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Functional Role of ClC-3 Chloride Channels in Myocardial Hypertrophy and Heart Failure
AdvisorDuan, Dayue D.
Biochemistry and Molecular Biology
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Background: In hypertrophied cardiac myocytes the volume-regulated chloride channels (VRCCs) are activated constitutively. But the functional role and molecular mechanism of the constitutively activated VRCCs in myocardial hypertrophy and heart failure are not well known. In this study a novel heart-specific inducible ClC-3 knockout (doxyhsClcn3-/-) mouse was developed to specifically test the hypothesis that ClC-3, a member of the ClC voltage-gated chloride channel superfamily, may be responsible for the constitutively activated VRCCs and may play a protective role against heart failure. Methods: A pressure overload model through a minimally invasive transverse aortic banding (MTAB) was established in the doxyhsClcn3-/- mice when doxycycline in the diet was either maintained (on-Doxy, to preserve Clcn3 gene expression) or removed (off-Doxy, to activate Cre recombinase and inactivate the Clcn3 gene expression). Changes in cardiac function and whole-cell VRCCs in cardiac myocytes of the doxyhsClcn3-/- mice during on-Doxy and off-Doxy were monitored using echocardiograph and whole-cell voltage-clamp techniques. Results: 1) Compared to age-matched on-Doxy control mice native cardiac VRCCs current densities of the off-Doxy mice were significantly reduced at week 1.5 and were completely eliminated at week 3. The changes in VRCCs activities were closely correlated to the changes in molecular expression of ClC-3 and cardiac function. 2) Global anatomy and histological analysis of isolated hearts revealed dramatically enlarged hearts from the off-Doxy doxyhsClcn3-/- mice at week 3 compared to the age-matched on-Doxy mice. 3) Echocardiography revealed a significant increase in left ventricular mass (LVM) and chamber dimensions and a decrease in left ventricular ejection fraction (LVEF) and fractional shortening (%FS) in the doxyhsClCn3-/- mice at both 1.5 and 3 weeks off-Doxy. 4) While on-Doxy preserved the compensatory myocardial hypertrophy and cardiac function for ~10 weeks after MTAB, off-Doxy accelerated the MTAB-induced increase in LVM (within 1 week) and the progression from myocardial hypertrophy to dilated heart failure (in < 3 weeks) during pressure overload. Conclusions: ClC-3 is a key component of native VRCCs in mammalian heart and plays a significant cardioprotective role against myocardial hypertrophy and heart failure.