Alveolar macrophages release an insulin-like growth factor I-type molecule

Identification of Key Candidate Genes Involved in the Progression of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal, agnogenic interstitial lung disease with limited therapeutic options. To investigate vital genes involved in the development of IPF, we integrated and compared four expression profiles (GSE110147, GSE53845, GSE24206, and GSE10667), including 87 IPF samples and 40 normal samples. By reanalyzing these datasets, we managed to identify 62 upregulated genes and 20 downregulated genes in IPF samples compared with normal samples. Differentially expressed genes (DEGs) were analyzed by gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to illustrate relevant pathways of IPF, biological processes, molecular function, and cell components. The DEGs were then subjected to protein-protein interaction (PPI) for network analysis, serving to find 11 key candidate genes (ANXA3, STX11, THBS2, MMP1, MMP9, MMP7, MMP10, SPP1, COL1A1, ITGB8, IGF1). The result of RT-qPCR and immunohistochemical staining verified our finding as well. In summary, we identified 11 key candidate genes related to the process of IPF, which may contribute to novel treatments of IPF.

PAPP-A and the IGF system in atherosclerosis: what's up, what's down?

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase with a well-established role in releasing bioactive insulin-like growth factor-1 (IGF-1) from IGF-binding protein-2, -4, and -5 by proteolytic processing of these. The IGF system has repeatedly been suggested to be involved in the pathology of atherosclerosis, and both PAPP-A and IGF-1 are proposed biomarkers and therapeutic targets for this disease. Several experimental approaches based on atherosclerosis mouse models have been undertaken to obtain causative and mechanistic insight to the role of these molecules in atherogenesis. However, reports seem conflicting. The literature suggests that PAPP-A is detrimental, while IGF-1 is beneficial. This raises important questions that need to be addressed. Here we summarize the various studies and discuss potential underlying explanations for this seemingly inconsistency with the objective of better understanding complexities and limitations when manipulating the IGF system in mouse models of atherosclerosis. A debate clarifying what's up and what's down is highly warranted going forward with the ultimate goal of improving atherosclerosis therapy by targeting the IGF system.

Insulin-Like Growth Factor 1 in the Cardiovascular System

Non-communicable diseases, such as cardiovascular diseases, are the leading cause of mortality worldwide. For this reason, a tremendous effort is being made worldwide to effectively circumvent these afflictions, where insulin-like growth factor 1 (IGF1) is being proposed both as a marker and as a central cornerstone in these diseases, making it an interesting molecule to focus on. Firstly, at the initiation of metabolic deregulation by overfeeding, IGF1 is decreased/inhibited. Secondly, such deficiency seems to be intimately related to the onset of MetS and establishment of vascular derangements leading to atherosclerosis and finally playing a definitive part in cerebrovascular and myocardial accidents, where IGF1 deficiency seems to render these organs vulnerable to oxidative and apoptotic/necrotic damage. Several human cohort correlations together with basic/translational experimental data seem to confirm deep IGF1 implication, albeit with controversy, which might, in part, be given by experimental design leading to blurred result interpretation.

Molecular Mechanisms of Pulmonary Fibrogenesis and Its Progression to Lung Cancer: A Review

Idiopathic pulmonary fibrosis (IPF) is defined as a specific form of chronic, progressive fibrosing interstitial pneumonia of unknown cause, occurring primarily in older adults, and limited to the lungs. Despite the increasing research interest in the pathogenesis of IPF, unfavorable survival rates remain associated with this condition. Recently, novel therapeutic agents have been shown to control the progression of IPF. However, these drugs do not improve lung function and have not been tested prospectively in patients with IPF and coexisting lung cancer, which is a common comorbidity of IPF. Optimal management of patients with IPF and lung cancer requires understanding of pathogenic mechanisms and molecular pathways that are common to both diseases. This review article reflects the current state of knowledge regarding the pathogenesis of pulmonary fibrosis and summarizes the pathways that are common to IPF and lung cancer by focusing on the molecular mechanisms.

Increased Levels of IGF-1 and Beta2-Microglobulin in Epithelial Lining Fluid of Preterm Newborns Developing Chronic Lung Disease: Effects of rhG-CSF

Insulin-like growth factor-1 (IGF-1) is involved in regulating the TH-l/TH-2 balance, favoring the development of the TH-2 compartment which enhances fibrosis, one of the main characteristics of Chronic Lung Disease (CLD) in premature newborns. Limited data is available concerning a possible association between early epithelial lining fluid (ELF) concentrations of IGF-1 (total and free forms), IGF-binding protein-3 (IGFBP-3), b2-microglobulin (B2M) and subsequent development of CLD in preterm neonates. If neutropenic, preterm neonates are frequently treated with recombinant human Granulocyte Colony Stimulating Factor (rhG-CSF). The objective of the study was to correlate ELF concentrations of IGF-1 and B2M during the first week of life both in non-neutropenic and in rhG-CSF-treated neutropenic preterm neonates, with subsequent development in CLD. Thirty preterm neonates with Respiratory Distress Syndrome (6 with neutropenia) were studied. Eleven out of 24 non-neutropenic preterm infants (46%) and all of the six neutropenic subjects (100%) developed CLD. With the exception of first day values, there was a clear similarity in the behaviors of assayed molecules between non-neutropenic and neutropenic patients developing CLD. Non-neutropenic patients without CLD showed significantly lower values of free IGF-1 and B2M both on days 1 and 3. Total IGF-I and cell counts were different only on the 3rd day. Conclusions: 1) the mechanisms leading to CLD might be mediated by high levels of IGF-family molecules soon after birth 2) B2M could be a marker of increased bronchoalveolar lavage fluid cellularity with potential inflammatory properties 3) G-CSF treatment induces an increased synthesis of IGF-1 molecules by cells recruited in the lung, with possible enhancement of the fibrogenic mechanisms.

Insulin-Like Growth Factor-1 Signaling in Lung Development and Inflammatory Lung Diseases

Insulin-like growth factor-1 (IGF-1) was firstly identified as a hormone that mediates the biological effects of growth hormone. Accumulating data have indicated the role of IGF-1 signaling pathway in lung development and diseases such as congenital disorders, cancers, inflammation, and fibrosis. IGF-1 signaling modulates the development and differentiation of many types of lung cells, including airway basal cells, club cells, alveolar epithelial cells, and fibroblasts. IGF-1 signaling deficiency results in alveolar hyperplasia in humans and disrupted lung architecture in animal models. The components of IGF-1 signaling pathways are potentiated as biomarkers as they are dysregulated locally or systemically in lung diseases, whereas data may be inconsistent or even paradoxical among different studies. The usage of IGF-1-based therapeutic agents urges for more researches in developmental disorders and inflammatory lung diseases, as the majority of current data are collected from limited number of animal experiments and are generally less exuberant than those in lung cancer. Elucidation of these questions by further bench-to-bedside researches may provide us with rational clinical diagnostic approaches and agents concerning IGF-1 signaling in lung diseases.

