Role of D and E domains in the migration of vascular smooth muscle cells into fibrin gels

Fibrin and Transforming Growth Factor Alpha Affect Prostatic Smooth Muscle Cell's Phenotype and Motility

Smooth muscle cells (SMCs) are dynamic and transition from a contractile to a synthetic phenotype under different circumstances. Plasma factors (fibrin and transforming growth factors, TGFs) are possible components affecting SMCs differentiation and behavior. Thus, the objective of this work was to investigate how the fibrin matrix and TGFs affect SMCs differentiation and motility behavior. SMCs invaded the fibrin gel and adopted a stellate phenotype while reducing the expression of differentiation markers (Acta2, Myh11, and Smtn). At the ultrastructural level, SMCs did not assemble a basal lamina and showed numerous blebs along the entire cell surface. This transition was not associated with changes in focal adhesion kinase (FAK) content and phosphorylation status but reflected a marked change in FAK distribution in the cytoplasm. After 48 h in culture, SMCs caused an active degradation of the fibrin gel. Additionally, we tested the SMCs response to TGFs in a cell layer wound repair assay. TGFα, but not TGFβ1 or TGFβ3, had significantly increased motility. In conclusion, prostatic SMCs present a phenotypical transition when cultured on fibrin, adopting a micro-blebbing based motility behavior and increasing migration in response to TGFα.

Fibrin fragment E potentiates TGF-β-induced myofibroblast activation and recruitment

Fibrin is an essential constituent of the coagulation cascade, and the formation of hemostatic fibrin clots is central to wound healing. Fibrin clots are over time degraded into fibrin degradation products as the injured tissue is replaced by granulation tissue. Our goal was to study the role of the fibrin degradation product fragment E (FnE) in fibroblast activation and migration. We present evidence that FnE is a chemoattractant for fibroblasts and that FnE can potentiate TGF-β-induced myofibroblast formation. FnE forms a stable complex with α_Vβ₃ integrin, and the integrin β₃ subunit is required both for FnE-induced fibroblast migration and for potentiation of TGF-β-induced myofibroblast formation. Finally, subcutaneous infusion of FnE in mice results in a fibrotic response in the hypodermis. These results support a model where FnE released from clots in wounded tissue promote wound healing and fibrosis by both recruitment and activation of fibroblasts. Fibrin fragment E could thus represent a therapeutic target for treatment of pathological fibrosis.

The role of fibrin E on the modulation of endothelial progenitors adhesion, differentiation and angiogenic growth factor production and the promotion of wound healing

Severe skin loss constitutes a major unsolved clinical problem worldwide. For this reason, in the last decades there has been a major push towards the development of novel therapeutic approaches to enhance skin wound healing. Neo-vessel formation through angiogenesis is a critical step during the wound healing process. Besides the contribution of pre-existing endothelial cells (EC), endothelial progenitor cells (EPCs) have also been implicated in wound healing acting either by differentiating into EC that incorporate the neo-vessels, or via the production of paracrine factors that improve angiogenesis. Here we tested the importance of different extracellular matrices (ECM) in regulating the angiogenic and wound healing potential of cord blood-derived EPC (CB-EPC). We compared the properties of several ECM and particularly of fibrin fragment E (FbnE) in regulating EPC adhesion, proliferation, differentiation and healing-promotion in vitro and in vivo. Our results show that CB-EPCs have increased adhesion and endothelial differentiation when plated on FbnE compared to collagens, fibronectin or fibrin. Using integrin neutralizing antibodies, we show that CB-EPC adhesion to FbnE is mediated by integrin α5β1. Gene expression analysis of CB-EPCs plated on different substrates revealed that CB-EPC grown on FbnE shows increased expression of paracrine factors such as VEGF-A, TGF-β1, SDF-1, IL-8 and MIP-1α. Accordingly, conditioned media from CB-EPC grown on FbnE induced EC tube formation and monocyte migration in vitro. To test the wound healing effects of FbnE in vivo we used an FbnE enriched scaffold in a cutaneous wound healing mouse model. In accordance with our in vitro data, co-administration of the FbnE enriched scaffold with CB-EPC significantly accelerated wound closure and wound vascularization, compared FbnE enriched scaffold alone or to using collagen-based scaffolds. Our results show that FbnE modulates several CB-EPC properties in vivo and in vitro, and as such promotes wound healing. We suggest the use of FbnE-based scaffolds represents a promising approach to resolve wound healing complications arising from different pathologies.

