FGFR4 and hepatocellular carcinoma: We found that receptors for FGF21 were expressed in human (h) primary retinal microvascular endothelial cells (HRMECs) in vitro: Fibroblast growth factor receptor 1 (FGFR1) at a high level, FGFR3 and co-receptor β-KLOTHO (validated with Huh7, a human hepatocellular carcinoma cell line as a positive control and water as a negative control) at moderate levels, and FGFR2 and FGFR4 at low levels (Supplementary Figure S1A–E).