Assemblies of JAG1 and JAG2 determine tracheobronchial cell fate in mucosecretory lung disease

Mucosecretory lung disease compromises airway epithelial function and is characterized by goblet cell hyperplasia and ciliated cell hypoplasia. Goblet and ciliated cell types are derived from tracheobronchial stem/progenitor cells via a Notch-dependent mechanism. Although specific arrays of Notch receptors regulate cell fate determination, the function of the ligands Jagged1 (JAG1) and JAG2 is unclear. This study examined JAG1 and JAG2 function using human air-liquid-interface cultures that were treated with γ-secretase complex (GSC) inhibitors, neutralizing peptides/antibodies, or WNT/β-catenin pathway antagonists/agonists. These experiments revealed that JAG1 and JAG2 regulated cell fate determination in the tracheobronchial epithelium; however, their roles did not adhere to simple necessity and sufficiency rules. Biochemical studies indicated that JAG1 and JAG2 underwent posttranslational modifications that resulted in generation of a JAG1 C-terminal peptide and regulated the abundance of full-length JAG2 on the cell surface. GSC and glycogen synthase kinase 3 were implicated in these posttranslational events, but WNT agonist/antagonist studies and RNA-Seq indicated a WNT-independent mechanism. Collectively, these data suggest that posttranslational modifications create distinct assemblies of JAG1 and JAG2, which regulate Notch signal strength and determine the fate of tracheobronchial stem/progenitor cells.

Repeated injury promotes tracheobronchial tissue stem cell attrition

Chronic lung disease has been attributed to stem cell aging and/or exhaustion. We investigated these mechanisms using mouse and human tracheobronchial tissue‐specific stem cells (TSC). In mouse, chromatin labeling and flow cytometry demonstrated that naphthalene (NA) injury activated a subset of TSC. These activated TSC continued to proliferate after the epithelium was repaired and a clone study demonstrated that ~96% of activated TSC underwent terminal differentiation. Despite TSC attrition, epithelial repair after a second NA injury was normal. The second injury accelerated proliferation of previously activated TSC and a nucleotide‐label retention study indicated that the second injury recruited TSC that were quiescent during the first injury. These mouse studies indicate that (a) injury causes selective activation of the TSC pool; (b) activated TSC are predisposed to further proliferation; and (c) the activated state leads to terminal differentiation. In human TSC, repeated proliferation also led to terminal differentiation and depleted the TSC pool. A clone study identified long‐ and short‐lived TSC and showed that short‐lived TSC clones had significantly shorter telomeres than their long‐lived counterparts. The TSC pool was significantly depleted in dyskeratosis congenita donors, who harbor mutations in telomere biology genes. The remaining TSC had short telomeres and short lifespans. Collectively, the mouse and human studies support a model in which epithelial injury increases the biological age of the responding TSC. When applied to chronic lung disease, this model suggests that repeated injury accelerates the biological aging process resulting in abnormal repair and disease initiation.

Airway epithelial stem cell chimerism in cystic fibrosis lung transplant recipients

BACKGROUND

The conducting airway epithelium is repaired by tissue specific stem cells (TSC). In response to mild/moderate injury, each TSC repairs a discrete area of the epithelium. In contrast, severe epithelial injury stimulates TSC migration and expands the stem cell's reparative domain. Lung transplantation (LTx) can cause a moderate/severe airway injury and the remodeled airway contains a chimeric mixture of donor and recipient cells. These studies supported the hypothesis, LTx stimulates TSC migration resulting in epithelial chimerism. We tested this hypothesis in cystic fibrosis (CF) LTx patients.

METHODS

Airway mucosal injury was quantified using bronchoscopic imaging and a novel grading system. Bronchial brushing was used to recover TSC from 10 sites in the recipient and allograft airways. TSC chimerism was quantified by short tandem repeat analysis. TSC self-renewal and differentiation potential were assayed using the clone forming cell frequency and air-liquid-interface methods. Electrophysiology was used to determine if TSC chimerism altered epithelial ion channel activity.

RESULTS

LTx caused a mild to moderate airway mucosal injury. Donor and recipient TSC were identified in 91% of anastomotic sites and 93% of bronchial airways. TSC chimerism did not alter stem cell self-renewal or differentiation potential. The frequency of recipient TSC was proportional to CF Transmembrane Conductance Regulator (CFTR)-dependent ion channel activity and 33% of allograft regions were at risk for abnormal CFTR activity.

