Autoantibodies are associated with disease progression in idiopathic pulmonary fibrosis.

Several reports have highlighted a potential role of autoreactive B-cells and autoantibodies that correlates with increased disease severity in patients with idiopathic pulmonary fibrosis (IPF). Here we show that patients with IPF have an altered B-cell phenotype and that those subjects who have autoantibodies against the intermediate filament protein periplakin (PPL) have a significantly worse outcome in terms of progression-free survival. Using a mouse model of lung fibrosis, we demonstrate that introducing antibodies targeting the endogenous protein PPL (mimicking naturally occurring autoantibodies seen in patients) directly in the lung increases lung injury, inflammation, collagen and fibronectin expression through direct activation of follicular dendritic cells, which in turn activates and drives proliferation of fibroblasts. This fibrocyte population was also observed in fibrotic foci of patients with IPF and was increased in peripheral blood of IPF patients compared to aged-matched controls. This study reiterates the complex and heterogeneous nature of IPF, identifying new pathways that may prove suitable for therapeutic intervention.

Sensitization of the UPR by loss of PPP1R15A promotes fibrosis and senescence in IPF.

The unfolded protein response (UPR) is a direct consequence of cellular endoplasmic reticulum (ER) stress and a key disease driving mechanism in IPF. The resolution of the UPR is directed by PPP1R15A (GADD34) and leads to the restoration of normal ribosomal activity. While the role of PPP1R15A has been explored in lung epithelial cells, the role of this UPR resolving factor has yet to be explored in lung mesenchymal cells. The objective of the current study was to determine the expression and role of PPP1R15A in IPF fibroblasts and in a bleomycin-induced lung fibrosis model. A survey of IPF lung tissue revealed that PPP1R15A expression was markedly reduced. Targeting PPP1R15A in primary fibroblasts modulated TGF-ß-induced fibroblast to myofibroblast differentiation and exacerbated pulmonary fibrosis in bleomycin-challenged mice. Interestingly, the loss of PPP1R15A appeared to promote lung fibroblast senescence. Taken together, our findings demonstrate the major role of PPP1R15A in the regulation of lung mesenchymal cells, and regulation of PPP1R15A may represent a novel therapeutic strategy in IPF.

Inhibition of mast cells: a novel mechanism by which nintedanib may elicit anti-fibrotic effects.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease which presents a grave prognosis for diagnosed patients. Nintedanib (a triple tyrosine kinase inhibitor) and pirfenidone (unclear mechanism of action) are the only approved therapies for IPF, but have limited efficacy. The pathogenic mechanisms of this disease are not fully elucidated; however, a role for mast cells (MCs) has been postulated. OBJECTIVES: The aim of this work was to investigate a role for MCs in IPF and to understand whether nintedanib or pirfenidone could impact MC function. METHODS AND RESULTS: MCs were significantly elevated in human IPF lung and negatively correlated with baseline lung function (FVC). Importantly, MCs were positively associated with the number of fibroblast foci, which has been linked to increased mortality. Furthermore, MCs were increased in the region immediately surrounding the fibroblast foci, and co-culture studies confirmed a role for MC-fibroblast crosstalk in fibrosis. Nintedanib but not pirfenidone inhibited recombinant stem cell factor (SCF)-induced MC survival. Further evaluation of nintedanib determined that it also inhibited human fibroblast-mediated MC survival. This was likely via a direct effect on ckit (SCF receptor) since nintedanib blocked SCF-stimulated ckit phosphorylation, as well as downstream effects on MC proliferation and cytokine release. In addition, nintedanib ablated the increase in lung MCs and impacted high tissue density frequency (HDFm) in a rat bleomycin model of lung fibrosis. CONCLUSION: Nintedanib inhibits MC survival and activation and thus provides a novel additional mechanism by which this drug may exert anti-fibrotic effects in patients with IPF.

FPR-1 is an important regulator of neutrophil recruitment and a tissue-specific driver of pulmonary fibrosis.

