Background: Hematopoietic mosaic loss of Y chromosome (mLOY) increases with age and associates with increased cardiovascular disease incidence. Very recent experimental murine studies revealed that mLOY may enhance cardiac fibrosis by activation and infiltration of bone marrow-derived macrophages. Yet, specific signatures of hematopoietic LOY cells in HFrEF patients are missing.

Objective: Single-cell RNA sequencing (scRNAseq) offers unique potential to decode the genetic signature of circulating hematopoietic cells and assess the effects of mLOY in human leukocytes.

Methods and results: Transcriptomic profiles of immune cells were analyzed in 10 male patients with chronic HFrEF by scRNAseq. Cells of HFrEF patients were sorted by Y-chromosome carrier status as determined by expression of any of the Y-chromosome associated genes (Y-carriers), whereas cells lacking expression of these genes were classified as LOY cells. To gain insights as to how mLOY macrophages might mediate cardiac fibrosis and heart failure, we focused on the analysis of monocytes with and without Y-carrier status from HFrEF patients (29810 Y-carrier monocytes, 2205 LOY monocytes). Using a patient specific, paired data analysis, monocytes from LOY cells showed significantly reduced expression of TGF-B inhibiting genes (SMAD7, TGIF2) in LOY cells vs. Y-carrier cells. Opposingly, LOY cells showed elevated inflammation markers like S100A8 and CXCL8 as well as cell survival genes like NAMPT. GO terms derived from upregulated genes in LOY cells furthermore indicated enhanced RAGE and TLR signaling, both of which are known to enhance profibrotic signaling.

To model further how mLOY cells might influence healthy cardiac tissue, we added data from a public snRNA-seq dataset and assessed cell-cell communication, finding that Progranulin-Sortilin1 and Resistin signaling are strikingly increased in mLOY myeloid cells, which has consequences for endothelial dysfunction and mesenchymal cell activation.

Conclusions: This is the first study to decipher the genetic signature of LOY monocytes cells in HFrEF patients. Our results considerably extend very recent experimental findings in mice that LOY sensitizes macrophages to enhanced profibrotic signaling. The profibrotic transcriptome in monocytes due to diminished TGF-B inhibitory molecules and enhanced TLR4 signaling may causally contribute to the aggravation of heart failure by mLOY in patients with HFrEF.