Uncoupled Respiration Research Articles

Fatty acids promote uncoupled respiration via the ATP/ADP carrier in white adipocytes.

Adipocytes store energy as triglycerides, while mobilizing energy when needed via lipolysis. Triglyceride lipolysis releases fatty acids and glycerol into the circulation to fuel other tissues. However, a significant fraction of fatty acids released by lipolysis are retained within the white adipose tissue and handled by adipocytes. While some of these retained fatty acids are re-esterified in white adipocytes 1-6 , the a substantial amount undergo oxidative metabolism via a pathway regulated by the nongenomic effects of STAT3 7-10 . Here we report that fatty acids promote uncoupled oxidative metabolism in white adipocytes via the ATP/ADP carrier, contributing to thermogenesis and cold tolerance in obese thermoneutral-adapted mice, independent of brown adipose tissue and muscle activity. Our results suggest that uncoupled respiration in white adipocytes significantly contributes to whole-body energy expenditure and could be a promising target for obesity treatment.

Abstract P180: Female mice with systemic lupus erythematosus produce antibodies to mitochondrial antigens and have impaired renal mitochondrial function

Patients with autoimmune disorders like systemic lupus erythematosus (SLE) are at significant risk for renal and cardiovascular mortality. The pathology of SLE is driven by a loss of immune tolerance with the subsequent production of autoantibodies (IgG), and our laboratory previously demonstrated a mechanistic role for autoantibodies in autoimmune mediated hypertension. While anti-double stranded DNA (dsDNA) antibodies are pathognomonic for SLE, a breadth of autoantibodies may contribute to disease pathology. The goal of this study is to identify autoantibodies that may contribute to the renal and cardiovascular consequences associated with SLE. To accomplish this goal, an antigen array was performed (University of Texas Southwestern Genomics & Microarray Core Facility) using plasma samples collected from an established experimental mouse model of SLE (30 week old female NZBWF1, n=8) and healthy controls (30 week old female NZWLacJ, n=7). As anticipated, autoantibodies raised to nuclear antigens were prominently represented in the array and were significantly increased relative to control mice. This includes antibodies to dsDNA, ssRNA, chromatin, and histones (total) (p<0.02). In addition, SLE mice produce antibodies to mitochondrial antigens including cardiolipin and cytochrome C (p<0.02 vs control mice), critical components of the inner mitochondrial membrane and respiratory chain, respectively. In a separate study, renal mitochondrial function was tested using high resolution respirometry (Oroboros Instruments) in whole kidney homogenates from 30 week old female SLE (n=6) and control mice (n=5). Results show that coupled respiration, an estimation of oxidative phosphorylation, is significantly impaired at Complex I in kidneys from SLE mice compared to healthy controls (62±9 vs. 90±7 pmol/s/mg tissue, p<0.05). Uncoupled respiration, an estimation of maximal electron transport, is also reduced in the kidneys of female SLE mice compared to controls (157±23 vs. 212±14 pmol/s/mg tissue, p=0.07). These data provide insight for new mechanistic pathways to pursue in understanding the underlying mechanisms promoting cardiovascular risk factors like hypertension during SLE.

Insulin sensitivity and skeletal muscle mitochondrial respiration in Black and White women with obesity.

Non-Hispanic black women (BW) have a greater risk of type 2 diabetes (T2D) and insulin resistance (IR) compared to non-Hispanic white women (WW). The mechanisms leading to these differences are not understood, and it is unclear whether synergistic effects of race and obesity impact disease risk. To understand the interaction of race and weight, hepatic and peripheral IR were compared in WW and BW with and without obesity. Hepatic and peripheral IR was measured by a labeled, hyperinsulinemic-euglycemic clamp in BW (n=32) and WW (n=32) with and without obesity. Measurements of body composition, cardiorespiratory fitness, and skeletal muscle (SM) respiration were completed. Data were analyzed by mixed model ANOVA. Subjects with obesity had greater hepatic and peripheral IR and lower SM respiration (P<0.001). Despite 14% greater insulin (P=0.066), BW tended to have lower peripheral glucose disposal (Rd; P=0.062), which was driven by women without obesity (P=0.002). BW had significantly lower glucose production (P=0.005), hepatic IR (P=0.024), and maximal coupled and uncoupled respiration (P<0.001) than WW. Maximal coupled and uncoupled SM mitochondrial respiration was strongly correlated with peripheral and hepatic IR (P<0.01). While BW without obesity had lower Rd than WW, race and obesity did not synergistically impact peripheral IR. Paradoxically, WW with obesity had greater hepatic IR compared to BW. Relationships between SM respiration and IR persisted across a range of body weight. These data provide support for therapies in BW, like exercise, that improve SM mitochondrial respiration to reduce IR and T2D risk.

