherwise ATP would block KATP, while H2O2 would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed KATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca2+ channels. Open synergic NSCCs or Cl- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca2+-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca2+-influx (fortified by endoplasmic reticulum Ca2+). ATP plus H2O2 are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H2O2 diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.
Aims: Glucose-stimulated insulin secretion (GSIS) in pancreatic β cells was expected to enhance mitochondrial superoxide formation. Hence, we elucidated relevant redox equilibria. Results: Unexpectedly, INS-1E cells at transitions from 3 (11 mM; pancreatic islets from 5 mM) to 25 mM glucose decreased matrix superoxide release rates (MitoSOX Red monitoring validated by MitoB) and H2O2 (mitoHyPer, subtracting mitoSypHer emission). Novel double-channel fluorescence lifetime imaging, approximating free mitochondrial matrix NADHF, indicated its ∼20% decrease. Matrix NAD+F increased on GSIS, indicated by the FAD-emission lifetime decrease, reflecting higher quenching of FAD by NAD+F. The participation of pyruvate/malate and pyruvate/citrate redox shuttles, elevating cytosolic NADPHF (iNAP1 fluorescence monitoring) at the expense of matrix NADHF, was indicated, using citrate (2-oxoglutarate) carrier inhibitors and cytosolic malic enzyme silencing: All changes vanished on these manipulations. 13C-incorporation from 13C-L-glutamine into 13C-citrate reflected the pyruvate/isocitrate shuttle. Matrix NADPHF (iNAP3 monitored) decreased. With decreasing glucose, the suppressor of Complex III site Q electron leak (S3QEL) suppressor caused a higher Complex I IF site contribution, but a lower superoxide fraction ascribed to the Complex III site IIIQo. Thus, the diminished matrix NADHF/NAD+F decreased Complex I flavin site IF superoxide formation on GSIS. Innovation: Mutually validated methods showed decreasing superoxide release into the mitochondrial matrix in pancreatic β cells on GSIS, due to the decreasing matrix NADHF/NAD+F (NADPHF/NADP+F) at increasing cytosolic NADPHF levels. The developed innovative methods enable real-time NADH/NAD+ and NADPH/NADP+ monitoring in any distinct cell compartment. Conclusion: The export of reducing equivalents from mitochondria adjusts lower mitochondrial superoxide production on GSIS, but it does not prevent oxidative stress in pancreatic β cells.
- Klíčová slova
- Complex I, NADH/NAD+ ratio, fluorescence lifetime imaging, glucose-stimulated insulin secretion, mitochondrial superoxide generation, pancreatic β cells,
- MeSH
- adenosintrifosfát metabolismus MeSH
- beta-buňky metabolismus MeSH
- buněčné dýchání MeSH
- chromatografie kapalinová MeSH
- energetický metabolismus MeSH
- flavinadenindinukleotid metabolismus MeSH
- glukosa metabolismus MeSH
- hmotnostní spektrometrie MeSH
- krysa rodu Rattus MeSH
- kyselina citronová metabolismus MeSH
- membránový potenciál mitochondrií MeSH
- metabolické sítě a dráhy MeSH
- metabolomika metody MeSH
- mitochondrie metabolismus MeSH
- NAD metabolismus MeSH
- peroxid vodíku metabolismus MeSH
- sekrece inzulinu * MeSH
- signální transdukce MeSH
- superoxidy metabolismus MeSH
- zvířata MeSH
- Check Tag
- krysa rodu Rattus MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- adenosintrifosfát MeSH
- flavinadenindinukleotid MeSH
- glukosa MeSH
- kyselina citronová MeSH
- NAD MeSH
- peroxid vodíku MeSH
- superoxidy MeSH
