Age and sex-specific changes in mitochondrial quality control in skeletal and cardiac muscle

Abstract

Introduction: Skeletal and cardiac muscle mitochondria exist in a dynamic reticulum that is maintained by a balance of mitochondrial biogenesis, fusion, fission, and mitophagy. This balance is crucial for adequate ATP production, and alterations in skeletal muscle mitochondria have been implicated in aging-associated declines in mitochondrial function.

Methods: We sought to determine whether age and biological sex affect mitochondrial content [Complex IV (CIV)], biogenesis (PGC-1ɑ), fusion (MFN2, OPA1), fission (DRP1, FIS1), and mitophagy (Parkin, Pink1) markers in skeletal and cardiac muscle by assessing protein expression in tibialis anterior (TA) and ventricular tissue from 16 young (≤6 months) and 16 old (≥20 months) male and female Sprague-Dawley rats.

Results: In the TA, CIV expression was 40% lower in old vs. young rats (p < 0.001), indicating lower mitochondrial content, and coincided with higher expression of Parkin (+4-fold, p < 0.001). Further, MFN2 expression was higher (+2-fold, p < 0.005) and DRP1 expression was lower (-40%, p = 0.014) in older rats. In cardiac muscle, mitochondrial content was maintained in old vs. young rats, and this occurred concomitantly with higher expression of both PGC-1ɑ and Parkin. MFN2 and OPA1 expression were also 1.2-5-fold higher in older rats (p < 0.05 for all). Largely, protein expression did not differ between male and female rats, with the exception of Pink1 and FIS1 expression in the TA.

Discussion: Collectively, older skeletal and cardiac muscle demonstrated higher expression of fusion and mitophagy proteins, which indicates age alters the balance of biogenesis, fission, fusion, and mitophagy. This may, in turn, affect the ability to provide ATP to these metabolically active tissues.

Keywords: biological sex; fission; fusion; mitophagy; muscle health.

FIGURE 1

Complex IV [CIV, (A)] protein expression is lower, glyceraldehyde-3-phosphate dehydrogenase [GAPDH, (B)] and Parkin (C,D) protein expression are higher, and Pink1 (E,F) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha [PGC-1α, (G)] protein expression are not different in old vs. young tibialis anterior muscle. Data in (A–C,E,G) are normalized to total protein. Data in (D,F) are normalized to total protein and subsequently expressed relative to CIV expression. Legend = AU, arbitrary units; YF, young female; YM, young male; OF, old female; OM, old male. #Main effect of sex (P < 0.05), *Main effect of age (P < 0.05). Data are presented as means +SEM, n = 6-8 per group.

FIGURE 2

Mitofusin 2 [MFN2, (A,B)] protein expression is higher, optic atrophy 1-short [OPA1-Short, (C,D)] and OPA1-Long (E,F) protein expression are not different, dynamin-related protein 1 [DRP1, panels (G,H)] protein expression is lower in old vs. young tibialis anterior muscle, while there was an age*sex interaction for fission 1 [FIS1, (I,J)] protein expression. Data in (A,C,E,G,I) are normalized to total protein. Data in (B,D,F,H,J) are normalized to total protein and subsequently expressed relative to CIV expression. Legend = AU, arbitrary units; YF, young female; YM, young male; OF, old female; OM, old male. *Main effect of age (P < 0.05), #Interaction effect (P < 0.05). Data are presented as means +SEM, n = 7-8 per group.

FIGURE 3

Complex IV [CIV, (A)] protein expression is not different, while glyceraldehyde-3-phosphate dehydrogenase [GAPDH, (B)] Parkin (C,D), and peroxisome proliferator-activated receptor gamma coactivator 1-alpha [PGC-1α, (E)] protein expression are higher in old vs. young cardiac muscle. Data in (A,B,C,E) are normalized to total protein. Data in (D) are normalized to total protein and subsequently expressed relative to CIV expression. Legend = AU, arbitrary units; YF, young female; YM, young male; OF, old female; OM, old male. *Main effect of age (P < 0.05). Data are presented as means ± SEM, n = 5-8 per group.

FIGURE 4

Mitofusin 2 [MFN2, (A,B)], optic atrophy 1-short [OPA1-Short, (C,D)] and OPA1-Long (E,F) protein expression are higher, while dynamin-related protein 1 [DRP1, (G,H)] and fission 1 [FIS1, (I,J)] protein expression are not different in old vs. young cardiac muscle. Data in (A,C,E,G,I) are normalized to total protein. Data in (B,D,F,H,J) are normalized to total protein and subsequently expressed relative to CIV expression. Legend = AU, arbitrary units; YF, young female; YM, young male; OF, old female; OM, old male. *Main effect of age (P < 0.05). Data are presented as means ± SEM, n = 7-8 per group.