The R120G Knock-in Mutation in αB-Crystallin is Insufficient to Induce Cardiomyopathy in Mice

The SMYD1 p.Asn101Ser is a partial loss-of-function variant that impairs mitochondrial function and leads to early-onset cardiomyopathy

The first functional characterization of the cardiomyopathy-associated SMYD1 N101S variant identified in a child with severe infantile cardiomyopathy is provided, establishing a mechanistic link between SMYD1 dysfunction and infantile cardiomyopathy and highlighting the importance of integrating genomic and functional approaches in rare cardiovascular disease.

Alpha protein kinase 3 gene therapy restores heart function in mouse and human models of cardiomyopathy.

Truncating variants in the ALPK3 gene (encoding alpha protein kinase 3) cause severe cardiomyopathy for which no curative treatment exists1-3. Here we establish an adeno-associated virus (AAV)-mediated gene replacement therapy to deliver full-length human ALPK3. AAV-ALPK3 prevented disease in neonatal Alpk3-mutant mice and reversed established pathology in adults, with proteomic analysis demonstrating reversal of more than 95% of the molecular disease signature. Beyond ALPK3 deficiency, we explored broader therapeutic potential based on ALPK3's regulatory role in proteostasis, a pathway commonly disrupted across cardiomyopathies. ALPK3 expression is reduced in cardiomyocytes with TTN-truncating variants, the most prevalent cause of dilated cardiomyopathy, and the encoded titin protein has a protein quality control network in common with ALPK3. AAV-ALPK3 restored contractile function in human cardiac organoids with an ALPK3- or TTN-truncating variant. These findings provide proof of concept for ALPK3 gene therapy in patients with ALPK3 cardiomyopathy and reveal potential for indication expansion to cardiomyopathies associated with TTN-truncating variants, which are not amenable to gene replacement therapy due to size limitations.

LMNA p.H222P mutation causes contractile dysfunction via impaired mitochondrial calcium uptake in human cardiac laminopathy.

AIMS Mutations in the LMNA gene, which encodes lamin A/C, cause a variety of diseases known as laminopathies. Some mutations are particularly associated with the occurrence of dilated cardiomyopathy and heart failure, but the genotype-phenotype relationship and underlying mechanisms are unclear. METHODS AND RESULTS Induced pluripotent stem cells (hiPSCs) from a patient carrying a LMNA point mutation (c.665A>C, p.His222Pro) and a CRISPR/Cas9 corrected isogenic control hiPSCs clones were differentiated into cardiomyocytes (hiPSC-CMs), with no difference in the differentiation yield and in sarcomere organisation between the two cell lines. However, 3D cardiac organoids generated with LMNA p.H222P hiPSC-CMs showed an impaired contractility compared to control organoids. Calcium transient recordings in LMNA p.H222P mutant cardiomyocytes showed a significantly higher calcium transient amplitude with a significantly slower calcium re-uptake. Transcriptomic analyses suggested a global mitochondrial dysfunction and in particular an impaired mitochondrial calcium uptake with a significantly decreased expression of the mitochondrial calcium uniporter (MCU). This decrease in MCU expression was confirmed by western blot and was accompanied by an increased MICU1:MCU ratio, as well as an increased PDH Ser232 and PDH Ser300 phosphorylation, indicating an altered mitochondrial calcium uptake in the LMNA mutant hiPSC-CMs. Consistently, lower mitochondrial respiration and ATP levels were found in LMNA p.H222P hiPSC-CMs as compared to isogenic controls. Strikingly, treatment with the MCU activator amorolfine restored mitochondrial calcium uptake and improved contractility in LMNA mutant hiPSC-CMs. CONCLUSIONS Our results establish a direct mechanistic link between nuclear envelope dysfunction and impaired mitochondrial function, and highlight the MCU complex as a potential therapeutic target in LMNA-related cardiomyopathy. More broadly, this work provides a paradigm for connecting gene-specific nuclear defects to mitochondrial dysfunction in inherited cardiomyopathies.

Vitronectin-driven amyloid deposition disrupts mitochondrial homeostasis via integrin-mediated pathway in a humanized mouse model of transthyretin cardiac amyloidosis.

Characterization of the frameshift c.515dupC knock-in mouse model of HSPB8-associated myopathy (MFM13) and evaluation of Trehalose as autophagy-modulating therapy

These findings support the value of preclinical models for translational studies, and autophagy enhancement as a potential therapeutic strategy for HSPB8-related myopathy, and evaluated trehalose, a natural disaccharide that induces HSPB8 and enhances autophagy.

The Maine Coon Cat Harboring the MYBPC3-A31P Mutation: A Genotype-Stratified Phenotypic Characterization of Hypertrophic Cardiomyopathy

Background Most animal models of HCM are mouse-based, but the thin interventricular septum in mice makes it difficult to clearly distinguish pathological hypertrophy, which introduces substantial errors and constrains basic HCM research. Cats develop HCM spontaneously, and the common MYBPC3-A31P variant in cats is homologous to human mutations in both genetics and pathology, with a larger body size that makes them suitable as large-animal models. This study examines how heterozygosity or homozygosity for the p.A31P mutation (c.91G>C) in the MYBPC3 gene affects the phenotype and severity of HCM in affected cats, with the aim of establishing an ideal large-animal model for clinical risk stratification and precision diagnosis and treatment of human HCM. Methods Forty-nine Maine Coon cats were enrolled and stratified into homozygous mutant (HOM, n=8), heterozygous mutant (HET, n=26), and wild-type (WT, n=15) groups. All cats underwent echocardiography, blood pressure measurement, physiological assessment, hematological and biochemical analyses, and cross-species sequence conservation analysis. Results No significant differences in baseline characteristics including age and body weight were observed among groups (P>0.05). HOM cats exhibited significantly higher left ventricular outflow tract pressure gradients and greater basal septal thickness compared to WT cats (P<0.05), with HET cats showing intermediate values. Analysis of hematological and serum biochemical parameters revealed no evidence of systemic inflammation or hepatic injury. Sequence conservation analysis confirmed that the A31 residue is highly conserved across mammalian species. Conclusions This study provides a phenotypic characterization of Maine Coon cats carrying the MYBPC3-A31P mutation, revealing marked gene-dose effects on cardiac structure and function, with homozygous individuals exhibiting more severe phenotypic features. This model serves as a large-animal translational platform that not only clarifies genotype–phenotype correlations but also supports risk stratification and precision therapeutic strategies in human HCM. Its spontaneous nature and genetic homology to human disease make it particularly valuable for bridging preclinical findings to clinical application. RESEARCH PERSPECTIVE What Is New? This study provides a genotype-stratified phenotypic characterization of MYBPC3-A31P mutation in Maine Coon cats, covering echocardiographic and laboratory parameters across homozygous, heterozygous, and wild-type groups. The results suggest a gene-dose effect, with homozygotes showing more pronounced cardiac changes, heterozygotes showing intermediate features, and wild-types remaining unaffected. All cats were raised under uniform environmental and dietary conditions, which may reduce the confounding effects of extrinsic factors compared with studies using cats from varied sources. What Question Should Be Addressed Next? Longitudinal follow-up of this cohort could help determine whether the observed genotype-related differences progress to clinical events over time. Protein-level and functional studies would be useful to explore the molecular mechanisms underlying the gene-dose-dependent phenotype. The utility of this feline model for evaluating genotype-specific therapeutic approaches remains to be examined.