Human Valve Research Articles

17 Numerical study of imaged-based human mitral valve coupled with the left ventricle

Mitral valve (MV) disease due to rheumatic fever is probably the greatest heart valve problem, leading to scarring and distortion of the valve tissue with consequent incompetence and stenosis. For example, MV regurgitation (MR), a condition in which MV cannot close tightly, allows blood to flow backward in heart and may induce heart dilatation. If left untreated, severe MR can cause left ventricular failure, atrial fibrillation, pulmonary hypertension, and even death. In this talk, we will present an integrated model of MV coupled with the left ventricle (LV). The model is derived from clinical images and takes into account of the important valvular features, left ventricle contraction, nonlinear soft tissue mechanics, fluid structure interaction, and most importantly, the MV-LV interaction. The integrated MV and LV model can simulate the cardiac function both in diastole and systole with detailed structural and fluid dynamics. Although the model is a step towards simulating physiologically realistic situation, improvements are needed in order to achieve subject specific modelling, associated not only with geometry, but also with material properties and boundary conditions. We are eager to communicate with clinicians to improve our model and understand changes, due to various pathological conditions.

Toxic influence of detergents on human mesenchimal stromal cells during graft repopulation

Detergents are effective decellularization agents in order to obtain cell-free matrixes. However, the toxicity of residual detergent prevents the adhesion of cells to the matrix and the realization of their functions. In this study, the degree of influence of residual detergents on mesenchymal stromal cells after a series of washes was investigated. The human pulmonary valve were treated in three ways: 1% solution of sodium dodecyl sulfate, 1% solution of sodium deoxycholate and a combination of these solutions with the reduction of the concentration to 0.5%. After each of 8 steps washing buffer were collected. We investigated influence of residual detergents on cytotoxicity and effect on the metabolic activity of MSCs. Histologic analysis showed sufficient tissue decellularization in all groups. Matrixes were washed by successive incubations with 200 ml of phosphate buffer. Detergent concentrations in all samples ceased to be toxic only to the 4-cycle wash, and had no effect on the metabolism and viability of human MSCs. After 4-8 washing cycles decellularized pulmonary trunk fragments were successfully settled by mesenchymal stromal cells. Thus, a few successive washing fabrics pulmonary valve after decellularization reduce residual detergent to a safe level and lead to successful repopulation of acellular scaffolds with MSCs.

CD133 antibody conjugation to decellularized human heart valves intended for circulating cell capture

The long term efficacy of tissue based heart valve grafts may be limited by progressive degeneration characterized by immune mediated inflammation and calcification. To avoid this degeneration, decellularized heart valves with functionalized surfaces capable of rapid in vivo endothelialization have been developed. The aim of this study is to examine the capacity of CD133 antibody-conjugated valve tissue to capture circulating endothelial progenitor cells (EPCs). Decellularized human pulmonary valve tissue was conjugated with CD133 antibody at varying concentrations and exposed to CD133 expressing NTERA-2 cl.D1 (NT2) cells in a microflow chamber. The amount of CD133 antibody conjugated on the valve tissue surface and the number of NT2 cells captured in the presence of shear stress was measured. Both the amount of CD133 antibody conjugated to the valve leaflet surface and the number of adherent NT2 cells increased as the concentration of CD133 antibody present in the surface immobilization procedure increased. The data presented in this study support the hypothesis that the rate of CD133+ cell adhesion in the presence of shear stress to decellularized heart valve tissue functionalized by CD133 antibody conjugation increases as the quantity of CD133 antibody conjugated to the tissue surface increases.

Personalized screening intervals for biomarkers using joint models for longitudinal and survival data.

Screening and surveillance are routinely used in medicine for early detection of disease and close monitoring of progression. Motivated by a study of patients who received a human tissue valve in the aortic position, in this work we are interested in personalizing screening intervals for longitudinal biomarker measurements. Our aim in this paper is 2-fold: First, to appropriately select the model to use at the time point the patient was still event-free, and second, based on this model to select the optimal time point to plan the next measurement. To achieve these two goals, we combine information theory measures with optimal design concepts for the posterior predictive distribution of the survival process given the longitudinal history of the subject.

