A nasal cell atlas reveals heterogeneity of tuft cells and their role in directing olfactory stem cell proliferation

The olfactory neuroepithelium serves as a sensory organ for odors and forms part of the nasal mucosal barrier. Olfactory sensory neurons are surrounded and supported by epithelial cells. Among them, microvillous cells (MVCs) are strategically positioned at the apical surface, but their specific functions are enigmatic and their relationship to the other specialized epithelial cells, particularly the solitary chemosensory cell family, is unclear. Here, we establish that the family of MVCs comprises tuft cells and ionocytes in both mice and humans. Integrating analysis of the respiratory and olfactory epithelia, we define the unique receptor expression of TRPM5+ tuft-MVCs compared to Galpha-gustducinhigh respiratory tuft cells and characterize a new population of glandular DCLK1+ tuft cells. To establish how allergen sensing by tuft-MVCs might direct olfactory mucosal responses, we employed an integrated single-cell transcriptional and protein analysis. Inhalation of Alternaria induced mucosal epithelial effector molecules including Chil4, and a distinct pathway leading to proliferation of the quiescent olfactory horizontal basal stem cell (HBC) pool, both triggered in the absence of olfactory apoptosis. While the Chil4 pathway was dependent on STAT6 signaling and innate lymphocytes, neither were required for HBC proliferation. Alternaria- and ATP- elicited HBC proliferation was dependent on tuft-MVCs, establishing these specialized epithelial cells as regulators of olfactory stem cell responses. Together our data provide high resolution characterization of nasal tuft cell heterogeneity and uncover a novel function for TRPM5+ tuft-MVCs in directing the olfactory mucosal response to allergens. Saltanat, Ualiyeva嗅觉神经上皮（olfactory neuroepithelium）作为嗅觉感知气味的感官器官，亦是鼻黏膜屏障的组成部分。嗅觉感觉神经元被上皮细胞包裹并获得支持。其中，微绒毛细胞（microvillous cells, MVCs）定位于上皮顶侧表面，但其具体功能尚不明确，且其与其他特化上皮细胞（尤其是孤立化学感受细胞家族（solitary chemosensory cell family））的关系仍不清楚。本研究证实，在小鼠与人类体内，微绒毛细胞家族包含簇细胞（tuft cells）与离子细胞（ionocytes）。通过整合分析呼吸上皮与嗅觉上皮的相关数据，我们明确了TRPM5阳性簇-MVCs（TRPM5+ tuft-MVCs）相较于Gα-味导素高表达呼吸簇细胞（Gα-gustducinhigh respiratory tuft cells）的独特受体表达谱，并鉴定出一类全新的腺体DCLK1阳性簇细胞（glandular DCLK1+ tuft cells）。为阐明簇-MVCs的过敏原感知如何调控嗅觉黏膜应答的机制，我们采用了单细胞转录组与蛋白质组整合分析技术。吸入链格孢属（Alternaria）孢子可诱导黏膜上皮产生包括几丁质酶样蛋白4（Chil4）在内的上皮效应分子，并激活一条独特通路以促进静息嗅觉水平基底干细胞（horizontal basal stem cell, HBC）池增殖，且上述两种反应均未伴随嗅觉上皮细胞凋亡。尽管几丁质酶样蛋白4（Chil4）通路依赖STAT6信号通路（STAT6 signaling）与先天淋巴细胞（innate lymphocytes），但二者均不参与HBC增殖过程。链格孢属（Alternaria）与三磷酸腺苷（ATP）诱导的HBC增殖依赖簇-MVCs（TRPM5+ tuft-MVCs），这证实这类特化上皮细胞作为嗅觉干细胞应答的调控因子。综上，本研究实现了鼻簇细胞异质性的高分辨率表征，并揭示了TRPM5阳性簇-MVCs（TRPM5+ tuft-MVCs）在介导嗅觉黏膜过敏原应答中的全新功能。作者：萨纳塔特·乌利耶娃（Saltanat Ualiyeva）