Infrared radiation affects the mitochondrial pathway of apoptosis in human fibroblasts

J Invest Dermatol. 2004 Nov;123(5):823-31. doi: 10.1111/j.0022-202X.2004.23472.x.


We have previously observed that near-infrared (IR) pre-irradiation protects normal human dermal fibroblasts from ultraviolet (UV) cytotoxicity in vitro. Here, we show that IR pre-irradiation of human fibroblasts inhibited UVB activation of caspase-9 and -3, leading us to study early events in the mitochondrial apoptotic pathway after IR irradiation. IR irradiation led to a partial release of cytochrome c and Smac/Diablo but not apoptosis-inducing factor (AIF). This was accompanied by a slight but transient decrease in the mitochondrial membrane potential (Deltapsim) and by the insertion of Bax into mitochondrial membrane. Early apoptotic events in the mitochondrial pathway thus occurred after IR irradiation despite a lack of caspase-9 and -3 activation. This could be explained by the induction by IR of the expression of heat shock protein Hsp27, which is known to prevent apoptosome assembly. Furthermore, the balance between pro-apoptotic (i.e., Bax) and anti-apoptotic (i.e., Bcl-2 or Bcl-xL) proteins, which was rather pro-apoptotic after IR exposure, became anti-apoptotic 24 h later, suggesting a protective effect. Together, these actions could also contribute to prepare the cell to resist UVB-triggered apoptosis. Finally, isolated rat liver mitochondria-released cytochrome c in response to IR, demonstrating that mitochondria were a primary target of IR radiation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Apoptosis / radiation effects*
  • Caspase 3
  • Caspase 9
  • Caspases / metabolism
  • Cells, Cultured
  • Cytochromes c / metabolism
  • Dermis / cytology*
  • Female
  • Fibroblasts / cytology
  • Fibroblasts / metabolism
  • Fibroblasts / radiation effects*
  • HSP27 Heat-Shock Proteins
  • Heat-Shock Proteins / metabolism
  • Humans
  • Infrared Rays*
  • Membrane Potentials / radiation effects
  • Middle Aged
  • Mitochondria / metabolism
  • Mitochondria / radiation effects*
  • Molecular Chaperones
  • Neoplasm Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • bcl-2-Associated X Protein


  • BAX protein, human
  • HSP27 Heat-Shock Proteins
  • HSPB1 protein, human
  • Heat-Shock Proteins
  • Molecular Chaperones
  • Neoplasm Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2-Associated X Protein
  • Cytochromes c
  • CASP3 protein, human
  • CASP9 protein, human
  • Casp3 protein, rat
  • Casp9 protein, rat
  • Caspase 3
  • Caspase 9
  • Caspases