Citations

Abstract Repetitive injury is hypothesized to lead to progressive tissue fibrosis and end-stage organ failure. Whether tissue-resident mesenchymal cell populations retain epigenetic memory of prior injuries that contribute to this pathological process is unknown. Here we used a genetic lineage labeling approach to mark the lung mesenchyme prior to injury, then performed multimodal analyses on isolated lung mesenchyme during the initiation, progression, and resolution of the fibrotic response. Our results demonstrate the remarkable epigenetic and transcriptional plasticity of the lung mesenchyme during fibrotic activation and de-activation. Despite this plasticity, we also find that the lung mesenchyme exhibits an enhanced fibrotic program upon reinjury. We identify RUNX1 as a critical driver of both fibrotic activation and fibrotic memory. Comparison of fresh isolated and cultured lung mesenchyme demonstrates that RUNX1 is spontaneously activated in standard culture conditions, previously masking these roles of RUNX1. Targeted knockdown of RUNX1 dampens fibrotic mesenchymal cell activation immediately after cell isolation, but with reduced efficacy after only days of culture, confirming its functional importance to both early activation and long-term memory. Collectively, our findings implicate RUNX1 in the initiation and memory of fibrotic mesenchymal cell activation that together prime enhanced mesenchymal cell responses upon repeated injury.

This study uncovers a previously unrecognized role for NAV3 in TGF-β1-driven cardiac fibroblast activation. We show that NAV3 facilitates profibrotic remodeling through noncanonical signaling and cell cycle arrest, independently of SMAD2/3. These findings position NAV3 as a novel regulator of fibroblast phenotype and a potential modulator of cardiac fibrosis.

Pulmonary fibrosis is a devastating and progressive disease marked by replacement of gas-exchanging tissue with collagen-rich scar. The mechanical environment is profoundly altered in pulmonary fibrosis and contributes to disease progression via feedback relationships between cells, the extracellular matrix, and the evolving mechanical environment. Targeting these mechanobiological feedback loops has emerged as a promising approach to interrupt disease progression, though with challenges in how to intervene selectively, safely, and effectively. We posit that further delineation of cell–matrix mechanobiological interactions will be pivotal to promoting fibrosis resolution and should guide efforts to discover and implement new approaches that can preserve or even restore lung function. To set the stage for these advances, we first review the mechanobiology of the healthy lung and the feedback loops that promote fibrosis progression. We then lay out the challenges and opportunities for targeting the fibrotic matrix as an essential element for protecting or restoring lung function.

Recent studies highlight transcriptionally distinct fibroblast subpopulations in human lungs. We observed the loss of these native transcriptional programs as fresh isolated cells are maintained in traditional culture conditions. Identifying the signals defining native fibroblast identities will be pivotal to creating culture models that preserve unique subpopulations. The screening system developed here will allow the investigation of a broad selection of cues, leading to better culture models for studying human lung fibroblast function and plasticity.

Background: Cardiac fibrosis is a critical and independent driver of heart failure (HF), characterized by excessive extracellular matrix (ECM) deposition. Decreased CDCP1 (CUB domain-containing protein 1) expression has been associated with myocardial recovery in human genome wide association studies by attenuating PDGF-BB driven cardiac fibroblast proliferation with no effect on canonical TGF-beta mediated transdifferentiation in-vitro. In-vivo, Cdcp1 deletion significantly reduced cardiac fibrosis and dysfunction in an angiotensin II/phenylephrine-induced pressure overload mouse model. However, its upstream regulators and its downstream effects on molecular signaling pathways that modulate ECM remodeling are unknown. Hypothesis: CDCP1 promotes human cardiac fibroblast mediated ECM remodeling in the HF microenvironment. Methods: Human ventricular fibroblasts (HVF) were treated with PDGF-BB (20 ng/ml), TGF-β (10 ng/ml), or Angiotensin II (100 ng/ml) for 48 hours. CDCP1 knockdown (KD) was achieved through siRNA transfection. Gene expression analysis was performed using qRT-PCR and protein quantification by Western blot. Both intact HVF and decellularized ECM were immunostained for collagen 1 to evaluate for ECM compositional changes. Results: Individual and combination treatments with fibrotic stimuli significantly increased CDCP1 expression (Figure 1A-1B). CDCP1 KD resulted in reduction of key ECM markers COL1A1, CTGF, and LOX (Figure 1C) across all fibrotic stimuli . Immunostaining of HVF after treatment with fibrotic stimuli showed reduced collagen 1 production with CDCP1 KD (Figure 1D). Western blot analysis showed increased phosphorylation of Src (tyr416) with 6h of treatment with fibrotic stimuli which was nullified by silencing of CDCP1 (Figure 1E). Conclusion: Our findings demonstrate that CDCP1 is necessary for ECM synthesis and Src signaling across multiple profibrotic pathways. Selective targeting of CDCP1 to modulate Src signaling pathways could provide novel therapeutic avenues for HF and fibrosis treatment.

