P1618A polymethoxy flavonoid, Nobiletin, Has a therapeutic potency against the development of heart failure through NBP1 activation

Introduction

Maladaptive hypertrophy is being recognized as a critical event during the development of heart failure. The control of cardiac hypertrophy may be one of the therapeutic strategy for heart failure therapy. In our previous study, we screened natural compound library and found that a natural compound, Nobiletin, could inhibit cardiomyocyte hypertrophy in culture. Nobiletin has various useful effects such as anti-cancer, anti-inflammation, and anti-oxidant and may be applicable to pharmacological therapy for heart failure.

Hypothesis

We thought that nobiletin might prevent the development of heart failure in vivo and investigated the target molecule of Nobiletin in the heart.

Methods and results

In primary cardiomyocytes, Nobiletin significantly inhibited phenylephrine (PE)-induced hypertrophic responses such as increases in cell size and hypertrophic gene transcription, such as ANF and BNP. C57BL6 mice were subjected to sham or transarotic constriction (TAC). Oral administrations of Nobiletin (20 mg/kg/day) or vehicle were repeated for 8 weeks. Nobiletin treatment significantly prevented TAC-induced increases in PWT and systolic dysfunction. Nobiletin also suppressed TAC-induced myocardial cell hypertrophy, perivascular fibrosis, and hypertrophic gene transcriptions. To investigate the target molecule of Nobiletin, Nobiletin-binding proteins were purified from rat heart using biotin-conjugated Nobiletin. We identified 162 novel binding protein of Nobiletin by LC/MS-MS. One of them, Nobiletin-binding protein 1 (NBP1) related to cellular metabolic pathway. Pulldown assay demonstrated that biotin-conjugated Nobiletin, but not biotin, directly interacted with recombinant NBP1. In vitro enzyme assay showed that Nobiletin enhanced NBP1 activity. Although NBP1 knockdown could not affect PE-induced hypertrophic response gene transcriptions and cardiomyocyte hypertrophy, NBP1 knockdown failed to exhibit Nobiletin-mediated anti-hypertrophic effects. NBP1-KO mice and WT mice were subjected to sham or TAC and randomly divided into two groups: Nobiletin (20 mg/kg/day) and vehicle. After 8 weeks, Nobiletin significantly improved TAC-induced cardiac hypertrophy and systolic dysfunction in WT mice but not in NBP1-KO mice. Nobiletin also prevented TAC-induced increases in HW/BW rate, myocardial cell hypertrophy, and mRNA levels of ANF and β-MHC in WT mice but not in NBP1-KO mice.

Conclusions

In this study, we demonstrate that Nobiletin inhibits cardiomyocyte hypertrophy and the development of heart failure in vivo. NBP1 activity is required to exhibit therapeutic potency of Nobiletin for heart failure. These finding suggest that a natural compound, nobiletin, might be a candidate for heart failure agent in human.

Acknowledgement/Funding

This work was supported by JSPS KAKENHI Grant.

P1608Inhibition of GATA4 dimerization suppress hypertrophic responses

Introduction

Hypertrophic signals eventually reach the nuclei of cardiomyocytes, change patterns of gene expression, and cause the development of heart failure. During the development of heart failure, intrinsic histone acetyltransferase called p300 induce GATA4 acetylation. Acetylated GATA4 increases its DNA binding, up-regulates cardiac hypertrophic response genes, and lead to heart failure. A zinc finger protein, GATA4 is the transcription factor that expression level is high in heart. It has been reported that GATA1, the same GATA family, regulates transcriptional activity through its homo-dimerization. However, GATA4 homo-dimerization and its relationship to hypertrophic responses are still unknown.

Purpose

To clarify the relationship between GATA4 homo-dimerization and transcriptional activity and investigate whether inhibition of this homo-dimerization become therapeutic target for cardiac hypertrophy.