Neutrophils are the most abundant inflammatory cells at the earliest stages of wound healing and play important roles in wound repair and fibrosis. Formyl peptide receptor 1 (FPR-1) is abundantly expressed on neutrophils and has been shown to regulate their function, yet the importance of FPR-1 in fibrosis remains ill defined. FPR-1-deficient (fpr1-/-) mice were protected from bleomycin-induced pulmonary fibrosis but developed renal and hepatic fibrosis normally. Mechanistically, we observed a failure to effectively recruit neutrophils to the lungs of fpr1-/- mice, whereas neutrophil recruitment was unaffected in the liver and kidney. Using an adoptive transfer model we demonstrated that the defect in neutrophil recruitment to the lung was intrinsic to the fpr1-/- neutrophils, as C57BL/6 neutrophils were recruited normally to the damaged lung in fpr1-/- mice. Finally, C57BL/6 mice in which neutrophils had been depleted were protected from pulmonary fibrosis. In conclusion, FPR-1 and FPR-1 ligands are required for effective neutrophil recruitment to the damaged lung. Failure to recruit neutrophils or depletion of neutrophils protects from pulmonary fibrosis.

Discovery and characterisation of an antibody that selectively modulates the inhibitory activity of plasminogen activator inhibitor-1.

Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor (serpin) that regulates fibrinolysis, cell adhesion and cell motility via its interactions with plasminogen activators and vitronectin. PAI-1 has been shown to play a role in a number of diverse pathologies including cardiovascular diseases, obesity and cancer and is therefore an attractive therapeutic target. However the multiple patho-physiological roles of PAI-1, and understanding the relative contributions of these in any one disease setting, make the development of therapeutically relevant molecules challenging. Here we describe the identification and characterisation of fully human antibody MEDI-579, which binds with high affinity and specificity to the active form of human PAI-1. MEDI-579 specifically inhibits serine protease interactions with PAI-1 while conserving vitronectin binding. Crystallographic analysis reveals that this specificity is achieved through direct binding of MEDI-579 Fab to the reactive centre loop (RCL) of PAI-1 and at the same exosite used by both tissue and urokinase plasminogen activators (tPA and uPA). We propose that MEDI-579 acts by directly competing with proteases for RCL binding and as such is able to modulate the interaction of PAI-1 with tPA and uPA in a way not previously described for a human PAI-1 inhibitor.

Divergent roles for Clusterin in Lung Injury and Repair.

Lung fibrosis is an unabated wound healing response characterized by the loss and aberrant function of lung epithelial cells. Herein, we report that extracellular Clusterin promoted epithelial cell apoptosis whereas intracellular Clusterin maintained epithelium viability during lung repair. Unlike normal and COPD lungs, IPF lungs were characterized by significantly increased extracellular Clusterin whereas the inverse was evident for intracellular Clusterin. In vitro and in vivo studies demonstrated that extracellular Clusterin promoted epithelial cell apoptosis while intercellular Clusterin modulated the expression of the DNA repair proteins, MSH2, MSH6, OGG1 and BRCA1. The fibrotic response in Clusterin deficient (CLU-/-) mice persisted after bleomycin and it was associated with increased DNA damage, reduced DNA repair responses, and elevated cellular senescence. Remarkably, this pattern mirrored that observed in IPF lung tissues. Together, our results show that cellular localization of Clusterin leads to divergent effects on epithelial cell regeneration and lung repair during fibrosis.

The TGF-ß inhibitory activity of antibody 37E1B5 depends on its H-CDR2 glycan.

Excessive transforming growth factor (TGF)-ß is associated with pro-fibrotic responses in lung disease, yet it also plays essential roles in tissue homeostasis and autoimmunity. Therefore, selective inhibition of excessive and aberrant integrin-mediated TGF-ß activation via targeting the α-v family of integrins is being pursued as a therapeutic strategy for chronic lung diseases, to mitigate any potential safety concerns with global TGF-ß inhibition. In this work, we reveal a novel mechanism of inhibiting TGF-ß activation utilized by an αvß8 targeting antibody, 37E1B5. This antibody blocks TGF-ß activation while not inhibiting cell adhesion. We show that an N-linked complex-type Fab glycan in H-CDR2 of 37E1B5 is directly involved in the inhibition of latent TGF-ß activation. Removal of the Fab N-glycosylation site by single amino acid substitution, or removal of N-linked glycans by enzymatic digestion, drastically reduced the antibody's ability to inhibit latency-associated peptide (LAP) and αvß8 association, and TGF-ß activation in an αvß8-mediated TGF-ß signaling reporter assay. Our results indicate a non-competitive, allosteric inhibition of 37E1B5 on αvß8-mediated TGF-ß activation. This unique, H-CDR2 glycan-mediated mechanism may account for the potent but tolerable TGF-b activation inhibition and lack of an effect on cellular adhesion by the antibody.

