Effect of 2,5-hexanedione on rat ovarian granulosa cell apoptosis involves endoplasmic reticulum stress-dependent m-TOR signaling pathway

Abstract

ABSTRACT Occupational exposure to N-hexane/2,5-hexanedione (2,5-HD) was found to adversely affect reproductive functions in females. However, there are few studies regarding the mechanisms underlying reproductive system damage initiated by 2,5-HD. Several studies demonstrated that 2,5-HD exerts hormonal dysfunctions in females by promoting apoptosis using rat ovarian granulosa cells (GCs) as a model. The endoplasmic reticulum (ER) plays a key role in cellular processes such as protein folding and modification, Ca2+ storage, and lipid synthesis, which are known to involve the activation of stress (ERS)-dependent m-TOR signaling pathway. Thus, the aim of this study was to examine the effects of 2,5-HD on ER and the associated activation of stress (ERS)-dependent m-TOR signaling pathway resulting in consequent apoptosis of ovarian GCs. Data demonstrated that after intraperitoneal treatment with 100, 200, or 400 mg/kg 2,5-HD for 6 consecutive weeks, 5 times per week, a decrease in body weight, ovarian weight, and relative ovary weight was found. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed that 2,5-HD promoted apoptosis of ovarian GCs, which involved enhanced relative protein expression levels of m-TOR/p-mTOR. Our findings demonstrated that 2,5-HD (1) elevated expression levels of pro-apoptosis-related genes Bax and Caspase 3, (2) decreased expression levels of the anti-apoptosis gene Bcl-2, and (3) activated the protein expression of glucose-regulatory protein 78 (GRP78), inositol-requiring enzyme-1 (IRE1), and c-Jun terminal kinase (JNK) associated with increased apoptosis. Evidence indicates that chronic exposure to 2,5-HD induced apoptosis of ovarian GCs, and the possible mechanism underlying this effect involves the ERS-dependent m-TOR signaling pathway.