Ultraviolet B (UVB) radiation has profound effects upon skin and generates systemic consequences from fever to immunosuppression to vitamin D production. The ability of UVB to serve as both an immunosuppressant and mutagen allows this environmental agent to serve as a complete carcinogen, and is the cause for non-melanoma skin cancer and melanoma. Skin cancer is the most common diagnosis in VA Dermatology clinics, and this is expected to increase as our military forces are often stationed in areas with a high UV index. Thus, understanding the mechanisms by which UVB generates skin cancer is relevant to our veterans. As UVB only penetrates the epidermis, a major question in photobiology is how UVB-treated skin sends systemic signals. Recent studies have indicated that small membrane-bound vesicles known as microvesicle particles (MVP) released from cells in response to various stressors can act as potent signaling agents due to their ability to carry nuclear and cytoplasmic components. We have demonstrated that UVB generates MVP release from epithelial cells and skin, which could provide a potential mechanism for UVB-mediated systemic signaling. Our group and others have previously reported that UVB radiation generates high levels of the lipid mediator Platelet-activating factor (PAF) produced enzymatically and PAF-receptor (PAFR) agonists produced non-enzymatically via reactive oxygen species. Recent studies using antioxidants and PAFR-expressing/null cell lines and pharmacologic/genetic inhibition of the enzyme acid sphingomyelinase (aSMase) have implicated involvement of PAFR signaling resulting in aSMase activation in UVB generated MVP (UVB-MVP). Finally, we provide evidence that UVB-MVP carry bioactive PAF agonists, which we hypothesize mediate the delayed immunosuppressive effects of UVB. Yet knowledge gaps exist as to how UVB-MVP are generated and if this new pathway can be exploited to address UVB-induced immunosuppression involved in skin tumor generation/progression.
Two aims are planned for the renewal of this long-running and highly productive VA Merit grant which is centered around the role of oxidized glycerophosphocholines in UV-induced immunosuppression.
These aims are designed to test the hypothesis that UVB generates MVP in human skin in a PAF-dependent manner involving aSMase and transfers both local and systemic effects via their carried PAF agonists.
Aim 1 will use in vitro cell lines and murine genetic and pharmacologic models to determine the mechanisms of UVB-MVP generation.
Aim 2 will use tools (in part validated in Aim 1) to define the roles of UVB- MVP in delayed immunosuppressive and tumor-promoting effects of UVB. Successful completion of this project will (i) address an important question in photobiology as to how a keratinocyte-specific stimulus can generate systemic signaling effects, (ii) offer pharmacologic mechanisms to block UVB local and systemic effects.
The primary long-term goal of our research is to characterize the role of the lipid mediator Platelet-activating factor (PAF) in ultraviolet B (UVB) radiation-induced immunosuppression which is responsible for skin cancers. We have shown that UVB generates subcellular microvesicle particles (MVP) which are not only dependent upon PAF, they appear to carry PAF agonists from the epidermal keratinocytes. These studies will define the mechanisms by which UVB generates MVP and define if this novel pathway can be exploited pharmacologically to block UVB-induced immunosuppression.
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