The Role of Bmp- and Fgf Signaling Modulating Mouse Proepicardium Cell Fate

Bmp and Fgf signaling are widely involved in multiple aspects of embryonic development. More recently non coding RNAs, such as microRNAs have also been reported to play essential roles during embryonic development. We have previously demonstrated that microRNAs, i.e., miR-130, play an essential role modulating Bmp and Fgf signaling during early stages of cardiomyogenesis. More recently, we have also demonstrated that microRNAs are capable of modulating cell fate decision during proepicardial/septum transversum (PE/ST) development, since over-expression of miR-23 blocked while miR-125, miR-146, miR-223 and miR-195 enhanced PE/ST-derived cardiomyogenesis, respectively. Importantly, regulation of these microRNAs is distinct modulated by Bmp2 and Fgf2 administration in chicken. In this study, we aim to dissect the functional role of Bmp and Fgf signaling during mouse PE/ST development, their implication regulating post-transcriptional modulators such as microRNAs and their impact on lineage determination. Mouse PE/ST explants and epicardial/endocardial cell cultures were distinctly administrated Bmp and Fgf family members. qPCR analyses of distinct microRNAs, cardiomyogenic, fibrogenic differentiation markers as well as key elements directly epithelial to mesenchymal transition were evaluated. Our data demonstrate that neither Bmp2/Bmp4 nor Fgf2/Fgf8 signaling is capable of inducing cardiomyogenesis, fibrogenesis or inducing EMT in mouse PE/ST explants, yet deregulation of several microRNAs is observed, in contrast to previous findings in chicken PE/ST. RNAseq analyses in mouse PE/ST and embryonic epicardium identified novel Bmp and Fgf family members that might be involved in such cell fate differences, however, their implication on EMT induction and cardiomyogenic and/or fibrogenic differentiation is limited. Thus our data support the notion of species-specific differences regulating PE/ST cardiomyogenic lineage commitment.

Extracellular mechanical forces drive endocardial cell volume decrease during cardiac valve morphogenesis

Organ morphogenesis involves dynamic changes of tissue properties at the cellular scale. In addition, cells need to adapt to their mechanical environment through mechanosensitive pathways. How mechanical cues influence cell behaviors during morphogenesis, however, remains poorly understood. Here we studied the influence of mechanical forces during the formation of the atrioventricular canal (AVC) where cardiac valves develop. We show that in zebrafish the AVC forms within a zone of tissue convergence between the atrium and the ventricle which is associated with increased activation of the actomyosin meshwork and endocardial cell orientation changes. We demonstrate that tissue convergence occurs with a major reduction of endocardial cell volume triggered by mechanical forces and the mechanosensitive channels TRPP2/TRPV4. In addition, we show that the extracellular matrix component hyaluronic acid controls cell volume changes. Together, our data suggest that cell volume change is a key cellular feature activated by mechanical forces during cardiovascular morphogenesis. This work further unravels how mechanical forces and extracellular matrix can influence tissue remodeling in developing organs.

Computational Model based Approach to Analyse Calcium (Ca2+) Channel in Ventricular Cells for Normal and Cardiac Arrhythmias Using Euler Integration Method – A Simulation Study

Aim: In this paper, analysis of ventricular arrhythmias are made with respect to the Calcium (Ca2+) ion channel dysfunction (generating improper electrical activity). Many cases can make arrhythmias and most of them are related to generation or conduction of Action Potential (AP) in cardiac myocardium. Materials and method: Human ventricular cell based on the model of the human endocardial cell by Ten Tusscher (TT). The TT model data is modified based on the experimental data of Han, describing the properties of Ca2+ currents and its channel dynamics in human ventricular cells. Euler integration method is used to analyse the human ventricular model for different channel failure conditions in the same group of 50 samples. Results: Our research findings focus with respect to normal and deviant Ca2+ conductance (GCaL). The normal GCaL 0.000175nS and deviant GCaL increase like (10%=0.000218nS, 25%=0.000182nS, 50%=0.000262nS and 100%=0.000350nS) having the normal AP average value ranges between 26.0mV to -74.0mV and 12.0mV to -88.0mV for 10% GCaL, 18.0mV to -78.0mV for 25% GCaL, 18.0mV to -78.0mV for 50% GCaL and 21.0mV to -75.0mV for 100% GCaL deviants. Similarly, deviant GCaL decrease like (10%=0.000158nS, 25%=0.000131nS, 50%=0.000088nS and 100%=0.000001nS) having the deviant AP mean values ranges between 10.0mV to -90.0mV for 10% GCaL, 7.0mV to -92.0mV for 25% GCaL, -9.0mV to -96.0mV for 50% GCaL and -51.0mV to 100.0mV for 100% GCaL. Simultaneously its membrane Ca2+ currents are having significant variations. Conclusion: The results show clearly for the affirmation for Excitation and Coupling (EC) failures. EC failures lead to a systole phase that is more prolonged, that in turns to produce QT syndrome and hypertrophic cardiomyopathy.

