A role for C-C chemokines in fibrotic lung disease

Crosstalk between fibroblasts and immunocytes in fibrosis: From molecular mechanisms to clinical trials

BACKGROUND

The impact of fibroblasts on the immune system provides insight into the function of fibroblasts. In various tissue microenvironments, multiple fibroblast subtypes interact with immunocytes by secreting growth factors, cytokines, and chemokines, leading to wound healing, fibrosis, and escape of cancer immune surveillance. However, the specific mechanisms involved in the fibroblast-immunocyte interaction network have not yet been fully elucidated.

MAIN BODY AND CONCLUSION

Therefore, we systematically reviewed the molecular mechanisms of fibroblast-immunocyte interactions in fibrosis, from the history of cellular evolution and cell subtype divisions to the regulatory networks between fibroblasts and immunocytes. We also discuss how these communications function in different tissue and organ statuses, as well as potential therapies targeting the reciprocal fibroblast-immunocyte interplay in fibrosis. A comprehensive understanding of these functional cells under pathophysiological conditions and the mechanisms by which they communicate may lead to the development of effective and specific therapies targeting fibrosis.

Homeostatic chemokines as putative therapeutic targets in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal chronic interstitial lung disease (ILD) that affects lung mechanical functions and gas exchange. IPF is caused by increased fibroblast activity and collagen deposition that compromise the alveolar-capillary barrier. Identifying an effective therapy for IPF remains a clinical challenge. Chemokines are key proteins in cell communication that have functions in immunity as well as in tissue homeostasis, damage, and repair. Chemokine receptor signaling induces the activation and proliferation of lung-resident cells, including alveolar macrophages (AMs) and fibroblasts. AMs are an important source of chemokines and cytokines during IPF. We highlight the complexity of this system and, based on insights from genetic and transcriptomic studies, propose a new role for homeostatic chemokine imbalance in IPF, with implications for putative therapeutic targets.

MKP-1 Deficiency Exacerbates Skin Fibrosis in a Mouse Model of Scleroderma

Scleroderma is a chronic fibrotic disease, where proinflammatory and profibrotic events precede collagen accumulation. MKP-1 [mitogen-activated protein kinase (MAPK) phosphatase-1] downregulates inflammatory MAPK pathways suppressing inflammation. MKP-1 also supports Th1 polarization, which could shift Th1/Th2 balance away from profibrotic Th2 profile prevalent in scleroderma. In the present study, we investigated the potential protective role of MKP-1 in scleroderma. We utilized bleomycin-induced dermal fibrosis model as a well-characterized experimental model of scleroderma. Dermal fibrosis and collagen deposition as well as the expression of inflammatory and profibrotic mediators were analyzed in the skin samples. Bleomycin-induced dermal thickness and lipodystrophy were increased in MKP-1-deficient mice. MKP-1 deficiency enhanced collagen accumulation and increased expression of collagens, 1A1 and 3A1, in the dermis. Bleomycin-treated skin from MKP-1-deficient mice also showed enhanced expression of inflammatory and profibrotic factors IL-6, TGF-β1, fibronectin-1 and YKL-40, and chemokines MCP-1, MIP-1α and MIP-2, as compared to wild-type mice. The results show, for the first time, that MKP-1 protects from bleomycin-induced dermal fibrosis, suggesting that MKP-1 favorably modifies inflammation and fibrotic processes that drive the pathogenesis of scleroderma. Compounds enhancing the expression or activity of MKP-1 could thus prevent fibrotic processes in scleroderma and possess potential as a novel immunomodulative drug.

Immune Mechanisms of Pulmonary Fibrosis with Bleomycin

Fibrosis and structural remodeling of the lung tissue can significantly impair lung function, often with fatal consequences. The etiology of pulmonary fibrosis (PF) is diverse and includes different triggers such as allergens, chemicals, radiation, and environmental particles. However, the cause of idiopathic PF (IPF), one of the most common forms of PF, remains unknown. Experimental models have been developed to study the mechanisms of PF, and the murine bleomycin (BLM) model has received the most attention. Epithelial injury, inflammation, epithelial-mesenchymal transition (EMT), myofibroblast activation, and repeated tissue injury are important initiators of fibrosis. In this review, we examined the common mechanisms of lung wound-healing responses after BLM-induced lung injury as well as the pathogenesis of the most common PF. A three-stage model of wound repair involving injury, inflammation, and repair is outlined. Dysregulation of one or more of these three phases has been reported in many cases of PF. We reviewed the literature investigating PF pathogenesis, and the role of cytokines, chemokines, growth factors, and matrix feeding in an animal model of BLM-induced PF.

Biological Mechanisms and Therapeutic Opportunities in Mammographic Density and Breast Cancer Risk

Mammographic density is an important risk factor for breast cancer; women with extremely dense breasts have a four to six fold increased risk of breast cancer compared to women with mostly fatty breasts, when matched with age and body mass index. High mammographic density is characterised by high proportions of stroma, containing fibroblasts, collagen and immune cells that suggest a pro-tumour inflammatory microenvironment. However, the biological mechanisms that drive increased mammographic density and the associated increased risk of breast cancer are not yet understood. Inflammatory factors such as monocyte chemotactic protein 1, peroxidase enzymes, transforming growth factor beta, and tumour necrosis factor alpha have been implicated in breast development as well as breast cancer risk, and also influence functions of stromal fibroblasts. Here, the current knowledge and understanding of the underlying biological mechanisms that lead to high mammographic density and the associated increased risk of breast cancer are reviewed, with particular consideration to potential immune factors that may contribute to this process.

Molecular pathways underlying tissue injuries in the bladder with ketamine cystitis

Ketamine cystitis (KC) is a chronic bladder inflammation leading to urinary urgency, frequency, and pain. The pathogenesis of KC is complicated and involves multiple tissue injuries in the bladder. Recent studies indicated that urothelium disruption, lamina propria fibrosis and inflammation, microvascular injury, neuropathological alterations, and bladder smooth muscle (BSM) abnormalities all contribute to the pathogenesis of KC. Ketamine has been shown to induce these tissue injuries by regulating different signaling pathways. Ketamine can stimulate antiproliferative factor, adenosine triphosphate, and oxidative stress to disrupt urothelium. Lamina propria fibrosis and inflammation are associated with the activation of cyclooxygenase-2, nitric oxide synthase, immunoglobulin E, and transforming growth factor β1. Ketamine contributes to microvascular injury via the N-methyl-D aspartic receptor (NMDAR), and multiple inflammatory and angiogenic factors such as tumor necrosis factor α and vascular endothelial growth factor. For BSM abnormalities, ketamine can depress the protein kinase B, extracellular signal-regulated kinase, Cav1.2, and muscarinic receptor signaling. Elevated purinergic signaling also plays a role in BSM abnormalities. In addition, ketamine affects neuropathological alterations in the bladder by regulating NMDAR- and brain-derived neurotrophic factor-dependent signaling. Inflammatory cells also contribute to neuropathological changes via the secretion of chemical mediators. Clarifying the role and function of these signaling underlying tissue injuries in the bladder with KC can contribute to a better understanding of the pathophysiology of this disease and to the design of effective treatments for KC.

Protective and anti-inflammatory effect of selenium nano-particles against bleomycin-induced pulmonary injury in male rats

Pulmonary fibrosis (PF) is an interstitial lung disease, in which the exact pathologic mechanisms are not fully understood. Drug trials for the treatment of PF have shown disappointing results and controversial. Recently, selenium nanoparticles (SeNPs) have received great attention for potential use in treatments, due to high bioactivity features and lower toxicity. This study evaluated the protective effect of SeNPs against pulmonary injury induced by bleomycin (single dose, 4 mg/kg, intratracheal) in male rats in early and late phases of the disease. The rats were treated with SeNPs by intraperitoneal injection (0.5 mg SeNP/kg) for five consecutive days in the early phase (a day after injection of bleomycin) and late phase (a week after injection of bleomycin). The results showed that injection of SeNPs in the early phase improved the degree of alveolitis and inflammation and lung structure damage. Also, led to significant decreases in density of transforming growth factor- β1 (TGF-β1) in the lung and tumor necrosis factor-α (TNF-α) levels in the serum and lung homogenates compared with bleomycin-administrated group. Notably, treatment with the SeNP during the late phase did not show any ameliorative effects. Thus, the data suggest that SeNP has a protective effect against bleomycin-induced pulmonary injury in rats in the early phase of the disease. This might mean that SeNPs may be a new therapeutic agent for the improvement of this disease in the early phases.

