CerS6-dependent ceramide synthesis in hypothalamic neurons promotes ER/mitochondrial stress and impairs glucose homeostasis in obese mice

Dysregulation of hypothalamic ceramides has been associated with disrupted neuronal pathways in control of energy and glucose homeostasis. However, the specific ceramide species promoting neuronal lipotoxicity in obesity have remained obscure. Here, we find increased expression of the C$_{16:0}$ ceramide-producing ceramide synthase (CerS)6 in cultured hypothalamic neurons exposed to palmitate in vitro and in the hypothalamus of obese mice. Conditional deletion of CerS6 in hypothalamic neurons attenuates high-fat diet (HFD)-dependent weight gain and improves glucose metabolism. Specifically, CerS6 deficiency in neurons expressing pro-opiomelanocortin (POMC) or steroidogenic factor 1 (SF-1) alters feeding behavior and alleviates the adverse metabolic effects of HFD feeding on insulin sensitivity and glucose tolerance. POMC-expressing cell-selective deletion of CerS6 prevents the diet-induced alterations of mitochondrial morphology and improves cellular leptin sensitivity. Our experiments reveal functions of CerS6-derived ceramides in hypothalamic lipotoxicity, altered mitochondrial dynamics, and ER/mitochondrial stress in the deregulation of food intake and glucose metabolism in obesity

Unraveling the Role of Sirtuin 2 in Metabolic Homeostasis

CORREIA, Marta Quatorze - Unraveling the Role of Sirtuin 2 in Metabolic Homeostasis. Coimbra : [s.n.], 2016. Dissertação de Mestrado.Sirtuin 2 (SIRT2) is one of the seven members (SIRT1-7) of the sirtuin family. Sirtuins are NAD+-dependent deacetylases with homology to the silent information regulator 2 (Sir2), found to extend longevity in yeast. Although it is still controversial whether sirtuins play a role in longevity, increasing evidence supports that they modulate homeostasis by sensing energy needs and restoring homeostasis during stress conditions. Metabolic diseases, such as obesity and type 2 diabetes, are one of the main causes of mortality and morbidity worldwide and their prevalence is increasing at an alarming rate. SIRT2 is particularly expressed in metabolic relevant tissues, such as adipose tissue, liver and brain, and has emerged as an important regulator of mammalian metabolism. SIRT2 regulates key processes of the lipid and glucose metabolism, such as adipogenesis, gluconeogenesis, fatty acid oxidation, lipogenesis and insulin sensitivity. Moreover, SIRT2 expression is modulated by energy availability, being downregulated during states of energy excess and overexpressed under low-energy conditions. Taking into account these previous findings, the present study aimed to evaluate the role of SIRT2 in the regulation of metabolic homeostasis in vivo. This study provides the first comprehensive metabolic characterization of SIRT2 knockout (SIRT2-KO) mice. SIRT2-KO mice developed no obvious phenotype when fed a normal chow diet (CD). Interestingly, when subjected to metabolic stress induced by short-term high fat diet (HFD) feeding, SIRT2-KO mice developed severe metabolic abnormalities, including increased body weight gain and energy intake, hyperglycemia, hypertriglyceridemia, glucose intolerance and insulin resistance. Thus, our data suggest that SIRT2 plays a key role during metabolic stress conditions. Taking into account the present findings, SIRT2 modulation may be a potential therapeutic strategy to counteract the metabolic dysfunction associated with the early onset of metabolic disorders.A Sirtuína 2 (SIRT2) é uma das sete proteínas que constituem a família das sirtuínas (SIRT1-7). As sirtuínas são desacetilases dependentes de NAD+, homólogas do gene regulador de informação silenciosa 2 (Sir2), conhecido por prolongar a longevidade em leveduras. É cada vez mais evidente que as sirtuínas modulam a homeostasia detectando necessidades energéticas e restaurando a homeostasia em condições de stress. A obesidade e a diabetes tipo 2 são duas das maiores causas mundiais de mortalidade e a sua prevalência tem vindo a aumentar a um ritmo acelerado. A SIRT2 encontra-se particularmente expressa em órgãos com relevância metabólica, tais como o tecido adiposo, o fígado e o cérebro, e o seu papel na regulação do metabolismo tem vindo a ser alvo de grande atenção. Sabe-se que a SIRT2 regula processos tais como a adipogénese, gliconeogénese, oxidação de ácidos gordos, lipogénese e sensibilidade à insulina. Além disso, a expressão da SIRT2 é modulada pela disponibilidade energética, sendo suprimida em condições de excesso de energia e estimulada em situações de energia limitada. Tendo em conta o conhecimento até agora adquirido, o objectivo deste estudo é avaliar o papel da SIRT2 na regulação do metabolismo in vivo. Este é o primeiro estudo a revelar a caracterização metabólica de murganhos knockout para SIRT2 (SIRT2-KO). Estes murganhos não desenvolveram um fenótipo metabólico significativo quando alimentados com uma dieta normal. No entanto, quando sujeitos a uma condição de stresse causada por uma dieta rica em lípidos durante 4 semanas, estes animais desenvolveram alterações metabólicas, tais como ganho de peso e consumo energético aumentados, hiperglicemia, hipertrigliceridemia, intolerância à glucose e resistência à insulina. Assim, a SIRT2 parece desempenhar um papel importante durante situações de stresse metabólico. Os resultados aqui apresentados sugerem a modulação da SIRT2 como uma estratégia promissora na prevenção da disfunção metabólica associada à fase inicial de desenvolvimento de doenças metabólic

CerS6-dependent ceramide synthesis in hypothalamic neurons promotes ER/mitochondrial stress and impairs glucose homeostasis in obese mice

Abstract Dysregulation of hypothalamic ceramides has been associated with disrupted neuronal pathways in control of energy and glucose homeostasis. However, the specific ceramide species promoting neuronal lipotoxicity in obesity have remained obscure. Here, we find increased expression of the C16:0 ceramide-producing ceramide synthase (CerS)6 in cultured hypothalamic neurons exposed to palmitate in vitro and in the hypothalamus of obese mice. Conditional deletion of CerS6 in hypothalamic neurons attenuates high-fat diet (HFD)-dependent weight gain and improves glucose metabolism. Specifically, CerS6 deficiency in neurons expressing pro-opiomelanocortin (POMC) or steroidogenic factor 1 (SF-1) alters feeding behavior and alleviates the adverse metabolic effects of HFD feeding on insulin sensitivity and glucose tolerance. POMC-expressing cell-selective deletion of CerS6 prevents the diet-induced alterations of mitochondrial morphology and improves cellular leptin sensitivity. Our experiments reveal functions of CerS6-derived ceramides in hypothalamic lipotoxicity, altered mitochondrial dynamics, and ER/mitochondrial stress in the deregulation of food intake and glucose metabolism in obesity