Biology subjects

Timek, T. A.

Publications and source records attributed to Timek, T. A..

8 recordsLinked to original sources

bioRxiv2026

No Strings Attached: Predicting Tricuspid Valve Deformation Without In Vivo Chordal Geometry

Predictive biomechanical models of the tricuspid valve require accurate representation of the chordae tendineae, yet subject-specific chordal geometry is difficult to reconstruct from non-invasive imaging. Here, we adopt a framework for generating functionally equivalent synthetic chordae without prior knowledge of in vivo chordal attachments. To this end, we first adapt an anatomy-informed hyperelastic shape-matching method that establishes correspondence between end-diastolic and end-systolic leaflet configurations using chordal-mimicking forces, a rigid contact template, and a Gaussian-smoothed locally corrective pressure field. We then generate synthetic chordal insertion sites using zone-based rejection sampling and calibrate the unloaded length of each chord by combining reaction forces with the chordal stress-stretch relationship. The framework was evaluated using Texas TriValve 1.1, a high-fidelity finite element model of a human tricuspid valve validated against beating-heart echocardiography. We found that shape matching reproduced the target end-systolic geometry with a mean inter-surface distance of 0.29 {+/-} 0.35 mm. Moreover, synthetic chordal insertions faithfully reproduce end-systolic leaflet deformations. We subsequently examined synthetic chordal configurations containing 202, 225, and 450 insertions, informed by measurements from eight explanted human tricuspid valves. Here, increasing insertion number reduced mean inter-surface distance from 0.63 {+/-} 0.52 mm to 0.49 {+/-} 0.44 mm and reduced contact area errors from 3.52% to 0.59%. Across all configurations, mean maximum principal stretch errors in leaflet belly regions remained below 2.4%, while areal strain errors ranged from 0.34% to 10.01%. These results demonstrate that anatomically informed shape matching coupled with stress-based chordal calibration can reproduce tricuspid valve closure without explicit subject-specific chordal geometry. This framework provides a foundation for generating synthetic subvalvular anatomy for future imaging-derived, predictive tricuspid valve models.

bioengineering↗

bioRxiv2026

Sex-Specific Remodeling Phenotypes of the Tricuspid Valve Leaflets in an Ovine Model of Functional Tricuspid Regurgitation

