Pluripotent stem cell-derived retinal pigment epithelial (RPE) cells holds great promise for the treatment of age-related macular degeneration (AMD) and retinitis pigmentosa (RP), but the poor induction efficiency and the according high cost of RPE differentiation hindere its clinical applications. Curcumin is proved to have a promoting effect on the induced differentiation of embryonic stem cells (ESCs). However, the mechanism of curcumin on differentiation of human ESCs into RPE-like cells remains unclear.

This study aimed to explore the underlying molecular mechanism of curcumin on directed differentiation of human ESCs into RPE-like cells.

Human ESCs strains were cultured in the Matrigel-coated 6-well plate with mTeSR™1 medium until over-confluence, and basic fibroblast growth factor was withdrawn there after to induce automatic differentiation. Curcumin at the final concentration 1 μmol/L was added in the first day of differentiation for 24 hours, and the cells without curcumin in the medium served as the control group. Total RNA and protein were extracted at 3 weeks and 5 weeks after induction. RT-PCR, Western blot and immunofluorescence were performed to examine the expressions of the biomarks of stem cells and RPE cells as well as Wnt/β-catenin signaling pathway components. The endocytosis of polystyrene microsphere by induced RPE (iRPE) cells was investigated to verify their function of phagocytosis which features RPE cells.

Pigmented cells were found from 3 weeks through 5 weeks after induction in the curcumin group, but only less pigmented cells were seen in the fifth week after induction in the control group. In the third and fifth week after induction, the relative expression levels of NANOG mRNA in the iRPE cells were significantly lower than those in the control group (t=13. 086, P=0. 022; t=34. 186, P=0. 004), and the relative expression levels of Pax6, RX, CRALBP and RPE65 mRNA were higher in the curcumin group than those of the control group (all at P<0. 01). Western blot assay showed that the expressing bands for CRALBP, RPE65 and MITF enhanced in iRPE cells with a similar appearance in human RPE cells. However, these expressions were all absent in human ESCs. Immunofluorescence staining showed the positive expressions of Pax6, MITF and ZO-1 in cytoplasm of iRPE cells in the curcumin group with a purified efficacy 100%. The fluorescence dye-doped polystyrene microspheres in cytoplasm were obvious in the iRPE cells like positive controls, but the polystyrene microsphere was absent in the negative controls. From 3 weeks through 5 weeks after induced, the relative expression levels of Lef1, MYC and TCF7 mRNA (the dwnstream target genes of Wnt signaling pathway), FZD3 mRNA (Wnt receptor), Wnt2B mRNA (Wnt ligand) and Wnt7B mRNA were significantly reduced in the curcumin group compared with the control group (all at P<0. 01).

Curcumin promotes the differentiation of human ESCs into RPE-like cells by stimulating the activation of Wnt signaling pathway, and therefore accelerate the differentiation and mature of iRPE cells.

Curcumin; Humans; Embryoid bodies/drug effects; Stem cells; Cell differentiation/drug effects; Gene expression/drug effect; Pigment epithelium, Eye; Wnt proteins/metabolism