Inhaled Kathon may induce eosinophilia-mediated disease in the lung

In 2011, a link between humidifier disinfectants and patients with idiopathic pulmonary fibrosis was identified in Korea, and Kathon was suggested as one of the causative agents. In this study, Kathon induced apoptotic cell death along with membrane damage at 24 h post-exposure. Additionally, on day 14 after a single instillation with Kathon, the total number of pulmonary cells and the levels of TNF-α, IL-5, IL-13, MIP-1α, and MCP-1α clearly increased in the lung of mice. The proportion of natural killer cells and eosinophils were significantly elevated in the spleen and the bloodstream, respectively, and the level of immunoglobulin (Ig) A, but not IgG, IgM, and IgE, dose-dependently increased. Therefore, we suggest that inhaled Kathon may induce eosinophilia-mediated disease in the lung by disrupting homeostasis of pulmonary surfactants. Considering that eosinophilia is closely related to cancer and fibrosis, further studies are needed to understand the relationship between them.

Mechanism of pulmonary immunosuppression: extrapulmonary burn injury suppresses bacterial endotoxin-induced pulmonary neutrophil recruitment and neutrophil extracellular trap (NET) formation

Pulmonary immunosuppression often occurs after burn injury (BI). However, the reasons for BI-induced pulmonary immunosuppression are not clearly understood. Neutrophil recruitment and neutrophil extracellular trap (NET) formation (NETosis) are important components of a robust pulmonary immune response, and we hypothesized that pulmonary inflammation and NETosis are defective after BI. To test this hypothesis, we established a mouse model with intranasal LPS instillation in the presence or absence of BI (15% of body surface burn) and determined the degree of immune cell infiltration, NETosis, and the cytokine levels in the airways and blood on d 2. Presence of LPS recruited monocytes and large numbers of neutrophils to the airways and induced NETosis (citrullinated histone H3, DNA, myeloperoxidase). By contrast, BI significantly reduced LPS-mediated leukocyte recruitment and NETosis. This BI-induced immunosuppression is attributable to the reduction of chemokine (C-C motif) ligand (CCL) 2 (monocyte chemoattractant protein 1) and CCL3 (macrophage inflammatory protein 1α). BI also suppressed LPS-induced increase in IL-17A, IL-17C, and IL-17E/IL-25 levels in the airways. Therefore, BI-mediated reduction in leukocyte recruitment and NETosis in the lungs are attributable to these cytokines. Regulating the levels of some of these key cytokines represents a potential therapeutic option for mitigating BI-mediated pulmonary immunosuppression.-Sakuma, M., Khan, M. A. S., Yasuhara, S., Martyn, J. A., Palaniyar, N. Mechanism of pulmonary immunosuppression: extrapulmonary burn injury suppresses bacterial endotoxin-induced pulmonary neutrophil recruitment and neutrophil extracellular trap (NET) formation.

Targeting metabolic dysregulation for fibrosis therapy

Fibrosis is the abnormal deposition of extracellular matrix, which can lead to organ dysfunction, morbidity, and death. The disease burden caused by fibrosis is substantial, and there are currently no therapies that can prevent or reverse fibrosis. Metabolic alterations are increasingly recognized as an important pathogenic process that underlies fibrosis across many organ types. As a result, metabolically targeted therapies could become important strategies for fibrosis reduction. Indeed, some of the pathways targeted by antifibrotic drugs in development - such as the activation of transforming growth factor-β and the deposition of extracellular matrix - have metabolic implications. This Review summarizes the evidence to date and describes novel opportunities for the discovery and development of drugs for metabolic reprogramming, their associated challenges, and their utility in reducing fibrosis. Fibrotic therapies are potentially relevant to numerous common diseases such as cirrhosis, non-alcoholic steatohepatitis, chronic renal disease, heart failure, diabetes, idiopathic pulmonary fibrosis, and scleroderma.

Targeted delivery of YSA-functionalized and non-functionalized polymeric nanoparticles to injured pulmonary vasculature

Ephrin type-A receptor 2 (EphA2) is a transmembrane receptor which is upregulated in injured lungs, including those treated with bleomycin. YSA peptide (YSAYPDSVPMMS), a mimic of ephrin ligands, binds to EphA2 receptors on cell surface with high affinity. In this study, we assessed the ability of YSA-functionalized and non-functionalized poly (dl-lactide-co-glycolide) (PLGA) nanoparticles to enhance delivery to bleomycin treated cultured vascular endothelial cells and, in a bleomycin induced lung injury mouse model. Nanoparticles were loaded with a lipophilic fluorescent dye. Human umbilical vein endothelial cells (HUVEC) with or without 2-day bleomycin pretreatment (25 µg/ml) and adult mice with or without intratracheal instillation of bleomycin (0.1 U) were dosed with nanoparticles. Mice received nanoparticles via tail vein injection 4 days after bleomycin treatment. Three days after nanoparticle injection, tissues (lung, heart, kidney, spleen, liver, brain, eyes and whole blood) were harvested and quantified for fluorescence using IVIS imaging. Mean particle uptake increased with time and concentration for both types of particles in HUVEC, with the uptake being higher for YSA-functionalized nanoparticles. Bleomycin treatment increased the 3-h uptake of both types of nanoparticles in HUVEC by about two-fold, with the YSA-functionalized nanoparticle uptake being 1.66-fold compared to non-functionalized nanoparticles (p < .05). In mice, bleomycin injury resulted in 2.3- and 4.7-fold increase in the lung levels of non-functionalized and YSA-functionalized nanoparticles (p < .05), respectively, although the differences between the two particle types were not significant. In conclusion, PLGA nanoparticle delivery to cultured vascular endothelial cells and mouse lungs in vivo is higher following bleomycin treatment, with the delivery tending to be higher for YSA functionalized nanoparticles.

A review of current studies on cellular and molecular mechanisms underlying pulmonary fibrosis induced by chemicals

Several studies showed that the inflammatory and fibrotic responses induced by polyhexamethylene guanidine phosphate (PHMG-p) were similar to those observed for idiopathic pulmonary fibrosis in South Korea in 2011. "Omic" technologies can be used to understand the mechanisms underlying chemical-induced diseases. Studies to determine the toxicity of chemicals may facilitate understanding of the mechanisms underlying the development of pulmonary fibrosis at a molecular level; thus, such studies may provide information about the toxic characteristics of various substances. In this review, we have outlined the cellular and molecular mechanisms underlying idiopathic pulmonary fibrosis and described pulmonary fibrosis induced by various chemicals, including bleomycin, paraquat, and PHMG-p, based on the results of studies performed to date.

Dietary NaCl affects bleomycin-induced lung fibrosis in mice

PURPOSE

High levels of NaCl in the diet are associated with both cardiac and renal fibrosis, but whether salt intake affects pulmonary fibrosis has not been examined.

AIM OF THE STUDY

To test the hypothesis that salt intake might affect pulmonary fibrosis.

MATERIALS AND METHODS

Mice were fed low, normal, or high salt diets for 2 weeks, and then treated with oropharyngeal bleomycin to induce pulmonary fibrosis, or oropharyngeal saline as a control.

RESULTS

As determined by collagen staining of lung sections, and protein levels and cell numbers in the bronchoalveolar lavage (BAL) fluid at 21 days after bleomycin, the high salt diet did not exacerbate bleomycin-induced fibrosis, while the low salt diet attenuated fibrosis. For the bleomycin-treated mice, staining of the post-BAL lung sections indicated that compared to the regular salt diet, high salt increased the number of Ly6c-positive macrophages and decreased the number of CD11c and CD206-positive macrophages and dendritic cells. The low salt diet caused bleomycin-induced leukocyte numbers to be similar to control saline-treated mice, but reduced numbers of CD45/collagen-VI positive fibrocytes. In the saline controls, low dietary salt decreased CD11b and CD11c positive cells in lung sections, and high dietary salt increased fibrocytes.

