Biology subjects

Zaffran, S.

Publications and source records attributed to Zaffran, S..

9 recordsLinked to original sources

bioRxiv2026

Morphogenesis of the muscular ventricular septum of the mouse heart is driven by retinoic acid signalling to myocardium

The mammalian heart is divided into four chambers by septa that isolate systemic and pulmonary circulation and are hotspots of congenital heart defects (CHD). The muscular ventricular septum develops between left and right ventricular cardiomyocytes derived from the first and second heart fields. Despite its clinical importance, mechanisms underlying development of the ventricular septum are poorly understood. Here we show that myocardial reception of retinoic acid (RA) signalling regulates formation of the compact septal core. Activation of a dominant negative RA receptor in second heart field-derived myocardium during septal morphogenesis results in a deep interventricular cleft and bifid cardiac apex. This phenotype is preceded by ectopic trabecular contributions to a RA-independent septal primordium. Molecular analysis implicates defective cardiomyocyte maturation and impaired RAC1 activation in mutant hearts. These results support an infolding and RA-dependent fusion model of septal morphogenesis, providing new insights into ventricular development and the origins of CHD.

developmental biology↗

bioRxiv2025

EGFR-Mediated Mechanotransduction in Aortic Valve Cells: A Key Pathway in Response to Wall Shear Stress

AimBlood flow-induced mechanical forces, particularly wall shear stress (WSS), play a fundamental role in aortic valve remodeling and maturation. Dysregulation of these processes contributes to age-related valve diseases, such as aortic stenosis and regurgitation. While epidermal growth factor receptor (EGFR) signaling has been implicated in valve development, its role in mechanotransduction remains unclear. This study aims to investigate how EGFR regulates WSS-induced signaling in valvular cells and explore its interaction with the mechanosensitive ion channel PIEZO1. Methods and ResultsTo investigate the role of EGFR in valvular cell mechanotransduction, we used conditional Egfrflox allele to selectively delete Egfr in valvular cells. Histological analysis revealed increased valve leaflet thickness and hyperproliferation of mesenchymal cells when Egfr was deleted both endothelial (Tie2-Cre lineage) and mesenchymal (Sm22-Cre lineage) cells. This was accompanied by a reduction in maturation-related genes (Egr1, Nos3, Tgf-{beta}) and extracellular matrix (ECM) components. We previously demonstrated that Egr1 expression is regulated by WSS in valvular endothelial cells, prompting further exploration of Egr1s role in valvular cells. In vitro, Egr1 overexpression and shRNA-mediated knockdown confirmed its role in regulating Nos3, Col1a1, and Tgf-{beta}, key mediators of valve remodeling. Using a pulsatile WSS-mimicking device, we found that WSS induces Erk1/2 phosphorylation and Egr1 expression in valvular cells, both of which were abolished by EGFR inhibition. However, direct EGFR activation via EGF failed to replicate WSS-induced Egr1 expression, suggesting the involvement of additional mechanosensitive pathways. Pharmacological studies further revealed that PIEZO1 inhibition impaired WSS-induced Egr1 expression, while PIEZO1 activation (via YODA) mimicked WSS effects on Erk1/2 phosphorylation and Egr1 expression. These findings suggest a functional interaction between EGFR and PIEZO1 in mechanotransduction, linking mechanical forces to key molecular pathways in valve remodeling. ConclusionOur findings establish EGFR as a critical mediator of WSS-induced mechanotransduction in valve remodeling, working in synergy with PIEZO1 to regulate flow-sensitive transcription factors such as Egr1. This study provides new insights into the molecular mechanisms governing valve maturation and highlights potential therapeutic targets for age-related valve pathologies linked to abnormal WSS responses. Translational PerspectiveOur study highlights the pivotal role of EGFR and the mechanosensitive ion channel PIEZO1 in aortic valve cell responses to wall shear stress (WSS), offering new insights into valve remodeling. The findings suggest that dysregulated EGFR signaling contributes to valve thickening and stenosis, key factors in age-related valvular heart disease. By identifying EGFR-PIEZO1 as a critical mechanotransduction pathway, our work provides a potential therapeutic target for early intervention in aortic valve disease. Modulating EGFR or PIEZO1 activity could help mitigate pathological valve remodeling, presenting novel strategies for treating or preventing degenerative valve disorders.

developmental biology↗

bioRxiv2024

Multi-modal refinement of the human heart atlas during the first gestational trimester

1.Forty first-trimester human hearts were studied to lay groundwork for further studies of principles underlying congenital heart defects. We first sampled 49,227 cardiac nuclei from three fetuses at 8.6, 9.0, and 10.7 post-conceptional weeks (pcw) for single-nucleus RNA sequencing, enabling distinction of six classes comprising 21 cell types. Improved resolution led to identification of novel cardiomyocytes and minority autonomic and lymphatic endothelial transcriptomes, among others. After integration with 5-7 pcw heart single-cell RNAseq, we identified a human cardiomyofibroblast progenitor preceding diversification of cardiomyocyte and stromal lineages. Analysis of six Visium sections from two additional hearts was aided by deconvolution, and key spatial markers validated on sectioned and whole hearts in two- and three-dimensional space and over time. Altogether, anatomical-positional features including innervation, conduction and subdomains of the atrioventricular septum translate latent molecular identity into specialized cardiac functions. This atlas adds unprecedented spatial and temporal resolution to the characterization of human-specific aspects of early heart formation.

developmental biology↗

bioRxiv2023

Cardiopharyngeal Mesoderm specification into cardiac and skeletal muscle lineages in gastruloids.

