Upregulation of the mineralocorticoid system in obesity-associated diabetes leads to increased adipocyte Rho kinase activation and dysregulation of adipocytokines
Increased activation of the renin-angiotensin-aldosterone (RAAS) system is often associated with obesity and metabolic syndrome. We previously reported that aldosterone (aldo) produced by adipocytes regulate vascular function. Despite the fact that aldo production by adipocytes is increased in obesity, the role of aldo and its receptor, the mineralocorticoid receptor (MR), in the regulation of adipocytes biology and their downstream signaling remain elusive. Since Rho kinase (Rock) signaling has recently been implicated in the development of obesity, we tested the hypothesis that MR upregulation leads to dysregulation of adipokines through Rock-dependent mechanisms in obesity. Here we used obese db/db and lean db/+ mice, treated for 4 weeks with K canrenoate (MR antagonist, 30 mg/kg/day) and fasudil (Rock inhibitor, 30 mg/kg/day). Aldo production and Rock activation were measured by ELISA. mRNA and protein levels of adipokines and Rock signaling were assayed by real time PCR and immunoblotting. Plasma and adipocyte-derived aldo levels were increased in db/db mice (plasma: pg/mL, db/+ 310±33, db/db 567±43, p<0.05; adipocytes: pg/mL/μgRNA, db/+ 329±130, db/db 3125±494, p<0.002), an effect partially prevented by MR blockade (pg/mL/μgRNA: db/db 1278±176, p<0.01) and not by fasudil. Aldosterone synthase mRNA levels were increased (2.3 fold) as well as Nr3c2 (MR) (1.8 fold) and markers of MR activation (Sgk1 and Ngal- 2.3 and 2.9 fold) in mature adipocytes from db/db mice. In mature adipocytes from db/db, adiponectin mRNA levels were decreased (2.6 fold; p<0.01), whereas leptin and IL-6 mRNA levels were increased (2 and 4.8 fold; p<0.01). All changes were blocked by K canrenoate. Rock activity and downstream effectors, such as activation of MYPT1 and ERM, were increased in perivascular adipose tissue from db/db mice, an effect prevented by MR blockade. In conclusion, our data demonstrate that in db/db mice adipocyte MR-dependent activation of Rock is associated with a pro-inflammatory adipose phenotype that is normalized by MR blockade. Our results implicate a potential role of adipocyte aldo/MR through RhoA/Rock in adipocyte dysfunction in obesity/diabetes, important co-morbidities often associated with metabolic syndrome and hypertension
