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Biofilm Infection Dysregulates Ceramide Metabolism Compromising Functional Wound Closure Of The Skin
Nandini Ghosh1, Mithun Sinha, Ph.D2, Shomita Steiner, Ph.D2, Dayanjan S. Wijesinghe, Ph.D3, Savita Khanna, Ph.D2, Daniel J. Wozniak, Ph.D1, Gayle M. Gordillo, MD2, Sashwati Roy, Ph.D2, Chandan K. Sen, Ph.D2.
1The Ohio State University, Columbus, OH, USA, 2Indiana University, Indianapolis, IN, USA, 3Virginia Commonwealth University, Richmond, VA, USA.

Background: Cutaneous lipids, 50% of which are ceramides (Cer), have structural and signaling roles in skin. The current study is based on our previous finding that biofilm infected wounds may appear visually closed but remain functionally open because of lack of barrier function of the repaired skin. Such defectively closed wounds display high trans-epidermal water loss (TEWL). The objective of this study was to test whether cutaneous ceramide depletion following wound biofilm infection compromises skin barrier function. Methods: Full thickness burn wounds (2”x2”) were created on pigs and followed up to 56 days post-wounding with or without infection of Pseudomonas aeruginosa or Pseudomonas ceramidase mutant strains. Analyses of wound closure (digital planimetry), skin barrier function (TEWL), ceramide levels (lipidomics), PPARδ, ABCA12, expression (IHC, quantitative RT-PCR) was performed. Results: Bacterial ceramidases were over expressed (~500 fold, n=4, p<0.05) in biofilm-infected pig wound tissues. Immunohistochemical studies demonstrated that biofilm-infection caused focal erosion of ceramides in the porcine skin. Lipidomic analyses showed that long chain ceramides were depleted in biofilm-infected wounds. Such depletion of ceramide was however absent in biofilm-infection caused by ceramidase mutant of Pseudomonas. Depletion of cutaneous ceramides downregulated the transcription factor PPARδ resulting in compromised transport of lipid molecules to stratum corneum by ABCA12, a lipid transporter. We further observed that such depletion of ceramide could be rescued by bacterial ceramidase inhibitor ceramidastin (n=5, p<0.05). Conclusion: Excessive microbial ceramidases in biofilm infected wounds deplete host skin ceramides. Such disruption of ceramide homeostasis in the skin causes compromised barrier function of the skin. Considering that two-thirds of all chronic wounds are estimated to be biofilm infected, this study provides a mechanistic insight to the observation that biofilm infected wounds remain functionally open.

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