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1.
Mol Cell ; 81(18): 3820-3832.e7, 2021 09 16.
Artículo en Inglés | MEDLINE | ID: mdl-34233158

RESUMEN

A metabolic imbalance between lipid synthesis and degradation can lead to hepatic lipid accumulation, a characteristic of patients with non-alcoholic fatty liver disease (NAFLD). Here, we report that high-fat-diet-induced sterol regulatory element-binding protein (SREBP)-1c, a key transcription factor that regulates lipid biosynthesis, impairs autophagic lipid catabolism via altered H2S signaling. SREBP-1c reduced cystathionine gamma-lyase (CSE) via miR-216a, which in turn decreased hepatic H2S levels and sulfhydration-dependent activation of Unc-51-like autophagy-activating kinase 1 (ULK1). Furthermore, Cys951Ser mutation of ULK1 decreased autolysosome formation and promoted hepatic lipid accumulation in mice, suggesting that the loss of ULK1 sulfhydration was directly associated with the pathogenesis of NAFLD. Moreover, silencing of CSE in SREBP-1c knockout mice increased liver triglycerides, confirming the connection between CSE, autophagy, and SREBP-1c. Overall, our results uncover a 2-fold mechanism for SREBP-1c-driven hepatic lipid accumulation through reciprocal activation and inhibition of hepatic lipid biosynthesis and degradation, respectively.


Asunto(s)
Homólogo de la Proteína 1 Relacionada con la Autofagia/metabolismo , Hígado Graso/metabolismo , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/metabolismo , Animales , Autofagia , Homólogo de la Proteína 1 Relacionada con la Autofagia/genética , Homólogo de la Proteína 1 Relacionada con la Autofagia/fisiología , Línea Celular Tumoral , Dieta Alta en Grasa/efectos adversos , Hígado Graso/fisiopatología , Humanos , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Metabolismo de los Lípidos/fisiología , Lípidos/fisiología , Lipogénesis , Hígado/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Enfermedad del Hígado Graso no Alcohólico/metabolismo , Transducción de Señal/fisiología , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/genética , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/fisiología , Triglicéridos/metabolismo
2.
Pflugers Arch ; 476(2): 151-161, 2024 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-37940681

RESUMEN

Pancreatic beta cells utilize Ca2+ to secrete insulin in response to glucose. The glucose-dependent increase in cytosolic Ca2+ concentration ([Ca2+]C) activates a series of insulin secretory machinery in pancreatic beta cells. Therefore, the amount of insulin secreted in response to glucose is determined in a [Ca2+]C-dependent manner, at least within a moderate range. However, the demand for insulin secretion may surpass the capability of beta cells. Abnormal elevation of [Ca2+]C levels beyond the beta-cell endurance capacity can damage them by inducing endoplasmic reticulum (ER) stress and cell death programs such as apoptosis. Therefore, while Ca2+ is essential for the insulin secretory functions of beta cells, it could affect their survival at pathologically higher levels. Because an increase in beta-cell [Ca2+]C is inevitable under certain hazardous conditions, understanding the regulatory mechanism for [Ca2+]C is important. Therefore, this review discusses beta-cell function, survival, ER stress, and apoptosis associated with intracellular and ER Ca2+ homeostasis.


Asunto(s)
Células Secretoras de Insulina , Células Secretoras de Insulina/metabolismo , Señalización del Calcio , Insulina/metabolismo , Retículo Endoplásmico/metabolismo , Calcio/metabolismo , Glucosa/metabolismo
3.
Gastroenterology ; 164(3): 439-453, 2023 03.
Artículo en Inglés | MEDLINE | ID: mdl-36402191