CONCLUSIONS

Together, these data suggest the possibility that a low salt diet might attenuate pulmonary fibrosis.

Therapeutic pro-fibrogenic signaling pathways in fibroblasts

Myofibroblasts (MFs) play a critical role in the progression of chronic inflammatory and fibroproliferative diseases in different tissues/organs, whatever the etiology. Fibrosis is preceded and sustained by persistent injury and inflammatory response in a profibrogenic scenario involving mutual interactions, operated by several mediators and pathways, of MFs and related precursor cells with innate immunity cells and virtually any cell type in a defined tissue. These interactions, mediators and related signaling pathways are critical in initiating and perpetuating the differentiation of precursor cells into MFs that in different tissues share peculiar traits and phenotypic responses, including the ability to proliferate, produce ECM components, migrate and contribute to the modulation of inflammatory response and tissue angiogenesis. Literature studies related to liver, lung and kidney fibrosis have outlined a number of MF-related core regulatory fibrogenic signaling pathways conserved across these different organs and potentially targetable in order to develop effective antifibrotic therapeutic strategies.

Macrophages are necessary for epimorphic regeneration in African spiny mice

How the immune system affects tissue regeneration is not well understood. In this study, we used an emerging mammalian model of epimorphic regeneration, the African spiny mouse, to examine cell-based inflammation and tested the hypothesis that macrophages are necessary for regeneration. By directly comparing inflammatory cell activation in a 4 mm ear injury during regeneration (Acomys cahirinus) and scarring (Mus musculus), we found that both species exhibited an acute inflammatory response, with scarring characterized by stronger myeloperoxidase activity. In contrast, ROS production was stronger and more persistent during regeneration. By depleting macrophages during injury, we demonstrate a functional requirement for these cells to stimulate regeneration. Importantly, the spatial distribution of activated macrophage subtypes was unique during regeneration with pro-inflammatory macrophages failing to infiltrate the regeneration blastema. Together, our results demonstrate an essential role for inflammatory cells to regulate a regenerative response.

Deficiency of α7 nicotinic acetylcholine receptor attenuates bleomycin-induced lung fibrosis in mice

α7 nicotinic acetylcholine receptor (α7 nAChR, coded by Chrna7) is indispensible in dampening proinflammatory responses. However, whether α7 nAChR would play a role in regulating bleomycin (BLM)-induced lung fibrosis is less investigated. Here, we intratracheally challenged wildtype and Chrna7^-/- mice with BLM to elicit lung fibrosis. Taken advantage of this model, we measured body weight loss, lung fibrogenic genes (Acta2, Col1a1, Fsp1, and Fstl1), histology, Masson's trichrome staining, hydroxyproline levels, and expression of α-SMA at protein levels in the BLM-challenged lung for evaluating severity of lung fibrosis. We also pretreated human fibroblasts (MRC5 cell line) and isolated mouse lung fibroblasts with GTS-21 (an α7 nAChR agonist) to study its effects on TGF-β-stimulated profibrotic profiles. We found that lung Chrna7 expression and CD4⁺CHAT⁺ (Choline acetyltransferase, an enzyme for local acetylcholine synthesis) cells were 12-fold and 4.5-fold respectively elevated in the early stage of lung fibrosis. Deletion of Chrna7 prevented body weight loss and reduced lung fibrogenic genes (Acta2, Col1a1, Fsp1, and Fstl1) and Arg 1 (coding arginase 1). Deletion of Chrna7 attenuated lung arginase 1⁺Ly6C⁺ cells, Masson's trichrome staining, hydroxyproline levels, and expression of α-SMA at protein levels in BLM-challenged mice. Mechanistically, activation of α7 nAChR in human fibroblasts increased TGF-β-induced phosphorylation of Smad2/3 and transcription of fibrogenic genes (Acta2, Col1a1). In isolated mouse lung fibroblasts, activation of α7 nAChR also enhanced TGF-β induced-transcription of fibrogenic genes; however, deletion of Chrna7 diminished these effects. Taken together, deficiency of α7 nAChR could suppress the development of BLM-induced lung fibrosis. Thus, α7 nAChR might be a novel therapeutic target for treating lung fibrosis.

Silencing of Carbohydrate Sulfotransferase 15 Hinders Murine Pulmonary Fibrosis Development

Pulmonary fibrosis is a progressive lung disorder characterized by interstitial fibrosis, for which no effective treatments are available. Chondroitin sulfate proteoglycan (CSPG) has been shown to be a mediator, but the specific component of glycosaminoglycan chains of CSPG has not been explored. We show that chondroitin sulfate E-type (CS-E) is involved in fibrogenesis. Small interfering RNA (siRNA) targeting carbohydrate sulfotransferase 15 (CHST15) was designed to inhibit CHST15 mRNA and its product, CS-E. CS-E augments cell contraction and CHST15 siRNA inhibits collagen production. We found that bleomycin treatment increased CHST15 expression in interstitial fibroblasts at day 14. CHST15 siRNA was injected intranasally on days 1, 4, 8, and 11, and CHST15 mRNA was significantly suppressed by day 14. CHST15 siRNA reduced lung CSPG and the grade of fibrosis. CHST15 siRNA repressed the activation of fibroblasts, as evidenced by suppressed expression of α smooth muscle actin (αSMA), connective tissue growth factor (CTGF), lysyl oxidase like 2 (LOXL2), and CC-chemokine ligand 2 (CCL2)/monocyte chemoattractant protein-1 (MCP-1). Inflammatory infiltrates in the bronchoalveolar lavage fluid (BALF) and interstitium were diminished by CHST15 siRNA. These results indicate a pivotal role for CHST15 in fibroblast-mediated lung fibrosis and suggest a possible new therapeutic role for CHST15 siRNA in pulmonary fibrosis.

Respiratory toxicity and immunotoxicity evaluations of microparticle and nanoparticle C60 fullerene aggregates in mice and rats following nose-only inhalation for 13 weeks

C60 fullerene (C60), or buckminsterfullerene, is a spherical arrangement of 60 carbon atoms, having a diameter of approximately 1 nm, and is produced naturally as a by-product of combustion. Due to its small size, C60 has attracted much attention for use in a variety of applications; however, insufficient information is available regarding its toxicological effects. The effects on respiratory toxicity and immunotoxicity of C60 aggregates (50 nm [nano-C60] and 1 μm [micro-C60] diameter) were examined in B6C3F1/N mice and Wistar Han rats after nose-only inhalation for 13 weeks. Exposure concentrations were selected to allow for data evaluations using both mass-based and particle surface area-based exposure metrics. Nano-C60 exposure levels selected were 0.5 and 2 mg/m³ (0.033 and 0.112 m²/m³), while micro-C60 exposures were 2, 15 and 30 mg/m³ (0.011, 0.084 and 0.167 m²/m³). There were no systemic effects on innate, cell-mediated, or humoral immune function. Pulmonary inflammatory responses (histiocytic infiltration, macrophage pigmentation, chronic inflammation) were concentration-dependent and corresponded to increases in monocyte chemoattractant protein (MCP)-1 (rats) and macrophage inflammatory protein (MIP)-1α (mice) in bronchoalveolar lavage (BAL) fluid. Lung overload may have contributed to the pulmonary inflammatory responses observed following nano-C60 exposure at 2 mg/m³ and micro-C60 exposure at 30 mg/m³. Phenotype shifts in cells recovered from the BAL were also observed in all C60-exposed rats, regardless of the level of exposure. Overall, more severe pulmonary effects were observed for nano-C60 than for micro-C60 for mass-based exposure comparisons. However, for surface-area-based exposures, more severe pulmonary effects were observed for micro-C60 than for nano-C60, highlighting the importance of dosimetry when evaluating toxicity between nano- and microparticles.