Analysis of the IGF-system in milk from farm animals - Occurrence, regulation, and biomarker potential

IGFs and IGF-binding proteins (IGFBPs) are abundantly present in milk and in dairy products. Compared to the IGFs, the IGFBP have received less attention in milk, although truncated IGFBPs and IGFBP-glycosylation have been described in milk. Thereby, complex control of local IGF-effects can be assumed on the levels of IGFBPs, proteases, and protease inhibitors. The present review collects the current knowledge both on presence and regulation of IGFs and IGFBPs in milk particularly from dairy animal species. As a rule higher levels of IGF-I, IGF-II, and IGFBPs are measured around parturition if compared to later time-points of lactation. In all farm animal species included in this review, it is found that the relative abundancies of IGFBPs in milk and serum are similar, with IGFBP-3 and -2 characterized by higher concentrations if compared to IGFBP-4 or -5. The concentrations of IGFs and IGFBPs in milk or dairy products can be altered by hormones, dairy processing, or fermentation. Because milk can be used for non-invasive biomarker research, quality management, and health monitoring, we discuss novel directions of IGF-analysis and potential on-site biomarker research in milk.

Complications of acromegaly: cardiovascular, respiratory and metabolic comorbidities

Acromegaly is associated with an enhanced mortality, with cardiovascular and respiratory complications representing not only the most frequent comorbidities but also two of the main causes of deaths, whereas a minor role is played by metabolic complications, and particularly diabetes mellitus. The most prevalent cardiovascular complications of acromegaly include a cardiomyopathy, characterized by cardiac hypertrophy and diastolic and systolic dysfunction together with arterial hypertension, cardiac rhythm disorders and valve diseases, as well as vascular endothelial dysfunction. Biochemical control of acromegaly significantly improves cardiovascular disease, albeit completely recovering to normal mainly in young patients with short disease duration. Respiratory complications, represented mainly by sleep-breathing disorders, particularly sleep apnea, and respiratory insufficiency, frequently occur at the early stage of the disease and, although their severity decreases with disease control, this improvement does not often change the indication for a specific therapy directed to improve respiratory function. Metabolic complications, including glucose and lipid disorders, are variably reported in acromegaly. Treatments of acromegaly may influence glucose metabolism, and the presence of diabetes mellitus in acromegaly may affect the choice of treatments, so that glucose homeostasis is worth being monitored during the entire course of the disease. Early diagnosis and prompt treatment of acromegaly, aimed at obtaining a strict control of hormone excess, are the best strategy to limit the development or reverse the complications and prevent the premature mortality.

Tissue-specific contribution of macrophages to wound healing

Macrophages are present in all tissues, either as resident cells or monocyte-derived cells that infiltrate into tissues. The tissue site largely determines the phenotype of tissue-resident cells, which help to maintain tissue homeostasis and act as sentinels of injury. Both tissue resident and recruited macrophages make a substantial contribution to wound healing following injury. In this review, we evaluate how macrophages in two fundamentally distinct tissues, i.e. the lung and the skin, differentially contribute to the process of wound healing. We highlight the commonalities of macrophage functions during repair and contrast them with distinct, tissue-specific functions that macrophages fulfill during the different stages of wound healing.

The History of the Bellevue Hospital Chest Service (1903-2015)

For more than 100 years, the Bellevue Hospital Chest Service in New York City has contributed major advances in our understanding of pulmonary disease. Research from the cardiopulmonary laboratory of the Chest Service by Drs. Cournand and Richards resulted in the shared Nobel Prize in Physiology or Medicine in 1956 for the development of human cardiac catheterization. In more recent years, continuing its mission to serve the underserved and respond to health crises, the Bellevue Chest Service has served as a leader in the management of HIV infections, multiple drug-resistant tuberculosis epidemics, early detection of lung cancer, and management of urban asthma. Members of the Chest Service founded the World Trade Center Environmental Health Center shortly after collapse of the towers in 2001. The Chest Service became New York's infectious isolation unit caring for the first patient in New York infected with Ebola virus. Recent research has focused on disease management, with the first in-house Directly Observed Therapy Clinic for treatment of tuberculosis, clinical trials of aerosolized IFN-γ, and translational research on host defense against tuberculosis infection. Studies of the airway mucosa have revealed mechanisms by which ambient pollutants promote asthma. Studies on the World Trade Center firefighters and community populations have promoted understanding of systemic inflammation and small airways function. Today, the partnership between a public hospital and an academic institution promotes the synergy that leads to cost-effective and state-of-the art care for an underserved population as well as cutting-edge training and research.

Macrophage and adipocyte IGF1 maintain adipose tissue homeostasis during metabolic stresses

OBJECTIVE

Insulin-like growth factor-1 (IGF1) regulates differentiation and growth of tissues and reduces stress and injury. IGF1 also in a tissue-specific manner modulates the differentiation and lipid storage capacity of adipocytes in vitro, but its roles in adipose tissue development and response to stress are not known.

METHODS

To study IGF1 in vivo, the cellular sources of adipose tissue Igf1 expression were identified and mice were generated with targeted deletion in adipocytes and macrophages. The effects of adipocyte and macrophage deficiency of IGF1 on adipose tissue development and the response to chronic (high-fat feeding) and acute (cold challenge) stress were studied.

RESULTS

The expression of Igf1 by adipose tissue was derived from multiple cell types including adipocytes and macrophages. In lean animals, adipocytes were the primary source of IGF1, but in obesity expression by adipocytes was reduced and by macrophages increased, so as to maintain overall adipose tissue Igf1 expression. Genetic deletion studies revealed that adipocyte-derived IGF1 regulated perigonadal but not subcutaneous adipose tissue mass during high-fat feeding and the development of obesity. Conversely, macrophage-derived IGF1 acutely modulated perigonadal adipose tissue mass during thermogenic challenges.

CONCLUSIONS

Local IGF1 is not required in lean adipose tissue development but is required to maintain homeostasis during both chronic and acute metabolic stresses.

Roles of Proteoglycans and Glycosaminoglycans in Wound Healing and Fibrosis

A wound is a type of injury that damages living tissues. In this review, we will be referring mainly to healing responses in the organs including skin and the lungs. Fibrosis is a process of dysregulated extracellular matrix (ECM) production that leads to a dense and functionally abnormal connective tissue compartment (dermis). In tissues such as the skin, the repair of the dermis after wounding requires not only the fibroblasts that produce the ECM molecules, but also the overlying epithelial layer (keratinocytes), the endothelial cells, and smooth muscle cells of the blood vessel and white blood cells such as neutrophils and macrophages, which together orchestrate the cytokine-mediated signaling and paracrine interactions that are required to regulate the proper extent and timing of the repair process. This review will focus on the importance of extracellular molecules in the microenvironment, primarily the proteoglycans and glycosaminoglycan hyaluronan, and their roles in wound healing. First, we will briefly summarize the physiological, cellular, and biochemical elements of wound healing, including the importance of cytokine cross-talk between cell types. Second, we will discuss the role of proteoglycans and hyaluronan in regulating these processes. Finally, approaches that utilize these concepts as potential therapies for fibrosis are discussed.

Macrophage proliferation, provenance, and plasticity in macroparasite infection

Macrophages have long been center stage in the host response to microbial infection, but only in the past 10–15 years has there been a growing appreciation for their role in helminth infection and the associated type 2 response. Through the actions of the IL-4 receptor α (IL-4Rα), type 2 cytokines result in the accumulation of macrophages with a distinctive activation phenotype. Although our knowledge of IL-4Rα-induced genes is growing rapidly, the specific functions of these macrophages have yet to be established in most disease settings. Understanding the interplay between IL-4Rα-activated macrophages and the other cellular players is confounded by the enormous transcriptional heterogeneity within the macrophage population and by their highly plastic nature. Another level of complexity is added by the new knowledge that tissue macrophages can be derived either from a resident prenatal population or from blood monocyte recruitment and that IL-4 can increase macrophage numbers through proliferative expansion. Here, we review current knowledge on the contribution of macrophages to helminth killing and wound repair, with specific attention paid to distinct cellular origins and plasticity potential.

