SORBS2 is a genetic factor contributing to cardiac malformation of 4q deletion syndrome patients

Impact of Sorbs2 dysfunction on cardiovascular diseases

Despite significant advancements in prevention and treatment over the past decades, cardiovascular diseases (CVDs) remain the leading cause of death worldwide. CVDs involve multifactorial inheritance, but our understanding of the genetic impact on these diseases is still incomplete. Sorbin and SH3 domain-containing protein 2 (Sorbs2) is ubiquitously expressed in various tissues, including the cardiovascular system. Increasing evidence suggests that Sorbs2 malfunction contributes to CVDs. This manuscript will review our current understanding of the potential mechanisms underlying Sorbs2 dysregulation in the development of CVDs.

Molecular genetics of congenital heart disease

Congenital heart disease (CHD) is the most prevalent human birth defect and remains a leading cause of mortality in childhood. Although advancements in surgical and medical interventions have significantly reduced mortality rates among infants with critical CHDs, many survivors experience substantial cardiac and extracardiac comorbidities that affect their quality of life. The etiology of CHD is multifactorial, involving both genetic and environmental factors, yet a definitive cause remains unidentified in many cases. Recent advancements in genetic testing technologies have improved our ability to identify the genetic causes of CHD. This review presents an updated summary of the established genetic contributions to CHD, including chromosomal aberrations and mutations in genes associated with transcription factors, cardiac structural proteins, chromatin modifiers, cilia-related proteins, and cell signaling pathways. Furthermore, we discuss recent findings that support the roles of non-coding mutations and complex inheritance in the etiology of CHD.

Cardiomyocyte SORBS2 expression increases in heart failure and regulates integrin interactions and extracellular matrix composition

AIMS

In this study, we aimed to uncover genes associated with stressed cardiomyocytes by combining single-cell transcriptomic datasets from failing cardiac tissue from both humans and mice.

METHODS AND RESULTS

Our bioinformatic analysis identified SORBS2 as conserved NPPA correlated gene. Using mouse models and cardiac tissue from human heart failure patients, we demonstrated that SORBS2 expression is consistently increased during pathological remodeling, correlates to disease severity and is regulated by GATA4. By affinity-purification mass-spectrometry, we showed SORBS2 to interact with the integrin-cytoskeleton connections. Cardiomyocyte-specific genetic loss of Sorbs2 in adult mice changed integrin interactions, indicated by the increased expression of several integrins and altered extracellular matrix components connecting to these integrins, leading to an exacerbated fibrotic response during pathological remodeling.

CONCLUSIONS

Sorbs2 is a cardiomyocyte-enriched gene that is increased during progression to heart failure in a GATA4-dependent manner and correlates to phenotypical hallmarks of cardiac failure.Our data indicate SORBS2 to function as a crucial regulator of integrin interactions and cardiac fibrosis.

Increased cardiac macrophages in Sorbs2-deficient hearts: revealing a potential role for macrophage in responding to embryonic myocardial abnormalities

Macrophages are known to support cardiac development and homeostasis, contributing to tissue remodeling and repair in the adult heart. However, it remains unclear whether embryonic macrophages also respond to abnormalities in the developing heart. Previously, we reported that the structural protein Sorbs2 promotes the development of the second heart field, with its deficiency resulting in atrial septal defects (ASD). In analyzing RNA-seq data, we noted an upregulation of macrophage-related genes in Sorbs2 -/- hearts. Immunostaining and lineage-tracing confirmed an increase in macrophage numbers, underscoring a macrophage response to myocardial abnormalities. Partial depletion of macrophages led to downregulation of genes involved in lipid metabolism, muscle development and organ regeneration, alongside upregulation of genes associated with DNA damage-induced senescence and cardiomyopathy. Additionally, a non-significant increase in septal defects in macrophage-depleted Sorbs2 -/- hearts suggests a potential reparative function for macrophages in maintaining structural integrity. Valve formation, however, remained unaffected. Our findings suggest that embryonic macrophages might sense abnormalities in embryonic cardiomyocytes and could adaptively support cardiac structure and function development in response to myocardial abnormalities.

Gene Commonality in Arterial Circuits Throughout the Body

The common genetic underpinnings of thoracic aortic aneurysms and aneurysms and dissections of several other major arterial circuits have been described in the literature. These include thoracic and abdominal aortic aneurysms, thoracic and intracranial aneurysms, thoracic aortic aneurysms, and spontaneous coronary artery dissections. In this study, we provide a unified report of these observations and investigate any genetic commonality between the above four arterial circulations.

