Hypoxia Sensing in Resident Cardiac Macrophages Regulates Monocyte Fate Specification following Ischemic Heart Injury

Myocardial infarction initiates cardiac remodeling and is central to heart failure pathogenesis. Following myocardial ischemia reperfusion injury, monocytes enter the heart and differentiate into diverse subpopulations of macrophages. The mechanisms and dynamics of monocyte differentiation within this context are unknown. We investigated the role of macrophage hypoxia sensing on monocyte differentiation following reperfused myocardial infarction. We show that deletion of Hif1a, a hypoxia response transcription factor, in resident cardiac macrophages led to increased remodeling and overrepresentation of a macrophage subset marked by arginase 1 (Arg1) expression. Arg1+ macrophages displayed an inflammatory gene signature and were predicted to represent an intermediate state within the monocyte differentiation cascade. Lineage tracing of Arg1+ macrophages revealed the existence of a monocyte differentiation trajectory consisting of multiple transcriptionally distinct macrophage states. We further showed that deletion of Hif1a in resident cardiac macrophages resulted in arrested progression through this trajectory and accumulation of an inflammatory intermediate state marked by persistent Arg1 expression. Depletion of the Arg1+ trajectory also results in increased heart remodeling following ischemic injury, likely due to the beneficial effects of macrophages downstream of Arg1+ macrophage differentiation. Collectively, our findings unveil distinct trajectories of monocyte differentiation and identify hypoxia sensing as an important determinant of monocyte differentiation following myocardial infarction. Overall design: Monocytes, macrophages, and dendritic cells from hearts were isolated via FACS and analzyed via scRNAseq using the 10x genomics platform. For macHif1aKO samples, experimental conditions were control and Hif1a KO monocytes/macrophages/dendritic cells 5 days after myocardial infarction. For Arg1ZsGr samples, fate labeled (ZsGr+) and non labeled (ZsGr-) monocytes/macrophages/dendritics cells were isolated from one of the two following experimental conditions. 1.) Hearts 2 and 30 days after myocardial infarction. 2.) control and Hif1a KO hearts 5 days after heart transplant. For Arg1DTR samples, monocytes, macrophages, and DCs were FACS sorted from control and Arg1DTR hearts 3 days aftermyocardial infarction. For resHif1aKO experiments, nuclei were isolated from control and resHif1aKO hearts 3 days after myocardial infarction using the 10X genomics nuclei isolation kit and FACS sorted based on DRAQ5 staining.