Molecular determinants of inhibition of UCP-1 mediated respiratory uncoupling

Molecular determinants of inhibition of UCP-1 mediated respiratory uncoupling

Mitochondrial free radicals contribute to cigarette smoke condensate-induced impairment of oxidative phosphorylation in the skeletal muscle in situ

Oxidative stress plays a critical role in cellular dysfunction associated with cigarette smoke exposure and aging. Some chemicals from tobacco smoke have the potential to amplify mitochondrial ROS (mROS) production, which, in turn, may impair mitochondrial respiratory function. Accordingly, the present study tested the hypothesis that a mitochondria-targeted antioxidant (MitoTEMPO, MT) would attenuate the inhibitory effects of cigarette smoke on skeletal muscle respiratory capacity of middle-aged mice. Specifically, mitochondrial oxidative phosphorylation was assessed using high-resolution respirometry in permeabilized fibers from the fast-twitch gastrocnemius muscle of middle-aged C57Bl/6J mice. Before the assessment of respiration, tissues were incubated for 1hr with a control buffer (CON), cigarette smoke condensate (2 % dilution, SMOKE), or MitoTEMPO (10 μM) combined with cigarette smoke condensate (MT + SMOKE). Cigarette smoke condensate (CSC) decreased maximal-ADP stimulated respiration (CON: 60 ± 15 pmolO2.s−1.mg−1 and SMOKE: 33 ± 8 pmolO2.s−1.mg−1; p = 0.0001), and this effect was attenuated by MT (MT + SMOKE: 41 ± 7 pmolO2.s−1.mg−1; p = 0.02 with SMOKE). Complex-I specific respiration was inhibited by CSC, with no significant effect of MT (p = 0.35). Unlike CON, the addition of glutamate (ΔGlutamate) had an additive effect on respiration in fibers exposed to CSC (CON: 0.9 ± 1.1 pmolO2.s−1.mg−1 and SMOKE: 5.4 ± 3.7 pmolO2.s−1.mg−1; p = 0.008) and MT (MT + SMOKE: 8.2 ± 3.8 pmolO2.s−1.mg−1; p ≤ 0.01). Complex-II specific respiration was inhibited by CSC but was partially restored by MT (p = 0.04 with SMOKE). Maximal uncoupled respiration induced by FCCP was inhibited by CSC, with no significant effect of MT. These findings underscore that mROS contributes to cigarette smoke condensate-induced inhibition of mitochondrial respiration in fast-twitch gastrocnemius muscle fibers of middle-aged mice thus providing a potential target for therapeutic treatment of smoke-related diseases. In addition, this study revealed that CSC largely impaired muscle respiratory capacity by decreasing metabolic flux through mitochondrial pyruvate transporter (MPC) and/or the enzymes upstream of α-ketoglutarate in the Krebs cycle.

Distinct mitochondrial respiration profiles in pediatric patients with febrile illness versus sepsis.

