Diabetes Mellitus induces epigenetic alterations in the slc2a4 gene in skeletal muscle that relate to gene repression and can be reversed by insulinotherapy or resveratrol.

A principal característica do diabetes mellitus (DM) é a perda da homeostasia glicêmica. O músculo esquelético desempenha papel chave e a adequada expressão do transportador de glicose GLUT4 (gene Slc2a4) é fundamental. Regulações epigenéticas do Slc2a4, como acetilação/trimetilação de histona H3, nunca foram investigadas no DM; e o resveratrol, sugerido como sensibilizador da insulina, poderia modular essas regulações, pois ativa a desacetilase sirtuína 1 (SIRT1). O objetivo foi avaliar em modelos de DM o efeito do tratamento com resveratrol sobre a homeostasia glicêmica, a expressão de Slc2a4/GLUT4 em músculo esquelético, a regulação epigenética do Slc2a4, e a possível participação da SIRT1. Os dados revelam a ocorrência de regulações epigenéticas no gene Slc2a4 em músculo de animais diabéticos e mostra que o tratamento com insulina ou resveratrol modula algumas dessas alterações, melhorando o controle glicêmico. Esses resultados apoiam o resveratrol como um sensibilizador da insulina, e constroem bases para o desenvolvimento de terapias epigenéticas para o DM.The main characteristic of diabetes mellitus (DM) is the loss of glycemic homeostasis. The skeletal muscle plays a key role and the maintenance expression of the GLUT4 glucose transporter (encoded by the Slc2a4 gene) is fundamental. Epigenetic regulations of Slc2a4, such as histone H3 acetylation/trimethylation, have never been investigated in DM; and resveratrol, suggested as an insulin sensitizer, could modulate these regulations, as it is an activator of the deacetylase sirtuin 1 (SIRT1). The aim was to evaluate in skeletal muscle of diabetic animals the effect of resveratrol treatment on glycemic homeostasis, Slc2a4/GLUT4 expression in skeletal muscle, the epigenetic regulation of Slc2a4, and the possible participation of SIRT1. The data reveals the occurrence of epigenetic regulation in the Slc2a4 gene in muscle of diabetic animals and the insulin or resveratrol treatment modulates some of these changes, improving glycemic control. These results support resveratrol as an insulin sensitizer, and build bases for the development of epigenetic therapies for DM

Chronic supplementation of beta hydroxy beta methylbutyrate (HMB) reduces insulin sensitivity of rats in tissue-specific manner.

O beta hidroxi beta metilbutirato (HMB), metabólito do aminoácido leucina, é utilizado para reduzir a degradação e/ou aumentar a síntese proteica. Nosso grupo demonstrou que ratos submetidos à suplementação crônica de HMB apresentaram hiperinsulinemia e normoglicemia, sugerindo um quadro de resistência à ação da insulina (RI). Em paralelo, observamos um aumento da síntese e secreção de GH e da concentração plasmática de IGF-I, sugerindo um possível envolvimento do eixo somatotrófico na RI, considerando seus efeitos diabetogênicos. No presente estudo, após sobrecarga de glicose (0,75g/kg), observamos uma redução da taxa de decaimento de glicose, com uma hiperinsulinemia (Teste de tolerância à glicose - GTT); bem como redução da ação da insulina, em resposta e este hormônio (10 U), no fígado e músculos esqueléticos, detectados por western blotting, confirmando uma RI. Não encontramos evidências do envolvimento do GH neste quadro, uma vez que, no fígado, não detectamos alterações na expressão de pSTAT5 e SOCS3. No tecido adiposo branco, observamos aumento na expressão de mRNA e proteína da lipase hormônio sensível (LHS), bem como aumento da concentração de ácidos graxos livres (AGL) plasmáticos, podendo este ser um mecanismo de RI promovido pelo GH, nesta situação.HMB is a metabolite of leucine able to increase protein synthesis and/or reduce protein degradation. Studies carried out in our laboratory have shown that HMB-supplemented rats although normoglycemic, exhibited hyperinsulinemia, suggesting an insulin resistance status. In parallel, it was observed an increased activity of the GH-IGF-I axis, reinforcing the possibility of alterations on glucose sensitivity, since GH is recognized as being diabetogenic effects. The results demonstrate that HMB-supplemented rats, after glucose overload (0,75g/kg) present reduced glucose decay rate and increased plasma insulin levels (glucose tolerance test GTT), confirming the insulin resistance status. By western blotting, was detected reduced insulin action (liver and skeletal muscle), after insulin stimulus. No alterations were detected in retroperitoneal white adipose tissue. No significant alterations were detected on pSTAT5 and SOCS3 after HMB supplementation indicating that GH could act by another mechanism to induce insulin resistance. Additionally, was detected increased on mRNA and protein expression of hormone sensitive lipase (HSL), and plasma concentrations of non-esterified fat acids (NEFA) in HMB-supplemented rats, which could be a mechanism mediated by GH, contributing to insulin resistance