Methods

GST pull-down and DNA pull-down assay were performed using GST fusion full length and deletion mutants of GATA4 and biotin-conjugated ET-1 promoter probe including a GATA element. Recombinant C-zinc finger domain (256–326), including C-zinc finger motif (256–295) and acetylation site (308–326) was cross-linked using glutaraldehyde and subjected to silver staining. An expression plasmid with three GATA4-acetylation site mutant-conjugated with nuclear localization sequence (3xG4D) was constructed. Immunoprecipitation and western blotting were performed using nuclear extract from HEK293T cells expressing p300, GATA4, and 3xG4D. Luciferase assay was using ANF and ET-1 promoter sequences. Neonatal rat cultured cardiomyocyte expressed 3xG4D and then stimulated with phenylephrine (PE) for 48 hours. Next cardiomyocytes stained with α-actinin antibody and measured the cell surface area.

Results

The acetylation site of GATA4 was required for the dimerization of GATA4. But, C-zinc finger motif (256–295) and the acetylation site were required for the DNA binding. Recombinant C-zinc finger domain formed not only a homo-dimer but also a multimer. Co-expression of p300 increased the formation of homo-dimer as well as the acetylation of GATA4 in HEK293T cells. The GATA4 homo-dimer was disrupted by acetyl-deficient GATA4 or HAT-deficient p300 mutant. Overexpression of 3xG4D prevented the dimerization of GATA4, but not acetylation of GATA4. The result of luciferase assay showed that overexpression of 3xG4D prevented p300/GATA-induced ANF and ET-1 promoter activities. Furthermore, overexpression of 3xG4D inhibited phenylephrine-induced cardiomyocyte hypertrophy.

Conclusions

These results suggest that GATA4 dimerization may play an important role in hypertrophy-response gene activation. Thus, it is likely that inhabitation of GATA4 dimerization become therapeutic target for cardiac hypertrophy.

P4998Novel GATA4 binding proteins, RbAp48/46, regulate cardiomyocyte hypertrophy with depending on the phosphorylate State of GATA4

Introduction

Cardiac hypertrophy is being recognized as a critical event during the development of heart failure. A zinc finger protein GATA4 associates with an intrinsic histone acetyltransferase p300 and regulates myocardial transcriptional activities in response to hypertrophic stimuli. Here, we show that Retinoblastoma protein (Rb)-associated protein 48 and 46 (RbAp48, RbAp46) are novel components of p300/GATA4 complex. Both RbAp48 and 46 form a repressor complex with HDACs and has been implicated in chromatin remodeling and transcriptional repression. However, the precise functional relationships among p300, GATA4, RbAp48, and RbAp46 remain unknown.

Hypothesis

We assessed the hypothesis that RbAp48/46 form a functional complex with p300/GATA4 and regulated hypertrophic responses in cardiomyocytes.

Methods and results

IP-WB using nuclear extract from rat heart demonstrated that GATA4 formed a complex with RbAp48, RbAp46, HDAC1, and HDAC2. GST pull down assay using recombinant proteins showed that GATA4 physically interacted with both RbAp48 and RbAp46 but not HDAC1 and HDAC2. Deletion mutant assay revealed that N-terminal domain of GATA4 interacted with RbAp48/46. In HEK293T cell, overexpression of RbAp48/46 recruited HDAC1/2 to GATA4, inhibited p300-induced GATA4 acetylation and suppressed p300/GATA4-dependent ANF and ET-1 promoter activations. Conversely, the knockdown of RbAp48/46 reversed these changes. Although overexpression of HDAC1/2 did not change p300/GATA4-induced these promoter activities, co-expression of HDAC1 or HDAC2 with RbAp48/46 enhanced RbAp48/46-mediated inhibitory actions. In cardiomyocytes, overexpression of RbAp48/46 significantly inhibited phenylephrine (PE)-induced GATA4 acetylation, activation of ANF and ET-1 promoters, and cardiomyocyte hypertrophy. The knockdown of RbAp48/46 reversed these changes. Moreover, the knockdown of HDAC1/2 deteriorated PE-induced hypertrophy-responsive events and did not exhibit RbAp48/46-induced inhibitory actions. Finally, MEK1/ERK-mediated S105 phosphorylation of GATA4 by PE stimulus induced the dissociation of RbAp48/46 with GATA4, the increase of p300-induced GATA4-acetylation, the synergistic activation of ANF and ET-1 promoters with p300/GATA4, and the decrease of RbAp48/46 recruitments onto the GATA element of the ANF promoter. Conversely, PD98059, a MEK1 inhibitor, treatment inhibited GATA4-phosphorylation and these changes.

