Global MicroRNA Profiling of the Mouse Ventricles during Development of Severe Hypertrophic Cardiomyopathy and Heart Failure

<div><p>MicroRNAs (miRNAs) regulate post-transcriptional gene expression during development and disease. We have determined the miRNA expression levels of early- and end-stage hypertrophic cardiomyopathy (HCM) in a severe, transgenic mouse model of the disease. Five miRNAs were differentially expressed at an early stage of HCM development. Time-course analysis revealed that decreased expression of miR-1 and miR-133a commences at a pre-disease stage, and precedes upregulation of target genes causal of cardiac hypertrophy and extracellular matrix remodelling, suggesting a role for miR-1 and miR-133a in early disease development. At end-stage HCM, 16 miRNA are dysregulated to form an expression profile resembling that of other forms of cardiac hypertrophy, suggesting common responses. Analysis of the mRNA transcriptome revealed that miRNAs potentially target 15.7% upregulated and 4.8% downregulated mRNAs at end-stage HCM, and regulate mRNAs associated with cardiac hypertrophy and electrophysiology, calcium signalling, fibrosis, and the TGF-β signalling pathway. Collectively, these results define the miRNA expression signatures during development and progression of severe HCM and highlight critical miRNA regulated gene networks that are involved in disease pathogenesis.</p> </div

Potential impact of miRNA regulation on mRNA transcript levels.

<p>mRNAs upregulated (left) and downregulated (right) during late-stage HCM are represented. Proportion of mRNAs with conserved target sites for conversely expressed miRNAs is shown in black.</p

Differentially expressed miRNAs during development of HCM.

<p>Fold change is shown for DBL mice; <b>A</b>) age 10 days, and <b>b</b>) age 16 days v age matched NTG mice. (1) miRNAs are part of the same family, (2) and (3) part of the same transcription unit, or (4) clustered.</p

Validated mRNA targets of miRNA regulation.

<p>Validated mRNA targets of miRNA regulation.</p

RT-qPCR validation of changes in mRNA expression levels.

<p>Extended time course analysis of mRNA expression levels. Fold change is shown compared to NTG mice age 5 days. *P<0.05.</p

Validated miRNAs differentially expressed in DBL mice.

<p>MicroRNAs significantly upregulated (top panel) or downregulated (bottom panel) (<i>P</i><0.05).</p

Cardiac troponin I mutations in Australian families with hypertrophic cardiomyopathy : clinical, genetic and functional consequences

Background. - Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder caused by mutations in sarcomeric proteins. Cardiac troponin I (cTnI) is a key switch molecule in the sarcomere. Mutations in cTnI have been identified in <1% of genotyped HCM families. Methods. - To study the prevalence, clinical significance and functional consequences of cTnI mutations, genetic testing was performed in 120 consecutive Australian families with HCM referred to a tertiary referral centre, and results correlated with clinical phenotype. Each cTnI mutation identified was tested in a mammalian two-hybrid system to evaluate the functional effects of these mutations on troponin complex interactions. Results. - Disease-causing missense mutations were identified in four families (3.3%). Two mutations were located at the same codon in exon 7 (R162G, R162P), and two in exon 8 (L198P, R204H). All four mutations change amino acid residues which are highly conserved and were not found in normal populations. Follow-up family screening has identified a total of seven clinically affected members in these four families, with a further four members who carry the gene mutation but have no clinical evidence of disease. Age at clinical presentation was variable (range 15-68 years) and the mean septal wall thickness was 19.3 ± 4.6 mm (range 7-33 mm) in clinically affected individuals, including children. In all four families, at least one member had a sudden cardiac death event, including previous cardiac arrest, indicating a more malignant form of HCM. All four mutations disrupted functional interactions with troponin C and T and this may account for the increased severity of disease in these families. Conclusions. - Gene mutations in cTnI occur in Australian families with HCM with a prevalence higher than previously reported and may be associated with a clinically more malignant course, reflecting significant disruptions to troponin complex interactions