Background

Skeletal muscle has extraordinary regenerative capabilities against challenge, mainly owing to its resident muscle stem cells, commonly identified by Pax7⁺, which expediently donate nuclei to the regenerating multinucleated myofibers. This local reserve of stem cells in damaged muscle tissues is replenished by undifferentiated bone marrow stem cells (CD34⁺) permeating into the surrounding vascular system.

Objective

The purpose of the study was to provide a quantitative estimate for the changes in Pax7⁺ muscle stem cells (satellite cells) in humans following an acute bout of exercise until 96 h, in temporal relation to circulating CD34⁺ bone marrow stem cells. A subgroup analysis of age was also performed.

Methods

Four databases (Web of Science, PubMed, Scopus, and BASE) were used for the literature search until February 2022. Pax7⁺ cells in human skeletal muscle were the primary outcome. Circulating CD34⁺ cells were the secondary outcome. The standardized mean difference (SMD) was calculated using a random-effects meta-analysis. Subgroup analyses were conducted to examine the influence of age, training status, type of exercise, and follow-up time after exercise.

Results

The final search identified 20 studies for Pax7⁺ cells comprising a total of 370 participants between the average age of 21 and 74 years and 26 studies for circulating CD34⁺ bone marrow stem cells comprising 494 participants between the average age of 21 and 67 years. Only one study assessed Pax7⁺ cells immediately after aerobic exercise and showed a 32% reduction in exercising muscle followed by a fast repletion to pre-exercise level within 3 h. A large effect on increasing Pax7⁺ cell content in skeletal muscles was observed 24 h after resistance exercise (SMD = 0.89, p < 0.001). Pax7⁺ cells increased to ~ 50% above pre-exercise level 24–72 h after resistance exercise. For a subgroup analysis of age, a large effect (SMD = 0.81, p < 0.001) was observed on increasing Pax7⁺ cells in exercised muscle among adults aged > 50 years, whereas adults at younger age presented a medium effect (SMD = 0.64, p < 0.001). Both resistance exercise and aerobic exercise showed a medium overall effect in increasing circulating CD34⁺ cells (SMD = 0.53, p < 0.001), which declined quickly to the pre-exercise baseline level after exercise within 6 h.

Conclusions

An immediate depletion of Pax7⁺ cells in exercising skeletal muscle concurrent with a transient release of CD34⁺ cells suggest a replenishment of the local stem cell reserve from bone marrow. A protracted Pax7⁺ cell expansion in the muscle can be observed during 24–72 h after resistance exercise. This result provides a scientific basis for exercise recommendations on weekly cycles allowing for adequate recovery time. Exercise-induced Pax7⁺ cell expansion in muscle remains significant at higher age, despite a lower stem cell reserve after age 50 years. More studies are required to confirm whether Pax7⁺ cell increment can occur after aerobic exercise.

Clinical Trial Registration

Registered at the International Prospective Register of Systematic Reviews (PROSPERO) [identification code CRD42021265457].

中文翻译：

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运动后人体骨骼肌中的 Pax7+ 卫星细胞：系统评价和荟萃分析

背景

骨骼肌具有非凡的再生能力来应对挑战，这主要归功于它常驻的肌肉干细胞，通常由 Pax7 ⁺鉴定，它可以方便地向再生的多核肌纤维提供细胞核。渗透到周围血管系统中的未分化骨髓干细胞 (CD34 ^{+ ) 补充了受损肌肉组织中干细胞的局部储备。}

客观的

^{该研究的目的是对人类 Pax7 +}肌肉干细胞（卫星细胞）在急性运动后直到 96 小时的变化提供定量估计，与循环 CD34 ⁺骨髓干细胞的时间关系。还进行了年龄亚组分析。

方法

直到 2022 年 2 月，使用四个数据库（Web of Science、PubMed、Scopus 和 BASE）进行文献检索。人类骨骼肌中的Pax7 ^{+细胞是主要结果。}循环 CD34 ⁺细胞是次要结果。使用随机效应荟萃分析计算标准化均值差 (SMD)。进行亚组分析以检查年龄、训练状态、运动类型和运动后随访时间的影响。

结果

最终搜索确定了 20 项针对 Pax7 ⁺细胞的研究，共包括 370 名平均年龄在 21 至 74 岁之间的参与者，以及 26 项针对循环 CD34 ⁺骨髓干细胞的研究，包括 494 名平均年龄在 21 至 67 岁之间的参与者。只有一项研究在有氧运动后立即评估了 Pax7 ⁺细胞，并显示运动肌肉减少了 32%，随后在 3 小时内快速恢复到运动前水平。在阻力运动后 24 小时观察到对增加骨骼肌中Pax7 ⁺细胞含量的巨大影响（SMD = 0.89， p  < 0.001）。大人7 ⁺阻力运动后 24-72 小时，细胞增加到比运动前水平高出约 50%。对于年龄的亚组分析，在年龄 > 50 岁的成年人中 观察到运动肌肉中 Pax7 ^{+细胞增加的较大影响（SMD = 0.81，} p < 0.001） ，而较年轻的成年人则呈现中等影响（SMD = 0.64，p  < 0.001）。^{抗阻运动和有氧运动在增加循环 CD34 +}细胞方面显示出中等的总体效果（SMD = 0.53，p  < 0.001），在运动后 6 小时内迅速下降到运动前的基线水平。

结论

运动骨骼肌时Pax7 ⁺细胞的立即耗尽与 CD34 ⁺细胞的瞬时释放同时表明来自骨髓的局部干细胞储备得到补充。在阻力运动后 24-72 小时内可以观察到肌肉中持久的 Pax7 ^{+细胞扩张。}这一结果为每周周期的锻炼建议提供了科学依据，以提供足够的恢复时间。尽管 50 岁后干细胞储备较低，但运动诱导的肌肉 Pax7 ^{+细胞扩张在较高年龄时仍然显着。Pax7 +}细胞是否会在有氧运动后增加，还需要更多的研究来证实。

临床试验注册

在国际前瞻性系统评价登记册 (PROSPERO) 注册[识别码 CRD42021265457]。