Impact of cGMP generated by NO-sensitive guanylyl cyclases on vascular smooth muscle remodelling

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In the vascular system, the NO/cGMP signalling cascade has established functions in the regulation of smooth muscle tone and inhibition of platelet aggregation and a role of NO/cGMP in smooth muscle proliferation which results in vascular remodelling, is anticipated. Cyclic GMP is generated by the cGMP-forming guanylyl cyclases (GC) in response to NO formed by the endothelial NO synthase activated by shear stress. Two isoforms of the NO-sensitive GC exist (NO-GC1, NO-GC2) and both of them occur in smooth muscle cells and mediate vascular relaxation. We generated knockout (KO) mice in which either one of the NO-GC isoforms is deleted. The lack of the NO-GC1 isoform leads to a more than 90% reduction of NO-stimulated cGMP-forming activity. However, the NO-GC1 KO mice do not develop hypertension. As the complete KO lacking both NO-GC isoforms shows a pronounced increase of blood pressure, our results show that only a low amount of cGMP is required to prevent hypertension under physiological conditions. It is generally accepted that the vasodilatory effect of the NO/cGMP pathway is counter-balanced by the vasoconstrictor Angiotensin II (Ang II) that also induces proliferation of smooth muscle cells. In the current project, NO-GC1 KO mice will be treated with AngII (2 and 4 weeks) to find out whether the decreased cGMP-forming capacity promotes vascular remodelling. After AngII treatment, vascular remodelling will be assessed by histological inspection of vessel architecture (wall thickness, lumen diameter), and biochemical analysis of cellular processes (cell growth, death, migration and reorganization of extracellular matrix). The comparison of AngII-induced changes in WT and NO-GC1 KO mice should show whether and how cGMP interacts with networks promoting proliferation. The role of NO/cGMP in vascular remodelling will also be evaluated in the context of atherosclerosis in NO-GC1 KO mice crossbred with LDL receptor KO mice and challenged with a high fat diet. The relevance of NO-induced cGMP in vascular remodelling will be assessed in further mouse models, i.e. lack of both NO-GC isoforms or pharmacological inhibition of NO/cGMP signalling. In sum, this project will increase our understanding of cGMP's role in vascular smooth muscle cell growth under various conditions and will analyse its possible interplay with proliferation-related processes at the molecular level and in the (patho-)physiological context.