BMP-SMAD signalling output is highly regionalized in cardiovascular and lymphatic endothelial networks

BACKGROUND

Bone morphogenetic protein (BMP) signalling has emerged as a fundamental pathway in endothelial cell biology and deregulation of this pathway is implicated in several vascular disorders. BMP signalling output in endothelial cells is highly context- and dose-dependent. Phosphorylation of the BMP intracellular effectors, SMAD1/5/9, is routinely used to monitor BMP signalling activity. To better understand the in vivo context-dependency of BMP-SMAD signalling, we investigated differences in BMP-SMAD transcriptional activity in different vascular beds during mouse embryonic and postnatal stages. For this, we used the BRE::gfp BMP signalling reporter mouse in which the BMP response element (BRE) from the ID1-promotor, a SMAD1/5/9 target gene, drives the expression of GFP.

RESULTS

A mosaic pattern of GFP was present in various angiogenic sprouting plexuses and in endocardium of cardiac cushions and trabeculae in the heart. High calibre veins seemed to be more BRE::gfp transcriptionally active than arteries, and ubiquitous activity was present in embryonic lymphatic vasculature. Postnatal lymphatic vessels showed however only discrete micro-domains of transcriptional activity. Dynamic shifts in transcriptional activity were also observed in the endocardium of the developing heart, with a general decrease in activity over time. Surprisingly, proliferative endothelial cells were almost never GFP-positive. Patches of transcriptional activity seemed to correlate with vasculature undergoing hemodynamic alterations.

CONCLUSION

The BRE::gfp mouse allows to investigate selective context-dependent aspects of BMP-SMAD signalling. Our data reveals the highly dynamic nature of BMP-SMAD mediated transcriptional regulation in time and space throughout the vascular tree, supporting that BMP-SMAD signalling can be a source of phenotypic diversity in some, but not all, healthy endothelium. This knowledge can provide insight in vascular bed or organ-specific diseases and phenotypic heterogeneity within an endothelial cell population.

Developmental SHP2 dysfunction underlies cardiac hypertrophy in Noonan syndrome with multiple lentigines

Hypertrophic cardiomyopathy is a common cause of mortality in congenital heart disease (CHD). Many gene abnormalities are associated with cardiac hypertrophy, but their function in cardiac development is not well understood. Loss-of-function mutations in PTPN11, which encodes the protein tyrosine phosphatase (PTP) SHP2, are implicated in CHD and cause Noonan syndrome with multiple lentigines (NSML), a condition that often presents with cardiac hypertrophic defects. Here, we found that NSML-associated hypertrophy stems from aberrant signaling mechanisms originating in developing endocardium. Trabeculation and valvular hyperplasia were diminished in hearts of embryonic mice expressing a human NSML-associated variant of SHP2, and these defects were recapitulated in mice expressing NSML-associated SHP2 specifically in endothelial, but not myocardial or neural crest, cells. In contrast, mice with myocardial- but not endothelial-specific NSML SHP2 expression developed ventricular septal defects, suggesting that NSML-associated mutations have both cell-autonomous and nonautonomous functions in cardiac development. However, only endothelial-specific expression of NSML-associated SHP2 induced adult-onset cardiac hypertrophy. Further, embryos expressing the NSML-associated SHP2 mutation exhibited aberrant AKT activity and decreased downstream forkhead box P1 (FOXP1)/FGF and NOTCH1/EPHB2 signaling, indicating that SHP2 is required for regulating reciprocal crosstalk between developing endocardium and myocardium. Together, our data provide functional and disease-based evidence that aberrant SHP2 signaling during cardiac development leads to CHD and adult-onset heart hypertrophy.

Probing chromatin landscape reveals roles of endocardial TBX20 in septation

Mutations in the T-box transcription factor TBX20 are associated with multiple forms of congenital heart defects, including cardiac septal abnormalities, but our understanding of the contributions of endocardial TBX20 to heart development remains incomplete. Here, we investigated how TBX20 interacts with endocardial gene networks to drive the mesenchymal and myocardial movements that are essential for outflow tract and atrioventricular septation. Selective ablation of Tbx20 in murine endocardial lineages reduced the expression of extracellular matrix and cell migration genes that are critical for septation. Using the assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), we identified accessible chromatin within endocardial lineages and intersected these data with TBX20 ChIP-seq and chromatin loop maps to determine that TBX20 binds a conserved long-range enhancer to regulate versican (Vcan) expression. We also observed reduced Vcan expression in Tbx20-deficient mice, supporting a direct role for TBX20 in Vcan regulation. Further, we show that the Vcan enhancer drove reporter gene expression in endocardial lineages in a TBX20-binding site-dependent manner. This work illuminates gene networks that interact with TBX20 to orchestrate cardiac septation and provides insight into the chromatin landscape of endocardial lineages during septation.

