Fibroblast growth factor 2 enhances early stages of in vitro endothelial repair by microfilament bundle reorganization and cell elongation

Lymphangiogenic responses of lymphatic endothelial cells to steady direct-current electric fields

Lymphangiogenesis plays pivotal roles in diverse physiological and pathological conditions. Steady direct-current electric fields (DC EFs) induce vascular endothelial behaviors related to angiogenesis have been observed. This study investigated the effects of DC EFs on the lymphangiogenic response of lymphatic endothelial cells (LECs). We demonstrated that EFs stimulation induced directional migration, reorientation, and elongation of human LECs in culture. These lymphangiogenic responses required VEGF receptor 3 (VEGFR-3) activation and were mediated through the PI3K-Akt, Erk1/2, and p38 MAPK signaling pathways in relation to the reorganization of the actin cytoskeleton. Our results indicate that endogenous EFs may play a role in lymphangiogenesis in vivo, and VEGFR-3 signaling activation may be involved in the cellular function of LECs driven by EFs.

Effects of incorporation of granule-lyophilised platelet-rich fibrin into polyvinyl alcohol hydrogel on wound healing

Dressings are commonly used to treat skin wounds. In this study, we aimed to develop a new scaffold composed of a polyvinyl alcohol (PVA) hydrogel containing granule-lyophilised platelet-rich fibrin (G-L-PRF) as a dressing. G-L-PRF was prepared by freeze-drying and was then incorporated into PVA hydrogel by freezing-thawing. Notably, the mechanical strength and degradation rate of the scaffold were found to be related to G-L-PRF concentrations, reaching 6.451 × 10⁻² MPa and 17–22%, respectively, at a concentration of 1%. However, the strength decreased and the degradation was accelerated when the G-L-PRF concentration was over 1%. The elastic properties and biocompatibility of the scaffold were independent of G-L-PRF concentration, and both showed excellent elasticity and biocompatibility. The release of vascular endothelial growth factor and platelet-derived growth factor-AB was no significant time dependent. Additionally, application of 1% G-L-PRF/PVA to acute full-thickness dorsal skin wounds accelerated wound closure at days 7 and 9. Healing also increased on day 11. Histological and immunohistochemical analyses showed that the scaffold enhanced granulation tissue, maturity, collagen deposition, and new vessel formation. These results demonstrated that the prepared G-L-PRF/PVA scaffolds accelerated wound healing in acute full-thickness skin wounds, suggesting potential applications as an ideal wound dressing.

Hybrid scaffolding strategy for dermal tissue reconstruction: a bioactive glass/chitosan/silk fibroin composite

Regeneration of deep burn wounds is a very complex process that strongly relies on the tissue response between the dermal substitute and the newly-formed dermis.

Silk fibroin/chondroitin sulfate/hyaluronic acid ternary scaffolds for dermal tissue reconstruction

The fabrication of new dermal substitutes providing mechanical support and cellular cues is urgently needed in dermal reconstruction. Silk fibroin (SF)/chondroitin sulfate (CS)/hyaluronic acid (HA) ternary scaffolds (95-248μm in pore diameter, 88-93% in porosity) were prepared by freeze-drying. By the incorporation of CS and HA with the SF solution, the chemical potential and quantity of free water around ice crystals could be controlled to form smaller pores in the SF/CS/HA ternary scaffold main pores and improve scaffold equilibrium swelling. This feature offers benefits for cell adhesion, survival and proliferation. In vivo SF, SF/HA and SF/CS/HA (80/5/15) scaffolds as dermal equivalents were implanted onto dorsal full-thickness wounds of Sprague-Dawley rats to evaluate wound healing. Compared to SF and SF/HA scaffolds, the SF/CS/HA (80/5/15) scaffolds promoted dermis regeneration, related to improved angiogenesis and collagen deposition. Further, vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) expression in the SF/CS/HA (80/5/15) groups were investigated by immunohistochemistry to assess the mechanisms involved in the stimulation of secretion of VEGF, PDGF and bFGF and accumulation of these growth factors related to accelerated wound process. These new three-dimensional ternary scaffolds offer potential for dermal tissue regeneration.

