Mast cell/fibroblast interactions

HIV-Related Myocardial Fibrosis: Inflammatory Hypothesis and Crucial Role of Immune Cells Dysregulation

Although the underlying mechanisms driving human immunodeficiency virus (HIV)-mediated cardiovascular diseases (CVD) onset and progression remain unclear, the role of chronic immune activation as a significant mediator is increasingly being highlighted. Chronic inflammation is a characteristic feature of CVD and considered a contributor to diastolic dysfunction, heart failure, and sudden cardiac death. This can trigger downstream effects that result in the increased release of pro-coagulant, pro-fibrotic, and pro-inflammatory cytokines. Subsequently, this can lead to an enhanced thrombotic state (by platelet activation), endothelial dysfunction, and myocardial fibrosis. Of note, recent studies have revealed that myocardial fibrosis is emerging as a mediator of HIV-related CVD. Together, such factors can eventually result in systolic and diastolic dysfunction, and an increased risk for CVD. In light of this, the current review article will focus on (a) the contributions of a chronic inflammatory state and persistent immune activation, and (b) the role of immune cells (mainly platelets) and cardiac fibrosis in terms of HIV-related CVD onset/progression. It is our opinion that such a focus may lead to the development of promising therapeutic targets for the treatment and management of CVD in HIV-positive patients.

Cardiac fibrosis: Cell biological mechanisms, molecular pathways and therapeutic opportunities

Cardiac fibrosis is a common pathophysiologic companion of most myocardial diseases, and is associated with systolic and diastolic dysfunction, arrhythmogenesis, and adverse outcome. Because the adult mammalian heart has negligible regenerative capacity, death of a large number of cardiomyocytes results in reparative fibrosis, a process that is critical for preservation of the structural integrity of the infarcted ventricle. On the other hand, pathophysiologic stimuli, such as pressure overload, volume overload, metabolic dysfunction, and aging may cause interstitial and perivascular fibrosis in the absence of infarction. Activated myofibroblasts are the main effector cells in cardiac fibrosis; their expansion following myocardial injury is primarily driven through activation of resident interstitial cell populations. Several other cell types, including cardiomyocytes, endothelial cells, pericytes, macrophages, lymphocytes and mast cells may contribute to the fibrotic process, by producing proteases that participate in matrix metabolism, by secreting fibrogenic mediators and matricellular proteins, or by exerting contact-dependent actions on fibroblast phenotype. The mechanisms of induction of fibrogenic signals are dependent on the type of primary myocardial injury. Activation of neurohumoral pathways stimulates fibroblasts both directly, and through effects on immune cell populations. Cytokines and growth factors, such as Tumor Necrosis Factor-α, Interleukin (IL)-1, IL-10, chemokines, members of the Transforming Growth Factor-β family, IL-11, and Platelet-Derived Growth Factors are secreted in the cardiac interstitium and play distinct roles in activating specific aspects of the fibrotic response. Secreted fibrogenic mediators and matricellular proteins bind to cell surface receptors in fibroblasts, such as cytokine receptors, integrins, syndecans and CD44, and transduce intracellular signaling cascades that regulate genes involved in synthesis, processing and metabolism of the extracellular matrix. Endogenous pathways involved in negative regulation of fibrosis are critical for cardiac repair and may protect the myocardium from excessive fibrogenic responses. Due to the reparative nature of many forms of cardiac fibrosis, targeting fibrotic remodeling following myocardial injury poses major challenges. Development of effective therapies will require careful dissection of the cell biological mechanisms, study of the functional consequences of fibrotic changes on the myocardium, and identification of heart failure patient subsets with overactive fibrotic responses.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

The pathogenesis of cardiac fibrosis

Cardiac fibrosis is characterized by net accumulation of extracellular matrix proteins in the cardiac interstitium, and contributes to both systolic and diastolic dysfunction in many cardiac pathophysiologic conditions. This review discusses the cellular effectors and molecular pathways implicated in the pathogenesis of cardiac fibrosis. Although activated myofibroblasts are the main effector cells in the fibrotic heart, monocytes/macrophages, lymphocytes, mast cells, vascular cells and cardiomyocytes may also contribute to the fibrotic response by secreting key fibrogenic mediators. Inflammatory cytokines and chemokines, reactive oxygen species, mast cell-derived proteases, endothelin-1, the renin/angiotensin/aldosterone system, matricellular proteins, and growth factors (such as TGF-β and PDGF) are some of the best-studied mediators implicated in cardiac fibrosis. Both experimental and clinical evidence suggests that cardiac fibrotic alterations may be reversible. Understanding the mechanisms responsible for initiation, progression, and resolution of cardiac fibrosis is crucial to design anti-fibrotic treatment strategies for patients with heart disease.