Abstract Pulmonary fibrosis is increasingly understood to involve dysfunction within and across multiple cellular compartments, with recent attention highlighting the involvement of pulmonary vascular dysfunction in failed repair and progression of fibrosis. Formulation and delivery of lung-targeting lipid nanoparticles (LNPs) may provide a means to selectively target the lung but not systemic vasculature. However, the feasibility and efficacy of such approaches in the fibrotic lung are unknown. We sought to test whether intravenously administered lung-targeting LNPs can safely deliver mRNA to the healthy and fibrotic lung vasculature in young and aged mice and whether delivery of mRNA encoding a matricellular protein could promote fibrosis resolution. We used a selective organ targeting LNP formulation and characterized cell-specificity of delivery after bleomycin-induced lung fibrosis. We then delivered Ccn3 mRNA (encoding cellular communication network factor 3) to aged mice in the setting of established lung fibrosis and evaluated fibrotic regression and vascular repair. The matricellular protein encoded by Ccn3 was previously identified by our group as an important regulator of lung endothelial function. We found that LNP delivery was lung specific and predominantly endothelial targeting in the setting of lung fibrosis. Delivery of Ccn3 mRNA to aged mice via LNPs modestly reduced fibrosis and improved microvascular density in the lungs. Our results support the concept that cell-specific and repair-promoting cargos delivered via lung-targeting LNPs may have utility for treatment of established fibrosis.

This study demonstrates that circulating extracellular vesicles (cEVs) isolated from young mice reverse the transcriptional alterations of the aged mouse pulmonary vasculature, leading to a more youthful endothelial transcriptional phenotype. As a result of this vascular phenotype, aged mice are protected from bleomycin-induced pulmonary fibrosis. These findings highlight the therapeutic potential of targeting vascular aging to alleviate pulmonary fibrosis.

