Mitral Valve Prolapse is a common disease affecting 2 to 3% of the population, characterized by a myxomatous mitral valve dystrophy (MVD). Based on the analysis of the FlnA-P637Q KI rat model of non-syndromic MVD, we highlighted that chemotaxis and immune cell migration played a central role in the pathogenesis of MVD, although MVD has been considered so far as a non-inflammatory disease.

To delineate the role of immune cells, specifically macrophages, in MVD pathophysiology.

MVD samples from 78 patients with sporadic severe MV regurgitation were sequenced by bulk RNA-seq. KI and WT animals were then studied from birth (D0) to D21 by histology, immunohistology, and flow cytometry to characterize the kinetic of MVD development and the activation/recruitment of macrophages. Bulk RNA-seq was also performed at D7.

The transcriptomic analysis of human “end-stage” MVD samples highlighted the activation of signaling pathways related to myxomatous ECM remodeling, valvular cell activation, and TGF-β/BMP, as well as the involvement of leucocyte migration and immune response. Deconvolution algorithm confirmed an enrichment in macrophages. Interestingly, human and D21 rat MVD shared common molecular signature (51% concordance between the top 2000 highly expressed genes), confirming the pertinence of the rat model. Flow cytometry at D21 revealed a 2-fold increase of macrophage in KI MV compared to WT (13% vs 7%, P<0.05). At the early timepoint (D0 and D2), no MVD was detected, although molecular markers of the disease were already overexpressed. At D7, we reported the presence of MVD in KI rats (histological score: 7 vs 4, P<0.001), without increased proportion of macrophages (7% vs 6%, P=0.63). Transcriptomic analysis of D7 MV revealed an enrichment in GO-Terms related to morphogenesis, ECM and cytoskeleton organization, cell activation, as well as a consistent activation of chemotaxis and cytokines activity.

This study confirmed a significant contribution of macrophages in the process leading to human MVD. Relying on the sequential analysis of the rat model, we reported a gradual activation of the MVD pathophysiological mechanisms following birth, that further translated to a detectable MVD as early as D7, and in turn lead to the recruitment of macrophages. This study supports the central role of macrophages in the disease development and progression, and open new avenues to develop medical therapy.