Identification of a Novel cGas/STING/Type I Interferon Specific Murine Cardiac Immune Landscape Following Radiation Therapy

Abstract

<h3>Purpose/Objective(s)</h3> Cardiotoxicity from radiation treatment to the chest is a late toxicity that has been shown to increase with radiation dose. While clinical parameters and advances in radiation techniques have resulted in lower doses to the heart, the pathophysiologic mechanisms of radiation cardiotoxicity remains a debated topic. We have previously demonstrated that, in murine models, radiation activates a delayed, fibroblast-specific type I interferon response that is dependent on the cytosolic nucleic acid sensor, cGas and its downstream signaling protein STING. Indeed, STING knockout mice exhibit a survival advantage in comparison to wild type mice following a radiation challenge to the heart (20Gy x 1). In this study, we sought to evaluate the consequences of the type I interferon activation on cardiac tissue-specific white blood cell population and identify novel radiation-dependent changes of cardiac immune infiltrates. <h3>Materials/Methods</h3> All animal experiments were performed in accordance with IACUC guidelines. C57BL/6 wild type mice and C57BL/6 Tmem173^gt (catalytically inactive STING) were treated with either sham or 12 Gy single dose to the heart using opposing tangents. At 1 month, hearts were harvested and CD45+ positive cells were immunoprecipitated and sent for 3' single cell RNA (scRNA) sequencing using 10X genomics. ScRNA data was analyzed using Seurat 3.0 <h3>Results</h3> Our results show that radiation induces the upregulation of a subset of cardiac macrophages, interferon inducible cardiac (IFNIC) macrophages. This effect is that is abrogated in mice lacking a functional STING. Furthermore, we observed a general activation of innate immunity as evidenced by increases in the dendritic cell population as well as upregulation of non-classical class I MHC molecules in non-IFNIC macrophages. More surprisingly, we find that there is a marked increase in tissue specific B cell population following radiation, an effect that is completely abolished in mice lacking a functional STING. <h3>Conclusion</h3> We describe for the first time the immune landscape of heart tissue following radiation. We find a previously undescribed infiltration of IFNIC macrophages and a robust activation of an innate immunity. Furthermore, we find a strong effector humoral adaptive response, likely downstream. These findings open the possibility to further understand the role of immune infiltrates in mediation of normal tissue toxicity following radiation.