Ceramides and mitochondrial fatty acid oxidation in obesity

: Obesity is an epidemic, complex disease that is characterized by increased glucose, lipids, and low-grade inflammation in the circulation, among other factors. It creates the perfect scenario for the production of ceramide, the building block of the sphingolipid family of lipids, which is involved in metabolic disorders such as obesity, diabetes, and cardiovascular disease. In addition, obesity causes a decrease in fatty acid oxidation (FAO), which contributes to lipid accumulation within the cells, conferringmore susceptibility to cell dysfunction. C16:0 ceramide, a specific ceramide species, has been identified recently as the principal mediator of obesity-derived insulin resistance, impaired fatty acid oxidation, and hepatic steatosis. In this review, we have sought to cover the importance of the ceramide species and their metabolism, the main ceramide signaling pathways in obesity, and the link between C16:0 ceramide, FAO, and obesity.¿Fucho, R., Casals, N., Serra, D., Herrero, L. Ceramides and mitochondrial fatty acid oxidation in obesity. FASEB J. 31, 000-000 (2017). www.fasebj.or

Estratègies de modulació de l'oxidació d'àcids grassos com a tractament per combatre l'obesitat

L'estil de vida actual, amb dietes d'alt contingut calòric i falta d'exercici físic, fa que la incidència d'obesitat s'incrementi notablement. Augmentar la degradació de greixos o bé reduir la ingesta calòrica poden ser potencials estratègies terapèutiques. L'enzim carnitina palmitoïltransferasa I (CPT1) és el pas limitant de l'oxidació dels àcids grassos. En aquest article, es mostra com la modulació de la seva activitat en diferents teixits, com el fetge, el teixit adipós o l'hipotàlem, pot ser clau a l'hora d'augmentar la despesa energètica i controlar la ingesta d'aliments

Fatty acid metabolism and the basis of brown adipose tissue function

Obesity has reached epidemic proportions, leading to severe associated pathologies such as insulin resistance, cardiovascular disease, cancer and type 2 diabetes. Adipose tissue has become crucial due to its involvement in the pathogenesis of obesity-induced insulin resistance, and traditionally white adipose tissue has captured the most attention. However in the last decade the presence and activity of heat-generating brown adipose tissue (BAT) in adult humans has been rediscovered. BAT decreases with age and in obese and diabetic patients. It has thus attracted strong scientific interest, and any strategy to increase its mass or activity might lead to new therapeutic approaches to obesity and associated metabolic diseases. In this review we highlight the mechanisms of fatty acid uptake, trafficking and oxidation in brown fat thermogenesis. We focus on BAT's morphological and functional characteristics and fatty acid synthesis, storage, oxidation and use as a source of energy

Mitochondrial GSH determines the toxic or therapeutic potential of superoxide scavenging in steatohepatitis

BACKGROUND & AIMS: Steatohepatitis (SH) is associated with mitochondrial dysfunction and excessive production of superoxide, which can then be converted into H(2)O(2) by SOD2. Since mitochondrial GSH (mGSH) plays a critical role in H(2)O(2) reduction, we explored the interplay between superoxide, H(2)O(2), and mGSH in nutritional and genetic models of SH, which exhibit mGSH depletion. METHODS: We used isolated mitochondria and primary hepatocytes, as well as in vivo SH models showing mGSH depletion to test the consequences of superoxide scavenging. RESULTS: In isolated mitochondria and primary hepatocytes, superoxide scavenging by SOD mimetics or purified SOD decreased superoxide and peroxynitrite generation but increased H(2)O(2) following mGSH depletion, despite mitochondrial peroxiredoxin/thioredoxin defense. Selective mGSH depletion sensitized hepatocytes to cell death induced by SOD mimetics, and this was prevented by RIP1 kinase inhibition with necrostatin-1 or GSH repletion with GSH ethyl ester (GSHee). Mice fed the methionine-choline deficient (MCD) diet or MAT1A(-/-) mice exhibited reduced SOD2 activity; in vivo treatment with SOD mimetics increased liver damage, inflammation, and fibrosis, despite a decreased superoxide and 3-nitrotyrosine immunoreactivity, effects that were ameliorated by mGSH replenishment with GSHee, but not NAC. As a proof-of-principle of the detrimental role of superoxide scavenging when mGSH was depleted transgenic mice overexpressing SOD2 exhibited enhanced susceptibility to MCD-mediated SH. CONCLUSIONS: These findings underscore a critical role for mGSH in the therapeutic potential of superoxide scavenging in SH, and suggest that the combined approach of superoxide scavenging with mGSH replenishment may be important in SH

Enhanced fatty acid oxidation in adipocytes and macrophages reduces lipid-induced triglyceride accumulation and inflammation

