Issa Rita, Boeving Michael, Kinter Michael, Griffin Timothy M
Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, 825 NE 13th St, Oklahoma City, Oklahoma 73104.
Department of Geriatric Medicine, Reynolds Oklahoma Center on Aging, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma.
J Orthop Res. 2018 Feb;36(2):760-769. doi: 10.1002/jor.23728. Epub 2017 Oct 17.
Mechanosensitve pathways in chondrocytes are essential for maintaining articular cartilage homeostasis. Traumatic loading increases cartilage oxidation and causes cell death and osteoarthritis. However, sub-lethal doses of the pro-oxidant molecule tert-Butyl hydroperoxide (tBHP) protects against loading-induced chondrocyte death. We hypothesized that compressive cyclic loading at moderate strains (<20%) causes sub-lethal cartilage oxidation that induces an adaptive increase in the endogenous antioxidant defense network. We tested this hypothesis by subjecting healthy bovine articular cartilage explants to in vitro static or cyclic (1 Hz) compressive loading at 50 kPa (15% strain, "physiologic") versus 300 kPa (40% strain, "hyper-physiologic") for 12 h per day for 2 days. We also treated unloaded explants with 100 μM tBHP for 12 h per day for 2 days to differentiate between biomechanical and chemical pro-oxidant stimulation. All loading conditions induced glutathione oxidation relative to unloaded controls, but only the 50 kPa cyclic loading condition increased total glutathione content (twofold). This increase was associated with a greater expression of glutamate-cysteine ligase, the rate-limiting step in glutathione synthesis, compared to 300 kPa cyclic loading. 50 kPa cyclic loading also increased the expression of superoxide dismutase-1 and peroxiredoxin-3. Like 50 kPa loading, tBHP treatment also increased total glutathione content. However, tBHP treatment and 50 kPa cyclic loading differed in their effect on the expression of genes regulating antioxidant defense and cartilage matrix synthesis and degradation. These findings suggest that glutathione metabolism is a mechanosensitive antioxidant defense pathway in chondrocytes and that intermittent pro-oxidant treatment alone is insufficient to account for all changes in mediators of cartilage homeostasis associated with cyclic loading. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:760-769, 2018.
软骨细胞中的机械敏感通路对于维持关节软骨的稳态至关重要。创伤性负荷会增加软骨氧化，导致细胞死亡和骨关节炎。然而，亚致死剂量的促氧化分子叔丁基过氧化氢（tBHP）可保护软骨细胞免受负荷诱导的死亡。我们推测，中等应变（<20%）下的周期性压缩负荷会导致亚致死性软骨氧化，从而诱导内源性抗氧化防御网络的适应性增加。我们通过将健康的牛关节软骨外植体每天在50 kPa（15%应变，“生理状态”）与300 kPa（40%应变，“超生理状态”）下进行体外静态或周期性（1 Hz）压缩负荷处理12小时，持续2天来验证这一假设。我们还将未加载的外植体每天用100 μM tBHP处理12小时，持续2天，以区分生物力学和化学促氧化刺激的差异。相对于未加载的对照组，所有负荷条件均诱导了谷胱甘肽氧化，但只有50 kPa的周期性负荷条件增加了总谷胱甘肽含量（两倍）。与300 kPa的周期性负荷相比，这种增加与谷胱甘肽合成的限速步骤——谷氨酸 - 半胱氨酸连接酶的表达增加有关。50 kPa的周期性负荷还增加了超氧化物歧化酶 - 1和过氧化物酶体增殖物激活受体 - 3的表达。与50 kPa负荷一样，tBHP处理也增加了总谷胱甘肽含量。然而，tBHP处理和50 kPa周期性负荷在调节抗氧化防御以及软骨基质合成和降解的基因表达方面存在不同影响。这些发现表明，谷胱甘肽代谢是软骨细胞中的一种机械敏感抗氧化防御途径，并且单独的间歇性促氧化处理不足以解释与周期性负荷相关的软骨稳态介质的所有变化。© 2017骨科学研究协会。由威利期刊公司出版。《矫形外科学研究》36:760 - 769，2018。
