Regular Endurance Exercise Promotes Fission, Mitophagy, and Oxidative Phosphorylation in Human Skeletal Muscle Independently of Age

Abstract

This study investigated whether regular endurance exercise maintains basal mitophagy and mitochondrial function during aging. Mitochondrial proteins and total mRNA were isolated from vastus lateralis biopsies (n = 33) of young sedentary (YS), old sedentary (OS), young active (YA), and old active (OA) men. Markers for mitophagy, fission, fusion, mitogenesis, and mitochondrial metabolism were assessed using qRT-PCR, Western blot, and immunofluorescence staining. Independently of age, fission protein Fis1 was higher in active vs. sedentary subjects (+80%; P < 0.05). Mitophagy protein PARKIN was more elevated in OA than in OS (+145%; P = 0.0026). mRNA expression of Beclin1 and Gabarap, involved in autophagosomes synthesis, were lower in OS compared to YS and OA (P < 0.05). Fusion and oxidative phosphorylation proteins were globally more elevated in the active groups (P < 0.05), while COx activity was only higher in OA than in OS (P = 0.032). Transcriptional regulation of mitogenesis did not vary with age or exercise. In conclusion, physically active lifestyle seems to participate in the maintenance of lifelong mitochondrial quality control by increasing fission and mitophagy.

Keywords: OXPHOS; endurance exercise; fusion; mitochondria; mitogenesis; physical activity.

FIGURE 1

Regulation of fission and mitophagy protein markers by age and physical activity in human skeletal muscle. Mitochondrial protein expression of (A) Fis1, (B) BNIP3, (C) PARKIN, cytosolic protein expression of (D) PARKIN, mitochondrial protein expression of (E) LC3b II, and (F) p62/SQSTM1 in young and old men in response to sedentary vs. active lifestyle. YS, young sedentary; OS, old sedentary; YA, young active; OA, old active. Values are expressed as means ± SEM. ^∗P < 0.05, ^∗∗∗P < 0.001.

FIGURE 2

Regulation of mitophagy transcriptional markers by age and physical activity in human skeletal muscle. mRNA levels of (A) Beclin1, (B) Gabarap, and (C) p62 in young and old men in response to sedentary vs. active lifestyle. YS, young sedentary; OS, old sedentary; YA, young active; OA, old active. Values are expressed as means ± SEM. ^∗P < 0.05.

FIGURE 3

Regulation of fusion, import, and oxidative phosphorylation protein markers by age and physical activity in human skeletal muscle. Mitochondrial protein expression of (A) Mfn2, (B) OPA1, (C) TOM20, (D) CS, (E) OXPHOS, and (F) protein activity of COx in young and old men in response to sedentary vs. active lifestyle. YS, young sedentary; OS, old sedentary; YA, young active; OA, old active. Values are expressed as means ± SEM. ^∗P < 0.05, ^∗∗P < 0.01. (G) Representative muscle cross sections stained for COx protein activity according to age and physical activity. YS, young sedentary; OS, old sedentary; YA, young active; OA, old active. 100 fibers were analyzed per subject. Scale bar is 120 μM.

FIGURE 4

Regulation of mitogenesis transcriptional markers by age and physical activity in human skeletal muscle. Mitochondria copy number (A), mRNA levels of (B) PGC1α, (C) Tfam, (D) NRF1, and (E) NRF2 in young and old men in response to sedentary vs. active lifestyle. YS, young sedentary; OS, old sedentary; YA, young active; OA, old active. Values are expressed as means ± SEM. ^∗∗P < 0.01.