Emerging evidence indicates that nonylphenol (NP), a widely diffused and stable environmental contaminant, causes damage to the central nervous system (CNS). Although NP could cross the blood-brain barrier (BBB) and accumulate in key brain regions, little is known about the direct effects of NP on neurons. In this study, we aimed to investigate the direct effects of NP exposure on induction of apoptosis and autophagy in primary cortical neurons. Results showed that exposure to NP decreased the cell viability in a concentration-dependent manner. The exposure led to both the increase of TUNEL-positive neurons and the activation of caspase-3. Increased levels of endoplasmic reticulum (ER) stress-related proteins, GRP78, CHOP, ATF4, and casepase-12, were observed in neurons exposed to NP. At the same time, the exposure decreased Bcl-2/Bax ratio and mitochondrial transmembrane potential, and increased the release of Cytochrome-C. In addition, NP exposure enhanced LC3-II conversion, decreased levels of SQSTM1/p62, and increased levels of Beclin-1 and LAMP2. NP exposure also reduced the protein levels of p-mTOR, and did not change the levels of total mTOR. Furthermore, to investigate the role of autophagy in NP-induced apoptosis, both the autophagy inhibitor chloroquine (CQ) and the autophagy inducer rapamycin (RAP) were applied to modulate autophagy activation in primary cortical neurons. The inhibition of autophagy caused by CQ enhanced NP-induced apoptosis; conversely, RAP-induced autophagy remarkably suppressed it. In conclusion, our findings demonstrate that NP exposure induced apoptosis with a concomitant increase of autophagic flux in primary cortical neurons, which supports the idea that this potential neurotoxin has direct effects of on neurons. Both ER stress and mitochondrial pathways may be involved in NP-induced apoptosis in neurons. Furthermore, our results also suggest that autophagy activation might be a protective strategy to ameliorate NP-induced apoptosis in neurons.

中文翻译：

---

自噬激活减轻了壬基酚诱导的皮质神经元凋亡。

新兴证据表明，壬基酚（NP）是一种广泛分布且稳定的环境污染物，会对中枢神经系统（CNS）造成损害。尽管NP可以穿过血脑屏障（BBB）并聚集在关键的大脑区域，但对于NP对神经元的直接作用知之甚少。在这项研究中，我们旨在调查NP暴露对原代皮层神经元凋亡和自噬诱导的直接影响。结果表明，暴露于NP以浓度依赖的方式降低了细胞活力。暴露导致TUNEL阳性神经元的增加和caspase-3的激活。在暴露于NP的神经元中观察到内质网（ER）应激相关蛋白，GRP78，CHOP，ATF4和casepase-12的水平增加。同时，暴露降低了Bcl-2 / Bax比和线粒体跨膜电位，并增加了细胞色素C的释放。此外，NP暴露增强了LC3-II的转化，降低了SQSTM1 / p62的水平，并增加了Beclin-1和LAMP2的水平。NP暴露也降低了p-mTOR的蛋白质水平，并且没有改变总mTOR的水平。此外，为了研究自噬在NP诱导的细胞凋亡中的作用，自噬抑制剂氯喹（CQ）和自噬诱导剂雷帕霉素（RAP）均被用于调节初级皮层神经元的自噬活化。CQ对自噬的抑制作用增强了NP诱导的细胞凋亡；相反，RAP诱导的自噬显着抑制了它。综上所述，我们的发现表明，NP暴露可诱导凋亡，并伴有原代皮层神经元自噬通量的增加，这支持了这种潜在的神经毒素对神经元具有直接作用的想法。内质网应激和线粒体途径都可能参与NP诱导的神经元凋亡。此外，我们的结果还表明自噬激活可能是减轻NP诱导的神经元凋亡的一种保护策略。