Characterization of cellular senescence in photoreceptor cells treated with cholesterol in vitro. mRNA expression of Abca1, Abcg1 (A), and senescence markers (p16 and p21) (B) in photoreceptor cell line 661W treated with cholesterol for 24 hours. (C) ISH (p16 and p21) (red) of photoreceptor cell line treated with cholesterol. (D) mRNA expression of inflammatory cytokines (Tnf-α, Cxcl12b, and Ccl2) in a photoreceptor cell line treated with cholesterol. (E) qPCR senescence array. (F) Immunofluorescence of photoreceptor cell line stained for Ki67 (green). Nuclei were stained with DAPI (blue). (G) The quantification of Ki67-positive cells. *P < 0.05; **P < 0.01, ***P < 0.001, ****P < 0.0001, t-test for comparison between two groups, one-way ANOVA followed by Bonferroni correction for multiple comparisons.