Primary skin keratinocytes were treated with gremlin (1-100 ng/mL) for 8 hours, mRNA expression of listed genes was tested by RT-qPCR assay A. Primary skin keratinocytes were pretreated with 1 μM of SU5416 or 10 μM of MK-2206 for 30 min, cells were then treated with gremlin (25 ng/mL) for 8 hours, HO1 mRNA expression was tested B. Primary skin keratinocytes expressing the Nrf2 shRNA (“shNrf2”), dominant negative Nrf2 (S40T, “dnNrf2”, Flag-tagged) or empty vector (“Vector”, pSV2 puro-Flag) were treated with gremlin (25 ng/mL) for indicated time, expressions of listed protein and mRNA were tested by Western blot assay C. and RT-qPCR assay D. respectively. Above cells were also subjected to UV (20 mJ/cm2) radiation, or plus gremlin (25 ng/mL, 30 min prior UV), cell viability E. and apoptosis F. were tested. *P < 0.05 vs. “C” group (A). #P < 0.05 vs. “DMSO (0.1%)” group (B).#P < 0.05 vs. “Vector” group (D-F).