Effects of hyperglycemia on angiotensin II receptor type 1 expression and insulin secretion in an INS-1E pancreatic beta-cell line.
BACKGROUND
A local pancreatic islet renin-angiotensin system has been identified and found to be upregulated in type 2 diabetes mellitus. Inhibition of this system improves beta-cell function and structure. The effects of hyperglycemia, a condition observed in diabetes, on angiotensin II type 1 receptor (AT1R) expression and beta-cell secretory function have yet to be explored.


OBJECTIVE
This study investigated the effects of chronic hyperglycemia (glucotoxicity) on the expression of AT1Rs, and possibly thereby on oxidative stress-induced insulin release, in an INS-1E beta-cell line.


METHODS
INS-1E beta-cells cultured and incubated in different glucose concentrations with a varying time course.


METHODS
Immunocytochemistry was employed for the precise localization of AT1Rs in INS-1E cells. The effects of hyperglycemia-induced AT1R expression changes in gene and protein levels were examined by real-time RT-PCR and Western blot analysis, respectively. AT1R activation-mediated oxidative stress was assessed by changes in NADPH oxidase expression, and the level of superoxide production was determined by nitroblue tetrazolium (NBT) assay. Glucotoxicity-induced AT1R activation-mediated secretory dysfunction was also assessed by insulin release from INS-1E cells.


RESULTS
AT1R immunoreactivity was found to be localized specifically on the cell membrane. Chronic hyperglycemia resulted in dose-dependent upregulation of AT1R gene and protein expression accompanied by concomitantly-enhanced oxidative stress. Glucose-stimulated insulin secretion via AT1R activation was impaired by hyperglycemia.


CONCLUSIONS
These data indicate that hyperglycemia-induced AT1R activation impairs insulin secretion; this impairment may be mediated via AT1R-dependent oxidative stress.
Leung
Kwan Keung
KK
Department of Physiology, Faculty of Medicine, The Chinese University of Hong Kong. Shatin, Hong Kong, China.
Leung
Po Sing
PS
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology*; D006943:Hyperglycemia / Q000235:genetics* / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D018384:Oxidative Stress / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D044140:Receptor, Angiotensin, Type 1 / Q000235:genetics* / Q000378:metabolism; D014018:Tissue Distribution
D007328:Insulin; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D000804:Angiotensin II; D005947:Glucose