Increased Infiltration of Extra-Cardiac Cells in Myxomatous Valve Disease.

Mutations in the actin-binding gene Filamin-A have been linked to non-syndromic myxomatous valvular dystrophy and associated mitral valve prolapse. Previous studies by our group traced the adult valve defects back to developmental errors in valve interstitial cell-mediated extracellular matrix remodeling during fetal valve gestation. Mice deficient in Filamin-A exhibit enlarged mitral leaflets at E17.5, and subsequent progression to a myxomatous phenotype is observed by two months. For this study, we sought to define mechanisms that contribute to myxomatous degeneration in the adult Filamin-A-deficient mouse. In vivo experiments demonstrate increased infiltration of hematopoietic-derived cells and macrophages in adolescent Filamin-A conditional knockout mice. Concurrent with this infiltration of hematopoietic cells, we show an increase in Erk activity, which localizes to regions of MMP2 expression. Additionally, increases in cell proliferation are observed at two months, when hematopoietic cell engraftment and signaling are pronounced. Similar changes are observed in human myxomatous mitral valve tissue, suggesting that infiltration of hematopoietic-derived cells and/or increased Erk signaling may contribute to myxomatous valvular dystrophy. Consequently, immune cell targeting and/or suppression of pErk activities may represent an effective therapeutic option for mitral valve prolapse patients.

Ischemic postconditioning altered microRNAs in human valve replacement

BackgroundAlthough the involvement of microRNAs (miRNAs) has been intensively studied in myocardial infarction, there is no report on the regulation of miRNAs by ischemic postconditioning in patients undergoing cardiac surgery. We aim to explore the regulation of miRNAs by ischemic postconditioning in double valve replacement. Materials and methodsIn this prospective, controlled clinical study, consecutive 30 patients undergoing double valve replacement were enrolled. The patients were randomized into two groups, namely an ischemic postconditioning (IPO) group (n = 15) and a control (CON) group (n = 15). For ethical considerations, samples of right atrial muscle were harvested, respectively, 10 min before cardiopulmonary bypass (pre-CPB) and 5 min after aortic declamping (post-CPB) for analysis of miRNAs, genes and apoptosis. ResultsCompared with the CON group, miR-1 was downregulated, whereas miR-21 was upregulated, and BCL2 messenger RNA (mRNA) was upregulated, whereas BAX mRNA and programmed cell death 4 mRNA remained unchanged in the IPO group. Likewise, a significant increase in BCL2 protein and a striking decrease in BAX protein were observed in the IPO group when compared with those in the CON group. The IPO group showed a significantly smaller increase of terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling-positive myocytes after CPB than CON group. ConclusionsIschemic postconditioning could regulate miR-1, miR-21, and downstream effectors and resulted in actual attenuation of apoptosis in patients undergoing valvular heart surgery.

Cardiac telocytes are double positive for CD34/PDGFR‐α

Telocytes (TCs) are a distinct type of interstitial cells, which are featured with a small cellular body and long and thin elongations called telopodes (Tps). TCs have been widely identified in lots of tissues and organs including heart. Double staining for CD34/PDGFR-β (Platelet-derived growth factor receptor β) or CD34/Vimentin is considered to be critical for TC phenotyping. It has recently been proposed that CD34/PDGFR-α (Platelet-derived growth factor receptor α) is actually a specific marker for TCs including cardiac TCs although the direct evidence is still lacking. Here, we showed that cardiac TCs were double positive for CD34/PDGFR-α in primary culture. CD34/PDGFR-α positive cells (putative cardiac TCs) also existed in mice ventricle and human cardiac valves including mitral valve, tricuspid valve and aortic valve. Over 87% of cells in a TC-enriched culture of rat cardiac interstitial cells were positive for PDGFR-α, while CD34/PDGFR-α double positive cells accounted for 30.25% of the whole cell population. We show that cardiac TCs are double positive for CD34/PDGFR-α. Better understanding of the immunocytochemical phenotypes of cardiac TCs might help using cardiac TCs as a novel source in cardiac repair.

