Decreased cardiolipin synthesis corresponds with cytochrome c release in palmitate-induced cardiomyocyte apoptosis

Death and the desaturase: Implication of Stearoyl-CoA desaturase-1 in the mechanisms of cell stress, apoptosis, and ferroptosis

Growth and proliferation of normal and cancerous cells necessitate a finely-tuned regulation of lipid metabolic pathways to ensure the timely supply of structural, energetic, and signaling lipid molecules. The synthesis and remodeling of lipids containing fatty acids with an appropriate carbon length and insaturation level are required for supporting each phase of the mechanisms of cell replication and survival. Mammalian Stearoyl-CoA desaturases (SCD), particularly SCD1, play a crucial role in modulating the fatty acid composition of cellular lipids, converting saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA) in the endoplasmic reticulum (ER). Extensive research has elucidated in great detail the participation of SCD1 in the molecular mechanisms that govern cell replication in normal and cancer cells. More recently, investigations have shed new light on the functional and regulatory role of the Δ9-desaturase in the processes of cell stress and cell death. This review will examine the latest findings on the involvement of SCD1 in the molecular pathways of cell survival, particularly on the mechanisms of ER stress and autophagy, as well in apoptotic and non-apoptotic cell death.

Cardiolipin remodeling maintains the inner mitochondrial membrane in cells with saturated lipidomes

Cardiolipin (CL) is a unique, four-chain phospholipid synthesized in the inner mitochondrial membrane (IMM). The acyl chain composition of CL is regulated through a remodeling pathway, whose loss causes mitochondrial dysfunction in Barth syndrome (BTHS). Yeast has been used extensively as a model system to characterize CL metabolism, but mutants lacking its two remodeling enzymes, Cld1p and Taz1p, exhibit mild structural and respiratory phenotypes compared to mammalian cells. Here, we show an essential role for CL remodeling in the structure and function of the IMM in yeast grown under reduced oxygenation. Microaerobic fermentation, which mimics natural yeast environments, caused the accumulation of saturated fatty acids and, under these conditions, remodeling mutants showed a loss of IMM ultrastructure. We extended this observation to HEK293 cells, where phospholipase A2 inhibition by Bromoenol lactone resulted in respiratory dysfunction and cristae loss upon mild treatment with exogenous saturated fatty acids. In microaerobic yeast, remodeling mutants accumulated unremodeled, saturated CL, but also displayed reduced total CL levels, highlighting the interplay between saturation and CL biosynthesis and/or breakdown. We identified the mitochondrial phospholipase A1 Ddl1p as a regulator of CL levels, and those of its precursors phosphatidylglycerol and phosphatidic acid, under these conditions. Loss of Ddl1p partially rescued IMM structure in cells unable to initiate CL remodeling and had differing lipidomic effects depending on oxygenation. These results introduce a revised yeast model for investigating CL remodeling and suggest that its structural functions are dependent on the overall lipid environment in the mitochondrion.

Triphenylphosphonium-Conjugated Palmitic Acid for Mitochondrial Targeting of Pancreatic Cancer Cells: Proteomic and Molecular Evidence

Pancreatic ductal adenocarcinoma (PDAC)'s resistance to therapies is mainly attributed to pancreatic cancer stem cells (PCSCs). Mitochondria-impairing agents can be used to hamper PCSC propagation and reduce PDAC progression. Therefore, to develop an efficient vector for delivering drugs to the mitochondria, we synthesized tris(3,5-dimethylphenyl)phosphonium-conjugated palmitic acid. Triphenylphosphonium (TPP) is a lipophilic cationic moiety that promotes the accumulation of conjugated agents in the mitochondrion. Palmitic acid (PA), the most common saturated fatty acid, has pro-apoptotic activity in different types of cancer cells. TPP-PA was prepared by the reaction of 16-bromopalmitic acid with TPP, and its structure was characterized by 1H and 13C NMR and HRMS. We compared the proteomes of TPP-PA-treated and untreated PDAC cells and PCSCs, identifying dysregulated proteins and pathways. Furthermore, assessments of mitochondrial membrane potential, intracellular ROS, cardiolipin content and lipid peroxidation, ER stress, and autophagy markers provided information on the mechanism of action of TPP-PA. The findings showed that TPP-PA reduces PDAC cell proliferation through mitochondrial disruption that leads to increased ROS, activation of ER stress, and autophagy. Hence, TPP-PA might offer a new approach for eliminating both the primary population of cancer cells and PCSCs, which highlights the promise of TPP-derived compounds as anticancer agents for PDAC.

Genetic evidence for functional diversification of gram-negative intermembrane phospholipid transporters

The outer membrane of gram-negative bacteria is a barrier to chemical and physical stress. Phospholipid transport between the inner and outer membranes has been an area of intense investigation and, in E. coli K-12, it has recently been shown to be mediated by YhdP, TamB, and YdbH, which are suggested to provide hydrophobic channels for phospholipid diffusion, with YhdP and TamB playing the major roles. However, YhdP and TamB have different phenotypes suggesting distinct functions. It remains unclear whether these functions are related to phospholipid metabolism. We investigated a synthetic cold sensitivity caused by deletion of fadR, a transcriptional regulator controlling fatty acid degradation and unsaturated fatty acid production, and yhdP, but not by ΔtamB ΔfadR or ΔydbH ΔfadR. Deletion of tamB recuses the ΔyhdP ΔfadR cold sensitivity further demonstrating the phenotype is related to functional diversification between these genes. The ΔyhdP ΔfadR strain shows a greater increase in cardiolipin upon transfer to the non-permissive temperature and genetically lowering cardiolipin levels can suppress cold sensitivity. These data also reveal a qualitative difference between cardiolipin synthases in E. coli, as deletion of clsA and clsC suppresses cold sensitivity but deletion of clsB does not. Moreover, increased fatty acid saturation is necessary for cold sensitivity and lowering this level genetically or through supplementation of oleic acid suppresses the cold sensitivity of the ΔyhdP ΔfadR strain. Together, our data clearly demonstrate that the diversification of function between YhdP and TamB is related to phospholipid metabolism. Although indirect regulatory effects are possible, we favor the parsimonious hypothesis that YhdP and TamB have differential phospholipid-substrate transport preferences. Thus, our data provide a potential mechanism for independent control of the phospholipid composition of the inner and outer membranes in response to changing conditions based on regulation of abundance or activity of YhdP and TamB.

Genetic evidence for functional diversification of gram-negative intermembrane phospholipid transporters

The outer membrane of Gram-negative bacteria is a barrier to chemical and physical stress. Phospholipid transport between the inner and outer membranes has been an area of intense investigation and, in E. coli K-12, it has recently been shown to be mediated by YhdP, TamB, and YdbH, which are suggested to provide hydrophobic channels for phospholipid diffusion, with YhdP and TamB playing the major roles. However, YhdP and TamB have different phenotypes suggesting distinct functions. We investigated these functions using synthetic cold sensitivity (at 30 °C) caused by deletion of yhdP and fadR, a transcriptional regulator controlling fatty acid degradation and unsaturated fatty acid production, but not by ΔtamB ΔfadR or ΔydbH ΔfadR,. Deletion of tamB suppresses the ΔyhdP ΔfadR cold sensitivity suggesting this phenotype is related to phospholipid transport. The ΔyhdP ΔfadR strain shows a greater increase in cardiolipin upon transfer to the non-permissive temperature and genetically lowering cardiolipin levels can suppress cold sensitivity. These data also reveal a qualitative difference between cardiolipin synthases in E. coli, as deletion of clsA and clsC suppresses cold sensitivity but deletion of clsB does not despite lower cardiolipin levels. In addition to increased cardiolipin, increased fatty acid saturation is necessary for cold sensitivity and lowering this level genetically or through supplementation of oleic acid suppresses the cold sensitivity of the ΔyhdP ΔfadR strain. Although indirect effects are possible, we favor the parsimonious hypothesis that YhdP and TamB have differential substrate transport preferences, most likely with YhdP preferentially transporting more saturated phospholipids and TamB preferentially transporting more unsaturated phospholipids. We envision cardiolipin contributing to this transport preference by sterically clogging TamB-mediated transport of saturated phospholipids. Thus, our data provide a potential mechanism for independent control of the phospholipid composition of the inner and outer membranes in response to changing conditions.

