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Molecular weight fibrinogen variants alter gene expression and functional characteristics of human endothelial cells

Summary.  Background: Fibrin is a temporary matrix that not only seals a wound, but also provides a temporary matrix structure for invading cells during wound healing. Two naturally occurring fibrinogen variants, high molecular weight (HMW) and low molecular weight (LMW) fibrinogen, display different properties in supporting angiogenesis in vivo and in vitro. Objectives: This study was aimed at investigating the functional characteristics and molecular mechanisms of human microvascular endothelial cells (HMVECs) cultured on HMW and LMW fibrin matrices. Methods and results: HMVECs on HMW fibrin matrices showed increased proliferation and tube formation as compared with their counterparts on unfractionated and LMW fibrin. Degradation of HMW fibrin was markedly enhanced by the presence of HMVECs, that of LMW fibrin was enhanced only slightly. However, the expression levels of fibrinolysis‐regulating proteins and integrins were similar. Subsequent microarray analysis revealed that the expression of 377 genes differed significantly between HMVECs cultured on HMW fibrin and those cultured on LMW fibrin. Among these genes, UNC5B, DLL4 and the DLL4–Notch downstream targets Hey1, Hey2 and Hes1 showed increased expression in HMVECs on LMW fibrin. However, pharmacologic and genetic (DLL4 small interfering RNA) inhibition of DLL4–Notch signaling blunted rather than enhanced proliferation and tube formation by HMVECs on both fibrin variants. Conclusions: Heterogeneity in naturally occurring fibrinogen strongly influences endothelial cell proliferation and tube formation, and causes alterations in gene expression, including that of DLL4–Notch. The higher fibrinolytic sensitivity of HMW fibrin in the presence of HMVECs contributes to increased tube formation. Although the expression of DLL4–Notch was altered, it did not explain the enhanced tube formation in HMW fibrin. This study provides new perspectives for biological and tissue engineering applications.