Thesis defense Benjamin Le Vély

Equipe

Team I - Human Genetics

Directeur de thèse

Romain Capoulade

Co-directrice :

Elvira Mass

Rapporteurs

Nabila Bouatia-Naji, PhD, DR - Paris Cardiovascular Research Center, Paris
Elvira Mass, PhD, Professor - Developmental biology of the immune system, LIMES, Bonn
Stéphane Zaffran, PhD, DR - Marseille Medical Genetics, Marseille

Examinateurs

Lucie Hénaut, PhD, IR  - MP3CV, Amiens
Ana Ivonne Vazquez, PhD, Professor - Organoid biology, LIMES, Bonn 
Falk Nimmerjahn, PhD, Professor - Chair of genetics, Erlangen
Sebastian Zimmer, PhD, Herzzentrum Bonn, Bonn

Abstract

Myxomatous mitral valve dystrophy (MVD) is the first cause of mitral valve prolapse (MVP), a common disease affecting 2 to 3 % of the population. The first causal mutation in the FLNA gene (FLNA-P637Q), was associated with MVD in 2007. Recently, the FLNA-P637Q KI rat model was generated and phenotyped. Using multimodality imaging, MVD was diagnosed as early as 3 weeks and signature of chemotaxis and myeloid cell migration was described at the transcriptomic level. This thesis has attached to determine the dynamic and the role of macrophages in the pathophysiology of MVD.

With a combination of histology, flow cytometry and transcriptomic analysis, the dynamic of MVD development in the FLNA-KI rat model was clarified. Extracellular matrix dysregulation, marked with increased expression of the Hyaluronan synthase Has1, is present as early as birth, quickly followed by endothelial dysfunction by two days post-natal, and marked by overexpression of the endothelial stress marker Esm1.  Morphological remodeling of the MV is detectable from seven days post-natal, and is  accompanied by an upregulation of chemotactic signaling as assessed by bulk RNA sequencing. However, no differences in the proportion of macrophages or immune cells is observed at this timepoint. The proportion of macrophages is significantly increase in the MV of KI rats at the age of three weeks along with severe remodeling of the MV leaflets. The contributions of macrophages to MVD was also corroborated in a large cohort of Human MVD samples. Macrophages core function, phagocytosis, was assessed in vitro upon FLNA-P637Q mutation and no differences were found. However we found that FLNA-KI valvular intestitial cells were more prone to monocyte adhesion than WT, consistent with the chemotactic microenvironment observed at the transcriptomic level. Finally, using single nuclei RNA-seq, the cellular landscape of the MV at steady state and during MVD was analyzed as well as the interactions between macrophages and the other cell types contributing to the disease. We found that the immune activation is temporally and spatially regulated, starting early in endothelial cells, then propagating to interstitial cells in more advanced stage of MVD.

Overall, this thesis highlight the contribution of macrophages to the myxomatous remodeling of the mitral valve, and pave the way to the study of macrophages interactions within the MV niche to better understand what role do they play in the development and the maintenance of MVD. This could potentially lead to the identification of new therapeutic targets.