This study examined how sex and circulating testosterone modify remodeling of the tricuspid valve leaflets during right-sided pressure overload produced by pulmonary artery banding (PAB) in an ovine model. Although the PAB protocol induced equivalent moderate-to-severe tricuspid regurgitation (TR) across groups, the subsequent leaflet responses diverged by sex and castration status, indicating intrinsic valve remodeling programs that differ between females, castrated males, and non-castrated males.
Adult Dorset sheep (n = 45) were assigned to female, castrated male (C-Male), or non-castrated male (NC-Male) groups. All animals underwent pulmonary artery banding to impose right-sided pressure overload and were observed for a mean of 13 ± 1.5 weeks. The model produced a uniform hemodynamic stimulus and equivalent degrees of moderate-to-severe TR across the sex groups, providing a controlled setting to compare valve-intrinsic remodeling responses.
Tricuspid leaflets were evaluated using a multimodal approach: gross morphometry and 3D profilometry to assess leaflet size and shape, biaxial mechanical testing to quantify regional mechanical behavior, histology for cellular and matrix-level structure, and bulk RNA sequencing to profile transcriptional changes. Sex-stratified differential gene expression and pathway enrichment analyses were performed to compare biological processes activated in each group.
Despite comparable TR severity, leaflet structural remodeling differed substantially between groups. Castrated males (C-Males) developed the most extensive remodeling phenotype, characterized by diffuse growth across multiple leaflets, generalized leaflet thickening, and increased nuclei counts—findings consistent with broad tissue growth and cellular proliferation or infiltration.
Females exhibited a more restricted remodeling pattern, with structural and cellular changes that were leaflet- and region-specific rather than diffuse. Non-castrated males (NC-Males) showed preferential remodeling of the septal leaflet, including growth and thickening with increased nuclei counts, indicating localized leaflet adaptation in the presence of endogenous male sex hormones.
Mechanical testing revealed sex- and region-specific alterations in leaflet stiffness. C-Males demonstrated low-strain stiffening distributed across leaflets, consistent with alterations affecting tissue behavior at physiological low-strain ranges. Females showed circumferential low-strain stiffening, indicating changes primarily in the circumferential mechanical response of the leaflet tissue at low strains.
By contrast, NC-Males developed radial high-strain stiffening, notably in the septal leaflet, indicating altered mechanical behavior at higher strains in the radial direction. These distinct mechanical signatures suggest sex- and testosterone-dependent remodeling mechanisms that differentially affect leaflet load-bearing behavior under physiologic and supra-physiologic deformation.
Histologic analyses corroborated morphometric and mechanical findings. Increased nuclei counts were observed in groups with notable growth and thickening (C-Males and NC-Males septal leaflet), suggesting elevated cellularity accompanying structural remodeling. Females exhibited more localized cellular changes aligned with their region-specific structural remodeling. The source text reports these cellular differences but does not specify cell types, proliferation markers, or detailed matrix composition changes beyond increased nuclei and thickening.
Bulk RNA sequencing revealed distinct sex-stratified transcriptional responses to the PAB-induced pressure overload. Females upregulated a relatively focused matricellular remodeling program, with pathway enrichment for extracellular space organization (67 differentially expressed genes [DEGs]; false discovery rate, FDR = 0.025). This suggests targeted modulation of extracellular matrix organization in females.
Castrated males (C-Males) activated coordinated programs involving extracellular matrix regulation and apoptosis control (388 DEGs; FDR = 0.009), pointing to a broader, coordinated remodeling and cell survival/apoptosis regulatory response in the absence of circulating testosterone. Non-castrated males (NC-Males) exhibited a broad transcriptional response (406 DEGs) but without statistically significant pathway enrichment reported in the source, indicating widespread gene expression changes that did not coalesce into enriched pathways detectable by the analyses performed.
The findings indicate that tricuspid leaflet maladaptation in response to right-sided pressure overload is both sex-dependent and testosterone-sensitive. Despite identical hemodynamic insult and comparable TR severity, female, castrated male, and non-castrated male leaflets followed distinct structural, mechanical, and transcriptional remodeling programs. C-Males demonstrated diffuse growth and low-strain stiffening with coordinated extracellular matrix and apoptosis gene activation; females showed focused extracellular space remodeling and circumferential low-strain stiffening; and NC-Males had septal-predominant growth with radial high-strain stiffening and a broad, non-enriched transcriptional response.
These valve-intrinsic differences may contribute to the clinical observation that women have higher TR prevalence and faster disease progression than men. The data implicate circulating testosterone as a modulator of remodeling phenotype, but the source does not provide mechanistic interventions or causal proof beyond associations between castration status and remodeling patterns.
This work used an ovine PAB model with a follow-up of approximately 13 weeks; applicability to human TR progression and chronicity requires further study. The source did not report detailed cellular phenotyping beyond nuclei counts or specific matrix component quantification in this summary. One author disclosed a speaking arrangement with Edwards Lifesciences; other authors declared no conflicts. Funding was provided by the American Heart Association and the National Institutes of Health, as reported in the source.
Overall, the study identifies sex and testosterone status as under-recognized modulators of tricuspid valve remodeling and presents structural, mechanical, and transcriptional evidence supporting sex-specific leaflet maladaptation during pressure overload, which may help explain sex disparities in clinical TR progression.