Alberta Diabetes Institute, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Canada.
Departments of Pharmacology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Canada.
J Physiol. 2020 Oct;598(19):4321-4338. doi: 10.1113/JP279961. Epub 2020 Aug 13.
25-Hydroxyvitamin D (25OHD) is a partial agonist of TRPV1 whereby 25OHD can weakly activate TRPV1 yet antagonize the stimulatory effects of the full TRPV1 agonists capsaicin and oleoyl dopamine. 25OHD binds to TRPV1 within the same vanilloid binding pocket as capsaicin. 25OHD inhibits the potentiating effects of PKC-mediated TRPV1 activity. 25OHD reduces T-cell activation and trigeminal neuron calcium signalling mediated by TRPV1 activity. These results provide evidence that TRPV1 is a novel receptor for the biological actions of vitamin D in addition to the well-documented effects of vitamin D upon the nuclear vitamin D receptor. The results may have important implications for our current understanding of certain diseases where TRPV1 and vitamin D deficiency have been implicated, such as chronic pain and autoimmune diseases, such as type 1 diabetes.
The capsaicin receptor TRPV1 plays an important role in nociception, inflammation and immunity and its activity is regulated by exogenous and endogenous lipophilic ligands. As vitamin D is lipophilic and involved in similar biological processes as TRPV1, we hypothesized that it directly regulates TRPV1 activity and function. Our calcium imaging and electrophysiological data demonstrate that vitamin D (25-hydroxyvitamin D (25OHD) and 1,25-hydroxyvitamin D (1,25OHD)) can weakly activate TRPV1 at physiologically relevant concentrations (100 nM). Furthermore, both 25OHD and 1,25OHD can inhibit capsaicin-induced TRPV1 activity (IC = 34.3 ± 0.2 and 11.5 ± 0.9 nM, respectively), but not pH-induced TRPV1 activity, suggesting that vitamin D interacts with TRPV1 in the same region as the TRPV1 agonist capsaicin. This hypothesis is supported by our in silico TRPV1 structural modelling studies, which place 25OHD in the same binding region as capsaicin. 25OHD also attenuates PKC-dependent TRPV1 potentiation via interactions with a known PKC phospho-acceptor residue in TRPV1. To provide evidence for a physiological role for the interaction of vitamin D with TRPV1, we employed two different cellular models known to express TRPV1: mouse CD4 T-cells and trigeminal neurons. Our results indicate that 25OHD reduces TRPV1-induced cytokine release from T-cells and capsaicin-induced calcium activity in trigeminal neurons. In summary, we provide evidence that vitamin D is a novel endogenous regulator of TRPV1 channel activity that may play an important physiological role in addition to its known effects through the canonical nuclear vitamin D receptor pathway.
25-羟维生素 D（25OHD）是 TRPV1 的部分激动剂，25OHD 可以弱激活 TRPV1，但拮抗全 TRPV1 激动剂辣椒素和油酰基多巴胺的刺激作用。25OHD 在与辣椒素相同的香草素结合口袋内结合 TRPV1。25OHD 抑制 PKC 介导的 TRPV1 活性的增强作用。25OHD 降低 TRPV1 活性介导的 T 细胞激活和三叉神经神经元钙信号。这些结果提供了证据，表明 TRPV1 是维生素 D 生物学作用的新型受体，除了维生素 D 对核维生素 D 受体的已有作用之外。这些结果可能对我们目前对某些疾病的理解具有重要意义，在这些疾病中，TRPV1 和维生素 D 缺乏与慢性疼痛和自身免疫性疾病（如 1 型糖尿病）有关。
辣椒素受体 TRPV1 在痛觉、炎症和免疫中起重要作用，其活性受外源性和内源性亲脂配体调节。由于维生素 D 是亲脂的，并参与与 TRPV1 相似的生物学过程，我们假设它直接调节 TRPV1 活性和功能。我们的钙成像和电生理数据表明，维生素 D（25-羟维生素 D（25OHD）和 1,25-羟维生素 D（1,25OHD））可以在生理相关浓度（100 nM）下弱激活 TRPV1。此外，25OHD 和 1,25OHD 均可抑制辣椒素诱导的 TRPV1 活性（IC 50 值分别为 34.3 ± 0.2 和 11.5 ± 0.9 nM），但不抑制 pH 诱导的 TRPV1 活性，表明维生素 D 与 TRPV1 相互作用的区域与 TRPV1 激动剂辣椒素相同。这一假设得到了我们 TRPV1 结构建模研究的支持，该研究将 25OHD 置于与辣椒素相同的结合区域。25OHD 还通过与 TRPV1 中已知的 PKC 磷酸化接受残基相互作用，减弱 PKC 依赖性 TRPV1 增强作用。为了提供维生素 D 与 TRPV1 相互作用的生理作用的证据，我们使用了两种已知表达 TRPV1 的不同细胞模型：小鼠 CD4 T 细胞和三叉神经神经元。我们的结果表明，25OHD 降低了 TRPV1 诱导的 T 细胞细胞因子释放和 TRPV1 诱导的三叉神经神经元钙活性。总之，我们提供的证据表明，维生素 D 是 TRPV1 通道活性的新型内源性调节剂，除了通过已知的核维生素 D 受体途径之外，它可能在生理上发挥重要作用。
