Biology subjects

Butcher, J. T.

Publications and source records attributed to Butcher, J. T..

5 recordsLinked to original sources

bioRxiv2026

Geometry-Encoded Microtrenches Stabilize Endothelium on High Shear Biomaterial Surfaces

Maintaining a confluent, antithrombotic endothelium on cardiovascular biomaterial surfaces remains a major barrier to long-term hemocompatibility, as endothelial cells (ECs) rapidly denude under supraphysiological shear in prosthetic devices. Here, we hypothesized that mesoscale surface geometry ([~]100-200 {micro}m) could reorganize near-wall hemodynamics, preserving endothelial coverage and function under extreme shear. Engineered microtrenches were introduced onto an implant biomaterial to generate spatially defined shear environments. Under supraphysiological near-wall shear ([~]250 dyn/cm{superscript 2}), microtrenched geometries created attenuated shear and vorticity gradients. Endothelial monolayers were sustained in these flow domains for 120 hours, whereas flat controls rapidly denuded. Endothelial retention in 22.5{degrees} angled trenches increased dramatically, from an EC of 33 to 101 dyn/cm{superscript 2}. 45{degrees} angled trenches further increased endothelial shear resistance to an EC of 207 dyn/cm{superscript 2}. Endothelial monolayers demonstrated collective mechano-adaptation to ultra-high shear through VE-cadherin junction thickening and coordinated cytoskeletal and nuclear alignment. Mechanoadapted monolayers exhibited increased eNOS expression correlated with local shear and elevated nitrite production (45{degrees}: 50.4 {+/-} 6.1 {micro}M; 22.5{degrees}: 35.7 {+/-} 3.3 {micro}M; 0{degrees}: 28.4 {+/-} 6.8 {micro}M). In contrast, interfaces with abrupt shear transitions or elevated rotational flow exhibited reduced coverage, junctional thinning, and re-emergence of VCAM-1 and PAI-1, indicating inflammatory and pro-thrombotic activation. Structural, functional, and inflammatory readouts exhibited peak responses within a shared shear-vorticity regime. Multivariate regression identified shear-vorticity coupling as the dominant predictor of endothelial persistence, with optima clustering within a mechanical range ({approx}0.8-2.9 x 10 dyn{middle dot}cm-{superscript 2}{middle dot}s-{superscript 1}). These findings establish geometry-driven modulation of near-wall flow as a predictive, material-agnostic strategy for endothelialization and vasoprotection of high-shear cardiovascular implants.

bioengineering↗

bioRxiv2022

Shear and hydrostatic stress regulate fetal heart valve remodeling through YAP-mediated mechanotransduction

Clinically serious congenital heart valve defects arise from improper growth and remodeling of endocardial cushions into leaflets. Genetic mutations have been extensively studied but explain less than 20% of cases. Mechanical forces generated by beating hearts drive valve development, but how these forces collectively determine valve growth and remodeling remains incompletely understood. Here we decouple the influence of those forces on valve size and shape, and study the role of YAP pathway in determining the size and shape. The low oscillatory shear stress promotes YAP nuclear translocation in valvular endothelial cells (VEC), while the high unidirectional shear stress restricts YAP in cytoplasm. The hydrostatic compressive stress activated YAP in valvular interstitial cells (VIC), whereas the tensile stress deactivated YAP. YAP activation by small molecules promoted VIC proliferation and increased valve size. YAP inhibition suppressed the VIC proliferation and reduced valve size, but enhanced cell-cell adhesions between VEC thus maintaining an elongated shape. Finally, left atrial ligation was performed in chick embryonic hearts to manipulate the shear and hydrostatic stress in-vivo. The restricted flow in the left ventricle induced a globular and hypoplastic left atrioventricular (AV) valves with an inhibited YAP expression. By contrast, the right AV valves with sustained YAP expression grew and elongated normally. This study establishes a simple yet elegant mechanobiological system by which transduction of local stresses regulates valve growth and remodeling. This system guides leaflets to grow into proper sizes and shapes with the ventricular development, without the need of a genetically prescribed timing mechanism. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/517814v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@167b319org.highwire.dtl.DTLVardef@11f2f07org.highwire.dtl.DTLVardef@4894f1org.highwire.dtl.DTLVardef@12a66ab_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2021

