Messenger RNA expression of the genes encoding receptors for bone morphogenetic protein (BMP) and transforming growth factor-β (TGF-β) 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 the mechanism of the pathological triggering of the disease has not yet been clarified, the cells in PLL have been reported to express osteotropic cytokines such as BMP-2 and TGF-β. However, it has not been known whether the cells in PLL express receptors for these cytokines. We examined the expression of the messenger RNAs of the genes encoding receptors for BMP-2/4 and TGF-β in the PLL cells. Tissues from three OPLL (ossification of the posterior longitudinal ligament) patients who underwent anterior decompression surgery with removal of the ossified PLL were dissected microscopically and were subjected to explant cultures; the cells outgrown from the explants were examined. Type I BMP receptor (BMPR) mRNA was expressed at moderate levels in the cells derived from both ossifying PLL tissues as well as nonossifying adjacent fibrous tissues. Type II TGF-β receptor (TβR) mRNA and α1(I) collagen mRNA were also constitutively expressed in these PLL cells from either regions. Treatment with BMP-2 enhanced the expression of BMPR mRNA in five out of ten of the cell cultures, suggesting that functional BMP receptors were expressed in at least a part of the PLL cells. The BMP-2 effect on BMPR was specific since no such enhancement was observed with regard to the levels of TβR 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-β were expressed in the cells derived from human PLL cells.