Matrix regulation of idiopathic pulmonary fibrosis: the role of enzymes.

Repairing damaged tissues is an essential homeostatic mechanism that enables clearance of dead or damaged cells after injury, and the maintenance of tissue integrity. However, exaggeration of this process in the lung can lead to the development of fibrotic scar tissue. This is characterized by excessive accumulation of extracellular matrix (ECM) components such as fibronectin, proteoglycans, hyaluronic acid, and interstitial collagens. After tissue injury, or a breakdown of tissue integrity, a cascade of events unfolds to maintain normal tissue homeostasis. Inflammatory mediators are released from injured epithelium, leading to both platelet activation and inflammatory cell migration. Inflammatory cells are capable of releasing multiple pro-inflammatory and fibrogenic mediators such as transforming growth factor (TGF)ß and interleukin (IL)-13, which can trigger myofibroblast proliferation and recruitment. The myofibroblast population is also expanded as a result of epithelial cells undergoing epithelial-to-mesenchymal transition and of the activation of resident fibroblasts, leading to ECM deposition and tissue remodeling. In the healthy lung, wound healing then proceeds to restore the normal architecture of the lung; however, fibrosis can develop when the wound is severe, the tissue injury persists, or the repair process becomes dysregulated. Understanding the processes regulating aberrant wound healing and the matrix in the chronic fibrotic lung disease idiopathic pulmonary fibrosis (IPF), is key to identifying new treatments for this chronic debilitating disease. This review focuses primarily on the emerging role of enzymes in the lungs of patients with IPF. Elevated expression of a number of enzymes that can directly modulate the ECM has been reported, and recent data indicates that modulating the activity of these enzymes can have a downstream effect on fibrotic tissue remodeling.

An anti-human ICAM-1 antibody inhibits rhinovirus-induced exacerbations of lung inflammation.

Human rhinoviruses (HRV) cause the majority of common colds and acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD). Effective therapies are urgently needed, but no licensed treatments or vaccines currently exist. Of the 100 identified serotypes, ∼90% bind domain 1 of human intercellular adhesion molecule-1 (ICAM-1) as their cellular receptor, making this an attractive target for development of therapies; however, ICAM-1 domain 1 is also required for host defence and regulation of cell trafficking, principally via its major ligand LFA-1. Using a mouse anti-human ICAM-1 antibody (14C11) that specifically binds domain 1 of human ICAM-1, we show that 14C11 administered topically or systemically prevented entry of two major groups of rhinoviruses, HRV16 and HRV14, and reduced cellular inflammation, pro-inflammatory cytokine induction and virus load in vivo. 14C11 also reduced cellular inflammation and Th2 cytokine/chemokine production in a model of major group HRV-induced asthma exacerbation. Interestingly, 14C11 did not prevent cell adhesion via human ICAM-1/LFA-1 interactions in vitro, suggesting the epitope targeted by 14C11 was specific for viral entry. Thus a human ICAM-1 domain-1-specific antibody can prevent major group HRV entry and induction of airway inflammation in vivo.

Development of a homogeneous high-throughput screening assay for biological inhibitors of human rhinovirus infection.

Infection with human rhinovirus (HRV) is thought to result in acute respiratory exacerbations of chronic obstructive pulmonary disorder (COPD). Consequently, prevention of HRV infection may provide therapeutic benefit to these patients. As all major group HRV serotypes infect cells via an interaction between viral coat proteins and intercellular adhesion molecule-1 (ICAM-1), it is likely that inhibitors of this interaction would prevent or reduce infections. Our objective was to use phage display technology in conjunction with naive human antibody libraries to identify anti-ICAM-1 antibodies capable of functional blockade of HRV infection. Key to success was the development of a robust, functionally relevant high-throughput screen (HTS) compatible with the specific challenges of antibody screening. In this article, we describe the development of a novel homogeneous time-resolved fluorescence (HTRF) assay based on the inhibition of soluble ICAM-1 binding to live HRV16. We describe the implementation of the method in an antibody screening campaign and demonstrate the biological relevance of the assay by confirming the activity of resultant antibodies in a cell-based in vitro HRV infection assay.