BackgroundModerate to severe tricuspid regurgitation (TR) affects approximately 1.6 million Americans, yet more than 90% of patients with significant TR remain untreated. Women exhibit higher TR prevalence and more rapid disease progression than men, but the valve-intrinsic mechanisms underlying these sex disparities remain unclear. We hypothesized that sex and circulating testosterone influence tricuspid leaflet remodeling during right-sided pressure overload. MethodsFemale, castrated male (C-Male), and non-castrated male (NC-Male) adult Dorset sheep (n = 45) underwent pulmonary artery banding (PAB) and were followed for 13 {+/-} 1.5 weeks. Tricuspid leaflets were evaluated using morphometry, 3D profilometry, biaxial mechanical testing, histology, and bulk RNA sequencing. Sex-stratified differential gene expression was performed, and pathway enrichment of key biological processes were compared between sexes. ResultsPAB produced a uniform hemodynamic stimulus and equivalent moderate-to-severe TR across sex groups. Despite similar TR burden, leaflet remodeling diverged substantially by sex and castration status. C-Males developed the broadest remodeling phenotype, characterized by diffuse multi-leaflet growth, thickening, increased nuclei count, and low-strain stiffening. Females demonstrated more restricted leaflet and region-specific structural and cellular changes, along with circumferential low-strain stiffening. NC-Males exhibited preferential septal remodeling characterized by growth, thickening, increased nuclei count, and radial high-strain stiffening. Transcriptomic analysis revealed that females upregulated a focused matricellular remodeling program enriched for extracellular space organization (67 DEGs; FDR=0.025), whereas C-Males activated coordinated extracellular matrix and apoptosis-regulatory programs (388 DEGs; FDR=0.009). In contrast, NC-Males exhibited broad transcriptional response (406 DEGs) without significant pathway enrichment. ConclusionsTricuspid leaflet maladaptation during pressure overload is sex-dependent and testosterone-sensitive, involving distinct structural, mechanical, and transcriptional remodeling programs. These findings identify sex and testosterone status as previously under-recognized modulators of tricuspid valve remodeling and may help explain clinical sex disparities in TR progression. NOVELTY AND SIGNIFICANCE What is known?O_LIPulmonary hypertension and right ventricular pressure overload are linked to tricuspid leaflet remodeling through leaflet thickening, enlargement, and altered mechanical properties. C_LIO_LISex and sex-steroid hormones regulate fibrosis and extracellular matrix remodeling in cardiovascular tissues, but their role in tricuspid leaflet remodeling remains poorly understood. C_LI What new information does this article contribute?O_LISex and circulating testosterone status influence the magnitude, spatial distribution, biomechanical behavior, and transcriptional organization of tricuspid leaflet remodeling during pressure overload. C_LIO_LIFemales, castrated males, and non-castrated males develop distinct remodeling programs characterized by focused matricellular remodeling, coordinated extracellular matrix/apoptosis signaling, and diffuse transcriptional activation, respectively. C_LIO_LIThese findings identify sex and hormonal status as biological regulators of tricuspid valve maladaptation during functional tricuspid regurgitation. C_LI SummarySex differences in tricuspid regurgitation progression are recognized clinically, yet the mechanobiological basis underlying these disparities remains poorly understood. Using a controlled ovine model of pressure overload-induced secondary tricuspid regurgitation, we demonstrated that tricuspid leaflet maladaptation is a sex-specific and testosterone-sensitive process spanning structural, mechanical, and transcriptional scales. Under comparable hemodynamic overload, all animals developed significant tricuspid regurgitation, but leaflet remodeling patterns diverged substantially across sexes. Castrated male sheep exhibited the broadest maladaptive phenotype, characterized by diffuse multi-leaflet growth and thickening, increased low-stretch stiffness, and coordinated extracellular matrix and apoptosis-regulatory transcriptional programs. Female sheep developed more spatially restricted remodeling accompanied by a focused matricellular and extracellular matrix secretory response, whereas non-castrated male sheep demonstrated selective leaflet remodeling with broad, but less coordinated, transcriptional activation. Different remodeling patterns emerged in females and castrated males despite comparable testosterone levels, suggesting that testosterone depletion alone does not fully explain these tricuspid valve remodeling phenotypes. These findings establish sex and testosterone status as previously underrecognized biological regulators of tricuspid leaflet maladaptation and support the emerging view that valve leaflets are active, mechanobiologically responsive, participants in functional tricuspid regurgitation progression.

bioengineering↗

bioRxiv2026

The Tricuspid Valve Maladapts in a Pulmonary Hypertension Rat Model

Tricuspid valve regurgitation is a frequent valve lesion and, if severe, an independent predictor of mortality. In most patients, the valve itself has historically been considered intact. Yet, we have previously shown that the valve may not be an innocent bystander. In multiple sheep models, we have shown that the tricuspid valve thickens and stiffens. This remodeling may contribute to valve disease. Our goal is to extend our investigation of tricuspid valve remodeling to a rodent model, potentially opening scientific opportunity and enabling scaling our studies. To this end, we used pulmonary artery banding (PAB) in male rats to induce pressure overload and right ventricular remodeling. After excising the tricuspid valve, we quantified anterior leaflet morphology, mapped anterior leaflet thickness using optical coherence tomography, and evaluated anterior leaflet belly mechanics using a custom bulge testing system. Compared with SHAM controls, PAB increased anterior leaflet area. Moreover, anterior leaflets in PAB animals exhibited region-specific thickening, with the largest increases near the annulus. Finally, anterior leaflets in PAB animals were significantly less compliant. However, leaflet stiffening stemmed from aforementioned thickening, i.e., structural stiffening, not constitutive stiffening. Our findings demonstrate that we can reliably quantify leaflet area, thickness, and stiffness in the minuscule tricuspid valves of rats. We also show that tricuspid valve remodeling is not ovine-specific, but also affects the tricuspid valves of rats. Together, our findings support our hypothesis that tricuspid valves are not innocent bystanders in regurgitation, and that rats may serve as a scalable model system for future investigations. NEW & NOTEWORTHYUsing a rat pulmonary artery banding model of pulmonary hypertension, we show that chronic right ventricular pressure overload induces leaflet enlargement and region-specific thickness remodeling of the tricuspid valve. Although structural mechanical metrics change under pressure loading, normalization by thickness reveals that geometric remodeling rather than intrinsic material stiffening predominates. These findings highlight leaflet structural (mal)adaptation as a potential contributor to functional tricuspid regurgitation and underscore the importance of considering leaflet geometry in therapeutic strategies.

