628 Activation of the alpha7 nicotinic acetylcholine receptor improves skin fibrosis

Abstract

Previously we showed an inhibitory effect of tropisetron on transforming growth factor (TGF)-beta1-induced collagen synthesis in human dermal fibroblasts (HDFs) which was alpha7 nicotinic acetylcholine receptors (alpha7nAchR) dependent. In vivo data disclose that tropisetron not only reduced but also prevented experimentally-induced skin fibrosis in the bleomycin (BLM) mouse model of scleroderma. To elucidate the role of the alpha7nAchR in fibrosis, we tested PHA-543613, a full agonist of the alpha7nAchR in the BLM mouse model of scleroderma. A preventive model with simultaneous treatment with BLM and PHA-543613 and a therapeutic model with application of the agonist after induction of fibrosis were used. PHA-543613 treatment resulted in a significant suppression of BLM-induced mRNA expression of murine collagen type I and extracellular matrix genes in mouse skin. Moreover, the α7nAchR agonist dramatically improved fibrosis when added in a therapeutic approach. These results were confirmed at protein level where skin samples injected with PHA-543613 in a preventive as well as therapeutic fashion had significantly lower collagen type I deposition compared to BLM-treated skin. Accordingly, histological analyses disclosed a reduction of dermal thickness after treatment with the alpha7nAchR agonist PHA-543613 in both the preventive and therapeutic approach. These anti-collagen effects could be imitated in vitro where HDFs were treated with the profibrotic factor TGF-beta1 alone and in comparison with PHA-543613 and another full alpha7nAchR agonist AR-R17779. Mechanistically, PHA-543613 and AR-R17779 elicit their anti-TGF-beta1 effect on collagen synthesis via modulation of specific microRNA (miRNAs), such as the profibrotic miR-21 and the antifibrotic miR-29a. In summary the alpha7nAchR agonist PHA-543613 is a novel potent antifibrotic agent, which further underlines the role of the alpha7nAchR in skin fibrosis. Experiments with alpha7nAchR deficient animals lacking this gene are in preparation in our laboratory to further clarify the role of this receptor in fibrosclerotic diseases.