An Investigation into the Effects of Macrophage Polarisation on Interleukin-1 Expression

Macrophages are innate immune cells characterised by functional heterogeneity and plasticity. The prevailing dogma divides macrophages into two opposing subtypes: the pro-inflammatory M1 and anti-inflammatory M2 macrophages. Macrophages are also the main cell type that produces two powerful cytokines that drive chronic inflammation and adaptive immunity - interleukin (IL)-1α and IL-1β. Although the role of M1 macrophages as drivers of inflammation has been extensively studied, unravelling the function of M2s in inflammation still requires further investigation. The work presented in this thesis challenges the dogmatic division of M1/M2 cells as pro/anti-inflammatory, respectively. We demonstrate that M2 macrophages produced substantially more IL-1α and IL-1β following LPS treatment, compared to M0 or M1 macrophages, and we have validated these findings in vivo. This may have important implications for diseases with heightened M2 polarisation, where they could contribute to previously unrecognised pro-inflammatory, IL-1-driven phenomena. In addition, we identified novel mechanisms of IL-1 regulation in macrophages. We show that HECT E3 ligase inhibition led to dose-dependent stabilisation of IL-1α, and we also identified AREL1 and TRIP12 as prospective candidates that target IL-1α for degradation. These findings suggest that a reduced rate of IL-1 degradation resulting from defects in E3 ligase expression and/or activity might have detrimental effects in inflammatory diseases. Further investigations to identify the cause of amplified IL-1 in M2s guided us to explore TBK1 signalling, which revealed that TBK1 inhibition significantly decreased IL-1α in M2s, but increased IL-1β in M0 and M1 macrophages. We also observed that this subtype-specific effect on IL-1 was not dependent on type I interferon or IRF3 signalling. Thus, understanding the subtype and context-specific effects of TBK1 inhibition may have important implications in, for example, TBK1-driven diseases. Finally, we used mRNA sequencing to examine transcriptional changes potentially underlying IL-1α/β expression in LPS-treated M1/M2 macrophages, particularly to identify the molecular mechanism behind the heightened IL-1 expression in M2s. The analysis revealed that LPS-treated M2 macrophages retained the characteristic M2 polarisation markers and importantly, identified IGF-1 signalling as a candidate regulator of IL-1. We show that LPS-treated M2 macrophages secreted high levels of IGF-1 and that IGF-1R inhibition reduced IL-1α/β expression in M2s. Therefore, targeting IL-1 signalling in inflammatory diseases characterised by high levels of IGF-1 might be an important therapeutic strategy. To conclude, the work presented in this thesis enhances our understanding of IL-1α and IL-1β regulation in macrophages and should enable revaluation of the roles of macrophages in health and disease.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Krzyzanska, Dominika

Advisor dc:contributor.advisor

• Clarke, Murray

• innate immunity
• interleukin-1
• macrophage
• macrophage polarisation

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/225b8615-3826-4bca-8e97-afed51caee9f/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.99101

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/352954