Boon and Bane of Inflammation in Bone Tissue Regeneration and Its Link with Angiogenesis

Delayed healing or nonhealing of bone is an important clinical concern. Although bone, one of the two tissues with scar-free healing capacity, heals in most cases, healing is delayed in more than 10% of clinical cases. Treatment of such delayed healing condition is often painful, risky, time consuming, and expensive. Tissue healing is a multistage regenerative process involving complex and well-orchestrated steps, which are initiated in response to injury. At best, these steps lead to scar-free tissue formation. At the onset of healing, during the inflammatory phase, stationary and attracted macrophages and other immune cells at the fracture site release cytokines in response to injury. This initial reaction to injury is followed by the recruitment, proliferation, and differentiation of mesenchymal stromal cells, synthesis of extracellular matrix proteins, angiogenesis, and finally tissue remodeling. Failure to heal is often associated with poor revascularization. Since blood vessels mediate the transport of circulating cells, oxygen, nutrients, and waste products, they appear essential for successful healing. The strategy of endogenous regeneration in a tissue such as bone is interesting to analyze since it may represent a blueprint of successful tissue formation. This review highlights the interdependency of the time cascades of inflammation, angiogenesis, and tissue regeneration. A better understanding of these inter-relations is mandatory to early identify patients at risk as well as to overcome critical clinical conditions that limit healing. Instead of purely tolerating the inflammatory phase, modulations of inflammation (immunomodulation) might represent a valid therapeutic strategy to enhance angiogenesis and foster later phases of tissue regeneration.

Enhanced production of IGF-I in the lungs of fibroproliferative ARDS patients

Insulin‐Like Growth Factor I (IGF‐I) has been identified in the lungs of individuals with fibrotic lung diseases. In a previous retrospective study, we showed enhanced IGF‐I immunoreactivity in individuals with fibroproliferative acute respiratory distress syndrome (FP‐ARDS), but we were unable to determine if this correlation was causative. This study was undertaken to prospectively investigate whether IGF‐I expression correlated with the fibroproliferative process and whether IGF‐I was induced and made in the lungs. We measured IGF‐I and procollagen III peptide (PCP‐III) in the epithelial lining fluid (ELF) from controls, early ALI/ARDS patients and FP‐ARDS patients. We also measured IGF‐I mRNA and immunoreactivity from controls and FP‐ARDS patient lung biopsies. We determined the level of lung permeability by measuring albumin and urea levels in ELF and serum. Our data show that IGF‐I is significantly increased in the ELF in FP‐ARDS patients. A significant correlation between IGF‐I and PCP‐III in the ELF of FP‐ARDS patients is found. IGF‐I mRNA is elevated in the FP‐ARDS lung biopsies. Our data suggest that IGF‐I found in the lungs of FP‐ARDS patients results from both increased lung permeability and local production of IGF‐I. The role of IGF‐I in the fibroproliferative process in the lungs has recently been confirmed in an animal model of lung fibroproliferation. This study importantly suggest that IGF‐I protein is made in the lungs of FP‐ARDS patients and correlates with increased levels of ELF PCP‐III, implicating a role for IGF‐I in the fibroproliferative process in humans.

The role of IGF‐I in the fibroproliferative process in the lungs has recently been confirmed in an animal model of lung fibroproliferation. This study importantly shows that IGF‐I protein is made in the lungs of FP‐ARDS patients and correlates with increased levels of ELF PCP‐III, implicating a role for IGF‐I in the fibroproliferative process in humans.

Neutrophil gelatinase-associated lipocalin (NGAL) and insulin-like growth factor (IGF)-1 association with a Mannheimia haemolytica infection in sheep

This study was aimed at mapping the tissue distribution of some inflammatory parameters associated with a Mannheimia haemolytica (M. haemolytica) infection in sheep. The M. haemolytica was isolated and characterized from the affected lungs of slaughtered animals. Cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-10, insulin-like growth factor (IGF)-1, as well as the acute-phase protein, neutrophil gelatinase-associated lipocalin (NGAL), were identified in the lung tissues, the serum, and the lymph nodes of M. haemolytica infected sheep, by enzyme-linked immunosorbent assay (ELISA). NGAL and IGF-1 pointed to an innate immune response, and epithelial cell repairing, respectively. The adaptive immune response was identified through the type of cytokines present in the affected sheep, as TNF-α represents the pro-inflammatory cytokines, and IL-10 represents the anti-inflammatory cytokines. M. haemolytica isolates were confirmed by polymerase chain reaction (PCR) and DNA sequences. There was a significant difference in the concentrations of NGAL, IGF-1, TNF-α, and IL-10, as observed in the affected sheep when compared to the healthy sheep. This study, for the first time, closely describes the distribution of some key and new inflammatory parameters in the tissue homogenate of affected lungs.

Leukotriene C4 aggravates bleomycin-induced pulmonary fibrosis in mice

BACKGROUND AND OBJECTIVE

Synthesis of cysteinyl leukotrienes (cys-LT) is thought to cause inflammatory disorders such as bronchial asthma and allergic rhinitis. Recent reports have suggested that leukotriene C4 (LTC4 ) is an important regulator of pulmonary fibrosis. This study examined the effect of LTC4 in LTC4 synthase-overexpressed transgenic mice with bleomycin-induced pulmonary fibrosis. The function of lung-derived fibroblasts from transgenic mice was also investigated.

METHODS

Bleomycin was administrated to transgenic mice and wild-type (WT) mice by intratracheal instillation. Concentrations of interleukin (IL)-4 and -13, interferon-γ, and transforming growth factor (TGF)-β1 in bronchoalveolar lavage fluid were measured 1, 3, 7 and 14 days after the administration of bleomycin. Lung tissue was examined histopathologically on day 14. In addition, lung-derived fibroblasts from transgenic and WT mice were cultured for 7 days. Expression of TGF-β1 mRNA was measured by real-time polymerase chain reaction.

RESULTS

Both the pathological scores for pulmonary fibrosis (3.8 ± 0.4 vs 2.0 ± 0.1, P < 0.05) and the levels of IL-4 (12.1 ± 2.3 vs <7.8 pg/mL, P < 0.05), IL-13 (26.5 ± 5.2 vs <7.8 pg/mL, P < 0.01) and TGF-β1 (211.1 ± 30.2 vs 21.3 ± 1.2 pg/mL, P < 0.01) on day 14 were significantly greater in transgenic than in WT mice. Furthermore, the reduction of LTC4 by pranlukast hydrate, a cys-LT1 receptor antagonist, in fibroblasts from transgenic significantly (P < 0.05) decreased the expression of TGF-β1 mRNA (by ∼50%) compared with those from WT mice.

CONCLUSIONS

Overexpression of LTC4 , amplifies bleomycin-induced pulmonary fibrosis in mice. Our findings suggest a role for LTC4 in lung fibrosis.

