Caveolin-3 is Up-Regulated in the Physiological Left Ventricular Hypertrophy Induced by Voluntary Exercise Training in Rats

Abstract

Various substances have been introduced in relation with cardiac hypertrophy almost always with controversy in their roles in signal transduction. Those controversies may attribute to the diversity of cardiac hypertrophy. We previously showed that calcineurin was activated in physiological left ventricular hypertrophy (LVH) induced by voluntary exercise training, but not in decompensated pressure-overload LVH. In the current study, we advanced our search for the differences between the voluntary exercise-induced LVH and the pressure-overload LVH into several other hypertrophy-related substances including caveolin. Wistar rats were assigned to one of the following three groups: 10 weeks of voluntary exercise (EX), sedentary regimen (SED), and 4 weeks of ascending aortic constriction (AC). The EX rats voluntarily ran 1.6 ± 1.1 km/day in the specially manufactured cages resulting in LVH (24 % increase in left ventricular weight per body weight ratio). Myocardial tissue homogenate of the EX rats revealed different characteristics in signal transduction of hypertrophy from that of the AC. The EX rats had normal sarcoplasmic reticulum (SR) Ca(2+)ATPase mRNA level and normal myosin heavy chain isozyme pattern assessed by RNA protection assay, while AC rats had decreased SR Ca(2+)ATPase mRNA level and increased beta myosin heavy chain mRNA level. Myocardial caveolin-3 protein levels assessed by Western blotting increased in the EX rats but decreased in the AC rats. The voluntary exercise-induced LVH differed in signal transduction from the decompensated pressure-overload LVH. Caveolin-3 was induced in the voluntary exercise-induced LVH, while it was decreased in the decompensated pressure-overload LVH.

Keywords: Exercise; hypertrophy; signal transduction.

Figure 1.

Myocardial gene expression regarding hypertrophy. The mRNA levels based on the RNase protection assay of each gene related with cardiac hypertrophy are expressed as relative values to that of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). * p < 0.05 versus SED. (a1) and (a2): skeletal and cardiac α- actin, respectively. (b1) and (b2): atrial- (ANP) and brain-types of natriuretic peptides (BNP), respectively. (c1) and (c2): α- and β-isoforms of myosin heavy chains (MyHC), respectively. (d): sarcoplasmic reticulum calcium ATPase. Abbreviations: SED = sedentary group, EX = voluntary exercise group, AC = ascending aortic constriction group.

Figure 2.

Myocardial Caveolin-3 protein levels assessed by Western blot analysis. Heart homogenates were subjected to immunoblotting, and the signals were quantitated by a densitometer. Abbreviations: SED = sedentary group, EX = voluntary exercise group, AC = ascending aortic constriction group. * p < 0.05 vs. SED.