Regular Exercise Rescues Heart Function Defects and Shortens the Lifespan of Drosophila Caused by dMnM Downregulation

Abstract

Although studies have shown that myomesin 2 (MYOM2) mutations can lead to hypertrophic cardiomyopathy (HCM), a common cardiovascular disease that has a serious impact on human life, the effect of MYOM2 on cardiac function and lifespan in humans is unknown. In this study, dMnM (MYOM2 homologs) knockdown in cardiomyocytes resulted in diastolic cardiac defects (diastolic dysfunction and arrhythmias) and increased cardiac oxidative stress. Furthermore, the knockdown of dMnM in indirect flight muscle (IFM) reduced climbing ability and shortened lifespan. However, regular exercise significantly ameliorated diastolic cardiac dysfunction, arrhythmias, and oxidative stress triggered by dMnM knockdown in cardiac myocytes and also reversed the reduction in climbing ability and shortening of lifespan caused by dMnM knockdown in Drosophila IFM. In conclusion, these results suggest that Drosophila cardiomyocyte dMnM knockdown leads to cardiac functional defects, while dMnM knockdown in IFM affects climbing ability and lifespan. Furthermore, regular exercise effectively upregulates cardiomyocyte dMnM expression levels and ameliorates cardiac functional defects caused by Drosophila cardiomyocyte dMnM knockdown by increasing cardiac antioxidant capacity. Importantly, regular exercise ameliorates the shortened lifespan caused by dMnM knockdown in IFM.

Keywords: IFM; cardiac function; dMnM; lifespan; regular exercise.

Figure 1

Effects of dMnM knockdown in cardiomyocytes on cardiac function. (A–H) M HR, AI, FS, SD, DD, DI, SI, HP, and FL in the W1118 > Hand-Gal4 group and the dMnM^RNAi > Hand-Gal4 group; all Drosophila females, n = 30. (I) Drosophila fibrillation level in Drosophila. (J,K) ECG pattern. Long and short black lines represent diastolic diameter and systolic diameter, respectively. The red square shows fibrillation. All M-mode ECGs were intercepted at 10 s. An independent-samples t-test was used to evaluate the differences between the two groups, * p < 0.05, ** p < 0.01, *** p < 0.001, ns is not statistically significant.

Figure 2

Effect of dMnM knockdown in cardiomyocytes on myofibrillar F-actin in cardiac myocytes. (A) Fluorescence images of the heart in the W1118 > Hand-Gal4 group; (B) fluorescence images of the heart in the dMnM^RNAi > Hand-Gal4 group, n = 5. A confocal microscope was used to observe the Drosophila heart tube with ghost pen cyclic peptide-labeled F-actin, scale bar = 100 μm.

Figure 3

Effects of dMnM knockdown in cardiac myocytes on oxidative stress in the heart and mRNA expression of dMnM, upheld, sod2, cat, and phgpx. (A,B) Fluorescence images of cardiac DHE staining in the W1118 > Hand-Gal4 and dMnM^RNAi > Hand-Gal4 groups, respectively, n = 5. (C) Relative fluorescence intensity of the heart. (D–H) Relative expression levels of dMnM, upheld, sod2, cat, and phgpx mRNA in Drosophila cardiomyocytes, respectively, n = 30. T-test for differences between the two groups using independent samples, * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 4

Effects of dMnM knockdown in cardiomyocytes and IFM on climbing and lifespan of Drosophila. (A) Climbing results for the W1118 > Hand-Gal4 group; (B,C) lifespan and survival curves for the W1118 > Hand-Gal4 group and dMnM^RNAi > Hand-Gal4 group, respectively; (D) climbing results for the W1118 > Act88F-Gal4 and dMnM^RNAi > Act88F-Gal4 group; (E,F) lifespan and survival curves for dMnM^RNAi > Hand-Gal4 group, respectively. Climbing sample n = 100; lifespan sample n = 200. The difference between the two groups was tested using an independent-samples t-test, ** p < 0.01, *** p < 0.001, ns is not statistically significant.

Figure 5

Effect of regular exercise on dMnM-specific knockdown of cardiac function in Drosophila cardiomyocytes. (A–H) HR, AI, FS, SD, DD, DI, SI, HP, and FL in the dMnM^RNAi > Hand-Gal4 group and the dMnM^RNAi > Hand-Gal4 + E group, n= 30. (I) Fibrillation levels in Drosophila. (J,K) Drosophila M-mode ECG pattern. Long and short black lines represent diastolic diameter and systolic diameter, respectively. The red square shows fibrillation. Rectangular area represents fibrillation. All M-mode ECGs were intercepted for 10 s. An independent-samples t-test and nonparametric test were used to assess the differences between the two groups, * p < 0.05, ** p < 0.01, *** p < 0.001, ns is not statistically significant.

Figure 6

Effect of regular exercise on F-actin in myogenic fibers of cardiac myocytes after dMnM knockdown. (A) Fluorescence images of the heart in the dMnM^RNAi > Hand-Gal4 group. (B) Fluorescence images of the heart in the dMnM^RNAi > Hand-Gal4 + E group, n = 5. F-actin was labeled with ghostwritten cyclic peptide. Confocal microscopy was used to observe the changes in the Drosophila heart tube.

Figure 7

Effects of regular exercise on ROS produced by specific knockdown of cardiac dMnM and mRNA expression levels of dMnM, upheld, phgpx, sod2, and cat. (A,B) DHE-stained images of hearts in the dMnM^RNAi > Hand-Gal4 group and dMnM^RNAi > Hand-Gal4 + E group, respectively; n = 5. (C) Relative fluorescence intensity of the heart. (D–H) Relative expression levels of dMnM, upheld, sod2, cat, and phgpx mRNA; n = 30. An independent-samples t-test was used to assess differences between the two groups, * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 8

Effects of regular exercise on climbing and lifespan of Drosophila melanogaster after dMnM knockdown in cardiac myocytes and IFM. (A) Climbing results for the dMnM^RNAi > Hand-Gal4 group. (B,C) Lifespan and survival curves for the dMnM^RNAi > Hand-Gal4 group and dMnM^RNAi > Hand-Gal4 + E group, respectively. (D) Climbing results for the dMnM^RNAi > Act88F-Gal4 and dMnM^RNAi > Act88F-Gal4 + E group. (E,F) Lifespan and survival curves of the dMnM^RNAi > Hand-Gal4 and dMnM^RNAi > Act88F-Gal4 + E groups, respectively, Climbing sample n = 100; lifespan sample n = 200. An independent-samples t-test was used to assess the difference between the two groups, ** p < 0.01, ns is not statistically significant.