Abstract 122: Pharmacological Inhibition Of Macrophage Infiltration Prevents Myxomatous Valve Degeneration In Marfan Syndrome

Abstract

Introduction: Myxomatous valve degeneration (MVD) is the most common cause of mitral regurgitation, characterized by valve leaflet thickening and progressive valve degeneration, leading to impaired cardiac function and heart failure. Currently, there is no medical therapy for the treatment of MVD. MVD in a mouse model of Marfan syndrome (MFS) is characterized leaflet thickening and increased macrophage infiltration, which are reduced with loss of C-C chemokine receptor type 2 (CCR2). However, the specific contributions of macrophages to pathological extracellular matrix (ECM) remodeling and underlying mechanisms are unknown. Hypothesis: Inhibition of macrophage infiltration by a CCR2 inhibitor blocks ECM abnormalities and MVD progression in mitral valves of MFS mice by suppressing the response to cytokine/chemokines. Methods: Mice with the mutation of Fibrillin 1 (Fbn1 C1039G/+ ) recapitulate histopathological features of MFS. Here, we tested the efficacy of a selective CCR2 antagonist RS504393 in the valves of MFS mice in the initiation (1-month-old) and the progression (2-month-old) of MVD, respectively. MFS mice were intraperitoneally injected with RS504393 at 2 mg/kg/d for 30 days. Histological evaluation and immunofluorescence for macrophages and ECM were performed. RNAseq was performed in mitral valves from 2-month old Fbn1 C1039G/+ mice with CCR2 knockout (CCR2 RFP/RFP ). Results: MFS valves revealed ECM abnormalities characterized by collagen fragmentation and proteoglycan accumulation. RS504393 treatment reduced infiltrating macrophages (MHCII+, CCR2+) in myxomatous valves. Remarkably, RS504393 was protective against both the initiation and the progression of MVD, detected by decreased mitral valve thickness and prevention of pathological ECM remodeling in MFS mice. RNAseq data confirmed increased leukocyte activation involved in immune response and abnormal extracellular matrix remodeling in MFS valves. CCR2 deficiency blocked macrophage infiltration and inhibited the response to cytokines in Fbn1 C1039G/+ valves. Conclusions: Our results show that macrophage infiltration is critical for progressive MVD. Moreover, CCR2 inhibition ameliorates MVD progression by preventing immune response. Thus, the CCR2 inhibitor RS504393 is a potential pharmacological candidate to treat MVD in MFS.