Endocardium Minimally Contributes to Coronary Endothelium in the Embryonic Ventricular Free Walls

RATIONALE

There is persistent uncertainty regarding the developmental origins of coronary vessels, with 2 principal sources suggested as ventricular endocardium or sinus venosus (SV). These 2 proposed origins implicate fundamentally distinct mechanisms of vessel formation. Resolution of this controversy is critical for deciphering the programs that result in the formation of coronary vessels and has implications for research on therapeutic angiogenesis.

OBJECTIVE

To resolve the controversy over the developmental origin of coronary vessels.

METHODS AND RESULTS

We first generated nuclear factor of activated T cells (Nfatc1)-Cre and Nfatc1-Dre lineage tracers for endocardium labeling. We found that Nfatc1 recombinases also label a significant portion of SV endothelial cells in addition to endocardium. Therefore, restricted endocardial lineage tracing requires a specific marker that distinguishes endocardium from SV. By single-cell gene expression analysis, we identified a novel endocardial gene natriuretic peptide receptor 3 (Npr3). Npr3 is expressed in the entirety of the endocardium but not in the SV. Genetic lineage tracing based on Npr3-CreER showed that endocardium contributes to a minority of coronary vessels in the free walls of embryonic heart. Intersectional genetic lineage tracing experiments demonstrated that endocardium minimally contributes to coronary endothelium in the embryonic ventricular free walls.

CONCLUSIONS

Our study suggested that SV, but not endocardium, is the major origin for coronary endothelium in the embryonic ventricular free walls. This work thus resolves the recent controversy over the developmental origin of coronary endothelium, providing the basis for studying coronary vessel formation and regeneration after injury.

ETA and ETB receptors contribute to neuropeptide Y-induced secretion of endothelin-1 in right but not left human ventricular endocardial endothelial cells

Our recent work showed that neuropeptide Y-induced secretion of endothelin-1 (ET-1) in left and right human ventricular endocardial endothelial cells (hLEECs or hREECs respectively) via the activation of neuropeptide Y2 or Y5 receptors depending on the cell type. The aim of this study was to verify whether hLEECs or hREECs secretion of ET-1 induced by NPY is due, in part, to the activation of ETA and/or ETB receptors by the secreted ET-1. Using the technique of indirect immunofluorescence coupled to real 3-D confocal microscopy, as well as ELISA, our results show that in hREECs, the NPY-induced release of ET-1 seems to be due, in part, to the activation of both ETA and ETB receptors. On the other hand, in hLEECs, ETA and ETB receptors do not contribute to the ET-1 released by NPY. Therefore, our results suggest that the NPY-induced release of ET-1 in EECRs is due to NPY receptor activation and the subsequent activation of the ETA and ETB receptors by the released ET-1. However, the release of ET-1 by NPY in hLEECs is mainly due to NPY receptor activation. Furthermore, this secretory process of ET-1 is different between the right and left ventricular cells and highlights the important tuning roles that right and left ventricular EECs possess as well as their contribution to the physiological and pathophysiological states of the underlying heart muscle.

Cardiac Telocytes in Regeneration of Myocardium After Myocardial Infarction

Recent research progress has revealed that a novel type of interstitial cells termed cardiac telocytes (CTs) is found in the interstitium of the heart. We demonstrated that CTs are distributed both longitudinally and within the cross network in the myocardium and that the density of CTs in the atrium-atria and base of the myocardium is higher than that in the middle of the myocardium, while the density of CTs in the epicardium is higher than that in the endocardium. In addition, we documented, for the first time, that the network of CTs in the infarct zone of the myocardium is destroyed during myocardial infarction (MI). This fact shows that, in addition to the death of cardiac myocytes, the previously unrecognized death of CTs is an important mechanism that contributes to the structural damage and poor healing and regeneration observed in the infarcted myocardium. Furthermore, we demonstrated, for the first time, that transplantation of CTs in cases of MI decreases the infarct size and improves myocardial function. The mechanisms behind the beneficial effects of CT transplantation are increased angiogenesis at the infarct site and the border zone, decreased fibrosis in the infarct and non-infarct zones, improved pathological reconstruction of the left ventricle, and increased regeneration of CTs in the infarct zone. Our findings reveal that CTs can be specifically identified by the following characteristics: very small cell bodies, extreme prolongation with some dilation, predisposition to cell death under ischemia, and expression of molecular markers such as c-Kit, CD34, vimentin, and PDGFR-β. CTs act as a structural and functional niche microenvironment in the myocardium and play an essential role in maintaining the integrity of the myocardium and in the regeneration of damaged myocardium.

