Myeloid cell populations and fibrogenic parameters in bleomycin- and HOCl-induced fibrosis

Characteristics and impact of infiltration of B-cells from systemic sclerosis patients in a 3D healthy skin model

Introduction

In systemic sclerosis (SSc), B-cells are activated and present in the skin and lung of patients where they can interact with fibroblasts. The precise impact and mechanisms of the interaction of B-cells and fibroblasts at the tissular level are poorly studied.

Objective

We investigated the impact and mechanisms of B-cell/fibroblast interactions in cocultures between B-cells from patients with SSc and 3-dimensional reconstituted healthy skin model including fibroblasts, keratinocytes and extracellular matrix.

Methods

The quantification and description of the B-cell infiltration in 3D cocultures were performed using cells imagery strategy and cytometry. The effect of coculture on the transcriptome of B-cells and fibroblasts was studied with bulk and single-cell RNA sequencing approaches. The mechanisms of this interaction were studied by blocking key cytokines like IL-6 and TNF.

Results

We showed a significant infiltration of B-cells in the 3D healthy skin model. The amount but not the depth of infiltration was higher with B-cells from SSc patients and with activated B-cells. B-cell infiltrates were mainly composed of naïve and memory cells, whose frequencies differed depending on B-cells origin and activation state: infiltrated B-cells from patients with SSc showed an activated profile and an overexpression of immunoglobulin genes compared to circulating B-cells before infiltration. Our study has shown for the first time that activated B-cells modified the transcriptomic profile of both healthy and SSc fibroblasts, toward a pro-inflammatory (TNF and IL-17 signaling) and interferon profile, with a key role of the TNF pathway.

Conclusion

B-cells and 3D skin cocultures allowed the modelization of B-cells infiltration in tissues observed in SSc, uncovering an influence of the underlying disease and the activation state of B-cells. We showed a pro-inflammatory effect on skin fibroblasts and pro-activation effect on infiltrating B-cells during coculture. This reinforces the role of B-cells in SSc and provide potential targets for future therapeutic approach in this disease.

The antifibrotic effects of naringin in a hypochlorous acid (HOCl)-induced mouse model of skin fibrosis

OBJECTIVES

Fibrosis is a chronic inflammation caused by the loss of innate compensational mechanisms. Naringin (NR) is a flavonoid with antineoplastic and anti-inflammatory effects. Here, we aimed to investigate the antifibrotic effects of NR and underlying mechanisms in a Hypochlorous acid (HOCl)-induced mouse model of skin fibrosis.

MATERIALS AND METHODS

A total of 24 six-week-old female BALB/c mice were randomly allocated into five groups: HOCl, Sham, PBS, HOCl + NR and DMSO and selected skin regions were treated for 6 weeks, until sacrifice. The histopathologic and collagenesis of skin resections were analyzed using H&E and PR staining. The mRNA levels of COL1, COL3 and αSMA genes were quantified. Serum samples were also used to evaluate TGF-β levels and LDH activity.

RESULTS

HOCl could increase the relative collagen content, while NR administration on HOCl-treated biopsies decreased collagenesis. COL1, COL3 and αSMA mRNA levels were significantly increased among HOCl-treated skin samples, while NR treatment could decrease these mRNA levels of genes to the extent equal to the levels in the Sham group. Similarly, Naringin-treated samples could decrease TGF-β levels.

CONCLUSIONS

We demonstrated that Naringin could exert protective effects against fibrotic complications of HOCL in skin tissue in vivo, by reducing the collagenesis and decreasing the levels of fibrosis-associated genes.

Generation of a novel CD30+ B cell subset producing GM-CSF and its possible link to the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is a T helper type 2 (Th2)-associated autoimmune disease characterized by vasculopathy and fibrosis. Efficacy of B cell depletion therapy underscores antibody-independent functions of B cells in SSc. A recent study showed that the Th2 cytokine interleukin (IL)-4 induces granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing effector B cells (GM-Beffs ) in humans. In this study, we sought to elucidate the generation mechanism of GM-Beffs and also determine a role of this subset in SSc. Among Th-associated cytokines, IL-4 most significantly facilitated the generation of GM-Beffs within memory B cells in healthy controls (HCs). In addition, the profibrotic cytokine transforming growth factor (TGF)-β further potentiated IL-4- and IL-13-induced GM-Beffs . Of note, tofacitinib, a Janus kinase (JAK) inhibitor, inhibited the expression of GM-CSF mRNA and protein in memory B cells induced by IL-4, but not by TGF-β. GM-Beffs were enriched within CD20+ CD30+ CD38-/low cells, a distinct population from plasmablasts, suggesting that GM-Beffs exert antibody-independent functions. GM-Beffs were also enriched in a CD30+ fraction of freshly isolated B cells. GM-Beffs generated under Th2 conditions facilitated the differentiation from CD14+ monocytes to DC-SIGN+ CD1a+ CD14- CD86+ cells, which significantly promoted the proliferation of naive T cells. CD30+ GM-Beffs were more pronounced in patients with SSc than in HCs. A subpopulation of SSc patients with the diffuse type and concomitant interstitial lung disease exhibited high numbers of GM-Beffs . Together, these findings suggest that human GM-Beffs are enriched in a CD30+ B cell subset and play a role in the pathogenesis of SSc.

