The ATP-sensitive potassium channel is a key molecular complex for glucose-stimulated insulin secretion in pancreatic ␤ cells. In humans, mutations in either of the two subunits for this channel, the sulfonylurea type 1 receptor (Sur1) or Kir6.2, cause persistent hyperinsulinemic hypoglycemia of infancy. We have generated and characterized Sur1 null mice. Interestingly, these animals remain euglycemic for a large portion of their life despite constant depolarization of membrane, elevated cytoplasmic free Ca 2؉ concentrations, and intact sensitivity of the exocytotic machinery to Ca 2؉ . A comparison of glucose-and meal-stimulated insulin secretion showed that, although Sur1 null mice do not secrete insulin in response to glucose, they secrete nearly normal amounts of insulin in response to feeding. Because Sur1 null mice lack an insulin secretory response to GLP-1, even though their islets exhibit a normal rise in cAMP by GLP-1, we tested their response to cholinergic stimulation. We found that perfused Sur1 null pancreata secreted insulin in response to the cholinergic agonist carbachol in a glucose-dependent manner. Together, these findings suggest that cholinergic stimulation is one of the mechanisms that compensate for the severely impaired response to glucose and GLP-1 brought on by the absence of Sur1, thereby allowing euglycemia to be maintained.Glucose-stimulated insulin secretion by the pancreatic ␤ cell requires the coupling of changes in glucose metabolism to alterations in membrane potential (1-4). In response to a rise in the intracellular ATP/ADP ratio that occurs with glucose metabolism the closure of ATP-sensitive potassium (K ATP ) 1 channels causes the ␤ cell membrane to depolarize. This, in turn, leads to the opening of voltage-gated L-type Ca 2ϩ channels, a rise in the cytoplasmic free Ca 2ϩ concentration ([Ca 2ϩ ] i ), and the subsequent exocytosis of insulin (5). The ␤ cell K ATP channel is an octameric complex of two proteins: an inward-rectifier K ϩ channel, Kir6.2, and the sulfonylurea receptor type 1 (Sur1), which are present in a 4:4 stoichiometry (6, 7). Kir6.2, which forms the channel pore, possesses intrinsic ATP sensitivity (8, 9), whereas Sur1, a member of a superfamily of ATPbinding cassette transporter proteins, provides sites for interaction with Mg-ADP (10). Sulfonylureas, which are widely used for treatment of patients with type 2 diabetes mellitus, act by binding to K ATP channels and stimulating their closure (10).Mutations in Sur1 are a frequent cause of persistent hyperinsulinemic hypoglycemia of infancy (PHHI), an autosomal recessive disorder characterized by excess and unregulated secretion of insulin. Because initial identification of Sur1 as a candidate gene for PHHI by , more than 50 different mutations in this gene, as well as 2 mutations in Kir6.2, have been identified in PHHI patients (12). Analyses of pancreatic ␤ cells from PHHI patients, as well as functional studies of mutated K ATP channels introduced into cultured cells, suggest that impaired K ATP channel...

We have identified two possible pathogenic mutations of PAX4, R164W, and IVS7-1G>A. For one of these, we have shown evidence of segregation with diabetes and a functional impact on PAX4 activity. Single-nucleotide polymorphism R192H might influence the age at onset of diabetes.

Type 2 diabetes is characterized by islet dysfunction resulting in hyperglycemia, which can then lead to further deterioration in islet function. A possible mechanism for hyperglycemia-induced islet dysfunction is the accumulation of advanced glycation end products (AGE). The DBA/2 mouse develops pancreatic islet dysfunction when exposed to a high glucose environment and/or obesity-induced insulin resistance. To determine the biochemical cause of dysfunction, DBA/2 and C57BL/6 control islets were incubated in 11·1 mM or 40 mM glucose in the absence or presence of the AGE inhibitor aminoguanidine (AG) for 10 days. Basal (2·8 mM glucose) insulin release was increased in both DBA/2 and C57BL/6 islets incubated with 40 mM vs 11·1 mM glucose for 10 days. Chronic exposure to hyperglycemia decreased glucose (20 mM)-stimulated insulin secretion in DBA/2 but not in C57BL/6 islets. AG significantly increased fold-induced insulin release in high glucose cultured DBA/2 mouse islets, but did not affect C57BL/6 islet function. DBA/2 islet glucokinase was significantly reduced following 40 mM glucose culture, compared with 11·1 mM glucose cultured DBA/2 islets and 40 mM glucose cultured C57BL/6 islets. Incubation of islets with AG resulted in a normalization of DBA/2 islet glucokinase levels. In conclusion, chronic high glucose-induced increases in AGE can result in islet dysfunction and this is associated with reduced glucokinase levels in a mouse model with susceptibility to islet failure.

