Alterações do diabetes mellitus no sistema nervoso central : avaliação de parâmetros astrocitários, comportamentais, da funcionalidade das barreiras hematoencefálica e hematoliquórica e o papel da exendina-4 na neuroproteção

O Diabetes mellitus (DM) é uma desordem metabólica caracterizada principalmente por hiperglicemia crônica. Durante o DM, a atenção está voltada principalmente para doenças que afetam sistemas periféricos, contudo, as complicações do DM podem resultar em danos ao sistema nervoso central (SNC), podendo levar a prejuízos cognitivos. Em vista disso, o objetivo desta tese foi investigar alterações no SNC, particularmente relacionadas às funções astrocitárias e do funcionamento das barreiras encefálicas em modelo animal de DM baseando-se nas alterações periféricas. Além disso, foi analisado o efeito da exendina-4 (EX-4), um agonista dos receptores do peptídeo semelhante ao glucagon (GLP-1), em reverter os parâmetros avaliados. Os resultados observados mostraram prejuízos periféricos e no SNC decorrentes do DM. O DM foi responsável pela excessiva produção de AGEs e alterações em parâmetros periféricos como peso corporal, glicemia, hemoglobina glicada (HbA1c) e peptídeo C. Ao analisar o SNC, observamos prejuízo nas funções cognitivas, em parâmetros astrocitários, disfunções nas barreiras encefálicas e diminuição do conteúdo da subunidade GluN1 do receptor N-metil D-Aspartato (NMDA). O tratamento com EX-4 reverteu o prejuízo cognitivo, o dano nas barreiras encefálicas, a captação de glutamato e o conteúdo de GluN1. No entanto, a EX-4 não teve efeito sobre a glicemia e formação de AGEs. O dano em funções astrocitárias e nas barreiras encefálicas observado no DM pode ser decorrente da ativação de vias de sinalização desencadeadas pelos elevados níveis de AGEs. Da mesma maneira, o prejuízo no comportamento cognitivo provavelmente possa ser atribuído aos danos astrocitários e nas barreiras encefálicas observados no DM. O efeito da EX-4 na melhora cognitiva possivelmente seja devido aos seus efeitos na captação de glutamato, no conteúdo de GluN1 e na recuperação das barreiras do encéfalo. Ainda, os papéis já estabelecidos da EX-4 na ativação de vias de sinalização relacionadas com a aprendizagem e memória e na diminuição da expressão de mediadores inflamatórios, podem ter atenuado os danos causados pela hiperglicemia e pelo acúmulo de AGEs. No entanto, mais estudos são necessários para estabelecer o mecanismo de ação da EX-4 na recuperação dos danos causados pelo DM no SNC.Diabetes mellitus (DM) is a metabolic disorder characterized primarily by chronic hyperglycemia. During the DM, attention is mainly focused on diseases affecting peripheral systems. However, DM complications may result in damage to the central nervous system (CNS), leading to cognitive impairments. In view of this, the aim of this thesis was to investigate changes in the CNS, particularly related to astrocytic functions and the functioning of the brain barriers in animal model of DM relying on the peripheral changes and to analyze the effect of exendin-4 (EX-4), an agonist of glucagon like peptide-1 (GLP-1) receptors, in reversing the parameters evaluated. The observed results showed peripheral and CNS damage resulting from DM. The DM was responsible for the excessive production of AGEs and changes in peripheral parameters such as body weight, blood glucose, glycated hemoglobin (HbA1c) and C-peptide When assessing the CNS, we observed impairment in cognitive functions, astrocytic parameters, dysfunctions in the brain barriers and decrease in N-methyl-D-aspartate (NMDA) GluN1 subunit content. Treatment with EX-4 reversed the cognitive impairment, damage in brain barriers, glutamate uptake and GluN1 content. However, the EX-4 had no effect in the glycemia and ADEs formation. The loss of astrocytic and brain barriers functions observed in DM may be due to the activation of signalling pathways triggered by high levels of AGEs. In addition, impairment in cognitive behavior can probably be attributed to astrocyte and brain barriers damage observed in DM. The effect of EX-4 on the cognitive improvement possibly be due to its effects on glutamate uptake, in the GluN1 content and in the recovery of the brain barriers. In addition, the EX-4 established roles in the activation of signalling pathways associated with learning and memory and in the decrease expression of inflammatory mediators, can attenuate the damage caused by hyperglycemia and by accumulation of AGE. However, further studies are needed to establish the mechanism of EX-4 action in the recovery of damage caused by DM in CNS

