Brookins Elysse, Serrano Sophia E, Yacu George S, Finer Gal, Thomson Benjamin R
bioRxiv. 2024 Mar 12:2024.03.08.584133. doi: 10.1101/2024.03.08.584133.
Endomucin (EMCN) is a 261 AA 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, mRNA expression was present in choroidal pericytes and a subset of fibroblasts, but not vascular smooth muscle cells. Besides , 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 -expressing fibroblasts exhibited high levels of chemokine and interferon signaling genes, while -negative fibroblasts were enriched in genes encoding extracellular matrix proteins. expressing fibroblasts were also detected in published datasets from mouse brain and human choroid, suggesting that stromal 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 angiogenesis and immune cell recruitment.
内黏液素（EMCN）是一种含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表达，在血管内皮生长因子（VEGF）介导的血管生成以及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，由于有在多种条件下和许多组织中都能发挥作用的高质量抗体可供商业购买，它已广泛应用。EMCN染色的特异性在视网膜血管中已得到充分验证，但尽管它在包括脉络膜在内的眼睛其他组织中被广泛用作标志物，其表达模式尚未得到详细描述。在这里，除了在脉络膜毛细血管层和更深层血管层中的内皮表达外，我们还鉴定了小鼠脉络膜中一群EMCN阳性的血管周围细胞，这些细胞与表达其他内皮标志物（如血小板内皮细胞黏附分子1或Podocalyxin样蛋白）的细胞不共定位。为了证实这些细胞代表了一群新的表达EMCN的基质细胞，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，脉络膜周细胞和成纤维细胞亚群中存在mRNA表达，但血管平滑肌细胞中没有。此外，在这些细胞群体中未检测到已知的内皮基因表达，证实它们不代表内皮-基质双联体，这是单细胞RNA测序数据集中常见的技术假象。相反，表达EMCN的脉络膜成纤维细胞表现出高水平的趋化因子和干扰素信号基因，而不表达EMCN的成纤维细胞则富含编码细胞外基质蛋白的基因。在小鼠脑和人类脉络膜的已发表数据集中也检测到了表达EMCN的成纤维细胞，这表明基质EMCN表达并非脉络膜所特有，且在进化上是保守的。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在血管生成和免疫细胞募集中的作用提供了新的背景信息。
