Elevated gelatinase activity in pulmonary alveolar proteinosis: role of macrophage-colony stimulating factor

Donor-defined mesenchymal stem cell antimicrobial potency against nontuberculous mycobacterium

Chronic nontuberculous mycobacterial infections with Mycobacterium avium and Mycobacterium intracellulare complicate bronchiectasis, chronic obstructive airway disease, and the health of aging individuals. These insidious intracellular pathogens cause considerable morbidity and eventual mortality in individuals colonized with these bacteria. Current treatment regimens with antibiotic macrolides are both toxic and often inefficient at providing infection resolution. In this article, we demonstrate that human marrow‐derived mesenchymal stem cells are antimicrobial and anti‐inflammatory in vitro and in the context of an in vivo sustained infection of either M. avium and/or M. intracellulare.

Alveolar macrophages of GM-CSF knockout mice exhibit mixed M1 and M2 phenotypes

Background

Activin A is a pleiotrophic regulatory cytokine, the ablation of which is neonatal lethal. Healthy human alveolar macrophages (AMs) constitutively express activin A, but AMs of patients with pulmonary alveolar proteinosis (PAP) are deficient in activin A. PAP is an autoimmune lung disease characterized by neutralizing autoantibodies to Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF). Activin A can be stimulated, however, by GM-CSF treatment of AMs in vitro. To further explore pulmonary activin A regulation, we examined AMs in bronchoalveolar lavage (BAL) from wild-type C57BL/6 compared to GM-CSF knockout mice which exhibit a PAP-like histopathology. Both human PAP and mouse GM-CSF knockout AMs are deficient in the transcription factor, peroxisome proliferator activated receptor gamma (PPARγ).

Results

In sharp contrast to human PAP, activin A mRNA was elevated in mouse GM-CSF knockout AMs, and activin A protein was increased in BAL fluid. Investigation of potential causative factors for activin A upregulation revealed intrinsic overexpression of IFNγ, a potent inducer of the M1 macrophage phenotype, in GM-CSF knockout BAL cells. IFNγ mRNA was not elevated in PAP BAL cells. In vitro studies confirmed that IFNγ stimulated activin A in wild-type AMs while antibody to IFNγ reduced activin A in GM-CSF knockout AMs. Both IFNγ and Activin A were also reduced in GM-CSF knockout mice in vivo after intratracheal instillation of lentivirus-PPARγ compared to control lentivirus vector. Examination of other M1 markers in GM-CSF knockout mice indicated intrinsic elevation of the IFNγ-regulated gene, inducible Nitrogen Oxide Synthetase (iNOS), CCL5, and interleukin (IL)-6 compared to wild-type. The M2 markers, IL-10 and CCL2 were also intrinsically elevated.

Conclusions

Data point to IFNγ as the primary upregulator of activin A in GM-CSF knockout mice which in addition, exhibit a unique mix of M1-M2 macrophage phenotypes.

Measuring matrix metalloproteinase activity in macrophages and polymorphonuclear leukocytes

Macrophages and polymorphonuclear cells (PMNs) represent an essential part of the innate immune system. These cells mediate a wide spectrum of immunological functions including bacterial defense, immune modulation, and inflammation; they are necessary for tissue homeostasis and also contribute to pathologies such as malignancy, autoimmunity, and chronic inflammation. Both macrophages and PMNs express a set of matrix metalloproteinases (MMPs), zinc-dependent endopeptidases that are involved in a variety of biological functions such as the turnover of extracellular matrix (ECM) components, angiogenesis, and the regulation of inflammation. Given the link between unregulated MMP function and diseases such as chronic inflammation or cancer, it is not surprising that these enzymes have been implicated as key effectors in clinical studies. Thus, it is important to widen our knowledge about the role of these enzymes in macrophage and PMN biology. Here, we briefly discuss the general role of inflammatory cell-derived MMPs and describe methods to analyze their activity in macrophages and PMN.

Pulmonary alveolar proteinosis: a bench-to-bedside story of granulocyte-macrophage colony-stimulating factor dysfunction

Pulmonary alveolar proteinosis (PAP) is a rare disorder characterized by ineffective clearance of surfactant by alveolar macrophages. Through recent studies with genetically altered mice, the etiology of this idiopathic disease is becoming clearer. Functional deficiency of granulocyte-macrophage colony-stimulating factor (GM-CSF) appears to contribute to disease pathogenesis because mutant mice deficient in GM-CSF or its receptor spontaneously develop PAP. Recent human studies further suggest a connection between PAP and defective GM-CSF activity because inactivating anti-GM-CSF autoantibodies are observed in all patients with idiopathic PAP, and additional rare cases of PAP in children have been accompanied by genetic defects in the alpha chain of the GM-CSF receptor. In patients and mouse models of PAP, deficient GM-CSF activity appears to result in defective alveolar macrophages that are unable to maintain pulmonary surfactant homeostasis and display defective phagocytic and antigen-presenting capabilities. The most recent studies also suggest that neutrophil dysfunction additionally contributes to the increased susceptibility to lung infections seen in PAP. Because the phenotypic and immunologic abnormalities of PAP in mouse models can be corrected by GM-CSF reconstituting therapies, early clinical trials are underway utilizing administration of GM-CSF to potentially treat human PAP. The development of novel treatment approaches for PAP represents a dramatic illustration in pulmonary medicine of the "bench-to-bedside" process, in which basic scientists, translational researchers, and clinicians have joined together to rapidly take advantage of the unexpected observations frequently made in the modern molecular biology research laboratory.

