Alternative splicing plays a major role in the adaptation of cardiac function exemplified by the isoform switch of titin, which adjusts ventricular filling. We previously identified a rat strain deficient in titin splicing. Using genetic mapping, we found a loss-of-function mutation in RBM20 as the underlying cause for the pathological titin isoform expression. Mutations in human RBM20 have previously been shown to cause dilated cardiomyopathy. We showed that the phenotype of Rbm20 deficient rats resembles the human pathology. Deep sequencing of the human and rat cardiac transcriptome revealed an RBM20 dependent regulation of alternative splicing. Additionally to titin we identified a set of 30 genes with conserved regulation between human and rat. This network is enriched for genes previously linked to cardiomyopathy, ion-homeostasis, and sarcomere biology. Our studies emphasize the importance of posttranscriptional regulation in cardiac function and provide mechanistic insights into the pathogenesis of human heart failure.

Mutations in dystrophin cause Duchenne muscular dystrophy (DMD), but absent dystrophin does not invariably cause necrosis in all muscles, life stages and species. Using DNA microarray, we established a molecular signature of dystrophinopathy in the mdx mouse, with evidence that secondary mechanisms are key contributors to pathogenesis. We used variability controls, adequate replicates and stringent analytic tools, including significance analysis of microarrays to estimate and manage false positive rates. In leg muscle, we identified 242 differentially expressed genes, >75% of which have not been previously reported as altered in human or animal dystrophies. Data provide evidence for coordinated activity of numerous components of a chronic inflammatory response, including cytokine and chemokine signaling, leukocyte adhesion and diapedesis, invasive cell type-specific markers, and complement system activation. Selective chemokine upregulation was confirmed by RT-PCR and immunoblot, and may be a key determinant of the nature of the inflammatory response in dystrophic muscle. Up-regulation of secreted phosphoprotein 1 (minopontin, osteopontin) mRNA and protein in dystrophic muscle identified a novel linkage between inflammatory cells and repair processes. Extracellular matrix genes were up-regulated in mdx to levels similar to those in DMD. Since, unlike DMD, mdx exhibits little fibrosis, data suggest that collagen regulation at post-transcriptional stages mediates extensive fibrosis in DMD. Taken together, these data identify a relatively neglected aspect of DMD, suggest new treatment avenues, and highlight the value of genome-wide profiling in study of complex disease processes.

Titin, a sarcomeric protein expressed primarily in striated muscles, is responsible for maintaining the structure and biomechanical properties of muscle cells. Cardiac titin undergoes developmental size reduction from 3.7 megadaltons in neonates to primarily 2.97 megadaltons in the adult. This size reduction results from gradually increased exon skipping between exons 50 and 219 of titin mRNA. Our previous study reported that Rbm20 is the splicing factor responsible for this process. In this work, we investigated its molecular mechanism. We demonstrate that Rbm20 mediates exon skipping by binding to titin pre-mRNA to repress the splicing of some regions; the exons/introns in these Rbm20-repressed regions are ultimately skipped. Rbm20 was also found to mediate intron retention and exon shuffling. The two Rbm20 speckles found in nuclei from muscle tissues were identified as aggregates of Rbm20 protein on the partially processed titin pre-mRNAs. Cooperative repression and alternative 3′ splice site selection were found to be used by Rbm20 to skip different subsets of titin exons, and the splicing pathway selected depended on the ratio of Rbm20 to other splicing factors that vary with tissue type and developmental age.

High blood pressure (BP) is more prevalent and contributes to more severe manifestations of cardiovascular disease (CVD) in African Americans than in any other United States ethnic group. Several small African-ancestry (AA) BP genome-wide association studies (GWASs) have been published, but their findings have failed to replicate to date. We report on a large AA BP GWAS meta-analysis that includes 29,378 individuals from 19 discovery cohorts and subsequent replication in additional samples of AA (n = 10,386), European ancestry (EA) (n = 69,395), and East Asian ancestry (n = 19,601). Five loci (EVX1-HOXA, ULK4, RSPO3, PLEKHG1, and SOX6) reached genome-wide significance (p < 1.0 × 10(-8)) for either systolic or diastolic BP in a transethnic meta-analysis after correction for multiple testing. Three of these BP loci (EVX1-HOXA, RSPO3, and PLEKHG1) lack previous associations with BP. We also identified one independent signal in a known BP locus (SOX6) and provide evidence for fine mapping in four additional validated BP loci. We also demonstrate that validated EA BP GWAS loci, considered jointly, show significant effects in AA samples. Consequently, these findings suggest that BP loci might have universal effects across studied populations, demonstrating that multiethnic samples are an essential component in identifying, fine mapping, and understanding their trait variability.

Two obsessive-compulsive disorder (OCD) genome-wide association studies (GWASs) have been published by independent OCD consortia, the International Obsessive-Compulsive Disorder Foundation Genetics Collaborative (IOCDF-GC) and the OCD Collaborative Genetics Association Study (OCGAS), but many of the top-ranked signals were supported in only one study. We therefore conducted a meta-analysis from the two consortia, investigating a total of 2688 individuals of European ancestry with OCD and 7037 genomically matched controls. No single-nucleotide polymorphisms (SNPs) reached genome-wide significance. However, in comparison with the two individual GWASs, the distribution of P-values shifted toward significance. The top haplotypic blocks were tagged with rs4733767 (P=7.1 × 10; odds ratio (OR)=1.21; confidence interval (CI): 1.12-1.31, CASC8/CASC11), rs1030757 (P=1.1 × 10; OR=1.18; CI: 1.10-1.26, GRID2) and rs12504244 (P=1.6 × 10; OR=1.18; CI: 1.11-1.27, KIT). Variants located in or near the genes ASB13, RSPO4, DLGAP1, PTPRD, GRIK2, FAIM2 and CDH20, identified in linkage peaks and the original GWASs, were among the top signals. Polygenic risk scores for each individual study predicted case-control status in the other by explaining 0.9% (P=0.003) and 0.3% (P=0.0009) of the phenotypic variance in OCGAS and the European IOCDF-GC target samples, respectively. The common SNP heritability in the combined OCGAS and IOCDF-GC sample was estimated to be 0.28 (s.e.=0.04). Strikingly, ∼65% of the SNP-based heritability in the OCGAS sample was accounted for by SNPs with minor allele frequencies of ⩾40%. This joint analysis constituting the largest single OCD genome-wide study to date represents a major integrative step in elucidating the genetic causes of OCD.