CRISPR‐MI and scRNA‐Seq Reveal TREM2's Function in Monocyte Infiltration and Macrophage Apoptosis During Abdominal Aortic Aneurysm Development

Abdominal aortic aneurysm (AAA) is a life-threatening aortic disease without effective medication. The infiltration of monocytes into the aortic wall is critical for AAA development, but the genes and pathways regulating this process remain to be elucidated. A novel method is developed for in vivo genome-wide CRISPR/Cas9 screening of monocyte infiltration (CRISPR-MI). By combining CRISPR-MI with single-cell RNA sequencing (scRNA-Seq), this study finds that Triggering receptor expressed on myeloid cells 2 (Trem2) is a negative regulator of monocyte infiltration into the aortic wall in early AAA induction. Trem2 knockout (KO) increases the expression of adhesion molecules, chemotactic receptors, and cytokines in monocytes. Trem2 KO promotes monocyte adhesion and migration in vitro and increases monocyte infiltration into the aortic wall in vivo. However, Trem2 KO attenuates AAA development because of prominent macrophage death at the late stage. In conclusion, CRISPR-MI is a powerful tool for studying genes underlying monocyte infiltration in disease conditions in vivo. These findings reveal a dichotomous role of Trem2 in monocyte recruitment and macrophage survival during AAA.