HMGB1异常调控肺干细胞增殖分化在IPF发病中的作用及机制研究

The central mechanism of idiopathic pulmonary fibrosis (IPF) is deficiencies in regeneration of normal alveolar structure and aberrant lung repair with fibroblast activation. Lung stem cell has been proved to play a crucial role in the regeneration of lung after injury. However, the function and mechanisms of lung stem cell involved in the pathogenesis of IPF are still unclear. Our group have recently reported that there was a dramatic reduction of epithelial progenitor cells and a relative increase of the mesenchymal progenitor cells in IPF patients. In addition, we found high mobility group box 1(HMGB1) was a causal link between lung injury and abnormal repair in the pathogenesis of IPF,and the niches caused by HMGB1 could be a key issue of IPF. Based on these findings, we hypothesis that HMGB1,released by damaged lung, binds to related receptors,then activates downstream signaling pathway(ERK1/2, AKT、STAT3, Wnt), eventually drives c-kit+ lung stem cell away from terminal differentiation conducive to local alveolar tissue regeneration, towards effector fibroblast/myofibroblast development. These strategies based on investigation of the altered differentiation and role of lung stem cell in IPF may hold promise for illustrating the mechanism and developing novel treatment approaches for pulmonary fibrosis.

特发性肺纤维化（IPF）发病机制的核心问题是损伤的功能性肺上皮细胞的再生障碍以及异常的纤维化修复。业已证实，肺干细胞在损伤后肺的再生修复中发挥了关键作用，然而这群肺干细胞在IPF发病中的作用及机制尚不清楚。我们前期研究发现IPF病人的肺上皮前体细胞大量减少，间质前体细胞相对增多，而进一步发现HMGB1是链接纤维化过程中炎症损伤-异常修复的关键桥梁分子,其介导的异常免疫微环境是IPF发病的核心事件。基于此我们提出假说：IPF发病过程中，肺损伤介导HMGB1的释放，通过与相应受体结合，活化了下游ERK1/2、AKT、STAT3、Wnt信号，进而导致c-kit+肺干细胞无法向正常终末肺泡结构分化，转而向效应成纤维细胞或肌纤维母细胞的异常分化。这可能是IPF发病的关键机制。深入探讨IPF过程中肺干细胞的异常分化及机理，有望为阐明肺纤维化的发生机制，开发有效治疗策略提供新思路。

特发性肺纤维化（IPF）是一种慢性、进行性、高致死性的间质性肺疾病，其发病的核心问题是损伤的功能性肺上皮细胞的再生障碍以及异常的纤维化修复。业已证实，肺干细胞在损伤后肺的再生修复中发挥了关键作用，然而这群肺干细胞在IPF发病中的作用及机制尚不清楚。我们前期研究发现IPF病人的肺上皮前体细胞大量减少，间质前体细胞相对增多，而进一步发现高迁移率族蛋白B-1（HMGB1）是链接纤维化过程中炎症损伤-异常修复的关键桥梁分子,其介导的异常免疫微环境是IPF发病的核心事件。本研究中，我们利用磁珠分选法，成功分离培养了人肺c-kit+细胞，该群细胞呈梭形，高表达干细胞相关基因SOX2、SEEA3、OCT4；同时，在特定的诱导条件下，可分化为表达TTF1、pro-SPC、PECAM-1、α-SMA的子代细胞。接着利用博莱霉素诱导的肺纤维化小鼠模型发现，尽管c-kit+在博莱霉素诱导的肺纤维化小鼠肺组织中表达并无明显改变，但c-kit+α-SMA+细胞明显增多；利用构建的c-kit-EGFP-SV40pA BAC小鼠模型发现，c-kit+细胞在体内并不能向pro-SPC+及CC-10+的肺上皮细胞分化，但可向PECAM-1+的内皮细胞及α-SMA+的间质细胞分化。 进一步发现，HMGB1在肺纤维化小鼠肺组织及IPF患者肺组织中的表达明显升高；利用已成功构建的HMGB1-shRNA小鼠，给予博莱霉素（bleomycin）诱导发现该组小鼠肺纤维化的病变明显减轻，死亡率明显降低。HMGB1-shRNA-c-kit-EGFP双转基因小鼠，给予bleomycin后，小鼠肺纤维化的病变较c-kit-EGFP小鼠组明显减轻，死亡率降低，c-kit+α-SMA+的细胞明显减少，体外实验也证实，HMGB1可活化STAT3、Wnt/β-catenin信号，诱导c-kit+表达α-SMA和Febronectin等间质标志物，进而参与肺纤维化的发生发展。本研究提示，IPF发病过程中异常释放的HMGB1，可导致c-kit+肺干细胞效应成纤维细胞或肌纤维母细胞的异常分化，这可能是IPF发病的核心机制，有望为开发IPF治疗策略提供新思路。