Krox20 and Bone Mass. We propose to delineate the role of the transcription factor Krox20 in the regulation of osteoblast function and bone mass control. During the previous funding cycle of this project, we discovered that Krox20 expression and transcriptional activity were strongly inhibited by glucocorticoids (GCs), contributing to the repression of osteocalcin transcription in cultured osteoblasts. We propose to expand the project beyond the problem of GC-induced osteoporosis (GIO) and study the role of Krox20 in basic osteoblast biology in vivo and in vitro. Such a role is suggested by: (i) developmental arrest of trabecular bone formation in Krox20-/- mice; (ii) low trabecular bone mass and decreased bone formation rate in mature Krox20 mice; (iii) impaired mineralization in Krox20 and Krox20-/- osteoblast cultures; (iv) stimulation of Krox20 expression and activity by the Wnt signaling pathway; and (v) expression pattern in vivo and in vitro consistent with a role for Krox20 in osteoblast function. We will analyze as a function of age the skeletal phenotype of mice with insufficient and/or osteoblast-specific excess of Krox20. In vivo approaches will include microcomputed tomography (mu CT) as well as histological and serological analyses. The cellular and molecular targets of Krox20 will be determined analyzing osteoblast cultures in which Krox20 expression has been altered by either genetic manipulations or viral infection. The in vitro analyses will be performed at short intervals during the development of the osteoblast phenotype to identify the Krox20-sensitive differentiation stage. The specific roles of Krox20 will be determined with respect to cell cycle progression, apoptosis, development of biochemical markers and expression of genes that promote the osteoblast phenotype, including genes potentially regulated directly by Krox20 and indirectly by the Wnt signaling pathway. Finally, we will return to the investigation of GIO. We will assess the effect of GCs on Krox20 expression in vivo in the context of a detailed description (including mu CT and apoptosis) of GIO development in the mouse; and, we will determine whether treatment with a Krox20 virus or recombinant Wnt3A antagonize adverse effects of GCs in osteoblasts. These studies will elucidate novel regulatory mechanisms that control osteoblast function and bone formation in health and disease, and open new avenues in the pursuit of bone anabolics. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
2R01AR047052-05A2
Application #
7145189
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Sharrock, William J
Project Start
2000-09-01
Project End
2011-07-31
Budget Start
2006-08-01
Budget End
2007-07-31
Support Year
5
Fiscal Year
2006
Total Cost
$359,251
Indirect Cost
Name
University of Southern California
Department
Orthopedics
Type
Schools of Medicine
DUNS #
072933393
City
Los Angeles
State
CA
Country
United States
Zip Code
90089
Baniwal, Sanjeev K; Little, Gillian H; Chimge, Nyam-Osor et al. (2012) Runx2 controls a feed-forward loop between androgen and prolactin-induced protein (PIP) in stimulating T47D cell proliferation. J Cell Physiol 227:2276-82
Baniwal, S K; Shah, P K; Shi, Y et al. (2012) Runx2 promotes both osteoblastogenesis and novel osteoclastogenic signals in ST2 mesenchymal progenitor cells. Osteoporos Int 23:1399-413
Gabet, Yankel; Noh, Tommy; Lee, Christopher et al. (2011) Developmentally regulated inhibition of cell cycle progression by glucocorticoids through repression of cyclin A transcription in primary osteoblast cultures. J Cell Physiol 226:991-8
Ofek, Orr; Attar-Namdar, Malka; Kram, Vardit et al. (2011) CB2 cannabinoid receptor targets mitogenic Gi protein-cyclin D1 axis in osteoblasts. J Bone Miner Res 26:308-16
Gabet, Yankel; Baniwal, Sanjeev K; Leclerc, Nathalie et al. (2010) Krox20/EGR2 deficiency accelerates cell growth and differentiation in the monocytic lineage and decreases bone mass. Blood 116:3964-71
Warotayanont, Rungnapa; Frenkel, Baruch; Snead, Malcolm L et al. (2009) Leucine-rich amelogenin peptide induces osteogenesis by activation of the Wnt pathway. Biochem Biophys Res Commun 387:558-63
Noh, Tommy; Gabet, Yankel; Cogan, Jon et al. (2009) Lef1 haploinsufficient mice display a low turnover and low bone mass phenotype in a gender- and age-specific manner. PLoS One 4:e5438
Baniwal, Sanjeev K; Khalid, Omar; Sir, Donna et al. (2009) Repression of Runx2 by androgen receptor (AR) in osteoblasts and prostate cancer cells: AR binds Runx2 and abrogates its recruitment to DNA. Mol Endocrinol 23:1203-14
Luppen, Cynthia A; Chandler, Ronald L; Noh, Tommy et al. (2008) BMP-2 vs. BMP-4 expression and activity in glucocorticoid-arrested MC3T3-E1 osteoblasts: Smad signaling, not alkaline phosphatase activity, predicts rescue of mineralization. Growth Factors 26:226-37
Leclerc, Nathalie; Noh, Tommy; Cogan, Jon et al. (2008) Opposing effects of glucocorticoids and Wnt signaling on Krox20 and mineral deposition in osteoblast cultures. J Cell Biochem 103:1938-51

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