Fibrocytes in Asthma and Chronic Obstructive Pulmonary Disease: Variations on the Same Theme

The role of macrophages in asthma-related fibrosis and remodelling

Airway remodelling significantly contributes to the progressive loss of lung function and heightened symptom severity in chronic asthma. Additionally, it often persists and demonstrates reduced responsiveness to the mainstay treatments. The excessive deposition of collagen and extracellular matrix proteins leads to subepithelial fibrosis and airway remodelling, resulting in increased stiffness and decreased elasticity in the airway. Studies have emphasized the crucial role of subepithelial fibrosis in the pathogenesis of asthma. Fibrotic processes eventually cause airway narrowing, reduced lung function, and exacerbation of asthma symptoms. Macrophages play a crucial role in this process by producing pro-fibrotic cytokines, growth factors, and enzymes such as matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Additionally, identification of novel genetic markers has provided evidence for a strong genetic component in fibrosis within macrophage regulated fibrosis. Although macrophages contribute to the progression of airway remodelling and subepithelial fibrosis, interventions targeting macrophage-driven fibrotic changes have not yet been developed. This review synthesizes research on the intricate pathways through which macrophages contribute to subepithelial fibrosis in chronic asthma and its' pathological features. Understanding the interplay between macrophages, fibrosis, and asthma pathogenesis is essential for developing effective therapeutic strategies to manage severe asthma and improve patient outcomes.

Respiratory symptoms, sensitisation and occupational exposure in the shrimp processing industry

Introduction

Shellfish processing workers are highly susceptible to respiratory illnesses such as allergies and asthma. This study examined respiratory symptoms and biomarkers of allergy and asthma in Norwegian shrimp processing plant workers and evaluated allergenic and irritant protein exposures in the workplace.

Material and methods

The study included 35 shrimp processing workers and 21 controls. Respiratory symptoms were assessed via questionnaire; blood samples were analysed for allergy and asthma biomarkers and specific IgE levels. Air samples were analysed for protein levels and composition.

Results

Shrimp processing workers had four to five times higher odds of reporting acute upper and chronic lower respiratory symptoms than the controls. They also had significantly higher plasma levels of IL4, CCL20, CSF2 and MMP12, with 11% of the exposed workers showing elevated levels of shrimp and crab specific IgE. Furthermore, exposed workers showed increased plasma levels of SFTPD and CHI3L1 post-shift. The median total protein exposure was 6 µg/m3, with peaks up to 66 µg/m3 in the cooking and peeling department. Total protein levels were correlated with CCL20, IL13, and basophil counts. Ninety-five shrimp proteins were identified, including seven known and eight potential allergens. Tropomyosin levels were generally high, particularly in the cooking and peeling department.

Conclusion

Shrimp workers had a higher prevalence of respiratory symptoms and biomarkers of allergy and asthma. The work environment contained tropomyosin and other allergenic proteins as well as irritants, highlighting the need for protective measures, especially in the cooking and peeling departments.

Cell-in-cell-mediated intercellular communication exacerbates the pro-inflammatory progression in asthma

Cell-in-cell (CIC) structures have been suggested to mediate intracellular substance transport between cells and have been found widely in inflammatory lung tissue of asthma. The aim of this study was to investigate the significance of CIC structures in inflammatory progress of asthma. CIC structures and related inflammatory pathways were analyzed in asthmatic lung tissue and normal lung tissue of mouse model. In vitro, the activation of inflammatory pathways by CIC-mediated intercellular communication was analyzed by RNA-Seq and verified by Western blotting and immunofluorescence. Results showed that CIC structures of lymphocytes and alveolar epithelial cells in asthmatic lung tissue mediated intercellular substance (such as mitochondria) transfer and promoted pro-inflammation in two phases. At early phase, internal lymphocytes triggered inflammasome-dependent pro-inflammation and cell death of itself. Then, degraded lymphocytes released cellular contents such as mitochondria inside alveolar epithelial cells, further activated multi-pattern-recognition receptors and NF-kappa B signaling pathways of alveolar epithelial cells, and thereby amplified pro-inflammatory response in asthma. Our work supplements the mechanism of asthma pro-inflammation progression from the perspective of CIC structure of lymphocytes and alveolar epithelial cells, and provides a new idea for anti-inflammatory therapy of asthma.

