Unveiling Alternate Pathways for SARS-CoV-2 Infection via Extracellular Vesicle-Mediated Transfer of ACE2 and TMPRSS2

The COVID-19 pandemic, caused by SARS-CoV-2, has underscored the urgency of understanding viral entry mechanisms to develop effective therapeutic strategies. SARS-CoV-2 primarily exploits angiotensin-converting enzyme 2 (ACE2) as its entry receptor and relies on the serine protease TMPRSS2 to prime its spike protein, enabling membrane fusion and infection. Traditionally, TMPRSS2 has been described as a cell surface protein, but our study reveals that in human lung epithelial cells, TMPRSS2 is largely absent from the plasma membrane and instead resides intracellularly. We show that TMPRSS2 is secreted together with ACE2 in extracellular vesicles (EVs) from lung epithelial cells, which are subsequently taken up by non-epithelial cells, specifically alveolar macrophages, endothelial cells, and pericytes, that do not express TMPRSS2 or ACE2 mRNA under homeostatic conditions. This EV uptake deposits ACE2 and TMPRSS2 protein onto recipient cells, equipping them for SARS-CoV-2 entry. By transferring these viral entry proteins, EVs expand the spectrum of susceptible cell types in the lung, offering a new explanation for how the virus can infect diverse cell populations and cause widespread tissue damage. Identifying EVs as vehicles for delivering functional ACE2 and TMPRSS2 across cell types reveals previously unrecognized pathway of viral entry with important implications for COVID-19 pathogenesis. These findings open new avenues for therapeutic intervention aimed at disrupting EV-mediated protein transfer, potentially limiting viral dissemination and severity, and may also represent a generalizable mechanism exploited by other viral pathogens, highlighting the potential relevance of EV-mediated protein transfer beyond SARS-CoV-2.

由严重急性呼吸综合征冠状病毒2型（SARS-CoV-2）引发的新型冠状病毒肺炎（COVID-19）大流行，凸显了阐明病毒入侵机制以开发有效治疗策略的紧迫性。SARS-CoV-2主要以血管紧张素转换酶2（ACE2）作为入侵受体，并依赖丝氨酸蛋白酶TMPRSS2对其刺突蛋白进行酶切激活，从而实现膜融合与细胞感染。传统观点认为TMPRSS2是一种细胞表面蛋白，但本研究发现，在人肺上皮细胞中，TMPRSS2大多并不存在于质膜，而是定位于细胞内。本研究证实，TMPRSS2可与ACE2一同通过肺上皮细胞分泌的细胞外囊泡（EVs）被释放，随后被非上皮细胞摄取，具体包括肺泡巨噬细胞、内皮细胞与周细胞——这类细胞在稳态条件下并不会表达TMPRSS2或ACE2的mRNA。这种细胞外囊泡介导的摄取过程将ACE2与TMPRSS2蛋白递送至受体细胞，使这些细胞获得SARS-CoV-2入侵的能力。通过传递这类病毒入侵相关蛋白，细胞外囊泡拓宽了肺部易感细胞类型的范围，为病毒如何感染多种细胞群体并引发广泛组织损伤提供了全新的解释。确定细胞外囊泡作为跨细胞类型递送功能性ACE2与TMPRSS2的载体，揭示了此前未被认知的病毒入侵途径，这对COVID-19的发病机制具有重要意义。这些发现为靶向阻断细胞外囊泡介导的蛋白转移的治疗干预开辟了新方向，有望限制病毒的传播与致病严重程度；同时，该机制或可被其他病毒病原体所利用，凸显了细胞外囊泡介导的蛋白转移在SARS-CoV-2之外的潜在相关性。