School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong.
Department of Ophthalmology & Visual Science, The Chinese University of Hong Kong, Hong Kong.
Exp Eye Res. 2019 Apr;181:277-284. doi: 10.1016/j.exer.2019.02.021. Epub 2019 Mar 1.
The receptor for growth hormone-releasing hormone (GHRH-R) has been shown to upregulate specifically in the ciliary and iris epithelial cells and infiltrating cells in the aqueous humor in a rat model of acute anterior uveitis. Treatment with GHRHR-R antagonist alleviates significantly these inflammatory responses. Herein we investigated whether the ciliary and iris epithelial cells can respond directly to lipopolysaccharide (LPS) without the influences of circulating leukocytes to produce inflammatory mediators through a GHRH-R mediated mechanism. In explant cultures of rat ciliary body and iris, LPS caused a substantial increase of GHRH-R in 24 h. Immunohistochemistry showed a localization of TLR4, the receptor for LPS, and an elevated expression of IL-6 and IL-1β in ciliary and iris epithelial cells after LPS treatment. LPS also elevated the level of IL-1β, IL-6, and iNOS and increased secretion of IL-1β and IL-6 from the explants. The GHRH-R antagonist, MIA-602, suppressed the elevated expression of IL-1β and IL-6, and reduced the release of IL-6. Such effects were not seen for the GHRHR agonist, MR-409. When co-cultured with leukocytes, expression of GHRH-R in the ocular explants was further enhanced during LPS treatment. Our results demonstrate a direct action of LPS on ciliary and iris epithelial cells to produce pro-inflammatory factors through a GHRH-R mediated mechanism, and suggest a role of these epithelial cells, in addition to the resident antigen presenting cells, in immune surveillance of the eye. Infiltrating leukocytes may enhance these inflammatory responses by regulating GHRH-R in ciliary and iris epithelial cells, in addition to their functions of synthesizing proinflammatory cytokines.
生长激素释放激素受体 (GHRH-R) 的受体已被证明在大鼠急性前葡萄膜炎模型中特异性地上调睫状和虹膜上皮细胞以及房水中的浸润细胞。用 GHRHR-R 拮抗剂治疗可显著缓解这些炎症反应。在此，我们研究了睫状和虹膜上皮细胞是否可以直接对脂多糖 (LPS) 作出反应，而无需循环白细胞的影响，通过 GHRH-R 介导的机制产生炎症介质。在大鼠睫状体和虹膜的离体培养物中，LPS 在 24 小时内导致 GHRH-R 大量增加。免疫组织化学显示 TLR4（LPS 的受体）定位以及 LPS 处理后睫状和虹膜上皮细胞中 IL-6 和 IL-1β 的表达升高。LPS 还升高了 IL-1β、IL-6 和 iNOS 的水平，并增加了 IL-1β 和 IL-6 从外植体的分泌。GHRH-R 拮抗剂 MIA-602 抑制了 IL-1β 和 IL-6 的升高表达，并减少了 IL-6 的释放。而 GHRHR 激动剂 MR-409 则没有这种作用。当与白细胞共培养时，LPS 处理期间眼外植体中 GHRH-R 的表达进一步增强。我们的结果表明，LPS 通过 GHRH-R 介导的机制对睫状和虹膜上皮细胞直接发挥作用，产生促炎因子，并提示这些上皮细胞除了作为固有抗原呈递细胞外，在眼睛的免疫监视中发挥作用。浸润的白细胞可能通过调节睫状和虹膜上皮细胞中的 GHRH-R 来增强这些炎症反应，除了它们合成促炎细胞因子的功能。