physiology↗

bioRxiv2026

Transcatheter Edge-to-Edge Repair Increases Annular Forces in In Vitro Whole Heart Preparations

BackgroundTricuspid transcatheter edge-to-edge repair (TEER) can induce an acute annuloplasty effect. While this has a therapeutic benefit, the mechanisms driving the reduction in annular size remain unclear. ObjectivesWe quantify the annular force induced by TEER in vitro in whole porcine heart preparations. We explore the impact of clipping different leaflet pairs on the TEER-induced annular forces. MethodsWe performed 49 interventions in 13 porcine hearts using a MitraClip XT. The clip was implanted between either the anterior-septal (AS), anterior-posterior (AP), or posterior-septal (SP) leaflet pairs. We also considered two-clip interventions between the combination of the AS-AP, AS-PS, or AP-PS leaflet pairs. For each intervention, we measured the right ventricular pressure, transvalvular flow rate, and force at eight locations around the annulus. ResultsTEER induced significant inward-pulling forces on the annulus. The maximum force was induced following an AS-PS two-clip intervention. A single AS clip induced the largest force among the one-clip interventions. Furthermore, the AP and AS-AP interventions induced the smallest annular forces. ConclusionsThe magnitude of the TEER-induced force depends on the intervention and number of clips implanted.

bioengineering↗

bioRxiv2025

The Tricuspid Valve is Transcriptionally Active During Prolonged Pressure Overload, Right-Sided Heart Failure, and Valve Regurgitation

