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Mechanism of mitochondrial stress-induced resistance to apoptosis in mitochondrial DNA-depleted C2C12 myocytes

G Biswas1, H K Anandatheerthavarada, N G Avadhani

  • 1Department of Animal Biology and the Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.

Cell Death and Differentiation
|January 15, 2005
PubMed

Insights

Mitochondrial stress from partial mitochondrial DNA depletion makes C2C12 cells resistant to apoptosis. Restoring mitochondrial DNA levels reversed this resistance, suggesting a link between mitochondrial health and cell death pathways.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mitochondrial DNA (mtDNA) plays a crucial role in cellular energy production and apoptosis regulation.
  • Mitochondrial dysfunction is implicated in various diseases, but its direct impact on apoptosis resistance is not fully understood.
  • C2C12 myoblasts are a widely used cell line for studying muscle differentiation and apoptosis.

Purpose of the Study:

  • To investigate the effect of partial mitochondrial DNA depletion (mitochondrial stress) on apoptosis sensitivity in C2C12 myoblasts.
  • To identify the molecular mechanisms underlying mitochondrial stress-induced apoptosis resistance.
  • To explore the relationship between mitochondrial integrity and cell proliferation/invasion.

Main Methods:

  • Induction of partial mitochondrial DNA depletion in C2C12 myoblasts.
  • Assessment of apoptosis resistance using staurosporine (STP) treatment.
  • Analysis of proapoptotic (Bax, BAD, Bid) and antiapoptotic (Bcl-2, Bcl-X(L)) protein levels.
  • Evaluation of caspase activation (caspases 3, 9, and 8).
  • Examination of protein localization within mitochondrial compartments.
  • Restoration of mtDNA levels and assessment of apoptosis sensitivity in reverted cells.

Main Results:

  • Partial mtDNA depletion significantly increased resistance to STP-induced apoptosis in C2C12 myoblasts.
  • MtDNA-depleted cells exhibited altered expression of proapoptotic and antiapoptotic proteins, including increased Bax, BAD, Bid, and Bcl-2.
  • Reduced processing of Bid to its active form (tBid) and sequestration of Bax, Bid, and BAD in the mitochondrial inner membrane were observed.
  • Inhibition of apoptosis correlated with increased Bcl-2 and Bcl-X(L) levels and decreased activation of caspases 3, 9, and 8.
  • Restoration of near-normal mtDNA levels and mitochondrial transmembrane potential reversed apoptosis resistance.
  • MtDNA-depleted cells displayed enhanced proliferative and invasive behavior.

Conclusions:

  • Partial mitochondrial DNA depletion induces significant resistance to apoptosis in C2C12 myoblasts.
  • This resistance is mediated by alterations in the balance of pro- and antiapoptotic proteins, impaired Bid processing, and altered protein localization.
  • Restoration of mitochondrial integrity effectively reverses apoptosis resistance.
  • Mitochondrial stress-induced apoptosis resistance may contribute to the observed proliferative and invasive behavior of mtDNA-depleted cells.

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