Division of Molecular Pathology, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
J Immunol. 2011 May 15;186(10):5983-92. doi: 10.4049/jimmunol.1002244. Epub 2011 Apr 11.
Close apposition of nerve and mast cells is viewed as a functional unit of neuro-immune mechanisms, and it is sustained by trans-homophilic binding of cell adhesion molecule-1 (CADM1), an Ig superfamily member. Cerebral nerve-mast cell interaction might be developmentally modulated, because the alternative splicing pattern of four (a-d) types of CADM1 transcripts drastically changed during development of the mouse cerebrum: developing cerebrums expressed CADM1b and CADM1c exclusively, while mature cerebrums expressed CADM1d additionally and predominantly. To probe how individual isoforms are involved in nerve-mast cell interaction, Neuro2a neuroblastoma cells that express CADM1c endogenously were modified to express additionally either CADM1b (Neuro2a-CADM1b) or CADM1d (Neuro2a-CADM1d), and they were cocultured with mouse bone marrow-derived mast cells (BMMCs) and BMMC-derived cell line IC-2 cells, both of which expressed CADM1c. BMMCs were found to adhere to Neuro2a-CADM1d neurites more firmly than to Neuro2a-CADM1b neurites when the adhesive strengths were estimated from the femtosecond laser-induced impulsive forces minimally required for detaching BMMCs. GFP-tagging and crosslinking experiments revealed that the firmer adhesion site consisted of an assembly of CADM1d cis-homodimers. When Neuro2a cells were specifically activated by histamine, intracellular Ca(2+) concentration was increased in 63 and 38% of CADM1c-expressing IC-2 cells that attached to the CADM1d assembly site and elsewhere, respectively. These results indicate that CADM1d is a specific neuronal isoform that enhances nerve-mast cell interaction, and they suggest that nerve-mast cell interaction may be reinforced as the brain grows mature because CADM1d becomes predominant.
神经细胞与肥大细胞紧密相邻被视为神经免疫机制的一个功能单位，这种紧密相邻状态是通过细胞黏附分子-1（CADM1）的同种细胞黏附实现的，CADM1 是免疫球蛋白超家族的成员之一。脑内神经-肥大细胞的相互作用可能存在发育调节，因为在小鼠大脑发育过程中，CADM1 四种（a-d）转录本的选择性剪接模式发生了显著变化：发育中的大脑仅表达 CADM1b 和 CADM1c，而成熟的大脑则额外且主要表达 CADM1d。为了研究各个同种型如何参与神经-肥大细胞的相互作用，我们将内源表达 CADM1c 的Neuro2a 神经母细胞瘤细胞修饰为额外表达 CADM1b（Neuro2a-CADM1b）或 CADM1d（Neuro2a-CADM1d），然后将其与表达 CADM1c 的小鼠骨髓来源的肥大细胞（BMMCs）和 BMMC 衍生的细胞系 IC-2 共培养。当从最小化分离 BMMC 所需的飞秒激光诱导的脉冲力估计黏附强度时，发现 BMMC 更牢固地黏附于表达 CADM1d 的 Neuro2a 神经突上，而非表达 CADM1b 的 Neuro2a 神经突上。GFP 标记和交联实验表明，更牢固的黏附部位由 CADM1d 顺式同源二聚体的组装体构成。当神经细胞被组胺特异性激活时，分别附着于 CADM1d 组装部位和其他部位的表达 CADM1c 的 IC-2 细胞中，细胞内 Ca(2+)浓度分别增加了 63%和 38%。这些结果表明，CADM1d 是增强神经-肥大细胞相互作用的特定神经元同种型，并且提示随着大脑的成熟，CADM1d 变得占主导地位，神经-肥大细胞的相互作用可能会增强。
