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Osteoblastic RAR Inhibition Causes VAD-Like Craniofacial Skeletal Deformity
Q Dai1,2,3,4,5,6, S Sun2,3,4,5,7, A Jin2,3,4,5,7
1The 2nd Dental Center, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Insights
Maternal vitamin A deficiency (VAD) causes craniofacial deformities. Inhibiting retinoic acid receptor (RAR) in osteoblasts in mice mimicked VAD skeletal defects, revealing RAR
Area of Science:
- Developmental Biology
- Genetics
- Orthopedics
Background:
- Retinoid signaling disorders, particularly vitamin A deficiency (VAD), are linked to craniofacial deformities in infants.
- Previous studies elucidated eye and palate defects in VAD mice but faced challenges in understanding craniofacial skeletal deformities, their cellular origins, and mechanisms.
- Retinoic acid receptor (RAR) is crucial for retinoid signaling, yet individual gene knockouts do not fully replicate pathway inhibition.
Purpose of the Study:
- To investigate the role of osteoblastic retinoic acid receptor (RAR) activity in craniofacial skeletal development.
- To elucidate the mechanisms by which RAR dysfunction in osteoblasts leads to craniofacial deformities mimicking VAD.
- To establish a mouse model that conditionally inhibits RAR transcription activity in osteoblasts.
Main Methods:
- Conditional expression of a dominant-negative RARα mutation (dnRARα) in osteoblasts of mice to specifically inhibit RAR transcription activity.
- Micro-computed tomography (micro-CT) for 3D reconstruction and analysis of craniofacial bone morphology, size, and ossification.
- Histological analysis and transcriptome sequencing of calvaria to assess bone formation, resorption, and gene expression changes.
- Cell-autonomous and crosstalk mechanisms involving osteoblast and osteoclast differentiation were investigated.
Main Results:
- Osteoblastic dnRARα expression successfully mimicked VAD-associated craniofacial skeletal deformities, including cranial bone hypomineralization, mandibular deformity, and clavicular hypoplasia.
- Micro-CT confirmed significant abnormalities in the shape, size, and ossification of craniofacial bones.
- Histology and transcriptome data revealed impaired osteoblast differentiation (cell-autonomous) and osteoclast differentiation (via impaired Rankl transcription and osteoblast-osteoclast crosstalk).
Conclusions:
- Osteoblastic RAR activity is essential for normal craniofacial skeletal development.
- Inhibition of osteoblastic RAR leads to skeletal deformities that closely resemble clinical VAD craniofacial defects.
- This study provides novel insights into the pathogenesis of VAD-induced craniofacial skeletal malformations by highlighting the critical role of RAR signaling in osteoblasts.
Abstract:
Retinoid signaling disorders cause craniofacial deformity, among which infants with maternal vitamin A deficiency (VAD) exhibited malformation of the eye, nose, palate, and parietal and jaw bone. Previous research uncovered the pathogenesis of eye defect and cleft palate of VAD in mice, but the studies on craniofacial skeletal deformity met obstacles, and the cell/lineage and underlying mechanism remain unclear. The retinoic acid receptor (RAR) is the key transcription factor in retinoid signaling, but individual knockout cannot simulate pathway inhibition. Here, we conditionally expressed dominant-negative RARα mutation (dnRARα) in osteoblasts to specifically inhibit the transcription activity of RAR in mice, which mimics the craniofacial deformities caused by VAD in clinical cases: hypomineralization of cranial bones, mandibular deformity, and clavicular hypoplasia. Furthermore, we performed 3-dimensional reconstruction based on micro-computed tomography and confirmed the abnormalities in the shape, size, and ossification of craniofacial bones due to osteoblastic RAR inhibition. Histological analysis indicated that inhibition of RAR in osteoblasts impaired both bone formation and bone resorption, which was confirmed by transcriptome sequencing of the calvaria. Furthermore, mechanism investigation showed that inhibition of RAR in osteoblasts directly decreased osteoblast differentiation in a cell-autonomous manner by impairing osteogenic gene transcription and also inhibited osteoclast differentiation via osteoblast-osteoclast crosstalk by impairing Rankl transcription. In summary, osteoblastic RAR activity is critical to craniofacial skeletal development, and its dysfunction leads to skeletal deformities mimicking VAD craniofacial defects, providing a new insight for VAD pathogenesis.
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