Regulation of CS1 fibronectin expression and function by IL-1 in endothelial cells

The extra domain A of fibronectin facilitates osteoclastogenesis in radicular cysts through vascular endothelial growth factor

AIM

To analyse the effects of the alternatively spliced fibronectin (FN) gene and its isoforms on osteoclastogenesis in radicular cysts.

METHODOLOGY

Specimens of radicular cysts were collected surgically from 22 patients whose radiolucent periapical areas were measured on digital panoramic radiographs before surgery. The associations between the radiolucent areas and FN isoforms, vascular endothelial growth factor (VEGF) expression or micro-vessel density, as well as the relationships amongst them, were analysed by immunohistochemical staining using the antibodies IST-9, BC-1, P1F11, VEGF and CD34. Fibroblasts isolated from those specimens were used to induce Trap + MNCs, and the effects of induction were assessed by blocking FN containing extra domain A (EDA + FN), COX-2 or VEGF in vitro. The effects of EDA exon knockout using CRISPR/Cas system were also assessed. Quantitative PCR was used to analyse relative expression of FN isoforms and osteoclastogenic genes. Data were analysed using linear regression, Spearman's rank correlation analysis, chi-square test and Student's t-test; P < 0.05 was considered significant.

RESULTS

Micro-vessel density and EDA + FN staining were positively associated with the size of radiolucent periapical areas (mm² ; P < 0.05), consistent with a positive association between Trap + MNCs and VEGF expression in fibroblasts (P < 0.05). Blocking the interaction between EDA + FN and fibroblasts inhibited Trap + MNC formation. In addition, EDA exon knockout decreased VEGF expression and inhibited Trap + MNC formation to the extent of blocking VEGF by bevacizumab, but osteoclastogenic induction was restored by recombinant VEGF. Using retrospective clinicopathological data, VEGF staining was shown to be positively associated with EDA + FN staining, micro-vessel density and the size of radiolucent areas (P < 0.05).

CONCLUSION

In fibrous capsules of radicular cysts, the alternatively spliced isoform EDA + FN generated by fibroblasts stimulated VEGF expression via an autocrine effect and then facilitated osteoclastogenesis. Both blockage of VEGF and EDA exon knockout could be used to inhibit bone destruction.

Atheroprone hemodynamics regulate fibronectin deposition to create positive feedback that sustains endothelial inflammation

RATIONALE

The extracellular matrix protein fibronectin (FN) is focally deposited in regions of atherosclerosis, where it contributes to inflammatory signaling.

OBJECTIVE

To elucidate the mechanism by which FN deposition is regulated by local shear stress patterns, its dependence on platelet-endothelial cell adhesion molecule (PECAM)-1 mechanotransduction and the role this pathway plays in sustaining an atheroprone/proinflammatory phenotype.

METHODS AND RESULTS

Human endothelial cells were exposed in vitro to atheroprone or atheroprotective shear stress patterns derived from human carotid arteries. Onset of atheroprotective flow induced a transient increase in FN deposition, whereas atheroprone flow caused a steady increase in FN expression and integrin activation over time, leading to a significant and sustained increase in FN deposition relative to atheroprotective conditions. Comparing FN staining in ApoE(-/-) and ApoE(-/-)PECAM(-/-) mice showed that PECAM-1 was essential for FN accumulation in atheroprone regions of the aortic arch. In vitro, small interfering RNA against PECAM-1 blocked the induction of FN and the activation of nuclear factor (NF)-kappaB by atheroprone flow, which was rescued by the addition of exogenous FN. Additionally, blocking NF-kappaB activation attenuated the flow-induced FN expression. Small interfering RNA against FN significantly reduced NF-kappaB activity, which was rescued by the addition of exogenous FN.

CONCLUSIONS

These results indicate that FN gene expression and assembly into matrix fibrils is induced by atheroprone fluid shear stress. This effect is mediated at least in part by the transcription factor NF-kappaB. Additionally, because FN promotes activation of NF-kappaB, atheroprone shear stress creates a positive feedback to maintain inflammation.

