Mitochondrial dysfunction and endoplasmic reticulum stress involved in oocyte aging: an analysis using single-cell RNA-sequencing of mouse oocytes

To explore the mechanisms of ovarian aging, we performed overall analysis on the age-related alterations of gene expression profiles in mouse germinal vesicle (GV) stage oocytes by means of single-cell RNA-sequencing method (scRNA-seq).Two age groups (5-week-old and 32-week-old) female KM mice were used as young and old models. Subsequently, GV oocytes were collected for scRNA-seq. The bioinformatics was performed to analyze and compare the differences of gene expression profile between GV oocytes of young and old mice.The analysis of scRNA-seq data showed that there were 624 differential expressed genes (DEGs) between two age groups of mouse GV stage oocytes. Four hundred forty-nine DEGs were up-regulated while 175 DEGs were down-regulated in the GV oocytes of the old group. KEGG pathway analysis revealed that the genes involved in mitochondrial function including oxidative phosphorylation and ATP production pathway were significantly down-regulated in GV oocytes of 32-week-old mice, especially the mitochondrial encoded NADH dehydrogenase (mt-Nd), including mt-Nd2, mt-Nd3, mt-Nd4, mt-Nd4L and mt-Nd5. Analysis of DEGs revealed that endoplasmic reticulum stress-related genes including AdipoR2, IRAK-1, RCAN1 and MsrB1 were significantly down-regulated in GV oocytes of 32-week-old mice. Also, analysis of DEGs demonstrated that anti-oxidation-related genes including Erbb3、Rcan1、Gsto2 and Msrb1 were significantly down-regulated in GV oocytes of old group.The disorder of mitochondrial function, endoplasmic reticulum stress and the reduced antioxidant capability might be involved in the progression of oocyte aging. Especially, the down regulation of mitochondrial encoded subunits of respiratory chain complexes might play critical roles in the relevant mechanisms.