Endocardial Endothelial Dysfunction Progressively Disrupts Initially Anti then Pro-Thrombotic Pathways in Heart Failure Mice

Objective

An experimental model of endocardial thrombosis has not been developed and endocardial endothelial dysfunction in heart failure (HF) is understudied. We sought to determine whether disruption of the endothelial anti-coagulant activated protein C (APC) pathway in CREB_A133 HF mice promotes endocardial thrombosis in the acute decompensated phase of the disease, and whether alterations in von Willebrand factor (vWF) secretion from HF endocardium reduces thrombus formation as HF stabilizes.

Approach and results

Echocardiography was used to follow HF development and to detect endocardial thrombi in CREB_A133 mice. Endocardial thrombi incidence was confirmed with immunohistochemistry and histology. In early and acute decompensated phases of HF, CREB_A133 mice had the highest incidence of endocardial thrombi and these mice also had a shorter tail-bleeding index consistent with a pro-thrombotic milieu. Both APC generation, and expression of receptors that promote APC function (thrombomodulin, endothelial protein C receptor, protein S), were suppressed in the endocardium of acute decompensated HF mice. However, in stable compensated HF mice, an attenuation occurred for vWF protein content and secretion from endocardial endothelial cells, vWF-dependent platelet agglutination (by ristocetin), and thrombin generation on the endocardial surface.

Conclusions

CREB_A133 mice develop HF and endocardial endothelial dysfunction. Attenuation of the anti-coagulant APC pathway promotes endocardial thrombosis in early and acute decompensated phases of HF. However, in stable compensated HF mice, disruptions in endothelial vWF expression and extrusion may actually reduce the incidence of endocardial thrombosis.

A mouse model of endocardial fibroelastosis

BACKGROUND

Endocardial fibroelastosis (EFE) is a pathologic condition of abnormal deposition of collagen and elastin within the endocardium of the heart. It is seen in conjunction with a variety of diseases including hypoplastic left heart syndrome and viral endocarditis. While an experimental model using heterotopic heart transplant in rats has been described, we sought to fully describe a mouse model that can be used to further elucidate the potential mechanisms of and treatments for EFE.

MATERIALS AND METHODS

The hearts of 2-day-old C57BL/6 mice were transplanted into the abdomen of 7-week-old C57BL/6 mice. At 2 weeks, the hearts were harvested and histologic analysis was performed using hematoxylin and eosin, Masson's trichrome, Russell-Movat's pentachrome, Picrosirius red, Hart's, Verhoeff-Van Gieson, and Weigert's Resorcin-Fuchsin stains. Additionally, one heart was analyzed using transmission electron microscopy (TEM).

RESULTS

Specimens demonstrated abnormal accumulation of both collagen and elastin within the endocardium with occasional expansion into the myocardium. Heterogeneity in extracellular matrix deposition was noted in the histologic specimens. In addition, TEM demonstrated the presence of excess collagen within the endocardium.

CONCLUSIONS

The heterotopic transplantation of an immature heart into a mouse results in changes consistent with EFE. This model is appropriate to investigate the etiology and treatment of EFE.

Endothelial plasticity drives arterial remodeling within the endocardium after myocardial infarction

RATIONALE

Revascularization of injured, ischemic, and regenerating organs is essential to restore organ function. In the postinfarct heart, however, the mechanisms underlying the formation of new coronary arteries are poorly understood.

OBJECTIVE

To study vascular remodeling of coronary arteries after infarction.

METHODS AND RESULTS

We performed permanent left coronary ligation on Connexin40-GFP mice expressing green fluorescent protein (GFP) in endothelial cells of coronary arteries but not veins, capillaries, or endocardium. GFP(+) endothelial foci were identified within the endocardium in the infarct zone. These previously undescribed structures, termed endocardial flowers, have a distinct endothelial phenotype (Cx40(+), VEGFR2(+), and endoglin(-)) to the surrounding endocardium (Cx40(-), VEGFR2(-), and endoglin(+)). Endocardial flowers are contiguous with coronary vessels and associated with subendocardial smooth muscle cell accumulation. Genetic lineage tracing reveals extensive endothelial plasticity in the postinfarct heart, showing that endocardial flowers develop by arteriogenesis of Cx40(-) cells and by outgrowth of pre-existing coronary arteries. Finally, endocardial flowers exhibit angiogenic features, including early VEGFR2 expression and active proliferation of adjacent endocardial and smooth muscle cells.

