VLA-5-mediated interaction with fibronectin induces cytokine production by human chondrocytes

SPECT Imaging of Acute Disc Herniation by Targeting Integrin α5β1 in Rat Models

Objective

Traditional morphological imaging of intervertebral disc herniation (IVDH) is challenging in early disease diagnosis. Aiming at the early diagnosis of IVD by non-invasive molecular imaging targeting of integrin α5β1, we performed novel imaging in rats with acute IVDH for the first time.

Methods

Animal models were prepared by conducting an established needle puncture procedure through the normal intervertebral disc (IVD). The disc-injured rats underwent SPECT/CT imaging of the ^99mTc-3PisoDGR2 peptide at 1 day to 2 months postinjury. The expression change of integrin α5β1 was determined by anti-integrin α5 and anti-integrin α5β1 immunohistochemistry (IHC). Magnetic resonance imaging (MRI) was performed for comparison during disease progression. The morphological changes of the disc were determined by safranin-O staining.

Results

Rats with acute IVDH showed gradually increased disc uptake of ^99mTc-3PisoDGR2 from 1 to 7 days posttreatment, which was a significantly higher level than that of the normal disks in degenerative diseases. IHC results showed the expression of integrin α5β1 on the surface of annulus fibrosus (AF) cells and nucleus pulposus (NP) cells, which agreed with the uptake data. MRI showed a progressively decreased T2 density and MRI index throughout the investigation. Hematoxylin and eosin (HE) staining and safranin-O staining revealed a disorganized structure of the IVD as well as loss of proteoglycans after puncture.

Conclusions

The present study demonstrated a good correlation between integrin α5β1 expression and acute disc herniation. The SPECT/CT imaging of ^99mTc-3PisoDGR2 targeting integrin α5β1 may diagnose IVDH in an acute phase for early disease management.

Surface modification of the cubic micro-cartilage by collagenase treatment and its efficacy in cartilage regeneration for ear tissue engineering

BACKGROUND

In order to enhance cartilage regeneration, surface modification of the cubic micro-cartilage with the collagenase treatment was tested and its efficacy to tissue engineer ear cartilage was investigated.

MATERIALS AND METHODS

Harvested cubic micro-cartilages were treated with collagenase with different digestion time (0, 15, 60, and 120 min). Histological, ultrastructural (SEM and TEM), and Western blot analyses were carried out. Subsequently, A total of 45 dogs were used to tissue engineer ear cartilage. Using collagenase-treated micro-cartilage, the ear cartilage regeneration with the prepared dilution (8, 12.5, 25, 50, 100%) of micro-cartilage block seeding was performed to determine the minimum amount of cartilage tissue required for ear tissue-engineering (n = 6 at each point in each group). At 10 weeks after surgery, samples were resected and subjected to histochemical and immune-histological evaluation for cartilage regeneration.

RESULTS

In vitro study on micro-cartilage morphology and western blot analysis showed that collagenase digestion was optimal at 60 min for cartilage regeneration. In vivo evaluation on the reduced proportions of micro-cartilage block seeding onto implant scaffolds under 60-min collagenase digestion determined the minimum amount of cartilage tissue necessary to initiate a one-step ear cartilage regeneration in a canine autologous model, which was 12.5-25% of the original ear size.

CONCLUSION

Tissue-engineering ear cartilage from limited volume of donor cartilage can possibly be achieved by the collagenase treatment on micro-cartilage to expand cartilage regeneration capacity, application of cytokine sustained-release system, and seeding on a suitable ear scaffold material.

Combination of ascorbate and growth factor (TGF β‐3) in thermo‐reversible hydrogel constructs embedded with rabbit chondrocytes for neocartilage formation

This study evaluated the potential of using poly(NiPAAm-co-AAc) as an injectable drug delivery carrier and a cell therapeutic agent in the form of a supporting matrix for the chondrogenic differentiation of rabbit chondrocytes. In particular, rabbit chondrocytes were embedded in hydrogels containing a combination of ascorbate and transforming growth factor beta-3 (TGF beta-3). Hydrogel constructs containing embedded cells either without ascorbate or a combination of ascorbate and TGF beta-3 were used as controls to determine the effects of ascorbate and TGF beta-3 on chondrogenic differentiation. The level of cartilage associated ECM proteins was examined using immunohistochemical staining for collagen type II as well as by Safranin-O and Alcian blue (GAG) staining. The results showed that ascorbate is an important factor for preparing cartilage constructs because of its action on chondrocyte phenotype modulation and proliferation.

Osteopontin: an intrinsic inhibitor of inflammation in cartilage

OBJECTIVE

To identify extracellular and intraarticular matrix components that are differentially expressed in normal and osteoarthritis (OA)-affected cartilage and to investigate their functions with respect to regulation of mediators of inflammation.