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.

Phosphatidylserine decarboxylase downregulation in uric acid‑induced hepatic mitochondrial dysfunction and apoptosis

The molecular mechanisms underlying uric acid (UA)-induced mitochondrial dysfunction and apoptosis have not yet been elucidated. Herein, we investigated underlying mechanisms of UA in the development of mitochondrial dysfunction and apoptosis. We analyzed blood samples of individuals with normal UA levels and patients with hyperuricemia. Results showed that patients with hyperuricemia had significantly elevated levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, which may indicate liver or mitochondrial damage in patients with hyperuricemia. Subsequently, lipidomic analysis of mouse liver tissue mitochondria and human liver L02 cell mitochondria was performed. Compared with control group levels, high UA increased mitochondrial phosphatidylserine (PS) and decreased mitochondrial phosphatidylethanolamine (PE) levels, whereas the expression of mitochondrial phosphatidylserine decarboxylase (PISD) that mediates PS and PE conversion was downregulated. High UA levels also inhibited signal transducer and activator of transcription 3 （STAT3） phosphorylation as well as mitochondrial respiration, while inducing apoptosis both in vivo and in vitro. Treatment with allopurinol, overexpression of PISD, and lyso-PE (LPE) administration significantly attenuated the three above-described effects in vitro. In conclusion, UA may induce mitochondrial dysfunction and apoptosis through mitochondrial PISD downregulation. This study provides a new perspective on liver damage caused by hyperuricemia.

Structural insights into cardiolipin replacement by phosphatidylglycerol in a cardiolipin-lacking yeast respiratory supercomplex

Cardiolipin is a hallmark phospholipid of mitochondrial membranes. Despite established significance of cardiolipin in supporting respiratory supercomplex organization, a mechanistic understanding of this lipid-protein interaction is still lacking. To address the essential role of cardiolipin in supercomplex organization, we report cryo-EM structures of a wild type supercomplex (IV1III2IV1) and a supercomplex (III2IV1) isolated from a cardiolipin-lacking Saccharomyces cerevisiae mutant at 3.2-Å and 3.3-Å resolution, respectively, and demonstrate that phosphatidylglycerol in III2IV1 occupies similar positions as cardiolipin in IV1III2IV1. Lipid-protein interactions within these complexes differ, which conceivably underlies the reduced level of IV1III2IV1 and high levels of III2IV1 and free III2 and IV in mutant mitochondria. Here we show that anionic phospholipids interact with positive amino acids and appear to nucleate a phospholipid domain at the interface between the individual complexes, which dampen charge repulsion and further stabilize interaction, respectively, between individual complexes.

Sorting-free metabolic profiling uncovers the vulnerability of fatty acid β-oxidation in in vitro quiescence models

Quiescent cancer cells are rare nondiving cells with the unique ability to evade chemotherapies and resume cell division after treatment. Despite the associated risk of cancer recurrence, how cells can reversibly switch between rapid proliferation and quiescence remains a long-standing open question. By developing a unique methodology for the cell sorting-free separation of metabolic profiles in cell subpopulations in vitro, we unraveled metabolic characteristics of quiescent cells that are largely invariant to basal differences in cell types and quiescence-inducing stimuli. Consistent with our metabolome-based analysis, we show that impairing mitochondrial fatty acid β-oxidation (FAO) can induce apoptosis in quiescence-induced cells and hamper their return to proliferation. Our findings suggest that in addition to mediating energy and redox balance, FAO can play a role in preventing the buildup of toxic intermediates during transitioning to quiescence. Uncovering metabolic strategies to enter, maintain, and exit quiescence can reveal fundamental principles in cell plasticity and new potential therapeutic targets beyond cancer.

A Hypothesis Concerning the role of PPAR family on Cardiac Energetics in Adriamycin-Induced Cardiomyopathy

Adriamycin is an effective anti-neoplastic drug against a variety of cancer types. However, the drug causes adverse side-effects in a number of organ systems. Cardiomyopathy is one of the life-threatening side-effects of Adriamycin. In the current work, we have derived the possible involvement of PPAR family members in the development of Adriamycin-induced cardiomyopathy. Dysregulation of PPAR family by Adriamycin causes impairment in the transport and β-oxidation of fatty acids, the key substrate for ATP synthesis in heart. Evidences suggest that dysregulation of PPAR family results in alters the recruitment of glucose transporters. Furthermore, Hemeoxygenase-1 is a crucial enzyme regulating the iron homeostasis in the heart whose expression is regulated by PPAR family. Inverse relationship exists between the expression levels of PPARγ and hemeoxygenase-1. Adriamycin upregulates the expression of hemeoxygenase-1 which in turn disrupts the iron homeostasis in cardiomyocytes. Our molecular docking results show that Adriamycin has high affinity for iron binding sites of hemeoxygenase-1, thereby hindering formation of iron-sulfur complex. Lack of iron-sulfur complex impairs the electron transport chain. In addition, succinate dehydrogenase subunit A is downregulated by Adriamycin. The lack of this subunit uncouples Krebs cycle from ETC. Further lack of this subunit causes increases the concentration of succinate which further alters the mitochondrial membrane potential. Overall, in the present work we hypothesize that alteration in the expression of PPAR family members is one of the major causes of metabolic chaos and oxidative stress caused by Adriamycin during the development of cardiomyopathy.

The Role of Mitochondria in Metabolic Syndrome–Associated Cardiomyopathy

With the rapid development of society, the incidence of metabolic syndrome (MS) is increasing rapidly. Evidence indicated that patients diagnosed with MS usually suffered from cardiomyopathy, called metabolic syndrome–associated cardiomyopathy (MSC). The clinical characteristics of MSC included cardiac hypertrophy and diastolic dysfunction, followed by heart failure. Despite many studies on this topic, the detailed mechanisms are not clear yet. As the center of cellular metabolism, mitochondria are crucial for maintaining heart function, while mitochondria dysfunction plays a vital role through mechanisms such as mitochondrial energy deprivation, calcium disorder, and ROS (reactive oxygen species) imbalance during the development of MSC. Accordingly, in this review, we will summarize the characteristics of MSC and especially focus on the mechanisms related to mitochondria. In addition, we will update new therapeutic strategies in this field.

Mitochondrial Lipids: From Membrane Organization to Apoptotic Facilitation

Mitochondria are the most complex intracellular organelles, their function combining energy production for survival and apoptosis facilitation for death. Such a multivariate physiology is structurally and functionally reflected upon their membrane configuration and lipid composition. Mitochondrial double membrane lipids, with cardiolipin as the protagonist, show an impressive level of complexity that is mandatory for maintenance of mitochondrial health and protection from apoptosis. Given that lipidomics is an emerging field in cancer research and that mitochondria are the organelles with the most important role in malignant maintenance knowledge of the mitochondrial membrane, lipid physiology in health is mandatory. In this review, we will thus describe the delicate nature of the healthy mitochondrial double membrane and its role in apoptosis. Emphasis will be given on mitochondrial membrane lipids and the changes that they undergo during apoptosis induction and progression.