Beyond TGFβ--novel ways to target airway and parenchymal fibrosis

Within the lungs, fibrosis can affect both the parenchyma and the airways. Fibrosis is a hallmark pathological change in the parenchyma in patients with idiopathic pulmonary fibrosis (IPF), whilst in asthma or chronic obstructive pulmonary disease (COPD) fibrosis is a component of the remodelling of the airways. In the past decade, significant advances have been made in understanding the disease behaviour and pathogenesis of parenchymal and airway fibrosis and as a result a variety of novel therapeutic targets for slowing or preventing progression of these fibrotic changes have been identified. This review highlights a number of these targets and discusses the potential for treating parenchymal or airway fibrosis through these mediators/pathways in the future.

Passion fruit peel extract attenuates bleomycin-induced pulmonary fibrosis in mice

Idiopathic pulmonary fibrosis is a progressive fatal lung disease characterized by excessive collagen deposition, with no effective treatments. We investigated the efficacy of natural products with high anti-inflammatory activity, such as passion fruit peel extract (PFPE), in a mouse model of bleomycin-induced pulmonary fibrosis (PF). C57BL/6J mice were subjected to a single intratracheal instillation of bleomycin to induce PF. Daily PFPE treatment significantly reduced loss of body mass and mortality rate in mice compared with those treated with bleomycin. While bleomycin-induced PF resulted in elevated total numbers of inflammatory cells, macrophages, lymphocytes, and neutrophils in bronchoalveolar lavage fluid on both days 7 and 21, PFPE administration significantly attenuated these phenomena compared with bleomycin group. On day 7, the decreased superoxide dismutase and myeloperoxidase activities observed in the bleomycin group were significantly restored with PFPE treatment. On day 21, enhanced hydroxyproline deposition in the bleomycin group was also suppressed by PFPE administration. PFPE treatment significantly attenuated extensive inflammatory cell infiltration and accumulation of collagen in lung tissue sections of bleomycin-induced mice on days 7 and 21, respectively. Our results indicate that administration of PFPE decreased bleomycin-induced PF because of anti-inflammatory and antioxidant activities.

Effects of lentiviral vector-mediated TRADD expression on the inhibition of hypertrophic scar formation

The tumor necrosis factor receptor-associated death domain protein (TRADD) regulates cell proliferation and apoptosis via tumor necrosis factor alpha (TNF-α)-mediated signaling pathways. Low levels of TRADD expression may result in the excessive proliferation of hypertrophic scar fibroblasts (HSFb). This study investigated the effects of a lentiviral vector carrying the human tradd gene on the proliferation, apoptosis and type I collagen synthesis of HSFb and embryonic fibroblasts (EFb) and further explored the resulting effects on hypertrophic scars (HS). We utilized cytoimmunofluorescence and Western blotting to confirm the expression of TRADD in HSFb and EFb. A PLVX-TRADD-EGFP lentivirus was prepared and transfected into EFb and HSFb, and then the expression of a TRADD-GFP-FLAG fusion protein was detected in HSFb and EFb. After stimulation with 10 ng/mL TNF-α, cell proliferation, apoptosis, and the synthesis of type I collagen were assessed. Our results show that the expression level of TRADD was significantly lower in HSFb than in EFb. A biologically active PLVX-TRADD-EGFP lentivirus was constructed and transfected into HSFb and EFb. The TRADD-GFP-FLAG fusion protein was effectively expressed in HSFb and EFb. Either alone or in combination with 10 ng/mL TNF-α, the PLVX-TRADD-EGFP lentivirus inhibited proliferation, caused a G2/M phase arrest, induced the appearance of a sub-G1 apoptotic peak and inhibited the secretion of type I collagen by HSFb without significantly affecting EFb. These results suggest that the low expression of TRADD in HSFb is a principal reason for their excessive proliferation. The transfection of a PLVX-TRADD-EGFP lentivirus led to the normal expression of TRADD in HSFb. When combined with 10 ng/mL TNF-α, a PLVX-TRADD-EGFP lentivirus transfection could inhibit cell proliferation, promote apoptosis, and reduce the secretion of type I collagen in HSFb, thereby reducing HS formation.

The relation between oxidative stress, inflammation, and neopterin in the paraquat-induced lung toxicity

Paraquat (PQ) is a well-known quaternary nitrogen herbicide. The major target organ in PQ poisoning is the lung. Reactive oxygen species (ROS) and inflammation play a crucial role in the development of PQ-induced pulmonary injury. Neopterin is synthesized in macrophage by interferon γ and other cytokines. We aimed to evaluate the utility of neopterin as a diagnostic marker in PQ-induced lung toxicity. Sprague Dawley rats were randomly divided into two groups (sham and PQ), administered intraperitoneally 1 mL saline and PQ (15 mg/kg/mL) respectively. Blood samples and lungs were collected for analyses. Lung injury and fibrosis were seen in the PQ group. Serum total antioxidant capacity, lactate dehydrogenase (LDH), and lung transforming growth factor-1β (TGF-1β) levels were significantly higher than the sham group (in all, p < 0.001). In addition, in the PQ group, serum neopterin and lung malondialdehyde (MDA) levels were also significantly higher than the sham group (in all, p = 0.001). Serum neopterin levels were correlated with LDH activities, lung MDA, lung TGF-1β levels, and the degree of lung injury. These findings demonstrated that oxidative stress, reduction of antioxidant capacity, and inflammation play a crucial role in the PQ-induced lung injury. Elevated serum neopterin levels may be a prognostic parameter to determine extends of PQ-induced lung toxicity. Further studies may be performed to clarify the role of neopterin by different doses of PQ.

Genome-wide transcriptional response during the development of bleomycin-induced pulmonary fibrosis in sprague-dawley rats

Pulmonary fibrosis is a common consequence of many lung diseases and a leading cause of morbidity and mortality. The molecular mechanisms underlying the development of pulmonary fibrosis remain poorly understood. One model used successfully to study pulmonary fibrosis over the past few decades is the bleomycin-induced pulmonary fibrosis model. We aimed to identify the genes associated with fibrogenesis using an Affymetrix GeneChip system in a bleomycin-induced rat model for pulmonary fibrosis. To confirm fibrosis development, several analyses were performed, including cellular evaluations using bronchoalveolar lavage fluid, measurement of lactate dehydrogenase activity, and histopathological examinations. Common aspects of pulmonary fibrosis such as prolonged inflammation, immune cell infiltration, emergence of fibroblasts, and deposition of extracellular matrix and connective tissue elements were observed. Global gene expression analysis revealed significantly altered expression of genes (≥ 1.5-fold, p < 0.05.) in a time-dependent manner during the development of pulmonary fibrosis. Our results are consistent with previous results of well-documented gene expression. Interestingly, the expression of triggering receptor expressed on myeloid cells 2 (Trem2) , secreted phosphoprotein 1 (Spp1) , and several proteases such as Tpsab1, Mcpt1, and Cma1 was considerably induced in the lung after bleomycin treatment, despite little evidence that they are involved in pulmonary fibrogenesis. These data will aid in our understanding of fibrogenic mechanisms and contribute to the identification of candidate biomarkers of fibrotic disease development.

Chemokines and Their Receptors Are Key Players in the Orchestra That Regulates Wound Healing

SIGNIFICANCE

Normal wound healing progresses through a series of overlapping phases, all of which are coordinated and regulated by a variety of molecules, including chemokines. Because these regulatory molecules play roles during the various stages of healing, alterations in their presence or function can lead to dysregulation of the wound-healing process, potentially leading to the development of chronic, nonhealing wounds.

RECENT ADVANCES

A discovery that chemokines participate in a variety of disease conditions has propelled the study of these proteins to a level that potentially could lead to new avenues to treat disease. Their small size, exposed termini, and the fact that their only modifications are two disulfide bonds make them excellent targets for manipulation. In addition, because they bind to G-protein-coupled receptors (GPCRs), they are highly amenable to pharmacological modulation.

