Engineering Interactions between Growth Factors and the Extracellular Matrix

Abstract

In natural situations, growth factors such as VEGF and PDGF are present bound to the ECM, yet therapeutic use of such growth factors has focused on application in soluble forms. To explore ECM immobilization of growth factors, we have explored complexation with recombinant variants of EMC proteins such as fibronectin and engineering growth factors fused to a domain that binds strongly to ECM proteins. To explore noncovalent immobilization upon matrices, we have engineered a fibrin‐binding domain of fibronectin, containing the 12th‐14th type III repeat (which was known to bind VEGF‐A). In studies of the 12th‐14th type III repeat, we determined that the growth factor binding activity of this domain was promiscuous. Incorporation of this domain into fibrin, through engineered transglutaminase activity, provides a powerful and generalizable method to retain such growth factors into surgical matrices. Examination of promiscuous growth factor binding to ECM proteins revealed broad binding to not only fibronectin but also fibrinogen, vitronectin, osteopontin, and tenascin C, among others. We examined these affinities to determine that placenta growth factor‐2 (PlGF‐2) binds the mentioned ECM molecules very strongly. We identified the binding domain and engineered it into other growth factors to confer nM affinity to them, demonstrating enhanced efficacy in the context of angiogenesis, skin repair in chronic wound models, and bone repair. In this way, using variant growth factors that have super‐affinity for ECM proteins, either a fibrin matrix or a tissue itself may be turned into a reservoir for growth factor sequestration and presentation.