Smoking-dependent reprogramming of alveolar macrophage polarization: implication for pathogenesis of chronic obstructive pulmonary disease

When exposed to a specific microenvironment, macrophages acquire either M1- or M2-polarized phenotypes associated with inflammation and tissue remodeling, respectively. Alveolar macrophages (AM) directly interact with environmental stimuli such as cigarette smoke, the major risk factor for chronic obstructive pulmonary disease (COPD), a disease characterized by lung inflammation and remodeling. Transcriptional profiling of AM obtained by bronchoalveolar lavage of 24 healthy nonsmokers, 34 healthy smokers, and 12 COPD smokers was performed to test the hypothesis whether smoking alters AM polarization, resulting in a disease-relevant activation phenotype. The analysis revealed that AM of healthy smokers exhibited a unique polarization pattern characterized by substantial suppression of M1-related inflammatory/immune genes and induction of genes associated with various M2-polarization programs relevant to tissue remodeling and immunoregulation. Such reciprocal changes progressed with the development of COPD, with M1-related gene expression being most dramatically down-regulated (p < 0.0001 vs healthy nonsmokers, p < 0.002 vs healthy smokers). Results were confirmed with TaqMan real-time PCR and flow cytometry. Among progressively down-regulated M1-related genes were those encoding type I chemokines CXCL9, CXCL10, CXCL11, and CCL5. Progressive activation of M2-related program was characterized by induction of tissue remodeling and immunoregulatory genes such as matrix metalloproteinase (MMP)2, MMP7, and adenosine A3 receptor (ADORA3). Principal component analysis revealed that differential expression of polarization-related genes has substantial contribution to global AM phenotypes associated with smoking and COPD. In summary, the data provide transcriptome-based evidence that AM likely contribute to COPD pathogenesis in a noninflammatory manner due to their smoking-induced reprogramming toward M1-deactivated, partially M2-polarized macrophages.

Peroxisome proliferator-activated receptor-gamma regulates the expression of alveolar macrophage macrophage colony-stimulating factor

Macrophage CSF (M-CSF) regulates monocyte differentiation, activation, and foam cell formation. We have observed that it is elevated in human pulmonary alveolar proteinosis (PAP) and in the GM-CSF knockout mouse, a murine model for PAP. A potential regulator of M-CSF, peroxisome proliferator-activated receptor-gamma (PPARgamma), is severely deficient in both human PAP and the GM-CSF knockout mouse. To investigate the role of PPARgamma in alveolar macrophage homeostasis, we generated myeloid-specific PPARgamma knockout mice using the Lys-Cre method to knock out the floxed PPARgamma gene. Similar to the GM-CSF-deficient mouse, absence of alveolar macrophage PPARgamma resulted in development of lung pathology resembling PAP in 16-wk-old mice, along with excess M-CSF gene expression and secretion. In ex vivo wild-type alveolar macrophages, we observed that M-CSF itself is capable of inducing foam cell formation similar to that seen in PAP. Overexpression of PPARgamma prevented LPS-stimulated M-CSF production in RAW 264.7 cells, an effect that was abrogated by a specific PPARgamma antagonist, GW9662. Use of proteasome inhibitor, MG-132 or a PPARgamma agonist, pioglitazone, prevented LPS-mediated M-CSF induction. Using chromatin immunoprecipitation, we found that PPARgamma is capable of regulating M-CSF through transrepression of NF-kappaB binding at the promoter. Gel-shift assay experiments confirmed that pioglitazone is capable of blocking NF-kappaB binding. Taken together, these data suggest that M-CSF is an important mediator of alveolar macrophage homeostasis, and that transcriptional control of M-CSF production is regulated by NF-kappaB and PPARgamma.

Matrix metalloproteinases in lung: multiple, multifarious, and multifaceted

The matrix metalloproteinases (MMPs), a family of 25 secreted and cell surface-bound neutral proteinases, process a large array of extracellular and cell surface proteins under normal and pathological conditions. MMPs play critical roles in lung organogenesis, but their expression, for the most part, is downregulated after generation of the alveoli. Our knowledge about the resurgence of the MMPs that occurs in most inflammatory diseases of the lung is rapidly expanding. Although not all members of the MMP family are found within the lung tissue, many are upregulated during the acute and chronic phases of these diseases. Furthermore, potential MMP targets in the lung include all structural proteins in the extracellular matrix (ECM), cell adhesion molecules, growth factors, cytokines, and chemokines. However, what is less known is the role of MMP proteolysis in modulating the function of these substrates in vivo. Because of their multiplicity and substantial substrate overlap, MMPs are thought to have redundant functions. However, as we explore in this review, such redundancy most likely evolved as a necessary compensatory mechanism given the critical regulatory importance of MMPs. While inhibition of MMPs has been proposed as a therapeutic option in a variety of inflammatory lung conditions, a complete understanding of the biology of these complex enzymes is needed before we can reasonably consider them as therapeutic targets.