A Human Hereditary Cardiomyopathy Shares a Genetic Substrate With Bicuspid Aortic Valve

Abstract

BACKGROUND: The complex genetics underlying human cardiac disease is evidenced by its heterogenous manifestation, multigenic basis, and sporadic occurrence. These features have hampered disease modeling and mechanistic understanding. Here, we show that 2 structural cardiac diseases, left ventricular noncompaction (LVNC) and bicuspid aortic valve, can be caused by a set of inherited heterozygous gene mutations affecting the NOTCH ligand regulator MIB1 (MINDBOMB1) and cosegregating genes. METHODS: We used CRISPR-Cas9 gene editing to generate mice harboring a nonsense or a missense MIB1 mutation that are both found in LVNC families. We also generated mice separately carrying these MIB1 mutations plus 5 additional cosegregating variants in the ASXL3 , APCDD1 , TMX3, CEP192 , and BCL7A genes identified in these LVNC families by whole exome sequencing. Histological, developmental, and functional analyses of these mouse models were carried out by echocardiography and cardiac magnetic resonance imaging, together with gene expression profiling by RNA sequencing of both selected engineered mouse models and human induced pluripotent stem cell–derived cardiomyocytes. Potential biochemical interactions were assayed in vitro by coimmunoprecipitation and Western blot. RESULTS: Mice homozygous for the MIB1 nonsense mutation did not survive, and the mutation caused LVNC only in heteroallelic combination with a conditional allele inactivated in the myocardium. The heterozygous MIB1 missense allele leads to bicuspid aortic valve in a NOTCH-sensitized genetic background. These data suggest that development of LVNC is influenced by genetic modifiers present in affected families, whereas valve defects are highly sensitive to NOTCH haploinsufficiency. Whole exome sequencing of LVNC families revealed single-nucleotide gene variants of ASXL3 , APCDD1 , TMX3, CEP192 , and BCL7A cosegregating with the MIB1 mutations and LVNC. In experiments with mice harboring the orthologous variants on the corresponding Mib1 backgrounds, triple heterozygous Mib1 Apcdd1 Asxl3 mice showed LVNC, whereas quadruple heterozygous Mib1 Cep192 Tmx3;Bcl7a mice developed bicuspid aortic valve and other valve-associated defects. Biochemical analysis suggested interactions between CEP192, BCL7A, and NOTCH. Gene expression profiling of mutant mouse hearts and human induced pluripotent stem cell–derived cardiomyocytes revealed increased cardiomyocyte proliferation and defective morphological and metabolic maturation. CONCLUSIONS: These findings reveal a shared genetic substrate underlying LVNC and bicuspid aortic valve in which MIB1-NOTCH variants plays a crucial role in heterozygous combination with cosegregating genetic modifiers.

Novel Association of the NOTCH Pathway Regulator MIB1 Gene With the Development of Bicuspid Aortic Valve

“…Our data are in full agreement with the results of a report showing that double heterozygous Mib1 V943F/+ ; Notch1 +/− mice show highly significant BAV. 37 Previously, our group and others demonstrated that deleterious MIB1 variants associated with LVNC, 40,53 atrial septal defects and VSDs, and patent ductus arteriosus. 54 A complex phenotype of BAV and cardiac muscle malformation, as found in 1 case in the discovery cohort, has also been described.…”

“…We have described recently the generation of the mice harboring the Mib1 V943F variant. 37 Mice heterozygous for Notch 38 (denoted as Notch1 +/− ) and Rbp 39 (denoted as Rbp +/− ) variant lines were used for genetic sensitization studies with Mib1 alleles.…”

“…We then excluded genes that are not expressed during cardiac development or involved in congenital heart valve defect (eTable 2 in Supplement 2). [33][34][35] Following, we used in silico gene prioritization tools (Endeavor and VarElect) 36,37 (eTable 7 in Supplement 2) to further prune the remaining genes. The top 10 ranked genes from each tool were chosen for further qualitative analysis based on population rarity, gene recurrence in families, and known or potential impact of each variant.…”

A cooperative response to endocardial NOTCH signaling stimulation regulates transcriptional activity during cardiac valve development and disease

“…Jagged1 (Jag1) signaling is dispensable for this process, but the later remodeling of the valve primordia requires induction of Notch activity by Jag1 expressed on endocardial cells 6 . Dysregulation of NOTCH signaling is associated with human valvular congenital heart disease (CHD) 7,8,9,10,11 and acquired calcific aortic valve disease (CAVD) 12,13,14 .…”

BCL7 proteins, metazoan-specific subunits of the mammalian SWI/SNF complex, bind the nucleosome core particle

“…Without exception, these proteins do not exist in yeast, and only participate in the metazoan complexes. The molecular function of most accessory subunits and their role within mSWI/SNF remain incompletely defined 8,9,10,11,12,13,14 . It has been reported that BCL7 proteins accumulate at sites of DNA damage, but the role they may play in DNA damage repair (DDR) is unknown 15 .…”