Early effects of LPS-induced neuroinflammation on the rat hippocampal glycolytic pathway

Neuroinflammation is a common feature during the development of neurological disorders and neurodegenerative diseases, where glial cells, such as microglia and astrocytes, play key roles in the activation and maintenance of inflammatory responses in the central nervous system. Neuroinflammation is now known to involve a neurometabolic shift, in addition to an increase in energy consumption. We used two approaches (in vivo and ex vivo) to evaluate the effects of lipopolysaccharide (LPS)-induced neuroinflammation on neurometabolic reprogramming, and on the modulation of the glycolytic pathway during the neuroinflammatory response. For this, we investigated inflammatory cytokines and receptors in the rat hippocampus, as well as markers of glial reactivity. Mitochondrial respirometry and the glycolytic pathway were evaluated by multiple parameters, including enzymatic activity, gene expression and regulation by protein kinases. Metabolic (e.g., metformin, 3PO, oxamic acid, fluorocitrate) and inflammatory (e.g., minocycline, MCC950, arundic acid) inhibitors were used in ex vivo hippocampal slices. The induction of early inflammatory changes by LPS (both in vivo and ex vivo) enhanced glycolytic parameters, such as glucose uptake, PFK1 activity and lactate release. This increased glucose consumption was independent of the energy expenditure for glutamate uptake, which was in fact diverted for the maintenance of the immune response. Accordingly, inhibitors of the glycolytic pathway and Krebs cycle reverted neuroinflammation (reducing IL-1β and S100B) and the changes in glycolytic parameters induced by LPS in acute hippocampal slices. Moreover, the inhibition of S100B, a protein predominantly synthesized and secreted by astrocytes, inhibition of microglia activation and abrogation of NLRP3 inflammasome assembly confirmed the role of neuroinflammation in the upregulation of glycolysis in the hippocampus. Our data indicate a neurometabolic glycolytic shift, induced by inflammatory activation, as well as a central and integrative role of astrocytes, and suggest that interference in the control of neurometabolism may be a promising strategy for downregulating neuroinflammation and consequently for diminishing negative neurological outcomes

Glycolysis-Derived Compounds From Astrocytes That Modulate Synaptic Communication

Based on the concept of the tripartite synapse, we have reviewed the role of glucose-derived compounds in glycolytic pathways in astroglial cells. Glucose provides energy and substrate replenishment for brain activity, such as glutamate and lipid synthesis. In addition, glucose metabolism in the astroglial cytoplasm results in products such as lactate, methylglyoxal, and glutathione, which modulate receptors and channels in neurons. Glucose has four potential destinations in neural cells, and it is possible to propose a crossroads in “X” that can be used to describe these four destinations. Glucose-6P can be used either for glycogen synthesis or the pentose phosphate pathway on the left and right arms of the X, respectively. Fructose-6P continues through the glycolysis pathway until pyruvate is formed but can also act as the initial compound in the hexosamine pathway, representing the left and right legs of the X, respectively. We describe each glucose destination and its regulation, indicating the products of these pathways and how they can affect synaptic communication. Extracellular L-lactate, either generated from glucose or from glycogen, binds to HCAR1, a specific receptor that is abundantly localized in perivascular and post-synaptic membranes and regulates synaptic plasticity. Methylglyoxal, a product of a deviation of glycolysis, and its derivative D-lactate are also released by astrocytes and bind to GABAA receptors and HCAR1, respectively. Glutathione, in addition to its antioxidant role, also binds to ionotropic glutamate receptors in the synaptic cleft. Finally, we examined the hexosamine pathway and evaluated the effect of GlcNAc-modification on key proteins that regulate the other glucose destinations

