Cytosolic DNA sensors in cutaneous wound healing and host defense

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ABSTRACT The cutaneous innate immune system is the first line of defense against pathogenic microorganisms, but also plays a key role in healing injured skin. Pattern recognition receptors (PRRs) orchestrate the molecular and cellular events that occur following the recognition of pathogen or danger associated molecular patterns (PAMPs and DAMPs, respectively) in the skin. While Toll-like receptors have long been known to trigger immune cell activation in response to extracellular and endosomal PAMPs and DAMPs, cytosolic nucleic acid sensors are emerging as major regulators of immune mediated diseases in the skin. These cytosolic sensors include cytosolic DNA sensors that can recognize both endogenous and exogenous DNA and RNA species. In fact, recognition of dsRNA by Toll-like receptor 3 (TLR3) was shown to affect UV-radiation induced skin damage, and regulate cutaneous regeneration following wounding. Whether the recognition of DNA in the cytosol regulates cutaneous immunity is poorly understood. Two major cytosolic DNA sensor systems trigger the majority of cellular signaling events. The cyclic GMP-AMP synthase and Stimulator of Interferon Genes (cGAS-STING) pathway results in potent induction of type I interferon (IFN), and has been shown to participate in lupus and lupus-like disease. The other cytosolic DNA sensor, absent in melanoma 2 (AIM2), activates the AIM2 inflammasome to induce interleukin 1β (IL-1β) and IL-18 and was shown to be involved in psoriasis pathogenesis. While these pathways are aberrantly induced in inflammatory skin disease, how these pathways contribute to normal cutaneous immunity is less understood. We recently showed that Staphylococcus aureus subverts cutaneous host defense by activating the cGAS-STING pathway to induce type I interferon and limit IL-1β. We hypothesize that the cGAS-STING and AIM2 pathways differentially regulate cutaneous immunity following S. aureus infection and during wound healing. In Aim 1, we will test the hypothesis that the AIM2 inflammasome is a major regulator of cutaneous IL-1β production and neutrophil recruitment, playing a critical role in host defense following cutaneous S. aureus infection. In Aim 2, we will test the hypothesis that the two cytosolic DNA pathways play opposing roles during wound healing with activation of the cGAS-STING-IFN pathway resulting in improved wound healing and tissue regeneration and activation of AIM2 resulting in more inflammation, poor wound healing, and impaired tissue regeneration. The experiments described herein will provide evidence whether targeting cytosolic DNA sensor pathways can result in new treatments for wound healing or protection against microbial organisms.