Advanced lung organoids for respiratory system and pulmonary disease modeling

Abstract

Amidst the recent coronavirus disease 2019 (COVID-19) pandemic, respiratory system research has made remarkable progress, particularly focusing on infectious diseases. Lung organoid, a miniaturized structure recapitulating lung tissue, has gained global attention because of its advantages over other conventional models such as two-dimensional (2D) cell models and animal models. Nevertheless, lung organoids still face limitations concerning heterogeneity, complexity, and maturity compared to the native lung tissue. To address these limitations, researchers have employed co-culture methods with various cell types including endothelial cells, mesenchymal cells, and immune cells, and incorporated bioengineering platforms such as air-liquid interfaces, microfluidic chips, and functional hydrogels. These advancements have facilitated applications of lung organoids to studies of pulmonary diseases, providing insights into disease mechanisms and potential treatments. This review introduces recent progress in the production methods of lung organoids, strategies for improving maturity, functionality, and complexity of organoids, and their application in disease modeling, including respiratory infection and pulmonary fibrosis.

Keywords: Lung organoid; bioengineeing platform; cellular niches; pulmonary fibrosis; respiratory infection.

Figure 1.

Development of lung organoids simulating the cellular components of the human respiratory system. Various epithelial cells known to exist in human conducting airway and alveoli are illustrated. Progenitor cells and adult stem cells within lung tissue can be used to generate airway organoid (bronchosphere), bronchioalveolar organoid, and alveolar organoid (alveolosphere). Pluripotent stem cells can differentiate into lung organoids containing mesenchymal cells through the stages of definitive endoderm and anterior foregut endoderm.

Figure 2.

The engineering platforms and cellular niches for culturing lung organoids to model the pulmonary infection and fibrosis. The organoid culture platforms, such as air-liquid interface (ALI), hydrogel, and microfluidic chip, have been employed in a combination with various niche cells like endothelial cells, mesenchymal cells, and immune cells. These engineered lung organoid models can be used for studying pulmonary infection and fibrosis.

Figure 3.

Lung organoid culture platforms based on air-liquid interface (ALI): (a) lung organoids cultured on permeable inserts exposed to air exhibited cystic and branched morphologies with lung epithelial markers (CC-10, EpCAM, and RT2-70). The images are reproduced from Laube et al. with a permission from publisher, (b) alveolar organoids cultured on ALI using artificial basement membrane showed high expression of alveolar cell specific proteins and tight junction. The images are reproduced from He et al. with a permission from publisher, and (c) the bronchioalveolar ALI system, established by seeding fetal lung bud tip organoids onto a transwell membrane and co-culturing mesenchymal cells on the bottom side of a well plate. This system increased the susceptibility to SARS-CoV-2 infection in AEC2 due to higher expression of the TMPRSS2, a pivotal factor in SARS-CoV-2 infection. The images are reproduced from Lamers et al. with a permission from publisher.

Figure 4.

Lung organoid culture platforms based on microfluidic devices: (a) establishment of 3D lung-on-a-chip model with alveoli-like curved microwell structure and lung epithelial cell monolayer. The microwell retained a complete lining of the epithelial layer, and the expression of epithelial marker (CK8) and AEC2 marker (pro-SPC) was observed across the entire culture area. The images are reproduced from Baptista et al. with a permission from publisher, (b) multi-organ-on-a-chip platform to recapitulate multi-tissue interactions among lung, heart, and liver organoids. The images are reproduced from Skardal et al. with a permission from publisher, and (c) microfluidic devices with 3D lung cancer organoids used for testing the sensitivity of anti-cancer drugs. Cleaved caspase 3-positive cells were detected in lung cancer organoids treated for 48 h with anti-cancer drugs (cisplatin and etoposide), indicating apoptosis of cancer cells in a concentration-dependent manner. The images are reproduced from Jung et al. with a permission from publisher.

Figure 5.

Lung organoid culture platforms based on functional hydrogels: (a) PEG-4MAL hydrogel functionalized with RGD exhibited not only the enhanced cytocompatibility, but also the potential to support lung organoids comparable to Matrigel, as evidenced by the organized expression of lung epithelium (E-cadherin) and lung-specific markers (NKX2-1 and P63). The images are reproduced from Cruz-Acuna et al. with a permission from publisher, (b) decellularized human lung alveolar-enriched ECM hydrogel for culturing human AEC2-derived alveolospheres. This ECM hydrogel enhanced AEC2 proliferation and upregulated expression of AEC2-derived transitional cell state genetic markers. The images are reproduced from Hoffman et al. with a permission from publisher, and (c) the expansion and growth of lung organoids in decellularized bovine lung-derived dECM hydrogel. Lung dECM hydrogels were prepared with different decellularization methods, including freeze-thaw cycles or Triton-X-100 treatment, and compared by evaluating the morphology and viability of lung organoids. The images are reproduced from Kusoglu et al. with a permission from publisher.

Figure 6.

Engineering strategies using advancing organoid platforms: (a) direct organoid assembly and simultaneous development of different types of organoids to study interactions between different tissues and boost the structural and functional maturation of lung organoids and (b) fabrication of large-scale lung organoid structures with enhanced complexity and functionality using 3D bioprinting in conjunction with hydrogel.