Abstract 1392 Juxtacrine signaling of cell surface IL-1α is an important driver of early atherosclerosis in hyperlipidemic mice

Previous studies suggest a differential effect of interleukin (IL)-1α and β signaling during atherogenesis. IL-1α, in contrast to IL-1ß, can be presented on the cell surface (csIL-1α) of immune cells. We characterized the role of IL-1α as the driver of atherosclerosis in a non-genetic PCSK9-AAV8 hyperlipidemia mouse model and investigated whether its surface expression on immune cells is responsible for their adhesion to endothelial cells.

Atherosclerosis was induced in wildtype mice (WT), Il1a^-/-, Nlrp3^-/-, and Il1b^-/- mice by a single injection of a mutant PSCK9-AAV8 virus and a high-fat Western diet (WTD, 21% fat, 0.2% cholesterol) for 12 weeks (1). Cholesterol levels were similarly increased in the four groups. Il1a was expressed independently of Nlrp3 in various tissues including aorta, liver, and adipose tissue. Il1a^-/- mice showed markedly reduced atherosclerosis development after 12 weeks WTD (-62% plaque size in the aortic root vs WTD control mice, p<0.05) and lower fat accumulation (Oil red O, -64%, p<0.05). In contrast, atherosclerosis development and plaque size did not differ between Nlrp3^-/-, Il1b^-/-, and hyperlipidemic WT mice (WTD control). While WTD control mice showed significantly increased serum concentrations of pro-inflammatory cytokines such as IL-1α, IL-1β and IL-6, no elevation of inflammatory cytokines was detected in the Il1a^-/-, Nlrp3^-/-, and Il1b^-/- animals, suggesting that the development of marked atherosclerosis in Nlrp3^-/-and Il1b^-/-mice is independent of the circulating secreted inflammatory cytokines.

To test the importance of cell-surface bound IL-1α, BMDCs from WT WTD, Nlrp3^-/-and Il1b^-/- mice were stimulated with LPS and showed a translocation of pro-IL-1α to the plasma membrane. Using a close proximity ligation assay (PLA), we found that activated monocytes bind to the IL-1 receptor on endothelial cells leading to the adhesion of monocytes to the endothelium. The addition of a neutralizing anti-IL-1α monoclonal antibody and an IL-1 receptor polyclonal antibody abolished monocyte adhesion.

In conclusion, this study indicates that IL-1α, but not Nlrp3 or IL-1β, is the main driver in early atherosclerosis development in mice. In particular, cell-surface bound IL-1α, but not the secreted form of IL-1α, is responsible for monocyte adhesion on endothelial cells. These data highlight the importance of juxtacrine signaling by cs-IL1α that is able to drive atherogenesis in the absence of circulating IL-1α, IL-1β and IL-6.

(1) Gaul S, Shahzad K, Medert R et al., Front Cardiovasc Med. 2022 Mar 8;9:813215. PMID: 35350534

Clin Res Cardiol (2023). https://doi.org/10.1007/s00392-023-02180-w
Juxtacrine signaling of cell surface IL-1α is an important driver of early atherosclerosis in hyperlipidemic mice
C. Mäder¹, T. Speer², A. Wirth³, J.-N. Boeckel¹, I. Gadi⁴, K. Shahzad⁴, B. Isermann⁴, M. Freichel³, S. Gaul¹, U. Laufs¹
¹Klinik und Poliklinik für Kardiologie, Universitätsklinikum Leipzig, Leipzig; ²Nephrologie, Universitätsklinikum Frankfurt, Frankfurt am Main; ³Pharmakologisches Institut, Universitätsklinikum Heidelberg, Heidelberg; ⁴Institut für Laboratoriumsmedizin, Klinische Chemie und Molekulare Diagnostik, Universitätsklinikum Leipzig, Leipzig;
Previous studies suggest a differential effect of interleukin (IL)-1α and β signaling during atherogenesis. IL-1α, in contrast to IL-1ß, can be presented on the cell surface (csIL-1α) of immune cells. We characterized the role of IL-1α as the driver of atherosclerosis in a non-genetic PCSK9-AAV8 hyperlipidemia mouse model and investigated whether its surface expression on immune cells is responsible for their adhesion to endothelial cells. Atherosclerosis was induced in wildtype mice (WT), Il1a^-/-, Nlrp3^-/-, and Il1b^-/- mice by a single injection of a mutant PSCK9-AAV8 virus and a high-fat Western diet (WTD, 21% fat, 0.2% cholesterol) for 12 weeks (1). Cholesterol levels were similarly increased in the four groups. Il1a was expressed independently of Nlrp3 in various tissues including aorta, liver, and adipose tissue. Il1a^-/- mice showed markedly reduced atherosclerosis development after 12 weeks WTD (-62% plaque size in the aortic root vs WTD control mice, p<0.05) and lower fat accumulation (Oil red O, -64%, p<0.05). In contrast, atherosclerosis development and plaque size did not differ between Nlrp3^-/-, Il1b^-/-, and hyperlipidemic WT mice (WTD control). While WTD control mice showed significantly increased serum concentrations of pro-inflammatory cytokines such as IL-1α, IL-1β and IL-6, no elevation of inflammatory cytokines was detected in the Il1a^-/-, Nlrp3^-/-, and Il1b^-/- animals, suggesting that the development of marked atherosclerosis in Nlrp3^-/-and Il1b^-/-mice is independent of the circulating secreted inflammatory cytokines. To test the importance of cell-surface bound IL-1α, BMDCs from WT WTD, Nlrp3^-/-and Il1b^-/- mice were stimulated with LPS and showed a translocation of pro-IL-1α to the plasma membrane. Using a close proximity ligation assay (PLA), we found that activated monocytes bind to the IL-1 receptor on endothelial cells leading to the adhesion of monocytes to the endothelium. The addition of a neutralizing anti-IL-1α monoclonal antibody and an IL-1 receptor polyclonal antibody abolished monocyte adhesion. In conclusion, this study indicates that IL-1α, but not Nlrp3 or IL-1β, is the main driver in early atherosclerosis development in mice. In particular, cell-surface bound IL-1α, but not the secreted form of IL-1α, is responsible for monocyte adhesion on endothelial cells. These data highlight the importance of juxtacrine signaling by cs-IL1α that is able to drive atherogenesis in the absence of circulating IL-1α, IL-1β and IL-6. (1) Gaul S, Shahzad K, Medert R et al., Front Cardiovasc Med. 2022 Mar 8;9:813215. PMID: 35350534
https://dgk.org/kongress_programme/jt2023/aP2215.html