Molecular Bases of Activated Myofibroblast (MYF) to Lipofibroblast (LIF) Phenotype switching during Fibrosis Resolution.

特发性肺纤维化（IPF）是一种病因不明的间质性肺病。由于其进行性和缺乏有效治疗，IPF与高死亡率有关。本病的显著特征是活化的肌成纤维细胞积聚，过度沉积细胞外基质蛋白，从而损害肺结构和功能，阻碍气体交换。因此，了解活化的肌成纤维细胞的细胞起源和控制纤维化形成和消退的分子机制是迫切的临床需要。在第一个资助期内，使用多个转基因和敲入小鼠系在时间控制的方式下标记肺成纤维细胞的脂肪生成或肌生成群体，并在纤维化形成和分解过程中监测它们。我们发表的数据表明，在纤维化形成过程中，成纤维细胞表型存在脂肪生成到肌生成的转换。我们确定常驻脂肪成纤维细胞是IPF发病机制中肌成纤维细胞池的新贡献者。相反，在纤维化消退期间，在这些小鼠的肺部观察到肌生成到脂肪生成的转换，支持肌成纤维细胞去分化模型。对人肺组织和原代人肺成纤维细胞的功能分析表明，这一机制参与了IPF的发病机制，这表明操纵这一开关可能为IPF患者提供一种新的治疗选择。在这个DFG项目中，我们将使用博来霉素模型诱导年轻和老年小鼠的纤维化形成，使用体内谱系追踪方法和单细胞RNA测序，研究“纤维化病变”中活化的肌成纤维细胞的细胞和转录组学特征，以及它们在正常（年轻小鼠）和受损（老年小鼠）纤维化消退期间的命运。我们的目标是定义在分解过程中激活的MYF的分化轨迹。这些结果将有助于增强IPF的纤维化消退。

Idiopathic pulmonary fibrosis (IPF) is a form of interstitial lung disease with unknown etiology. Due to its progressive nature and lack of effective treatment, IPF is associated with a high mortality rate. The hallmark feature of this disease is the accumulation of activated myofibroblasts that excessively deposit extracellular matrix proteins, thus compromising lung architecture and function, and hindering gas exchange. Therefore, understanding the cellular origin of activated myofibroblasts and the molecular mechanisms governing fibrosis formation and resolution is an urgent clinical need. During the first funding period, multiple transgenic and knock-in mouse lines were used to label lipogenic or myogenic populations of lung fibroblasts in a time-controlled manner, and monitor them during fibrosis formation and resolution. Our published data demonstrate a lipogenic-to-myogenic switch in fibroblast phenotype during fibrosis formation. We identify the resident lipofibroblast as a novel contributor to the myofibroblast pool in the pathogenesis of IPF. Conversely during fibrosis resolution, a myogenic-to-lipogenic switch was observed in the lungs of these mice supporting the myofibroblast dedifferentiation model. Analysis of human lung tissues and functional analysis of primary human lung fibroblasts revealed that this mechanism is involved in the pathogenesis of IPF, suggesting that manipulating this switch might offer a novel therapeutic option for IPF patients. In this DFG project, we will use the bleomycin model to induce fibrosis formation in young and aged mice to investigate, using an in vivo lineage-tracing approach and single cell RNA sequencing, the cellular and transcriptomic characteristics of the activated myofibroblasts in the "fibrotic lesions" and their fate during normal (in young mice) and impaired (in aged mice) fibrosis resolution. Our goal is to define trajectories of differentiation for the activated MYF during the resolution process. These results will be instrumental in enhancing fibrosis resolution in IPF.