Reduced supply of monocyte-derived macrophages leads to a transition from nodular to diffuse lesions and tissue cell activation in silica-induced pulmonary fibrosis in mice

Molecular imaging in experimental pulmonary fibrosis reveals that nintedanib unexpectedly modulates CCR2 immune cell infiltration

BACKGROUND

Pulmonary fibrosis is a challenging clinical problem with lung pathology featuring immune cell infiltrates, fibroblast expansion, and matrix deposition. Molecular analysis of diseased lungs and preclinical models have uncovered C-C chemokine receptor type 2 (CCR2)+ monocyte egress from the bone marrow into the lung, where they acquire profibrotic activities. Current drug treatment is focused on fibroblast activity. Alternatively, therapeutic targeting and monitoring CCR2+ cells may be an effective patient management strategy.

METHODS

Inhibition of CCR2+ cells and, as a benchmark, the clinical antifibrotic agent, nintedanib, were used in mouse lung fibrosis models. Lungs were evaluated directly for CCR2+ cell infiltration and by non-invasive CCR2+ positron emission tomography imaging (CCR2-PET).

FINDINGS

Lung CCR2+ cells were significantly elevated in the bleomycin model as determined by tissue evaluation and CCR2-PET imaging. A protective treatment protocol with an oral CCR2 inhibitor was compared to oral nintedanib. While we expected disparate effects on CCR2+ cells, each drug similarly decreased lung CCR2+ cells and fibrosis. Chemotaxis assays showed nintedanib indirectly inhibited C-C motif chemokine 2 (CCL2)-mediated migration of CCR2+ cells. Even delayed therapeutic administration of nintedanib in bleomycin and the silicosis progressive fibrosis models decreased the accumulation of CCR2+ lung cells. In these treatments early CCR2-PET imaging predicted the later development of fibrosis.

INTERPRETATION

The inhibition of CCR2+ cell egress is likely a critical controller for stabilising lung fibrosis, as provided by nintedanib. Imaging with CCR2-PET may be useful to monitor nintedanib treatment responses, guide decision-making in the treatment of patients with progressive pulmonary fibrosis, and as a biomarker for drug development.

FUNDING

National Institutes of Health (NIH), R01HL131908 (SLB), R35HL145212 (YL), P41EB025815 (YL), K01DK133670 (DHK); Barnes Jewish Hospital Foundation (SLB).

Results from omic approaches in rat or mouse models exposed to inhaled crystalline silica: a systematic review

BACKGROUND

Crystalline silica (cSiO2) is a mineral found in rocks; workers from the construction or denim industries are particularly exposed to cSiO2 through inhalation. cSiO2 inhalation increases the risk of silicosis and systemic autoimmune diseases. Inhaled cSiO2 microparticles can reach the alveoli where they induce inflammation, cell death, auto-immunity and fibrosis but the specific molecular pathways involved in these cSiO2 effects remain unclear. This systematic review aims to provide a comprehensive state of the art on omic approaches and exposure models used to study the effects of inhaled cSiO2 in mice and rats and to highlight key results from omic data in rodents also validated in human.

METHODS

The protocol of systematic review follows PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Eligible articles were identified in PubMed, Embase and Web of Science. The search strategy included original articles published after 1990 and written in English which included mouse or rat models exposed to cSiO2 and utilized omic approaches to identify pathways modulated by cSiO2. Data were extracted and quality assessment was based on the SYRCLE's Risk of Bias tool for animal studies.

RESULTS

Rats and male rodents were the more used models while female rodents and autoimmune prone models were less studied. Exposure of animals were both acute and chronic and the timing of outcome measurement through omics approaches were homogeneously distributed. Transcriptomic techniques were more commonly performed while proteomic, metabolomic and single-cell omic methods were less utilized. Immunity and inflammation were the main domains modified by cSiO2 exposure in lungs of mice and rats. Less than 20% of the results obtained in rodents were finally verified in humans.

CONCLUSION

Omic technics offer new insights on the effects of cSiO2 exposure in mice and rats although the majority of data still need to be validated in humans. Autoimmune prone model should be better characterised and systemic effects of cSiO2 need to be further studied to better understand cSiO2-induced autoimmunity. Single-cell omics should be performed to inform on pathological processes induced by cSiO2 exposure.

