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Mutant activated FGFR3 impairs endochondral bone growth by preventing SOX9 downregulation in differentiating

Zi-Qiang Zhou1, Sara Ota1, Chuxia Deng2

  • 1Shriners Hospitals for Children, 3101 SW Sam Jackson Park Road, Portland, OR 97239, USA.

Human Molecular Genetics
|November 30, 2014
PubMed

Insights

Mutant fibroblast growth factor receptor 3 (FGFR3) causes a differentiation block in chondrocytes, hindering bone growth. Reducing SOX9 levels rescues this block and improves endochondral ossification in developmental disorders.

Area of Science:

  • Skeletal biology
  • Developmental genetics
  • Molecular endocrinology

Background:

  • Fibroblast growth factor receptor 3 (FGFR3) is crucial for endochondral ossification and bone growth.
  • Mutations leading to FGFR3 hyperactivation cause developmental disorders with impaired bone growth.
  • FGFR3 is expressed in growth plate chondrocytes, including those in the prehypertrophic phase.

Purpose of the Study:

  • To investigate the role of FGFR3 in chondrocyte differentiation independent of proliferation.
  • To determine the mechanism by which mutant FGFR3 impairs endochondral bone growth.
  • To identify potential therapeutic targets for FGFR3-associated skeletal dysplasias.

Main Methods:

  • Generated a knockin mouse model with a constitutively active FGFR3 allele (FGFR3K650E) specifically in prehypertrophic chondrocytes.
  • Analyzed chondrocyte proliferation, differentiation, and gene expression.
  • Assessed endochondral bone growth and SOX9 (master regulator of chondrogenesis) expression levels.
  • Manipulated SOX9 dosage to evaluate its impact on differentiation and bone growth.

Main Results:

  • Mutant FGFR3 induced a differentiation block in prehypertrophic chondrocytes, independent of proliferation changes.
  • This block was associated with persistent SOX9 expression.
  • Reducing SOX9 dosage rescued the differentiation defect and significantly improved endochondral bone growth in the FGFR3K650E model.

Conclusions:

  • A proliferation-independent, SOX9-dependent differentiation block is a key mechanism in FGFR3-associated skeletal disorders.
  • Targeting SOX9 may offer a therapeutic strategy for improving bone growth in conditions like Thanatophoric Dysplasia Type II.
  • These findings refine our understanding of FGFR3's role in skeletal development and disease.

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