ALCAT1 Overexpression Affects Supercomplex Formation and Increases ROS in Respiring Mitochondria

In Vitro Hypoxia/Reoxygenation Induces Mitochondrial Cardiolipin Remodeling in Human Kidney Cells

Renal ischemia/reperfusion is a serious condition that not only causes acute kidney injury, a severe clinical syndrome with high mortality, but is also an inevitable part of kidney transplantation or other kidney surgeries. Alterations of oxygen levels during ischemia/reperfusion, namely hypoxia/reoxygenation, disrupt mitochondrial metabolism and induce structural changes that lead to cell death. A signature mitochondrial phospholipid, cardiolipin, with many vital roles in mitochondrial homeostasis, is one of the key players in hypoxia/reoxygenation-induced mitochondrial damage. In this study, we analyze the effect of hypoxia/reoxygenation on human renal proximal tubule epithelial cell (RPTEC) cardiolipins, as well as their metabolism and mitochondrial functions. RPTEC cells were placed in a hypoxic chamber with a 2% oxygen atmosphere for 24 h to induce hypoxia; then, they were replaced back into regular growth conditions for 24 h of reoxygenation. Surprisingly, after 24 h, hypoxia cardiolipin levels substantially increased and remained higher than control levels after 24 h of reoxygenation. This was explained by significantly elevated levels of cardiolipin synthase and lysocardiolipin acyltransferase 1 (LCLAT1) gene expression and protein levels. Meanwhile, hypoxia/reoxygenation decreased ADP-dependent mitochondrial respiration rates and oxidative phosphorylation capacity and increased reactive oxygen species generation. Our findings suggest that hypoxia/reoxygenation induces cardiolipin remodeling in response to reduced mitochondrial oxidative phosphorylation in a way that protects mitochondrial function.

Anomalous peroxidase activity of cytochrome c is the primary pathogenic target in Barth syndrome

Barth syndrome (BTHS) is a life-threatening genetic disorder with unknown pathogenicity caused by mutations in TAFAZZIN (TAZ) that affect remodeling of mitochondrial cardiolipin (CL). TAZ deficiency leads to accumulation of mono-lyso-CL (MLCL), which forms a peroxidase complex with cytochrome c (cyt c) capable of oxidizing polyunsaturated fatty acid-containing lipids. We hypothesized that accumulation of MLCL facilitates formation of anomalous MLCL-cyt c peroxidase complexes and peroxidation of polyunsaturated fatty acid phospholipids as the primary BTHS pathogenic mechanism. Using genetic, biochemical/biophysical, redox lipidomic and computational approaches, we reveal mechanisms of peroxidase-competent MLCL-cyt c complexation and increased phospholipid peroxidation in different TAZ-deficient cells and animal models and in pre-transplant biopsies from hearts of patients with BTHS. A specific mitochondria-targeted anti-peroxidase agent inhibited MLCL-cyt c peroxidase activity, prevented phospholipid peroxidation, improved mitochondrial respiration of TAZ-deficient C2C12 myoblasts and restored exercise endurance in a BTHS Drosophila model. Targeting MLCL-cyt c peroxidase offers therapeutic approaches to BTHS treatment.

A tail of their own: regulation of cardiolipin and phosphatidylinositol fatty acyl profile by the acyltransferase LCLAT1

Cardiolipin and phosphatidylinositol along with the latter's phosphorylated derivative phosphoinositides, control a wide range of cellular functions from signal transduction, membrane traffic, mitochondrial function, cytoskeletal dynamics, and cell metabolism. An emerging dimension to these lipids is the specificity of their fatty acyl chains that is remarkably distinct from that of other glycerophospholipids. Cardiolipin and phosphatidylinositol undergo acyl remodeling involving the sequential actions of phospholipase A to hydrolyze acyl chains and key acyltransferases that re-acylate with specific acyl groups. LCLAT1 (also known as LYCAT, AGPAT8, LPLAT6, or ALCAT1) is an acyltransferase that contributes to specific acyl profiles for phosphatidylinositol, phosphoinositides, and cardiolipin. As such, perturbations of LCLAT1 lead to alterations in cardiolipin-dependent phenomena such as mitochondrial respiration and dynamics and phosphoinositide-dependent processes such as endocytic membrane traffic and receptor signaling. Here we examine the biochemical and cellular actions of LCLAT1, as well as the contribution of this acyltransferase to the development and specific diseases.