Fat and Protein Combat Triggers Immunological Weapons of Innate and Adaptive Immune Systems to Launch Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second-most common neurodegenerative disease in the world, affecting up to 10 million people. This disease mainly happens due to the loss of dopaminergic neurons accountable for memory and motor function. Partial glucocerebrosidase enzyme deficiency and the resultant excess accumulation of glycosphingolipids and alpha-synuclein (α-syn) aggregation have been linked to predominant risk factors that lead to neurodegeneration and memory and motor defects in PD, with known and unknown causes. An increasing body of evidence uncovers the role of several other lipids and their association with α-syn aggregation, which activates the innate and adaptive immune system and sparks brain inflammation in PD. Here, we review the emerging role of a number of lipids, i.e., triglyceride (TG), diglycerides (DG), glycerophosphoethanolamines (GPE), polyunsaturated fatty acids (PUFA), sphingolipids, gangliosides, glycerophospholipids (GPL), and cholesterols, and their connection with α-syn aggregation as well as the induction of innate and adaptive immune reactions that trigger neuroinflammation in PD.

Adipose tissue-heart crosstalk as a novel target for treatment of cardiometabolic diseases

Cardiometabolic disorders, such as diabetes, obesity, or metabolic syndrome, are often considered as key comorbidities, leading to the development of different forms of cardiovascular diseases such as heart failure or diabetic cardiomyopathy. Although the causal relationship between the pathophysiological status of white adipose tissue (WAT) and cardiac lipotoxicity is still elusive, elevated lipolytic rate in WAT has been demonstrated to participate in the overall augmentation of plasma lipid levels, as observed in most of the patients suffering from heart failure. In the present overview, we discuss current therapeutic approaches, as well as new treatment options targeting lipolysis and cardiac lipid metabolism in different forms of heart failure and diabetic cardiomyopathy.

Dietary Intake and Serum Selenium Levels Influence the Outcome of HTLV-1 Infection

Human T cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP), as the most common neurological emersion related to HTLV-1, is a debilitating and lifelong treating disease with no definitive treatment. Furthermore, it has been determined that dietary compositions (inflammatory and anti-inflammatory) and some micronutrients (such as vitamin D and selenium) have an effect on inflammatory and immune processes and with this background; the study was done to compare the nutritional status between age- and sex-matched with infected and non-infected HTLV-1. In a multi-center setting, 70 healthy controls (HCs), 35 asymptomatic carriers (ACs), and 35 HAM/TSP patients were recruited in the HTLV-1 Foundation, Ghaem Hospital, Mashhad University of Medical Sciences, Mashhad, Iran. Nutritional status including anthropometric indices, dietary (micro- and macronutrient) intake, and serum vitamin D, vitamin B12, zinc, and selenium were measured. In anthropometric indices, mean waist circumference (WC) in the carrier group was significantly higher than the patient and the control groups (p = 0.008). In the dietary intake, the patient group received less energy, protein, mono-unsaturated fatty acids (MUFA), and oleic, but more fat than the HTLV-1 carrier and control groups, and these differences were remarkable in three groups (p = 0.002, 0.005, 0.001, 0.01, and 0.001, respectively), whereas the carrier group received more saturated fatty acid and less poly-unsaturated fatty acids (PUFA), linoleic, and linolenic than patient and control groups with a different significant (p = 0.01, 0.007, 0.005, and 0.006, respectively) in three groups. In micronutrient intake, although selenium, zinc, and vitamins B12 and D were lower in the patient group than the carrier and control group, however, no significant differences were observed. In comparison with micronutrient serum concentrations, vitamins B12 and D and selenium in the patient group were lower than the carrier and control groups, but statistically, the considerable difference was found only in the selenium concentration (p = 0.001). The study showed that there were differences in dietary intake (including energy, macronutrients, and fatty acids), WC, and selenium serum levels between HAM/TSP patients and HTLV-1 carriers, suggesting that nutritional statues influence the inflammatory immune response in HTLV-1 infection.

Inhibition of Stearoyl-CoA Desaturase by Sterculic Oil Reduces Proliferation and Induces Apoptosis in Prostate Cancer Cell Lines

Prostate cancer (PCa) is a common type of cancer affecting male population. PCa treatments have side effects and are temporarily effective, so new therapeutic options are being investigated. Due to the high demand of energy for cell proliferation, an increase in the expression and activity of lipogenic enzymes such as the stearoyl-CoA desaturase (SCD) have been observed in PCa. Sterculic acid, contained in the seed's oil of Malvales, is a natural inhibitor of SCD. The objective of our investigation was to evaluate the effects of sterculic oil (SO) from Sterculia apetala seeds on proliferation, cell cycle and apoptosis in prostate cancer cells. SO was administered to PC3 and LNCaP cells, and to prostate normal cells; cell viability, cell cycle, apoptosis, SCD gene and protein expression and enzymatic activity were analyzed. SO administration (4 mM sterculic acid) diminished cell viability in LNCaP and PC3 cells, arrested cell cycle in G2 and promoted apoptosis. SO diminished SCD enzymatic activity with no effects on gene nor protein expression. Our results suggest that SO might offer benefits as an adjuvant in hormonal and chemotherapy prostate cancer treatments. This is the first study to analyze the effect of SO on cancer cells.

Pharmacological inhibition of adipose tissue adipose triglyceride lipase by Atglistatin prevents catecholamine-induced myocardial damage

AIMS

Heart failure (HF) is characterized by an overactivation of β-adrenergic signalling that directly contributes to impairment of myocardial function. Moreover, β-adrenergic overactivation induces adipose tissue lipolysis, which may further worsen the development of HF. Recently, we demonstrated that adipose tissue-specific deletion of adipose triglyceride lipase (ATGL) prevents pressure-mediated HF in mice. In this study, we investigated the cardioprotective effects of a new pharmacological inhibitor of ATGL, Atglistatin, predominantly targeting ATGL in adipose tissue, on catecholamine-induced cardiac damage.

METHODS AND RESULTS

Male 129/Sv mice received repeated injections of isoproterenol (ISO, 25 mg/kg BW) to induce cardiac damage. Five days prior to ISO application, oral Atglistatin (2 mmol/kg diet) or control treatment was started. Two and twelve days after the last ISO injection cardiac function was analysed by echocardiography. The myocardial deformation was evaluated using speckle-tracking-technique. Twelve days after the last ISO injection, echocardiographic analysis revealed a markedly impaired global longitudinal strain, which was significantly improved by the application of Atglistatin. No changes in ejection fraction were observed. Further studies included histological-, WB-, and RT-qPCR-based analysis of cardiac tissue, followed by cell culture experiments and mass spectrometry-based lipidome analysis. ISO application induced subendocardial fibrosis and a profound pro-apoptotic cardiac response, as demonstrated using an apoptosis-specific gene expression-array. Atglistatin treatment led to a dramatic reduction of these pro-fibrotic and pro-apoptotic processes. We then identified a specific set of fatty acids (FAs) liberated from adipocytes under ISO stimulation (palmitic acid, palmitoleic acid, and oleic acid), which induced pro-apoptotic effects in cardiomyocytes. Atglistatin significantly blocked this adipocytic FA secretion.

CONCLUSION

This study demonstrates cardioprotective effects of Atglistatin in a mouse model of catecholamine-induced cardiac damage/dysfunction, involving anti-apoptotic and anti-fibrotic actions. Notably, beneficial cardioprotective effects of Atglistatin are likely mediated by non-cardiac actions, supporting the concept that pharmacological targeting of adipose tissue may provide an effective way to treat cardiac dysfunction.

