Macrophage-enriched Sectm1a promotes efficient efferocytosis to attenuate ischemia/reperfusion-induced cardiac injury

Efficient clearance and degradation of apoptotic cardiomyocytes by macrophages (termed efferocytosis) are critical for inflammation resolution and restoration of cardiac function after myocardial ischemia/reperfusion (I/R). Here, we define secreted and transmembrane protein 1a (Sectm1a), a cardiac macrophage-enriched gene, as a modulator of macrophage efferocytosis in I/R hearts. Upon myocardial I/R, Sectm1a-KO mice exhibit impaired macrophage efferocytosis, leading to massive accumulation of apoptotic cardiomyocytes, cardiac inflammation, fibrosis, and consequently, exaggerated cardiac dysfunction. By contrast, therapeutic administration of recombinant SECTM1A protein significantly enhances macrophage efferocytosis and improves cardiac function. Mechanistically, SECTM1A can elicit autocrine effects on the activation of glucocorticoid-induced TNF receptor (GITR) at the surface of macrophages, leading to the upregulation of liver X receptor alpha (LXRa) and its downstream efferocytosis-related genes and lysosomal enzyme genes. Our study suggests that Sectm1a-mediated activation of Gitr/LXRa axis could be a promising approach to enhance macrophage efferocytosis for the treatment of myocardial I/R injury. Overall design: To dissect the potential mechanism underlying the established link between Sectm1a and macrophage efferocytosis, we re-analyzed our previous RNA-sequencing data generated from (wilde type) WT and Sectm1a knockout (KO) macrophages (M?s). RNA files of bone marrow derived M?s from WT and Sectm1a KO mice were generated. Directional polyA RNA-sequencing was performed by the Genomics, Epigenomics and Sequencing Core (GESC) at the University of Cincinnati. To fully capitalize the gene signature of the whole transcriptome, especially to capture lower amplitude signals (e.g., lower fold changes) from expression variation that would otherwise fall below the signal-to-noise significance cutoff, we first performed unbiased gene set enrichment analysis (GSEA) using whole M? transcriptomes. The volcano plot was created using the R package “EnhancedVolcano” and showed that there were 2117 significantly changed genes (FDR<0.1) out of 12987 genes used as input. We then performed gene ontology (GO) enrichment analysis on differentially expressed genes and focused on GO pathways related to efferocytosis. Our analysis results demonstrated that ablation of Sectm1a in M?s significantly reduced the expression of several sets of genes that are associated with the regulation of endocytosis and phagocytosis, phagocytotic engulfment, apoptotic cell clearance, and lysosome function.