340 - Contribution of Cardiac Macrophages and Interferon Signaling to the Therapeutic Effects of Cardiac Radiation in Heart Failure

L. Pedersen¹, Z. Guo¹, C. V. Ripoll¹, M. Ozcan¹, M. Pennino², D. Abhyankar², A. Klaas¹, F. Grogan¹, A. Sargazi¹, O. Ajijola², A. Javaheri¹, and C. Bergom¹; ¹Washington University School of Medicine, St. Louis, MO, ²University of California Los Angeles, Los Angeles, CA

Purpose/Objective(s): Heart failure (HF) affects ~2% of American adults and has a poor prognosis (50 % mortality <5 years), highlighting the need for new therapies. We recently published that over short timescales, 5 Gy cardiac radiation (RT) attenuates left ventricular (LV) dysfunction in humans with cardiomyopathy and in mice with HF, including mice with cardiomyocyte-specific overexpression of acyl CoA synthetase 1 (ACSL1). As failing hearts generally display more inflammation than healthy hearts, we investigated the impact of RT on cardiac inflammation and found that 5 Gy cardiac RT decreased cardiac macrophage abundance and non-cardiomyocyte cell proliferation in ACSL1. Thus, we hypothesized that reduced inflammation is important to the short-term cardioprotection induced by RT. In the current study, we aimed to validate our echocardiographic (echo) findings in ACSL1 mice at another major academic institution and to use RNA sequencing and macrophage depletion to interrogate inflammation after RT in this HF model. Materials/

Methods: Six-wk-old ACSL1 mice received 5 Gy cardiac RT or sham and were sent to our collaborator at another major academic institution. Echo was performed at 12 wks of age. In a second experiment, ACSL1 mice received the macrophage-depleting CSF1R mAb or control IgG beginning at 6-wks-old and continuing for 6 wks, at which time echo was used to assess cardiac function. Finally, bulk RNA seq and qPCR were performed on LV tissue collected from ACSL1 mice 6 wks after sham vs. 5 Gy cardiac RT. Unpaired student’s t-test (echo parameters) and 2-way ANOVA with Sidak’s correction (RNA seq, qPCR) were used to analyze data with alpha=0.05.
Results: RT significantly improved survival vs. sham treatment (p=0.0086). Echo revealed that RT ACSL1 mice had greater ejection fraction (p=0.0002) vs. sham mice. Macrophage depletion with CSF1R mAb improved ejection fraction (p=0.016) and end diastolic volume (p<0.0001) vs. IgG treatment. RNA seq revealed upregulation of genes related to interferon (IFN)-alpha and IFN-gamma in RT ACSL1 vs. sham, and qPCR showed upregulation of the IFN-responsive genes Isg15, Mx1, Ifit1, and Oas1a in RT ACSL1 mice vs. sham (p(RT)=0.0174).
Conclusion: In mice with HF, 5 Gy cardiac RT improved survival and attenuated cardiac dysfunction over short timescales. Macrophage depletion recapitulated RT-induced cardioprotection, suggesting that modulation of inflammation is a mechanism through which RT attenuates HF. Furthermore, irradiated ACSL1 mice had increased IFN signaling. These findings suggest that cardiac macrophages, as well as IFN signaling which can be related to macrophage function, may mediate the therapeutic effects of RT in our HF model. Future investigation should continue to interrogate the contribution of IFN signaling to the protective effect of RT on HF, which will inform potential translation to human patients with HF.