Vascular growth factor binding kinetics to the endothelial cell basement membrane, with a kinetics-based correction for substrate binding

Fibroblast Growth Factor-2 Binding to Heparan Sulfate Proteoglycans Varies with Shear Stress in Flow-Adapted Cells

Fibroblast growth factor 2 (FGF2), an important regulator of angiogenesis, binds to endothelial cell (EC) surface FGF receptors (FGFRs) and heparan sulfate proteoglycans (HSPGs). FGF2 binding kinetics have been predominantly studied in static culture; however, the endothelium is constantly exposed to flow which may affect FGF2 binding. We therefore used experimental and computational techniques to study how EC FGF2 binding changes in flow. ECs adapted to 24 h of flow demonstrated biphasic FGF2-HSPG binding, with FGF2-HSPG complexes increasing up to 20 dynes/cm2 shear stress and then decreasing at higher shear stresses. To understand how adaptive EC surface remodeling in response to shear stress may affect FGF2 binding to FGFR and HSPG, we implemented a computational model to predict the relative effects of flow-induced surface receptor changes. We then fit the computational model to the experimental data using relationships between HSPG availability and FGF2-HSPG dissociation and flow that were developed from a basement membrane study, as well as including HSPG production. These studies suggest that FGF2 binding kinetics are altered in flow-adapted ECs due to changes in cell surface receptor quantity, availability, and binding kinetics, which may affect cell growth factor response.

Laminin heparin-binding peptides bind to several growth factors and enhance diabetic wound healing

Laminin, as a key component of the basement membrane extracellular matrix (ECM), regulates tissue morphogenesis. Here, we show that multiple laminin isoforms promiscuously bind to growth factors (GFs) with high affinity, through their heparin-binding domains (HBDs) located in the α chain laminin-type G (LG) domains. These domains also bind to syndecan cell-surface receptors, promoting attachment of fibroblasts and endothelial cells. We explore the application of these multifunctional laminin HBDs in wound healing in the type-2 diabetic mouse. We demonstrate that covalent incorporation of laminin HBDs into fibrin matrices improves retention of GFs and significantly enhances the efficacy of vascular endothelial cell growth factor (VEGF-A165) and platelet-derived growth factor (PDGF-BB) in promoting wound healing in vivo, under conditions where the GFs alone in fibrin are inefficacious. This laminin HBD peptide may be clinically useful by improving biomaterial matrices as both GF reservoirs and cell scaffolds, leading to effective tissue regeneration.

Laminins are important regulators of epidermal wound healing. Here, the authors show that laminins bind to multiple growth factors via their heparin-binding domains, and that incorporation of these domains into fibrin matrices increases growth factor retention, promoting wound healing in type 2 diabetic mouse models.

The vascular basement membrane in the healthy and pathological brain

The vascular basement membrane contributes to the integrity of the blood-brain barrier (BBB), which is formed by brain capillary endothelial cells (BCECs). The BCECs receive support from pericytes embedded in the vascular basement membrane and from astrocyte endfeet. The vascular basement membrane forms a three-dimensional protein network predominantly composed of laminin, collagen IV, nidogen, and heparan sulfate proteoglycans that mutually support interactions between BCECs, pericytes, and astrocytes. Major changes in the molecular composition of the vascular basement membrane are observed in acute and chronic neuropathological settings. In the present review, we cover the significance of the vascular basement membrane in the healthy and pathological brain. In stroke, loss of BBB integrity is accompanied by upregulation of proteolytic enzymes and degradation of vascular basement membrane proteins. There is yet no causal relationship between expression or activity of matrix proteases and the degradation of vascular matrix proteins in vivo. In Alzheimer's disease, changes in the vascular basement membrane include accumulation of Aβ, composite changes, and thickening. The physical properties of the vascular basement membrane carry the potential of obstructing drug delivery to the brain, e.g. thickening of the basement membrane can affect drug delivery to the brain, especially the delivery of nanoparticles.

