Department of Ophthalmology and Feinberg Cardiovascular and Renal Research Inst. Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
Lurie Children's Hospital Department of Nephrology and Stanley Manne Children's Research Inst., Chicago, IL, USA.
Exp Eye Res. 2024 Oct;247:110054. doi: 10.1016/j.exer.2024.110054. Epub 2024 Aug 15.
Endomucin (EMCN) is a 261 amino acid transmembrane glycoprotein that is highly expressed by venous and capillary endothelial cells where it plays a role in VEGF-mediated angiogenesis and regulation of immune cell recruitment. However, it is better known as a histological marker, where it has become widespread due to the commercial availability of high-quality antibodies that work under a wide range of conditions and in many tissues. The specificity of EMCN staining has been well-validated in retinal vessels, but while it has been used extensively as a marker in other tissues of the eye, including the choroid, the pattern of expression has not been described in detail. Here, in addition to endothelial expression in the choriocapillaris and deeper vascular layers, we characterize a population of EMCN-positive perivascular cells in the mouse choroid that did not co-localize with cells expressing other endothelial markers such as PECAM1 or PODXL. To confirm that these cells represented a new population of EMCN-expressing stromal cells, we then performed single cell RNA sequencing in choroids from adult wild-type mice. Analysis of this new dataset confirmed that, in addition to endothelial cells, Emcn mRNA expression was present in choroidal pericytes and a subset of fibroblasts, but not vascular smooth muscle cells. Besides Emcn, no known endothelial gene expression was detected in these cell populations, confirming that they did not represent endothelial-stromal doublets, a common technical artifact in single cell RNA seq datasets. Instead, choroidal Emcn-expressing fibroblasts exhibited high levels of chemokine and interferon signaling genes, while Emcn-negative fibroblasts were enriched in genes encoding extracellular matrix proteins. Emcn expressing fibroblasts were also detected in published datasets from mouse brain and human choroid, suggesting that stromal Emcn expression was not unique to the choroid and was evolutionarily conserved. Together, these findings highlight unique fibroblast and pericyte populations in the choroid and provide new context for the role of EMCN in the eye.
内皮黏蛋白（EMCN）是一种 261 个氨基酸的跨膜糖蛋白，在静脉和毛细血管内皮细胞中高度表达，在 VEGF 介导的血管生成和免疫细胞募集的调节中发挥作用。然而，它作为一种组织学标志物更为人所知，由于高质量的抗体的商业可用性，它在广泛的条件下和许多组织中都得到了广泛应用。EMCN 染色的特异性在视网膜血管中已经得到了很好的验证，但尽管它在眼部的其他组织中被广泛用作标志物，包括脉络膜，但它的表达模式并没有详细描述。在这里，除了在脉络膜毛细血管和更深的血管层中表达内皮细胞外，我们还描述了在小鼠脉络膜中存在一群 EMCN 阳性的血管周细胞，这些细胞与表达其他内皮标志物如 PECAM1 或 PODXL 的细胞没有共定位。为了确认这些细胞代表了一种新的 EMCN 表达基质细胞群体，我们随后对成年野生型小鼠的脉络膜进行了单细胞 RNA 测序。对这个新数据集的分析证实，除了内皮细胞外，Emcn mRNA 表达还存在于脉络膜周细胞和一部分成纤维细胞中，但不存在于血管平滑肌细胞中。除了 Emcn，在这些细胞群体中没有检测到已知的内皮基因表达，这证实了它们不是内皮-基质二联体，这是单细胞 RNA seq 数据集中常见的技术假象。相反，脉络膜中表达 Emcn 的成纤维细胞表现出高水平的趋化因子和干扰素信号基因，而 Emcn 阴性的成纤维细胞富含编码细胞外基质蛋白的基因。在发表的来自小鼠大脑和人脉络膜的数据集也检测到了表达 Emcn 的成纤维细胞，这表明基质中 Emcn 的表达并非脉络膜所特有，而是在进化上保守的。总之，这些发现突出了脉络膜中独特的成纤维细胞和周细胞群体，并为 EMCN 在眼睛中的作用提供了新的背景。