Astaxanthin ameliorates lung fibrosis in vivo and in vitro by preventing transdifferentiation, inhibiting proliferation, and promoting apoptosis of activated cells

Astaxanthin, a member of the carotenoid family, is the only known ketocarotenoid transported into the brain by transcytosis through the blood-brain barrier. However, whether astaxanthin has antifibrotic functions is unknown. In this study, we investigated the effects of astaxanthin on transforming growth factor β1-mediated and bleomycin-induced pulmonary fibrosis in vitro and in vivo. The results showed that astaxanthin significantly improved the structure of the alveoli and alleviated collagen deposition in vivo. Compared with the control group, the astaxanthin-treated groups exhibited downregulated protein expressions of α-smooth muscle actin, vimentin, hydroxyproline, and B cell lymphoma/leukemia-2 as well as upregulated protein expressions of E-cadherin and p53 in vitro and in vivo. Astaxanthin also inhibited the proliferation of activated A549 and MRC-5 cells at median inhibitory concentrations of 40 and 30 μM, respectively. In conclusion, astaxanthin could relieve the symptoms and halt the progression of pulmonary fibrosis, partly by preventing transdifferentiation, inhibiting proliferation, and promoting apoptosis of activated cells.

Monocytes: super cells for bone regeneration

Monocytes are progenitor cells that lead the inflammatory cascade reaction responsible for guiding revascularization and regeneration of tissue at injury sites. They do this by secreting inductive cytokines responsible for endothelial cell migration. When released into the peripheral blood, monocytes enter tissues and become macrophages. Monocytes also trigger the body's defense mechanism against microbial invasion by lysing and removing cell debris and dead tissue. The aim of this article is to explain the role of monocytes in the processes of bone healing and regeneration and describe their interaction with stem cells and other entities. Results of a pilot histomorphometric study in which concentrated monocytes were combined with demineralized allograft material to augment implant-placement sites in 2 patients also are presented.

An essential role for TH2-type responses in limiting acute tissue damage during experimental helminth infection

Helminths induce potent Th2-type immune responses that can mediate worm expulsion but the importance of this response in controlling acute tissue damage caused by migrating multi-cellular parasites through vital tissues remains uncertain. We used a helminth infection model where parasitic nematode larvae migrate transiently through the lung causing damage resulting in hemorrhage and inflammation. Our findings showed initial elevations in IL-17 contributed to inflammation and lung damage while subsequent IL-4R signaling controlled IL-17 elevations, enhanced expression of insulin-like growth factor 1 and IL-10 and stimulated development of M2 cells, each of which contributed to rapid resolution of tissue damage. These studies indicate an essential role for the Th2-type immune response in mediating acute wound healing during helminth infection.

Role of oxidants in interstitial lung diseases: pneumoconioses, constrictive bronchiolitis, and chronic tropical pulmonary eosinophilia

Oxidants such as superoxide anion, hydrogen peroxide, and myeloperoxidase from activated inflammatory cells in the lower respiratory tract contribute to inflammation and injury. Etiologic agents include inorganic particulates such as asbestos, silica, or coal mine dust or mixtures of inorganic dust and combustion materials found in World Trade Center dust and smoke. These etiologic agents are phagocytosed by alveolar macrophages or bronchial epithelial cells and release chemotactic factors that recruit inflammatory cells to the lung. Chemotactic factors attract and activate neutrophils, eosinophils, mast cells, and lymphocytes and further activate macrophages to release more oxidants. Inorganic dusts target alveolar macrophages, World Trade Center dust targets bronchial epithelial cells, and eosinophils characterize tropical pulmonary eosinophilia (TPE) caused by filarial organisms. The technique of bronchoalveolar lavage in humans has recovered alveolar macrophages (AMs) in dust diseases and eosinophils in TPE that release increased amounts of oxidants in vitro. Interestingly, TPE has massively increased eosinophils in the acute form and after treatment can still have ongoing eosinophilic inflammation. A course of prednisone for one week can reduce the oxidant burden and attendant inflammation and may be a strategy to prevent chronic TPE and interstitial lung disease.

Stimulation of neoplastic mouse lung cell proliferation by alveolar macrophage-derived, insulin-like growth factor-1 can be blocked by inhibiting MEK and PI3K activation

Background

Worldwide, lung cancer kills more people than breast, colon and prostate cancer combined. Alterations in macrophage number and function during lung tumorigenesis suggest that these immune effector cells stimulate lung cancer growth. Evidence from cancer models in other tissues suggests that cancer cells actively recruit growth factor-producing macrophages through a reciprocal signaling pathway. While the levels of lung macrophages increase during tumor progression in mouse models of lung cancer, and high pulmonary macrophage content correlates with a poor prognosis in human non-small cell lung cancer, the specific role of alveolar macrophages in lung tumorigenesis is not clear.

Methods

After culturing either an immortalized lung macrophage cell line or primary murine alveolar macrophages from naïve and lung-tumor bearing mice with primary tumor isolates and immortalized cell lines, the effects on epithelial proliferation and cellular kinase activation were determined. Insulin-like growth factor-1 (IGF-1) was quantified by ELISA, and macrophage conditioned media IGF-1 levels manipulated by IL-4 treatment, immuno-depletion and siRNA transfection.

Results

Primary macrophages from both naïve and lung-tumor bearing mice stimulated epithelial cell proliferation. The lungs of tumor-bearing mice contained 3.5-times more IGF-1 than naïve littermates, and media conditioned by freshly isolated tumor-educated macrophages contained more IGF-1 than media conditioned by naïve macrophages; IL-4 stimulated IGF-1 production by both macrophage subsets. The ability of macrophage conditioned media to stimulate neoplastic proliferation correlated with media IGF-1 levels, and recombinant IGF-1 alone was sufficient to induce epithelial proliferation in all cell lines evaluated. Macrophage-conditioned media and IGF-1 stimulated lung tumor cell growth in an additive manner, while EGF had no effect. Macrophage-derived factors increased p-Erk1/2, p-Akt and cyclin D1 levels in neoplastic cells, and the combined inhibition of both MEK and PI3K ablated macrophage-mediated increases in epithelial growth.

Conclusions

Macrophages produce IGF-1 which directly stimulates neoplastic proliferation through Erk and Akt activation. This observation suggests that combining macrophage ablation therapy with IGF-1R, MEK and/or PI3K inhibition could improve therapeutic response in human lung cancer. Exploring macrophage-based intervention could be a fruitful avenue for future research.

Transcriptomic analysis reveals a mechanism for a prefibrotic phenotype in STAT1 knockout mice during severe acute respiratory syndrome coronavirus infection

Severe acute respiratory syndrome coronavirus (SARS-CoV) infection can cause the development of severe end-stage lung disease characterized by acute respiratory distress syndrome (ARDS) and pulmonary fibrosis. The mechanisms by which pulmonary lesions and fibrosis are generated during SARS-CoV infection are not known. Using high-throughput mRNA profiling, we examined the transcriptional response of wild-type (WT), type I interferon receptor knockout (IFNAR1-/-), and STAT1 knockout (STAT1-/-) mice infected with a recombinant mouse-adapted SARS-CoV (rMA15) to better understand the contribution of specific gene expression changes to disease progression. Despite a deletion of the type I interferon receptor, strong expression of interferon-stimulated genes was observed in the lungs of IFNAR1-/- mice, contributing to clearance of the virus. In contrast, STAT1-/- mice exhibited a defect in the expression of interferon-stimulated genes and were unable to clear the infection, resulting in a lethal outcome. STAT1-/- mice exhibited dysregulation of T-cell and macrophage differentiation, leading to a TH2-biased immune response and the development of alternatively activated macrophages that mediate a profibrotic environment within the lung. We propose that a combination of impaired viral clearance and T-cell/macrophage dysregulation causes the formation of prefibrotic lesions in the lungs of rMA15-infected STAT1-/- mice.

