Activation of liver X receptor α protects amyloid β induced inflammatory and senescent responses in human retinal pigment epithelial cells.

Objective: To investigate whether activation of the liver X receptors (LXRs) inhibits amyloid β (Aβ) induced inflammatory and senescent responses in human retinal pigment epithelial (RPE) cells.

Materials And Methods: Confluent cultures of human primary RPE and ARPE-19 cells pretreated with 5 μΜ of TO901317 (TO90), a synthetic agonist of LXR, or vehicle were incubated with 1 μΜ of Aβ or Aβ. The optimum concentrations of Aβ and TO90 were determined by cell viability assay. Pro-inflammatory cytokines IL-6, IL-8, MCP-1 were detected by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Expression and localization of an aging protein p16INK4a (p16) were analyzed by western blotting and immunofluorescence. Expressions of LXRs and one of their target genes ATP-binding cassette transporter A1 (ABCA1) were examined by real-time PCR and western blotting. Phosphorylated transcription inhibition factor-κB-α (p-IκB-α) was assessed by western blotting.

Results: A negative linear relationship between the Aβ concentration and the cell viability was evident, indicating Aβ decreased ARPE-19 cell viability in a dose-dependent manner. Aβ enhanced the expression of IL-6, IL-8, MCP-1 as well as p16 in both RPE cell lines at both mRNA and protein levels, whereas TO90 counteracted the detrimental effects. TO90 upregulated the expression of LXRα and its target gene ABCA1, but it did not affect the expression of LXRβ. Meanwhile, TO90 inhibited the phosphorylation of IκB-α mediated by Aβ stimulation.

Conclusion: Activation of the LXRα-ABCA1 axis may alleviate Aβ induced inflammatory and senescent responses in RPE cells. The beneficial effect appears associated with the inhibition of the NF-κB signaling pathway.