CRITICAL ISSUES

Chemokines are multifunctional, and in many situations, their functions are highly dependent on the microenvironment. Moreover, each specific chemokine can bind to several GPCRs to stimulate the function, and both can function as monomers, homodimers, heterodimers, and even oligomers. Activation of one receptor by any single chemokine can lead to desensitization of other chemokine receptors, or even other GPCRs in the same cell, with implications for how these proteins or their receptors could be used to manipulate function.

FUTURE DIRECTIONS

Investment in better understanding of the functions of chemokines and their receptors in a local context can reveal new ways for therapeutic intervention. Understanding how different chemokines can activate the same receptor and vice versa could identify new possibilities for drug development based on their heterotypic interactions.

Cytokines in chronic respiratory diseases

Cytokines are small, secreted proteins that control immune responses. Within the lung, they can control host responses to injuries or infection, resulting in clearance of the insult, repair of lung tissue, and return to homeostasis. Problems can arise when this response is over exuberant and/or cytokine production becomes dysregulated. In such cases, chronic and repeated inflammatory reactions and cytokine production can be established, leading to airway remodeling and fibrosis with unintended, maladaptive consequences. In this report, we describe the cytokines and molecular mechanisms behind the pathology observed in three major chronic diseases of the lung: asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. Overlapping mechanisms are presented as potential sites for therapeutic intervention.

Sequential expression of IGF-IB followed by active TGF-β1 induces synergistic pulmonary fibroproliferation in vivo

Pulmonary fibrosis, the end stage of a variety of fibroproliferative lung diseases, is usually induced after repetitive or chronic lung injury or inflammation. The mechanisms of fibroproliferation are poorly understood. Insulin-like growth factor-I (IGF-I) is significantly elevated in patients with pulmonary fibrosis and fibroproliferative acute respiratory distress syndrome. However, we showed that IGF-I overexpression alone in wild-type mouse lungs does not cause fibroproliferation. We therefore questioned whether IGF-I, acting together with active TGF-β1, a known profibrotic cytokine, enhances pulmonary fibroproliferation caused by active TGF-β1. A unique sequential adenoviral transgene mouse model was used expressing AdEmpty/AdTGF-β1 or AdhIGF-IB/AdTGF-β1 transgenes. IGF-IB plus active TGF-β1 transgene expression synergistically increased collagen deposition in the lung parenchyma compared with active TGF-β1 expression alone. The enhanced fibrosis was accompanied by an increased recruitment of macrophages and lymphocytes into the bronchoalveolar lavage fluid (BALF) and inflammatory cells in the lungs. α-Smooth muscle actin expression, a marker of myofibroblast proliferation and differentiation, was also increased. Finally, fibroblasts exposed ex vivo to BALF isolated from AdhIGF-IB/AdTGF-β1-transduced mice showed synergistic collagen induction compared with BALF from AdEmpty/AdTGF-β1-transduced mice. This study provides the first direct evidence that IGF-I is able to synergistically enhance pulmonary fibroproliferation in cooperation with TGF-β1.

Aberrant innate immune sensing leads to the rapid progression of idiopathic pulmonary fibrosis

Novel approaches are needed to define subgroups of patients with Idiopathic pulmonary fibrosis (IPF) at risk for acute exacerbations and/or accelerated progression of this generally fatal disease. Progression of disease is an integral component of IPF with a median survival of 3 to 5 years. Conversely, a high degree of variability in disease progression has been reported among series. The characteristics of patients at risk of earlier death predominantly rely on baseline HRCT appearance, but this concept that has been challenged. Disparate physiological approaches have also been taken to identify patients at risk of mortality, with varying results. We hypothesized that the rapid decline in lung function in IPF may be a consequence of an abnormal host response to pathogen-associated molecular patterns (PAMPs), leading to aberrant activation in fibroblasts and fibrosis. Analysis of upper and lower lobe surgical lung biopsies (SLBs) indicated that TLR9, a hypomethylated CpG DNA receptor, is prominently expressed at the transcript and protein level, most notably in biopsies from rapidly progressive IPF patients. Surprisingly, fibroblasts appeared to be a major cellular source of TLR9 expression in IPF biopsies from this group of progressors. Further, CpG DNA promoted profibrotic cytokine and chemokine synthesis in isolated human IPF fibroblasts, most markedly again in cells from patients with the rapidly progressive IPF phenotype, in a TLR9-dependent manner. Finally, CpG DNA exacerbated fibrosis in an in vivo model initiated by the adoptive transfer of primary fibroblasts derived from patients who exhibited rapidly progressing fibrosis. Together, these data suggested that TLR9 activation via hypomethylated DNA might be an important mechanism in promoting fibrosis particularly in patients prone to rapidly progressing IPF.

Protective effect of 4,4'-diaminodiphenylsulfone against paraquat-induced mouse lung injury

Although 4,4'-diaminodiphenylsulfone (DDS, dapsone) has been used to treat several dermatologic conditions, including Hansen disease, for the past several decades, its mode of action has remained a topic of debate. We recently reported that DDS treatment significantly extends the lifespan of the nematode C. elegans by decreasing the generation of reactive oxygen species. Additionally, in in vitro experiments using non-phagocytic human fibroblasts, we found that DDS effectively counteracted the toxicity of paraquat (PQ). In the present study, we extended our work to test the protective effect of DDS against PQ in vivo using a mouse lung injury model. Oral administration of DDS to mice significantly attenuated the lung tissue damage caused by subsequent administration of PQ. Moreover, DDS reduced the local expression of mRNA transcripts encoding inflammation-related molecules, including endothelin-1 (ET-1), macrophage inflammatory protein-1α (MIP-1α), and transforming growth factor-β (TGF-β). In addition, DDS decreased the PQ-induced expression of NADPH oxidase mRNA and activation of protein kinase Cμ (PKCμ). DDS treatment also decreased the PQ-induced generation of superoxide anions in mouse lung fibroblasts. Taken together, these data suggest the novel efficacy of DDS as an effective protective agent against oxidative stress-induced tissue damages.

Distinct spatio-temporal extracellular matrix accumulation within demyelinated spinal cord lesions in Theiler's murine encephalomyelitis

The accumulation of extracellular matrix (ECM) and glial scar formation are considered important factors for the failure of regeneration in central nervous system (CNS) injury and multiple sclerosis. Theiler's murine encephalomyelitis (TME) as a model of multiple sclerosis served to evaluate the spatio-temporal course of ECM alterations in demyelinating conditions. Microarray analysis revealed only mildly upregulated gene expression of ECM molecules, their biosynthesis pathways and pro-fibrotic factors, while upregulation of matrix remodeling enzymes was more prominent. Immunohistochemistry demonstrated progressive accumulation of chondroitin sulfate proteoglycans, glycoproteins and collagens within demyelinated TME lesions, paralleling the development of astrogliosis. Deposition of collagen IV, laminin, perlecan and tenascin-C started 28 days postinfection (dpi), collagen I, decorin, entactin and neurocan accumulated from 56 dpi on, and fibronectin from 98 dpi on. The basement membrane (BM) molecules collagen IV, entactin, fibronectin, laminin and perlecan showed perivascular and parenchymal deposition, while the non-BM components collagen I, decorin, neurocan and tenascin-C only accumulated in a nonvascular pattern in demyelinated areas. Contrary, phosphacan expression progressively decreased during TME. The immunoreactivity of aggrecan and brevican remained unchanged. The spatio-temporal association of matrix accumulation with astrogliosis suggests a mainly astrocytic origin of ECM deposits, which in turn may contribute to remyelination failure in TME.

PPARs in alveolar macrophage biology

PPARs, most notably PPAR-gamma, play a crucial role in regulating the activation of alveolar macrophages, which in turn occupy a pivotal place in the immune response to pathogens and particulates drawn in with inspired air. In this review, we describe the dual role of the alveolar macrophage as both a first-line defender through its phagocytotic activity and a regulator of the immune response. Depending on its state of activation, the alveolar macrophage may either enhance or suppress different aspects of immune function in the lung. We then review the role of PPAR-gamma and its ligands in deactivating alveolar macrophages-thus limiting the inflammatory response that, if unchecked, could threaten the essential respiratory function of the alveolus-while upregulating the cell's phagocytotic activity. Finally, we examine the role that inadequate or inappropriate PPAR-gamma responses play in specific lung diseases.

