Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.
PLoS One. 2011 Mar 9;6(3):e17392. doi: 10.1371/journal.pone.0017392.
Although the satellite cell (SC) is a key regulator of muscle growth during development and muscle adaptation following exercise, the regulation of human muscle SC function remains largely unexplored. STAT3 signalling mediated via interleukin-6 (IL-6) has recently come to the forefront as a potential regulator of SC proliferation. The early response of the SC population in human muscle to muscle-lengthening contractions (MLC) as mediated by STAT3 has not been studied.
METHODOLOGY/PRINCIPAL FINDINGS: Twelve male subjects (21±2 y; 83±12 kg) performed 300 maximal MLC of the quadriceps femoris at 180°•s(-1) over a 55° range of motion with muscle samples (vastus lateralis) and blood samples (antecubital vein) taken prior to exercise (PRE), 1 hour (T1), 3 hours (T3) and 24 hours (T24) post-exercise. Cytoplasmic and nuclear fractions of muscle biopsies were purified and analyzed for total and phosphorylated STAT3 (p-STAT3) by western blot. p-STAT3 was detected in cytoplasmic fractions across the time course peaking at T24 (p<0.01 vs. PRE). Nuclear total and p-STAT3 were not detected at appreciable levels. However, immunohistochemical analysis revealed a progressive increase in the proportion of SCs expressing p-STAT3 with ∼60% of all SCs positive for p-STAT3 at T24 (p<0.001 vs. PRE). Additionally, cMyc, a STAT3 downstream gene, was significantly up-regulated in SCs at T24 versus PRE (p<0.05). Whole muscle mRNA analysis revealed induction of the STAT3 target genes IL-6, SOCS3, cMyc (peaking at T3, p<0.05), IL-6Rα and GP130 (peaking at T24, p<0.05). In addition, Myf5 mRNA was up-regulated at T24 (p<0.05) with no appreciable change in MRF4 mRNA.
CONCLUSIONS/SIGNIFICANT FINDINGS: We demonstrate that IL-6 induction of STAT3 signaling occurred exclusively in the nuclei of SCs in response to MLC. An increase in the number of cMyc+ SCs indicated that human SCs were induced to proliferate under the control of STAT3 signaling.
卫星细胞（SC）是发育过程中肌肉生长和运动后肌肉适应的关键调节因子，但人类肌肉 SC 功能的调节仍在很大程度上未被探索。最近，白细胞介素 6（IL-6）介导的 STAT3 信号转导已成为调节 SC 增殖的潜在调节剂。STAT3 介导的人类肌肉中 SC 群体对肌肉拉长收缩（MLC）的早期反应尚未研究。
方法/主要发现：12 名男性受试者（21±2 岁；83±12 千克）以 180°•s(-1) 的速度进行 300 次最大 MLC，运动范围为 55°，在运动前（PRE）、1 小时（T1）、3 小时（T3）和 24 小时（T24）时采集股四头肌的肌肉样本（股外侧肌）和血液样本（肘前静脉）。通过 Western blot 分析肌肉活检的细胞质和核部分中总 STAT3（t-STAT3）和磷酸化 STAT3（p-STAT3）。在整个时间过程中，p-STAT3 均在细胞质部分中检测到，在 T24 时达到峰值（p<0.01 比 PRE）。核总 STAT3 和 p-STAT3 未检测到可观水平。然而，免疫组织化学分析显示，表达 p-STAT3 的 SC 比例逐渐增加，T24 时约有 60%的 SC 呈 p-STAT3 阳性（p<0.001 比 PRE）。此外，SC 中 STAT3 下游基因 cMyc 的表达在 T24 时明显上调，与 PRE 相比（p<0.05）。全肌 mRNA 分析显示，STAT3 靶基因 IL-6、SOCS3、cMyc（在 T3 时达到峰值，p<0.05）、IL-6Rα 和 GP130（在 T24 时达到峰值，p<0.05）的诱导。此外，Myf5mRNA 在 T24 时上调（p<0.05），而 MRF4mRNA 没有明显变化。
结论/重要发现：我们证明，IL-6 诱导的 STAT3 信号转导仅发生在 MLC 后 SC 的细胞核中。cMyc+ SC 数量的增加表明，人类 SC 在 STAT3 信号的控制下被诱导增殖。