Endothelial alpha globin is a nitrite reductase

Small artery vasodilation in response to hypoxia is essential for matching oxygen supply to tissue oxygen demand. One source of hypoxic dilation via nitric oxide (NO) signaling is nitrite reduction by erythrocytic hemoglobin (2{beta}2). However, the alpha subunit of hemoglobin is also expressed in resistance artery endothelium and localized to myoendothelial junctions, a subcellular domain that contacts underlying vascular smooth muscle cells. We hypothesized that nitrite reduction mediated by endothelial alpha globin may occur at myoendothelial junctions to regulate hypoxic vasodilation. To test this concept, we created two novel mouse strains: one lacking alpha globin specifically in endothelium (EC Hba1{Delta}/{Delta}) and one where alpha globin is mutated such that its inhibitory association with endothelial NO synthase (eNOS) is prevented (Hba1WT/{Delta}36-39). In EC Hba1{Delta}/{Delta} or Hba1WT/{Delta}36-39 mice hemoglobin levels, hematocrit and erythrocyte counts were unchanged from littermate controls. Loss of the full alpha globin protein from the endothelium in the EC Hba1{Delta}/{Delta} model was associated with decreased exercise capacity and decreased intracellular nitrite utilization in hypoxic conditions. These effects were not seen in Hba1WT/{Delta}36-39 animals. Hypoxia induced vasodilation was decreased by 60% in isolated thoracodorsal arteries from EC Hba1{Delta}/{Delta}, while infusion of erythrocytes only partially rescued the dilatory response. Lastly, unlike other models where blood pressure is decreased, EC Hba1{Delta}/{Delta} blood pressure was not altered in response to hypoxia. Overall, we conclude that alpha globin in the resistance artery endothelium can act as a nitrite reductase to provide a local vasodilatory response to hypoxia.

physiology↗

bioRxiv2020

Uncovering Transcriptional Dark Matter via Gene Annotation Independent Single-Cell RNA Sequencing Analysis

Single-cell RNA sequencing (scRNA-seq) enables the study of cell biology with high resolution. scRNA-seq expression analyses rely on the availability of a high quality annotation of genes in the genome. Yet, as we show here with scRNA-seq experiments and analyses spanning human, mouse, chicken, mole rat, lemur and sea urchin, gene annotations often fail to cover the full transcriptome of every cell type at every stage of development, in particular for organisms that are not routinely studied. To overcome this hurdle, we created a scRNA-seq analysis routine that recovers biologically relevant information beyond the scope of the best available gene annotation. This is achieved by performing single-cell expression analysis on any region in the genome for which transcriptional products are detected. Our routine identifies transcriptionally active regions (TARs) using a hidden Markov model, generates a matrix of expression levels for all TARs across all cells in a dataset, performs single-cell TAR expression analysis to identify TARs that are biologically significant, and then annotates biologically significant TARs using gene homology analysis. This procedure leverages single-cell expression analyses as a filter to direct annotation efforts to biologically significant transcripts in complex tissues and thereby uncovers biology to which scRNA-seq would otherwise be in the dark.

bioinformatics↗

bioRxiv2020

Spatiotemporal single-cell RNA sequencing of developing hearts reveals interplay between cellular differentiation and morphogenesis

Single-cell RNA sequencing is a powerful tool to study developmental biology but does not preserve spatial information about cellular interactions and tissue morphology. Here, we combined single-cell and spatial transcriptomics with new algorithms for data integration to study the early development of the chicken heart. We collected data from four key ventricular development stages, ranging from the early chamber formation stage to the late four-chambered stage. We created an atlas of the diverse cellular lineages in developing hearts, their spatial organization, and their interactions during development. Spatial mapping of differentiation transitions revealed the intricate interplay between cellular differentiation and morphogenesis in cardiac cellular lineages. Using spatially resolved expression analysis, we identified anatomically restricted gene expression programs. Last, we discovered a stage-dependent role for the small secreted peptide, thymosin beta-4, in the coordination of multi-lineage cellular populations. Overall, our study identifies key stage-specific regulatory programs that govern cardiac development.

genomics↗