SOX7 suppresses endothelial-to-mesenchymal transitions by enhancing VE-cadherin expression during outflow tract development

The endothelial-to-mesenchymal transition (EndMT) is a critical process that occurs during the development of the outflow tract (OFT). Malformations of the OFT can lead to the occurrence of conotruncal defects (CTD). SOX7 duplication has been reported in patients with congenital CTD, but its specific role in OFT development remains poorly understood. To decipher this, histological analysis showed that SOX7 was regionally expressed in the endocardial endothelial cells and in the mesenchymal cells of the OFT, where EndMT occurs. Experiments, using invitro collagen gel culture system, revealed that SOX7 was a negative regulator of EndMT that inhibited endocardial cell migration and resulted in decreased number of mesenchymal cells. Forced expression of SOX7 in endothelial cells blocked further migration and improved the expression of the adhesion protein vascular endothelial (VE)-cadherin. Moreover, a VE-cadherin knockdown could partly reverse the SOX7-mediated repression of cell migration. Luciferase and electrophoretic mobility shift assays demonstrated that SOX7 up-regulated VE-cadherin by directly binding to the gene’s promoter in endothelial cells. The coding exons and splicing regions of the SOX7 gene were also scanned in the 536 sporadic CTD patients and in 300 unaffected controls, which revealed four heterozygous SOX7 mutations. Luciferase assays revealed that two SOX7 variants weakened the transactivation of the VE-cadherin promoter. In conclusion, SOX7 inhibited EndMT during OFT development by directly upregulating the endothelial-specific adhesion molecule VE-cadherin. SOX7 mutations can lead to impaired EndMT by regulating VE-cadherin, which may give rise to the molecular mechanisms associated with SOX7 in CTD pathogenesis.

Endocardial/endothelial angiocrines regulate cardiomyocyte development and maturation and induce features of ventricular non-compaction

Non-compaction cardiomyopathy is a devastating genetic disease caused by insufficient consolidation of ventricular wall muscle that can result in inadequate cardiac performance. Despite being the third most common cardiomyopathy, the mechanisms underlying the disease, including the cell types involved, are poorly understood. We have previously shown that endothelial cell-specific deletion of the chromatin remodeler gene Ino80 results in defective coronary vessel development that leads to ventricular noncompaction in embryonic mouse hearts. Here, we used single-cell RNA-sequencing to characterize endothelial and endocardial defects in Ino80-deficient hearts. We observed a pathological endocardial cell population in the non-compacted hearts, and identified multiple dysregulated angiocrine factors that dramatically affected cardiomyocyte behavior. We identified Col15A1 as a coronary vessel-secreted angiocrine factor, downregulated by Ino80-deficiency, that functioned to promote cardiomyocyte proliferation. Furthermore, mutant endocardial and endothelial cells (ECs) upregulated expression of secreted factors, such as Tgfbi, Igfbp3, Isg15, and Adm, which decreased cardiomyocyte proliferation and increased maturation. These findings support a model where coronary ECs normally promote myocardial compaction through secreted factors, but that endocardial and ECs can secrete factors that contribute to non-compaction under pathological conditions.

Cardiac function modulates endocardial cell dynamics to shape the cardiac outflow tract

ABSTRACTPhysical forces are important participants in the cellular dynamics that shape developing organs. During heart formation, for example, contractility and blood flow generate biomechanical cues that influence patterns of cell behavior. Here, we address the interplay between function and form during the assembly of the cardiac outflow tract (OFT), a crucial connection between the heart and vasculature that develops while circulation is underway. In zebrafish, we find that the OFT expands via accrual of both endocardial and myocardial cells. However, when cardiac function is disrupted, OFT endocardial growth ceases, accompanied by reduced proliferation and reduced addition of cells from adjacent vessels. The TGFβ receptor Acvrl1 is required for addition of endocardial cells, but not for their proliferation, indicating distinct regulation of these essential cell behaviors. Together, our results suggest that cardiac function modulates OFT morphogenesis by triggering endocardial cell accumulation that induces OFT lumen expansion and shapes OFT dimensions.