State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, Guangzhou, China.
Invest Ophthalmol Vis Sci. 2022 May 2;63(5):6. doi: 10.1167/iovs.63.5.6.
Inflammation contributes to the development of meibomian gland dysfunction (MGD) under specific disease conditions, but the underlying mechanisms remain elusive. We examined whether lipopolysaccharide (LPS) induced a proinflammatory cytokine response and lipogenesis in human meibomian gland epithelial cells (HMGECs) and whether melatonin (MLT), a powerful anti-inflammatory regent in the eyes, could protect against LPS-induced disorders.
Human meibomian gland (MG) tissues and immortalized HMGECs were stained to identify Toll-like receptor (TLR) 4 and MLT receptors (MT1 and MT2). HMGECs were pretreated with or without MLT and then stimulated with LPS. Then, TLR4 activation, cytokine levels, lipid synthesis, apoptosis, autophagy, and MAPK/NF-κB factor phosphorylation in HMGECs were analyzed.
TLR4, MT1, and MT2 were expressed in human MG acini and HMGECs. Pretreatment with MLT inhibited the TLR4/MyD88 signaling and attenuated proinflammatory cytokine response and lipogenesis in LPS-stimulated HMGECs, which manifested as decreased production of cytokines (IL-1β, IL-6, IL-8, and TNF-α), reduced lipid droplet formation, and downregulated expression of meibum lipogenic proteins (ADFP, ELOVL4, and SREBP-1). Phospho-histone H2A.X foci, lysosome accumulation, and cytoplasmic cleaved caspase 3/LC3B-II staining were increased in LPS-stimulated HMGECs, indicating enhanced cell death mediated by apoptosis and autophagy during LPS-induced lipogenesis. MLT downregulated cleaved caspase 3 levels and the Bax/Bcl-2 ratio to alleviate apoptosis and ameliorated the expression of Beclin 1 and LC3B-II to inhibit autophagy. The protective mechanisms of MLT include the inhibition of MAPK and NF-κB phosphorylation.
MLT attenuated lipogenesis, apoptosis, and autophagy in HMGECs induced by proinflammatory stimuli, indicating the protective potential of MLT in MGD.
在特定疾病条件下，炎症会导致睑板腺功能障碍（MGD）的发生，但潜在机制尚不清楚。本研究旨在探讨脂多糖（LPS）是否会诱导人睑板腺上皮细胞（HMGEC）产生促炎细胞因子和脂生成，以及眼部强大的抗炎调节剂褪黑素（MLT）是否可以预防 LPS 诱导的异常。
对人睑板腺（MG）组织和永生化 HMGEC 进行染色，以鉴定 Toll 样受体（TLR）4 和 MLT 受体（MT1 和 MT2）。用或不用 MLT 预处理 HMGEC 后，用 LPS 刺激。然后分析 TLR4 激活、细胞因子水平、脂质合成、细胞凋亡、自噬以及 HMGEC 中 MAPK/NF-κB 因子磷酸化。
TLR4、MT1 和 MT2 均在人 MG 腺泡和 HMGEC 中表达。MLT 预处理抑制了 TLR4/MyD88 信号通路，并减弱了 LPS 刺激的 HMGEC 中促炎细胞因子反应和脂生成，表现为细胞因子（IL-1β、IL-6、IL-8 和 TNF-α）产生减少、脂滴形成减少以及睑脂生成蛋白（ADFP、ELOVL4 和 SREBP-1）表达下调。LPS 刺激的 HMGEC 中磷酸组蛋白 H2A.X 焦点、溶酶体积累和细胞质裂解的 caspase 3/LC3B-II 染色增加，表明 LPS 诱导的脂生成过程中细胞凋亡和自噬介导的细胞死亡增加。MLT 下调裂解的 caspase 3 水平和 Bax/Bcl-2 比值以减轻细胞凋亡，并改善 Beclin 1 和 LC3B-II 的表达以抑制自噬。MLT 的保护机制包括抑制 MAPK 和 NF-κB 磷酸化。
MLT 减弱了促炎刺激诱导的 HMGEC 中的脂生成、凋亡和自噬，表明 MLT 在 MGD 中具有保护潜力。