Lung regeneration: diverse cell types and the therapeutic potential

Lung tissue has a certain regenerative ability and triggers repair procedures after injury. Under controllable conditions, lung tissue can restore normal structure and function. Disruptions in this process can lead to respiratory system failure and even death, causing substantial medical burden. The main types of respiratory diseases are chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and acute respiratory distress syndrome (ARDS). Multiple cells, such as lung epithelial cells, endothelial cells, fibroblasts, and immune cells, are involved in regulating the repair process after lung injury. Although the mechanism that regulates the process of lung repair has not been fully elucidated, clinical trials targeting different cells and signaling pathways have achieved some therapeutic effects in different respiratory diseases. In this review, we provide an overview of the cell type involved in the process of lung regeneration and repair, research models, and summarize molecular mechanisms involved in the regulation of lung regeneration and fibrosis. Moreover, we discuss the current clinical trials of stem cell therapy and pharmacological strategies for COPD, IPF, and ARDS treatment. This review provides a reference for further research on the molecular and cellular mechanisms of lung regeneration, drug development, and clinical trials.

CD147 induces asthmatic airway remodeling and activation of circulating fibrocytes in a mouse model of asthma

BACKGROUND

Airway remodeling is a poorly reversible feature of asthma which lacks effective therapeutic interventions. CD147 can regulate extracellular matrix (ECM) remodeling and tissue fibrosis, and participate in the pathogenesis of asthma. In this study, the role of CD147 in airway remodeling and activation of circulating fibrocytes was investigated in asthmatic mice.

METHODS

Asthmatic mouse model was established by sensitizing and challenging mice with ovalbumin (OVA), and treated with anti-CD147 or Isotype antibody. The number of eosinophils in bronchoalveolar lavage fluid (BALF) was examined by microscope, and the levels of interleukin-4 (IL-4), IL-5 and IL-13 in BALF were detected by enzyme-linked immunosorbent assay (ELISA). The number of CD45+ and collagen I (COL-I)+ circulating fibrocytes in BALF was detected by flow cytometry. Lung tissue sections were respectively stained with hematoxylin and eosin (HE), periodic acid-Schiff (PAS) or Masson trichrome staining, or used for immunohistochemistry of CD31 and immunohistofluorescence of α-smooth muscle actin (α-SMA), CD45 and COL-I. The protein expression of α-SMA, vascular endothelial growth factor (VEGF), transforming growth factor-β1 (TGF-β1), Fibronectin, and COL-I was determined by western blotting.

RESULTS

Anti-CD147 treatment significantly reduced the number of eosinophils and the levels of IL-4, IL-13, and IL-5 in BALF, and repressed airway inflammatory infiltration and airway wall thickening in asthmatic mice. Anti-CD147 treatment also reduced airway goblet cell metaplasia, collagen deposition, and angiogenesis in asthmatic mice, accompanied by inhibition of VEGF and α-SMA expression. The number of CD45+COL-I+ circulating fibrocytes was increased in BALF and lung tissues of OVA-induced asthmatic mice, but was decreased by anti-CD147 treatment. In addition, anti-CD147 treatment also reduced the protein expression of COL-I, fibronectin, and TGF-β1 in lung tissues of asthmatic mice.

CONCLUSION

OVA-triggered airway inflammation and airway remodeling in asthmatic mice can be repressed by anti-CD147 treatment, along with inhibiting the accumulation and activation of circulating fibrocytes.

