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Genetic Basis of Left Ventricular Noncompaction

Rojanasopondist, Pakdee; Nesheiwat, Leigh; Piombo, Sebastian; Porter, George A; Ren, Mindong; Phoon, Colin K L
BACKGROUND:Left ventricular noncompaction (LVNC) is the third most common pediatric cardiomyopathy characterized by a thinned myocardium and prominent trabeculations. Next-generation genetic testing has led to a rapid increase in the number of genes reported to be associated with LVNC, but we still have little understanding of its pathogenesis. We sought to grade the strength of the gene-disease relationship for all genes reported to be associated with LVNC and identify molecular pathways that could be implicated. METHODS:Following a systematic PubMed review, all genes identified with LVNC were graded using a validated, semi-quantitative system based on all published genetic and experimental evidence created by the Clinical Genome Resource (ClinGen). Genetic pathway analysis identified molecular processes and pathways associated with LVNC. RESULTS:We identified 189 genes associated with LVNC: 11 (6%) were classified as definitive, 21 (11%) were classified as moderate, and 140 (74%) were classified as limited, but 17 (9%) were classified as no evidence. Of the 32 genes classified as definitive or moderate, the most common gene functions were sarcomere function (n=11; 34%), transcriptional/translational regulator (n=6; 19%), mitochondrial function (n=3; 9%), and cytoskeletal protein (n=3; 9%). Furthermore, 18 (56%) genes were implicated in noncardiac syndromic presentations. Lastly, 3 genetic pathways (cardiomyocyte differentiation via BMP receptors, factors promoting cardiogenesis in vertebrates, and Notch signaling) were found to be unique to LVNC and not overlap with pathways identified in dilated cardiomyopathy and hypertrophic cardiomyopathy. CONCLUSIONS:LVNC is a genetically heterogeneous cardiomyopathy. Distinct from dilated or hypertrophic cardiomyopathies, LVNC appears to arise from abnormal developmental processes.
PMID: 35549379
ISSN: 2574-8300
CID: 5214612

The remarkable Harriet Lane

Phoon, Colin KL
ISSN: 2155-3017
CID: 5295612

LPGAT1 controls the stearate/palmitate ratio of phosphatidylethanolamine and phosphatidylcholine in sn-1 specific remodeling

Xu, Yang; Miller, Paighton C; Phoon, Colin K L; Ren, Mindong; Nargis, Titli; Rajan, Sujith; Hussain, M Mahmood; Schlame, Michael
Most mammalian phospholipids contain a saturated fatty acid at the sn-1 carbon atom and an unsaturated fatty acid at the sn-2 carbon atom of the glycerol backbone group. While the sn-2 linked chains undergo extensive remodeling by deacylation and reacylation (Lands cycle), it is not known how the composition of saturated fatty acids is controlled at the sn-1 position. Here, we demonstrate that lysophosphatidylglycerol acyltransferase 1 (LPGAT1) is an sn-1 specific acyltransferase that controls the stearate/palmitate ratio of phosphatidylethanolamine (PE) and phosphatidylcholine. Bacterially expressed murine LPGAT1 transferred saturated acyl-CoAs specifically into the sn-1 position of lysophosphatidylethanolamine (LPE) rather than lysophosphatidylglycerol and preferred stearoyl-CoA over palmitoyl-CoA as the substrate. In addition, genetic ablation of LPGAT1 in mice abolished 1-LPE:stearoyl-CoA acyltransferase activity and caused a shift from stearate to palmitate species in PE, dimethyl-PE, and phosphatidylcholine. Lysophosphatidylglycerol acyltransferase 1 KO mice were leaner and had a shorter life span than their littermate controls. Finally, we show that total lipid synthesis was reduced in isolated hepatocytes of LPGAT1 knockout mice. Thus, we conclude that LPGAT1 is an sn-1 specific LPE acyltransferase that controls the stearate/palmitate homeostasis of PE and the metabolites of the PE methylation pathway and that LPGAT1 plays a central role in the regulation of lipid biosynthesis with implications for body fat content and longevity.
PMID: 35131264
ISSN: 1083-351x
CID: 5175992

