43 - Retinoic Acid Regulates Commitment of Osteoprogenitor Cells During Bone Development

Poster Board Number: 43
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Co-authors:

Paul Trainor - Stowers Institute for Medical Research; Maureen Kane - University of Maryland; Andrew Wilkie - University of Oxford; Alexander Moise - Northern Ontario School of Medicine University

Abstract Body : Introduction: Vitamin A is an essential nutrient for a wide range of biological processes during both embryonic development and postnatal life. Retinoic acid (RA), the main active metabolite of vitamin A mediates a variety of signaling pathways as well as regulates the expression levels of more than 500 genes through activating its nuclear receptors, retinoic acid receptor (RAR). RA is also a key regulator of cell differentiation and fate determination throughout life. Alterations in vitamin A metabolism or signaling pathways contribute to congenital disorders. Therefore, RA levels need to be precisely regulated by a complex network of enzymes, binding proteins, and transporters. The interconversion of all-trans-retinol to all-trans-retinaldehyde is primarily controlled by RA through a negative feedback mechanism via regulation of the expression levels of short-chain dehydrogenase (SDR) enzymes, RDH10 and DHRS3. Disruption of the activity of these enzymes results in RA deficiency or excess, respectively, both of which result in birth defects and embryonic lethality. Mutations in DHRS3 are associated with craniosynostosis, a birth defect characterized by the premature fusion of cranial sutures. Exposure to elevated levels of RA can contribute to craniosynostosis but the pathological mechanisms involved are not known. In this study, we explored the mechanisms by which perturbations in RA signaling affect the differentiation of calvarial osteoprogenitor cells using physiological levels of RA or genetic modification and inhibition of RA metabolic enzymes.

Material and methods: We employed both genetic and biochemical means to disrupt RA metabolism. We disrupted Dhrs3 in mouse MC3T3-E1 calvarial preosteoblasts to induce excess RA formation and mimic the human disorder caused by DHRS3 mutations. Alternatively, we developed a protocol to block RA formation using WIN 18,446, a specific inhibitor of the RA synthetic enzyme, RALDH2.

Results: Administration of 10 µM WIN 18446, 50 nM exogenous RA, or disruption of Dhrs3, all caused significant changes in the expression levels of osteogenic markers and mineralization during the process of osteogenic differentiation of MC3T3-E1 preosteoblasts.

Conclusion: Together, our data show important roles for RA in the regulation of the osteogenesis process by controlling the fate of progenitor cells. Our result revealed either excess or deficiency of RA has multiple effects on bone development and disturbs the transition of pre-osteoblasts toward osteocytes.