Objective: To investigate the effect of estradiol (E2)/estrogen receptor 1 (ESR1) on the proliferation of human chondrocytes in vitro and explore the molecular mechanism.
Methods: The Ad-Easy adenovirus packaging system was used to construct and package the ESR1-overexpressing adenovirus Ad-ESR1. Western blotting and qPCR were used to detect the expression of ESR1 protein and mRNA in human chondrocyte C28I2 cells. In the cells treated with different adenoviruses, the effects of E2 were tested on the expressions of proteins related with cell autophagy and apoptosis and the phosphorylation of ERK signaling pathway using Western blotting. Immunofluorescence assay was used to observe the intracellular autophagic flow, flow cytometry was performed to analyze the cell apoptosis rate and the cell cycle changes, and qPCR was used to detect the expressions of PCNA, cyclin B1 and cyclin D1 mRNAs. The inhibitory effect of the specific inhibitor of ERK on the expressions of autophagy- and apoptosis-related genes at both the protein and mRNA levels were detected using Western blotting and qPCR.
Results: Transfection with the recombinant adenovirus overexpressing ESR1 and E2 treatment of C28I2 cells significantly enhanced the expressions of autophagy-related proteins LC3, ATG7, promoted the colocalization of LC3 and LAMP1 in the cytoplasm, increased the expressions of the proliferation-related marker genes PCNA, cyclin B1 and cyclin D1, and supressed the expressions of cleaved caspase-3, caspase-12 and pERK. RNA interference of ESR1 obviously lowered the expression levels of autophagy-related proteins in C28I2 cells, causing also suppression of the autophagic flow, increments of the expressions of apoptosis-related proteins and pERK, and down-regulated the expressions of the proliferation marker genes. Blocking ERK activation with the ERK inhibitor obviously inhibited the effects of E2/ESR1 on autophagy, proliferationrelated gene expressions and cell apoptosis.
Conclusions: The targeted binding of E2 with ESR1 promotes the proliferation of human chondrocytes in vitro possibly by inhibiting the activation of ERK signaling pathway to promote cell autophagy and induce cell apoptosis.
目的: 探讨雌二醇（E2）/ESR1（ERα）对C28I2软骨细胞增殖的影响及可能的分子机制。
方法: 应用Ad-Easy腺病毒包装系统构建和包装过表达腺病毒Ad-ESR1，Western blot及QPCR检测该基因在细胞中蛋白及RNA表达情况。在E2处理下，设立不同病毒感染组处理C28I2细胞，Western blot检测各处理组C28I2细胞的自噬、凋亡相关蛋白的表达及ERK信号通路的磷酸化水平；免疫荧光实验观察细胞内自噬流的强弱；FCM检测各组细胞凋亡率及周期；QPCR检测mRNA水平增殖相关标志基因（PCNA）、细胞周期蛋白B1（CyclinB1）和细胞周期蛋白D1（CyclinD1）表达。ERK特异性抑制剂处理细胞，Western blot检测抑制ERK通路后自噬及凋亡相关蛋白表达，QPCR检测增殖相关标志基因表达。
结果: 成功构建过表达腺病毒Ad-ESR1。过表达ESR1能够促进E2处理后LC3和ATG7的表达，促进LC3和LAMP1在细胞质中共定位，抑制cleaved caspase3、cleaved caspase12的表达并且促进PCNA、cyclinB1和cyclinD1表达，且细胞内pERK明显减少；而干扰ESR1表达后，自噬相关蛋白表达减少，自噬流减弱，凋亡蛋白表达增加，增殖标志基因表达下调，细胞内pERK相对增加。特异性抑制剂阻断ERK活化，E2/ ESR1诱导的自噬增加以及凋亡减少被抑制，增殖相关基因表达被抑制。
结论: E2与ESR1的靶向结合可促进软骨细胞的增殖，其作用机制可能与抑制ERK信号通路活化从而促进自噬、抑制凋亡有关。
Keywords: ERK signaling pathway; ESR1; apoptosis; autophagy; estradiol; proliferation.