Limbal stem/progenitor cells (LSPCs) play a crucial role in maintaining corneal health by regulating epithelial homeostasis. Although PM2.5 is associated with the occurrence of several corneal diseases, its effects on LSPCs are not clearly understood. In this study, we explored the correlation between PM2.5 exposure and human limbal epithelial thickness measured by Fourier-domain Optical Coherence Tomography in the ophthalmologic clinic. Long- and short-term PM2.5 exposed-rat models were established to investigate the changes in LSPCs and the associated mechanisms. We found that people living in regions with higher PM2.5 concentrations had thinner limbal epithelium, indicating the loss of LSPCs. In rat models, long-term PM2.5 exposure impairs LSPCs renewal and differentiation, manifesting as corneal epithelial defects and thinner epithelium in the cornea and limbus. However, LSPCs were activated in short-term PM2.5-exposed rat models. RNA sequencing implied that the circadian rhythm in LSPCs was perturbed during PM2.5 exposure. The mRNA level of circadian genes including Per1, Per2, Per3, and Rev-erbα was upregulated in both short- and long-term models, suggesting circadian rhythm was involved in the activation and dysregulation of LSPCs at different stages. PM2.5 also disturbed the limbal microenvironment as evidenced by changes in corneal subbasal nerve fiber density, vascular density and permeability, and immune cell infiltration, which further resulted in the circadian mismatches and dysfunction of LSPCs. This study systematically demonstrates that PM2.5 impairs LSPCs and their microenvironment. Moreover, we show that circadian misalignment of LSPCs may be a new mechanism by which PM2.5 induces corneal diseases. Therapeutic options that target circadian rhythm may be viable options for improving LSPC functions and alleviating various PM2.5-associated corneal diseases.

中文翻译：

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长期暴露于 PM2.5 会损害人类和大鼠模型的角膜缘干/祖细胞，从而破坏角膜上皮稳态

角膜缘干/祖细胞（LSPC）通过调节上皮稳态在维持角膜健康中发挥着至关重要的作用。尽管 PM2.5 与多种角膜疾病的发生有关，但其对 LSPC 的影响尚不清楚。在本研究中，我们探讨了眼科诊所中通过傅里叶域光学相干断层扫描测量的 PM2.5 暴露与人体角膜缘上皮厚度之间的相关性。建立长期和短期PM2.5暴露大鼠模型来研究LSPC的变化及其相关机制。我们发现生活在 PM2.5 浓度较高地区的人角膜缘上皮较薄，表明 LSPC 丢失。在大鼠模型中，长期接触 PM2.5 会损害 LSPC 的更新和分化，表现为角膜上皮缺陷以及角膜和角膜缘上皮变薄。然而，LSPC 在短期暴露于 PM2.5 的大鼠模型中被激活。RNA 测序表明 LSPC 的昼夜节律在 PM2.5 暴露期间受到干扰。Per1、Per2、Per3 和 Rev-erbα 等昼夜节律基因的 mRNA 水平在短期和长期模型中均上调，表明昼夜节律参与了 LSPC 在不同阶段的激活和失调。PM2.5还扰乱角膜缘微环境，表现为角膜基底神经纤维密度、血管密度和通透性以及免疫细胞浸润的变化，进一步导致LSPC的昼夜节律不匹配和功能障碍。这项研究系统地证明了 PM2.5 会损害 LSPC 及其微环境。此外，我们发现LSPC的昼夜节律失调可能是PM2.5诱发角膜疾病的新机制。针对昼夜节律的治疗方案可能是改善 LSPC 功能和减轻各种 PM2.5 相关角膜疾病的可行选择。