Altering aspects of mitochondrial quality to improve musculoskeletal outcomes in disuse atrophy

Abstract

Muscle atrophy is a significant moderator for disease prognosis; as such, interventions to mitigate disuse-induced muscle loss are imperative to improve clinical interventions. Mitochondrial deteriorations may underlie disuse-induced myopathies; therefore, improving mitochondrial quality may be an enticing therapeutic intervention. However, different mitochondria-based treatments may have divergent impacts on the prognosis of disuse atrophy. Therefore, the purpose of this study was to investigate different mitochondria-centered interventions during disuse atrophy in hindlimb unloaded male and female mice. Male and female mice overexpressing peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) or mitochondrially targeted catalase (MCAT) and their respective wild-type (WT) littermate controls were hindlimb unloaded for 7 days to induce disuse atrophy or allowed normal ambulatory activity (cage control; CON). After designated interventions, animals were euthanized, and tissues were collected for measures of mitochondrial quality control and protein turnover. Although PGC-1α overexpression mitigated ubiquitin-proteasome activation (MuRF1 and Atrogin mRNA content), this did not correspond to phenotypic protections from disuse-induced atrophy. Rather, PGC-1α mice appeared to have a greater reliance on autophagic protein breakdown compared with WT mice. In MCAT mice, females exhibited a mitigated response to disuse atrophy; however, this effect was not noted in males. Despite these phenotypic differences, there were no clear cellular signaling differences between MCAT hindlimb unloaded females and MCAT fully loaded females. PGC-1α overexpression does not protect against phenotypic alterations during disuse atrophy but appears to shift catabolic pathways moderating atrophy. However, increased mitochondrially targeted catalase activity appears to blunt disuse atrophy within highly oxidative muscles specifically in female mice.NEW & NOTEWORTHY We present data suggesting that mitochondria-based interventions may mitigate disuse atrophy. However, the efficacy of mitochondria-based interventions may vary depending on the specific target of the intervention and the sex of the organism. Females appear to be more responsive to increased mitochondrial catalase as a potential therapeutic for mitigating disuse atrophy.

Keywords: PGC1α; catalase; females; mitochondria; muscle atrophy.

Conflict of interest statement

No conflicts of interest, financial or otherwise, are declared by the authors.

Figures

Fig. 1.

Muscle phenotypic data for males and females from PGC colony portion of this study. A: plantaris cross-sectional area (CSA) quantification for males. B: representative images for CSA for males. C: plantaris cross-sectional area (CSA) quantification for females. D: representative images for CSA for females. E: pMitoTimer red/green ratio in males. F: representative images of pMitoTimer in males. G: pMitoTimer red/green ratio in females. H: representative images of pMitoTimer in females. *Tukey-adjusted P < 0.05. All CSA images were taken at ×20 magnification. pMitoTimer images were taken at ×100 magnification. Males had the following sample sizes: WT-CON = 9, WT-HU = 10, PGC-CON = 9, and PGC-HU = 9. Females had the following samples sizes: WT-CON = 8, WT-HU = 9, PGC-CON = 9, and PGC-HU = 9. PGC, peroxisome proliferator-activated receptor gamma coactivator 1-alpha; PGC-CON, peroxisome proliferator-activated receptor gamma coactivator 1-alpha-cage control; PGC-HU, peroxisome proliferator-activated receptor gamma coactivator 1-alpha-humanized; WT-CON, wild-type-cage control; WT-HU, wild-type-humanized.

Fig. 2.

mRNA and protein content of moderators of ubiquitin-proteasome and autophagy-mediated catabolism from the PGC colony portion of this study. A: Atrogin mRNA content in males. B: Atrogin mRNA content in females. C: MurF1 mRNA content in males. D: MurF1 mRNA content in females. E: LC3II protein content in males. F: LCII protein content in females. G: total LC3 protein content in males. H: total LC3 protein content in females. I: representative image of immunoblotting targets. J: p62 mRNA content in males. K: p62 mRNA content in females. L: p62 protein content in males. M: p62 protein content in females. All values are normalized within sex to WT-CON. *Tukey-adjusted P < 0.05. ME denotes main effect. Males had the following sample sizes: WT-CON = 9, WT-HU = 10, PGC-CON = 9, and PGC-HU = 9. Females had the following samples sizes: WT-CON = 8, WT-HU = 9, PGC-CON = 9, and PGC-HU = 9. PGC, peroxisome proliferator-activated receptor gamma coactivator 1-alpha; PGC-CON, peroxisome proliferator-activated receptor gamma coactivator 1-alpha-cage control; PGC-HU, peroxisome proliferator-activated receptor gamma coactivator 1-alpha-humanized; WT-CON, wild-type-cage control; WT-HU, wild-type-humanized.