CONCLUSIONS

Arterial endothelial foci within the endocardium reveal extensive endothelial cell plasticity in the infarct zone and identify the endocardium as a site of endogenous arteriogenesis and source of endothelial cells to promote vascularization in regenerative strategies.

Hand2 is an essential regulator for two Notch-dependent functions within the embryonic endocardium

The basic-helix-loop-helix (bHLH) transcription factor Hand2 plays critical roles during cardiac morphogenesis via expression and function within myocardial, neural crest, and epicardial cell populations. Here, we show that Hand2 plays two essential Notch-dependent roles within the endocardium. Endocardial ablation of Hand2 results in failure to develop a patent tricuspid valve, intraventricular septum defects, and hypotrabeculated ventricles, which collectively resemble the human congenital defect tricuspid atresia. We show endocardial Hand2 to be an integral downstream component of a Notch endocardium-to-myocardium signaling pathway and a direct transcriptional regulator of Neuregulin1. Additionally, Hand2 participates in endocardium-to-endocardium-based cell signaling, with Hand2 mutant hearts displaying an increased density of coronary lumens. Molecular analyses further reveal dysregulation of several crucial components of Vegf signaling, including VegfA, VegfR2, Nrp1, and VegfR3. Thus, Hand2 functions as a crucial downstream transcriptional effector of endocardial Notch signaling during both cardiogenesis and coronary vasculogenesis.

Blood flow and Bmp signaling control endocardial chamber morphogenesis

During heart development, the onset of heartbeat and blood flow coincides with a ballooning of the cardiac chambers. Here, we have used the zebrafish as a vertebrate model to characterize chamber ballooning morphogenesis of the endocardium, a specialized population of endothelial cells that line the interior of the heart. By combining functional manipulations, fate mapping studies, and high-resolution imaging, we show that endocardial growth occurs without an influx of external cells. Instead, endocardial cell proliferation is regulated, both by blood flow and by Bmp signaling, in a manner independent of vascular endothelial growth factor (VEGF) signaling. Similar to myocardial cells, endocardial cells obtain distinct chamber-specific and inner- versus outer-curvature-specific surface area sizes. We find that the hemodynamic-sensitive transcription factor Klf2a is involved in regulating endocardial cell morphology. These findings establish the endocardium as the flow-sensitive tissue in the heart with a key role in adapting chamber growth in response to the mechanical stimulus of blood flow.

Specification of the mouse cardiac conduction system in the absence of Endothelin signaling

Coordinated contraction of the heart is essential for survival and is regulated by the cardiac conduction system. Contraction of ventricular myocytes is controlled by the terminal part of the conduction system known as the Purkinje fiber network. Lineage analyses in chickens and mice have established that the Purkinje fibers of the peripheral ventricular conduction system arise from working myocytes during cardiac development. It has been proposed, based primarily on gain-of-function studies, that Endothelin signaling is responsible for myocyte-to-Purkinje fiber transdifferentiation during avian heart development. However, the role of Endothelin signaling in mammalian conduction system development is less clear, and the development of the cardiac conduction system in mice lacking Endothelin signaling has not been previously addressed. Here, we assessed the specification of the cardiac conduction system in mouse embryos lacking all Endothelin signaling. We found that mouse embryos that were homozygous null for both ednra and ednrb, the genes encoding the two Endothelin receptors in mice, were born at predicted Mendelian frequency and had normal specification of the cardiac conduction system and apparently normal electrocardiograms with normal QRS intervals. In addition, we found that ednra expression within the heart was restricted to the myocardium while ednrb expression in the heart was restricted to the endocardium and coronary endothelium. By establishing that ednra and ednrb are expressed in distinct compartments within the developing mammalian heart and that Endothelin signaling is dispensable for specification and function of the cardiac conduction system, this work has important implications for our understanding of mammalian cardiac development.