Cardiopharyngeal mesoderm contributes to the formation of the heart and head muscles. However, the mechanisms governing cardiopharyngeal mesoderm specification remain unclear. Indeed, there is a lack of an in vitro model replicating the differentiation of both heart and head muscles to study these mechanisms. Such models are required to allow live-imaging and high throughput genetic and drug screening. Here, we show that the formation of self-organizing or pseudo-embryos from mouse embryonic stem cells (mESCs), also called gastruloids, reproduces cardiopharyngeal mesoderm specification towards cardiac and skeletal muscle lineages. By conducting a comprehensive temporal analysis of cardiopharyngeal mesoderm establishment and differentiation in gastruloids and comparing it to mouse embryos, we present the first evidence for skeletal myogenesis in gastruloids. By inferring lineage trajectories from the gastruloids single-cell transcriptomic data, we further suggest that heart and head muscles formed in gastruloids derive from cardiopharyngeal mesoderm progenitors. We identify different subpopulations of cardiomyocytes and skeletal muscles, which most likely correspond to different states of myogenesis with "head-like" and "trunk-like" skeletal myoblasts. These findings unveil the potential of mESC-derived gastruloids to undergo specification into both cardiac and skeletal muscle lineages, allowing the investigation of the mechanisms of cardiopharyngeal mesoderm differentiation in development and how this could be affected in congenital diseases.

developmental biology↗

bioRxiv2021

Clinical and Genetic insights in a tertiary care center cohort of patients with bicuspid aortic valve

BACKGROUNDto describe spectrum of valve function in bicuspid aortic valve (BAV) patients referred to a tertiary care center and to investigate genetic pathways associated with valve degeneration. METHODSAll consecutive patients with BAV were prospectively included from 2014 to 2018. BAV was defined according to embryologic and Sievers classifications. Clinical and echo variables were compared according to aortic valve function. Aortic valve tissues were collected from BAV patients (n=15) operated for severe aortic stenosis (AS-BAV, n=7) or aortic regurgitation (AR-BAV, n=8). RT-qPCR was performed to compare gene expression level in AS-BAV, AR-BAV and controls corresponding to healthy tricuspid aortic valves collected on human heart explant immediately after transplantation (n=5). RESULTSOut of 223 adults with BAV, mean age 53{+/-}17 years, 83% had left-right coronary cusps fusion, 80% Sievers type 1 BAV and 49% aortopathy. Twenty-four patients had normal valve function, 66 patients had AS-BAV, 91 patients had AR-BAV and 40 patient had AR+AS BAV. BAV phenotype did not predict neither AS-BAV nor AR-BAV (all p>0.1). By multivariable analysis, age >50 (41.6[10.3-248.2],p<0.001) and presence of raphe(12.8[2.4-87.4],p<0.001) were significantly associated with AS-BAV and male gender of AR-BAV(5[1.6-16.4], p=0.005). RT-qPCR revealed overexpression of RUNX2 in AS-BAV (17.67{+/-}1.83 vs 3.25{+/-}0.93, p=0.04), and overexpression of COL1A1 (4.01{+/-}0.6vs2.25{+/-}0.5,p=0.03) and FLNA (23.31{+/-}7.5vs1.97{+/-}0.3,p=0.03) in AR-BAV. CONCLUSIONSThis prospective study confirmed high prevalence of valve dysfunction at first diagnosis of BAV in a referred population. Clinical and echo variables are poorly associated with BAV dysfunction. The leaking or stenotic processes could be both supported by dysregulation of specific genetic pathways

genetics↗

bioRxiv2020

Hox-dependent coordination of cardiac progenitor cell patterning and differentiation

Perturbation of addition of second heart field (SHF) cardiac progenitor cells to the poles of the heart tube results in congenital heart defects (CHD). The transcriptional programs and upstream regulatory events operating in different subpopulations of the SHF remain unclear. Here, we profile the transcriptome and chromatin accessibility of anterior and posterior SHF sub-populations at genome-wide levels and demonstrate that Hoxb1 negatively regulates differentiation in the posterior SHF. Spatial mis-expression of Hoxb1 in the anterior SHF results in hypoplastic right ventricle. Activation of Hoxb1 in embryonic stem cells arrests cardiac differentiation, whereas Hoxb1-deficient embryos display premature cardiac differentiation. Moreover, ectopic differentiation in the posterior SHF of embryos lacking both Hoxb1 and its paralog Hoxa1 results in atrioventricular septal defects. Our results show that Hoxb1 plays a key role in patterning cardiac progenitor cells that contribute to both cardiac poles and provide new insights into the pathogenesis of CHD.

developmental biology↗

bioRxiv2019

Piezo1 is required for outflow tract and aortic valve development.