An effective placental cotyledons proteins extraction method for 2D gel electrophoresis

Effective protein extraction is essential especially in producing a well-resolved proteome on 2D gels. A well-resolved placental cotyledon proteome, with good reproducibility, have allowed researchers to study the proteins underlying the physiology and pathophysiology of pregnancy. The aim of this study is to determine the best protein extraction protocol for the extraction of protein from placental cotyledons tissues for a two-dimensional gel electrophoresis (2D-GE). Based on widely used protein extraction strategies, 12 different extraction methodologies were carefully selected, which included one chemical extraction, two mechanical extraction coupled protein precipitations, and nine chemical extraction coupled protein precipitations. Extracted proteins were resolved in a one-dimensional gel electrophoresis and 2D-GE; then, it was compared with set criteria: extraction efficacy, protein resolution, reproducibility, and recovery efficiency. Our results revealed that a better profile was obtained by chemical extraction in comparison to mechanical extraction. We further compared chemical extraction coupled protein precipitation methodologies, where the DNase/lithium chloride-dense sucrose homogenization coupled dichloromethane-methanol precipitation (DNase/LiCl-DSH-D/MPE) method showed good protein extraction efficiency. This, however, was carried out with the best protein resolution and proteome reproducibility on 2D-gels. DNase/LiCl-DSH-D/MPE was efficient in the extraction of proteins from placental cotyledons tissues. In addition, this methodology could hypothetically allow the protein extraction of any tissue that contains highly abundant lipid and glycogen.

A computational model of fibroblast growth factor-2 binding to endothelial cells under fluid flow

Fibroblast growth factor-2 (FGF2) is an angiogenic growth factor that binds to cell surface receptors (FGFR) and heparan sulfate proteoglycans (HSPG), as well as HSPG in the basement membrane. FGF2 plays a critical role in angiogenesis, yet clinical FGF2 trials demonstrated limited success perhaps due to inadequate understanding of FGF2 binding in physiological conditions. We developed a computational model of FGF2 binding to isolated (HSPG or FGFR) or combined (HSPG and FGFR) binding sites under physiological fluid flow and predicted the effects of FGF2 concentration, binding site density, fluid flow rate, and delivery mode (continuous vs. bolus) on FGF2 complex formation. The isolated binding site models showed increased binding with FGF2 and binding site density. However, in the triad model, increasing FGF2 concentration decreased triads (FGF2-HSPG-FGFR) and increased FGF2-HSPG complexes. Fluid flow decreased time to equilibrium and dissociation in isolated binding site models, yet flow effect in the triad model depended on binding site density. Similarly, FGF2 capture and complex stability in bolus delivery depended on bolus size, flow rate, association and dissociation rate constants, as well as binding site density. This model shows the integrated effects of FGF2 binding stoichiometry, fluid flow, and delivery mode, and enhances our understanding of FGF2 complex formation under physiological conditions.

Fibroblast growth factor-2 binding to the endothelial basement membrane peaks at a physiologically relevant shear stress

Fibroblast growth factor-2 (FGF2) is produced and released by endothelial cells and binds to heparan sulfate proteoglycans in the endothelial basement membrane (BM), an important FGF2 storage reservoir. Experimental and computational models of FGF2 binding kinetics to both cells and BM under static conditions are well established in the literature but remain largely unexplored under flow. We now examine BM-FGF2 binding kinetics in fluid flow conditions. We hypothesized that FGF2 binding to the endothelial BM would decrease as fluid shear stress increased. To investigate this, BM-FGF2 equilibrium, associative, and dissociative bindings were measured at various shear stresses. Surprisingly, FGF2 binding increased up to a physiological arterial shear stress of 25 dynes/cm², after which it decreased to a level similar to the 1 dyne/cm² condition. Both BM-FGF2 dissociation and BM binding site availability increased with flow, while association remained constant. This suggests that force-dependent FGF2 equilibrium binding varies with shear stress due to a combination of an increase in binding site availability and FGF2 dissociation with flow. This improved understanding of BM-FGF2 binding with flow enriches current knowledge of FGF2 binding kinetics under physiologic conditions, which may contribute to improved growth factor therapy development.