Changes in Clara cell 10 kDa protein (CC10)-positive cell distribution in acute lung injury following repeated lipopolysaccharide challenge in the rat

Club Cells-A Guardian against Occupational Hazards

Club cells have a distinct role in the epithelial repair and defense mechanisms of the lung. After exposure to environmental pollutants, during chronic exposure, the secretion of club cells secretory protein (CCSP) decreases. Exposure to occupational hazards certainly has a role in a large number of interstitial lung diseases. According to the American Thoracic Society and the European Respiratory Society, around 40% of the all interstitial lung disease is attributed to occupational hazards. Some of them are very well characterized (pneumoconiosis, hypersensitivity pneumonitis), whereas others are consequences of acute exposure (e.g., paraquat) or persistent exposure (e.g., isocyanate). The category of vapors, gases, dusts, and fumes (VGDF) has been proven to produce subclinical modifications. The inflammation and altered repair process resulting from the exposure to occupational respiratory hazards create vicious loops of cooperation between epithelial cells, mesenchymal cells, innate defense mechanisms, and immune cells. The secretions of club cells modulate the communication between macrophages, epithelial cells, and fibroblasts mitigating the inflammation and/or reducing the fibrotic process. In this review, we describe the mechanisms by which club cells contribute to the development of interstitial lung diseases and the potential role for club cells as biomarkers for occupational-related fibrosis.

Extracellular vesicle-encapsulated CC16 as novel nanotherapeutics for treatment of acute lung injury

Acute lung injury (ALI) is still associated with high mortality. Growing evidence suggests that Club Cell Protein 16 (CC16) plays a protective role against ALI. However, the doses of recombinant CC16 (rCC16) used in preclinical studies are supraphysiological for clinical applications. Extracellular vesicles (EVs) are nanovesicles endogenously generated by mammalian cells. Our study demonstrated that CC16 is released via small EVs and EV-encapsulated CC16 (sEV-CC16) and has anti-inflammatory activities, which protect mice from lipopolysaccharide (LPS) or bacteria-induced ALI. Additionally, sEV-CC16 can activate the DNA damage repair signaling pathways. Consistent with this activity, we observed more severe DNA damage in lungs from Cc16 knockout (KO) than wild-type (WT) mice. Mechanistically, we elucidated that CC16 suppresses nuclear factor κB (NF-κB) signaling activation by binding to heat shock protein 60 (HSP60). We concluded that sEV-CC16 could be a potential therapeutic agent for ALI by inhibiting the inflammatory and DNA damage responses by reducing NF-κB signaling.

Aspirin Attenuates Hyperoxia-Induced Acute Respiratory Distress Syndrome (ARDS) by Suppressing Pulmonary Inflammation via the NF-κB Signaling Pathway

Acute respiratory distress syndrome (ARDS) is a common destructive syndrome with high morbidity and mortality rates. Currently, few effective therapeutic interventions for ARDS are available. Clinical trials have shown that the effectiveness of aspirin is inconsistent. The contribution of platelets to the inflammatory response leading to the development of ARDS is increasingly recognized. The antiplatelet agent aspirin reportedly exerts a protective effect on acid- and hyperoxia-induced lung injury in murine models. Our previous study showed that pretreatment with aspirin exerts protective effects on hyperoxia-induced lung injury in mice. However, the mechanisms and therapeutic efficacy of aspirin in the posttreatment of hyperoxia-induced acute lung injury (ALI) remain unclear. In this study, we used a homozygous NF-κB-luciferase^+/+ transgenic mouse model and treated mice with low-dose (25 μg/g) or high-dose (50 μg/g) aspirin at 0, 24, and 48 h after exposure to hyperoxia (inspired oxygen fraction (FiO₂) > 95%). Hyperoxia-induced lung injury significantly increased the activation of NF-κB in the lung and increased the levels of macrophages infiltrating the lung and reactive oxygen species (ROS), increased the HO-1, NF-κB, TNF-α, IL-1β, and IL-4 protein levels, and reduced the CC10, SPC, eNOS, Nrp-1, and IκBα protein levels in the lung tissue. Pulmonary edema and alveolar infiltration of neutrophils were also observed in the lung tissue of mice exposed to hyperoxia. However, in vivo imaging revealed that posttreatment with aspirin reduced luciferase expression, suggesting that aspirin might reduce NF-κB activation. Posttreatment with aspirin also reduced hyperoxia-induced increases in the numbers of lung macrophages, intracellular ROS levels, and the expression of TNF-α, IL-1β, and IL-4; it also increased CC10, SPC and Nrp-1 levels compared with hyperoxia exposure alone. Lung histopathology also indicated that the aspirin posttreatment significantly reduced neutrophil infiltration and lung edema compared with hyperoxia exposure alone. Aspirin effectively induces an anti-inflammatory response in a model of hyperoxia-induced lung injury. Thus, aspirin may have potential as a novel treatment for hyperoxia-induced ALI.