RESUMEN

BACKGROUND & AIMS: Obesity predisposes to type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD), but underlying mechanisms are incompletely understood. Potassium channel tetramerization domain-containing protein 17 (Kctd17) levels are increased in livers from obese mice and humans. In this study, we investigated the mechanism of increased Kctd17 and whether it is causal to obesity-induced metabolic complications. METHODS: We transduced Rosa26-LSL-Cas9 knockin mice with AAV8-TBG-Cre (Control), AAV8-U6-Kctd17 sgRNA-TBG-Cre (L-Kctd17), AAV8-U6-Oga sgRNA-TBG-Cre (L-Oga), or AAV8-U6-Kctd17/Oga sgRNA-TBG-Cre (DKO). We fed mice a high-fat diet (HFD) and assessed for hepatic glucose and lipid homeostasis. We generated Kctd17, O-GlcNAcase (Oga), or Kctd17/Oga-knockout hepatoma cells by CRISPR-Cas9, and Kctd17-directed antisense oligonucleotide to test therapeutic potential in vivo. We analyzed transcriptomic data from patients with NAFLD. RESULTS: Hepatocyte Kctd17 expression was increased in HFD-fed mice due to increased Srebp1c activity. HFD-fed L-Kctd17 or Kctd17 antisense oligonucleotide-treated mice show improved glucose tolerance and hepatic steatosis, whereas forced Kctd17 expression caused glucose intolerance and hepatic steatosis even in lean mice. Kctd17 induced Oga degradation, resulting in increasing carbohydrate response element-binding protein (Chrebp) protein, so concomitant Oga knockout negated metabolic benefits of hepatocyte Kctd17 deletion. In patients with NAFLD, KCTD17 messenger RNA was positively correlated with expression of Chrebp target and other lipogenic genes. CONCLUSIONS: Srebp1c-induced hepatocyte Kctd17 expression in obesity disrupted glucose and lipid metabolism by stabilizing Chrebp, and may represent a novel therapeutic target for obesity-induced T2D and NAFLD.


Asunto(s)
Diabetes Mellitus Tipo 2 , Intolerancia a la Glucosa , Resistencia a la Insulina , Enfermedad del Hígado Graso no Alcohólico , Humanos , Animales , Ratones , Enfermedad del Hígado Graso no Alcohólico/metabolismo , Diabetes Mellitus Tipo 2/complicaciones , Resistencia a la Insulina/fisiología , Factores de Transcripción/genética , Hígado/metabolismo , Hepatocitos/metabolismo , Obesidad/complicaciones , Glucosa/metabolismo , Dieta Alta en Grasa , Ratones Endogámicos C57BL , Proteínas Adaptadoras Transductoras de Señales/metabolismo
4.
Proc Natl Acad Sci U S A ; 115(52): E12228-E12234, 2018 12 26.
Artículo en Inglés | MEDLINE | ID: mdl-30530672

RESUMEN

There is a growing appreciation for a fundamental connection between lipid metabolism and the immune response. Macrophage phagocytosis is a signature innate immune response to pathogen exposure, and cytoplasmic membrane expansion is required to engulf the phagocytic target. The sterol regulatory element binding proteins (SREBPs) are key transcriptional regulatory proteins that sense the intracellular lipid environment and modulate expression of key genes of fatty acid and cholesterol metabolism to maintain lipid homeostasis. In this study, we show that TLR4-dependent stimulation of macrophage phagocytosis requires mTORC1-directed SREBP-1a-dependent lipid synthesis. We also show that the phagocytic defect in macrophages from SREBP-1a-deficient mice results from decreased interaction between membrane lipid rafts and the actin cytoskeleton, presumably due to reduced accumulation of newly synthesized fatty acyl chains within major membrane phospholipids. We show that mTORC1-deficient macrophages also have a phagocytic block downstream from TLR4 signaling, and, interestingly, the reduced level of phagocytosis in both SREBP-1a- and mTORC1-deficient macrophages can be restored by ectopic SREBP-1a expression. Taken together, these observations indicate SREBP-1a is a major downstream effector of TLR4-mTORC1 directed interactions between membrane lipid rafts and the actin cytoskeleton that are required for pathogen-stimulated phagocytosis in macrophages.


Asunto(s)
Lípidos/biosíntesis , Macrófagos/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , Fagocitosis , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/metabolismo , Receptor Toll-Like 4/metabolismo , Animales , Células Cultivadas , Diana Mecanicista del Complejo 1 de la Rapamicina/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/genética , Receptor Toll-Like 4/genética
5.
Int J Mol Sci ; 22(11)2021 Jun 05.
Artículo en Inglés | MEDLINE | ID: mdl-34198910

