MechanoBiology Laboratory, Department of Orthopaedic Surgery, School of Medicine, University of Pittsburgh, 210 Lothrop St BST E1640, PA, 15213, Pittsburgh, USA.
Department of Electrical and Computer Engineering, University of Pittsburgh, Pittsburgh, PA, 15213, USA.
Cell Tissue Res. 2021 May;384(2):367-387. doi: 10.1007/s00441-020-03379-3. Epub 2021 Jan 26.
This study aimed to characterize porcine Achilles tendon (PAT) in terms of its structural components, vascularity, and resident tendon cells. We found that PAT is composed of a paratenon sheath, a core of fascicles, and an endotenon/interfascicular matrix (IFM) that encases the fascicle bundles. We analyzed each of these three tendon components structurally using tissue sections and by isolating cells from each component and analyzing in vitro. Many blood vessel-like tissues were present in the paratenon and IFM but not in fascicles, and the vessels in the paratenon and IFM appeared to be inter-connected. Cells isolated from the paratenon and IFM displayed characteristics of vascular stem/progenitor cells expressing the markers CD105, CD31, with α-smooth muscle actin (α-SMA) localized surrounding blood vessels. The isolated cells from paratenon and IFM also harbored abundant stem/progenitor cells as evidenced by their ability to form colonies and express stem cell markers including CD73 and CD146. Furthermore, we demonstrate that both paratenon and IFM-isolated cells were capable of undergoing multi-differentiation. In addition, both paratenon and IFM cells expressed elastin, osteocalcin, tubulin polymerization promoting protein (TPPP), and collagen IV, whereas fascicle cells expressed none of these markers, except collagen I. The neurotransmitter substance P (SP) was also found in the paratenon and IFM-localized surrounding blood vessels. The findings of this study will help us to better understand the vascular and cellular mechanisms of tendon homeostasis, injury, healing, and regeneration.
本研究旨在从结构成分、血管分布和固有肌腱细胞等方面对猪跟腱（PAT）进行特征描述。我们发现 PAT 由腱旁组织鞘、纤维束核心和包绕纤维束的腱内膜/束间基质（IFM）组成。我们通过组织切片以及从每个组成部分分离细胞并进行体外分析，对这三个肌腱成分进行了结构分析。许多类似血管的组织存在于腱旁组织和 IFM 中，但不存在于纤维束中，且腱旁组织和 IFM 中的血管似乎相互连通。从腱旁组织和 IFM 分离得到的细胞表达 CD105、CD31 等血管干/祖细胞标志物，α-平滑肌肌动蛋白（α-SMA）定位于血管周围。从腱旁组织和 IFM 分离得到的细胞还含有丰富的干/祖细胞，这可通过其形成集落和表达 CD73 和 CD146 等干细胞标志物的能力来证明。此外，我们证明了腱旁组织和 IFM 分离得到的细胞均具有多向分化能力。此外，腱旁组织和 IFM 细胞均表达弹性蛋白、骨钙素、微管聚合促进蛋白（TPPP）和Ⅳ型胶原，而纤维束细胞除了表达Ⅰ型胶原外，不表达这些标志物。神经递质 P 物质（SP）也存在于腱旁组织和 IFM 中，位于周围血管附近。本研究的结果将有助于我们更好地理解肌腱稳态、损伤、愈合和再生的血管和细胞机制。
