Modulation of the microenvironment by senescent biliary epithelial cells may be involved in the pathogenesis of primary biliary cirrhosis

Background & aims

Biliary epithelial cells (BECs) in damaged small bile ducts in primary biliary cirrhosis (PBC) show senescent features. Given that senescent cells modulate the microenvironment by expressing senescence-associated secretory phenotypes (SASP), including inflammatory cytokines and chemokines, we investigated the possible involvement of SASP in the pathogenesis of PBC.

Methods

We examined the chemokine profiles and the induced migration of RAW264.7 cells in senescent BECs induced by oxidative stress, DNA damage, and serum deprivation. We also immunohistochemically examined the expression of CCL2 and CX3CX1 in livers taken from patients with PBC (n=37) and control livers (n=75).

Results

Senescent BECs induced by oxidative stress, DNA damage, or serum deprivation expressed a significantly higher level of chemokines to various degrees, when compared with control BECs. Senescent BECs significantly facilitated the migration of RAW264.7 cells (p<0.01), and neutralizing antibodies against CCL2 and CX3CX1 partially blocked the migration induced by senescent BECs (p<0.01). The expression of CCL2 and CX3CL1 was significantly higher in BECs in inflamed and damaged small bile ducts in PBC, when compared with non-inflamed bile ducts and control livers (p<0.01). The expression of CCL2 and CX3CL1 was co-localized with the expression of senescent markers.

Conclusions

Senescent BECs displayed an upregulated expression of various chemokines and chemotactic activities. The expression of CCL2 and CX3CL1 was increased in senescent BECs in PBC. These findings suggest that the senescent BECs may modulate the microenvironment around bile ducts by expressing SASP and contribute to the pathogenesis of bile duct lesions in PBC.

Keywords: Chemokine, Cellular senescence, Senescence-associated secretory phenotype, p16^INK4a, p21^WAF1/Cip1

Abbreviations: BEC, biliary epithelial cell, CNSDC, chronic non-suppurative destructive cholangitis, CVH, chronic viral hepatitis, DAPI, 4′-6-diamidino- 2-phenylindole, EBO, extrahepatic biliary obstruction, ELISA, enzyme-linked immunosorbent assay, FITC, fluorescent isothiocyanate, HBsAg, hepatitis B surface B antigen, HCVAb, anti-hepatitis C viral antibody, IgG, immunoglobulin G, IL, Interleukin, MCP-1, monocyte chemotactic protein-1, NASH, non-alcoholic steatohepatitis, PBC, primary biliary cirrhosis, PBS, phosphate-buffered saline, RT-PCR, reverse transcriptase-polymerase chain reaction, SA-β-gal, senescence-associated β-galactosidase, SASP, senescence-associated secretory phenotypes