Insulin-Like Growth Factor Helps Regulate Bone Growth

Protein factor regulates growth of epiphyseal chondrocytes

MONDAY, July 16 (HealthDay News) -- The growth factor insulin-like growth factor-I (IGF-I) is a major regulator of bone growth by regulating epiphyseal chondrocyte growth, with some cell types more sensitive to IGF-I than others, according to study findings published in the July issue of Endocrinology.

Michele R. Hutchison, M.D., Ph.D., and colleagues from the University of Texas Southwestern Medical Center in Dallas examined the effect of IGF-I on the growth of juvenile bovine epiphyseal chondrocytes.

The researchers found that high-density cells corresponding to the reserve zone proliferated the most in response to IGF-I, while low-density cells in the hypertrophic zone proliferated only in response to both IGF-I and basic fibroblast growth factor (FGF). The differential response to IGF-I was due to differences in the number of IGF-I receptors, with reserve zone cells containing 10-fold more receptors than hypertrophic zone cells. FGF appeared to increase the number of IGF-I receptors in the hypertrophic zone, according to the study.

"These results suggest that the major regulator of chondrocyte proliferation is systemic IGF-I; FGFs may influence the actions of IGF-I at the growth plate by altering its receptor number in chondrocytes," Hutchison and colleagues conclude.

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