Abstract Body (Do not enter title and authors here): Background: Atherosclerosis is the development of lipid-rich plaques in the medial layer of arteries. Atherosclerosis is the underlying pathology leading to myocardial infarction and stroke. Atherosclerotic plaques start to develop at a young age and increase over the lifespan. Age is the strongest clinical risk factor for development of atherosclerosis. Atherosclerosis is characterized by chronic inflammation. As a result of inflammation there is infiltration of different immune cells including macrophages and T cells. Recent studies have shown that cytotoxic CD8⁺ T cells are pro-atherogenic; however, CD8⁺ T cells are a diverse class of cells. Subset-specific phenotypes and mechanisms are unknown.
Methods and Results: To test the hypothesis that aging affects T-cell phenotype and its functions, we performed high throughput RNA sequencing on spleens from young (3-months, n=3) and aged (21-months, n=3) mice. We performed differential gene expression and pathway analysis and validated gene expression by qPCR. We also analyzed our single cell sequencing data from human and mouse atherosclerotic plaques. We identified that inflammation, blood coagulation, and activation of complement cascade pathways are upregulated in aged mice. Furthermore, we found increased expression of Granzyme K in the spleens of aged mice. In our single cell sequencing data from atherosclerotic plaques we found enrichment of CD8+T-cells expressing Granzyme k in mice. Expression of Granzyme K was also significantly higher in plaques from older (> 65 years) compared to the younger cohorts (< 65 years) in human patients. We further validated that effector memory CD8⁺ T cells express very high granzyme K compared to naïve CD8⁺ T cells. Interestingly, effector memory cells also express transcription factors Tigit and Eomes.
Conclusion: Granzyme K expressing CD8⁺ T cells are novel class of immune cells that accumulates with age in atherosclerotic plaques in mice and humans. Future research will explore how targeting these cells can be used to manipulate atherogenesis.