J. Cardiovasc. Dev. Dis.2015, 2(4), 282-298; doi:10.3390/jcdd2040282 - published 30 November 2015 Show/Hide Abstract
Abstract: The definitive sinoatrial node (SAN), the primary pacemaker of the mammalian heart, develops from part of pro-pacemaking embryonic venous pole that expresses both Hcn4 and the transcriptional factor Shox2. It is noted that ectopic pacemaking activities originated from the myocardial sleeves of the pulmonary vein and systemic venous return, both derived from the Shox2+ pro-pacemaking cells in the venous pole, cause atrial fibrillation. However, the developmental link between the pacemaker properties in the embryonic venous pole cells and the SAN remains largely uncharacterized. Furthermore, the genetic program for the development of heterogeneous populations of the SAN is also under-appreciated. Here, we review the literature for a better understanding of the heterogeneous development of the SAN in relation to that of the sinus venosus myocardium and pulmonary vein myocardium. We also attempt to revisit genetic models pertinent to the development of pacemaker activities in the perspective of a Shox2-Nkx2-5 epistatic antagonism. Finally, we describe recent efforts in deciphering the regulatory networks for pacemaker development by genome-wide approaches.
J. Cardiovasc. Dev. Dis.2015, 2(4), 273-281; doi:10.3390/jcdd2040273 - published 16 November 2015 Show/Hide Abstract
Abstract: Only sparse data was available on long-term of Takotusbo Cardiomyopathy (TC). Previous studies suggested prognosis is not necessarily benign. We report the long-term follow-up of 12 TC patients actively managed with risk factor reduction. Retrospective analysis of all patients diagnosed with TC at our hospital between 1998 and 2010. We identified 12 patients with TC among 1651 cases of emergent left heart catheterization over 12 years. Mean follow-up time was 8.3 ± 3.6 years. All were female, 87% had hypertension, 25% had history of Coronary Artery Disease (CAD), 67% had hyperlipidemia, 44% had some preceding emotional trauma, and 44% had some physical/physiological stress. Previous studies have shown that over 50% of TC patients experience future cardiac events, and 10% have a recurrence of TC. Patients were prescribed therapeutic lifestyle changes (TLC) and guideline directed medical therapy (GDMT) for aggressive risk factor reduction. TLC included diet, exercise, and cardiac rehabilitation. GDMT often included aspirin, beta-blockers, ACE-inhibitors, and statins. Follow-up echocardiograms showed recovery and maintenance of the ejection fraction. There was no cardiac mortality and no recurrences of TC. Aggressive risk factor reduction with TLC and GDMT may be effective in improving the long term outcomes of patients with TC.
J. Cardiovasc. Dev. Dis.2015, 2(4), 248-272; doi:10.3390/jcdd2040248 - published 2 October 2015 Show/Hide Abstract
Abstract: Bicuspid aortic valve (BAV) is the most common congenital valvular heart defect with an overall frequency of 0.5%–1.2%. BAVs result from abnormal aortic cusp formation during valvulogenesis, whereby adjacent cusps fuse into a single large cusp resulting in two, instead of the normal three, aortic cusps. Individuals with BAV are at increased risk for ascending aortic disease, aortic stenosis and coarctation of the aorta. The frequent occurrence of BAV and its anatomically discrete but frequent co-existing diseases leads us to suspect a common cellular origin. Although autosomal-dominant transmission of BAV has been observed in a few pedigrees, notably involving the gene NOTCH1, no single-gene model clearly explains BAV inheritance, implying a complex genetic model involving interacting genes. Several sequencing studies in patients with BAV have identified rare and uncommon mutations in genes of cardiac embryogenesis. But the extensive cell-cell signaling and multiple cellular origins involved in cardiac embryogenesis preclude simplistic explanations of this disease. In this review, we examine the series of events from cellular and transcriptional embryogenesis of the heart, to development of the aortic valve.
J. Cardiovasc. Dev. Dis.2015, 2(3), 233-247; doi:10.3390/jcdd2030233 - published 8 September 2015 Show/Hide Abstract
Abstract: Although the genetic basis of mitral valve prolapse (MVP) has now been clearly established, the molecular and cellular mechanisms involved in the pathological processes associated to a specific mutation often remain to be determined. The FLNA gene (encoding Filamin A; FlnA) was the first gene associated to non-syndromic X-linked myxomatous valvular dystrophy, but the impacts of the mutations on its function remain un-elucidated. Here, using the first repeats (1–8) of FlnA as a bait in a yeast two-hybrid screen, we identified the tyrosine phosphatase PTPN12 (PTP-PEST) as a specific binding partner of this region of FlnA protein. In addition, using yeast two-hybrid trap assay pull down and co-immunoprecipitation experiments, we showed that the MVP-associated FlnA mutations (G288R, P637Q, H743P) abolished FlnA/PTPN12 interactions. PTPN12 is a key regulator of signaling pathways involved in cell-extracellular matrix (ECM) crosstalk, cellular responses to mechanical stress that involve integrins, focal adhesion transduction pathways, and actin cytoskeleton dynamics. Interestingly, we showed that the FlnA mutations impair the activation status of two PTPN12 substrates, the focal adhesion associated kinase Src, and the RhoA specific activating protein p190RhoGAP. Together, these data point to PTPN12/FlnA interaction and its weakening by FlnA mutations as a mechanism potentially involved in the physiopathology of FlnA-associated MVP.
J. Cardiovasc. Dev. Dis.2015, 2(3), 214-232; doi:10.3390/jcdd2030214 - published 17 August 2015 Show/Hide Abstract
Abstract: The heart valve interstitial cell (VIC) population is dynamic and thought to mediate lay down and maintenance of the tri-laminar extracellular matrix (ECM) structure within the developing and mature valve throughout life. Disturbances in the contribution and distribution of valve ECM components are detrimental to biomechanical function and associated with disease. This pathological process is associated with activation of resident VICs that in the absence of disease reside as quiescent cells. While these paradigms have been long standing, characterization of this abundant and ever-changing valve cell population is incomplete. Here we examine the expression pattern of Smooth muscle α-actin, Periostin, Twist1 and Vimentin in cultured VICs, heart valves from healthy embryonic, postnatal and adult mice, as well as mature valves from human patients and established mouse models of disease. We show that the VIC population is highly heterogeneous and phenotypes are dependent on age, species, location, and disease state. Furthermore, we identify phenotypic diversity across common models of mitral valve disease. These studies significantly contribute to characterizing the VIC population in health and disease and provide insights into the cellular dynamics that maintain valve structure in healthy adults and mediate pathologic remodeling in disease states.
J. Cardiovasc. Dev. Dis.2015, 2(3), 200-213; doi:10.3390/jcdd2030200 - published 24 July 2015 Show/Hide Abstract
Abstract: 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.