Mosaic deletion of claudin-5 reveals rapid non-cell-autonomous consequences of blood-brain barrier leakage

Claudin-5 (CLDN5) is an endothelial tight junction protein essential for blood-brain barrier (BBB) formation. Abnormal CLDN5 expression is common in brain disease, and knockdown of Cldn5 at the BBB has been proposed to facilitate drug delivery to the brain. To study the consequences of CLDN5 loss in the mature brain, we induced mosaic endothelial-specific Cldn5 gene ablation in adult mice (Cldn5iECKO). These mice displayed increased BBB permeability to tracers up to 10 kDa in size from 6 days post induction (dpi) and ensuing lethality from 10 dpi. Single-cell RNA sequencing at 11 dpi revealed profound transcriptomic differences in brain endothelial cells regardless of their Cldn5 status in mosaic mice, suggesting major non-cell-autonomous responses. Reactive microglia and astrocytes suggested rapid cellular responses to BBB leakage. Our study demonstrates a critical role for CLDN5 in the adult BBB and provides molecular insight into the consequences and risks associated with CLDN5 inhibition.

Titin M-line insertion sequence 7 is required for proper cardiac function in mice

Titin is a giant sarcomeric protein that is involved in a large number of functions, with a primary role in skeletal and cardiac sarcomere organization and stiffness. The titin gene (TTN) is subject to various alternative splicing events, but in the region that is present at the M-line, the only exon that can be spliced out is Mex5, which encodes for the insertion sequence 7 (is7). Interestingly, in the heart, the majority of titin isoforms are Mex5+, suggesting a cardiac role for is7. Here, we performed comprehensive functional, histological, transcriptomic, microscopic and molecular analyses of a mouse model lacking the Ttn Mex5 exon (ΔMex5), and revealed that the absence of the is7 is causative for dilated cardiomyopathy. ΔMex5 mice showed altered cardiac function accompanied by increased fibrosis and ultrastructural alterations. Abnormal expression of excitation-contraction coupling proteins was also observed. The results reported here confirm the importance of the C-terminal region of titin in cardiac function and are the first to suggest a possible relationship between the is7 and excitation-contraction coupling. Finally, these findings give important insights for the identification of new targets in the treatment of titinopathies.

Phospholamban antisense oligonucleotides improve cardiac function in murine cardiomyopathy

Heart failure (HF) is a major cause of morbidity and mortality worldwide, highlighting an urgent need for novel treatment options, despite recent improvements. Aberrant Ca2+ handling is a key feature of HF pathophysiology. Restoring the Ca2+ regulating machinery is an attractive therapeutic strategy supported by genetic and pharmacological proof of concept studies. Here, we study antisense oligonucleotides (ASOs) as a therapeutic modality, interfering with the PLN/SERCA2a interaction by targeting Pln mRNA for downregulation in the heart of murine HF models. Mice harboring the PLN R14del pathogenic variant recapitulate the human dilated cardiomyopathy (DCM) phenotype; subcutaneous administration of PLN-ASO prevents PLN protein aggregation, cardiac dysfunction, and leads to a 3-fold increase in survival rate. In another genetic DCM mouse model, unrelated to PLN (Cspr3/Mlp-/-), PLN-ASO also reverses the HF phenotype. Finally, in rats with myocardial infarction, PLN-ASO treatment prevents progression of left ventricular dilatation and improves left ventricular contractility. Thus, our data establish that antisense inhibition of PLN is an effective strategy in preclinical models of genetic cardiomyopathy as well as ischemia driven HF.

An epigenetic circuit linking oxidative stress and DNA hydroxymethylation in heart failure

Background

Heart failure is a major cause of morbidity and mortality worldwide, but the underlying molecular mechanisms remain not well defined. Reactive oxygen species (ROS) in heart failure (HF) alter multitudes of mitochondrial enzymes and metabolites, such as α-ketoglutarate and its oxidised form L-2-hydroxyglutarate (L-2HG). These metabolites are cofactors for ten eleven translocation (TET) enzymes that convert DNA's 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC).

Aim

We hypothesize that oxidative stress during heart failure alters mitochondrial function through epigenetic remodeling, and that reduction of oxidative stress will improve cardiac function.

Methods and results

Targeted LC-MS/MS analysis of dilated cardiomyopathy (DCM) hearts obtained from MLP−/− and WT littermate controls showed a significant increase in the oxidized metabolite L-2HG (∼30%, p=0.004), with significant reduction of multiple TCA cycle intermediates. RNA sequencing revealed a significant reduction in mRNA levels of IDH2 in human TTN related DCM and MLP−/− HF mice. The altered activity of IDH2 contributes to ROS production in these hearts and to the production of L-2HG. No alteration in the mitochondria structures was observed. HF biopsies show decreased TET activity most likely due to increased L-2HG levels. Whole genome single base pair 5mC and 5hmC deep sequencing of gDNA from explanted human DCM heart biopsies and MLP−/− mouse model revealed significantly altered global distribution of both 5mC and 5hmC in comparison to control samples. Genes involved in hypertrophy, such as Myh7 and Fhl2 were among the top genes with differential 5mC levels. Global loss of 5hmC level was observed, especially in the intronic regions of genes involved in redox hemostasis. Reducing oxidative stress in vivo in MLP−/− using a small molecule (AZ14117925) improves heart function (EF) by 13% [EF=(Treated:47,44%, Placebo: 34,54%), n=5 (males per group), p=0.0373, unpaired t-test]. Additional bioinformatic analysis revealed that reduction of ROS most likely leads to activation of TET and activation of pro-survival pathways, anti-oxidative stress response, and significantly less activation of apoptotic pathways.