Combined dynamic predictions using joint models of two longitudinal outcomes and competing risk data.

Nowadays there is an increased medical interest in personalized medicine and tailoring decision making to the needs of individual patients. Within this context our developments are motivated from a Dutch study at the Cardio-Thoracic Surgery Department of the Erasmus Medical Center, consisting of patients who received a human tissue valve in aortic position and who were thereafter monitored echocardiographically. Our aim is to utilize the available follow-up measurements of the current patients to produce dynamically updated predictions of both survival and freedom from re-intervention for future patients. In this paper, we propose to jointly model multiple longitudinal measurements combined with competing risk survival outcomes and derive the dynamically updated cumulative incidence functions. Moreover, we investigate whether different features of the longitudinal processes would change significantly the prediction for the events of interest by considering different types of association structures, such as time-dependent trajectory slopes and time-dependent cumulative effects. Our final contribution focuses on optimizing the quality of the derived predictions. In particular, instead of choosing one final model over a list of candidate models which ignores model uncertainty, we propose to suitably combine predictions from all considered models using Bayesian model averaging.

A translational “humanised” porcine model for transcatheter mitral valve interventions: the neo inferior vena cava approach

Preclinical studies and translational animal models are fundamental for the development of new clinical interventions. Compared to human anatomy, pigs present a more anterior heart position in the chest which may jeopardise the imaging and testing of devices designed to be delivered to the human mitral valve. To imitate human anatomy, we developed a novel model to "humanise" a pig heart. The creation of a neo inferior vena cava with a Dacron tube grafted to the right atrium was tested for transseptal delivery of an experimental mitral annuloplasty device in 35 animals. In 15 animals with native anatomy a conventional right transfemoral access was used. Imaging guidance was achieved with intracardiac or epicardial echocardiography. In all transfemoral approaches (n=15), the delivery of the device was unsuccessful and the handling was dissimilar to a human implant. In all neo-cava approaches (n=35), the handling and manoeuvring were as expected in humans, the targets were reached as intended and all procedures but one were successful. A translational "humanised" animal model with the creation of a neo cava eliminates the differences between pig and human anatomy and is suitable for testing human grade devices.

Abstract 440: Increased Migration and Proliferation of Human Venous Valve Wall Smooth Muscle Cells are Mediated by FGF2

Introduction: Lesions causing coronary and peripheral vein graft failure often occur at valves. To test the hypothesis that intrinsic differences in cells of the valve wall contribute to graft failure we measured cell migration from tissue explants and migration and proliferation of cultured cells from valve and non-valve sections of human saphenous vein (HSV). Methods: After removal of endothelium, HSVs were dissected into an outer wall with adventitia and some media and an inner wall with intima and some media. Cell migration from explants and migration (microchemotaxis chambers) and proliferation of cultured cells at passage 6 were measured. Results: Cells migrated faster from valve compared to non-valve tissue of the inner wall (Figure A; P<0.01, N=24 veins), but not the outer wall (not shown). PDGF-BB- or serum-mediated migration of valve inner wall smooth muscle cells (VSMC) was greater than with non-valve SMCs (NVSMC; P<0.05, N=6 pairs, 6.5 ± 1.2 vs. 4.2 ± 0.8 fold of control for PDGF-BB and 4.7 ± 0.6 vs. 3.4 ± 0.4 for serum). VSMC also proliferated faster than NVSMC after stimulation with PDGF-BB plus 2% serum (P<0.01, N=6 pairs, 3.3 ± 0.4 vs. 2.2 ± 0.2 fold of control). Finally, a blocking antibody to FGF2 had no effect on PDGF-mediated migration or proliferation of NVSMC (migration: IgG 2.2 ± 0.3 vs anti-FGF2 2.0 ± 0.4, N=6; proliferation: IgG 2.6 ± 0.1 vs anti-FGF2 2.5 ± 0.2, N=7), but largely blocked the enhanced migration and proliferation of VSMC (migration: Figure B; P<0.01, N=6; proliferation: control IgG 3.4 ± 0.3 vs. Anti-FGF2 Ab 2.7 ± 0.3 fold; P<0.01, N=7). Conclusion: The increased migration and proliferation of VSMC compared to NVSMC is largely mediated by FGF2.