bFGF regulates PI3-kinase-Rac1-JNK pathway and promotes fibroblast migration in wound healing

Fibroblast proliferation and migration play important roles in wound healing. bFGF is known to promote both fibroblast proliferation and migration during the process of wound healing. However, the signal transduction of bFGF-induced fibroblast migration is still unclear, because bFGF can affect both proliferation and migration. Herein, we investigated the effect of bFGF on fibroblast migration regardless of its effect on fibroblast proliferation. We noticed involvement of the small GTPases of the Rho family, PI3-kinase, and JNK. bFGF activated RhoA, Rac1, PI3-kinase, and JNK in cultured fibroblasts. Inhibition of RhoA did not block bFGF-induced fibroblast migration, whereas inhibition of Rac1, PI3-kinase, or JNK blocked the fibroblast migration significantly. PI3-kinase-inhibited cells down-regulated the activities of Rac1 and JNK, and Rac1-inhibited cells down-regulated JNK activity, suggesting that PI3-kinase is upstream of Rac1 and that JNK is downstream of Rac1. Thus, we concluded that PI3-kinase, Rac1, and JNK were essential for bFGF-induced fibroblast migration, which is a novel pathway of bFGF-induced cell migration.

Generation of a Specific Immunological Response to FGF‐2 Does Not Affect Wound Healing or Reproduction

Angiogenesis, the process of new capillary formation from pre-existing vessels, has been established as an important mechanism involved in pathologic processes, such as cancer, as well as in normal physiology (Ribatti, D.; Vacca, A.; Roncali, L.; Dammacco, F. Angiogenesis under normal and pathological conditions. Haematologica 1991, 76 (4), 311-320). Basic fibroblast growth factor (FGF-2) is a critical mediator of angiogenesis that is important for normal reproduction and wound healing. FGF-2 mediates its pro-angiogenic effects by binding to heparin sulfate proteoglycan in addition to a tyrosine kinase receptor (Baird, A.; Schubert, D.; Ling, N.; Guillemin, R. Receptor and heparin-binding domain of basic fibroblast growth factor. Proc. Natl. Acad. Sci. U. S. A. 1998, 5 (7), 2324-2328; Richard, C.; Roghani, M.; Moscatelli, D. Fibroblast growth factor (FGF)-2 mediates cell attachment through interactions with two FGF receptor-1 isoforms and extracellular matrix or cell-associated heparin sulfate proteoglycans. Biochem. Biophys. Res. Commun. 2000, 276 (2), 399-405; Casu, B.; Guerrini, M.; Naggi, A.; Perez, M.; Torri, G.; Ribatti, D.; Carminati, P.; Giannini, G.; Penco, S.; Pisano, C.; Belleri, M.; Rusnati, M.; Presta, M. Short heparin sequences spaced by glycol-split urinate residues are antagonists of fibroblast growth factor 2 and angiogenesis inhibitors. Biochemistry 2002, 41 (33), 10519-10528; Murphy, P.V.; Pitt, N.; O'Brien, A.; Enright, P.M.; Dunne, A.; Wilson, S.J.; Duane, R.M.; O'Boyle, K.M. Identification of novel inhibitors of fibroblast growth factor (FGF-2) binding to heparin and endothelial cell survival from a structurally diverse carbohybrid library. Bioorg. Med. Chem. Lett. 2002, 12 (22), 3287-3290). We developed a liposomal-based peptide vaccine, L(HBD) that targets the heparin binding domain of the FGF-2 molecule. This vaccine, when inoculated into mice, inhibits angiogenesis in response to FGF-2 in a hepatic sponge model as well as tumor progression in two models of pulmonary metastatic disease. In the present studies, we further characterize the immunological and physiological responses to this vaccine. Vaccinated animals generated a specific anti-FGF-2 antibody (titer of 1:5000) that was able to inhibit FGF-2 binding to heparin sulfate in a dose dependent fashion. Cell mediated immunity was evidenced by a delayed type hypersensitivity response following challenge with the heparin binding domain peptide. Despite an immune response toward FGF-2, vaccination with L(HBD) did not result in alterations in mean time to wound healing when compared to unvaccinated animals or those treated with a liposome control. In reproductive studies, vaccinated females were not impaired in their ability to: 1) become pregnant, 2) support the growth and development of their embryos, and 3) deliver viable offspring. Furthermore, when assessed histologically, these offspring did not demonstrate any alterations in organogenesis when compared to pups born to untreated or liposome control treated females. Thus, while vaccination against FGF-2 induces a specific FGF-2 antibody response, and inhibits angiogenesis and tumor development in a pathological setting, it does not adversely alter normal physiological events dependent on FGF-2.