An arterial-specific enhancer of the human endothelin converting enzyme 1 (ECE1) gene is synergistically activated by Sox17, FoxC2, and Etv2

Endothelin-converting enzyme-1 (Ece-1), a crucial component of the Endothelin signaling pathway, is required for embryonic development and is an important regulator of vascular tone, yet the transcriptional regulation of the ECE1 gene has remained largely unknown. Here, we define the activity and regulation of an enhancer from the human ECE1 locus in vivo. The enhancer identified here becomes active in endothelial progenitor cells shortly after their initial specification and is dependent on a conserved FOX:ETS motif, a composite binding site for Forkhead transcription factors and the Ets transcription factor Etv2, for activity in vivo. The ECE1 FOX:ETS motif is bound and cooperatively activated by FoxC2 and Etv2, but unlike other described FOX:ETS-dependent enhancers, ECE1 enhancer activity becomes restricted to arterial endothelium and endocardium by embryonic day 9.5 in transgenic mouse embryos. The ECE1 endothelial enhancer also contains an evolutionarily-conserved, consensus SOX binding site, which is required for activity in transgenic mouse embryos. Importantly, the ECE1 SOX site is bound and activated by Sox17, a transcription factor involved in endothelial cell differentiation and an important regulator of arterial identity. Moreover, the ECE1 enhancer is cooperatively activated by the combinatorial action of FoxC2, Etv2, and Sox17. Although Sox17 is required for arterial identity, few direct transcriptional targets have been identified in endothelial cells. Thus, this work has important implications for our understanding of endothelial specification and arterial subspecification.

Resident fibroblast lineages mediate pressure overload-induced cardiac fibrosis

Activation and accumulation of cardiac fibroblasts, which result in excessive extracellular matrix deposition and consequent mechanical stiffness, myocyte uncoupling, and ischemia, are key contributors to heart failure progression. Recently, endothelial-to-mesenchymal transition (EndoMT) and the recruitment of circulating hematopoietic progenitors to the heart have been reported to generate substantial numbers of cardiac fibroblasts in response to pressure overload-induced injury; therefore, these processes are widely considered to be promising therapeutic targets. Here, using multiple independent murine Cre lines and a collagen1a1-GFP fusion reporter, which specifically labels fibroblasts, we found that following pressure overload, fibroblasts were not derived from hematopoietic cells, EndoMT, or epicardial epithelial-to-mesenchymal transition. Instead, pressure overload promoted comparable proliferation and activation of two resident fibroblast lineages, including a previously described epicardial population and a population of endothelial origin. Together, these data present a paradigm for the origins of cardiac fibroblasts during development and in fibrosis. Furthermore, these data indicate that therapeutic strategies for reducing pathogenic cardiac fibroblasts should shift from targeting presumptive EndoMT or infiltrating hematopoietically derived fibroblasts, toward common pathways upregulated in two endogenous fibroblast populations.

Zebrafish Crip2 plays a critical role in atrioventricular valve development by downregulating the expression of ECM genes in the endocardial cushion

The initial step of atrioventricular (AV) valve development involves the deposition of extracellular matrix (ECM) components of the endocardial cushion and the endocardial-mesenchymal transition. While the appropriately regulated expression of the major ECM components, Versican and Hyaluronan, that form the endocardial cushion is important for heart valve development, the underlying mechanism that regulates ECM gene expression remains unclear. We found that zebrafish crip2 expression is restricted to a subset of cells in the AV canal (AVC) endocardium at 55 hours post-fertilization (hpf). Knockdown of crip2 induced a heart-looping defect in zebrafish embryos, although the development of cardiac chambers appeared to be normal. In the AVC of Crip2-deficient embryos, the expression of both versican a and hyaluronan synthase 2 (has2) was highly upregulated, but the expression of bone morphogenetic protein 4 (bmp4) and T-box 2b (tbx2b) in the myocardium and of notch1b in the endocardium in the AVC did not change. Taken together, these results indicate that crip2 plays an important role in AV valve development by downregulating the expression of ECM components in the endocardial cushion.

Transmural heterogeneity of cellular level power output is reduced in human heart failure