NOTCH1 regulates matrix gla protein and calcification gene networks in human valve endothelium

Valvular and vascular calcification are common causes of cardiovascular morbidity and mortality. Developing effective treatments requires understanding the molecular underpinnings of these processes. Shear stress is thought to play a role in inhibiting calcification. Furthermore, NOTCH1 regulates vascular and valvular endothelium, and human mutations in NOTCH1 can cause calcific aortic valve disease. Here, we determined the genome-wide impact of altering shear stress and NOTCH signaling on human aortic valve endothelium. mRNA-sequencing of primary human aortic valve endothelial cells (HAVECs) with or without knockdown of NOTCH1, in the presence or absence of shear stress, revealed NOTCH1-dependency of the atherosclerosis-related gene connexin 40 (GJA5), and numerous repressors of endochondral ossification. Among these, matrix gla protein (MGP) is highly expressed in aortic valve and vasculature, and inhibits soft tissue calcification by sequestering bone morphogenetic proteins (BMPs). Altering NOTCH1 levels affected MGP mRNA and protein in HAVECs. Furthermore, shear stress activated NOTCH signaling and MGP in a NOTCH1-dependent manner. NOTCH1 positively regulated endothelial MGP in vivo through specific binding motifs upstream of MGP. Our studies suggest that shear stress activates NOTCH1 in primary human aortic valve endothelial cells leading to downregulation of osteoblast-like gene networks that play a role in tissue calcification.

The Effect of Mechanotransduction and ECM Proteins on the Development of Calcific Nodules: A Model System for CAVD

Test an in vitro model of calcific aortic valve nodule growth that modulates stiffness and substrate composition in polyacrylamide (PAAM) gels to understand progression of calcific aortic valve disease (CAVD). Isolated valve interstitial cells (VICs) were used to seed PAAM gels incorporated with either collagen I or hyaluronic acid (HA). To induce calcification, TFG-β1 was added to the culture medium. Additional murine leaflets were isolated and placed in culture media with TFG-β1. Nodule formation has been shown in both the rat leaflet model systems and the PAAM gel system using three separate visualization techniques: the calcium fluorescence indicator fluo-4 AM, Alizarin red staining, and two photon excited fluorescence (TPEF). This is also confirmed in human valves with CAVD. Nodule formation, as measured by fluo-4 imaging, shows an increase in average nodule size with an increase in Young's modulus, but also a dependence on the type of binding protein used. Preliminary studies looking at fiber organization in explanted rat leaflets shows an increase in nodule formation with a decreased in collagen organization – shown using second harmonic generation (SHG) signal. Using silk films to mimic the natural valve environment, we aim to study the effect of fiber alignment on nodule growth. Average nodule size is affected by both the stiffness of the PAAM gel and the binding protein indicating that changes in valve extracellular matrix (ECM) content during disease progression may lead to CAVD advancement. Additionally, preliminary studies indicate that fiber orientation may play a role in initial nodule formation that may be exacerbated by changes in ECM composition.

0268 : Involvement of LRRFip1 gene and canonical Wnt pathway in Mitral Valve Prolapse (MVP)

