Abstract Body: Contemporary evidence supports neutrophils' complex roles beyond being the simple and powerful destruction tools in MI. However, our understanding remains limited. We especially lack the knowledge of how cGAS-STING regulates neutrophil functions in acute ischemia. The cGAS-STING pathway senses cytosolic DNA to produce IFN and ISGs and is a pillar of innate immunity. Early evidence suggested neutrophils did not express cGAS. Taking advantage of the improved detecting method, we revisited this topic because this pathway can play an essential role in neutrophil function in MI. Using purified neutrophils from WT and knockout mice (as control), we detected cGAS, STING, and IRF3 in these cells. To determine if cGAS-STING regulates neutrophil function, we first generated MI model in cGAS^-/-, STING^-/- mice, and their WT littermates and performed flow cytometry and RNA-seq analyses. We uncovered that inhibiting cGAS-STING decreases neutrophil production in bone marrow (BM) after ischemia. Interestingly, cGAS- and STING-deficient neutrophils express significantly higher levels of primary granule molecules such as MPO, Prtn3, Elane, Cts- (s, g, b, l) but much lower levels of the secondary and tertiary granule components, including Mmp9, Mmp8, Olfm4, Cd177, Lyz2, and Lyz1. Neutrophils acquire granules sequentially during differentiation. Therefore, our data suggest inhibiting cGAS-STING leads to a stagnated neutrophil differentiation in the BM and mobilizes CD101^- immature neutrophils into the circulation and MI hearts. Consistently, cGAS- and STING-deficient neutrophils release less MMP8 and MMP9 into the ischemic area. Ischemia does not trigger the degranulation of primary granules, as indicated by the minimal changes of CD63. Our data further suggest that TF C/EBP𝜹 functions downstream of cGAS-STING to promote neutrophil differentiation. Adoptive transfer experiments suggest the neutrophil-specific function of cGAS-STING. In conclusion, we identify cGAS-STING as a novel mechanism promoting emergency granulopoiesis and neutrophil differentiation after MI and uncover its functional implications in ischemia-induced remodeling. Studies using Mrp8-Cre-mediated cGAS-STING deletion in granulocyte/macrophage progenitors are in progress.