A simple mechanistic explanation for Barth syndrome and cardiolipin remodeling

Xu, Yang; Phoon, Colin K L; Ren, Mindong; Schlame, Michael
Barth syndrome is a multisystem disorder caused by an abnormal metabolism of the mitochondrial lipid cardiolipin. In this review, we discuss physical properties, biosynthesis, membrane assembly, and function of cardiolipin. We hypothesize that cardiolipin reduces packing stress in the inner mitochondrial membrane, which arises as a result of protein crowding. According to this hypothesis, patients with Barth syndrome are unable to meet peak energy demands because they fail to concentrate the proteins of oxidative phosphorylation to a high surface density in the inner mitochondrial membrane.
PMID: 34611930
ISSN: 1573-2665
CID: 5067722

Truncus Arteriosus

Chapter by: Bhansali, Suneet; Phoon, Colin
in: StatPearls by
Treasure Island FL : StatPearls, 2022
pp. -
CID: 5295662

Condensed Mitochondria Assemble Into the Acrosomal Matrix During Spermiogenesis

Ren, Mindong; Xu, Yang; Phoon, Colin K L; Erdjument-Bromage, Hediye; Neubert, Thomas A; Rajan, Sujith; Hussain, M Mahmood; Schlame, Michael
Mammalian spermatogenesis is associated with the transient appearance of condensed mitochondria, a singularity of germ cells with unknown function. Using proteomic analysis, respirometry, and electron microscopy with tomography, we studied the development of condensed mitochondria. Condensed mitochondria arose from orthodox mitochondria during meiosis by progressive contraction of the matrix space, which was accompanied by an initial expansion and a subsequent reduction of the surface area of the inner membrane. Compared to orthodox mitochondria, condensed mitochondria respired more actively, had a higher concentration of respiratory enzymes and supercomplexes, and contained more proteins involved in protein import and expression. After the completion of meiosis, the abundance of condensed mitochondria declined, which coincided with the onset of the biogenesis of acrosomes. Immuno-electron microscopy and the analysis of sub-cellular fractions suggested that condensed mitochondria or their fragments were translocated into the lumen of the acrosome. Thus, it seems condensed mitochondria are formed from orthodox mitochondria by extensive transformations in order to support the formation of the acrosomal matrix.
PMID: 35531097
ISSN: 2296-634x
CID: 5214072

Neurological & psychological aspects of Barth syndrome: Clinical manifestations and potential pathogenic mechanisms

Olivar-Villanueva, Melissa; Ren, Mindong; Phoon, Colin K L
Barth syndrome is a rare X-linked multisystem mitochondrial disease that is caused by variants in the tafazzin gene leading to deficient and abnormal cardiolipin. Previous research has focused on the cardiomyopathy and neutropenia in individuals with Barth syndrome, yet just as common are the least explored neurological aspects of Barth syndrome. This review focuses on the major neuropsychological and neurophysiological phenotypes that affect the quality of life of individuals with Barth syndrome, including difficulties in sensory perception and feeding, fatigue, and cognitive and psychological challenges. We propose selected pathogenetic mechanisms underlying these phenotypes and draw parallels to other relevant disorders. Finally, avenues for future research are also suggested.
PMID: 34197965
ISSN: 1872-8278
CID: 5003722

Cardiolipin remodeling enables protein crowding in the inner mitochondrial membrane

Xu, Yang; Erdjument-Bromage, Hediye; Phoon, Colin K L; Neubert, Thomas A; Ren, Mindong; Schlame, Michael
Mitochondrial cristae are extraordinarily crowded with proteins, which puts stress on the bilayer organization of lipids. We tested the hypothesis that the high concentration of proteins drives the tafazzin-catalyzed remodeling of fatty acids in cardiolipin, thereby reducing bilayer stress in the membrane. Specifically, we tested whether protein crowding induces cardiolipin remodeling and whether the lack of cardiolipin remodeling prevents the membrane from accumulating proteins. In vitro, the incorporation of large amounts of proteins into liposomes altered the outcome of the remodeling reaction. In yeast, the concentration of proteins involved in oxidative phosphorylation (OXPHOS) correlated with the cardiolipin composition. Genetic ablation of either remodeling or biosynthesis of cardiolipin caused a substantial drop in the surface density of OXPHOS proteins in the inner membrane of the mouse heart and Drosophila flight muscle mitochondria. Our data suggest that OXPHOS protein crowding induces cardiolipin remodelling and that remodeled cardiolipin supports the high concentration of these proteins in the inner mitochondrial membrane.
PMID: 34661298
ISSN: 1460-2075
CID: 5043122