RESUMEN

Changes in structural and functional neuroplasticity have been implicated in various neurological disorders. Sterol regulatory element-binding protein (SREBP)-1c is a critical regulatory molecule of lipid homeostasis in the brain. Recently, our findings have shown the potential involvement of SREBP-1c deficiency in the alteration of novel modulatory molecules in the hippocampus and occurrence of schizophrenia-like behaviors in mice. However, the possible underlying mechanisms, related to neuronal plasticity in the hippocampus, are yet to be elucidated. In this study, we investigated the hippocampus-dependent memory function and neuronal architecture of hippocampal neurons in SREBP-1c knockout (KO) mice. During the passive avoidance test, SREBP-1c KO mice showed memory impairment. Based on Golgi staining, the dendritic complexity, length, and branch points were significantly decreased in the apical cornu ammonis (CA) 1, CA3, and dentate gyrus (DG) subregions of the hippocampi of SREBP-1c KO mice, compared with those of wild-type (WT) mice. Additionally, significant decreases in the dendritic diameters were detected in the CA3 and DG subregions, and spine density was also significantly decreased in the apical CA3 subregion of the hippocampi of KO mice, compared with that of WT mice. Alterations in the proportions of stubby and thin-shaped dendritic spines were observed in the apical subcompartments of CA1 and CA3 in the hippocampi of KO mice. Furthermore, the corresponding differential decreases in the levels of SREBP-1 expression in the hippocampal subregions (particularly, a significant decrease in the level in the CA3) were detected by immunofluorescence. This study suggests that the contributions of SREBP-1c to the structural plasticity of the mouse hippocampus may have underlain the behavioral alterations. These findings offer insights into the critical role of SREBP-1c in hippocampal functioning in mice.


Asunto(s)
Espinas Dendríticas/genética , Memoria/fisiología , Neuronas/metabolismo , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/genética , Animales , Región CA1 Hipocampal/metabolismo , Región CA1 Hipocampal/fisiología , Espinas Dendríticas/patología , Regulación de la Expresión Génica/genética , Hipocampo/metabolismo , Hipocampo/patología , Humanos , Ratones , Ratones Noqueados , Plasticidad Neuronal/genética , Neuronas/patología , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/deficiencia
6.
Biochem Biophys Res Commun ; 529(1): 70-76, 2020 08 13.
Artículo en Inglés | MEDLINE | ID: mdl-32560822

RESUMEN

Pathogenic bacteria acquire the acquisition of iron from the host to ensure their survival. Salmonella spp. utilizes siderophores, including salmochelin, for high affinity aggressive import of iron. Although the iroBCDEN operon is reportedly responsible for the production and the transport of salmochelin, the molecular mechanisms underlying the regulation of its gene expression have not yet been characterized. Here, we analyzed the expression pattern of iroB using the lacZY transcriptional reporter system and determined the transcription start site in response to iron availability using primer extension analysis. We further examined the regulation of iroB expression by the ferric uptake regulator (Fur), a key regulatory protein involved in the maintenance of iron homeostasis in various bacteria, including Salmonella. Using sequence analysis followed by a gel shift assay, we verified that the Fur box lies within the promoter region of iroBCDE. The Fur box contained the consensus sequence (GATATTGGTAATTATTATC) and overlapped with the -10-element region. The expression of iroB was repressed by Fur in the presence of iron, as determined using an in vitro transcription assay. Therefore, we found that the iron acquisition system is regulated in a Fur-dependent manner in Salmonella.


Asunto(s)
Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Enterobactina/análogos & derivados , Glucosiltransferasas/genética , Glucosiltransferasas/metabolismo , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Salmonella typhimurium/genética , Salmonella typhimurium/metabolismo , Proteínas Bacterianas/química , Secuencia de Bases , Ciencias Bioconductuales , Secuencia de Consenso , ADN Bacteriano/genética , Enterobactina/metabolismo , Regulación Bacteriana de la Expresión Génica , Humanos , Hierro/metabolismo , Regiones Promotoras Genéticas , Unión Proteica , Multimerización de Proteína , Proteínas Represoras/química , Sideróforos/metabolismo , Transcripción Genética
7.
Proc Natl Acad Sci U S A ; 114(45): 11926-11931, 2017 11 07.
Artículo en Inglés | MEDLINE | ID: mdl-29078297

