Chondrocyte suppression is mediated by miR‐129‐5p via GDF11/SMAD3 signaling in developmental dysplasia of the hip

Recent studies have shown that developmental dysplasia of the hip (DDH) during childhood and in animal models is associated with impaired endochondral ossification of the roof of the acetabulum, yet the molecular mechanism of this pathology remains unknown. To address this, an animal model of DDH was established in 4-week-old New Zealand white rabbits by cast immobilization of knee extension. Fifty-six rabbits of DDH were involved in this study, including 21 male rabbits and 25 female rabbits. High-throughput RNA sequencing identified 18 differentially expressed microRNAs; miR-129-5p downregulation was further confirmed by quantitative polymerase chain reaction. Bioinformatics and luciferase reporter assay identified growth differentiation factor 11 (GDF11) as the target gene of miR-129-5p in vitro. miR-129-5p downregulation increased GDF11 expression, which induced the phosphorylation of SMAD family member 3. As a result, the expression of runt-related transcription factor 2, Indian hedgehog homolog, and collagen type X was inhibited in vitro. Meanwhile, Alizarin Red S and Von Kossa staining revealed reduced formation of mineralized nodules by chondrocytes after miR-129-5P downregulation compared with the control. Additionally, proliferation assays and flow cytometry confirmed the suppression of chondrocyte proliferation and G1 cell cycle arrest following miR-129-5p downregulation. These findings indicate that miR-129-5p is able to suppress chondrocyte proliferation and hypertrophic differentiation and decrease mineralization via the miR-129-5p/GDF11/SMAD3 axis. This could present the underlying cause for the observed DDH-associated ossification impairment of the acetabular roof.