Endogenous Glucocorticoids and Bone

Abstract

While the adverse effects of glucocorticoids on bone are well described, positive effects of glucocorticoids on the differentiation of osteoblasts are also observed. These paradoxical effects of glucocorticoids are dose dependent. At both physiologicaland supraphysiological levels of glucocorticoids, osteoblasts and osteocytes are the major glucocorticoid target cells. However, the response of the osteoblasts to each of these is quite distinct. At physiology levels, glucocorticoids direct mesenchymal progenitor cells to differentiate towards osteoblasts and thus increase bone formation in a positive way. In contrast with ageing, the excess production of glucocorticoids, at both systemic and intracellular levels, appear to impact on osteoblast and osteocytes in a negative way in a similar fashion to that seen with therapeutic glucocorticoids. This review will focus on therole of glucocorticoids in normal bone physiology, with particular emphasis on the mechanism by which endogenous glucocorticoids impact on bone and its constituent cells.

References

[1] Hench PS, Kendall EC. The effect of a hormone of the adrenal cortex (17-hydroxy-11-dehydrocorticosterone; compound E) and of pituitary adrenocorticotropic hormone on rheumatoid arthritis. Proc Staff Meet Mayo Clin, 1949, 24:181-197

[2] Tronche F, Kellendonk C, Kretz O, Gass P, Anlag K, Orban PC, Bock R, Klein R, Schütz G. Disruption of the glucocorticoid receptor gene in the nervous system results in reduced anxiety. Nat Genet, 1999, 23 1 99-103

[3] Adinoff AD, Hollister JR. Steroid-induced fractures and bone loss in patients with asthma. N Engl J Med, 1983, 309:265-268

[4] Turner RT, Hannon KS, Greene VS, Bell NH. Prednisone inhibits formation of cortical bone in sham-operated and ovariectomized female rats. Calcif Tissue Int, 1995, 56:311-315

[5] Altman A, Hochberg Z, Silbermann M. Interactions between growth hormone and dexamethasone in skeletal growth and bone structure of the young mouse. Calcif Tissue Int, 1992, 51:298-304

[6] Weinstein RS, Jilka RL, Parfitt AM, Manolagas SC. Inhibition of osteoblastogenesis and promotion of apoptosis of osteoblasts and osteocytes by glucocorticoids. Potential mechanisms of their deleterious effects on bone. J Clin Invest, 1998, 102:274-282

[7] Jia D, O'Brien CA, Stewart SA, Manolagas SC, Weinstein RS. Glucocorticoids act directly on osteoclasts to increase their life span and reduce bone density. Endocrinology, 2006, 147:5592-5599

[8] Reid IR, Chapman GE, Fraser TR, Davies AD, Surus AS, Meyer J, Huq NL, Ibbertson HK. Low serum osteocalcin levels in glucocorticoid-treated asthmatics. J Clin Endocrinol Metab, 1986, 62:379-383

[9] Prummel MF, Wiersinga WM, Lips P, Sanders GT, Sauerwein HP. The course of biochemical parameters of bone turnover during treatment with corticosteroids. J Clin Endocrinol Metab, 1991, 72:382-386

[10] Henneicke H, Herrmann M, Kalak R, Brennan-Speranza TC, Heinevetter U, Bertollo N, Day RE, Huscher D, Buttgereit F, Dunstan CR, Seibel MJ, Zhou H. Corticosterone selectively targets endo-cortical surfaces by an osteoblast-dependent mechanism. Bone, 2011, 49:733-742

[11] O'Brien CA, Jia D, Plotkin LI, Bellido T, Powers CC, Stewart SA, Manolagas SC, Weinstein RS. Glucocorticoids act directly on osteoblasts and osteocytes to induce their apoptosis and reduce bone formation and strength. Endocrinology, 2004, 145:1835-1841

[12] Xia X, Kar R, Gluhak-Heinrich J, Yao W, Lane NE, Bonewald LF, Biswas SK, Lo WK, Jiang JX. Glucocorticoid-induced autophagy in osteocytes. J Bone Miner Res, 2010, 25:2479-2488

[13] Jia J, Yao W, Guan M, Dai W, Shahnazari M, Kar R, Bonewald L, Jiang JX, Lane NE. Glucocorticoid dose determines osteocyte cell fate. FASEB J, 2011, 25:3366-3376