Architecture and the extracellular matrix: the still unappreciated components of the adipose tissue

Fibrosis is usually characterized by the modification of both the amount and composition of a wide panel of extracellular matrix (ECM) proteins. In the liver, pancreas, kidney and lung the accumulation of fibrosis disrupts cellular processes and appears detrimental for organ function. This review highlights the available evidence supporting an important ECM remodelling in adipose tissue (AT) and, in particular, during the development of obesity. The modifications and occurrence of new adipose ECM components leads to an abnormal accumulation of fibrosis in this tissue. This phenomenon was well described in rodent models and evidence is beginning to emerge in humans; however, the origin and potential impact of these depots in AT biology are unclear. Two animal models with disruptions in ECM components (secreted proteins acidic in nature rich in cysteine null mice and ob/ob collagen VI null mice) suggest that fibrosis limits adipocyte hypertrophy and may cause the metabolic disorders associated with obesity. Over-expression of Hypoxia-inducible factor 1 leading to an increase in collagen expression suggests a role for hypoxia in fibrosis development. We conclude this review with possible hypotheses regarding the cellular and molecular contributors of fibrosis initiation.

Adrenomedullin in inflammatory process associated with experimental pulmonary fibrosis

BACKGROUND

Adrenomedullin (AM), a 52-amino acid ringed-structure peptide with C-terminal amidation, was originally isolated from human pheochromocytoma. AM are widely distributed in various tissues and acts as a local vasoactive hormone in various conditions.

METHODS

In the present study, we investigated the efficacy of AM on the animal model of bleomycin (BLM)-induced lung injury. Mice were subjected to intratracheal administration of BLM and were assigned to receive AM daily by an intraperitoneal injection of 200 ngr/kg.

RESULTS AND DISCUSSION

Myeloperoxidase activity, lung histology, immunohistochemical analyses for cytokines and adhesion molecules expression, inducible nitric oxide synthase (iNOS), nitrotyrosine, and poly (ADP-ribose) polymerase (PARP) were performed one week after fibrosis induction. Lung histology and transforming growth factor beta (TGF-β) were performed 14 and 21 days after treatments. After bleomycin administration, AM-treated mice exhibited a reduced degree of lung damage and inflammation compared with BLM-treated mice, as shown by the reduction of (1) myeloperoxidase activity (MPO), (2) cytokines and adhesion molecules expression, (3) nitric oxide synthase expression, (4) the nitration of tyrosine residues, (5) poly (ADP-ribose) (PAR) formation, a product of the nuclear enzyme poly (ADP-ribose) polymerase (PARP) (6) transforming growth factor beta (TGF-β) (7)and the degree of lung injury.

CONCLUSIONS

Our results indicate that AM administration is able to prevent bleomycin induced lung injury through the down regulation of proinflammatory factors.

Pulmonary fibrosis in response to environmental cues and molecular targets involved in its pathogenesis

Chronic lung injury resulting from a variety of different causes is frequently associated with the develop ment of pulmonary fibrosis in humans. Although the etiology of pulmonary fibrosis is generally unknown, several sources of evidence support the hypothesis that a number of environmental and occupational agents play an etiologic role in the pathogenesis of this disease. The agents discussed in this review include beryllium, nylon flock, textile printing aerosols, polyvinyl chloride and didecyldimethylammonium chloride. The authors also describe a variety of animal models, including genetically modified mice, in order to investigate the molecular mechanism of pulmonary fibrosis, focusing on chemokine receptors, regulatory T cells and transforming growth factor-β and bone morphogenetic protein signaling. Overall, we propose the concept of toxicological pulmonary fibrosis as a lung disease induced in response to environmental cues.

Collagen I induces discoidin domain receptor (DDR) 1 expression through DDR2 and a JAK2-ERK1/2-mediated mechanism in primary human lung fibroblasts

Discoidin domain receptors (DDRs) DDR1 and DDR2 are receptor tyrosine kinases with the unique ability among receptor tyrosine kinases to respond to collagen. Several signaling molecules have been implicated in DDR signaling, including Shp-2, Src, and MAPK pathways, but a detailed understanding of these pathways and their transcriptional targets is still lacking. Similarly, the regulation of the expression of DDRs is poorly characterized with only a few inflammatory mediators, such as lipopolysaccharide and interleukin-1β identified as playing a role in DDR1 expression. DDRs have been reported to induce the expression of various genes including matrix metalloproteinases and bone morphogenetic proteins, but the regulatory mechanisms underlying DDR-induced gene expression remain to be determined. The aim of the present work was to elucidate the molecular mechanisms implicated in the expression of DDRs and to identify DDR-induced signaling pathways and target genes. Our data show that collagen I induces the expression of DDR1 in a dose- and time-dependent manner in primary human lung fibroblasts. Furthermore, activation of DDR2, JAK2, and ERK1/2 MAPK signaling pathways was essential for collagen I-induced DDR1 and matrix metalloproteinase 10 expression. Finally, inhibition of the ERK1/2 pathway abrogated DDR1 expression by blocking the recruitment of the transcription factor polyoma enhancer A-binding protein 3 to the DDR1 promoter. Our data provide new insights into the molecular mechanisms of collagen I-induced DDR1 expression and demonstrate an important role for ERK1/2 activation and the recruitment of polyoma enhancer-A binding protein 3 to the DDR1 promoter.

Distinct severe acute respiratory syndrome coronavirus-induced acute lung injury pathways in two different nonhuman primate species

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), caused by influenza A virus H5N1 and severe acute respiratory syndrome coronavirus (SARS-CoV), supposedly depend on activation of the oxidative-stress machinery that is coupled with innate immunity, resulting in a strong proinflammatory host response. Inflammatory cytokines, such as interleukin 1β (IL-1β), IL-8, and IL-6, play a major role in mediating and amplifying ALI/ARDS by stimulating chemotaxis and activation of neutrophils. To obtain further insight into the pathogenesis of SARS-CoV-associated ALI, we compared SARS-CoV infections in two different nonhuman primate species, cynomolgus macaques and African green monkeys. Viral titers in the upper and lower respiratory tract were not significantly different in SARS-CoV-infected macaques and African green monkeys. Inflammatory cytokines that play a major role in mediating and amplifying ALI/ARDS or have neutrophil chemoattractant activity, such as IL-6, IL-8, CXCL1, and CXCL2, were, however, induced only in macaques. In contrast, other proinflammatory cytokines and chemokines, including osteopontin and CCL3, were upregulated in the lungs of African green monkeys to a significantly greater extent than in macaques. Because African green monkeys developed more severe ALI than macaques, with hyaline membrane formation, some of these differentially expressed proinflammatory genes may be critically involved in development of the observed pathological changes. Induction of distinct proinflammatory genes after SARS-CoV infection in different nonhuman primate species needs to be taken into account when analyzing outcomes of intervention strategies in these species.

Synergistic induction of CX3CL1 by interleukin-1β and interferon-γ in human lung fibroblasts: involvement of signal transducer and activator of transcription 1 signaling pathways

CX3CL1 (fractalkine), a membrane-bound chemokine that induces both the adhesion and the migration of leukocytes, is involved in the recruitment of cells into tissues undergoing inflammatory responses. To explore the regulation of CX3CL1 in pulmonary inflammation and fibrosis, CX3CL1 expression in lung fibroblasts was examined. Normal human fibroblasts were obtained from Promocell (Lonza Walkersville Inc, Md) and were incubated in the presence or absence of various inflammatory stimuli. Culture supernatants were collected, and the soluble CX3CL1 levels were determined with an enzyme-linked immunosorbent assay. The expression of CX3CL1 mRNA transcripts in lung fibroblasts was assessed using quantitative TaqMan real-time polymerase chain reaction. Interleukin (IL)-1β or interferon (IFN)-γ individually induced negligible soluble CX3CL1 secretion by human lung fibroblasts after 24 h. However, the combination of IL-1β and IFN-γ induced dramatic increases in both soluble CX3CL1 protein and mRNA transcripts in a dose- and time-dependent manner. Synergistic up-regulation of cell-associated CX3CL1 protein also was observed after treatment with IL-1β and IFN-γ. The secretion and expression of lung fibroblast-derived CX3CL1 were markedly reduced by specific inhibitors of the STAT-1 transcription factor. These findings suggest that lung fibroblasts are an important cellular source of CX3CL1 and may play a role in pulmonary inflammation and fibrosis.

