LAUSR

Endogenous cardiotonic steroid, marinobufagenin (MBG), induces Fli1-dependent tissue fibrosis. We hypothesized that an increase in MBG initiates the development of aortic fibrosis in salt-loaded rats with type 2 diabetes mellitus (DM2) via pressure-independent mechanism.DM2 was induced by a single intraperitoneal administration of 65 mg/kg streptozotocin to neonatal (4-5 days) male Wistar rats. Eight weeks old DM2 rats received water or 1.8% NaCl (DM-NaCl) solution for 4 weeks (n=16); half of DM-NaCl rats were treated with anti-MBG monoclonal antibody (mAb) (DM-NaCl-AB) during week 4 of salt loading; control intact rats received water (n=8/group). Blood pressure (BP), MBG, erythrocyte Na/K-ATPase activity, aortic weights and levels of fibrosis markers (Fli1, PKCδ, TGFβ1, SMAD5, fibronectin, collagen-1), and sensitivity of the aortic explants to the vasorelaxant effect of sodium nitroprusside were assessed. No changes in systolic BP were observed while erythrocyte Na/K-ATPase was inhibited by 30%, plasma MBG was doubled, and aortic markers of fibrosis became elevated in DM-NaCl rats vs. control. Treatment of DM-NaCl rats with anti-MBG mAb activated Na/K-ATPase, prevented increases in aortic weights, and the levels of fibrosis markers returned to the control levels. The responsiveness of the aortic rings from DM-NaCl rats to the relaxant effect of sodium nitroprusside was reduced (EC50=29 nmol/L) vs. control rings (EC50=7 nmol/L) and was restored by anti-MBG mAb (EC50=9 nmol/L). Our results suggest that in salt-loaded diabetic rats MBG stimulates aortic collagen synthesis in a pressure-independent fashion, and that two pro-fibrotic mechanisms, Fli1-dependent and TGFβ-dependent, underlie its effects.