Short-range interactions between fibrocytes and CD8+ T cells in COPD bronchial inflammatory response

Bronchi of chronic obstructive pulmonary disease (COPD) are the site of extensive cell infiltration, allowing persistent contact between resident cells and immune cells. Tissue fibrocytes interaction with CD8⁺ T cells and its consequences were investigated using a combination of in situ, in vitro experiments and mathematical modeling. We show that fibrocytes and CD8⁺ T cells are found in the vicinity of distal airways and that potential interactions are more frequent in tissues from COPD patients compared to those of control subjects. Increased proximity and clusterization between CD8⁺ T cells and fibrocytes are associated with altered lung function. Tissular CD8⁺ T cells from COPD patients promote fibrocyte chemotaxis via the CXCL8-CXCR1/2 axis. Live imaging shows that CD8⁺ T cells establish short-term interactions with fibrocytes, that trigger CD8⁺ T cell proliferation in a CD54- and CD86-dependent manner, pro-inflammatory cytokines production, CD8⁺ T cell cytotoxic activity against bronchial epithelial cells and fibrocyte immunomodulatory properties. We defined a computational model describing these intercellular interactions and calibrated the parameters based on our experimental measurements. We show the model's ability to reproduce histological ex vivo characteristics, and observe an important contribution of fibrocyte-mediated CD8⁺ T cell proliferation in COPD development. Using the model to test therapeutic scenarios, we predict a recovery time of several years, and the failure of targeting chemotaxis or interacting processes. Altogether, our study reveals that local interactions between fibrocytes and CD8⁺ T cells could jeopardize the balance between protective immunity and chronic inflammation in the bronchi of COPD patients.

Fibrocytes enhance mammary gland fibrosis in obesity

Obesity rates continue to rise, and obese individuals are at higher risk for multiple types of cancer, including breast cancer. Obese mammary fat is a site of chronic, macrophage-driven inflammation, which enhances fibrosis within adipose tissue. Elevated fibrosis within the mammary gland may contribute to risk for obesity-associated breast cancer. To understand how inflammation due to obesity enhanced fibrosis within mammary tissue, we utilized a high-fat diet model of obesity and elimination of CCR2 signaling in mice to identify changes in immune cell populations and their impact on fibrosis. We observed that obesity increased a population of CD11b+ cells with the ability to form myofibroblast-like colonies in vitro. This population of CD11b+ cells is consistent with fibrocytes, which have been identified in wound healing and chronic inflammatory diseases but have not been examined in obesity. In CCR2-null mice, which have limited ability to recruit myeloid lineage cells into obese adipose tissue, we observed reduced mammary fibrosis and diminished fibrocyte colony formation in vitro. Transplantation of myeloid progenitor cells, which are the cells of origin for fibrocytes, into the mammary glands of obese CCR2-null mice resulted in significantly increased myofibroblast formation. Gene expression analyses of the myeloid progenitor cell population from obese mice demonstrated enrichment for genes associated with collagen biosynthesis and extracellular matrix remodeling. Together these results show that obesity enhances recruitment of fibrocytes to promote obesity-induced fibrosis in the mammary gland.

Cellular interplay in skeletal muscle regeneration and wasting: insights from animal models