Determinants of CCL5-driven mononuclear cell migration across the blood-brain barrier. Implications for therapeutically modulating neuroinflammation

Chemokine receptors and adhesion molecules are used selectively for the transmigration of leukocytes across the blood-brain barrier (BBB) during neuroinflammation. We established an activated in vitro BBB (aIVBBB) using physiological concentrations of cytokines. We studied CCL5-driven migration as a model to determine how chemokine receptors and adhesion molecules regulate T-cell and monocyte migration across the aIVBBB. Increased expression of CCL5 and its receptors, CCR1 and CCR5 have been described in the perivascular space of multiple sclerosis (MS) lesions. Elucidating the determinants of CCL5-mediated mononuclear cell migration may clarify appropriate targets for therapeutic modulation in neuroinflammatory conditions. In response to CCL5, there was a significant increase in total mononuclear cell migration across the aIVBBB. Neutralizing monoclonal antibodies to CCR1 and CCR5 abrogated CCL5-driven transmigration, suggestive of non-redundant receptor usage in mononuclear cell migration to this chemokine in vitro. CCL5-driven transmigration was also dependent on alpha(4)beta(1) integrin/fibronectin connecting segment-1 (FN CS-1) and alpha(L)beta(2) integrin/intercellular adhesion molecule (ICAM-1) interactions. Monocyte migration to CCL5 was solely dependent on alpha(4)beta(1) integrin/FN CS-1 while T-cell migration required both alpha(L)beta(2) integrin/ICAM-1 and alpha(4)beta(1) integrin/FN CS-1 interactions. These findings provide plausible molecular targets for the selective inhibition of mononuclear cell trafficking during the acute immune effector phases of MS and other neuroinflammatory diseases.

Hypoxia induces adhesion molecules on cancer cells: A missing link between Warburg effect and induction of selectin-ligand carbohydrates

Cancer cells undergo distinct metabolic changes to cope with their hypoxic environment. These changes are achieved at least partly by the action of transcriptional factors called hypoxia-inducible factors (HIFs). We investigated gene expression in cultured human colon cancer cells induced by hypoxic conditions with special reference to cell-adhesion molecules and carbohydrate determinants having cell-adhesive activity by using DNA-microarray and RT-PCR techniques. Hypoxic culture of colon cancer cells induced a marked increase in expression of selectin ligands, the sialyl Lewis x and sialyl Lewis a determinants at the cell surface, which led to a definite increase in cancer cell adhesion to endothelial E-selectin. The transcription of genes for fucosyltransferase VII (FUT7), sialyltransferase ST3Gal-I (ST3O), and UDP-galactose transporter-1 (UGT1), which are all known to be involved in the synthesis of the carbohydrate ligands for E-selectin, was significantly induced in cancer cells by hypoxic culture. In addition, a remarkable induction was detected in the genes for syndecan-4 (SDC4) and alpha5-integrin (ITGA5), the cell-adhesion molecules involved in the enhanced adhesion of cancer cells to fibronectin. The transcriptional induction by hypoxia was reproduced in the luciferase-reporter assays for these genes, which were significantly suppressed by the co-transfection of a dominant-negative form of HIF. These results indicate that the metabolic shifts of cancer cells partly mediated by HIFs significantly enhance their adhesion to vascular endothelial cells, through both selectin- and integrin-mediated pathways, and suggest that this enhancement further facilitates hematogenous metastasis of cancers and tumor angiogenesis.

Functional expression of CXCR4 (CD184) on small-cell lung cancer cells mediates migration, integrin activation, and adhesion to stromal cells

