Saito Keiichi, Mori Shiro, Date Fumiko, Hong Guang
a Liaison Centre for Innovative Dentistry, Tohoku University Graduate School of Dentistry , Sendai , Japan .
Autoimmunity. 2015;48(6):379-88. doi: 10.3109/08916934.2015.1030617.
The water channel aquaporin 5 (AQP5) plays a crucial role in regulating salivary flow rates. Xerostomia is often observed in patients with Sjögren's syndrome, and this is attributed to reduced AQP5 expression in the salivary glands. Recently, anti-type 3 muscarinic cholinergic receptors (M3R) autoantibodies and nuclear factor κB (NF-κB) have been found to be negative regulators of AQP5 expression in the salivary gland. Anti-M3R autoantibodies desensitize M3R to salivary secretagogues in Sjögren's syndrome, while activated NF-κB translocates to nuclei and binds to the AQP5 gene promoter, resulting in the suppression of AQP5 expression. We previously documented that epigallocatechin gallate (EGCG), which is a robust antioxidant contained in green tea, ameliorates oxidative stress-induced tissue damage to the salivary glands of MRL/MpJ-lpr/lpr (MRL-Fas(lpr)) mice, which are widely used as a model of Sjögren's syndrome. Reactive oxygen species (ROS) can activate NF-κB and inactivate protein kinase A (PKA), which is a key driver of AQP5 expression. In this study, we examined the effects of administering EGCG to MRL-Fas(lpr) mice with autoimmune sialadenitis on the levels of AQP5, activated NF-κB p65 subunit, activated PKA, activated c-Jun N-terminal kinase (JNK) (an activator of NF-κB), inhibitor κB (IκB) and histone deacetylase 1 (HDAC1) (an inhibitor of NF-κB). In EGCG-treated mice, intense aster-like immunostaining for AQP5 was observed on the apical plasma membranes (APMs) of submandibular gland acinar cells. Likewise, PKA, IκB and HDAC1 were highly expressed in salivary gland tissues, whereas the expression of JNK and NF-κB p65 was negligible. Rank correlation and partial correlation analyses revealed that treatment with EGCG upregulated AQP5 expression on the APM of acinar cells through activation of PKA and inactivation of NF-κB, while IκB and HDAC1 played a pivotal role in the induction of AQP5 expression by PKA. Our study indicates that EGCG may have therapeutic potential for Sjögren's syndrome patients.
水通道蛋白5（AQP5）在调节唾液流速方面起着关键作用。口干症在干燥综合征患者中经常出现，这归因于唾液腺中AQP5表达的降低。最近，抗3型毒蕈碱胆碱能受体（M3R）自身抗体和核因子κB（NF-κB）已被发现是唾液腺中AQP5表达的负调节因子。在干燥综合征中，抗M3R自身抗体使M3R对唾液分泌刺激剂脱敏，而活化的NF-κB易位至细胞核并与AQP5基因启动子结合，导致AQP5表达受到抑制。我们之前记录到，表没食子儿茶素没食子酸酯（EGCG）是绿茶中含有的一种强大抗氧化剂，可改善氧化应激诱导的对MRL/MpJ-lpr/lpr（MRL-Fas(lpr)）小鼠唾液腺的组织损伤，该小鼠被广泛用作干燥综合征的模型。活性氧（ROS）可激活NF-κB并使蛋白激酶A（PKA）失活，而PKA是AQP5表达的关键驱动因子。在本研究中，我们检测了给患有自身免疫性涎腺炎的MRL-Fas(lpr)小鼠施用EGCG后，其AQP5、活化的NF-κB p65亚基、活化的PKA、活化的c-Jun氨基末端激酶（JNK）（NF-κB的激活剂）、抑制蛋白κB（IκB）和组蛋白去乙酰化酶1（HDAC1）（NF-κB的抑制剂）水平的变化。在经EGCG处理的小鼠中，在下颌下腺腺泡细胞的顶端质膜（APM）上观察到了强烈的AQP5星状免疫染色。同样，PKA、IκB和HDAC1在唾液腺组织中高表达，而JNK和NF-κB p65的表达可忽略不计。等级相关分析和偏相关分析显示，EGCG处理通过激活PKA和使NF-κB失活，上调了腺泡细胞APM上的AQP5表达，而IκB和HDAC1在PKA诱导AQP5表达中起关键作用。我们的研究表明，EGCG可能对干燥综合征患者具有治疗潜力。
