Dr. Dylan Ryan

Macrophages are key innate immune cells essential for the detection of invading pathogens and in promoting protective host immunity. Following infection, pattern recognition receptor (PRR) activation is triggered by pathogen-associated molecular patterns (PAMPs). Notable examples of PRRs are the toll-like (TLR), RIG-like (RLR) and NOD-like (NLR) receptor families, which initiate remodelling of cellular metabolism in macrophages. Mitochondria are central to pathogen sensing and metabolic rewiring, serving as vital signalling hubs for the execution of macrophage effector functions. These effector functions range from mitochondrial reactive oxygen species (mtROS)-mediated bacterial killing to the activation of the NLRP3 inflammasome signalling complex, which triggers pyroptosis to limit bacterial dissemination. However, aberrant activation of the NLRP3 inflammasome can also exacerbate systemic immune responses and promote sepsis progression. NLRP3 activation is dependent on the release of newly synthesised and oxidised mitochondrial DNA (mtDNA), a process supported by the pyrimidine salvage enzyme cytidine/uridine monophosphate kinase 2 (CMPK2). My recent unpublished data has uncovered an unappreciated increase in de novo pyrimidine biosynthesis in macrophages, a pathway reliant on the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH). In parallel, pyrimidine salvage is promoted via induction of the cytosolic enzyme, uridine phosphorylase 1 (UPP1), which is also significantly increased in critically ill sepsis patients. How these pathways regulate macrophage function and septic shock is currently unknown. The main aim of this research is to understand how pyrimidine synthesis and salvage pathways regulate macrophage function, with a focus on mtDNA, NLRP3 inflammasome activation and sepsis.

This project will explore why people with inherited mitochondrial disease are often more vulnerable to severe infections. Mitochondria are widely known as the structures that generate energy inside our cells, but they also play an important role in controlling the immune system. The research will focus on harmful mutations in mitochondrial DNA, a major cause of primary mitochondrial disease, and investigate how these mutations alter the behaviour of immune cells. Although patients with these disorders frequently experience recurrent infections and inflammatory complications, the reasons for this remain poorly understood. This project aims to uncover the biological link between mitochondrial dysfunction and impaired host defence. The study will centre on macrophages, frontline immune cells that help the body detect and eliminate pathogens, such as bacteria and viruses. By combining advanced metabolic profiling, infection models and preclinical studies, the research will test whether mitochondrial DNA mutations drive these immune cells into a persistent `false alarm" state that weakens antibacterial defence and promotes damaging inflammation. It will also assess whether these abnormalities can be reversed using targeted therapeutic strategies. The findings are expected to provide new insight into infection risk in mitochondrial disease and may have wider relevance for understanding immune dysfunction in conditions such as sepsis, autoimmunity and ageing.