The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

Oxidative damage is exacerbated by dysregulation of proteasomal activity in naturally aged oocytes (#327)

Bettina P Mihalas 1 , Elizabeth G Bromfield 1 , Jessie M Sutherland 1 , Geoffry N Deluiis 1 , Eileen A McLaughlin 2 , Robert J Aitken 1 , Brett Nixon 1
  1. University of Newcastle, Callaghan, NSW, Australia
  2. Biological Sciences, The University of Auckland, Auckland, New Zealand

An increase in oxidative protein damage is a leading contributor to age-associated decline in oocyte quality. Through the removal of such damaged and / or dysfunctional proteins, the proteasome plays an essential role in maintaining the fidelity of oocyte meiosis. Our study reveals a decrease in proteasome activity in the naturally aged germinal vesicle (GV) mouse oocyte that is positively correlated with increased protein modification by the lipid aldehyde, 4-hydroxynonenal (4-HNE). This highly reactive lipid aldehyde, generated as a by-product of lipid peroxidation cascades, can covalently adduct and dysregulate the function of key oocyte proteins including α-tubulin, a structural component of the oocyte’s meiotic spindle; thus, contributing to a reduction in the integrity of oocyte meiosis. Further, we have shown that inhibition of proteasome activity (MG132; 50 μM) in oxidatively stressed GV oocytes obtained from young animals leads to an attendant increase in the accumulation of 4-HNE-modified proteins, including α-tubulin. Among alternative protein targets for 4-HNE adduction, we identified several subunits of the proteasome as being particularly vulnerable. Accordingly, proteasomal activity was also significantly attenuated in a dose-dependent manner in young oocytes exposed to an acute oxidative insult (H2O2 or 4-HNE). Notably, the inclusion of the antioxidant, penicillamine, to limit propagation of oxidative stress cascades led to a complete recovery of proteasome activity and enhanced clearance of 4-HNE adducted α-tubulin during a 6 h post-H2O2 treatment recovery period. This strategy also proved effective in reducing the incidence of oxidative stress-induced aneuploidy following in vitro oocyte maturation. Taken together, our data implicates proteasome dysfunction as an important factor in the accumulation of oxidatively induced damage in the female germline.