Project description:Pathological growth of cardiomyocytes during hypertrophy is characterized by excess protein synthesis; however, the regulatory mechanism remains largely unknown. Using a neonatal rat ventricular myocyte (NRVMs) model, here we find that the expression of nucleosome assembly protein 1 like 5 (Nap1l5) is upregulated in phenylephrine (PE)-induced hypertrophy. Knockdown of Nap1l5 expression by siRNA significantly blocks cell size enlargement and pathological gene induction after PE treatment. In contrast, Adenovirus-mediated Nap1l5 overexpression significantly aggravates the pro-hypertrophic effects of PE on NRVMs. RNA-seq analysis reveals that Nap1l5 knockdown reverses the pro-hypertrophic transcriptome reprogramming after PE treatment. Whereas immune response is dominantly enriched in the upregulated genes, oxidative phosphorylation, cardiac muscle contraction and ribosome related pathways are remarkably enriched in the down-regulated genes. Although PRC2 and PRC1 are involved in Nap1l5-mediated gene regulation, Nap1l5 does not directly alter the levels of global histone methylations. However, puromycin incorporation assay shows that Nap1l5 is both necessary and sufficient to drive the increased protein synthesis rate in cardiomyocyte hypertrophy. This is attributable to a direct regulation of ribosome assembly by Nap1l5. Our findings demonstrate a previously unrecognized role of Nap1l5 in translation control during cardiac hypertrophy.
Project description:Zinc dyshomeostasis has been involved in the pathogenesis of cardiac hypertrophy; however, the dynamic regulation of intracellular zinc and its downstream signaling in cardiac hypertrophy remain largely unknown. Here we screened ZIP (SLC39) family members that were responsible for zinc uptake in a phenylephrine (PE)-induced cardiomyocyte hypertrophy model. We found that Slc39a2 was the only member that was altered at mRNA level by PE treatment in neonatal rat ventricular myocytes (NRVMs), but its protein level was not affected. Zincpyr1 staining showed a significant decrease in zinc uptake after PE treatment or after Slc39a2 knockdown in NRVMs, indicating an inhibition of its transport activity during hypertrophy. Slc39a2 deficiency caused spontaneous hypertrophy in NRVMs, and further exacerbated the hypertrophic responses after PE treatment. RNA sequencing analysis confirmed a largely aggravated pro-hypertrophic transcriptome reprogramming after Slc39a2 knockdown. Interestingly, the innate immune pathways, including NOD signaling, TOLL-like receptor, NFB, and IRFs, were substantially enriched after Slc39a2 knockdown. Whereas IRF7, the most sensitive among all IRFs, did not mediate the effect of Slc39a2 in hypertrophy, pro-hypertrophy phosphorylations of NFB and STAT3 were significantly enhanced after Slc39a2 knockdown, in parallel with degradation of IkBα protein. Our data demonstrate that SLC39A2-mediated zinc homeostasis contributes to the remodeling of innate immune signaling in cardiomyocyte hypertrophy, and provide novel insights into the pathogenesis of heart failure and its treatment.
Project description:Background: Although myocardial hypertrophy is an essential component of heart’s response to many forms of stress, prolonger excessive hypertrophy contributes importantly to the pathogenesis of heart disease. The pimobendan is a drug that both inhibits phosphodiesterase 3 (PDE3) and acts as a calcium sensitizer, which has been used to treat heart failure. The effects of pimobendan on myocardial hypertrophy is controversial. Objective: This study aims to evaluate the therapeutic effect of pimobendan on myocardial hypertrophy. Methods: Mice were treated with low oral doses of pimobendan (1mg/kg/d) for 4 weeks after transaortic constriction. Heart structure and function was assessed using ultrasound, hemodynamic measurements and histology combined with biochemical assessments of myocardial hypertrophy. We also examined the effects of pimobendan (100 µM) on hypertrophy in cultured neonatal rat cardiomyocytes (NRCMs) induced by 50 µM phenylephrine (PE). Results: The doses pimobendan used in our studies had no effect on baseline contractility. Nevertheless, pimobendan administration of mice subjected to TAC decreased heart weights (normalized to either tibia length or body weight) ventricular wall thickness, cardiomyocyte sizes, myocardial fibrosis and the levels of a number of key myocardial hypertrophy markers (WHICH ONES). In cultured neonatal cardiomyocytes, pimobendan attenuated the PE-induced hypertrophy. In both hypertrophy models pimobendan reduced the phosphorylation levels of several essential proteins in the MAPK pathway, PI3K-AKT pathway, and calcineurin signaling pathway. Conclusion: Low pimobendan may attenuate myocardial hypertrophy. Although the underlying mechanisms remain to be elucidated, the MAPK pathway is likely to play a role.
