Department of Orthopaedics with Integrated Chinese and Western Medicine, Liyi People's Hospital, Linyi, China.
Eur Rev Med Pharmacol Sci. 2020 Sep;24(18):9246-9255. doi: 10.26355/eurrev_202009_23006.
Osteoarthritis (OA) is associated with decreased autophagy activity and imbalance of cell homeostasis in chondrocytes (CHs). Sirtuin 7 (Sirt7) is claimed to have the ability to activate the autophagy response. The aim of this study was to explore the function of Sirt7 in the development of OA involving autophagy by culturing human chondrocytes (CHs).
We collected knee joint cartilage from patients undergoing traumatic amputation and arthroscopic knee replacement. Protein and mRNA levels of collagen II, Sirt7, ULK1, Lc3, and Beclin1 were analyzed by Western blot and RT-PCR. CHs were isolated from the traumatic cartilage as a control group, and IL-1β was used to induce CHs degeneration. The expression of Sirt7 gene was silenced by siRNA and upregulated by recombinant human Sirt7 protein (rh-Sirt7). An autophagy activator Tat-beclin 1 (Tat) was used to activate autophagy in cultural CHs. Expression of collagen II, Sirt7, ULK1, Lc3, and Beclin1 was determined by immunofluorescence, Western blot, and RT-PCR, respectively.
The protein and mRNA levels of Collagen II, Sirt7, ULK1, Lc3-II, and Beclin1 expressions were decreased in OA cartilage compared with those in healthy cartilage. IL-1β degenerated the CHs resulting in a reduction of collagen II, which also downregulated Sirt7, ULK1, Lc3-II, and Beclin1. Sirt7 deficiency accelerated the catabolism of collagen II and weakened the expression of ULK1, Lc3-II, and Beclin1. On the contrary, exogenous rh-Sirt7 played a positive role in these gene expressions. Finally, Tat alleviated the CHs degeneration by upregulating collagen II and activating ULK1, Lc3-II, and Beclin1, but incapable to mediate Sirt7 expression.
Overall, these findings suggested that Sirt7 was suppressed in the degenerated cartilage. Sirt7 deficiency does harm to the autophagy level, affecting CHs metabolism, while the upregulation of Sirt7 activated autophagy and protected CHs degeneration. An appropriate increase in autophagy can protect CHs but has no effect on Sirt7 expression.
骨关节炎（OA）与软骨细胞（CHs）中自噬活性降低和细胞内稳态失衡有关。据称，Sirtuin 7（Sirt7）具有激活自噬反应的能力。本研究旨在通过培养人软骨细胞（CHs）来探讨 Sirt7 在涉及自噬的 OA 发展中的功能。
我们从接受创伤截肢和关节镜膝关节置换术的患者膝关节采集软骨。通过 Western blot 和 RT-PCR 分析胶原蛋白 II、Sirt7、ULK1、Lc3 和 Beclin1 的蛋白和 mRNA 水平。从创伤性软骨中分离 CHs 作为对照组，并使用 IL-1β诱导 CHs 退变。通过 siRNA 沉默 Sirt7 基因，并使用重组人 Sirt7 蛋白（rh-Sirt7）上调 Sirt7 基因表达。使用自噬激活剂 Tat-beclin 1（Tat）激活培养 CHs 的自噬。通过免疫荧光、Western blot 和 RT-PCR 分别测定胶原蛋白 II、Sirt7、ULK1、Lc3 和 Beclin1 的表达。
与健康软骨相比，OA 软骨中胶原蛋白 II、Sirt7、ULK1、Lc3-II 和 Beclin1 的蛋白和 mRNA 水平降低。IL-1β 使 CHs 退化，导致胶原蛋白 II 减少，同时下调 Sirt7、ULK1、Lc3-II 和 Beclin1。Sirt7 缺乏加速了胶原蛋白 II 的分解代谢，削弱了 ULK1、Lc3-II 和 Beclin1 的表达。相反，外源性 rh-Sirt7 对这些基因表达起到了积极作用。最后，Tat 通过上调胶原蛋白 II 并激活 ULK1、Lc3-II 和 Beclin1 来缓解 CHs 退化，但不能介导 Sirt7 的表达。
总的来说，这些发现表明 Sirt7 在退化的软骨中受到抑制。Sirt7 缺乏会损害自噬水平，影响 CHs 代谢，而 Sirt7 的上调则激活自噬并保护 CHs 退化。适当增加自噬可以保护 CHs，但对 Sirt7 表达没有影响。