Intervention of Inflammatory Monocyte Activity Limits Dermal Fibrosis

Monocytes and monocyte-derived cells are important players in the initiation, progression, and resolution of inflammatory skin reactions. As inflammation is a prerequisite for fibrosis development, we focused on the role of monocytes in cutaneous fibrosis, the clinical hallmark of patients suffering from systemic sclerosis. Investigating the function of monocytes in reactive oxygen species-induced dermal fibrosis, we observed that early monocyte depletion partially reduced disease severity. Low numbers of inflammatory Ly6C^high monocytes, as well as inhibition of CCR2 and CCL2 in wild type animals by a specific L-RNA aptamer, mitigated disease parameters, indicating a pivotal role for CCR2⁺ inflammatory monocytes and the CCR2/CCL2 axis in fibrosis development. Of note, mice lacking splenic reservoirs failed to recruit monocytes to the skin and developed less fibrosis. Furthermore, enforced monocyte conversion into noninflammatory, patrolling Ly6C^low monocytes by a nuclear receptor Nur77-agonist also resulted in significantly impaired cutaneous inflammation and dermal fibrosis. Most evident, pronounced monocyte conversion in interferon stimulated gene 12-deficient mice with pronounced nuclear Nur77 signaling completely protected from dermal fibrosis. Our study shows that inflammatory monocytes that are recruited from splenic reservoirs play a key role in the development of skin fibrosis and can be therapeutically challenged by forced conversion via the Nur77/interferon stimulated gene 12 axis.

Attenuating Effects of Nortrachelogenin on IL-4 and IL-13 Induced Alternative Macrophage Activation and on Bleomycin-Induced Dermal Fibrosis

Excessive alternative macrophage activation contributes to fibrosis. We studied the effects of nortrachelogenin, the major lignan component of Pinus sylvestris knot extract, on alternative (M2) macrophage activation. J774 murine and THP-1 human macrophages were cultured with IL-4+IL-13 to induce alternative activation, together with the extract and its components. Effects of nortrachelogenin were also studied in bleomycin-induced murine dermal fibrosis model. Knot extract significantly decreased the expression of alternative activation markers-arginase 1 in murine macrophages (97.4 ± 1.3% inhibition at 30 μg/mL) and CCL13 and PDGF in human macrophages-as did nortrachelogenin (94.9 ± 2.4% inhibition of arginase 1 at 10 μM). Nortrachelogenin also decreased PPARγ expression but had no effect on STAT6 phosphorylation. In vivo, nortrachelogenin reduced bleomycin-induced increase in skin thickness as well as the expression of collagens COL1A1, COL1A2, and COL3A1 (all by >50%). In conclusion, nortrachelogenin suppressed IL-4+IL-13-induced alternative macrophage activation and ameliorated bleomycin-induced fibrosis, indicating therapeutic potential in fibrosing conditions.

Regulatory T cell deficient scurfy mice exhibit a Th2/M2-like inflammatory response in the skin

BACKGROUND

Scurfy mice have a functional defect in regulatory T cells (Treg), which leads to lethal multi-organ inflammation. The missing Treg function results in uncontrolled autoimmune cellular and humoral inflammatory responses. We and others have previously shown that during the course of disease scurfy mice develop severe skin inflammation and autoantibodies including anti-nuclear autoantibodies (ANA).

OBJECTIVE

Autoimmune skin inflammation and ANA are hallmarks for the diagnosis of autoimmune connective tissue diseases; therefore we analyzed scurfy mice for typical signs of these diseases.

METHODS

Indirect immunofluorescence was used to specify the ANA pattern in scurfy mice. Skin fibrosis was assessed by cutaneous collagen accumulation (Goldeners trichrome staining), collagen crosslinking/disorganization (Sirus red polarimetry) and quantitative PCR for fibrosis-related transcripts. The cellular components of the inflammatory infiltrates in scurfy skin were analyzed by flow cytometry and intracellular cytokine staining.