Small-cell lung cancer (SCLC) is an aggressive, rapidly metastasizing neoplasm. The chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) is constitutively secreted by marrow stromal cells and plays a key role for homing of hematopoietic cells to the marrow. Here, we report that tumor cells from patients with SCLC express high levels of functional CXCR4 receptors for the chemokine CXCL12. Reverse transcriptase-polymerase chain reaction and flow cytometry demonstrated CXCR4 mRNA and CXCR4 surface expression in SCLC cell lines. Immunohistochemistry of primary tumor samples from SCLC patients revealed high expression of CXCR4. CXCL12 elicited CXCR4 receptor endocytosis, actin polymerization, and a robust activation of phospho-p44/42 mitogen-activated protein kinase in SCLC cells. Furthermore, CXCL12 induced SCLC cell invasion into extracellular matrix and firm adhesion to marrow stromal cells. Stromal cell adhesion of SCLC cells was significantly inhibited by the specific CXCR4 antagonist T140, pertussis toxin, antivascular cell adhesion molecule-1(VCAM-1) antibodies, and CS-1 peptide, demonstrating the importance of CXCR4 chemokine receptor activation and alpha4beta1 integrin binding, respectively. In addition, CXCL12 enhanced the adhesion of SCLC cells to immobilized VCAM-1, demonstrating that CXCR4 chemokine receptors can induce integrin activation on SCLC cells. As SCLC has a high propensity for bone marrow involvement, our findings suggest that CXCR4 chemokine receptors and alpha4beta1 integrins play a critical role in the interaction of SCLC cells with stromal cells in the tumor microenvironment.

Novel approaches to treating inflammatory bowel disease: targeting alpha-4 integrin

Crohn's disease involves persistent recruitment of leukocytes into gut tissue, coupled with dysregulated activation of specific immune cell function. Adhesion molecules expressed by circulating leukocytes, such as alpha 4 integrin, mediate their attachment to vascular endothelial cells lining blood vessels within the intestine and facilitate their migration into the tissue. Through interactions with extracellular matrix molecules, adhesion molecules then support immune cell activation and survival within the intestinal wall. Agents that interfere with these adhesive interactions hold great potential for suppressing the cycle of leukocyte infiltration and activation, and thereby, for ameliorating chronic inflammation. This article will discuss clinical data for a humanized monoclonal antibody against alpha 4 integrin, natalizumab, which is the first alpha 4 integrin antagonist in a new class of biotechnology agents referred to as selective adhesion molecule inhibitors.

CXCR4 chemokine receptors (CD184) and alpha4beta1 integrins mediate spontaneous migration of human CD34+ progenitors and acute myeloid leukaemia cells beneath marrow stromal cells (pseudoemperipolesis)

Marrow stromal cells play an important role in regulating the development and proliferation of haematopoietic stem cells (HSC) within the marrow microenvironment. However, the molecular mechanisms of stem cell-stromal cell interactions are not fully understood. We observed that mobilized peripheral blood and cord-blood-derived CD34+ progenitor cells, or CD34+ acute myeloid leukaemia (AML) cells spontaneously migrated beneath marrow stromal cells, an in vitro migration phenomenon termed pseudoemperipolesis. In contrast, the CD34+ myeloid leukaemia cell line, Kasumi-1, did not display pseudoemperipolesis. Cord blood CD34+ cells had a higher capacity than granulocyte-colony-stimulating-factor-mobilized CD34+ cells for pseudoemperipolesis (28.7 +/- 12%vs 18.1 +/- 6.1% of input cells within 24 h, mean +/- SD, n = 8), whereas 9.4 +/- 12.6% (mean +/- SD, n = 10) of input AML cells displayed this phenomenon. Pseudoemperipolesis of CD34+ progenitor and AML cells was significantly inhibited by pertussis toxin and antibodies to the CXCR4 chemokine receptor (CXCR4, CD184), but not control antibodies. Moreover, CD34+ and AML cell migration was significantly inhibited by a CS1 peptide that blocks alpha4beta1 integrin binding, but not by a control peptide, in which the fibronectin binding motif was scrambled. Pseudoemperipolesis was associated with an increased proliferation of migrated CD34+ progenitor cells but not AML cells within the stromal layer, demonstrated by cell cycle analysis and cell division tracking. We conclude that alpha4beta1 integrin binding and CXCR4 chemokine receptor activation are prerequisites for the migration of CD34+ haematopoietic progenitors and AML cells beneath marrow stromal cells. These observations suggest a central role of marrow stromal cells for HSC trafficking and homing within the marrow microenvironment.

