Bile acids and bilirubin effects on osteoblastic gene profile. Implications in the pathogenesis of osteoporosis in liver diseases

Susana Jurado,Albert Parés,Andres Combalia,Ana Monegal,Marta Dubreuil,Nuria Guañabens,Silvia Ruiz-Gaspà,Pilar Peris

doi:10.1016/j.gene.2019.144167

Abstract

Osteoporosis in advanced cholestatic and end-stage liver disease is related to low bone formation. Previous studies have demonstrated the deleterious consequences of lithocholic acid (LCA) and bilirubin on osteoblastic cells. These effects are partially or completely neutralized by ursodeoxycholic acid (UDCA). We have assessed the differential gene expression of osteoblastic cells under different culture conditions. The experiments were performed in human osteosarcoma cells (Saos-2) cultured with LCA (10 μM), bilirubin (50 μM) or UDCA (10 and 100 μM) at 2 and 24 h. Expression of 87 genes related to bone metabolism and other signalling pathways were assessed by TaqMan micro fluidic cards. Several genes were up-regulated by LCA, most of them pro-apoptotic (BAX, BCL10, BCL2L13, BCL2L14), but also MGP (matrix Gla protein), BGLAP (osteocalcin), SPP1 (osteopontin) and CYP24A1, and down-regulated bone morphogenic protein genes (BMP3 and BMP4) and DKK1 (Dickkopf-related protein 1). Parallel effects were observed with bilirubin, which up-regulated apoptotic genes and CSF2 (colony-stimulating factor 2) and down-regulated antiapoptotic genes (BCL2 and BCL2L1), BMP3, BMP4 and RUNX2. UDCA 100 μM had specific consequences since differential expression was observed, up-regulating BMP2, BMP4, BMP7, CALCR (calcitonin receptor), SPOCK3 (osteonectin), BGLAP (osteocalcin) and SPP1 (osteopontin), and down-regulating pro-apoptotic genes. Furthermore, most of the differential expression changes induced by both LCA and bilirubin were partially or completely neutralized by UDCA. Conclusion: Our observations reveal novel target genes, whose regulation by retained substances of cholestasis may provide additional insights into the pathogenesis of osteoporosis in cholestatic and end-stage liver diseases.

Highlights

Osteoporosis is a skeletal disease characterized by low bone mass and micro-architectural deterioration of bone tissue, leading to an increased fragility and susceptibility to fracture.It is a common complication of liver diseases, in chronic cholestasis and especially in those patients with primary biliary cholangitis (PBC) [1,2,3,4]
Caspase 1 (CASP1) was overexpressed under lithocholic acid (LCA) treatment and bilirubin decreased the expression of caspase 9 (CASP9)
The effects of substances retained in chronic cholestasis on bone cells have been previously described, suggesting direct harmful effects of bilirubin and LCA on human osteoblastic cells

Summary

Introduction

Osteoporosis is a skeletal disease characterized by low bone mass and micro-architectural deterioration of bone tissue, leading to an increased fragility and susceptibility to fracture. It is a common complication of liver diseases, in chronic cholestasis and especially in those patients with primary biliary cholangitis (PBC) [1,2,3,4]. In bone cells UDCA increases survival and improves differentiation of human osteoblasts, neutralizing the detrimental effects of LCA and bilirubin on osteoblast survival, differentiation and mineralization [12]. While bilirubin and LCA act as pro-apoptotic agents in human osteoblasts, UDCA has anti-apoptotic effects and neutralizes the apoptosis induced by LCA and bilirubin in osteoblastic cells [12]

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Conclusion