Extracellular vesicles in cardiomyopathies: A narrative review

Extracellular vesicles (EVs) are membrane-bound particles released by all cells under physiological and pathological conditions. EVs constitute a potential tool to unravel cell-specific pathophysiological mechanisms at the root of disease states and retain the potential to act as biomarkers for cardiac diseases. By being able to carry bioactive cargo (such as proteins and miRNAs), EVs harness great potential as accessible "liquid biopsies", given their ability to reflect the state of their cell of origin. Cardiomyopathies encompass a variety of myocardial disorders associated with mechanical, functional and/or electric dysfunction. These diseases exhibit different phenotypes, including inappropriate ventricular hypertrophy, dilatation, scarring, fibro-fatty replacement, dysfunction, and may stem from multiple aetiologies, most often genetic. Thus, the aims of this narrative review are to summarize the current knowledge on EVs and cardiomyopathies (e.g., hypertrophic, dilated and arrhythmogenic), to elucidate the potential role of EVs in the paracrine cell-to-cell communication among cardiac tissue compartments, in aiding the diagnosis of the diverse subtypes of cardiomyopathies in a minimally invasive manner, and finally to address whether certain molecular and phenotypical characteristics of EVs may correlate with cardiomyopathy disease phenotype and severity.

TNF-α-induced Inhibition of Protein Myristoylation Via Binding Between NMT1 and Sorbs2 in Osteoblasts

BACKGROUND/AIM

Bone resolution due to tumor invasion often occurs on the surface of the jaw and is important for clinical prognosis. Although cytokines, such as TNF-α are known to impair osteoblasts, the underlying mechanism remains unclear. Protein myristoylation, a post-translational modification, plays an important role in the development of immune responses and cancerization of cells. A clear understanding of the mechanisms underlying this involvement will provide insights into molecular-targeted therapies. N-myristoyltransferase1 (NMT1), a specific enzyme involved in myristoylation, is expressed in cancer cells and in other normal cells, suggesting that changes in myristoylation may result from the regulation of NMT1 in cancer cells.

MATERIALS AND METHODS

Using newly emerging state-of-the-art techniques such as the Click-it assay, RNA interference, mass spectrometry, immunoprecipitation, immunocytochemistry, and western blotting, the expression of myristoylated proteins and the role of TNF-α stimulation on NMT1 and Sorbs2 binding were evaluated in a murine osteoblastic cell line (MC3T3-E1).

RESULTS

The expression of myristoylated proteins was detected; however, TNF-α stimulation resulted in their inhibition in MC3T3-E1 cells. The expression of NMT1 also increased. Immunoprecipitation and mass spectrometry identified Sorbs2 as a novel binding protein of NMT1, which upon TNF-α stimulation, inhibited myristoylation.

CONCLUSION

The binding between NMT1 and Sorbs2 can regulate myristoylation, and NMT1 can be considered as a potential target molecule for tumor invasion.

Novel dominant-negative FOXJ1 mutation in a family with heterotaxy plus mouse model

Background

Primary ciliary dyskinesia (PCD) is a clinically heterogeneous group of autosomal or, less frequently, X-chromosomal recessive inheritance syndrome of motile cilia dysfunction characterized by neonatal respiratory distress, oto-sino-pulmonary disease, infertility and situs inversus. Recently, type 43 PCD (CILD43, OMIM#618699) was established by autosomal-dominant loss-of-function mutations identified in Forkhead box J1 (FOXJ1). However, the functional validation of FOXJ1 mutations in humans and mice has not been fully performed. Here we studied a three-generation family with heterotaxy and proband with complex congenital heart disease (CHD).

Methods

We performed whole-exome sequencing to investigate the causative variant of this family and generated gene knock-in mice carrying the human equivalent mutation by homologous recombination. Then, microscopy analysis was used to characterize the phenotype and ciliary ultrastructure of the model. Effects of the variant on heart anomaly were preliminarily explored through transcriptome sequencing.

Results

A novel heterozygous deletion variant (c.1129delC/p.Leu377Trpfs*76) of FOXJ1 was discovered that exerts a dominant-negative effect (DNE) in vitro. Notably, both homozygous (Foxj1c.1129delT/c.1129delT) and heterozygous (Foxj1+/c.1129delT) mice developed situs inversus, hydrocephalus and showed a disruption of trachea cilia structure, whereas these abnormalities were only observed in previously reported Foxj1-/-, not Foxj1+/- mice. Thus, a more severe phenotype and higher expressivity of our mouse model further indicated the DNE of this mutation. Meanwhile, several cardiomyopathy-related genes were differentially expressed in the homozygous Foxj1 knock-in mouse hearts, pointing to a probable function in cardiac pathology.

Conclusions

Overall, our study results showed that c.1129delC mutation in FOXJ1 was regarded as the cause of situs inversus in this family and this mutant showed a capacity of DNE over wild-type FOXJ1, causing more serious consequences than the allelic deletion of Foxj1.

Knockout of Sorbin And SH3 Domain Containing 2 (Sorbs2) in Cardiomyocytes Leads to Dilated Cardiomyopathy in Mice

Background

Sorbin and SH3 domain containing 2 (Sorbs2) protein is a cytoskeletal adaptor with an emerging role in cardiac biology and disease; yet, its potential relevance to adult‐onset cardiomyopathies remains underexplored. Sorbs2 global knockout mice display lethal arrhythmogenic cardiomyopathy; however, the causative mechanisms remain unclear. Herein, we examine Sorbs2 dysregulation in heart failure, characterize novel Sorbs2 cardiomyocyte‐specific knockout mice (Sorbs2‐cKO), and explore associations between Sorbs2 genetic variations and human cardiovascular disease.

