Bone Abstracts

Low bone formation is considered to be the main feature in osteoporosis associated with cholestatic and end-stage liver diseases. Previous studies have demonstrated the deleterious consequences of retained substances such as lithocholic acid (LCA) and bilirubin (Bil) on osteoblastic cells. These effects are neutralized by ursodeoxycholic acid (UDCA). To gain new insights into cholestatic-induced osteoporosis, we have assessed the differential gene expression of osteoblastic cells under varied culture conditions.

The experiments were performed in human osteosarcoma cells (Saos-2), cultured with LCA (10 μM), Bil (50 μM) or UDCA (10/100 μM) at 2 and 24 h. Expression of several signalling pathways and related bone genes were assessed by TaqMan microfluidic cards. The 88 genes covered a broad range of functional activities including apoptosis, osteoclast and osteoblast differentiation and mineralization and expression of genes involved in collagen synthesis and degradation, growth factors and vascularisation.

LCA up-regulated several genes, most of them involved in apoptosis (BAX, BCL10, BCL2L13, BCL2L14) but also MGP, BGLAP, SPP1 and CYP24A1, and down-regulated BMP3, BMP4 and DKK1. Parallel effects were observed by Bil, which up-regulated apoptotic genes and CSF2, and down-regulated antiapoptotic genes BCL2 and BCL2L1. Moreover, Bil down-regulated BMP3, BMP4, DPP1 and SMAD6. UDCA has specific consequences since differential expression was observed particularly at 100 μM up-regulating BMP2, BMP4, BMP7, CALCR, SPOCK3, SPP1 and DMP1, and down-regulating antiapoptotic genes and RANKL. UDCA down-regulated collagen genes with no changes in metalloproteinases. Furthermore, most of the differential expression changes induced by LCA and Bil were partially or completely neutralized by UDCA. No differential expression effects of LCA and Bil were observed regarding metalloproteinases, MAPKs, growth factors, vascularisation and oncogenes.

These observations reveal novel target genes, whose regulation by retained substances of cholestasis may provide new approaches for understanding the pathogenesis of osteoporosis in cholestatic and end-stage liver diseases.