Characterizing the role of Staphylococcus aureus V8 protease in skin barrier damage and neuroimmune responses during host-pathogen interaction

Abstract

Atopic dermatitis (AD) is a skin disorder that is characterized by itch and flares of inflamed skin lesions. Pathophysiology is associated with impaired epidermal barrier function, immunological abnormalities, and an altered skin microbiota. Staphylococcus aureus, a Gram-positive opportunistic bacterium, is rarely isolated from the skin of healthy adults but is frequently found on eczematous skin lesions of patients with AD. We have developed a murine epicutaneous exposure and infection model using methicillin-resistant S. aureus USA 300 (LAC) strain. Previous work by Deng et al.[1] has identified the S. aureus V8 protease (SspA) as both necessary and sufficient to drive itch during epicutaneous infection. We also observed that, compared to mice infected with wild-type (WT) MRSA, infection with sspA mutant isogenic strain which lacks V8 protease resulted in significantly reduced inflammation. Currently, V8 protease-driven host skin barrier and neuroimmune responses during infection remain poorly understood. Flow cytometric immune cell profiling shows differential neutrophil infiltration during infection with WT and sspA MRSA. Additionally, we found decreased expression of pro-inflammatory cytokines and neutrophil-recruiting chemokines in the infected skin with sspA MRSA compared to WT. We have also observed changes in S. aureus-induced epidermal and dermal innervation with Nav1.8+ sensory nerve fibers that we hope to further quantify in the context of microbe-neuron-immune crosstalk for host defense. Overall, we hypothesize that V8 protease plays a critical role in host-pathogen interaction by inducing inflammation with rapid innate immune response, dysregulating epidermal barrier by cleaving tight junction proteins and targeting cell death via caspase-dependent mechanisms, and promoting hyperinnervation of ii sensory nerves in the skin proximal to bacterial colonization. The aims of this thesis are to 1) characterize the skin barrier and immune responses to V8 protease, 2) determine how V8 protease impacts cell death mechanisms in keratinocytes and 3) quantify sensory innervation with bacteria localization in infected skin. Ultimately, understanding the role of V8 protease in S. aureus pathogenesis can inform the development of therapeutics to reduce itch, inflammation, and skin barrier damage in cutaneous diseases like atopic dermatitis.