Fine-tuning of a three-dimensional microcarrier-based angiogenesis assay for the analysis of endothelial-mesenchymal cell co-cultures in fibrin and collagen gels

A prerequisite for successful tissue engineering is the existence of a functional microvascular network. We hypothesized that such networks can be created and quantified in an in vitro setting by co-culturing endothelial cells (ECs) with tissue-specific 'bystander cells' in 3-D gel matrices. To test this hypothesis we adapted a previously described in vitro microcarrier-based angiogenesis assay (V. Nehls and D. Drenckhahn, 1995, Microvasc Res 50: 311-322). On optimizing this assay, we noted that the initial EC-microcarrier coverage depended on EC type and seeding technique employed to coat the microcarrier beads with the ECs. A confluent EC monolayer on the microcarrier surfaces formed only when bovine aortic endothelial cells (BAECs) were admixed to the beads under gentle agitation on an orbital shaker. After embedding BAEC-covered microcarrier beads into a sandwich-like arrangement of collagen or fibrin gels, we assessed cellular outgrowth at different serum concentrations in terms of migration distance and sprout formation. Quantifiable sprout formation was highest at 1% fetal bovine serum (FBS) in collagen matrices and at 0.1% FBS in fibrin matrices. At higher serum concentration, excess cell migration and formation of clusters prevented quantitative analysis of sprouting. Following the fine-tuning of this angiogenesis assay, we co-cultured BAECs with adipose tissue-derived fibroblasts (FBs) and vascular smooth muscle cells (SMCs). While FBs were able to increase the average migration distance of BAECs in both matrices, SMCs enhanced BAEC migration in fibrin, but not in collagen gels. By contrast, the number of newly formed sprouts in fibrin gels was increased by both cell types. We conclude that in this model bystander cells enhance EC network formation in a matrix-dependent manner. Additionally, these results stress the importance of carefully selecting the experimental parameters of a given in vitro angiogenesis model.

Autologous morphogen gradients by subtle interstitial flow and matrix interactions

Cell response to extracellular cues is often driven by gradients of morphogenetic and chemotactic proteins, and therefore descriptions of how such gradients arise are critical to understanding and manipulating these processes. Many of these proteins are secreted in matrix-binding form to be subsequently released proteolytically, and here we explore how this feature, along with small dynamic forces that are present in all tissues, can affect pericellular protein gradients. We demonstrate that 1), pericellular gradients of cell-secreted proteins can be greatly amplified when secreted by the cell in matrix-binding form as compared to a nonmatrix-interacting form; and 2), subtle flows can drive significant asymmetry in pericellular protein concentrations and create transcellular gradients that increase in the direction of flow. This study thus demonstrates how convection and matrix-binding, both physiological characteristics, combine to allow cells to create their own autologous chemotactic gradients that may drive, for example, tumor cells and immune cells into draining lymphatic capillaries.

An ex vivo model for functional studies of myofibroblasts

Migration, proliferation and invasive growth of myofibroblasts are key cellular events during formation of granulation tissue in situations of wound healing, arteriosclerosis and tumor growth. To study the invasive phenotype of myofibroblasts, we established an assay where arterial tissue from chicken embryos was embedded in fibrin gels and stimulated with growth factors. Addition of serum, PDGF-BB and FGF-2, but not VEGF-A, resulted in an outgrowth of cellular sprouts with a pattern that was similar to the organization of cells invading a provisional matrix in an in vivo model of wound healing using the chicken chorioallantoic membrane. Sprouting cells were defined as myofibroblasts based on being alpha-smooth muscle actin-positive but desmin-negative. There was no contribution of endothelial cells in outgrowing sprouts. The acquired myofibroblastic phenotype was stable since sprout-derived cells resumed sprouting in a growth factor-independent manner when re-embedded as spheroids in a fibrin matrix. Invasive growth and sprouting of vascular smooth muscle cells was not limited to chicken cells since a similar response was seen when spheroids composed of purified primary human aortic smooth muscle cells were embedded in fibrin. Finally, a technique for flat visualization of the three-dimensional sprouting and a quantification method is described. This ex vivo model allows quantitative analysis of invasive growth and differentiation of vascular smooth muscle cells and fibroblasts into myofibroblasts.

Fibrinolysis in LPS-induced chronic airway disease

To examine the role of the fibrinolytic system in LPS-induced airway disease, we compared the effect of a chronic LPS challenge in plasminogen activator inhibitor-deficient (C57BL/6JPAI-1-/-) mice and wild-type (WT) C57BL/6J mice. Physiological and biological assessments were performed, immediately after, and 4 wk after an 8-wk exposure to LPS or saline. Immediately after the LPS exposure, WT mice had increased estimates of airway reactivity to methacholine compared with C57BL/6JPAI-1-/- mice; however, airway inflammation was similar in both LPS-exposed groups. Significant increases in both active transforming growth factor (TGF)-beta1 and active matrix metalloproteinase (MMP)-9 was detected after LPS exposure in WT but not C57BL/6JPAI-1-/- mice. C57BL/6JPAI-1-/- mice showed significantly less TGF-beta1 in the lavage and higher MMP-9 in the lung tissue than WT mice at the end of exposure and 4 wk later. After LPS exposure, both WT and C57BL/6JPAI-1-/- mice had substantial expansion of the subepithelial area of the medium [diameter (d) = 90-129 microm]- and large (d > 129 microm)-size airways when compared with saline-exposed mice. Subepithelial fibrin deposition was prevalent in WT mice but diminished in C57BL/6JPAI-1-/-. PAI-1 expression by nonciliated bronchial epithelial cells was enhanced in LPS-exposed WT mice compared with the saline-exposed group. Four weeks after LPS inhalation, airway hyperreactivity and the expansion of the subepithelial area in the medium and large airways persisted in WT but not C57BL/6JPAI-1-/- mice. We conclude that an active fibrinolytic system can substantially alter the development and resolution of the postinflammatory airway remodeling observed after chronic LPS inhalation.