Transcriptomes in healthy and CHB fetal hearts

Given that diseases associated with anti-SSA/Ro autoantibodies such as systemic lupus erythematosus and Sjögren’s syndrome are linked with an upregulation of IFN and type I IFN-stimulated genes, including Sialic Acid-Binding Ig-Like Lectin 1 (Siglec-1), a receptor on monocytes/macrophages, recent attention has focused on a potential role for IFN and IFN-stimulated genes in the pathogenesis of congenital heart block (CHB). Accordingly, three approaches were leveraged to address the association of IFN, IFN-stimulated genes, and the phenotype of macrophages in affected fetal cardiac tissue: a) cultured healthy human macrophages transfected with hY3, an anti-SSA/Ro-associated single-stranded RNA, b) RNA isolated from freshly sorted human leukocytes/macrophages after Langendorff perfusion of three fetal hearts dying with CHB and three healthy gestational age-matched hearts, and c) autopsy tissue from three additional human CHB hearts and one healthy heart. TLR ligation of macrophages with hY3 led to the upregulation of a panel of IFN transcripts, including SIGLEC1, a result corroborated using qPCR. Utilizing independent and agnostic bioinformatics approaches, CD45+CD11c+ and CD45+CD11c- human leukocytes flow sorted from the CHB hearts highly expressed type I IFN response genes inclusive of SIGLEC1. Furthermore, Siglec-1 expression was identified in the septal region of several affected fetal hearts. These data now provide a link between IFN, IFN-stimulated genes, and the inflammatory and possibly fibrosing components of CHB, positioning Siglec-1-positive macrophages as integral to the process. three CHB hearts of gestational ages 19, 20 and 23 and three healthy hearts of gestational ages 18, 22, and 23 weeks were utilized.