Attenuated T cell activation and rearrangement of T cell receptor β repertoire in silica nanoparticle-induced pulmonary fibrosis of mice

An amphiregulin reporter mouse enables transcriptional and clonal expansion analysis of reparative lung Treg cells

Regulatory T (Treg) cells are known to play critical roles in tissue repair via provision of growth factors such as amphiregulin (Areg). Areg-producing Treg cells have previously been difficult to study because of an inability to isolate live Areg-producing cells. In this report, we created a novel reporter mouse to detect Areg expression in live cells ( Areg Thy1.1 ). We employed influenza A and bleomycin models of lung damage to sort Areg-producing and -non-producing Treg cells for transcriptomic analyses. Single cell RNA-seq revealed distinct subpopulations of Treg cells and allowed transcriptomic comparisons of damage-induced populations. Single cell TCR sequencing showed that Treg cell clonal expansion is biased towards Areg-producing Treg cells, and largely occurs within damage-induced subgroups. Gene module analysis revealed functional divergence of Treg cells into immunosuppression-oriented and tissue repair-oriented groups, leading to identification of candidate receptors for induction of repair activity in Treg cells. We tested these using an ex vivo assay for Treg cell-mediated tissue repair, identifying 4-1BB agonism as a novel mechanism for reparative activity induction. Overall, we demonstrate that the Areg Thy1.1 mouse is a promising tool for investigating tissue repair activity in leukocytes.

Silica's silent threat: Contributing to skin fibrosis in systemic sclerosis by targeting the HDAC4/Smad2/3 pathway

Nowadays, silica products are widely used in daily life, especially in skin applications, which inevitably increases the risk of silica exposure in general population. However, inadequate awareness of silica's potential hazards and lack of self-protection are of concern. Systemic sclerosis (SSc) is characterized by progressive tissue fibrosis under environmental and genetic interactions. Silica exposure is considered an important causative factor for SSc, but its pathogenesis remains unclear. Within this study, we showed that lower doses of silica significantly promoted the proliferation, migration, and activation of human skin fibroblasts (HSFs) within 24 h. Silica injected subcutaneously into mice induced and exacerbated skin fibrosis. Notably, silica increased histone deacetylase-4 (HDAC4) expression by inducing its DNA hypomethylation in normal HSFs. The elevated HDAC4 expression was also confirmed in SSc HSFs. Furthermore, HDAC4 was positively correlated with Smad2/3 phosphorylation and COL1, α-SMA, and CTGF expression. The HDAC4 inhibitor LMK235 mitigated silica-induced upregulation of these factors and alleviated skin fibrosis in SSc mice. Taken together, silica induces and exacerbates skin fibrosis in SSc patients by targeting the HDAC4/Smad2/3 pathway. Our findings provide new insights for evaluating the health hazards of silica exposure and identify HDAC4 as a potential interventional target for silica-induced SSc skin fibrosis.

Crystalline silica-induced recruitment and immuno-imbalance of CD4+ tissue resident memory T cells promote silicosis progression

Occupational crystalline silica (CS) particle exposure leads to silicosis. The burden of CS-associated disease remains high, and treatment options are limited due to vague mechanisms. Here we show that pulmonary CD4+ tissue-resident memory T cells (TRM) accumulate in response to CS particles, mediating the pathogenesis of silicosis. The TRM cells are derived from peripheral lymphocyte recruitment and in situ expansion. Specifically, CD69+CD103+ TRM-Tregs depend more on circulating T cell replenishment. CD69 and CD103 can divide the TRM cells into functionally distinct subsets, mirroring the immuno-balance within CD4+ TRM cells. However, targeting CD103+ TRM-Tregs do not mitigate disease phenotype since the TRM subsets exert immunosuppressive but not pro-fibrotic roles. After identifying pathogenic CD69+CD103- subsets, we highlight IL-7 for their maintenance and function, that present a promising avenue for mitigating silicosis. Together, our findings highlight the distinct role of CD4+ TRM cells in mediating CS-induced fibrosis and provide potential therapeutic strategies.

Epithelium-derived exosomes promote silica nanoparticles-induced pulmonary fibroblast activation and collagen deposition via modulating fibrotic signaling pathways and their epigenetic regulations

BACKGROUND

In the context of increasing exposure to silica nanoparticles (SiNPs) and ensuing respiratory health risks, emerging evidence has suggested that SiNPs can cause a series of pathological lung injuries, including fibrotic lesions. However, the underlying mediators in the lung fibrogenesis caused by SiNPs have not yet been elucidated.

