title: Aldosterone suppresses insulin signaling via the downregulation of insulin receptor substrate-1 in vascular smooth muscle cells.
abstract: Clinical reports indicate that patients with primary aldosteronism commonly have impaired glucose tolerance; however, the relationship between aldosterone and insulin signaling pathway has not been clarified. In this study, we examined the effects of aldosterone treatment on insulin receptor substrate-1 expression and insulin signaling pathway including Akt phosphorylation and glucose uptake in rat vascular smooth muscle cells. Insulin receptor substrate-1 protein expression and Akt phosphorylation were determined by Western blot analysis with anti-insulin receptor substrate-1 and phosphorylated-Akt antibodies, respectively. Glucose metabolism was evaluated using (3)H-labeled 2-deoxy-d-glucose uptake. Aldosterone (1-100 nmol/L) dose-dependently decreased insulin receptor substrate-1 protein expression with a peak at 18 hours (n=4). Aldosterone-induced degradation of insulin receptor substrate-1 was markedly attenuated by treatment with the selective mineralocorticoid receptor antagonist eplerenone (10 micromol/L; n=4). Furthermore, degradation was blocked by the Src inhibitor PP1 (20 micromol/L; n=4). Treatment with antioxidants, N-acetylcysteine (10 mmol/L), or ebselen (40 micromol/L) also attenuated aldosterone-induced insulin receptor substrate-1 degradation (n=4). In addition, proteasome inhibitor MG132 (1 micromol/L) prevented insulin receptor substrate-1 degradation (n=4). Aldosterone treatment abolished insulin-induced Akt phosphorylation (100 nmol/L; 5 minutes; n=4). Furthermore, aldosterone pretreatment decreased insulin-stimulated (100 nmol/L; 60 minutes; n=4) glucose uptake by 50%, which was reversed by eplerenone (10 micromol/L; n=4). These data indicate that aldosterone decreases insulin receptor substrate-1 expression via Src and reactive oxygen species stimulation by proteasome-dependent degradation in vascular smooth muscle cells; thus, aldosterone may be involved in the pathogenesis of vascular insulin resistance via oxidative stress.
authors.affiliation: Department of Cardiorenal and Cerebrovascular Medicine, Faculty of Medicine, Kagawa University, Kita-gun, Japan. hitomi@kms.ac.jp
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Hitomi
authors.forename: Hideyasu
authors.initials: H
authors.lastname: Kiyomoto
authors.forename: Akira
authors.initials: A
authors.lastname: Nishiyama
authors.forename: Taiga
authors.initials: T
authors.lastname: Hara
authors.forename: Kumiko
authors.initials: K
authors.lastname: Moriwaki
authors.forename: Kumiko
authors.initials: K
authors.lastname: Kaifu
authors.forename: Genei
authors.initials: G
authors.lastname: Ihara
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Fujita
authors.forename: Toyomu
authors.initials: T
authors.lastname: Ugawa
authors.forename: Masakazu
authors.initials: M
authors.lastname: Kohno
mesh_terms: D000450:Aldosterone / Q000502:physiology*; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D015536:Down-Regulation; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000502:physiology; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D019061:src-Family Kinases / Q000502:physiology
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D017382:Reactive Oxygen Species; D000804:Angiotensin II; D000450:Aldosterone; D019061:src-Family Kinases; D051058:Oncogene Protein v-akt; D046988:Proteasome Endopeptidase Complex