The Impact of Aging on Macroautophagy in the Pre-ovulatory Mouse Oocyte.

Alexandra E Peters,Elizabeth G Bromfield,Eileen A Mclaughlin,Brett Nixon,Shaun D Roman,Shandelle J Caban,Jessie M Sutherland

doi:10.3389/fcell.2021.691826

Abstract

Accompanying the precipitous age-related decline in human female fertility is an increase in the proportion of poor-quality oocytes within the ovary. The macroautophagy pathway, an essential protein degradation mechanism responsible for maintaining cell health, has not yet been thoroughly investigated in this phenomenon. The aim of this study was to characterize the macroautophagy pathway in an established mouse model of oocyte aging using in-depth image analysis-based methods and to determine mechanisms that account for the observed changes. Three autophagy pathway markers were selected for assessment of gene and protein expression in this model: Beclin 1; an initiator of autophagosome formation, Microtubule-associated protein 1 light chain 3B; a constituent of the autophagosome membrane, and lysosomal-associated membrane protein 1; a constituent of the lysosome membrane. Through quantitative image analysis of immunolabeled oocytes, this study revealed impairment of the macroautophagy pathway in the aged oocyte with an attenuation of both autophagosome and lysosome number. Additionally, an accumulation of amphisomes greater than 10 μm2 in area were observed in aging oocytes, and this accumulation was mimicked in oocytes treated with lysosomal inhibitor chloroquine. Overall, these findings implicate lysosomal dysfunction as a prominent mechanism by which these age-related changes may occur and highlight the importance of macroautophagy in maintaining mouse pre-ovulatory oocyte quality. This provides a basis for further investigation of dysfunctional autophagy in poor oocyte quality and for the development of therapeutic or preventative strategies to aid in the maintenance of pre-ovulatory oocyte health.

Highlights

Infertility is a major health burden affecting an estimated 15% of couples globally, with a female factor implicated in approximately half of all cases (Vayena et al, 2002; Agarwal et al, 2005; Vander Borght and Wyns, 2018)
The initial goal of this study was to characterize the macroautophagy pathway in mouse pre-ovulatory oocytes
Relative Expression of Macroautophagy Marker Genes Map1lc3, Becn1, and Lamp1 Is Not Altered in Aged Mouse Oocytes

Summary

INTRODUCTION

Infertility is a major health burden affecting an estimated 15% of couples globally, with a female factor implicated in approximately half of all cases (Vayena et al, 2002; Agarwal et al, 2005; Vander Borght and Wyns, 2018). This prolonged stage of cell cycle arrest renders the oocyte vulnerable to damage from a variety of insults such as the oxidative stress and inflammation associated with folliculogenesis and ovulation (Chao et al, 2005; Goud et al, 2008; Miyamoto et al, 2010; Lliberos et al, 2021) Chronic exposure to these factors throughout a female’s reproductive life can cause damage to the intracellular environment of the oocyte and its immediate supportive cells, contributing to reduced oocyte quality. Despite various pathways’ involvement in oocyte aging, there are minimal therapeutic or preventative treatments available to maintain or improve oocyte quality or enhance the success of interventions such as assisted reproductive technologies (Newman et al, 2019; Peters et al, 2020) This situation provides a clear imperative for further investigation into the molecular pathways that underpin female age-related infertility.

MATERIALS AND METHODS

RESULTS

DISCUSSION

ETHICS STATEMENT