Loss of decorin from the surface zone of articular cartilage in a chick model of osteoarthritis

Assessment of specific mRNA levels in cartilage regions in a lapine model of osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis and patients with meniscal and ligament injuries of the knee are at high risk to develop the disease. The purpose of this study was to evaluate molecular and structural changes occurring in four articular cartilage (AC) regions from the knees of anterior cruciate ligament (ACL)-transected rabbits at 3 and 8 weeks post-surgery. Rabbit AC from the lateral and medial femoral condyles (LFC and MFC) as well as from the medial and lateral tibial plateau (MTP and LTP) were processed for histology and for semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for a subset of relevant molecules (collagen II, aggrecan. biglycan, decorin, fibromodulin, MMP-1, -3, -13, and TIMP-1). While the most severe histological changes were observed in the MTP starting as early as 3 weeks post-ACL transection based on Mankin scores, histological examination demonstrated a progression of osteoarthritic changes in the MFC from 3 to 8 weeks post-surgery. In contrast, very few changes were observed within both the LFC and LTP, and these changes did not worsen with increasing time after surgery. The water content increased significantly in the MFC at 8 weeks post-ACL transection and at both 3 and 8 weeks post-ACL transection in the MTP. Significant decreases in DNA content were observed for the MFC, LTP and MTP at 8 weeks post-ACL transection. Total RNA yields from the MFC and MTP were significantly elevated at 8 weeks post-ACL transection, while in the lateral compartment total RNA was unchanged following ACL transection. Analysis of mRNA levels for a subset of matrix molecules, proteinases and proteinase inhibitors, by RT-PCR demonstrated significant region-specific changes at the mRNA level following ACL transection. These results show that following ACL transection, complex molecular, as well as structural changes occur early in cartilage and that the observed changes are both region-specific and time-dependent.

Perturbations in factors that modulate osteoblast functions in vitamin B6 deficiency

It was hypothesized that the widespread structural defect of collagen in connective tissue of vitamin B6deficient-animals and the consequent alteration in bone biomechanical properties cause an additional stress to their inflammed swollen tibiotarsometatarsal joints. The present study showed a 32% elevation (P &lt 0.02) in mean plasma free cortisol concentration. Vitamin D metabolism was impaired but without changing plasma calcium homeostasis and bone mineral content. Mean plasma calcitriol [1,25(OH)2D] concentration was significantly reduced (P < 0.001). Because plasma calcidiol concentration did not change, we speculated that either renal 25-hydroxycalciferol-1α-hydroxylase activity was reduced or 1,25(OH)2D turnover was increased. Plasma osteocalcin, an index of osteoblast function related to bone formation, was significantly decreased (P < 0.05). This adverse effect on osteoblasts was consistent with the reduction of bone specific alkaline phosphatase activity (another index of bone formation) found in a previous study. The excess of cortisol may have impaired these bone cells functions directly and (or) indirectly via the decline in calcitriol synthesis. Plasma hydroxyproline concentrations in B6-deficient animals were found to be significantly reduced (P < 0.001), suggesting that cortisol in excess had also a suppressive effect on another hydroxylase, namely tissue (mainly bone and liver) prolyl hydroxylase. The bone uncoupling (in formation and resoption) associated with vitamin B6deficiency seems to be due to secondary hypercortisolism and (or) another unknown factors but not related to a change in bone modulators such as IGF-1 and eicosanoids.Key words: collagen, vitamin B6, vitamin D, cortisol, osteocalcin, IGF-1, eicosanoids, PGE2.

Effects of interleukin-1beta and tumor necrosis factor-alpha on expression of matrix-related genes by cultured equine articular chondrocytes

OBJECTIVE

To determine the effects of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) on expression and regulation of several matrix-related genes by equine articular chondrocytes.

SAMPLE POPULATION

Articular cartilage harvested from grossly normal joints of 8 foals, 6 yearling horses, and 8 adult horses.

PROCEDURE

Chondrocytes maintained in suspension cultures were treated with various doses of human recombinant IL-1beta or TNF-alpha. Northern blots of total RNA from untreated and treated chondrocytes were probed with equine complementary DNA (cDNA) probes for cartilage matrix-related genes. Incorporation of 35S-sulfate, fluorography of 14C-proline labeled medium, zymography, and western blotting were used to confirm effects on protein synthesis.

RESULTS

IL-1beta and TNF-alpha increased steady-state amounts of mRNA of matrix metalloproteinases 1, 3, and 13 by up to 100-fold. Amount of mRNA of tissue inhibitor of metalloproteinase-1 also increased but to a lesser extent (1.5- to 2-fold). Amounts of mRNA of type-II collagen and link protein were consistently decreased in a dose-dependent manner. Amount of aggrecan mRNA was decreased slightly; amounts of biglycan and decorin mRNA were minimally affected.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment of cultured equine chondrocytes with IL-1beta or TNF-alpha resulted in marked alterations in expression of various matrix and matrix-related genes consistent with the implicated involvement of these genes in arthritis. Expression of matrix metalloproteinases was increased far more than expression of their putative endogenous inhibitor. Results support the suggestion that IL-1beta and TNF-alpha play a role in the degradation of articular cartilage in arthritis.

Age-associated changes in decorin in rat mandibular condylar cartilage

The small proteoglycan decorin strongly binds the fibrils of collagen types I and II; this interaction is thought to play a part in the maintenance of tissue integrity and biomechanical properties. In limb articular cartilage, there is evidence that decorin synthesis increases with age and that it is elevated in response to increased loading or in osteoarthritic cartilage. The aim here was to characterize the presence and relative amount of decorin in the condylar cartilage of the temporomandibular joint (TMJ) with maturation by Western blotting, and to assess its tissue localization by immunohistochemistry. Comparative data were obtained from tibial articular cartilage, which has been extensively studied. Cartilage from the mandibular condyle and tibial plateau was harvested from 24-day-old (growing) and 161-day-old (young adult) female Sprague-Dawley rats. In growing animals, decorin appeared slightly more abundant in the mandibular condylar cartilage than in articular cartilage, whereas in young adult animals the decorin content in the TMJ cartilage was noticeably less than in limb articular cartilage. Although there was an increase in decorin abundance with age at the TMJ, the increase in decorin with age in limb articular cartilage was considerably more pronounced. These data indicate that, although decorin is present in mandibular condylar cartilage, its abundance in adults is less than in limb articular cartilage; thus, maturation-associated changes may be dissimilar in magnitude from those documented for limb articular cartilage.