Endoplasmic reticulum stress contributes to beta cell apoptosis in type 2 diabetes.
OBJECTIVE
Increased lipid supply causes beta cell death, which may contribute to reduced beta cell mass in type 2 diabetes. We investigated whether endoplasmic reticulum (ER) stress is necessary for lipid-induced apoptosis in beta cells and also whether ER stress is present in islets of an animal model of diabetes and of humans with type 2 diabetes.


METHODS
Expression of genes involved in ER stress was evaluated in insulin-secreting MIN6 cells exposed to elevated lipids, in islets isolated from db/db mice and in pancreas sections of humans with type 2 diabetes. Overproduction of the ER chaperone heat shock 70 kDa protein 5 (HSPA5, previously known as immunoglobulin heavy chain binding protein [BIP]) was performed to assess whether attenuation of ER stress affected lipid-induced apoptosis.


RESULTS
We demonstrated that the pro-apoptotic fatty acid palmitate triggers a comprehensive ER stress response in MIN6 cells, which was virtually absent using non-apoptotic fatty acid oleate. Time-dependent increases in mRNA levels for activating transcription factor 4 (Atf4), DNA-damage inducible transcript 3 (Ddit3, previously known as C/EBP homologous protein [Chop]) and DnaJ homologue (HSP40) C3 (Dnajc3, previously known as p58) correlated with increased apoptosis in palmitate- but not in oleate-treated MIN6 cells. Attenuation of ER stress by overproduction of HSPA5 in MIN6 cells significantly protected against lipid-induced apoptosis. In islets of db/db mice, a variety of marker genes of ER stress were also upregulated. Increased processing (activation) of X-box binding protein 1 (Xbp1) mRNA was also observed, confirming the existence of ER stress. Finally, we observed increased islet protein production of HSPA5, DDIT3, DNAJC3 and BCL2-associated X protein in human pancreas sections of type 2 diabetes subjects.


CONCLUSIONS
Our results provide evidence that ER stress occurs in type 2 diabetes and is required for aspects of the underlying beta cell failure.
Laybutt
D R
DR
Diabetes and Obesity Research Program, Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, NSW, Australia.
Preston
A M
AM
Akerfeldt
M C
MC
Kench
J G
JG
Busch
A K
AK
Biankin
A V
AV
Biden
T J
TJ
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism* / Q000473:pathology*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation; D006360:Heat-Shock Proteins / Q000235:genetics / Q000502:physiology; D006801:Humans; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000473:pathology*; D008055:Lipids / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018832:Molecular Chaperones / Q000235:genetics / Q000502:physiology; D018384:Oxidative Stress; D012333:RNA, Messenger / Q000378:metabolism
D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D008055:Lipids; D018832:Molecular Chaperones; D012333:RNA, Messenger