In vitro studies on the expansion of endothelial cell monolayers on components of the basement membrane

Targeting Fibronectin to Overcome Remyelination Failure in Multiple Sclerosis: The Need for Brain- and Lesion-Targeted Drug Delivery

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease with unknown etiology that can be characterized by the presence of demyelinated lesions. Prevailing treatment protocols in MS rely on the modulation of the inflammatory process but do not impact disease progression. Remyelination is an essential factor for both axonal survival and functional neurological recovery but is often insufficient. The extracellular matrix protein fibronectin contributes to the inhibitory environment created in MS lesions and likely plays a causative role in remyelination failure. The presence of the blood–brain barrier (BBB) hinders the delivery of remyelination therapeutics to lesions. Therefore, therapeutic interventions to normalize the pathogenic MS lesion environment need to be able to cross the BBB. In this review, we outline the multifaceted roles of fibronectin in MS pathogenesis and discuss promising therapeutic targets and agents to overcome fibronectin-mediated inhibition of remyelination. In addition, to pave the way for clinical use, we reflect on opportunities to deliver MS therapeutics to lesions through the utilization of nanomedicine and discuss strategies to deliver fibronectin-directed therapeutics across the BBB. The use of well-designed nanocarriers with appropriate surface functionalization to cross the BBB and target the lesion sites is recommended.

Increased expression of fibronectin and the alpha 5 beta 1 integrin in angiogenic cerebral blood vessels of mice subject to hypobaric hypoxia

The extracellular matrix (ECM) is an important regulator of angiogenesis and vascular remodeling. We showed previously that angiogenic capillaries in the developing CNS express high levels of fibronectin and its receptor alpha5beta1 integrin, and that this expression is developmentally downregulated. As cerebral hypoxia leads to an angiogenic response, we sought to determine whether angiogenic vessels in the adult CNS re-express fibronectin and the alpha5beta1 integrin. Ten-week old mice were subject to hypobaric hypoxia for 0, 4, 7 and 14 days, and fibronectin/integrin expression examined. Fibronectin and the alpha5 integrin subunit were strongly upregulated on capillaries in the hypoxic CNS, with the effect maximal at the earliest time point examined (4 days). Immunofluorescent studies demonstrated that the alpha5 integrin was expressed by angiogenic endothelial cells. In light of the defined angiogenic role for fibronectin in other systems, this work suggests that induction of fibronectin-alpha5beta1 integrin expression may be an important molecular switch driving angiogenesis in the hypoxic CNS.

Fibronectin promotes brain capillary endothelial cell survival and proliferation through alpha5beta1 and alphavbeta3 integrins via MAP kinase signalling

We showed previously that blood vessel maturation in the CNS is associated with a developmental switch in brain capillary endothelial cells (BCEC), from fibronectin signalling during angiogenesis to laminin signalling in the adult. To investigate the functional significance of this switch, we have examined the response of BCEC to different extracellular matrix (ECM) proteins. This showed that BCEC proliferation was significantly promoted by fibronectin (28.2 +/- 4.0%) and by vitronectin (14.8 +/- 2.1%) compared with uncoated glass (7.2 +/- 0.7%), while BCEC survival was significantly promoted by fibronectin (1130 +/- 131 cells), vitronectin (830 +/- 63 cells), collagen IV (703 +/- 77 cells) and laminin (680 +/- 34 cells) compared with the uncoated glass (367 +/- 48 cells). Biochemical studies showed that BCEC express a limited repertoire of integrins, including the beta1 integrins, alpha3beta1, alpha5beta1 and alpha6beta1, and the alphavbeta3 integrin. Function-blocking studies showed that the response to fibronectin was mediated equally by the alpha5beta1 and alphavbeta3 integrins. Analysis of signalling pathways revealed that fibronectin stimulated activation of the p44/p42 MAP kinase signalling pathway and pharmacological inhibitors of this pathway blocked BCEC proliferation on fibronectin. Taken together, these findings show that fibronectin exerts a strong angiogenic influence on endothelial cells (EC) in the CNS, and that this is mediated through the alpha5beta1 and alphavbeta3 integrins via MAP kinase signalling. In addition to a fundamental role in development, these findings may also have implications in pathological conditions of the CNS where fibronectin is re-expressed.

