Differential expression of apoptosis-related factors induces the age-related apoptosis of the gracilis muscle in humans

Int J Mol Med. 2014 May;33(5):1110-6. doi: 10.3892/ijmm.2014.1675. Epub 2014 Feb 27.

Abstract

In the normal aging process, apoptosis has been implicated as a mechanism responsible for the loss of muscle cells and plays an important role in age-related muscle loss. Several signaling pathways involved in skeletal muscle apoptosis are currently under intense investigation, particularly the caspase-independent pathway. This study investigated the age-related apoptotic changes occurring in the gracilis muscle in humans between 10 and 50 years of age. For this purpose, muscle samples were divided into 5 groups (n=8). Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and immunofluorescence detection were performed to determine the number of apoptotic muscle cells in each group. In addition, the expression levels of apoptosis-related factors, such as Bcl-2, Bax, apoptosis-inducing factor (AIF), caspase-3 and calpain-1 were determined by RT-PCR and western blot analysis. TUNEL assay revealed a significant increase in gracilis muscle apoptosis with aging. The activity of caspase-3 in the gracilis muscle tended to change with age, although the changes were not significant, while the increase in DNA nuclei in muscle from 50 years of age (5.419±0.97) was associated with an increase in the expression of AIF, as observed both at protein (10-30%) and mRNA level (10-60%) in gracilis tissues. Taken together, our results demonstrated that the relative Bcl-2 expression decreased with aging, while Bax expression was upregulated compared to 10-year-olds. In addition, a double-labeling experiment with TUNEL staining and immunofluorescence revealed the co-localization of nuclear AIF-positive and TUNEL-labeled cells. This study suggests that apoptosis in gracilis skeletal muscle in the elderly is partly mediated through the expression of Bcl-2/Bax and the degradation of AIF.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Apoptosis / genetics
  • Apoptosis / physiology*
  • Apoptosis Inducing Factor / metabolism
  • Caspase 3 / metabolism
  • Child
  • Female
  • Humans
  • In Situ Nick-End Labeling
  • Male
  • Middle Aged
  • Muscle, Skeletal / metabolism*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Young Adult
  • bcl-2-Associated X Protein / metabolism

Substances

  • Apoptosis Inducing Factor
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2-Associated X Protein
  • Caspase 3