Understanding fibrosis pathogenesis via modeling macrophage-fibroblast interplay in immune-metabolic context

Macrophage plasticity: signaling pathways, tissue repair, and regeneration

Macrophages are versatile immune cells with remarkable plasticity, enabling them to adapt to diverse tissue microenvironments and perform various functions. Traditionally categorized into classically activated (M1) and alternatively activated (M2) phenotypes, recent advances have revealed a spectrum of macrophage activation states that extend beyond this dichotomy. The complex interplay of signaling pathways, transcriptional regulators, and epigenetic modifications orchestrates macrophage polarization, allowing them to respond to various stimuli dynamically. Here, we provide a comprehensive overview of the signaling cascades governing macrophage plasticity, focusing on the roles of Toll-like receptors, signal transducer and activator of transcription proteins, nuclear receptors, and microRNAs. We also discuss the emerging concepts of macrophage metabolic reprogramming and trained immunity, contributing to their functional adaptability. Macrophage plasticity plays a pivotal role in tissue repair and regeneration, with macrophages coordinating inflammation, angiogenesis, and matrix remodeling to restore tissue homeostasis. By harnessing the potential of macrophage plasticity, novel therapeutic strategies targeting macrophage polarization could be developed for various diseases, including chronic wounds, fibrotic disorders, and inflammatory conditions. Ultimately, a deeper understanding of the molecular mechanisms underpinning macrophage plasticity will pave the way for innovative regenerative medicine and tissue engineering approaches.

Retroductal dexamethasone administration promotes the recovery from obstructive and inflammatory salivary gland dysfunction

Introduction

Salivary gland dysfunction, often resulting from salivary gland obstruction-induced inflammation, is a prevalent condition. Corticosteroid, known for its anti-inflammatory and immunomodulatory properties, is commonly prescribed in clinics. This study investigates the therapeutic implications and potential side effects of dexamethasone on obstructive sialadenitis recovery using duct ligation mice and salivary gland organoid models.

Methods

Functional and pathological changes were assessed after administering dexamethasone to the duct following deligation 2 weeks after maintaining ligation of the mouse submandibular duct. Additionally, lipopolysaccharide- and tumor necrosis factor-induced salivary gland organoid inflammation models were established to investigate the effects and underlying mechanisms of action of dexamethasone.

Results

Dexamethasone administration facilitated SG function restoration, by increasing salivary gland weight and saliva volume while reducing saliva lag time. Histological evaluation revealed, reduced acinar cell atrophy and fibrosis with dexamethasone treatment. Additionally, dexamethasone suppressed pro-inflammatory cytokines IL-1β and TNF expression. In a model of inflammation in salivary gland organoids induced by inflammatory substances, dexamethasone restored acinar markers such as AQP5 gene expression levels, while inhibiting pro-inflammatory cytokines TNF and IL6, as well as chemokines CCL2, CXCL5, and CXCL12 induction. Macrophages cultured in inflammatory substance-treated media from salivary gland organoid cultures exhibited pro-inflammatory polarization. However, treatment with dexamethasone shifted them towards an anti-inflammatory phenotype by reducing M1 markers (Tnf, Il6, Il1b, and Cd86) and elevating M2 markers (Ym1, Il10, Cd163, and Klf4). However, high-dose or prolonged dexamethasone treatment induced acino-ductal metaplasia and had side effects in both in vivo and in vitro models.

Conclusions

Our findings suggest the effectiveness of corticosteroids in treating obstructive sialadenitis-induced salivary gland dysfunction by regulating pro-inflammatory cytokines.

Identification of tyrosine brominated extracellular matrix proteins in normal and fibrotic lung tissues

