Role of cGMP signalling in pericytes during lung fibrosis

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Mice lacking NO-sensitive guanylyl cyclase (NO-GC) globally or in specific cell types have been proven to be excellent models to study NO/cGMP-mediated signalling in many cellular functions including contraction, growth and survival. Based on our work in the previous three years, we will now concentrate on lung physiology and pathophysiology with a special focus on fibrosis. Although NO-GC has been first isolated from rat and bovine lung, the cell type that expresses high levels of the enzyme has not been identified to date. In the last funding period, we have found NO-GC to be highly expressed in lung pericytes. Pericytes are mural cells found in precapillary arterioles, capillaries and postcapillary venules. The identification of NO-GC in pericytes is clinically intriguing as these cells are found in virtually all organs and tissues. The exact function of pericytes is still under investigation. Based on their ability to contract and relax, pericytes have been postulated to regulate capillary diameter and thus possibly contribute to blood pressure regulation. Pericytes are also thought to be involved in the development of lung fibrosis. Interestingly, a role of NO-GC in fibrotic processes has been demonstrated recently using our global KO mice. We have acquired a mouse strain that expresses Cre recombinase in pericyte precursor cells under the control of the Foxd1 promotor. In lineage tracing experiments, Foxd1-expressing cells have been shown to develop into lung pericytes which contribute significantly to extracellular matrix deposition and scarring during bleomycin-induced lung fibrosis. Foxd1-Cre mice are currently being crossed with our floxed NO-GC mice. Using these animals, we will elucidate the role of NO-GC in the development of bleomycin-induced lung fibrosis. This will include 1) the isolation and culture of pericytes for identification of members of the NO/cGMP cascade as well as contraction/relaxation studies, 2) bleomycin induction of lung fibrosis in our cell-specific KO strains, including the clinically relevant evaluation of novel NO-GC activators and stimulators as agents to prevent/relieve fibrotic processes and 3) the effect of NO-GC on cigarette smoke-exposed animals in conjunction with lung fibrosis. In addition, we will try to dissect which of the NO-GC isoforms (NO-GC1 or NO-GC2) has the major impact in the disease. In collaboration with other groups of this research unit, these data will be complemented using mice lacking cGKI and BK channel. Furthermore, we will use transgenic mice expressing a cGMP biosensor in Foxd1-derived pericytes to monitor cGMP kinetics in culture and in whole lung during disease development. In sum, our project will provide valuable information on the function of cGMP in a so far neglected cell type, the pericyte, and will shed light on the role of NO-GC during lung fibrosis.