Phosphoinositide 3-kinase γ plays a critical role in bleomycin-induced pulmonary inflammation and fibrosis in mice

PI3Kγ is central in signaling diverse arrays of cellular functions and inflammation. Pulmonary fibrosis is associated with pulmonary inflammation, angiogenesis, and deposition of collagen and is modeled by instillation of bleomycin. The role of PI3Kγ in mediating bleomycin-induced pulmonary inflammation and fibrosis in mice and potential mechanisms involved was investigated here. WT or PI3Kγ KO mice were instilled with bleomycin and leukocyte subtype influx, cytokine and chemokine levels, and angiogenesis and tissue fibrosis evaluated. The activation of lung-derived leukocytes and fibroblasts was evaluated in vitro. The relevance of PI3Kγ for endothelial cell function was evaluated in HUVECs. PI3Kγ KO mice had greater survival and weight recovery and less fibrosis than WT mice after bleomycin instillation. This was associated with decreased production of TGF-β(1) and CCL2 and increased production of IFN-γ and IL-10. There was reduced expression of collagen, fibronectin, α-SMA, and von Willebrand factor and decreased numbers and activation of leukocytes and phosphorylation of AKT and IκB-α. PI3Kγ KO mice had a reduced number and area of blood vessels in the lungs. In vitro, treatment of human endothelial cells with the PI3Kγ inhibitor AS605240 decreased proliferation, migration, and formation of capillary-like structures. AS605240 also decreased production of collagen by murine lung-derived fibroblasts. PI3Kγ deficiency confers protection against bleomycin-induced pulmonary injury, angiogenesis, and fibrosis through the modulation of leukocyte, fibroblast, and endothelial cell functions. Inhibitors of PI3Kγ may be beneficial for the treatment of pulmonary fibrosis.

Antifibrosis: to reverse the irreversible

Fibrosis is a pathological process that includes scar formation and overproduction of extracellular matrix by the connective tissue as a response to tissue damage. The fibrotic process involves multiple organs and results in progressive life-threatening diseases. Today, we know more about the molecular mechanism that leads to fibrosis involving different type of cells, cytokines, chemokines, and tissue enzymes. Fibrosis was considered an irreversible process, at least clinically, and is still usually treated by anti-inflammatory and immunosuppressive agents. No proven antifibrotic therapy has shown efficacy in ameliorating the clinical course of fibrotic diseases, but our current understanding led to the development of different drugs with promising results, like: mycophenolate mofetil, interferon, relaxin, and intravenous immunoglobulin. This review will provide a glance to this heavily investigated subject.

Amphiregulin attenuates bleomycin-induced pneumopathy in mice

Amphiregulin, an EGF receptor (EGFR) ligand, is essential for epithelial development in various organs. A recent report suggested that amphiregulin acts as a protective factor in a liver injury model. Little is known about the roles of amphiregulin in lung injury and pulmonary fibrosis. The purpose of the present study was to investigate the role of amphiregulin in an experimental model of bleomycin-induced pneumopathy in mice. C57BL/6 mice were administered a bleomycin hydrochloride solution intratracheally. Recombinant human amphiregulin was injected intraperitoneally at 6, 8, 10, and 12 days after the bleomycin instillation. The grades of inflammation and fibrosis were assessed histologically and biochemically, and the numbers of apoptotic cells were counted after TdT-mediated dUTP nick end labeling (TUNEL) staining in the lung tissues. We also examined downstream survival signals of EGFR, namely phosphorylated Akt and phosphorylated Erk, in lung tissues by Western blotting analysis and immunohistochemistry. Expression of intrinsic amphiregulin was increased in murine lung tissues after bleomycin instillation. Administration of recombinant amphiregulin improved the survival rate and suppressed the degrees of inflammation and fibrosis and the number of TUNEL-positive cells in lung tissues. Amphiregulin treatment enhanced the activation of Akt and Erk in lung epithelial cells. Amphiregulin may play a protective role in bleomycin-induced pneumopathy in mice, probably through the activation of survival signals. Administration of amphiregulin may be a novel therapeutic strategy against lung injury and fibrosis.

Latent herpesvirus infection augments experimental pulmonary fibrosis

RATIONALE

No effective treatment exists for idiopathic pulmonary fibrosis, and its pathogenesis remains unclear. Accumulating evidence implicates herpesviruses as cofactors (either initiating or exacerbating agents) of fibrotic lung disease, but a role for latent herpesvirus infection has not been studied.

OBJECTIVES

To develop a murine model to determine whether latent herpesvirus infection can augment fibrotic responses and to gain insight into potential mechanisms of enhanced fibrogenesis.

METHODS

Mice were infected with murine gammaherpesvirus 14 to 70 days before a fibrotic challenge with fluorescein isothiocyanate or bleomycin so that the virus was latent at the time of fibrotic challenge. Measurements were made after viral infection alone or after the establishment of fibrosis.

MEASUREMENTS AND MAIN RESULTS

gammaHerpesvirus is latent by 14 days post infection, and infection 14 to 70 days before fibrotic challenge augmented fibrosis. Fibrotic augmentation was not dependent on reactivation of the latent virus to a lytic state. Total cell numbers and fibrocyte numbers were increased in the lungs of latently infected mice administered fibrotic challenge compared with mock-infected mice that received fibrotic challenge. Latent infection up-regulates expression of proinflammatory chemokines, transforming growth factor-beta1, and cysteinyl leukotrienes in alveolar epithelial cells.

CONCLUSIONS

Latent gammaherpesvirus infection augments subsequent fibrotic responses in mice. Enhanced fibrosis is associated with the induction of profibrotic factors and the recruitment of fibrocytes. Our data complement existing human and animal data supporting the hypothesis that gammaherpesviruses can serve as initiating cofactors in the pathogenesis of pulmonary fibrosis.

Bronchoalveoloar lavage fluid cytokines and chemokines as markers and predictors for the outcome of interstitial lung disease in systemic sclerosis patients

Introduction

Interstitial lung disease (ILD) is a frequent manifestation of systemic sclerosis (SSc), and cytokines can contribute to the disease pathology. The aim of the current study was to identify specific changes in cytokine levels that may serve as disease markers and possible targets for therapy.

Methods

Cytokines were measured with bioplex analysis in 38 bronchoalveolar fluids (BALFs) from 32 SSc patients (27 with alveolitis and 11 without alveolitis) and 26 control patients. In the case of SSc patients, cytokines were correlated with the respective bronchoalveolar lavage (BAL) cell differentiation, lung function, and thoracic HR-CT score. For 35 BALF samples derived from 29 SSc patients, follow-up investigations of clinical data, lung-function parameter, or thoracic HR-CT scans were available to evaluate the predictive capacity of BALF cytokines and chemokines.

Results

High IL-7 levels were characteristic of SSc-associated interstitial lung disease (ILD) and, in addition, when compared with ILD-negative SSc patients, ILD-positive SSc patients revealed higher IL-4, IL-6, IL-8, and CCL2 (MCP-1) BALF levels. High CCL2 and IL-8 BALF concentrations were associated with neutrophilic and mixed alveolitis. Cytokine levels of IL-4, IL-8, and CCL2 correlated negatively with lung-function parameters; CCL2 concentrations also correlated with HR-CT scores. High concentrations of several cytokines were associated with the progress of ILD and end-stage ILD. Univariate analyses revealed high IL-2 and tumor necrosis factor-alpha (TNF-α) levels as the best predictors for progressive disease, together with lung-function parameters, young age, and neutrophilic alveolitis. Multivariate analyses partially confirmed these results but did not sufficiently converge because of the limited number of patients.