Activated MCTC mast cells infiltrate diseased lung areas in cystic fibrosis and idiopathic pulmonary fibrosis

Background

Although mast cells are regarded as important regulators of inflammation and tissue remodelling, their role in cystic fibrosis (CF) and idiopathic pulmonary fibrosis (IPF) has remained less studied. This study investigates the densities and phenotypes of mast cell populations in multiple lung compartments from patients with CF, IPF and never smoking controls.

Methods

Small airways, pulmonary vessels, and lung parenchyma were subjected to detailed immunohistochemical analyses using lungs from patients with CF (20 lung regions; 5 patients), IPF (21 regions; 7 patients) and controls (16 regions; 8 subjects). In each compartment the densities and distribution of MC_T and MC_TC mast cell populations were studied as well as the mast cell expression of IL-6 and TGF-β.

Results

In the alveolar parenchyma in lungs from patients with CF, MC_TC numbers increased in areas showing cellular inflammation or fibrosis compared to controls. Apart from an altered balance between MC_TC and MC_T cells, mast cell in CF lungs showed elevated expression of IL-6. In CF, a decrease in total mast cell numbers was observed in small airways and pulmonary vessels. In patients with IPF, a significantly elevated MC_TC density was present in fibrotic areas of the alveolar parenchyma with increased mast cell expression of TGF-β. The total mast cell density was unchanged in small airways and decreased in pulmonary vessels in IPF. Both the density, as well as the percentage, of MC_TC correlated positively with the degree of fibrosis. The increased density of MC_TC, as well as MC_TC expression of TGF-β, correlated negatively with patient lung function.

Conclusions

The present study reveals that altered mast cell populations, with increased numbers of MC_TC in diseased alveolar parenchyma, represents a significant component of the histopathology in CF and IPF. The mast cell alterations correlated to the degree of tissue remodelling and to lung function parameters. Further investigations of mast cells in these diseases may open for new therapeutic strategies.

Ultrastructural injury to interstitial cells of Cajal and communication with mast cells in Crohn's disease

Crohn's disease associated dysmotility has been attributed to fibrosis and damage to enteric nerves but injury to interstitial cells of Cajal (ICC) could also be involved. We assessed ICC in specimens obtained from patients with Crohn's disease and determined the relation between ICC and the inflammatory infiltrate, particularly mast cells (MC) using quantitative immunohistochemistry and electron microscopy. Ultrastructural injury to ICC was patchy in all ICC subtypes but ICC-Auerbach's plexus (AP) showed damage more frequently, i.e. swelling of mitochondria, decreased electron density, autophagosomes and partial depletion of the cytoplasm. Light microscopy confirmed a significant decrease in c-kit immunoreactivity for ICC-AP and an increased number of MC in the muscularis externa. Electron microscopy showed MC exhibiting piecemeal degranulation and making frequent and selective membrane-to-membrane contact with all types of injured ICC which suggests chronic release of granule content to affect ICC. Extent of ICC injury was not associated with duration of the disease. In conclusion, ultrastructural injury and loss of ICC-AP is evident in Crohn's disease. Epidemiological and morphological data suggest that ICC have the capacity to regenerate in spite of the chronic insult. The muscularis hosts a marked number of MC that exhibit piecemeal degranulation associated with ICC and may facilitate ICC maintenance.