Project description:The long-non coding RNA NRON is enriched in cardiomyocytes where it localizes in the nucleus. Unexpectedly, NRON-overexpression in a transverse aortic constriction-induced hypertrophy mouse model exacerbated hypertrophy, whereas cardiomyocyte-specific NRON-deletion attenuated cardiac hypertrophy, thereby suggesting a novel regulatory role of NRON in the heart.
Project description:Aims: Cardiomyocyte-specific nitric oxide synthase 3 (NOS3) overexpression reduces left ventricular (LV) remodelling after myocardial infarction in mice, but its effect on sustained LV pressure-overload remains incompletely understood. We investigated LV structural and functional adaptation to elevated afterload in mice with cardiomyocyte-restricted NOS3 overexpression (NOS3TG) and wild type littermates (WT). Methods and Results: Hemodynamic indices, cardiac hypertrophy and interstitial fibrosis were measured 10 weeks after transverse aortic constriction (TAC). After 10 weeks TAC, NOS3TG had better preserved systolic function (maximum rates of pressure development normalized to maximal pressure 77±6 versus 65±2 ms-1, P=0.05), reduced heart weight-body weight ratio (HW/BW, 5.0±0.3 versus 5.8±0.1, P<0.05), and cardiomyocyte width than WT (14.9±0.4 vs 16.7±0.2 ?m, P<0.05). After 10 weeks TAC, a 44k cDNA chip-based microarray analysis was validated using real time PCR and revealed significantly altered expression pattern of genes involved in cellular growth, matrix remodelling, and inflammation between genotypes. Conclusions: Cardiomyocyte-restricted NOS3 overexpression attenuates TAC-induced hypertrophy via autocrine inhibition of cardiomyocyte cell growth, but does not mitigate myocardial fibrosis. The subsequent diastolic dysfunction suggests that inhibition of matrix producing cells during hypertrophic stress is necessary to prevent functional and structural deterioration of the pressure-overloaded heart. Left ventricular mRNA expression profiles were compared between alpha-myosin heavy chain driven nitric oxide synthase 3 (alpha-MHC-NOS3) transgenic and wild type (WT) littermate mice at baseline and 10 weeks after transversal aortic constrcition-induced pressure-overload. Biological repeats: n=4, two males and two females, for each group and condition. Transgenic mice were backcrossed for seven generations (F7) to a C57Bl/6 N background and age and weight matched animals were used for microarray experiments.
Project description:The HECT domain E3 ubiquitin protein ligase 3 (HectD3) is highly expressed in the heart, but its cardiac function is still unknown. Here, we identified SUMO2 and Stat1 as novel cardiac substrates for HectD3. SUMO2 is a potent inducer of Calcineurin-NFAT mediated cardiomyocyte hypertrophy, whereas, Stat1 is an interferon responsive transcription factor that plays crucial role in cellular immune responses. HectD3 overexpression on one hand attenuated SUMO2-Calcineurin-NFAT signaling driven cardiomyocyte hypertrophy, on the other hand, it abrogated the pro-inflammatory actions of LPS or interferon-γ in cardiomyocytes in vitro. Consistently, AAV9-mediated overexpression of HectD3 in mice in vivo not only reduced cardiac SUMO2/Stat1 levels and pathological hypertrophy but also alleviated macrophage infiltration and fibrosis induced by pressure overload. In conclusion, we describe a novel cardioprotective mechanism involving the ubiquitin ligase HectD3, which exerts anti-hypertrophic and anti-inflammatory effects via dual regulation of SUMO2 and Stat1.
