Abstract Body: Background: The human heart contains diverse cell types whose composition and gene expression change during development, aging, and disease. Notable sex differences exist in these processes, but the underlying genetic and cellular mechanisms remain incompletely understood.
Hypothesis: We hypothesize that these cardiac sex differences are initiated during development and are further shaped and maintained as the heart matures and ages. Characterizing these differences can provide mechanistic insight into sex biases in cardiovascular diseases.
Aims: To generate an age- and sex-resolved atlas of healthy human heart cells and identify sex-biased differences in cell type compositions and transcriptional programs.
Methods: We integrated and reanalyzed single-cell and single-nucleus RNA sequencing datasets comprising ~1 million cells from 64 healthy hearts (7 post-conception weeks to 75 years). Differential expression between male and female hearts was assessed using DESeq2 software, and cell-type proportion differences were evaluated using the propeller test.
Results: Sex-biased transcriptional and compositional differences were detected across multiple cardiac cell types, with the strongest seen in ventricular cardiomyocytes (vCMs). Subpopulation analysis identified a sex difference in the fatty acid-utilizing vCM subtype. Female vCMs showed increased expression of genes related to gap junction formation and less mature states, whereas male vCMs showed upregulation of genes involved in extracellular matrix organization and cell adhesion. These pathways are linked to cardiovascular diseases with known sex biases.
Conclusions: Our analysis of this age- and sex-resolved cell atlas reveals sex biases in transcription and composition of ventricular cardiomyocytes, highlighting potential molecular mechanisms underlying sex differences in cardiac physiology and disease susceptibility.