Role of growth factors in acute lung injury induced by paraquat in a rat model

Paraquat (PQ) can cause acute lung injury in humans and experimental animals. However, the role of growth factors in the progression of injury has not been clearly established. We developed an animal model of PQ-induced lung injury using Wistar rats. One milliliter of PQ solution (30, 60, and 120 mg/kg) was applied through the lavage, while the same amount of vehicle was applied to control rats. Based on histopathology, the lungs of some animals exposed to PQ showed acute fulmination, resulting in death, while others showed a more protracted injury, resulting in typical pulmonary fibrosis at 21 days. Using this PQ-poisoned rat model, we examined the intrapulmonary gene expression and circulatory level of cytokines and growth factors at 8 hours, 24 hours, 3 days, 7 days, 14 days, and 21 days after PQ administration. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that the gene expression levels of interleukin-1 beta and interleukin-6 were significantly increased at 21 days after PQ challenge compared with the controls. The mRNA expression of tumor necrosis factor-alpha was also significantly increased except on days 14 and 21 after PQ treatment. Moreover, PQ-treated rats showed enhanced gene expression of growth factors such as platelet-derived growth factor-A and insulin-like growth factor-1 at 21 days and transforming growth factor-beta 1 at 14 days. ELISA results showed the circulatory level of cytokines and growth factors coincided with intrapulmonary gene expression. The synergistic effects of these molecules are presumed to cause pulmonary damage due to PQ challenge and may become targets of treatment.

Insulin-like growth factor-I regulation of immune function: a potential therapeutic target in autoimmune diseases?

This topically limited review explores the relationship between the immune system and insulin-like growth factors (IGF-I and IGF-II) and the proteins through which they act, including IGF-I receptor (IGF-IR) and the IGF-I binding proteins. The IGF/IGF-IR pathway plays important and diverse roles in tissue development and function. It regulates cell cycle progression, apoptosis, and the translation of proteins. Many of the consequences ascribed to IGF-IR activation result from its association with several accessory proteins that are either identical or closely related to those involved in insulin receptor signaling. Relatively recent awareness that IGF-I and IGF-IR regulate immune function has cast this pathway in an unexpected light; it may represent an important switch governing the quality and amplitude of immune responses. IGF-I/IGF-IR signaling may also participate in the pathogenesis of autoimmune diseases, although its relationship with these processes seems complex and relatively unexplored. On the one hand, IGF-I seems to protect experimental animals from developing insulin-deficient diabetes mellitus. In contrast, activating antibodies directed at IGF-IR have been detected in patients with Graves' disease, where the receptor is overexpressed by multiple cell types. The frequency of IGF-IR+ B and T cells is substantially increased in patients with that disease. Potential involvement of IGF-I and IGF-IR in the pathogenesis of autoimmune diseases suggests that this pathway might constitute an attractive therapeutic target. IGF-IR has been targeted in efforts directed toward drug development for cancer, employing both small-molecule and monoclonal antibody approaches. These have been generally well-tolerated. Recognizing the broader role of IGF-IR in regulating both normal and pathological immune responses may offer important opportunities for therapeutic intervention in several allied diseases that have proven particularly difficult to treat.

Effects of Th2 pulmonary inflammation in mice with bleomycin-induced pulmonary fibrosis

BACKGROUND AND OBJECTIVE

Leucocytes, especially lymphocytes and neutrophils, as well as alveolar macrophages, that infiltrate into the lung are involved in the development of pulmonary fibrosis. However, the role of T helper (Th)2-type inflammation, mediated by Th2 cells and eosinophils, in fibrosis remains unknown. Transgenic mice deficient in the transcriptional repressor, Bcl6, display an attenuation of Th2 cytokine production. We studied the effects of Th2-type pulmonary inflammation on bleomycin-induced pulmonary fibrosis using Bcl6 transgenic mice.

METHODS

Bleomycin was administered to ovalbumin (OVA)-sensitized Bcl6 transgenic and wild-type mice by intratracheal instillation during sequential OVA antigen challenge. Concentrations of transforming growth factor-beta1 in the BAL fluid were measured 2 weeks after bleomycin administration. At the same time lung tissue was examined histopathologically, and homogenized to assess collagen levels and Th1/Th2 cytokine mRNA expression.

RESULTS

Although OVA-sensitized, bleomycin-treated Bcl6 transgenic mice had markedly lower numbers of eosinophils in both BAL and lung tissue compared with OVA-sensitized, bleomycin-treated wild-type mice, the development of pulmonary fibrosis in response to bleomycin was similar in Bcl6 transgenic mice and wild-type mice.

CONCLUSION

These results suggest that Th2-dominant inflammation in the lung is not essential for the development of bleomycin-induced pulmonary fibrosis.

Insulin-like growth factor-I receptor blockade improves outcome in mouse model of lung injury

RATIONALE

The insulin-like growth factor-I (IGF-I) pathway is an important determinant of survival and proliferation in many cells. However, little is known about the role of the IGF-I pathway in lung injury. We previously showed elevated levels of IGF-I in bronchoalveolar lavage fluid from patients with acute respiratory distress syndrome. Furthermore, immunodepletion of IGF from acute respiratory distress syndrome bronchoalveolar lavage increased fibroblast apoptosis.

OBJECTIVES

We examined the effect of blockade of type 1 IGF tyrosine kinase receptor (IGF-IR) in a murine model of bleomycin-induced lung injury and fibrosis.

METHODS

Mice were treated with a monoclonal antibody against the IGF-I receptor (A12) or vehicle after intratracheal bleomycin instillation.

MEASUREMENTS AND MAIN RESULTS

Mice treated with A12 antibody had significantly improved survival after bleomycin injury compared with control mice. Both groups of mice had a similar degree of fibrosis on days 7 and 14, but by Day 28 the A12-treated group had significantly less fibrosis. Delayed treatment with A12 also resulted in decreased fibrosis. A12-treated mice had significantly decreased apoptotic cells on Day 28 compared with control mice. We confirmed that A12 treatment induced mouse lung fibroblast apoptosis in vitro. In addition, IGF-I increased lung fibroblast migration. The primary pathway activated by IGF-I in lung fibroblasts was the insulin receptor substrate-2/phosphatidylinositol 3-kinase/Akt axis.

CONCLUSIONS

IGF-I regulated survival and migration of fibrogenic cells in the lung. Blockade of the IGF pathway increased fibroblast apoptosis and subsequent resolution of pulmonary fibrosis. Thus, IGF-IR may be a potential target for treatment of lung injury and fibrosis.

Insulin-like growth factor-I in wound healing of rat skin

Growth factors play an important role in orchestrating and enabling the cellular responses required for successful wound healing. In the present study, rat surgical incision was used to investigate insulin-like growth factor-I (IGF-I) expression in skin cells as well as its systemic and cutaneous tissue concentrations during acute phase of wound healing. Thirty two animals were sacrificed at days 2, 3, 5 and 9 after surgery. Eight animals were used as control. Tissue expression of IGF-I in both incisional and periincisional skin areas, as well as in skin of control unwounded animals was determined by immunohistochemistry. Serum and tissue concentrations of IGF-I were measured using RIA. Immunohistochemical analysis revealed enhanced IGF-I immunostaining in the incisional area at day 2 post-wounding. Presence of IGF-I immunoreactivity in the epidermis, as well as in dermal fibroblasts and monocytes within perivascular inflammatory infiltrate suggests its local synthesis. Although serum levels of IGF-I were not altered during wound healing, their tissue contents in the incisional area were significantly increased compared with periincisional area at days 2 and 3 after injury, as well as compared with skin content of unwounded control rats in all examined time points. Obtained results support a paracrine role of IGF-I during the acute phase of wound healing by primary intention in the rat.