Extracellular vesicles: emerging roles, biomarkers and therapeutic strategies in fibrotic diseases

Extracellular vesicles (EVs), a cluster of cell-secreted lipid bilayer nanoscale particles, universally exist in body fluids, as well as cell and tissue culture supernatants. Over the past years, increasing attention have been paid to the important role of EVs as effective intercellular communicators in fibrotic diseases. Notably, EV cargos, including proteins, lipids, nucleic acids, and metabolites, are reported to be disease-specific and can even contribute to fibrosis pathology. Thus, EVs are considered as effective biomarkers for disease diagnosis and prognosis. Emerging evidence shows that EVs derived from stem/progenitor cells have great prospects for cell-free therapy in various preclinical models of fibrotic diseases and engineered EVs can improve the targeting and effectiveness of their treatment. In this review, we will focus on the biological functions and mechanisms of EVs in the fibrotic diseases, as well as their potential as novel biomarkers and therapeutic strategies.

Mass cytometry identifies characteristic immune cell subsets in bronchoalveolar lavage fluid from interstitial lung diseases

Immune cells have been implicated in interstitial lung diseases (ILDs), although their phenotypes and effector mechanisms remain poorly understood. To better understand these cells, we conducted an exploratory mass cytometry analysis of immune cell subsets in bronchoalveolar lavage fluid (BALF) from patients with idiopathic pulmonary fibrosis (IPF), connective-tissue disease (CTD)-related ILD, and sarcoidosis, using two panels including 64 markers. Among myeloid cells, we observed the expansion of CD14⁺ CD36^hi CD84^hiCCR2^- monocyte populations in IPF. These CD14⁺ CD36^hi CD84^hi CCR2^- subsets were also increased in ILDs with a progressive phenotype, particularly in a case of acute exacerbation (AEx) of IPF. Analysis of B cells revealed the presence of cells at various stages of differentiation in BALF, with a higher percentage of IgG memory B cells in CTD-ILDs and a trend toward more FCRL5⁺ B cells. These FCRL5⁺ B cells were also present in the patient with AEx-IPF and sarcoidosis with advanced lung lesions. Among T cells, we found increased levels of IL-2R⁺ TIGIT⁺ LAG3⁺ CD4⁺ T cells in IPF, increased levels of CXCR3⁺ CD226⁺ CD4⁺ T cells in sarcoidosis, and increased levels of PD1⁺ TIGIT⁺ CD57⁺ CD8⁺ T cells in CTD-ILDs. Together, these findings underscore the diverse immunopathogenesis of ILDs.

Continuous infiltration of small peritoneal macrophages in the mouse peritoneum through CCR2-dependent and -independent routes during fibrosis and mesothelioma development induced by a multiwalled carbon nanotube, MWNT-7

Although toxicities of multiwalled carbon nanotube (MWCNT) have been found to be related with activities of macrophages phagocytosing the fibers, the exact relationship between macrophage population and pathogenesis of fibrosis and mesotheliomas induced by MWCNTs is largely unknown. CCL2-CCR2 axis, a major monocyte/macrophage infiltration route, is thought to be involved in not only acute inflammation but also the formation of tumor microenvironment. We therefore described a time-course of alteration of macrophage population in an attempt to clarify the contribution of the Ccr2 gene to mesotheliomagenesis. Wild-type (WT) C57BL/6 mice and Ccr2-knockout (KO) mice were intraperitoneally administered with MWNT-7 and were sequentially necropsied at 1, 7, 28, 90, and 245 day(s) after the injection. Peritoneal fibrosis was prominent in all MWCNT-treated mice, with a lower severity in the KO mice. No differences were observed in the incidences of neoplastic lesions of mesothelia between WT and KO mice. A flow cytometric analysis revealed that after gross disappearance of macrophages after MWCNT exposure, small peritoneal macrophages (SPMs) were exclusively refurbished by the CCR2-dependent route at day 1 (as Ly-6C+MHC class II- cells), followed by additional CCR2-independent routes (as Ly-6C-MHC class II- cells); i.e., the only route in KO mice; with a delay of 1-7 days. The SPMs derived from both routes appeared to differentiate into maturated cells as Ly-6C-MHC class II+, whose ratio increased in a time-dependent manner among the total SPM population. Additionally, most macrophages expressed M1-like features, but a small fraction of macrophages exhibited an M1/M2 mixed status in MWCNT-treated animals. Our findings demonstrate a long-persistent activation of the CCL2-CCR2 axis after MWCNT exposure and enable a better understanding of the participation and potential roles of SPMs in fibrous material-induced chronic toxicities.

