Evaluation of endoplasmic reticulum stress (ERS) associated protein expressions in Stz-induced diabetic mouse ovary

Main function of endoplasmic reticulum (ER) is to facilitate the proper folding of newly synthesized secretory and membrane proteins into native three-dimensional structures. Various triggers result in the onset of accumulation of unfolded or misfolded proteins in ER lümen including inhibition of N-linked glycosylation, perturbations in Ca2+ homeostasis, hipoxia, oxidative stress, glucose deprivation, viral infections and environmental conditions like ambient temperature, condition known as ER stress. In response to ER stress, unfolded protein response (UPR) signalling pathway is activated to retain cellular homeostasis. Although, UPR or ER stress response is an efficient adaptation mechanism for the cells, it was shown that it is also related to various pathophysiology of diseases, including diabetes. Diabetes-induced hyperglysemia or glucose absorbation inefficiency consistently causes granulosa cell apoptosis and reduced meiosis resumption rate in oocytes and low oocyte quality. Both ER stress and UPR may have a role in series of negative impacts on mice ovaries caused by hyperglycemic conditions by determining the cell fate. In this study, 24-days-old BalbC female mice (N=31) were used and designed as three groups: Control (n=10, no treatment), Vehicle (n=6, i.p. 100 µl natrium citrate injected group), Diabetic (n=15, STZ-injected group (i.p. 90 mg/kg BW in 100 µl natrium citrate). To control STZ-induced diabetic model, blood glucose level was measured following the injection days on 2nd, 7th and 14th. Mice whose blood sugar is over 300 mg/dl were accepted as the diabetic. The day of 14th, mice were sacrificed and ovary samples were examined with immunohistochemical staining and western blot analysis to show localisation and the expression levels of ER stress proteins (GRP78, Caspase 12, p-PERK and DDIT3). Additionally, with using qRT-PCR analysis mRNA level of Grp78 and Ddit3 genes which are the indicators for ER stress were examined. It was observed that the immun reaction for p-PERK and DDIT3 was significantly increased in diabetic ovaries, especially in atretic follicles, apoptotic granulosa cells and degenerated oocytes. In ovaries, protein expression of Caspase 12, p-PERK and GRP78 was not showed any statistically differences among experimental groups. There was no significant differences among experimental groups for an amount of Grp78 mRNA. Compair to control and vehicle group, Ddit3 mRNA was significantly increased in diabetic group while amount of DDIT3 protein was not significantly differences among groups. XBP1s protein expression was increased in diabetic group which were statistically significant than control and vehicle. In conclusion, it is detected that diabetes can initiate ERS and stimulate UPR in mice ovaries. Keywords: ERS, Diabetes mellitus, UPR, Mice, Ovary