The C-type Natriuretic Peptide: a new player in the development of the Marfan syndrome?

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): CHUV Background Marfan Syndrome (MFS) is an autosomal dominant inherited connective tissue disorder affecting the cardio-vascular system. Aortic dissections and ruptures are the primary cause of morbidity and mortality in these patients. MFS is a genetic disorder due to mutations in the Fibrillin1 gene or in genes coding for the proteins of the TGF-beta signaling pathway. No treatment really cures Marfan patients. Interestingly, in humans, mutations in the gene coding for the C-type natriuretic peptide (CNP) or its receptors lead to a "Marfan-like syndrome". CNP is a local regulator of skeletal growth and of vascular homeostasis, remodeling and angiogenesis. CNP binds to two receptors, NPR-B and NPR-C, expressed on endothelial and smooth muscle cells (SMCs). CNP is constitutively released by endothelial cells, whereas TGF-beta stimulates its secretion by SMCs. The aim of this project is to determine whether altered CNP signaling pathway contributes to the development and progression of the vascular dysfunctions in MFS. Methods Plasma and vessel biopsies were taken from Marfan patients (RAVAD registery, CHUV Lausanne) and from Fbn1C1041G/+ mice, a mouse model which recapitulates several of the human phenotypes, including aortic wall degeneration and aneurysm development. CNP and TGF-beta concentrations were measured in the plasma. CNP, NPR-B and NPR-C protein levels were evaluated by Western blot analysis in aortic tissue during the development of MFS. In parallel, human and mouse SMCs were isolated and cultured in vitro with different CNP concentrations. Results CNP plasma concentration was decreased in Marfan patients compared to age and sex-matched non-Marfan patients (18 pmol/l versus 310; p=0.07). Two fold less CNP protein level was detected in the abdominal aorta of a Marfan patient. In 6-7 week-old male Fbn1C1041G/+ mice, CNP protein levels were 1.5 and 2.5-fold increased in the ascending and descending aorta, respectively. NPR-B and NPR-C protein levels remained unchanged. In 24 week-old Marfan male mice, CNP protein level was normalized. In female mice, we detected no alterations of the CNP protein level but the NPR-B and NPR-C protein levels were decreased in the descending aorta 6 and 24 weeks after birth, respectively. In vitro, CNP simulates both human and mouse SMC proliferation in a dose-dependent manner (+ 40% for human SMCs stimulated with 0.02 nM CNP). Conclusion Our results suggest that the early step of the syndrome is associated with high level of CNP (detected in 6 week-old male mice), whereas the late advanced stage of the disease is associated with decreased CNP protein level (detected in Marfan patients). These results could open the door to new therapies for Marfan patients.