Skeletal muscle wasting, whether related to physiological ageing, muscle disuse or to an underlying chronic disease, is a key determinant to quality of life and mortality. However, cellular basis responsible for increased catabolism in myocytes often remains unclear. Although myocytes represent the vast majority of skeletal muscle cellular population, they are surrounded by numerous cells with various functions. Animal models, mostly rodents, can help to decipher the mechanisms behind this highly dynamic process, by allowing access to every muscle as well as time-course studies. Satellite cells (SCs) play a crucial role in muscle regeneration, within a niche also composed of fibroblasts and vascular and immune cells. Their proliferation and differentiation is altered in several models of muscle wasting such as cancer, chronic kidney disease or chronic obstructive pulmonary disease (COPD). Fibro-adipogenic progenitor cells are also responsible for functional muscle growth and repair and are associated in disease to muscle fibrosis such as in chronic kidney disease. Other cells have recently proven to have direct myogenic potential, such as pericytes. Outside their role in angiogenesis, endothelial cells and pericytes also participate to healthy muscle homoeostasis by promoting SC pool maintenance (so-called myogenesis-angiogenesis coupling). Their role in chronic diseases muscle wasting has been less studied. Immune cells are pivotal for muscle repair after injury: Macrophages undergo a transition from the M1 to the M2 state along with the transition between the inflammatory and resolutive phase of muscle repair. T regulatory lymphocytes promote and regulate this transition and are also able to activate SC proliferation and differentiation. Neural cells such as terminal Schwann cells, motor neurons and kranocytes are notably implicated in age-related sarcopenia. Last, newly identified cells in skeletal muscle, such as telocytes or interstitial tenocytes could play a role in tissular homoeostasis. We also put a special focus on cellular alterations occurring in COPD, a chronic and highly prevalent respiratory disease mainly linked to tobacco smoke exposure, where muscle wasting is strongly associated with increased mortality, and discuss the pros and cons of animal models versus human studies in this context. Finally, we discuss resident cells metabolism and present future promising leads for research, including the use of muscle organoids.

Muscarinic receptor M3 activation promotes fibrocytes contraction

Fibrocytes are monocyte-derived cells able to differentiate into myofibroblasts-like cells. We have previously shown that they are increased in the bronchi of Chronic Obstructive Pulmonary Disease (COPD) patients and associated to worse lung function. COPD is characterized by irreversible airflow obstruction, partly due to an increased cholinergic environment. Our goal was to investigate muscarinic signalling in COPD fibrocytes. Fibrocytes were isolated from 16 patients with COPD's blood and presence of muscarinic M3 receptor was assessed at the transcriptional and protein levels. Calcium signalling and collagen gels contraction experiments were performed in presence of carbachol (cholinergic agonist) ± tiotropium bromide (antimuscarinic). Expression of M3 receptor was confirmed by Western blot and flow cytometry in differentiated fibrocytes. Immunocytochemistry showed the presence of cytoplasmic and membrane-associated pools of M3. Stimulation with carbachol elicited an intracellular calcium response in 35.7% of fibrocytes. This response was significantly blunted by the presence of tiotropium bromide: 14.6% of responding cells (p < 0.0001). Carbachol induced a significant contraction of fibrocytes embedded in collagen gels (13.6 ± 0.3% versus 2.5 ± 4.1%; p < 0.0001), which was prevented by prior tiotropium bromide addition (4.1 ± 2.7% of gel contraction; p < 0.0001). Finally, M3-expressing fibrocytes were also identified in situ in the peri-bronchial area of COPD patients' lungs, and there was a tendency to an increased density compared to healthy patient's lungs. In conclusion, around 1/3 of COPD patients' fibrocytes express a functional muscarinic M3 receptor. Cholinergic-induced fibrocyte contraction might participate in airway diameter reduction and subsequent increase of airflow resistance in patients with COPD. The inhibition of these processes could participate to the beneficial effects of muscarinic antagonists for COPD treatment.

Blood fibrocytes are associated with severity and prognosis in COVID-19 pneumonia

