Exercise-induced cardioprotection through sex-specific remodelling in ageing murine hearts

Introduction

Ageing is an independent risk factor for heart failure, whereas exercise serves as a cardioprotective intervention. Sex differences influence age- and exercise-related cardiac remodelling. However, the underlying molecular regulation remains insufficiently characterised.

Purpose

This study aimed to identify sex-specific pathways influenced by exercise in the ageing heart.

Methods

Eight-week-old female (F) and male (M) C57BL/6J mice were randomly assigned to either voluntary wheel running (run) or sedentary (sed) conditions for 18 months (n=10/group). Cardiac function was assessed by serial echocardiography at baseline, 6, 12, and 18 months. At the 18-month endpoint, hearts were harvested for gravimetric and histological analyses. Single-nucleus RNA sequencing (snRNA-Seq) of whole hearts was performed to characterise exercise-responsive transcriptional programmes across cardiac cell populations for both sexes.

Results

Over the 18-month period, female mice ran significantly more than males. Exercise improved global systolic function in both sexes and partly mitigated the age-related decline in cardiac performance. Males exhibited a more pronounced hypertrophic response to exercise, reflected by increased changes in cross-sectional area of cardiomyocytes. In both sexes, exercise significantly reduced myocardial fibrosis (Masson's trichrome staining) and cardiac inflammation, as demonstrated by a lower accumulation of CD45-positive cells per mm². Notably, these effects were more prominent in females compared to males.

sn-RNASeq analysis revealed cardiomyocytes and fibroblasts as the cell populations with the greatest transcriptional response to exercise. In cardiomyocytes, relevant sex differences hint at divergent molecular cascades with exercise. Genes enriched in cardiomyocytes of females were related to pathways of energy metabolism, while genes differentially regulated in male cardiomyocytes were enriched for extracellular matrix organisation and contractile function, consistent with the more pronounced structural remodelling observed histologically in males. Ongoing in-depth bioinformatic analyses and validation will further reveal the upstream regulatory networks and key driver genes underlying these sex-specific transcriptional adaptations, thereby clarifying the molecular mechanisms by which long-term exercise differentially modulates cardiac remodelling and function in ageing female and male mice.

Conclusion

Exercise induces distinct and sex-specific remodelling mechanisms in the ageing heart, highlighting the importance of sex as a biological variable when developing therapeutic strategies to harness the cardioprotective benefits of exercise.