Amiodarone but not propafenone impairs bioenergetics and autophagy of human myocardial cells

Cardiac and extra-cardiac side effects of common antiarrhythmic agents might be related to drug-induced mitochondrial dysfunction. Supratherapeutic doses of amiodarone have been shown to impair mitochondria in animal studies, whilst influence of propafenone on cellular bioenergetics is unknown. We aimed to assess effects of protracted exposure to pharmacologically relevant doses of amiodarone and propafenone on cellular bioenergetics and mitochondrial biology of human and mouse cardiomyocytes. In this study, HL-1 mouse atrial cardiomyocytes and primary human cardiomyocytes derived from the ventricles of the adult heart were exposed to 2 and 7 μg/mL of either amiodarone or propafenone. After 24 h, extracellular flux analysis and confocal laser scanning microscopy were used to measure mitochondrial functions. Autophagy was assessed by western blots and live-cell imaging of lysosomes. In human cardiomyocytes, amiodarone significantly reduced mitochondrial membrane potential and ATP production, in association with an inhibition of fatty acid oxidation and impaired complex I- and II-linked respiration in the electron transport chain. Expectedly, this led to increased anaerobic glycolysis. Amiodarone increased the production of reactive oxygen species and autophagy was also markedly affected. In contrast, propafenone-exposed cardiomyocytes did not exert any impairment of cellular bioenergetics. Similar changes after amiodarone treatment were observed during identical experiments performed on HL-1 mouse cardiomyocytes, suggesting a comparable pharmacodynamics of amiodarone among mammalian species. In conclusion, amiodarone but not propafenone in near-therapeutic concentrations causes a pattern of mitochondrial dysfunction with affected autophagy and metabolic switch from oxidative metabolism to anaerobic glycolysis in human cardiomyocytes.

Irisin and ALCAT1 mediated aerobic exercise-alleviated oxidative stress and apoptosis in skeletal muscle of mice with myocardial infarction

Skeletal muscle in patients with heart failure (HF) exhibits altered structure, function and metabolism. Myocardial infarction (MI) is the most common cause of HF. Oxidative stress and cell apoptosis are involved in the pathophysiology of MI/HF-induced skeletal muscle atrophy. It is well recognized that aerobic exercise (AE) could prevent skeletal muscle atrophy after MI, but the underlying mechanism and molecular targets are still not fully clarified. In this study, Fndc5^-/- and Alcat1^-/- mice were used to establish the MI model and subjected to six weeks of moderate-intensity AE. C2C12 cells were treated with H₂O₂ and recombinant human Irisin (rhIrisin), or transduced with a lentiviral vector to mediate the overexpression of ALCAT1 (LV-Alcat1). Results showed that MI reduced Irisin expression and antioxidant capacity of skeletal muscle, increased ALCAT1 expression, induced protein degradation and cell apoptosis, which were partly reversed by AE; Knockout of Fndc5 further aggravated MI-induced oxidative stress and cell apoptosis in skeletal muscle, and partly weakened the beneficial effects of AE. In contrast, knockout of Alcat1 reduced MI-induced oxidative stress and cell apoptosis and strengthened the beneficial effects of AE. rhIrisin and AICAR intervention inhibited ALCAT1 expression, oxidative stress and cell apoptosis, which induced by H₂O₂ or LV-Alcat1 in C2C12 cells. These findings reveal that AE could alleviate the levels of oxidative stress and apoptosis in skeletal muscle following MI, partly via up-regulating Irisin and inhibiting ALCAT1 expression.