Conclusion

Alterations in TCA cycle metabolites may underlie changes in DNA methylation and gene expression in end-stage human DCM and mouse models and indicate a role for epigenetic regulation of mitochondrial function in HF. NRF2 activation may pose a novel therapeutic approach to treat this devastating disease.

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): AstraZeneca

Titin splicing regulates cardiotoxicity associated with calpain 3 gene therapy for limb-girdle muscular dystrophy type 2A

Limb-girdle muscular dystrophy type 2A (LGMD2A or LGMDR1) is a neuromuscular disorder caused by mutations in the calpain 3 gene (CAPN3). Previous experiments using adeno-associated viral (AAV) vector-mediated calpain 3 gene transfer in mice indicated cardiac toxicity associated with the ectopic expression of the calpain 3 transgene. Here, we performed a preliminary dose study in a severe double-knockout mouse model deficient in calpain 3 and dysferlin. We evaluated safety and biodistribution of AAV9-desmin-hCAPN3 vector administration to nonhuman primates (NHPs) with a dose of 3 × 10¹³ viral genomes/kg. Vector administration did not lead to observable adverse effects or to detectable toxicity in NHP. Of note, the transgene expression did not produce any abnormal changes in cardiac morphology or function of injected animals while reaching therapeutic expression in skeletal muscle. Additional investigation on the underlying causes of cardiac toxicity observed after gene transfer in mice and the role of titin in this phenomenon suggest species-specific titin splicing. Mice have a reduced capacity for buffering calpain 3 activity compared to NHPs and humans. Our studies highlight a complex interplay between calpain 3 and titin binding sites and demonstrate an effective and safe profile for systemic calpain 3 vector delivery in NHP, providing critical support for the clinical potential of calpain 3 gene therapy in humans.

P5435Epigenetic modifications and gene expressions in Mybpc3 knockout mice

Background

DNA methylation and hydroxymethylation plays critical role in important biological processes, including differentiation of tissues in the embryo and cellular response to different diseases and diverse environmental factors. The epigenetic landscape in heart failure might be altered.

Purpose

Our objective was to determine how Mybpc3 deficiency, which produces hypertrophic cardiomyopathy, affects epigenetic landscape, gene expression, and regulation.

Methods

We generated and analysed genome-wide DNA methylomes and hydroxymethylomes from cardiac tissues of 12-week old Mybpc3−/− mice and littermate controls, and performed whole genome RNA sequencing (RNA-seq) for gene expression and validated the findings using qPCR.

Results

Single base resolution revealed overall lower 5-mC level in Mybpc3 deficient mice. In deficient mice, different genic regions including transcription start site, exons, and introns, had low levels of 5-mC. Although there was no overall difference in 5-hmC content, knockout mice had lower levels of 5-hmC in the distal part of the genes (last exon, transcription termination site, and 3'-flanking regions). The 5-hmC enrichment in the intronic regions was associated with higher gene expression, whereas, the presence of 5-mC in the 5'-flanking regions was associated with lower gene expression in both knockout and wildtype mice. Ingenuity pathway analysis (IPA) of differentially expressed genes revealed overrepresentation of genes involved in axonal-guidance pathway. Tet activity was downregulated in Mybpc3−/− mice, and it may explain the overall difference of 5-mC in deficient mice. We also observed that Mybpc3 ablation affected alternative splicing of Myh6 and Myh7.

Conclusion

This study establishes that knocking out of Mybpc3 changes epigenetic landscape in cardiac tissue, which is tightly linked to gene expression and regulation.

Acknowledgement/Funding

LeDucq 13CVD04, Hjärt och Lungfonden (Sweden)

Association of intronic DNA methylation and hydroxymethylation alterations in the epigenetic etiology of dilated cardiomyopathy

In this study, we investigated the role of DNA methylation [5-methylcytosine (5mC)] and 5-hydroxymethylcytosine (5hmC), epigenetic modifications that regulate gene activity, in dilated cardiomyopathy (DCM). A MYBPC3 mutant mouse model of DCM was compared with wild type and used to profile genomic 5mC and 5hmC changes by Chip-seq, and gene expression levels were analyzed by RNA-seq. Both 5mC-altered genes (957) and 5hmC-altered genes (2,022) were identified in DCM hearts. Diverse gene ontology and KEGG pathways were enriched for DCM phenotypes, such as inflammation, tissue fibrosis, cell death, cardiac remodeling, cardiomyocyte growth, and differentiation, as well as sarcomere structure. Hierarchical clustering of mapped genes affected by 5mC and 5hmC clearly differentiated DCM from wild-type phenotype. Based on these data, we propose that genomewide 5mC and 5hmC contents may play a major role in DCM pathogenesis. NEW & NOTEWORTHY Our data demonstrate that development of dilated cardiomyopathy in mice is associated with significant epigenetic changes, specifically in intronic regions, which, when combined with gene expression profiling data, highlight key signaling pathways involved in pathological cardiac remodeling and heart contractile dysfunction.