Jonathan L. McQualter

Serum amyloid A opposes lipoxin A4 to mediate glucocorticoid refractory lung inflammation in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) will soon be the third most common cause of death globally. Despite smoking cessation, neutrophilic mucosal inflammation persistently damages the airways and fails to protect from recurrent infections. This maladaptive and excess inflammation is also refractory to glucocorticosteroids (GC). Here, we identify serum amyloid A (SAA) as a candidate mediator of GC refractory inflammation in COPD. Extrahepatic SAA was detected locally in COPD bronchoalveolar lavage fluid, which correlated with IL-8 and neutrophil elastase, consistent with neutrophil recruitment and activation. Immunohistochemistry detected SAA was in close proximity to airway epithelium, and in vitro SAA triggered release of IL-8 and other proinflammatory mediators by airway epithelial cells in an ALX/FPR2 (formyl peptide receptor 2) receptor-dependent manner. Lipoxin A4 (LXA4) can also interact with ALX/FPR2 receptors and lead to allosteric inhibition of SAA-initiated epithelial responses (pA2 13 nM). During acute exacerbation, peripheral blood SAA levels increased dramatically and were disproportionately increased relative to LXA4. Human lung macrophages (CD68+) colocalized with SAA and GCs markedly increased SAA in vitro (THP-1, pEC50 43 nM). To determine its direct actions, SAA was administered into murine lung, leading to induction of CXC chemokine ligand 1/2 and a neutrophilic response that was inhibited by 15-epi-LXA4 but not dexamethasone. Taken together, these findings identify SAA as a therapeutic target for inhibition and implicate SAA as a mediator of GC-resistant lung inflammation that can overwhelm organ protective signaling by lipoxins at ALX/FPR2 receptors.

Functional Analysis of Two Distinct Bronchiolar Progenitors during Lung Injury and Repair

Air spaces of the mammalian lung are lined by a specialized epithelium that is maintained by endogenous progenitor cells. Within bronchioles, the abundance and distribution of progenitor cells that contribute to epithelial homeostasis change as a function of maintenance versus repair. It is unclear whether functionally distinct progenitor pools or a single progenitor cell type maintain the epithelium and how the behavior is regulated in normal or disease states. To address these questions, we applied fractionation methods for the enrichment of distal airway progenitors. We show that bronchiolar progenitor cells can be subdivided into two functionally distinct populations that differ in their susceptibility to injury and contribution to repair. The proliferative capacity of these progenitors is confirmed in a novel in vitro assay. We show that both populations give rise to colonies with a similar dependence on stromal cell interactions and regulation by TGF-β. These findings provide additional insights into mechanisms of epithelial remodeling in the setting of chronic lung disease and offer hope that pharmacologic interventions may be developed to mitigate tissue remodeling.

TGF-β signaling in stromal cells acts upstream of FGF-10 to regulate epithelial stem cell growth in the adult lung

Tissue resident mesenchymal stromal cells (MSCs) contribute to tissue regeneration through various mechanisms, including the secretion of trophic factors that act directly on epithelial stem cells to promote epithelialization. However, MSCs in tissues constitute a heterogeneous population of stromal cells and different subtypes may have different functions. In this study we show that CD166(neg) and CD166(pos) lung stromal cells have different proliferative and differentiative potential. CD166(neg) lung stromal cells exhibit high proliferative potential with the capacity to differentiate along the lipofibroblastic and myofibroblastic lineages, whereas CD166(pos) lung stromal cells have limited proliferative potential and are committed to the myofibroblastic lineage. Moreover, we show that CD166(pos) lung stromal cells do not share the same epithelial-supportive capacity as their CD166(neg) counterparts, which support the growth of lung epithelial stem cell (EpiSPC) colonies in vitro. In addition, ex vivo expansion of lung stromal cells also resulted in the loss of epithelial-supportive capacity, which could be reinstated by inhibition of the TGF-β signaling pathway. We show that epithelial-supportive capacity correlated with the level of FGF-10 expression and the reactivation of several lung development-associated genes. In summary, these studies suggest that TGF-β signaling in stromal cells acts upstream of FGF-10 to regulate epithelial stem cell growth in the adult lung.

Concise Review: Deconstructing the Lung to Reveal Its Regenerative Potential

Despite burgeoning interest in the potential of cellular therapies in lung regenerative medicine, progress in delivering these therapies has been confounded by a lack of knowledge about the identity of appropriate targets which can be harnessed to repair the lung, and the cellular and molecular factors which regulate their regenerative potential. While systematic analysis of lung development and cell lineage tracing studies in normal and perturbed animal models provides a framework for understanding the complex interplay of the multiple cell types, biomatrix elements and soluble and insoluble cytokines and factors that regulate lung structure and function, a reductionist approach is also required to analyze the organization of regenerative cells in the adult lung and identify the factors and molecular pathways which regulate their capacity to generate descendent lineages. In this review we describe recent progress in identifying and characterizing endogenous epithelial, mesenchymal and endothelial stem/progenitor cells in the adult lung using multiparameter cell separative strategies and functional in vitro clonogenic assays. STEM CELLS 2012;30:811–816

COPD and squamous cell lung cancer: aberrant inflammation and immunity is the common link.