Mitochondrial dysfunction, linked to sepsis-related organ failure, is unknown in febrile illness. Prospective study of children in an Emergency Department (ED) with febrile illness or without infection (ED controls); secondary analysis of ICU patients with sepsis or without infection (ICU controls). Mitochondrial oxygen consumption measured in peripheral blood mononuclear cells using respirometry, with primary outcome of spare respiratory capacity (SRC). Mitochondrial content measured as citrate synthase (CS: febrile illness and ED controls) and mitochondrial to nuclear DNA ratio (mtDNA:nDNA: all groups). SRC was lower in febrile illness (6.7 ± 3.0 pmol/sec/106 cells) and sepsis (5.7 ± 4.7) than ED/PICU controls (8.5 ± 3.7; both p < 0.05), but not different between febrile illness and sepsis (p = 0.26). Low SRC was driven by increased basal respiration in febrile illness and decreased maximal uncoupled respiration in sepsis. Differences were no longer significant after adjustment for patient demographics. Febrile illness demonstrated lower CS activity than ED controls (p = 0.07) and lower mtDNA:nDNA than both ED/PICU controls and sepsis (both p < 0.05). Mitochondrial SRC was reduced in both febrile illness and sepsis, but due to distinct mitochondrial profiles and impacted by demographics. Further work is needed to determine if mitochondrial profiles could differentiate febrile illness from early sepsis. Mitochondrial dysfunction has been linked to organ failure in sepsis, but whether mitochondrial alterations are evident in febrile illness without sepsis is unknown. In our study, while mitochondrial spare respiratory capacity (SRC), an index of cellular bioenergetic reserve under stress, was reduced in children with both febrile illness and sepsis compared to children without infections, low SRC was driven by increased basal respiration in febrile illness compared with decreased maximal uncoupled respiration in sepsis. Additional research is needed to understand if distinct mitochondrial profiles could be used to differentiate febrile illness from early sepsis in children.

Single-nucleus transcriptomics identifies separate classes of UCP1 and futile cycle adipocytes

Adipose tissue can recruit catabolic adipocytes that utilize chemical energy to dissipate heat. This process occurs either by uncoupled respiration through uncoupling protein 1 (UCP1) or by utilizing ATP-dependent futile cycles (FCs). However, it remains unclear how these pathways coexist since both processes rely on the mitochondrial membrane potential. Utilizing single-nucleus RNA sequencing to deconvolute the heterogeneity of subcutaneous adipose tissue in mice and humans, we identify at least 2 distinct subpopulations of beige adipocytes: FC-adipocytes and UCP1-beige adipocytes. Importantly, we demonstrate that the FC-adipocyte subpopulation is highly metabolically active and utilizes FCs to dissipate energy, thus contributing to thermogenesis independent of Ucp1. Furthermore, FC-adipocytes are important drivers of systemic energy homeostasis and linked to glucose metabolism and obesity resistance in humans. Taken together, our findings identify a noncanonical thermogenic adipocyte subpopulation, which could be an important regulator of energy homeostasis in mammals.

Development of a functional beige fat cell line uncovers independent subclasses of cells expressing UCP1 and the futile creatine cycle

Although uncoupling protein 1 (UCP1) is established as a major contributor to adipose thermogenesis, recent data have illustrated an important role for alternative pathways, particularly the futile creatine cycle (FCC). How these pathways co-exist in cells and tissues has not been explored. Beige cell adipogenesis occurs invivo but has been difficult to model invitro; here, we describe the development of a murine beige cell line that executes a robust respiratory response, including uncoupled respiration and the FCC. The key FCC enzyme, tissue-nonspecific alkaline phosphatase (TNAP), is localized almost exclusively to mitochondria in these cells. Surprisingly, single-cell cloning from this cell line shows that cells with the highest levels of UCP1 express little TNAP, and cells with the highest expression of TNAP express little UCP1. Immunofluorescence analysis of subcutaneous fat from cold-exposed mice confirms that the highest levels of these critical thermogenic components are expressed in distinct fat cell populations.

Mitochondrial functions and fatty acid profiles in fish heart: an insight into physiological limitations linked to thermal tolerance and age.

Heart failure is among the first major consequences of heat stress in aquatic ectotherms. Mitochondria produce most of the ATP used by the heart and represent almost half of the volume in cardiac cells. It has therefore been hypothesized that mitochondrial dysfunction may be a major cause of heart failure associated with heat stress. The present study aims to investigate if CTmax is linked to the thermal sensitivity of cardiac mitochondria in the three-spined stickleback (Gasterosteus aculeatus), and if it is influenced by heart fatty acid composition and age. To do so, we measured the CTmax of 30 fish. The cardiac mitochondrial oxygen consumption was measured by high resolution respirometry at three temperatures and heart lipid profiles were obtained by gas chromatography (GC) coupled with a flame ionization detector (FID). Fish age was estimated via otolith readings. Fatty acid profiles showed no correlation with CTmax, but EPA levels were higher in older individuals. Mitochondrial respiration was measured in 35 fish using high-resolution respirometry. It was strongly affected by temperature and showed a drastic drop in OXPHOS respiration fed by complex I and complex I+complex II, while uncoupled respiration plateaued at CTmax temperature. Our results suggest that complex I is an important modulator of the impact of temperature on mitochondrial respiration at high temperatures but is not the main limiting factor in physiological conditions (maximal OXPHOS). Mitochondrial respiration was also affected by fish age, showing a general decrease in older individuals.

