Disruption of insulin-like growth factor-I expression in type IIalphaI collagen-expressing cells reduces bone length and width in mice - PubMed (original) (raw)

Disruption of insulin-like growth factor-I expression in type IIalphaI collagen-expressing cells reduces bone length and width in mice

Kristen E Govoni et al. Physiol Genomics. 2007.

Abstract

It is well established that insulin-like growth factor (IGF)-I is critical for the regulation of peak bone mineral density (BMD) and bone width. However, the role of systemic vs. local IGF-I is not well understood. To determine the role local IGF-I plays in regulating BMD and bone width, we crossed IGF-I flox/flox mice with procollagen, typeIIalphaI-Cre mice to generate conditional mutants in which chondrocyte-derived IGF-I was disrupted. Bone parameters were measured by dual X-ray absorptiometry at 2, 4, 8, and 12 wk of age and peripheral quantitative computed tomography at 12 wk of age. Body length, areal BMD, and bone mineral content (BMC) were reduced (P < 0.05) between 4 and 12 wk in the conditional mutant mice. Bone width was reduced 7% in the vertebrae and femur (P < 0.05) of conditional mutant mice at 12 wk. Gains in body length and total body BMC and BMD were reduced by 27, 22, and 18%, respectively (P < 0.05) in conditional mutant mice between 2 and 4 wk of age. Expression of parathyroid hormone related protein, parathyroid hormone receptor, distal-less homeobox (Dlx)-5, SRY-box containing gene-9, and IGF binding protein (IGFBP)-5 were reduced 27, 36, 45, 33, and 45%, respectively, in the conditional mutant cartilage (P < 0.05); however, no changes in Indian hedgehog, Dlx-3, growth hormone receptor, IGF-I receptor, and IGFBP-3 expression were observed (P > or = 0.20). In conclusion, IGF-I from cells expressing procollagen type IIalphaI regulates bone accretion that occurs during postnatal growth period.

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Figures

Fig. 1

Reduced insulin-like growth factor (IGF)-I expression in the bones of conditional mutant mice at 2 wk of age. Gene expression was determined by real-time RT-PCR and expressed as a percent of controls. A 50% change is equal to a 2-fold change in expression. Data are presented as means ± SE. *Significant difference from controls at P < 0.05. Conditional mutant mice (n = 7) and control mice (n = 8). Dia/Met, diaphysis/metaphysis of femur/tibia.

Fig. 2

Cre expression is specific to chondrocyte cells. Image presented is the PCR product of Cre and GAPDH for primary chondrocytes (C) and osteoblasts (O). We amplified 30 and 15 ng of RNA for 40 cycles for Cre and GAPDH, respectively. Cre expression was not detectable in primary osteoblast cells by PCR analysis or real-time RT-PCR.

Fig. 3

Body weight and length are reduced in conditional mutant mice. Body weights (A) and lengths (B) were determined between 2 and 12 wk of age. Diamond with solid line, conditional mutant females; diamond with dashed line, conditional mutant males; circle with solid line, control females; circle with dashed line, control males. *Significant difference between conditional mutant and control mice at P < 0.05.

Fig. 4

Reduced rate of gain in body length, total body bone mineral density (BMD), and total body bone mineral content (BMC) in conditional mutant mice during prepubertal growth. Growth and bone parameters were determined by dual X-ray absorptiometry analysis and rate of gain was calculated between 2 and 4 wk of age. Data are expressed as conditional mutants as a percent of controls and presented as means ± SE. *Significant difference from controls at P < 0.05. At 2 wk of age [conditional mutant female mice (n = 6), conditional mutant male mice (n = 4), control female mice (n = 4), control male mice (n = 4)]. At 4 wk of age, n = 8 mice/sex/treatment group.

Fig. 5

Reduced PTHrP, PTH1R, Sox9, Dlx5, and IGFBP-5 expression in the cartilage of conditional mutant mice at 2 wk of age. Gene expression was determined by real-time RT-PCR and expressed as a percent of control. A 50% change is equal to a 2-fold change in expression. Data are presented as means ± SE. *Significant difference from controls at P < 0.05. Conditional mutant mice (n = 7) and control mice (n = 8). Ihh, Indian hedgehog; PTHrP, parathyroid hormone-related protein; PTH1R, PTHrP/PTH receptor; Sox, SRY-box containing gene; Dlx, distal-less homeobox; GHR, growth hormone receptor; IGF-IR, IGF-I receptor; BP, IGF binding protein.

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Disruption of insulin-like growth factor-I expression in type IIalphaI collagen-expressing cells reduces bone length and width in mice - PubMed (original) (raw)