How the brain fights fatty acids' toxicity

Neurons spurn hydrogen-rich fatty acids for energizing oxidative ATP synthesis, contrary to other cells. This feature has been mainly attributed to a lower yield of ATP per reduced oxygen, as compared to glucose. Moreover, the use of fatty acids as hydrogen donor is accompanied by severe β-oxidation-associated ROS generation. Neurons are especially susceptible to detrimental activities of ROS due to their poor antioxidative equipment. It is also important to note that free fatty acids (FFA) initiate multiple harmful activities inside the cells, particularly on phosphorylating mitochondria. Several processes enhance FFA-linked lipotoxicity in the cerebral tissue. Thus, an uptake of FFA from the circulation into the brain tissue takes place during an imbalance between energy intake and energy expenditure in the body, a situation similar to that during metabolic syndrome and fat-rich diet. Traumatic or hypoxic brain injuries increase hydrolytic degradation of membrane phospholipids and, thereby elevate the level of FFA in neural cells. Accumulation of FFA in brain tissue is markedly associated with some inherited neurological disorders, such as Refsum disease or X-linked adrenoleukodystrophy (X-ALD). What are strategies protecting neurons against FFA-linked lipotoxicity? Firstly, spurning the β-oxidation pathway in mitochondria of neurons. Secondly, based on a tight metabolic communication between neurons and astrocytes, astrocytes donate metabolites to neurons for synthesis of antioxidants. Further, neuronal autophagy of ROS-emitting mitochondria combined with the transfer of degradation-committed FFA for their disposal in astrocytes, is a potent protective strategy against ROS and harmful activities of FFA. Finally, estrogens and neurosteroids are protective as triggers of ERK and PKB signaling pathways, consequently initiating the expression of various neuronal survival genes via the formation of cAMP response element-binding protein (CREB).

High-fructose diet initially promotes increased aortic wall thickness, liver steatosis, and cardiac histopathology deterioration, but does not increase body fat index

BACKGROUND

Dietary fats and fructose have been responsible for inducing obesity and body tissues damage due to the consequence of metabolic syndrome through several mechanisms. The body fat index (BFI) is one of the anthropometric measures used to detect obesity in rats. This study aims to examine the correlation between high-fat high-fructose diet and liver steatosis cell count, early atherosclerosis characteristics, and BFI in Sprague Dawley Rats.

DESIGN AND METHODS

This was an experimental design using 2 groups of 12-weeks-old Sprague Dawley (SD) rats. The control group received a standard diet and tap water beverages for 17 weeks. The intervention group was fed with high-fat diet from modified AIN 93-M and additional 30% fructose drink. We analyzed the foam cell count, aortic wall thickness, cardiac histopathology, and liver steatosis cell count after the sacrifice process.

RESULTS

The rats in the intervention group had a higher aortic wall thickness, liver steatosis, and foam cell count (+125%, p<0.01; +317%, p<0.01 and +165%, p<0.01 respectively) compared to the control group. The intervention group also showed higher mononuclear inflammatory and hypertrophic cell count. A significant positive correlation was found between dietary fructose with premature atherosclerosis by increasing foam cell count (r=0.66) and aortic wall thickness (r=0.68). In addition, 30% dietary fructose increased liver steatosis (r =0.69) and mononuclear inflammatory cardiac cell count (r=0.61). Interestingly, the intervention had no effect on BFI (p>0.5; r=0.13).

CONCLUSIONS

Dietary fat and fructose consumption for 17 weeks promote atherosclerosis, liver steatosis, and cardiac histopathology alteration without increasing BFI.

Investigation of cardiolipin oxidation products as a new endpoint for oxidative stress in C. elegans by means of online two-dimensional liquid chromatography and high-resolution mass spectrometry

The investigation of neurodegenerative and age-related diseases is a highly relevant topic in current research. Especially oxidative stress is thought to be the common underlying mechanism in diseases such as Parkinson's or Alzheimer's disease. The nematode Caenorhabditis elegans (C. elegans) is a prominent model organism, which is often used for such investigations and has gained extensive recognition in research regarding the linkage of reactive oxygen species (ROS) and neurodegeneration. Not only studies regarding genomics and proteomics have been increasingly conducted, also the number of studies based on the lipidome is rising. The phospholipid class of cardiolipin (CL) is a unique lipid class, which is exclusively located in mitochondria and is therefore of great relevance regarding oxidative stress and associated diseases. CL oxidation products have become a prominent marker for oxidative stress in various organisms. However, the CL distribution in the nematode C. elegans is still scarcely known on the molecular level and oxidation products have not yet been identified. In this work, we demonstrate the importance of CL distribution and the applicability of CL oxidation products as a sensitive marker for oxidative stress in C. elegans. For this reason, the CL distribution was determined by means of online two-dimensional liquid chromatography hyphenated with high-resolution mass spectrometry (2D-LC/HRMS). Subsequently, worms were treated with tert-butyl hydroperoxide (tBOOH) in order to provoke oxidative stress and induce the artificial formation of oxidized CL. We were able to detect increasing amounts of CL oxidation products of highly unsaturated CL species in a concentration-dependent manner. This finding emphasizes the great potential of CL oxidation products as a sensitive marker substance of oxidative stress in C. elegans, which is not only directly linked to mitochondria function but also favourable to other oxidative stress markers in terms of the needed sample material, relative substance stability and specificity of the oxidation site.

Metabolic Alterations Caused by Defective Cardiolipin Remodeling in Inherited Cardiomyopathies

The heart is the most energy-consuming organ in the human body. In heart failure, the homeostasis of energy supply and demand is endangered by an increase in cardiomyocyte workload, or by an insufficiency in energy-providing processes. Energy metabolism is directly associated with mitochondrial redox homeostasis. The production of toxic reactive oxygen species (ROS) may overwhelm mitochondrial and cellular ROS defense mechanisms in case of heart failure. Mitochondria are essential cell organelles and provide 95% of the required energy in the heart. Metabolic remodeling, changes in mitochondrial structure or function, and alterations in mitochondrial calcium signaling diminish mitochondrial energy provision in many forms of cardiomyopathy. The mitochondrial respiratory chain creates a proton gradient across the inner mitochondrial membrane, which couples respiration with oxidative phosphorylation and the preservation of energy in the chemical bonds of ATP. Akin to other mitochondrial enzymes, the respiratory chain is integrated into the inner mitochondrial membrane. The tight association with the mitochondrial phospholipid cardiolipin (CL) ensures its structural integrity and coordinates enzymatic activity. This review focuses on how changes in mitochondrial CL may be associated with heart failure. Dysfunctional CL has been found in diabetic cardiomyopathy, ischemia reperfusion injury and the aging heart. Barth syndrome (BTHS) is caused by an inherited defect in the biosynthesis of cardiolipin. Moreover, a dysfunctional CL pool causes other types of rare inherited cardiomyopathies, such as Sengers syndrome and Dilated Cardiomyopathy with Ataxia (DCMA). Here we review the impact of cardiolipin deficiency on mitochondrial functions in cellular and animal models. We describe the molecular mechanisms concerning mitochondrial dysfunction as an incitement of cardiomyopathy and discuss potential therapeutic strategies.

Early disruption of nerve mitochondrial and myelin lipid homeostasis in obesity-induced diabetes

Diabetic neuropathy is a major complication of diabetes. Current treatment options alleviate pain but do not stop the progression of the disease. At present, there are no approved disease-modifying therapies. Thus, developing more effective therapies remains a major unmet medical need. Seeking to better understand the molecular mechanisms driving peripheral neuropathy, as well as other neurological complications associated with diabetes, we performed spatiotemporal lipidomics, biochemical, ultrastructural, and physiological studies on PNS and CNS tissue from multiple diabetic preclinical models. We unraveled potentially novel molecular fingerprints underlying nerve damage in obesity-induced diabetes, including an early loss of nerve mitochondrial (cardiolipin) and myelin signature (galactosylceramide, sulfatide, and plasmalogen phosphatidylethanolamine) lipids that preceded mitochondrial, myelin, and axonal structural/functional defects; started in the PNS; and progressed to the CNS at advanced diabetic stages. Mechanistically, we provided substantial evidence indicating that these nerve mitochondrial/myelin lipid abnormalities are (surprisingly) not driven by hyperglycemia, dysinsulinemia, or insulin resistance, but rather associate with obesity/hyperlipidemia. Importantly, our findings have major clinical implications as they open the door to novel lipid-based biomarkers to diagnose and distinguish different subtypes of diabetic neuropathy (obese vs. nonobese diabetics), as well as to lipid-lowering therapeutic strategies for treatment of obesity/diabetes-associated neurological complications and for glycemic control.

