Abstract MP173: Loss of DCHS1 Promotes Mitral Valve Prolapse Through Cytoskeleton Destabilization

Abstract

Introduction: Mitral valve prolapse (MVP) is a major source of morbidity and mortality and is becoming one of the most common indications for cardiac surgery. Our group has previously reported that MVP is associated with missense mutations in DCHS1 , a gene widely implicated in tissue development and organization. Purpose: We recently performed two-hybrid screens and co-immunoprecipitation assays that define a novel complex between DCHS1, LIX1L, and SEPT9 (DLS). Our current studies investigate the role of this interaction in mitral valve morphogenesis. Methods: Wild-type (WT), DCHS1, and/or LIX1L heterozygous neonate murine heart tissue was isolated for primary culture of cardiac fibroblasts (CFs) and analyzed with immunocytochemistry, collagen, compaction, fibrin pillar to post assays, and actin sedimentation assays. Nuclear morphology and chromatin density were conducted for functional read-outs of cytoskeletal aberrations. Morphologic and functional analyses of murine mitral valves were completed. Results: Loss of actin architecture and collagen compaction capability were seen in CFs deficient of DCHS1 and/or LIX1L. Delivery of a peptide that disrupted the LIX1L-SEPT9 binding domain likewise destroyed actin architecture and reduced ECM compaction. In-vivo epistasis studies support these findings as mitral valve enlargement was exacerbated in DCHS1/LIX1L compound heterozygote mice compared to DCHS1 and LIX1L heterozygotes. Echocardiography of 11-month DCHS1/LIX1L compound heterozygote mice revealed pronounced MVP and increased left atrium diameter relative to DCHS1 and LIX1L heterozygotes. Filamentous SEPTIN9 localized to the actin ultrastructure and was also lost with disturbance of the DLS complex. Nuclei stretch and chromatin compaction were reduced in DCHS1/LIX1L compound heterozygote CFs. Further, histone H4 modifications were observed in DCHS1 KO mouse embryonic fibroblasts that indicate reductions in gene expression. Conclusion: DCHS1, through its interaction with the septin cytoskeleton, must regulate and stabilize actin dynamics in mitral VICs leading to proper valve development. Non-surgical interventions for MVP may be identified through establishing the downstream effects of DCHS1 mutations in our model.