Discussion
In recent years, significant progress has been made in the study of PF and its related fibrotic mechanisms. PF is generally caused by multiple pathogenic factors, triggering a wound-healing process that leads to an inflammatory response in macrophages. Subsequently, dysregulated epithelial cells interact with various cells, including mesenchymal cells, immune cells, and endothelial cells, through multiple signaling mechanisms. This process ultimately recruits fibroblasts and activates myofibroblasts, resulting in excessive deposition of collagen-rich ECM and the formation of fibrosis(55). In this review, we focus on the application and research of in vitro models in PF, specifically exploring strategies for uncovering disease pathways, repurposing drugs, and investigating cell-cell interactions.
Throughout our literature review, we found that different cellular models have been used to study the various pathogenic aspects of PF, although there is a lack of strict uniform criteria for selecting cell types in mechanistic studies. Macrophages persist during inflammation and injury, while monocyte-derived macrophages are recruited to aid in repair. Researchers commonly employ macrophages to construct inflammatory models of PF to investigate its pathogenesis in terms of inflammation and immunity. The repair process driven by airway epithelial cells leads to epithelial hyperplasia and the emergence of abnormal basal-like cells around the lungs. Bronchial epithelial cells are commonly used to construct pathological models of lung fibrosis, focusing on the pathogenesis of tracheal, bronchial, and fine bronchial-associated lung fibrosis. Chronic damage to AECs impairs the effective repair of damaged epithelium by AT2 cells. AECs are often employed to construct pathological models of PF, primarily studying the pathogenesis of epithelial-mesenchymal transition (EMT), cellular senescence, endoplasmic reticulum stress, mitochondrial dysfunction, and telomere shortening. Abnormally activated fibroblasts and myofibroblasts contribute to excessive ECM production in the alveolar interstitial space, ultimately leading to PF. Developing in vitro models of fibroblasts is crucial for studying excessive ECM deposition and tissue remodeling in lung fibrosis. Current studies often utilize multiple cell lines for comparison, enhancing the scientific validity and accuracy of experiments compared to using a single cell line.
However, the complex and diverse pathogenesis of PF necessitates new disease models for more intricate mechanism studies. The advent of co-culture systems enables the study of intercellular relationships and cell-environment interactions in vitro. Traditional culture systems consist of single cell types isolated from naturally or complexly growing in vivo environments, resulting in simplified characteristics. However, cells require information exchange and substance metabolism within their survival microenvironment. Intercellular signal transduction plays a vital role in cellular behaviors. Understanding the crosstalk mechanisms between different cell types is significant for investigating the pathogenesis of certain diseases. Thus, comprehending PF should be based on a multi-organ, multi-level, and multi-perspective understanding, rather than solely relying on a single cell type or organ. While the research paradigm traditionally involves studying in vivo models and extrapolating findings to humans, in vitro co-culture models offer a simpler and reproducible system for researching PF, providing a more comprehensive cellular characterization compared to single-cell models.
In conclusion, this article reviews the construction and application of in vitro models for PF and their relevance to mechanistic studies. In the future, optimizing co-culture systems in disease research, particularly in the early stages, will enable better understanding of disease mechanisms and support the development of new therapeutic strategies for PF.