Single-cell atlas of ABCA7 loss-of-function reveals impaired neuronal respiration via choline-dependent lipid imbalances.

Loss-of-function (LoF) variants in the lipid transporter ABCA7 significantly increase the risk of Alzheimer's disease (odds ratio ∼2), yet the pathogenic mechanisms and the neural cell types affected by these variants remain largely unknown. Here, we performed single-nuclear RNA sequencing of 36 human post-mortem samples from the prefrontal cortex of 12 ABCA7 LoF carriers and 24 matched non-carrier control individuals. ABCA7 LoF was associated with gene expression changes in all major cell types. Excitatory neurons, which expressed the highest levels of ABCA7, showed transcriptional changes related to lipid metabolism, mitochondrial function, cell cycle-related pathways, and synaptic signaling. ABCA7 LoF-associated transcriptional changes in neurons were similarly perturbed in carriers of the common AD missense variant ABCA7 p.Ala1527Gly (n = 240 controls, 135 carriers), indicating that findings from our study may extend to large portions of the at-risk population. Consistent with ABCA7's function as a lipid exporter, lipidomic analysis of isogenic iPSC-derived neurons (iNs) revealed profound intracellular triglyceride accumulation in ABCA7 LoF, which was accompanied by a relative decrease in phosphatidylcholine abundance. Metabolomic and biochemical analyses of iNs further indicated that ABCA7 LoF was associated with disrupted mitochondrial bioenergetics that suggested impaired lipid breakdown by uncoupled respiration. Treatment of ABCA7 LoF iNs with CDP-choline (a rate-limiting precursor of phosphatidylcholine synthesis) reduced triglyceride accumulation and restored mitochondrial function, indicating that ABCA7 LoF-induced phosphatidylcholine dyshomeostasis may directly disrupt mitochondrial metabolism of lipids. Treatment with CDP-choline also rescued intracellular amyloid β -42 levels in ABCA7 LoF iNs, further suggesting a link between ABCA7 LoF metabolic disruptions in neurons and AD pathology. This study provides a detailed transcriptomic atlas of ABCA7 LoF in the human brain and mechanistically links ABCA7 LoF-induced lipid perturbations to neuronal energy dyshomeostasis. In line with a growing body of evidence, our study highlights the central role of lipid metabolism in the etiology of Alzheimer's disease.

SEPTIC SHOCK: LPS TOLERANCE PROTECTS MITOCHONDRIAL BIOGENESIS AND RESPIRATION.

Mitochondrial dysfunction is a recognized feature of sepsis, characterized by ultrastructural damage, diminished oxidative phosphorylation, and depletion of mitochondrial antioxidant capacity observed in deceased septic patients. LPS tolerance induces a controlled response to sepsis. This study aimed to evaluate the function of tolerant mitochondria after cecal ligation and puncture (CLP)-induced sepsis. Mytochondrial oxygen consumption was determined using polarography. Extraction and quantification of RNA for the expression of Tfam, Nrf-1, and Ppargc-1α, and respiratory complex activity were measured. CLP-tolerant animals presented preserved respiratory rates of S3 and S4 and a ratio of respiratory control (RCR) compared to CLP-nontolerant animals with reduced oxidative phosphorylation and increased uncoupled respiration. Complex I Vmax was reduced in septic animals; however, CLP animals sustained normal Vmax. Mitochondrial biogenesis was preserved in CLP-tolerant animals compared to the CLP-nontolerant group, likely due to increased TFAM expression. LPS tolerance protected septic animals from mitochondrial dysfunction, favoring mitochondrial biogenesis and preserving mitochondrial respiration and respiratory complex I activity.

