Genetic and Epigenetic Basis for Brain Abnormalities and Neurobehavioral Deficits in a Mouse Model of Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS), a critical congenital heart disease (CHD), is associated with high risk for neurodevelopmental disabilities (NDD), with over 50% of HLHS survivors experiencing neurocognitive impairment. While NDD in HLHS patients is typically thought to arise secondary to circulatory disturbance, our recent recovery of HLHS mutant mice with brain abnormalities point to a shared genetic etiology for CHD and NDD. HLHS and brain abnormalities in the Ohia mouse line have a digenic etiology, arising from mutations in Sin3a-associated protein 130 (Sap130), a chromatin modifying protein, and protocadherin-a9 (Pcdha9), a protein involved in cell-cell adhesion. Ohia mice exhibit brain defects with 80% penetrance, with severe mutants exhibiting microcephaly. This is associated with cortical thinning involving loss of intermediate progenitors, decreased cell proliferation, increased apoptosis, and mitotic block with multipolar spindle formation. Molecular profiling the Ohia mutant mouse brain using RNAseq, ChIPseq and genome-wide DNA methylation analysis revealed dysregulation of genes associated with neurodevelopment including many in pathways relevant to the cognitive deficits found in CHD patients. As Ohia mice die at birth, precluding assessment of neurodevelopmental outcomes, we also generated adult animals either homozygous for the Pchda9 mutation or with forebrain specific deletion of Sap130 using Emx1cre and a floxed Sap130 allele. MRI analysis of Pcdha9m/m adult mice revealed bicuspid aortic valve with normal brain structure, while Emx1-cre:Sap130f/- mice displayed microcephaly without heart defects. Behavioral assessments showed both have associative learning deficits and autism-like behavior. To translate these neurodevelopmental findings to an animal model with brain structure more similar to human, we developed a SAP130 mutant pig, and separately a PCDHA mutant pig. The SAP130 mutant pig displays CHD and craniofacial deficits, while PCDHA mutant pigs appear normal. Intercrossing these pigs is underway to generate double mutants to possibly replicate the HLHS phenotype. Overall, these findings show the HLHS heart phenotype and poor neurodevelopment share a common genetic etiology, and link epigenetic modulation of gene expression with HLHS associated NDD. The concepts proposed and models generated in this work will have broad relevance for insights into brain and behavioral deficits associated with CHD, but also in other NDD