Loss-of-function mutations in the co-chaperone protein BAG5 cause dilated cardiomyopathy requiring heart transplantation

Adeno-associated virus-mediated gene therapy for cardiac tachyarrhythmia: A systematic review and meta-analysis

Cardiac tachyarrhythmia presents a significant health care challenge, causing notable morbidity and mortality. Conventional treatments have limitations and potential risks, resulting in an elevated disease burden. Adeno-associated virus (AAV)-mediated gene therapy holds promise as a potential future treatment option. Therefore, we aimed to provide a measured overview of the latest developments in this rapidly growing field. PubMed and Embase databases were searched up to January 2024. Studies that employed AAV as a vector for delivery of therapeutic agents to treat cardiac tachyarrhythmia were included. Of the 26 studies included, 20 published in the last 5 years. There were 22 novel molecular targets identified. More than 80% of the included studies employed small-animal models or used AAV9. In atrial fibrillation preclinical studies, AAV-mediated gene therapy reduced atrial fibrillation inducibility by 81% (odds ratio, 0.19 [0.08-0.45]; P < .01). Similarly, for acquired and inherited ventricular arrhythmia, animal models receiving gene therapy had less inducible ventricular arrhythmia (odds ratio, 0.06 [0.03-0.11]; P < .01). This review highlights the rapid progress of AAV-mediated gene therapy for cardiac tachyarrhythmia. Although these investigations are currently in the early stages of clinical application, they present promising prospects for gene therapy. (PROSPERO registry: CRD42023479448).

A novel BAG5 variant impairs the ER stress response pathway, causing dilated cardiomyopathy and arrhythmia

Pathogenic BAG5 variants recently linked to dilated cardiomyopathy (DCM) prompt further investigation into phenotypic, mutational, and pathomechanistic aspects. We explored the clinical and molecular characteristics of DCM associated with BAG5 variants, uncovering the consistently severe manifestations of the disease and its impact on the endoplasmic reticulum (ER) stress response. The analysis involved three siblings affected by DCM and arrhythmia, along with their four unaffected siblings, their unaffected father, and their mother who exhibited arrhythmia. The parents were consanguineous. Exome and Sanger sequencing identified a novel BAG5 variant, c.444_445delGA (p.Lys149AsnfsTer6), homozygous in affected siblings and heterozygous in parents and unaffected siblings. We generated heterozygous and homozygous Bag5 point mutant knock-in (KI) mice and evaluated cardiac pathophysiology under stress conditions, including tunicamycin (TN) administration. Bag5-/- mice displayed no abnormalities up to 12 months old and showed no anomalies during an exercise stress test. However, following TN injection, Bag5-/- mice exhibited significantly reduced left ventricular fractional shortening (LVFS) and ejection fraction (LVEF). Their cardiac tissues exhibited a notable increase in apoptotic cells, despite non-distinctive changes in CHOP and GRP78 levels. Interestingly, only Bag5 KI male mice demonstrated arrhythmia, which was more pronounced in Bag5-/- than in Bag5+/-males. Here, our study reveals a novel BAG5 mutation causing DCM by impairing the ER stress response, with observed sex-specific arrhythmia differences.

BAG5 regulates HSPA8-mediated protein folding required for sperm head-tail coupling apparatus assembly

Teratozoospermia is a significant cause of male infertility, but the pathogenic mechanism of acephalic spermatozoa syndrome (ASS), one of the most severe teratozoospermia, remains elusive. We previously reported Spermatogenesis Associated 6 (SPATA6) as the component of the sperm head-tail coupling apparatus (HTCA) required for normal assembly of the sperm head-tail conjunction, but the underlying molecular mechanism has not been explored. Here, we find that the co-chaperone protein BAG5, expressed in step 9-16 spermatids, is essential for sperm HTCA assembly. BAG5-deficient male mice show abnormal assembly of HTCA, leading to ASS and male infertility, phenocopying SPATA6-deficient mice. In vivo and in vitro experiments demonstrate that SPATA6, cargo transport-related myosin proteins (MYO5A and MYL6) and dynein proteins (DYNLT1, DCTN1, and DNAL1) are misfolded upon BAG5 depletion. Mechanistically, we find that BAG5 forms a complex with HSPA8 and promotes the folding of SPATA6 by enhancing HSPA8's affinity for substrate proteins. Collectively, our findings reveal a novel protein-regulated network in sperm formation in which BAG5 governs the assembly of the HTCA by activating the protein-folding function of HSPA8.

