Pseudomonas aeruginosa elastase down-regulates host inflammatory responses by degrading cytokines and chemokines: a non-healing wound perspective

Mariena J.A. van der Plas^1,2*Manoj Puthia¹Seow Theng Ong³Kajsa Arkelius¹Ann-Charlotte Strömdahl¹Marta Butrym¹Magnus Rasmussen^4,5Navin Kumar Verma³Artur Schmidtchen^1,6

• ¹Division of Dermatology and Venereology, Department of Clinical Sciences, Lund University, Lund, Sweden
• ²LEO Foundation Center for Cutaneous Drug Delivery, Department of Pharmacy, University of Copenhagen, Copenhagen, Denmark
• ³Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
• ⁴Division of Infection Medicine, Department of Clinical Sciences, Faculty of Medicine, Lund University, Lund, Skane County, Sweden
• ⁵Department of Infectious Diseases, Skåne University Hospital, Lund, Sweden
• ⁶Dermatology, Skane University Hospital, Lund, Sweden

Non-healing venous leg ulcers are characterized by dysfunctional wound healing and frequently exhibit an absence of classical inflammatory signs, despite substantial bacterial loads of the Gram-negative pathogen Pseudomonas aeruginosa. To investigate this clinical observation, we used a porcine wound infection model and complementary in vitro cell and enzymatic activity assays. In vivo, P. aeruginosa infected wounds resulted in attenuated inflammatory responses compared to those infected with Staphylococcus aureus. Protease activity was elevated in P. aeruginosa-infected wounds relative to uninfected controls, while pro-inflammatory cytokine levels decreased over time. In vitro analyses employing cell cultures, wildtype and mutant strains, and clinical isolates from venous ulcers and blood, revealed that P. aeruginosa elastase (LasB) degrades a range of pro-inflammatory cytokines (G-CSF, GM-CSF, IFN-γ, IL-1ra, IL-6, IL-12p40, IL-23, TNF-α) and chemokines (Gro-α, IL-8, IP-10, MCP-1, MIP-1α, MIP-1β) in the extracellular milieu, without impacting cell morphology, transcription factor activation, or subsequent intracellular cytokine production. Correspondingly, wound fluids from non-healing ulcers colonized/infected with P. aeruginosa degraded cytokines, whereas fluids from uninfected wounds did not. Collectively, our findings indicate that P. aeruginosa modulates host inflammation by degrading cytokines and chemokines.