Heart valves diseases affect 3% of world population, and surgery is often the only therapeutic mean. A genetic study performed on a family in which several members exhibited a MVP identified a R94G mutation on LRRFip1 gene. LRRFip1 alternative transcription splicing gives rise to five isoforms in humans, three of which are targeted by the mutation (Iso1, 3 and 4). Previous studies only focused on LRRFip1-iso5 that was first described as a transcription factor interacting with positive (Dishevelled) and negative (Flightless-1) regulators of the canonical Wnt β-catenin dependant pathway. As it may participate and regulate crucial events of cardiac valve development and homeostasis involving Wnt pathway, we hypothesised that LRRFip1 could be involved in MVP pathology. We first analysed the expression of LRRFip1 in valves by RNA sequencing and quantitative PCR and showed that LRRFip1- iso1 is expressed in human valves. In mouse, it prevails during embryonic development and then levels down to that other isoforms expression. We thus focused on LRRFip-iso1. Using cell fractionation, we showed a nuclear localization of LRRFip1-iso1 while other isoforms are strictly cytoplasmic. Using luciferase-based Wnt reporter assays and co-IP, we further demonstrated that out of the five isoforms, LRRFip1-iso1 is the strongest interactor of Dvl-1 and Fli-1, and the strongest activator of the canonical Wnt pathway. Although activation requires beta-catenin, it does not involve beta-catenin stabilization nor activation. Using site directed mutagenesis, we mapped the domain responsible for Wnt pathway activation to the 25 amino-acids region surrounding arginine 94 and showed that R94G mutation also decreases Wnt activation. This work demonstrates the involvement of LRRFip1-iso1 in canonical Wnt pathway activation. Taken together, our results suggest a potential role for LRRFip1 in valvulogenesis and/or valve homeostasis regulation that may be impeded by the R94G mutation.

0077 : DOCK1 a new candidate gene in inherited form of mitral valve prolapse

Mitral valve prolapse (MVP) affects 2-4% of the general population and remains one of the most frequent indications for valvular surgery. So far, the only gene described in MVP, with an X-linked form of inheritance, is FLNA but only represents a small part of MVP. To this respect, we investigated a french MVP pedigree to uncover new molecular insights associated to the disease. We focus on a family of 5 affected patients characterized by a dysmorphic myxomatous phenotype with 2 operated patients. From 4 MVP patients, we performed a Whole Exome Sequencing screening. From bioinformatics analysis, we focused on rare (MAF<0.1%) functional variants shared by the 4 affected patients. Among 25 variants of interest, 11 were novel. One of them, found in a highly conserved residue (GERP=4.88), in DOCK1 (c.4646G>A; p. R1549Q) co-segregates in all affected members in the family. DOCK1 is highly expressed in the mitral valve as evidenced by RNA sequencing experiments using human mitral valve tissue. DOCK1 , encodes an atypical Rac exchange factor, Dock180, which acts as a guanine exchange factors (GEF) for small Rho family G proteins. Interestingly, Sanematsu et al. (2010) described a major role of Dock180 during cardiovascular development. Mitral valves of Dock1 depleted mice are thickened and lead to blood retention in left atrium. We currently investigate repercussions of p. R1549Q (located in GEF activity domain of Dock180) on Dock180 activity in the cellular adhesion phenotype (XCELLigence; IF assays) and GEF activity (Pull-Down assays) using a heterologous transfection system. Finally, a cohort of 285 MVP affected patients is screened to evaluate the prevalence of DOCK1 in the disease. This study reports a familial approach, coupled to an exome sequencing strategy which identifies a novel DOCK1 missense mutation associated with MVP phenotype. In vivo previous studies and cellular mechanisms learning will allow us to better understand mechanisms involved in the MVP pathogenesis.

Evidence for time‐dependent and adaptive mechanisms in the mitral valve following prolonged Angiotensin II infusion