Project description:Kinase-catalyzed phosphorylation plays crucial roles in numerous biological processes. CDC-like kinases (CLKs) are a group of evolutionarily conserved dual-specificity kinases that have been implicated in RNA splicing, glucose metabolism, diet-induced thermogenesis and so on. However, it is still largely unknown whether CLKs are involved in pathologic cardiac hypertrophy. This study aimed to investigate the role of CLKs in pathologic cardiac hypertrophy and the underlying mechanisms. Using small RNA interference, we discovered that defects in CLK4, but not CLK1, CLK2 or CLK3, were associated with the pathogenesis of pathological cardiomyocyte hypertrophy, while overexpression of CLK4 exerted resistance to isoproterenol-induced pathological cardiomyocyte hypertrophy. Moreover, the expression of CLK4 was significantly reduced in the failed myocardia of mice subjected to either transverse aortic constriction or isoproterenol infusion. Through the Cre/loxP system, we constructed cardiac-specific Clk4-knockout (Clk4-cKO) mice, which manifested pathological myocardial hypertrophy with progressive left ventricular systolic dysfunction and heart dilation. Phosphoproteomic analysis revealed significant changes in phosphorylation of sarcomere-related proteins in Clk4-cKO mice. Further experiments identified nexilin (NEXN), an F-actin binding protein, as the direct substrate of CLK4, and overexpression of a phosphorylation-mimic mutant of NEXN was sufficient to reverse the hypertrophic growth of cardiomyocytes induced by Clk4 knockdown. Importantly, restoring the phosphorylated NEXN significantly ameliorated the myocardial hypertrophy in Clk4-cKO mice. CLK4 phosphorylates NEXN to regulate the development of pathological cardiac hypertrophy. CLK4 may serve as a potential intervention target for the prevention and treatment of heart failure.
Project description:Pathological cardiac hypertrophy is featured by enhanced protein synthesis. Translation inhibition is effective in treating cardiac hypertrophy, yet with systematic side effect. We identified a cardiac-enriched LncRNA CARDINAL, when over-expressed in cardiomyocyte using AAV9 driven by cTNT promoter, ameliorate transaortic constriction (TAC) induced hypertrophy.
Project description:An important event in the pathogenesis of heart failure is the development of pathological cardiac hypertrophy. In cultured cardiac cardiomyocytes, the transcription factor Gata4 is required for agonist-induced cardiomyocyte hypertrophy. We hypothesized that in the intact organism Gata4 is an important regulator of postnatal heart function and of the hypertrophic response of the heart to pathological stress. To test this hypothesis, we studied mice heterozygous for deletion of the second exon of Gata4 (G4D). At baseline, G4D mice had mild systolic and diastolic dysfunction associated with reduced heart weight and decreased cardiomyocyte number. After transverse aortic constriction (TAC), G4D mice developed overt heart failure and eccentric cardiac hypertrophy, associated with significantly increased fibrosis and cardiomyocyte apoptosis. Inhibition of apoptosis by overexpression of the insulin-like growth factor 1 receptor prevented TAC-induced heart failure in G4D mice. Unlike WT-TAC controls, G4D-TAC cardiomyocytes hypertrophied by increasing in length more than width. Gene expression profiling revealed upregulation of genes associated with apoptosis and fibrosis, including members of the TGF? pathway. Our data demonstrate that Gata4 is essential for cardiac function in the postnatal heart. After pressure overload, Gata4 regulates the pattern of cardiomyocyte hypertrophy and protects the heart from load-induced failure. Experiment Overall Design: We reasoned that if Gata4 was a crucial regulator of pathways necessary for cardiac hypertrophy, then modest reductions of Gata4 activity should result in an observable cardiac phenotype. To test this hypothesis, we used gene targeted mice that express reduced levels of Gata4. We characterized these mice at baseline and after pressure Experiment Overall Design: overload.