Electrical stimulation directly induces pre-angiogenic responses in vascular endothelial cells by signaling through VEGF receptors

Controlling angiogenesis is crucial. Growth factors and cytokines are key regulators but a full understanding remains elusive. Endogenous electrical potential differences exist within and around the vasculature, both in relation to blood flow and in situations where active angiogenesis occurs, such as wound healing, development and tumor growth. Recent work shows that electrical stimulation induces significant angiogenesis in vivo, through enhanced vascular endothelial growth factor (VEGF) production by muscle cells. We report that applied electric fields (EFs) of small physiological magnitude directly stimulate VEGF production by endothelial cells in culture without the presence of any other cell type. EFs as low as 75-100 mV mm-1 (1.5-2.0 mV across an endothelial cell) directed the reorientation, elongation and migration of endothelial cells in culture. These pre-angiogenic responses required VEGF receptor activation and were mediated through PI3K-Akt and Rho-ROCK signaling pathways, resulting in reorganization of the actin cytoskeleton. This indicates that endogenous EFs might play a role in angiogenesis in vivo by stimulating the VEGF receptor signaling pathway, to induce key pre-angiogenic responses. In addition, it raises the feasibility of using applied EFs to initiate and guide angiogenesis through direct effects on endothelial cells.

Vessel injury and capillary leak

OBJECTIVE

To understand the mechanism of pathologic capillary leak in the critically ill patient.

DESIGN

Review of normal and altered physiology of the microvasculature. Review of recent literature describing pathogenesis, mediators, and interventions influencing capillary leak and microvascular repair.

SETTING

In vitro and in vivo studies, the latter including animal and human subjects.

MEASUREMENTS AND MAIN RESULTS

Capillary leak with resultant edema develops in the critical care setting on the basis of perturbations in Starling's equation, primarily as a result of increased capillary permeability to larger molecules. This process is most likely fueled by inflammatory mediators or mechanical stress. Attempts to prevent or treat this process remain largely unsuccessful; resuscitation is more often symptomatic than therapeutic. Models of microvascular repair focus on discrete injury and may not be applicable to the recovery of capillary damage secondary to a systemic leak

CONCLUSIONS

Our understanding of capillary leak syndrome remains fragmented and weighted toward specific mediators contributing to the leak. The implications of extensive edema and the mechanism by which it resolves continue to be the subject of speculation rather than study.

Fibroblast growth factor 2 regulation of mitral valve interstitial cell repair in vitro

OBJECTIVE

Because elongated mitral valve interstitial cells have features of myofibroblasts, it is likely that these cells are essential for the repair of injured valve leaflets. We characterized the cellular morphology and pattern of repair of these interstitial cells in wounds produced in vitro and tested the hypothesis that fibroblast growth factor 2 enhances interstitial cell repair.

METHODS

Mitral valve interstitial cells were plated onto glass coverslips, reached confluence after 1 week, and were wounded by passage of a spatula along the center of a monolayer, which created a linear wound with two edges. The wounds were observed from 0 to 96 hours by phase-contrast microscopy. Wounds were also fixed at 0, 2, and 24 hours and stained for fibroblast growth factor 2 and fibroblast growth factor receptor 1 by means of immunofluorescence and laser confocal microscopy.

