Department of Neurobiology, Physiology, & Behavior, University of California Davis, United States.
Department of Neurobiology, Physiology, & Behavior, University of California Davis, United States; Department of Physical Medicine and Rehabilitation, University of California Davis, United States.
Acta Biomater. 2024 Oct 1;187:227-241. doi: 10.1016/j.actbio.2024.08.035. Epub 2024 Aug 30.
Collagen fiber architecture within the skeletal muscle extracellular matrix (ECM) is significant to passive muscle mechanics. While it is thought that collagen fibers re-orient themselves in response to changes in muscle length, this has not been dynamically visualized and quantified within a muscle. The goal of this study was to measure changes in collagen alignment across a range of muscle lengths and compare the corresponding alignment to muscle mechanics. We hypothesized that collagen fibers dynamically increase alignment in response to muscle stretching, and this change in alignment is related to passive muscle stiffness. Further, we hypothesized that digesting collagen fibers with collagenase would reduce the re-alignment response to muscle stretching. Using DBA/2J and D2.mdx mice, we isolated extensor digitorum longus (EDL), soleus, and diaphragm muscles for collagenase or sham treatment and decellularization to isolate intact or collagenase-digested decellularized muscles (DCMs). These DCMs were mechanically tested and imaged using second harmonic generation microscopy to measure collagen alignment across a range of strains. We found that collagen alignment increased in a strain-dependent fashion, but collagenase did not significantly affect the strain-dependent change in alignment. We also saw that the collagen fibers in the diaphragm epimysium (surface ECM) and perimysium (deep ECM) started at different angles, but still re-oriented in the same direction in response to stretching. These robust changes in collagen alignment were weakly related to passive DCM stiffness. Overall, we demonstrated that the architecture of muscle ECM is dynamic in response to strain and is related to passive muscle mechanics. STATEMENT OF SIGNIFICANCE: Our study presents a unique visualization and quantification of strain-induced changes in muscle collagen fiber alignment as they relate to passive mechanics. Using dynamic imaging of collagen in skeletal muscle we demonstrate that as skeletal muscle is stretched, collagen fibers re-orient themselves along the axis of stretch and increase their alignment. The degree of alignment and the increase in alignment are each weakly related to passive muscle stiffness. Collagenase treatments further demonstrate that the basis for muscle Extracellular matrix stiffness is dependent on factors beyond collagen crosslinking and alignment. Together the study contributes to the knowledge of the structure-function relationships of muscle extracellular matrix to tissue stiffness relevant to conditions of fibrosis and aberrant stiffness.
骨骼肌细胞外基质（ECM）中的胶原纤维结构对被动肌肉力学很重要。虽然人们认为胶原纤维会在肌肉长度发生变化时重新定向，但这在肌肉内尚未被动态可视化和量化。本研究的目的是测量胶原排列在一系列肌肉长度下的变化，并将相应的排列与肌肉力学进行比较。我们假设胶原纤维在肌肉拉伸时会动态增加排列，这种排列的变化与被动肌肉硬度有关。此外，我们假设用胶原酶消化胶原纤维会减少肌肉拉伸时的重新排列反应。我们使用 DBA/2J 和 D2.mdx 小鼠，分离伸趾长肌（EDL）、比目鱼肌和膈肌进行胶原酶或假处理以及去细胞化以分离完整或胶原酶消化的去细胞化肌肉（DCM）。这些 DCM 进行机械测试并使用二次谐波产生显微镜进行成像，以测量一系列应变下的胶原排列。我们发现胶原排列以应变依赖的方式增加，但胶原酶并没有显著影响排列的应变依赖性变化。我们还观察到膈肌筋膜（表面 ECM）和肌束膜（深部 ECM）中的胶原纤维从不同的角度开始，但在拉伸时仍向同一方向重新定向。胶原排列的这些强烈变化与被动 DCM 硬度弱相关。总的来说，我们证明了肌肉 ECM 的结构在应变下是动态的，与被动肌肉力学有关。意义陈述：我们的研究提出了一种独特的可视化和量化方法，用于研究应变引起的骨骼肌胶原纤维排列变化及其与被动力学的关系。我们使用骨骼肌肉中的胶原动态成像，证明当骨骼肌被拉伸时，胶原纤维会沿着拉伸轴重新定向并增加它们的排列。排列的程度和排列的增加都与被动肌肉硬度弱相关。胶原酶处理进一步表明，肌肉细胞外基质硬度的基础取决于胶原交联和排列以外的因素。总的来说，该研究有助于了解肌肉细胞外基质的结构-功能关系，这与纤维化和异常硬度等条件下的组织硬度有关。
