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

The Bace1 product sAPPβ induces ER stress and inflammation and impairs insulin signaling

Objective -secretase/-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a key enzyme involved in Alzheimer's disease that has recently been implicated in insulin-independent glucose uptake in myotubes. However, it is presently unknown whether BACE1 and the product of its activity, soluble APPsAPPcontribute to lipid-induced inflammation and insulin resistance in skeletal muscle cells. Materials/Methods Studies were conducted in mouse C2C12 myotubes, skeletal muscle from Bace1-/-mice and mice treated with sAPP and adipose tissue and plasma from obese and type 2 diabetic patients. Results We show that BACE1 inhibition or knockdown attenuates palmitate-induced endoplasmic reticulum (ER) stress, inflammation, and insulin resistance and prevents the reduction in Peroxisome Proliferator- Activated Receptor Co-activator 1 (PGC-1) and fatty acid oxidation caused by palmitate in myotubes. The effects of palmitate on ER stress, inflammation, insulin resistance, PGC-1 down-regulation, and fatty acid oxidation were mimicked by soluble APP in vitro. BACE1 expression was increased in subcutaneous adipose tissue of obese and type 2 diabetic patients and this was accompanied by a decrease in PGC-1 mRNA levels and by an increase in sAPPplasma levels of obese type 2 diabetic patients compared to obese non-diabetic subjects. Acute sAPP administration to mice reduced PGC-1 levels and increased inflammation in skeletal muscle and decreased insulin sensitivity. Conclusions Collectively, these findings indicate that the BACE1 product sAPP is a key determinant in ER stress, inflammation and insulin resistance in skeletal muscle and gluconeogenesis in liver

Estrès del reticle endoplasmàtic, inflamació i resistència a la insulina en cèl•lules musculars esquelètiques

[cat] L’objectiu d’aquesta tesi doctoral ha estat elucidar nous mecanismes moleculars que expliquessin els efectes antiinflamatoris i antidiabètics de l’oleat. A més, també s’ha volgut aprofundir en l’estudi dels mecanismes moleculars mitjançant els quals l’activació del PPARß/d evita processos inflamatoris i de resistència a la insulina. Així doncs, el primer objectiu d’aquesta tesi doctoral ha estat estudiar si l’oleat és capaç d’exercir els seus efectes antiinflamatoris i antidiabètics mitjançant mecanismes que modulin l’estrès del RE en cèl•lules musculars esquelètiques. A més, tenint en compte que l’AMPK inhibeix l’estrès del RE, en aquest estudi es va voler elucidar si l’oleat, mitjançant l’activació de l’AMPK, evitava l’estrès del RE responsable de l’aparició de la inflamació i RI induïda pel palmitat. Els resultats obtinguts mostren que l’oleat evita l’estrès del RE induït pel palmitat en miotubs murins C2C12 i humans LHCN-M2. Els efectes de l’oleat sobre l’estrès del RE, així com els seus efectes antiinflamatoris i antidiabètics semblen involucrar la cinasa AMPK, atès que la inhibició farmacològica i molecular d’aquesta proteïna, va revertir els efectes de l’oleat sobre els nivells d’expressió gènica dels marcadors d’estrès del RE, d’inflamació i de RI. En resum, les dades d’aquest estudi indiquen que l’oleat evita l’estrès del RE, la inflamació i la RI produïda pel palmitat en cèl•lules musculars esquelètiques, mitjançant mecanismes que involucren l’activació de l’AMPK. El segon objectiu d’aquesta tesi doctoral ha estat determinar si l’activació de PPARß/d és capaç d’evitar la inflamació i la RI en múscul esquelètic mitjançant mecanismes que involucren l’estrès del RE, així com elucidar si la cinasa AMPK està involucrada en aquest procés. Els resultats obtinguts evidencien que l’activació farmacològica de PPARß/d redueix l’estrès del RE induït per lípids en cèl•lules musculars esquelètiques. Tanmateix, l’activació farmacològica de PPARß/d també va evitar l’estrès del RE, la inflamació i la RI induïda per coneguts activadors d’estrès del RE en cèl•lules musculars esquelètiques mitjançant mecanismes que involucraven l’AMPK. Com a resum, podem concloure que l’activació de PPARß/d evita la inflamació i la RI induïdes per l’estrès del RE en cèl•lules musculars esquelètiques mitjançant mecanismes que involucren l’activació de l’AMPK. Per tant, els resultats obtinguts en aquesta tesi doctoral destaquen el paper de l’AMPK com a proteïna clau a l’hora d’inhibir la inflamació i la RI secundària a l’estrès del RE. Així, podem proposar que el seguiment d’una dieta mediterrània, la qual conté l’oli d’oliva com a greix essencial, juntament amb la pràctica d’exercici físic, podria ser una bona estratègia per a la prevenció de la DM2. De la mateixa manera que l’oleat, l’activació farmacològica de PPARß/d inhibeix l’estrès del RE responsable de la inflamació i la RI en múscul esquelètic mitjançant l’activació de l’AMPK. Així doncs, els resultats d’aquesta tesi doctoral aporten nous mecanismes antidiabètics de l’oleat i dels activadors de PPARß/d que podrien ser bones estratègies futures per a la prevenció de la RI i de la DM2.[eng] Although it is known that oleate has many beneficial effects for the prevention of type 2 diabetes mellitus, the mechanisms by which oleate improves insulin resistance are not completely known. The first objective of this thesis was to examine whether oleate could prevent palmitate-induced endoplasmic reticulum (ER) stress, which is involved in the link between lipid-induced inflammation and insulin resistance. The studies were conducted in mouse C2C12 and human LHCN-M2 myotubes. Palmitate increased the levels of ER stress markers, whereas oleate did not. In palmitate-exposed cells incubated with a lower concentration of oleate, the effects of palmitate were prevented. Moreover, the ability of oleate to prevent palmitate-induced ER stress, inflammation and insulin resistance was reversed in the presence of the AMP-activated protein kinase (AMPK) inhibitor, compound C, or by overexpression of a dominant negative AMPK construct. Overall, these findings indicate that oleate prevents ER stress, inflammation and insulin resistance in palmitate-exposed skeletal muscle cells by activating AMPK. The second objective of this thesis was to examine whether peroxisome proliferator-activated receptor (PPAR)ß/d could prevent ER stress-associated inflammation and insulin resistance in skeletal muscle cells. Studies were conducted in mouse C2C12 and human LHCN-M2 myotubes, and in skeletal muscle from wild-type and PPARß/d-deficient mice and mice exposed to a high-fat diet. The PPARß/d agonist GW501516 prevented lipid-induced ER stress in mouse and human myotubes and in skeletal muscle of mice fed a high-fat diet. PPARß/d activation also prevented thapsigargin- and tunicamycin-induced ER stress in human and murine skeletal muscle cells. In agreement with this, PPARß/d activation prevented ER stress-associated inflammation and insulin resistance, and glucose-intolerant PPARß/d-deficient mice showed increased phosphorylated levels of inositol-requiring 1 transmembrane kinase/endonuclease-1a in skeletal muscle. Our findings demonstrate that PPARß/d activation prevents ER stress through the activation of AMPK, and the subsequent inhibition of extracellular-signal-regulated kinase (ERK)1/2 due to the inhibitory crosstalk between AMPK and ERK1/2, since overexpression of a dominant negative AMPK construct (K45R) reversed the effects attained by PPARß/d activation. These findings indicate that PPARß/d prevents ER stress, inflammation and insulin resistance in skeletal muscle cells by activating AMPK

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