Increased blood fibrocytes are associated with a poor prognosis in fibrotic lung diseases. We aimed to determine whether the percentage of circulating fibrocytes could be predictive of severity and prognosis during coronavirus disease 2019 (COVID-19) pneumonia. Blood fibrocytes were quantified by flow cytometry as CD45⁺/CD15^-/CD34⁺/collagen-1⁺ cells in patients hospitalized for COVID-19 pneumonia. In a subgroup of patients admitted in an intensive care unit (ICU), fibrocytes were quantified in blood and bronchoalveolar lavage (BAL). Serum amyloid P (SAP), transforming growth factor-β1 (TGF-β1), CXCL12, CCL2, and FGF2 concentrations were measured. We included 57 patients in the hospitalized group (median age = 59 yr [23-87]) and 16 individuals as healthy controls. The median percentage of circulating fibrocytes was higher in the patients compared with the controls (3.6% [0.2-9.2] vs. 2.1% [0.9-5.1], P = 0.04). Blood fibrocyte count was lower in the six patients who died compared with the survivors (1.6% [0.2-4.4] vs. 3.7% [0.6-9.2], P = 0.02). Initial fibrocyte count was higher in patients showing a complete lung computed tomography (CT) resolution at 3 mo. Circulating fibrocyte count was decreased in the ICU group (0.8% [0.1-2.0]), whereas BAL fibrocyte count was 6.7% (2.2-15.4). Serum SAP and TGF-β1 concentrations were increased in hospitalized patients. SAP was also increased in ICU patients. CXCL12 and CCL2 were increased in ICU patients and negatively correlated with circulating fibrocyte count. We conclude that circulating fibrocytes were increased in patients hospitalized for COVID-19 pneumonia, and a lower fibrocyte count was associated with an increased risk of death and a slower resolution of lung CT opacities.

Pharmacological properties and underlying mechanisms of curcumin and prospects in medicinal potential

Curcumin, isolated from Curcuma longa L., is a fat-soluble natural compound that can be obtained from ginger plant tuber roots, which accumulative evidences have demonstrated that it can resist viral and microbial infection and has anti-tumor, reduction of blood lipid and blood glucose, antioxidant and removal of free radicals, and is active against numerous disorders various chronic diseases including cardiovascular, pulmonary, neurological and autoimmune diseases. In this article is highlighted the recent evidence of curcuminoids applied in sevral aspects of medical problem particular in COVID-19 pandemics. We have searched several literature databases including MEDLINE (PubMed), EMBASE, the Web of Science, Cochrane Library, Google Scholar, and the ClinicalTrials.gov website via using curcumin and medicinal properties as a keyword. All studies published from the time when the database was established to May 2021 was retrieved. This review article summarizes the growing confirmation for the mechanisms related to curcumin's physiological and pharmacological effects with related target proteins interaction via molecular docking. The purpose is to provide deeper insight and understandings of curcumin's medicinal value in the discovery and development of new drugs. Curcumin could be used in the prevention or therapy of cardiovascular disease, respiratory diseases, cancer, neurodegeneration, infection, and inflammation based on cellular biochemical, physiological regulation, infection suppression and immunomodulation.

Development of improved method to identify and analyze lung fibrocytes with flow cytometry in a reporter mouse strain

Introduction

Fibrocytes are emerging myeloid‐derived circulating cells that can migrate into damaged tissues and usually contribute to their repair. Key features of fibrocytes include the expression myeloid markers, production of extracellular matrix proteins, and secretion of various humoral factors that activate resident fibroblasts; they also have the potential to differentiate into fibroblasts. However, no specific surface markers have been identified to identify fibrocytes in vivo. One reason could be that the method used to detect fibrocytes requires intracellular collagen staining.

Methods

In the present study, to establish an improved method for the detection of lung fibrocytes and to analyze viable fibrocytes, we used collagen I(α)2‐green fluorescent protein (Col‐GFP) reporter mice, which had undergone the intratracheal instillation of bleomycin (BLM).

Results

Using flow cytometry to gate out cells with autofluorescence, we clearly found that CD45⁺ GFP⁺ cells resided in the lungs of Col‐GFP mice at a steady state and these cells increased after BLM injury, peaking at Day 14. These cells expressed not only known cell surface markers of fibrocytes, but also some novel markers, in addition to a low level of collagen I in comparison to CD45⁻ GFP⁺ cells.

Conclusion

Our findings suggest that the improved method can be a useful for the detection of pure lung fibrocytes and allows us to further analyze the characteristics of viable fibrocytes.