METHODS

Differential-display reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of a pool of messenger RNA (mRNA) from 10 human OA cartilage samples and 5 normal cartilage samples was performed using arbitrary primers. Confirmatory analysis of the up-regulated transcripts of fibronectin (FN) and osteopontin (OPN) was performed by RT-PCR of individual RNA samples from a separate set of donors. The effect of recombinant OPN (or anti-OPN antiserum) on chondrocyte function was examined by analyzing the spontaneous or interleukin-1 (IL-1)-induced release of nitric oxide (NO) and prostaglandin E2 (PGE2) from human OA-affected cartilage under ex vivo conditions.

RESULTS

Up-regulation (300-700%) of FN and OPN mRNA was observed in human OA-affected cartilage as compared with normal cartilage. Functional analysis of the role of OPN in OA cartilage showed that 1) Addition of 1 microg/ml (20 nM) of recombinant OPN to human OA-affected cartilage under ex vivo conditions inhibited spontaneous and IL-1beta-induced NO and PGE2 production, and 2) neutralization of intraarticular OPN with anti-OPN antiserum augmented NO production.

CONCLUSION

The data indicate that one of the functions of intraarticular OPN, which is overexpressed in OA cartilage, is to act as an innate inhibitor of IL-1, NO, and PGE2 production. These findings suggest that the production of pleiotropic mediators of inflammation that influence cartilage homeostasis, such as NO and PGE2, is regulated by the interaction of chondrocytes with differentially expressed proteins within the extracellular matrix.

Functional genomic analysis in arthritis-affected cartilage: yin-yang regulation of inflammatory mediators by alpha 5 beta 1 and alpha V beta 3 integrins

Osteoarthritis-affected cartilage exhibits enhanced expression of fibronectin (FN) and osteopontin (OPN) mRNA in differential display and bioinformatics screen. Functional genomic analysis shows that the engagement of the integrin receptors alpha 5 beta 1 and alpha v beta 3 of FN and OPN, respectively, have profound effects on chondrocyte functions. Ligation of alpha 5 beta 1 using activating mAb JBS5 (which acts as agonist similar to FN N-terminal fragment) up-regulates the inflammatory mediators such as NO and PGE2 as well as the cytokines, IL-6 and IL-8. Furthermore, up-regulation of these proinflammatory mediators by alpha 5 beta1 integrin ligation is mediated via induction and autocrine production of IL-1 beta, because type II soluble IL-1 decoy receptor inhibits their production. In contrast, alpha v beta 3 complex-specific function-blocking mAb (LM609), which acts as an agonist similar to OPN, attenuates the production of IL-1 beta, NO, and PGE2 (triggered by alpha 5 beta 1, IL-1 beta, IL-18, or IL-1 beta, TNF-alpha, plus LPS) in a dominant negative fashion by osteoarthritis-affected cartilage and activated bovine chondrocytes. These data demonstrate a cross-talk in signaling mechanisms among integrins and show that integrin-mediated "outside in" and "inside out" signaling very likely influences cartilage homeostasis, and its deregulation may play a role in the pathogenesis of osteoarthritis.

Integrin expression by primary and immortalized human chondrocytes: evidence of a differential role for alpha1beta1 and alpha2beta1 integrins in mediating chondrocyte adhesion to types II and VI collagen

OBJECTIVE

Chondrocytes have been shown to express beta1-containing integrins both in vitro and in situ, but their role in regulating chondrocyte function is poorly understood. The objective of this study was to determine how the relative expression of different integrins may be modulated in relation to the differentiated state and proliferative capacity of the chondrocyte.

DESIGN

Integrin expression by four different cell lines of human chondrocytes immortalized with Simian virus 40 large T-antigen (SV40-TAg) was studied and compared to primary chondrocytes. Differences in alpha1 and alpha2 integrin subunit expression were utilized to further study the role of these integrins in mediating adhesion to types II and VI collagen.

RESULTS

The overall cell-surface levels of beta1-containing integrins were higher on all four immortalized cell lines which expressed over 10-fold higher levels of alpha2 and alpha3 integrin subunits compared to primary cells. However, primary cells expressed higher levels of the alpha1 integrin subunit which was not expressed by T/C28a4 cells and expressed at variable and lower levels in the other lines. Levels of the alpha3 integrin subunit were significantly greater on the highly proliferative juvenile costal chondrocyte lines (T/C-28a4, C-2812, and C-20a4) compared to primary articular chondrocytes and tsT/AC-62 cells which were derived from adult articular chondrocytes. Expression of alpha5 was similar among primary cells and cell lines except on C-20/A4 cells which had an average of over 4-fold higher levels. None of the primary or immortalized chondrocytes tested expressed significant levels of alpha4. Cell adhesion assays revealed that both alpha1beta1 and alpha2beta1 could serve as chondrocyte adhesion receptors for types II and VI collagen. In cell lines expressing both integrins, alpha1beta1 was the preferential receptor for type VI collagen while alpha2beta1 was the preferential receptor for type II collagen. Rather than inhibiting adhesion, incubation with the alpha3 blocking antibody P1B5 increased adhesion of C-28/12 cells to both fibronectin and type II collagen by 67% and 100% respectively.