[14] Xiong J, Onal M, Jilka RL, Weinstein RS, Manolagas SC, O'Brien CA. Matrix-embedded cells control osteoclast formation. Nat Med, 2011, 17:1235-1241

[15] Hofbauer LC, Gori F, Riggs BL, Lacey DL, Dunstan CR, Spelsberg TC, Khosla S. Stimulation of osteoprotegerin ligand and inhibition of osteoprotegerin production by glucocorticoids in human osteoblastic lineage cells: potential paracrine mechanisms of glucocorticoid-induced osteoporosis. Endocrinology, 1999, 140:4382-4389

[16] Kondo T, Kitazawa R, Yamaguchi A, Kitazawa S. Dexamethasone promotes osteoclastogenesis by inhibiting osteoprotegerin through multiple levels. J Cell Biochem, 2008, 103:335-345

[17] Rubin J, Biskobing DM, Jadhav L, Fan D, Nanes MS, Perkins S, Fan X. Dexamethasone promotes expression of membrane-bound macrophage colony-stimulating factor in murine osteoblast-like cells. Endocrinology, 1998, 139:1006-1012

[18] Lekamwasam S, Adachi JD, Agnusdei D, Bilezikian J, Boonen S, Borgström F, Cooper C, Diez Perez A, Eastell R, Hofbauer LC, Kanis JA, Langdahl BL, Lesnyak O, Lorenc R, McCloskey E, Messina OD, Napoli N, Obermayer-Pietsch B, Ralston SH, Sambrook PN, Silverman S, Sosa M, Stepan J, Suppan G, Wahl DA, Compston JE. Joint IOF-ECTS GIO Guidelines Working Group. A framework for the development of guidelines for the management of glucocorticoid-induced osteoporosis. Osteoporos Int, 2012, 23:2257-2276

[19] Rhen T, Cidlowski JA. Antiinflammatory action of glucocorticoids—new mechanisms for old drugs. N Engl J Med, 2005, 353:1711-1723

[20] Diamond MI, Miner JN, Yoshinaga SK, Yamamoto KR. Transcription factor interactions: selectors of positive or negative regulation from a single DNA element. Science, 1990, 249:1266-1272

[21] Pearce D, Matsui W, Miner JN, Yamamoto KR. Glucocorticoid receptor transcriptional activity determined by spacing of receptor and nonreceptor DNA sites. J Biol Chem, 1998, 273:30081-30085

[22] Buttgereit F, Burmester GR, Straub RH, Seibel MJ, Zhou H. Exogenous and endogenous glucocorticoids in rheumatic diseases. Arthritis Rheum, 2011, 63:1-9

[23] Stewart PM, Krozowski ZS. 11 beta-Hydroxysteroid dehydrogenase. Vitam Horm, 1999, 57:249-324

[24] Draper N, Stewart PM. 11beta-hydroxysteroid dehydrogenase and the pre-receptor regulation of corticosteroid hormone action. J Endocrinol, 2005, 186:251-271

[25] Funder JW, Pearce PT, Smith R, Smith AI. Mineralocorticoid action: target tissue specificity is enzyme, not receptor, mediated. Science, 1988, 242:583-585

[26] Webster JC, Oakley RH, Jewell CM, Cidlowski JA. Proinflammatory cytokines regulate human glucocorticoid receptor gene expression and lead to the accumulation of the dominant negative beta isoform: a mechanism for the generation of glucocorticoid resistance. Proc Natl Acad Sci U S A, 2001, 98:6865-6870

[27] Albiston AL, Obeyesekere VR, Smith RE, Krozowski ZS. Cloning and tissue distribution of the human 11 beta-hydroxysteroid dehydrogenase type 2 enzyme. Mol Cell Endocrinol, 1994, 105:R11-R17

[28] Krozowski Z. The 11beta-hydroxysteroid dehydrogenases: functions and physiological effects. Mol Cell Endocrinol, 1999, 151:121-127

[29] Edwards CR, Stewart PM, Burt D, Brett L, McIntyre MA, Sutanto WS, De Kloet ER, Monder C. Localisation of 11 beta-hydroxysteroid dehydrogenase—tissue specific protector of the mineralocorticoid receptor. Lancet, 1988, 2:986-989

[30] Woitge H, Harrison J, Ivkosic A, Krozowski Z, Kream B. Cloning and in vitro characterization of alpha 1(I)-collagen 11 beta-hydroxysteroid dehydrogenase type 2 transgenes as models for osteoblast-selective inactivation of natural glucocorticoids. Endocrinology, 2001, 142:1341-1348

