Insulin-mediated regulation of the endothelial renin-angiotensin system and vascular cell growth.
OBJECTIVE
Insulin has a growth-stimulating effect for vascular tissue. At the tissue level, the vascular renin-angiotensin system (RAS) may be involved in the progression of atherosclerosis or vascular hypertrophy. We previously reported that the vascular RAS activity is activated in vascular smooth muscle cells (SMC) by insulin stimulation. However, the effect of insulin on the RAS in endothelial cells (EC) is not fully understood.


METHODS
Cultured human EC were incubated with or without insulin. After incubation for 48 h, cellular angiotensinogen and renin mRNA expression and levels in the cells were quantified by slot-blot hybridization and radioimmunoassay. Angiotensin I converting enzyme (ACE) activity in EC homogenates was measured by modified Cushman and Cheung method. EC growth and SMC with or without EC using co-culture were assessed by 3H-thymidine uptake for evaluation of their growth.


RESULTS
All doses of insulin (10, 100, 1000 microU/ml) decreased angiotensinogen and renin mRNA expression (angiotensinogen: 19.3%, P < 0.05; 25.4%, P < 0.01; 26.2%, P < 0.01, renin: 12.9%, P < 0.05; 21.3%, P < 0.01; 14.3%, P < 0.05, respectively). Both cellular angiotensinogen and renin level were also reduced by high levels of insulin. Neither 10 nor 100 microU/ml insulin increased cellular angiotensin converting enzyme (ACE) activity (2.17 to 3.48-folds, P = 0.077, 0.125, respectively) significantly, but 1000 microU/ml insulin strongly up-regulated ACE activity by 16.67-folds (P = 0.001) in cultured EC. For the co-culture with EC and SMC, 100 microU/ml insulin was not able to induce SMC but 1000 microU/ml insulin accelerated SMC growth in the co-culture. In contrast insulin that was over 100 microU/ml induced SMC growth in the sole culture of SMC.


CONCLUSIONS
Either low or high levels of insulin suppressed angiotensinogen and renin expression, however, high doses of insulin stimulated ACE activity in cultured human aortic EC. This may indicate that insulin regulates vascular cell growth and endothelial function via bifunctional modification of the vascular angiotensin generation.
Kamide
Kei
K
Department of Geriatric Medicine, Osaka University Graduate School of Medicine, Suita, Japan. kamide@hsp.ncvc.go.jp
Rakugi
Hiromi
H
Nagai
Michiko
M
Takiuchi
Shin
S
Matsukawa
Naomichi
N
Higaki
Jitsuo
J
Kawano
Yuhei
Y
Ogihara
Toshio
T
Tuck
Michael L
ML
D000808:Angiotensinogen / Q000096:biosynthesis / Q000187:drug effects; D001011:Aorta / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage*; D007328:Insulin / Q000008:administration & dosage*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D007703:Peptidyl-Dipeptidase A / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects; D044140:Receptor, Angiotensin, Type 1 / Q000096:biosynthesis / Q000187:drug effects; D012083:Renin / Q000096:biosynthesis / Q000187:drug effects; D012084:Renin-Angiotensin System / Q000187:drug effects* / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects
D007004:Hypoglycemic Agents; D007328:Insulin; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D000808:Angiotensinogen; D007703:Peptidyl-Dipeptidase A; D012083:Renin