Boron Attenuates Heat Stress-Induced Apoptosis by Inhibiting Endoplasmic Reticulum Stress in Mouse Granulosa Cells.

: Heat stress-induced apoptosis in granulosa cells is mediated by multiple apoptotic signaling pathways, including endoplasmic reticulum (ER) stress. Boron is a naturally occurring trace element with several cytoprotective properties. Nonetheless, the molecular mechanisms involved in the protective functions of boron in granulosa cells undergoing apoptosis caused by heat stress (HS) remain unclear. In this study, we investigated the role of boric acid, a predominant chemical form of boron, in HS-induced apoptotic damage in mouse granulosa cells (mGCs) and explored the underlying mechanisms. We found that HS treatment suppressed cell viability; increased the apoptotic rate of cells; potentiated the activity of caspase-3, a key player in the caspase-mediated apoptotic signaling pathway; and activated ER stress markers, including glucose-regulated protein 78 (GRP78) and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) in mGCs. However, boric acid treatment effectively alleviated the effects of both HS-induced and thapsigargin (an ER stress agonist)-induced apoptosis, such as the enhanced activity of caspase-3 and increase in GRP78 and CHOP expression. Moreover, treatment with 4-phenylbutyrate (4-PBA), an ER stress antagonist, significantly attenuated these HS-induced adverse effects in mGCs. In addition, boric acid supplementation in the culture medium significantly restored the decreased estradiol levels in heat-treated mGCs. The administration of boric acid to female mice previously exposed to hyperthermal conditions effectively restored the levels of serum estradiol in vivo. Collectively, these findings suggest that HS induces apoptosis in mGCs via ER stress pathways and that boron has a protective effect against these adverse effects. This study provides novel insights into the benefits of using boron against heat-induced apoptosis.