Enhancers are activated by p300/CBP activity-dependent PIC assembly, RNAPII recruitment, and pause release.

The metazoan-specific acetyltransferase p300/CBP is involved in activating signal-induced, enhancer-mediated transcription of cell-type-specific genes. However, the global kinetics and mechanisms of p300/CBP activity-dependent transcription activation remain poorly understood. We performed genome-wide, time-resolved analyses to show that enhancers and super-enhancers are dynamically activated through p300/CBP-catalyzed acetylation, deactivated by the opposing deacetylase activity, and kinetic acetylation directly contributes to maintaining cell identity at very rapid (minutes) timescales. The acetyltransferase activity is dispensable for the recruitment of p300/CBP and transcription factors but essential for promoting the recruitment of TFIID and RNAPII at virtually all enhancers and enhancer-regulated genes. This identifies pre-initiation complex assembly as a dynamically controlled step in the transcription cycle and reveals p300/CBP-catalyzed acetylation as the signal that specifically promotes transcription initiation at enhancer-regulated genes. We propose that p300/CBP activity uses a "recruit-and-release" mechanism to simultaneously promote RNAPII recruitment and pause release and thereby enables kinetic activation of enhancer-mediated transcription.

Coordinated demethylation of H3K9 and H3K27 is required for rapid inflammatory responses of endothelial cells.

Histone H3 lysine-9 di-methylation (H3K9me2) and lysine-27 tri-methylation (H3K27me3) are linked to repression of gene expression, but the functions of repressive histone methylation dynamics during inflammatory responses remain enigmatic. Here, we report that lysine demethylases 7A (KDM7A) and 6A (UTX) play crucial roles in tumor necrosis factor (TNF)-α signaling in endothelial cells (ECs), where they are regulated by a novel TNF-α-responsive microRNA, miR-3679-5p. TNF-α rapidly induces co-occupancy of KDM7A and UTX at nuclear factor kappa-B (NF-κB)-associated elements in human ECs. KDM7A and UTX demethylate H3K9me2 and H3K27me3, respectively, and are both required for activation of NF-κB-dependent inflammatory genes. Chromosome conformation capture-based methods furthermore uncover increased interactions between TNF-α-induced super enhancers at NF-κB-relevant loci, coinciding with KDM7A and UTX recruitments. Simultaneous pharmacological inhibition of KDM7A and UTX significantly reduces leukocyte adhesion in mice, establishing the biological and potential translational relevance of this mechanism. Collectively, these findings suggest that rapid erasure of repressive histone marks by KDM7A and UTX is essential for NF-κB-dependent regulation of genes that control inflammatory responses of ECs.

Lysine demethylase 2B regulates angiogenesis via Jumonji C dependent suppression of angiogenic transcription factors.

Vascular endothelial growth factor (VEGF) signaling plays a central role in vascular development and maintenance of vascular homeostasis. In endothelial cells (ECs), VEGF activates the gene expression of angiogenic transcription factors (TFs), followed by induction of downstream angiogenic responsive genes. Recent findings support that histone modification dynamics contribute to the transcriptional control of genes that are important for EC functions. Lysine demethylase 2B (KDM2B) demethylates histone H3K4me3 and H3K36me2/3 and mediates the monoubiquitination of histone H2AK119. KDM2B functions as a transcriptional repressor in somatic cell reprogramming and tumor development. However, the role of KDM2B in VEGF signaling remains to be elucidated. Here, we show that KDM2B knockdown enhances VEGF-induced angiogenesis in cultured human ECs via increased migration and proliferation. In contrast, ectopic expression of KDM2B inhibits angiogenesis. The function of KDM2B may depend on its catalytic Jumonji C domain. Genome-wide analysis further reveals that KDM2B selectively controls the transcription of VEGF-induced angiogenic TFs that are associated with increased H3K4me3/H3K36me3 and decreased H2AK119ub. These findings suggest an essential role of KDM2B in VEGF signaling in ECs. As dysregulation of VEGF signaling in ECs is involved in various diseases, including cancer, KDM2B may be a potential therapeutic target in VEGF-mediated vasculopathic diseases.

Molecular mechanistic insights: The emerging role of SOXF transcription factors in tumorigenesis and development.

Over the last decade, the development and progress of next-generation sequencers incorporated with classical biochemical analyses have drastically produced novel insights into transcription factors, including Sry-like high-mobility group box (SOX) factors. In addition to their primary functions in binding to and activating specific downstream genes, transcription factors also participate in the dedifferentiation or direct reprogramming of somatic cells to undifferentiated cells or specific lineage cells. Since the discovery of SOX factors, members of the SOXF (SOX7, SOX17, and SOX18) family have been identified to play broad roles, especially with regard to cardiovascular development. More recently, SOXF factors have been recognized as crucial players in determining the cell fate and in the regulation of cancer cells. Here, we provide an overview of research on the mechanism by which SOXF factors regulate development and cancer, and discuss their potential as new targets for cancer drugs while offering insight into novel mechanistic transcriptional regulation during cell lineage commitment.

