Insulin receptor substrate-1 in osteoblast is indispensable for maintaining bone turnover
Naoshi Ogata, … , Kozo Nakamura, Hiroshi Kawaguchi
Naoshi Ogata, … , Kozo Nakamura, Hiroshi Kawaguchi
Published April 1, 2000
Citation Information: J Clin Invest. 2000;105(7):935-943. https://doi.org/10.1172/JCI9017.
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Article

Insulin receptor substrate-1 in osteoblast is indispensable for maintaining bone turnover

Abstract

Insulin receptor substrates (IRS-1 and -2) are essential for intracellular signaling by insulin and IGF-I, anabolic regulators of bone metabolism. Mice lacking the IRS-1 gene IRS-1–/– showed severe osteopenia with low bone turnover. IRS-1 was expressed in osteoblasts, but not in osteoclasts, of wild-type (WT) mice. IRS-1–/– osteoblasts treated with insulin or IGF-I failed to induce tyrosine phosphorylation of cellular proteins, and they showed reduced proliferation and differentiation. Osteoclastogenesis in the coculture of hemopoietic cells and osteoblasts depended on IRS-1 expression in osteoblasts and could not be rescued by IRS-1 expression in hemopoietic cells in the presence of not only IGF-I but also 1,25(OH)2D3. In addition, osteoclast differentiation factor (RANKL/ODF) was not induced by these factors in IRS-1–/– osteoblasts. We conclude that IRS-1 deficiency in osteoblasts impairs osteoblast proliferation, differentiation, and support of osteoclastogenesis, resulting in low-turnover osteopenia. Osteoblastic IRS-1 is essential for maintaining bone turnover, because it mediates signaling by IGF-I and insulin and, we propose, also by other factors, such as 1,25(OH)2D3.

Authors

Naoshi Ogata, Daichi Chikazu, Naoto Kubota, Yasuo Terauchi, Kazuyuki Tobe, Yoshiaki Azuma, Tomohiro Ohta, Takashi Kadowaki, Kozo Nakamura, Hiroshi Kawaguchi

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The expression of IRS-1 and -2 and the phosphorylation of cellular prote...
The expression of IRS-1 and -2 and the phosphorylation of cellular proteins in cell cultures. (a) Messenger RNA expression patterns of IRS-1 and IRS-2 in osteoblasts and osteoclasts from WT and IRS-1–/– littermates and mouse osteoclast progenitor C7 cells at various differentiation stages were determined by semiquantitative RT-PCR within an exponential phase of the amplification. Total RNA was extracted from cultured osteoblasts from neonatal calvariae, osteoclasts formed in the coculture of marrow cells and osteoblasts, and C7 cells cultured for 2, 4, and 6 days in the presence of RANKL/ODF and M-CSF. IRS-1 expression was seen only in osteoblasts but not in cells of osteoclastic lineage, even when the amount of template cDNA or the number of amplification cycles was increased. (b) Induction of tyrosine phosphorylation of cellular proteins and IRS-1 in osteoblasts from WT and IRS-1–/– mice by IGF-I and insulin. Osteoblasts from neonatal calvariae of WT (lanes 1–3, 7–9, 13–15) and IRS-1–/– (lanes 4–6, 10–12, 16–18) littermates were treated with vehicle (lanes 1, 4, 7, 10, 13, and 16), IGF-I (lanes 2, 5, 8, 11, 14, and 17) or insulin (lanes 3, 6, 9, 12, 15, and 18) for 2 minutes, and extracted cellular proteins were subjected to SDS-PAGE. Lanes 1–6: immunoblotting with an anti-phosphotyrosine antibody; lanes 7–12: immunoblotting with an anti–IRS-1 antibody; lanes 13–18: immunoblotting with an anti–IRS-1 antibody for the osteoblast extracts immunoprecipitated with an anti-phosphotyrosine antibody. Arrowheads indicate 185-kD protein (IRS-1).