CONCLUSIONS

Immortalization with SV40-TAg results in altered integrin expression by chondrocytes. Changes in the relative levels of alpha1, alpha2, and alpha3 subunits may significantly alter the manner in which chondrocytes interact with types II and VI collagen in the extracellular matrix.

The incidence of enlarged chondrons in normal and osteoarthritic human cartilage and their relative matrix density

OBJECTIVE

To quantitate changes in the pericellular matrix in osteoarthritic (OA) articular cartilage.

DESIGN

Chondrons were enzymatically isolated from normal and OA human cartilage. The cross-sectional area of the chondrons were measured. After immunolabeling for keratan sulfate, type VI collagen and type II collagen, the relative matrix density was determined for different size classes of chondrons with quantitative fluorescence microscopy.

RESULTS

For individual chondrons, the average cross-sectional area (344+/-28 microm(2), mean+/-SE) for the normal specimens was significantly smaller than the average area (439+/-30 microm(2)) for the OA specimens. Using 496 microm(2) (mean+2 SD of the normal area) as the cut-off for enlarged chondrons, 33% of individual OA chondrons were enlarged compared to 16% for the normal. Chondrons under 300 microm(2) had a significantly higher density of keratan sulfate and type VI collagen than larger chondrons, while chondrons over 400 microm(2) had similar matrix densities.

CONCLUSIONS

There is a higher incidence of enlarged chondrons in OA cartilage than in normal cartilage. The enlargement may initially be due to hydrodynamic swelling but further increases in size are due to increased matrix deposition.

Vascular cell adhesion molecule 1 (CD106) on primary human articular chondrocytes: functional regulation of expression by cytokines and comparison with intercellular adhesion molecule 1 (CD54) and very late activation antigen 2

OBJECTIVE

To investigate the expression of adhesion molecules belonging to the immunoglobulin superfamily on human primary articular chondrocytes and to determine their response pattern to cytokines with respect to the adhesion of lymphocytes.

METHODS

The expression of adhesion molecules was studied by flow cytometry (cultured cells), immunohistochemistry (cartilage), reverse transcription-polymerase chain reaction, and Northern blotting. Adhesion of T cells to chondrocytes was measured using the Jurkat T cell line.

RESULTS

Vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) were found to be constitutively expressed on large percentages of unstimulated chondrocytes in culture and in cartilage ex vivo. ICAM-2, ICAM-3, and very late activation antigen 4 (VLA-4; alpha4beta1 integrin), the ligand for VCAM-1, were not detected. Interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) further induced VCAM-1 and ICAM-1 messenger RNA and protein expression. Transforming growth factor beta (TGFbeta) had no effect on ICAM-1 and decreased the expression of VCAM-1. Another adhesion molecule, VLA-2 alpha2beta1 integrin) that was also expressed on unstimulated chondrocytes, was differentially regulated by cytokines. While neither IL-1beta nor TNFalpha had any effect on expression of VLA-2, TGFbeta markedly increased the alpha2 subunit of VLA-2. Adhesion of Jurkat T cells to chondrocytes was further induced by IL-1beta and TNFalpha. Pretreatment of chondrocytes with monoclonal antibodies to VCAM-1 and ICAM-1 inhibited adhesion of T cells to chondrocytes.

CONCLUSION

VCAM-1, ICAM-1, and VLA-2 are constitutively expressed by human articular chondrocytes. Expression is regulated by cytokines. As shown for other chondrocyte genes, IL-1beta/TNFalpha and TGFbeta antagonistically modulate the expression of adhesion molecules. VCAM-1 and ICAM-1 contribute to adhesion of T lymphocytes to chondrocytes, and may thus participate in host defense mechanisms during inflammatory joint conditions such as rheumatoid arthritis and after cartilage transplantation.

Expression of alpha and beta subunits of the integrin superfamily in articular cartilage from macroscopically normal and osteoarthritic human femoral heads

OBJECTIVE

The objective of this study was to detail the topographical and zonal distribution of alpha and beta subunits of the integrin superfamily in normal and osteoarthritic cartilage.

