Department of Basic Medical Sciences, The University of Arizona College of Medicine-Phoenix, Phoenix, Arizona, USA.
J Appl Physiol (1985). 2012 Aug;113(3):465-72. doi: 10.1152/japplphysiol.01545.2011. Epub 2012 Jun 7.
Cyclic short-duration stretches (CSDS) such as those resulting from repetitive motion strain increase the risk of musculoskeletal injury. Myofascial release is a common technique used by clinicians that applies an acyclic long-duration stretch (ALDS) to muscle fascia to repair injury. When subjected to mechanical strain, fibroblasts within muscle fascia secrete IL-6, which has been shown to induce myoblast differentiation, essential for muscle repair. We hypothesize that fibroblasts subjected to ALDS following CSDS induce myoblast differentiation through IL-6. Fibroblast conditioned media and fibroblast-myoblast cocultures were used to test fibroblasts' ability to induce myoblast differentiation. The coculture system applies strain to fibroblasts only but still allows for diffusion of potential differentiation mediators to unstrained myoblasts on coverslips. To determine the role of IL-6, we utilized myoblast unicultures ± IL-6 (0-100 ng/ml) and cocultures ± α-IL-6 (0-200 μg/ml). Untreated uniculture myoblasts served as a negative control. After 96 h, coverslips (n = 6-21) were microscopically analyzed and quantified by blinded observer for differentiation endpoints: myotubes per square millimeter (>3 nuclei/cell), nuclei/myotube, and fusion efficiency (%nuclei within myotubes). The presence of fibroblasts and fibroblast conditioned media significantly enhanced myotube number (P < 0.05). However, in coculture, CSDS applied to fibroblasts did not reproduce this effect. ALDS following CSDS increased myotube number by 78% and fusion efficiency by 96% vs. CSDS alone (P < 0.05). Fibroblasts in coculture increase IL-6 secretion; however, IL-6 secretion did not correlate with enhanced differentiation among strain groups. Exogenous IL-6 in myoblast uniculture failed to induce differentiation. However, α-IL-6 attenuated differentiation in all coculture groups (P < 0.05). Fibroblasts secrete soluble mediators that have profound effects on several measures of myoblast differentiation. Specific biophysical strain patterns modify these outcomes, and suggest that myofascial release after repetitive strain increases myoblast differentiation and thus may improve muscle repair in vivo. Neutralization of IL-6 in coculture significantly reduced differentiation, suggesting fibroblast-IL-6 is necessary but not sufficient in this process.
周期性短时间拉伸（CSDS），如重复运动引起的拉伸，会增加肌肉骨骼损伤的风险。肌筋膜松解术是临床医生常用的一种技术，它对肌肉筋膜施加非周期性长时间拉伸（ALDS），以修复损伤。当肌肉筋膜受到机械应变时，其中的成纤维细胞会分泌白细胞介素 6（IL-6），它已被证明能诱导成肌细胞分化，这对肌肉修复至关重要。我们假设 CSDS 后接受 ALDS 的成纤维细胞通过 IL-6 诱导成肌细胞分化。使用成纤维细胞条件培养基和成纤维细胞-成肌细胞共培养物来测试成纤维细胞诱导成肌细胞分化的能力。共培养系统仅对成纤维细胞施加应变，但仍允许潜在的分化介质扩散到盖玻片上未受应变的成肌细胞。为了确定白细胞介素 6 的作用，我们利用成肌细胞单培养物±白细胞介素 6（0-100ng/ml）和共培养物±α-白细胞介素 6（0-200μg/ml）。未经处理的单培养物成肌细胞作为阴性对照。96 小时后，通过显微镜对盖玻片（n=6-21）进行分析，并由盲法观察者对分化终点进行定量：每平方毫米的肌管数（>3 个细胞核/细胞）、细胞核/肌管和融合效率（%细胞核在肌管内）。成纤维细胞和成纤维细胞条件培养基的存在显著增加了肌管数量（P<0.05）。然而，在共培养中，CSDS 施加于成纤维细胞并未再现这种效果。CSDS 后施加 ALDS 将肌管数量增加了 78%，融合效率增加了 96%，而 CSDS 单独作用时仅增加了 78%（P<0.05）。共培养中的成纤维细胞增加了白细胞介素 6 的分泌；然而，白细胞介素 6 的分泌与应变组之间增强的分化无关。成肌细胞单培养物中的外源性白细胞介素 6 未能诱导分化。然而，α-白细胞介素 6 减弱了所有共培养组的分化（P<0.05）。成纤维细胞分泌可溶性介质，对成肌细胞分化的几个测量值有深远影响。特定的生物物理应变模式改变了这些结果，并表明重复应变后的肌筋膜松解术增加了成肌细胞的分化，从而可能改善体内肌肉修复。在共培养中中和白细胞介素 6 显著降低了分化，这表明成纤维细胞-白细胞介素 6 是必要的，但不是这个过程所必需的。
