BET bromodomain inhibition attenuates cardiac phenotype in myocyte-specific lamin A/C-deficient mice.

Mutation in the LMNA gene, encoding lamin A/C, causes a diverse group of diseases called laminopathies. Cardiac involvement is the major cause of death and manifests as dilated cardiomyopathy, heart failure, arrhythmias, and sudden death. There is no specific therapy for LMNA-associated cardiomyopathy. We report that deletion of Lmna in cardiomyocytes in mice leads to severe cardiac dysfunction, conduction defect, ventricular arrhythmias, fibrosis, apoptosis, and premature death within 4 weeks. The phenotype is similar to LMNA-associated cardiomyopathy in humans. RNA sequencing, performed before the onset of cardiac dysfunction, led to identification of 2338 differentially expressed genes (DEGs) in Lmna-deleted cardiomyocytes. DEGs predicted activation of bromodomain-containing protein 4 (BRD4), a regulator of chromatin-associated proteins and transcription factors, which was confirmed by complementary approaches, including chromatin immunoprecipitation sequencing. Daily injection of JQ1, a specific BET bromodomain inhibitor, partially reversed the DEGs, including those encoding secretome; improved cardiac function; abrogated cardiac arrhythmias, fibrosis, and apoptosis; and prolonged the median survival time 2-fold in the myocyte-specific Lmna-deleted mice. The findings highlight the important role of LMNA in cardiomyocytes and identify BET bromodomain inhibition as a potential therapeutic target in LMNA-associated cardiomyopathy, for which there is no specific effective therapy.

Cardiac Fibro-Adipocyte Progenitors Express Desmosome Proteins and Preferentially Differentiate to Adipocytes Upon Deletion of the Desmoplakin Gene.

RATIONALE: Mutations in desmosome proteins cause arrhythmogenic cardiomyopathy (AC), a disease characterized by excess myocardial fibroadipocytes. Cellular origin(s) of fibroadipocytes in AC is unknown. OBJECTIVE: To identify the cellular origin of adipocytes in AC. METHODS AND RESULTS: Human and mouse cardiac cells were depleted from myocytes and flow sorted to isolate cells expressing platelet-derived growth factor receptor-α and exclude those expressing other lineage and fibroblast markers (CD32, CD11B, CD45, Lys76, Ly(-6c) and Ly(6c), thymocyte differentiation antigen 1, and discoidin domain receptor 2). The PDGFRA(pos):Lin(neg):THY1(neg):DDR2(neg) cells were bipotential as the majority expressed collagen 1 α-1, a fibroblast marker, and a subset CCAAT/enhancer-binding protein α, a major adipogenic transcription factor, and therefore, they were referred to as fibroadipocyte progenitors (FAPs). FAPs expressed desmosome proteins, including desmoplakin, predominantly in the adipogenic but not fibrogenic subsets. Conditional heterozygous deletion of Dsp in mice using Pdgfra-Cre deleter led to increased fibroadipogenesis in the heart and mild cardiac dysfunction. Genetic fate mapping tagged 41.4±4.1% of the cardiac adipocytes in the Pdgfra-Cre:Eyfp:Dsp(W/F) mice, indicating an origin from FAPs. FAPs isolated from the Pdgfra-Cre:Eyfp:Dsp(W/F) mouse hearts showed enhanced differentiation to adipocytes. Mechanistically, deletion of Dsp was associated with suppressed canonical Wnt signaling and enhanced adipogenesis. In contrast, activation of the canonical Wnt signaling rescued adipogenesis in a dose-dependent manner. CONCLUSIONS: A subset of cardiac FAPs, identified by the PDGFRA(pos):Lin(neg):THY1(neg):DDR2(neg) signature, expresses desmosome proteins and differentiates to adipocytes in AC through a Wnt-dependent mechanism. The findings expand the cellular spectrum of AC, commonly recognized as a disease of cardiac myocytes, to include nonmyocyte cells in the heart.

Human molecular genetic and functional studies identify TRIM63, encoding Muscle RING Finger Protein 1, as a novel gene for human hypertrophic cardiomyopathy.