Fig. 3.

Muscle size data in MCAT male and female mice. A: percent difference tissue loss in female hindlimb-unloaded mice. B: percent difference tissue loss in male hindlimb-unloaded mice. C: percent difference in plantaris fiber cross-sectional area (CSA) in MCAT male mice. D: percent difference in plantaris fiber cross-sectional area (CSA) in MCAT female mice. *Tukey-adjusted P < 0.05. Males had the following sample sizes: WT-CON = 8, WT-HU = 7, MCAT-CON = 4, and MCAT-HU = 3. Females had the following samples sizes: WT-CON = 5, WT-HU = 6, MCAT-CON = 6, and MCAT-HU = 6. MCAT, mitochondrially targeted catalase; MCAT-CON, mitochondrially targeted catalase-cage control; MCAT-HU, mitochondrially targeted catalase-humanized; WT-CON, wild-type-cage control; WT-HU, wild-type-humanized.

Fig. 4.

mRNA content of moderators of ubiquitin-proteasome and autophagy-mediated catabolism from the soleus muscle of MCAT animals. A: atrogin mRNA response and basal content in males. B: atrogin mRNA response and basal content in females. C: MuRF1 mRNA response and basal content in males. D: MuRF1 mRNA response and basal content in females. E: Lc3 mRNA response and basal content in males. F: Lc3 mRNA response and basal content in females. G: p62 mRNA response and basal content in males. H: p62 mRNA response and basal content in females. Larger graphs show the responses of WT-HU and MCAT-HU, with the inset containing comparisons between WT-CON and MCAT-CON. To demonstrate responses compared with control, 1 (indicating the within genotype basal levels) is graphed with a dotted line. *P < 0.05 from a Student’s t test between genotypes. Males had the following sample sizes: WT-CON = 8, WT-HU = 7, MCAT-CON = 4, and MCAT-HU = 3. Females had the following samples sizes: WT-CON = 5, WT-HU = 6, MCAT-CON = 6, and MCAT-HU = 6. MCAT-CON, mitochondrially targeted catalase-cage control; MCAT-HU, mitochondrially targeted catalase-humanized; WT-CON, wild-type-cage control; WT-HU, wild-type-humanized.

Fig. 5.

mRNA content of moderators of protein anabolism the soleus of MCAT mice. A: Igf1 mRNA content in males. B: Igf1 mRNA content in females. C: deptor mRNA content in males. D: deptor mRNA content in females. E: Redd1 mRNA content in males. F: Redd1 mRNA content in females. Larger graphs show the responses of WT-HU and MCAT-HU, with the inset containing comparisons between WT-CON and MCAT-CON. To demonstrate responses compared with control, 1 (indicating the within genotype basal levels) is graphed with a dotted line. *P < 0.05 from a Student’s t test between genotypes. Males had the following sample sizes: WT-CON = 8, WT-HU = 7, MCAT-CON = 4, and MCAT-HU = 3. Females had the following samples sizes: WT-CON = 5, WT-HU = 6, MCAT-CON = 6, and MCAT-HU = 6. MCAT, mitochondrially targeted catalase; MCAT-CON, mitochondrially targeted catalase-cage control; MCAT-HU, mitochondrially targeted catalase-humanized; WT-CON, wild-type-cage control; WT-HU, wild-type-humanized.

Fig. 6.

pMitoTimer from males and females from the MCAT portion of this study. A: percent difference between CON and HU animal with each genotype in red/green ratio in males. B: percent difference between CON and HU animals with each genotype in red/green ratio in females. C: percent difference between CON and HU animals with each genotype in red puncta in males. D: percent difference between CON and HU animals with each genotype in red puncta in females. E: representative images of pMitoTimer in males. F: representative images of pMitoTimer in females. To demonstrate responses compared with control, 1 (indicating the within genotype basal levels) is graphed with a dotted line. *Tukey-adjusted P < 0.05. pMitoTimer images were taken at ×100 magnification. Males had the following sample sizes: WT-CON = 8, WT-HU = 7, MCAT-CON = 4, and MCAT-HU = 3. Females had the following samples sizes: WT-CON = 5, WT-HU = 6, MCAT-CON = 6, and MCAT-HU = 6. MCAT, mitochondrially targeted catalase; MCAT-CON, mitochondrially targeted catalase-cage control; MCAT-HU, mitochondrially targeted catalase-humanized; WT-CON, wild-type-cage control; WT-HU, wild-type-humanized.