Endurance exercise rescues progeroid aging and induces systemic mitochondrial rejuvenation in mtDNA mutator mice

Abstract

A causal role for mitochondrial DNA (mtDNA) mutagenesis in mammalian aging is supported by recent studies demonstrating that the mtDNA mutator mouse, harboring a defect in the proofreading-exonuclease activity of mitochondrial polymerase gamma, exhibits accelerated aging phenotypes characteristic of human aging, systemic mitochondrial dysfunction, multisystem pathology, and reduced lifespan. Epidemiologic studies in humans have demonstrated that endurance training reduces the risk of chronic diseases and extends life expectancy. Whether endurance exercise can attenuate the cumulative systemic decline observed in aging remains elusive. Here we show that 5 mo of endurance exercise induced systemic mitochondrial biogenesis, prevented mtDNA depletion and mutations, increased mitochondrial oxidative capacity and respiratory chain assembly, restored mitochondrial morphology, and blunted pathological levels of apoptosis in multiple tissues of mtDNA mutator mice. These adaptations conferred complete phenotypic protection, reduced multisystem pathology, and prevented premature mortality in these mice. The systemic mitochondrial rejuvenation through endurance exercise promises to be an effective therapeutic approach to mitigating mitochondrial dysfunction in aging and related comorbidities.

Fig. 1.

Endurance exercise mitigates the exercise intolerance and systemic pathology observed in PolG-SED mice. (A) The time to exhaustion (in min) of PolG-END mice in monthly endurance stress test trials was significantly greater compared with both PolG-SED and WT mice (n = 10/group). (B and C) Weights of skeletal muscle (quadriceps femoris and gastrocnemius) (B) and brain (C) from WT, PolG-SED, and PolG-END mice at 8 mo of age (n = 18/group). (D) Trichrome-stained cross-sections of heart from WT, PolG-SED, and PolG-END mice (n = 6/group). Representative images of heart from each group are displayed. (Scale bar: 50 mm.) (E) Weight of abdominal (ABDO) and retroperitoneal (RETRO) fat pads from WT, PolG-SED, and PolG-END mice (n = 10/group). (F) H&E-stained sections of dorsal skin from WT, PolG-SED, and PolG-END mice (n = 3/group). Open arrowheads indicate dermal skin; closed arrowheads, subcutaneous fat; diamond arrowheads, subcutaneous muscle. (G) Weights of gonads (ovaries and testes) from WT, PolG-SED, and PolG-END mice (n = 10/group). (H) Hemoglobin values in from WT, PolG-SED, and PolG-END mice (n = 10/group). *P < 0.05, **P < 0.01, and ***P < 0.001, PolG-SED versus both WT and PolG-END; ^†P < 0.05, ^‡P < 0.01, PolG-END versus WT. Error bars represent SEM.

Fig. 2.

Endurance exercise rescues mtDNA depletion, mitigates mtDNA random point mutations, and enhances COX assembly in PolG mice. (A) Quantification of mtDNA levels relative to diploid nuclear genome in skeletal muscle (soleus) from WT, PolG-SED, and PolG-END mice at 8 mo of age (n = 10/group). (B) Frequency of mtDNA point mutations in 3,325, 2,473, and 3,842 reads of mtDNA sequences from multiple mtDNA populations, yielding 1.46 × 10⁶, 1.25 × 10⁶, and 9.21 × 10⁵ bp of mtDNA sequences from the PolG-SED, PolG-END, and WT mice, respectively. (C) COX assembly in skeletal muscle (quadriceps femoris) from WT, PolG-SED, and PolG-END mice (n = 4–6/group) using 2D Blue-Native PAGE. Blots were probed with COX subunits I, IV, Vb, and VIc. *P < 0.05, **P < 0.01, and ***P < 0.001, PolG-SED versus both WT and PolG-END; ^†P < 0.05, PolG-END versus WT. Error bars represent SEM.

Fig. 3.

Endurance exercise induces systemic mitochondrial biogenesis, enhances systemic COX activity, and mitigates dysregulated systemic apoptosis in PolG mice. (A) Gene expression and protein content of nuclear PGC-1α and Tfam in skeletal muscle (tibialis anterior) of PolG-SED and PolG-END mice versus WT mice (n = 10/group) at 8 mo of age. (B) Representative Western blot of PGC-1α–mediated downstream proteins—(i) complex V ATP synthase subunit α, (ii) complex III subunit core 2, (iii) complex IV subunit I, (iv) complex II subunit 30 kDa, and (v) complex I subunit NADH-ubiquinone oxidoreductase 1β subcomplex 8—in skeletal muscle (quadriceps femoris), lung, and heart extracts from WT, PolG-SED (PS), and PolG-END (PE) mice (n = 8/group). (vi) Actin was used as a housekeeping loading control. (C) COX activity in skeletal muscle (quadriceps femoris), heart, and ovary of PolG-SED and PolG-END mice versus WT mice (n = 10/group). (D) Nuclear DNA fragmentation (apoptotic index) in the cytosolic fractions prepared from skeletal muscle (quadriceps femoris), heart, and liver from WT, PolG-SED, and PolG-END mice (n = 4–6/group). *P < 0.05, **P < 0.01, and ***P < 0.001, PolG-SED versus both WT and PolG-END; ^†P < 0.05, PolG-END versus WT. Error bars represent SEM.

Fig. 4.

Endurance exercise restores mitochondrial abundance and morphology in PolG mice. (A–C) Electron micrographs of myofibers (quadriceps femoris) from WT (A), PolG-SED (B), and PolG-END (C) mice (n = 6/group) at 8 mo of age. (Scale bar: 1 μm.) (D–I) Myofibers of PolG-SED mice (D–G) are populated with enlarged, abnormally shaped mitochondria containing vacuoles, fragmented cristae, disrupted external membranes, and large myelin-like figures compared with mitochondria observed in WT (H) and PolG-END (I) mice. (Scale bar: 100 nm.)