The role of osteoprotegerin (OPG) in fibrosis:its potential as a biomarker and/or biological target for the treatment of fibrotic diseases

Fibrosis is defined by excessive formation and accumulation of extracellular matrix proteins, produced by myofibroblasts, that supersedes normal wound healing responses to injury and results in progressive architectural remodelling. Fibrosis is often detected in advanced disease stages when an organ is already severely damaged and can no longer function properly. Therefore, there is an urgent need for reliable and easily detectable markers to identify and monitor fibrosis onset and progression as early as possible; this will greatly facilitate the development of novel therapeutic strategies. Osteoprotegerin (OPG), a well-known regulator of bone extracellular matrix and most studied for its role in regulating bone mass, is expressed in various organs and functions as a decoy for receptor activator of nuclear factor kappa-B ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Recently, OPG has been linked to fibrosis and fibrogenesis, and has been included in a panel of markers to diagnose liver fibrosis. Multiple studies now suggest that OPG may be a general biomarker suitable for detection of fibrosis and/or monitoring the impact of fibrosis treatment. This review summarizes our current understanding of the role of OPG in fibrosis and will discuss its potential as a biomarker and/or novel therapeutic target for fibrosis

Non-genomic Effects of Glucocorticoids: An Updated View

Glucocorticoid (GC) anti-inflammatory effects generally require a prolonged onset of action and involve genomic processes. Because of the rapidity of some of the GC effects, however, the concept that non-genomic actions may contribute to GC mechanisms of action has arisen. While the mechanisms have not been completely elucidated, the non-genomic effects may play a role in the management of inflammatory diseases. For instance, we recently reported that GCs ‘rapidly’ enhanced the effects of bronchodilators, agents used in the treatment of allergic asthma. In this review article, we discuss (i) the non-genomic effects of GCs on pathways relevant to the pathogenesis of inflammatory diseases and (ii) the putative role of the membrane GC receptor. Since GC side effects are often considered to be generated through its genomic actions, understanding GC non-genomic effects will help design GCs with a better therapeutic index

Role of contractile prostaglandins and Rho-kinase in growth factor-induced airway smooth muscle contraction

Background: In addition to their proliferative and differentiating effects, several growth factors are capable of inducing a sustained airway smooth muscle (ASM) contraction. These contractile effects were previously found to be dependent on Rho-kinase and have also been associated with the production of eicosanoids. However, the precise mechanisms underlying growth factor-induced contraction are still unknown. In this study we investigated the role of contractile prostaglandins and Rho-kinase in growth factor-induced ASM contraction.Methods: Growth factor-induced contractions of guinea pig open-ring tracheal preparations were studied by isometric tension measurements. The contribution of Rho-kinase, mitogen-activated protein kinase ( MAPK) and cyclooxygenase ( COX) to these reponses was established, using the inhibitors Y-27632 ( 1 mu M), U-0126 ( 3 mu M) and indomethacin ( 3 mu M), respectively. The Rho-kinase dependency of contractions induced by exogenously applied prostaglandin F-2 alpha (PGF(2 alpha)) and prostaglandin E-2 (PGE(2)) was also studied. In addition, the effects of the selective FP-receptor antagonist AL-8810 (10 mu M) and the selective EP1-antagonist AH-6809 (10 mu M) on growth factor-induced contractions were investigated, both in intact and epithelium-denuded preparations. Growth factor-induced PGF(2 alpha)- and PGE(2)-release in the absence and presence of Y-27632, U-0126 and indomethacin, was assessed by an ELISA-assay.Results: Epidermal growth factor (EGF)- and platelet-derived growth factor ( PDGF)- induced contractions of guinea pig tracheal smooth muscle preparations were dependent on Rho-kinase, MAPK and COX. Interestingly, growth factor-induced PGF(2 alpha)- and PGE(2)-release from tracheal rings was significantly reduced by U-0126 and indomethacin, but not by Y-27632. Also, PGF2a- and PGE(2)-induced ASM contractions were largely dependent on Rho-kinase, in contrast to other contractile agonists like histamine. The FP-receptor antagonist AL-8810 ( 10 mu M) significantly reduced ( approximately 50 %) and the EP1-antagonist AH-6809 ( 10 mu M) abrogated growth factor-induced contractions, similarly in intact and epithelium-denuded preparations.Conclusion: The results indicate that growth factors induce ASM contraction through contractile prostaglandins - not derived from the epithelium - which in turn rely on Rho-kinase for their contractile effects.</p

Mevalonate Cascade Regulation of Airway Mesenchymal Cell Autophagy and Apoptosis: A Dual Role for p53