Death by lipids: The role of small nucleolar RNAs in metabolic stress

Excess fatty acid accumulation in nonadipose tissues leads to cell dysfunction and cell death that is linked to the pathogenesis of inherited and acquired human diseases. Study of this process, known as lipotoxicity, has provided new insights into the regulation of lipid homeostasis and has revealed new molecular pathways involved in lipid-induced cellular stress. The discovery that disruption of specific small nucleolar RNAs protects against fatty acid-induced cell death and remodels metabolism in vivo opens new opportunities for understanding how nutrient signals influence cellular and systemic metabolic homeostasis through RNA biology.

Analysis of artificially oxidized cardiolipins and monolyso-cardiolipins via liquid chromatography/high-resolution mass spectrometry and Kendrick mass defect plots after hydrophilic interaction liquid chromatography based sample preparation

RATIONALE

Cardiolipins (CL) are a special lipid class which plays a main role in energy metabolism in mitochondria and is involved in apoptosis. In contrast to other glycerophospholipids, they contain four fatty acyl residues which results in a high structural diversity. Oxidation, for example by reactive oxygen species, or lyso forms such as monolyso-CL (MLCL), increases this diversity. Mass spectrometric analysis and computational identification of CL, MLCL and their oxidation products is therefore a challenging task.

METHODS

In order to distinguish CL, MLCL and their oxidation products, a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed. A hydrophilic interaction liquid chromatography (HILIC)-based solid-phase extraction (SPE) clean-up approach was developed for CL enrichment. Graphical analysis of CL, MLCL and their oxidation products was carried out by a three-dimensional Kendrick mass defect (3D-KMD) plot module, as well as a refined lipid search module of the open-source metabolomics data mining software MZmine 2.

RESULTS

The HILIC-based SPE clean-up enabled complete separation of polar and nonpolar lipid classes. A yeast (Saccharomyces cerevisiae) lipid extract, which was artificially oxidized by means of the Fenton reaction, was analyzed by the developed LC/MS/MS method. CL species with differences in chain length and degree of unsaturation have been separated by high-performance liquid chromatography (HPLC). In total 66 CL, MLCL and oxidized species have been identified utilizing 3D-KMD plots in combination with database matching using MZmine 2. For further characterization of annotated species, MS/MS experiments have been utilized.

CONCLUSIONS

3D-KMD plots capturing chromatographic and high-resolution mass spectrometry data have been successfully used for graphical identification of CL, MLCL as well as their oxidized species. Therefore, we chose multiple KMD bases such as hydrogen and oxygen to visualize the degree of unsaturation and oxidation capturing chromatographic data by means of a color-coded paint scale as the third dimension. In combination with database matching, the analysis of low concentrated lipid species in complex samples has been significantly improved.

Proliferation of C6 glioma cells requires the phospholipid remodeling enzyme tafazzin independent of cardiolipin composition

The mitochondrial phospholipid (CL) has been linked to mitochondrial and cellular functions. It has been postulated that the composition of CL is of impact for mitochondrial energy metabolism and cell proliferation. Although a correlation between CL composition and proliferation could be demonstrated for several cell types, evidence for a causal relationship remains obscure. Here, we applied two independent approaches, i) supplementation of fatty acids and ii) knock-out of the phospholipid remodeling enzyme tafazzin, to manipulate CL composition and analyzed the response on proliferation of C6 glioma cells. Both strategies caused substantial changes in the distribution of cellular fatty acids as well as in the distribution of fatty acids incorporated in CL that were accompanied by changes of the composition of molecular CL species. These changes did not correlate with cell proliferation. However, knock-out of tafazzin caused dramatic reduction in proliferation of C6 glioma cells independent of CL composition. The mechanism of tafazzin-dependent restriction of proliferation remains unclear. Among the various fatty acids administered only palmitic acid restricted cell proliferation by induction of cell death.

Myocardial Adaptation in Pseudohypoxia: Signaling and Regulation of mPTP via Mitochondrial Connexin 43 and Cardiolipin

Therapies intended to mitigate cardiovascular complications cannot be applied in practice without detailed knowledge of molecular mechanisms. Mitochondria, as the end-effector of cardioprotection, represent one of the possible therapeutic approaches. The present review provides an overview of factors affecting the regulation processes of mitochondria at the level of mitochondrial permeability transition pores (mPTP) resulting in comprehensive myocardial protection. The regulation of mPTP seems to be an important part of the mechanisms for maintaining the energy equilibrium of the heart under pathological conditions. Mitochondrial connexin 43 is involved in the regulation process by inhibition of mPTP opening. These individual cardioprotective mechanisms can be interconnected in the process of mitochondrial oxidative phosphorylation resulting in the maintenance of adenosine triphosphate (ATP) production. In this context, the degree of mitochondrial membrane fluidity appears to be a key factor in the preservation of ATP synthase rotation required for ATP formation. Moreover, changes in the composition of the cardiolipin’s structure in the mitochondrial membrane can significantly affect the energy system under unfavorable conditions. This review aims to elucidate functional and structural changes of cardiac mitochondria subjected to preconditioning, with an emphasis on signaling pathways leading to mitochondrial energy maintenance during partial oxygen deprivation.

Proteolytic Control of Lipid Metabolism

Synthesis and regulation of lipid levels and identities is critical for a wide variety of cellular functions, including structural and morphological properties of organelles, energy storage, signaling, and stability and function of membrane proteins. Proteolytic cleavage events regulate and/or influence some of these lipid metabolic processes and as a result help modulate their pleiotropic cellular functions. Proteins involved in lipid regulation are proteolytically cleaved for the purpose of their relocalization, processing, turnover, and quality control, among others. The scope of this review includes proteolytic events governing cellular lipid dynamics. After an initial discussion of the classic example of sterol regulatory element-binding proteins, our focus will shift to the mitochondrion, where a range of proteolytic events are critical for normal mitochondrial phospholipid metabolism and enforcing quality control therein. Recently, mitochondrial phospholipid metabolic pathways have been implicated as important for the proliferative capacity of cancers. Thus, the assorted proteases that regulate, monitor, or influence the activity of proteins that are important for phospholipid metabolism represent attractive targets to be manipulated for research purposes and clinical applications.

Resveratrol prevents palmitic-acid-induced cardiomyocyte contractile impairment

Long-chain saturated fatty acids, especially palmitic acid (PA), contribute to cardiomyocyte lipotoxicity. This study tests the effects of PA on adult rat cardiomyocyte contractile function and proteins associated with calcium regulating cardiomyocyte contraction and relaxation. Adult rat cardiomyocytes were pretreated with resveratrol (Resv) and then treated with PA. For the reversal study, cardiomyocytes were incubated with PA prior to treatment with Resv. Cardiomyocyte contractility, ratio of rod- to round-shaped cardiomyocytes, and Hoechst staining were used to measure functional and morphological changes in cardiomyocytes. Protein expression of sarco-endoplasmic reticulum ATPase 2a (SERCA2a), native phospholamban (PLB) and phosphorylated PLB (pPLB ser16 and pPLB thr17), and troponin I (TnI) and phosphorylated TnI (pTnI) were measured. SERCA2a activity was also measured. Our results show that PA (200 μM) decreased the rate of cardiomyocyte relaxation, reduced the number of rod-shaped cardiomyocytes, and increased the number of cells with condensed nuclei; pre-treating cardiomyocytes with Resv significantly prevented these changes. Post-treatment with Resv did not reverse morphological changes induced by PA. Protein expression levels of SERCA2a, PLB, pPLBs, TnI, and pTnI were unchanged by PA or Resv. SERCA2a activity assay showed that V_max and Iono ratio were increased with PA and pre-treatment with Resv prevented this increase. In conclusion, our results show that Resv protect cardiomyocytes from contractile dysfunction induced by PA.

