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 t o understanding events such as distraction osteogenesis. The goal of this s tudy was to determine the effect of continuous cyclic mechanical stretch as a fundamental event in distraction osteogenesis on the expression of 3 bon e growth factors, transforming growth factor-beta 1 (TGF-beta 1), insulin-l ike growth factor 1 (IGF-1), basic fibroblast growth factor (bFGF) and 2 cy tokines, interleukin (IL)-1 (IL-1) and 6 (IL-6) in human osteoblast-like ce lls. 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 conflu ence and either subjected to tensile stretch for different time intervals o r used as the control group. RNA was isolated to conduct Northern blot anal ysis 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 expe rimental 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 signifi cant 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, where as catabolic cytokines are unaffected. These findings suggest a direct effe ct of mechanical strain on osteoblasts and may be the driving factors of bo ne growth during distraction.