Methods and Results

Bioinformatic analyses show myocardial Sorbs2 mRNA is consistently upregulated in humans with adult‐onset cardiomyopathies and in heart failure models. We generated Sorbs2‐cKO mice and report that they develop progressive systolic dysfunction and enlarged cardiac chambers, and they die with congestive heart failure at about 1 year old. After 3 months, Sorbs2‐cKO mice begin to show atrial enlargement and P‐wave anomalies, without dysregulation of action potential–associated ion channel and gap junction protein expressions. After 6 months, Sorbs2‐cKO mice exhibit impaired contractility in dobutamine‐treated hearts and skinned myofibers, without dysregulation of contractile protein expressions. From our comprehensive survey of potential mechanisms, we found that within 4 months, Sorbs2‐cKO hearts have defective microtubule polymerization and compensatory upregulation of structural cytoskeletal and adapter proteins, suggesting that this early intracellular structural remodeling is responsible for contractile dysfunction. Finally, we identified genetic variants that associate with decreased Sorbs2 expression and human cardiac phenotypes, including conduction abnormalities, atrial enlargement, and dilated cardiomyopathy, consistent with Sorbs2‐cKO mice phenotypes.

Conclusions

Our studies show that Sorbs2 is essential for maintaining structural integrity in cardiomyocytes, likely through strengthening the interactions between microtubules and other cytoskeletal proteins at cross‐link sites.

Sequencing of a Chinese tetralogy of fallot cohort reveals clustering mutations in myogenic heart progenitors

Tetralogy of Fallot (TOF) is the most common cyanotic heart defect, yet the underlying genetic mechanisms remain poorly understood. Here, we performed whole-genome sequencing analysis on 146 nonsyndromic TOF parent-offspring trios of Chinese ethnicity. Comparison of de novo variants and recessive genotypes of this data set with data from a European cohort identified both overlapping and potentially novel gene loci and revealed differential functional enrichment between cohorts. To assess the impact of these mutations on early cardiac development, we integrated single-cell and spatial transcriptomics of early human heart development with our genetic findings. We discovered that the candidate gene expression was enriched in the myogenic progenitors of the cardiac outflow tract. Moreover, subsets of the candidate genes were found in specific gene coexpression modules along the cardiomyocyte differentiation trajectory. These integrative functional analyses help dissect the pathogenesis of TOF, revealing cellular hotspots in early heart development resulting in cardiac malformations.

Cytogenomic characterization of a de novo 4q34.1 deletion in a girl with mild dysmorphic features and a coagulation disorder

BACKGROUND

4q deletion syndrome is a rare chromosomal disorder that mostly arises de novo. The syndrome is characterized by craniofacial dysmorphism, digital abnormalities, skeletal alterations, heart malformations, developmental delay, growth retardation, Pierre Robin sequence, autistic spectrum and attention deficit-hyperactivity disorder, although not every patient shows the same features. Array comparative genomic hybridization (aCGH) use improves the detection of tiny chromosomal deletions and allows for a better understanding of genotype-phenotype correlations in affected patients. We report the case of a 6-year-old female patient showing mild dysmorphic features, mild mental disabilities and a coagulation disorder as a consequence of a de novo del(4)(q34.1) characterized by aCGH.

CASE PRESENTATION

A 6-year-old female patient exhibited special craniofacial features, such as backward-rotated ears, upslanted palpebral fissures, broad nasal bridges, anteverted nares, broad nasal alae, smooth philtrums, smooth nasolabial folds, thin lips, horizontal labial commissures, and retrognathia. In the oral cavity, maxillary deformation, a high arched palate, agenesis of both mandibular canines and fusion of two mandibular incisors were observed. She also displayed bilateral implantation of the proximal thumbs, widely spaced nipples, dorsal kyphosis, hyperlordosis, and clitoral hypertrophy. In addition, the patient presented with coagulopathy, psychomotor delay, attention deficit-hyperactivity disorder, and mild mental disability. A chromosomal study showed the karyotype 46,XX,del(4)(q34.1), while an aCGH analysis revealed an 18.9 Mb deletion of a chromosome 4q subtelomeric region spanning 93 known genes.

CONCLUSION

The clinical manifestations of this patient were similar to those reported in other individuals with 4q deletion syndrome. Although most of the patients with a 4q34 terminal deletion share similarities, variations in phenotype are also common. In general, clinical effects of chromosomal deletion syndromes depend on the length of the deleted chromosomal segment and, consequently, on the number of lost genes; however, in all of these syndromes, there is no simple correlation between the phenotype and the chromosomal region involved, particularly in cases of 4q deletion.