No abstract

No abstract

Male hypogonadism associates with type 2 diabetes, and T can protect pancreatic β-cells from glucotoxicity. However, the protective mechanism is still unclear. This study thus aims to examine the antiapoptotic mechanism of T in pancreatic β cells cultured in high-glucose medium. T (0.0005-2 μg/mL) was added to INS-1 cells cultured in basal glucose or high-glucose media. Then cellular apoptosis, oxidative stress, and cell viability were measured. Endoplasmic reticulum (ER) stress markers and sensors and the antiapoptotic protein (B-cell lymphoma 2) were investigated by real-time PCR and Western blot analysis. ER stress markers were also measured in male mouse pancreatic islet cultured in similar conditions. T (0.05 and 0.5 μg/mL) did not have any effect on apoptosis and viability of INS-1 cells cultured in basal glucose medium, but it could reduce apoptosis and increase viability of INS-1 cells cultured in high-glucose medium. The protective effect of T is diminished by androgen receptor inhibitor. T (0.05 μg/mL) could significantly reduce nitrotyrosine levels, mRNA, and protein levels of the ER stress markers and sensor those that were induced when INS-1 cells were cultured in high-glucose medium. It could also significantly increase the survival proteins, sarco/endoplasmic reticulum Ca(2+) ATPase-2, and B-cell lymphoma 2 in INS-1 cells cultured in the same conditions. Similarly, it could reduce ER stress markers and increase sarco/endoplasmic reticulum Ca(2+) ATPase protein levels in male mouse pancreatic islets cultured in high-glucose medium. T can protect against male pancreatic β-cell apoptosis from glucotoxicity via the reduction of both oxidative stress and ER stress.

Hypogonadism in men is associated with an increased incidence of type 2 diabetes. Supplementation with testosterone has been shown to protect pancreatic b-cell against apoptosis due to toxic substances including streptozotocin and high glucose. One of the pathological mechanisms of glucose-induced pancreatic b-cell apoptosis is the induction of the local rennin-angiotensin-aldosterone system (RAAS). The role of testosterone in regulation of the pancreatic RAAS is still unknown. This study aims to investigate the protective action of testosterone against glucotoxicity-induced pancreatic b-cell apoptosis via alteration of the pancreatic RAAS pathway. Rat insulinoma cell line (INS-1) cells or isolated male mouse islets were cultured in basal and high-glucose media in the presence or absence of testosterone, losartan, and angiotensin II (Ang II), then cell apoptosis, cleaved caspase 3 expression, oxidative stress, and expression of angiotensin II type 1 receptor (AGTR1) and p47 phox mRNA and protein were measured. Testosterone and losartan showed similar effects in reducing pancreatic b-cell apoptosis. Testosterone significantly reduced expression of AGTR1 protein in INS-1 cells cultured in high-glucose medium or high-glucose medium with Ang II. Testosterone decreased the expression of AGTR1 and p47 phox mRNA and protein in comparison with levels in cells cultured in high-glucose medium alone. Furthermore, testosterone attenuated superoxide production when co-cultured with high-glucose medium. In contrast, when cultured in basal glucose, supplementation of testosterone did not have any effect on cell apoptosis, oxidative stress, and expression of AGT1R and p47 phox .In addition, high-glucose medium did not increase cleaved caspase 3 in AGTR1 knockdown experiments. Thus, our results indicated that testosterone prevents pancreatic b-cell apoptosis due to glucotoxicity through reduction of the expression of ATGR1 and its signaling pathway.

No abstract