Effects of 6-week aerobic exercise on calcium regulation in skeletal muscle of ApoE knockout mice fed by high-fat diet

Abstract

Objective: To investigate the effects of 6 weeks of aerobic exercise on the sarcoplasmic reticulum calcium regulatory proteins in skeletal muscle of apolipoprotein E (ApoE) knockout mice fed by high-fat diet. Methods: There were a total of twenty five 9-week-old ApoE knockout mice (ApoE knockout mice, ApoE KO), five of which were selected randomly for the maximum running speed test. The running speed would be increased by 1.2 m/min every 3 min after a 5-min duration of initial speed of 4.8 m/min without slope until exhaustion, then the final speed was set as maximal speed, and the test result of the maximum running speed was (27.0±2.4)m/min. The remaining 20 ApoE KO mice were randomly divided into ApoE KO mouse high-fat diet group (KO) and ApoE KO mouse high-fat diet + aerobic exercise group (KE), 10 mice per group. Ten 9-week-old wild-type C57BL/6J mice were used as a blank control group (wild-type, WT). High fat diet composition: fat content was 21% (w/w) and cholesterol content was 1.5% (w/w). Exercise intervention was initiated 1 week after adaptive training in the KE group with an exercise protocol consisting of 40% maximal running speed (10.8 m/min), 40 min/d and a frequency of 3 d/w for a total of 6 weeks. All mice were anesthetized and sacrificed by cardiac puncture then bilateral gastrocnemius muscles were isolated immediately 48 h after the final exercise. Skeletal muscle Ca2+ concentration was detected by visible light colorimetry; the expression levels of RyR, CaM, CaMK Ⅱ, SERCA1 and SERCA2, which are calcium regulated proteins of sarcoplasmic reticulum, in mouse skeletal muscle, was detected by Western blotting. Results: Compared with WT mice, the Ca2+ concentration, the expression levels of the sarcoplasmic reticulum calcium releasing proteins RyR, CaMKⅡ, and the calcium recycling proteins SERCA1 and SERCA2 were decreased significantly in skeletal muscle of the KO mice (P＜0.05, P＜0.01), while the expression of CaM protein did not change. Skeletal muscle Ca2+ concentration and the levels of sarcoplasmic reticulum calcium recycling proteins SERCA1 and SERCA2 were increased significantly (P＜0.05) in KE mice compared with KO mice, but there were no significant differences in the expressions of the sarcoplasmic reticulum calcium release proteins RyR, CaM and CaMK II. Conclusion: High fat diet can reduce the concentration of Ca2+ in skeletal muscle and weaken the release and recovery of sarcoplasmic reticulum calcium in ApoE knockout mice. 6-week aerobic exercise training can significantly increase its Ca2+concentration and promote the recovery of sarcoplasmic reticulum calcium.