Osteoarthritis (OA) is one of the most characterized joint diseases associated with chondrocyte apoptosis. JNK plays an important role in apoptosis in many pathological conditions, but systemic inhibition of JNK was shown to result in detrimental side effects. MAPK kinase 7 (MKK7) is a direct upstream kinase that regulates JNK and has been shown to activate JNK specifically under toxic conditions. In this study, we investigated the effect of GADD45β-I, a cell-permeable inhibitor targeted for MKK7, on IL-1β-induced cytotoxicity in rat chondrocytes. The results showed that IL-1β exposure resulted in toxicity in a dose-dependent manner, which was nullified by endoplasmic reticulum (ER) stress inhibitors. GADD45β-I significantly preserved cell survival, inhibited oxidative injury and reduced apoptosis after IL-1β treatment. ER stress in chondrocytes was attenuated by GADD45β-I, as evidenced by reduced levels of GRP78 and CHOP, as well as decreased caspase-12 cleavage. In addition, GADD45β-I increased the enzymatic activities of mitochondrial antioxidant enzymes, including IDH2, GSH-Px and SOD2. GADD45β-I significantly upregulated the expression of Sirt3 and attenuated IL-1β-induced acetylation of SOD2. Furthermore, GADD45β-I-induced inhibition of ER stress and protection in chondrocytes were partially reversed by knockdown of Sirt3. In conclusion, our data indicated that GADD45β-I protected chondrocytes against IL-1β through Sirt3-mediated inhibition of ER stress. Targeting MKK7 might be an ideal therapeutic strategy for reducing chondrocyte apoptosis in OA.

骨关节炎（OA）是与软骨细胞凋亡相关的最典型的关节疾病之一。在许多病理条件下，JNK在细胞凋亡中都起着重要作用，但是JNK的系统性抑制显示会导致有害的副作用。MAPK激酶7（MKK7）是直接上游激酶，可调节JNK，并已证明在毒性条件下能特异性激活JNK。在这项研究中，我们研究了针对MKK7的细胞渗透性抑制剂GADD45β-I对IL-1β诱导的大鼠软骨细胞毒性的影响。结果表明，IL-1β暴露以剂量依赖性方式产生毒性，而内质网（ER）应激抑制剂可消除这种毒性。在IL-1β处理后，GADD45β-I可显着保留细胞存活，抑制氧化损伤并减少细胞凋亡。GDD78β-I降低了软骨细胞的内质网应激，GRP78和CHOP的水平降低以及caspase-12裂解的降低证明了这一点。另外，GADD45β-1增加了线粒体抗氧化剂酶的酶活性，包括IDH2，GSH-Px和SOD2。GADD45β-1明显上调Sirt3的表达，并减弱IL-1β诱导的SOD2的乙酰化。此外，通过敲除Sirt3可以部分逆转GADD45β-I诱导的对ER应激的抑制和对软骨细胞的保护。总之，我们的数据表明GADD45β-I通过Sirt3介导的ER应激抑制作用保护软骨细胞抵抗IL-1β。靶向MKK7可能是减少OA中软骨细胞凋亡的理想治疗策略。以及caspase-12切割减少。另外，GADD45β-1增加了线粒体抗氧化剂酶的酶活性，包括IDH2，GSH-Px和SOD2。GADD45β-1明显上调Sirt3的表达，并减弱IL-1β诱导的SOD2的乙酰化。此外，通过敲除Sirt3可以部分逆转GADD45β-I诱导的对ER应激的抑制和对软骨细胞的保护。总之，我们的数据表明GADD45β-I通过Sirt3介导的ER应激抑制作用保护软骨细胞抵抗IL-1β。靶向MKK7可能是减少OA中软骨细胞凋亡的理想治疗策略。以及caspase-12切割减少。另外，GADD45β-1增加了线粒体抗氧化剂酶的酶活性，包括IDH2，GSH-Px和SOD2。GADD45β-1明显上调Sirt3的表达，并减弱IL-1β诱导的SOD2的乙酰化。此外，通过敲除Sirt3可以部分逆转GADD45β-I诱导的对ER应激的抑制和对软骨细胞的保护。总之，我们的数据表明GADD45β-I通过Sirt3介导的ER应激抑制作用保护软骨细胞抵抗IL-1β。靶向MKK7可能是减少OA中软骨细胞凋亡的理想治疗策略。GADD45β-1明显上调Sirt3的表达，并减弱IL-1β诱导的SOD2的乙酰化。此外，通过敲除Sirt3可以部分逆转GADD45β-I诱导的对ER应激的抑制和对软骨细胞的保护。总之，我们的数据表明GADD45β-I通过Sirt3介导的ER应激抑制作用保护软骨细胞抵抗IL-1β。靶向MKK7可能是减少OA中软骨细胞凋亡的理想治疗策略。GADD45β-1明显上调Sirt3的表达，并减弱IL-1β诱导的SOD2的乙酰化。此外，通过敲除Sirt3可以部分逆转GADD45β-I诱导的对ER应激的抑制和对软骨细胞的保护。总之，我们的数据表明GADD45β-I通过Sirt3介导的ER应激抑制作用保护软骨细胞抵抗IL-1β。靶向MKK7可能是减少OA中软骨细胞凋亡的理想治疗策略。