The Role of Fatty Acid Signaling in Islet Beta-Cell Adaptation to Normal Pregnancy

BackgroundMaintenance of a normal fetal nutrient supply requires major adaptations in maternal metabolic physiology, including of the islet beta-cell. The role of lipid signaling processes in the mechanisms of islet beta-cell adaptation to pregnancy has been minimally investigated.ObjectiveTo determine the effects of pregnancy on islet fatty acid (FA) metabolic partitioning and FA augmentation of glucose-stimulated insulin secretion (GSIS).MethodsAge matched virgin, early pregnant (gestational day-11, G11) and late pregnant (G19) Sprague-Dawley rats were studied. Fasted and fed state biochemistry, oral glucose tolerance tests (OGTT), and fasted and post-OGTT liver glycogen, were determined to assess in vivo metabolic characteristics. In isolated islets, FA (BSA-bound palmitate 0.25 mmol/l) augmentation of GSIS, FA partitioning into esterification and oxidation processes using metabolic tracer techniques, lipolysis by glycerol release, triacylglycerols (TG) content, and the expression of key beta-cell genes were determined.ResultsPlasma glucose in pregnancy was lower, including during the OGTT (glucose area under the curve 0-120 min (AUC0-120); 655±24 versus 849±13 mmol.l-1.min; G19 vs virgin; P<0.0001), with plasma insulin concentrations equivalent to those of virgin rats (insulin AUC0-120; 97±7 versus 83±7 ng.ml-1.min; G19 vs virgin; not significant). Liver glycogen was depleted in fasted G19 rats with full recovery after oral glucose. Serum TG increased during pregnancy (4.4±0.4, 6.7±0.5; 17.1±1.5 mmol/l; virgin, G11, G19, P<0.0001), and islet TG content decreased (147±42, 172±27, 73±13 ng/µg protein; virgin, G11, G19; P<0.01). GSIS in isolated islets was increased in G19 compared to virgin rats, and this effect was augmented in the presence of FA. FA esterification into phospholipids, monoacylglycerols and TG were increased, whereas FA oxidation was reduced, in islets of pregnant compared to virgin rats, with variable effects on lipolysis dependent on gestational age. Expression of Ppargc1a, a key regulator of mitochondrial metabolism, was reduced by 51% in G11 and 64% in G19 pregnant rat islets compared to virgin rat islets (P<0.001).ConclusionA lowered set-point for islet and hepatic glucose homeostasis in the pregnant rat has been confirmed. Islet adaptation to pregnancy includes increased FA esterification, reduced FA oxidation, and enhanced FA augmentation of glucose-stimulated insulin secretion.

Inverse relationship between serum adenosine deaminase levels and islet beta cell function in patients with type 2 diabetes

Objective Type 2 diabetes (T2D) is a chronic low-grade inflammatory disease, which characterized by islet beta cell dysfunction. Serum adenosine deaminase (ADA) is an important enzyme that regulates the biological activity of insulin, and its levels are greatly increased in inflammatory diseases with insulin resistance. The present study was designed to explore the relationship between serum ADA levels and islet beta cell function in patients with T2D. Methods This cross-sectional study recruited 1573 patients with T2D from the Endocrinology Department of the Affiliated Hospital 2 of Nantong University between 2015 and 2018. All participants were received serum ADA test and oral glucose tolerance test (OGTT). Insulin sensitivity index (assessed by Matsuda index using C-peptide, ISIM-cp), insulin secretion index (assessed by ratio of area under the C-peptide curve to glucose curve, AUCcp/glu) and islet beta cell function (assessed by insulin secretion-sensitivity index 2 using C-peptide, ISSI2cp) were derived from OGTT. And other clinical parameters, such as HbA1c, were also collected. Results It was showed that HbA1c was significantly increased, while ISIM-cp, AUCcp/glu and ISSI2cp significantly decreased, across ascending quartiles of serum ADA levels. Moreover, serum ADA levels were negatively correlated with ISSI2cp (r = − 0.267, p < 0.001). Furthermore, after adjusting for other clinical parameters by multiple linear regression analysis, serum ADA levels were still independently associated with ISSI2cp (β = − 0.125, t = − 5.397, p < 0.001, adjusted R2 = 0.459). Conclusions Serum ADA levels are independently associated with islet beta cell function in patients with T2D.

