Effect of Exercise on the Expression of HSP20 in the Hypertensive Rat Heart

Abstract

Previous observations show that levels of Hsp20, a small heat shock protein, are elevated in the rat left ventricle by exercise training. PURPOSE: To determine whether exercise training would induce an increase in the levels of Hsp20 in hearts of spontaneously hypertensive rats (SHR). METHODS: SHR were randomly assigned to a sedentary (SHR-SED) or trained (SHR-TRN) group. The trained group was exercised on a treadmill at 0% grade for eight weeks, using a high intensity interval training protocol. After 3 weeks of introductory running, 2.5 min of sprint running at 29–45 m/min was interspersed with steady running at 24 m/min for five minutes for a total duration of 37 minutes. The number of sprints was increased progressively so that the duration was approximately 60 minutes after eight weeks. During the last week of the study, sedentary rats were habituated to the treadmill for 5 days for 10 min each at 15 m/min. On the last day of the study, sedentary and exercise-trained rats were run for 10 minutes at 15 or 25 m/min respectively, and hearts were harvested at various times (t=0,10,30,60,180 min) after the last bout of exercise. From groups of SHR-SED and SHR-TRN rats, heart left (LV) and right ventricle (RV) free walls and septum (SEP) were used to measure the levels of Hsp20. Western blotting was performed using 12% gels, PVDF membranes, and an enhanced chemiluminescent detection method. A rabbit polyclonal anti- HSP20 antibody was used to detect the protein. Levels of Hsp20 were normalized to those of glyceraldehyde-3-phosphate dyhydrogenase (GAPDH). RESULTS: The level of HSP20 expression was significantly increased in response to exercise training in the soluble fraction (+61%) and whole homogenate (+70%) of the RV. In the SEP, the increase in HSP20 expression level was observed only in the soluble fraction (+54%) while the expression level was not statistically different in the whole homogenate. Exercise training did not trigger increased expression of HSP20 in the hypertensive LV free wall. In the RV and LV free walls, the level of HSP20 was higher in the soluble fraction than in the whole homogenate, and the ratio of the two measurements was unchanged by exercise-training. On the other hand, the level of HSP20 in the SEP was greater in the whole homogenate, and the soluble-to-whole homogenate ratio was increased as a result of exercise training (p < 0.05). CONCLUSION: Exercise training triggers increased expression of HSP20 in the unaffected RV free wall of hypertensive rats, but not in the pressure-overloaded LV free wall. Supported by the American Heart Association Midwest Affiliate and the Undergraduate Research Opportunity Program at the University of Michigan