[31] Yu K, Xu J, Liu Z, Sosic D, Shao J, Olson EN, Towler DA, Ornitz DM. Conditional inactivation of FGF receptor 2 reveals an essential role for FGF signaling in the regulation of osteoblast function and bone growth. Development, 2003, 130:3063-3074

[32] Li A, Hardy R, Stoner S, Tuckermann J, Seibel MJ, Zhou H. Deletion of mesenchymal glucocorticoid receptor attenuates embryonic lung development and abdominal wall closure. PLoS One, 2013, 8:e63578

[33] Rauch A, Seitz S, Baschant U, Schilling AF, Illing A, Stride B, Kirilov M, Mandic V, Takacz A, Schmidt-Ullrich R, Ostermay S, Schinke T, Spanbroek R, Zaiss MM, Angel PE, Lerner UH, David JP, Reichardt HM, Amling M, Schütz G, Tuckermann JP. Glucocorticoids suppress bone formation by attenuating osteoblast differentiation via the monomeric glucocorticoid receptor. Cell Metab, 2010, 11:517-531

[34] Yang M, Trettel LB, Adams DJ, Harrison JR, Canalis E, Kream BE. Col3.6-HSD2 transgenic mice: a glucocorticoid loss-of-function model spanning early and late osteoblast differentiation. Bone, 2010, 47:573-582

[35] Sher LB, Woitge HW, Adams DJ, Gronowicz GA, Krozowski Z, Harrison JR, Kream BE. Transgenic expression of 11beta-hydroxysteroid dehydrogenase type 2 in osteoblasts reveals an anabolic role for endogenous glucocorticoids in bone. Endocrinology, 2004, 145:922-929

[36] Sher LB, Harrison JR, Adams DJ, Kream BE. Impaired cortical bone acquisition and osteoblast differentiation in mice with osteoblast-targeted disruption of glucocorticoid signaling. Calcif Tissue Int, 2006, 79:118-125

[37] Zhou H, Mak W, Zheng Y, Dunstan CR, Seibel MJ. Osteoblasts directly control lineage commitment of mesenchymal progenitor cells through Wnt signaling. J Biol Chem, 2008, 283:1936-1945

[38] Zhou H, Mak W, Kalak R, Street J, Fong-Yee C, Zheng Y, Dunstan CR, Seibel MJ. Glucocorticoid-dependent Wnt signaling by mature osteoblasts is a key regulator of cranial skeletal development in mice. Development, 2009, 136:427-436

[39] Mak W, Shao X, Dunstan CR, Seibel MJ, Zhou H. Biphasic glucocorticoid-dependent regulation of Wnt expression and its inhibitors in mature osteoblastic cells. Calcif Tissue Int, 2009, 85:538-545

[40] Kalak R, Zhou H, Street J, Day RE, Modzelewski JR, Spies CM, Liu PY, Li G, Dunstan CR, Seibel MJ. Endogenous glucocorticoid signaling in osteoblasts is necessary to maintain normal bone structure in mice. Bone, 2009, 45:61-67

[41] Cole TJ, Blendy JA, Monaghan AP, Krieglstein K, Schmid W, Aguzzi A, Fantuzzi G, Hummler E, Unsicker K, Schütz G. Targeted disruption of the glucocorticoid receptor gene blocks adrenergic chromaffin cell development and severely retards lung maturation. Genes Dev, 1995, 9:1608-1621

[42] Zhou H, Mak W, Zheng Y, Dunstan CR, Seibel MJ. Osteoblasts Directly Control Lineage Commitment of Mesenchymal Progenitor Cells through Wnt Signaling. Journal of Biological Chemistry, 2008, 283:1936-1945

[43] Shalhoub V, Conlon D, Tassinari M, Quinn C, Partridge N, Stein GS, Lian JB. Glucocorticoids promote development of the osteoblast phenotype by selectively modulating expression of cell growth and differentiation associated genes. J Cell Biochem, 1992, 50:425-440

[44] Herbertson A, Aubin JE. Dexamethasone alters the subpopulation make-up of rat bone marrow stromal cell cultures. J Bone Miner Res, 1995, 10:285-294

[45] Haynesworth SE, Goshima J, Goldberg VM, Caplan AI. Characterization of cells with osteogenic potential from human marrow. Bone, 1992, 13:81-88

