The Acute Effects of Exercise and Temperature on Regional mtDNA

Abstract

A reduced mitochondrial DNA (mtDNA) copy number, the ratio of mitochondrial DNA to genomic DNA (mtDNA:gDNA), has been linked with dysfunctional mitochondria. Exercise can acutely induce mtDNA damage manifested as a reduced copy number. However, the influence of a paired (exercise and temperature) intervention on regional mtDNA (MINor Arc and MAJor Arc) are unknown. Thus, the purpose of this study was to determine the acute effects of exercise in cold (7 °C), room temperature (20 °C), and hot (33 °C) ambient temperatures, on regional mitochondrial copy number (MINcn and MAJcn). Thirty-four participants (24.4 ± 5.1 yrs, 87.1 ± 22.1 kg, 22.3 ± 8.5 %BF, and 3.20 ± 0.59 L·min^-1 VO₂peak) cycled for 1 h (261.1 ± 22.1 W) in either 7 °C, 20 °C, or 33 °C ambient conditions. Muscle biopsy samples were collected from the vastus lateralis to determine mtDNA regional copy numbers via RT-qPCR. mtDNA is sensitive to the stressors of exercise post-exercise (MIN fold change, -1.50 ± 0.11; MAJ fold change, -1.70 ± 0.12) and 4-h post-exercise (MIN fold change, -0.82 ± 0.13; MAJ fold change, -1.54 ± 0.11). The MAJ Arc seems to be more sensitive to heat, showing a temperature-trend (p = 0.056) for a reduced regional copy number ratio after exercise in the heat (fold change -2.81 ± 0.11; p = 0.019). These results expand upon our current knowledge of the influence of temperature and exercise on the acute remodeling of regional mtDNA.

Keywords: ambient temperature; copy number; exercise; mitochondria; mtDNA; thermoregulation.

Figure 1

Heart rate data. Heart rate during the exercise trial. Data are reported in mean ± SE. * p < 0.05 different from previous time-point.

Figure 2

Temperature Data. (A) Core temperature during the exercise trial. (B) Skin temperature during the exercise trial. Data are reported in mean ± SE. * p < 0.05, all groups different. † p < 0.05, 7 °C different from other temperatures. ‡ p < 0.05, 33 °C different from other temperatures.

Figure 3

Regional mtDNA copy number. (A) mtDNA Minor Arc copy number (MINcn) data relative to reference gene B2M. (B) mtDNA Major Arc copy number (MAJcn) data relative to reference gene B2M. Data are reported in mean ± SE. * p < 0.05, less than Pre, main effect over time. † p < 0.001, greater than 20 °C and 33 °C, main effect for temperature.

Figure 4

Regional mtDNA copy number change from Pre (A) Minor Arc mtDNA change from Pre. (B) Major Arc mtDNA change from Pre. Fold change bars present the negative inverse mean change ± SE, relative to (1.0) the reference gene B2M.