Facult� de m�decine et des sciences de la sant�


1) Role of osteoclastogenesis and osteoclast activation in joint destruction, in degenerative, and inflammatory joint diseases

2) Anabolic properties of PGD2 in human bone- Summary



1) Role of osteoclastogenesis and osteoclast activation in joint destruction, in degenerative, and inflammatory joint diseases

Bone is a central element in the pathophysiology of degenerative and inflammatory arthropathies. Rheumatoid arthritis (RA) is associated with periarticular bone loss and erosions which contribute to joint destruction. Subchondral bone sclerosis, bone cysts and osteophytes are hallmarks of osteoarthritis (OA). It has been clearly shown that osteoclasts (OCs) are critical in joint destruction in RA and there is indirect evidence implicating OCs in the pathogenesis of OA. Periodontal disease (PD) is now emerging as a disease with remarkable analogy to arthropathies. Similar to RA, PD bone loss is associated with inflammation, with the subset of PD, refractory periodontitis (RP), exhibiting persistent degenerative bone loss. The involvement of OCs in bone and joint destruction in these diseases has been confirmed, yet their role in disease onset and progression has not been previously addressed.

Working hypothesis: Human peripheral blood mononuclear cells (PBMCs) can differentiate into OCs capable of bone resorption. We have recently observed that the capacity for in vitro osteoclastogenesis varies widely in a normal human population, distinguishing two subgroups, high and low differentiators, regardless of age, gender, weight, or other demographic variables. We hypothesize that variations in osteoclastogenic capacity in OA, RA, and PD populations could underlie variation in predisposition for disease and disease severity.

: This Team is targeted at prevention, detection and, management of bone loss, through a multidisciplinary approach combining in vitro and clinical studies. We propose to use PBMCs from OA, RA and PD patients evaluated according to validated criteria and from a control population, to address the following questions:

1) For OC precursors, does their frequency, osteoclastogenic capacity, or motility correlate with the presence and severity of RA, OA and PD?

2) Can differences in cytokine and chemokine receptor expression and signalling account for differences in osteoclastogenesis, and, consequently, in the presence and severity of these diseases?

3) Do characteristics of mature OCs formed from patients’ PBMCs correlate with the presence and severity of these diseases?

Research Design: The project will comprise two consecutive phases: Phase 1, an exploratory analysis of a transverse cohort including 4 populations: OA, RA, and PD patients and a normal cohort, and Phase 2, a prospective analysis to test predictive value of parameters identified in Phase 1 for progression of disease and responsiveness to medications. OA and RA patients satisfying the appropriate ACR criteria will be recruited from the Centre Hospitalier Universitaire de Sherbrooke (CHUS). PD patients will be recruited from the periodontal clinic at the Faculty of Dentistry of the University of Toronto. The normal cohort will be recruited from the Sherbrooke and Toronto population. The quotas of PBMCs from blood samples will be distributed between the laboratories of participants to allow a multidisciplinary study of their characteristics. We will study the frequency of OC precursors, in vitro osteoclastogenesis, receptor expression and signaling, resorptive activity, motility and survival of OCs. We have confirmed that material can be distributed successfully among participating laboratories. The data will be analyzed by a combination of novel data mining approaches and statistical tests to discover related biomarkers.

Significance: This work will allow us to: 1) establish osteoclastic parameters strongly related to presence and severity of bone and joint destruction; 2) determine if these biomarkers are predictors of patient progression and responsiveness to different treatment regimens; and 3) identify new targets for development of antiresorptive therapies specifically aimed at arresting inflammation-induced bone loss.

Integration of these structural, functional, and molecular data, obtained from the same common models, will advance the understanding of bone loss in inflammatory diseases, with direct relevance to human health. The assembled team of junior and senior investigators has the expertise, commitment, and enthusiasm to ensure the success of this multi-pillar research program.

2) Anabolic properties of PGD2 in human bone- Summary

I. Introduction: Our last grant was based on the original working hypothesis that Prostaglandin D2 (PGD2) could act as an autocrine or paracrine agent in bone and have a positive impact on bone anabolism, which was supported by our results. The general objective of the present proposal is to further explore this working hypothesis as we believe that targeting PGD2 production or action on specific receptors may lead to the identification of new and improved therapeutic approaches to bone and joint diseases. Our specific objectives are to study :

A) The roles of PGD2 in bone fracture repair as an in vivo model of bone remodeling.

B) The mechanisms implicated in the control of PGD2 production.

C) The roles of PGD2 on the birth, life, and death of human OCs.

D) The implication of PGD2 in human joint diseases.

Research Plan:

A. Implication of PGD2 receptors in in vivo bone remodeling: Using experimental fracture in mice as an in vivo model of bone remodeling and specific PGD2 receptor antagonists, we will determine the implication of the DP and CRTH2 receptors in fracture repair and bone remodeling by studying histologic, radiologic, and mechanical characteristics of the fracture site.

B. Control of PGD2 production: Since PGD2 may have an impact on bone metabolism, identifying the sites and controls of its production may lead to the identification of interesting pharmacologic targets. In this section we will study 1) The production of PGD2 by human osteoclasts differentiated in vitro from CD14+ precursors, and 2) The regulation of LPGDS activity by proteins that interact with this enzyme.

C. Implication of PGD2 in the birth, life, and death of human osteoclasts: We will extend our observations on the effects of PGD2 on osteoclastogenesis, mature OC function and apoptosis, with a special emphasis on the intracellular mechanisms implicated in these actions. More specifically, we will study 1) the genes implicated in osteoclastogenesis and affected by PGD2, 2) PGD2 signaling, gene expression, and cellular effects on mature human OCs, 3) the control of osteoclast apoptosis by PGD2, and 4) the mechanisms of PGD2 receptors desensitization and phosphorilation.

D. PGD2 in human joint diseases: PGD2 may have a positive effect on bone metabolism by activating osteoblasts and repressing osteoclast differentiation and function. Consequently, in joint diseases such as RA, where inflammation and peri-articular bone resorption are present, we hypothesize that PGD2 levels relative to PGE2 would be lower than in OA and in spondylarthritis, clinical situations where new bone formation is seen. We will determine PGE2, PGD2, and its metabolites in synovial fluids from a synovial fluid and serum bank from the laboratory of the Division of Rheumatology of the CHUS, and study the expression of LPGDs and HPGDS in synovial membrane samples from the Dep. of Pathology.

III. Conclusion:

This is a bench to bedside grant proposal based on an original and solid working hypothesis. Unveiling the fine mechanisms implicated in the actions of PGD2 on bone will lead to a better understanding of bone and joint pathology and physiology, and to the identification of new pharmacologic targets. Further development of original therapeutic interventions based on this research will be facilitated by the chemical nature of PGD2 analogues, which can be synthesized, tested, and administered without the limitations imposed by the protein nature of many hormones and growth factors. This project may have an impact on different bone and joint diseases such as osteoporosis, periodontal disease, fracture repair, rheumatoid arthritis and spondylarthropathies, only to cite a few ones.