Activation of angiotensin II (AngII) signaling has been implicated in the pathogenesis of human myxomatous mitral valve prolapse (MVP). To determine whether chronic AngII infusion can elicit molecular and phenotypic manifestations of MVP, we implanted C57BL/6J mice with osmotic minipumps delivering AngII (1000ng/kg/min) or saline for 2 or 4 weeks. We probed changes in mRNA (qRT-PCR) and protein (immunohistochemistry) levels in mitral valves, and assessed valve function by echocardiography. In line with previous findings from human MVP, 2-week AngII infusion was associated with increased pro-fibrotic (e.g. TGFβ2 and CTGF) and “classical” pro-calcific (Wnt/β-catenin) gene expression in mouse mitral valves. Increased immunofluorescence of phospho-SMAD2 and nuclear β-catenin suggested canonical activation of these pathways. Increased gene expression of the transcription factor Runx2 (1.8 fold-change [FC]) and the proliferation marker KI67 (3.9 FC) were also recaptured by AngII. Surprisingly, we found that increases in Runx2 and KI67 mRNA were attenuated (both ~1.3FC) following 4 weeks of AngII, and transcriptional changes in TGFβ and Wnt/β-catenin pathway target genes were no longer evident. The incidence of mitral regurgitation after 2 weeks of AngII (38%) did not increase when mice were treated for 4 weeks (40%). Collectively, these data suggest that there may be adaptive molecular changes occurring following prolonged AngII treatment, which oppose fibrogenic and proliferative signaling pathways. Future studies aimed at identifying key protective and deleterious molecular changes following prolonged AngII infusion will be critical to understanding mechanisms contributing to evolution of MVP.

Loss of axin2 in murine aortic valves leads to myxomatous disease

In the older population, calcific and myxomatous valve diseases are the two main heart valve diseases. Mechanisms involved in aortic valve calcification are similar to bone formation while myxomatous valves display cartilaginous features with proteoglycan accumulation and increased chondrogenic markers; Sox9, Hapln1 and aggrecan. Similarly, increased Wnt/β‐catenin signaling is measured in calcific aortic valve while loss of Wnt/β‐catenin signaling promotes chondrogenic differentiation in aortic valves. This indicates a major role of Wnt/β‐catenin signaling in heart valve homeostasis although underlying mechanisms are still poorly understood. To further investigate the role of Wnt/β‐catenin signaling, we analyzed heart valves from mice deficient in axin2, a negative regulator of β‐catenin. X‐gal staining performed on Axin2‐lacZ knockout mice (KO) indicates that axin2 is expressed in endothelial and interstitial cells in adult heart valves. At 2 months, KO mice demonstrate thickened proteoglycan‐rich aortic valves with increased Sox9 and Hapln1 expression while focal aggrecan‐rich areas are observed in 4 months old KO mice. Surprisingly thickened aortic valves do not calcify as indicated by lack of alizarin red staining in 1 year old KO mice. These markers are consistent with increased chondrogenic features observed in human myxomatous mitral valves. Interestingly, melanocyte accumulation also is observed in thickened aortic valve, suggesting that axin2 regulates neural crest cells contribution to heart valves. Altogether these data indicate a role for axin2 in heart valve homeostasis and in myxomatous disease. Ongoing in vivo and in vitro studies are investigating the specific functions of axin2 in valve diseases mechanisms.

Score: N = 1/Tricuspid regurgitation = 0

Compassionate use of a percutaneous mitral valve repair technology to treat tricuspid regurgitation yielded the first human transcatheter tricuspid valve repair.

Nonbiased Molecular Screening Identifies Novel Molecular Regulators of Fibrogenic and Proliferative Signaling in Myxomatous Mitral Valve Disease.

Pathological processes underlying myxomatous mitral valve degeneration (MMVD) remain poorly understood. We sought to identify novel mechanisms contributing to the development of this condition. Microarrays were used to measure gene expression in 11 myxomatous and 11 nonmyxomatous human mitral valves. Differential gene expression (thresholds P<0.05; fold-change >1.5) and pathway activation (Ingenuity) were confirmed using quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. Contributions of bone morphogenetic protein 4 and transforming growth factor (TGF)-β2 to differential gene expression were evaluated in vitro. Contributions of angiotensin II to differential pathway activation were examined in mice in vivo. A total of 2602 genes were differentially expressed between myxomatous and nonmyxomatous valves. Canonical TGF-β signaling was increased in MMVD because of increased ligand expression and derepression of SMA mothers against decapentaplegic 2/3 signaling and was confirmed with quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. Myxomatous valves demonstrated activation of canonical bone morphogenetic protein and Wnt/β-catenin signaling and upregulation of their common target runt-related transcription factor 2. Our data set provided transcriptional and immunohistochemical evidence for activated immune cell infiltration. In vitro treatment of mitral valve interstitial cells with TGF-β2 increased β-catenin signaling at mRNA and protein levels, suggesting interactions between TGF-β2 and Wnt signaling. In vivo infusion of mice with angiotensin II recaptured several changes in signaling pathways characteristic of human MMVD. These data support a new disease framework whereby activation of TGF-β2, bone morphogenetic protein 4, Wnt/β-catenin, or immune signaling plays major roles in the pathogenesis of MMVD. We propose these pathways act in a context-dependent manner to drive phenotypic changes that fundamentally differ from those observed in aortic valve disease and open novel avenues guiding future research into the pathogenesis of MMVD.

