Serum-Dependence of Affinity-Mediated VEGF Release from Biomimetic Microspheres

Abstract

Vascular endothelial growth factor (VEGF) activity is highly regulated via sequestering within the ECM and cell-demanded proteolysis to release the sequestered VEGF. Numerous studies have demonstrated that VEGF activity mediates cellular events leading to angiogenesis and capillary formation in vivo. This has motivated the study of biomaterials to sustain VEGF release, and in many cases, the materials are inspired by the structure and function of the native ECM. However, there remains a need for materials that can bind to VEGF with high specificity, as the in vivo environment is rich in a variety of growth factors (GFs) and GF-binding moieties. Here we describe a strategy to control VEGF release using hydrogel microspheres with tethered peptides derived from VEGF receptor 2 (VEGFR2). Using biomaterials covalently modified with varying concentrations of two distinct VEGFR2-derived peptides with varying serum stability, we analyzed both biomaterial and environmental variables that influence VEGF release and activity. The presence of tethered VEGF-binding peptides (VBPs) resulted in significantly extended VEGF release relative to control conditions, and the resulting released VEGF significantly increased the expansion of human umbilical vein endothelial cells in culture. VEGF release rates were also strongly influenced by the concentration of serum. The presence of Feline McDonough Sarcoma-like tyrosine kinase 1 (sFlt-1), a serum-borne receptor fragment derived from VEGF receptor 1, increased VEGF release rates, although sFlt-1 was not sufficient to recapitulate the release profile of VEGF in serum. Further, the influence of serum on VEGF release was not due to protease activity or nonspecific VEGF interactions in the presence of serum-borne heparin. VEGF release kinetics correlated well with a generalizable mathematical model describing affinity-mediated release of VEGF from hydrogel microspheres in defined conditions. Modeling results suggest a potential mechanism whereby competition between VEGF and multiple VEGF-binding serum proteins including sFlt-1, soluble kinase insert domain receptor (sKDR), and α2-macroglobulin (α2-M) likely influenced VEGF release from microspheres. The materials and mathematical model described in this approach may be useful in a range of applications in which sustained, biologically active GF release of a specific GF is desirable.

Regulating VEGF signaling in platelet concentrates via specific VEGF sequestering

“…2), we conclude that VBP microspheres reduced VEGF-dependent HUVEC proliferation by decreasing the concentration of free soluble VEGF relative to control microspheres. This conclusion is substantiated by previous evidence that VBP microspheres sequestered and reduced VEGF activity in culture 13 and retained VEGF over a much longer time-frame than either Scramble or Blank microspheres 29 .…”

Human iPSC-derived endothelial cell sprouting assay in synthetic hydrogel arrays

“…Eight-arm poly(ethylene glycol) (PEG) terminated on each arm with hydroxyl groups was derivatized with norbornene using a modified procedure[31] and as previously described in detail[32]. All subsequent reagents were purchased from Sigma-Aldrich unless otherwise indicated.…”

Thiol–norbornene photoclick hydrogels for tissue engineering applications

“…For example, Murphy and his colleagues prepared thiol-norbornene microgels using multi-arm PEGNB macromers and di-thiol containing linkers from an aqueous two-phase separation system. 60-65 These microgels also were immobilized with affinity peptides capable of sequestering vascular endothelial growth factor (VEGF). By increasing affinity peptide concentration, VEGF was sequestered in the microgels for a prolonged period of time and was delivered slowly from the microgels.…”