The endoplasmic reticulum in pancreatic beta cells of type 2 diabetes patients.
OBJECTIVE
Pancreatic beta cells have highly developed endoplasmic reticulum (ER) due to their role in insulin secretion. Since ER stress has been associated with beta cell dysfunction, we studied several features of beta cell ER in human type 2 diabetes.


METHODS
Pancreatic samples and/or isolated islets from non-diabetic controls (ND) and type 2 diabetes patients were evaluated for insulin secretion, apoptosis (electron microscopy and ELISA), morphometric ER assessment (electron microscopy), and expression of ER stress markers in beta cell prepared by laser capture microdissection and in isolated islets.


RESULTS
Insulin release was lower and beta cell apoptosis higher in type 2 diabetes than ND islets. ER density volume was significantly increased in type 2 diabetes beta cells. Expression of alpha-mannosidase (also known as mannosidase, alpha, class 1A, member 1) and UDP-glucose glycoprotein glucosyl transferase like 2 (UGCGL2), assessed by microarray and/or real-time reverse transcriptase polymerase chain reaction (RT-PCR), differed between ND and type 2 diabetes beta cells. Expression of immunoglobulin heavy chain binding protein (BiP, also known as heat shock 70 kDa protein 5 [glucose-regulated protein, 78 kDa] [HSPA5]), X-box binding protein 1 (XBP-1, also known as XBP1) and C/EBP homologous protein (CHOP, also known as damage-inducible transcript 3 [DDIT3]) was not higher in type 2 diabetes beta cell or isolated islets cultured at 5.5 mmol/l glucose (microarray and real-time RT-PCR) than in ND samples. When islets were cultured for 24 h at 11.1 mmol/l glucose, there was induction of BiP and XBP-1 in type 2 diabetes islets but not in ND islets.


CONCLUSIONS
Beta cell in type 2 diabetes showed modest signs of ER stress when studied in pancreatic samples or isolated islets maintained at physiological glucose concentration. However, exposure to increased glucose levels induced ER stress markers in type 2 diabetes islet cells, which therefore may be more susceptible to ER stress induced by metabolic perturbations.
Marchetti
P
P
Department of Endocrinology and Metabolism, Metabolic Unit, Ospedale Cisanello, University of Pisa, Via Paradisa 2, 56100, Pisa, Italy. marchant@immr.med.unipi.it
Bugliani
M
M
Lupi
R
R
Marselli
L
L
Masini
M
M
Boggi
U
U
Filipponi
F
F
Weir
G C
GC
Eizirik
D L
DL
Cnop
M
M
D000368:Aged; D017209:Apoptosis / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000473:pathology* / Q000502:physiology* / Q000648:ultrastructure; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D020869:Gene Expression Profiling; D005947:Glucose / Q000494:pharmacology; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000473:pathology / Q000502:physiology / Q000648:ultrastructure*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D000071701:Regulatory Factor X Transcription Factors; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1
C497249:DDIT3 protein, human; D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D007328:Insulin; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D051742:Transcription Factor CHOP; D005947:Glucose