ZC3H4 regulates infiltrating monocytes, attenuating pulmonary fibrosis through IL-10

Silicosis is a pulmonary fibrosis-associated disease caused by the inhalation of large amounts of free silicon dioxide (SiO₂) that mainly manifests as early inflammation and late pulmonary fibrosis. As macrophage precursors, monocytes accumulate in the lung during early inflammation, but their role in the development of silicosis is unclear. Single-cell sequencing (cell numbers = 25,002), Western blotting, quantitative real-time PCR, ELISA and cell functional experiments were used to explore the specific effects of monocytes on fibroblasts. The CRISPR/Cas9 system was used to specifically knock down ZC3H4, a novel member of the CCCH zinc finger protein family, and was combined with pharmacological methods to explore the mechanism by which ZC3H4 affects chemokine and cytokine secretion. The results indicated that (1) SiO₂ induced an infiltrating phenotype in monocytes; (2) infiltrating monocytes inhibited the activation, viability and migration of fibroblasts by regulating IL-10 but not IL-8; and (3) SiO₂ downregulated IL-10 via ZC3H4-induced autophagy. This study revealed that ZC3H4 regulated the secretion function of monocytes, which, in turn, inhibited fibroblast function in early inflammation through autophagy signaling, thereby reducing pulmonary fibrosis. These findings provide a new idea for the clinical treatment of silicosis.

Profibrotic properties of C1q+ interstitial macrophages in silica-induced pulmonary fibrosis in mice

Pulmonary fibrosis (PF) is a progressive fibrotic disease with poor prognosis and suboptimal therapeutic options. Although macrophages have been implicated in PF, the role of macrophage subsets, particularly interstitial macrophages (IMs), remains unknown. We performed a time-series single-cell RNA sequencing analysis of the silica-induced mouse PF model. Among the macrophage subsets in fibrotic lungs, Lyve1lo MHC IIhi IMs increased with fibrosis, and highly expressed profibrotic genes. Additionally, we identified C1q as an IM-specific marker. Experiments with C1q-diphtheria toxin receptor-GFP knock-in (C1qKI) mice revealed that IMs are distributed around fibrotic nodules. Depletion of C1q+ IMs in C1qKI mice decreased activated fibroblasts and epithelial cells; however, bodyweight loss and neutrophil infiltration were exacerbated in silica-induced PF. Collectively, these results suggest that IMs have profibrotic and anti-inflammatory properties and that the selective inhibition of the profibrotic function of IMs without compromising their anti-inflammatory effects is a potential novel therapeutic strategy for PF.

Temporal and Spatial Characterization of Mononuclear Phagocytes in Circulating, Pulmonary Alveolar, and Interstitial Compartments in LPS-Induced Acute Lung Injury

Peripheral circulating monocytes and resident macrophages are heterogeneous effector cells that play a critical role in the maintenance and restoration of pulmonary integrity. However, their detailed dynamic changes in lipopolysaccharide (LPS)-induced acute lung injury (ALI) remain unclear. Here, we investigated the impact of mononuclear phagocyte cells in the development of LPS-induced ALI/Acute respiratory distress syndrome (ARDS) and described the relations between the dynamic phenotypic changes and pulmonary pathological evolution. In this study, mice were divided into two groups and intraperitoneally injected with normal saline (NS) or LPS, respectively. A series of flow cytometry assay was performed for the quantification of peripheral circulating monocyte subpopulations, detection of the polarization state of bronchoalveolar lavage fluid (BALF)-isolated alveolar macrophages (AMϕ) and pulmonary interstitial macrophages (IMϕ) separated from lung tissues. Circulating Ly6Clo monocytes expanded rapidly after the LPS challenge on day 1 and then decreased to day 7, while Ly6Chi monocytes gradually increased and returned to normal level on the 7th day. Furthermore, the expansion of M2-like AMϕ (CD64+CD206+) was peaked on day 1 and remained high on the third day, while the polarization state of IMϕ (CD64+ CD11b+) was not influenced by the LPS challenge at all the time points. Taken together, our findings show that Ly6Clo monocytes and M2-like AMϕ form the major peripheral circulation and pulmonary immune cell populations, respectively. The dynamic changes of mononuclear phagocyte in three compartments after the LPS challenge may provide novel protective strategies for mononuclear phagocytes.

Expression of Fibrosis-Related Genes in Liver and Kidney Fibrosis in Comparison to Inflammatory Bowel Diseases

Fibrosis is an important feature of inflammatory bowel diseases (IBD), but its pathogenesis is incompletely understood. Our aim was to identify genes important for fibrosis in IBD by comparison with kidney and liver fibrosis. First, we performed bioinformatics analysis of Gene Expression Omnibus datasets of liver and kidney fibrosis and identified CXCL9, THBS2, MGP, PTPRC, CD52, GZMA, DPT and DCN as potentially important genes with altered expression in fibrosis. We then performed qPCR analysis of the selected genes’ expression on samples of fibrotic kidney, liver, Crohn’s disease (CD) with and without fibrosis and ulcerative colitis (UC), in comparison to corresponding normal tissue. We found significantly altered expression in fibrosis for all selected genes. A significant difference for some genes was observed in CD with fibrosis in comparison to CD without fibrosis and UC. We conclude that similar changes in the expression of selected genes in liver, kidney fibrosis and IBD provide further evidence that fibrosis in IBD might share common mechanisms with other organs, supporting the hypothesis that fibrosis is the common pathway in diseases of various organs. Some genes were already active in IBD with inflammation without fibrosis, suggesting the early activation of profibrotic pathways or overlapping function in fibrosis and inflammation.

Macrophages in lung fibrosis

Pulmonary fibrosis (PF) is a disease in which excessive extracellular matrix (ECM) accumulation occurs in the lungs, which induces thickening of the alveolar walls, ultimately leading to the destruction of alveolar structures and respiratory failure. Idiopathic PF, the cause of which is unknown, has a poor prognosis with a median survival of 2–4 years after diagnosis. There is currently no known curative treatment. The mechanism underlying PF is thought to be initiated by the dysfunction of type II alveolar epithelial cells, which leads to ECM overproduction through the activation of fibroblasts. In addition, it has been suggested that a variety of cells contribute to fibrotic processes. In particular, clinical and basic research findings examining the roles of macrophages suggest that they may be pivotal regulators of PF. In this review, we discuss the characteristics, functions and origins of subsets of macrophages involved in PF, including resident alveolar, interstitial and monocyte-derived macrophages.

Silica dust exposure induces pulmonary fibrosis through autophagy signaling

Silicosis is a well-acknowledged occupational lung disease caused by inhalation of a large amount of free silica dust during the production period and eventually a considerable negative impact on the patients' quality of life. Autophagy exerts a critical influence on immune and inflammatory responses during the pathogenesis of pulmonary fibrosis. In this study, we sought to determine whether autophagy is involved in silicosis's pathogenesis and how it may affect pulmonary cellular physiology. In the animal experiments, we found persistent activation of autophagy in the development of pulmonary fibrosis, which was also accompanied by tumor necrosis factor and transforming growth factor expression increased. Therefore, the autophagy signaling pathway may regulate the inflammatory response and affect the progression of fibrosis. Further, in vitro experiments, we used LY294002, RAPA, and N-acetylcysteine (NAC) intervened autophagy. Our results showed that PI3K/Akt/mTOR signaling pathway is involved in the autophagy changed mediated by SiO₂ exposed, and autophagy might play a protective role in the progression of pulmonary fibrosis. Additionally, NAC's effect is not apparent on SiO₂ -mediated autophagy through the PI3K/Akt/mTOR signaling pathway, but it can reduce the inflammatory response on NR8383 cells mediated by SiO2-exposed. Nevertheless, it's interesting that NAC can reduce the inflammatory response on NR8383 cells mediated by SiO₂ -exposed. Taken together, our data demonstrated that SiO₂ -exposed can induce pulmonary fibrosis along with autophagy both in vivo and in vitro, NAC could alleviate the inflammatory response NR8383 cells by SiO₂ -exposed through non PI3K/Akt/mTOR signaling pathway, and the specific mechanism of its action needs further studying.

Ac-SDKP Attenuates Activation of Lung Macrophages and Bone Osteoclasts in Rats Exposed to Silica by Inhibition of TLR4 and RANKL Signaling Pathways

Background

Silica-induced inflammatory activation is associated with silicosis and various non-respiratory conditions. The present study was designed to examine the anti-inflammatory effects of N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) on lung macrophages and bone osteoclasts after silica inhalation in rats.

Methods

Wistar rats and NR8383 and RAW 264.7 cell lines were used in the present study. The receptor activator of nuclear factor kappa-B ligand (RANKL) and toll-like receptor 4 (TLR4) signaling pathways was measured in the lung tissue of rats or NR8383/RAW 264.7 cells exposed to silica. The microarchitecture of the trabecular bone in the tibia and femur was evaluated in silicotic rats. Furthermore, the roles of Ac-SDKP on silicotic rats, silica-treated NR8383/RAW 264.7 cells, and RANKL-induced osteoclast differentiation were studied.

Results

The data indicated that silica inhalation might activate the RANKL and TLR4 signaling pathways in lung macrophages, thus inducing the lung inflammatory and proteolytic phenotype of macrophages and osteoclasts in lung and bone. Ac-SDKP maintained the lung elastin level by inhibiting lung inflammation and macrophage activation via the RANKL and TLR4 signaling pathways. Ac-SDKP also attenuated the reduction in femoral bone mineral density in silicotic rats by inhibiting osteoclast differentiation via the RANKL signaling pathway.

Conclusion

Our findings support the hypothesis that inhalation of crystalline silica induces activation of lung macrophages and bone osteoclasts via the RANKL and TLR4 signaling pathways. Ac-SDKP has the potential to stabilize lung homeostasis and bone metabolism.

Matrix metalloproteinase: An upcoming therapeutic approach for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a debilitating condition where excess collagen deposition occurs in the extracellular matrix. At first sight, it is expected that the level of different kinds of matrix metalloproteinases might be downregulated in IPF as it is a matrix degrading collagenase. However, the role of some matrix metalloproteinases (MMPs) is profibrotic where others have anti-fibrotic functions. These profibrotic MMPs effectively promote fibrosis development by stimulating the process of epithelial to mesenchymal transition. These profibrotic groups also induce macrophage polarization and fibrocyte migration. All of these events ultimately disrupt the balance between profibrotic and antifibrotic mediators, resulting aberrant repair process. Therefore, inhibition of these matrix metalloproteinases functions in IPF is a potential therapeutic approach. In addition to the use of synthetic inhibitor, various natural compounds, gene silencing act as potential natural MMP inhibitor to recover IPF.

Kaempferol Modulates Autophagy and Alleviates Silica-Induced Pulmonary Fibrosis

Silicosis is an occupational disease characterized as inflammatory cells infiltration and severe progressive pulmonary fibrosis. Kaempferol (Kae), a flavonoid that exists in many plants and fruits, has been proved to have anti-inflammatory and antifibrosis functions. However, the effects of Kae on silicosis remain unclear. In the present study, we analyzed the therapeutic effects of Kae in 1-, 7-, and 28-day silicosis models, respectively. In the 1-day model, Kae treatment did not vary the wet-to-dry weight ratios of the lung, apoptotic rate, autophagy, or the expression of inflammatory factors. In contrast, Kae significantly inhibited pulmonary inflammation in the 7-day silicosis models and inhibited silica-induced pulmonary fibrosis in the 28-day models. Besides, we found that Kae partially restored silica-induced LC3 lipidation without increasing the p62 levels. Blocking autophagy with chloroquine antagonized the inhibitory effects of Kae on inflammation, suggesting that autophagy might be required in the therapeutic effects of Kae on silicosis. These findings indicated that Kae inhibits the progression of silica-induced pulmonary fibrosis, which may provide experimental evidences for Kae in the treatment of silicosis.

Transcriptome network analysis identifies protective role of the LXR/SREBP-1c axis in murine pulmonary fibrosis

Pulmonary fibrosis (PF) is an intractable disorder with a poor prognosis. Although lung fibroblasts play a central role in PF, the key regulatory molecules involved in this process remain unknown. To address this issue, we performed a time-course transcriptome analysis on lung fibroblasts of bleomycin- and silica-treated murine lungs. We found gene modules whose expression kinetics were associated with the progression of PF and human idiopathic PF (IPF). Upstream analysis of a transcriptome network helped in identifying 55 hub transcription factors that were highly connected with PF-associated gene modules. Of these hubs, the expression of Srebf1 decreased in line with progression of PF and human IPF, suggesting its suppressive role in fibroblast activation. Consistently, adoptive transfer and genetic modification studies revealed that the hub transcription factor SREBP-1c suppressed PF-associated gene expression changes in lung fibroblasts and PF pathology in vivo. Moreover, therapeutic pharmacological activation of LXR, an SREBP-1c activator, suppressed the Srebf1-dependent activation of fibroblasts and progression of PF. Thus, SREBP-1c acts as a protective hub of lung fibroblast activation in PF. Collectively, the findings of the current study may prove to be valuable in the development of effective therapeutic strategies for PF.

Lung fibroblasts express a miR-19a-19b-20a sub-cluster to suppress TGF-β-associated fibroblast activation in murine pulmonary fibrosis

Lung fibroblasts play a pivotal role in pulmonary fibrosis, a devastating lung disease, by producing extracellular matrix. MicroRNAs (miRNAs) suppress numerous genes post-transcriptionally; however, the roles of miRNAs in activated fibroblasts in fibrotic lungs remain poorly understood. To elucidate these roles, we performed global miRNA-expression profiling of fibroblasts from bleomycin- and silica-induced fibrotic lungs and investigated the functions of miRNAs in activated lung fibroblasts. Clustering analysis of global miRNA-expression data identified miRNA signatures exhibiting increased expression during fibrosis progression. Among these signatures, we found that a miR-19a-19b-20a sub-cluster suppressed TGF-β-induced activation of fibroblasts in vitro. Moreover, to elucidate whether fibroblast-specific intervention against the sub-cluster modulates pathogenic activation of fibroblasts in fibrotic lungs, we intratracheally transferred the sub-cluster-overexpressing fibroblasts into bleomycin-treated lungs. Global transcriptome analysis of the intratracheally transferred fibroblasts revealed that the sub-cluster not only downregulated expression of TGF-β-associated pro-fibrotic genes, including Acta2, Col1a1, Ctgf, and Serpine1, but also upregulated expression of the anti-fibrotic genes Dcn, Igfbp5, and Mmp3 in activated lung fibroblasts. Collectively, these findings indicated that upregulation of the miR-19a-19b-20a sub-cluster expression in lung fibroblasts counteracted TGF-β-associated pathogenic activation of fibroblasts in murine pulmonary fibrosis.

Reduction of Proliferating Olfactory Cells and Low Expression of Extracellular Matrix Genes Are Hallmarks of the Aged Olfactory Mucosa

Background: The incidence of olfactory impairment increases with age; however, the detailed molecular and cellular mechanisms underlying this increase are yet to be determined. Methods: We examined the influence of aging on olfactory receptor neurons (ORNs), which are maintained by a unique stem cell system, from olfactory progenitor cells to mature ORNs, by histological comparisons of the physiological status of the olfactory epithelium between young adult and aged mice. Furthermore, we clarified the expression of genes encoding inflammatory cytokines, neurotrophins, growth factors, and extracellular matrix proteins to reveal the molecular mechanisms underlying olfactory impairment caused by aging. Results: The numbers of mature and immature ORNs, but not olfactory progenitors, decreased in the aged olfactory epithelium, with a concurrent reduction in Ki-67-positive proliferating cells. Transcriptome analyses revealed an increase in Il6, encoding a component of senescence-associated secretary phenotypes (SASP), and a decrease in Igf1, encoding a growth factor for ORNs, in the aged nasal mucosa. Interestingly, expression levels of several extracellular matrix genes, including Col1a2, decreased in the aged nasal mucosa. Consistent with the transcriptional changes, the number of Col1a2-GFP-positive cells decreased in the aged lamina propria. Conclusions: Our data suggest that reduction in ORN number and cell proliferation, reduced extracellular matrix gene expression, and increased SASP contribute to olfactory impairment during aging.