Heart failure is associated with pump dysfunction and remodeling but it is not yet known if the condition affects different transmural regions of the heart in the same way. We tested the hypotheses that the left ventricles of non-failing human hearts exhibit transmural heterogeneity of cellular level contractile properties, and that heart failure produces transmural region-specific changes in contractile function. Permeabilized samples were prepared from the sub-epicardial, mid-myocardial, and sub-endocardial regions of the left ventricular free wall of non-failing (n=6) and failing (n=10) human hearts. Power, an in vitro index of systolic function, was higher in non-failing mid-myocardial samples (0.59±0.06μWmg(-1)) than in samples from the sub-epicardium (p=0.021) and the sub-endocardium (p=0.015). Non-failing mid-myocardial samples also produced more isometric force (14.3±1.33kNm(-2)) than samples from the sub-epicardium (p=0.008) and the sub-endocardium (p=0.026). Heart failure reduced power (p=0.009) and force (p=0.042) but affected the mid-myocardium more than the other transmural regions. Fibrosis increased with heart failure (p=0.021) and mid-myocardial tissue from failing hearts contained more collagen than matched sub-epicardial (p<0.001) and sub-endocardial (p=0.043) samples. Power output was correlated with the relative content of actin and troponin I, and was also statistically linked to the relative content and phosphorylation of desmin and myosin light chain-1. Non-failing human hearts exhibit transmural heterogeneity of contractile properties. In failing organs, region-specific fibrosis produces the greatest contractile deficits in the mid-myocardium. Targeting fibrosis and sarcomeric proteins in the mid-myocardium may be particularly effective therapies for heart failure.

Accelerated coronary angiogenesis by vegfr1-knockout endocardial cells

During mouse heart development, ventricular endocardial cells give rise to the coronary arteries by angiogenesis. Myocardially-derived vascular endothelial growth factor-a (Vegfa) regulates embryonic coronary angiogenesis through vascular endothelial growth factor-receptor 2 (Vegfr2) expressed in the endocardium. In this study, we investigated the role of endocardially-produced soluble Vegfr1 (sVegfr1) in the coronary angiogenesis. We deleted sVegfr1 in the endocardium of the developing mouse heart and found that this deletion resulted in a precocious formation of coronary plexuses. Using an ex vivo coronary angiogenesis assay, we showed that the Vegfr1-null ventricular endocardial cells underwent excessive angiogenesis and generated extensive endothelial tubular networks. We also revealed by qPCR analysis that expression of genes involved in the Vegf-Notch pathway was augmented in the Vegfr1-null hearts. We further showed that inhibition of Notch signaling blocked the formation of coronary plexuses by the ventricular endocardial cells. These results establish that Vegfr1 produced in the endocardium negatively regulates embryonic coronary angiogenesis, possibly by limiting the Vegf-Notch signaling.

Endocardial to myocardial notch-wnt-bmp axis regulates early heart valve development

Endocardial to mesenchymal transformation (EMT) is a fundamental cellular process required for heart valve formation. Notch, Wnt and Bmp pathways are known to regulate this process. To further address how these pathways coordinate in the process, we specifically disrupted Notch1 or Jagged1 in the endocardium of mouse embryonic hearts and showed that Jagged1-Notch1 signaling in the endocardium is essential for EMT and early valvular cushion formation. qPCR and RNA in situ hybridization assays reveal that endocardial Jagged1-Notch1 signaling regulates Wnt4 expression in the atrioventricular canal (AVC) endocardium and Bmp2 in the AVC myocardium. Whole embryo cultures treated with Wnt4 or Wnt inhibitory factor 1 (Wif1) show that Bmp2 expression in the AVC myocardium is dependent on Wnt activity; Wnt4 also reinstates Bmp2 expression in the AVC myocardium of endocardial Notch1 null embryos. Furthermore, while both Wnt4 and Bmp2 rescue the defective EMT resulting from Notch inhibition, Wnt4 requires Bmp for its action. These results demonstrate that Jagged1-Notch1 signaling in endocardial cells induces the expression of Wnt4, which subsequently acts as a paracrine factor to upregulate Bmp2 expression in the adjacent AVC myocardium to signal EMT.

Living high training low induces physiological cardiac hypertrophy accompanied by down-regulation and redistribution of the renin-angiotensin system

AIM

Living high training low" (LHTL) is an exercise-training protocol that refers living in hypoxia stress and training at normal level of O2. In this study, we investigated whether LHTL caused physiological heart hypertrophy accompanied by changes of biomarkers in renin-angiotensin system in rats.

METHODS

Adult male SD rats were randomly assigned into 4 groups, and trained on living low-sedentary (LLS, control), living low-training low (LLTL), living high-sedentary (LHS) and living high-training low (LHTL) protocols, respectively, for 4 weeks. Hematological parameters, hemodynamic measurement, heart hypertrophy and plasma angiotensin II (Ang II) level of the rats were measured. The gene and protein expression of angiotensin-converting enzyme (ACE), angiotensinogen (AGT) and angiotensin II receptor I (AT1) in heart tissue was assessed using RT-PCR and immunohistochemistry, respectively.

