Developmental Toxicology Division, Council of Scientific and Industrial Research-Indian Institute of Toxicology Research (CSIR-IITR), Lucknow-226001, India.
Toxicol Sci. 2012 Feb;125(2):473-87. doi: 10.1093/toxsci/kfr303. Epub 2011 Nov 1.
Cypermethrin is reported to affect astrocytes in rat brain; however, its mechanism of action is obscure. Here, we observed an increase in apoptosis in the cortical astrocytes upon treatment of rats with cypermethrin. We then characterized the mechanism governing the apoptosis. Because the epidermal growth factor receptor (EGFR) signaling regulates the survival of astrocytes, we investigated the effect of cypermethrin on EGFR activation. The astrocytes exhibited an early and irreversible attenuation in the basal EGFR phosphorylation. Supportively, molecular docking studies revealed considerable homology in the docking mode of cypermethrin and the known EGFR inhibitors, erlotinib and AG1478, to the kinase domain of EGFR. Furthermore, treatment with cypermethrin demonstrated a downregulation in the intracellular and secreted levels of heparin-binding epidermal growth factor (HB-EGF), an EGFR ligand. AG1478 reduced the synthesis of HB-EGF, suggesting the dependence of HB-EGF on EGFR activation. In addition, a neutralizing antibody against HB-EGF diminished the basal EGFR levels, indicating ligand-dependent expression of EGFR. Likewise, cypermethrin caused irreversible suppression in the basal EGFR levels, which induced apoptosis in astrocytes. The apoptosis was prevented by exogenous HB-EGF. These data imply an autocrine/paracrine mode of action of HB-EGF-EGFR in astrocyte survival. Consequently, cypermethrin induced a mitochondria-mediated apoptosis, characterized by rise in Bax/Bcl-2 ratio and cleavage of caspase-9, -3, and -7, and the effect was prevented by HB-EGF. HB-EGF activated the extracellular signal-regulated kinases and AKT pathways that protected against apoptosis. Together, these data demonstrate that cypermethrin induces astrocyte apoptosis by disrupting the autocrine/paracrine mode of HB-EGF-EGFR signaling at two levels, irreversible loss of basal EGFR and downregulation of HB-EGF.
氯菊酯据报道会影响大鼠大脑中的星形胶质细胞；然而，其作用机制尚不清楚。在这里，我们观察到用氯菊酯处理大鼠会导致皮质星形胶质细胞凋亡增加。然后，我们描述了调控凋亡的机制。因为表皮生长因子受体（EGFR）信号调节星形胶质细胞的存活，我们研究了氯菊酯对 EGFR 激活的影响。星形胶质细胞表现出基础 EGFR 磷酸化的早期和不可逆转的衰减。支持性的是，分子对接研究显示氯菊酯和已知的 EGFR 抑制剂厄洛替尼（erlotinib）和 AG1478 与 EGFR 激酶结构域的对接模式具有相当大的同源性。此外，用氯菊酯处理会导致细胞内和分泌的肝素结合表皮生长因子（HB-EGF）水平下调，这是 EGFR 的配体。AG1478 降低了 HB-EGF 的合成，表明 HB-EGF 依赖于 EGFR 激活。此外，针对 HB-EGF 的中和抗体降低了基础 EGFR 水平，表明 EGFR 的配体依赖性表达。同样，氯菊酯会导致基础 EGFR 水平的不可逆抑制，从而诱导星形胶质细胞凋亡。外源性 HB-EGF 可预防这种凋亡。这些数据表明 HB-EGF-EGFR 在星形胶质细胞存活中具有自分泌/旁分泌作用模式。因此，氯菊酯通过线粒体介导的凋亡诱导星形胶质细胞凋亡，其特征是 Bax/Bcl-2 比值升高，caspase-9、-3 和 -7 被切割，而 HB-EGF 可预防这种作用。HB-EGF 激活细胞外信号调节激酶和 AKT 通路，从而防止凋亡。总之，这些数据表明氯菊酯通过破坏 HB-EGF-EGFR 信号的自分泌/旁分泌模式在两个水平上诱导星形胶质细胞凋亡：基础 EGFR 的不可逆丧失和 HB-EGF 的下调。
