Biomimetic hydrogels for controlled biomolecule delivery to augment bone regeneration.

Macrophage migration inhibitory factor (MIF) is a pleiotropic inflammatory cytokine that was recently identified as a non-cognate ligand of the CXC-family chemokine receptors 2 and 4 (CXCR2 and CXCR4). MIF is expressed and secreted from endothelial cells (ECs) following atherogenic stimulation, exhibits chemokine-like properties and promotes the recruitment of leucocytes to atherogenic endothelium. CXCR4 expressed on endothelial progenitor cells (EPCs) and EC-derived CXCL12, the cognate ligand of CXCR4, have been demonstrated to be critical when EPCs are recruited to ischemic tissues. Here we studied whether hypoxic stimulation triggers MIF secretion from ECs and whether the MIF/CXCR4 axis contributes to EPC recruitment. Exposure of human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAoECs) to 1% hypoxia led to the specific release of substantial amounts of MIF. Hypoxia-induced MIF release followed a biphasic behaviour. MIF secretion in the first phase peaked at 60 min. and was inhibited by glyburide, indicating that this MIF pool was secreted by a non-classical mechanism and originated from pre-formed MIF stores. Early hypoxia-triggered MIF secretion was not inhibited by cycloheximide and echinomycin, inhibitors of general and hypoxia-inducible factor (HIF)-1α-induced protein synthesis, respectively. A second phase of MIF secretion peaked around 8 hrs and was likely due to HIF-1α-induced de novo synthesis of MIF. To functionally investigate the role of hypoxia-inducible secreted MIF on the recruitment of EPCs, we subjected human AcLDL+ KDR+ CD31+ EPCs to a chemotactic MIF gradient. MIF potently promoted EPC chemotaxis in a dose-dependent bell-shaped manner (peak: 10 ng/ml MIF). Importantly, EPC migration was induced by supernatants of hypoxia-conditioned HUVECs, an effect that was completely abrogated by anti-MIF- or anti-CXCR4-antibodies. Thus, hypoxia-induced MIF secretion from ECs might play an important role in the recruitment and migration of EPCs to hypoxic tissues such as after ischemia-induced myocardial damage.

Hypoxia‐induced endothelial secretion of macrophage migration inhibitory factor and role in endothelial progenitor cell recruitment

Regeneration deficiency is one of the main obstacles limiting the effectiveness of tissue-engineered scaffolds. To develop scaffolds that are capable of accelerating regeneration, we created a heparin/chitosan nanoparticle-immobilized decellularized bovine jugular vein scaffold to increase the loading capacity and allow for controlled release of vascular endothelial growth factor (VEGF). The vascularization of the scaffold was evaluated in vitro and in vivo. The functional nanoparticles were prepared by physical self-assembly with a diameter of 67-132 nm, positive charge, and a zeta potential of ∼30 mV and then the nanoparticles were successfully immobilized to the nanofibers of scaffolds by ethylcarbodiimide hydrochloride/hydroxysulfosuccinimide modification. The scaffolds immobilized with heparin/chitosan nanoparticles exhibited highly effective localization and sustained release of VEGF for several weeks in vitro. This modified scaffold significantly stimulated endothelial cells' proliferation in vitro. Importantly, utilization of heparin/chitosan nanoparticles to localize VEGF significantly increased fibroblast infiltration, extracellular matrix production, and accelerated vascularization in mouse subcutaneous implantation model in vivo. This study provided a novel and promising system for accelerated regeneration of tissue-engineering scaffolds.

https://www.dovepress.com/getfile.php?fileID=9947

Controlled release of chitosan/heparin nanoparticle-delivered VEGF enhances regeneration of decellularized tissue-engineered scaffolds.

Induction of angiogenesis using VEGF releasing genipin-crosslinked electrospun gelatin mats

Fibrocytes were first described in 1994 as fibroblast-like, peripheral blood cells. These bone marrow-derived mesenchymal progenitor cells migrate into regions of tissue injury. They are unique in their expression of hematopoietic and monocyte lineage markers and extracellular matrix proteins. Several studies have focused on the specific role of fibrocytes in the process of wound repair and tissue regeneration. We discuss herein the biology and mechanistic action of fibrocytes in wound healing, scar formation, and maintenance of tissue integrity. Fibrocytes synthesize and secrete different cytokines, chemokines, and growth factors, providing a wound milieu that supports tissue repair. They further promote angiogenesis and contribute to wound closure via pathways involving specific cytokines, leukocyte-specific protein-1, serum amyloid P, and adenosine A(2A) receptors. Fibrocytes are involved in inflammatory fibrotic processes in such diseases as systemic fibrosis, atherosclerosis, asthma, hypertrophic scarring, and keloid formation. Accumulating literature has emphasized the important role of fibrocytes in wound healing and fibrosis. Detailed mechanisms nevertheless remain to be investigated to elucidate the full therapeutic potential of fibrocytes in the treatment of fibrosing disorders and the enhancement of tissue repair.

Circulating fibrocytes--biology and mechanisms in wound healing and scar formation.

The use of implantable biomaterials, such as artificial skin substitutes used for dermal defects, remains limited by the low angiogenic potential of these products. The rapid in vivo degradation of growth factors contributes to the limiting of angiogenesis in biomaterials. Here, we report on collagen sponges in which vascular endothelial growth factor (VEGF) was immobilized through physical binding to heparin, covalently incorporated in the matrix via cross-linking with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide. The in vitro release of VEGF over time and endothelial cell proliferation were investigated in matrices modified at varying heparin to EDC ratios either nonloaded or loaded with VEGF. ELISA demonstrated a significantly slower in vitro release of VEGF over a period of 5 days from heparinized matrices as compared to their unmodified and cross-linked counterparts. The effects of these modifications on the proliferation of endothelial cells and endothelial progenitor cells were evaluated after 1, 3 and 5 days either according to the bromodeoxyuridine assay or total cell counting with a Neubauer chamber. The endothelial and endothelial progenitor cells cultured in contact with heparinized matrices loaded with VEGF revealed both the highest rate of DNA synthesis and the highest total cell count. Furthermore, these results show that the cross-linking of collagen matrices - both in the presence and absence of heparin - leads to increases of the proliferative activities. We can assume that these changes lead to matrices with increased angiogenic capabilities.

G Grieb

Papers

Tissue substitutes with improved angiogenic capabilities: an in vitro investigation with endothelial cells and endothelial progenitor cells.