Intermittently injected parathyroid hormone (PTH) is a key anabolic therapy for osteoporosis, stimulating bone formation more than resorption. Paradoxically, continuously elevated PTH causes bone loss. We have identified a factor that may explain the paradox. PTH is a potent inducer in osteoblastic lineage cells of both cyclooxygenase 2 (Cox2), the major enzyme producing prostaglandin E2 (PGE2), and receptor activator of nuclear factor ?B ligand (RANKL), which is required to commit bone marrow macrophages (BMMs) to become osteoclasts. RANKL and Cox2/PGE2 together cause BMMs to secrete a factor that suppresses the ability of continuous PTH to stimulate differentiation of osteoblasts. Using in vitro cell models, we identified the inhibitory factor as serum amyloid A3 (Saa3), an acute phase protein generally associated with inflammation or infection, and showed that Saa3 inhibited PTH-stimulated osteoblast differentiation by blocking PTH-stimulated cAMP production. As predicted by the in vitro models, PTH infusion in wild type (WT) mice suppressed bone formation and caused bone loss, but PTH infusion in in Cox2 knockout (KO) mice was markedly anabolic for bone. In contrast to the effects on formation, PTH infusion stimulated bone resorption equally in WT and Cox2 KO mice. We have generated a mouse with global KO of Saa3. We will test the hypothesis that Saa3 suppresses the anabolic, but not the catabolic, responses to continuously elevated PTH in vivo.
Specific aim 1 will examine effects on bone formation and resorption of Saa3 in in vivo models for elevating PTH.
Aim 2 will examine the effect of Saa3 on PTH-stimulated osteoblast and osteoclast differentiation in vitro and the cAMP- dependent actions by which PTH regulates Wnt signaling and the cAMP?independent signaling pathways by which PTH regulates RANKL signaling in our models.
Aim 3 will examine the requirement for PGE2 and its EP4 receptor in the induction of Saa3 in BMMs and the role of Saa3 in stimulating other cytokines that can regulate the bone environment. We are proposing a novel role for Saa3; a new means by which osteoclasts regulate osteoblasts; and a novel role for Cox2/PGE2. The results of this study should strengthen our understanding of the molecular mechanisms underlying actions of PTH and may help us target bone remodeling more effectively to treat osteoporosis and other skeletal diseases.

Public Health Relevance

PTH is a major stimulator of bone resorption and formation. We have identified serum amyloid A3 as a factor that, when elevated, can suppress the bone formation response to continuous PTH, resulting in bone loss. Understanding how Saa3 inhibits responses to PTH and how Saa3 is regulated may lead to development of new agents to treat osteoporosis and other skeletal defects and be the basis for enhancing the current clinical therapy with intermittent PTH.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR060286-07
Application #
9273372
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Nicks, Kristy
Project Start
2011-07-01
Project End
2021-06-30
Budget Start
2017-07-01
Budget End
2018-06-30
Support Year
7
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Connecticut
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
022254226
City
Farmington
State
CT
Country
United States
Zip Code
06032
Deb Roy, Abhijit; Yin, Taofei; Choudhary, Shilpa et al. (2017) Optogenetic activation of Plexin-B1 reveals contact repulsion between osteoclasts and osteoblasts. Nat Commun 8:15831
Hewett, Sandra J; Shi, Jingxue; Gong, Yifan et al. (2016) Spontaneous Glutamatergic Synaptic Activity Regulates Constitutive COX-2 Expression in Neurons: OPPOSING ROLES FOR THE TRANSCRIPTION FACTORS CREB (cAMP RESPONSE ELEMENT BINDING) PROTEIN AND Sp1 (STIMULATORY PROTEIN-1). J Biol Chem 291:27279-27288
Choudhary, Shilpa; Goetjen, Alexandra; Estus, Thomas et al. (2016) Serum Amyloid A3 Secreted by Preosteoclasts Inhibits Parathyroid Hormone-stimulated cAMP Signaling in Murine Osteoblasts. J Biol Chem 291:3882-94
Estus, Thomas L; Choudhary, Shilpa; Pilbeam, Carol C (2016) Prostaglandin-mediated inhibition of PTH-stimulated ?-catenin signaling in osteoblasts by bone marrow macrophages. Bone 85:123-30
Choudhary, Shilpa; Canalis, Ernesto; Estus, Thomas et al. (2015) Cyclooxygenase-2 suppresses the anabolic response to PTH infusion in mice. PLoS One 10:e0120164
Choudhary, Dharamainder; Hegde, Poornima; Voznesensky, Olga et al. (2015) Increased expression of L-selectin (CD62L) in high-grade urothelial carcinoma: A potential marker for metastatic disease. Urol Oncol 33:387.e17-27
Lalla, Rajesh V; Choquette, Linda E; Curley, Kathleen F et al. (2014) Randomized double-blind placebo-controlled trial of celecoxib for oral mucositis in patients receiving radiation therapy for head and neck cancer. Oral Oncol 50:1098-103
Choudhary, Shilpa; Blackwell, Katherine; Voznesensky, Olga et al. (2013) Prostaglandin E2 acts via bone marrow macrophages to block PTH-stimulated osteoblast differentiation in vitro. Bone 56:31-41
Choudhary, Shilpa; Hegde, Poornima; Pruitt, James R et al. (2013) Macrophage migratory inhibitory factor promotes bladder cancer progression via increasing proliferation and angiogenesis. Carcinogenesis 34:2891-9
Xu, Manshan; Choudhary, Shilpa; Voznesensky, Olga et al. (2010) Basal bone phenotype and increased anabolic responses to intermittent parathyroid hormone in healthy male COX-2 knockout mice. Bone 47:341-52

Showing the most recent 10 out of 13 publications