Aims-During embryogenesis, the onset of circulatory blood flow generates a variety of hemodynamic forces which reciprocally induce changes in cardiovascular development and performance. It has been known for some time that these forces can be detected by as yet unknown mechanosensory systems which in turn promote cardiogenic events such as outflow tract and aortic valve development. PIEZO1 is a mechanosensitive ion channel present in endothelial cells where it serves to detect hemodynamic forces making it an ideal candidate to play a role during cardiac development. We sought to determine whether PIEZO1 is required for outflow tract and aortic valve development. Methods and results-By analysing heart development in zebrafish we have determined that piezo1 is expressed in the developing outflow tract where it serves to detect hemodynamic forces. In particular, we have found that mechanical forces generated during the cardiac cycle activate Piezo1 which triggers nitric oxide to be released in the outflow tract. Consequently, disrupting Piezo1 signalling leads to defective outflow tract and aortic valve development and indicates this gene may be involved in the etiology of congenital heart diseases. Based on these findings, we analysed genomic data generated from a cohort of bicuspid aortic valve patients and identified 3 probands who each harboured a novel variant in PIEZO1. Subsequent in vitro and in vivo assays indicates that these variants behave as dominant negatives leading to an inhibition of normal PIEZO1 mechanosensory activity and defective aortic valve development. Conclusion-These data indicate that the mechanosensitive ion channel piezo1 is required for OFT and aortic valve development and, furthermore, dominant negative variants of PIEZO1 appear to be associated with BAV in humans.

developmental biology↗

bioRxiv2018

A human cell model of cardiac pathophysiological valvulogenesis

Genetically modified mice have advanced our understanding of valve development and related pathologies. Yet, little is known regarding human valvulogenesis in health and diseases. Genuine human in vitro models that reproduce valvular (patho)biology are thus needed. We here developed a human pluripotent stem cell-derived model fit to decode the early steps of human valvulogenesis and to recapitulate valve disease traits in a dish.\n\nUsing cellular based, single cell omics-informed and in vivo-validated approaches, we derived a population of pre-valvular endocardial cells from a pluripotent stem cell source. These human prevalvular cells (HPVCs) expressed gene patterns conforming to the atrio-ventricular canal (AVC) endocardium signature originally established in E9.0 mouse embryos. In fact, HPVC treated with BMP2, cultured onto mouse AVC cushions, or transplanted into the AVC of embryonic mouse hearts, underwent endothelial-to-mesenchymal transition and expressed markers of valve interstitial cells of different valvular layers demonstrating tissue functionality. HPVCs also differentiated into tendinous/chondrogenic cells in line with the valvular repertoire. Extending this valvulogenic model to patient specific iPS cells, we recapitulated features of mitral valve prolapse and uncovered that dysregulation of the SHH pathway is likely to be at the origin of the disease thus providing a putative therapeutic target.\n\nHuman pluripotent stem cells recapitulate early valvulogenesis and provide a powerful model to systematically decipher the origin and lineage contribution of different valvular cell types in humans as well as to study valve diseases in a dish.

developmental biology↗

bioRxiv2018

Ectopic expression of Hoxb1 induces cardiac and craniofacial malformations

Members of the large family of Hox transcription factors are encoded by genes whose tightly regulated expression in development and in space within different embryonic tissues confer positional identity from the neck to the tips of the limbs. Many structures of the face, head and heart develop from cell populations expressing few or no Hox genes. Hoxb1 is the member of its chromosomal cluster expressed in the most rostral domain during vertebrate development, but never by the multipotent neural crest cell population anterior to the cerebellum. We have developed a novel floxed transgenic mouse line, CAG-Hoxb1,-EGFP (CAG-Hoxb1), which upon recombination by Cre recombinase conditionally induces robust Hoxb1 and eGFP over-expression. When induced within the neural crest lineage, pups die at birth. A variable phenotype develops from E11.5 on, associating frontonasal hypoplasia/aplasia, micrognathia/agnathia, major ocular and forebrain anomalies, and cardiovascular malformations. Neural crest derivatives in the body appear unaffected. Transcription of effectors of developmental signaling pathways (Bmp, Shh, Vegfa) and transcription factors (Pax3, Sox9) is altered in mutants. These outcomes emphasize that repression of Hoxb1, along with other paralog group 1 and 2 Hox genes, is strictly necessary in anterior cephalic NC for craniofacial, visual, auditory and cardiovascular development.

developmental biology↗