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Direct visualization of cardiac transcription factories reveals regulatory principles of nuclear architecture during pathological remodeling.

ABSTRACT: Heart failure is associated with hypertrophying of cardiomyocytes and changes in transcriptional activity. Studies from rapidly dividing cells in culture have suggested that transcription may be compartmentalized into factories within the nucleus, but this phenomenon has not been tested in vivo and the role of nuclear architecture in cardiac gene regulation is unknown. While alterations to transcription have been linked to disease, little is known about the regulation of the spatial organization of transcription and its properties in the pathological setting. In the present study, we investigate the structural features of endogenous transcription factories in the heart and determine the principles connecting chromatin structure to transcriptional regulation in vivo. Super-resolution imaging of endogenous RNA polymerase II clusters in neonatal and adult cardiomyocytes revealed distinct properties of transcription factories in response to pathological stress: neonatal nuclei demonstrated changes in number of clusters, with parallel increases in nuclear area, while the adult nuclei underwent changes in size and intensity of RNA polymerase II foci. Fluorescence in situ hybridization-based labeling of genes revealed locus-specific relationships between expression change and anatomical localization-with respect to nuclear periphery and heterochromatin regions, both sites associated with gene silencing-in the nuclei of cardiomyocytes in hearts (but not liver hepatocytes) of mice subjected to pathologic stimuli that induce heart failure. These findings demonstrate a role for chromatin organization and rearrangement of nuclear architecture for cell type-specific transcription in vivo during disease. RNA polymerase II ChIP and chromatin conformation capture studies in the same model system demonstrate formation and reorganization of distinct nuclear compartments regulating gene expression. These findings reveal locus-specific compartmentalization of stress-activated, housekeeping and silenced genes in the anatomical context of the endogenous nucleus, revealing basic principles of global chromatin structure and nuclear architecture in the regulation of gene expression in healthy and diseased conditions.

SUBMITTER: Karbassi E

PROVIDER: S-EPMC6644685 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Direct visualization of cardiac transcription factories reveals regulatory principles of nuclear architecture during pathological remodeling.

Karbassi Elaheh E Rosa-Garrido Manuel M Chapski Douglas J DJ Wu Yong Y Ren Shuxun S Wang Yibin Y Stefani Enrico E Vondriska Thomas M TM

Journal of molecular and cellular cardiology 20190208

Heart failure is associated with hypertrophying of cardiomyocytes and changes in transcriptional activity. Studies from rapidly dividing cells in culture have suggested that transcription may be compartmentalized into factories within the nucleus, but this phenomenon has not been tested in vivo and the role of nuclear architecture in cardiac gene regulation is unknown. While alterations to transcription have been linked to disease, little is known about the regulation of the spatial organization ...[more]

PMID: 30742811

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Project description:Heart failure (HF) is a functional lack of myocardial performance due to a loss of molecular control over increases in calcium and ROS, resulting in proteolytic degradative advances and cardiac remodeling. Mitochondria are the molecular powerhouse of cells, shifting the sphere of cardiomyocyte stability and performance. Functional mitochondria rely on the molecular abilities of safety factors such as TFAM to maintain physiological parameters. Mitochondrial transcription factor A (TFAM) creates a mitochondrial nucleoid structure around mtDNA, protecting it from mutation, inhibiting NFAT (ROS activator/hypertrophic stimulator), and transcriptionally activates Serca2a to decrease calcium mishandling. Calpain1 and MMP9 are proteolytic degratory factors that play a major role in cardiomyocyte decline in HF. Current literature depicts major decreases in TFAM as HF progresses. We aim to assess TFAM function against Calpain1 and MMP9 proteolytic activity and its role in cardiac remodeling. To this date, no publication has surfaced describing the effects of aortic banding (AB) as a surgical HF model in TFAM-TG mice. HF models were created via AB in TFAM transgenic (TFAM-TG) and C57BLJ-6 (WT) mice. Eight weeks post AB, functional analysis revealed a successful banding procedure, resulting in cardiac hypertrophy as observed via echocardiography. Pulse wave and color doppler show increased aortic flow rates as well as turbulent flow at the banding site. Preliminary results of cardiac tissue immuno-histochemistry of HF-control mice show decreased TFAM and compensatory increases in Serca2a fluorescent expression, along with increased Calpain1 and MMP9 expression. Protein, RNA, and IHC analysis will further assess TFAM-TG results post-banding. Echocardiography shows more cardiac stability and functionality in HF-induced TFAM-TG mice than the control counterpart. These findings complement our published in vitro results. Overall, this suggests that TFAM has molecular therapeutic potential to reduce protease expression.

