Upregulation of Receptor Interacting Protein 1 Induced by UVB Contributes to Photodamage of the Skin Through NF-κB Pathway In Vivo and In Vitro.

Background: Ultraviolet (UV) B can reach the epidermis and superficial dermis of the skin, inducing sunburn, inflammation, immunosuppression, cancer, and so on. Our former research found that receptor interacting protein (RIP) 1 could be upregulated in human dermal fibroblasts(HDFs) after UVB irradiation by using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry techniques. Besides, our further research found that RIP1 was involved in the UVB-induced production of ROS and MMPs in HDFs. So far, the mechanisms of skin photodamage induced by UV mainly include DNA damage, oxidative stress, inflammation, apoptosis, and necroptosis. The NF-κB pathway can be activated eventually in the occurrence of inflammation and thus produce inflammatory cytokines such as IL-1, TNF-α, IL-6, and IL-8. However, the mechanism by which the upregulation of RIP 1 induced by UVB contributes to photodamage is still unclear.

Aims: To explore the role of RIP1 in UVB-induced skin inflammation and the related signal pathways and molecular mechanism, thus providing possible molecular markers for the diagnosis and prevention of skin photodamage.

Methods: Human dermal fibroblasts were cultured in vitro from normal human skin tissues. Besides, HaCaT cell lines and Balb/c nude mice were also the research objects. First, cellular models of UVB-induced upregulation of RIP1 were established. Then, the expression of RIP1 and localization of RIP1 before and after UVB irradiation of the cells were studied through western blot and immunofluorescence. Then, the change in the expression of the nuclear factor (NF)-kappaB (NF-κB) pathway, along with RIP1 in these cells before and after UVB irradiation was detected, including NF-κB p50/p65, p-p65, IκB and cytokines such as IL-1, IL-6, IL-8, and TNF-α. Next, the effects of the RIP1 inhibitor Nec-1 and RIP1 siRNA on the expression of RIP1, p-RIP1, NF-κB p50/p65, inflammatory cytokines, and nuclear translocation of p-p65 in vitro cells after UVB irradiation were explored. At last, the expression of RIP1 and NF-κB pathway-related proteins such as p65/p50 was detected by western blot and immunohistochemistry before and after UVB radiation with or without subcutaneous injection of Nec-1 in the Balb/c nude mice were detected.

Result: We provide that RIP1 involved in the photodamage of human dermal fibroblasts, HaCaT cell lines, and the skin tissues of Balb/c nude mice induced by UVB. Upregulated RIP1 induced by UVB ultimately upregulates inflammatory cytokines, including IL-1, IL-6, IL-8, and TNF-α by triggering the expression of NF-κB p65/p50 and activating nuclear translocation of p-p65 in cells. RIP1 inhibitor Nec-1 or RIP1 siRNA can inhibit the function of RIP1. We first illustrate that the upregulated RIP1 induced by UVB contributes to photodamage of the skin via the NF-κB signaling pathway in vivo and in vitro.

Conclusion: The study reveals the molecular mechanism by which upregulated RIP induced by UVB contributes to the occurrence of inflammation of the skin and also provides possible molecular markers for the diagnosis and prevention of skin photodamage.