High-density lipoprotein ameliorates palmitic acid-induced lipotoxicity and oxidative dysfunction in H9c2 cardiomyoblast cells via ROS suppression

Background

High levels circulating saturated fatty acids are associated with diabetes, obesity and hyperlipidemia. In heart, the accumulation of saturated fatty acids has been determined to play a role in the development of heart failure and diabetic cardiomyopathy. High-density lipoprotein (HDL) has been reported to possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, anti-oxidative and anti-inflammatory activities. However, the underlying mechanisms are still largely unknown. Therefore, the aim of the present study is to test whether HDL could protect palmitic acid (PA)-induced cardiomyocyte injury and explore the possible mechanisms.

Results

H9c2 cells were pretreated with HDL (50–100 μg/ml) for 2 h followed by PA (0.5 mM) for indicated time period. Our results showed that HDL inhibited PA-induced cell death in a dose-dependent manner. Moreover, HDL rescued PA-induced ROS generation and the phosphorylation of JNK which in turn activated NF-κB-mediated inflammatory proteins expressions. We also found that PA impaired the balance of BCL₂ family proteins, destabilized mitochondrial membrane potential, and triggered subsequent cytochrome c release into the cytosol and activation of caspase 3. These detrimental effects were ameliorated by HDL treatment.

Conclusion

PA-induced ROS accumulation and results in cardiomyocyte apoptosis and inflammation. However, HDL attenuated PA-induced lipotoxicity and oxidative dysfunction via ROS suppression. These results may provide insight into a possible molecular mechanism underlying HDL suppression of the free fatty acid-induced cardiomyocyte apoptosis.

Decrease in membrane phospholipids unsaturation correlates with myocardial diastolic dysfunction

Increase in saturated fatty acid (SFA) content in membrane phospholipids dramatically affects membrane properties and cellular functioning. We sought to determine whether exogenous SFA from the diet directly affects the degree of membrane phospholipid unsaturation in adult hearts and if these changes correlate with contractile dysfunction. Although both SFA-rich high fat diets (HFDs) and monounsaturated FA (MUFA)-rich HFDs cause the same degree of activation of myocardial FA uptake, triglyceride turnover, and mitochondrial FA oxidation and accumulation of toxic lipid intermediates, the former induced more severe diastolic dysfunction than the latter, which was accompanied with a decrease in membrane phospholipid unsaturation, induction of unfolded protein response (UPR), and a decrease in the expression of Sirt1 and stearoyl-CoA desaturase-1 (SCD1), catalyzing the conversion of SFA to MUFA. When the SFA supply in the heart overwhelms the cellular capacity to use it for energy, excess exogenous SFA channels to membrane phospholipids, leading to UPR induction, and development of diastolic dysfunction.

Mitochondria Released by Apoptotic Cell Death Initiate Innate Immune Responses

In solid organ transplantation, cell death arising from ischemia/reperfusion leads to the release of several damage-associated molecular patterns derived from mitochondria. Mitochondrial damage-associated molecular patterns (mtDAMPs) initiate proinflammatory responses, but it remains unknown whether the mode of cell death affects the inflammatory properties of mitochondria. Murine and human cell lines induced to selectively undergo apoptosis and necroptosis were used to examine the extracellular release of mitochondria during programmed cell death. Mitochondria purified from healthy, apoptotic, and necroptotic cells were used to stimulate macrophage inflammasome responses in vitro and neutrophil chemotaxis in vivo. Inhibition of specific mtDAMPs was performed to identify those responsible for macrophage inflammasome activation. A rat liver transplant model was used to identify apoptotic and necroptotic cell death in graft tissue following ischemia/reperfusion. Both apoptotic and necroptotic cell death occur in parallel in graft tissue. Apoptotic cells released more mitochondria than necroptotic cells. Moreover, mitochondria from apoptotic cells were significantly more inflammatory in terms of macrophage inflammasome activation and neutrophil recruitment. Inhibition of cellular synthesis of cardiolipin, a mitochondria-specific lipid and mtDAMP, significantly reduced the inflammasome-activating properties of apoptosis-derived mitochondria. Mitochondria derived from apoptotic cells are potent activators of innate immune responses, whereas mitochondria derived from healthy or necroptotic cells are significantly less inflammatory. Cardiolipin appears to be a key mtDAMP-regulating inflammasome activation by mitochondria. Methods of inhibiting apoptotic cell death in transplant grafts may be beneficial for reducing graft inflammation and transplant allosensitization.

Omega-3 and omega-6 fatty acid differentially impact cardiolipin remodeling in activated macrophage

Background

The macrophage plays an important role in innate immunity to induce immune responses. Lipid replacement therapy has been shown to change the lipid compositions of mitochondria and potentially becomes an alternative to reduce the inflammatory response.

Methods

We examined the effects of omega-6 arachidonic acid (AA), omega-3 eicosapentaenoic acid (EPA), and omega-3 docosahexaenoic acid (DHA) supplementation on the activated the macrophage cell line RAW264.7 via KdO₂-lipid A (KLA). The mitochondrial cardiolipin (CL) and monolysocardiolipin (MLCL) were analyzed by LC-MS.

Results

After macrophage activation by KLA, CL shifted to saturated species, but did not affect the quantity of CL. Inhibition of delta 6 desaturase also resulted in the same trend of CL species shift. We further examined the changes in CL and MLCL species induced by polyunsaturated fatty acid supplementation during inflammation. After supplementation of AA, EPA and DHA, the MLCL/CL ratio increased significantly in all treatments. The percentages of the long-chain species highly elevated and those of short-chain species reduced in both CL and MLCL.

Conclusions

Comparisons of AA, EPA and DHA supplementation revealed that the 20-carbon EPA (20:5) and AA (20:4) triggered higher incorporation and CL remodeling efficiency than 22-carbon DHA (22:6). EPA supplementation not only efficiently extended the chain length of CL but also increased the unsaturation of CL.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0845-y) contains supplementary material, which is available to authorized users.

Palmitate lipotoxicity in enteric glial cells: Lipid remodeling and mitochondrial ROS are responsible for cyt c release outside mitochondria

Enteric glial cells (EGCs) are components of the enteric nervous system, an organized structure that controls gut functions. EGCs may be vulnerable to different agents, such as bacterial infections that could alter the intestinal epithelial barrier, allowing bacterial toxins and/or other agents possessing intrinsic toxic effect to access cells. Palmitate, known to exhibit lipotoxicity, is released in the gut during the digestion process. In this study, we investigated the lipotoxic effect of palmitate in cultured EGCs, with particular emphasis on palmitate-dependent intracellular lipid remodeling. Palmitate but not linoleate altered mitochondrial and endoplasmic reticulum lipid composition. In particular, the levels of phosphatidic acid, key precursor of phospholipid synthesis, increased, whereas those of mitochondrial cardiolipin (CL) decreased; in parallel, phospholipid remodeling was induced. CL remodeling (chains shortening and saturation) together with palmitate-triggered mitochondrial burst, caused cytochrome c (cyt c) detachment from its CL anchor and accumulation in the intermembrane space as soluble pool. Palmitate decreased mitochondrial membrane potential and ATP levels, without mPTP opening. Mitochondrial ROS permeation into the cytosol and palmitate-induced ER stress activated JNK and p38, culminating in Bim and Bax overexpression, factors known to increase the outer mitochondrial membrane permeability. Overall, in EGCs palmitate produced weakening of cyt c-CL interactions and favoured the egress of the soluble cyt c pool outside mitochondria to trigger caspase-3-dependent viability loss. Elucidating the mechanisms of palmitate lipotoxicity in EGCs may be relevant in gut pathological conditions occurring in vivo such as those following an insult that may damage the intestinal epithelial barrier.

