title: Tight regulation of wingless-type signaling in the articular cartilage - subchondral bone biomechanical unit: transcriptomics in Frzb-knockout mice.
abstract: BACKGROUND
  The aim of this research was 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 three wild-type and three Frzb-/- mice was performed by microarray. Data from three wild-type and two Frzb-/- samples could be used for pathway analysis of differentially expressed genes and were explored with PANTHER, DAVID and GSEA bioinformatics tools. Activation of the wingless-type (WNT) pathway was analysed using Western blot. The effects of Frzb gain and loss of function on chondrogenesis and cell proliferation was examined using ATDC5 micro-masses and mouse ribcage chondrocytes.
  
  
  RESULTS
  Extracellular matrix-associated integrin and cadherin pathways, as well as WNT pathway genes were up-regulated in Frzb-/- samples. Several WNT receptors, target genes and other antagonists were up-regulated, but no difference in active β-catenin was found. Analysis of ATDC5 cell micro-masses overexpressing FRZB indicated an up-regulation of aggrecan and Col2a1, and down-regulation of molecules related to damage and repair in cartilage, Col3a1 and Col5a1. Silencing of Frzb resulted in down-regulation of aggrecan and Col2a1. Pathways associated with cell cycle were down-regulated in this transcriptome analysis. Ribcage chondrocytes derived from Frzb-/- mice showed decreased proliferation compared to wild-type cells.
  
  
  CONCLUSIONS
  Our analysis provides evidence for tight regulation of WNT signalling, 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.
authors.affiliation: Laboratory for Skeletal Development and Joint Disorders, Department of Development and Regeneration, KU Leuven, Belgium. Rik.Lories@med.kuleuven.be
authors.forename: Liesbet
authors.initials: L
authors.lastname: Lodewyckx
authors.forename: Frédéric
authors.initials: F
authors.lastname: Cailotto
authors.forename: Sarah
authors.initials: S
authors.lastname: Thysen
authors.forename: Frank P
authors.initials: FP
authors.lastname: Luyten
authors.forename: Rik J
authors.initials: RJ
authors.lastname: Lories
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001842:Bone and Bones / Q000378:metabolism*; D002358:Cartilage, Articular / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics; D002460:Cell Line; D049109:Cell Proliferation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D020219:Chondrogenesis / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling / Q000706:statistics & numerical data; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007719:Knee Joint / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D035683:MicroRNAs / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D060449:Wnt Signaling Pathway / Q000235:genetics*; D000099274:Frizzled-Related Proteins
chemical_list: D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D035683:MicroRNAs; D000099274:Frizzled-Related Proteins; C544772:Mirn147 microRNA, mouse