Mast Cells: Not Only in Allergy

The past decade has confronted us with a striking abundance of novel findings regarding the roles of mast cells in immune responses in health and disease. Newly developed models and techniques have enabled clear-cut dissection of the mast cell contribution in these settings. We now understand that mast cells possess critical effector functions not only within the traditional context of allergic reactions. It is likely that mast cells played pivotal roles in primitive immune systems, yet these functions have been masked in the recent eras by newer immune functions, such as adaptive immunity. Conceivably, mast cells should be refocused on so as to obtain new insights about diverse pathologic conditions, ultimately leading to novel therapeutic approaches targeting these fascinating cells.

Mast cell chymase is a possible mediator of neurogenic bladder fibrosis

AIMS

Urinary bladders of patients with myelomeningocele, owing to spina bifida, are often functionally impaired, fibrotic organs. Common to this condition are repeated occurrences of bladder infection and inflammation. Since mast cells have been associated with a fibrogenic response in inflammatory conditions, we investigated the role of mast cell granule product, chymase, as a mediator of myleodysplastic bladder fibrosis.

METHODS

Human control and myelodysplastic bladder tissues were stained with Unna's stain and chymase antibody to determine mast cell number and localization. Cell specific localization of collagen mRNAs was determined by in situ hybridization (ISH). In vitro, normal human bladder fibroblasts were treated with recombinant chymase, heparin and inhibitors, and collagen subtype concentration was determined by enzyme linked immunosorbent assay (ELISA).

RESULTS

Myelodysplastic bladders were characterized by increased mast cells in the detrusor muscle layer compared to control bladders, as well as mast cell degranulation and increased connective tissue deposition. Both types I and III collagen mRNA localized to fibroblasts surrounding detrusor muscle fascicles, whereas only collagen III mRNA localized to cells within connective tissue infiltrated muscle bundles in myelomeningocele bladder tissue. Chymase treatment of bladder fibroblasts, in vitro, was dose-dependent and resulted in significant increases in both types I and III collagen. Heparin did not alter collagen protein expression, whereas heparin-chymase combination modulated type III collagen expression. Serine protease inhibitor, phenylmethylsulfonlyfluoride, did not inhibit collagen synthesis, whereas denatured chymase resulted in decreased collagenous protein levels.

CONCLUSIONS

Bladder fibrosis may be mediated by mast cell chymase stimulation of collagen synthesis.

Histamine-induced cytokine production and ICAM-1 expression in human conjunctival fibroblasts

PURPOSE

Conjunctival fibroblasts stimulated with histamine (H) may be directly involved in the inflammatory and remodeling processes of chronic allergic conjunctival diseases.

METHODS

Proinflammatory cytokine and growth factor production, and the expression of intercellular adhesion molecule-1 (ICAM-1) were studied in conjunctival fibroblast cultures challenged with different concentrations of H (from 10(-9) M to 10(-) (4) M). Interleukin (IL)-1, IL-4, IL-6, IL-8, tumor necrosis factor-alfa (TNF-alpha), fibroblast growth factor (FGF), epidermal growth factor (EGF) and transforming growth factor-beta (TGFbeta-1) were measured in supernatants. ICAM-1 expression was evaluated by a fluorescence activated cell sorter (FACS). Inhibitory effects of the H-1 antagonists (antiH): emedastine, levocabastine, and azelastine, and of the antiH-2, cimetidine, on H-stimulated fibroblasts were evaluated by measuring both cytokines in supernatants and the cellular expression of ICAM-1.

RESULTS

Histamine increased the production of IL-1, IL-6 and IL-8, and ICAM-1 expression. TNF-alpha, IL-4 and growth factor production were not modified by histamine. The antiH-1, emedastine, significantly reduced H-induced production of IL-1, IL-6 and IL-8, while azelastine reduced only IL-1. Levocabastine and cimetidine were less effective. The histamine-induced increase in ICAM-1 expression was inhibited by emedastine but not by azelastine and levocabastine.

CONCLUSIONS

Histamine has pro-inflammatory effects on conjunctival fibroblasts, inducing the production of cytokines and the expression of ICAM-1. Emedastine significantly reduced cytokine and ICAM-1 expression from H-stimulated fibroblasts. Conjunctival fibroblasts may contribute to the maintenance of inflammation in chronic allergic diseases.