Effect of noradrenaline on propofol-induced mitochondrial dysfunction in human skeletal muscle cells

Background

Mitochondrial dysfunction is a hallmark of both critical illness and propofol infusion syndrome and its severity seems to be proportional to the doses of noradrenaline, which patients are receiving. We comprehensively studied the effects of noradrenaline on cellular bioenergetics and mitochondrial biology in human skeletal muscle cells with and without propofol-induced mitochondrial dysfunction.

Methods

Human skeletal muscle cells were isolated from vastus lateralis biopsies from patients undergoing elective hip replacement surgery (n = 14) or healthy volunteers (n = 4). After long-term (96 h) exposure to propofol (10 µg/mL), noradrenaline (100 µM), or both, energy metabolism was assessed by extracellular flux analysis and substrate oxidation assays using [14C] palmitic and [14C(U)] lactic acid. Mitochondrial membrane potential, morphology and reactive oxygen species production were analysed by confocal laser scanning microscopy. Mitochondrial mass was assessed both spectrophotometrically and by confocal laser scanning microscopy.

Results

Propofol moderately reduced mitochondrial mass and induced bioenergetic dysfunction, such as a reduction of maximum electron transfer chain capacity, ATP synthesis and profound inhibition of exogenous fatty acid oxidation. Noradrenaline exposure increased mitochondrial network size and turnover in both propofol treated and untreated cells as apparent from increased co-localization with lysosomes. After adjustment to mitochondrial mass, noradrenaline did not affect mitochondrial functional parameters in naïve cells, but it significantly reduced the degree of mitochondrial dysfunction induced by propofol co-exposure. The fatty acid oxidation capacity was restored almost completely by noradrenaline co-exposure, most likely due to restoration of the capacity to transfer long-chain fatty acid to mitochondria. Both propofol and noradrenaline reduced mitochondrial membrane potential and increased reactive oxygen species production, but their effects were not additive.

Conclusions

Noradrenaline prevents rather than aggravates propofol-induced impairment of mitochondrial functions in human skeletal muscle cells. Its effects on bioenergetic dysfunctions of other origins, such as sepsis, remain to be demonstrated.

Cardioprotection Attributed to Aerobic Exercise-Mediated Inhibition of ALCAT1 and Oxidative Stress-Induced Apoptosis in MI Rats

Cardiolipin (CL) plays a pivotal role in mitochondria-mediated apoptosis. Acyl-CoA: lysocardiolipin acyltransferase 1 (ALCAT1) can accelerate CL reactive oxygen production and cause mitochondrial damage. Although we have demonstrated that aerobic exercise significantly reduced ALCAT1 levels in MI mice, what is the temporal characteristic of ALCAT1 after MI? Little is known. Based on this, the effect of exercise on ALCAT1 in MI rats needs to be further verified. Therefore, this paper aimed to characterize ALCAT1 expression, and investigate the possible impact of exercise on ALCAT1 and its role in fibrosis, antioxidant capacity, and apoptosis in MI rats. Our results indicated that the potential utility of MI increased ALCAT1 expression within 1–6 h of MI, and serum CK and CKMB had significant effects in MI at 24 h, while LDH exerted an effect five days after MI. Furthermore, ALCAT1 expression was upregulated, oxidative capacity and excessive apoptosis were enhanced, and cardiac function was decreased after MI, and aerobic exercise can reverse these changes. These findings revealed a previously unknown endogenous cardiac injury factor, ALCAT1, and demonstrated that ALCAT1 damaged the heart of MI rats, and aerobic exercise reduced ALCAT1 expression, oxidative stress, and apoptosis after MI-induced cardiac injury in rats.

