Determining the contributions of protein synthesis and breakdown to muscle atrophy requires non-steady-state equations.
Determining the contributions of protein synthesis and breakdown to muscle atrophy requires non-steady-state equations.
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DOI：
10.1002/jcsm.12772
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发表时间：
2021-12
期刊：
影响因子：
--
通讯作者：
Miller BF
中科院分区：
文献类型：
--
作者：
Kobak KA;Lawrence MM;Pharaoh G;Borowik AK;Peelor FF 3rd;Shipman PD;Griffin TM;Van Remmen H;Miller BF
随着时间的推移，衰老和恶病质会导致肌肉质量损失，这表明蛋白质分解超过了蛋白质合成。由于长期标记的优点，氧化氘 (D2O) 用于研究蛋白质周转，但这些方法引入了在研究蛋白质增益或损失条件时很大程度上被忽视的考虑因素。本研究的目的是证明在 D2O 标记研究期间考虑蛋白质质量（非稳态）变化的重要性，同时探索蛋白质合成和分解对去神经诱导的肌肉萎缩的贡献。成年（6 个月）雄性 C57BL/6 小鼠（n = 14）在单侧坐骨神经横断后用 D2O 标记总共 7 天，以诱导后肢肌肉去神经支配。对侧假肢和非手术小鼠 (n = 5) 用作两个不同的对照，以解释去神经支配的潜在交叉效应。我们在假设稳态或使用非稳态模型的情况下计算了腓肠肌肌原纤维和胶原蛋白的合成和分解。我们测量了 RNA 合成率，以进一步了解萎缩过程中核糖体的周转。与假手术组（174 ± 15 mg；P < 0.0001）或非手术对照组（162 ± 5 mg；P < 0.0001）相比，去神经肌肉中腓肠肌质量较小（137 ± 9 mg）。通过稳态计算，与假手术组（1.81±0.09%/天；P<0.0001）或非手术对照组（2.27±0.04%/天；P<0.0001）相比，去神经肌肉的合成分数和分解率（FSR和FBR）较低（1.49±0.06%/天）。当调整蛋白质质量的变化时，去神经肢体的 FSR 为 4.21 ± 0.19%/天，而 FBR 为 4.09 ± 0.22%/天。当考虑蛋白质质量（ksyn）的变化时，与假手术（3.43±0.22毫克/天；P<0.0001）和非手术对照（3.74±0.12毫克/天；P<0.0001）相比，去神经肢体的肌原纤维合成较低（2.44±0.14毫克/天），而蛋白质分解率与假手术组 (0.019 ± 0.001；P < 0.0001) 和非手术对照组 (0.023 ± 0.000；P < 0.0001) 相比，去神经肢体 (kdeg，1/t) 更大 (0.050 ± 0.003)。去神经期间肌肉胶原蛋白的分解被完全抑制。假手术肌肉中的 RNA 和肌原纤维蛋白合成之间存在很强的相关性（r = 0.83，P < 0.001），但去神经肌肉中却没有。我们显示了肌肉损失期间肌原纤维蛋白合成和分解的稳态和非稳态计算之间相互矛盾的结果。我们还发现胶原蛋白的积累主要是由于胶原蛋白分解的减少。假手术和非手术控制之间的比较表明，去神经支配对肌原纤维蛋白合成和核糖体生物发生的交叉效应，这影响单侧萎缩研究的研究设计。这些考虑因素很重要，因为不考虑它们可能会误导维持肌肉质量的治疗尝试。
Ageing and cachexia cause a loss of muscle mass over time, indicating that protein breakdown exceeds protein synthesis. Deuterium oxide (D2O) is used for studies of protein turnover because of the advantages of long‐term labelling, but these methods introduce considerations that have been largely overlooked when studying conditions of protein gain or loss. The purpose of this study was to demonstrate the importance of accounting for a change in protein mass, a non‐steady state, during D2O labelling studies while also exploring the contribution of protein synthesis and breakdown to denervation‐induced muscle atrophy. Adult (6 months) male C57BL/6 mice (n = 14) were labelled with D2O for a total of 7 days following unilateral sciatic nerve transection to induce denervation of hindlimb muscles. The contralateral sham limb and nonsurgical mice (n = 5) were used as two different controls to account for potential crossover effects of denervation. We calculated gastrocnemius myofibrillar and collagen protein synthesis and breakdown assuming steady‐state or using non‐steady‐state modelling. We measured RNA synthesis rates to further understand ribosomal turnover during atrophy. Gastrocnemius mass was less in denervated muscle (137 ± 9 mg) compared with sham (174 ± 15 mg; P < 0.0001) or nonsurgical control (162 ± 5 mg; P < 0.0001). With steady‐state calculations, fractional synthesis and breakdown rates (FSR and FBR) were lower in the denervated muscle (1.49 ± 0.06%/day) compared with sham (1.81 ± 0.09%/day; P < 0.0001) or nonsurgical control (2.27 ± 0.04%/day; P < 0.0001). When adjusting for change in protein mass, FSR was 4.21 ± 0.19%/day in denervated limb, whereas FBR was 4.09 ± 0.22%/day. When considering change in protein mass (ksyn), myofibrillar synthesis was lower in denervated limb (2.44 ± 0.14 mg/day) compared with sham (3.43 ± 0.22 mg/day; P < 0.0001) and non‐surgical control (3.74 ± 0.12 mg/day; P < 0.0001), whereas rate of protein breakdown (kdeg, 1/t) was greater in denervated limb (0.050 ± 0.003) compared with sham (0.019 ± 0.001; P < 0.0001) and nonsurgical control (0.023 ± 0.000; P < 0.0001). Muscle collagen breakdown was completely inhibited during denervation. There was a strong correlation (r = 0.83, P < 0.001) between RNA and myofibrillar protein synthesis in sham but not denervated muscle. We show conflicting results between steady‐ and non‐steady‐state calculations on myofibrillar protein synthesis and breakdown during periods of muscle loss. We also found that collagen accumulation was largely from a decrease in collagen breakdown. Comparison between sham and non‐surgical control demonstrated a crossover effect of denervation on myofibrillar protein synthesis and ribosomal biogenesis, which impacts study design for unilateral atrophy studies. These considerations are important because not accounting for them can mislead therapeutic attempts to maintain muscle mass.
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影响因子：
5.5
作者：
Miller, BF;Olesen, JL;Rennie, MJ
通讯作者：
Rennie, MJ
影响因子：
5.5
作者：
Gillies, Allison R.;Chapman, Mark A.;Lieber, Richard L.
通讯作者：
Lieber, Richard L.
影响因子：
4.1
作者：
GOLDSPINK, DF;GARLICK, PJ;MCNURLAN, MA
通讯作者：
MCNURLAN, MA
影响因子：
2.8
作者：
GOLDSPINK, G;FERNANDES, K;WELLS, DJ
通讯作者：
WELLS, DJ
影响因子：
4.9
作者：
Mann CJ;Perdiguero E;Kharraz Y;Aguilar S;Pessina P;Serrano AL;Muñoz-Cánoves P
通讯作者：
Muñoz-Cánoves P