Peroxidasin (PXDN) is a secreted heme peroxidase that catalyzes the oxidative crosslinking of collagen IV within the extracellular matrix (ECM) via intermediate hypobromous acid (HOBr) synthesis from hydrogen peroxide and bromide, but recent findings have also suggested alternative ECM protein modifications by PXDN, including incorporation of bromide into tyrosine residues. In this work, we sought to identify the major target proteins for tyrosine bromination by HOBr or by PXDN-mediated oxidation in ECM from mouse teratocarcinoma PFHR9 cells. We detected 61 bromotyrosine (BrY)-containing peptides representing 23 proteins in HOBr-modified ECM from PFHR9 cells, among which laminins displayed the most prominent bromotyrosine incorporation. Moreover, we also found that laminin α1, laminin β1, and tubulointerstitial nephritis antigen-like (TINAGL1) contained BrY in untreated PFHR9 cells, which depended on PXDN. We extended these analyses to lung tissues from both healthy mice and mice with experimental lung fibrosis, and in lung tissues obtained from human subjects. Analysis of ECM-enriched mouse lung tissue extracts showed that 83 ECM proteins were elevated in bleomycin-induced fibrosis, which included various collagens and laminins, and PXDN. Similarly, mRNA and protein expression of PXDN and laminin α/β1 were enhanced in fibrotic mouse lung tissues, and also in mouse bone-marrow-derived macrophages or human fibroblasts stimulated with transforming growth factor β1, a profibrotic growth factor. We identified 11 BrY-containing ECM proteins, including collagen IV α2, collagen VI α1, TINAGL1, and various laminins, in both healthy and mouse fibrotic lung tissues, although the relative extent of tyrosine bromination of laminins was not significantly increased during fibrosis. Finally, we also identified 7 BrY-containing ECM proteins in human lung tissues, again including collagen IV α2, collagen VI α1, and TINAGL1. Altogether, this work demonstrates the presence of several bromotyrosine-modified ECM proteins, likely involving PXDN, even in normal lung tissues, suggesting a potential biological function for these modifications.

Therapeutic potential of stem cells in regeneration of liver in chronic liver diseases: Current perspectives and future challenges

The deposition of extracellular matrix and hyperplasia of connective tissue characterizes chronic liver disease called hepatic fibrosis. Progression of hepatic fibrosis may lead to hepatocellular carcinoma. At this stage, only liver transplantation is a viable option. However, the number of possible liver donors is less than the number of patients needing transplantation. Consequently, alternative cell therapies based on non-stem cells (e.g., fibroblasts, chondrocytes, keratinocytes, and hepatocytes) therapy may be able to postpone hepatic disease, but they are often ineffective. Thus, novel stem cell-based therapeutics might be potentially important cutting-edge approaches for treating liver diseases and reducing patient' suffering. Several signaling pathways provide targets for stem cell interventions. These include pathways such as TGF-β, STAT3/BCL-2, NADPH oxidase, Raf/MEK/ERK, Notch, and Wnt/β-catenin. Moreover, mesenchymal stem cells (MSCs) stimulate interleukin (IL)-10, which inhibits T-cells and converts M1 macrophages into M2 macrophages, producing an anti-inflammatory environment. Furthermore, it inhibits the action of CD4+ and CD8+ T cells and reduces the activity of TNF-α and interferon cytokines by enhancing IL-4 synthesis. Consequently, the immunomodulatory and anti-inflammatory capabilities of MSCs make them an attractive therapeutic approach. Importantly, MSCs can inhibit the activation of hepatic stellate cells, causing their apoptosis and subsequent promotion of hepatocyte proliferation, thereby replacing dead hepatocytes and reducing liver fibrosis. This review discusses the multidimensional therapeutic role of stem cells as cell-based therapeutics in liver fibrosis.

Identifying key genes related to the peritubular capillary rarefaction in renal interstitial fibrosis by bioinformatics

Renal interstitial fibrosis (RIF) is a key feature of progressive chronic kidney disease (CKD), characterized by tubular epithelial cell (TEC) hypoxia and peritubular capillary (PTC) rarefaction. However, the mechanisms underlying these processes remain poorly understood. To address this knowledge gap, we conducted a comparative transcriptome analysis of hypoxic and normoxic HK-2 cells, identifying 572 differentially expressed genes (DEGs). Subsequent Gene Ontology (GO), protein‒protein interaction (PPI) network, and hub gene analyses revealed significant enrichment of DEGs in the HIF-1 signaling pathway based on KEGG enrichment analysis. To further explore TEC modulation under hypoxic conditions, we performed chromatin immunoprecipitation (ChIP) sequencing targeting HIF-1α, identifying 2915 genes potentially regulated by HIF-1α. By comparing RNA sequencing and ChIP sequencing data, we identified 43 overlapping DEGs. By performing GO analysis and peak annotation with IGV, we identified two candidate molecules, VEGFA and BTG1, that are associated with angiogenesis and whose gene sequences were reliably bound by HIF-1α. Our study elucidates the molecular mechanisms underlying RIF, providing valuable insights for potential therapeutic interventions.