The Roles of FGF21 and ALCAT1 in Aerobic Exercise-Induced Cardioprotection of Postmyocardial Infarction Mice

Aerobic exercise mitigates oxidative stress and apoptosis caused by myocardial infarction (MI) even though the precise mechanisms remain completely elusive. In this study, we investigated the potential mechanisms of aerobic exercise in ameliorating the cardiac function of mice with MI. In vivo, MI was induced by left anterior descending (LAD) coronary artery ligation in wild-type mice, alcat1 knockout, and fgf21 knockout mice. The mice were exercised under a moderate-intensity protocol for 6 weeks at one week later post-MI. In vitro, H9C2 cells were treated with lentiviral vector carrying alcat1 gene, recombinant human FGF21 (rhFGF21), PI3K inhibitor, and H₂O₂ to explore the potential mechanisms. Our results showed that aerobic exercise significantly increased the FGF21 expression and decreased the ALCAT1 expression in the hearts of mice with MI. fgf21 knockout weakened the inhibitory effects of aerobic exercise on oxidative stress, endoplasmic reticulum (ER) stress, and apoptosis in mice with MI. Both/either alcat1 knockout and/or aerobic exercise improved cardiac function by inhibiting oxidative stress and apoptosis in the MI heart. rhFGF21 inhibited both H₂O₂ and overexpression of ALCAT1-induced oxidative stress and apoptosis by activating the PI3K/AKT pathway in H9C2 cells. In conclusion, our results showed that aerobic exercise alleviated oxidative stress and apoptosis by activating the FGF21/FGFR1/PI3K/AKT pathway or inhibiting the hyperexpression of ALCAT1, which ultimately improved the cardiac function in MI mice.

Protein Supercomplex Recording in Living Cells Via Position-Specific Fluorescence Lifetime Sensors

Our group has previously established a strategy utilizing fluorescence lifetime probes to image membrane protein supercomplex (SC) formation in situ. We showed that a probe at the interface between individual mitochondrial respiratory complexes exhibits a decreased fluorescence lifetime when a supercomplex is formed. This is caused by electrostatic interactions with the adjacent proteins. Fluorescence lifetime imaging microscopy (FLIM) records the resulting decrease of the lifetime of the SC-probe. Here we present the details of our method for performing SC-FLIM, including the evaluation of fluorescence lifetimes from the FLIM images. To validate the feasibility of the technique for monitoring adaptive SC formation, we compare data obtained under different metabolic conditions. The results confirm that SC formation is dynamic.

Molecular and Supramolecular Structure of the Mitochondrial Oxidative Phosphorylation System: Implications for Pathology

Under aerobic conditions, mitochondrial oxidative phosphorylation (OXPHOS) converts the energy released by nutrient oxidation into ATP, the currency of living organisms. The whole biochemical machinery is hosted by the inner mitochondrial membrane (mtIM) where the protonmotive force built by respiratory complexes, dynamically assembled as super-complexes, allows the F1FO-ATP synthase to make ATP from ADP + Pi. Recently mitochondria emerged not only as cell powerhouses, but also as signaling hubs by way of reactive oxygen species (ROS) production. However, when ROS removal systems and/or OXPHOS constituents are defective, the physiological ROS generation can cause ROS imbalance and oxidative stress, which in turn damages cell components. Moreover, the morphology of mitochondria rules cell fate and the formation of the mitochondrial permeability transition pore in the mtIM, which, most likely with the F1FO-ATP synthase contribution, permeabilizes mitochondria and leads to cell death. As the multiple mitochondrial functions are mutually interconnected, changes in protein composition by mutations or in supercomplex assembly and/or in membrane structures often generate a dysfunctional cascade and lead to life-incompatible diseases or severe syndromes. The known structural/functional changes in mitochondrial proteins and structures, which impact mitochondrial bioenergetics because of an impaired or defective energy transduction system, here reviewed, constitute the main biochemical damage in a variety of genetic and age-related diseases.

A Metabolic Gene Signature to Predict Overall Survival in Head and Neck Squamous Cell Carcinoma

Background

Head and neck squamous cell carcinoma (HNSCC) is a common malignancy that emanates from the lips, mouth, paranasal sinuses, oropharynx, larynx, nasopharynx, and from other pharyngeal cancers. The availability of high-throughput expression data has made it possible to use global gene expression data to analyze the relationship between metabolic-related gene expression and clinical outcomes in HNSCC patients.