Effects of crocidolite asbestos on human bronchoepithelial-dependent fibroblast stimulation in coculture: the role of IL-6 and GM-CSF

Cocultures of human pulmonary epithelial cells (BEAS-2B) and lung fibroblasts (WISTAR-38), representing two cell types of central regulatory potential in (chronic) lung disease, were used as an in vitro model to study the role of interleukin 6 (IL-6) and of granulocyte macrophage-colony stimulating factor (GM-CSF) in early fibrogenesis. For this purpose, epithelial cells were pre-exposed to UICC crocidolite asbestos fibers or titanium dioxide (TiO2) particles for 96 h and subsequently cocultured with fibroblasts for additional 72 h. Gene expression of IL-6 or GM-CSF in both cell types as well as of alpha1 procollagens types I and III in fibroblasts was determined by RT-PCR. Synthesis of IL-6, GM-CSF or collagen I was quantified using IL-6 bioassay or ELISA tests, respectively. Both mediators were directly induced in bronchoepithelial cells by crocidolite but not by TiO2. Likewise, steady-state mRNA levels of procollagens as well as collagen synthesis were upregulated in cocultured fibroblasts. As a result of coculture, cytokine concentrations were synergistically enhanced and further increased by crocidolite in a dose-dependent manner. Suppression of cytokine induction by corresponding neutralizing antibodies consistently abrogated collagen enhancement. Direct stimulation of fibroblast monocultures with recombinant human IL-6 or GM-CSF significantly increased collagen synthesis and transcription in a dose-dependent manner. Thus, our results demonstrate that crocidolite selectively stimulated production of IL-6 and GM-CSF in bronchoepithelial cells. In epithelial-fibroblast interactions, these mediators appear to play a key role in regulating fibroblast activity, indicating a close correlation between these cytokines and the fibrogenic potential of particulates.

Histamine effects on conjunctival fibroblasts from patients with vernal conjunctivitis

Histamine, an important mast cell mediator in allergic disorders, may affect extracellular matrix production and cell growth in vernal keratoconjunctivitis (VKC). In the present study, the histamine reactivity of conjunctival fibroblasts derived from VKC patients was investigated in vitro. Conjunctival fibroblast cultures were derived from biopses of 8 tarsal VKC patients and 5 normal subjects. These cells were maintained in vitro and stimulated with different concentrations of histamine with and without H1 (clorpheniramine) and H2 (cimetidine) receptor antagonists. Comparisons were made to fibroblasts grown in the same media without histamine and to fibroblasts stimulated with just antihistamine. The effects of histamine were evaluated by: (1) the MTT test to assess cell proliferation; (2) an in vitro wound model for cell migration and (3) the measurement of procollagen I (PIP) and procollagen III (PIIIP) in supernatants for collagen production. Results showed: (1) While VKC-derived fibroblasts proliferated at a faster rate than normal cells in unstimulated media, after histamine stimulation, VKC and normal cells grew at a similar rate. Both H1 and H2 antagonists significantly inhibited (P<0.05) histamine-induced cell proliferation. (2) Histamine enhanced cell migration after wounding; this effect was inhibited only by H2 antagonism. (3) When stimulated with histamine, VKC fibroblasts produced significantly more PIP than those in control media. Furthermore, VKC-derived fibroblasts were more sensitive to histamine challenge, producing significantly more PIP than normal fibroblasts. H1 and H2 antagonists did not modify histamine-stimulated PIP production. The enhanced proliferative and productive capacity of VKC fibroblasts may be the result of a selective overgrowth of one or more fibroblast subpopulations in a chronically inflamed tissue. Histamine increased proliferation, migration and collagen production in both normal and VKC fibroblasts. Since H2 antagonism modulated both cell growth and migration, but not histamine-induced collagen production, the latter may be mediated by a different receptor. These results showed that histamine is at least partially responsible for fibroblast stimulation.

