DREADDs-Gi mediated inhibition of myeloid cells leads to anti-inflammatory signalling, shrinkage of microglia and acute heart failure in Cx3cr1Cre mice.

Little is known about the functional consequences of real-time changes to innate immune-cell states. While chemogenetic tools have become increasingly used for probing immune-brain interactions, the consequences of manipulating myeloid cell activity states remain poorly understood. In this study, we found that acute activation of Gi-coupled DREADDs (hM4Di) in Cx3cr1⁺ myeloid cells severely supresses cardiac function and induces a predominantly anti-inflammatory signalling state in mice. This surprising finding prompted further investigation. Using high-resolution ultrasound and electrocardiography, we show that although Cx3cr1⁺ mice have some reduced cardiac function already prior intervention, activation of hM4Di in Cx3cr1+ cells markedly reduces cardiac output and ejection fraction, and induces arrhythmias and increased heart-rate variability, which is absent in Cx3cr1Cre controls. hM4Di activation leads to decreased soma size, but not number, of IBA1⁺ microglia in the hypothalamus, while sections containing nucleus of the solitary tract remained unaffected. Plasma proteomic profiling using the Olink Mouse Exploratory panel revealed increased IL-10 alongside reductions in IL-23R and CCL20, indicating a shift toward systemic anti-inflammatory signalling. Furthermore, Olink analysis revealed a complex systemic signalling profile characterized by changes in several proteins associated with extracellular matrix remodelling, vascular regulation, and cell death pathways. Collectively, these findings demonstrate that Gi-DREADD inhibition of Cx3cr1⁺ myeloid cells produce coordinated central and peripheral immune changes and causes fatal cardiac dysfunction.