FGF10/FGFR2b signaling in lung emphysema as a target for lung regeneration
Final Report Abstract
Our research proposal can be divided into three major parts: (i) the first part focussing on Fgf10+/- and Fgfr2b+/- animals exposed for 3 and 8 months to cigarette smoke, (ii) the second part focussing on the Fgf10 mediated regeneration of cigarette smoke-induced pulmonary emphysema and pulmonary hypertension and (iii) the third part examining the FGF related signalling pathways in human lung tissue from COPD patient and donors. In the first part, we report that Fgf10 signalling in the lung appears to be involved in adult lung homeostasis and its impairment led to higher susceptibility towards cigarette smoke-induced lung injury and spontaneous development of pulmonary emphysema and PH with aging. At the advanced stage of the disease, Fgf10+/- and Fgfr2b+/- animals exhibit numerous hallmarks of COPD (pulmonary emphysema, pulmonary hypertension, increased inflammatory response, nitrotyrosine accumulation, collagen deposition in septal walls etc.) witch do not worsen when exposed to cigarette smoke. Fgf10 expression in the lung homogenate of animals exposed 8 months to cigarette smoke was significantly decreased and on the same level as in the lungs from Fgf10+/- animals. Fgf10 was not further decreased by cigarette smoke in Fgf10+/- animals. This suggests that impaired Fgf10 signalling in the adult lung could be an underlying mechanism of cigarette smoke-induced lung injury and in future; these animals could be used as a model of COPD. Interestingly, even though the FGF10 was downregulated on protein level in the lung homogenate of cigarette smokeexposed mice, IHC staining and compartment specific analysis of mRNA levels revealed Fgf10 upregulation in the vessel area. The mechanisms of cigarette smoke-induced downregulation of Fgf10 are still under investigation. In the second part, we have used an inducible Fgf10 overexpressing mouse line [Rosa26rtT/rtTA; Tg(tet(O)Fgf10)/+]. After stable induction of emphysema and pulmonary hypertension by exposing animals to cigarette smoke for 8 months, Fgf10 was overexpressed and animals were sacrificed in different timepoints. We observed that Fgf10 overexpression after cigarette smoke-induced lung injury leads to regeneration of lung parenchyma and reversion of pulmonary hypertension phenotype. Interestingly, in our regenerative model, reversion of pulmonary hypertension precedes the parenchyma regeneration. Reduction of pulmonary-vasculature resistance and right ventricular pressure consecutively lead to reverse remodelling of the right ventricular wall hypertrophy. The underlying mechanisms and the target cells of the Fgf10 signalling in our regenerative approach are under investigation. In the third part, we examined FGF signalling in COPD patient and donor lung tissue. The samples were divided in 3 groups: (i) healthy donor non-smokers, (ii) healthy smokers and (iii) end stage COPD patients. Signs of emphysema and vascular alterations were histologically examined. Several FGF ligands and receptors appeared to be altered in the lung homogenate of healthy smokers compared to the non-smokers, but most of the targets were not changed in COPD patients compared to the donors. This could be due to smoker status of COPD patients who were required to stop smoking for certain time prior to the lung transplantation. Interestingly, in IHC analysis, FGF10 expression was increased in the vessel area in lungs of smokers and COPD patients. These both findings, cigarette smoke-induced FGF10 expression and increased expression in the vessel area, are consistent with the results obtained in our animal model. Further compartment specific evaluation of different targets is required in order to reveal a relevant pattern of changes in the COPD pathology.
