MESSENGER-RNA EXPRESSION OF THE GENES ENCODING RECEPTORS FOR BONE MORPHOGENETIC PROTEIN (BMP) AND TRANSFORMING GROWTH-FACTOR-BETA (TGF-BETA) IN THE CELLS FROM THE POSTERIOR LONGITUDINAL LIGAMENT IN CERVICAL-SPINE

Posterior longitudinal ligament (PLL) in cervical spine is one of the sites of ossification in idiopathic hyperostotic diseases. Although th e mechanism of the pathological triggering of the disease has not yet been clarified, the cells in PLL have been reported to express osteotr opic cytokines such as BMP-2 and TGF-beta. However, it has not been kn own whether the cells in PLL express receptors for these cytokines. We examined the expression of the messenger RNAs of the genes encoding r eceptors for BMP-2/4 and TGF-beta in the PLL cells. Tissues from three OPLL (ossification of the posterior longitudinal ligament) patients w ho underwent anterior decompression surgery with removal of the ossifi ed PLL were dissected microscopically and were subjected to explant cu ltures; the cells outgrown from the explants were examined. Type I BMP receptor (BMPR) mRNA was expressed at moderate levels in the cells de rived from both ossifying PLL tissues as well as nonossifying adjacent fibrous tissues. Type II TGF-beta receptor (T beta R) mRNA and alpha 1(l) collagen mRNA were also constitutively expressed in these PLL cel ls from either regions. Treatment with BMP-2 enhanced the expression o f BMPR mRNA in five out of ten of the cell cultures, suggesting that f unctional BMP receptors were expressed in at least a part of the PLL c ells. The BMP-2 effect on BMPR was specific since no such enhancement was observed with regard to the levels of T beta R mRNA in all of the ten cultures. These results indicated for the first time that mRNAs of the genes encoding receptors for BMP-2/4 and TGF-beta were expressed in the cells derived from human PLL cells.