Fibulin-2 is essential for angiotensin II-induced myocardial fibrosis mediated by transforming growth factor (TGF)-β.
Fibrosis is an ominous pathological process in failing myocardium, but its pathogenesis is poorly understood. We recently reported that loss of an extracellular matrix (ECM) protein, fibulin-2, protected against ventricular dysfunction after myocardial infarction (MI) in association with absence of activation of transforming growth factor (TGF)-β signaling and suppressed upregulation of ECM protein expression during myocardial remodeling. Here we investigated the role of fibulin-2 in the development of myocardial hypertrophy and fibrosis induced by continuous pressor-dosage of angiotensin II (Ang II) infusion. Both wild type (WT) and fibulin-2 null (Fbln2KO) mice developed comparable hypertension and myocardial hypertrophy by Ang II infusion. However, myocardial fibrosis with significant upregulation of collagen type I and III mRNA was only seen in WT but not in Fbln2KO mice.Transforming growth factor (TGF)-β1 mRNA and its downstream signal, Smad2, were significantly upregulated in WT by Ang II, whereas there were no Ang II-induced changes in Flbn2KO, suggesting fibulin-2 is necessary for Ang II-induced TGF-β signaling that induces myocardial fibrosis. To test whether fibulin-2 is sufficient for Ang II-induced TGF-β upregulation, isolated Flbn2KO cardiac fibroblasts were treated with Ang II after transfecting with fibulin-2 expression vector or pretreating with recombinant fibulin-2 protein. Ang II-induced TGF-β signaling in Fbln2KO cells was partially rescued by exogenous fibulin-2, suggesting that fibulin-2 is required and probably sufficient for Ang II-induced TGF-β activation. Smad2 phosphorylation was induced just by adding recombinant fibulin-2 to KO cells, suggesting that extracellular interaction between fibulin-2 and latent TGF-β triggered initial TGF-β activation. Our study indicates that Ang II cannot induce TGF-β activation without fibulin-2 and that fibulin-2 has an essential role in Ang II-induced TGF-β signaling and subsequent myocardial fibrosis. Fibulin-2 can be considered as a critical regulator of TGF-β that induces myocardial fibrosis.
Nemours Biomedical Research and Nemours Cardiac Center, Nemours/Alfred I. duPont Hospital for Children, Wilmington, DE, USA.
Shaukat A
SA
Khan
Nemours Biomedical Research and Nemours Cardiac Center, Nemours/Alfred I. duPont Hospital for Children, Wilmington, DE, USA.
Hailong
H
Dong
Nemours Biomedical Research and Nemours Cardiac Center, Nemours/Alfred I. duPont Hospital for Children, Wilmington, DE, USA.
Jennifer
J
Joyce
Department of Biochemistry, Oita University School of Medicine, Oita, Japan.
Takako
T
Sasaki
Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, PA, USA.
Mon-Li
ML
Chu
Nemours Biomedical Research and Nemours Cardiac Center, Nemours/Alfred I. duPont Hospital for Children, Wilmington, DE, USA.
Takeshi
T
Tsuda
D000804:Angiotensin II / Q000008:administration & dosage / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006332:Cardiomegaly / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D016326:Extracellular Matrix Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005355:Fibrosis; D006333:Heart Failure / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology*; D015398:Signal Transduction; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D020257:Ventricular Remodeling
D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; C508961:Tgfb1 protein, mouse; D053773:Transforming Growth Factor beta1; C084612:fibulin 2; D000804:Angiotensin II