Lipid overload in obesity and type 2 diabetes is associated with adipocyte dysfunction, inflammation, macrophage infiltration, and decreased fatty acid oxidation (FAO). Here, we report that the expression of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme in mitochondrial FAO, is higher in human adipose tissue macrophages than in adipocytes and that it is differentially expressed in visceral vs. subcutaneous adipose tissue in both an obese and a type 2 diabetes cohort. These observations led us to further investigate the potential role of CPT1A in adipocytes and macrophages. We expressed CPT1AM, a permanently active mutant form of CPT1A, in 3T3-L1 CARΔ1 adipocytes and RAW 264.7 macrophages through adenoviral infection. Enhanced FAO in palmitate-incubated adipocytes and macrophages reduced triglyceride content and inflammation, improved insulin sensitivity in adipocytes, and reduced endoplasmic reticulum stress and ROS damage in macrophages. We conclude that increasing FAO in adipocytes and macrophages improves palmitate-induced derangements. This indicates that enhancing FAO in metabolically relevant cells such as adipocytes and macrophages may be a promising strategy for the treatment of chronic inflammatory pathologies such as obesity and type 2 diabetes

Mitochondrial and autophagic alterations in skin fibroblasts from Parkinson disease patients with Parkin mutations.

PRKN encodes an E3-ubiquitin-ligase involved in multiple cell processes including mitochondrial homeostasis and autophagy. Previous studies reported alterations of mitochondrial function in fibroblasts from patients with PRKN mutation-associated Parkinson's disease (PRKN-PD) but have been only conducted in glycolytic conditions, potentially masking mitochondrial alterations. Additionally, autophagy flux studies in this cell model are missing.We analyzed mitochondrial function and autophagy in PRKN-PD skin-fibroblasts (n=7) and controls (n=13) in standard (glucose) and mitochondrial-challenging (galactose) conditions.In glucose, PRKN-PD fibroblasts showed preserved mitochondrial bioenergetics with trends to abnormally enhanced mitochondrial respiration that, accompanied by decreased CI, may account for the increased oxidative stress. In galactose, PRKN-PD fibroblasts exhibited decreased basal/maximal respiration vs. controls and reduced mitochondrial CIV and oxidative stress compared to glucose, suggesting an inefficient mitochondrial oxidative capacity to meet an extra metabolic requirement. PRKN-PD fibroblasts presented decreased autophagic flux with reduction of autophagy substrate and autophagosome synthesis in both conditions.The alterations exhibited under neuron-like oxidative environment (galactose), may be relevant to the disease pathogenesis potentially explaining the increased susceptibility of dopaminergic neurons to undergo degeneration. Abnormal PRKN-PD phenotype supports the usefulness of fibroblasts to model disease and the view of PD as a systemic disease where molecular alterations are present in peripheral tissues

Asmase Regulates autophagy and lysosomal membrane permeabilization and its inhibition prevents early stage nonalcoholic steatohepatitis

Background & Aims: Acid sphingomyelinase (ASMase) is activated in nonalcoholic steatohepatitis (NASH). However, ASMase's contribution to NASH is poorly understood and limited to hepatic steatosis and glucose metabolism. Here we examined ASMase's role in high fat diet (HFD)-induced NASH. Methods: Autophagy, endoplasmic reticulum (ER) stress and lysosomal membrane permeabilization (LMP) were determined in ASMase-/- mice fed HFD. The impact of pharmacological ASMase inhibition on NASH was analyzed in wild type mice fed HFD. Results: ASMase deficiency determined resistance to HFD or methionine and choline deficient diet-mediated hepatic steatosis. ASMase-/- mice were resistant to HFD-induced hepatic ER stress, but sensitive to tunicamycin-mediated ER stress and steatosis, indicating selectivity in the resistance of ASMase-/- mice to ER stress. Autophagic flux determined in the presence of rapamycin and/or chloroquine was lower in primary mouse hepatocytes (PMH) from ASMase-/- mice and accompanied by increased p62 levels, suggesting autophagic impairment. Moreover, autophagy suppression by chloroquine and brefeldinA caused ER stress in PMH from ASMase+/+ mice but not ASMase-/- mice. ASMase-/- PMH exhibited increased lysosomal cholesterol loading, decreased LMP and apoptosis resistance induced by O-methyl-serine dodecylamide hydrochloride or palmitic acid, effects that were reversed by decreasing cholesterol levels by the oxysterol 25-hydroxycholesterol. In vivo pharmacological ASMase inhibition by amitriptyline, a widely used tricyclic antidepressant, protected wild type mice against HFD- induced hepatic steatosis, fibrosis, and liver damage, effects indicative of early-stage NASH. Conclusions: These findings underscore a critical role for ASMase in diet-induced NASH and suggest the potential of amitriptyline as a treatment for patients with NASH

