Protective role of Gremlin-1 in myocardial function.

Abstract

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. 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-β proteins by confocal microscopy and co-immunoprecipitation experiments. The interaction between Gremlin-1 and TGF-β was analysed by photon correlation spectroscopy. Gremlin-1 modulation of the TGF-β-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. 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-β (TGF-β) expressed in fibroblasts and inflammatory cell infiltrates (P<.05). Gremlin-1 reduces TGF-β-induced collagen production of myocardial fibroblasts by approximately 20% (P<.05). We found that Gremlin-1 binds with high affinity to TGF-β (KD =54nmol/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). The present data disclose Gremlin-1 as an antagonist of TGF-β and presume a role for Gremlin-1/TGF-β interaction in myocardial remodelling following myocardial ischaemia.