Rajaram Gopalakrishnan - US grants

DESCRIPTION (provided by applicant): Mineralization of bone and teeth is a complex process controlled by the interplay between various nucleators and inhibitors of hydroxyapatite crystal formation. Among these proteins, matrix Gla protein (MGP) is the most important with in vivo evidence for a role in regulating mineralization. Recently, we showed that MGP is induced by parathyroid hormone (PTH), and this response might play a crucial role in PTH-mediated inhibition of mineralization in osteoblasts. However, the transcriptional mechanisms involved in PTH regulation of MGP are not known. Detailed knowledge of this regulation will help in understanding a factor that can be used as a target for preventive and therapeutic interventions for patients with mineralization defects. The overall goal of this project is to use genetic and molecular approaches to determine the importance of MGP in the regulation of osteoblast mineralization by PTH; and to determine the transcriptional mechanisms involved in this regulation. This project will test two hypotheses: (a) induction of MGP is responsible for the inhibition of mineralization seen in osteoblasts following parathyroid hormone treatment, and (b) stimulation of MGP is mediated through activation of second messenger(s) which regulate specific cis-acting response elements in the promoter of the MGP gene. The following two specific aims will be pursued: 1. Determine the response of Mgp-deficient or -suppressed osteoblasts to parathyroid hormone treatment, and 2. Identify the DNA response elements necessary for MGP responsiveness to parathyroid hormone in osteoblasts. Aim 1 will use both Mgp-deficient (Mgp -/-) mice and osteoblasts in which MGP synthesis is suppressed using RNAi to determine the regulation of mineralization by PTH. We expect that PTH treatment of MGP-deficient/suppressed osteoblasts will not inhibit mineralization. Aim 2 will characterize the MGP promoter to understand the regulatory mechanisms involved in PTH induction. We expect, based on our preliminary data that CRE and AP-1 sites are key to PTH induced transcription of MGP. Our long-range goal, which will be tested in a future R01 application, is to characterize specific transcriptional factors involved in PTH-mediated regulation of MGP, and perform detailed structure-function analyses of MGP as it relates to PTH-mediated inhibition of mineralization.

DESCRIPTION (provided by applicant): Osteonecrosis of the jaw (ONJ) is a recently described major complication of long-term bisphosphonate (BP) treatment. BPs are potent inhibitors of bone resorption used in the treatment of multiple myeloma, skeletal metastases of solid tumors, hypercalcemia of malignancy and osteoporosis. Most patients present with painful exposed avascular bone in either or both jaws that simulates "tooth-ache" or bone infection. Currently, there is no effective treatment for ONJ. Periodontal disease is a commonly reported risk factor for ONJ. However, most of the information about these risk factors has been obtained through case reports, and there is an immediate need for matched case-control and prospective studies to confirm this association. The overall goal of current exploratory proposal is to perform a matched case-control study to test the hypothesis that periodontal disease and periodontal pathogens are risk factors for ONJ in cancer patients receiving intravenous BPs. To test our hypothesis and accomplish our goal, we plan to enroll 50 cancer patients receiving intravenous BP with ONJ and 100 controls (cancer patients on intravenous BP who have not developed ONJ) matched according to type of cancer, type of BP, duration of BP, age and sex. Two specific aims will be pursued. (a) To determine the association between clinical and microbiological measures of periodontitis and risk of ONJ development. We will perform a thorough intraoral and periodontal exam in cases and matched controls to test if clinical measures of periodontitis are associated with ONJ. Further, we will also evaluate the prevalence of putative periodontal pathogens in subgingival plaque samples collected from these same cases and controls. (b) To determine whether ONJ is associated with increased mucosal invasion of putative periodontal pathogens and Actinomyces species. We will evaluate if putative periodontal pathogens and Actinomyces species colonize the oral mucosa cells near the ONJ lesion and contribute to its development. The findings will be used to define the role of periodontal disease in ONJ pathogenesis and contribute towards development of prevention and intervention strategies. PUBLIC HEALTH RELEVANCE: Intravenous bisphosphonates are routine components of treatment protocols for multiple myeloma, and breast and prostate cancer patients with bone metastasis due to their ability to reduce cancer-induced destruction of bone. Osteonecrosis of the jaw is a recently identified devastating adverse effect of bisphosphonate treatment. In this exploratory proposal we will evaluate whether periodontal disease is a risk factor in osteonecrosis of jaw.

