Cartilage is an essential tissue in developing and adult humans. Sadly, this is best illustrated by the prevalence and severity of birth defects due to cartilage malformations, growth retardations due to growth plate defects in children, and articular cartilage degeneration diseases in adults. Today, however, no suitable treatments exist for most of these diseases, and this is largely due to incomplete understanding of the mechanisms underlying chondrogenesis. The main goal of this project is to help lift this barrier by increasing knowledge of the action and regulation of Sox9, a master transcription factor in chondrogenesis. Sox9 is well known to activate the early chondrocyte differentiation program, and our recent data reveal that it remains a master transcription factor in the growth plate throughout chondrocyte hypertrophy. It sustains columnar chondrocyte proliferation, delays prehypertrophy, and ensures hypertrophy. Based on these data, we propose that important mechanisms must exist to determine the specific activity of Sox9 at each chondrocyte developmental stage from early to hypertrophic differentiation.
Aim 1 is to test the hypothesis that the redundant proteins Sox5 and Sox6 boost the ability of Sox9 to activate the differentiation program of early chondrocytes by increasing the efficiency of Sox9 binding to gene enhancers.
Aim 2 is to test the hypothesis that Sox9 phosphorylation by the cAMP-dependent protein kinase A critically contributes to delaying chondrocyte maturation downstream of parathyroid hormone-related protein signaling.
Aim 3 is to test the hypothesis that specific transcriptional mechanisms allow Sox9 to activate the hypertrophic chondrocyte program and most specifically the Col10a1 gene.
All aims will be reached using genetic approaches in the developing mouse and state-of-the-art genomics, cellular and molecular approaches in vitro. We anticipate that the achievement of this project will lead to a deeper knowledge of the mechanisms that govern the multi-step differentiation pathway of chondrocytes. This knowledge will provide novel insights into mechanisms underlying cartilage malformation and degeneration diseases and will help find suitable treatments.

Public Health Relevance

This project is relevant to multiple types of cartilage malformation diseases (chondrodysplasias) and cartilage degeneration diseases (mainly osteoarthritis). Together, these diseases are highly prevalent in the human population and can have devastating consequences on life expectancy and quality from birth until senior age. Our studies are designed to increase understanding of the modes of action and regulation of Sox9, a protein with master roles in the control of genes required for cartilage development and function. We anticipate that the results of our studies will provide important new insights into mechanisms underlying cartilage diseases and will suggest novel, efficient ways to prevent and cure these diseases.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-MOSS-S (03))
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Tyree, Bernadette
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Cleveland Clinic Lerner
Other Basic Sciences
Schools of Medicine
United States
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Mead, Timothy J; Lefebvre, VĂ©ronique (2014) Proliferation assays (BrdU and EdU) on skeletal tissue sections. Methods Mol Biol 1130:233-43
Mead, Timothy J; Wang, Qiuqing; Bhattaram, Pallavi et al. (2013) A far-upstream (-70 kb) enhancer mediates Sox9 auto-regulation in somatic tissues during development and adult regeneration. Nucleic Acids Res 41:4459-69
Dy, Peter; Wang, Weihuan; Bhattaram, Pallavi et al. (2012) Sox9 directs hypertrophic maturation and blocks osteoblast differentiation of growth plate chondrocytes. Dev Cell 22:597-609
Dy, Peter; Smits, Patrick; Silvester, Amber et al. (2010) Synovial joint morphogenesis requires the chondrogenic action of Sox5 and Sox6 in growth plate and articular cartilage. Dev Biol 341:346-59
Lefebvre, Veronique; Bhattaram, Pallavi (2010) Vertebrate skeletogenesis. Curr Top Dev Biol 90:291-317
Lefebvre, Veronique (2010) The SoxD transcription factors--Sox5, Sox6, and Sox13--are key cell fate modulators. Int J Biochem Cell Biol 42:429-32
Han, Yu; Lefebvre, Veronique (2008) L-Sox5 and Sox6 drive expression of the aggrecan gene in cartilage by securing binding of Sox9 to a far-upstream enhancer. Mol Cell Biol 28:4999-5013
Lefebvre, Veronique; Dumitriu, Bogdan; Penzo-Mendez, Alfredo et al. (2007) Control of cell fate and differentiation by Sry-related high-mobility-group box (Sox) transcription factors. Int J Biochem Cell Biol 39:2195-214
Dumitriu, Bogdan; Dy, Peter; Smits, Patrick et al. (2006) Generation of mice harboring a Sox6 conditional null allele. Genesis 44:219-24
Lefebvre, Veronique; Smits, Patrick (2005) Transcriptional control of chondrocyte fate and differentiation. Birth Defects Res C Embryo Today 75:200-12

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