IGF-1 reduces inflammatory responses, suppresses oxidative stress, and decreases atherosclerosis progression in ApoE-deficient mice

OBJECTIVE

Whereas growth factors, via their ability to stimulate vascular smooth muscle cell (VSMC) proliferation and migration, have been thought to play a permissive role in atherosclerosis initiation and progression, the role of insulin-like growth factor-1 (IGF-1) is unknown. Here we report for the first time that IGF-1 infusion decreased atherosclerotic plaque progression in ApoE-deficient mice on a Western diet.

METHODS AND RESULTS

ApoE-null mice (8 weeks) were infused with vehicle or recombinant human IGF-1 and fed a high-fat diet for 12 weeks. Analysis of aortic sinuses revealed that IGF-1 infusion decreased atherosclerotic plaque progression and macrophage infiltration into lesions. Furthermore, IGF-1 decreased vascular expression of the proinflammatory cytokines interleukin-6 and tumor necrosis factor-alpha, reduced aortic superoxide formation and urinary 8-isoprostane levels, and increased aortic pAkt and eNOS expression and circulating endothelial progenitor cells, consistent with an antiinflammatory, antioxidant, and prorepair effect on the vasculature.

CONCLUSIONS

Our data indicate that an increase in circulating IGF-1 reduces vascular inflammatory responses, systemic and vascular oxidant stress and decreases atherosclerotic plaque progression. These findings have major implications for the treatment of atherosclerosis.

Regulation of interleukin-8 expression in human prostate cancer cells by insulin-like growth factor-I and inflammatory cytokines

OBJECTIVE

Since serum IGF-I levels are related to risks of prostate cancer and cytokines like interleukin (IL)-6 and IL-8 have been implicated in prostate cancer progression, we investigated the effects of IGF-I on IL-6 and IL-8 expression in the prostate cancer cell.

DESIGN

In order to address the regulation by IGF-I of cytokine expression in prostate cancer cells we used cell cultures of established androgen dependent (LNCaP) and androgen-independent cell lines (DU-145 and PC-3).

RESULTS

We found that IGF-I stimulates IL-8 mRNA expression and secretion in DU-145 cells, whereas the secretion of IL-6 was hardly affected. IGF-I enhances IL-8 expression in synergy with IL-1beta, but not with tumour necrosis factor (TNF)alpha. Similarly, on IL-8 promoter activity, IGF-I exerted synergistic effects with IL-1beta, but not with TNFalpha. Although IGF-I stimulated the phosphorylation of both Akt (protein kinase B) and extracellular-regulated kinase (ERK), the effect of IGF-I at IL-8 expression was inhibited only by U0126, a pharmacological inhibitor of MAPK/ERK kinase (MEK) and not by inhibition of the upstream activator of Akt, phosphatidylinositol-3 kinase (PI3K).

CONCLUSIONS

Our results indicate that IGF-I stimulates IL-8 expression through the MEK-ERK pathway in DU-145 cells, at least in part, by augmentation of transcriptional activity. This finding is in accordance with our observations that IGF-I did not influence cytokine secretion and phosphorylation of ERK in LNCaP or PC-3 cells. It remains to be established whether IL-8 mediates certain effects of IGF-I on prostate cancer cells and whether differential responsiveness of prostate cancer cells to IGF-I relates to certain stages of prostate cancer.

A distinctive alveolar macrophage activation state induced by cigarette smoking

RATIONALE

Macrophages are believed to play a central role in emphysema based largely on data from mouse models. However, the relevance of these models to smoking-related lung disease in humans is uncertain.

OBJECTIVES

We sought to comprehensively characterize the effects of smoking on gene expression in human alveolar macrophages and to compare these with effects seen in transgenic mouse models of emphysema.

METHODS

We used DNA microarrays with genomewide coverage to analyze alveolar macrophages from 15 smokers, 15 nonsmokers, and 15 subjects with asthma (disease control). Selected gene expression changes were validated by polymerase chain reaction and ELISA. Expression changes were compared with those identified by microarray analysis of interleukin-13-overexpressing and integrin-beta6-deficient mice, which both develop emphysema.

MEASUREMENTS AND MAIN RESULTS

All 15 smokers shared a common pattern of macrophage gene expression that distinguished them from nonsmokers, a finding not observed in subjects with asthma. We identified 110 genes as differentially expressed in smokers despite using conservative statistical methods. Matrix metalloproteinase 12, a proteinase that plays a critical role in mouse models, was the third most highly induced gene in smokers (ninefold, p < 0.0001). However, most changes in smokers were not reflected in mouse models. One such finding was increased osteopontin expression in smokers (fourfold, p = 0.006), which was confirmed at the protein level and correlated with the degree of airway obstruction.

CONCLUSIONS

Smoking induces a remarkably consistent and distinctive pattern of alveolar macrophage activation. These studies identify aspects of mouse models that are directly relevant to human smokers and also reveal novel potential mediators of smoking-related diseases.

Transcription of macrophage IGF-I exon 1 is positively regulated by the 5′-untranslated region and negatively regulated by the 5′-flanking region

Idiopathic pulmonary fibrosis (IPF) is an insidious lung disease with no known cure or effective therapy. Macrophage-derived insulin-like growth factor-I (IGF-I) is thought to play a role in the pathogenesis of IPF; however, little is known about the control of IGF-I expression in macrophages. In this report we investigated the cis-regulatory elements that control basal expression using luciferase reporter constructs in RAW 264.7 macrophages. We show that the +95 to +329 region contains elements necessary to direct maximal promoter activity, whereas the +251 to +329 region contains the minimal promoter. Mapping transcriptional start sites for endogenous IGF-I in primary macrophages revealed that the major transcriptional start site is centered at +150, whereas the most 3′-transcriptional start site is centered at +255. Nuclear proteins from primary and RAW 264.7 macrophages bind specifically to the region required for maximal promoter activity (+134 to +173) and to the region required for minimal promoter activity (+267 to +299). Antibody supershift assays indicate that Sp3 bound to the +267 to +299 region. Moreover, mutation of the putative binding site reduced Sp3 binding in EMSAs and increased promoter activity in luciferase reporter gene assays. We also found that the regions from −1711 to −855 and −855 to −337 contain putative macrophage-specific suppressor elements that do not function in HeLa or COS-7 epithelial cell lines. These data support the view that macrophage IGF-I expression is positively regulated by elements located in the 5′-untranslated region and negatively regulated by elements in the 5′-flanking region of the IGF-I gene.

