Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Anatomy and Cell Biology

Supervisor

Whitehead, Shawn N.

2nd Supervisor

Cregan, Sean P

Co-Supervisor

Abstract

Microglia undergo a dynamic pro-inflammatory phenotypic shift in response to acute injury and disease. However, inappropriate microglia reactivity impairs homeostatic resolution and exacerbates neurodegeneration. The integrated stress response (ISR) is a putative signalling pathway mediating intrinsic and extracellular stress. Thus, the ISR is an attractive target for investigation as a novel modulator of microglia reactivity. In the present study, ISR activation is stimulated via toxin-mediated perturbations to proteostasis and validate the efficacy of pharmacological ISR inhibition in primary microglia in vitro. This study demonstrates that ISR-dependent, non-canonical priming and inflammasome activation are sufficient to induce pro-inflammatory cytokines release and paracrine stimulation of naïve microglia—further, ISR inhibition rescues survival, homeostatic morphology, and upregulation in phagocytic activity. These results implicate the ISR as a novel affecter of microglial activation. Therapeutic ISR manipulation may be a tangible target for mediating microglia behaviour, restoring brain homeostasis, and mitigating the deleterious effects of sustained neuroinflammation.

Summary for Lay Audience

Microglia are the immune cells of the central nervous system and first responders to injury and disease. While their transient activity is essential for maintaining brain health, sustained reactivity can lead to neuroinflammation and toxicity. Inappropriate microglia activation is commonly seen following brain trauma and disease and can exacerbate neurodegeneration. No therapies currently exist to mitigate inflammation, and the mechanisms contributing to microglia reactivity remain elusive. The Integrated Stress Response (ISR) is a stress signalling pathway that responds to various signals to restore homeostasis. However, sustained ISR activation can lead to the induction of proteins, which cause dysfunction and cell death. ISR activation is seen after stroke, brain trauma and in many neurodegenerative diseases. However, the ISR has not been studied well in microglia. Given the role of ISR in mediating cell homeostasis, this study aims to determine if ISR activity impacts inflammation in microglia. In the current study, the ISR is activated in microglia using toxins which cause protein dysfunction. Drugs that inhibit different proteins involved in ISR signalling were used to modulate ISR activity. This study demonstrates that ISR activation induced pro-inflammatory signalling and behaviour in microglia. Further, sustained ISR signalling results in the propagation of inflammation and cell death. Importantly, inhibition of the ISR leads to increased microglia survival, reduced inflammation and restoration of important behaviours required for brain health. The results of this study implicate the novel role of ISR activation in stimulating inflammatory microglia activation. Further, the ISR is a tangible therapeutic target to restore healthy microglia function and decrease neurodegeneration and toxicity caused by inflammatory microglia in the brain.

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Available for download on Saturday, August 30, 2025

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