Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Chem Senses. 2012 Nov;37(9):859-68. doi: 10.1093/chemse/bjs069. Epub 2012 Sep 5.
The main olfactory epithelium consists of 4 major cell types: sensory neurons, supporting cells, microvillar cells, and basal progenitor cells. Several populations of microvillar olfactory cells have been described, whose properties are not yet fully understood. In this study, we aimed to clarify the classification of microvillar cells by introducing a specific marker, CD73. Furthermore, we investigated the turnover of CD73-microvillar cells during adult life. Using direct and indirect immunofluorescence in adult main olfactory epithelium, we first demonstrate that ecto-5'-nucleotidase (CD73) is a reliable marker for microvillar cells reported previously to express phospholipase C β2 (PLC β2) along with type 3 IP(3) receptors (IP(3)R3) and transient receptor potential channels 6 (TRPC6), as well as for cells labeled by transgenic expression of tauGFP driven by the IP(3)R3 promoter. The ubiquitous CD73 immunoreactivity in the microvilli of these 2 cell populations indicates that they correspond to the same cell type (CD73-microvillar cell), endowed with a signal transduction cascade mobilizing Ca(++) from intracellular stores. These microvillar cells respond to odors, possess a basal process, and do not degenerate after bulbectomy, suggesting that they contribute to cellular homeostasis in the olfactory epithelium. Next, we examined whether CD73-microvillar cells undergo turnover in the adult olfactory epithelium. By combining CD73 immunofluorescence and BrdU pulse labeling, we show delayed BrdU incorporation in a small fraction of CD73-positive microvillar cells, which persists for several weeks after BrdU administration. These findings indicate that CD73-microvillar cells likely differentiate from proliferating progenitor cells and have a slow turnover despite their apical position in the olfactory epithelium. These combined properties are unique among olfactory cells, in line with the possibility that they might regulate cellular homeostasis driven by extracellular ATP and adenosine.
嗅上皮主要由 4 种主要细胞类型组成：感觉神经元、支持细胞、微绒毛细胞和基底祖细胞。已经描述了几种微绒毛嗅细胞群体，但其特性尚未完全了解。在这项研究中，我们旨在通过引入特定标记物 CD73 来阐明微绒毛细胞的分类。此外，我们还研究了成年期 CD73-微绒毛细胞的更新。通过成年嗅上皮的直接和间接免疫荧光，我们首先证明，外核苷酸酶（CD73）是一种可靠的微绒毛细胞标记物，先前的研究表明，它表达磷脂酶 Cβ2（PLCβ2）以及 3 型 IP3 受体（IP3R3）和瞬时受体电位通道 6（TRPC6），以及由 IP3R3 启动子驱动的 tauGFP 转基因表达标记的细胞。这 2 种细胞群体的微绒毛中无处不在的 CD73 免疫反应性表明，它们对应于相同的细胞类型（CD73-微绒毛细胞），具有动员细胞内储存的 Ca++的信号转导级联。这些微绒毛细胞对气味有反应，具有基底过程，并且在球囊切除后不会退化，这表明它们有助于嗅上皮的细胞内稳态。接下来，我们检查了成年嗅上皮中 CD73-微绒毛细胞是否发生更新。通过结合 CD73 免疫荧光和 BrdU 脉冲标记，我们发现 BrdU 在一小部分 CD73 阳性微绒毛细胞中的掺入延迟，并且在 BrdU 给药后数周内持续存在。这些发现表明，CD73-微绒毛细胞可能来自于增殖的祖细胞分化而来，尽管它们位于嗅上皮的顶端，但具有缓慢的更新率。这些综合特性在嗅细胞中是独一无二的，与它们可能调节由细胞外 ATP 和腺苷驱动的细胞内稳态的可能性一致。
