title: Circulating levels of IGF-1 directly regulate bone growth and density.
abstract: IGF-1 is a growth-promoting polypeptide that is essential for normal growth and development. In serum, the majority of the IGFs exist in a 150-kDa complex including the IGF molecule, IGF binding protein 3 (IGFBP-3), and the acid labile subunit (ALS). This complex prolongs the half-life of serum IGFs and facilitates their endocrine actions. Liver IGF-1-deficient (LID) mice and ALS knockout (ALSKO) mice exhibited relatively normal growth and development, despite having 75% and 65% reductions in serum IGF-1 levels, respectively. Double gene disrupted mice were generated by crossing LID+ALSKO mice. These mice exhibited further reductions in serum IGF-1 levels and a significant reduction in linear growth. The proximal growth plates of the tibiae of LID+ALSKO mice were smaller in total height as well as in the height of the proliferative and hypertrophic zones of chondrocytes. There was also a 10% decrease in bone mineral density and a greater than 35% decrease in periosteal circumference and cortical thickness in these mice. IGF-1 treatment for 4 weeks restored the total height of the proximal growth plate of the tibia. Thus, the double gene disruption LID+ALSKO mouse model demonstrates that a threshold concentration of circulating IGF-1 is necessary for normal bone growth and suggests that IGF-1, IGFBP-3, and ALS play a prominent role in the pathophysiology of osteoporosis.
authors.affiliation: Section on Cellular and Molecular Physiology, Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health, Bethesda, Maryland 20892, USA.
authors.forename: Shoshana
authors.initials: S
authors.lastname: Yakar
authors.forename: Clifford J
authors.initials: CJ
authors.lastname: Rosen
authors.forename: Wesley G
authors.initials: WG
authors.lastname: Beamer
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Ackert-Bicknell
authors.forename: Yiping
authors.initials: Y
authors.lastname: Wu
authors.forename: Jun-Li
authors.initials: JL
authors.lastname: Liu
authors.forename: Guck T
authors.initials: GT
authors.lastname: Ooi
authors.forename: Jennifer
authors.initials: J
authors.lastname: Setser
authors.forename: Jan
authors.initials: J
authors.lastname: Frystyk
authors.forename: Yves R
authors.initials: YR
authors.lastname: Boisclair
authors.forename: Derek
authors.initials: D
authors.lastname: LeRoith
mesh_terms: D000818:Animals; D015519:Bone Density / Q000502:physiology*; D001846:Bone Development / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D013006:Growth Hormone / Q000097:blood; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D013977:Tibia / Q000166:cytology / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D018969:Insulin-Like Growth Factor Binding Proteins; C075944:insulin-like growth factor binding protein, acid labile subunit; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone