Colin K.L. Phoon

Onset of Cardiac Function During Early Mouse Embryogenesis Coincides With Entry of Primitive Erythroblasts Into the Embryo Proper

When cardiac function and blood flow are first established are fundamental questions in mammalian embryogenesis. The earliest erythroblasts arise in yolk sac blood islands and subsequently enter the embryo proper to initiate circulation. Embryos staged 0 to 30 somites (S) were examined in utero with 40- to 50-MHz ultrasound biomicroscopy (UBM)-Doppler, to determine onset of embryonic heartbeat and blood flow and to characterize basic physiology of the very early mouse embryonic circulation. A heartbeat was first detected at 5 S, and blood vascular flow at 7 S. Heart rate, peak arterial velocity, and velocity-time integral showed progressive increases that indicated a dramatically increasing cardiac output from even the earliest stages. In situ hybridization revealed an onset of the heartbeat coincident with the appearance of yolk sac–derived erythroblasts in the embryo proper at 5 S. Early maturation of the circulation follows a tightly coordinated program.

Evaluation of fetuses in a study of intravenous immunoglobulin as preventive therapy for congenital heart block: Results of a multicenter, prospective, open-label clinical trial†

OBJECTIVE The recurrence rate of anti-SSA/Ro-associated congenital heart block (CHB) is 17%. Sustained reversal of third-degree block has never been achieved. Based on potential reduction of maternal autoantibody titers as well as fetal inflammatory responses, intravenous immunoglobulin (IVIG) was evaluated as preventive therapy for CHB. METHODS A multicenter, prospective, open-label study based on Simons 2-stage optimal design was initiated. Enrollment criteria included the presence of anti-SSA/Ro antibodies in the mother, birth of a previous child with CHB/neonatal lupus rash, current treatment with < or = 20 mg/day of prednisone, and <12 weeks pregnant. IVIG (400 mg/kg) was given every 3 weeks from week 12 to week 24 of gestation. The primary outcome was the development of second-degree or third-degree CHB. RESULTS Twenty mothers completed the IVIG protocol before the predetermined stopping rule of 3 cases of advanced CHB in the study was reached. CHB was detected at 19, 20, and 25 weeks; none of the cases occurred following the finding of an abnormal PR interval on fetal Doppler monitoring. One of these mothers had 2 previous children with CHB. One child without CHB developed a transient rash consistent with neonatal lupus. Sixteen children had no manifestations of neonatal lupus at birth. No significant changes in maternal titers of antibody to SSA/Ro, SSB/La, or Ro 52 kd were detected over the course of therapy or at delivery. There were no safety issues. CONCLUSION This study establishes the safety of IVIG and the feasibility of recruiting pregnant women who have previously had a child with CHB. However, IVIG at low doses consistent with replacement does not prevent the recurrence of CHB or reduce maternal antibody titers.

Metabolism and function of mitochondrial cardiolipin.

Since it has been recognized that mitochondria are crucial not only for energy metabolism but also for other cellular functions, there has been a growing interest in cardiolipin, the specific phospholipid of mitochondrial membranes. Indeed, cardiolipin is a universal component of mitochondria in all eukaryotes. It has a unique dimeric structure comprised of two phosphatidic acid residues linked by a glycerol bridge, which gives rise to unique physicochemical properties. Cardiolipin plays an important role in the structural organization and the function of mitochondrial membranes. In this article, we review the literature on cardiolipin biology, focusing on the most important discoveries of the past decade. Specifically, we describe the formation, the migration, and the degradation of cardiolipin and we discuss how cardiolipin affects mitochondrial function. We also give an overview of the various phenotypes of cardiolipin deficiency in different organisms.

40 MHz Doppler characterization of umbilical and dorsal aortic blood flow in the early mouse embryo.

Physiological study of the developing mouse circulation has lagged behind advances in molecular cardiology. Using an innovative high-frequency Doppler system, we noninvasively characterized circulatory hemodynamics in early mouse embryos. We used image-guided 43 MHz pulsed-wave (PW) Doppler ultrasound to study the umbilical artery and vein, or dorsal aorta in 109 embryos. Studies were conducted on embryonic days (E) 9.5-14.5. Heart rate, peak blood flow velocities, and velocity time integrals in all vessels increased from E9.5-14.5, indicating increasing stroke volume and cardiac output. Heart rate, ranging from 192 bpm (E9.5) to 261 bpm (E14.5), was higher than previously reported. Placental impedance, assessed by the time delay between the peaks of the umbilical arterial and venous waveforms and by venous pulsatility, decreased with gestation. Acceleration time, a load-independent Doppler index of cardiac contractility, remained constant but seemed sensitive to heart rate. High-frequency PW Doppler is a powerful tool for the quantitative, noninvasive investigation of early mouse circulatory development.

Embryonic Heart Failure in NFATc1-/- Mice. Novel Mechanistic Insights From In Utero Ultrasound Biomicroscopy

Gene targeting in the mouse has become a standard approach, yielding important new insights into the genetic factors underlying cardiovascular development and disease. However, we still have very limited understanding of how mutations affect developing cardiovascular function, and few studies have been performed to measure altered physiological parameters in mouse mutant embryos. Indeed, although in utero lethality due to embryonic heart failure is one of the most common results of gene targeting experiments in the mouse, the underlying physiological mechanisms responsible for embryonic demise remain elusive. Using in utero ultrasound biomicroscopy (UBM), we studied embryonic day (E) 10.5 to 14.5 NFATc1−/− embryos and control littermates. NFATc1−/−mice, which lack outflow valves, die at mid-late gestation from presumed defects in forward blood flow with resultant heart failure. UBM showed increasing abnormal regurgitant flow in the aorta and extending into the embryonal–placental circulation, which was evident after E12.5 when outflow valves normally first develop. Reduced NFATc1−/− net volume flow and diastolic dysfunction contributed to heart failure, but contractile function remained unexpectedly normal. Among 107 NFATc1−/− embryos imaged, only 2 were observed to be in acute decline with progressive bradyarrhythmia, indicating that heart failure occurs rapidly in individual NFATc1−/− embryos. This study is among the first linking a specific physiological phenotype with a defined genotype, and demonstrates that NFATc1−/−embryonic heart failure is a complex phenomenon not simply attributable to contractile dysfunction.

Cardiovascular dysregulation of miR-17-92 causes a lethal hypertrophic cardiomyopathy and arrhythmogenesis

MicroRNA cluster miR‐17‐92 has been implicated in cardiovascular development and function, yet its precise mechanisms of action in these contexts are uncertain. This study aimed to investigate the role of miR‐17‐92 in morphogenesis and function of cardiac and smooth muscle tissues. To do so, a mouse model of conditional overexpression of miR‐17‐92 in cardiac and smooth muscle tissues was generated. Extensive cardiac functional studies identified a dose‐dependent induction of dilated, hypertrophic cardiomyopathy, and arrhythmia inducibility in transgenic animals, which correlated with premature mortality (98.3±42.5 d, P<0.0001). Expression analyses revealed the abundance of Pten transcript, a known miR‐17‐92 target, to be inversely correlated with miR‐17‐92 expression levels and heart size. In addition, we demonstrated through 3′‐UTR luciferase assays and expression analyses that Connexin43 (Cx43) is a novel direct target of miR‐19a/b and its expression is suppressed in transgenic hearts. Taken together, these data demonstrate that dysregulated expression of miR‐17‐92 during cardiovascular morphogenesis results in a lethal cardiomyopathy, possibly in part through direct repression of Pten and Cx43. This study highlights the importance of miR‐17‐92 in both normal and pathological functions of the heart, and provides a model that may serve as a useful platform to test novel antiarrhythmic therapeutics.—Danielson, L. S., Park, D. S., Rotllan, N., Chamorro‐Jorganes, A., Guijarro, M. V., Fernandez‐Hernando, C., Fishman, G. I., Phoon, C. K. L., Hernando, E. Cardiovascular dysregulation of miR‐17‐92 causes a lethal hypertrophic cardiomyopathy and arrhythmogenesis. FASEB J. 27, 1460–1467 (2013). www.fasebj.org

Imaging tools for the developmental biologist: ultrasound biomicroscopy of mouse embryonic development.

Progress has been rapid in the elucidation of genes responsible for cardiac development. Strategies to ascertain phenotypes, however, have lagged behind advances in genomics, particularly in the in vivo mouse embryo, considered a model organism for mammalian development, and for human development and disease. Over the past several years, our laboratory and others have pioneered a variety of ultrasound biomicroscopy (UBM)-Doppler approaches to study in vivo development in both normal and mutant mouse embryos. This state-of-the-art review will discuss the development and potential of ultrasound biomicroscopy as a tool for the in vivo imaging and phenotyping of both cardiac and non-cardiac organ systems in the early developing mouse. Broad, long-term research objectives are to define living structure-function relationships during critical periods of mammalian morphogenesis.

Tafazzin knockdown in mice leads to a developmental cardiomyopathy with early diastolic dysfunction preceding myocardial noncompaction.

Background Barth syndrome is a rare, multisystem disorder caused by mutations in tafazzin that lead to cardiolipin deficiency and mitochondrial abnormalities. Patients most commonly develop an early-onset cardiomyopathy in infancy or fetal life. Methods and Results Knockdown of tafazzin (TAZKD) in a mouse model was induced from the start of gestation via a doxycycline-inducible shRNA transgenic approach. All liveborn TAZKD mice died within the neonatal period, and in vivo echocardiography revealed prenatal loss of TAZKD embryos at E12.5-14.5. TAZKD E13.5 embryos and newborn mice demonstrated significant tafazzin knockdown, and mass spectrometry analysis of hearts revealed abnormal cardiolipin profiles typical of Barth syndrome. Electron microscopy of TAZKD hearts demonstrated ultrastructural abnormalities in mitochondria at both E13.5 and newborn stages. Newborn TAZKD mice exhibited a significant reduction in total mitochondrial area, smaller size of individual mitochondria, reduced cristae density, and disruption of the normal parallel orientation between mitochondria and sarcomeres. Echocardiography of E13.5 and newborn TAZKD mice showed good systolic function, but early diastolic dysfunction was evident from an abnormal flow pattern in the dorsal aorta. Strikingly, histology of E13.5 and newborn TAZKD hearts showed myocardial thinning, hypertrabeculation and noncompaction, and defective ventricular septation. Altered cellular proliferation occurring within a narrow developmental window accompanied the myocardial hypertrabeculation-noncompaction. Conclusions In this murine model, tafazzin deficiency leads to a unique developmental cardiomyopathy characterized by ventricular myocardial hypertrabeculation-noncompaction and early lethality. A central role of cardiolipin and mitochondrial functioning is strongly implicated in cardiomyocyte differentiation and myocardial patterning required for heart development. (J Am Heart Assoc. 2012;1:jah3-e000455 doi: 10.1161/JAHA.111.000455.)

Cognitive-behavioral Treatment of Persistent Functional Somatic Complaints and Pediatric Anxiety: An Initial Controlled Trial

Background: Children and adolescents who seek medical treatment for persistent physical distress often suffer from co‐occurring anxiety disorders. Treatment options for this impaired population are limited. This study tests the feasibility and potential efficacy of a cognitive‐behavioral intervention targeting pain and anxiety for youth with impairing functional physical symptoms and anxiety disorders presenting to pediatricians for medical care. Methods: Children and adolescents (aged 8–16) experiencing somatic complaints, without an explanatory medical disorder (i.e., functional), were recruited from primary care and specialty (gastroenterologists and cardiologists) pediatricians. Forty children, primarily with gastrointestinal symptoms, who met criteria for a co‐occurring anxiety disorder, were randomly assigned to a cognitive‐behavioral treatment addressing pain and anxiety, Treatment of Anxiety and Physical Symptoms (TAPS), or to a waiting list control. Results: TAPS was found to be an acceptable treatment for this population and was superior to the waiting list condition. Eighty percent of children in TAPS were rated as treatment responders by independent evaluators compared with none of the controls. Overall, self‐ and parent ratings indicated reductions in childrens somatic discomfort and anxiety following intervention. TAPS participants maintained clinical gains 3 months following treatment. Conclusions: The study supports the feasibility and preliminary efficacy of a cognitive‐behavioral intervention targeting co‐occurring physical distress and anxiety in youth presenting for medical treatment. Such an approach has the potential to exert broad impact on childrens dysfunction and to minimize exposure to invasive, ineffective, and costly medical procedures and treatments. Depression and Anxiety, 2011.

Outflow tract cushions perform a critical valve-like function in the early embryonic heart requiring BMPRIA-mediated signaling in cardiac neural crest

Neural crest-specific ablation of BMP type IA receptor (BMPRIA) causes embryonic lethality by embryonic day (E) 12.5, and this was previously postulated to arise from a myocardial defect related to signaling by a small population of cardiac neural crest cells (cNCC) in the epicardium. However, as BMP signaling via cNCC is also required for proper development of the outflow tract cushions, precursors to the semilunar valves, a plausible alternate or additional hypothesis is that heart failure may result from an outflow tract cushion defect. To investigate whether the outflow tract cushions may serve as dynamic valves in regulating hemodynamic function in the early embryo, in this study we used noninvasive ultrasound biomicroscopy-Doppler imaging to quantitatively assess hemodynamic function in mouse embryos with P0-Cre transgene mediated neural crest ablation of Bmpr1a (P0 mutants). Similar to previous studies, the neural crest-deleted Bmpr1a P0 mutants died at approximately E12.5, exhibiting persistent truncus arteriosus, thinned myocardium, and congestive heart failure. Surprisingly, our ultrasound analyses showed normal contractile indices, heart rate, and atrioventricular conduction in the P0 mutants. However, reversed diastolic arterial blood flow was detected as early as E11.5, with cardiovascular insufficiency and death rapidly ensuing by E12.5. Quantitative computed tomography showed thinning of the outflow cushions, and this was associated with a marked reduction in cell proliferation. These results suggest BMP signaling to cNCC is required for growth of the outflow tract cushions. This study provides definitive evidence that the outflow cushions perform a valve-like function critical for survival of the early mouse embryo.