In vitro platform to model the function of ionocytes in the human airway epithelium

BACKGROUND

Pulmonary ionocytes have been identified in the airway epithelium as a small population of ion transporting cells expressing high levels of CFTR (cystic fibrosis transmembrane conductance regulator), the gene mutated in cystic fibrosis. By providing an infinite source of airway epithelial cells (AECs), the use of human induced pluripotent stem cells (hiPSCs) could overcome some challenges of studying ionocytes. However, the production of AEC epithelia containing ionocytes from hiPSCs has proven difficult. Here, we present a platform to produce hiPSC-derived AECs (hiPSC-AECs) including ionocytes and investigate their role in the airway epithelium.

METHODS

hiPSCs were differentiated into lung progenitors, which were expanded as 3D organoids and matured by air-liquid interface culture as polarised hiPSC-AEC epithelia. Using CRISPR/Cas9 technology, we generated a hiPSCs knockout (KO) for FOXI1, a transcription factor that is essential for ionocyte specification. Differences between FOXI1 KO hiPSC-AECs and their wild-type (WT) isogenic controls were investigated by assessing gene and protein expression, epithelial composition, cilia coverage and motility, pH and transepithelial barrier properties.

RESULTS

Mature hiPSC-AEC epithelia contained basal cells, secretory cells, ciliated cells with motile cilia, pulmonary neuroendocrine cells (PNECs) and ionocytes. There was no difference between FOXI1 WT and KO hiPSCs in terms of their capacity to differentiate into airway progenitors. However, FOXI1 KO led to mature hiPSC-AEC epithelia without ionocytes with reduced capacity to produce ciliated cells.

CONCLUSION

Our results suggest that ionocytes could have role beyond transepithelial ion transport by regulating epithelial properties and homeostasis in the airway epithelium.

Simultaneous depletion of RB, RBL1 and RBL2 affects endoderm differentiation of human embryonic stem cells

RB is a well-known cell cycle regulator controlling the G1 checkpoint. Previous reports have suggested that it can influence cell fate decisions not only by regulating cell proliferation and survival but also by interacting with transcription factors and epigenetic modifiers. However, the functional redundancy of RB family proteins (RB, RBL1 and RBL2) renders it difficult to investigate their roles during early development, especially in human. Here, we address this problem by generating human embryonic stem cells lacking RB family proteins. To achieve this goal, we first introduced frameshift mutations in RBL1 and RBL2 genes using the CRISPR/Cas9 technology, and then integrated the shRNA-expression cassette to knockdown RB upon tetracycline treatment. The resulting RBL1/2_dKO+RB_iKD cells remain pluripotent and efficiently differentiate into the primary germ layers in vitro even in the absence of the RB family proteins. In contrast, we observed that subsequent differentiation into foregut endoderm was impaired without the expression of RB, RBL1 and RBL2. Thus, it is suggested that RB proteins are dispensable for the maintenance and acquisition of cell identities during early development, but they are essential to generate advanced derivatives after the formation of primary germ layers. These results also indicate that our RBL1/2_dKO+RB_iKD cell lines are useful to depict the detailed molecular roles of RB family proteins in the maintenance and generation of various cell types accessible from human pluripotent stem cells.

hiPSC hepatocyte model demonstrates the role of unfolded protein response and inflammatory networks in α1-antitrypsin deficiency

BACKGROUND & AIMS

α1-Antitrypsin deficiency (A1ATD) is an autosomal recessive disorder caused by mutations in the SERPINA1 gene. Individuals with the Z variant (Gly342Lys) retain polymerised protein in the endoplasmic reticulum (ER) of their hepatocytes, predisposing them to liver disease. The concomitant lack of circulating A1AT also causes lung emphysema. Greater insight into the mechanisms that link protein misfolding to liver injury will facilitate the design of novel therapies.

METHODS

Human-induced pluripotent stem cell (hiPSC)-derived hepatocytes provide a novel approach to interrogate the molecular mechanisms of A1ATD because of their patient-specific genetic architecture and reflection of human physiology. To that end, we utilised patient-specific hiPSC hepatocyte-like cells (ZZ-HLCs) derived from an A1ATD (ZZ) patient, which faithfully recapitulated key aspects of the disease at the molecular and cellular level. Subsequent functional and "omics" comparisons of these cells with their genetically corrected isogenic-line (RR-HLCs) and primary hepatocytes/human tissue enabled identification of new molecular markers and disease signatures.

