α-Synuclein impairs ferritinophagy in the retinal pigment epithelium: Implications for retinal iron dyshomeostasis in Parkinson's disease

Sci Rep. 2017 Oct 9;7(1):12843. doi: 10.1038/s41598-017-12862-x.

Abstract

Retinal degeneration is prominent in Parkinson's disease (PD), a neuromotor disorder associated with aggregation of α-synuclein (α-syn) in the substantia-nigra (SN). Although α-syn is expressed in the neuroretina, absence of prominent aggregates suggests altered function as the likely cause of retinal pathology. We demonstrate that α-syn impairs ferritinophagy, resulting in the accumulation of iron-rich ferritin in the outer retina in-vivo and retinal-pigment-epithelial (RPE) cells in-vitro. Over-expression of Rab1a restores ferritinophagy, suggesting that α-syn impairs lysosomal function by disrupting the trafficking of lysosomal hydrolases. Surprisingly, upregulation of ferritin in RPE cells by exogenous iron in-vitro stimulated the release of ferritin and α-syn in exosomes, suggesting that iron overload due to impaired ferritinophagy or other cause(s) is likely to initiate prion-like spread of α-syn and ferritin, creating retinal iron dyshomeostasis and associated cytotoxicity. Since over-expression of α-syn is a known cause of PD, these results explain the likely cause of PD-associated retinal degeneration.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Autophagosomes / metabolism
  • Autophagosomes / radiation effects
  • Autophagy* / radiation effects
  • Exosomes / metabolism
  • Ferritins / metabolism*
  • Homeostasis*
  • Humans
  • Iron / metabolism*
  • Light
  • Lysosomes / metabolism
  • Lysosomes / radiation effects
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Microtubule-Associated Proteins / metabolism
  • Models, Biological
  • Parkinson Disease / metabolism*
  • Parkinson Disease / pathology
  • Photoreceptor Cells, Vertebrate / metabolism
  • Photoreceptor Cells, Vertebrate / radiation effects
  • Proteolysis / radiation effects
  • RNA, Small Interfering / metabolism
  • Retinal Pigment Epithelium / metabolism*
  • Retinal Pigment Epithelium / pathology
  • Retinal Pigment Epithelium / radiation effects
  • alpha-Synuclein / metabolism*
  • rab1 GTP-Binding Proteins / metabolism

Substances

  • Map1lc3b protein, mouse
  • Microtubule-Associated Proteins
  • RNA, Small Interfering
  • alpha-Synuclein
  • Ferritins
  • Iron
  • rab1 GTP-Binding Proteins