Department of Pathology, Kindai University Faculty of Medicine, Osaka-sayama, Japan,
Center for Clinical Research, Toyama University Hospital, Toyama, Japan.
Cells Tissues Organs. 2024;213(4):326-337. doi: 10.1159/000534892. Epub 2023 Oct 30.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first infects the host nasal mucosa, where the viral spike protein binds to angiotensin-converting enzyme 2 (ACE2) on the mucosal cells. This study aimed at searching host cell surface molecules that could contribute to the infection in two views; abundance on host cells and affinity to the spike protein. Since the nasal mucosa is lined by respiratory and olfactory epithelia, and both express an immunoglobulin superfamily member cell adhesion molecule 1 (CADM1), whether CADM1 would participate in the spike protein binding was examined. Immunohistochemistry on the mouse nasal cavity detected CADM1 strongly in the olfactory epithelium at cell-cell contacts and on the apical surface but just faintly in the respiratory epithelium. In contrast, ACE2 was detected in the respiratory, not olfactory, epithelium. When mice were administered intranasally with SARS-CoV-2 S1 spike protein and an anti-CADM1 ectodomain antibody separately, both were detected exclusively on the olfactory, not respiratory, epithelium. Then, the antibody and S1 spike protein were administered intranasally to mice in this order with an interval of 1 h. After 3 h, S1 spike protein was detected as a protein aggregate floating in the nasal cavity. Next, S1 spike protein labeled with fluorescein was added to the monolayer cultures of epithelial cells exogenously expressing ACE2 or CADM1. Quantitative detection of fluorescein bound to the cells revealed that S1 spike protein bound to CADM1 with affinity half as high as to ACE2. Consistently, docking simulation analyses revealed that S1 spike protein could bind to CADM1 three-quarters as strongly as to ACE2 and that the interface of ACE2 was similar in both binding modes. Collectively, intranasal S1 spike protein appeared to prefer to accumulate on the olfactory epithelium, and CADM1 was suggested to contribute to this preference of S1 spike protein based on the molecular abundance and affinity.
严重急性呼吸综合征冠状病毒 2 (SARS-CoV-2) 首先感染宿主鼻腔黏膜,病毒刺突蛋白与黏膜细胞上的血管紧张素转换酶 2 (ACE2) 结合。本研究旨在从两个方面寻找可能有助于感染的宿主细胞表面分子;在宿主细胞中的丰度和与刺突蛋白的亲和力。由于鼻腔黏膜由呼吸和嗅觉上皮细胞组成,并且两者都表达免疫球蛋白超家族成员细胞黏附分子 1 (CADM1),因此检查了 CADM1 是否会参与刺突蛋白结合。对小鼠鼻腔的免疫组织化学检测发现,CADM1 在嗅觉上皮细胞的细胞-细胞连接处和顶表面强烈表达,但在呼吸上皮细胞中仅微弱表达。相比之下,ACE2 在呼吸上皮细胞中表达,而在嗅觉上皮细胞中不表达。当用 SARS-CoV-2 S1 刺突蛋白和抗 CADM1 外显子抗体分别鼻内给药给小鼠时,两种蛋白都仅在嗅觉上皮细胞中检测到,而在呼吸上皮细胞中未检测到。然后,以 1 小时的间隔先后将抗体和 S1 刺突蛋白鼻内给药给小鼠。3 小时后,S1 刺突蛋白作为漂浮在鼻腔中的蛋白聚集体被检测到。接下来,将用荧光素标记的 S1 刺突蛋白添加到表达 ACE2 或 CADM1 的上皮细胞的单层培养物中。定量检测结合到细胞上的荧光素发现,S1 刺突蛋白与 CADM1 的亲和力是与 ACE2 的亲和力的一半。一致地,对接模拟分析表明,S1 刺突蛋白与 CADM1 的结合强度是与 ACE2 的结合强度的四分之三,并且 ACE2 的结合模式相似。总之,鼻内 S1 刺突蛋白似乎更喜欢在嗅觉上皮细胞上积累,并且 CADM1 基于分子丰度和亲和力被认为有助于 S1 刺突蛋白的这种偏好。