Fibulin-2 deficiency attenuates angiotensin II-induced cardiac hypertrophy by reducing transforming growth factor-β signalling

Angll (angiotensin II) is a potent neurohormone responsible for cardiac hypertrophy, in which TGF (transforming growth factor)-beta serves as a principal downstream mediator. We recently found that ablation of fibulin-2 in mice attenuated TGF-beta signalling, protected mice against progressive ventricular dysfunction, and significantly reduced the mortality after experimental MI (myocardial infarction). In the present study, we investigated the role of fibulin-2 in Angll-induced TGF-beta signalling and subsequent cardiac hypertrophy. We performed chronic subcutaneous infusion of Angll in fibulin-2 null (FbIn2(-/-)), heterozygous (FbIn2(+/-)) and WT (wild-type) mice by a mini-osmotic pump. After 4 weeks of subpressor dosage of Angll infusion (0.2 mu g/kg of body weight per min), WT mice developed significant hypertrophy, whereas the FbIn2(-/-) showed no response. In WT, Angll treatment significantly up-regulated mRNAs for fibulin-2, ANP (atrial natriuretic peptide), TGF-beta 1, Col I (collagen type l), Col III (collagen type III), MMP (matrix metalloproteinase)-2 and MMP-9, and increased the phosphorylation of TGF-beta-downstream signalling markers, Smad2, TAK1 (TGF-beta-activated kinase 1) and p38 MAPK (mitogen-activated protein kinase), which were all unchanged in Angll-treated FbIn2(-/-) mice. The FbIn2+/- mice consistently displayed Angll-induced effects intermediate between WT and FbIn2(-/-). Pressor dosage of Angll (2 mg/kg of body weight per min) induced significant fibrosis in WT but not in FbIn2(-/-) mice with comparable hypertension and hypertrophy in both groups. Isolated CFs (cardiac fibroblasts) were treated with Angll, in which direct Angll effects and TGF-beta-mediated autocrine effects was observed in WT. The latter effects were totally abolished in FbIn2(-/-) - cells, suggesting that fibulin-2 is essential for Angll-induced TGF-beta activation. In conclusion our data indicate that fibulin-2 is essential for Angll-induced TGF-beta-mediated cardiac hypertrophy via enhanced TGF-beta activation and suggest that fibulin-2 is a potential therapeutic target to inhibit Angll-induced cardiac remodelling.