BackgroundRight-sided heart failure (RHF), in the presence of tricuspid valve regurgitation (TR), can result from left-sided heart failure (LHF), pulmonary hypertension (PH), or heart malformations. The occurrence of RHF and TR represents a critical indicator of hospitalization rates and all-cause mortality. However, RHF has remained understudied, specifically with respect to the tricuspid valve, with few animal models to investigate the transformative processes and identify novel interventions. MethodsUsing the outbred sheep (Ovis aries) model of pulmonary artery banding (PAB) that induces RHF and TR, we generated three batches of ribosomal reduced RNA sequencing for 354 samples (NCBI SRA PRJNA1182691) containing right ventricle, left ventricle, each tricuspid valve leaflet, each mitral valve leaflet, and the pulmonary artery that represents both male and female sheep. The reads were assembled into a de novo sheep heart transcriptome for differential analysis. ResultsThe de novo sheep heart transcriptome enhanced transcript mapping of reads by 43-45% in the heart valves relative to the known sheep reference transcriptome. The identified transcripts produce validated tissue-specific pathways in ventricles (2,756 isoforms), pulmonary arteries (535 isoforms), and valves (1,215 isoforms), with transcript differences between the mitral and tricuspid valve involved in extracellular and endocrine signaling. The transcriptome also produced robust sex differences encoded by sex chromosomes and autosomes, highlighting epigenetic and sex hormone differences in the heart. Echocardiography and differential expression suggest that 8 weeks after PAB, the right ventricle has extensive morphological changes and known stress-induced lipid processing dysregulation. At 16-weeks post-PAB, tricuspid valve leaflets show the most significant transcriptional changes, with alterations in endocrine and immune pathway genes involved in cellular and extracellular remodeling. Genes within the tricuspid valve with differential expression and known human or mouse heart phenotypes include FLNA, LTBP4, VDR, CR2, PIGQ, CENPF, ACKR3, CR1, KLF2, and HIF3A. ConclusionsThis project highlights the complexity of heart valve tissues and their transcriptional activity in a sheep model of RHF. It suggests potential therapeutic interventions in heart valve remodeling in PAH, RHF, and TR. This work highlights the need for further human and model organism research into the dynamic valve cells and genes. Clinical PerspectiveO_ST_ABSWhat Is New?C_ST_ABS- Improved cardiac and valve specific transcriptome mapping through de novo transcriptome for clinically relevant ovine model. - Tricuspid valves show a sex dependent and active transcriptional response to pulmonary artery banding induced pulmonary hypertension and right sided heart failure. - Transcriptional phenotypes in ovine model mirror known human heart disease phenotypes. - Several transcripts identified with therapeutic potential for treating pressure overload conditions such as pulmonary hypertension. What Are the Clinical Implications?- Tricuspid valve remodeling due to pulmonary hypertension is accompanied by transcriptional alterations, and mechanical alterations alone may not be sufficient to address valve insufficiency. - Valve and ventricle sex specific gene expression changes following pulmonary hypertension indicate a potential role for hormonal influences and a need for personalized treatment strategies. - Improved patient outcomes for right heart failure, including diagnosis, early detection, and improved treatment strategies can be elucidated through the ovine model and supported through expanded interrogation of human tissues.

genomics↗

bioRxiv2024

Tricuspid valve maladaptation in sheep with biventricular heart failure: The posterior and septal leaflets

Tricuspid valve leaflets are dynamic tissues that can respond to altered biomechanical and hemodynamic loads. Each leaflet has unique structural and mechanical properties, leading to differential in vivo strains. We hypothesized that these intrinsic differences drive heterogeneous, disease-induced remodeling between the leaflets. Although we previously reported significant remodeling changes in the anterior leaflet, the responses among the other two leaflets have not been reported. Using a sheep model of biventricular heart failure, we compared the remodeling responses between all tricuspid leaflets. Our results show that the anterior leaflet underwent the most significant remodeling, while the septal and posterior leaflets exhibited similar but less pronounced changes. We found several between-leaflet differences in key structural and mechanical metrics that have been shown to contribute to valvular dysfunction. These findings underscore the need to consider leaflet-specific remodeling to fully understand tricuspid valve dysfunction and to develop targeted therapies for its treatment and more accurate computational models. STATEMENT OF SIGNIFICANCEOur study is significant as it advances our understanding of tricuspid valve remodeling by providing a comprehensive analysis of all three leaflets in a sheep model of biventricular heart failure. Unlike prior works that focused primarily on the anterior leaflet or generalized leaflet changes, we integrated morphological, histological, immunohistochemistry, biaxial mechanical testing, and two-photon microscopy to quantify differences between all three tricuspid valve leaflets (anterior, posterior, and septal) across multiple functional scales. This comprehensive approach highlights the unique remodeling response of each leaflet. Our findings offer critical insights for developing targeted therapeutic strategies and improving computational models of disease progression. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/613284v2_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@1e8efaforg.highwire.dtl.DTLVardef@1cfee04org.highwire.dtl.DTLVardef@136956org.highwire.dtl.DTLVardef@68c488_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2023

Untangling the mechanisms of pulmonary hypertension-induced right ventricular stiffening in a large animal model