BIOTECHNOLOGICAL CONDITIONS OF VALVE PROSTHESES CREATING BY TISSUE ENGINEERING METHOD

Tissue engineering is the advanced biotechnology area focusing on invention of artificial substitutes of biological origin to repair, support and activity improvement of the defective organ or its part [1, 2]. In this case the therapeu tic reconstruction is achieved by delivering support structures (matrix), cells as well as regenerative molecular and mechanical signals to the specific area [3, 4]. Today the tissue engineering covers a range of materials studied as matrices [1, 5]. Nominally they can be divided into two categories: polymer matrix, including biological and synthetic polymers, and connective tissue frameworks of human (allogeneic) and animal (xenogeneic) tissues [6, 7]. According to one of the m ost inspiring hypotheses in cardiological surgery the tissue engineering is an opportunity to create a perfect valvular prosthesis — live, growable, adaptive, autologous and functionally optimally adjustable [8, 9]. The point of this hypothe sis is to use the valvular connective tissue frameworks, which after decellularization [10, 11] become perfect for prosthesis repopulation with recipient cells and creation of a live autologous tissue [12, 13]. Using allogeneic decel lularized grafts is limited by insufficient amount of transplants. That is why xenogeneic tissue becomes increasingly popular as a basis for manufacturing tissue-engineered valvular prostheses [14, 15]. This biotechnological approach will make valvular prosthetic repair procedure more widely applicable due to material availability [6, 16, 17]. It is especially convenient to use porcine valves regarding their 3D structure and extracellular matrix structure, which are much similar to the relevant parameters of the human valve [17]. It is also important that molecules of the extracellular matrix refer to the class of highly conserved proteins (their amino acid composition has low variability among different species), that almost completely explains the absence of immune response after decellularized tissue xenografting [18, 19]. Additionally it is presumed that except immune response decrease the decellularization will contribute to life improvement of valvular transplants [20–22]. Decellularization is an intentional initiation of cell death in the biological tissue [23–25]. It is significan t that there are two basic ways of tissue and human/animal SHORT REVIEWS

Evidence of Aortopathy in Mice with Haploinsufficiency of Notch1 in Nos3-Null Background.

Thoracic aortic aneurysms (TAA) are a significant cause of morbidity and mortality in humans. While the exact etiology is unknown, genetic factors play an important role. Mutations in NOTCH1 have been linked to bicuspid aortic valve (BAV) and aortopathy in humans. The aim of this study was to determine if haploinsufficiency of Notch1 contributes to aortopathy using Notch1+/−; Nos3−/− mice. Echocardiographic analysis of Notch1+/−; Nos3−/− mice reveals effacement of the sinotubular junction and a trend toward dilation of the aortic sinus. Furthermore, examination of the proximal aorta of Notch1+/−; Nos3−/− mice reveals elastic fiber degradation, a trend toward increased matrix metalloproteinase 2 expression, and increased smooth muscle cell apoptosis, features characteristic of aneurysmal disease. Although at a lower penetrance, we also found features consistent with aortopathic changes in Notch1 heterozygote mice and in Nos3-null mice. Our findings implicate a novel role for Notch1 in aortopathy of the proximal aorta.