Post-weaning epiphysiolysis causes distal femur dysplasia and foreshortened hindlimbs in fetuin-A-deficient mice

Fetuin-A / α(2)-Heremans-Schmid-glycoprotein (gene name Ahsg) is a systemic inhibitor of ectopic calcification. Due to its high affinity for calcium phosphate, fetuin-A is highly abundant in mineralized bone matrix. Foreshortened femora in fetuin-A-deficient Ahsg(-/-) mice indicated a role for fetuin-A in bone formation. We studied early postnatal bone development in fetuin-A-deficient mice and discovered that femora from Ahsg(-/-) mice exhibited severely displaced distal epiphyses and deformed growth plates, similar to the human disease slipped capital femoral epiphysis (SCFE). The growth plate slippage occurred in 70% of Ahsg(-/-) mice of both sexes around three weeks postnatal. At this time point, mice weaned and rapidly gained weight and mobility. Epiphysis slippage never occurred in wildtype and heterozygous Ahsg(+/-) mice. Homozygous fetuin-A-deficient Ahsg(-/-) mice and, to a lesser degree, heterozygous Ahsg(+/-) mice showed lesions separating the proliferative zone from the hypertrophic zone of the growth plate. The hypertrophic growth plate cartilage in long bones from Ahsg(-/-) mice was significantly elongated and V-shaped until three weeks of age and thus prior to the slippage. Genome-wide transcriptome analysis of laser-dissected distal femoral growth plates from 13-day-old Ahsg(-/-) mice revealed a JAK-STAT-mediated inflammatory response including a 550-fold induction of the chemokine Cxcl9. At this stage, vascularization of the elongated growth plates was impaired, which was visualized by immunofluorescence staining. Thus, fetuin-A-deficient mice may serve as a rodent model of growth plate pathologies including SCFE and inflammatory cartilage degradation.