CDK11 Promotes Cytokine-Induced Apoptosis in Pancreatic Beta Cells Independently of Glucose Concentration and Is Regulated by Inflammation in the NOD Mouse Model

BackgroundPancreatic islets are exposed to strong pro-apoptotic stimuli: inflammation and hyperglycemia, during the progression of the autoimmune diabetes (T1D). We found that the Cdk11(Cyclin Dependent Kinase 11) is downregulated by inflammation in the T1D prone NOD (non-obese diabetic) mouse model. The aim of this study is to determine the role of CDK11 in the pathogenesis of T1D and to assess the hierarchical relationship between CDK11 and Cyclin D3 in beta cell viability, since Cyclin D3, a natural ligand for CDK11, promotes beta cell viability and fitness in front of glucose.MethodsWe studied T1D pathogenesis in NOD mice hemideficient for CDK11 (N-HTZ), and, in N-HTZ deficient for Cyclin D3 (K11HTZ-D3KO), in comparison to their respective controls (N-WT and K11WT-D3KO). Moreover, we exposed pancreatic islets to either pro-inflammatory cytokines in the presence of increasing glucose concentrations, or Thapsigargin, an Endoplasmic Reticulum (ER)-stress inducing agent, and assessed apoptotic events. The expression of key ER-stress markers (Chop, Atf4 and Bip) was also determined.ResultsN-HTZ mice were significantly protected against T1D, and NS-HTZ pancreatic islets exhibited an impaired sensitivity to cytokine-induced apoptosis, regardless of glucose concentration. However, thapsigargin-induced apoptosis was not altered. Furthermore, CDK11 hemideficiency did not attenuate the exacerbation of T1D caused by Cyclin D3 deficiency.ConclusionsThis study is the first to report that CDK11 is repressed in T1D as a protection mechanism against inflammation-induced apoptosis and suggests that CDK11 lies upstream Cyclin D3 signaling. We unveil the CDK11/Cyclin D3 tandem as a new potential intervention target in T1D.

Pharmacological inhibition of thioredoxin reductase increases insulin secretion and diminishes beta cell viability

Apparently, both a decrease in beta cell function and in beta cell mass contribute to the progressive worsening of type 2 diabetes. So, it is of particular interest to define factors which are relevant for the regulation of insulin secretion and at the same time for the maintenance of beta cell mass. The NADPH-thioredoxin system has a candidate role for such a dual function. Here, we have characterized the effects of a highly specific inhibitor of thioredoxin reductase, AM12, on the viability and function of insulin-secreting MIN6 cells and isolated NMRI mouse islets. Viability was checked by MTT testing and the fluorescent live-dead assay. Apoptosis was assessed by annexin V assay. Insulin secretion of perifused islets was measured by ELISA. The cytosolic Ca2+ concentration was measured by the Fura technique. Acute exposure of perifused pancreatic islets to 5 μM AM12 was without significant effect on insulin secretion. Islets cultured for 24 h in 0.5 or 5 μM AM12 showed unchanged basal secretion during perifusion, but the response to 30 mM glucose was significantly enhanced by 5 μM. Twenty-four-hour exposure to 5 μM AM12 proved to be without effect on the viability of MIN6 cells, whereas longer exposure was clearly toxic. Islets were more susceptible, showing initial signs of apoptosis after 24-h exposure to 5 μM AM12. The activity of the NADPH-thioredoxin system is indispensable for beta cell viability but may have a limiting effect on glucose-induced insulin secretion.

The role of coffee derivatives in the regulation of pancreatic beta cell function in Type 2 Diabetes

Coffee contains several components other than caffeine such as chlorogenic acids (CGAs), which are a family of polyphenols. Non-caffeinated coffee has been shown to reduce the risk of Type 2 diabetes, but it is unclear whether this effect is primarily due to a beneficial action on glucose regulation in peripheral tissues or whether it is partly mediated via a direct, functional modulation of insulin-secreting beta cells from the pancreas. This study aims to explore the specific role of coffee compounds derived from the polyphenolic family of CGAs (caffeic acid (CA) and ferulic acid (FA)) and their metabolites (dihydroferulic acid (diFA) and ferulic acid 4-O-sulphate (FA-4-OS)) in the regulation of beta cell survival and secretory function. To investigate this role, the cells were initially exposed to conditions of glucotoxicity (30mmol/l glucose), lipotoxicity (0.5mmol/l palmitate), glucolipotoxicity (30mmol/l glucose + 0.5mmol/l palmitate) and cytokine-induced cell toxicity (25U/ml IL1b + 500U/ml TNFα) for 20 and 48 h. INS1 beta cells were subsequently treated with or without 100nmol/l of the CGA compounds for 48 h followed by 20 h exposure to glucolipotoxicity to measure cellular ATP content and 3/7 caspase activity, respectively, as an indication of cell viability and apoptosis. Additionally, insulin release was assessed by radioimmunoassay following 1 h static incubations with or without CA, FA and metabolites. Data were analysed by One-Way ANOVA using GraphPad prism software (version 8). Glucotoxicity, lipotoxicity and glucotoxicity or glucolipotoxicity combined with cytokines significantly reduced INS1 cell viability compared to control at 20 and 48 h (p < 0.001 vs 11mmol/l glucose, p < 0.05; Glucotoxicity vs 11mmol/l glucose at 20 h, n = 6), whereas cytokines alone did not significantly affect cellular ATP content. Moreover, pre-treatment for 48 h with CGAs alone or in combination did not affect INS1 beta-cell viability under basal conditions (n = 3, p > 0.2). Additional exposure to glucolipotoxicity for 20 h significantly decreased beta cell viability and survival and was not alleviated by pre- or co-treatment with CGAs (n = 3, p > 0.05). However, insulin release in response to 1 h incubation with 20 mmol/l glucose + 10μmol/l forskolin (FSK) + 100μmol/l 3-isobutyl-1-methylxanthine (IBMX) was significantly higher from cells pre-treated with CA and FA combined compared to controls (7.64 + 2.89pg insulin/5,000 cells/h vs 2.17 + 0.35pg insulin/5,000 cells/h; p < 0.01 vs. 20mmol/l glucose + 10μmol/l FSK + 100μmol/l IBMX only, n = 5). The results suggest that CGA derivatives from coffee do not directly modulate INS1 beta cell viability and apoptosis whereas the compounds may play a role in the regulation of beta cell secretory function.