Melatonin attenuates palmitic acid-induced mouse granulosa cells apoptosis via endoplasmic reticulum stress

Background: Palmitic acid (PA), the main component of dietary saturated fat, causes Apoptosis in many cell types, including mouse granulosa cell. Melatonin, an important endogenous hormone, has beneficial effects on female reproductive processes. Since elevated PA levels are present in follicular fluid (FF) of patients with infertility and are shown to be toxic for granulosa cells, we investigated the molecular mechanisms of PA toxicity in mouse granulosa cells and explored the effects of melatonin on PA-induced Apoptosis.

Methods: Granulosa cells from immature female mice were cultured for 24 h in medium containing PA and/or melatonin. Then, the effects of PA alone or combined with melatonin on viability, Apoptosis and endoplasmic reticulum (ER) stress in granulosa cells were detected by methyl thiazolyl tetrazolium (MTT) assay, flow cytometry assay and western blot. After 48 h of PA and/or melatonin treatment, the concentrations of estradiol (E2) and progesterone (P4) in the culture supernatants were measured with ELISA kits.

Results: In this study, we explored the effects of melatonin on cell viability and Apoptosis in PA-treated mouse granulosa cells and uncovered the signaling pathways involved in these processes. Our results showed that 200-800 μM PA treatment reduces cell viability, induces cell Apoptosis, enhances the expression of apoptosis-related genes (Caspase 3 and B-cell lymphoma-2 (Bcl-2) associated X protein (Bax)), and activates the expression of ER stress marker genes (glucose-regulated protein 78 (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP)). Melatonin treatment (1-10 μM) suppresses 400 μM PA-induced cell viability decrease, cell Apoptosis, Caspase 3 activation, and Bax, CHOP, and GRP78 expression. In addition, we found that 10 μM melatonin successfully attenuated the 400 μM PA-induced estrogen (E2) and progesterone (P4) decreases.

Conclusions: This study suggests that PA triggers cell Apoptosis via ER stress and that melatonin protects cells against Apoptosis by inhibiting ER stress in mouse granulosa cells.