RESULTS

Cells in confluent monolayers and in the monolayer behind the wound edge formed a multilayered orthogonal pattern of elongated cells similar to fibroblasts. Cells along the wound edge migrated into the wound after 4 hours, and at 24 hours single cells with prominent lamellipodia and tails were present within the wound. There was overlapping of cells as well, similar to smooth muscle cells. Fibroblast growth factor 2 and fibroblast growth factor receptor 1 were present in the cells of the undisturbed confluent monolayer. They were upwardly regulated relative to the unwounded monolayer in the cells along the wound edge at 2 hours and in the monolayer behind the wound edge at 24 hours. In single cells that migrated into the wound, fibroblast growth factor 2 and fibroblast growth factor receptor 1 were prominent. Fibroblast growth factor 2 showed a 6-fold increase in concentration relative to unwounded cultures in conditioned medium from wounded cultures at 2 hours after wounding. Addition of a neutralizing antibody to fibroblast growth factor 2 significantly delayed wound closure at 24 to 96 hours. Addition of exogenous fibroblast growth factor 2 to cultures at the time of wounding did not enhance wound repair.

CONCLUSION

Mitral valve interstitial cells have the ability to repair wounds, and fibroblast growth factor 2 is a modulator of these repair processes.

Rho and basic fibroblast growth factor involvement in centrosome redistribution and actin microfilament remodeling during early endothelial wound repair

OBJECTIVE

We have shown that centrosome redistribution to the front of the cell and actin microfilament remodeling occurs during the initiation of early porcine aortic endothelial wound repair even before cell migration. Because Ras homologous protein (Rho) induces actin microfilament polymerization, interacts with microtubules, and is believed to be activated by growth factors, we set forth to study the regulatory roles of basic fibroblast growth factor (bFGF) and Rho signaling on centrosome redistribution and actin microfilament remodeling in endothelial cells at an in vitro wound edge.

STUDY DESIGN

With double immunofluorescent confocal microscopy, we studied the distribution of various cytoskeletal proteins in wounded porcine aortic endothelial cells in response to bFGF and exoenzyme C3 treatments.

RESULTS

We showed that the addition of 10 ng/mL bFGF for 3 hours after wounding resulted in a significant increase (P <.05) in cells at the wound edge with central microfilaments oriented perpendicular to the wound. Rho inhibition with 2 microg/mL C3 resulted in the reduction of phosphotyrosine, paxillin, and central microfilament staining. Centrosome redistribution and endothelial cell elongation also were significantly inhibited (P <.05) with C3, resulting in decreased wound closure. However, inhibition was reduced with coincubation of bFGF with C3, which also returned the rate of endothelial wound closure toward control values. This Rho-independent bFGF-induced centrosome redistribution was associated with the cells showing a significant increase (P <.05) in acetylated microtubules that extended from the centrosome to the posterior cell border.

CONCLUSION

We conclude that Rho regulates centrosome redistribution and central microfilament remodeling during early endothelial wound repair, and bFGF promotes actin remodeling through a downstream Rho-dependent pathway and promotes centrosome redistribution, at least in part, with a Rho-independent pathway.

Advances towards understanding heart valve response to injury

BACKGROUND

Composed of endocardial endothelial, valvular interstitial, cardiac muscle, and smooth muscle cells (SMC), heart valves are prone to various pathologic conditions the morphology of which has been well described. The morphology of diseased valves suggest that the "response to injury" process occurs in these valves, and is associated with an accumulation of interstitial cells and matrix, valvular inflammation and calcification, conditions that lead to dysfunction. The purpose of this study is to describe the current knowledge of the regulation of the valvular "response to injury" process, since we feel that this paradigm is essential to understanding valve disease.

METHODS

The pertinent literature relating to the cell and molecular biology of valvular repair, and specifically interstitial cell function in valve repair, is reviewed.

