High glucose-induced impairment in insulin secretion is associated with reduction in islet glucokinase in a mouse model of susceptibility to islet dysfunction

Abstract

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.

Cellular responses of novel human pancreatic β-cell line, 1.1B4 to hyperglycemia

“…[16][17][18][19][20][21][22] Basal insulin release at 5.6 mM glucose was not affected by hyperglycemia but the secretory response to 16.7 mM glucose was impaired by 48 and 72 h exposure to 25 mM glucose. We also observed that insulin release from 1.1B4 cells chronically exposed to hyperglycemia for 48 and 72 h was significantly reduced in response to alanine, GLP-1, KCl, elevated Ca 2+ , or forskolin.…”

“…29 This is supported by observations in INS-1E cells exposed to hyperglycemia and isolated human islets. 19,[30][31][32][33][34] Such downregulation could be due to concomitant reduction in PDX1, which is involved in regulation of insulin gene transcription and expression of other important genes involved in β-cell secretory function. 16 Reduced PDX1 levels have been observed also in HIT-T15 cells, INS-1E cells and human islets treated with high glucose.…”

Identification of ABCC8 as a contributory gene to impaired early-phase insulin secretion in NZO mice

“…Western blotting was performed to determine protein expression levels of SUR1 and Kir6.2 in the pellet fraction of homogenised pancreata as previously described (Kooptiwut et al 2005). Protein was loaded onto a 10% resolving gel (Kir6.2) or a 7.5% resolving gel (SUR1) and immunodetected using their respective specific primary antibodies from Santa Cruz Biotechnology, Inc. at a 1:500 dilution overnight at 4 8C; anti-Kir6.2 (H-55) (sc-20809) and anti-SUR1 (C-16) (sc-5789) antibodies respectively.…”

“…Islets were isolated and incubated for insulin secretion studies as previously described (Kooptiwut et al 2005, Zraika, et al 2006. Islets were prepared for cDNA synthesis and subsequent mRNA analysis using the method as previously described (Aston-Mourney et al 2007).…”

Too much of a good thing: why it is bad to stimulate the beta cell to secrete insulin

“…We have recently completed a 7-year study on the DBA/2 mouse, a strain that is susceptible to beta cell failure and diabetes when genetically stressed with obesity [15] or exposed to a high-glucose environment [16,17]. We found that in contrast to C57BL/6 mice, which have a genetic disruption in Nnt, and the 129T2 mice, which show low levels of expression, the diabetes-susceptible DBA/2 mice show a fivefold overexpression of this gene, which encodes the mitochondrial proton pump known as nicotinamide nucleotide transhydrogenase.…”