Bisphenols A and F, but not S, induce apoptosis in bovine granulosa cells via the intrinsic mitochondrial pathway

Abstract

With the gradual decline in global fertility rates, there is a need to identify potential contributing factors, their mechanisms of actions and investigate possible solutions to reverse the trend. Endocrine disrupting compounds (EDCs), such as bisphenol A (BPA), are environmental toxicants that are known to negatively impact reproductive functions. As such, the use of BPA in the manufacturing industry has slowly been replaced by analogs, including bisphenol S (BPS) and bisphenol F (BPF), despite limited knowledge available regarding their impact on health and their safety. The following study investigates the effects of BPA, BPS and BPF at a concentration of 0.5 μg/mL and 50 μg/mL on bovine granulosa cell apoptosis, with the ultimate goal of determining how they may impact oocyte competence and, thus, overall fertility. The underlying hypothesis is that bisphenols disrupt the granulosa cell environment surrounding the oocyte inducing excessive apoptosis via the intrinsic mitochondrial pathway. To test this hypothesis, apoptosis was measured following a time- and dose-dependent exposure to all three bisphenols by flowcytometry paired with annexin V/PI staining as well as by quantification of key genes belonging to the intrinsic apoptotic pathway both at the mRNA and protein levels. The results of this study report that BPA and BPF reduce cell viability through reduced cell counts and increased apoptosis. This increase is due, in part, to the induction of apoptotic genes of the intrinsic pathway of apoptosis. Additionally, this study also suggests that BPS may not act on the intrinsic mitochondrial apoptotic pathway in bovine granulosa cells. Overall, this study allows us to establish potential apoptotic pathways activated by bisphenols as well as compare the relative apoptotic activities of BPA to its most widespread analogs.

SMAD signaling pathway is disrupted by BPA via the AMH receptor in bovine granulosa cells

“…Furthermore, BPS use in the industry has increased drastically to levels similar to BPA [53], therefore further endorsing its use at a dose of 0.05 mg/mL. This dose has been extensively validated in the literature and by several previously published studies by our group [29,[31][32][33][34][35].…”

“…Previous studies by our group show that bovine oocytes and embryos exposed to BPA display significantly reduced cleavage and blastocyst rates resulting in poor oocyte competence and embryo development [29]. Furthermore, additional studies show the effects of BPA on apoptosis rates, epigenetic regulators, spindle formation, and oxidative stress, through alterations in gene expression [30][31][32][33][34][35]. In vitro BPA exposure has also been shown to disrupt steroidogenesis and decrease sex hormone levels [36].…”