Redox mechanisms in retinal cells

Oxidative stress is a key underlying component in the pathogenesis of retinal diseases, including glaucoma, diabetic retinopathy and age related macular degeneration (AMD). Intracellular and extracellular anti-oxidants counteract oxidative stress to prevent tissue damage and subsequent disease. The transcription factor Nrf2 is found in mammalian cells and is a major sensor of redox changes. In response to oxidative stress, it activates numerous intracellular anti-oxidant enzymes and cytoprotective proteins. Exogenous antioxidants also utilise this pathway to amplify the anti-oxidant response in cells. In retinal pigment epithelial cells and photoreceptor cells, the Nrf2 pathway has been involved in providing cytoprotection and delaying degeneration within the eye. Mueller cells play a supportive role within the retina, protecting the surrounding cells from oxidative stress. However, the effects of oxidative stress and the Nrf2 pathway have not previously been investigated in retinal Mueller cells. In this study, the effects of a range of pro-oxidants and the dietary antioxidant sulforaphane (SFN) on the Nrf2 pathway were investigated in the human Mueller MIO-M1 cell line. None of the pro-oxidants investigated, including hydrogen peroxide, high glucose concentrations, oxygen and glucose deprivation, lipopolysaccharide and TNF-α, activated Nrf2-mediated gene expression in MIO-M1 cells. Hydrogen peroxide however, induced the Nrf2- driven cellular anti-oxidant heme oxygenase-1 (HO-1) in the human ARPE-19 retinal epithelial cell line In contrast, SFN significantly increased HO-1 and NAD(P)H:quinine oxidoreductase 1 (NQO1), but not ferritin or Thioredoxin (Trx1) expression in MIO-M1 cells, which are Nrf2 target genes. SFN also increased Nrf2 protein expression but not Nrf2 de novo synthesis in MIO-M13 cells. SFN-induced Nrf2 and HO-1 expression was dose-dependently suppressed by Bisindolylmaleimide I (a protein kinase C inhibitor) and LY294002 (a phosphionositide 3-Kinase (PI3K) inhibitor). These results suggest that Mueller cells may be more resistant to oxidative stress than other retinal cell types and that SFN utilises the Nrf2 pathway to amplify the anti-oxidant response in these cells via PI3K and PKC regulation of Nrf2. In conclusion, the Nrf2 pathway may have a key role in amplifying neuroprotection in the diseased retina through SFN in the Mueller cells.

Name dc:type.qualificationname

mphil

Level dc:type.qualificationlevel

other

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2012

Author dc:creator

• Wherry, Lydia Elspeth

Language dc:language

en