Knowledge of mechanisms and mediators which regulate the anabolic effectof PTH will permit a more rational approach to using PTH to treatosteoporosis, and may suggest new approaches to increasing bone mass tocompensate for pathologic bone loss. We hypothesize that the anabolic effect of PTH in vivo is mediated bygrowth hormone-dependent insulin-like growth factor I IGF-I. The goalof the first study is to determine if PTH selectively increases mRNA andprotein for IGF-I and IGF-binding proteins IGF-BPs in trabecular boneof young intact and hypophysectomized HX rats treated with vehicle orPTH alone or in combination with GH for 1, 3, 5 or 12 days distalfemurs will be separated into trabecular, cortical and marrowcompartments and changes in IGF-I will be correlated in time withpossible changes in mRNA for PTH receptor, alternate putative mediators, IGF-II, TGFbeta and PGH synthase, matrix proteins, procollagen 1alphaIand osteocalcin, measured using semi-quantitative RT-PCR, solution- hybridizationnuclease protection assays or Northern blot hybridization. Changes in these mRNAs with time will be related to the increase inpercent of bone forming surfaces. In the second study, in situhistohybridization will be used to detect the spatial expression of theselected mRNAs and to determine the relative locations of cellsexpressing growth factor mRNA and those expressing the PTH receptor orthe bone matrix proteins in trabecular bone of lumbar vertebrae. Spatiallocation of trabecular bone cells secreting IGF-I and IGF-BPs will beidentified using immunocytochemistry the goal of the third study is todetermine if IGF-I monoclonal antibody or excess IGF-BPs will block theanabolic effect of PTH when infused locally into one distal femur invivo. Bone density will be monitored by quantitative radiography; bonemineral content will be measured by single photon absorptiometry SPA; and bone formation by bone histomorphometry. The goal of the fourthstudy is to determine if there are shifts in time or location in mRNA forIGF-I, IGF-II, IGF-BPs, TGFbeta, PGH synthase and PTH receptor or inprotein synthesis of IGF-I, IGF-BPs or PGH synthase in animal models, such as thyroid-parathyroidectomized rats infused with PTH or aged ratsgiven intermittent PTH, in which we have shown the anabolic response toPTH to be absent or blunted.
Our research is directed to the mechanisms of regulated and unregulated growth in bone, using genetically modified and mutant mice as experimental models, and focusing on the role of apoptosis. Regulated growth is studied based on anabolic mechanisms of action of parathyroid hormone and mechanisms of successful regeneration after bone fracture, using a variety of molecular and cell-based assays in conjunction with in vivo protocols. Constitutive activation of the ras signal transduction pathway, which occurs in diseases such as Neurofibromatosis Type 1 (NF1), perturbs bone cell proliferation and function in genetically modified Nf1 mice, and impairs fracture healing (bone regeneration) in affected humans. Unregulated growth resulting in bone cancer or osteosarcoma is a new direction of research and will focus on the role of stromal cells in supporting cancer growth and metastases. We are also interested in women's health issues and sex-based differences in bone biology, and study the effects of androgens on the developing skeleton of transgenic female mice with high circulating levels of androgen.
,, Aging, Bone Development, Calcium Metabolism, Dihydroxycholecalciferol, Hormone Receptor, Hormone Regulation Control Mechanism, Immunocytochemistry, Insulinlike Factor, Laboratory Rat, Messenger Rna, Northern Blotting, Osteoporosis, Parathyroid Hormone, Pathologic Bone Resorption, Rna Binding Protein, Rnase Protection Assay, Scanning Electron Microscopy;, Transforming Growth Factor