Project description:Heart Failure (HF) is the leading cause of death worldwide. Myocardial fibrosis, one of the clinical manifestations implicated in almost every form of heart disease, contributes significantly to HF development. However, there is no approved drug specifically designed to target cardiac fibrosis. Nintedanib (NTB) is an FDA approved tyrosine kinase inhibitor for idiopathic pulmonary fibrosis (IPF) and chronic fibrosing interstitial lung diseases (ILD). The favorable clinical outcome of NTB in IPF patients is well established. Furthermore, NTB is well tolerated in IPF patients irrespective of cardiovascular comorbidities. However, there is a lack of direct evidence to support the therapeutic efficacy and safety of NTB in cardiac diseases. In this study we examined the effects of NTB treatment on cardiac fibrosis and dysfunction using a murine model of HF. Specifically, 10 weeks old C57BL/6J male mice were subjected to Transverse Aortic Constriction (TAC) surgery. NTB was administered once daily by oral gavage (50 mg/kg) till 16 weeks post-TAC. Cardiac function was monitored by serial echocardiography. Histological analysis and morphometric studies were performed at 16 weeks post-TAC. In the control group, systolic dysfunction started developing from 4 weeks post-surgery and progressed till 16 weeks. However, NTB treatment prevented TAC-induced cardiac functional decline. In another experiment, NTB treatment was stopped at 8 weeks, and animals were followed till 16 weeks post-TAC. Surprisingly, NTB's beneficial effect on cardiac function was maintained even after treatment interruption. NTB treatment remarkably reduced cardiac fibrosis as confirmed by Masson's trichrome staining and decreased expression of collagen genes (COL1A1, COL3A1). Compared to the TAC group, NTB treated mice showed a lower HW/TL ratio and cardiomyocyte cross-sectional area. NTB treatment reduced myocardial and systemic inflammation by inhibiting pro-inflammatory subsets and promoting regulatory T cells (Tregs). Our in vitro studies demonstrated that NTB prevents myofibroblast transformation, TGFβ1-induced SMAD3 phosphorylation, and the production of fibrogenic proteins (Fibronectin-1, α-SMA). However, NTB promoted immunosuppressive phenotype in Tregs, and altered vital signaling pathways in isolated cardiac fibroblast and cardiomyocytes, suggesting that its biological effect and underlying cardiac protection mechanisms are not limited to fibroblast and fibrosis alone. Our findings provide a proof of concept for repurposing NTB to combat adverse myocardial fibrosis and encourage the need for further validation in large animal models and subsequent clinical development for HF patients.

Project description:BackgroundHomeodomain-Interacting Protein Kinase 2 (HIPK2) has been reported to maintain basal cardiac function, however, its role in pathological cardiac remodeling remains unclear.MethodsHIPK2 inhibitors (tBID and PKI1H) treated mice and two lines of HIPK2-/- mice were subjected to transverse aortic constriction (TAC). HIPK2 knockdown were performed in neonatal rat cardiomyocytes (NRCMs), neonatal rat cardiac fibroblasts (NRCFs), and human embryonic stem cell-derived cardiomyocytes (hESC-CMs). Microarray analysis was used to screen HIPK2 targets. Overexpression of early growth response 3 (EGR3) and C-type lectin receptor 4D (CLEC4D) were performed in NRCMs, while an activator of Smad3 was used in NRCFs, to rescue the effects of HIPK2 knockdown. Finally, the effects of EGR3 and CLEC4D knockdown by AAV9 in TAC were determined.FindingsHIPK2 was elevated in TAC mice model, as well as cardiomyocyte hypertrophy and NRCFs fibrosis model. Pharmacological and genetic inhibition of HIPK2 improved cardiac function and suppressed cardiac hypertrophy and fibrosis induced by TAC. In vitro, HIPK2 inhibition prevented cardiomyocyte hypertrophic growth and NRCFs proliferation and differentiation. At the mechanistic level, we identified EGR3 and CLEC4D as new targets of HIPK2, which were regulated by ERK1/2-CREB and mediated the protective function of HIPK2 inhibition in cardiomyocytes. Meanwhile, inhibition of phosphorylation of Smad3 was responsible for the suppression of cardiac fibroblasts proliferation and differentiation by HIPK2 inhibition. Finally, we found that inhibition of EGR3 or CLEC4D protected against TAC.InterpretationHIPK2 inhibition protects against pathological cardiac remodeling by reducing EGR3 and CLEC4D with ERK1/2-CREB inhibition in cardiomyocytes, and by suppressing the phosphorylation of Smad3 in cardiac fibroblasts.FundingThis work was supported by the grants from National Key Research and Development Project (2018YFE0113500 to J.X.), National Natural Science Foundation of China (82020108002 and 81911540486 to J.X., 81400647 to MJ Xu), the grant from Science and Technology Commission of Shanghai Municipality (21XD1421300 and 20DZ2255400 to J.X.), the "Dawn" Program of Shanghai Education Commission (19SG34 to J.X.), and Shanghai Sailing Program (21YF1413200 to Q.Z.).

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Direct visualization of cardiac transcription factories reveals regulatory principles of nuclear architecture during pathological remodeling.

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Direct visualization of cardiac transcription factories reveals regulatory principles of nuclear architecture during pathological remodeling.

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