Transforming Growth Factor-β₂ mRNA Level in Unloaded Bone Analyzed by Quantitative In Situ Hybridization

Abstract

The effects of tail suspension hypokinesia on the gene expression for TGF-β₂ at different sites within bone were evaluated. TGF-β₂ mRNA signal levels were determined quantitatively by an image analysis system. The osteopenia induced by tail suspension was verified by histomorphometry. In the periosteum of nonsuspended control rats, TGF-β₂ mRNA was highly expressed in the preosteoblasts and osteoblast-rich cambial layers; very little signal was present within the middle and outer fibroblastic layers. Gene expression was significantly reduced in suspended rats, and this was evident both in terms of the number of silver grains in unit area or length of tissue and in each osteoblast and preosteoblast. Hypokinesia also reduced the expression of TGF-β₂ mRNA level in cortical and trabecular bone osteocytes, but did not adversely affect the mRNA level in chondrocytes in growth plate. The results affirm the site-specific response of TGF-β₂ gene expression in rats, and suggest that the cortical and trabecular bone osteopenia associated with hypokinesia in rats may be associated with a deficit in osteoblastic and osteocytic TGF-β₂ level.