Epithelial regeneration is modulated by chitin and chitinase activity

Epithelial injury underlies fibrotic and inflammatory lung diseases during which regenerative responses become dysregulated or recurrently engaged. Although environmental exposures are risk factors for severe lung disease, specific drivers of persistent epithelial and immune dysfunction are poorly understood. Here we identify a feedback circuit triggered by chitin, a common component of airborne particulate matter, that impacts lung health and regeneration after epithelial injury. In mice, damage to epithelial cells results in loss of homeostatic lung chitinase activity and accumulation of environmental chitin substrates; these disturbances impair epithelial renewal and drive activation of group 2 innate lymphoid cells (ILC2s). ILC2s, in turn, restore chitinase activity by inducing acidic mammalian chitinase (AMCase) in regenerating epithelial cells, thereby promoting chitin degradation, epithelial differentiation, and inflammatory resolution. Mice lacking AMCase or ILC2s fail to clear airway chitin and exhibit exacerbated inflammation, impaired epithelial regeneration, and increased mortality following epithelial injury. These effects are ameliorated by chitinase replacement therapy or AMCase overexpression, demonstrating that chitin degradation is crucial for restoring lung homeostasis after perturbation. The ILC2-chitinase response circuit thus comprises a tissue adaptation to a widespread environmental constituent and may be a target for alleviating persistent post-injury lung epithelial and immune dysfunction. Overall design: To investigatae whether chitin treatment in WT and AMCase deficient epithelial cells alters differentiation proliferation program, mice were intransally challenged with chitin particles prior to sacrifice after 12 hours for isolation and analysis of mature lung or progenitor-like epithelial cells through RNA sequencing.

上皮损伤是纤维化与炎症性肺部疾病的核心病理基础，此类疾病中再生应答会出现失调或反复激活。尽管环境暴露是重症肺部疾病的危险因素，但目前对持续性上皮与免疫功能异常的具体驱动机制仍知之甚少。本研究鉴定出一条由几丁质（chitin）——空气颗粒物的常见组分——触发的反馈环路，该环路可影响上皮损伤后的肺部健康与再生过程。
在小鼠模型中，上皮细胞损伤会导致稳态肺几丁质酶活性丧失，并伴随环境几丁质底物蓄积；这些异常会削弱上皮更新能力，并驱动2型天然淋巴细胞（group 2 innate lymphoid cells，ILC2s）活化。反过来，2型天然淋巴细胞可通过在再生上皮细胞中诱导酸性哺乳动物几丁质酶（acidic mammalian chitinase，AMCase）的表达，恢复几丁质酶活性，从而促进几丁质降解、上皮分化与炎症消退。
缺失酸性哺乳动物几丁质酶或2型天然淋巴细胞的小鼠无法清除气道内的几丁质，会出现炎症加重、上皮再生受损以及上皮损伤后死亡率升高的表型。通过几丁质酶替代疗法或酸性哺乳动物几丁质酶过表达可缓解上述异常，这表明几丁质降解对于扰动后的肺部稳态恢复至关重要。
综上，2型天然淋巴细胞-几丁质酶应答环路代表了机体对一类广泛存在的环境组分的组织适应性调节机制，或可作为缓解损伤后持续性肺部上皮与免疫功能异常的潜在靶点。
实验整体设计：为探究几丁质处理对野生型（Wild Type，WT）与酸性哺乳动物几丁质酶缺陷型上皮细胞的分化与增殖程序是否存在影响，研究人员先向小鼠鼻腔内滴注几丁质颗粒，于12小时后处死小鼠，分离成熟肺上皮细胞或祖细胞样上皮细胞，并通过RNA测序开展相关分析。