Protective role of Gremlin-1 in myocardial function

Background Gremlin-1 is a cystine knot protein and is expressed in organs developing fibrosis. Transient ischaemia leads to myocardial fibrosis, a major determinant of impaired myocardial function. Materials and methods Expression of Gremlin-1 was investigated in infarcted myocardium by real-time PCR, Western blot analysis, histological and immunohistochemistry staining. We further elaborated the colocalization of Gremlin-1 and TGF-beta proteins by confocal microscopy and co-immunoprecipitation experiments. The interaction between Gremlin-1 and TGF-beta was analysed by photon correlation spectroscopy. Gremlin-1 modulation of the TGF-beta-dependent collagen I synthesis in fibroblasts was investigated using ELISA and immunohistochemistry experiments. The effect of prolonged administration of recombinant Gremlin-1 on myocardial function following ischaemia/reperfusion was accessed by echocardiography and immunohistochemistry. Results Gremlin-1 is expressed in myocardial tissue and infiltrating cells after transient myocardial ischaemia (P < .05). Gremlin-1 colocalizes with the pro-fibrotic cytokine transforming growth factor-beta (TGF-beta) expressed in fibroblasts and inflammatory cell infiltrates (P < .05). Gremlin-1 reduces TGF-beta-induced collagen production of myocardial fibroblasts by approximately 20% (P < .05). We found that Gremlin-1 binds with high affinity to TGF-beta (K-D = 54 nmol/L) as evidenced by photon correlation spectroscopy and co-immunoprecipitation. intravenous administration of (m)Gremlin-1-Fc, but not of equivalent amount of Fc control, significantly reduced infarct size by approximately 20%. In the (m)Gremlin-1-Fc group, infarct area was reduced by up to 30% in comparison with mice treated with Fc control (I/LV: 4.8 +/- 1.2% vs 6.0 +/- 1.2% P < .05; I/AaR: 15.2 +/- 1.5% vs 21.1 +/- 5%, P < .05). Conclusions The present data disclose Gremlin-1 as an antagonist of TGF-beta and presume a role for Gremlin-1/TGF-beta interaction in myocardial remodelling following myocardial ischaemia.