Conclusion

In this study, we demonstrate that RbAp48/46 mediate the binding between GATA4 and HDAC1/2 and regulate p300/GATA4 axis. The phosphorylation of S105 GATA4 has a critical role on the dissociation of GATA4/RbAp48/46/HDAC repressor complex, the formation of 300/GATA4 activator complex, and the increase of GATA4 acetylation and hypertrophic responses. These findings suggest that RbAp48/46 may regulate hypertrophic responses involved in modulating the posttranslational modification crosstalk of GATA4.

Acknowledgement/Funding

This work was supported by JSPS KAKENHI Grant.

P1607Epigenetic modifications via histone acetylation by p300 are changed during the transition from cardiac hypertrophy to heart failure

Background

An intrinsic histone acetyltransferase (HAT), p300, is required for acetylation and the transcriptional activity of GATA4, as well as pathological left ventricular hypertrophy (LVH) and the development of heart failure (HF) in vivo. Recently, studies of histone modification have been performed within the flexible tails, such as H3K9 and H3K14. Although most previously studied histone modifications are within the flexible tails of histones, H3K122 is reportedly a novel site of the histone globular domain acetylated by p300, and its acetylation activates gene transcriptions by destabilizing histone-DNA binding and increasing the accessibility of transactional factors to DNA. However, little is known about the extent histone modifications directly affect LVH and HF.

Hypothesis

We hypothesized that p300 could induce epigenetic changes by acetylation of the globular domain as well as tail domain of histone during the development of LVH and HF.

Methods

First, to investigate whether the acetylation of H3K122 in the globular domain of histones as well as those of H3K9 and H3K14 in the tail domain of histones increased in cardiomyocytes hypertrophy, western blotting and chromatin-immunoprecipitation (ChIP) assays were performed using neonatal rat cultured cardiomyocytes with phenylephrine (PE) stimulus. Second, neonatal rat cultured cardiomyocytes were treated with p300 knockdown by siRNA or curcumin, a p300-specific HAT inhibitor. Third, to investigate the role of p300 HAT activity in histone acetylation in vivo, we utilized mice overexpressing p300 in the heart, which induced LVH. Final, to investigate whether these acetylation changes during the development of LVH and HF, in vivo ChIP assay was performed using hypertensive heart disease model of Dahl salt-sensitive rats.

Results

Western blotting indicated that treatment with PE increased the acetylation of H3K122 as well as those of H3K9 and H3K14 in cardiomyocytes hypertrophy. ChIP assay demonstrated that PE increased the recruitment of acetylated H3K122 and H3K9 onto ANF and BNP promoters containing the GATA element and peaks of acetylation of these domains were 4 hours after PE stimulation. Next, these acetylations were significantly inhibited by p300 knockdown by siRNA or treatment with curcumin. Conversely, in vivo ChIP assays in mice overexpressing p300 indicated that p300 overexpression increased recruitment of acetylated H3K122 and H3K9 onto ANF and BNP promoters containing the GATA element. Next, in hypertensive heart disease model of Dahl salt-sensitive rats, in vivo ChIP assays reviled that acetylation of H3K9 was increased around ANF and BNP promoters containing the GATA element at the LVH stage but that of H3K122 was increased at the HF stage.

Conclusion

Our data indicate that acetylation of H3K122 in globular domain of histones by p300 is the key event of the transition from LVH to HF.