Regulated splicing of the fibronectin EDA exon is essential for proper skin wound healing and normal lifespan

Fibronectins (FNs) are multifunctional high molecular weight glycoproteins present in the blood plasma and in the ECMs of tissues. The FN primary transcript undergoes alternative splicing in three regions generating up to 20 main different variants in humans. However, the precise role of the FN isoforms is poorly understood. One of the alternatively spliced exons is the extra domain A (EDA) or extra type III homology that is regulated spatially and temporally during development and aging. To study its in vivo function, we generated mice devoid of EDA exon-regulated splicing. Constitutive exon inclusion was obtained by optimizing the splice sites, whereas complete exclusion was obtained after in vivo CRE-loxP-mediated deletion of the exon. Homozygous mouse strains with complete exclusion or inclusion of the EDA exon were viable and developed normally, indicating that the alternative splicing at the EDA exon is not necessary during embryonic development. Conversely, mice without the EDA exon in the FN protein displayed abnormal skin wound healing, whereas mice having constitutive inclusion of the EDA exon showed a major decrease in the FN levels in all tissues. Moreover, both mutant mouse strains have a significantly shorter lifespan than the control mice, suggesting that EDA splicing regulation is necessary for efficient long-term maintenance of biological functions.

Correlating fibronectin adsorption with endothelial cell adhesion and signaling on polymer substrates

Fibronectin (Fn) adsorption was studied on different commercial polymer surface chemistries, including tissue culture polystyrene (TCPS), bacteriologic polystyrene (BPS), fluoropolymer Teflon AF, and poly-L-lactide (PLLA). Antibody probes detected the availability of Fn's cell binding domain on adsorbed Fn in the competitive presence and absence of bovine serum albumin (BSA). Domain availability was highest for Fn adsorbed on TCPS, especially in the presence of either serum albumin or dilute serum. Attachment and growth efficiencies for human umbilical venous endothelial cells (HUVECs) cultured on surfaces preadsorbed with Fn in serum and serum-free media correlated with antibody cell-binding domain availability: TCPS > BPS, Teflon AF > PLLA. Intracellular signaling from the GTPase, RhoA, was highest (RhoA:RhoGDI inhibitor ratio) in cells cultured on the Teflon AF surfaces, indicating that despite lower attached cell numbers on Teflon AF compared to TCPS, cell signaling remained activated after 24 h of growth. Up-regulated cellular Fn mRNA messages, assessed using RT-PCR techniques, supported HUVECs' producing the endogenous extracellular matrix (ECM) protein Fn in order to attach and survive on the suboptimal Teflon AF culture surfaces.

Fibroblast-like synoviocytes support B-cell pseudoemperipolesis via a stromal cell-derived factor-1- and CD106 (VCAM-1)-dependent mechanism

B-cell accumulation and formation of ectopic germinal centers are characteristic changes in the diseased joints of patients with rheumatoid arthritis (RA). Earlier studies suggested that interactions between B lymphocytes and specialized synovial "nurse-like" cells peculiar to the RA synovium may be responsible for the homing and sustained survival of B cells in the synovium. However, in this study, we found that B cells spontaneously migrate beneath ordinary fibroblast-like synoviocytes (FLSs) and then experience prolonged survival. FLSs isolated from joints of patients with osteoarthritis also supported this activity, termed B-cell pseudoemperipolesis. We found that FLSs constitutively expressed the chemokine stromal cell-derived factor-1 (SDF-1), and that pertussis toxin or antibodies to the SDF-1 receptor (CXCR4) could inhibit B-cell pseudoemperipolesis. However, expression of SDF-1 is not sufficient, as dermal fibroblasts also expressed this chemokine but were unable to support B-cell pseudoemperipolesis unless previously stimulated with IL-4 to express CD106 (VCAM-1), a ligand for the alpha(4)beta(1) integrin, very-late-antigen-4 (VLA-4 or CD49d). Furthermore, mAb's specific for CD49d and CD106, or the synthetic CS1 fibronectin peptide, could inhibit B-cell pseudoemperipolesis. We conclude that ordinary FLSs can support B-cell pseudoemperipolesis via a mechanism dependent upon fibroblast expression of SDF-1 and CD106.