RESULTS

Our studies showed that abnormal A1AT polymer processing (immobilised ER components, reduced luminal protein mobility and disrupted ER cisternae) occurred heterogeneously within hepatocyte populations and was associated with disrupted mitochondrial structure, presence of the oncogenic protein AKR1B10 and two upregulated molecular clusters centred on members of inflammatory (IL-18 and Caspase-4) and unfolded protein response (Calnexin and Calreticulin) pathways. These results were validated in a second patient-specific hiPSC line.

CONCLUSIONS

Our data identified novel pathways that potentially link the expression of Z A1AT polymers to liver disease. These findings could help pave the way towards identification of new therapeutic targets for the treatment of A1ATD.

LAY SUMMARY

This study compared the gene expression and protein profiles of healthy liver cells and those affected by the inherited disease α1-antitrypsin deficiency. This approach identified specific factors primarily present in diseased samples which could provide new targets for drug development. This study also demonstrates the interest of using hepatic cells generated from human-induced pluripotent stem cells to model liver disease in vitro for uncovering new mechanisms with clinical relevance.

Macrophage recruitment by fibrocystin-defective biliary epithelial cells promotes portal fibrosis in congenital hepatic fibrosis

Congenital hepatic fibrosis (CHF) is a disease of the biliary epithelium characterized by bile duct changes resembling ductal plate malformations and by progressive peribiliary fibrosis, in the absence of overt necroinflammation. Progressive liver fibrosis leads to portal hypertension and liver failure; however, the mechanisms leading to fibrosis in CHF remain elusive. CHF is caused by mutations in PKHD1, a gene encoding for fibrocystin, a ciliary protein expressed in cholangiocytes. Using a fibrocystin-defective (Pkhd1(del4/del4)) mouse, which is orthologous of CHF, we show that Pkhd1(del4/del4) cholangiocytes are characterized by a β-catenin-dependent secretion of a range of chemokines, including chemokine (C-X-C motif) ligands 1, 10, and 12, which stimulate bone marrow-derived macrophage recruitment. We also show that Pkhd1(del4/del4) cholangiocytes, in turn, respond to proinflammatory cytokines released by macrophages by up-regulating αvβ6 integrin, an activator of latent local transforming growth factor-β1. While the macrophage infiltrate is initially dominated by the M1 phenotype, the profibrogenic M2 phenotype increases with disease progression, along with the number of portal myofibroblasts. Consistent with these findings, clodronate-induced macrophage depletion results in a significant reduction of portal fibrosis and portal hypertension as well as of liver cysts.

CONCLUSION

Fibrosis can be initiated by an epithelial cell dysfunction, leading to low-grade inflammation, macrophage recruitment, and collagen deposition; these findings establish a new paradigm for biliary fibrosis and represent a model to understand the relationship between cell dysfunction, parainflammation, liver fibrosis, and macrophage polarization over time.

Notch signaling and new therapeutic options in liver disease

Notch signaling is a crucial determinant of cell fate decision during development and disease in several organs. Notch effects are strictly dependent on the cellular context in which it is activated. In the liver, Notch signaling is involved in biliary tree development and tubulogenesis. Recent advances have shed light on Notch as a critical player in liver regeneration and repair, as well as in liver metabolism and inflammation and cancer. Notch signaling is finely regulated at several levels. The complexity of the pathway provides several possible targets for development of therapeutic agents able to inhibit Notch. Recent reports have shown that persistent activation of Notch signaling is associated with liver malignancies, particularly hepatocellular with stem cell features and cholangiocarcinoma. These novel findings suggest that interfering with the aberrant activation of the Notch pathway may have therapeutic relevance. However, further studies are needed to clarify the mechanisms regulating physiologic and pathologic Notch activation in the adult liver, to better understand the mechanistic role(s) of Notch in liver diseases and to develop safe and specific therapeutic agents.

Notch signalling beyond liver development: emerging concepts in liver repair and oncogenesis

Notch signalling is an evolutionarily conserved intercellular pathway involved in many aspects of development and tissue renewal in several organs. The importance of Notch signalling in liver development and morphogenesis is well established. However, the post-natal role of Notch in liver repair/regeneration is only now beginning to be unveiled. Despite the simplicity of the pathway activation, a fine spatial-temporal regulation of Notch signalling is required to avoid pathologic effects. This review highlights recent advances in the field indicating that Notch signalling is involved in the reparative morphogenesis of the biliary tree and in liver carcinogenesis. Defective Notch signalling leads to impaired ability of the liver to repair liver damage, while excessive activation may be involved in liver cancer. Even though much remains to be understood about these mechanisms, including the cross-talk between Notch signalling and other liver morphogens, current evidence suggests that the modulation of the Notch pathway may represent a therapeutic target in chronic liver disease.