Ambulatory fetal heart rate monitoring (FHRM) to surveil pregnancies at risk for congenital heart block [Meeting Abstract]

Masson, M; Phoon, C; Sinkovskaya, E; Howley, L; Acherman, R; Makhoul, M; Pinto, N; Chang, M; Clancy, R; Drewes, B; Cuneo, B; Buyon, J
Background/Purpose: Congenital Heart Block (CHB) complicates 2% of anti-Ro/ SSA antibody positive pregnancies and carries substantial perinatal morbidity and mortality. Almost all survivors require lifelong pacing. Data suggests the potential of anti-inflammatory treatment of 1degree and 2degree CHB in preventing progression to immutable complete block. However, the optimal surveillance strategy to detect rapidly transitioning and potentially reversible conduction disease is unknown. This study addresses the feasibility, acceptance and accuracy of the fetal heart rate and rhythm technique (FHRM) in high risk mothers.
Method(s): Prospective data from the Surveillance To Prevent AV Block Likely to Occur Quickly (STOP BLOQ) study were leveraged. Mothers referred to the study all had commercially positive anti-Ro/ SSA antibodies and were stratified into high and low titers of anti-Ro60 and Ro52 based on a research ELISA which used a threshold cutoff defined as the titer above or below that obtained for 50 mothers with a previous CHB offspring. Mothers with anti-Ro60 or 52 antibodies at or above 1,000 I.U or with a previous CHB offspring, were trained to perform FHRM with an educational video and personal instruction from a pediatric cardiologist. From 17-25 weeks of gestation, FHRM was completed 3x/day in addition to weekly or biweekly fetal echocardiograms (echo). Mothers texted all FHRM sounds to the study's data coordinating center. For those FHRM deemed abnormal by the mothers, texts were immediately sent to an on call pediatric cardiologist who either reassured if FHRM was normal or referred for emergency fetal echo in < 6 hours if abnormal. Postnatal electrocardiograms were evaluated for CHB.
Result(s): Fifty-six mothers with commercial anti-Ro/ SSA positivity were consented to the study. Of these, 37 (inclusive of 6 with previous CHB) performed FRHM since they had high titer anti-Ro60 (n=8) or 52 antibodies (n=7) or both (n=21), albeit one mother had unexpectedly low titer antibodies to both Ro60 and 52 and a child with incomplete CHB 4 yrs prior to enrollment. In total 3,360 FHRM audiotexts were received during the monitoring period. Of these, 39 recordings from 5 concerned mothers prompted an immediate call with the cardiologist. All but 2 recordings were deemed to be normal based on review of the audiotext alone; the cardiologist requested that the patient send repeat recordings after review as part of re-training and to provide additional reassurance. In the 2 cases an emergency echo was completed in < 6 hrs. In both there were premature atrial contractions which confirmed the mother's perception of the FHRM abnormality. However, there was no evidence of conduction disease. All surveillance echoes were normal. Thus, the overall rate of false positive recordings for the concern of a conduction defect perceived by the mothers was 1.1% (38/3360). There were no cases of CHB at birth.
Conclusion(s): These data support that FHRM is feasible and accurate. Mothers can be empowered to detect rhythm abnormalities with very few false perceptions thus supporting this technique to substantially enhance the management of anti-Ro/ SSA pregnancies
ISSN: 2326-5205
CID: 5164622

Is My Mouse Pregnant? High-Frequency Ultrasound Assessment

Phoon, Colin K L; Ren, Mindong
The mouse is the mammalian animal model of choice for many human diseases and biological processes. Developmental biology often requires staged-pregnant mice to determine evolving processes at various timepoints. Moreover, optimal and efficient breeding of model mice requires an assessment of timed pregnancies. Most commonly, mice are mated overnight, and the presence of a vaginal plug is determined; however, the positive predictive value of this technique is suboptimal, and one needs to wait to know if the mouse is truly pregnant. High-resolution ultrasound biomicroscopy is an effective and efficient tool for imaging: 1) Whether a mouse is pregnant; 2) What gestational stage the mouse has reached; and 3) Whether there are intrauterine losses. In addition to the embryos and fetuses, the investigator must also recognize common artifacts in the abdominal cavity so as not to mistake these for a gravid uterus. This article provides a protocol for imaging along with illustrative examples.
PMID: 33818561
ISSN: 1940-087x
CID: 5295652