Mitochondria Transplantation: Rescuing Innate Muscle Bioenergetic Impairment in a Model of Aging and Exercise Intolerance

Abstract

Arroum, T, Hish, GA, Burghardt, KJ, Ghamloush, M, Bazzi, B, Mrech, A, Morse, PT, Britton, SL, Koch, LG, McCully, JD, Hüttemann, M, and Malek, MH. Mitochondria transplantation: Rescuing innate muscle bioenergetic impairment in a model of aging and exercise intolerance. J Strength Cond Res 38(7): 1189-1199, 2024-Mitochondria, through oxidative phosphorylation, are crucial for energy production. Disease, genetic impairment, or deconditioning can harm muscle mitochondria, affecting energy production. Endurance training enhances mitochondrial function but assumes mobility. Individuals with limited mobility lack effective treatments for mitochondrial dysfunction because of disease or aging. Mitochondrial transplantation replaces native mitochondria that have been damaged with viable, respiration-competent mitochondria. Here, we used a rodent model selectively bred for low-capacity running (LCR), which exhibits innate mitochondrial dysfunction in the hind limb muscles. Hence, the purpose of this study was to use a distinct breed of rats (i.e., LCR) that display hereditary skeletal muscle mitochondrial dysfunction to evaluate the consequences of mitochondrial transplantation. We hypothesized that the transplantation of mitochondria would effectively alleviate mitochondrial dysfunction in the hind limb muscles of rats when compared with placebo injections. In addition, we hypothesized that rats receiving the mitochondrial transplantation would experience an improvement in their functional capacity, as evaluated through incremental treadmill testing. Twelve aged LCR male rats (18 months old) were randomized into 2 groups (placebo or mitochondrial transplantation). One LCR rat of the same age and sex was used as the donor to isolate mitochondria from the hindlimb muscles. Isolated mitochondria were injected into both hindlimb muscles (quadriceps femoris, tibialis anterior (TA), and gastrocnemius complex) of a subset LCR (n = 6; LCR-M) rats. The remaining LCR (n = 5; LCR-P) subset received a placebo injection containing only the vehicle without the isolated mitochondria. Four weeks after mitochondrial transplantation, rodents were euthanized and hindlimb muscles harvested. The results indicated a significant (p < 0.05) increase in mitochondrial markers for glycolytic (plantaris and TA) and mixed (quadricep femoris) muscles, but not oxidative muscle (soleus). Moreover, we found significant (p < 0.05) epigenetic changes (i.e., hypomethylation) at the global and site-specific levels for a key mitochondrial regulator (transcription factor A mitochondrial) between the placebo and mitochondrial transplantation groups. To our knowledge, this is the first study to examine the efficacy of mitochondrial transplantation in a rodent model of aging with congenital skeletal muscle dysfunction.

Figure 1.

Comparison of maximal treadmill test at 11 weeks and 18 months old (left panels) and pre- and post-injection (right panels) for the two LCR groups (mean ± SEM).

Figure 2.

Basal cytochrome c oxidase activity (left panel A) and [ATP] (right panel A) in the quadriceps femoris muscle. Representative BN-PAGE of supercomplex activity and SDS PAGE of α-VDAC (panel B). Quantitative representation of supercomplex: CIV-m (monomeric); CIV-2 (dimeric); CIV-sc (supercomplex [SC I + III₂ + IV_n]) (panel C). Quantitative representation of supercomplex band 1 and band 2 for Complex I IGA (SC I + III₂ + IV_n) (panel D). (mean ± SEM).

Figure 3.

Representative Western Blots and quantification for key mitochondrial markers for the soleus and plantaris muscles (mean ± SEM). Bands obtained run at the expected protein size. Note that the two parkin bands represent the precursor and cleaved forms of the protein and multiple bands seen for Opa1 are splice isoforms. Loading control for target proteins were normalized to α-tubulin.

Figure 4.

Epigenetic results for the quadriceps femoris muscles for NFe2L2, PPAGC-1β, and SIRT. No significant (p > 0.05) mean differences between groups (mean ± SEM).

Figure 5.

Epigenetic results for the quadriceps femoris muscles for TFAM as well as site specific CpG islands (mean ± SEM).