[46] Amlal H, Sheriff S, Faroqui S, Ma L, Barone S, Petrovic S, Soleimani M. Regulation of acid-base transporters by vasopressin in the kidney collecting duct of Brattleboro rat. Am J Nephrol, 2006, 26:194-205

[47] Li X, Liu P, Liu W, Maye P, Zhang J, Zhang Y, Hurley M, Guo C, Boskey A, Sun L, Harris SE, Rowe DW, Ke HZ, Wu D. Dkk2 has a role in terminal osteoblast differentiation and mineralized matrix formation. Nat Genet, 2005, 37:945-952

[48] Spater D, Hill TP, O'Sullivan RJ, Gruber M, Conner DA, Hartmann C. Wnt9a signaling is required for joint integrity and regulation of Ihh during chondrogenesis. Development, 2006, 133:3039-3049

[49] Bennett CN, Longo KA, Wright WS, Suva LJ, Lane TF, Hankenson KD, MacDougald OA. Regulation of osteoblastogenesis and bone mass by Wnt10b. Proc Natl Acad Sci U S A, 2005, 102:3324-3329

[50] Tu X, Joeng KS, Nakayama KI, Nakayama K, Rajagopal J, Carroll TJ, McMahon AP, Long F. Noncanonical Wnt signaling through G protein-linked PKCdelta activation promotes bone formation. Dev Cell, 2007, 12:113-127

[51] Bennett CN, Ouyang H, Ma YL, Zeng Q, Gerin I, Sousa KM, Lane TF, Krishnan V, Hankenson KD, MacDougald OA. Wnt10b increases postnatal bone formation by enhancing osteoblast differentiation. J Bone Miner Res, 2007, 22:1924-1932

[52] Maupin KA, Droscha CJ, Williams BO. A Comprehensive Overview of Skeletal Phenotypes Associated with Alterations in Wnt/β-catenin Signaling in Humans and Mice. Bone Research, 2013, 1:27-71

[53] Jiang J, Lichtler AC, Gronowicz GA, Adams DJ, Clark SH, Rosen CJ, Kream BE. Transgenic mice with osteoblast-targeted insulinlike growth factor-I show increased bone remodeling. Bone, 2006, 39:494-504

[54] Hill TP, Spater D, Taketo MM, Birchmeier W, Hartmann C. Canonical Wnt/beta-catenin signaling prevents osteoblasts from differentiating into chondrocytes. Dev Cell, 2005, 8:727-738

[55] Day TF, Guo X, Garrett-Beal L, Yang Y. Wnt/beta-catenin signaling in mesenchymal progenitors controls osteoblast and chondrocyte differentiation during vertebrate skeletogenesis. Dev Cell, 2005, 8:739-750

[56] Holmbeck K, Bianco P, Chrysovergis K, Yamada S, BirkedalHansen H. MT1-MMP-dependent, apoptotic remodeling of unmineralized cartilage: a critical process in skeletal growth. J Cell Biol, 2003, 163:661-671

[57] Owen TA, Aronow M, Shalhoub V, Barone LM, Wilming L, Tassinari MS, Kennedy MB, Pockwinse S, Lian JB, Stein GS. Progressive development of the rat osteoblast phenotype in vitro: reciprocal relationships in expression of genes associated with osteoblast proliferation and differentiation during formation of the bone extracellular matrix. J Cell Physiol, 1990, 143:420-430

[58] Zhou H, Choong P, McCarthy R, Chou ST, Martin TJ, Ng KW. In situ hybridization to show sequential expression of osteoblast gene markers during bone formation in vivo. J Bone Miner Res, 1994, 9:1489-1499

[59] Pavlov EP, Harman SM, Chrousos GP, Loriaux DL, Blackman MR. Responses of plasma adrenocorticotropin, cortisol, and dehydro-epiandrosterone to ovine corticotropin-releasing hormone in healthy aging men. J Clin Endocrinol Metab, 1986, 62:767-772

[60] Purnell JQ, Brandon DD, Isabelle LM, Loriaux DL, Samuels MH. Association of 24-hour cortisol production rates, cortisol-binding globulin, and plasma-free cortisol levels with body composition, leptin levels, and aging in adult men and women. J Clin Endocrinol Metab, 2004, 89:281-287

[61] Deuschle M, Gotthardt U, Schweiger U, Weber B, Körner A, Schmider J, Standhardt H, Lammers CH, Heuser I. With aging in humans the activity of the hypothalamus-pituitary-adrenal system increases and its diurnal amplitude flattens. Life Sci, 1997, 61:2239-2246