Method

In this study, we used RNA sequencing (RNA-seq) data from the cancer genome atlas (TCGA), with validation in the GEO dataset to profile the metabolic microenvironment and define potential biomarkers for metabolic therapy.

Results

We extracted data for 529 patients and 327 metabolic genes (198 upregulated and 129 downregulated genes) in the TCGA database. Carbonic anhydrase 9 (CA9) and CA6 had the largest logFCs in the upregulated and downregulated genes, respectively. Our Cox regression model data showed 51 prognostic-related genes with lysocardiolipin acyltransferase 1 (LCLAT1) and choline dehydrogenase (CHDH) being associated with the highest risk (HR = 1.144, 95% CI = 1.044 ~ 1.251) and the lowest risk (HR = 0.580, 95% CI = 0.400 ~ 0.839) in HNSCC, respectively. We next used the ROC curve to evaluate whether the differentially expressed metabolic-related genes could serve as early predictors of HNSCC. The findings showed an AUC of 0.745 and 0.618 in the TCGA and GEO analysis, respectively. Besides, the ability for the genes to predict clinicopathological HNSCC status was analyzed and the data showed that the AUC for age, gender, grade, stage, T, M, and N was 0.520, 0.495, 0.568, 0.606, 0.577, 0.476, and 0.673, respectively, in the TCGA dataset. On the other hand, the AUC for age, gender, stage, T, M, N, smoking, and HPV16-pos was 0.599, 0.531, 0.622, 0.606, 0.616, 0.550, 0.614, 0.519, and 0.397, respectively, in the GEO dataset.

Conclusion

Taken together, our study unearths a novel metabolic gene signature for the prediction of HNSCC prognosis based on the TCGA dataset. Our signature might point out the metabolic microenvironment disorders and provides potential treatment targets and prognostic biomarkers.

Intimate Relations-Mitochondria and Ageing

Mitochondrial dysfunction is associated with ageing, but the detailed causal relationship between the two is still unclear. We review the major phenomenological manifestations of mitochondrial age-related dysfunction including biochemical, regulatory and energetic features. We conclude that the complexity of these processes and their inter-relationships are still not fully understood and at this point it seems unlikely that a single linear cause and effect relationship between any specific aspect of mitochondrial biology and ageing can be established in either direction.

Aerobic exercise alleviates oxidative stress-induced apoptosis in kidneys of myocardial infarction mice by inhibiting ALCAT1 and activating FNDC5/Irisin signaling pathway

Aerobic exercise involves in ameliorating kidney injury, but the underlying mechanisms are not fully clarified. In this study, we elucidated the potential mechanisms of aerobic exercise in ameliorating kidney injury following myocardial infarction (MI). In vivo, wildtype and alcat1 knockout mice were used to establish the MI model, and subjected to six-week moderate-intensity aerobic exercise. In vitro, Normal Rat Kidney (NRK) cells treated with H₂O₂ and recombinant human Irisin (rhIrisin) were used for exploring potential mechanisms. Our results showed that Irisin expression was up-regulated by aerobic exercise in kidneys after MI, while ALCAT1 was reduced. In alcat1 knockout mice, we found that ALCAT1 involved in the progressions of oxidative stress and apoptosis in impaired kidney tissues of MI mice, but aerobic exercise reversed these changes. Furthermore, in vitro, we observed that Irisin inhibited both H₂O₂-treatment or overexpression of alcat1-induced oxidative stress and apoptosis in NRK cells, partially via AMPK-Sirt1-PGC-1α pathway. These findings reveal that aerobic exercise participates in alleviating the levels of oxidative stress and apoptosis in impaired kidney tissues following MI, partially via activating FNDC5/Irisin-AMPK-Sirt1-PGC-1α signaling pathway and inhibiting ALCAT1 expression.