The changes we detected are not limited to the articu lar cartilage. Increased WNT signaling in the subchon dral bone can also contribute to OA development. In this context, local regulatory mechanisms may be differ ent from tissue to tissue. Frzb mice appear selleck products to have normal subchondral bone but increased cortical bone thickness. Also, anabolic responses in the cortical bone Inhibitors,Modulators,Libraries to cyclic loading are much greater in Frzb mice compared to wild types. Absence of FRZB resulted in shifts in collagens, integ rins and cadherins. Among these, changes in type III and type V collagen are of interest. As articular cartilage matures and ages, collagen fibrils become thicker, the amount of types IX and XI Inhibitors,Modulators,Libraries collagens decreases relative to type II collagen, and these minor collagens are progressively replaced by type V collagen.

Type III collagen can be detected Inhibitors,Modulators,Libraries in small but significant amounts in articular Inhibitors,Modulators,Libraries cartilage of mature joints and is cross linked to the surface of type II collagen. Its presence is more prominent in OA. The type III collagen content in articular cartilage tends to vary between individual joints, anatomical location and tissue microanatomy. It may also be dependent on the history of injuries and the wear and tear experienced by a nor mal joint. Therefore, it seems likely that type III collagen is synthesised as a modifier of existing fibril networks in response to tissue and matrix damage. Although no increased cartilage damage was found in unchallenged Frzb mice, the significant up regulation of Col5a1, Col5a3 and Col3a1 in the articular cartilage and subchondral bone from Frzb mice, suggests increased damage and repair in the Frzb mice at the molecular level.

These observations were further corroborated by com plementary experiments where FRZB was overexpressed in the ATDC5 in vitro chondrogenesis model. Under these conditions, expression of both Col3a1 and Col5a1 was decreased during chondrogenic differentiation, sug gesting that either FRZB by itself, or by modulating WNT Inhibitors,Modulators,Libraries selleck bio signaling, affects expression of these ECM mole cules in different systems. The additional observation that silencing of Frzb also results in a decrease in these collagens can be explained by lack of chondrogenic dif ferentiation in the latter system. We also found that overexpression of FRZB appeared to stimulate chondrogenesis in this model, as shown by increased aggrecan and col2a1 expression. Matured aggrecan monomers in the cartilage are glycosylated macro molecules in which the glycoconjugates are formed by sulphatation of GAG side chains on the core protein. The amount of sulphated GAGs in the micro masses, measured by Safranin O staining, was surprisingly decreased in FRZB overexpressing micro masses.