Statins inhibit the proximal steps of cholesterol biosynthesis, and are linked to health benefits in various conditions, including cancer and lung disease. We have previously investigated apoptotic pathways triggered by statins in airway mesenchymal cells, and identified reduced prenylation of small GTPases as a primary effector mechanism leading to p53-mediated cell death. Here, we extend our studies of statin-induced cell death by assessing endpoints of both apoptosis and autophagy, and investigating their interplay and coincident regulation. Using primary cultured human airway smooth muscle (HASM) and human airway fibroblasts (HAF), autophagy, and autophagosome formation and flux were assessed by transmission electron microscopy, cytochemistry (lysosome number and co-localization with LC3) and immunoblotting (LC3 lipidation and Atg12-5 complex formation). Chemical inhibition of autophagy increased simvastatin-induced caspase activation and cell death. Similarly, Atg5 silencing with shRNA, thus preventing Atg5-12 complex formation, increased pro-apoptotic effects of simvastatin. Simvastatin concomitantly increased p53-dependent expression of p53 up-regulated modulator of apoptosis (PUMA), NOXA, and damage-regulated autophagy modulator (DRAM). Notably both mevalonate cascade inhibition-induced autophagy and apoptosis were p53 dependent: simvastatin increased nuclear p53 accumulation, and both cyclic pifithrin-α and p53 shRNAi partially inhibited NOXA, PUMA expression and caspase-3/7 cleavage (apoptosis) and DRAM expression, Atg5-12 complex formation, LC3 lipidation, and autophagosome formation (autophagy). Furthermore, the autophagy response is induced rapidly, significantly delaying apoptosis, suggesting the existence of a temporally coordinated p53 regulation network. These findings are relevant for the development of statin-based therapeutic approaches in obstructive airway disease

Central role of Rho-kinase in the pathophysiology of allergic asthma

Allergisch astma is een chronisch inflammatoire luchtwegaandoening die gekenmerkt wordt door overgevoeligheid van de luchtwegen voor bronchusobstructieve prikkels. Deze luchtweghyperreactiviteit (LHR) wordt in belangrijke mate veroorzaakt door een verhoogde reactiviteit van het gladde spierweefsel rond de luchtwegen voor contractiele stimuli. De intracellulaire Ca2+-huishouding speelt een belangrijke rol bij de regulatie van contractie. Rho-kinase is een enzym dat in staat is om de gevoeligheid van (spier)cellen voor Ca2+ te verhogen (Ca2+-sensitisatie), hetgeen mogelijk bijdraagt aan de ontwikkeling of versterking van gladde spiercontractie. In dit proefschrift werd de rol van Rho-kinase in de ontwikkeling van LHR bestudeerd. De bevindingen beschreven in dit proefschrift tonen aan dat Rho-kinase inderdaad bijdraagt aan luchtweg-gladde spiercontractie, afhankelijk van de agonist en receptor in kwestie. Tevens werd aangetoond dat allergische sensitisatie deze bijdrage zowel in vitro als in vivo verhoogt, wat gepaard gaat met een toename in RhoA-expressie (Rho-kinase-activator). Zeer opmerkelijk bleek dat inhalatie van de Rho-kinase remmer Y-27632 de LHR na de allergeen-geïnduceerde vroege en late astmatische reactie acuut opheft. Tevens bleek voorbehandeling met geïnhaleerd Y-27632 te beschermen tegen acute allergeen-geïnduceerde bronchusconstrictie, ontwikkeling van LHR en luchtwegontsteking. Een andere opmerkelijke bevinding is dat groeifactoren, die een rol spelen bij luchtwegremodeling in astma, naast groei ook een volledig Rho-kinase afhankelijke contractie induceren. Van deze groeifactoren bleek insuline tevens in staat om op een Rho-kinase afhankelijke manier de grootte van spiercellen te doen laten toenemen, wat zou kunnen bijdragen aan een toegenomen spiermassa in de luchtwegwand. Aangezien Rho-kinase betrokken is bij verscheidene sleutelprocessen die ten grondslag liggen aan LHR, kan Rho-kinase beschouwd worden als een potentieel target in allergisch astma.

Monomeric G-proteins as signal transducers in airway physiology and pathophysiology

Monomeric G-proteins, also referred to as small GTPases, function as biological hubs being activated by extracellular stimuli and regulate downstream signalling events, which result in different cellular responses. The importance of these mechanisms is mirrored by the fact that several pathological conditions, including allergic asthma, are associated with derailed GTPases signalling. For this reason attention has been focused on the role of monomeric G-proteins and their effectors in airway (patho)physiology. In this article we review our current knowledge on the regulation and functions of Ras and Rho GTPase signalling under physiological and pathophysiological conditions in the pulmonary system. Based on recent findings concerning novel regulatory proteins for Ras family members, we further discuss potential future directions for therapeutical interventions in asthma. (C) 2008 Elsevier Inc. All rights reserved

Rho kinase inhibitors: A novel therapeutical intervention in asthma?

In asthma, inflammatory mediators that are released in the airways by recruited inflammatory cells and by resident structural cells result in airway hyperresponsiveness caused by increased bronchoconstriction. In addition, chronic inflammation appears to drive remodelling of the airways that contributes to the development of fixed airway obstruction and airway hyperresponsiveness in chronic asthma. Airway remodelling includes several key features such as excessive deposition of extracellular matrix proteins in the airway wall (fibrosis) and increased abundance of contractile airway smooth muscle encircling the airways. Current asthma therapy fails to inhibit these features satisfactorily. This review focuses on Rho kinase as a potential drug target in asthma, as compelling evidence from animal models and ex vivo studies suggests a central role for this enzyme and its associated signalling in acute and chronic airway hyperresponsiveness. (C) 2008 Elsevier B.V. All rights reserved