Chondrocyte survival and differentiation in situ are integrin mediated

Abstract

Chondrocytes in specific areas of the chick sternum have different developmental fates. Cephalic chondrocytes become hypertrophic and secrete type X collagen into the extracellular matrix prior to bone deposition. Middle and caudal chondrocytes remain cartilaginous throughout development and continue to secrete collagen types II, IX, and XI. The interaction of integrin receptors with extracellular matrix molecules has been shown to affect cytoskeleton organization, proliferation, differentiation, and gene expression in other cell types. We hypothesized that chondrocyte survival and differentiation including the deposition into interstitial matrix of type X collagen may be integrin receptor mediated. To test this hypothesis, a serum-free organ culture sternal model that recapitulates normal development and maintains the three-dimensional relationships of the tissue was developed. We examined chondrocyte differentiation by five parameters: type X collagen deposition into interstitial matrix, sternal growth, actin distribution, cell shape, and cell diameter changes. Additional sterna were analyzed for apoptosis using a fragmented DNA assay. Sterna were organ cultured with blocking antibodies specific for integrin subunits (alpha2, alpha3, or beta1). In the presence of anti-beta1 integrin (25 microg/ml, clone W1B10), type X collagen deposition into interstitial matrix and sternal growth were significantly inhibited. In addition, all chondrocytes were significantly smaller, the actin was disrupted, and there was a significant increase in apoptosis throughout the specimens. Addition of anti-alpha2 (10 microg/ml, clone P1E6) or anti-alpha3 (10 microg/ml, clone P1B5) integrin partially inhibited type X collagen deposition into interstitial matrix; however, sternal growth and cell size were significantly decreased. These data are the first obtained from intact tissue and demonstrate that the interaction of chondrocytes with extracellular matrix is required for chondrocyte survival and differentiation.

Integrity of the cortical actin ring is required for activation of the PI3K/Akt and p38 MAPK signaling pathways in redifferentiation of chondrocytes on chitosan

“…Disruption with cytochalasin D blocked BMP 7-mediated increase in type II collagen expression (Vinall et al, 2002). Moreover, actin cytoskeleton disruption by treatment with an anti-beta1 integrin antibody inhibited type X collagen deposition (Hirsch et al, 1997). In our study, cytochalasin D blocked the redifferentiation of chondrocytes on chitosan membrane (Fig.…”

Different Bone Growth Rates Are Associated With Changes in the Expression Pattern of Types II and X Collagens and Collagenase 3 in Proximal Growth Plates of the Rat Tibia

“…This suggestion is in accordance with several experimental evidences considering cell-matrix interactions as a basic process influencing chondrocyte differentiation. In this way, it has been reported that chondrocyte survival and differentiation is highly dependent on the interaction of cells with extracellular matrix molecules via integrins (37) and that exposition of early hypertrophic chondrocytes to a specific microenviroment composed of unique matrix-origininating signals and cellular cross-talks plays determines their differentiation to osteoblast-like cells at the perichondral bony collar. (38,39) Furthermore, studies of chondrocyte cultures have proved that many endocrine factors exert their effect on the growth plate, at least partially, affecting the genetic expression of matrix components.…”

Autocrine stimulation by insulin-like growth factor 1 and insulin-like growth factor 2 mediates chondrocyte survival in vitro

“…Maximum cell death was noted at 24 hours with 50 g/ml of the antibodies, with no additional cell death after longer incubation periods. For synthetic oligonucleotide studies, preliminary time course studies (1,2,4,8,24, and 48 hours) were used to determine the time required for chondrocyte uptake of fluorescein isothiocyanate-conjugated oligonucleotides, by observation on a fluorescent microscope. From these studies, 24 hours was found to be the time required for maximal uptake.…”

“…In previous work, we have shown that an additional survival factor, Gas-6, is produced by chondrocytes (9). Inhibition of ␤1 integrins in sternal cartilage has also been associated with apoptotic chondrocyte death (24). It is likely that several survival factors act in concert with signals from the extracellular matrix to maintain chondrocyte survival.…”