RESULTS

The cell and molecular biology of valve interstitial cells are poorly understood. Molecules regulating some of the aspects of the "response to injury" process have been studied, however, the signal transduction pathways, gene activation, and interactions of bioactive molecules with each other, with cells, and with the matrix have not been characterized. Initial studies identify the cell and molecular biology of interstitial cells to be an important area of research. Agents that have been studied include nitric oxide (NO) and FGF-2 and several matrix-related proteins including osteopontin. The present review suggests several directions for future study and a working model of valvular repair is presented.

DISCUSSION

The regulation of the "response to injury" process in the human heart valve is still largely unknown. The cell and molecular events and processes that occur in heart valve function and repair remain poorly understood. These events and processes are vital to our understanding of the pathobiology of heart valve disease, and to the successful design of tissue engineered replacement valves.

Response of bovine endothelial cells to FGF-2 and VEGF is dependent on their site of origin: Relevance to the regulation of angiogenesis

Angiogenesis, the formation of new capillary blood vessels, occurs almost exclusively in the microcirculation. This process is controlled by the interaction between factors with positive and negative regulatory activity. In this study, we have compared the effect of two well described positive regulators, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2) on bovine adrenal cortex-derived microvascular endothelial (BME) and bovine aortic endothelial (BAE) cells. The parameters we assessed included (a) cellular reorganization and lumen formation following exposure of the apical cell surface to a three-dimensional collagen gel; (b) organization of the actin cytoskeleton; (c) expression of thrombospondin-1 (TSP-1), an endogenous negative regulator of angiogenesis; and (d) extracellular proteolytic activity mediated by the plasminogen activator (PA)/plasmin system. We found that (a) collagen gel overlay induces rapid reorganization and lumen formation in BME but not BAE cells; (b) FGF-2 but not VEGF induced dramatic reorganization of actin microfilaments in BME cells, with neither cytokine affecting BAE cells; (c) FGF-2 decreased TSP-1 protein and mRNA expression in BME cells, an effect which was specific for FGF-2 and BME cells, since TSP-1 protein levels were unaffected by VEGF in BME cells, or by FGF-2 or VEGF in BAE cells; (d) FGF-2 induced urokinase-type PA (uPA) in BME and BAE cells, while VEGF induced uPA and tissue-type PA in BME cells with no effect on BAE cells. Taken together, these findings reveal endothelial cell-type specific responses to FGF-2 and VEGF, and point to the greater specificity of these cytokines for endothelial cells of the microvasculature than for large vessel (aortic) endothelial cells. Furthermore, when viewed in the context of our previous observation on the synergistic interaction between VEGF and FGF-2, our present findings provide evidence for complementary mechanisms which, when acting in concert, might account for the synergistic effect.

FGF signalling is required for differentiation-induced cytoskeletal reorganisation and formation of actin-based processes by podocytes

To examine the potential role of fibroblast growth factor (FGF) signalling during cell differentiation, we used conditionally immortalised podocyte cells isolated from kidneys of Fgf2 mutant and wild-type mice. Wild-type mouse podocyte cells upregulate FGF2 expression when differentiating in culture, as do maturing podocytes in vivo. Differentiating wild-type mouse podocyte cells undergo an epithelial to mesenchymal-like transition, reorganise their actin cytoskeleton and extend actin-based cellular processes; all of these activities are similar to the activity of podocytes in vivo. Molecular analysis of Fgf2 mutant mouse podocyte cells reveals a general disruption of FGF signalling as expression of Fgf7 and Fgf10 are also downregulated. These FGF mutant mouse podocyte cells in culture fail to activate mesenchymal markers and their post-mitotic differentiation is blocked. Furthermore, mutant mouse podocyte cells in culture fail to reorganise their actin cytoskeleton and form actin-based cellular processes. These studies show that FGF signalling is required by cultured podocytes to undergo the epithelial to mesenchymal-like changes necessary for terminal differentiation. Together with other studies, these results point to a general role for FGF signalling in regulating cell differentiation and formation of actin-based cellular processes during morphogenesis.