RESULTS

LLTL, LHS and LHTL significantly improved cardiac function, increased hemoglobin concentration and RBC. At the molecular level, LLTL, LHS and LHTL significantly decreased the expression of ACE, AGT and AT1 genes, but increased the expression of ACE and AT1 proteins in heart tissue. Moreover, ACE and AT1 protein expression was significantly increased in the endocardium, but unchanged in the epicardium.

CONCLUSION

LHTL training protocol suppresses ACE, AGT and AT1 gene expression in heart tissue, but increases ACE and AT1 protein expression specifically in the endocardium, suggesting that the physiological heart hypertrophy induced by LHTL is regulated by region-specific expression of renin-angiotensin system components.

Mef2c regulates transcription of the extracellular matrix protein cartilage link protein 1 in the developing murine heart

Cartilage Link Protein 1 (Crtl1) is an extracellular matrix (ECM) protein that stabilizes the interaction between hyaluronan and versican and is expressed in endocardial and endocardially-derived cells in the developing heart, including cells in the atrioventricular (AV) and outflow tract (OFT) cushions. Previous investigations into the transcriptional regulation of the Crtl1 gene have shown that Sox9 regulates Crtl1 expression in both cartilage and the AV valves. The cardiac transcription factor Mef2c is involved in the regulation of gene expression in cardiac and skeletal muscle cell lineages. In this study we have investigated the potential role of Mef2c in the regulation of ECM production in the endocardial and mesenchymal cell lineages of the developing heart. We demonstrate that the Crtl1 5′ flanking region contains two highly conserved Mef2 binding sites and that Mef2c is able to bind to these sites in vivo during cardiovascular development. Additionally, we show that Crtl1 transcription is dependent on Mef2c expression in fetal mitral valve interstitial cells (VICs). Combined, these findings highlight a new role for Mef2c in cardiac development and the regulation of cardiac extracellular matrix protein expression.

Differences in neuropeptide Y-induced secretion of endothelin-1 in left and right human endocardial endothelial cells

The aim of the study was to test the hypothesis that neuropeptide Y (NPY) may induce endothelin-1 (ET-1) secretion in left (hLEECs) and right (hREECs) human endocardial endothelial cells. Furthermore, the type of NPY receptor implicated could be different in NPY-induced secretion in hLEECs and hREECs. Using immunofluorescence coupled to real 3D confocal microscopy and ELISA, our results showed that stimulation of secretion by NPY induced the release of ET-1 from both right and left human ventricular endocardial endothelial cells (hEECs) in a time-dependent manner. Furthermore, the secretory capacity of hREECs was higher than that of hLEECs. In addition, our results showed that the effect of NPY on ET-1 secretion in hLEECs was only due to activation of Y(5) receptors. However, the effect of NPY on ET-1 secretion in hREECs was due to mainly Y(2) and partially Y(5) receptors activation. In conclusion, our results suggest that differences in excitation-secretion coupling exist between hREECS and hLEECs which may contribute to the functional differences between right and left ventricular muscle. Furthermore, high NPY level contributes to ET-1 release by hEECs and Y(2) and Y(5) receptors antagonists may be used for regulation of ET-1 secretion in the heart.

Multiple cerebral and cerebellar infarcts as the first clinical manifestation in a patient with Churg-Strauss syndrome: case report and literature review

PURPOSE

Churg-Strauss syndrome (CSS) is a rare autoimmune disease with small-vessel vasculitis. Neurological manifestation of CSS is common. Central nervous system is less frequently involved than that of peripheral nervous system.

CASE REPORT

We report a case of 60-year-old man who presented with acute onset of right hemiparesis and impaired cognition. The presence of hypereosinophilia, asthma, sinusitis and extravascular eosinophil accumulation led to the diagnosis of Churg-Strauss syndrome. Brain magnetic resonance imaging (MRI) revealed multiple infarcts in bilateral cerebral and cerebellar hemispheres. The neurophysiology study did not reveal peripheral neuropathy. The patient was effectively treated with methylprednisolone, cyclophosphamide and warfarin.

CONCLUSION

Symptoms and signs of central nervous system can be the initial neurological manifestation of CSS patients. CSS should be considered while patients have stroke and hypereosinophilia. In our patient, there is a good response to timely steroid, immunosuppressant and anticoagulant therapies.