Effects of insulin-like growth factors and insulin-like growth factor binding protein-2 on the in vitro proliferation of peripheral blood mononuclear cells

Increasing evidence has implicated that insulin-like growth factors (IGFs), polypeptides structurally related to proinsulin, are involved in the function and development of the immune system. To probe the relevance of IGF binding protein 2 (IGFBP-2) in T-cell activation and proliferation, we studied the role of IGFBP-2 in anti-CD3 monoclonal antibody (mAb)-activated peripheral blood mononuclear cells (PBMCs). Secretion of IGF-I, IGF-II, and IGFBP-2 by PBMCs from healthy adult donors was determined by radioimmunoassays (RIAs). The PBMC proliferative response after stimulation with anti-CD3 mAb and exposure to increasing concentrations of IGF-I, IGF-II, IGFBP-2, and anti-IGFBP-2 were determined by bromodeoxyuridine enzyme-linked immunosorbent assay. Observations were tested for significance by paired t-tests. We demonstrate an increase in IGFBP-2 secretion associated with both activation of PBMC by anti-CD3 mAb and increasing cell density. Incubation with exogenous IGFBP-2 increased the proliferation of PBMCs, whereas anti-IGFBP-2 had an antiproliferative effect on PBMCs that was reversed by simultaneous exposure to IGFBP-2. The stimulatory activity of IGFBP-2 (1-10 ng/ml) on anti-CD3 mAb-activated PBMCs was similar to that of IGF-I and IGF-II (1-100 ng/ml), with the mean increase in PBMC proliferative response ranging between 150% and 160% for IGFBP-2 (p = 0.03), 150% and 170% for IGF-I (p < 0.01), 133%-161% for IGF-II (p < 0.01), and 157% and 175% for IGF-I + IGF-II (p < 0.01). Thus, our data strongly suggest a role for IGFBP-2 as a local growth factor contributing to the proliferation and activation of mononuclear cells.

Idiopathic pulmonary fibrosis: new insights into pathogenesis

The combination of the unique pathologic features of usual interstitial pneumonia (UIP) on biopsy, the progressive clinical course, and resistance to anti-inflammatory therapy constitutes the cardinal manifestations of what is termed idiopathic pulmonary fibrosis (IFP)/usual interstitial pneumonia, and it has led to recent suggestions that new therapies should be directed at regulating fibroblast functions rather than targeting the inflammatory response. The observation that "early" UIP looks like "late" UIP but there is less of it has been largely responsible for re-evaluation of the paradigm that IPF is the result of uncontrolled lung inflammation. This article highlights aspects of current thoughts on pathogenesis of IFP and expands on recent reviews.

Inhaled Insulins

The inhalation of insulin was conceptualized by the mid-1920s, but the first successful testing of inhaled insulin occurred in the mid-1990s. The lung has proven to be an organ well capable of absorbing insulin in a reproducible and dose-dependent manner. At present, two concepts of pulmonary insulin delivery at relatively advanced stages of development have been investigated in several published studies. The first involves the Exubera device, a system consisting of a formulation of insulin in a dry and amorphous powder, which is then packaged into blisters. A special delivery system generates a pulse of compressed air, which causes the insulin to form a white fog in a transparent reservoir that can be inhaled by deep breathing. The second approach is the AERx insulin Diabetes Management System, which uses an aqueous formulation of insulin, delivered as an aerosol generated by a special, microprocessor-controlled, inhalation device. This device is capable of monitoring the patient's inspiratory flow and guiding the inhalation by a microelectronic feedback system. The therapeutic efficacy and safety of these inhaled insulins seem comparable to those of subcutaneous insulin regimens; however, inhaled insulins do not appear to achieve significantly better glycemic control. Several other concepts for the pulmonary delivery of insulin are also being developed. With the incidence of diabetes mellitus, especially type 2 diabetes, dramatically increasing worldwide, patients with type 2 diabetes appear to be an important target group for new modalities of insulin delivery. In this group, the onset of insulin treatment is frequently delayed due to the fear of self-injection, preventing effective glycemic control. Patient acceptance of inhaled insulins is excellent and no serious adverse effects have been observed to date. Further advantages of inhaled insulins are the more rapid onset of insulin action and a mitigation of postprandial glucose excursions. However, there are some open questions. The most important concerns the possible long-term effects of insulin inhalation on the lung, as insulin is known to have growth-promoting properties. Thus far, there are no observations of the effects of inhaled insulin on lung structure and function that extend beyond 10 years. In patients with pulmonary disease, the smaller cumulative alveolar surface may cause problems in absorption, and in smokers the action of inhaled insulin has been shown to be stronger and with a faster onset. Furthermore, treatment with inhaled insulin requires larger doses of insulin compared with the subcutaneous route of insulin administration to achieve the same systemic effect, and the costs of this therapy could therefore be significantly higher than the costs of present insulin therapies.

IL-4-induced macrophage-derived IGF-I protects myofibroblasts from apoptosis following growth factor withdrawal

The development of idiopathic pulmonary fibrosis (IPF) is associated with myofibroblast accumulation and collagen deposition in the lung parenchyma. Recent studies have suggested that the fibroproliferative response is associated with immune deviation toward a T helper cell type 2 (Th2) cytokine profile. In addition, myofibroblast accumulation may be the result of resistance to physiologic apoptosis. If and how these events are linked remain largely unknown. Insulin-like growth factor-I (IGF-I) is a fibroblast growth and survival factor that has long been implicated in the pathogenesis of IPF. We have previously shown that interstitial macrophage-derived IGF-I correlates with disease severity in IPF, and the Th2 cytokines interleukin (IL)-4 and IL-13 stimulate the expression and secretion of IGF-I by macrophages. In the present study, we tested the hypothesis that IL-4-induced, macrophage-derived IGF-I protects myofibroblasts from apoptosis. Using a growth factor withdrawal model of apoptosis in the myofibroblast cell line, CCL39, we demonstrate that conditioned media from IL-4-stimulated macrophages protect myofibroblasts from apoptosis. The survival effect is lost when IGF-I is immunodepleted from macrophage-conditioned media with IGF-I-specific antibodies. We also show that the protection of myofibroblasts by macrophage-derived IGF-I correlates with and is dependent on the activation of the prosurvival kinases Akt and extracellular signal-regulated kinase. These findings support the view that IL-4-stimulated, macrophage-derived IGF-I may contribute to the persistence of myofibroblasts in pulmonary fibrosis in the Th2-deviated environment of the fibrotic lung.

The role of transforming growth factor beta in lung development and disease

Transforming growth factor (TGF) beta plays an important role in normal pulmonary morphogenesis and function and in the pathogenesis of lung disease. The effect of TGFbeta is regulated via a selective pathway of TGFbeta synthesis and signaling that involves activation of latent TGFbeta, specific TGFbeta receptors, and intracellular signaling via Smad molecules. All three isoforms of TGFbeta are expressed at high levels during normal lung development, being particularly important for branching morphogenesis and epithelial cell differentiation with maturation of surfactant synthesis. Small amounts of TGFbeta are still present in the adult lung, and TGFbeta is involved in normal tissue repair following lung injury. However, in a variety of forms of pulmonary pathology, the expression of TGFbeta is increased. These include chronic lung disease of prematurity as well as several forms of acute and chronic adult lung disease. While TGFbeta1 appears to be the predominant isoform involved, elevated levels of all three isoforms have been demonstrated. The increase in TGFbeta precedes abnormalities in lung function and detectable lung pathology, but correlates with the severity of the disease. TGFbeta plays a key role in mediating fibrotic tissue remodeling by increasing the production and decreasing the degradation of connective tissue via several mechanisms.