CONCLUSIONS

LTx in CF patients stimulates bidirectional TSC migration across the anastomoses. TSC chimerism may alter ion homeostasis and compromise the host defense capability of the allograft airway epithelium.

Protein Abundance Determination: An Optimized Western Blot Workflow

We report that the quantitative western blot (qWB) analysis requires a target protein-specific approach, and we provide a workflow that streamlines development of this process. First, the optimal primary antibody dilution is determined. Blots containing 15 μg total protein per lane are probed with the primary antibody at three concentrations and a secondary antibody concentration that is defined by the manufacturer. The lowest primary antibody concentration that detects a discrete band at the correct molecular weight is used in the remaining two steps. Secondly, the optimal protein load is determined. Blots containing 3.75 to 60 μg protein per lane are probed using the antibody concentrations defined in step 1. A target protein band intensity vs. protein load plot is used to determine the linear dynamic range (LDR) for the target protein. The midpoint of the LDR is defined as the optimal protein load. Finally, an appropriate loading control (LC) is identified. We found that the LDR for β-actin, a commonly used LC, exhibited a narrow range, 3.75 to 15 μg. In contrast, the total protein assessed by a Ponceau staining method exhibited a broader LDR, 3.75 to 60 μg. Thus, the total protein is used as a LC. We conclude that the sensitivity and accuracy of the qWB method is dependent on the use of an optimal: 1) primary antibody dilution; 2) total protein load; 3) and LC. Our workflow simplifies the identification of these values.

Electrospun scaffolds limit the regenerative potential of the airway epithelium

Objective

Significant morbidity and mortality are associated with clinical use of synthetic tissue‐engineered tracheal grafts (TETG). Our previous work focused on an electrospun polyethylene terephthalate and polyurethane (PET/PU) TETG that was tested in sheep using a long‐segment tracheal defect model. We reported that graft stenosis and limited epithelialization contributed to graft failure. The present study determined if the epithelialization defect could be attributed to: 1) postsurgical depletion of native airway basal stem/progenitor cells; 2) an inability of the PET/PU‐TETG to support epithelial migration; or 3) compromised basal stem/progenitor cell proliferation within the PET/PU environment.

Study Design

Experimental.

Methods

Basal stem/progenitor cell frequency in sheep that underwent TETG implantation was determined using the clone‐forming cell frequency (CFCF) method. A novel migration model that mimics epithelial migration toward an acellular scaffold was developed and used to compare epithelial migration toward a control polyester scaffold and the PET/PU scaffold. Basal stem/progenitor cell proliferation within the PET/PU scaffold was evaluated using the CFCF assay, doubling‐time analysis, and mitotic cell quantification.

Results

We report that TETG implantation did not decrease basal stem/progenitor cell frequency. In contrast, we find that epithelial migration toward the PET/PU scaffold was significantly less extensive than migration toward a polyester scaffold and that the PET/PU scaffold did not support basal stem/progenitor cell proliferation.

Conclusions

We conclude that epithelialization of a PET/PU scaffold is compromised by poor migration of native tissue‐derived epithelial cells and by a lack of basal stem/progenitor cell proliferation within the scaffold.

Level of Evidence

NA

Maternal high-fat diet alters lung development and function in the offspring

The effects of maternal obesity on lung development have been recognized, and speculation is that these diseases are not simply because of accelerated pulmonary decline with aging but with a failure to achieve optimal lung development during early life. These studies tested the hypothesis that maternal obesity alters signaling pathways during the course of lung development that may affect life-long pulmonary health. Adult female mice were fed 60% fat [high-fat diet (HFD)] or 10% fat [control diet (CD)] for 8 wk before mating and through weaning. Pup lung tissues were collected at postnatal days (PN) 7, 21, and 90 (after receiving HFD or CD as adults). At PN7, body weights from HFD were greater than CD but lung weight-to-body weight ratios were lower. In lung tissues, NFκB-mediated inflammation was greater in HFD pups at PN21 and phospho-/total STAT3, phospho-/total VEGF receptor 2, and total AKT protein levels were lower with maternal HFD and protein tyrosine phosphatase B1 levels were increased. Decreased platelet endothelial cell adhesion molecule levels were observed at PN21 and at PN90 in the pups exposed to maternal HFD. Morphometry indicated that the pups exposed to maternal or adult HFD had fewer alveoli, and the effect was additive. Decreases in pulmonary resistance, elastance, and compliance were observed because of adult HFD diet and decreases in airway resistance and increases in inspiratory capacity because of maternal HFD. In conclusion, maternal HFD disrupts signaling pathways in the early developing lung and may contribute to deficiencies in lung function and increased susceptibility in adults.