Liver CPT1A gene therapy reduces diet-induced hepatic steatosis in mice and highlights potential lipid biomarkers for human NAFLD

The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased drastically due to the global obesity pandemic but at present there are no approved therapies. Here, we aimed to revert high-fat diet (HFD)-induced obesity and NAFLD in mice by enhancing liver fatty acid oxidation (FAO). Moreover, we searched for potential new lipid biomarkers for monitoring liver steatosis in humans. We used adeno-associated virus (AAV) to deliver a permanently active mutant form of human carnitine palmitoyltransferase 1A (hCPT1AM), the key enzyme in FAO, in the liver of a mouse model of HFD-induced obesity and NAFLD. Expression of hCPT1AM enhanced hepatic FAO and autophagy, reduced liver steatosis, and improved glucose homeostasis. Lipidomic analysis in mice and humans before and after therapeutic interventions, such as hepatic AAV9-hCPT1AM administration and RYGB surgery, respectively, led to the identification of specific triacylglyceride (TAG) specie (C50:1) as a potential biomarker to monitor NAFFLD disease. To sum up, here we show for the first time that liver hCPT1AM gene therapy in a mouse model of established obesity, diabetes, and NAFLD can reduce HFD-induced derangements. Moreover, our study highlights TAG (C50:1) as a potential noninvasive biomarker that might be useful to monitor NAFLD in mice and humans

Disrupted mitochondrial and metabolic plasticity underlie comorbidity between age-Related and degenerative disorders as parkinson disease and type 2 diabetes mellitus.

Idiopathic Parkinson's disease (iPD) and type 2 diabetes mellitus (T2DM) are chronic, multisystemic, and degenerative diseases associated with aging, with eventual epidemiological co-morbidity and overlap in molecular basis. This study aims to explore if metabolic and mitochondrial alterations underlie the previously reported epidemiologic and clinical co-morbidity from a molecular level. To evaluate the adaptation of iPD to a simulated pre-diabetogenic state, we exposed primary cultured fibroblasts from iPD patients and controls to standard (5 mM) and high (25 mM) glucose concentrations to further characterize metabolic and mitochondrial resilience. iPD fibroblasts showed increased organic and amino acid levels related to mitochondrial metabolism with respect to controls, and these differences were enhanced in high glucose conditions (citric, suberic, and sebacic acids levels increased, as well as alanine, glutamate, aspartate, arginine, and ornithine amino acids; p-values between 0.001 and 0.05). The accumulation of metabolites in iPD fibroblasts was associated with (and probably due to) the concomitant mitochondrial dysfunction observed at enzymatic, oxidative, respiratory, and morphologic level. Metabolic and mitochondrial plasticity of controls was not observed in iPD fibroblasts, which were unable to adapt to different glucose conditions. Impaired metabolism and mitochondrial activity in iPD may limit energy supply for cell survival. Moreover, reduced capacity to adapt to disrupted glucose balance characteristic of T2DM may underlay the co-morbidity between both diseases. Conclusions: Fibroblasts from iPD patients showed mitochondrial impairment, resulting in the accumulation of organic and amino acids related to mitochondrial metabolism, especially when exposed to high glucose. Mitochondrial and metabolic defects down warding cell plasticity to adapt to changing glucose bioavailability may explain the comorbidity between iPD and T2DM

A Predominant Role for Parenchymal c-Jun Amino Terminal Kinase (JNK) in the Regulation of Systemic Insulin Sensitivity

It has been established that c-Jun N-terminal kinase 1 (JNK1) is essential to the pathogenesis of insulin resistance and type 2 diabetes. Although JNK influences inflammatory signaling pathways, it remains unclear whether its activity in macrophages contributes to adipose tissue inflammation and ultimately to the regulation of systemic metabolism. To address whether the action of this critical inflammatory kinase in bone marrow-derived elements regulates inflammatory responses in obesity and is sufficient and necessary for the deterioration of insulin sensitivity, we performed bone marrow transplantation studies with wild type and JNK1-deficient mice. These studies illustrated that JNK1-deficiency in the bone marrow-derived elements (BMDE) was insufficient to impact macrophage infiltration or insulin sensitivity despite modest changes in the inflammatory profile of adipose tissue. Only when the parenchymal elements lacked JNK1 could we demonstrate a significant increase in systemic insulin sensitivity. These data indicate that while the JNK1 activity in BMDE is involved in metabolic regulation and adipose milieu, it is epistatic to JNK1 activity in the parenchymal tissue for regulation of metabolic homeostasis