Inhibition of B cell-dependent lymphoid follicle formation prevents lymphocytic bronchiolitis after lung transplantation

Lung transplantation (LTx) is the only therapeutic option for many patients with chronic lung disease. However, long-term survival after LTx is severely compromised by chronic rejection (chronic lung allograft dysfunction [CLAD]), which affects 50% of recipients after 5 years. The underlying mechanisms for CLAD are poorly understood, largely due to a lack of clinically relevant animal models, but lymphocytic bronchiolitis is an early sign of CLAD. Here, we report that lymphocytic bronchiolitis occurs early in a long-term murine orthotopic LTx model, based on a single mismatch (grafts from HLA-A2:B6-knockin donors transplanted into B6 recipients). Lymphocytic bronchiolitis is followed by formation of B cell-dependent lymphoid follicles that induce adjacent bronchial epithelial cell dysfunction in a spatiotemporal fashion. B cell deficiency using recipient μMT-/- mice prevented intrapulmonary lymphoid follicle formation and lymphocytic bronchiolitis. Importantly, selective inhibition of the follicle-organizing receptor EBI2, using genetic deletion or pharmacologic inhibition, prevented functional and histological deterioration of mismatched lung grafts. In sum, we provided what we believe to be a mouse model of chronic rejection and lymphocytic bronchiolitis after LTx and identified intrapulmonary lymphoid follicle formation as a target for pharmacological intervention of long-term allograft dysfunction after LTx.

Club cell 10-kDa protein attenuates airway mucus hypersecretion and inflammation

Bacterial lipopolysaccharide (LPS) and interleukin (IL)-13 increase mucus secretion and inflammatory cytokine production in normal human bronchial epithelial (NHBE) cells. We evaluated the effect of club cell 10-kDa protein (CC10), an anti-inflammatory protein produced by epithelial cells, on mucus secretion, cell morphology and inflammatory cytokine production.

NHBE cells were cultured at an air–liquid interface with CC10 or vehicle and exposed to LPS on day 14. Mucin MUC5AC, IL-8 and granulocyte-macrophage colony-stimulating factor were measured in cell supernatants. MUC5AC and IL-8 mRNA expression were measured by real-time PCR. Western blotting was used to evaluate nuclear factor (NF)-κB and extracellular signal-regulated kinase (ERK) activation. Cells were evaluated histologically. Additionally, NHBE cells were exposed to IL-13 and CC10 for 14 days, and secretion of the mucins MUC5AC and MUC5B was measured.

MUC5AC secretion stimulated either by LPS or by IL-13 was attenuated by CC10 at 20 ng·mL−1 (p<0.05). CC10 at 20 ng·mL−1 also attenuated IL-8 secretion (p<0.05). MUC5AC and IL-8 mRNA expression were also decreased by CC10 (p<0.05). CC10 attenuated phosphorylation of NF-κB (p<0.05) and ERK1/2 (p<0.05).

CC10 attenuates LPS-induced mucus secretion in airway cells, in part due to inhibition of NF-κB and ERK phosphorylation.

