Régulation de l'expression de PPARγ dans l'arthrose

Osteoarthritis (OA) is the most common degenerative joint disease. It is characterised by progressive destruction of articular cartilage, synovial inflammation and subchondral bone remodelling. The complete etiology of OA is still not well defined. Several studies have been carried out to elucidate the molecular and cellular mechanisms involved in OA development.           The protective effects of Peroxisome proliferator-activated receptor gamma (PPARγ) in OA have been well documented. It has been demonstrated that PPARγ exhibit anti-inflammatory and anti-catabolic properties. Although many stimuli have been reported to regulate the expression of PPARγ in several cell types. However, little information is available on the exact mechanisms that govern its regulation as well as the expression profile of this recepteur during the course of the disease.            In the first part of this work, we tried to elucidate the mechanisms involved in the alteration of PPARγ expression in OA. Our findings confirm that interleukin-1 beta (IL-1β), a proinflammatory cytokine, down regulate the expression of PPARγ in articular chondrocytes. This effect coincided with the induction of early growth response protein-1 (Egr-1) expression. In addition, down regulation of PPARγ expression was associated with Egr-1 recruitment to and concomitant reduction in Sp1 occupancy at PPARγ promoter.           In the second part of this work, we evaluated the expression profile of this receptor in cartilage during the progression of OA. Spontaneous Hartley guinea pig model and anterior cruciate ligament transection (ACLT) dog model were used to follow the expression of three isoforms of PPARs: PPAR alpha (α), PPAR beta (β) and PPAR gamma (γ) as well as hematopoietic prostaglandin D synthase (H-PGDS) and lipocalin-type prostaglandin D synthase (L-PGDS) two enzymes involved in the production of the natural agonist PAARγ, 15-Deoxy-delta(12,14)-prostaglandin J(2) (15d PGJ2).           Our reultats showed changes in the expression of PPARγ and L-PGDS. In contrast, the level of PPARα, PPARβ and H-PGDS was constant over time. The decrease in PPARγ levels in articular chondrocytes suggest that it may be a contributing factor in OA development in both animal models used in this study. Furthermore, siRNA silencing of PPARγ resulted in an enhanced production of osteoarthric mediators such as matrix metalloproteinase-13 (MMP-13) and nitric oxide (NO). Thus, confirming the anti-arthritic role of this receptor. In contrast, unlike the later, there was an increase in the expression level of L-PGDS during disease progression. The overexpression of L-PGDS in human chondrocytes was associated with reduced production of these osteoarthric mediators, suggesting its involvement in repair process.           In summary, our data suggest that the modulation of PPARγ, L-PGDS and Egr-1 expression levels in articular cartilage may be a potential therapeutic approach in the treatment of OA and probably other forms of arthritis.

Keyphrases: Cartilage, PPARs, PGDS, Egr-1, Sp1, Chondrocytes, Osteoarthritis, Cartilage, PPARs, PGDS, Egr-1, Sp1, Chondrocytes