65 - Nrf2 in Keratinocytes Modulates UVB-Induced DNA Damage and Apoptosis in Melanocytes through ROS-Dependent Mechanism

Abstract

Responses of melanocytes (MC) to ultraviolet (UV) irradiation can be regulated by their neighbouring keratinocytes (KC). Aims We investigated the role of Nrf2 in regulating paracrine effects of KC on UVB-induced MC responses through phosphorylation of MAPKs in association with oxidative stress in primary human MC co-cultured with primary human KC using a trans-well co-culture system and small-interfering RNA-mediated silencing of Nrf2 (siNrf2). The mechanisms by which Nrf2 modulated paracrine factors including α-melanocyte-stimulating hormone (α-MSH) and paracrine effects of KC on UVB-mediated apoptosis were also assessed. Results Co-culture of MC with siNrf2-transfected KC enhanced UVB-mediated cyclobutane pyrimidine dimer (CPD) formation, apoptosis and oxidant formation in correlation with phosphorylation of ERK, JNK and p38 in MC. MC damage induced by UVB was increased in MC treated with conditioned medium (CM) derived from Nrf2-depleted KC, suggesting that KC modulated UVB-mediated MC responses via paracrine effects. Additionally, at 30 min post-irradiation, depletion of Nrf2 in KC suppressed UVB-induced α-MSH levels, although pre-treatment with N-acetylcysteine (NAC) elevated its levels in CM from siNrf2-transfected KC. Furthermore, NAC reversed the effect of CM from Nrf2-depleted KC on UVB-induced apoptosis in MC. Conclusion Our study demonstrates for the first time that KC provided a rescue effect on UVB-mediated MC responses, although depletion of Nrf2 in KC reversed its protective effects on MC in a paracrine fashion in association with elevation of reactive oxygen species (ROS) levels and activation of MAPK pathways in MC. Nrf2 may indirectly regulate paracrine effect of KC probably by affecting levels of the paracrine factor α-MSH via a ROS-dependent mechanism.