Understanding the Role of Mitochondria in Driving Antiviral Inflammatory Responses

Aging is associated with immune dysfunction and increased risk of morbidity and mortality due to infectious diseases, as exemplified by the COVID-19 pandemic. To improve health outcomes in these populations we need novel therapeutics that can restore immune function. Targeting macrophages is a potential option. These cells are the first line of defence in most tissues and sense changes in the local microenvironment to initiate and regulate immune responses. Emerging evidence suggests aging induces an energy-deficient state that compromises macrophage function. It is unclear how these changes in cellular metabolism affect innate sensing and downstream antiviral responses. To investigate this, we developed young and old metabotypes for antiviral immune responses using murine bone marrow derived macrophages stimulated with viral ligands (TLR7 ligand; mimics ssRNA) and (TLR3 ligand; mimics dsRNA). In young cells, TLR7 engagement was associated with high levels of inflammatory cytokine production dependent on glycolysis for ATP production. TLR3 engagement was associated with a robust type I IFN response, requiring sustained OXPHOS activity for energy production. We found mitochondria superoxide production (mtROS) had differential effects on cytokine production following stimulation with these viral ligands, dampening cytokine production following TLR7 activation but increasing it following TLR3. In aging cells, reduced metabolic activity was associated with reduced cytokine production irrespective of the ligand used. This was linked to a reduced ability to modulate the main ROS producing ETC complexes and reduced mtROS production. We conducted a pilot study to evaluate if Bacillus Calmette-Guerin (BCG) can restore function in aged macrophages. BCG is a potent inducer of trained immunity and was used during the COVID-19 pandemic to protect against severe disease. Interestingly, we found that BCG treatment in vivo induced a trained phenotype in cells stimulated with TLR7 ligands and a tolerant phenotype following TLR3. In the old cells, these effects were more subtle, with indications of metabolic reprograming in favor of glycolysis. Collectively, our findings have the potential to inform novel therapeutic treatments to improve the innate response to viral infections, particularly in aging populations.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Health Sciences

Grantor dc:publisher

Carleton University

Year dc:date.issued

2025

Author dc:creator

• Sheridan, Mary-Elizabeth

Statement dc:rights

• Copyright © 2024 the author(s). Theses may be used for non-commercial research, educational, or related academic purposes only. Such uses include personal study, distribution to students, research and scholarship. Theses may only be shared by linking to the Carleton University Institutional Repository and no part may be copied without proper attribution to the author; no part may be used for commercial purposes directly or indirectly via a for-profit platform; no adaptation or derivative works are permitted without consent from the copyright owner.

Language dc:language.iso

en

DOI

10.22215/etd/2025-16457

OAI identifier oai:identifier

oai:carleton.scholaris.ca:20.500.14718/43600