RATIONALE: A delicate balance between protein synthesis and degradation maintains cardiac size and function. TRIM63 encoding Muscle RING Finger 1 (MuRF1) maintains muscle protein homeostasis by tagging the sarcomere proteins with ubiquitin for subsequent degradation by the ubiquitin-proteasome system (UPS). OBJECTIVE: To determine the pathogenic role of TRIM63 in human hypertrophic cardiomyopathy (HCM). METHODS AND RESULTS: Sequencing of TRIM63 gene in 302 HCM probands (250 white individuals) and 339 control subjects (262 white individuals) led to identification of 2 missense (p.A48V and p.I130M) and a deletion (p.Q247*) variants exclusively in the HCM probands. These 3 variants were absent in 751 additional control subjects screened by TaqMan assays. Likewise, rare variants were enriched in the white HCM population (11/250, 4.4% versus 3/262, 1.1%, respectively, P=0.024). Expression of the mutant TRIM63 was associated with mislocalization of TRIM63 to sarcomere Z disks, impaired auto-ubiquitination, reduced ubiquitination and UPS-mediated degradation of myosin heavy chain 6, cardiac myosin binding protein C, calcineurin (PPP3CB), and p-MTOR in adult cardiac myocytes. Induced expression of the mutant TRIM63 in the mouse heart was associated with cardiac hypertrophy, activation of the MTOR-S6K and calcineurin pathways, and expression of the hypertrophic markers, which were normalized on turning off expression of the mutant protein. CONCLUSIONS: TRIM63 mutations, identified in patients with HCM, impart loss-of-function effects on E3 ligase activity and are probably causal mutations in HCM. The findings implicate impaired protein degradation in the pathogenesis of HCM.

Molecular genetic and functional characterization implicate muscle-restricted coiled-coil gene (MURC) as a causal gene for familial dilated cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) are classic forms of systolic and diastolic heart failure, respectively. Mutations in genes encoding sarcomere and cytoskeletal proteins are major causes of HCM and DCM. MURC, encoding muscle-restricted coiled-coil, a Z-line protein, regulates cardiac function in mice. We investigated potential causal role of MURC in human cardiomyopathies. METHODS AND RESULTS: We sequenced MURC in 1199 individuals, including 383 probands with DCM, 307 with HCM, and 509 healthy control subjects. We found 6 heterozygous DCM-specific missense variants (p.N128K, p.R140W, p.L153P, p.S307T, p.P324L, and p.S364L) in 8 unrelated probands. Variants p.N128K and p.S307T segregated with inheritance of DCM in small families (χ(2)=8.5, P=0.003). Variants p.N128K, p.R140W, p.L153P, and p.S364L were considered probably or possibly damaging. Variant p.P324L recurred in 3 independent probands, including 1 proband with a TPM1 mutation (p.M245T). A deletion variant (p.L232-R238del) was present in 3 unrelated HCM probands, but it did not segregate with HCM in a family who also had a MYH7 mutation (p.L907V). The phenotype in mutation carriers was notable for progressive heart failure leading to heart transplantation in 4 patients, conduction defects, and atrial arrhythmias. Expression of mutant MURC proteins in neonatal rat cardiac myocytes transduced with recombinant adenoviruses was associated with reduced RhoA activity, lower mRNA levels of hypertrophic markers and smaller myocyte size as compared with wild-type MURC. CONCLUSIONS: MURC mutations impart loss-of-function effects on MURC functions and probably are causal variants in human DCM. The causal role of a deletion mutation in HCM is uncertain.

Determinants of plasma vitamin D levels in patients with acute coronary syndromes.

