Marr Neil, Zamboulis Danae E, Werling Dirk, Felder Alessandro A, Dudhia Jayesh, Pitsillides Andrew A, Thorpe Chavaunne T
Comparative Biomedical Sciences, Royal Veterinary College, London, United Kingdom.
Pathobiology and Population Sciences, Centre for Vaccinology and Regenerative Medicine, Royal Veterinary College, Hatfield, United Kingdom.
Front Cell Dev Biol. 2023 Jan 9;10:1094124. doi: 10.3389/fcell.2022.1094124. eCollection 2022.
The interfascicular matrix (IFM; also known as the endotenon) is critical to the mechanical adaptations and response to load in energy-storing tendons, such as the human Achilles and equine superficial digital flexor tendon (SDFT). We hypothesized that the IFM is a tendon progenitor cell niche housing an exclusive cell subpopulation. Immunolabelling of equine superficial digital flexor tendon was used to identify the interfascicular matrix niche, localising expression patterns of CD31 (endothelial cells), Desmin (smooth muscle cells and pericytes), CD146 (interfascicular matrix cells) and LAMA4 (interfascicular matrix basement membrane marker). Magnetic-activated cell sorting was employed to isolate and compare in vitro properties of CD146+ and CD146- subpopulations. Labelling for CD146 using standard histological and 3D imaging of large intact 3D segments revealed an exclusive interfascicular cell subpopulation that resides in proximity to a basal lamina which forms extensive, interconnected vascular networks. Isolated CD146+ cells exhibited limited mineralisation (osteogenesis) and lipid production (adipogenesis). This study demonstrates that the interfascicular matrix is a unique tendon cell niche, containing a vascular-rich network of basement membrane, CD31+ endothelial cells, Desmin+ mural cells, and CD146+ cell populations that are likely essential to tendon structure and/or function. Contrary to our hypothesis, interfascicular CD146+ subpopulations did not exhibit stem cell-like phenotypes. Instead, our results indicate CD146 as a pan-vascular marker within the tendon interfascicular matrix. Together with previous work demonstrating that endogenous tendon CD146+ cells migrate to sites of injury, our data suggest that their mobilisation to promote intrinsic repair involves changes in their relationships with local interfascicular matrix vascular and basement membrane constituents.
束间基质（IFM；也称为腱内膜）对于储能肌腱（如人类跟腱和马的浅屈肌腱[SDFT]）的机械适应性和对负荷的反应至关重要。我们假设IFM是一个肌腱祖细胞龛，容纳一个独特的细胞亚群。使用马浅屈肌腱的免疫标记来识别束间基质龛，定位CD31（内皮细胞）、结蛋白（平滑肌细胞和周细胞）、CD146（束间基质细胞）和层粘连蛋白4（束间基质基底膜标记物）的表达模式。采用磁激活细胞分选技术分离并比较CD146+和CD146-亚群的体外特性。使用标准组织学和大型完整三维节段的三维成像对CD146进行标记，发现一个独特的束间细胞亚群，其位于形成广泛、相互连接的血管网络的基底层附近。分离出的CD146+细胞表现出有限的矿化（成骨）和脂质生成（成脂）。本研究表明，束间基质是一个独特的肌腱细胞龛，包含一个富含血管的基底膜网络、CD31+内皮细胞、结蛋白+壁细胞和CD146+细胞群，这些可能对肌腱结构和/或功能至关重要。与我们的假设相反，束间CD146+亚群未表现出干细胞样表型。相反，我们的结果表明CD146是肌腱束间基质中的一种泛血管标记物。结合先前证明内源性肌腱CD146+细胞迁移到损伤部位的研究，我们的数据表明，它们动员以促进内在修复涉及它们与局部束间基质血管和基底膜成分关系的变化。
