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All‐trans retinoic acid attenuates ultraviolet radiation‐induced down‐regulation of aquaporin‐3 and water permeability in human keratinocytes

One of the major characteristics of human skin photoaging induced by ultraviolet (UV) radiation is the dehydration of the skin. Water movement across plasma membrane occurs via diffusion through lipid bilayer and via aquaporins (AQPs). We find that UV induces aquaporin‐3 (AQP3) down‐regulation in human skin keratinocytes. MEK/ERK inhibitors PD98059 and U0126 inhibit UV‐induced down‐regulation of AQP3. Antioxidant N‐acetyl‐L‐cysteine or NAC blocks UV‐induced MEK/ERK activation and down‐regulation of AQP3. All‐trans retinoic acid or atRA, while alone inducing AQP3 expression, attenuates UV‐induced down‐regulation of AQP3 and water permeability. Using special inhibitors, we find that activation of EGFR and inhibition on ERK activation are involved in atRA's protective effects against UV‐induced AQP3 down‐regulation. Using specific AQP3's water transport inhibitors and siRNA knockdown, we observe that AQP3 is involved in cell migration and in vitro wound healing. UV‐induced AQP3 down‐regulation results in reduced water permeability, decreased cell migration, and delayed wound healing, which are attenuated by atRA pretreatment. We conclude that atRA protects against UV‐induced down‐regulation AQP3 and decrease in water permeability, reduction in cell migration and delayed in vitro wound healing via trans‐activation of EGFR and inhibition on ROS‐mediated MEK/ERK pathway. This novel finding provides evidence to support possible involvement of AQP3 in UV induced skin dehydration. J. Cell. Physiol. 215: 506–516, 2008. © 2007 Wiley‐Liss, Inc.