Gene expression in articular cartilage - subchondral bone of FRZB knockout mice

Objective : To study molecular changes in the articular cartilage and subchondral bone of the tibial plateau from mice deficient in frizzled related protein (Frzb) compared to wild-type mice by transcriptome analysis. Methods : Gene-expression analysis of the articular cartilage and subchondral bone of 3 wild-type and 3 Frzb-/- mice was performed by microarray. Pathway analysis of differentially expressed genes between 3 wild-type and 2 Frzb-/- samples was explored with PANTHER, DAVID and GSEA bioinformatics tools. Activation of the WNT pathway was analyzed using western blot. The effects of Frzb gain and loss of function on chondrogenesis and cell proliferation was examined using ATDC5 micromasses and mouse ribcage chondrocytes. Results : Extracellular matrix-associated integrin and cadherin pathways, as well as WNT pathway genes were upregulated in Frzb-/- samples. Several WNT receptors, target genes, and other antagonists were upregulated, but no difference in active β-catenin was found. Analysis of ATDC5 cell micromasses overexpressing FRZB indicated an upregulation of aggrecan and Col2a1, and downregulation of molecules related to damage and repair in cartilage, Col3a1 and Col5a1. Silencing of Frzb resulted in downregulation of aggrecan and Col2a1. Pathways associated with cell cycle were downregulated. Ribcage chondrocytes derived from Frzb-/- mice showed decreased proliferation compared to wild-type cells. Conclusions : Our analysis provides evidence for tight regulation of WNT signaling, shifts in extracellular matrix components and effects on cell proliferation and differentiation in the articular cartilage - subchondral bone unit in Frzb-/- mice. These data further support an important role for FRZB in joint homeostasis and highlight the complex biology of WNT signaling in the joint. Gene-expression analysis of the articular cartilage and subchondral bone of 3 wild-type and 3 Frzb-/- mice was performed by microarray. Pathway analysis of differentially expressed genes between 3 wild-type and 2 Frzb-/- samples was explored with PANTHER, DAVID and GSEA bioinformatics tools.