Type IV collagen modulates angiogenesis and neovessel survival in the rat aorta model

Type IV collagen is a major basement membrane component that has been implicated in the regulation of angiogenesis. The purpose of this study was to evaluate the effect of type IV collagen on the angiogenic response of native endothelial cells in three-dimensional vascular organ culture. Rings of rat aorta were cultured under serum-free conditions in gels of type I collagen with or without type IV collagen. In the absence of type IV collagen, aortic rings generated neovessels, which proliferated until day 9 and gradually regressed during the second and third weeks of culture. Type IV collagen promoted neovessel elongation and survival in a dose-dependent manner. Microvascular length increased by 43, 57, and 119% over control values in cultures treated with 3, 30, and 300 microg/ml type IV collagen, respectively. When used at high concentrations (300 microg/ml) type IV collagen stabilized the neovascular outgrowths and prevented vascular regression. Type IV collagen also promoted the formation of neovessels, but significant stimulatory effects were observed only at an intermediate concentration (30 microg/ml) and were no longer significant at the high concentration (300 microg/ml). The observation that type IV collagen has dose-dependent effects on vascular elongation, proliferation, and stabilization, supports the concept that the developing basement membrane of neovessels acts as a solid-phase regulator of angiogenesis, whose function varies depending on the concentration of its molecular components.

Interaction of human malignant melanoma tumor spheroids with endothelium and reconstituted basement membrane: modulation by RGDS

Tumor-cell extravasation involves sequential adhesive interactions with vascular endothelium and the subendothelial basement membrane. We have established a 3-dimensional model in vitro to simulate these events and to elucidate targets of the anti-cell-adhesive synthetic peptide RGDS. Tumor spheroids of the melanoma cell line ST-ML-12 served as models of tumor-cell emboli and were transferred onto human umbilical vein endothelial cells. To imitate the vascular anatomy, the latter were grown on reconstituted basement membranes produced by dextran-stimulated bovine corneal endothelial cells. RGDS did not affect the homotypic aggregation of the tumor cells and only minimally inhibited the attachment of the spheroids to the reconstituted vessel. A short-term (20 min) inhibition of adhesion to denuded basement membranes was observed. The attachment was closely associated with damage to the endothelial cells by oxygen-derived free radicals. RGDS retarded endothelial injury for up to 3 hr. The most prominent effect was observed after penetration of the endothelium. RGDS suppressed the emigration of tumor cells from the attached tumor-cell cluster in a dose- and time-dependent fashion. After 12 hr, the inhibitory effect progressively declined. This was not due to loss of activity of the peptide, indicating a resistance mechanism in the melanoma cells. On purified components of the basement membrane, RGDS effectively inhibited the initial spheroid attachment to fibronectin and collagen IV but had no effect on attachment to laminin. By contrast, subsequent migration was significantly suppressed on all substrata. Our model permits the study of dynamic cell-cell and cell-extracellular-matrix interactions and indicates that RGDS might predominantly act on early tumor-cell locomotion after penetration of the endothelium.

Quantitative analysis of autocrine-regulated, matrix-induced, and tumor cell-stimulated endothelial cell migration using a silicon template compartmentalization technique

Autocrine-regulated, matrix-induced, and tumor cell-stimulated endothelial cell migration was quantitatively analyzed using a two-dimensional, two-compartment coculture system. Silicon templates were used to subdivide 35-mm tissue culture dishes into two separate compartments. Endothelial cells were grown to confluence in the inner compartment and released from growth arrest by removal of the silicon template. The distance of endothelial cell outgrowth from the monolayer was measured in 24-h intervals. Endothelial cells from different vascular beds migrated with different migration rates (large vessel endothelial cells greater than hemangioendothelioma cells greater than microvessel endothelial cells). Prior coating of tissue culture wells with fibronectin, type I collagen, or type IV collagen and increasing serum concentrations strongly enhanced endothelial cell migration. Seeding tumor cells into the outer compartment prior to removal of the silicon template permitted the direct coculture analysis of tumor cell-induced endothelial cell migration. Microvascular endothelial cell migration was stimulated in a tumor cell number-dependent fashion, whereas large vessel endothelial cells could not consistently be stimulated by coculture with tumor cells. It is concluded that silicon templates offer a useful approach for the quantitative study of migration of anchorage-dependent cells, permitting follow-up measurements over several days, the study of matrix effects, and the direct coculture analysis of cell migration.

New artificial connective matrix-like structure: thrombogenicity and use as endothelial cell culture support

The recently described artificial connective matrix made of elastin solubilized peptides, type I+III collagens and connective proteins is shown to have structural and biological properties very close to the natural arterial subendothelium: the capacity to promote endothelial cell cultures maintaining their phenotype expression and its non-thrombogenicity. This new bioactive composite material could be used to replace arteries.

Migration assay for endothelial cells in multiwells. Application to studies on the effect of opioids

An assay system is described which permits rapid and effective evaluation of endothelial cell repair, using cells growing in a monolayer. With this method it was possible to obtain highly significant results. For example, endothelial growth factor and heparin, significantly enhanced cell migration and/or proliferation, whereas beta-endorphin, an endogenous opioid, had no effect on the migration and/or proliferation of human umbilical vein endothelial cells. This model may be used to study the cell migration of a variety of cell types which under certain experimental conditions (e.g., irradiation) do not proliferate.