The ER Stress/UPR Axis in Chronic Obstructive Pulmonary Disease and Idiopathic Pulmonary Fibrosis

Cellular protein homeostasis in the lungs is constantly disrupted by recurrent exposure to various external and internal stressors, which may cause considerable protein secretion pressure on the endoplasmic reticulum (ER), resulting in the survival and differentiation of these cell types to meet the increased functional demands. Cells are able to induce a highly conserved adaptive mechanism, known as the unfolded protein response (UPR), to manage such stresses. UPR dysregulation and ER stress are involved in numerous human illnesses, such as metabolic syndrome, fibrotic diseases, and neurodegeneration, and cancer. Therefore, effective and specific compounds targeting the UPR pathway are being considered as potential therapies. This review focuses on the impact of both external and internal stressors on the ER in idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD) and discusses the role of the UPR signaling pathway activation in the control of cellular damage and specifically highlights the potential involvement of non-coding RNAs in COPD. Summaries of pathogenic mechanisms associated with the ER stress/UPR axis contributing to IPF and COPD, and promising pharmacological intervention strategies, are also presented.

Fibrocyte localisation to the ASM bundle in asthma: bidirectional effects on cell phenotype and behaviour

Objectives

Airway hyper‐responsiveness and persistent airflow obstruction contribute to asthma pathogenesis and symptoms, due in part to airway smooth muscle (ASM) hypercontractility and increased ASM mass. Fibrocytes have been shown to localise to the ASM in asthma however it is not known whether fibrocytes localise to the ASM in nonasthmatic eosinophilic bronchitis (NAEB) and chronic obstructive pulmonary disease (COPD). In addition, the potential consequences of fibrocyte localisation to ASM as regards asthma pathophysiology has not been widely studied.

Methods

Fibrocytes and proliferating cells were enumerated in ASM in bronchial tissue using immunohistochemistry. The effects of primary ASM and fibrocytes upon each other in terms of phenotype and behaviour following co‐culture were investigated by assessing cell number, size, apoptotic status, phenotype and contractility in in vitro cell‐based assays.

Results

Increased fibrocyte number in the ASM was observed in asthma versus NAEB, but not NAEB and COPD versus controls, and confirmed in asthma versus controls. ASM proliferation was not detectably different in asthmatics versus healthy controls in vivo. No difference in proliferation, apoptotic status or size of ASM was seen following culture with/without fibrocytes. Following co‐culture with ASM from asthmatics versus nonasthmatics, fibrocyte smooth muscle marker expression and collagen gel contraction were greater. Following co‐culture, fibrocyte CD14 expression was restored with the potential to contribute to asthma pathogenesis via monocyte‐mediated processes dependent on the inflammatory milieu.

Conclusion

Further understanding of mechanisms of fibrocyte recruitment to and/or differentiation within the ASM may identify novel therapeutic targets to modulate ASM dysfunction in asthma.

Role of circulating fibrocytes in the diagnosis of acute appendicitis

Background

Improved diagnostic biomarkers are required for acute appendicitis. The circulating fibrocyte percentage (CFP) is increased in inflammatory states, but has not been studied in acute appendicitis. This study aimed to determine CFP in acute appendicitis and compare diagnostic accuracy with standard serological biomarkers.

Methods

A prospective cohort study was carried out between June 2015 and February 2016 at University Hospital Limerick. The CFP was determined by dual‐staining peripheral venous samples for CD45 and collagen I using fluorescence‐activated cell sorting, and correlated with histopathological diagnoses. The accuracy of CFP in determining histological acute appendicitis was characterized and compared with the white cell count, C‐reactive protein concentration, neutrophil count, lymphocyte count and neutrophil : lymphocyte ratio.