Preclinical magnetic resonance imaging and spectroscopy in the fields of radiological technology, medical physics, and radiology

Magnetic resonance imaging (MRI) is an indispensable diagnostic imaging technique used in the clinical setting. MRI is advantageous over X-ray and computed tomography (CT), because the contrast provided depends on differences in the density of various organ tissues. In addition to MRI systems in hospitals, more than 100 systems are used for research purposes in Japan in various fields, including basic scientific research, molecular and clinical investigations, and life science research, such as drug discovery, veterinary medicine, and food testing. For many years, additional preclinical imaging studies have been conducted in basic research in the fields of radiation technology, medical physics, and radiology. The preclinical MRI research includes studies using small-bore and whole-body MRI systems. In this review, we focus on the animal study using small-bore MRI systems as "preclinical MRI". The preclinical MRI can be used to elucidate the pathophysiology of diseases and for translational research. This review will provide an overview of previous preclinical MRI studies such as brain, heart, and liver disease assessments. Also, we provide an overview of the utility of preclinical MRI studies in radiological physics and technology.

Exploring the complex spectrum of dominance and recessiveness in genetic cardiomyopathies

Discrete categorization of Mendelian disease genes into dominant and recessive models often oversimplifies their underlying genetic architecture. Cardiomyopathies (CMs) are genetic diseases with complex etiologies for which an increasing number of recessive associations have recently been proposed. Here, we comprehensively analyze all published evidence pertaining to biallelic variation associated with CM phenotypes to identify high-confidence recessive genes and explore the spectrum of monoallelic and biallelic variant effects in established recessive and dominant disease genes. We classify 18 genes with robust recessive association with CMs, largely characterized by dilated phenotypes, early disease onset and severe outcomes. Several of these genes have monoallelic association with disease outcomes and cardiac traits in the UK Biobank, including LMOD2 and ALPK3 with dilated and hypertrophic CM, respectively. Our data provide insights into the complex spectrum of dominance and recessiveness in genetic heart disease and demonstrate how such approaches enable the discovery of unexplored genetic associations.

Recent Advances in Translational Research for Heart Failure in Japan

Despite decades of intensive research and therapeutic development, heart failure remains a leading cause of death worldwide. However, recent advances in several basic and translational research fields, such as genomic analysis and single-cell analysis, have increased the possibility of developing novel diagnostic approaches to heart failure. Most cardiovascular diseases that predispose individuals to heart failure are caused by genetic and environmental factors. It follows that genomic analysis can contribute to the diagnosis and prognostic stratification of patients with heart failure. In addition, single-cell analysis has shown great potential for unveiling the pathogenesis and/or pathophysiology and for discovering novel therapeutic targets for heart failure. Here, we summarize the recent advances in translational research on heart failure in Japan, based mainly on our studies.

Genetic Testing for Cardiomyopathy in Japan 2022: Current Status and Issues of Precision Medicine

Although many causative genes for primary cardiomyopathy have been identified, the use of genetic testing in routine practice is limited in Japan presently. Genetic diagnosis has been reported to be useful for early diagnosis through cascade genetic screening in the family, differentiating secondary cardiomyopathies, and predicting prognosis in some patients; nonetheless, the acquisition of genetic information for cardiomyopathy is stagnating in actual clinical practice. There seem to be a number of reasons for this phenomenon, and although the use of next-generation sequencers has resolved some of the past issues, the importance of pathogenicity studies of variants that are identified is growing. To ensure that patients with cardiomyopathy and their relatives can receive precision medicine, the results of genetic analysis linked to clinical information need to be collected, and a database of variants in Japanese people needs to be established.

Disease modeling of desmosome-related cardiomyopathy using induced pluripotent stem cell-derived cardiomyocytes

Cardiomyopathy is a pathological condition characterized by cardiac pump failure due to myocardial dysfunction and the major cause of advanced heart failure requiring heart transplantation. Although optimized medical therapies have been developed for heart failure during the last few decades, some patients with cardiomyopathy exhibit advanced heart failure and are refractory to medical therapies. Desmosome, which is a dynamic cell-to-cell junctional component, maintains the structural integrity of heart tissues. Genetic mutations in desmosomal genes cause arrhythmogenic cardiomyopathy (AC), a rare inheritable disease, and predispose patients to sudden cardiac death and heart failure. Recent advances in sequencing technologies have elucidated the genetic basis of cardiomyopathies and revealed that desmosome-related cardiomyopathy is concealed in broad cardiomyopathies. Among desmosomal genes, mutations in PKP2 (which encodes PKP2) are most frequently identified in patients with AC. PKP2 deficiency causes various pathological cardiac phenotypes. Human cardiomyocytes differentiated from patient-derived induced pluripotent stem cells (iPSCs) in combination with genome editing, which allows the precise arrangement of the targeted genome, are powerful experimental tools for studying disease. This review summarizes the current issues associated with practical medicine for advanced heart failure and the recent advances in disease modeling using iPSC-derived cardiomyocytes targeting desmosome-related cardiomyopathy caused by PKP2 deficiency.

