Apoptosis and expression of stress protein (ORP150, HO1) during development of ischaemic osteonecrosis in the rat

Using in situ hybridisation and the terminal deoxynucleotidyl transferase-m ediated biotin-dUTP nick end-labelling (TUNEL) reaction in rats with osteon ecrosis of the femoral head we have studied the effect of ischaemia on the gene expression of the stress proteins oxygen-regulated protein 150 (ORP150 ) and haemoxygenase 1 (HO1) and the death mechanism of the cells involved i n osteonecrosis. Both ORP150 and HO1 have been reported to have important r oles in the successful adaptation to oxygen deprivation. ORP150 and HO1 mRNA expression was induced by ischaemia in osteoblasts and osteocytes. In proliferative chondrocytes, these signals were detected cons titutively. During the development of ischaemic osteonecrosis, the mechanis m of cell death was apoptosis as indicated by DNA fragmentation and the pre sence of apoptotic bodies in osteocytes, chondrocytes and bone-marrow cells . After the initial ischaemic event, expression of ORP150 and HO1 mRNA, the TUNEL-positive reaction and empty lacunae were found sequentially. These f indings were exclusive and may be considered to be markers for each stage i n the development of osteonecrosis.