Club cell secretory protein improves survival in a murine obliterative bronchiolitis model

Club cell secretory protein (CCSP) is an indirect phospholipase A2 inhibitor with some immunosuppressive and antiproliferative properties that is expressed in bronchiolar Club cells. In our murine bone marrow transplant (BMT) model of obliterative bronchiolitis (OB), CCSP is diminished; however, its role is unknown. To determine the role of CCSP, B6 wild-type (WT) or CCSP-deficient (CCSP(-/-)) mice were lethally conditioned and given allogeneic bone marrow with a sublethal dose of allogeneic splenic T cells to induce OB. We found that CCSP(-/-) mice demonstrated a higher mortality following BMT-induced OB compared with WT mice. Mice were analyzed 60 days post-BMT for protein expression, pulmonary function, and histology. CCSP levels were reduced in WT mice with BMT-induced OB, and lower levels correlated to decreased lung compliance. CCSP(-/-) had a higher degree of injury and fibrosis as measured by hydroxy proline, along with an increased lung resistance and the inflammatory markers, leukotriene B4 and CXCL1. Replacement with recombinant intravenous CCSP partially reversed the weight loss and improved survival in the CCSP(-/-) mice. In addition, CCSP replacement improved histology and decreased inflammatory cells and markers. These findings indicate that CCSP has a regulatory role in OB and may have potential as a preventive therapy.

Distribution and morphology of Clara cells in common marmosets (Callithrix jacchus)

BACKGROUND

The objective of this investigation was to define the phenotype and spatial distribution of Clara cells within the respiratory tract of common marmosets and to distinguish them from other non-ciliated cells (goblet cells, mixed type secretory cells).

METHODS

Non-ciliated cells were identified immunohistochemically using antibodies against Clara cell secretory protein and mucin 5AC. Transmission electron microscopy and scanning electron microscopy were performed to characterize Clara cells ultrastructurally.

RESULTS

Clara cells were present throughout the tracheobronchial tree, with lowest numbers in the trachea and highest numbers in bronchioles. Goblet cells and mixed type cells were scarce in the upper conducting airways and virtually absent within bronchioles. Ultrastructurally, Clara cells showed typical apical electron-dense granules and a prominent granular endoplasmatic reticulum.

CONCLUSIONS

Clara cells of common marmosets have species-specific morphological characteristics, which suggest grouping the common marmoset phenotypically between primates and rodents.

Claudin-3 and Clara cell 10 kDa protein as early signals of cigarette smoke-induced epithelial injury along alveolar ducts

Smoking-associated chronic obstructive pulmonary disease is characterized by inflammation, changes affecting small airways, and development of emphysema. Various short- and long-term models have been introduced to investigate these processes. The aim of the present study was to identify markers of early epithelial injury/adaptation in a short-term animal model of cigarette smoke exposure. Initially, male BALB/c mice were exposed to smoke from one to five cigarettes and lung changes were assessed 4 and 24 hr after smoking cessation. Subsequently, animals were exposed to smoke from five cigarettes for 2 consecutive days and lungs investigated daily until the seventh postexposure day. Lung homogenates cytokines were determined, bronchioloalveolar fluid cells were counted, and lung tissue was analyzed by immunohistochemistry. Exposure to smoke from a single cigarette induced slight pulmonary neutrophilia. Smoke from two cigarettes additionally induced de novo expression of tight junction protein, claudin-3, by alveolar duct (AD) epithelial cells. Further increases in smoke exposure induced epithelial changes in airway progenitor regions. During the recovery period, the severity/frequency of epithelial reactions slowly decreased, coinciding with the switch from acute to a chronic inflammatory reaction. Claudin-3 and Clara cell 10 kDa protein were identified as possible markers of early tobacco smoke-induced epithelial injury along ADs.

Transdifferentiation of Clara cell 10-kDa protein secreting cells in experimental allergic rhinitis

BACKGROUND

The reasons for the down-regulated Clara cell 10-kDa protein (CC10) expression in allergic rhinitis (AR) are unclear and the airway remodeling in AR has received little attention. This study explores epithelium remodeling and the change of CC10 secreting cells in AR by using a murine model.

METHODS

AR murine models were established by ovalbumin sensitization and challenge. In some mice, dexamethasone was given before each challenge. Histological changes of nasal mucosa were examined by means of hematoxylin and eosin and periodic acid-Schiff staining. CC10 and trefoil factor family (TFF) 1 expression were evaluated by immunohistochemistry.

