Endoplasmic reticulum stress induces apoptosis via IFN-γ production in pancreatic β-cells

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 834-867-Islet Biology
Bench to Bedside
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-845
Masashi Ichijo*, Hiroki Shimura, Fumihiko Furuya, Sayaka Ichijo, Shoichiro Tanaka, Soichi Takizawa, Kaoru Aida, Toyoshi Endo and Tetsuro Kobayashi
University of Yamanashi, Chuo, Yamanashi, Japan
Fulminant type 1 diabetes mellitus (FT1DM) is characterized by abrupt onset of severe hyperglycemia and rapid destruction of β-cells within one week from the onset of virus infection. Progressive destruction of pancreatic islets has been shown in a transgenic mouse model expressing IFN-γ driven by human insulin promoter. Therefore, we hypothesize that production of IFN-γ by β-cells itself is one of the leading candidates for destruction of cells in FT1DM. We recently reported that interferon (IFN)-γ was expressed in β-cells of FT1DM. The aim of the present study was to analyze underlying mechanisms determining secretion of IFN-γ in pancreatic β-cells of patients with FT1DM.

Since various cytokines have been shown to stimulate IFN-γ production in immune competent cells, we determined the effects of cytokines on IFN-γ production in MIN6 cells. However, expression of IFN-γ was not influenced in those treated with cytokines (TNFα, IL-1β, IL12+IL18, and IFN-α). Although we also reported the expression of RIG-I and MDA5, intracellular receptors for dsRNA, in pancreatic β-cells in FT1DM patients, treatment of MIN6 cells with poly(I:C) had no stimulatory effect on IFN-γ.

Endoplasmic reticulum (ER) stress is also one of cellular responses followed by virus infection. Therefore, we studied the effects of ER stress inducers on the IFN-γ expression in MIN6 cells. Treatment with 10 μg/ml of tunicamycin and 1 μM of thapsigargin exhibited a dose-dependent increase in IFN-γ mRNA expression up to 5.80±1.27-fold and 47.2±14.3-fold increase, respectively. Treatment with 10 μg/ml brefeldin A and 1 μM of palminate for 24 h also increased IFN-γ mRNA level 2.4±0.2-fold and 3.9±0.8-fold, respectively. In addition, glucose starvation by culturing MIN6 cells with no glucose for 24 h exhibited a 99.8±7.8-fold increase in IFN-γ mRNA expression. These ER stress inducers also increased IFN-γ protein levels analyzed by Western blot analysis. Experiments using kinase inhibitors demonstrated that expression of IFN-γ was mediated by JNK but not by p38 MAPK or MEK1/2. We further investigated the role of ER stress-induced IFN-γ production in pancreatic β-cells. In TUNEL staining, transfection of IFN-γ siRNA significantly suppressed thapsigargin-induced apoptosis in MIN6 cells. This result showed that ER stress-induced IFN-γ was involved in ER stress-induced apoptosis of pancreatic β-cells.

Our present study is the first report showing that ER stress induces IFN-γ expression in pancreatic β-cells. We suggest that ER stress-induced IFN-γ expression might play an important role in the abrupt β-cell apoptosis in FT1DM.

Nothing to Disclose: MI, HS, FF, SI, ST, ST, KA, TE, TK

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm