M2 macrophages have unique transcriptomes but conditioned media does not promote profibrotic responses in lung fibroblasts or alveolar epithelial cells in vitro

The role of macrophage polarization and cellular crosstalk in the pulmonary fibrotic microenvironment: a review

Pulmonary fibrosis (PF) is a progressive interstitial inflammatory disease with a high mortality rate. Patients with PF commonly experience a chronic dry cough and progressive dyspnoea for years without effective mitigation. The pathogenesis of PF is believed to be associated with dysfunctional macrophage polarization, fibroblast proliferation, and the loss of epithelial cells. Thus, it is of great importance and necessity to explore the interactions among macrophages, fibroblasts, and alveolar epithelial cells in lung fibrosis, as well as in the pro-fibrotic microenvironment. In this review, we discuss the latest studies that have investigated macrophage polarization and activation of non-immune cells in the context of PF pathogenesis and progression. Next, we discuss how profibrotic cellular crosstalk is promoted in the PF microenvironment by multiple cytokines, chemokines, and signalling pathways. And finally, we discuss the potential mechanisms of fibrogenesis development and efficient therapeutic strategies for the disease. Herein, we provide a comprehensive summary of the vital role of macrophage polarization in PF and its profibrotic crosstalk with fibroblasts and alveolar epithelial cells and suggest potential treatment strategies to target their cellular communication in the microenvironment.

Concentration Effects of Methylprednisolone in Human Vocal Fold Fibroblast-Macrophage Co-Culture

OBJECTIVE

The diversity of glucocorticoid (GC) properties may underlie variability of clinical efficacy for vocal fold (VF) disease. Optimized therapeutic approaches must account for tissue complexity as well as interactions between cell types. We previously reported that reduced GC concentrations inhibited inflammation without eliciting fibrosis in mono-cultured VF fibroblasts and macrophages. These data suggested that a refined approach to GC concentration may improve outcomes. In the current study, co-culture of VF fibroblasts and macrophages was employed to investigate the effects of different concentrations of methylprednisolone on fibrotic and inflammatory response genes in VF fibroblasts to optimize management paradigms.

STUDY DESIGN

In vitro.

METHODS

THP-1 monocyte-derived macrophages were stimulated with interferon-γ (IFN-γ), lipopolysaccharide (LPS), or transforming growth factor-β (TGF-β) to induce inflammatory (M(IFN/LPS)) and fibrotic (M(TGF)) phenotypes. Macrophages were then co-cultured with a human VF fibroblast cell line using a 0.4 μm pore membrane with or without 0.1-3000 nM methylprednisolone. Inflammatory (CXCL10, TNF, and PTGS2) and fibrotic (ACTA2, CCN2, and COL1A1) gene expression was quantified in fibroblasts.

RESULTS

Incubating VF fibroblasts with M(IFN/LPS) macrophages increased expression of TNF and PTGS2, and this effect was inhibited by methylprednisolone. Incubation of VF fibroblasts with M(TGF) macrophages increased expression of ACTA2, CCN2, and COL1A1, and this effect was enhanced by methylprednisolone. The concentration of methylprednisolone required to downregulate inflammatory genes (TNF and PTGS2) was lower than that to upregulate fibrotic genes (ACTA2, CCN2, and COL1A1).

CONCLUSION

Reduced concentration of methylprednisolone effectively suppressed inflammatory genes without enhancing fibrotic genes, suggesting that a refined approach to GC concentration may improve clinical outcomes.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:3116-3122, 2023.

αCGRP deficiency aggravates pulmonary fibrosis by activating the PPARγ signaling pathway

In order to explore whether αCGRP (Calca) deficiency aggravates pulmonary fibrosis (PF). Clinical data from patients with PF (n = 52) were retrospectively analyzed. Lung tissue from a bleomycin (BLM)-induced rat model was compared with that of Calca-knockout (KO) and wild type (WT) using immunohistochemistry, RNA-seq, and UPLC-MS/MS metabolomic analyses. The results showed that decreased αCGRP expression and activation of the type 2 immune response were detected in patients with PF. In BLM-induced and Calca-KO rats, αCGRP deficiency potentiated apoptosis of AECs and induced M2 macrophages. RNA-seq identified enrichment of pathways involved in nuclear translocation and immune system disorders in Calca-KO rats compared to WT. Mass spectrometry of lung tissue from Calca-KO rats showed abnormal lipid metabolism, including increased levels of LTB4, PDX, 1-HETE. PPAR pathway signaling was significantly induced in both transcriptomic and metabolomic datasets in Calca-KO rats, and immunofluorescence analysis confirmed that the nuclear translocation of PPARγ in BLM-treated and Calca-KO rats was synchronized with STAT6 localization in the cytoplasmic and nuclear fractions. In conclusion, αCGRP is protective against PF, and αCGRP deficiency promotes M2 polarization of macrophages, probably by activating the PPARγ pathway, which leads to activation of the type 2 immune response and accelerates PF development.

Alveolar macrophages drive lung fibroblast function in cocultures of IPF and normal patient samples

Idiopathic pulmonary fibrosis (IPF) is characterized by increased collagen accumulation that is progressive and nonresolving. Although fibrosis progression may be regulated by fibroblasts and alveolar macrophage (AM) interactions, this cellular interplay has not been fully elucidated. To study AM-fibroblast interactions, cells were isolated from IPF and normal human lung tissue and cultured independently or together in direct 2-D coculture, direct 3-D coculture, indirect transwell, and in 3-D hydrogels. AM influence on fibroblast function was assessed by gene expression, cytokine/chemokine secretion, and hydrogel contractility. Normal AMs cultured in direct contact with fibroblasts downregulated extracellular matrix (ECM) gene expression whereas IPF AMs had little to no effect. Fibroblast contractility was assessed by encapsulating cocultures in 3-D collagen hydrogels and monitoring gel diameter over time. Both normal and IPF AMs reduced baseline contractility of normal fibroblasts but had little to no effect on IPF fibroblasts. When stimulated with Toll-like receptor (TLR) agonists, IPF AMs increased production of pro-inflammatory cytokines TNFα and IL-1β, compared with normal AMs. TLR ligand stimulation did not alter fibroblast contraction, but stimulation with exogenous TNFα and TGFβ did alter contraction. To determine if the observed changes required cell-to-cell contact, AM-conditioned media and transwell systems were utilized. Transwell culture showed decreased ECM gene expression changes compared with direct coculture and conditioned media from AMs did not alter fibroblast contraction regardless of disease state. Taken together, these data indicate that normal fibroblasts are more responsive to AM crosstalk, and that AM influence on fibroblast behavior depends on cell proximity.

Update on the roles of macrophages in the degeneration and repair process of intervertebral discs

Intervertebral disc (IVD) degeneration is the common cause of lumbar degenerative diseases, causing severe social and economic burden. The process of IVD degeneration involves a complex of pathologic changes on both extracellular matrix degradation and resident cell apoptosis. In recent years, there is increasing evidence that macrophages play vital roles during the damage and repair process of IVD degeneration. Nevertheless, the interactions between macrophages and IVD are not well understood, even if the IVD has long been regarded as the immune privileged site. Therefore, this review mainly focuses on the progress and obstacles of studies investigating the blood supply, immune response and especially macrophages during the IVD degeneration process.

Myeloid- and Epithelial-derived Heparin-Binding Epidermal Growth Factor-like Growth Factor Promotes Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a poorly understood, progressive lethal lung disease with no known cure. In addition to alveolar epithelial cell (AEC) injury and excessive deposition of extracellular matrix proteins, chronic inflammation is a hallmark of IPF. Literature suggests that the persistent inflammation seen in IPF primarily consists of monocytes and macrophages. Recent work demonstrates that monocyte-derived alveolar macrophages (moAMs) drive lung fibrosis, but further characterization of critical moAM cell attributes is necessary. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is an important epidermal growth factor receptor ligand that has essential roles in angiogenesis, wound healing, keratinocyte migration, and epithelial-mesenchymal transition. Our past work has shown HB-EGF is a primary marker of profibrotic M2 macrophages, and this study seeks to characterize myeloid-derived HB-EGF and its primary mechanism of action in bleomycin-induced lung fibrosis using Hbegff/f;Lyz2Cre+ mice. Here, we show that patients with IPF and mice with pulmonary fibrosis have increased expression of HB-EGF and that lung macrophages and transitional AECs of mice with pulmonary fibrosis and humans all express HB-EGF. We also show that Hbegff/f;Lyz2Cre+ mice are protected from bleomycin-induced fibrosis and that this protection is likely multifactorial, caused by decreased CCL2-dependent monocyte migration, decreased fibroblast migration, and decreased contribution of HB-EGF from AEC sources when HB-EGF is removed under the Lyz2Cre promoter.

Macrophages alter inflammatory and fibrotic gene expression in human vocal fold fibroblasts

Macrophage phenotypes are simplistically classified as pro-inflammatory (M1) or anti-inflammatory/pro-fibrotic (M2). Phenotypically different macrophages are putatively involved in vocal fold (VF) fibrosis. The current study investigated interactions between macrophages and VF fibroblasts. THP-1 monocyte-derived macrophages were treated with interferon-gamma (IFN-γ), lipopolysaccharide (LPS)/IFN-γ, interleukin-10 (IL10), transforming growth factor-β1 (TGF-β), or interleukin-4 (IL4) for 24 h (M(IFN), M(IFN/LPS), M(IL10), M(TGF), and M(IL4), respectively; M(-) denotes untreated macrophages). Differentially activated macrophages and human VF fibroblasts were co-cultured ± direct contact. Expression of CXCL10, CCN2, ACTA2, FN1, TGM2, and LOX was quantified by real-time polymerase chain reaction. Type I collagen and smooth muscle actin (SMA) were observed by immunofluorescence. CXCL10 and PTGS2 were upregulated in fibroblasts indirectly co-cultured with M(IFN) and M(IFN/LPS). M(TGF) stimulated CCN2, ACTA2, and FN1 in fibroblasts. Enzymes involved in extracellular matrix crosslinking (TGM2, LOX) were increased in monocultured M(IL4) compared to M(-). Direct co-culture with all macrophages increased type I collagen and SMA in fibroblasts. Macrophage phenotypic shift was consistent with stimulation and had downstream differential effects on VF fibroblasts. Direct contact with macrophages, regardless of phenotype, stimulated a pro-fibrotic response in VF fibroblasts. Collectively, these data suggest meaningful interactions between macrophages and fibroblasts mediate fibrosis.

Fibrotic lung disease inhibits innate immune responses to Staphylococcal pneumonia via impaired neutrophil and macrophage function

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease characterized by collagen deposition within the lung interstitium. Bacterial infection is associated with increased morbidity and more rapid mortality in IPF patient populations, and pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) are commonly isolated from the lungs of hospitalized patients with IPF. Despite this, the effects of fibrotic lung injury on critical immune responses to infection remain unknown. In the present study, we show that, like humans with IPF, fibrotic mice infected with MRSA exhibit increased morbidity and mortality compared with uninfected fibrotic mice. We determine that fibrosis conferred a defect in MRSA clearance compared with nonfibrotic mice, resulting from blunted innate immune responses. We show that fibrosis inhibited neutrophil intracellular killing of MRSA through impaired neutrophil elastase release and oxidative radical production. Additionally, we demonstrate that lung macrophages from fibrotic mice have impaired phagocytosis of MRSA. Our study describes potentially novel impairments of antimicrobial responses upon pulmonary fibrosis development, and our findings suggest a possible mechanism for why patients with IPF are at greater risk of morbidity and mortality related to infection.