METHODS

Immunohistochemistry utilising antibodies towards alpha and beta subunits was performed on cryostat sections of human articular cartilage from macroscopically normal (n = 6) and osteoarthritic (n = 6) femoral heads. Samples of articular cartilage were obtained from 12 topographically distinct sites from each femoral head. Each section was divided into zones (superficial, middle, deep) and staining scores were recorded.

RESULTS

Normal cartilage stained for integrin subunits alpha 1, alpha 5, alpha V, beta 1, beta 4, and beta 5, but not for alpha 2, alpha 3, alpha 4, alpha 6, beta 2, beta 3, and beta 6. Intact and non-intact residual cartilage from osteoarthritic femoral heads stained for alpha 1, alpha 2, alpha 5, alpha V, beta 1, beta 4, and beta 5. Staining was occasionally seen for alpha 4 and beta 2, but not for alpha 3, alpha 6, beta 3, and beta 6. There was no topographical variation in the staining for any of the subunits in either normal or osteoarthritic cartilage. The only subunit that displayed a zonal variation was alpha V; staining for this subunit was most pronounced in the superficial zone compared with the middle and deep zones.

CONCLUSION

Chondrocytes in normal and osteoarthritic cartilage express the integrin subunits alpha 1, alpha 5, alpha V, beta 1, beta 4, and beta 5. Chondrocytes in osteoarthritic cartilage, in addition, express the alpha 2, alpha 4, and beta 2 subunits. The alpha v subunit is expressed by more chondrocytes in the superficial zone in comparison with cells in the deeper zones. None of the subunits display topographical variation in expression.

RGDN peptide interaction with endothelial alpha5beta1 integrin causes sustained endothelin-dependent vasoconstriction of rat skeletal muscle arterioles

The ability of an integrin-binding Arg-Gly-Asp-Asn (RGDN)- containing peptide to influence vascular tone by interacting with the alpha5beta1 integrin was studied using rat skeletal muscle arterioles. After blockade of beta3 integrin function, isolated arterioles with spontaneous tone showed concentration-dependent vasoconstrictions to topical application of GRGDNP, a peptide that shows a greater ability to interact with alpha5beta1 than with alphavbeta3. The constriction to GRGDNP (2.1 mM) was inhibited by blocking alpha5 integrin function, and was intensified by blocking beta3 integrin function. In contrast, GRGDSP, a peptide that interacts better with alphavbeta3, was unable to induce sustained constrictions. Removal of the endothelium abolished the vasoconstriction in response to GRGDNP, suggesting that the response was due to release of an endothelium-dependent factor. Indeed, blockade of ETA endothelin receptors with BQ-610 (1 microM), similar to removal of the endothelium and alpha5 integrin blockade, inhibited the vasoconstriction. These data indicate that interaction of RGD peptides, and in particular the RGDN sequence with endothelial cell alpha5beta1, causes endothelin-mediated arteriolar vasoconstriction. These results indicate that integrins are novel signaling receptors within the vascular wall that affect vasomotor tone, and may play an important role in vascular control.

Cartilage fibronectin isoforms: in search of functions for a special population of matrix glycoproteins

Fibronectins are a part of the repertoire of matrix molecules produced by the chondrocyte in order to assemble a functional cartilage matrix. They are encoded by a single gene, but significant protein heterogeneity results from alternative RNA splicing. The population of fibronectin isofroms in adult cartilage is significantly different from fibronectins in other tissues and includes relatively high levels (20-30%) of ED-B(+) fibronectins and high levels (50-80%) of the cartilage specific (V + C)- isoform which lacks the V, III-15 and I-10 segments. Less than 4% of the fibronectins in cartilage are ED-A(+). The synthesis and accumulation of cartilage fibronectins are modulated in response to matrix pathology and to biochemical and mechanical mediators. In addition, alternative splicing patterns are altered when chondrocytes are allowed to dedifferentiate in monolayer culture such that the (V + C)- isoform is lost but the ED-A(+) isoform is reexpressed at high levels. Cartilage fibronectins have the potential to participate in cell signalling via integrin mediated pathways and to interact with other cartilage matrix macromolecules. The tissue-specific splicing pattern gives rise to a unique population of fibronectins within the cartilage. Together, this points to a critical role for cartilage fibronectins in chondrocyte cell biology and the organization of a biomechanically sound matrix. However, the precise function (or functions) of the cartilage fibronectins has (or have) not been defined. This minireview examines current information about the structure, synthesis and interactions of cartilage fibronectins. When possible, potential consequences of the inclusion of the ED-B segment or the exclusion of the V, III-15 and I-10 segments are discussed. The goal is to stimulate critical thought and discussion in the field about cartilage fibronectin isoforms, their function(s) in normal cartilage, and their role(s) in the pathogenesis of cartilage diseases.