Reversible protein assemblies in the proteostasis network in health and disease

While proteins populating their native conformations constitute the functional entities of cells, protein aggregates are traditionally associated with cellular dysfunction, stress and disease. During recent years, it has become clear that large aggregate-like protein condensates formed via liquid-liquid phase separation age into more solid aggregate-like particles that harbor misfolded proteins and are decorated by protein quality control factors. The constituent proteins of the condensates/aggregates are disentangled by protein disaggregation systems mainly based on Hsp70 and AAA ATPase Hsp100 chaperones prior to their handover to refolding and degradation systems. Here, we discuss the functional roles that condensate formation/aggregation and disaggregation play in protein quality control to maintain proteostasis and why it matters for understanding health and disease.

VEZF1 loss-of-function mutation underlying familial dilated cardiomyopathy

Dilated cardiomyopathy (DCM), characteristic of left ventricular or biventricular dilation with systolic dysfunction, is the most common form of cardiomyopathy, and a leading cause of heart failure and sudden cardiac death. Aggregating evidence highlights the underlying genetic basis of DCM, and mutations in over 100 genes have been causally linked to DCM. Nevertheless, due to pronounced genetic heterogeneity, the genetic defects underpinning DCM in most cases remain obscure. Hence, this study was sought to identify novel genetic determinants of DCM. In this investigation, whole-exome sequencing and bioinformatics analyses were conducted in a family suffering from DCM, and a novel heterozygous mutation in the VEZF1 gene (coding for a zinc finger-containing transcription factor critical for cardiovascular development and structural remodeling), NM_007146.3: c.490A > T; p.(Lys164*), was identified. The nonsense mutation was validated by Sanger sequencing and segregated with autosome-dominant DCM in the family with complete penetrance. The mutation was neither detected in another cohort of 200 unrelated DCM patients nor observed in 400 unrelated healthy individuals nor retrieved in the Single Nucleotide Polymorphism database, the Human Gene Mutation Database and the Genome Aggregation Database. Biological analyses by utilizing a dual-luciferase reporter assay system revealed that the mutant VEZF1 protein failed to transactivate the promoters of MYH7 and ET1, two genes that have been associated with DCM. The findings indicate VEZF1 as a new gene responsible for DCM, which provides novel insight into the molecular pathogenesis of DCM, implying potential implications for personalized precisive medical management of the patients affected with DCM.

Clustering of Cardiac Transcriptome Profiles Reveals Unique

Dilated cardiomyopathy is a heterogeneous disease characterized by multiple genetic and environmental etiologies. The majority of patients are treated the same despite these differences. The cardiac transcriptome provides information on the patient's pathophysiology, which allows targeted therapy. Using clustering techniques on data from the genotype, phenotype, and cardiac transcriptome of patients with early- and end-stage dilated cardiomyopathy, more homogeneous patient subgroups are identified based on shared underlying pathophysiology. Distinct patient subgroups are identified based on differences in protein quality control, cardiac metabolism, cardiomyocyte function, and inflammatory pathways. The identified pathways have the potential to guide future treatment and individualize patient care.

Identification of BMP10 as a Novel Gene Contributing to Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM), characterized by left ventricular or biventricular enlargement with systolic dysfunction, is the most common type of cardiac muscle disease. It is a major cause of congestive heart failure and the most frequent indication for heart transplantation. Aggregating evidence has convincingly demonstrated that DCM has an underlying genetic basis, though the genetic defects responsible for DCM in a larger proportion of cases remain elusive, motivating the ongoing research for new DCM-causative genes. In the current investigation, a multigenerational family affected with autosomal-dominant DCM was recruited from the Chinese Han population. By whole-exome sequencing and Sanger sequencing analyses of the DNAs from the family members, a new BMP10 variation, NM_014482.3:c.166C > T;p.(Gln56*), was discovered and verified to be in co-segregation with the DCM phenotype in the entire family. The heterozygous BMP10 variant was not detected in 268 healthy volunteers enrolled as control subjects. The functional measurement via dual-luciferase reporter assay revealed that Gln56*-mutant BMP10 lost the ability to transactivate its target genes NKX2.5 and TBX20, two genes that had been causally linked to DCM. The findings strongly indicate BMP10 as a new gene contributing to DCM in humans and support BMP10 haploinsufficiency as an alternative pathogenic mechanism underpinning DCM, implying potential implications for the early genetic diagnosis and precision prophylaxis of DCM.

