During limb skeletogenesis, chondrocytes located at the epiphyseal ends of long bone anlagen develop into permanent articular chondrocytes that sustain joint function though life. Instead, the chondrocytes constituting the shaft are transient cells and are eventually replaced by bone via endochondral ossification. We initiated this project several years ago to identify the molecular mechanisms of formation and long-term phenotypic stabilization of articular chondrocytes and focused on transcriptional factor Erg. Erg belongs to the ets family of transcription factors that regulate several key processes, and is part of an ets subfamily that includes Fli-1. In the previous funding period, we showed that Erg is expressed during early synovial joint development along with Gdf5 and Wnt9a and its expression dwindles over time. To test function, we created floxed Erg mice and conditionally ablated Erg in developing joints by mating with Gdf5-Cre mice. Unexpectedly, limb joint development proceeded and the Erg-deficient mice survived to adulthood. To account for absence of a major joint developmental phenotype, we asked whether Fli-1 was co-expressed and in fact it was, and may have compensated for Erg absence. To test possible postnatal roles of Erg, we subjected 2 month-old Erg-deficient mice to knee's medial collateral ligament (MCL) transection to induce experimental osteoarthritis (OA). Strikingly, the Erg-deficient mice developed serious OA-like defects far sooner than operated wild type companions. Indeed, we observed similar severe OA-like defects in aging un-operated 7-11 month-old Erg-deficient mice, while control littermates displayed mild defects. To gain insights into how Erg maintains long-term articular chondrocyte function, we focused on parathyroid hormone-related protein (PTHrP) which is also expressed in developing joints, stabilizes the chondrocyte phenotype and prevents chondrocyte hypertrophy when over-expressed in cartilage (just as transgenic Erg over-expression does). We found that Erg (as well as Fli-1) stimulates PTHrP expression and the PTHrP gene promoter contains several conserved ets binding sites needed for responsiveness. These and other data lead to our central hypothesis is that Erg is essential for the development and long-term stabilization and function of articular chondrocytes and does so in cooperation with Fli-1 and PTHrP.
Our Aims are: (1) To uncover the respective roles of Erg and Fli-1 in joint formation and long-term articular cartilage stabilization;(2) To determine how Erg and Fli-1 regulate PTHrP expression;and (3) To determine if transgenic Erg expression protects joints from surgically-induced OA. The work will be carried out using diverse experimental approaches that include transgenic mouse genetics, microsurgery and cell phenotypic expression. It will produce fundamentally new data and insights into the biology and molecular biology of articular chondrocytes and will pave the way to create future repair and regeneration therapies by which function can be restored in articular chondrocytes affected by a variety of adverse conditions including osteoarthritis and natural aging.

Public Health Relevance

Articular cartilage is essential for joint function, unhindered body movement and quality of life, but is affected by common diseases including osteoarthritis and becomes non-functional during natural aging. This project will continue to clarify mechanisms by which the tissue normally maintains its function and will thus generate important information that can be used to create novel joint repair and regeneration therapies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR046000-14
Application #
8487366
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Tyree, Bernadette
Project Start
1999-04-15
Project End
2017-06-30
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
14
Fiscal Year
2013
Total Cost
$358,031
Indirect Cost
$144,281
Name
Children's Hospital of Philadelphia
Department
Type
DUNS #
073757627
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Usami, Yu; Gunawardena, Aruni T; Iwamoto, Masahiro et al. (2016) Wnt signaling in cartilage development and diseases: lessons from animal studies. Lab Invest 96:186-96
Candela, Maria Elena; Wang, Chao; Gunawardena, Aruni T et al. (2016) Alpha 5 Integrin Mediates Osteoarthritic Changes in Mouse Knee Joints. PLoS One 11:e0156783
Decker, Rebekah S; Koyama, Eiki; Pacifici, Maurizio (2015) Articular Cartilage: Structural and Developmental Intricacies and Questions. Curr Osteoporos Rep 13:407-14
Han, Rong; Pacifici, Maurizio; Iwamoto, Masahiro et al. (2015) Endothelial Erg expression is required for embryogenesis and vascular integrity. Organogenesis 11:75-86
Ohta, Yoichi; Okabe, Takahiro; Larmour, Colleen et al. (2015) Articular cartilage endurance and resistance to osteoarthritic changes require transcription factor Erg. Arthritis Rheumatol 67:2679-90
Candela, Maria Elena; Cantley, Leslie; Yasuaha, Rika et al. (2014) Distribution of slow-cycling cells in epiphyseal cartilage and requirement of β-catenin signaling for their maintenance in growth plate. J Orthop Res 32:661-8
Decker, Rebekah S; Koyama, Eiki; Enomoto-Iwamoto, Motomi et al. (2014) Mouse limb skeletal growth and synovial joint development are coordinately enhanced by Kartogenin. Dev Biol 395:255-67
Candela, Maria Elena; Yasuhara, Rika; Iwamoto, Masahiro et al. (2014) Resident mesenchymal progenitors of articular cartilage. Matrix Biol 39:44-9
Decker, Rebekah S; Koyama, Eiki; Pacifici, Maurizio (2014) Genesis and morphogenesis of limb synovial joints and articular cartilage. Matrix Biol 39:5-10
Iwamoto, Masahiro; Ohta, Yoichi; Larmour, Colleen et al. (2013) Toward regeneration of articular cartilage. Birth Defects Res C Embryo Today 99:192-202

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