BackgroundPulmonary arterial hypertension (PHT) is a devastating disease with low survival rates. In PHT, chronic pressure overload leads to right ventricle (RV) remodeling and stiffening; thus, impeding diastolic filling and ventricular function. Multiple mechanisms contribute to RV stiffening, including wall thickening, microstructural disorganization, and myocardial stiffening. The relative importance of each mechanism is unclear. Our objective is to use a large animal model as well as imaging, experimental, and computational approaches to untangle these mechanisms. MethodsWe induced PHT in eight sheep via pulmonary artery banding. After eight weeks, the hearts underwent anatomic and diffusion tensor MRI to characterize wall thickening and microstructural disorganization. Additionally, myocardial samples underwent histological and gene expression analyses to quantify compositional changes and mechanical testing to quantify myocardial stiffening. All findings were compared to 12 control animals. Finally, we used computational modeling to disentangle the relative importance of each stiffening mechanism. ResultsFirst, we found that the RVs of PHT animals thickened most at the base and the free wall. Additionally, we found that PHT induced excessive collagen synthesis and microstructural disorganization, consistent with increased expression of fibrotic genes. We also found that the myocardium itself stiffened significantly. Importantly, myocardial stiffening correlated significantly with excess collagen synthesis. Finally, our model of normalized RV pressure-volume relationships predicted that myocardial stiffness contributes to RV stiffening significantly more than other mechanisms. ConclusionsIn summary, we found that PHT induces wall thickening, microstructural disorganization, and myocardial stiffening. These remodeling mechanisms were both spatially and directionally dependent. Using modeling, we show that myocardial stiffness is the primary contributor to RV stiffening. Thus, myocardial stiffening may be an important predictor for PHT progression. Given the significant correlation between myocardial stiffness and collagen synthesis, collagen-sensitive imaging modalities may be useful for non-invasively estimating myocardial stiffness and predicting PHT outcomes.

physiology↗

bioRxiv2020

The tricuspid valve also maladapts: A multiscale study in sheep with biventricular heart failure

ObjectivesWe set out to determine the tricuspid valves propensity to (mal)adapt in disease. BackgroundTricuspid regurgitation (TR) is generally considered secondary to right and/or left ventricular disease without organic failure. Interestingly, we and others have previously shown the mitral valve (mal)adapts in functional mitral regurgitation, which may warrant reconsideration of its functional etiology. Whether the tricuspid valve similarly (mal)adapts is mostly unknown. MethodsWe evaluated the (mal)adaptive response of tricuspid valve anterior leaflets (TVALs) from an ovine model in which over-pacing (19 {+/-} 6 days) induced biventricular heart failure and TR (tachycardia-induced cardiomyopathy, TIC, n=33) and compared findings to those from a control group (n=17). In both groups, we performed proteomics, immunohistochemistry, histology, two-photon microscopy, collagen assays, leaflet thickness and morphology measurements, and biaxial mechanical tests. ResultsWe found metabolically active resident valvular cells in TIC TVALs which expressed activation and turnover markers. In TIC TVALs, we observed a 140% increase in collagen content (p=0.016), increased collagen dispersion regionally (p=0.017), a 130% increase in leaflet area (p=0.002), a 140% increase in thickness (p=0.006), and a 130% increase in radial stiffness (p=0.006). ConclusionsOur data suggest that TVALs (mal)adapt during TIC on all scales. This response is likely initiated by activated valvular cells, resulting in collagen turnover, and ultimately leading to thickening, area increase, and stiffening. Our data motivates future studies on the exact pathways leading to tricuspid (mal)adaptation and pharmacological therapeutic strategies for TR. Condensed AbstractIn most cases, tricuspid regurgitation is presumed to originate from valve extrinsic factors. We challenge this paradigm and hypothesize that the tricuspid valve maladapts, rendering the valve at least partially culpable for its dysfunction. As such, we set out to demonstrate that the tricuspid valve, indeed, maladapts in an ovine model of heart disease. In the anterior leaflets, we found alterations on the protein and cell-level, leading to maladaptation in the form of tissue growth, thickening, and stiffening. Our findings may initially motivate mechanistic pathway studies, and in the future, leaflet-targeted pharmacological therapeutic options for tricuspid regurgitation.

bioengineering↗