RESULTS

The in vivo investigation verified that long-term inhalation exposure to SiNPs induced fibroblast activation and collagen deposition in the rat lungs. In vitro, the uptake of exosomes derived from SiNPs-stimulated lung epithelial cells (BEAS-2B) by fibroblasts (MRC-5) enhanced its proliferation, adhesion, and activation. In particular, the mechanistic investigation revealed SiNPs stimulated an increase of epithelium-secreted exosomal miR-494-3p and thereby disrupted the TGF-β/BMPR2/Smad pathway in fibroblasts via targeting bone morphogenetic protein receptor 2 (BMPR2), ultimately resulting in fibroblast activation and collagen deposition. Conversely, the inhibitor of exosomes, GW4869, can abolish the induction of upregulated miR-494-3p and fibroblast activation in MRC-5 cells by the SiNPs-treated supernatants of BEAS-2B. Besides, inhibiting miR-494-3p or overexpression of BMPR2 could ameliorate fibroblast activation by interfering with the TGF-β/BMPR2/Smad pathway.

CONCLUSIONS

Our data suggested pulmonary epithelium-derived exosomes serve an essential role in fibroblast activation and collagen deposition in the lungs upon SiNPs stimuli, in particular, attributing to exosomal miR-494-3p targeting BMPR2 to modulate TGF-β/BMPR2/Smad pathway. Hence, strategies targeting exosomes could be a new avenue in developing therapeutics against lung injury elicited by SiNPs.

NF-κB pathway affects silica nanoparticle-induced fibrosis via inhibited inflammatory response and epithelial-mesenchymal transition in 3D co-culture

Long-term inhalation of silica nanoparticles (SiNPs) can induce pulmonary fibrosis (PF), nevertheless, the potential mechanisms remain elusive. Herein, we constructed a three-dimensional (3D) co-culture model by using Matrigel to investigate the interaction among different cells and potential regulatory mechanisms after SiNPs exposure. Methodologically, we dynamically observed the changes in cell morphology and migration after exposure to SiNPs by co-culturing mouse monocytic macrophages (RAW264.7), human non-small cell lung cancer cells (A549), and medical research council cell strain-5 (MRC-5) in Matrigel for 24 h. Subsequently, we detected the expression of nuclear factor kappa B (NF-κB), inflammatory factor and epithelial-mesenchymal transition (EMT) markers. The results showed that SiNPs produced toxic effects on cells. In the 3D co-culture state, the cell's movement velocity and displacement increased, and the cell migration ability was enhanced. Meanwhile, the expression of inflammatory factor tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) were upregulated, the epithelial marker E-cadherin (E-cad) was downregulated, the mesenchymal marker N-cadherin (N-cad) and myofibroblast marker alpha-smooth muscle actin (α-SMA) expression were upregulated, while NF-κB expression was also upregulated after SiNPs exposure. We further found that cells were more prone to transdifferentiate into myofibroblasts in the 3D co-culture state. Conversely, utilizing the NF-κB-specific inhibitor BAY 11-7082 effectively downregulated the expression of TNF-α, IL-6, interleukin-1β (IL-1β), N-cad, α-SMA, collagen-I (COL I), and fibronectin (FN), the expression of E-cad was upregulated. These findings suggest that NF-κB is involved in regulating SiNPs-induced inflammatory, EMT, and fibrosis in the 3D co-culture state.

Silica nanoparticles induce pulmonary damage in rats via VEGFC/D-VEGFR3 signaling-mediated lymphangiogenesis and remodeling

Silica nanoparticles (SiNPs) are widely used as drug carriers for improving drug delivery and retention. The lungs are highly sensitive to the toxicity of SiNPs entering the respiratory tract. Furthermore, pulmonary lymphangiogenesis, which is the growth of lymphatic vessels observed during multiple pulmonary diseases, plays a vital role in promoting the lymphatic transport of silica in the lungs. However, more research is required on the effects of SiNPs on pulmonary lymphangiogenesis. We investigated the effect of SiNP-induced pulmonary toxicity on lymphatic vessel formation in rats and evaluated the toxicity and possible molecular mechanisms of 20-nm SiNPs. Saline containing 3.0, 6.0, and 12.0mg/kg of SiNPs was instilled intrathecally into female Wistar rats once a day for five days, then sacrificed on day seven. Lung histopathology, pulmonary permeability, pulmonary lymphatic vessel density changes, and the ultrastructure of the lymph trunk were investigated using light microscopy, spectrophotometry, immunofluorescence, and transmission electron microscopy. CD45 expression in lung tissues was determined using immunohistochemical staining, and protein expression in the lung and lymph trunk was quantified using western blotting. We observed increased pulmonary inflammation and permeability, lymphatic endothelial cell damage, pulmonary lymphangiogenesis, and remodeling with increasing SiNP concentration. Moreover, SiNPs activated the VEGFC/D-VEGFR3 signaling pathway in the lung and lymphatic vessel tissues. SiNPs caused pulmonary damage, increased permeability and resulted in inflammation-associated lymphangiogenesis and remodeling by activating VEGFC/D-VEGFR3 signaling. Our findings provide evidence for SiNP-induced pulmonary damage and a new perspective for the prevention and treatment of occupational exposure to SiNPs. DATA AVAILABILITY: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.