RESUMEN

Insulin resistance, a key etiological factor in metabolic syndrome, is closely linked to ectopic lipid accumulation and increased intracellular Ca2+ concentrations in muscle and liver. However, the mechanism by which dysregulated intracellular Ca2+ homeostasis causes insulin resistance remains elusive. Here, we show that increased intracellular Ca2+ acts as a negative regulator of insulin signaling. Chronic intracellular Ca2+ overload in hepatocytes during obesity and hyperlipidemia attenuates the phosphorylation of protein kinase B (Akt) and its key downstream signaling molecules by inhibiting membrane localization of pleckstrin homology (PH) domains. Pharmacological approaches showed that elevated intracellular Ca2+ inhibits insulin-stimulated Akt phosphorylation and abrogates membrane localization of various PH domain proteins such as phospholipase Cδ and insulin receptor substrate 1, suggesting a common mechanism inhibiting the membrane targeting of PH domains. PH domain-lipid overlay assays confirmed that Ca2+ abolishes the binding of various PH domains to phosphoinositides (PIPs) with two adjacent phosphate groups, such as PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3 Finally, thermodynamic analysis of the binding interaction showed that Ca2+-mediated inhibition of targeting PH domains to the membrane resulted from the tight binding of Ca2+ rather than PH domains to PIPs forming Ca2+-PIPs. Thus, Ca2+-PIPs prevent the recognition of PIPs by PH domains, potentially due to electrostatic repulsion between positively charged side chains in PH domains and the Ca2+-PIPs. Our findings provide a mechanistic link between intracellular Ca2+ dysregulation and Akt inactivation in insulin resistance.


Asunto(s)
Calcio/metabolismo , Membrana Celular/metabolismo , Resistencia a la Insulina/fisiología , Fosfatidilinositoles/metabolismo , Dominios Homólogos a Pleckstrina/fisiología , Proteínas Proto-Oncogénicas c-akt/metabolismo , Animales , Dieta Alta en Grasa , Intolerancia a la Glucosa/patología , Hiperinsulinismo/patología , Insulina/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Obesidad/patología , Fosfolipasa C delta/metabolismo , Fosforilación , Unión Proteica
8.
Int J Mol Sci ; 21(11)2020 Jun 10.
Artículo en Inglés | MEDLINE | ID: mdl-32531902

RESUMEN

Lipid homeostasis is an important component of brain function, and its disturbance causes several neurological disorders, such as Huntington's, Alzheimer's, and Parkinson's diseases as well as mood disorders. Sterol regulatory element-binding protein-1c (SREBP-1c) is a key modulatory molecule involved in lipid homeostasis in the central nervous system. However, little is known about the biological effects of SREBP-1c in the brain. Our previous study uncovered that mice deficient in SREBP-1c exhibit schizophrenia-like behaviors. To investigate whether there are novel molecular mechanisms involved in the neurological aberrations caused by SREBP-1c deficiency, we analyzed the transcriptomes of the hippocampus of SREBP-1c knockout (KO) mice and wild-type mice. We found seven differentially expressed genes (three up-regulated and four down-regulated genes) in the hippocampus of SREBP-1c KO mice. For further verification, we selected the three most significantly changed genes: glucagon-like peptide 2 receptors (GLP2R) involved in hippocampal neurogenesis and neuroplasticity as well as in cognitive impairments; necdin (NDN) which is related to neuronal death and neurodevelopmental disorders; and Erb-B2 receptor tyrosine kinase 4 (ERBB4) which is a receptor for schizophrenia-linked protein, neuregulin-1. The protein levels of GLP2R and NDN were considerably decreased, but the level of ERBB4 was significantly increased in the hippocampus of SREBP-1c KO mice. However, further confirmation is warranted to establish the translatability of these findings from this rodent model into human patients. We suggest that these data provide novel molecular evidence for the modulatory role of SREBP-1c in the mouse hippocampus.


Asunto(s)
Conducta Animal/fisiología , Hipocampo/fisiología , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/genética , Animales , Diferenciación Celular/genética , Supervivencia Celular/genética , Perfilación de la Expresión Génica , Hipocampo/patología , Ratones Endogámicos C57BL , Ratones Noqueados , Mapas de Interacción de Proteínas/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Reproducibilidad de los Resultados , Esquizofrenia/genética , Transducción de Señal/genética , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/metabolismo
9.
Pflugers Arch ; 471(11-12): 1407-1418, 2019 12.
Artículo en Inglés | MEDLINE | ID: mdl-31667577

