Two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1) result from massive intracellular retention of mutant COMP (MT-COMP) in the endoplasmic reticulum (ER) which causes premature chondrocyte death during bone development. The focus of this research is to determine the cellular mechanism by which MT- COMP promotes the chondrocyte cellular pathology and to determine whether various pharmacologic agents inhibit or reverse the pathology. In previous studies, we have shown that: 1) mutations in COMP cause skeletal dysplasias, 2) mutant COMP interferes with the export of COMP as well as type IX collagen and matrilin-3 proteins to the extracellular matrix, 3) intracellular matrix is inappropriately assembled in giant rER cisternae, 4) the PSACH cartilage matrix is deficient in ECM proteins and 5) the intracellular retention of COMP causes premature chondrocyte cell death. While our in vitro chondrocyte model system indicates that mutant COMP is not degraded by the cellular quality control machinery, the lack of an animal model system has limited studies to define the molecular mechanisms that result in the cellular pathology created by MT-COMP. Importantly and critical for this proposal, we have created a transgenic mouse model in which inducible chondrocyte-specific MT-COMP expression recapitulates the PSACH chondrocyte pathology. This MT-COMP mouse shows intracellular growth plate pathology in vivo and the chondrocytes can be isolated and utilized for in vitro studies. In these studies, we will use this novel and unique transgenic mouse to focus our efforts on: 1) defining the role of the Unfolded Protein Response (UPR) and activation of apoptosis in response to MT-COMP retention in chondrocytes in vivo, 2) testing the efficacy of different pharmacologic agents on inhibiting or reversing the intracellular retention of MT-COMP and 3) characterizing the effect of MT-COMP on articular cartilage morphology and function in mice throughout life. The MT-COMP mouse model allows us to test the hypothesis that removal of MT-COMP from the ER will return the chondrocyte to normal functionality. This is a first step towards a therapeutic intervention which will be a significant step forward as only symptomatic treatment is currently available for the painful osteoarthritis that is associated with PSACH and MED. Altogether, the results of this work will provide important information that will ultimately lead to better care of individuals with PSACH, MED/EDM1 and osteoarthritis.

Public Health Relevance

The goals of the proposed studies are to understand the debilitating pathophysiology caused by mutations in cartilage oligomeric matrix protein (COMP) that leads to pseudoachondroplasia (PSACH), a severe dwarfing condition and to test therapeutic interventions to reverse this process. We have an inducible mouse model that mimics the human cellular process and this model will allow definition of the cellular mechanisms causing the disease. In addition, we can test pharmacologic agents that reduce cellular stress, thereby reducing the premature loss of growth plate chondrocytes that are needed for limb growth. This research will ultimately lead to treatments for the chronic life long problems related to severe short stature in PSACH and premature osteoarthritis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR057117-04
Application #
8475426
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Tyree, Bernadette
Project Start
2010-07-01
Project End
2015-05-31
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
4
Fiscal Year
2013
Total Cost
$307,800
Indirect Cost
$102,600
Name
University of Texas Health Science Center Houston
Department
Pediatrics
Type
Schools of Medicine
DUNS #
800771594
City
Houston
State
TX
Country
United States
Zip Code
77225
Posey, Karen L; Coustry, Francoise; Veerisetty, Alka C et al. (2014) Chondrocyte-specific pathology during skeletal growth and therapeutics in a murine model of pseudoachondroplasia. J Bone Miner Res 29:1258-68
Posey, Karen LaShea; Alcorn, Joseph L; Hecht, Jacqueline T (2014) Pseudoachondroplasia/COMP - translating from the bench to the bedside. Matrix Biol 37:167-73
Coustry, Francoise; Posey, Karen L; Liu, Peiman et al. (2012) D469del-COMP retention in chondrocytes stimulates caspase-independent necroptosis. Am J Pathol 180:738-48
Posey, Karen L; Coustry, Francoise; Veerisetty, Alka C et al. (2012) Chop (Ddit3) is essential for D469del-COMP retention and cell death in chondrocytes in an inducible transgenic mouse model of pseudoachondroplasia. Am J Pathol 180:727-37