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Wound healing signals mediated by Rho/ROCK activation in response to radiotherapy and consequences fot treatmeny of late damage within normal tissues

Abstract : Radiotherapy is the second most important treatment modality after surgery in the treatment of cancer. Recent technical advancements, such as intensity-modulated radiation therapy (IMRT) or image-guided radiation therapy (IGRT), combined with new targeted drugs have significant promise for therapeutic outcome. However radiation treatment could result in disabling normal tissue injury and in the development of progressive fibrosis in a subset of sensitive patients and in long-term cancer survivors. The main feature of tissue fibrosis is excessive accumulation of abnormal and cross-linked collagen mainly composed of fibrillar and immature extracellular matrix (ECM) components.The organs that can be affected by this phenomenon are liver, skin, intestine, kidneys and lungs. From a clinical point of view, fibrosis can be seen as an irreversible condition, without solution. We and others recently showed that beside the activation of the canonical TGF-β/Smad pathway, other intracellular signaling cascades including the Rho/ROCK pathway are switched on in fibrotic tissues. Interestingly, the Rho/ROCK pathway seems differentially activated in radiation-induced intestinal fibrosis, thereby providing a rationale for a specific, targeted anti-fibrotic strategy. Pharmacological inhibition of Rho using statins indeed prevent and even reverse intestinal radiation fibrosis.In our studies, we showed the role of Statin (Pravastatin e Simvastatin) and a specific inhibitor ROCK inhibitors (Y-27632) in a mice model of pulmonary induced-fibrosis obtained by a pharmacological approach (Bleomycin – BLM). Indeed, we developed a model of lung fibrosis by complete irradiation of chest and tested Pravastatin action. Confirmation of the involvement of Rho/ROCK/CTGF pathway in lung fibrosis are shown by immunohistochemistry: Pravastatin-treament normalized the expression of three markers: RhoB, TGF-RII and CTGF.Then, in models of radiation induced gut and lung fibrosis, we analysed, from a immunohistological point of view, the underlying mechanisms of the antifibrotic action of Pravastatin via MMP2-TIMP2 axis. Interestingly we found a different impact on fibrolysis when Pravastatin was administered preventively or curatively.Finally, in vitro, we investigate by zymography the expression of Gelatinases (MMP2 and MMP9) in primary lung fibroblasts cultures exposure at the different radiation and Pravastatin doses. Metalloproteases would appear to be in turn involved in pro-fibrolytic mechanisms induced by statin.The multiplicity of actors involved in the pathogenesis of fibrotic lesions explains why the definition of an effective therapeutic strategy is so complex.Researches in mechanistic processes of normal tissue damage paved the way for new therapeutic approaches. These new targets include reduction of vascular activation, inflammation and thrombosis and new molecular targets definition. Effective strategies are multiple on preclinical models, but numerous efforts have to be made to achieve the complicated goal of protection of normal tissues from the side effects of radiation therapy.
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Nadia Pasinetti. Wound healing signals mediated by Rho/ROCK activation in response to radiotherapy and consequences fot treatmeny of late damage within normal tissues. Human health and pathology. Université Paris Sud - Paris XI; Università degli studi (Brescia, Italie), 2012. English. ⟨NNT : 2012PA11T029⟩. ⟨tel-00714360⟩

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