Chemistry and Physics Faculty Proceedings, Presentations, Speeches, Lectures

Title

24,25-Dihydroxyvitamin D Promotes the Osteogenic Maturation of Human Mesenchymal Stem Cells through the Regulation of p63.

Event Name/Location

The Endocrine Society's 94th Annual Meeting and Expo / Houston, TX

Event Name

The Endocrine Society's 94th Annual Meeting and Expo

Event Location

Houston, Texas

Document Type

Conference Presentation

Publication Date

6-23-2012

Date Range

June 23-26, 2012

Abstract

Bone homeostasis and repair are regulated by vitamin D and its metabolites, of which 1α,25- dihydroxyvitamin D (1,25OHD) has been considered the most biologically active and relevant. Vitamin D metabolites include 24,25-dihydroxyvitamin D (24,25OHD), a major metabolite with heretofore unappreciated activity. We present here results showing that 24,25OHD regulates human mesenchymal stem cell (hMSC) osteogenic maturation. Our data establishes that 24,25OHD inhibits hMSC proliferation, increases alkaline phosphatase activity and mineralization, and decreases 1α-hydroxylase expression, potentially decreasing the ability to convert 25OHD to 1,25OHD. In addition, 24,25OHD but not 1,25OHD induced mineralization in the absence of dexamethasone -- commonly used for osteogenic induction and known to up-regulate the VDR. This data supports a role for 24,25OHD during osteogenic maturation, suggesting that previously published studies using dexamethasone are skewed toward a 1,25OHD response. Currently, we don't understand how 24,25OHD and 1,25OHD differentially mediate this process. During murine development, the transcription factor p63 is required for skeletal formation (1). In addition, our work (2) demonstrates that p63 is integral for 1,25OHD receptor, VDR expression in hMSC. Therefore, since p63 regulates 1,25OHD/VDR, the question is raised as to its regulation of 24,25OHD actions and overall osteogenic maturation. p63 gene expression is complex, leading to the formation of TA- and ΔNp63 isoforms, and three splice variants (α,β,γ). The p63 gene products can activate or repress growth and differentiation, however their role(s) during osteogenic maturation are not established. Our studies demonstrate that during the progression of immature hMSC toward the osteogenic phenotype, there is a switch from TAp63α,β to TAp63γ expression. The addition of 1,25OHD up-regulated the ΔNp63 isoforms, while 24,25OHD increased TA/ΔNp63γ mRNA expression and TAp63α protein expression. These results link 1,25OHD up-regulation of ΔNp63, required for terminal differentiation (3), and 24,25OHD up-regulation of p63γ, known to regulate VDR expression (4). These results support a generalized paradigm implicating p63 as a key player during hMSC osteogenic maturation and possibly bone repair in vivo. We hypothesize that the actions of vitamin D on osteogenic maturation and bone repair are due to a regulatory relationship between p63 gene products and unique 24,25OHD/1,25OHD effects.

Comments

(1) Yang A, Schweitzer R, Sun D, et al., p63 is essential for regenerative proliferation in limb, craniofacial and epithelial development. Nature, 1999. 398(6729): p. 714-8 (PMCID: 10227294). (2) Chen K, Roos BA, Howard GA: Hepatocyte Growth Factor (HGF) and 1,25-dihydroxyvitamin D Together Stimulate Human Bone Marrow-Derived Stem Cells Toward the Osteogenic Phenotype by HGF-induced UpRegulation of VDR. BONE 2012 (Under Revision). (3) Yang A, Kaghad M, Wang Y, et al., p63, a p53 homolog at 3q27-29, encodes multiple products with transactivating, death-inducing, and dominantnegative activities. Mol Cell, 1998. 2(3): p. 305-16 (PMCID: 9774969). (4) Kommagani R., Caserta TM., and Kadakia MP. Identification of vitamin D receptor as a target of p63. Oncogene (2006) 25, 3745-3751. Nothing to Disclose: KMC, KKA, KC, BAR, GAH Sources of Research Support: Veterans Affairs Merit Review Awards (GH, BR).

Conference Proceeding Title

Endocrine Reviews

ISSN

0163-769X

DOI

10.1093/edrv/34.supp.1

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