RESUMEN

Orexin A (OXA) is a neuropeptide associated with plasma insulin and leptin levels involved in body weight and appetite regulation. However, little is known about the effect of OXA on leptin secretion in adipocytes and its physiological roles. Leptin secretion and expression were analysed in 3T3-L1 adipocytes. Plasma leptin, adiponectin and insulin levels were measured by ELISA assay. Phosphorylated signal transducer and activator of transcription 3 (pSTAT3) levels in the hypothalamus were evaluated by western blotting. OXA dose-dependently suppressed leptin secretion from 3T3-L1 adipocytes by inhibiting its gene expression while facilitating adiponectin secretion. The leptin inhibition by OXA was mediated via orexin receptors (OXR1 and OXR2). In addition to the pathway via extracellular signal-regulated kinases, OXA triggered adenylyl cyclase-induced cAMP elevation, which results in protein kinase A-mediated activation of cAMP response element-binding proteins (CREB). Accordingly, CREB inhibition restored the OXA-induced downregulation of leptin gene expression and secretion. Exogenous OXA for 4 weeks decreased fasting plasma leptin levels and increased hypothalamic pSTAT3 levels in high-fat diet-fed mice, regardless of increase in body weight and food intake. These results suggest that high dose of OXA directly inhibits leptin mRNA expression and thus secretion in adipocytes, which may be a peripheral mechanism of OXA for its role in appetite drive during fasting. It may be also critical for lowering basal plasma leptin levels and thus maintaining postprandial hypothalamic leptin sensitivity.


Asunto(s)
Adipocitos/efectos de los fármacos , Adipocitos/metabolismo , Hipotálamo/efectos de los fármacos , Hipotálamo/metabolismo , Leptina/sangre , Leptina/metabolismo , Orexinas/farmacología , Células 3T3-L1 , Animales , Apetito/efectos de los fármacos , Peso Corporal/efectos de los fármacos , Línea Celular , Dieta Alta en Grasa , Masculino , Ratones , Ratones Endogámicos C57BL , Neuropéptidos/metabolismo , Receptores de Orexina/metabolismo
10.
Pflugers Arch ; 471(6): 829-843, 2019 06.
Artículo en Inglés | MEDLINE | ID: mdl-30617744

RESUMEN

Hydrogen peroxide (H2O2) produced endogenously can cause mitochondrial dysfunction and metabolic complications in various cell types by inducing oxidative stress. In the liver, oxidative and endoplasmic reticulum (ER) stress affects the development of non-alcoholic fatty liver disease (NAFLD). Although a link between both stresses and fatty liver diseases has been suggested, few studies have investigated the involvement of catalase in fatty liver pathogenesis. We examined whether catalase is associated with NAFLD, using catalase knockout (CKO) mice and the catalase-deficient human hepatoma cell line HepG2. Hepatic morphology analysis revealed that the fat accumulation was more prominent in high-fat diet (HFD) CKO mice compared to that in age-matched wild-type (WT) mice, and lipid peroxidation and H2O2 release were significantly elevated in CKO mice. Transmission electron micrographs indicated that the liver mitochondria from CKO mice tended to be more severely damaged than those in WT mice. Likewise, mitochondrial DNA copy number and cellular ATP concentrations were significantly lower in CKO mice. In fatty acid-treated HepG2 cells, knockdown of catalase accelerated cellular lipid accumulation and depressed mitochondrial biogenesis, which was recovered by co-treatment with N-acetyl cysteine or melatonin. This effect of antioxidant was also true in HFD-fed CKO mice, suppressing fatty liver development and improving hepatic mitochondrial function. Expression of ER stress marker proteins and hepatic fat deposition also increased in normal-diet, aged CKO mice compared to WT mice. These findings suggest that H2O2 production may be an important event triggering NAFLD and that catalase may be an attractive therapeutic target for preventing NAFLD.


Asunto(s)
Catalasa/metabolismo , Metabolismo de los Lípidos , Hígado/metabolismo , Enfermedad del Hígado Graso no Alcohólico/enzimología , Obesidad/complicaciones , Animales , Antioxidantes , Estrés del Retículo Endoplásmico , Células Hep G2 , Humanos , Peróxido de Hidrógeno/metabolismo , Hígado/ultraestructura , Masculino , Ratones Endogámicos C57BL , Ratones Noqueados , Mitocondrias Hepáticas/metabolismo , Enfermedad del Hígado Graso no Alcohólico/etiología , Obesidad/enzimología , Estrés Oxidativo
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