Вплив етанолу та циклоспорину А на дихання ізольованих гепатоцитів щурів

It is known that ethanol affects the oxidative processes in liver mitochondria, which can be one of the mechanisms of the development of the alcoholic liver disease. A well-known immunosuppressant cyclosporine A is also an inhibitor of mitochondrial permeabi­lity transition pore. However, the pharmacological interaction of ethanol and cyclosporin A is not sufficiently studied. The aim of the study was to investigate the effect of ethanol and cyclosporine A on the respiration rate of isolated rat hepatocytes. Five male Wistar rats were used in the study. Hepatocytes were isolated by perfusion with collagenase. Cell plasma membrane integrity was assessed with trypan blue staining (0.1 %). Intact cell number was 85.7±0.92 %. The rate of oxygen consumption was measured using a polarographic device based on a Clark electrode. Protonophore FCCP was used to study the uncoupled respiration. Cell respiration was studied in the presence of glucose, pyruvate or monomethylsuccinate in solution. Statistical analysis was performed with Origin Pro 2018 software. Significance of difference between groups was evaluated with analysis of variance test. After one hour incubation with ethanol (50 mM), the rate of basal respiration of hepatocytes oxidizing glucose increased by a meager 8 %. Similar result was obtained upon the presence of pyruvate in solution. Monomethylsuccinate, however, abolished the effect of ethanol on basal respiration. he but not uncoupled respiration of hepatocytes upon glucose or pyruvate oxidation. Ethanol did not affect the uncoupled respiration of hepatocytes in presence of glucose, pyruvate of monomethylsuccinate. Incubation with cyclocporin A did not cause any changes in cell oxygen consumption in all experiments. Cyclosporin A also did not modify the effects of ethanol on basal respiration of hepatocytes. Therefore, no pharmacological no interaction between ethanol and cyclosporin A was detected, which could be evidenced by the change of mitochondrial respiration of isolated hepatocytes.

Mitochondrial function in skeletal muscle contributes to reproductive endothermy in tegu lizards (Salvator merianae).

In cyclic climate variations, including seasonal changes, many animals regulate their energy demands to overcome critical transitory moments, restricting their high-demand activities to phases of resource abundance, enabling rapid growth and reproduction. Tegu lizards (Salvator merianae) are ectotherms with a robust annual cycle, being active during summer, hibernating during winter, and presenting a remarkable endothermy during reproduction in spring. Here, we evaluated whether changes in mitochondrial respiratory physiology in skeletal muscle could serve as a mechanism for the increased thermogenesis observed during the tegu's reproductive endothermy. We performed high-resolution respirometry and calorimetry in permeabilized red and white muscle fibers, sampled during summer (activity) and spring (high activity and reproduction), in association with citrate synthase measurements. During spring, the muscle fibers exhibited increased oxidative phosphorylation. They also enhanced uncoupled respiration and heat production via adenine nucleotide translocase (ANT), but not via uncoupling proteins (UCP). Citrate synthase activity was higher during the spring, suggesting greater mitochondrial density compared to the summer. These findings were consistent across both sexes and muscle types (red and white). The current results highlight potential cellular thermogenic mechanisms in an ectothermic reptile that contribute to transient endothermy. Our study indicates that the unique feature of transitioning to endothermy through nonshivering thermogenesis during the reproductive phase may be facilitated by higher mitochondrial density, function, and uncoupling within the skeletal muscle. This knowledge contributes significant elements to the broader picture of models for the evolution of endothermy, particularly in relation to the enhancement of aerobic capacity.

Angiotensin II participates in mitochondrial thermogenic functions via the activation of glycolysis in chemically induced human brown adipocytes