RESULTS

In AR mice, both in turbinate and in septal mucosa, total cell number and the number of basal cells did not change; however, the number of dome-shaped cells decreased and the number of ciliated and goblet cells increased in turbinate mucosa, and the number of ciliated cells decreased and the number of goblet cells increased in septal mucosa. In turbinate mucosa, the number of CC10(+) cells (mainly dome-shaped cells) decreased whereas the number of TFF1(+) cells (mainly ciliated cells) increased. In septal mucosa, the number of CC10(+) and TFF1(+) cells (mainly ciliated cells) decreased simultaneously. Intermediate phenotypic goblet cells could express CC10 and TFF1. CC10 and TFF1 could be localized in the same cells. Dexamethasone reversed the changes of epithelium significantly.

CONCLUSION

Allergen exposure leads to a possible transdifferentiation of CC10 secreting cells into TFF1 secreting cells and/or goblet cells in upper airways. Nasal turbinate and septal epithelium display different patterns of transdifferentiation.

FGF2 specifies hESC-derived definitive endoderm into foregut/midgut cell lineages in a concentration-dependent manner

Fibroblast growth factor (FGF) signaling controls axis formation during endoderm development. Studies in lower vertebrates have demonstrated that FGF2 primarily patterns the ventral foregut endoderm into liver and lung, whereas FGF4 exhibits broad anterior-posterior and left-right patterning activities. Furthermore, an inductive role of FGF2 during dorsal pancreas formation has been shown. However, whether FGF2 plays a similar role during human endoderm development remains unknown. Here, we show that FGF2 specifies hESC-derived definitive endoderm (DE) into different foregut lineages in a dosage-dependent manner. Specifically, increasing concentrations of FGF2 inhibits hepatocyte differentiation, whereas intermediate concentration of FGF2 promotes differentiation toward a pancreatic cell fate. At high FGF2 levels specification of midgut endoderm into small intestinal progenitors is increased at the expense of PDX1(+) pancreatic progenitors. High FGF2 concentrations also promote differentiation toward an anterior foregut pulmonary cell fate. Finally, by dissecting the FGF receptor intracellular pathway that regulates pancreas specification, we demonstrate for the first time to the best of our knowledge that induction of PDX1(+) pancreatic progenitors relies on FGF2-mediated activation of the MAPK signaling pathway. Altogether, these observations suggest a broader gut endodermal patterning activity of FGF2 that corresponds to what has previously been advocated for FGF4, implying a functional switch from FGF4 to FGF2 during evolution. Thus, our results provide new knowledge of how cell fate specification of human DE is controlled-facts that will be of great value for future regenerative cell therapies.

Characterisation of the proximal airway squamous metaplasia induced by chronic tobacco smoke exposure in spontaneously hypertensive rats

Background

Continuous exposure to tobacco smoke (TS) is a key cause of chronic obstructive pulmonary disease (COPD), a complex multifactorial disease that is difficult to model in rodents. The spontaneously hypertensive (SH) rat exhibits several COPD-associated co-morbidities such as hypertension and increased coagulation. We have investigated whether SH rats are a more appropriate animal paradigm of COPD.

Methods

SH rats were exposed to TS for 6 hours/day, 3 days/week for 14 weeks, and the lung tissues examined by immunohistochemistry.

Results

TS induced a CK13-positive squamous metaplasia in proximal airways, which also stained for Ki67 and p63. We hypothesise that this lesion arises by basal cell proliferation, which differentiates to a squamous cell phenotype. Differences in staining profiles for the functional markers CC10 and surfactant D, but not phospho-p38, indicated loss of ability to function appropriately as secretory cells. Within the parenchyma, there were also differences in the staining profiles for CC10 and surfactant D, indicating a possible attempt to compensate for losses in proximal airways. In human COPD sections, areas of CK13-positive squamous metaplasia showed sporadic p63 staining, suggesting that unlike the rat, this is not a basal cell-driven lesion.

Conclusion

This study demonstrates that although proximal airway metaplasia in rat and human are both CK13+ and therefore squamous, they potentially arise by different mechanisms.