BACKGROUND: Vitamin D is implicated in various biological functions ranging from cellular proliferation to immunity. Vitamin D deficiency is associated with an increased risk of several diseases including coronary atherosclerosis. MATERIALS AND METHODS: We measured plasma 25(OH)D3 level in 224 patients with acute coronary syndromes (ACS) and 209 control individuals by ELISA. We genotyped the study populations for 11 single nucleotide polymorphisms (SNPs) in seven genes involved in vitamin D biosynthesis and metabolism by 5' nuclease assays. RESULTS: The mean and median plasma 25(OH)D3 levels were not significantly different between patients with ACS and controls (median: 22·06 vs. 22·24 ng mL(-1) , respectively, P = 0·618). Plasma 25(OH)D3 level was < 20 ng mL(-1) in 175/433 (40%) and < 30 ng mL(-1) in 333/433 (77%) participants. Only four individuals had plasma 25(OH)D3 levels of above 60 ng mL(-1) . African-American and Hispanic populations, women and those with diabetes mellitus had significantly lower plasma 25(OH)D3 levels. In multivariable regression analysis, age, sex, diabetes mellitus, body weight, rs2762933 (CYP24A1) and rs6055987 (PLCB1) SNPs were independent predictors of plasma 25(OH)D3 level in the Caucasian population. CONCLUSIONS: We found no difference in mean plasma vitamin D levels between patients with ACS and controls. Differences in population characteristics between the two study groups including medications use and the lack of data on vitamin D, calcium and multivitamin supplements intake as well as the relatively small sample size of the populations could confound the results. Ethnic background, sex, age, body weight and SNPs in CYP24A1 and PLCB1 were independent determinants of plasma vitamin D levels.

Genome-wide mapping of modifier chromosomal loci for human hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is a disease of mutant sarcomeric proteins (except for phenocopy). Cardiac hypertrophy is the clinical diagnostic hallmark of HCM and a major determinant of morbidity and mortality in various cardiovascular diseases. However, there is remarkable variability in expression of hypertrophy, even among HCM patients with identical causal mutations. We hypothesized modifier genes are partly responsible for the variation in hypertrophic expressivity. To map the modifier loci, we typed 811 short-tandem repeat markers ( approximately 5 cMdense) in 100 members of an HCM family including 36 with the InsG791 mutation in MYBPC3. We performed oligogenic simultaneous segregation and linkage analyses using Markov Chain Monte Carlo methods and detected linkage on 3q26.2 (180 cM), 10p13 (41 cM), 17q24 (108 cM) with log of the posterior placement probability ratio (LOP) of 3.51, 4.86 and 4.17, respectively, and suggestive linkage (LOP of 2.40) on 16q12.2 (73 cM). The effect sizes varied according to the modifier locus, age and sex. It ranged from approximately 8 g shift in left ventricular mass for 10p13 locus heterozygosity for the common allele to approximately 90 g shift for 3q26.2 locus homozygosity for the uncommon allele. Refining the 10p13 locus restricted the candidate modifier genes to ITGA8, C10orf97 (CARP) and PTER. ITGA8 and CARP are biologically plausible candidates as they are implicated in cardiac fibrosis and apoptosis, respectively. Since cardiac hypertrophy is a major determinant of total and cardiovascular mortality and morbidity, regardless of the etiology, identification of the specific modifier genes could have significant prognostic and therapeutic implications for various cardiovascular diseases.

The cloning, genomic organization and tissue expression profile of the human DLG5 gene.

BACKGROUND: Familial atrial fibrillation, an autosomal dominant disease, was previously mapped to chromosome 10q22. One of the genes mapped to the 10q22 region is DLG5, a member of the MAGUKs (Membrane Associated Gyanylate Kinase) family which mediates intracellular signaling. Only a partial cDNA was available for DLG5. To exclude potential disease inducing mutations, it was necessary to obtain a complete cDNA and genomic sequence of the gene. METHODS: The Northern Blot analysis performed using 3' UTR of this gene indicated the transcript size to be about 7.2 KB. Using race technique and library screening the entire cDNA was cloned. This gene was evaluated by sequencing the coding region and splice functions in normal and affected family members with familial atrial fibrillation. Furthermore, haploid cell lines from affected patients were generated and analyzed for deletions that may have been missed by PCR. RESULTS: We identified two distinct alternately spliced transcripts of this gene. The genomic sequence of the DLG5 gene spanned 79 KB with 32 exons and was shown to have ubiquitous human tissue expression including placenta, heart, skeletal muscle, liver and pancreas. CONCLUSIONS: The entire cDNA of DLG5 was identified, sequenced and its genomic organization determined.