DESCRIPTION (provided by applicant): Twisted gastrulation (Twsg1) is a key extracellular regulator of bone morphogenetic protein (BMP) signaling. BMPs are potent inducers of bone formation and any dysregulation of BMP signaling can lead to defects in bone remodeling. To examine whether Twsg1 regulates bone remodeling, we generated a Twsg1-null mouse that showed profound osteopenia with significantly reduced histomorphometric parameters compared to wild type (WT) mice. Tetracycline labeling studies showed no significant decrease in mineral apposition rate in Twsg1-null mice compared to WT mice, indicating that osteopenia in Twsg1-/- mice are not due to reduced osteoblast function. On the other hand, Twsg1-/- mice showed increased bone resorption compared to WT mice characterized by larger and increased numbers of osteoclasts, increase in the area of resorption pits and increased serum CTX and TRAP levels. Enhanced osteoclastogenesis in vitro was associated with an increase in cell fusion and upregulation of key genes involved in osteoclast differentiation (NFATc1) and cell- cell fusion (DC-STAMP). We also show higher levels of phosphorylated Smad1/5/8 in Twsg1-/- osteoclasts and that the enhanced in vitro osteoclastogenesis can be reversed by increasing doses of Noggin, a BMP- specific antagonist. Further, we show that exogenous BMP2 increases pSmad1/5/8 levels in WT osteoclasts and also enhances RANKL stimulated osteoclast differentiation. These results provide compelling evidence for our hypothesis that Twsg1 inhibits osteoclast formation and function through regulation of BMP signaling. Thus in specific aim 1, we will determine if osteoclast precursors rather than stromal cell/osteoblasts are direct targets of Twsg1-/- disruption using (1A) reciprocal co-culture experiments with osteoblasts and osteoclast precursors from both WT and Twsg1-/- mice, and (1B) chimeric mice in which either WT or Twsg1-/- marrow will be transplanted into lethally irradiated Twsg1-/- or WT mice. In specific aim 2, we will evaluate whether enhanced osteoclastogenesis in Twsg1-/- mice is mediated through increased BMP signaling and elaborate the function of Twsg1 and BMP in osteoclastogenesis by (2A) determining if increased BMP signaling mediates the osteoclast phenotype in Twsg1-/- mice, and determine if BMPs can regulate RANKL stimulated osteoclastogenesis, and (2B) determining the function of Twsg1 as an inhibitor of osteoclastogenesis. In specific aim 3, we will elucidate molecular and cellular mechanisms mediating increased osteoclastogenesis in Twsg1-/- mice by (3A) recapitulating the osteoclast phenotype of Twsg1-/- mice using better defined osteoclast progenitor population from the bone marrow, and determining if osteoclast precursors are already primed to RANKL and/or M-CSF, (3B) determining whether Twsg1 disruption leads to altered RANK-mediated signaling pathways;and (3C) evaluating if NFAT-c1 is a target of Twsg1-deficiency . Completion of these aims will enable us to unequivocally determine the roles of Twsg1 in osteoclastogenesis and bone resorption. The impact of our work may not only provide an understanding of the mechanisms by which Twsg1 inhibit osteoclastogenesis but also first steps towards development of novel antiresorptive drugs that can be used in the treatment of osteoporosis and osteolytic bone tumors. PUBLIC HEALTH RELEVANCE: Twisted gastrulation (Twsg1) is a bone morphogenetic protein-binding protein whose function in skeletal development and remodeling is not known. Towards understanding its significance, we developed Twsg1-null mice by deleting part of its BMP-binding domain. Preliminary data show that Twsg1-/- mice show severe osteopenia due to enhanced osteoclastogenesis leading to increased bone resorption. The overall objective of this project is to identify the cellular targets of Twsg1-disruption and characterize the signaling and molecular mechanisms by which Twsg1 inhibits osteoclastogenesis.