High Glucose Causes Apoptosis in Cultured Human Pancreatic Islets of Langerhans

Abstract

Type 2 diabetes is characterized by insulin resistance and inadequate insulin secretion. In the advanced stages of the disease, ␤-cell dysfunction worsens and insulin therapy may be necessary to achieve satisfactory metabolic control. Studies in autopsies found decreased ␤-cell mass in pancreas of people with type 2 diabetes. Apoptosis, a constitutive program of cell death modulated by the Bcl family genes, has been implicated in loss of ␤-cells in animal models of type 2 diabetes. In this study, we compared the effect of 5 days' culture in high glucose concentration (16.7 mmol/l) versus normal glucose levels (5.5 mmol/l) or hyperosmolar control (mannitol 11 mmol/l plus glucose 5 mmol/l) on the survival of human pancreatic islets. Apoptosis, analyzed by flow cytometry and electron and immunofluorescence microscopy, was increased in islets cultured in high glucose (HG5) as compared with normal glucose (NG5) or hyperosmolar control (NG5؉MAN5). We also analyzed by reverse transcriptase-polymerase chain reaction and Western blotting the expression of the Bcl family genes in human islets cultured in normal glucose or high glucose. The antiapoptotic gene Bcl-2 was unaffected by glucose change, whereas Bcl-xl was reduced upon treatment with HG5. On the other hand, proapoptotic genes Bad, Bid, and Bik were overexpressed in the islets maintained in HG5. To define the pancreatic localization of Bcl proteins, we performed confocal immunofluorescence analysis on human pancreas. Bad and Bid were specifically expressed in ␤-cells, and Bid was also expressed, although at low levels, in the exocrine pancreas. Bik and Bcl-xl were expressed in other endocrine islet cells as well as in the exocrine pancreas. These data suggest that in human islets, high glucose may modulate the balance of proapoptotic and antiapoptotic Bcl proteins toward apoptosis, thus favoring ␤-cell death.

Glucagon-like peptide-1 prevents beta cell glucolipotoxicity

“…The addition of GLP-1 completely prevented lipotoxicity. The relatively high basal level of apoptosis is similar to that reported by previous studies of isolated intact human islets (9%) [14] or of islets after dispersion (22%) [10]. This might be due in part to: (i) the presence of a low concentration of serum in the incu- bation medium; (ii) the stress imposed by the dissociation process; and (iii) central necrosis of islets after their isolation.…”

“…Short-term exposure of the beta cell to elevated concentrations of glucose promotes insulin release and enhances insulin biosynthesis [1,5]. However, chronic hyperglycaemia causes beta cell dysfunction characterised by reduced insulin biosynthesis [6] and increased levels of apoptosis (glucotoxicity) [7,8,9,10,11]. Similarly, acute exposure to NEFA potentiates glucose-induced insulin secretion by beta cells [12], whereas prolonged exposure to high concentrations of NEFA triggers beta cell apoptosis (lipotoxicity) [13,14,15,16,17].…”

Differential beta cell responses to hyperglycaemia and insulin resistance in two novel congenic strains of diabetes (FVB-Lepr db ) and obese (DBA-Lep ob ) mice

“…In the case of beta-cell proliferation, it might be interesting to investigate expression of genes that have been implicated in controlling beta-cell mass, such as Igf1r, Insr, Irs2, and the MODY genes [34,35,36]. It would also be interesting to study the same set of genes in the regulation of cell death, in addition to the genes implicated in apoptosis, such as the BAD family of genes [37]. Further studies to measure the rates of beta-cell turnover will be required to find the relative contributions of these two processes to the beta-cell mass expansion of obese FVB mice.…”

Sustained insulin secretory response in human islets co-cultured with pancreatic duct-derived epithelial cells within a rotational cell culture system

“…This precisely controlled milieu is disturbed by islet processing, which results in the loss of many important physical, cellular and trophic signals required for beta cell differentiation, survival and function [11,12]. Notably, detachment from the ECM has been shown to leave islets prone to fragmentation [5] and susceptible to an increased frequency of apoptotic events [13,14]. Efforts to restore the vital associations between the endocrine and ECM compartments of the pancreas in vitro have yielded promising results, with numerous studies reporting improved beta cell viability of islets cultured in the presence of soluble components of the basement membrane or on artificial matrices [7,10,15].…”