Involvement of Hookworm Co-Infection in the Pathogenesis and Progression of Podoconiosis: Possible Immunological Mechanism

Podoconiosis is an endemic, non-infectious, geochemical and non-filarial inflammatory cause of tropical elephantiasis. The immunology of podoconiosis is not yet expressly understood. In spite of this, co-infection and co-morbidity with the infectious, soil-transmitted hookworm disease that causes iron deficiency anemia has been found to be predominant among affected individuals living in co-endemic settings, thus creating a more complex immunological interplay that still has not been investigated. Although deworming and iron-rich nutrient supplementation have been suggested in podoconiosis patients living under resource-poor conditions, and it is thought that hookworm infection may help to suppress inflammatory responses, the undisputed link that exists between a non-infectious and an infectious disease may create a scenario whereby during a co-infection, treatment of one exacerbates the other disease condition or is dampened by the debilitation caused by the other. In this paper, we elaborate on the immunopathogenesis of podoconiosis and examine the possible immunological dynamics of hookworm co-infection in the immunopathology of podoconiosis, with a view toward improved management of the disease that will facilitate its feasible elimination.

ATP Evokes Ca2+ Responses and CXCL5 Secretion via P2X4 Receptor Activation in Human Monocyte-Derived Macrophages

Leukocytes sense extracellular ATP, a danger-associated molecular pattern, released during cellular stress and death, via activation of cell surface P2X and P2Y receptors. Here, we investigate P2 receptor expression in primary human monocyte-derived macrophages and receptors that mediate ATP-evoked intracellular [Ca²⁺]_i signals and cytokine production in response to ATP concentrations that exclude P2X₇ receptor activation. Expression of P2X₁, P2X₄, P2X₅, P2X₇, P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, and P2Y₁₃ was confirmed by quantitative RT-PCR and immunocytochemistry. ATP elicited intracellular Ca²⁺ responses in a concentration-dependent fashion (EC₅₀ = 11.4 ± 2.9 μM, n = 3). P2Y₁₁ and P2Y₁₃ activations mediated the amplitude of [Ca²⁺]_i response, whereas P2X₄ activation, but not P2X₁ or P2X₇, determined the duration of Ca²⁺ response during a sustained phase. ATP mediated gene induction of CXCL5, a proinflammatory chemokine. P2X₄ antagonism (PSB-12062 or BX430) inhibited ATP-mediated induction of CXCL5 gene expression and secretion of CXCL5 by primary macrophage. Inhibition of CXCL5 secretion by P2X₄ antagonists was lost in the absence of extracellular Ca²⁺ Reciprocally, positive allosteric modulation of P2X₄ (ivermectin) augmented ATP-mediated CXCL5 secretion. P2X₇, P2Y₁₁, or P2Y₁₃ receptor did not contribute to CXCL5 secretion. Together, the data reveals a role for P2X₄ in determining the duration of ATP-evoked Ca²⁺ responses and CXCL5 secretion in human primary macrophage.