KLF13 Loss‐of‐Function Mutations Underlying Familial Dilated Cardiomyopathy

Background

Dilated cardiomyopathy (DCM), characterized by progressive left ventricular enlargement and systolic dysfunction, is the most common type of cardiomyopathy and a leading cause of heart failure and cardiac death. Accumulating evidence underscores the critical role of genetic defects in the pathogenesis of DCM, and >250 genes have been implicated in DCM to date. However, DCM is of substantial genetic heterogeneity, and the genetic basis underpinning DCM remains elusive in most cases.

Methods and Results

By genome‐wide scan with microsatellite markers and genetic linkage analysis in a 4‐generation family inflicted with autosomal‐dominant DCM, a new locus for DCM was mapped on chromosome 15q13.1–q13.3, a 4.77‐cM (≈3.43 Mbp) interval between markers D15S1019 and D15S1010, with the largest 2‐point logarithm of odds score of 5.1175 for the marker D15S165 at recombination fraction (θ)=0.00. Whole‐exome sequencing analyses revealed that within the mapping chromosomal region, only the mutation in the KLF13 gene, c.430G>T (p.E144X), cosegregated with DCM in the family. In addition, sequencing analyses of KLF13 in another cohort of 266 unrelated patients with DCM and their available family members unveiled 2 new mutations, c.580G>T (p.E194X) and c.595T>C (p.C199R), which cosegregated with DCM in 2 families, respectively. The 3 mutations were absent from 418 healthy subjects. Functional assays demonstrated that the 3 mutants had no transactivation on the target genes ACTC1 and MYH7 (2 genes causally linked to DCM), alone or together with GATA4 (another gene contributing to DCM), and a diminished ability to bind the promoters of ACTC1 and MYH7 . Add, the E144X‐mutant KLF13 showed a defect in intracellular distribution.

Conclusions

This investigation indicates KLF13 as a new gene predisposing to DCM, which adds novel insight to the molecular pathogenesis underlying DCM, implying potential implications for prenatal prevention and precision treatment of DCM in a subset of patients.

Autophagy in striated muscle diseases

Impaired biomolecules and cellular organelles are gradually built up during the development and aging of organisms, and this deteriorating process is expedited under stress conditions. As a major lysosome-mediated catabolic process, autophagy has evolved to eradicate these damaged cellular components and recycle nutrients to restore cellular homeostasis and fitness. The autophagic activities are altered under various disease conditions such as ischemia-reperfusion cardiac injury, sarcopenia, and genetic myopathies, which impact multiple cellular processes related to cellular growth and survival in cardiac and skeletal muscles. Thus, autophagy has been the focus for therapeutic development to treat these muscle diseases. To develop the specific and effective interventions targeting autophagy, it is essential to understand the molecular mechanisms by which autophagy is altered in heart and skeletal muscle disorders. Herein, we summarize how autophagy alterations are linked to cardiac and skeletal muscle defects and how these alterations occur. We further discuss potential pharmacological and genetic interventions to regulate autophagy activities and their applications in cardiac and skeletal muscle diseases.

Role of BAG5 in Protein Quality Control: Double-Edged Sword?

Cardiovascular disorder is the major health burden and cause of death among individuals worldwide. As the cardiomyocytes lack the ability for self-renewal, it is utmost necessary to surveil the protein quality in the cells. The Bcl-2 associated anthanogene protein (BAG) family and molecular chaperones (HSP70, HSP90) actively participate in maintaining cellular protein quality control (PQC) to limit cellular dysfunction in the cells. The BAG family contains a unique BAG domain which facilitates their interaction with the ATPase domain of the heat shock protein 70 (HSP70) to assist in protein folding. Among the BAG family members (BAG1-6), BAG5 protein is unique since it has five domains in tandem, and the binding of BD5 induces certain conformational changes in the nucleotide-binding domain (NBD) of HSP70 such that it loses its affinity for binding to ADP and results in enhanced protein refolding activity of HSP70. In this review, we shall describe the role of BAG5 in modulating mitophagy, endoplasmic stress, and cellular viability. Also, we have highlighted the interaction of BAG5 with other proteins, including PINK, DJ-1, CHIP, and their role in cellular PQC. Apart from this, we have described the role of BAG5 in cellular metabolism and aging.