[62] Van Cauter E, Leproult R, Plat L. Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA, 2000, 284:861-868

[63] Weinstein RS, Wan C, Liu Q, Wang Y, Almeida M, O'Brien CA, Thostenson J, Roberson PK, Boskey AL, Clemens TL, Manolagas SC. Endogenous glucocorticoids decrease skeletal angiogenesis, vascularity, hydration, and strength in aged mice. Aging Cell, 2010, 9:147-161

[64] Seeman TE, Singer B, Wilkinson CW, McEwen B. Gender differences in age-related changes in HPA axis reactivity. Psychoneuroendocrinology, 2001, 26:225-240

[65] Otte C, Hart S, Neylan TC, Marmar CR, Yaffe K, Mohr DC. A meta-analysis of cortisol response to challenge in human aging: importance of gender. Psychoneuroendocrinology, 2005, 30:80-91

[66] Tiganescu A, Walker EA, Hardy RS, Mayes AE, Stewart PM. Localization, age- and site-dependent expression, and regulation of 11beta-hydroxysteroid dehydrogenase type 1 in skin. J Invest Dermatol, 2011, 131:30-36

[67] Cooper MS, Rabbitt EH, Goddard PE, Bartlett WA, Hewison M, Stewart PM. Osteoblastic 11beta-hydroxysteroid dehydrogenase type 1 activity increases with age and glucocorticoid exposure. J Bone Miner Res, 2002, 17:979-986

[68] Greendale GA, Unger JB, Rowe JW, Seeman TE. The relation between cortisol excretion and fractures in healthy older people: results from the MacArthur studies-Mac. J Am Geriatr Soc, 1999, 47:799-803

[69] Raff H, Raff JL, Duthie EH, Wilson CR, Sasse EA, Rudman I, Mattson D. Elevated salivary cortisol in the evening in healthy elderly men and women: correlation with bone mineral density. J Gerontol A Biol Sci Med Sci, 1999, 54:M479-M483

[70] Fulzele K, Riddle RC, DiGirolamo DJ, Cao X, Wan C, Chen D, Faugere MC, Aja S, Hussain MA, Brüning JC, Clemens TL. Insulin Receptor Signaling in Osteoblasts Regulates Postnatal Bone Acquisition and Body Composition. Cell, 2010, 142:309-319

[71] Ferron M, McKee MD, Levine RL, Ducy P, Karsenty G. Intermittent injections of osteocalcin improve glucose metabolism and prevent type 2 diabetes in mice. Bone, 2012, 50:568-575

[72] Ferron M, Hinoi E, Karsenty G, Ducy P. Osteocalcin differentially regulates β cell and adipocyte gene expression and affects the development of metabolic diseases in wild-type mice. Proc Natl Acad Sci U S A, 2008, 105:5266-5270

[73] Lee NK, Sowa H, Hinoi E, Ferron M, Ahn JD, Confavreux C, Dacquin R, Mee PJ, McKee MD, Jung DY, Zhang Z, Kim JK, Mauvais-Jarvis F, Ducy P, Karsenty G. Endocrine regulation of energy metabolism by the skeleton. Cell, 2007, 130:456-469

[74] Ferron M, Wei J, Yoshizawa T, Del Fattore A, DePinho RA, Teti A, Ducy P, Karsenty G. Insulin signaling in osteoblasts integrates bone remodeling and energy metabolism. Cell, 2010, 142:296-308

[75] Booth SL, Centi A, Smith SR, Gundberg C. The role of osteocalcin in human glucose metabolism: marker or mediator?. Nat Rev Endocrinol, 2013, 9:43-55

[76] De Paula FJA, Rosen CJ. Bone remodeling and energy metabolism: new perspectives. Bone Res, 2013, 1:72-84

[77] Brennan-Speranza TC, Henneicke H, Gasparini SJ, Blankenstein KI, Heinevetter U, Cogger VC, Svistounov D, Zhang Y, Cooney GJ, Buttgereit F, Dunstan CR, Gundberg C, Zhou H, Seibel MJ. Osteoblasts mediate the adverse effects of glucocorticoids on fuel metabolism. J Clin Invest, 2012, 122:4172-4189

[78] Hofbauer LC, Khosla S, Dunstan CR, Lacey DL, Spelsberg TC, Riggs BL. Estrogen stimulates gene expression and protein production of osteoprotegerin in human osteoblastic cells. Endocrinology, 1999, 140:4367-4370