CCR2+ monocytic myeloid-derived suppressor cells (M-MDSCs) inhibit collagen degradation and promote lung fibrosis by producing transforming growth factor-β1

Monocytes infiltrating scar tissue are predominantly viewed as progenitor cells. Here, we show that tissue CCR2⁺ monocytes have specific immunosuppressive and profibrotic functions. CCR2⁺ monocytic cells are acutely recruited to the lung before the onset of silica-induced fibrosis in mice. These tissue monocytes are defined as monocytic myeloid-derived suppressor cells (M-MDSCs) because they significantly suppress T-lymphocyte proliferation in vitro. M-MDSCs collected from silica-treated mice also express transforming growth factor (TGF)-β1, which stimulates lung fibroblasts to release tissue inhibitor of metalloproteinase (TIMP)-1, an inhibitor of metalloproteinase collagenolytic activity. By using LysMCreCCR2^loxP/loxP mice, we show that limiting CCR2⁺ M-MDSC accumulation reduces the pulmonary contents of TGF-β1, TIMP-1 and collagen after silica treatment. M-MDSCs do not differentiate into lung macrophages, granulocytes or fibrocytes during pulmonary fibrogenesis. Collectively, our data indicate that M-MDSCs contribute to lung fibrosis by specifically promoting a non-degrading collagen microenvironment. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Loss of CCR2 signaling alters leukocyte recruitment and exacerbates γ-herpesvirus-induced pneumonitis and fibrosis following bone marrow transplantation

CCR2-expressing leukocytes are required for the progression of fibrosis in models of induced lung injury as well as models of bone marrow transplant (BMT)-related idiopathic pneumonia syndrome. Infection with murid γ-herpesvirus-68 (γHV-68) results in severe pneumonitis and pulmonary fibrosis following syngeneic BMT; however, the roles that various proinflammatory leukocyte populations play in this process remain unclear. Deletion of CCR2 in both non-BMT and BMT mice increased early lytic viral replication and resulted in a reduction in the numbers of lung-infiltrating GR1+,F4/80+ and CXCR1+ cells, while maintaining robust neutrophil infiltration. Similarly, in γHV-68-infected CCR2(-/-) BMT mice, recruitment of monocytes and lymphocytes were reduced whereas neutrophil recruitment was increased compared with wild-type (WT) BMT mice. Interestingly, levels of profibrotic IL-17 were increased in infected CCR2 BMT mice compared with WT BMT. Furthermore, an increase in lung-associated collagen was detected even though there was an overall decrease in the number of profibrotic CCR2+ fibrocytes detected in the lungs of CCR2(-/-) BMT mice. These data indicate that, contrary to most models of fibrosis, deletion of CCR2 offers no protection from γ-herpesvirus-induced pneumonitis and fibrosis, and, indeed, CCR2+ cells play a suppressive role during the development of pulmonary fibrosis following γ-herpesvirus infection post-BMT by limiting IL-7 and collagen production.

Dynamic changes of mononuclear phagocytes in circulating, pulmonary alveolar and interstitial compartments in a mouse model of experimental silicosis

CONTEXT

Silicosis is a devastating, irreversible lung fibrosis condition exposed to crystalline silica. The mononuclear phagocyte system plays an important role in the pathogenesis of silicosis.

OBJECTIVE

The present study was aimed to explore the dynamic changes of mononuclear phagocytes in circulating, pulmonary alveolar and interstitial compartments in experimental silicosis model.

MATERIALS AND METHODS

A mouse model of lung fibrosis was developed with crystalline silica particles (2 mg/40 μL via oropharyngeal instillation) using male C57BL/6 mice, and were killed on days 1, 3, 7, 14, and 28. The lung inflammation and fibrosis was investigated using hematoxylin-eosin staining and bronchoalveolar lavage fluid (BALF) analysis, Masson's trichrome staining, and immunofluorescence. Circulating monocyte subsets (Ly6C(hi) and Ly6C(lo)), polarization state of BALF-derived alveolar macrophages (AMϕ) and lung interstitial macrophages (IMϕ, derived from enzymatically digested lung tissue) were analyzed by flow cytometry.

RESULTS

The percentage of Ly6C(hi) monocytes significantly increased on day 1 after silica exposure, which reached the peak level from day 7 till day 28. Moreover, M2 (alternative activation) AMϕ (PI - CD64 + CD206+) was dramatically and progressively increased from day 1 to day 28. A parallel increase in IMϕ with M2 polarization (PI-CD64 + CD11b + CD206+) was also observed from day 1 to day 28.

CONCLUSION

Our data demonstrate a dynamic view of mononuclear phagocyte change in three compartments after silica challenge, which highlights the remodeling of mononuclear phagocyte system as a potential therapeutic target for silicosis.