Osteoblasts regulate the deposition of bone matrix protein and its subsequent mineralization. In situ, regulation of osteoblast proliferation, differentiation and function occurs via the complex interplay of extracellular signals mediated by steroid hormone and vitamin D receptors, receptor tyrosine kinases, and G protein-coupled receptors (GPCRs), such as those for parathyroid hormone (PTH) and prostaglandins. While it is clear that GPCRs transmit signals that are critical for the regulation of osteoblast metabolism, their significance as potential regulators of osteoblast growth and differentiation has only recently been appreciated. The broad goal of this research proposal is to determine how GPCRs regulate the growth and differentiation of osteoblasts through activation of the ERK mitogen-activated protein kinase (MAP) cascade, a key regulatory pathway in terms of both cell proliferation and differentiation. We provide preliminary data that demonstrate that GPCRs employ two novel mechanisms to direct the temporal and spatial activation of MAP kinases. First, matrix metalloprotease-mediated ectodomain shedding causes the release of autocrine ligands that induce """"""""transactivation"""""""" of epidermal growth factor receptors (EGFRs). Second, beta-arrestins, proteins which bind to agonist-occupied GPCRs and uncouple them from their cognate G proteins, function as scaffolds for the component kinases of the ERK cascade and lead to the targeted activation of MAP kinase within specific cellular compartments.
The first Aim of this proposal is to characterize the molecular mechanisms whereby PTH and prostaglandin receptors regulate the activity of MAP kinase cascades in osteoblasts.
The second Aim i s to determine the role of EGFR and beta-arrestin-dependent signals in regulating osteoblast proliferation, differentiation, and matrix production in vitro. These studies will employ osteoblastic cell lines and primary cultures of osteoblasts from mice in which EGFR or beta-arrestin function has been selectively inhibited.
The third Aim of the proposal is to determine the role of EGFR and beta-arrestin-dependent signals in the control of anabolic bone metabolism by PTH in vivo. These studies will employ transgenic mouse models, in which beta-arrestins have been knocked out by homologous recombination or EGFR function has been impaired through osteoblast-specific expression of a dominant inhibitory mutant EGFR. By increasing our understanding of the mechanisms of GPCR signaling in bone, these studies may permit the rational development of safe strategies for employing PTH analogues to modulate osteoblast number and/or function.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
7R01DK064353-03
Application #
6820556
Study Section
Orthopedics and Musculoskeletal Study Section (ORTH)
Program Officer
Malozowski, Saul N
Project Start
2002-09-15
Project End
2006-08-31
Budget Start
2003-10-01
Budget End
2004-08-31
Support Year
3
Fiscal Year
2003
Total Cost
$195,885
Indirect Cost
Name
Medical University of South Carolina
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
183710748
City
Charleston
State
SC
Country
United States
Zip Code
29425
Luttrell, Louis M; Maudsley, Stuart; Gesty-Palmer, Diane (2018) Translating in vitro ligand bias into in vivo efficacy. Cell Signal 41:46-55
Bohinc, Brittany N; Gesty-Palmer, Diane (2013) Arrestins in bone. Prog Mol Biol Transl Sci 118:335-58
Appleton, Kathryn M; Luttrell, Louis M (2013) Emergent biological properties of arrestin pathway-selective biased agonism. J Recept Signal Transduct Res 33:153-61
Gesty-Palmer, Diane; Yuan, Ling; Martin, Bronwen et al. (2013) ?-arrestin-selective G protein-coupled receptor agonists engender unique biological efficacy in vivo. Mol Endocrinol 27:296-314
Bohinc, B N; Gesty-Palmer, D (2012) Biased agonism at the parathyroid hormone receptor: a demonstration of functional selectivity in bone metabolism. Mini Rev Med Chem 12:856-65
Gesty-Palmer, Diane; Luttrell, Louis M (2011) 'Biasing' the parathyroid hormone receptor: a novel anabolic approach to increasing bone mass? Br J Pharmacol 164:59-67
Gesty-Palmer, Diane; Luttrell, Louis M (2011) Refining efficacy: exploiting functional selectivity for drug discovery. Adv Pharmacol 62:79-107
DuSell, Carolyn D; Nelson, Erik R; Wang, Xiaojuan et al. (2010) The endogenous selective estrogen receptor modulator 27-hydroxycholesterol is a negative regulator of bone homeostasis. Endocrinology 151:3675-85
Luttrell, Louis M; Gesty-Palmer, Diane (2010) Beyond desensitization: physiological relevance of arrestin-dependent signaling. Pharmacol Rev 62:305-30
Gesty-Palmer, Diane; Flannery, Pat; Yuan, Ling et al. (2009) A beta-arrestin-biased agonist of the parathyroid hormone receptor (PTH1R) promotes bone formation independent of G protein activation. Sci Transl Med 1:1ra1

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