Background:
Mosaic loss of Y chromosome (LOY) in blood cells is the most common acquired mutation, increases with age and has been linked to increased cardiovascular disease. Most recently, murine studies revealed that LOY induces cardiac fibrosis following left ventricular pressure overload by TAC mimicking aortic valve stenosis (AVS). As AVS is the prototypical age-related cardiovascular disease and diffuse cardiac fibrosis is the major determinant of impaired survival even after successful aortic valve replacement (TAVR), we hypothesized that LOY affects long-term outcome in male patients undergoing TAVR.

Methods: Using the previously validated digital droplet PCR (ddPCR) in DNA samples from peripheral blood cells (PBMC), the extent of LOY was assessed by quantifying the relative number of X and Y chromosomes by targeting a 6 bp sequence difference present between the AMELX and AMELY genes using a TaqMan-based method. For potential mechanistic insights, single cell RNA sequencing (scRNAseq) was used to differentiate the genetic signature of patient-derived monocytes lacking the Y chromosome from those harboring the Y chromosome.

Results: In a total of 362 male patients (median age = 82) with advanced AVS undergoing successful TAVR between February 2017 and August 2021 at the University Hospital of the Goethe University, Frankfurt. The extent of LOY ranged from -13.2 to 83.4%, and 48% of the patients had LOY > 10%. 3-year mortality increased with increasing extent of LOY. Using the ROC curve-derived Youden index revealed an optimal cut-off value of > 17% of LOY (X/Y ratio < 0.83) in blood cells to predict long-term mortality (see fig.A).  By multivariate analysis including all clinical and laboratory parameters reaching statistical significance in univariate analysis, the extent of LOY remained a significant (p<0.001) independent predictor of mortality in addition to EuroScore II and anemia. Mechanistically, scRNAseq analyses disclosed a pro-fibrotic polarization in gene signature of patient-derived circulating monocytes lacking the Y chromosome and activation of TGFß signalling via significant downregulation of TGFß inhibiting pathways (TGIF1/2,SMAD7) (see fig.B).

Conclusions: This is the first study to demonstrate that LOY in blood cells is associated with profoundly impaired long-term survival even after successful TAVR. Mechanistically, in line with very recent experimental data, the pro-fibrotic gene signature with enhanced TGFß signaling in patient-derived circulating monocytes supports a prominent role for cardiac fibrosis to contribute to the effects of LOY observed in male patients undergoing TAVR.