Glyoxalase I (GLO1) is the primary enzyme for detoxification of the reactive dicarbonyl methylglyoxal (MG). Loss of GLO1 promotes accumulation of MG resulting in a recapitulation of diabetic phenotypes. We previously demonstrated attenuated GLO1 protein in skeletal muscle from individuals with type 2 diabetes (T2D). However, whether GLO1 attenuation occurs prior to T2D and the mechanisms regulating GLO1 abundance in skeletal muscle are unknown. GLO1 expression and activity were determined in skeletal muscle tissue biopsies from 15 lean healthy individuals (LH, BMI: 22.4 ± 0.7) and 5 individuals with obesity (OB, BMI: 32.4 ± 1.3). GLO1 protein was attenuated by 26 ± 0.3 % in OB compared to LH skeletal muscle ( = 0.019). Similar reductions for GLO1 activity were observed ( = 0.102). NRF2 and Keap1 expression were equivocal between groups despite a 2-fold elevation in GLO1 transcripts in OB skeletal muscle ( = 0.008). GLO1 knock-down (KD) in human immortalized myotubes promoted downregulation of muscle contraction and organization proteins indicating the importance of GLO1 expression for skeletal muscle function. SIRT1 KD had no effect on GLO1 protein or activity whereas, SIRT2 KD attenuated GLO1 protein by 28 ± 0.29 % ( < 0.0001) and GLO1 activity by 42 ± 0.12 % ( = 0.0150). KD of NAMPT also resulted in attenuation of GLO1 protein (28 ± 0.069 %, p = 0.003), activity (67 ± 0.09 %, = 0.011) and transcripts (50 ± 0.13 %, = 0.049). Neither the provision of the NAD precursors NR nor NMN were able to prevent this attenuation in GLO1 protein. However, NR did augment GLO1 specific activity ( = 0.022 vs NAMPT KD). These perturbations did not alter GLO1 acetylation status. SIRT1, SIRT2 and NAMPT protein levels were all equivocal in skeletal muscle tissue biopsies from individuals with obesity and lean individuals. These data implicate NAD-dependent regulation of GLO1 in skeletal muscle independent of altered GLO1 acetylation and provide rationale for exploring NR supplementation to rescue attenuated GLO1 abundance and activity in conditions such as obesity.

中文翻译：

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NAMPT 和 SIRT2 的缺失而非 SIRT1 的缺失会减弱人类骨骼肌中 GLO1 的表达和活性


乙二醛酶 I (GLO1) 是活性二羰基甲基乙二醛 (MG) 解毒的主要酶。 GLO1 的缺失会促进 MG 的积累，从而导致糖尿病表型的重现。我们之前证明了 2 型糖尿病 (T2D) 患者骨骼肌中的 GLO1 蛋白减弱。然而，GLO1 衰减是否发生在 T2D 之前以及调节骨骼肌中 GLO1 丰度的机制尚不清楚。 GLO1 表达和活性是在 15 名瘦健康个体（LH，BMI：22.4 ± 0.7）和 5 名肥胖个体（OB，BMI：32.4 ± 1.3）的骨骼肌组织活检中测定的。与 LH 骨骼肌相比，OB 中的 GLO1 蛋白减弱了 26 ± 0.3% (= 0.019)。观察到 GLO1 活性的类似降低 (= 0.102)。尽管 OB 骨骼肌中 GLO1 转录物增加了 2 倍 (= 0.008)，但各组之间的 NRF2 和 Keap1 表达是模棱两可的。人类永生化肌管中的 GLO1 敲低 (KD) 促进了肌肉收缩和组织蛋白的下调，表明 GLO1 表达对骨骼肌功能的重要性。 SIRT1 KD 对 GLO1 蛋白或活性没有影响，而 SIRT2 KD 使 GLO1 蛋白减弱 28 ± 0.29 % (< 0.0001)，使 GLO1 活性减弱 42 ± 0.12 % (= 0.0150)。 NAMPT 的 KD 还导致 GLO1 蛋白（28 ± 0.069 %，p = 0.003）、活性（67 ± 0.09 %，= 0.011）和转录物（50 ± 0.13 %，= 0.049）减弱。提供 NAD 前体 NR 和 NMN 都无法阻止 GLO1 蛋白的这种减弱。然而，NR 确实增强了 GLO1 比活性（= 0.022 vs NAMPT KD）。这些扰动不会改变 GLO1 乙酰化状态。 在肥胖个体和瘦个体的骨骼肌组织活检中，SIRT1、SIRT2 和 NAMPT 蛋白水平均不明确。这些数据表明骨骼肌中 GLO1 的 NAD 依赖性调节与 GLO1 乙酰化的改变无关，并为探索 NR 补充剂以挽救肥胖等情况下 GLO1 丰度和活性减弱提供了理论依据。