Conclusions

The association of BALF cytokines with lung fibrosis and its progress suggests that cytokines contribute to the pathogenesis of ILD and hence could be regarded as potential therapeutic targets.

Role of MCP-1 in cardiovascular disease: molecular mechanisms and clinical implications

Many of the major diseases, including cardiovascular disease, are widely recognized as inflammatory diseases. MCP-1 (monocyte chemotactic protein-1) plays a critical role in the development of cardiovascular diseases. MCP-1, by its chemotactic activity, causes diapedesis of monocytes from the lumen to the subendothelial space where they become foam cells, initiating fatty streak formation that leads to atherosclerotic plaque formation. Inflammatory macrophages probably play a role in plaque rupture and the resulting ischaemic episode as well as restenosis after angioplasty. There is strong evidence that MCP-1 plays a major role in myocarditis, ischaemia/reperfusion injury in the heart and in transplant rejection. MCP-1 also plays a role in cardiac repair and manifests protective effects under certain conditions. Such protective effects may be due to the induction of protective ER (endoplasmic reticulum) stress chaperones by MCP-1. Under sustained ER stress caused by chronic exposure to MCP-1, the protection would break down resulting in the development of heart failure. MCP-1 is also involved in ischaemic angiogenesis. The recent advances in our understanding of the molecular mechanisms that might be involved in the roles that MCP-1 plays in cardiovascular disease are reviewed. The gene expression changes induced by the signalling events triggered by MCP-1 binding to its receptor include the induction of a novel zinc-finger protein called MCPIP (MCP-1-induced protein), which plays critical roles in the development of the pathophysiology caused by MCP-1 production. The role of the MCP-1/CCR2 (CC chemokine receptor 2) system in diabetes, which is a major risk factor for cardiovascular diseases, is also reviewed briefly. MCP-1/CCR2- and/or MCPIP-targeted therapeutic approaches to intervene in inflammatory diseases, including cardiovascular diseases, may be feasible.

Chemokines and cardiac fibrosis

Several members of the chemokine family play an important role in reparative fibrosis and are involved in the pathogenesis of remodeling following myocardial infarction. Chemokines may regulate the fibrotic process through recruitment and activation of mononuclear cell subsets and fibroblast progenitors (fibrocytes), by exerting direct effects on resident fibroblasts, and by modulating angiogenesis. Monocyte Chemoattractant Protein (MCP)-1/CCL2 is the best studied chemokine in cardiac fibrosis. Disruption of the MCP-1 axis reduces fibrosis attenuating dilation of the infarcted ventricle. In addition, MCP-1 signaling is activated in response to insults that do not cause cardiomyocyte death, such as brief ischemia or pressure overload and regulates fibrous tissue deposition in experimental models of fibrotic non-infarctive cardiomyopathy. Understanding the role of chemokine-mediated interactions in the development of cardiac fibrosis may identify novel therapeutic targets for treatment of patients with heart failure.

CD19 regulates the development of bleomycin-induced pulmonary fibrosis in a mouse model

OBJECTIVE

The contribution of CD19 and B lymphocytes to pulmonary fibrosis is controversial. The aim of this study was to address the role of CD19 during the development of pulmonary fibrosis.

METHODS

Mice lacking or overexpressing the B cell surface molecule CD19, which is known as a positive regulator of B cell activation, were used in a model of bleomycin-induced pulmonary fibrosis. Ten or sixteen days after intratracheal injection of bleomycin, lung sections from mice were evaluated by histologic analysis. Seven days after instillation, the total leukocyte count and the number of B cells in bronchoalveolar lavage fluid (BALF) were determined, using a hemocytometer and flow cytometry. Bleomycin was also administered into selectin-deficient or intercellular adhesion molecule 1-deficient mouse strains. The level of CXCR3 expression on B cells was determined by flow cytometry.

RESULTS

CD19 deficiency significantly reduced susceptibility to intratracheal bleomycin challenge on day 16, while CD19 overexpression augmented fibrosis even on day 10. Furthermore, the survival rate and number of B cells in BALF also correlated with CD19 expression levels. The accumulation of B cells in BALF was dependent on CD19 levels, whereas there was no association with the levels of selectins or intercellular adhesion molecule 1. Additionally, CXCR3 was up-regulated in BALF B cells, while it was rarely expressed on circulating B cells. Furthermore, CD19 signaling facilitated B cell CXCR3 up-regulation in response to stimulation in vitro.

CONCLUSION

These results suggest that CD19 signaling is associated with the development of pulmonary fibrosis by controlling B cell infiltration into lung tissue, which may be associated with CXCR3 up-regulation.

The adenosine a2a receptor inhibits matrix-induced inflammation in a novel fashion

Endogenous mediators within the inflammatory milieu play a critical role in directing the scope, duration, and resolution of inflammation. High-molecular-weight extracellular matrix hyaluronan (HA) helps to maintain homeostasis. During inflammation, hyaluronan is broken down into fragments that induce chemokines and cytokines, thereby augmenting the inflammatory response. Tissue-derived adenosine, released during inflammation, inhibits inflammation via the anti-inflammatory A2 adenosine receptor (A2aR). We demonstrate that adenosine modulates HA-induced gene expression via the A2aR. A2aR stimulation inhibits HA fragment-induced pro-fibrotic genes TNF-alpha, keratinocyte chemoattractant (KC), macrophage inflammatory protein (MIP)-2, and MIP-1alpha while simultaneously synergizing with hyaluronan fragments to up-regulate the TH1 cytokine IL-12. Interestingly, A2aR stimulation mediates these affects via the novel cAMP-activated guanine nucleotide exchange factor EPAC. In addition, A2aR-null mice are more susceptible to bleomycin-induced lung injury, consistent with a role for endogenous adenosine in inhibiting the inflammation that may lead to fibrosis. Indeed, the bleomycin treated A2aR-null mice demonstrate increased lung inflammation, HA accumulation, and histologic damage. Overall, our data elucidate the opposing roles of tissue-derived HA fragments and adenosine in regulating noninfectious lung inflammation and support the pursuit of A2aR agonists as a means of pharmacologically inhibiting inflammation that may lead to fibrosis.

Fc receptor engagement mediates differentiation of cardiac fibroblast precursor cells

We previously described a critical role for a fibroblast precursor population in the development of a murine fibrotic cardiomyopathy model (I/RC). These precursors arose from circulating bone marrow-derived cells of monocytic origin. Administration of serum amyloid P (SAP) prevented the presence of this cell population in the heart and the cardiomyopathy. Because SAP binds to Fc receptors (FcRs) expressed on monocytes, we investigated the involvement of FcR signaling. We chose mice lacking the FcRgamma chain protein (FcRgamma(-/-)), a common membrane-signaling component of activating FcRs. Like wild-type mice, FcRgamma(-/-) mice developed fibrosis and cardiac dysfunction when subjected to I/RC. However, unlike wild-type mice, SAP in FcRgamma(-/-) mice failed to inhibit the development of fibrosis and cardiac dysfunction and did not diminish the numbers of alpha-smooth muscle actin(+) and CD34(+), CD45(+) fibroblasts that were typical for I/RC. To further examine the role of SAP in monocyte-to-fibroblast transition, we performed in vitro assays in which human peripheral blood mononuclear cells (PBMCs) migrated through human umbilical vein endothelial cells (HUVECs). We found that MCP-1-dependent transendothelial migration of monocytes markedly accelerated their differentiation into fibroblasts. This monocyte differentiation to fibroblasts was eliminated when SAP was added to the PBMC suspension before endothelial transmigration. Adding SAP to cells after successful migration did not inhibit fibroblast maturation. These data indicate that SAP inhibits the differentiation of a blood-borne, myeloid cell population into fibroblasts by signaling through activating FcRs before transendothelial migration has occurred. We suggest that FcR activation of circulating precursor cells may represent a new treatment target for adverse remodeling and cardiac fibrosis.