Glucose Transport and Utilization in the Hippocampus: From Neurophysiology to Diabetes-Related Development of Dementia

The association of diabetes with cognitive dysfunction has at least 60 years of history, which started with the observation that children with type 1 diabetes mellitus (T1D), who had recurrent episodes of hypoglycemia and consequently low glucose supply to the brain, showed a deficit of cognitive capacity. Later, the growing incidence of type 2 diabetes mellitus (T2D) and dementia in aged populations revealed their high association, in which a reduced neuronal glucose supply has also been considered as a key mechanism, despite hyperglycemia. Here, we discuss the role of glucose in neuronal functioning/preservation, and how peripheral blood glucose accesses the neuronal intracellular compartment, including the exquisite glucose flux across the blood–brain barrier (BBB) and the complex network of glucose transporters, in dementia-related areas such as the hippocampus. In addition, insulin resistance-induced abnormalities in the hippocampus of obese/T2D patients, such as inflammatory stress, oxidative stress, and mitochondrial stress, increased generation of advanced glycated end products and BBB dysfunction, as well as their association with dementia/Alzheimer’s disease, are addressed. Finally, we discuss how these abnormalities are accompained by the reduction in the expression and translocation of the high capacity insulin-sensitive glucose transporter GLUT4 in hippocampal neurons, which leads to neurocytoglycopenia and eventually to cognitive dysfunction. This knowledge should further encourage investigations into the beneficial effects of promising therapeutic approaches which could improve central insulin sensitivity and GLUT4 expression, to fight diabetes-related cognitive dysfunctions

Postmortem Brains from Subjects with Diabetes Mellitus Display Reduced GLUT4 Expression and Soma Area in Hippocampal Neurons: Potential Involvement of Inflammation

Diabetes mellitus (DM) is an important risk factor for dementia, which is a common neurodegenerative disorder. DM is known to activate inflammation, oxidative stress, and advanced glycation end products (AGEs) generation, all capable of inducing neuronal dysfunctions, thus participating in the neurodegeneration progress. In that process, disturbed neuronal glucose supply plays a key role, which in hippocampal neurons is controlled by the insulin-sensitive glucose transporter type 4 (GLUT4). We investigated the expression of GLUT4, nuclear factor NF-kappa B subunit p65 [NFKB (p65)], carboxymethyllysine and synapsin1 (immunohistochemistry), and soma area in human postmortem hippocampal samples from control, obese, and obese+DM subjects (41 subjects). Moreover, in human SH-SY5Y neurons, tumor necrosis factor (TNF) and glycated albumin (GA) effects were investigated in GLUT4, synapsin-1 (SYN1), tyrosine hydroxylase (TH), synaptophysin (SYP) proteins, and respective genes; NFKB binding activity in the SLC2A4 promoter; effects of increased histone acetylation grade by histone deacetylase 3 (HDAC3) inhibition. Hippocampal neurons (CA4 area) of obese+DM subjects displayed reduced GLUT4 expression and neuronal soma area, associated with increased expression of NFKB (p65). Challenges with TNF and GA decreased the SLC2A4/GLUT4 expression in SH-SY5Y neurons. TNF decreased SYN1, TH, and SYP mRNAs and respective proteins, and increased NFKB binding activity in the SLC2A4 promoter. Inhibition of HDAC3 increased the SLC2A4 expression and the total neuronal content of CRE-binding proteins (CREB/ICER), and also counterbalanced the repressor effect of TNF upon these parameters. This study revealed reduced postmortem human hippocampal GLUT4 content and neuronal soma area accompanied by increased proinflammatory activity in the brains of DM subjects. In isolated human neurons, inflammatory activation by TNF reduced not only the SLC2A4/GLUT4 expression but also the expression of some genes related to neuronal function (SYN1, TH, SYP). These effects may be related to epigenetic regulations (H3Kac and H4Kac status) since they can be counterbalanced by inhibiting HDAC3. These results uncover the improvement in GLUT4 expression and/or the inhibition of HDAC3 as promising therapeutic targets to fight DM-related neurodegeneration