Fibulin-1 suppresses endothelial to mesenchymal transition in the proximal outflow tract

Abstract

Endothelial to mesenchymal transition (EMT) that occurs during cardiac outflow tract (OFT) development is critical for formation of the semilunar valves. Fibulin-1 (Fbln1) is an extra-cellular matrix protein that is present at several sites of EMT, including the OFT (i.e., E9.5–10.5). The aim of this study was to determine the role of Fbln1 in EMT during the earliest events of OFT development. Examination of proximal OFT cushions in Fbln1 null embryos detected hypercellularity at both E9.5 (93% increase; p = 0.002) and E10.5 (43% increase; p = 0.01) as compared to wild type, suggesting that Fbln1 normally suppresses OFT endocardial cushion EMT. This was supported by studies of proximal OFT cushion explants, which showed that explants from Fbln1 null embryos displayed a 58% increase in cells migrating from the explants as compared to wild type (p = 0.005). We next evaluated the effects of Fbln1 deficiency on the expression of factors that regulate proximal OFT EMT. At E9.5, Fbln1 null proximal OFT endocardium and EMT-derived mesenchyme showed increased TGFβ2 (58% increase; p = 0.01) and increased Snail1-positive nuclei (27% increase; p = 0.0003). Histological examination of OFT cushions in Fbln1 null embryos (E9.5) also detected cells present in the cushion that were determined to be erythrocytes based on round morphology, autofluorescence, and positive staining for hemoglobin. Erythrocytes were also detected in Fbln1 null OFT cushions at E10.5. Together, the findings indicate that Fbln1 normally suppresses proximal OFT EMT preventing proximal cushion hypercellularity and blood cell accumulation.

Widespread cis-regulatory convergence between the extinct Tasmanian tiger and gray wolf

“…Correspondingly, disruption of TGF beta signaling in Ltbp1-null mice results in reduced snout length and a more compact head shape (Drews et al 2008). Bioavailability of TGF beta ligands is further influenced by other fibrillin-interacting proteins, such as fibulins (Harikrishnan et al 2015;Radice et al 2015;Tian et al 2015). Genes encoding two fibulins (Fbln2 and Fbln5) were also associated with TWARs (TWAR15.Chr6 and TWAR8.Chr12, respectively).…”

Development and evolution of the metazoan heart

“…Endocardial cushions, beginning as acellular cardiac jelly, will develop in the AV canal as well as in the OFT. The cardiac jelly, sometimes considered the myocardial basement membrane, contains extracellular matrix components such as hyaluronan and aggrecan and will become cellularized by endocardial‐mesenchymal transition (EMT) primarily from the overlying endocardium . Secondarily, other cell populations take part in expanding the cushions.…”

“…The cardiac jelly, sometimes considered the myocardial basement membrane, contains extracellular matrix components such as hyaluronan and aggrecan 124 and will become cellularized by endocardial-mesenchymal transition (EMT) primarily from the overlying endocardium. [125][126][127][128] Secondarily, other cell populations take part in expanding the cushions. These include epicardial cells migrating from the AV junction in the case of AV cushions, [129][130][131] and epicardial cells and NCCs in the case of OFT cushions.…”

Proteomic Alterations Associated with Biomechanical Dysfunction are Early Processes in the Emilin1 Deficient Mouse Model of Aortic Valve Disease

“…Aged WT AVs (AgWT/AdWT) showed increased cell activation, immune response, and adhesion (Figure 5C), including increases in the proteins vitronectin (VTN, secreted protein associated with maintenance of valve integrity) 35,36 , VCAM1 (marker of inflammation), and FBLN1 (modulator of OFT endothelial mesenchymal transition) 37 , identifying multiple processes involved in alteration of AV structure. Overall, these findings are consistent with the observation that age is an independent risk factor for developing AV disease and that normal aging processes contribute to the pathogenesis of AV disease.…”