RESUMEN
OBJECTIVE: Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused in almost all cases by homozygosity for a GAA trinucleotide repeat expansion in the frataxin gene. Frataxin is a mitochondrial protein involved in iron homeostasis. FRDA patients have a high prevalence of diabetes, the pathogenesis of which is not known. We aimed to evaluate the relative contribution of insulin resistance and ß-cell failure and the pathogenic mechanisms involved in FRDA diabetes. METHODS: Forty-one FRDA patients, 26 heterozygous carriers of a GAA expansion, and 53 controls underwent oral and intravenous glucose tolerance tests. ß-Cell proportion was quantified in postmortem pancreas sections from 9 unrelated FRDA patients. Using an in vitro disease model, we studied how frataxin deficiency affects ß-cell function and survival. RESULTS: FRDA patients had increased abdominal fat and were insulin resistant. This was not compensated for by increased insulin secretion, resulting in a markedly reduced disposition index, indicative of pancreatic ß-cell failure. Loss of glucose tolerance was driven by ß-cell dysfunction, which correlated with abdominal fatness. In postmortem pancreas sections, pancreatic islets of FRDA patients had a lower ß-cell content. RNA interference-mediated frataxin knockdown impaired glucose-stimulated insulin secretion and induced apoptosis in rat ß cells and human islets. Frataxin deficiency sensitized ß cells to oleate-induced and endoplasmic reticulum stress-induced apoptosis, which could be prevented by the incretins glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. INTERPRETATION: Pancreatic ß-cell dysfunction is central to diabetes development in FRDA as a result of mitochondrial dysfunction and higher sensitivity to metabolic and endoplasmic reticulum stress-induced ß-cell death.
Asunto(s)
Diabetes Mellitus/etiología , Diabetes Mellitus/patología , Ataxia de Friedreich/complicaciones , Células Secretoras de Insulina/fisiología , Proteínas de Unión a Hierro/genética , Expansión de Repetición de Trinucleótido/genética , Tejido Adiposo/metabolismo , Adulto , Animales , Distribución de la Grasa Corporal , Metabolismo Energético/genética , Salud de la Familia , Femenino , Citometría de Flujo , Ataxia de Friedreich/genética , Prueba de Tolerancia a la Glucosa , Humanos , Hipoglucemiantes/farmacología , Insulina/farmacología , Resistencia a la Insulina/genética , Células Secretoras de Insulina/efectos de los fármacos , Células Secretoras de Insulina/patología , Modelos Lineales , Masculino , Persona de Mediana Edad , Ratas , FrataxinaRESUMEN
Trafficking of pancreatic K(ATP) channels to the plasma membrane critically depends on masking the endoplasmic reticulum (ER) retention signals of the SUR1 and Kir6.2 subunits upon their proper assembly into functional hetero-octamers. When expressed in the absence of the partner protein, each subunit might accumulate in the ER and trigger beta-cell ER stress and oxidative stress. To test this hypothesis, Kir6.2 localisation, ER ultra-structure and ER-stress- and oxidative-stress-response gene mRNA levels were evaluated in pancreatic endocrine cells from adult wild-type (WT) and Sur1 knockout (Sur1 ( -/- )) mice. As previously reported, Kir6.2 was mainly expressed on secretory granules and at the plasma membrane of WT islet cells. In contrast, like the ER chaperone calreticulin, Kir6.2 was primarily localised in the rough endoplasmic reticulum (RER) of Sur1 ( -/- ) islet cells. ER retention of Kir6.2 was demonstrated (electron microscopy) by a significant increase in the length and Kir6.2 density of RER in Sur1 ( -/- ) vs WT islet cells. Despite Kir6.2 retention in RER, Xbp1 mRNA splicing and mRNA levels of preproinsulin and ER-stress-response genes Bip, Edem and Gadd153 were similar in WT and Sur1 ( -/- ) islets. However, mRNA levels of the antioxidant enzymes Sod1, Sod2, Gpx2 and catalase were significantly up-regulated in Sur1 ( -/- ) islets. Sequestration of Kir6.2 in RER of Sur1 ( -/- ) islet cells is thus associated with an increase in RER length and mild oxidative stress without activation of the classical ER stress response.