Cell Therapy for Cystic Fibrosis Lung Disease: Regenerative Basal Cell Amplification

The human airway epithelium is regenerated by basal cells. Thus, basal cell therapy has the potential to cure cystic fibrosis (CF) lung disease. We previously reported that the human basal cells repopulated the mouse airway epithelium after transplantation, and we estimated that 60 million cells would be needed to treat a human patient. To further develop cell therapy, we compared the proliferation potential of non‐CF and CF tissue‐derived bronchial basal cells. Three methods were used: regenerative cell frequency, burst size, and cell division frequency. Second, we used a serial passage strategy to determine if CF basal cells could be amplified to the estimated therapeutic dose. These studies evaluated that tissue‐derived bronchial basal cells and the basal cells that were recovered by brushing bronchial airways or the nasal respiratory epithelium. Finally, we used the limiting dilution method to isolate non‐CF and CF basal cell clones. The proliferation assays and the air‐liquid‐interface differentiation method were used to determine if cell amplification altered the proliferation and/or differentiation potential of clonal isolates. We demonstrate that: (a) non‐CF and CF basal cell proliferation is similar, (b) CF basal cells can be amplified to a therapeutic cell dose, and (c) amplified non‐CF and CF basal cell clones differentiate normally. Despite these encouraging findings, we also find that the cell amplification process depletes the regenerative basal cell pool. Analysis of basal cell clones indicates that serial passage selects for long‐lived basal cells and raise the possibility that prospective isolation of these stem‐like cells will improve the efficacy of cell replacement therapy. stem cells translational medicine2019;8:225&235

Regulation of Human Airway Epithelial Tissue Stem Cell Differentiation by β-Catenin, P300, and CBP

The wingless/integrase-1 (WNT)/β-catenin signaling pathway is active in several chronic lung diseases including idiopathic pulmonary fibrosis, asthma, and chronic obstructive pulmonary disease. Although this WNT/β-catenin pathway activity is associated with an increase in mucus cell frequency and a decrease in ciliated cell frequency, a cause and consequence relationship between signaling and cell frequency has not been established. We previously demonstrated that genetic stabilization of β-catenin inhibited differentiation of mouse bronchiolar tissue stem cells (TSC). This study determined the effect of β-catenin and its co-factors P300 (E1A-binding protein, 300 kDa) and cAMP response element binding (CREB)-binding protein (CBP) on human bronchial epithelial TSC differentiation to mucus and ciliated cells. We developed a modified air-liquid interface (ALI) culture system in which mucus and ciliated cell frequency is similar. These cultures were treated with the β-catenin agonist CHIR99021 (CHIR) and antagonists to β-catenin (XAV939), P300 (IQ1), and CBP (ICG001). We report that human TSC differentiation to mucus and ciliated cells can be divided into two stages, specification and commitment. CHIR treatment inhibited mucus and ciliated cell commitment while XAV939 treatment demonstrated that β-catenin was necessary for mucus and ciliated cell specification. Additional studies demonstrate that a β-catenin/P300 complex promotes mucus cell specification and that β-catenin interacts with either P300 or CBP to inhibit ciliated cell commitment. These data indicate that activation of β-catenin-dependent signaling in chronic lung disease leads to changes in mucus and ciliated cell frequency and that P300 and CBP tune the β-catenin signal to favor mucus cell differentiation. Stem Cells 2018;36:1905-12.

