Histone deacetylase 4 in limb mesenchyme is essential for chondrocyte proliferation, growth plate maintenance and proper bone formation.

PURPOSE/AIM: Dysregulation of well-ordered chondrocyte proliferation and differentiation leads to distorted architecture of the growth plate, resulting in skeletal dysplasia with impaired longitudinal bone growth. Histone deacetylase 4 (HDAC4) is essential for chondrocyte hypertrophy and endochondral bone formation, but its role in postnatal bone development remains unexplored due to early lethality in Hdac4-ablated mice. Furthermore, a direct in vivo effect of Hdac4 on mesenchymal cell specification and bone development has not been investigated.

MATERIALS AND

METHODS

We generated Prx1-Cre;Hdac4fl/fl, Sp7-Cre;Hdac4fl/fl, Acan-CreERT2;Hdac4fl/fl, and Hdac4fl/fl transgenic mice, respectively. The genotyping of transgenic mice was performed via conventional PCR. Whole-body radiographs and x-ray analyses of limbs were conducted. Trabecular and cortical bone microstructures of tibias from 21-day-old mice were evaluated using micro-computed tomography. EdU label-retention assay investigated cell proliferation, while histological analyses included H&E, TRAP, and Von Kossa staining. RT-qPCR and Immunohistochemistry to detect the pro-osteogenic function of HDAC4.

RESULTS

Hdac4 inactivation in limb mesenchyme cells resulted in limb shortening, premature growth plate closure, abnormal bone morphologies, and loss of the rounded articular surface. HDAC4 was crucial for regulating chondrocyte proliferation and secondary ossification center formation. Micro-computed tomography showed increased trabecular and cortical bone Prx1-Cre;Hdac4fl/fl mice at 3 weeks, with altered microarchitecture. .

CONCLUSIONS

Hdac4 in limb mesenchymal cells plays an indispensable role in chondrocyte proliferation, maintenance of the growth plate and formation of secondary ossification centers, its pro-osteogenic role was accomplished through premature differentiation of chondrocytes, along with accelerated cartilage-to-bone conversion.