The tumor microenvironment shows a hierarchy of cell-cell interactions dominated by fibroblasts

The tumor microenvironment (TME) is comprised of non-malignant cells that interact with each other and with cancer cells, critically impacting cancer biology. The TME is complex, and understanding it requires simplifying approaches. Here we provide an experimental-mathematical approach to decompose the TME into small circuits of interacting cell types. We find, using female breast cancer single-cell-RNA-sequencing data, a hierarchical network of interactions, with cancer-associated fibroblasts (CAFs) at the top secreting factors primarily to tumor-associated macrophages (TAMs). This network is composed of repeating circuit motifs. We isolate the strongest two-cell circuit motif by culturing fibroblasts and macrophages in-vitro, and analyze their dynamics and transcriptomes. This isolated circuit recapitulates the hierarchy of in-vivo interactions, and enables testing the effect of ligand-receptor interactions on cell dynamics and function, as we demonstrate by identifying a mediator of CAF-TAM interactions - RARRES2, and its receptor CMKLR1. Thus, the complexity of the TME may be simplified by identifying small circuits, facilitating the development of strategies to modulate the TME.

Systems level identification of a matrisome-associated macrophage polarisation state in multi-organ fibrosis

Tissue fibrosis affects multiple organs and involves a master-regulatory role of macrophages which respond to an initial inflammatory insult common in all forms of fibrosis. The recently unravelled multi-organ heterogeneity of macrophages in healthy and fibrotic human disease suggests that macrophages expressing osteopontin (SPP1) associate with lung and liver fibrosis. However, the conservation of this SPP1+ macrophage population across different tissues and its specificity to fibrotic diseases with different etiologies remain unclear. Integrating 15 single-cell RNA-sequencing datasets to profile 235,930 tissue macrophages from healthy and fibrotic heart, lung, liver, kidney, skin, and endometrium, we extended the association of SPP1+ macrophages with fibrosis to all these tissues. We also identified a subpopulation expressing matrisome-associated genes (e.g., matrix metalloproteinases and their tissue inhibitors), functionally enriched for ECM remodelling and cell metabolism, representative of a matrisome-associated macrophage (MAM) polarisation state within SPP1+ macrophages. Importantly, the MAM polarisation state follows a differentiation trajectory from SPP1+ macrophages and is associated with a core set of regulon activity. SPP1+ macrophages without the MAM polarisation state (SPP1+MAM-) show a positive association with ageing lung in mice and humans. These results suggest an advanced and conserved polarisation state of SPP1+ macrophages in fibrotic tissues resulting from prolonged inflammatory cues within each tissue microenvironment.

Immunology of human fibrosis

Fibrosis, defined by the excess deposition of structural and matricellular proteins in the extracellular space, underlies tissue dysfunction in multiple chronic diseases. Approved antifibrotics have proven modest in efficacy, and the immune compartment remains, for the most part, an untapped therapeutic opportunity. Recent single-cell analyses have interrogated human fibrotic tissues, including immune cells. These studies have revealed a conserved profile of scar-associated macrophages, which localize to the fibrotic niche and interact with mesenchymal cells that produce pathological extracellular matrix. Here we review recent advances in the understanding of the fibrotic microenvironment in human diseases, with a focus on immune cell profiles and functional immune-stromal interactions. We also discuss the key role of the immune system in mediating fibrosis regression and highlight avenues for future study to elucidate potential approaches to targeting inflammatory cells in fibrotic disorders.

Another piece in the puzzle of kidney fibrosis

Kidney fibrosis is a chronic physiomorphologic transformation of the renal parenchyma. Despite the known characteristics of the related structural and cellular changes, the mechanisms responsible for the initiation and progression of renal fibrosis are not completely understood. Development of efficient therapeutic drugs aimed at preventing the progressive loss of renal function requires an in-depth understanding of the complex phenomena associated with the pathophysiology of human diseases. The investigation of Li et al. provides novel evidence in this direction.

Photothermal Controlled-Release Immunomodulatory Nanoplatform for Restoring Nerve Structure and Mechanical Nociception in Infectious Diabetic Ulcers

Infectious diabetic ulcers (IDU) require anti-infection, angiogenesis, and nerve regeneration therapy; however, the latter has received comparatively less research attention than the former two. In particular, there have been few reports on the recovery of mechanical nociception. In this study, a photothermal controlled-release immunomodulatory hydrogel nanoplatform is tailored for the treatment of IDU. Due to a thermal-sensitive interaction between polydopamine-reduced graphene oxide (pGO) and the antibiotic mupirocin, excellent antibacterial efficacy is achieved through customized release kinetics. In addition, Trem2⁺ macrophages recruited by pGO regulate collagen remodeling and restore skin adnexal structures to alter the fate of scar formation, promote angiogenesis, accompanied by the regeneration of neural networks, which ensures the recovery of mechanical nociception and may prevent the recurrence of IDU at the source. In all, a full-stage strategy from antibacterial, immune regulation, angiogenesis, and neurogenesis to the recovery of mechanical nociception, an indispensable neural function of skin, is introduced to IDU treatment, which opens up an effective and comprehensive therapy for refractory IDU.