Chlorella diet alters mitochondrial cardiolipin contents differentially in organs of Danio rerio analyzed by a lipidomics approach

The zebrafish (Danio rerio) is an important and widely used vertebrate model organism for the study of human diseases which include disorders caused by dysfunctional mitochondria. Mitochondria play an essential role in both energy metabolism and apoptosis, which are mediated through a mitochondrial phospholipid cardiolipin (CL). In order to examine the cardiolipin profile in the zebrafish model, we developed a CL analysis platform by using liquid chromatography-mass spectrometry (LC-MS). Meanwhile, we tested whether chlorella diet would alter the CL profile in the larval fish, and in various organs of the adult fish. The results showed that chlorella diet increased the chain length of CL in larval fish. In the adult zebrafish, the distribution patterns of CL species were similar between the adult brain and eye tissues, and between the heart and muscles. Interestingly, monolyso-cardiolipin (MLCL) was not detected in brain and eyes but found in other examined tissues, indicating a different remodeling mechanism to maintain the CL integrity. While the adult zebrafish were fed with chlorella for four weeks, the CL distribution showed an increase of the species of saturated acyl chains in the brain and eyes, but a decrease in the other organs. Moreover, chlorella diet led to a decrease of MLCL percentage in organs except the non-MLCL-containing brain and eyes. The CL analysis in the zebrafish provides an important tool for studying the mechanism of mitochondria diseases, and may also be useful for testing medical regimens targeting against the Barth Syndrome.

Role of Cardiolipin in Mitochondrial Signaling Pathways

The phospholipid cardiolipin (CL) is an essential constituent of mitochondrial membranes and plays a role in many mitochondrial processes, including respiration and energy conversion. Pathological changes in CL amount or species composition can have deleterious consequences for mitochondrial function and trigger the production of reactive oxygen species. Signaling networks monitor mitochondrial function and trigger an adequate cellular response. Here, we summarize the role of CL in cellular signaling pathways and focus on tissues with high-energy demand, like the heart. CL itself was recently identified as a precursor for the formation of lipid mediators. We highlight the concept of CL as a signaling platform. CL is exposed to the outer mitochondrial membrane upon mitochondrial stress and CL domains serve as a binding site in many cellular signaling events. During mitophagy, CL interacts with essential players of mitophagy like Beclin 1 and recruits the autophagic machinery by its interaction with LC3. Apoptotic signaling pathways require CL as a binding platform to recruit apoptotic factors such as tBid, Bax, caspase-8. CL required for the activation of the inflammasome and plays a role in inflammatory signaling. As changes in CL species composition has been observed in many diseases, the signaling pathways described here may play a general role in pathology.

Dysfunctional HDL in diabetes mellitus and its role in the pathogenesis of cardiovascular disease

Coronary artery disease, the leading cause of death in the developed and developing countries, is prevalent in diabetes mellitus with 68% cardiovascular disease (CVD)-related mortality. Epidemiological studies suggested inverse correlation between HDL and CVD occurrence. Therefore, low HDL concentration observed in diabetic patients compared to non-diabetic individuals was thought to be one of the primary causes of increased risks of CVD. Efforts to raise HDL level via CETP inhibitors, Torcetrapib and Dalcetrapib, turned out to be disappointing in outcome studies despite substantial increases in HDL-C, suggesting that factors beyond HDL concentration may be responsible for the increased risks of CVD. Therefore, recent studies have focused more on HDL function than on HDL levels. The metabolic environment in diabetes mellitus condition such as hyperglycemia-induced advanced glycation end products, oxidative stress, and inflammation promote HDL dysfunction leading to greater risks of CVD. This review discusses dysfunctional HDL as one of the mechanisms of increased CVD risks in diabetes mellitus through adversely affecting components that support HDL function in cholesterol efflux and LDL oxidation. The dampening of reverse cholesterol transport, a key process that removes cholesterol from lipid-laden macrophages in the arterial wall, leads to increased risks of CVD in diabetic patients. Therapeutic approaches to keep diabetes under control may benefit patients from developing CVD.

High density lipoprotein (HDL) reverses palmitic acid induced energy metabolism imbalance by switching CD36 and GLUT4 signaling pathways in cardiomyocyte

In our previous study palmitic acid (PA) induced lipotoxicity and switches energy metabolism from CD36 to GLUT4 in H9c2 cells. Low level of high density lipoprotein (HDL) is an independent risk factor for cardiac hypertrophy. Therefore, we in the present study investigated whether HDL can reverse PA induced lipotoxicity in H9c2 cardiomyoblast cells. In this study, we treated H9c2 cells with PA to create a hyperlipidemia model in vitro and analyzed for CD36 and GLUT4 metabolic pathway proteins. CD36 metabolic pathway proteins (phospho-AMPK, SIRT1, PGC1α, PPARα, CPT1β, and CD36) were decreased by high PA (150 and 200 μg/μl) concentration. Interestingly, expression of GLUT4 metabolic pathway proteins (p-PI3K and pAKT) were increased at low concentration (50 μg/μl) and decreased at high PA concentration. Whereas, phospho-PKCζ, GLUT4 and PDH proteins expression was increased in a dose dependent manner. PA treated H9c2 cells were treated with HDL and analyzed for cell viability. Results showed that HDL treatment induced cell proliferation efficiency in PA treated cells. In addition, HDL reversed the metabolic effects of PA: CD36 translocation was increased and reduced GLUT4 translocation, but HDL treatment significantly increased CD36 metabolic pathway proteins and reduced GLUT4 pathway proteins. Rat neonatal cardiomyocytes showed similar results. In conclusion, HDL reversed palmatic acid-induced lipotoxicity and energy metabolism imbalance in H9c2 cardiomyoblast cells and in neonatal rat cardiomyocyte cells.

Palmitate impairs angiogenesis via suppression of cathepsin activity

Angiogenesis requires the interaction of multiple variable factors to promote endothelial cell adhesion, migration and survival. Palmitate, a free fatty acid, exhibits an anti-angiogenic effect via interference with endothelial cell function, whereas cysteine proteases are important in protein turnover and are termed positive modulators of neovascularization. However, the association between these two factors regarding the regulation of human endothelial cell function remains to be elucidated. By using cell counting kit-8, the Transwell method and an annexin V-fluorescein isothiocyanate/propidium iodide apoptosis detection kit, the present study reported that high levels of palmitate result in a significant decrease in endothelial cell proliferation and invasion, and induced cell apoptosis; cathepsin L and S inhibitors may suppress palmitate-induced apoptosis. Conversely, the results of the cathepsin L and S activity assay and reverse-transcription-quantitative polymerase chain reaction indicated that palmitate inhibited cathepsin-induced endothelial cell invasion, partially via suppressing the expression and activity of cathepsin L and S. The findings of the present study suggested that the potent anti-angiogenic properties of palmitate may be mediated by cysteine proteases.

Copper Homeostasis for the Developmental Progression of Intraerythrocytic Malarial Parasite

Malaria is one of the world’s most devastating diseases, particularly in the tropics. In humans, Plasmodium falciparum lives mainly within red blood cells, and malaria pathogenesis depends on the red blood cells being infected with the parasite. Non-esterified fatty acids (NEFAs), including cis-9-octadecenoic acid, and phospholipids have been critical for complete parasite growth in serum-free culture, although the efficacy of NEFAs in sustaining the growth of P. falciparum has varied markedly. Hexadecanoic acid and trans-9-octadecenoic acid have arrested development of the parasite, in association with down-regulation of genes encoding copper-binding proteins. Selective removal of Cu⁺ ions has blockaded completely the ring–trophozoite–schizont progression of the parasite. The importance of copper homeostasis for the developmental progression of P. falciparum has been confirmed by inhibition of copper-binding proteins that regulate copper physiology and function by associating with copper ions. These data have provided strong evidence for a link between healthy copper homeostasis and successive developmental progression of P. falciparum. Perturbation of copper homeostasis may be, thus, instrumental in drug and vaccine development for the malaria medication. We review the importance of copper homeostasis in the asexual growth of P. falciparum in relation to NEFAs, copper-binding proteins, apoptosis, mitochondria, and gene expression.