[79] Cooper MS, Walker EA, Bland R, Fraser WD, Hewison M, Stewart PM. Expression and functional consequences of 11beta-hydroxysteroid dehydrogenase activity in human bone. Bone, 2000, 27:375-381

[80] Justesen J, Mosekilde L, Holmes M, Stenderup K, Gasser J, Mullins JJ, Seckl JR, Kassem M. Mice deficient in 11beta-hydroxysteroid dehydrogenase type 1 lack bone marrow adipocytes, but maintain normal bone formation. Endocrinology, 2004, 145:1916-1925

[81] Cooper MS, Syddall HE, Fall CH, Wood PJ, Stewart PM, Cooper C, Dennison EM. Circulating cortisone levels are associated with biochemical markers of bone formation and lumbar spine BMD: the hertfordshire cohort study. Clin Endocrinol (Oxf), 2005, 62:692-697

[82] Hwang JY, Lee SH, Kim GS, Koh JM, Go MJ, Kim YJ, Kim HC, Kim TH, Hong JM, Park EK, Lee JY, Kim SY. HSD11B1 polymorphisms predicted bone mineral density and fracture risk in postmenopausal women without a clinically apparent hypercortisolemia. Bone, 2009, 45:1098-1103

[83] Feldman K, Szappanos A, Butz H, Grolmusz V, Majnik J, Likó I, Kriszt B, Lakatos P, Tóth M, Rácz K, Patócs A. The rs4844880 polymorphism in the promoter region of the HSD11B1 gene associates with bone mineral density in healthy and postmenopausal osteoporotic women. Steroids, 2012, 77:1345-1351

[84] Cooper MS, Bujalska I, Rabbitt E, Walker EA, Bland R, Sheppard MC, Hewison M, Stewart PM. Modulation of 11beta-hydroxysteroid dehydrogenase isozymes by proinflammatory cytokines in osteoblasts: an autocrine switch from glucocorticoid inactivation to activation. J Bone Miner Res, 2001, 16:1037-1044

[85] Hardy R, Cooper MS. Bone loss in inflammatory disorders. J Endocrinol, 2009, 201:309-320

[86] Coutinho AE, Gray M, Brownstein DG, Salter DM, Sawatzky DA, Clay S, Gilmour JS, Seckl JR, Savill JS, Chapman KE. 11beta-Hydroxysteroid dehydrogenase type 1, but not type 2, deficiency worsens acute inflammation and experimental arthritis in mice. Endocrinology, 2012, 153:234-240

[87] Hardy R, Rabbitt EH, Filer A, Emery P, Hewison M, Stewart PM, Gittoes NJ, Buckley CD, Raza K, Cooper MS. Local and systemic glucocorticoid metabolism in inflammatory arthritis. Ann Rheum Dis, 2008, 67:1204-1210

[88] Karsenty G. Minireview: transcriptional control of osteoblast differentiation. Endocrinology, 2001, 142:2731-2733

[89] Komori T. Regulation of osteoblast differentiation by transcription factors. J Cell Biochem, 2006, 99:1233-1239

[90] Rodda SJ, McMahon AP. Distinct roles for Hedgehog and canonical Wnt signaling in specification, differentiation and maintenance of osteoblast progenitors. Development, 2006, 133:3231-3244

[91] Kalajzic I, Kalajzic Z, Kaliterna M, Gronowicz G, Clark SH, Lichtler AC, Rowe D. Use of type I collagen green fluorescent protein transgenes to identify subpopulations of cells at different stages of the osteoblast lineage. J Bone Miner Res, 2002, 17:15-25

[92] Kalajzic Z, Liu P, Kalajzic I, Du Z, Braut A, Mina M, Canalis E, Rowe DW. Directing the expression of a green fluorescent protein transgene in differentiated osteoblasts: comparison between rat type I collagen and rat osteocalcin promoters. Bone, 2002, 31:654-660

[93] Zhang M, Xuan S, Bouxsein ML, von Stechow D, Akeno N, Faugere MC, Malluche H, Zhao G, Rosen CJ, Efstratiadis A, Clemens TL. Osteoblast-specific knockout of the insulin-like growth factor (IGF) receptor gene reveals an essential role of IGF signaling in bone matrix mineralization. J Biol Chem, 2002, 277:44005-44012