Kato Mami, Takayama Yasunori, Sunagawa Masataka
Department of Physiology, Showa University School of Medicine, Tokyo, Japan.
Front Pharmacol. 2021 Apr 8;12:628968. doi: 10.3389/fphar.2021.628968. eCollection 2021.
The transmembrane 16 (TMEM16) family contains 10 subtypes, and the function of each protein is different. TMEM16A is a calcium-activated chloride channel involved in physiological and pathological situations. Liquiritigenin is an aglycone derived from , and it is generated via the metabolism of enterobacterial flora. It has been known that liquiritigenin reduces pain sensation involving TMEM16A activation in primary sensory neurons. In addition, other pharmacological effects of liquiritigenin in physiological functions involving TMEM16A have been reported. However, the relationship between TMEM16A and liquiritigenin is still unknown. Therefore, we hypothesized that TMEM16A is inhibited by liquiritigenin. To confirm this hypothesis, we investigated the effect of liquiritigenin on TMEM16A currents evoked by intracellular free calcium in HEK293T cells transfected with TMEM16A. In this study, we found that liquiritigenin inhibited the mouse and human TMEM16A currents. To further confirm its selectivity, we also investigated its pharmacological effects on other ion channels, including transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1), which are non-selective cation channels involved in pain sensation. However, liquiritigenin did not inhibit the currents of TRPV1 and TRPA1 induced by capsaicin and allyl isothiocyanate, respectively. Therefore, our findings indicate that selective TMEM16A inhibition could be one molecular mechanism that explains liquiritigenin-induced pain reduction. Additionally, we also investigated the inhibitory effects of estrogens on TMEM16A because liquiritigenin reportedly binds to the estrogen receptor. In this study, a pregnancy-dependent estrogen, estriol, significantly inhibited TMEM16A. However, the efficacy was weak. Although there is a possibility that TMEM16A activity could be suppressed during pregnancy, the physiological significance seems to be small. Thus, the inhibitory effect of estrogen might not be significant under physiological conditions. Furthermore, we investigated the effect of dihydrodaidzein, which is an analog of liquiritigenin that has a hydroxyphenyl at different carbon atom of pyranose. Dihydrodaidzein also inhibited mouse and human TMEM16A. However, the inhibitory effects were weaker than those of liquiritigenin. This suggests that the efficacy of TMEM16A antagonists depends on the hydroxyl group positions. Our finding of liquiritigenin-dependent TMEM16A inhibition could connect the current fragmented knowledge of the physiological and pathological mechanisms involving TMEM16A and liquiritigenin.
跨膜蛋白16（TMEM16）家族包含10个亚型，每个蛋白的功能各不相同。TMEM16A是一种钙激活氯离子通道，参与生理和病理过程。甘草素是一种来源于[此处原文缺失相关信息]的苷元，由肠道菌群代谢产生。已知甘草素可减轻疼痛感觉，这一过程涉及初级感觉神经元中TMEM16A的激活。此外，还报道了甘草素在涉及TMEM16A的生理功能方面的其他药理作用。然而，TMEM16A与甘草素之间的关系仍不清楚。因此，我们推测甘草素可抑制TMEM16A。为证实这一推测，我们研究了甘草素对转染TMEM16A的HEK293T细胞中细胞内游离钙诱发的TMEM16A电流的影响。在本研究中，我们发现甘草素可抑制小鼠和人类的TMEM16A电流。为进一步证实其选择性，我们还研究了其对其他离子通道的药理作用，包括瞬时受体电位香草酸亚型1（TRPV1）和锚蛋白1（TRPA1），它们是参与疼痛感觉的非选择性阳离子通道。然而，甘草素分别未抑制辣椒素和异硫氰酸烯丙酯诱导的TRPV1和TRPA1电流。因此，我们的研究结果表明，选择性抑制TMEM1蛋白6A可能是解释甘草素减轻疼痛的一种分子机制。此外，我们还研究了雌激素对TMEM16A的抑制作用，因为据报道甘草素可与雌激素受体结合。在本研究中，一种与妊娠相关的雌激素——雌三醇，可显著抑制TMEM16A。然而，其效果较弱。尽管在妊娠期间TMEM16A的活性有可能被抑制，但其生理意义似乎不大。因此，在生理条件下雌激素的抑制作用可能并不显著。此外，我们研究了二氢大豆苷元的作用，它是甘草素的类似物，在吡喃糖的不同碳原子上有一个羟基苯基。二氢大豆苷元也可抑制小鼠和人类的TMEM16A。然而，其抑制作用比甘草素弱。这表明TMEM16A拮抗剂的效果取决于羟基的位置。我们关于甘草素依赖性抑制TMEM16A的发现可能会将目前关于涉及TMEM16A和甘草素的生理和病理机制的零散知识联系起来。
