Cytokine-induced beta-cell death is independent of endoplasmic reticulum stress signaling.
OBJECTIVE
Cytokines contribute to beta-cell destruction in type 1 diabetes. Endoplasmic reticulum (ER) stress-mediated apoptosis has been proposed as a mechanism for beta-cell death. We tested whether ER stress was necessary for cytokine-induced beta-cell death and also whether ER stress gene activation was present in beta-cells of the NOD mouse model of type 1 diabetes.


METHODS
INS-1 beta-cells or rat islets were treated with the chemical chaperone phenyl butyric acid (PBA) and exposed or not to interleukin (IL)-1beta and gamma-interferon (IFN-gamma). Small interfering RNA (siRNA) was used to silence C/EBP homologous protein (CHOP) expression in INS-1 beta-cells. Additionally, the role of ER stress in lipid-induced cell death was assessed.


RESULTS
Cytokines and palmitate triggered ER stress in beta-cells as evidenced by increased phosphorylation of PKR-like ER kinase (PERK), eukaryotic initiation factor (EIF)2alpha, and Jun NH(2)-terminal kinase (JNK) and increased expression of activating transcription factor (ATF)4 and CHOP. PBA treatment attenuated ER stress, but JNK phosphorylation was reduced only in response to palmitate, not in response to cytokines. PBA had no effect on cytokine-induced cell death but was associated with protection against palmitate-induced cell death. Similarly, siRNA-mediated reduction in CHOP expression protected against palmitate- but not against cytokine-induced cell death. In NOD islets, mRNA levels of several ER stress genes were reduced (ATF4, BiP [binding protein], GRP94 [glucose regulated protein 94], p58, and XBP-1 [X-box binding protein 1] splicing) or unchanged (CHOP and Edem1 [ER degradation enhancer, mannosidase alpha-like 1]).


CONCLUSIONS
While both cytokines and palmitate can induce ER stress, our results suggest that, in contrast to lipoapoptosis, the PERK-ATF4-CHOP ER stress-signaling pathway is not necessary for cytokine-induced beta-cell death.
Akerfeldt
Mia C
MC
Diabetes and Obesity Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales, Australia.
Howes
Jennifer
J
Chan
Jeng Yie
JY
Stevens
Veronica A
VA
Boubenna
Nacer
N
McGuire
Helen M
HM
King
Cecile
C
Biden
Trevor J
TJ
Laybutt
D Ross
DR
D051701:Activating Transcription Factor 4 / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D020148:Butyric Acid / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology; D053583:Interleukin-1beta / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D010168:Palmitates / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects*; D013312:Stress, Physiological / Q000187:drug effects / Q000502:physiology; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000378:metabolism
D051701:Activating Transcription Factor 4; D020148:Butyric Acid; D016207:Cytokines; D015852:Eukaryotic Initiation Factor-2; D007371:Interferon-gamma; D053583:Interleukin-1beta; D048031:JNK Mitogen-Activated Protein Kinases; D010168:Palmitates; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C081452:Atf4 protein, mouse; C497250:Ddit3 protein, mouse