Results

Of 95 adults recruited, 15 were healthy individuals and 80 had suspected appendicitis at presentation. Forty‐six of these 80 patients had an appendicectomy, of whom 34 had histologically confirmed appendicitis. The CFP was statistically higher in patients with pathologically proven acute appendicitis than in healthy controls (median 6·1 (i.q.r. 1·6–11·6) versus 2·3 (0·9–3·4) per cent respectively; P = 0·008). The diagnostic accuracy of CFP, as determined using the area under the receiver operating characteristic (ROC) curve, was similar to that of standard biomarkers. In multinomial regression analysis, only raised CFP was retained as an independent prognostic determinant of acute appendicitis (odds ratio 1·57, 95 per cent c.i. 1·05 to 2·33; P = 0·027).

Conclusion

The CFP is increased in histologically confirmed acute appendicitis and is as accurate as standard serological biomarkers in terms of diagnosis.

Bidirectional interaction of airway epithelial remodeling and inflammation in asthma

Asthma is a chronic disease of the airways that has long been viewed predominately as an inflammatory condition. Accordingly, current therapeutic interventions focus primarily on resolving inflammation. However, the mainstay of asthma therapy neither fully improves lung function nor prevents disease exacerbations, suggesting involvement of other factors. An emerging concept now holds that airway remodeling, another major pathological feature of asthma, is as important as inflammation in asthma pathogenesis. Structural changes associated with asthma include disrupted epithelial integrity, subepithelial fibrosis, goblet cell hyperplasia/metaplasia, smooth muscle hypertrophy/hyperplasia, and enhanced vascularity. These alterations are hypothesized to contribute to airway hyperresponsiveness, airway obstruction, airflow limitation, and progressive decline of lung function in asthmatic individuals. Consequently, targeting inflammation alone does not suffice to provide optimal clinical benefits. Here we review asthmatic airway remodeling, focusing on airway epithelium, which is critical to maintaining a healthy respiratory system, and is the primary defense against inhaled irritants. In asthma, airway epithelium is both a mediator and target of inflammation, manifesting remodeling and resulting obstruction among its downstream effects. We also highlight the potential benefits of therapeutically targeting airway structural alterations. Since pathological tissue remodeling is likewise observed in other injury- and inflammation-prone tissues and organs, our discussion may have implications beyond asthma and lung disease.

Fibrocytes, Wound Healing, and Corneal Fibrosis

Purpose

This review highlights the roles of fibrocytes—their origin, markers, regulation and functions—including contributions to corneal wound healing and fibrosis.

Methods

Literature review.

Results

Peripheral blood fibroblast-like cells, called fibrocytes, are primarily generated as mature collagen-producing cells in the bone marrow. They are likely derived from the myeloid lineage, although the exact precursor remains unknown. Fibrocytes are identified by a combination of expressed markers, such as simultaneous expression of CD34 or CD45 or CD11b and collagen type I or collagen type III. Fibrocytes migrate into the wound from the blood where they participate in pathogen clearance, tissue regeneration, wound closure and angiogenesis. Transforming growth factor beta 1 (TGF-β₁) and adiponectin induce expression of α-smooth muscle actin and extracellular matrix proteins through activation of Smad3 and adenosine monophosphate-activated protein kinase pathways, respectively. Fibrocytes are important contributors to the cornea wound healing response and there are several mechanisms through which fibrocytes contribute to fibrosis in the cornea and other organs, such as their differentiation into myofibroblasts, production of matrix metalloproteinase, secretion of tissue inhibitor of metalloproteinase, and release of TGF-β₁. In some tissues, fibrocytes may also contribute to the basement membrane regeneration and to the resolution of fibrosis.

Conclusions

New methods that block fibrocyte generation, fibrocyte migration, and their differentiation into myofibroblasts, as well as their production of matrix metalloproteinases, tissue inhibitor of metalloproteinase, and TGF-β₁, have therapeutic potential to reduce the accumulation of collagens, maintain tissue integrity and retard or prevent the development of fibrosis.

