Modifiers of TGF-beta1 effector function as novel therapeutic targets of pulmonary fibrosis

Pulmonary fibrosis is a fatal progressive disease with no effective therapy. Transforming growth factor (TGF)-beta1 has long been regarded as a central mediator of tissue fibrosis that involves multiple organs including skin, liver, kidney, and lung. Thus, TGF-beta1 and its signaling pathways have been attractive therapeutic targets for the development of antifibrotic drugs. However, the essential biological functions of TGF-beta1 in maintaining normal immune and cellular homeostasis significantly limit the effectiveness of TGF-beta1-directed therapeutic approaches. Thus, targeting downstream mediators or signaling molecules of TGF-beta1 could be an alternative approach that selectively inhibits TGF-beta1-stimulated fibrotic tissue response while preserving major physiological function of TGF-beta1. Recent studies from our laboratory revealed that TGF-beta1 crosstalk with epidermal growth factor receptor (EGFR) signaling by induction of amphiregulin, a ligand of EGFR, plays a critical role in the development or progression of pulmonary fibrosis. In addition, chitotriosidase, a true chitinase in humans, has been identified to have modulating capacity of TGF-beta1 signaling as a new biomarker and therapeutic target of scleroderma-associated pulmonary fibrosis. These newly identified modifiers of TGF-beta1 effector function significantly enhance the effectiveness and flexibility in targeting pulmonary fibrosis in which TGF-beta1 plays a significant role.

Protective effects of basic fibroblast growth factor in the development of emphysema induced by interferon-gamma

Recent clinical evidence indicates that the non-eosinophilic subtype of severe asthma is characterized by fixed airway obstruction, which may be related to emphysema. Transgenic studies have demonstrated that high levels of IFN-gamma in the airways induce emphysema. Fibroblast growth factor 2 (FGF2), which is the downstream mediator of TGF-beta, is important in wound healing. We investigated the role of FGF2 in IFN-gamma-induced emphysema and the therapeutic effects of recombinant FGF2 in the prevention of emphysema in a severe non-eosinophilic asthma model. To evaluate the role of FGF2 in IFN-gamma-induced emphysema, lung targeted IFN-gamma transgenic mice were cross-bred with FGF2-deficient mice. A severe non-eosinophilic asthma model was generated by airway application of LPS-containing allergens twice a week for 4 weeks. To evaluate protective effects of FGF2, recombinant FGF2 (10 microg) was injected subcutaneously during allergen challenge in the severe asthma model. We found that non-eosinophilic inflammation and emphysema induced by transgenic overexpression of IFN-gamma in the airways were aggravated by the absence of FGF2. Airway challenge with LPS-containing allergens induced more inflammation in mice sensitized with LPS-containing allergens compared to challenge with allergens alone. In addition, LPS-induced lung inflammation and emphysema depended on IFN-gamma but not on IL-13. Interestingly, emphysema in the severe asthma model was significantly inhibited by treatment with recombinant FGF2 during allergen challenge, whereas lung inflammation was unaffected. Therefore, our present data suggest that FGF2 may help protect against IFN-gamma-induced emphysema, and that recombinant FGF2 may help lessen the severity of emphysema.

IL-12-STAT4-IFN-gamma axis is a key downstream pathway in the development of IL-13-mediated asthma phenotypes in a Th2 type asthma model

IL-4 and IL-13 are closely related cytokines that are produced by Th2 cells. However, IL-4 and IL-13 have different effects on the development of asthma phenotypes. Here, we evaluated downstream molecular mechanisms involved in the development of Th2 type asthma phenotypes. A murine model of Th2 asthma was used that involved intraperitoneal sensitization with an allergen (ovalbumin) plus alum and then challenge with ovalbumin alone. Asthma phenotypes, including airway-hyperresponsiveness (AHR), lung inflammation, and immunologic parameters were evaluated after allergen challenge in mice deficient in candidate genes. The present study showed that methacholine AHR and lung inflammation developed in allergen-challenged IL-4-deficient mice but not in allergen-challenged IL-13-deficient mice. In addition, the production of OVA-specific IgG2a and IFN-gamma-inducible protein (IP)-10 was also impaired in the absence of IL-13, but not of IL-4. Lung-targeted IFN-gamma over-expression in the airways enhanced methacholine AHR and non-eosinophilic inflammation; in addition, these asthma phenotypes were impaired in allergen-challenged IFN-gamma-deficient mice. Moreover, AHR, non-eosinophilic inflammation, and IFN-gamma expression were impaired in allergen-challenged IL-12Rbeta2- and STAT4-deficient mice; however, AHR and non-eosinophilic inflammation were not impaired in allergen-challenged IL-4Ralpha-deficient mice, and these phenomena were accompanied by the enhanced expression of IL-12 and IFN-gamma. The present data suggest that IL-13-mediated asthma phenotypes, such as AHR and non-eosinophilic inflammation, in the Th2 type asthma are dependent on the IL-12-STAT4-IFN-gamma axis, and that these asthma phenotypes are independent of IL-4Ralpha-mediated signaling.

Role of breast regression protein-39/YKL-40 in asthma and allergic responses

BRP-39 and its human homolog YKL-40 have been regarded as a prototype of chitinase-like proteins (CLP) in mammals. Exaggerated levels of YKL-40 protein and/or mRNA have been noted in a number of diseases characterized by inflammation, tissue remodeling, and aberrant cell growth. Asthma is an inflammatory disease characterized by airway hyperresponsiveness and airway remodeling. Recently, the novel regulatory role of BRP-39/YKL-40 in the pathogenesis of asthma has been demonstrated both in human studies and allergic animal models. The levels of YKL-40 are increased in the circulation and lungs from asthmatics where they correlate with disease severity, and CHI3L1 polymorphisms correlate with serum YKL-40 levels, asthma and abnormal lung function. Animal studies using BRP-39 null mutant mice demonstrated that BRP-39 was required for optimal allergen sensitization and Th2 inflammation. These studies suggest the potential use of BRP-39 as a biomarker as well as a therapeutic target for asthma and other allergic diseases. Here, we present an overview of chitin/chitinase biology and summarize recent findings on the role of BRP-39 in the pathogenesis of asthma and allergic responses.