Hypoxia Increases β-Cell Death by Activating Pancreatic Stellate Cells within the Islet

BackgroundHypoxia can occur in pancreatic islets in type 2 diabetes mellitus. Pancreatic stellate cells (PSCs) are activated during hypoxia. Here we aimed to investigate whether PSCs within the islet are also activated in hypoxia, causing β-cell injury.MethodsIslet and primary PSCs were isolated from Sprague Dawley rats, and cultured in normoxia (21% O2) or hypoxia (1% O2). The expression of α-smooth muscle actin (α-SMA), as measured by immunostaining and Western blotting, was used as a marker of PSC activation. Conditioned media (hypoxia-CM) were obtained from PSCs cultured in hypoxia.ResultsIslets and PSCs cultured in hypoxia exhibited higher expressions of α-SMA than did those cultured in normoxia. Hypoxia increased the production of reactive oxygen species. The addition of N-acetyl-L-cysteine, an antioxidant, attenuated the hypoxia-induced PSC activation in islets and PSCs. Islets cultured in hypoxia-CM showed a decrease in cell viability and an increase in apoptosis.ConclusionPSCs within the islet are activated in hypoxia through oxidative stress and promote islet cell death, suggesting that hypoxia-induced PSC activation may contribute to β-cell loss in type 2 diabetes mellitus.

Hypoxia Increases β-Cell Death by Activating Pancreatic Stellate Cells within the Islet

BackgroundHypoxia can occur in pancreatic islets in type 2 diabetes mellitus. Pancreatic stellate cells (PSCs) are activated during hypoxia. Here we aimed to investigate whether PSCs within the islet are also activated in hypoxia, causing β-cell injury.MethodsIslet and primary PSCs were isolated from Sprague Dawley rats, and cultured in normoxia (21% O2) or hypoxia (1% O2). The expression of α-smooth muscle actin (α-SMA), as measured by immunostaining and Western blotting, was used as a marker of PSC activation. Conditioned media (hypoxia-CM) were obtained from PSCs cultured in hypoxia.ResultsIslets and PSCs cultured in hypoxia exhibited higher expressions of α-SMA than did those cultured in normoxia. Hypoxia increased the production of reactive oxygen species. The addition of N-acetyl-L-cysteine, an antioxidant, attenuated the hypoxia-induced PSC activation in islets and PSCs. Islets cultured in hypoxia-CM showed a decrease in cell viability and an increase in apoptosis.ConclusionPSCs within the islet are activated in hypoxia through oxidative stress and promote islet cell death, suggesting that hypoxia-induced PSC activation may contribute to β-cell loss in type 2 diabetes mellitus.

Protective Effect of Heme Oxygenase-1 on High Glucose-Induced Pancreatic beta-Cell Injury

BACKGROUND: Glucose toxicity that is caused by chronic exposure to a high glucose concentration leads to islet dysfunction and induces apoptosis in pancreatic beta-cells. Heme oxygenase-1 (HO-1) has been identified as an anti-apoptotic and cytoprotective gene. The purpose of this study is to investigate whether HO-1 up-regulation when using metalloprotophyrin (cobalt protoporphyrin, CoPP) could protect pancreatic beta-cells from high glucose-induced apoptosis. METHODS: Reverse transcription-polymerase chain reaction was performed to analyze the CoPP-induced mRNA expression of HO-1. Cell viability of INS-1 cells cultured in the presence of CoPP was examined by acridine orange/propidium iodide staining. The generation of intracellular reactive oxygen species (ROS) was measured using flow cytometry. Glucose stimulated insulin secretion (GSIS) was determined following incubation with CoPP in different glucose concentrations. RESULTS: CoPP increased HO-1 mRNA expression in both a dose- and time-dependent manner. Overexpression of HO-1 inhibited caspase-3, and the number of dead cells in the presence of CoPP was significantly decreased when exposed to high glucose conditions (HG). CoPP also decreased the generation of intracellular ROS by 50% during 72 hours of culture with HG. However, decreased GSIS was not recovered even in the presence of CoPP. CONCLUSION: Our data suggest that CoPP-induced HO-1 up-regulation results in protection from high glucose-induced apoptosis in INS-1 cells; however, glucose stimulated insulin secretion is not restored.

Decreased Expression and Induced Nucleocytoplasmic Translocation of Pancreatic and Duodenal Homeobox 1 in INS-1 Cells Exposed to High Glucose and Palmitate

BACKGROUND: Type 2 diabetes mellitus (T2DM) is often accompanied by increased levels of circulating fatty acid. Elevations in fatty acids and glucose for prolonged periods of time have been suggested to cause progressive dysfunction or apoptosis of pancreatic beta cells in T2DM. However, the precise mechanism of this adverse effect is not well understood. METHODS: INS-1 rat-derived insulin-secreting cells were exposed to 30 mM glucose and 0.25 mM palmitate for 48 hours. RESULTS: The production of reactive oxygen species increased significantly. Pancreatic and duodenal homeobox 1 (Pdx1) expression was down-regulated, as assessed by reverse transcription-polymerase chain reaction and Western blot analyses. The promoter activities of insulin and Pdx1 were also diminished. Of note, there was nucleocytoplasmic translocation of Pdx1, which was partially prevented by treatment with an antioxidant, N-acetyl-L-cysteine. CONCLUSION: Our data suggest that prolonged exposure of beta cells to elevated levels of glucose and palmitate negatively affects Pdx1 expression via oxidative stress.

Transdifferentiation of Enteroendocrine K-cells into Insulin-expressing Cells / 당뇨병

BACKGROUND: Despite a recent breakthough in human islet transplantation for treating type 1 diabetes mellitus, the limited availability of donor pancreases remains a major obstacle. Endocrine cells within the gut epithelium (enteroendocrine cells) and pancreatic beta cells share similar pathways of differentiation during embryonic development. In particular, K-cells that secrete glucose-dependent insulinotropic polypeptide (GIP) have been shown to express many of the key proteins found in beta cells. Therefore, we hypothesize that K-cells can be transdifferentiated into beta cells because both cells have remarkable similarities in their embryonic development and cellular phenotypes. METHODS: K-cells were purified from heterogeneous STC-1 cells originating from an endocrine tumor of a mouse intestine. In addition, a K-cell subclone expressing stable Nkx6.1, called "Kn4-cells," was successfully obtained. In vitro differentiation of K-cells or Kn4-cells into beta cells was completed after exendin-4 treatment and serum deprivation. The expressions of insulin mRNA and protein were examined by RT-PCR and immunocytochemistry. The interacellular insulin content was also measured. RESULTS: K-cells were found to express glucokinase and GIP as assessed by RT-PCR and Western blot analysis. RT-PCR showed that K-cells also expressed Pdx-1, NeuroD1/Beta2, and MafA, but not Nkx6.1. After exendin-4 treatment and serum deprivation, insulin mRNA and insulin or C-peptide were clearly detected in Kn4-cells. The intracellular insulin content was also increased significantly in these cells. CONCLUSION: K-cells are an attractive potential source of insulin-producing cells for treatment of type 1 diabetes mellitus. However, more experiments are necessary to optimize a strategy for converting K-cells into beta cells.