COPD beyond proximal bronchial obstruction: phenotyping and related tools at the bedside

Chronic obstructive pulmonary disease (COPD) is characterised by nonreversible proximal bronchial obstruction leading to major respiratory disability. However, patient phenotypes better capture the heterogeneously reported complaints and symptoms of COPD. Recent studies provided evidence that classical bronchial obstruction does not properly reflect respiratory disability, and symptoms now form the new paradigm for assessment of disease severity and guidance of therapeutic strategies. The aim of this review was to explore pathways addressing COPD pathogenesis beyond proximal bronchial obstruction and to highlight innovative and promising tools for phenotyping and bedside assessment. Distal small airways imaging allows quantitative characterisation of emphysema and functional air trapping. Micro-computed tomography and parametric response mapping suggest small airways disease precedes emphysema destruction. Small airways can be assessed functionally using nitrogen washout, probing ventilation at conductive or acinar levels, and forced oscillation technique. These tests may better correlate with respiratory symptoms and may well capture bronchodilation effects beyond proximal obstruction.Knowledge of inflammation-based processes has not provided well-identified targets so far, and eosinophils probably play a minor role. Adaptative immunity or specific small airways secretory protein may provide new therapeutic targets. Pulmonary vasculature is involved in emphysema through capillary loss, microvascular lesions or hypoxia-induced remodelling, thereby impacting respiratory disability.

Fibrocyte accumulation in the airway walls of COPD patients

The remodelling mechanism and cellular players causing persistent airflow limitation in COPD remain largely elusive. We have recently demonstrated that circulating fibrocytes, a rare population of fibroblast-like cells produced by the bone marrow stroma, are increased in COPD patients during an exacerbation. We aimed to quantify fibrocyte density in situ in bronchial specimens from both control subjects and COPD patients, to define associations with relevant clinical, functional and computed tomography (CT) parameters, and to investigate the effect of the epithelial microenvironment on fibrocyte survival in vitro (“Fibrochir” study).

A total of 17 COPD patients and 25 control subjects, all requiring thoracic surgery, were recruited. Using co-immunostaining and image analysis, we identified CD45+ FSP1+ cells as tissue fibrocytes, and quantified their density in distal and proximal bronchial specimens. Fibrocytes, cultured from the blood samples of six COPD patients, were exposed to primary bronchial epithelial cell secretions from control subjects or COPD patients.

We demonstrate that fibrocytes are increased in both distal and proximal tissue specimens of COPD patients. The density of fibrocytes is negatively correlated with lung function parameters and positively correlated with bronchial wall thickness as assessed by CT scan. A high density of distal bronchial fibrocytes predicts the presence of COPD with a sensitivity of 83% and a specificity of 70%. Exposure of fibrocytes to COPD epithelial cell supernatant favours cell survival.

Our results thus demonstrate an increased density of fibrocytes within the bronchi of COPD patients, which may be promoted by epithelial-derived survival-mediating factors.

Chemokines in COPD: From Implication to Therapeutic Use

: Chronic Obstructive Pulmonary Disease (COPD) represents the 3rd leading cause of death in the world. The underlying pathophysiological mechanisms have been the focus of extensive research in the past. The lung has a complex architecture, where structural cells interact continuously with immune cells that infiltrate into the pulmonary tissue. Both types of cells express chemokines and chemokine receptors, making them sensitive to modifications of concentration gradients. Cigarette smoke exposure and recurrent exacerbations, directly and indirectly, impact the expression of chemokines and chemokine receptors. Here, we provide an overview of the evidence regarding chemokines involvement in COPD, and we hypothesize that a dysregulation of this tightly regulated system is critical in COPD evolution, both at a stable state and during exacerbations. Targeting chemokines and chemokine receptors could be highly attractive as a mean to control both chronic inflammation and bronchial remodeling. We present a special focus on the CXCL8-CXCR1/2, CXCL9/10/11-CXCR3, CCL2-CCR2, and CXCL12-CXCR4 axes that seem particularly involved in the disease pathophysiology.