PTRF/Cavin-1 Deficiency Causes Cardiac Dysfunction Accompanied by Cardiomyocyte Hypertrophy and Cardiac Fibrosis

<div><p>Mutations in the <i>PTRF/Cavin-1</i> gene cause congenital generalized lipodystrophy type 4 (CGL4) associated with myopathy. Additionally, long-QT syndrome and fatal cardiac arrhythmia are observed in patients with CGL4 who have homozygous <i>PTRF</i>/<i>Cavin-1</i> mutations. PTRF/Cavin-1 deficiency shows reductions of caveolae and caveolin-3 (Cav3) protein expression in skeletal muscle, and Cav3 deficiency in the heart causes cardiac hypertrophy with loss of caveolae. However, it remains unknown how loss of PTRF/Cavin-1 affects cardiac morphology and function. Here, we present a characterization of the hearts of <i>PTRF</i>/<i>Cavin-1</i>-null (<i>PTRF</i>^−/−) mice. Electron microscopy revealed the reduction of caveolae in cardiomyocytes of <i>PTRF</i>^−/− mice. <i>PTRF</i>^−/− mice at 16 weeks of age developed a progressive cardiomyopathic phenotype with wall thickening of left ventricles and reduced fractional shortening evaluated by echocardiography. Electrocardiography revealed that <i>PTRF</i>^−/− mice at 24 weeks of age had low voltages and wide QRS complexes in limb leads. Histological analysis showed cardiomyocyte hypertrophy accompanied by progressive interstitial/perivascular fibrosis. Hypertrophy-related fetal gene expression was also induced in <i>PTRF</i>^−/− hearts. Western blotting analysis and quantitative RT-PCR revealed that Cav3 expression was suppressed in <i>PTRF</i>^−/− hearts compared with that in wild-type (WT) ones. ERK1/2 was activated in <i>PTRF</i>^−/− hearts compared with that in WT ones. These results suggest that loss of PTRF/Cavin-1 protein expression is sufficient to induce a molecular program leading to cardiomyocyte hypertrophy and cardiomyopathy, which is partly attributable to Cav3 reduction in the heart.</p></div

Morphometric analysis of WT and <i>PTRF</i>^−/− female mice at 16 weeks of age.

<p>Morphometric analysis of WT and <i>PTRF</i>^−/− female mice at 16 weeks of age.</p

Echocardiographic analysis of WT and <i>PTRF</i>^−/− female mice at 16 weeks of age.

<p>Echocardiographic analysis of WT and <i>PTRF</i>^−/− female mice at 16 weeks of age.</p

Electrocardiogram of <i>PTRF</i>^−/− mice.

<p>(A) Left, representative ECG of WT and <i>PTRF</i>^−/− female mice at 24 weeks of age. Right, magnified waveforms of ECG in lead II. (B) ECG parameters in lead II of WT and <i>PTRF</i>^−/− female mice at 24 weeks of age. HR, heart rate; bpm, beats per minute. Values are expressed as means ± SEM. **<i>P</i> < 0.01 compared with WT mice.</p

mRNA and protein expression in the heart of <i>PTRF</i>^−/− mice.

<p>(A) mRNA expression of caveolins and cavins in WT and <i>PTRF</i>^−/− female hearts at 16 weeks of age. (B) mRNA expression of cardiac hypertrophy-related fetal genes and fibrosis-related genes in WT and <i>PTRF</i>^−/− female hearts at 16 weeks of age. (C) Expression of caveola-associated proteins in WT and <i>PTRF</i>^−/− female hearts at 16 weeks of age. Left, representative immunoblotting of heart lysates from WT and <i>PTRF</i>^−/− mice. Right, bar graph showing protein expression of WT and <i>PTRF</i>^−/− hearts. (D) Phosphorylation levels of MAPKs and Akt in WT and <i>PTRF</i>^−/− female hearts at 16 weeks of age. Left, representative immunoblotting of heart lysates from WT and <i>PTRF</i>^−/− mice. Right, bar graph showing phosphorylation levels of MAPKs and Akt in WT and <i>PTRF</i>^−/− hearts. *<i>P</i> < 0.05 and **<i>P</i> < 0.01.</p

Morphological changes in the heart of <i>PTRF</i>^−/− mice.

<p>(A) Left, representative electron microscopic images of WT and <i>PTRF</i>^−/− hearts from 12-week-old female mice. Caveolae were identified by their characteristic flask shape and location at the plasma membrane. White arrowheads indicate caveolae. Right, quantification of caveolae per μm of plasma membrane in atrial and ventricular cardiomyocytes of WT and <i>PTRF</i>^−/− hearts. Multiple electron micrographs were obtained for each heart, and both the number of caveolae and the total length of the plasma membrane were quantified in each image. Caveolae were counted as omega-shaped membrane profiles open at the cell surface. (B) Myocyte cross-sectional area of WT and <i>PTRF</i>^−/− hearts. Left, representative H&E staining sections of hearts from WT and <i>PTRF</i>^−/− female mice at 16 weeks of age. Right, bar graph showing cross-sectional area of cardiomyocytes of WT and <i>PTRF</i>^−/− hearts. (C) Fibrotic area of WT and <i>PTRF</i>^−/− female hearts. Left, representative Masson’s trichrome staining sections of hearts from WT and <i>PTRF</i>^−/− female mice at 16 weeks of age. Right, bar graph showing fibrotic area in WT and <i>PTRF</i>^−/− hearts. **<i>P</i> < 0.01.</p