IL-33-ST2 axis regulates myeloid cell differentiation and activation enabling effective club cell regeneration.

Evidence points to an indispensable function of macrophages in tissue regeneration, yet the underlying molecular mechanisms remain elusive. Here we demonstrate a protective function for the IL-33-ST2 axis in bronchial epithelial repair, and implicate ST2 in myeloid cell differentiation. ST2 deficiency in mice leads to reduced lung myeloid cell infiltration, abnormal alternatively activated macrophage (AAM) function, and impaired epithelial repair post naphthalene-induced injury. Reconstitution of wild type (WT) AAMs to ST2-deficient mice completely restores bronchial re-epithelialization. Central to this mechanism is the direct effect of IL-33-ST2 signaling on monocyte/macrophage differentiation, self-renewal and repairing ability, as evidenced by the downregulation of key pathways regulating myeloid cell cycle, maturation and regenerative function of the epithelial niche in ST2-/- mice. Thus, the IL-33-ST2 axis controls epithelial niche regeneration by activating a large multi-cellular circuit, including monocyte differentiation into competent repairing AAMs, as well as group-2 innate lymphoid cell (ILC2)-mediated AAM activation.

Uroplakin 3a+ Cells Are a Distinctive Population of Epithelial Progenitors that Contribute to Airway Maintenance and Post-injury Repair.

There is evidence that certain club cells (CCs) in the murine airways associated with neuroepithelial bodies (NEBs) and terminal bronchioles are resistant to the xenobiotic naphthalene (Nap) and repopulate the airways after Nap injury. The identity and significance of these progenitors (variant CCs, v-CCs) have remained elusive. A recent screen for CC markers identified rare Uroplakin3a (Upk3a)-expressing cells (U-CCs) with a v-CC-like distribution. Here, we employ lineage analysis in the uninjured and chemically injured lungs to investigate the role of U-CCs as epithelial progenitors. U-CCs proliferate and generate CCs and ciliated cells in uninjured airways long-term and, like v-CCs, after Nap. U-CCs have a higher propensity to generate ciliated cells than non-U-CCs. Although U-CCs do not contribute to alveolar maintenance long-term, they generate alveolar type I and type II cells after Bleomycin (Bleo)-induced alveolar injury. Finally, we report that Upk3a+ cells exist in the NEB microenvironment of the human lung and are aberrantly expanded in conditions associated with neuroendocrine hyperplasias.

Angiotensin receptors as sensitive markers of acute bronchiole injury after lung transplantation.

BACKGROUND: Although lung transplantation is the only means of survival for patients with end-stage pulmonary disease, outcomes from this intervention are inferior to other solid organ transplants. The reason for the poor outcomes may be linked to an early reaction, such as primary graft dysfunction, and associated with marked inflammatory response, bronchiole injury, and later fibrotic responses. Mediators regulating these effects include angiotensin II and matrix metalloproteinases (MMPs). METHODS: We investigated changes to these mediators over the course of cardiopulmonary bypass (CPB) and up to 72 h after lung transplantation, using immunohistochemistry, Western blot, and ELISA techniques. RESULTS: We found 4- and 16-fold increases in plasma angiotensin II and MMP-9, respectively, from pre-CPB to post-CPB. MMP-9 levels remained elevated 1 h after transplantation. MMP-2 levels were elevated 6-24 h after lung transplantation. Type 2 angiotensin II receptor (ATR2) expression was 3.5-fold higher in bronchoalveolar cells 1-6 h after transplantation than in controls. CONCLUSIONS: The study suggests that the combination of cardiopulmonary bypass and lung transplantation is associated with early changes in the angiotensin II receptor system and in MMPs, and that altered expression of these mediators may be a useful marker to examine pathological changes that occur in lungs during transplant surgery.

Late infusion of cloned marrow fibroblasts stimulates endogenous recovery from radiation-induced lung injury.

In the current study, we used a canine model of radiation-induced lung injury to test the effect of a single i.v. infusion of 10×10(6)/kg of marrow fibroblasts on the progression of damage following 15 Gy exposure to the right lung. The fibroblasts, designated DS1 cells, are a cloned population of immortalized cells isolated from a primary culture of marrow stromal cells. DS1 cells were infused at week 5 post-irradiation when lung damage was evident by imaging with high-resolution computed tomography (CT). At 13 weeks post-irradiation we found that 4 out of 5 dogs receiving DS1 cells had significantly improved pulmonary function compared to 0 out of 5 control dogs (p = 0.047, Fisher's Exact). Pulmonary function was measured as the single breath diffusion capacity-hematocrit (DLCO-Hct), the total inspiratory capacity (IC), and the total lung capacity (TLC), which differed significantly between control and DS1-treated dogs; p = 0.002, p = 0.005, and p = 0.004, respectively. The DS1-treated dogs also had less pneumonitis detected by CT imaging and an increased number of TTF-1 (thyroid transcription factor 1, NKX2-1) positive cells in the bronchioli and alveoli compared to control dogs. Endothelial-like progenitor cells (ELC) of host origin, detected by colony assays, were found in peripheral blood after DS1 cell infusion. ELC numbers peaked one day after infusion, and were not detectable by 7 days. These data suggest that infusion of marrow fibroblasts stimulates mobilization of ELC, which is associated with a reduction in otherwise progressive radiation-induced lung injury. We hypothesize that these two observations are related, specifically that circulating ELC contribute to increased angiogenesis, which facilitates endogenous lung repair.

Local small airway epithelial injury induces global smooth muscle contraction and airway constriction.

Small airway epithelial cells form a continuous sheet lining the conducting airways, which serves many functions including a physical barrier to protect the underlying tissue. In asthma, injury to epithelial cells can occur during bronchoconstriction, which may exacerbate airway hyperreactivity. To investigate the role of epithelial cell rupture in airway constriction, laser ablation was used to precisely rupture individual airway epithelial cells of small airways (<300-µm diameter) in rat lung slices (∼250-µm thick). Laser ablation of single epithelial cells using a femtosecond laser reproducibly induced airway contraction to ∼70% of the original cross-sectional area within several seconds, and the contraction lasted for up to 40 s. The airway constriction could be mimicked by mechanical rupture of a single epithelial cell using a sharp glass micropipette but not with a blunt glass pipette. These results suggest that soluble mediators released from the wounded epithelial cell induce global airway contraction. To confirm this hypothesis, the lysate of primary human small airway epithelial cells stimulated a similar airway contraction. Laser ablation of single epithelial cells triggered a single instantaneous Ca(2+) wave in the epithelium, and multiple Ca(2+) waves in smooth muscle cells, which were delayed by several seconds. Removal of extracellular Ca(2+) or decreasing intracellular Ca(2+) both blocked laser-induced airway contraction. We conclude that local epithelial cell rupture induces rapid and global airway constriction through release of soluble mediators and subsequent Ca(2+)-dependent smooth muscle shortening.