Induction of macrophage insulin-like growth factor-I expression by the Th2 cytokines IL-4 and IL-13

Macrophage-derived insulin-like growth factor-I (IGF-I) has long been implicated in the pathogenesis of the interstitial lung disease, idiopathic pulmonary fibrosis, in part, by its ability to 1) stimulate the proliferation and survival of fibroblasts and myofibroblasts and 2) promote collagen matrix synthesis by these cells. However, little is known about the mechanisms that stimulate the expression of IGF-I by macrophages. Previous studies have shown that the development of pulmonary fibrosis is accompanied by enhanced expression of Th2-profile cytokines, especially IL-4, and diminished expression of Th1 cytokines, including IFN-gamma. In addition, in vitro studies have shown that IFN-gamma down-regulates the expression of IGF-I. Thus, the paucity of IFN-gamma in the fibrotic lung may favor increased growth factor production by allowing Th2 cytokines to predominate. In view of these findings, we investigated the hypothesis that Th2 cytokines stimulate the expression of IGF-I by macrophages. Incubation with IL-4 or IL-13 led to concentration- and time-dependent increases in the expression of IGF-I mRNA and the secretion of IGF-I protein by mouse macrophages as a consequence of increased transcription of IGF-I pre-mRNA. Exposure of macrophages to IL-4 in the presence of IFN-gamma inhibited the increase in the expression of IGF-I. Studies using STAT6-deficient macrophages indicated that the increase in IGF-I expression was dependent on STAT6. In addition, the down-regulation of IGF-I expression by IFN-gamma was absent in STAT1-deficient macrophages. Collectively, these findings define a homeostatic mechanism in which Th2 cytokines promote, and Th1 cytokines inhibit, the expression of IGF-I by macrophages.

Characterization of leukocyte subtypes in chicken inner ear sensory epithelia

Human hearing and balance require intact inner ear sensory hair cells, which transduce mechanical stimuli into electrical signals that are transmitted to the brain. Loss of hair cells after birth in mammals is irreversible, whereas birds are able to regenerate hair cells after insult and demonstrate ongoing hair cell production in the vestibular epithelia. Leukocytes reside in undamaged sensory epithelia of the avian inner ear and increase in number after trauma, prior to the proliferation of hair cell progenitors. It has been hypothesized that leukocyte-produced growth factors or cytokines may be involved in triggering hair cell regeneration. Little is known about the specific leukocyte subtypes present in avian ear. Immunohistochemistry with a panel of monoclonal antibodies to chicken leukocytes was used to identify leukocyte subtypes in normal posthatch chicken ear sensory epithelia. The responsiveness of the leukocytes to aminoglycoside-induced damage was also observed. Based on immunocytochemical and morphological criteria, we quantified leukocyte subtypes in normal and drug-damaged auditory and vestibular sensory epithelia. Data indicate that lymphocytes (B and T cells) do not reside in normal or drug-damaged ear sensory epithelia at 1-3 days post insult but are present in adjacent nonsensory tissues. The most common leukocytes in inner ear sensory epithelia are ramified cells of the myeloid lineage. Many of these are MHC class II positive, and a small percentage are mature tissue macrophages. An absence of leukocytes in lesioned areas of the auditory sensory epithelium suggests they may not play a critical role in triggering hair cell regeneration.

Localization and regulation of pregnancy-associated plasma protein a expression in healing human skin

Pregnancy-associated plasma protein A (PAPP-A) is an IGF-binding protein-4 (IGFBP-4) metalloproteinase that cleaves inhibitory IGFBP-4 to amplify local IGF-I bioavailability in vitro. Thus it has functional implications in injury/repair responses. In this study we determined PAPP-A expression in healing human skin. Wounds were induced with a scalpel on the forearms of three normal subjects and were allowed to heal by first intention. Biopsies obtained on d 0, 2, 8, and 14 were processed for immunohistochemical detection of PAPP-A, IGF-I, and IGFBP-4. In uninjured skin (d 0), strong staining for PAPP-A was present in the epidermis, sweat and sebaceous gland epithelial cells, hair follicles, and blood vessels; no PAPP-A was detected in dermal fibroblasts or with mature collagen bundles. IGF-I localized strongly to epithelial cells of skin glands was weak to moderate in epidermis and blood vessels, and was absent in dermal cells. Weak focal staining for IGFBP-4 was found within uninjured epidermis. During wound healing, PAPP-A expression was induced in dermal granulation tissue within and adjacent to the injury. PAPP-A was present in dermis on d 2 and was increased in intensity and extent on d 8 and 14. PAPP-A expression also increased in the epidermis. PAPP-A expression in cells of granulation tissue colocalized with alpha-smooth actin staining of myofibroblasts and new blood vessels as well as with CD68 staining of macrophages and was associated with the compact, newly synthesized collagen of the healing wound. IGF-I staining was enhanced in the epidermis localized to the area of the incision and in granulation tissue associated with lymphoid cells. IGFBP-4 staining of the epidermis remained unchanged during wound healing, but was induced in the fibroblastic cells of granulation tissue over time. These data demonstrate localized and regulated expression of PAPP-A in human skin and suggest that PAPP-A may play an important role in an integrated IGF system in wound healing and tissue remodeling in vivo.

Injury and repair in lung and airways

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common causes of morbidity and mortality in the intensive care unit. ALI/ARDS occurs as a result of systemic inflammation, usually triggered by a microorganism. Activation of leukocytes and release of proinflammatory mediators from multiple cellular sources result in both local and distant tissue injury. Tumor necrosis factor-alpha and interleukin-1 beta are the best characterized of the proinflammatory cytokines contributing to ALI/ARDS and subsequent fibrosis. The ultimate clinical course of ALI/ARDS often is determined by the ability of the injured lung to repopulate the alveolar epithelium with functional cells. Death may occur when fibrosis predominates the healing response, as it results in worsening lung compliance and oxygenation. The rodent bleomycin model of lung fibrosis allows the use of molecular tools to dissect the cellular and subcellular processes leading to fibrosis. The elements of this response may provide therapeutic targets for the prevention of this devastating complication of ALI/ARDS.

Localization of insulin-like growth factor-I in lung tissues of patients with fibroproliferative acute respiratory distress syndrome

Insulin-like growth factor-I (IGF-I) is elevated in human fibrotic lung diseases and in animal models of pulmonary fibrosis, implicating IGF-I in the pathogenesis of fibrotic lung disease. We questioned whether IGF-I protein levels were enhanced in fibroproliferative acute respiratory distress syndrome (FP-ARDS). Serial lung tissue sections from a biopsy database were immunohistochemically stained for IGF-I, IGF-I receptor, CD68, alpha-smooth muscle actin, collagens I and III, and proliferating cell nuclear antigen. Our results show enhanced staining of IGF-I and IGF-I receptor, collagens I and III, smooth muscle actin, CD68, and proliferating cell nuclear antigen in FP-ARDS compared with control lung sections. In FP-ARDS specimens, prominent staining of IGF-I and IGF-I receptor was seen in alveolar and interstitial macrophages as well as in a variety of mesenchymal cells. There was a correlation between IGF-I staining and CD68-positive cells, suggesting macrophages as a potential source of the IGF-I protein present in lungs. IGF-I also correlated with enhanced collagen I, collagen III, and proliferating cell nuclear antigen immunoreactivity, suggesting that IGF-I may play a role in the extracellular matrix protein deposition and cellular proliferation seen in the lungs of individuals with FP-ARDS. Our results indicate that IGF-I is increased in FP-ARDS and may be an important mediator in the progression of acute lung injury to FP-ARDS.