Angiopoietin-like 4 (ANGPTL4) is a secreted protein of the Angiopoietins family involved in angiogenesis and vessel maintenance. We identified angptl4 as a hypoxia induced gene in endothelial cells in vitro. In humans, ANGPTL4 is expressed in hypoxic areas such as vascular cells of human critical leg ischemia samples. In the heart, focal expression in myocytes, vessels and infiltrating monocytes was also evidenced in infarcted areas.
Material & Methods
We used C57/Bl6 angptl4 knock-out mice (Regeneron pharmaceuticals, Tarrytown). The pattern of expression of angptl4 was determined during development using Lac Z staining allowed by the insertion of a beta-galactosidase cassette. At the adult stage, myocardial infarction was induced by ligation of the left coronary artery for 45mn. The hearts were analyzed 24 h, 48 h and 2 weeks after reperfusion.
During embryonic development, angptl4 is expressed in endothelial cells from intersomitic, limb bud (E10,5-E11,5) and heart vessels (E12,5-E14,5). At later stages (from E15,5), angptl4 is also expressed in skin vessels.
Angptl4 knock-out mice showed an increased infarcted area compared to wild type littermates mice (+31 %, p=0.01) 48h after reperfusion, suggesting a cardioprotective role of ANGPTL4. Immunohistological analyzes revealed dramatic tissue damages in the angptl4 knock-out mice in term of oedema, hemorragies and necrosis correlated with an increased circulating monocytes infiltration (+36 %, p=0.004). PECAM-1 stainings revealed morphologically modified angiogenic capillaries in angptl4 KO mice compared to controls suggesting a modulated vascular permeability. No difference was observed between isolated cardiomyocytes from both groups submitted to a survival assay under hypoxia.
Angptl4 is expressed by endothelial cells during embryonic and during adult stage following hypoxic stress. Experiments performed using the ischemia-reperfusion model show that ANGPTL4 has a cardioprotective role modulating both endothelium integrity and post-ischaemic inflammation.Le texte complet de cet article est disponible en PDF.