Brown adipocytes are potential therapeutic targets for the prevention of obesity-associated metabolic diseases because they consume circulating glucose and fatty acids for heat production. Angiotensin II (Ang II) peptide is involved in the pathogenesis of obesity- and cold-induced hypertension; however, the mechanism underlying the direct effects of Ang II on human brown adipocytes remains unclear. Our transcriptome analysis of chemical compound-induced brown adipocytes (ciBAs) showed that the Ang II type 1 receptor (AGTR1), but not AGTR2 and MAS1 receptors, was expressed. The Ang II/AGTR1 axis downregulated the expression of mitochondrial uncoupling protein 1 (UCP1). The simultaneous treatment with β-adrenergic receptor agonists and Ang II attenuated UCP1 expression, triglyceride lipolysis, and cAMP levels, although cAMP response element-binding protein (CREB) phosphorylation was enhanced by Ang II mainly through the protein kinase C pathway. Despite reduced lipolysis, both coupled and uncoupled mitochondrial respiration was enhanced in Ang II-treated ciBAs. Instead, glycolysis and glucose uptake were robustly activated upon treatment with Ang II without a comprehensive transcriptional change in glucose metabolic genes. Elevated mitochondrial energy status induced by Ang II was likely associated with UCP1 repression. Our findings suggest that the Ang II/AGTR1 axis participates in mitochondrial thermogenic functions via glycolysis.

Screening of Amino Acids as a Safe Energy Source for Isolated Rat Pancreatic Acini.

Amino acids play an essential role in protein synthesis, metabolism, and survival of pancreatic acini. Adequate nutritional support is important for acute pancreatitis treatment. However, high concentrations of arginine and lysine may induce acute pancreatitis. The study aimed to identify the most suitable l -amino acids as safe energy sources for pancreatic acinar cells. Pancreatic acini were isolated from male Wistar rats. Effects of amino acids (0.1-20 mM) on uncoupled respiration of isolated acini were studied with a Clark electrode. Cell death was evaluated with fluorescent microscopy and DNA gel electrophoresis. Among the tested amino acids, glutamate, glutamine, alanine, lysine, and aspartate were able to stimulate the uncoupled respiration rate of isolated pancreatic acini, whereas arginine, histidine, and asparagine were not. Lysine, arginine, and glutamine (20 mM) caused complete loss of plasma membrane integrity of acinar cells after 24 hours of incubation. Glutamine also caused early (2-4 hours) cell swelling and blebbing. Aspartate, asparagine, and glutamate only moderately decreased the number of viable cells, whereas alanine and histidine were not toxic. DNA fragmentation assay and microscopic analysis of nuclei showed no evidence of apoptosis in cells treated with amino acids. Alanine and glutamate are safe and effective energy sources for mitochondria of pancreatic acinar cells.

Oxidative Stress Induced by Cortisol in Human Platelets.

Hypercortisolism is known to affect platelet function. However, few studies have approached the effect of exogenous cortisol on human platelets, and the results obtained are conflicting and unconvincing. In this study, the effect of exogenous cortisol on several parameters indicative of oxidative status in human platelets has been analysed. We have found that cortisol stimulates ROS production, superoxide anion formation, and lipid peroxidation, with these parameters being in strict correlation. In addition, cortisol decreases GSH and membrane SH-group content, evidencing that the hormone potentiates oxidative stress, depleting platelet antioxidant defence. The involvement of src, syk, PI3K, and AKT enzymes in oxidative mechanisms induced by cortisol is shown. The main sources of ROS in cells can include uncontrolled increase of NADPH oxidase activity and uncoupled aerobic respiration during oxidative phosphorylation. Both mechanisms seem to be involved in ROS formation induced by cortisol, as the NADPH oxidase 1 inhibitor 2(trifluoromethyl)phenothiazine, and rotenone and antimycin A, complex I and III inhibitor, respectively, significantly reduce oxidative stress. On the contrary, the NADPH oxidase inhibitor gp91ds-tat, malate and NaCN, complex II and IV inhibitor, respectively, have a minor effect. It is likely that, in human platelets, oxidative stress induced by cortisol can be associated with venous and arterial thrombosis, greatly contributing to cardiovascular diseases.

Mitochondrial flashes are interlinked with adaptive thermogenesis in brown adipocytes

Mitochondrial flash (mitoflash) is the electrochemical excitation of a single mitochondrion and plays diverse signaling roles in a variety of cells. From the viewpoint of bioenergetics, it represents the transient uncoupling of mitochondrial respiration from ATP synthesis. Brown adipose tissue (BAT) produces heat, primarily via mitochondrial uncoupled respiration. Here, we aim to illustrate the mitoflash activity in BAT thermogenesis. We show that BAT mitochondria undergo stochastic and intermittent mitoflashes at the levels of isolated mitochondria, cultured brown adipocytes, and even intact BAT. A BAT mitoflash contains multiple signals, including transient depolarization of mitochondrial membrane potential, transient matrix alkalization, and bursting production of reactive oxygen species. Importantly, thermogenic activation by β3-adrenergic stimulation dramatically augments mitoflash incidence, with mild effects on its unitary characteristics. Ablation of the thermogenic uncoupling protein 1 (UCP1) showed little effect on mitoflash biogenesis during heat production. Collectively, our results suggest that mitoflash might constitute an elemental signaling activity of mitochondria to regulate BAT thermogenesis.