Abstract Rationale Extracellular matrix (ECM) accumulation results from an imbalance between ECM deposition and degradation, due to persistently increased ECM synthesis or reduced resorption. Fibroblasts, as key regulators of ECM homeostasis in both health and disease, are essential targets to rebalance ECM turnover. Recent findings indicate that fibroblasts are regulated by immune cells, which can influence ECM deposition. Specifically, myeloperoxidase (MPO), an enzyme produced by neutrophils, has been shown to enhance fibroblast-driven ECM accumulation in various diseases. In patients with radiographic Interstitial Lung Disease (ILD), elevated MPO levels have been correlated with reduced lung capacity (Cantin et al., 1987), while recent studies report increased MPO levels in the bronchoalveolar lavage fluid of ILD patients (Ngo et al., EJROR 2024). Additionally, MPO and related immune dysregulation proteins are found in fibrotic alveoli in Idiopathic Pulmonary Fibrosis (IPF) (Herrera et al., JCI Insight 2022). These findings suggest an association between MPO and lung fibrosis, yet it remains uncertain whether MPO directly influences ECM accumulation in fibrotic progression. Methods Patient tissue and serum samples were collected with consent, and MPO levels were quantified using ELISA and immunofluorescence techniques. Biochemical assays were performed using MPO isolated from human leukocytes, recombinant cathepsin K, and hydrogen peroxide to investigate whether MPO influences cathepsin K activity. Precision cut lung slices (PCLS) were prepared from untreated C57BL/6 mice and treated with transforming growth factor-beta (TGFβ) and/or MPO for four days, with cathepsin K activity assessed using fluorescence assays. Additionally, MPO-knockout and wild-type mice received intratracheal bleomycin, and after 14 days, cathepsin K activity was quantified via in vivo imaging. Collagen content, as an indicator of fibrosis, was measured by quantifying hydroxyproline in harvested lung tissue. Results/Discussion/Conclusion Increased MPO levels were observed in immunofluorescent-stained samples (57%; 4/7) and serum samples (30%; 3/10) from IPF patients. Biochemical assays demonstrated that physiological levels of MPO (0.2 µg/ml) combined with H2O2 reduced recombinant cathepsin K activity by 85%. In PCLS treated with MPO, cathepsin K activity decreased by 50% with or without TGFβ. After bleomycin treatment, wild-type mice showed reduced cathepsin K activity, while MPO-knockout mice maintained activity levels. Both survival and weight loss were similar between wild-type and MPO-knockout mice; however, collagen content was significantly higher in wild-type mice, whereas MPO-knockout mice were protected from bleomycin-induced collagen accumulation. These findings suggest that MPO contributes to ECM accumulation in lung fibrosis, potentially through inhibition of collagenolytic enzymes such as cathepsin K.

Abstract Rationale: Application of single cell RNAseq (scRNAseq) in idiopathic pulmonary fibrosis (IPF) and multiple murine models has revealed two unique disease associated fibroblast subsets, the Cthrc1+ fibrotic population, and a population expressing inflammatory markers whose function is unclear. We, and others, have demonstrated that inflammatory fibroblasts are derived from homeostatic fibroblasts and can differentiate to Cthrc1+ fibroblasts. There is also data in mice suggesting that TGFβ inhibition prevents the emergence of Cthrc1+ fibrotic fibroblasts without impacting the inflammatory fibroblast population. Using our inducible genetic murine model of PF, reductionist organoid systems, and scRNAseq from IPF we present evidence and mechanism for inflammatory fibroblasts as a potential regenerative population in the alveolar niche. Methods: Tamoxifen administration to SftpcI73T conditional allelic knock-in mice, induces expression of mutant protein and promotes an inflammatory cascade followed by fibrogenesis. ScRNA-seq and population RNA-seq of bleomycin and SftpcI73T murine models were compared with publicly available data sets from IPF to identify population specific surface marker expression and potential epithelial ligand-receptor pairs. Flow cytometry approaches developed to isolate fibroblast populations were applied for in-vitro organoid modeling and validation of signaling pathways. In-vivo murine intervention in TGFβ signaling was further applied to confirm functional biology of inflammatory fibroblasts. Results: Informatic analysis of human and mouse inflammatory fibroblasts identifies expression of multiple BMP antagonists that have previously been associated with epithelial proliferation. Furthermore, human inflammatory fibroblasts also express key epithelial growth factors including FGF2 and FGF7. Murine organoid modeling confirms that inflammatory fibroblasts support alveolar organoid formation through the inhibition of BMP signaling. As was previously demonstrated in bleomycin, the inhibition of TGFβ signaling in SftpcI73T does not alter the inflammatory fibroblast population, rather this population is sustained, and alveolar epithelial proliferation increases. Additionally, we did not find any evidence for increase inflammation in the mouse lung due to inflammatory fibroblasts preservation. Finally, human data suggests that two populations of inflammatory fibroblasts are present in the lung with only one subset found to express the BMP antagonists and growth factors required to promote alveolar epithelial proliferation. Conclusions: Our data identifies that inflammatory fibroblasts in the alveolar niche inhibit BMP signaling and allow for epithelial expansion. We also determine differences between murine and human inflammatory fibroblasts suggesting that human inflammatory fibroblasts have a greater potential to drive epithelial expansion. These data shed light on the functional role of inflammatory fibroblasts, further refining our understanding of fibroblast heterogeneity in IPF.