RhoG-Rac1 Signaling Pathway Mediates Metabolic Dysfunction of the Pancreatic Beta-Cells Under Chronic Hyperglycemic Conditions.

BACKGROUND/AIMS: Published evidence suggests regulatory roles for small G proteins (Cdc42 and Rac1) in glucose-stimulated insulin secretion (GSIS) from pancreatic beta-cells. More recent evidence suggests novel roles for these G proteins, specifically Rac1, in the induction of metabolic dysfunction of the islet beta-cell under the duress of a variety of stress conditions. However, potential upstream regulators of sustained activation of Rac1 have not been identified in the beta-cell. Recent studies in other cell types have identified RhoG, a small G protein, as an upstream regulator of Rac1 under specific experimental conditions. Herein, we examined putative roles for RhoG in islet beta-cell dysregulation induced by glucotoxic conditions. METHODS: Expression of RhoG or GDIγ was suppressed by siRNA transfection using the DharmaFect1 reagent. Subcellular fractions were isolated using NE-PER Nuclear and Cytoplasmic Extraction Reagent kit. The degree of activation of Rac1 was assessed using a pull-down assay kit. Extent of cell death was quantified using a Cell Death Detection ELISAplus kit. RESULTS: RhoG is expressed in human islets, rat islets, and clonal INS-1 832/13 cells. siRNA-RhoG markedly attenuated sustained activation of Rac1 and caspase-3 in INS-1 832/13 cells exposed to hyperglycemic conditions (20 mM; 24 hours). In a manner akin to Rac1, which has been shown to translocate to the nuclear fraction to induce beta-cell dysfunction under metabolic stress, a significant increase in the association of RhoG with the nuclear fraction was observed in beta-cells under the duress of metabolic stress. Interestingly, GDIγ, a known regulator of RhoG, remained associated with non-nuclear fraction under conditions RhoG and Rac1 translocated to the membrane. Lastly, siRNA-RhoG modestly attenuated pancreatic beta-cell demise induced by high glucose exposure conditions, but such an effect was not statistically significant. CONCLUSION: Based on these data we conclude that RhoG-Rac1 signaling module plays critical regulatory roles in promoting mitochondrial dysfunction (caspase-3 activation) of the islet beta cell under metabolic stress.

The Secretome of Mesenchymal Stem Cells Prevents Islet Beta Cell Apoptosis via an IL-10-Dependent Mechanism

Background: Type 1 Diabetes Mellitus (T1DM) is partly driven by autoimmune destruction of the pancreatic beta cell, facilitated by the release of inflammatory cytokines, including IFN-γ, TNF-α and IL-1β by cells of the innate immune system. Mesenchymal Stem Cells (MSCs) have been used to counteract autoimmunity in a range of therapeutic settings due to their secretion of trophic and immunomodulatory factors that ameliorate disease independently of the cells themselves. Objective: The aim of this study was to assess the effect of the secretome of human bone-marrow derived MSCs on cytokine-driven beta cell apoptosis. Methods: All experiments were conducted in two insulin-secreting islet cell lines (BRIN-BD11 and βTC1.6) with selected experiments confirmed in primary islets. MSC secretome was generated by conditioning serum-free media (MSC-CM) for 24 hours on sub-confluent MSC populations. The media was then removed and filtered in readiness for use. Results: Exposure to IFN-γ, TNF-α and IL-1β induced apoptosis in cell lines and primary islets. The addition of MSC-CM to cell lines and primary islets partially reversed cytokine-driven apoptosis. MSC-CM also restored glucose-stimulated insulin secretion in cytokine-treated cell lines, which was linked to improved cell viability following from cytokine challenge. Characterization of MSC-CM revealed significant concentrations of IL-4, IL-10, PIGF and VEGF. Of these, IL-10 alone prevented cytokine-driven apoptosis. Furthermore, the inhibition of IL-10 through the addition of a blocking antibody reversed the anti-apoptotic effects of MSC-CM. Conclusion: Overall, the protective effects of MSC-CM on islet beta cell survival appear to be largely IL-10-dependent.