Transcriptome analysis of human heart failure reveals dysregulated cell adhesion in dilated cardiomyopathy and activated immune pathways in ischemic heart failure.

BACKGROUND: Current heart failure (HF) treatment is based on targeting symptoms and left ventricle dysfunction severity, relying on a common HF pathway paradigm to justify common treatments for HF patients. This common strategy may belie an incomplete understanding of heterogeneous underlying mechanisms and could be a barrier to more precise treatments. We hypothesized we could use RNA-sequencing (RNA-seq) in human heart tissue to delineate HF etiology-specific gene expression signatures. RESULTS: RNA-seq from 64 human left ventricular samples: 37 dilated (DCM), 13 ischemic (ICM), and 14 non-failing (NF). Using a multi-analytic approach including covariate adjustment for age and sex, differentially expressed genes (DEGs) were identified characterizing HF and disease-specific expression. Pathway analysis investigated enrichment for biologically relevant pathways and functions. DCM vs NF and ICM vs NF had shared HF-DEGs that were enriched for the fetal gene program and mitochondrial dysfunction. DCM-specific DEGs were enriched for cell-cell and cell-matrix adhesion pathways. ICM-specific DEGs were enriched for cytoskeletal and immune pathway activation. Using the ICM and DCM DEG signatures from our data we were able to correctly classify the phenotypes of 24/31 ICM and 32/36 DCM samples from publicly available replication datasets. CONCLUSIONS: Our results demonstrate the commonality of mitochondrial dysfunction in end-stage HF but more importantly reveal key etiology-specific signatures. Dysfunctional cell-cell and cell-matrix adhesion signatures typified DCM whereas signals related to immune and fibrotic responses were seen in ICM. These findings suggest that transcriptome signatures may distinguish end-stage heart failure, shedding light on underlying biological differences between ICM and DCM.

Danon disease - dysregulation of autophagy in a multisystem disorder with cardiomyopathy.

Danon disease is a rare, severe X-linked form of cardiomyopathy caused by deficiency of lysosome-associated membrane protein 2 (LAMP-2). Other clinical manifestations include skeletal myopathy, cognitive defects and visual problems. Although individuals with Danon disease have been clinically described since the early 1980s, the underlying molecular mechanisms involved in pathological progression remain poorly understood. LAMP-2 is known to be involved in autophagy, and a characteristic accumulation of autophagic vacuoles in the affected tissues further supports the idea that autophagy is disrupted in this disease. The LAMP2 gene is alternatively spliced to form three splice isoforms, which are thought to play different autophagy-related cellular roles. This Commentary explores findings from genetic, histological, functional and tissue expression studies that suggest that the specific loss of the LAMP-2B isoform, which is likely to be involved in macroautophagy, plays a crucial role in causing the Danon phenotype. We also compare findings from mouse and cellular models, which have allowed for further molecular characterization but have also shown phenotypic differences that warrant attention. Overall, there is a need to better functionally characterize the LAMP-2B isoform in order to rationally explore more effective therapeutic options for individuals with Danon disease.

Genetic Infiltrative Cardiomyopathies.

Infiltrative cardiomyopathies are characterized by abnormal accumulation or deposition of substances in cardiac tissue leading to cardiac dysfunction. These can be inherited, resulting from mutations in specific genes, which engender a diverse array of extracardiac features but overlapping cardiac phenotypes. This article provides an overview of each inherited infiltrative cardiomyopathy, describing the causative genes, the pathologic mechanisms involved, the resulting cardiac manifestations, and the therapies currently offered or being developed.

Cardiac dopamine D1 receptor triggers ventricular arrhythmia in chronic heart failure.

Pathophysiological roles of cardiac dopamine system remain unknown. Here, we show the role of dopamine D1 receptor (D1R)-expressing cardiomyocytes (CMs) in triggering heart failure-associated ventricular arrhythmia. Comprehensive single-cell resolution analysis identifies the presence of D1R-expressing CMs in both heart failure model mice and in heart failure patients with sustained ventricular tachycardia. Overexpression of D1R in CMs disturbs normal calcium handling while CM-specific deletion of D1R ameliorates heart failure-associated ventricular arrhythmia. Thus, cardiac D1R has the potential to become a therapeutic target for preventing heart failure-associated ventricular arrhythmia.

FLNC Gene Splice Mutations Cause Dilated Cardiomyopathy.

OBJECTIVE: To identify novel dilated cardiomyopathy (DCM) causing genes, and to elucidate the pathological mechanism leading to DCM by utilizing zebrafish as a model organism. BACKGROUND: DCM, a major cause of heart failure, is frequently familial and caused by a genetic defect. However, only 50% of DCM cases can be attributed to a known DCM gene variant, motivating the ongoing search for novel disease genes. METHODS: We performed whole exome sequencing (WES) in two multigenerational Italian families and one US family with arrhythmogenic DCM without skeletal muscle defects, in whom prior genetic testing had been unrevealing. Pathogenic variants were sought by a combination of bioinformatic filtering and cosegregation testing among affected individuals within the families. We performed function assays and generated a zebrafish morpholino knockdown model. RESULTS: A novel filamin C gene splicing variant (FLNC c.7251+1 G>A) was identified by WES in all affected family members in the two Italian families. A separate novel splicing mutation (FLNC c.5669-1delG) was identified in the US family. Western blot analysis of cardiac heart tissue from an affected individual showed decreased FLNC protein, supporting a haploinsufficiency model of pathogenesis. To further analyze this model, a morpholino knockdown of the ortholog filamin Cb in zebrafish was created which resulted in abnormal cardiac function and ultrastructure. CONCLUSIONS: Using WES, we identified two novel FLNC splicing variants as the likely cause of DCM in three families. We provided protein expression and in vivo zebrafish data supporting haploinsufficiency as the pathogenic mechanism leading to DCM.