Nishiyama Tatsuaki, Nakamura Takeshi, Obara Kumi, Inoue Hiroko, Mishima Kenji, Matsumoto Nagisa, Matsui Minoru, Manabe Toshiya, Mikoshiba Katsuhiko, Saito Ichiro
Department of Pathology, Tsurumi University School of Dental Medicine, Tsurumi-ku, Yokohama, 230-8501, Japan.
J Pharmacol Exp Ther. 2007 Feb;320(2):516-24. doi: 10.1124/jpet.106.113092. Epub 2006 Oct 31.
Protease-activated receptor-2 (PAR-2) is expressed in the salivary glands and is expected to be a new target for the treatment of exocrine dysfunctions, such as dry mouth; however, the salivary secretory mechanism mediated by PAR-2 remains to be elucidated. Therefore, mechanism of the PAR-2-mediated salivary secretion was investigated in this study. We found that a PAR-2 agonist peptide, SLIGRL-OH, induced salivary flow in vivo and dose-dependent increase in Ca(2+) submandibular gland (SMG) acinar cells in wild-type (WT) mice and mice lacking M(3) or both M(1) and M(3) muscarinic acetylcholine receptors (mAChRs), whereas secretions in PAR-2 knockout (PAR-2KO) mice were completely abolished. The saliva composition secreted by SLIGRL-OH was similar to that secreted by mAChR stimulation. Ca(2+) imaging in WT acinar cells and beta-galactosidase staining in PAR-2KO mice, in which the beta-galactosidase gene (LacZ) was incorporated into the disrupted gene, revealed a nonubiquitous, sporadic distribution of PAR-2 in the SMG. Furthermore, compared with the secretion in WT mice, PAR-2-mediated salivary secretion and Ca(2+) response were enhanced in mice lacking M(3) or both M(1) and M(3) mAChRs, in which mAChR-stimulated secretion and Ca(2+) response in acinar cells were severely impaired. Although the mechanism underlying the enhanced PAR-2-mediated salivary secretion in M(3)-deficient mice is not clear, the result suggests the presence of some compensatory mechanism involving PAR-2 in the salivary glands deficient in cholinergic activation. These results indicate that PAR-2 present in the salivary glands mediates Ca(2+)-dependent fluid secretion, demonstrating potential usefulness of PAR-2 as a target for dry mouth treatment.
蛋白酶激活受体-2（PAR-2）在唾液腺中表达，有望成为治疗外分泌功能障碍（如口干）的新靶点；然而，由PAR-2介导的唾液分泌机制仍有待阐明。因此，本研究对PAR-2介导的唾液分泌机制进行了研究。我们发现，PAR-2激动剂肽SLIGRL-OH在野生型（WT）小鼠以及缺乏M3或同时缺乏M1和M3毒蕈碱型乙酰胆碱受体（mAChRs）的小鼠体内可诱导唾液分泌，并使下颌下腺（SMG）腺泡细胞内的[Ca(2+)]i呈剂量依赖性增加，而PAR-2基因敲除（PAR-2KO）小鼠的分泌则完全被消除。SLIGRL-OH分泌的唾液成分与mAChR刺激分泌的唾液成分相似。对WT腺泡细胞进行Ca(2+)成像以及对PAR-2KO小鼠（其中β-半乳糖苷酶基因（LacZ）已整合到被破坏的基因中）进行β-半乳糖苷酶染色，结果显示PAR-2在下颌下腺中的分布并非普遍存在，而是呈散在分布。此外，与WT小鼠的分泌情况相比，在缺乏M3或同时缺乏M1和M3 mAChRs的小鼠中，PAR-2介导的唾液分泌和Ca(2+)反应增强，而在这些小鼠中，腺泡细胞中mAChR刺激的分泌和Ca(2+)反应严重受损。尽管M3缺陷小鼠中PAR-2介导的唾液分泌增强的机制尚不清楚，但该结果表明，在胆碱能激活不足的唾液腺中，存在一些涉及PAR-2的代偿机制。这些结果表明，唾液腺中存在的PAR-2介导Ca(2+)依赖性液体分泌，并证明PAR-2作为口干治疗靶点具有潜在的应用价值。
