Pal-Ghosh Sonali, Tadvalkar Gauri, Stepp Mary Ann
Department of Anatomy and Regenerative Biology, The George Washington University Medical School, Washington, D.C., United States.
Department of Ophthalmology, The George Washington University Medical School, Washington, D.C., United States.
Invest Ophthalmol Vis Sci. 2017 Oct 1;58(12):4959-4975. doi: 10.1167/iovs.17-21531.
To determine the impact of the loss of syndecan 1 (SDC1) on intraepithelial corneal nerves (ICNs) during homeostasis, aging, and in response to 1.5-mm trephine and debridement injury.
Whole-mount corneas are used to quantify ICN density and thickness over time after birth and in response to injury in SDC1-null and wild-type (WT) mice. High-resolution three-dimensional imaging is used to visualize intraepithelial nerve terminals (INTs), axon fragments, and lysosomes in corneal epithelial cells using antibodies against growth associated protein 43 (GAP43), βIII tubulin, and LAMP1. Quantitative PCR was performed to quantify expression of SDC1, SDC2, SDC3, and SDC4 in corneal epithelial mRNA. Phagocytosis was assessed by quantifying internalization of fluorescently labeled 1-μm latex beads.
Intraepithelial corneal nerves innervate the corneas of SDC1-null mice more slowly. At 8 weeks, ICN density is less but thickness is greater. Apically projecting intraepithelial nerve terminals and lysosome-associated membrane glycoprotein 1 (LAMP1) are also reduced in unwounded SDC1-null corneas. Quantitative PCR and immunofluorescence studies show that SDC3 expression and localization are increased in SDC1-null ICNs. Wild-type and SDC1-null corneas lose ICN density and thickness as they age. Recovery of axon density and thickness after trephine but not debridement wounds is slower in SDC1-null corneas compared with WT. Experiments assessing phagocytosis show reduced bead internalization by SDC1-null epithelial cells.
Syndecan-1 deficiency alters ICN morphology and homeostasis during aging, reduces epithelial phagocytosis, and impairs reinnervation after trephine but not debridement injury. These data provide insight into the mechanisms used by sensory nerves to reinnervate after injury.
确定在稳态、衰老过程中以及对1.5毫米环钻和清创损伤的反应中，Syndecan 1（SDC1）缺失对角膜上皮内神经（ICN）的影响。
使用全层角膜来量化出生后不同时间以及SDC1基因敲除小鼠和野生型（WT）小鼠在受伤后ICN的密度和厚度。利用针对生长相关蛋白43（GAP43）、βIII微管蛋白和溶酶体相关膜蛋白1（LAMP1）的抗体，通过高分辨率三维成像来观察角膜上皮细胞中的上皮内神经末梢（INT）、轴突片段和溶酶体。进行定量PCR以量化角膜上皮mRNA中SDC1、SDC2、SDC3和SDC4的表达。通过量化荧光标记的1微米乳胶珠的内化来评估吞噬作用。
角膜上皮内神经对SDC1基因敲除小鼠角膜的支配速度较慢。在8周时，ICN密度较低但厚度较大。在未受伤的SDC1基因敲除角膜中，顶端突出的上皮内神经末梢和溶酶体相关膜糖蛋白1（LAMP1）也减少。定量PCR和免疫荧光研究表明，SDC1基因敲除的ICN中SDC3的表达和定位增加。野生型和SDC1基因敲除的角膜随着年龄增长会失去ICN密度和厚度。与WT相比，SDC1基因敲除的角膜在环钻损伤后轴突密度和厚度的恢复较慢，但清创伤口后则不然。评估吞噬作用的实验表明，SDC1基因敲除的上皮细胞对珠子的内化减少。
Syndecan-1缺乏会改变衰老过程中ICN的形态和稳态，降低上皮吞噬作用，并损害环钻损伤后的神经再支配，但不影响清创损伤后的神经再支配。这些数据为感觉神经在损伤后进行神经再支配所使用的机制提供了见解。
