Genetic resiliency associated with dominant lethal TPM1 mutation causing atrial septal defect with high heritability

Genetic and Environmental Contributors To Congenital Heart Disease

Purpose of Review

Paradigms surrounding congenital heart disease (CHD) etiology represent an evolving area of study. Traditionally, genetic causes of CHD have been classified into chromosomal abnormalities, copy number variation, and single-gene disorders, while environmental contributors include external and intrinsic maternal factors that impair cardiac development. Here, we summarize established causes of CHD and highlight emerging insights into CHD pathogenesis that may inform future treatment options.

Recent Findings

Recent advancements in next-generation sequencing technologies have uncovered novel genetic etiologies underlying CHD including oligogenic inheritance and pathogenic noncoding variation. In addition, industrialization and transformation of society has introduced new environmental risk factors that may contribute to CHD. Further, mechanistic insight into both genetic and environmental factors underlying CHD has led to discovery of novel therapeutic strategies.

Summary

New methodologies have greatly improved our comprehension of the heterogeneous mechanisms underlying CHD, catalyzing the discovery of effective therapeutic strategies to reduce CHD incidence.

Sex-specific response to A1BG loss results in female dilated cardiomyopathy

BACKGROUND

Cardiac disease often manifests with sex-specific differences in frequency, pathology, and progression. However, the molecular mechanisms underlying these differences remain incompletely understood. The glycoprotein A1BG has emerged as a female-specific regulator of cardiac structure and integrity, yet its precise role in the female heart is not well characterized.

METHODS

To investigate the sex-specific role of A1BG in the heart, we generated both a conditional A1bg knockout allele and an A1bg Rosa26 knockin allele. We employed histological analysis, electrocardiography, RNA sequencing (RNA-seq), transmission electron microscopy (TEM), western blotting, mass spectrometry, and immunohistochemistry to assess structural, functional, and molecular phenotypes.

RESULTS

Loss of A1BG in cardiomyocytes leads to persistent structural remodeling in female, but not male, hearts. Despite preserved systolic function in female A1bgCM/CM mice left ventricular dilation and wall thinning are evident and sustained over time, consistent with early-stage dilated cardiomyopathy (DCM). Transcriptomic analyses reveal that A1BG regulates key metabolic pathways in females, including glucose-6-phosphate and acetyl-CoA metabolism. TEM imaging highlights sex-specific disruption of intercalated disc architecture in female cardiomyocytes. These findings suggest that the absence of A1BG initiates chronic pathological remodeling in female hearts, potentially predisposing them to DCM under stress or aging.

CONCLUSION

A1BG is essential for maintaining ventricular structural integrity in female, but not male, hearts, leading to a chronic remodeling consistent with early-stage DCM.

High-fat stimulation induces atrial structural remodeling via the TPM1/P53/SHISA5 Axis

BACKGROUND

Atrial structural remodeling plays a central role in the development and progression of atrial fibrillation (AF) and significantly influences its course. Hyperlipidemia, a potential contributor to AF, affects cardiac function through multiple pathways. This study aimed to investigate the underlying mechanisms by which high lipid levels promote AF progression.

METHODS

In vitro cell models were established using palmitic acid (PA) stimulation, and in vivo rat models were generated by feeding a high-fat diet (HFD). Proteomic and transcriptomic sequencing analyses were conducted to identify differentially expressed proteins and genes. Extracellular vesicles (EVs) were isolated and characterized by differential centrifugation. Cell proliferation was assessed using EdU incorporation and flow cytometry, while transmission electron microscopy (TEM) was used to observe autophagy. Protein expression was analyzed by immunoblotting, immunohistochemistry, and immunofluorescence.

RESULTS

High lipid stimulation significantly increased the expression of tropomyosin 1 (TPM1) in cardiomyocytes, which was transferred to cardiac fibroblasts via EVs, activating the P53/SHISA5 signaling axis and inducing endoplasmic reticulum (ER) stress and autophagy, thereby promoting atrial structural remodeling. Activation of P53 and overexpression of SHISA5 in human cardiac fibroblast (HCF) cells reduced ER stress, autophagy, and fibrosis. Furthermore, ER stress and autophagy markers were significantly elevated in the atrial tissues of HFD-fed rats, while SHISA5 overexpression mitigated these effects.

CONCLUSION

High-fat stimulation may induce atrial fibrosis through the TPM1/P53/SHISA5 axis by modulating the ER stress-autophagy pathway.

The Role of Cilia and the Complex Genetics of Congenital Heart Disease

Congenital heart disease (CHD) can affect up to 1% of live births, and despite abundant evidence of a genetic etiology, the genetic landscape of CHD is still not well understood. A large-scale mouse chemical mutagenesis screen for mutations causing CHD yielded a preponderance of cilia-related genes, pointing to a central role for cilia in CHD pathogenesis. The genes uncovered by the screen included genes that regulate ciliogenesis and cilia-transduced cell signaling as well as many that mediate endocytic trafficking, a cell process critical for both ciliogenesis and cell signaling. The clinical relevance of these findings is supported by whole-exome sequencing analysis of CHD patients that showed enrichment for pathogenic variants in ciliome genes. Surprisingly, among the ciliome CHD genes recovered were many that encoded direct protein-protein interactors. Assembly of the CHD genes into a protein-protein interaction network yielded a tight interactome that suggested this protein-protein interaction may have functional importance and that its disruption could contribute to the pathogenesis of CHD. In light of these and other findings, we propose that an interactome enriched for ciliome genes may provide the genomic context for the complex genetics of CHD and its often-observed incomplete penetrance and variable expressivity.

Sex-Specific Response to A1BG Loss Results in Female Dilated Cardiomyopathy

Background

Cardiac disease often manifests differently in terms of frequency and pathology between men and women. However, the mechanisms underlying these differences are not fully understood. The glycoprotein A1BG is necessary for proper cardiac function in females but not males. Despite this, the role of A1BG in the female heart remains poorly studied.

Methods

To determine the sex differential function of A1BG, we generated a novel conditional A1bg allele and a novel conditional A1bg Rosa26 knockin allele. Histology, electrocardiography, transcriptional profiling (RNA-seq), transmission electron microscopy, western blot analyses, mass spectrometry, and immunohistochemistry were used to assess cardiac structure and function.

Results

The study reveals that the absence of A1BG results in significant cardiac dysfunction in female but not male mice. Gene expression underscores that A1BG plays a critical role in metabolic processes and the integrity of intercalated discs in female cardiomyocytes. This dysfunction may be related to sex-specific A1BG cardiac interactomes and manifests as structural and functional alterations in the left ventricle indicative of dilated cardiomyopathy, thus suggesting a sex-specific requirement for A1BG in cardiac health.

Conclusion

The loss of A1BG in cardiomyocytes leads to dilated cardiomyopathy in females, not males.

Insights into the genetic architecture of congenital heart disease from animal modeling

Congenital heart disease (CHD) is observed in up to 1% of live births and is one of the leading causes of mortality from birth defects. While hundreds of genes have been implicated in the genetic etiology of CHD, their role in CHD pathogenesis is still poorly understood. This is largely a reflection of the sporadic nature of CHD, as well as its variable expressivity and incomplete penetrance. We reviewed the monogenic causes and evidence for oligogenic etiology of CHD, as well as the role of de novo mutations, common variants, and genetic modifiers. For further mechanistic insight, we leveraged single-cell data across species to investigate the cellular expression characteristics of genes implicated in CHD in developing human and mouse embryonic hearts. Understanding the genetic etiology of CHD may enable the application of precision medicine and prenatal diagnosis, thereby facilitating early intervention to improve outcomes for patients with CHD.