Reduced autophagy leads to an impaired ferritin turnover in senescent fibroblasts

Free Radic Biol Med. 2016 Dec;101:325-333. doi: 10.1016/j.freeradbiomed.2016.10.492. Epub 2016 Oct 24.


Changes in the two main intracellular degradation systems, the Ubiquitin-Proteasome System and the Autophagy-Lysosome pathway (ALP) are widely discussed as a hallmark of the aging process. To follow the age-related behavior of both degradation systems we examined their impact on ferritin, known to be degradable by both. Ferritin H was analyzed in young and senescent human fibroblasts, revealing a higher steady-state level in the senescent cells. By blocking both proteolytic systems, we confirmed that particularly the ALP plays a crucial role in ferritin H turnover. However, an unexpected increase in lysosomal activity in the senescent cells, suggests a dysregulation in the autophagy pathway. To further investigate the impaired ferritin H turnover, confocal microscopic colocalization studies of ferritin H with lysosomal-associated membrane protein 2a (Lamp2a) and monodansylcadaverine (MDC) were performed and clearly revealed the degradation of ferritin by macroautophagy. By induction of autophagy via inhibition of mTOR using rapamycin an increase of ferritin H turnover was obtained in senescent cells, demonstrating a mTOR dependent reduction of autophagy in senescent human fibroblasts.

Keywords: 20S proteasome; ATGs; Aging; Autophagy-lysosome pathway; Ferritin; Fibroblasts; Rapamycin; Senescence; mTOR.

MeSH terms

  • Apoferritins / metabolism*
  • Autophagy / drug effects*
  • Autophagy / genetics
  • Cadaverine / analogs & derivatives
  • Cadaverine / pharmacology
  • Cellular Senescence / drug effects
  • Deferoxamine / pharmacology
  • Enzyme Inhibitors / pharmacology
  • Fibroblasts / cytology
  • Fibroblasts / drug effects*
  • Fibroblasts / metabolism
  • Foreskin / cytology
  • Foreskin / metabolism
  • Gene Expression
  • Hemin / pharmacology
  • Humans
  • Kinetics
  • Lysosomal-Associated Membrane Protein 2 / genetics
  • Lysosomal-Associated Membrane Protein 2 / metabolism
  • Lysosomes / drug effects*
  • Lysosomes / metabolism
  • Male
  • Primary Cell Culture
  • Proteasome Endopeptidase Complex / metabolism*
  • Proteolysis / drug effects
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases / antagonists & inhibitors
  • TOR Serine-Threonine Kinases / genetics*
  • TOR Serine-Threonine Kinases / metabolism


  • Enzyme Inhibitors
  • LAMP2 protein, human
  • Lysosomal-Associated Membrane Protein 2
  • Hemin
  • Apoferritins
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Proteasome Endopeptidase Complex
  • monodansylcadaverine
  • Deferoxamine
  • Cadaverine
  • Sirolimus