Growth factor and cytokine gene expression in mechanically strained human osteoblast-like cells: Implications for distraction osteogenesis

Objective. An understanding of bone cellular biology is a basic necessity to understanding events such as distraction osteogenesis. The goal of this study was to determine the effect of continuous cyclic mechanical stretch as a fundamental event in distraction osteogenesis on the expression of 3 bone growth factors, transforming growth factor-beta 1 (TGF-beta 1), insulin-like growth factor 1 (IGF-1), basic fibroblast growth factor (bFGF) and 2 cytokines, interleukin (IL)-1 (IL-1) and 6 (IL-6) in human osteoblast-like cells. Material and methods. A human osteoblast-like cell line, SaOS-2, capable of forming a ground substance and mineralizing it, was maintained. Cells were transferred to 6-well plates with flexible silicon bottoms grown to confluence and either subjected to tensile stretch for different time intervals or used as the control group. RNA was isolated to conduct Northern blot analysis for the expression of 3 bone growth factors, transforming TGF-beta 1, IGF-1, bFGF, and 2 cytokines, IL-1 and IL-6. Results. After 8 hours, mRNA for TGF-beta 1 and IGF-1 increased in the experimental group, whereas bFCF decreased but cytokines IL-1 and IL-6 were not affected. At 16 hours, TGF-beta 1, IGF-1, and bFCF showed increased levels of mRNA; IL-6 showed a slight increase, After 24 hours, TGF-beta 1, IGF-1, bFGF, and IL-6 had increased mRNA levels. IL-1 beta did never show significant alterations in mRNA production as compared with the control. Conclusion. Tensile stretch on osteoblast-like cells alter local regulation of bone formation, increasing the expression of bone growth factors, whereas catabolic cytokines are unaffected. These findings suggest a direct effect of mechanical strain on osteoblasts and may be the driving factors of bone growth during distraction.