4-Nonylphenol induces autophagy and attenuates mTOR-p70S6K/4EBP1 signaling by modulating AMPK activation in Sertoli cells

Abstract

The estrogenic chemical 4-nonylphenol (NP) is known to impair testicular devolopment and spermatogenesis in rodents. The objective of this study was to explore the effects of NP on autophagy induction and AMPK-mTOR signaling pathway in Sertoli cells (SCs), which are the "nursemaid cells" for meiosis of spermatocytes. In this study we exposed 7-week-old male rats to NP by intra-peritoneal injection at 0, 20, 50 or 100 mg/kg body weight/2 days for 20 consecutive days. Our results showed that exposure to NP dose-dependently induces the formation of autophagosomes in SCs, increases the expression of Beclin-1, the conversion of LC3-I to LC3-II and the mRNA expression of Atg3, Atg5, Atg7 and Atg12 in testis, and these effects are concomitant with the activation of AMPK, and the suppression of TSC2-mTOR-p70S6K/4EBP1 signaling cascade in testis. Furthermore, 10 µM Compound C or AMPKα1 siRNA pre-treatment effectively attenuated autophagy and reversed AMPK-mTOR-p70S6K/4EBP1 signaling in NP-treated SCs. Co-treatment with 1 mM AICAR remarkably strengthened NP-induced autophagy and mTOR inhibition in SCs. Together, these data suggest that NP stimulates Sertoli cell autophagy and inhibits mTOR-p70S6K/4EBP1 activity through AMPK activation, which is the potential mechanism responsible for the regulation of testis function and differentiation following NP exposure.

Upregulated Autophagy in Sertoli Cells of Ethanol-Treated Rats Is Associated with Induction of Inducible Nitric Oxide Synthase (iNOS), Androgen Receptor Suppression and Germ Cell Apoptosis

“…This was confirmed by upregulation of LC3-II using western blot, which was statistically significant (Figure 7C) and downregulation of p62 in ethanol-exposed SCs compared to the control (Figure S5). Blocking autophagy with 3-methyladenine (3-MA), an inhibitor of early autophagosome formation [44,45], resulted in a marked reduction of cell viability in cultured ethanol-treated SCs (Figure 7D), indicating the prosurvival role of autophagy as supported by other studies [19,20,34,41,44,45]. …”

“…This cytoprotective role for autophagy has also been observed in thymic macrophages [12], hepatocytes [31,44] and astrocytes [34] with the same animal model of acute ethanol toxicity. To provide direct proof for the prosurvival role of autophagy in SCs, the authors exposed cultured SCs to various concentrations of ethanol and found that blocking of autophagy by 3-MA resulted in reduction of viability, as also observed in similar studies of cultured SCs with various models of acute stress [19,20] and in cultured hepatocytes exposed to ethanol [44]. Blocking autophagy with 3-MA mitigated viability both in ethanol-exposed SCs and in untreated cells, indicating that autophagy is essential for the survival of SCs under normal and ethanol-exposed conditions [44].…”

“…This enhanced autophagic response in stressed SCs also accelerated the secretion of lactate (an essential substrate for germ cell survival) via the modulation of SLC2A3, LDHA and SLC16A1 expression levels [19]. Autophagy induction via mechanisms related to oxidative stress and mammalian target of rapamycin (mTOR) inhibition was also cytoprotective for cultured rat SCs acutely exposed to xenoestrogen 4-nonylphenol (a common environmental toxicant) [20]. Under normal conditions, autophagy upregulation in cultured rat SCs exposed to cell-derived substrates was required for phagocytosis of these substrates by SCs, indicating cooperation between the phagocytosis and autophagy mechanisms [21].…”

Identification of microRNAs for regulating adenosine monophosphate‐activated protein kinase expression in immature boar Sertoli cells in vitro

“…In addition, AMPK activation inhibits cell proliferation via the upregulation of the insulin receptor substrate (Fisher, Gao, Han, Holloszy, & Nolte, ; Harrington et al, ; Shah, Wang, & Hunter, ; Um et al, ) and the suppression of mTOR pathway (Johnson, Rabinovitch, & Kaeberlein, ; Mihaylova & Shaw, ; Patel et al, ). The AMPK signaling pathway is involved in the disruption of SC polarity (Tanwar, Kaneko‐Tarui, Zhang, & Teixeira, ), dysregulated energy metabolism (Bertoldo et al, ), autophagy, and apoptosis in SCs (Duan et al, ; Duan et al, ). These findings are coincided with AICAR‐induced inhibition of SC proliferation via the activation of AMPKα2 based on the GO enrichment and KEGG pathway analyses.…”

miR‐26a suppresses autophagy in swine Sertoli cells by targeting ULK2

“…Accumulating evidence has demonstrated that autophagy has a protective role in Sertoli cells under various pathological conditions (Aslani et al., ; Yin et al., ). The autophagy inhibitor 3‐MA enhances xenoestrogen 4‐nonylphenol‐induced rat Sertoli cell apoptosis and necrosis (Duan et al., ). Autophagy‐mediated degradation of PALIM1 in mouse Sertoli cells is important for the proper assembly of the ectoplasmic specialization (ES), and the ES is essential for Sertoli‐germ cell communication (Liu et al., ).…”