Elevated extracellular HSP72 and blunted heat shock response in severe covid-19 patients

Aims: We hypothesized that critically ill patients with SARS-CoV-2 infection and insulin resistance would present a reduced Heat Shock Response (HSR), which is a pathway involved in proteostasis and anti-inflammation, subsequently leading to worse outcomes and higher inflammation. In this work we aimed: (i) to measure the concentration of extracellular HSP72 (eHSP72) in patients with severe COVID-19 and in comparison with noninfected patients; (ii) to compare the HSR between critically ill patients with COVID-19 (with and without diabetes); and (iii) to compare the HSR in these patients with noninfected individuals. Methods: Sixty critically ill adults with acute respiratory failure with SARS-CoV-2, with or without diabetes, were selected. Noninfected subjects were included for comparison (healthy, n = 19 and patients with diabetes, n = 22). Blood samples were collected to measure metabolism (glucose and HbA1c); oxidative stress (lypoperoxidation and carbonyls); cytokine profile (IL-10 and TNF); eHSP72; and the HSR (in vitro). Results: Patients with severe COVID-19 presented higher plasma eHSP72 compared with healthy individuals and noninfected patients with diabetes. Despite the high level of plasma cytokines, no differences were found between critically ill patients with COVID-19 with or without diabetes. Critically ill patients, when compared to noninfected, presented a blunted HSR. Oxidative stress markers followed the same pattern. No differences in the HSR (extracellular/intracellular level) were found between critically ill patients, with or without diabetes. Conclusions: We demonstrated that patients with severe COVID-19 have elevated plasma eHSP72 and that their HSR is blunted, regardless of the presence of diabetes. These results might explain the uncontrolled inflammation and also provide insights on the increased risk in developing type 2 diabetes after SARS-CoV-2 infection

Polymorphisms in ACE1, TMPRSS2, IFIH1, IFNAR2, and TYK2 genes are associated with worse clinical outcomes in COVID-19

Although advanced age, male sex, and some comorbidities impact the clinical course of COVID-19, these factors only partially explain the inter-individual variability in disease severity. Some studies have shown that genetic polymorphisms contribute to COVID-19 severity; however, the results are inconclusive. Thus, we investigated the association between polymorphisms in ACE1, ACE2, DPP9, IFIH1, IFNAR2, IFNL4, TLR3, TMPRSS2, and TYK2 and the clinical course of COVID-19. A total of 694 patients with COVID-19 were categorized as: (1) ward inpatients (moderate symptoms) or patients admitted at the intensive care unit (ICU; severe symptoms); and (2) survivors or non-survivors. In females, the rs1990760/IFIH1 T/T genotype was associated with risk of ICU admission and death. Moreover, the rs1799752/ACE1 Ins and rs12329760/TMPRSS2 T alleles were associated with risk of ICU admission. In non-white patients, the rs2236757/IFNAR2 A/A genotype was associated with risk of ICU admission, while the rs1799752/ACE1 Ins/Ins genotype, rs2236757/IFNAR2 A/A genotype, and rs12329760/TMPRSS2 T allele were associated with risk of death. Moreover, some of the analyzed polymorphisms interact in the risk of worse COVID19 outcomes. In conclusion, this study shows an association of rs1799752/ACE1, rs1990760/IFIH1, rs2236757/IFNAR2, rs12329760/TMPRSS2, and rs2304256/TYK2 polymorphisms with worse COVID19 outcomes, especially among female and non-white patients