Airway Progenitor Clone Formation Is Enhanced by Y-27632-Dependent Changes in the Transcriptome

The application of conditional reprogramming culture (CRC) methods to nasal airway epithelial cells would allow more wide-spread incorporation of primary airway epithelial culture models into complex lung disease research. In this study, we adapted the CRC method to nasal airway epithelial cells, investigated the growth advantages afforded by this technique over standard culture methods, and determined the cellular and molecular basis of CRC cell culture effects. We found that the CRC method allowed the production of 7.1 × 10(10) cells after 4 passages, approximately 379 times more cells than were generated by the standard bronchial epithelial growth media (BEGM) method. These nasal airway epithelial cells expressed normal basal cell markers and could be induced to form a mucociliary epithelium. Progenitor cell frequency was significantly higher using the CRC method in comparison to the standard culture method, and progenitor cell maintenance was dependent on addition of the Rho-kinase inhibitor Y-27632. Whole-transcriptome sequencing analysis demonstrated widespread gene expression changes in Y-27632-treated basal cells. We found that Y-27632 treatment altered expression of genes fundamental to the formation of the basal cell cytoskeleton, cell-cell junctions, and cell-extracellular matrix (ECM) interactions. Importantly, we found that Y-27632 treatment up-regulated expression of unique basal cell intermediate filament and desmosomal genes. Conversely, Y-27632 down-regulated multiple families of protease/antiprotease genes involved in ECM remodeling. We conclude that Y-27632 fundamentally alters cell-cell and cell-ECM interactions, which preserves basal progenitor cells and allows greater cell amplification.

Maternal high fat diet exposure is associated with increased hepcidin levels, decreased myelination, and neurobehavioral changes in male offspring

Maternal obesity induces chronic inflammatory responses that impact the fetus/neonate during the perinatal period. Inflammation, iron regulation, and myelination are closely interconnected and disruptions in these processes may have deleterious effects on neurodevelopment. Hepcidin levels are increased in response to inflammation causing subsequent decreases in ferroportin and available iron needed for myelination. Our current studies were designed to test the hypotheses that: 1) maternal high fat diet (HFD) prior to and during pregnancy is sufficient to induce inflammation and alter iron regulation in the brain of the offspring, and 2) HFD exposure is associated with altered myelination and neurobehavioral deficits in the offspring. Our data revealed modest increases in inflammatory cytokines in the serum of dams fed HFD prior to pregnancy compared to dams fed a control diet (CD). Early increases in IL-5 and decreases in IL-10 were observed in serum at PN7 while IL-5 remained elevated at PN21 in the HFD-exposed pups. At PN0, most cytokine levels in whole brain homogenates were higher in the pups born to HFD-fed dams but were not different or were lower than in pups born to CD-fed dams at PN21. Conversely, the inflammation mediated transcription factor Nurr77 remained elevated at PN21. At birth, brain hepcidin, ferroportin, and l-ferritin levels were elevated in pups born to HFD-fed dams compared to pups born to CD-fed dams. Hepcidin levels remained elevated at PN7 and PN21 while ferroportin and l-ferritin levels were lower at PN7 and were not different at PN21. Decreases in myelination in the medial cortex were observed in male but not in female pups born to maternal HFD-fed dams at PN21. These structural changes correlated with changes in behavior (novel object recognition) in at 4months in males only. Our data indicate that maternal obesity (HFD) results in disruption of iron regulation in the brains of the offspring with structural and neurobehavioral deficits in males.

Enhanced Steatosis and Fibrosis in Liver of Adult Offspring Exposed to Maternal High-Fat Diet

Early life exposures can increase the risk of developing chronic diseases including nonalcoholic fatty liver disease. Maternal high-fat diet increases susceptibility to development of steatosis in the offspring. We determined the effect of maternal high-fat diet exposure in utero and during lactation on offspring liver histopathology, particularly fibrosis. Female C57Bl/6J mice were fed a control or high-fat diet (HFD) for 8 weeks and bred with lean males. Nursing dams were continued on the same diet with offspring sacrificed during the perinatal period or maintained on either control or high-fat diet for 12 weeks. Increased hepatocyte proliferation and stellate cell activation were observed in the liver of HFD-exposed pups. Offspring exposed to perinatal high-fat diet and high-fat diet postweaning showed extensive hepatosteatosis compared to offspring on high-fat diet after perinatal control diet. Offspring exposed to perinatal high-fat diet and then placed on control diet for 12 weeks developed steatosis and pericellular fibrosis. Importantly, we found that exposure to perinatal high-fat diet unexpectedly promotes more rapid disease progression of nonalcoholic fatty liver disease, with a sustained fibrotic phenotype, only in adult offspring fed a postweaning control diet.