Asunto(s)
Retículo Endoplásmico/metabolismo , Islotes Pancreáticos/metabolismo , Canales de Potasio de Rectificación Interna/deficiencia , Canales de Potasio de Rectificación Interna/metabolismo , Receptores de Droga/deficiencia , Estrés Fisiológico , Transportadoras de Casetes de Unión a ATP/genética , Transportadoras de Casetes de Unión a ATP/metabolismo , Animales , Especificidad de Anticuerpos/inmunología , Calreticulina/metabolismo , Retículo Endoplásmico/genética , Retículo Endoplásmico/ultraestructura , Regulación de la Expresión Génica , Islotes Pancreáticos/citología , Islotes Pancreáticos/ultraestructura , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Estrés Oxidativo/genética , Canales de Potasio de Rectificación Interna/genética , Transporte de Proteínas , ARN Mensajero/genética , ARN Mensajero/metabolismo , Receptores de Droga/genética , Receptores de Droga/metabolismo , Fracciones Subcelulares/metabolismo , Receptores de SulfonilureasRESUMEN
In congenital hyperinsulinism of infancy (CHI), the loss of K-ATP channels (composed of Kir6.2 and SUR1 subunits) in beta cells induces permanent insulin secretion and severe hypoglycaemia. By contrast, Sur1 ( -/- ) mice do not present such defects. We have investigated the impact of Sur1 gene inactivation on mouse islet cell morphology, structure and basic physiology. Pancreata were collected from young, adult and old wild-type (WT) and Sur1 ( -/- ) mice. After immunostaining for hormone, the total endocrine tissue, cell proportion, cell size and intra-insular distribution, hormone content and Glut-2 expression were quantified by morphometry. Basic physiological parameters were also measured. In young Sur1 ( -/- ) mice, the total endocrine tissue and proportion of beta cells were higher (P<0.05) than in WT mice, whereas the proportion of delta cells was lower (P<0.01). In old Sur1 ( -/- ) mice, alpha cells were frequently located in the central regions of islets (unlike WT islets) and their proportion was increased (P<0.05). Glut-2 protein and mRNA levels were lower in old Sur1 ( -/- ) islets (P<0.02). Insulinaemia, fasting insulin and glucagon contents were equivalent in both groups of pancreata. Thus, the islets of Sur1 ( -/- ) mice present morphological modifications that have not been described in CHI and that might reflect an adaptive mechanism controlling insulin secretion in these mice.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/genética , Islotes Pancreáticos/fisiología , Páncreas/fisiología , Canales de Potasio de Rectificación Interna/genética , Receptores de Droga/genética , Factores de Edad , Animales , Glucemia/metabolismo , Femenino , Silenciador del Gen , Glucagón/genética , Glucagón/metabolismo , Inmunohistoquímica , Insulina/sangre , Insulina/metabolismo , Secreción de Insulina , Islotes Pancreáticos/citología , Islotes Pancreáticos/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Páncreas/anatomía & histología , Páncreas/citología , Páncreas/metabolismo , Canales de Potasio de Rectificación Interna/deficiencia , Receptores de Droga/deficiencia , Receptores de SulfonilureasRESUMEN
Environmental factors such as diets rich in saturated fats contribute to dysfunction and death of pancreatic ß-cells in diabetes. Endoplasmic reticulum (ER) stress is elicited in ß-cells by saturated fatty acids. Here we show that palmitate-induced ß-cell apoptosis is mediated by the intrinsic mitochondrial pathway. By microarray analysis, we identified a palmitate-triggered ER stress gene expression signature and the induction of the BH3-only proteins death protein 5 (DP5) and p53-upregulated modulator of apoptosis (PUMA). Knockdown of either protein reduced cytochrome c release, caspase-3 activation, and apoptosis in rat and human ß-cells. DP5 induction depends on inositol-requiring enzyme 1 (IRE1)-dependent c-Jun NH2-terminal kinase and PKR-like ER kinase (PERK)-induced activating transcription factor (ATF3) binding to its promoter. PUMA expression is also PERK/ATF3-dependent, through tribbles 3 (TRB3)-regulated AKT inhibition and FoxO3a activation. DP5(-/-) mice are protected from high fat diet-induced loss of glucose tolerance and have twofold greater pancreatic ß-cell mass. This study elucidates the crosstalk between lipotoxic ER stress and the mitochondrial pathway of apoptosis that causes ß-cell death in diabetes.