RESULTS

The majority of scurfy mice developed ANA with a predominant AC-5 pattern typical for mixed connective tissue disease, especially scleroderma. Scurfy mice showed higher skin collagen content compared to WT controls with a significant tendency in upregulation of TIMP-1. CD3⁺CD4⁺ T cells in scurfy skin exhibited a strong Th2 deviation with a significant increase of IL-4, IL-5 and IL-13, and M2-polarized CD11b⁺MHCII⁺ macrophages compared to WT mice.

CONCLUSION

We show that Scurfy mice show a predominant AC-5 ANA pattern typical for mixed connective tissue disease as in scleroderma. The autoimmune inflammation in scurfy skin mainly consists of CD4⁺ T cells with Th2 differentiation and alternatively-activated (M2) macrophages as it is found in scleroderma with advanced fibrosis.

B Cell Homeostasis and Functional Properties Are Altered in an Hypochlorous Acid-Induced Murine Model of Systemic Sclerosis

Introduction

During systemic sclerosis (SSc), peripheral B cells display alterations in subset homeostasis and functional properties and are a promising therapeutic target. However, there is only few data regarding whether these anomalies are accurately reproduced in animal models of SSc.

Objective

In this work, we assessed the B cell homeostasis modifications in an experimental model of SSc [hypochlorous acid (HOCl)-induced mouse], both at a phenotypic and functional level, during the course of the disease.

Methods

Balb/c mice underwent daily intradermal injections of HOCl (or phosphate-buffered saline) and were then sacrificed at day 21 (early inflammatory stage) or day 42 (late fibrotic stage). For phenotypic studies, the distribution of the main spleen cell subsets (B cells, T CD4 and CD8 cells, NK cells, macrophages) and splenic B cell subsets (immature, mature naïve, germinal center, antibody-secreting, memory, B1) was assessed by flow cytometry. For functional studies, splenic B cells were immediately MACS-sorted. Production of interleukin (IL)-6, CCL3, IL-10, and transforming growth factor (TGF)-β was assessed ex vivo by RT-PCR and after 48 h of culture by ELISA. Regulatory B cell (Breg) counts were quantified by flow cytometry.

Results

Phenotypic analyses showed an early expansion of transitional B cells, followed by a late expansion of the mature naive subset and decrease in plasmablasts and memory B cells. These anomalies are similar to those encountered in SSc patients. Functional analyses revealed a B-cell overproduction of pro-inflammatory cytokines (IL-6 and CCL3) and an impairment of their anti-inflammatory capacities (decreased production of IL-10 and TGF-β, reduced levels of Bregs) at the early inflammatory stage; and an overproduction of pro-fibrotic cytokines (TGF-β and IL-6) at the late fibrotic stage. These results approximate the anomalies observed in human SSc.

Conclusion

This work reports the existence of anomalies in B cell homeostasis and functional properties in an animal model of SSc that approximate those displayed by SSc patients. These anomalies vary over the course of the disease, which pleads for their participation in inflammatory and fibrotic events. This makes the HOCl mouse a relevant experimental model for the study of B cells, and therefore, B-cell-targeted therapies in SSc.

Dendritic cells maintain dermal adipose-derived stromal cells in skin fibrosis

Scleroderma is a group of skin-fibrosing diseases for which there are no effective treatments. A feature of the skin fibrosis typical of scleroderma is atrophy of the dermal white adipose tissue (DWAT). Adipose tissue contains adipose-derived mesenchymal stromal cells (ADSCs) that have regenerative and reparative functions; however, whether DWAT atrophy in fibrosis is accompanied by ADSC loss is poorly understood, as are the mechanisms that might maintain ADSC survival in fibrotic skin. Here, we have shown that DWAT ADSC numbers were reduced, likely because of cell death, in 2 murine models of scleroderma skin fibrosis. The remaining ADSCs showed a partial dependence on dendritic cells (DCs) for survival. Lymphotoxin β (LTβ) expression in DCs maintained ADSC survival in fibrotic skin by activating an LTβ receptor/β1 integrin (LTβR/β1 integrin) pathway on ADSCs. Stimulation of LTβR augmented the engraftment of therapeutically injected ADSCs, which was associated with reductions in skin fibrosis and improved skin function. These findings provide insight into the effects of skin fibrosis on DWAT ADSCs, identify a DC-ADSC survival axis in fibrotic skin, and suggest an approach for improving mesenchymal stromal cell therapy in scleroderma and other diseases.