Barth syndrome cardiomyopathy

Barth syndrome (BTHS) is an inherited form of cardiomyopathy, caused by a mutation within the gene encoding the mitochondrial transacylase tafazzin. Tafazzin is involved in the biosynthesis of the unique phospholipid cardiolipin (CL), which is almost exclusively found in mitochondrial membranes. CL directly interacts with a number of essential protein complexes in the mitochondrial membranes including the respiratory chain, mitochondrial metabolite carriers, and proteins, involved in shaping mitochondrial morphology. Here we describe, how in BTHS CL deficiency causes changes in the morphology of mitochondria, structural changes in the respiratory chain, decreased respiration, and increased generation of reactive oxygen species. A large number of cellular and animal models for BTHS have been established to elucidate how mitochondrial dysfunction induces sarcomere disorganization and reduced contractility, resulting in dilated cardiomyopathy in vivo.

Cardiolipin promotes electron transport between ubiquinone and complex I to rescue PINK1 deficiency

Parkinson’s disease–causing mutations in PINK1 yield mitochondrial defects including inefficient electron transport between complex I and ubiquinone. Vos et al. show that genetic and pharmacological inhibition of fatty acid synthase bypass these complex I defects in fly, mouse, and human Parkinson’s disease models.

PINK1 is mutated in Parkinson’s disease (PD), and mutations cause mitochondrial defects that include inefficient electron transport between complex I and ubiquinone. Neurodegeneration is also connected to changes in lipid homeostasis, but how these are related to PINK1-induced mitochondrial dysfunction is unknown. Based on an unbiased genetic screen, we found that partial genetic and pharmacological inhibition of fatty acid synthase (FASN) suppresses toxicity induced by PINK1 deficiency in flies, mouse cells, patient-derived fibroblasts, and induced pluripotent stem cell–derived dopaminergic neurons. Lower FASN activity in PINK1 mutants decreases palmitate levels and increases the levels of cardiolipin (CL), a mitochondrial inner membrane–specific lipid. Direct supplementation of CL to isolated mitochondria not only rescues the PINK1-induced complex I defects but also rescues the inefficient electron transfer between complex I and ubiquinone in specific mutants. Our data indicate that genetic or pharmacologic inhibition of FASN to increase CL levels bypasses the enzymatic defects at complex I in a PD model.

Stearoyl CoA desaturase-1: New insights into a central regulator of cancer metabolism

The processes of cell proliferation, cell death and differentiation involve an intricate array of biochemical and morphological changes that require a finely tuned modulation of metabolic pathways, chiefly among them is fatty acid metabolism. The critical participation of stearoyl CoA desaturase-1 (SCD1), the fatty acyl Δ9-desaturing enzyme that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA), in the mechanisms of replication and survival of mammalian cells, as well as their implication in the biological alterations of cancer have been actively investigated in recent years. This review examines the growing body of evidence that argues for a role of SCD1 as a central regulator of the complex synchronization of metabolic and signaling events that control cellular metabolism, cell cycle progression, survival, differentiation and transformation to cancer.

Cell Death and Heart Failure in Obesity: Role of Uncoupling Proteins

Metabolic diseases such as obesity, metabolic syndrome, and type II diabetes are often characterized by increased reactive oxygen species (ROS) generation in mitochondrial respiratory complexes, associated with fat accumulation in cardiomyocytes, skeletal muscle, and hepatocytes. Several rodents studies showed that lipid accumulation in cardiac myocytes produces lipotoxicity that causes apoptosis and leads to heart failure, a dynamic pathological process. Meanwhile, several tissues including cardiac tissue develop an adaptive mechanism against oxidative stress and lipotoxicity by overexpressing uncoupling proteins (UCPs), specific mitochondrial membrane proteins. In heart from rodent and human with obesity, UCP2 and UCP3 may protect cardiomyocytes from death and from a state progressing to heart failure by downregulating programmed cell death. UCP activation may affect cytochrome c and proapoptotic protein release from mitochondria by reducing ROS generation and apoptotic cell death. Therefore the aim of this review is to discuss recent findings regarding the role that UCPs play in cardiomyocyte survival by protecting against ROS generation and maintaining bioenergetic metabolism homeostasis to promote heart protection.

Inhibition of fatty acid desaturation is detrimental to cancer cell survival in metabolically compromised environments

BACKGROUND

Enhanced macromolecule biosynthesis is integral to growth and proliferation of cancer cells. Lipid biosynthesis has been predicted to be an essential process in cancer cells. However, it is unclear which enzymes within this pathway offer the best selectivity for cancer cells and could be suitable therapeutic targets.

RESULTS

Using functional genomics, we identified stearoyl-CoA desaturase (SCD), an enzyme that controls synthesis of unsaturated fatty acids, as essential in breast and prostate cancer cells. SCD inhibition altered cellular lipid composition and impeded cell viability in the absence of exogenous lipids. SCD inhibition also altered cardiolipin composition, leading to the release of cytochrome C and induction of apoptosis. Furthermore, SCD was required for the generation of poly-unsaturated lipids in cancer cells grown in spheroid cultures, which resemble those found in tumour tissue. We also found that SCD mRNA and protein expression is elevated in human breast cancers and predicts poor survival in high-grade tumours. Finally, silencing of SCD in prostate orthografts efficiently blocked tumour growth and significantly increased animal survival.

CONCLUSIONS

Our data implicate lipid desaturation as an essential process for cancer cell survival and suggest that targeting SCD could efficiently limit tumour expansion, especially under the metabolically compromised conditions of the tumour microenvironment.

Cardiac mitochondrial energy metabolism in heart failure: Role of cardiolipin and sirtuins

Mitochondrial oxidation of fatty acids accounts for the majority of cardiac ATP production in the heart. Fatty acid utilization by cardiac mitochondria is controlled at the level of fatty acid uptake, lipid synthesis, mobilization and mitochondrial import and oxidation. Consequently defective mitochondrial function appears to be central to the development of heart failure. Cardiolipin is a key mitochondrial phospholipid required for the activity of the electron transport chain. In heart failure, loss of cardiolipin and tetralinoleoylcardiolipin helps to fuel the generation of excessive reactive oxygen species that are a by-product of inefficient mitochondrial electron transport chain complexes I and III. In this vicious cycle, reactive oxygen species generate lipid peroxides and may, in turn, cause oxidation of cardiolipin catalyzed by cytochrome c leading to cardiomyocyte apoptosis. Hence, preservation of cardiolipin and mitochondrial function may be keys to the prevention of heart failure development. In this review, we summarize cardiac energy metabolism and the important role that fatty acid uptake and metabolism play in this process and how defects in these result in heart failure. We highlight the key role that cardiolipin and sirtuins play in cardiac mitochondrial β-oxidation. In addition, we review the potential of pharmacological modulation of cardiolipin through the polyphenolic molecule resveratrol as a sirtuin-activator in attenuating mitochondrial dysfunction. Finally, we provide novel experimental evidence that resveratrol treatment increases cardiolipin in isolated H9c2 cardiac myocytes and tetralinoleoylcardiolipin in the heart of the spontaneously hypertensive rat and hypothesize that this leads to improvement in mitochondrial function. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.