Molecular determinants of inhibition of UCP1-mediated respiratory uncoupling

Molecular determinants of inhibition of UCP1-mediated respiratory uncoupling

Critical roles of tubular mitochondrial ATP synthase dysfunction in maleic acid-induced acute kidney injury.

Maleic acid (MA) induces renal tubular cell dysfunction directed to acute kidney injury (AKI). AKI is an increasing global health burden due to its association with mortality and morbidity. However, targeted therapy for AKI is lacking. Previously, we determined mitochondrial-associated proteins are MA-induced AKI affinity proteins. We hypothesized that mitochondrial dysfunction in tubular epithelial cells plays a critical role in AKI. In vivo and in vitro systems have been used to test this hypothesis. For the in vivo model, C57BL/6 mice were intraperitoneally injected with 400mg/kg body weight MA. For the in vitro model, HK-2 human proximal tubular epithelial cells were treated with 2mM or 5mM MA for 24h. AKI can be induced by administration of MA. In the mice injected with MA, the levels of blood urea nitrogen (BUN) and creatinine in the sera were significantly increased (p < 0.005). From the pathological analysis, MA-induced AKI aggravated renal tubular injuries, increased kidney injury molecule-1 (KIM-1) expression and caused renal tubular cell apoptosis. At the cellular level, mitochondrial dysfunction was found with increasing mitochondrial reactive oxygen species (ROS) (p < 0.001), uncoupled mitochondrial respiration with decreasing electron transfer system activity (p < 0.001), and decreasing ATP production (p < 0.05). Under transmission electron microscope (TEM) examination, the cristae formation of mitochondria was defective in MA-induced AKI. To unveil the potential target in mitochondria, gene expression analysis revealed a significantly lower level of ATPase6 (p < 0.001). Renal mitochondrial protein levels of ATP subunits 5A1 and 5C1 (p < 0.05) were significantly decreased, as confirmed by protein analysis. Our study demonstrated that dysfunction of mitochondria resulting from altered expression of ATP synthase in renal tubular cells is associated with MA-induced AKI. This finding provides a potential novel target to develop new strategies for better prevention and treatment of MA-induced AKI.

H+-slip correlated to rotor free-wheeling as cause of F1FO-ATPase dysfunction in primary mitochondrial disorders.

Inborn errors of metabolism are related to mitochondrial disorders caused by dysfunction of the oxidative phosphorylation (OXPHOS) system. Congenital hypermetabolism in the infant is a rare disease belonging to Luft syndrome, nonthyroidal hypermetabolism, arising from a singular example of a defect in OXPHOS. The mitochondria lose coupling of mitochondrial substrates oxidation from the ADP phosphorylation. Since Luft syndrome is due to uncoupled cell respiration responsible for deficient in ATP production that originates in the respiratory complexes, a de novo heterozygous variant in the catalytic subunit of mitochondrial F1FO-ATPase arises as the main cause of an autosomal dominant syndrome of hypermetabolism associated with dysfunction in ATP production, which does not involve the respiratory complexes. The F1FO-ATPase works as an embedded molecular machine with a rotary action using two different motor engines. The FO, which is an integral domain in the membrane, dissipates the chemical potential difference for H+, a proton motive force (Δp), across the inner membrane to generate a torsion. The F1 domain-the hydrophilic portion responsible for ATP turnover-is powered by the molecular rotary action to synthesize ATP. The structural and functional coupling of F1 and FO domains support the energy transduction for ATP synthesis. The dissipation of Δp by means of an H+ slip correlated to rotor free-wheeling of the F1FO-ATPase has been discovered to cause enzyme dysfunction in primary mitochondrial disorders. In this insight, we try to offer commentary and analysis of the molecular mechanism in these impaired mitochondria.