The use of silicone occlusive sheeting (Sil-K) and silicone occlusive gel (Epiderm) in the prevention of hypertrophic scar formation

The development of hypertrophic scars and keloids is an unsolved problem in the process of wound healing. For this reason, a successful treatment to prevent excessive scar formation still has not been found. Over the last decade, however, a promising new treatment has been introduced. Silicone materials have proved to reduce the amount of scar tissue and are believed even to prevent hypertrophic scar and keloid formation. In this study, the prophylactic effect of a silicone occlusive sheeting (Sil-K, Degania, Israel) and a silicone occlusive gel (Epiderm, Inamed B.V., The Netherlands) was investigated in a bilateral breast-reduction scar model in which the nontreated scars were supported by nonocclusive Micropore (3M, The Netherlands). The inframammary scars of 129 female patients with a mean age of 31 years ( 14 to 69 years) were studied up to 1 year after the operation. The width and height were measured, and B-scan ultrasound, laser-Doppler flowmetry, and color measurements were used as objective indicators to distinguish between normal and exuberant scars. Three months following the operation, 64.3 percent of the patients developed a hypertrophic scar, which was reduced to 56.6 percent after 6 months and down to 35.3 percent after 1 year. No keloids were seen. Patients with an easily tanning skin, nonsmokers, and patients with an allergy showed more hypertrophic scar formation. Neither Sil-K, used in 68 patients, nor Epiderm, used in 61 patients, could prevent the formation of hypertrophic scars. If both groups were taken together, the scars treated with silicone materials even developed significantly more hypertrophy compared with the Micropore-applicated scars.

Mast cells in clinical dermatology

Recent advances in cutaneous mast cell biology are briefly reviewed with special reference to our own studies on cultured human mast cells. Of note are the heterogeneity of mastocytosis, the important participation of mast cells in allergic inflammation by releasing cytokines and the inhibitory effect of histamine release from mast cells by phototherapy. It is also stressed that mast cells play a major role in tissue remodelling. These novel findings suggest that mast cells can no longer be regarded simply as cells that initiate immediate allergic reactions, but that they are responsible for various chronic inflammatory or immunological events through cytokine-dependent leucocyte recruitment. The regulation of mast cell activation should be a critical issue and, thus, a promising therapeutic approach in clinical dermatology.

Mast cells in bronchiolitis obliterans organizing pneumonia. Mast cell hyperplasia and evidence for extracellular release of tryptase

Idiopathic bronchiolitis obliterans organizing pneumonia (BOOP) is characterized by air space inflammation and fibrosis of unknown origin. The pathogenesis of the inflammatory reaction and fibrosis in fibrotic lung disorders remains unclear; however, recent attention has focused on the potential role of the mast cell in the genesis of fibrosis. To determine whether mast cells are implicated in the pathogenesis of BOOP, mast cells were identified in BAL fluid and in transbronchial lung biopsy specimens from 11 patients affected by BOOP and 17 control subjects. Mast cells and tryptase were significantly increased in BAL fluid of patients with BOOP (p = 0.001 and p = 0.03, respectively). In lung tissue of patients with BOOP, there was an increased number of mast cells per square millimeter of lung tissue with respect to control group (p = 0.001). Seventy-three percent of mast cells were found in the alveolar septa, 18% within alveoli often plunged in organizing pneumonia, 4% among alveolar lining cells, and 6% along blood vessels. No mast cells were located within alveoli in control subjects. Mast cell degranulation was evident in lung tissue specimens of patients with BOOP but not in those of control subjects (p = 0.01). This study shows the importance of mast cells and mast cell activation in the pathogenesis of BOOP.

Interleukin-2 inhibits 3T3 fibroblast proliferation

In order to clarify the role played by interleukin-2 (IL-2) in the regulation of fibroblast function, we investigated the effect of rat IL-2 and human recombinant IL-2 on 3T3 fibroblast proliferation and collagen synthesis. Fibroblasts were incubated with various concentrations of IL-2 for different periods of time. IL-2 was found to decrease in time- and dose-dependent manner the proliferation of 3T3 fibroblasts. This effect correlated with ability of IL-2 to enhance PGE2 production by 3T3 fibroblasts. When 3T3 fibroblasts were cocultured with rat peritoneal mast cells (MC), the growth-inhibiting effect of IL-2 was significantly less pronounced. Treatment of the cultures with IL-2 had no effect on collagen production by both 3T3 fibroblasts and fibroblasts cocultured with MC. In conclusion, in this study we provide evidence that IL-2, the key cytokine in T-cell growth and differentiation, can affect fibroblast functions.