The role of inflammation, the autonomic nervous system and classical cardiovascular disease risk factors on subendocardial viability ratio in patients with RA: a cross-sectional and longitudinal study

INTRODUCTION

Evidence indicates that rheumatoid arthritis (RA) patients have increased susceptibility to myocardial ischaemia that contributes to myocardial infarction. The subendocardial viability ratio (SEVR) can be measured using pulse wave analysis and reflects myocardial oxygen supply and demand. The objective of the present study was to examine specific predictors of SEVR in RA patients, with a specific focus on inflammation and classical cardiovascular disease (CVD) risk factors.

METHODS

Two patient cohorts were included in the study; a primary cohort consisting of 220 RA patients and a validation cohort of 127 RA patients. All patients underwent assessment of SEVR using pulse wave analysis. Thirty-one patients from the primary cohort who were about to start anti-inflammatory treatment were prospectively examined for SEVR at pretreatment baseline and 2 weeks, 3 months and 1 year following treatment. Systemic markers of disease activity and classical CVD risk factors were assessed in all patients.

RESULTS

The SEVR (mean ± standard deviation) for RA in the primary cohort was 148 ± 27 and in the validation cohort was 142 ± 25. Regression analyses revealed that all parameters of RA disease activity were associated with SEVR, along with gender, blood pressure and heart rate. These findings were the same in the validation cohort. Analysis of longitudinal data showed that C-reactive protein (P < 0.001), erythrocyte sedimentation rate (P < 0.005), Disease Activity Score in 28 joints (P < 0.001), mean blood pressure (P < 0.005) and augmentation index (P < 0.001) were significantly reduced after commencing anti-TNFα treatment. Increasing C-reactive protein was found to be associated with a reduction in SEVR (P = 0.02) and an increase in augmentation index (P = 0.001).

CONCLUSION

The present findings reveal that the SEVR is associated with markers of disease activity as well as highly prevalent classical CVD risk factors in RA, such as high blood pressure and diabetes. Further prospective studies are required to determine whether the SEVR predicts future cardiac events in RA.

Biomechanics of the chick embryonic heart outflow tract at HH18 using 4D optical coherence tomography imaging and computational modeling

During developmental stages, biomechanical stimuli on cardiac cells modulate genetic programs, and deviations from normal stimuli can lead to cardiac defects. Therefore, it is important to characterize normal cardiac biomechanical stimuli during early developmental stages. Using the chicken embryo model of cardiac development, we focused on characterizing biomechanical stimuli on the Hamburger–Hamilton (HH) 18 chick cardiac outflow tract (OFT), the distal portion of the heart from which a large portion of defects observed in humans originate. To characterize biomechanical stimuli in the OFT, we used a combination of in vivo optical coherence tomography (OCT) imaging, physiological measurements and computational fluid dynamics (CFD) modeling. We found that, at HH18, the proximal portion of the OFT wall undergoes larger circumferential strains than its distal portion, while the distal portion of the OFT wall undergoes larger wall stresses. Maximal wall shear stresses were generally found on the surface of endocardial cushions, which are protrusions of extracellular matrix onto the OFT lumen that later during development give rise to cardiac septa and valves. The non-uniform spatial and temporal distributions of stresses and strains in the OFT walls provide biomechanical cues to cardiac cells that likely aid in the extensive differential growth and remodeling patterns observed during normal development.

Vascular and mesenchymal factors during heart development: a chronological study

As heart development is an incomplete described area, and likewise an important source of intra- and post-partum morbidity and mortality, we have aimed at analyzing both vascular and cytoskeletal factors during early heart development in humans. The distribution of CD105, CD31, α-SMA, vimentin and desmin have been studied on a series of normal human heart tissues varying between five and 33 weeks of gestational age, utilizing both enzymatic single immunohistochemistry, as well as double immunofluorescence. We showed here that CD105 is already expressed at five weeks of gestational age in the future endocardium, and that between 9 and 10 weeks it shows clear-cut formed vessels. CD31 was also present diffusely at five weeks in the myocardium, while beginning with seven weeks, endocardium and vessels were clearly positive. Contrary to what it might be expected for striated muscle cells, cardiomyocytes were α-SMA positive between 9 and 20 weeks, a time window during which the marker showed clear-cut sarcomer formation. Desmin was first detected at nine weeks lining the cardiomyocyte plasma membrane, and after 17 weeks it showed the adult-like striated pattern of the protein. As expected, vimentin was already present in the mesenchymal cells from the first investigated time point, retaining a perivascular localization only towards higher ages. This is the first study that describes these vascular, muscular and mesenchymal factors on a large series of sequential human tissues, in an attempt to shed more light on the development of heart.