Cigarette smoking has reached epidemic proportions within many regions of the world and remains the highest risk factor for chronic obstructive pulmonary disease (COPD) and lung cancer. Squamous cell lung cancer is commonly detected in heavy smokers, where the risk of developing lung cancer is not solely defined by tobacco consumption. Although therapies that target common driver mutations in adenocarcinomas are showing some promise, they are proving ineffective in smoking‐related squamous cell lung cancer. Since COPD is characterized by an excessive inflammatory and oxidative stress response, this review details how aberrant innate, adaptive and systemic inflammatory processes can contribute to lung cancer susceptibility in COPD. Activated leukocytes release increasing levels of proteases and free radicals as COPD progresses and tertiary lymphoid aggregates accumulate with increasing severity. Reactive oxygen species promote formation of reactive carbonyls that are not only tumourigenic through initiating DNA damage, but can directly alter the function of regulatory proteins involved in host immunity and tumour suppressor functions. Systemic inflammation is also markedly increased during infective exacerbations in COPD and the interplay between tumour‐promoting serum amyloid A (SAA) and IL‐17A is discussed. SAA is also an endogenous allosteric modifier of FPR2 expressed on immune and epithelial cells, and the therapeutic potential of targeting this receptor is proposed as a novel strategy for COPD–lung cancer overlap.

SAA drives proinflammatory heterotypic macrophage differentiation in the lung via CSF-1R-dependent signaling

Serum amyloid A (SAA) is expressed locally in chronic inflammatory conditions such as chronic obstructive pulmonary disease (COPD), where macrophages that do not accord with the classic M1/M2 paradigm also accumulate. In this study, the role of SAA in regulating macrophage differentiation was investigated in vitro using human blood monocytes from healthy subjects and patients with COPD and in vivo using an airway SAA challenge model in BALB/c mice. Differentiation of human monocytes with SAA stimulated the proinflammatory monokines IL‐6 and IL‐1β concurrently with the M2 markers CD163 and IL‐10. Furthermore, SAA‐differentiated macrophages stimulated with lipopolysaccharide (LPS) expressed markedly higher levels of IL‐6 and IL1‐β. The ALX/FPR2 antagonist WRW4 reduced IL‐6 and IL‐1β expression but did not significantly inhibit phagocytic and efferocytic activity. In vivo, SAA administration induced the development of a CD11chighCD11bhigh macrophage population that generated higher levels of IL6, IL‐1β, and G‐CSF following ex vivo LPS challenge. Blocking CSF‐1R signaling effectively reduced the number of CD11chigh CD11bhigh macrophages by 71% and also markedly inhibited neutrophilic inflammation by 80%. In conclusion, our findings suggest that SAA can promote a distinct CD11chigh CD11bhigh macrophage phenotype, and targeting this population may provide a novel approach to treating chronic inflammatory conditions associated with persistent SAA expression.—Anthony, D., McQualter, J. L., Bishara, M., Lim, E. X., Yatmaz, S., Seow, H. J., Hansen, M., Thompson, M., Hamilton, J. A., Irving, L. B., Levy, B. D., Vlahos, R., Anderson, G. P., Bozinovski, S. SAA drives proinflammatory heterotypic macrophage differentiation in the lung via CSF‐1R‐dependent signaling. FASEB J. 28, 3867‐3877 (2014). www.fasebj.org

Innate cellular sources of interleukin-17A regulate macrophage accumulation in cigarette- smoke-induced lung inflammation in mice.

The present study has identified IL-17A as an alternative target to combat macrophage accumulation in cigarette smoke (CS)-related lung conditions and suggests that alternative innate cellular sources should be considered when developing strategies to combat excessive IL-17A signalling in chronic lung conditions.

Lung stem cells: Do they exist?

Recognition of the potential of stem cell‐based therapies for alleviating intractable lung diseases has provided the impetus for research aimed at identifying regenerative cells in the adult lung, understanding how they are organized and regulated, and how they could be harnessed in lung regenerative medicine. In this review, we describe the attributes of adult stem and progenitor cells in adult organs and how they are regulated by the permissive or restrictive microenvironment in which they reside. We describe the power and limitations of experimental models, cell separative strategies and functional assays used to model the organization and regulation of adult airway and alveolar stem cells in the adult lung. The review summarizes recent progress and obstacles in defining endogenous lung epithelial stem and progenitor cells in mouse models and in translational studies.

Rare SOX2+ Airway Progenitor Cells Generate KRT5+ Cells that Repopulate Damaged Alveolar Parenchyma following Influenza Virus Infection

Summary Recent studies have implicated keratin 5 (KRT5)+ cells in repopulation of damaged lung tissue following severe H1N1 influenza virus infection. However, the origins of the cells repopulating the injured alveolar region remain controversial. We sought to determine the cellular dynamics of lung repair following influenza infection and define whether nascent KRT5+ cells repopulating alveolar epithelium were derived from pre-existing alveolar or airway progenitor cells. We found that the wound-healing response begins with proliferation of SOX2+ SCGB1A1− KRT5− progenitor cells in airways. These cells generate nascent KRT5+ cells as an early response to airway injury and yield progeny that colonize damaged alveolar parenchyma. Moreover, we show that local alveolar progenitors do not contribute to nascent KRT5+ cells after injury. Repopulation of injured airway and alveolar regions leads to proximalization of distal airways by pseudostratified epithelium and of alveoli by airway-derived epithelial cells that lack the normal characteristics of mature airway or alveolar epithelium.

Isolation and Clonal Assay of Adult Lung Epithelial Stem/Progenitor Cells

Adult mouse lung epithelial stem/progenitor cells (EpiSPC) can be defined in vitro as epithelial colony-forming units that are capable of self-renewal, and which when co-cultured with lung mesenchymal stromal cells (MSC) are able to give rise to differentiated progeny comprising mature lung epithelial cells. This unit describes a protocol for the prospective isolation and in vitro propagation and differentiation of adult mouse lung EpiSPC. The strategy used for selection of EpiSPC and MSC from adult mouse lung by enzymatic digestion and flow cytometry is based on the differential expression of CD45, CD31, Sca-1, EpCAM, and CD24. The culture conditions required for the differentiation (co-culture with MSC) and expansion (stromal-free culture with FGF-10 and HGF) of EpiSPC are described.