Delayed wound healing can cause significant issues for immobile and ageing individuals as well as those living with co-morbid conditions such as diabetes, cardiovascular disease, and cancer. These delays increase a patient’s risk for infection and, in severe cases, can result in the formation of chronic, non-healing ulcers (e.g., diabetic foot ulcers, surgical site infections, pressure ulcers and venous leg ulcers). Chronic wounds are very difficult and expensive to treat and there is an urgent need to develop more effective therapeutics that restore healing processes. Sustained innate immune activation and inflammation are common features observed across most chronic wound types. However, the factors driving this activation remain incompletely understood. Emerging evidence suggests that the composition and structure of the wound microbiome may play a central role in driving this dysregulated activation but the cellular and molecular mechanisms underlying these processes require further investigation. In this review, we will discuss the current literature on: 1) how bacterial populations and biofilms contribute to chronic wound formation, 2) the role of bacteria and biofilms in driving dysfunctional innate immune responses in chronic wounds, and 3) therapeutics currently available (or underdevelopment) that target bacteria-innate immune interactions to improve healing. We will also discuss potential issues in studying the complexity of immune-biofilm interactions in chronic wounds and explore future areas of investigation for the field.

Pseudomonas aeruginosa is a Gram-negative environmental and human opportunistic pathogen highly adapted to many different environmental conditions. It can cause a wide range of serious infections, including wounds, lungs, the urinary tract, and systemic infections. The high versatility and pathogenicity of this bacterium is attributed to its genomic complexity, the expression of several virulence factors, and its intrinsic resistance to various antimicrobials. However, to thrive and establish infection, P. aeruginosa must overcome several barriers. One of these barriers is the presence of oxidizing agents (e.g., hydrogen peroxide, superoxide, and hypochlorous acid) produced by the host immune system or that are commonly used as disinfectants in a variety of different environments including hospitals. These agents damage several cellular molecules and can cause cell death. Therefore, bacteria adapt to these harsh conditions by altering gene expression and eliciting several stress responses to survive under oxidative stress. Here, we used PubMed to evaluate the current knowledge on the oxidative stress responses adopted by P. aeruginosa. We will describe the genes that are often differently expressed under oxidative stress conditions, the pathways and proteins employed to sense and respond to oxidative stress, and how these changes in gene expression influence pathogenicity and the virulence of P. aeruginosa. Understanding these responses and changes in gene expression is critical to controlling bacterial pathogenicity and developing new therapeutic agents.

Hypoxia-inducible factor-1α (HIF-1α) is an important regulator of glucose metabolism and inflammatory cytokine production in innate immune responses. Viruses modulate HIF-1α to support viral replication and the survival of infected cells, but it is unclear if this transcription factor also plays an important role in regulating antiviral immune responses. In this study, we found that short and long dsRNA differentially engage TLR3, inducing distinct levels of proinflammatory cytokine production (TNF-α and IL-6) in bone marrow–derived macrophages from C57BL/6 mice. These responses are associated with differential accumulation of HIF-1α, which augments NF-κB activation. Unlike TLR4 responses, increased HIF-1α following TLR3 engagement is not associated with significant alterations in glycolytic activity and was more pronounced in low glucose conditions. We also show that the mechanisms supporting HIF-1α stabilization may differ following stimulation with short versus long dsRNA and that pyruvate kinase M2 and mitochondrial reactive oxygen species play a central role in these processes. Collectively, this work suggests that HIF-1α may fine-tune proinflammatory cytokine production during early antiviral immune responses, particularly when there is limited glucose availability or under other conditions of stress. Our findings also suggest we may be able to regulate the magnitude of proinflammatory cytokine production during antiviral responses by targeting proteins or molecules that contribute to HIF-1α stabilization.

Chronic wounds are challenging to treat, cause significant pain, prolong hospitalization, and in the most severe cases, may lead to infection and/or amputations. Understanding the pathophysiology of chronic wounds is crucial for creating novel therapies that promote healing. Bacterial biofilms have been shown to impair wound healing and promote a low-grade inflammatory response. In chronic wounds, macrophages are chronically activated in a pro-inflammatory state and are unable to promote tissue repair. It is unclear what interactions occur between biofilms and macrophages to drive this persistent pro-inflammatory activation. Emerging evidence suggests that mitochondrial reprogramming plays a key role in fine-tuning the macrophage inflammatory response to bacterial infection. In this study, we found that treatment of bone marrow-derived macrophages with conditioned medium containing secreted factors from single-species biofilms of Staphylococcus aureus or Pseudomonas aeruginosa resulted in different patterns of mitochondrial reprogramming and inflammatory responses. S. aureus conditioned media induced a low-grade inflammatory response, associated with a transient reprogramming of the mitochondria to support mitochondrial reactive oxygen species and inflammatory cytokine production. Alternatively, P. aeruginosa conditioned media induced a stronger inflammatory response associated with sustained mitochondrial reprogramming that resulted in prolonged accumulation of mtROS, which eventually resulted in cell death. When macrophages were stimulated with an anti-inflammatory signal, IL-4, they were unable to repolarize to an antiinflammatory state and demonstrated terminal reprogramming towards sustained inflammation.Our findings imply that secreted factors from biofilms (e.g., LPS) may alter mitochondrial function to rewire macrophages to promote prolonged inflammation in chronic wounds. The bacterial species that are present in wounds have a significant impact on this reprogramming. imposter syndrome. When my experiments failed and I began to self-doubt, your patience and constructive feedback helped me continue to progress. You were always positive, motivational, and committed, so I could tackle complicated research problems with the support I needed. You encouraged me to take the initiative to seek solutions and be resilient despite facing setbacks. Not only was I able to work with a fantastic team of people in your lab, but you also fostered collaboration between several research groups that allowed me to target my project from a multidisciplinary approach and conduct high-impact translational research. I am indebted to my co-supervisor and thesis advisory committee members, Dr. Joerg Overhage and Dr. Daniel Pletzer for their infinite guidance and insightful discussions, comments, and expertise throughout my thesis that has helped to improve my scientific approach. I would also like to acknowledge the collaborative efforts of Drs. Katrina DeZeeuw and Jonah Marek.Your expertise greatly helped in the development of th...