Sodium-glucose cotransporter 2 inhibition normalizes glucose metabolism and suppresses oxidative stress in the kidneys of diabetic mice.

It is unclear whether long-term sodium-glucose cotransporter 2 (SGLT2) inhibition such as that during the treatment of diabetes has deleterious effects on the kidney. Therefore, we first sought to determine whether abnormal glucose metabolism occurs in the kidneys of 22-week-old BTBR ob/ob diabetic mice. Second, the cumulative effect of chronic SGLT2 inhibition by ipragliflozin and 30% calorie restriction, either of which lowered blood glucose to a similar extent, on renal glucose metabolism was evaluated. Mass spectrometry-based metabolomics demonstrated that these diabetic mice exhibited an abnormal elevation in the renal pools of tricarboxylic acid cycle metabolites. This was almost completely nullified by SGLT2 inhibition and calorie restriction. Moreover, imaging mass spectrometry indicated an increased level of the tricarboxylic acid cycle intermediate, citrate, in the cortex of the diabetic mice. SGLT2 inhibition as well as calorie restriction almost completely eliminated citrate accumulation in the cortex. Furthermore, imaging mass spectrometry revealed that the accumulation of oxidized glutathione in the cortex of the kidneys, prominent in the glomeruli, was also canceled by SGLT2 inhibition and calorie restriction. Effects of these beneficial interventions were consistent with improvements in glomerular damage, such as albuminuria, glomerular hyperfiltration, and mesangial expansion. Tubulointerstitial macrophage infiltration and fibrosis were ameliorated only by calorie restriction, which may have been due to autophagy activation, which was observed only with calorie restriction. Thus, chronic SGLT2 inhibition is efficient in normalizing the levels of accumulated tricarboxylic acid cycle intermediates and increased oxidative stress in the kidneys of diabetic mice.

Applications of the CRISPR-Cas9 system in kidney research.

The recently discovered clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated protein 9 (Cas9) is an RNA-guided DNA nuclease, and has been harnessed for the development of simple, efficient, and relatively inexpensive technologies to precisely manipulate the genomic information in virtually all cell types and organisms. The CRIPSR-Cas9 systems have already been effectively used to disrupt multiple genes simultaneously, create conditional alleles, and generate reporter proteins, even in vivo. The ability of Cas9 to target a specific genomic region has also been exploited for various applications, such as transcriptional regulation, epigenetic control, and chromosome labeling. Here we first describe the molecular mechanism of the RNA-guided DNA targeting by the CRISPR-Cas9 system and then outline the current applications of this system as a genome-editing tool in mice and other species, to better model and study human diseases. We also discuss the practical and potential uses of the CRISPR-Cas9 system in kidney research and highlight the further applications of this technology beyond genome editing. Undoubtedly, the CRISPR-Cas9 system holds enormous potential for revolutionizing and accelerating kidney research and therapeutic applications in the future.

Vascular adhesion protein-1 enhances neutrophil infiltration by generation of hydrogen peroxide in renal ischemia/reperfusion injury.

Vascular adhesion protein-1 (VAP-1) is a unique molecule since it acts as an adhesion molecule as well as an ectoenzyme catalyzing oxidative deamination of primary amines and generates hydrogen peroxide in the extracellular space. While VAP-1 is implicated in various inflammatory diseases, its role in acute kidney injury is less characterized. Here we studied VAP-1 expression in the kidney and the effect of its inhibition in a rat model of renal ischemia/reperfusion injury. VAP-1 was predominantly expressed in pericytes, which released enzymatically active enzyme. In vivo, a specific VAP-1 inhibitor, RTU-1096, significantly ameliorated rat renal ischemia/reperfusion injury and decreased neutrophil infiltration measured 12 hours after injury without altering macrophage or T lymphocyte populations. The protective effect of VAP-1 inhibition was lost in neutrophil-depleted rats, suggesting its inhibition ameliorated renal ischemia/reperfusion injury by suppressing neutrophil infiltration. To investigate whether hydrogen peroxide generated by VAP-1 enzyme reaction enhances neutrophil infiltration, we conducted an under-agarose migration assay with purified human neutrophils. Recombinant human VAP-1 significantly induced neutrophil migration, which was almost completely inhibited by RTU-1096 or catalase. Thus, VAP-1 plays a critical role in the pathophysiology of renal ischemia/reperfusion injury by enhancement of neutrophil infiltration generating a local hydrogen peroxide gradient. Hence, VAP-1 inhibition may be a novel therapy in ischemic acute kidney injury.

Anti-inflammatory role of DPP-4 inhibitors in a nondiabetic model of glomerular injury.

Dipeptidyl peptidase (DPP)-4 is an enzyme that cleaves and inactivates incretin hormones capable of stimulating insulin secretion from pancreatic ß-cells. DPP-4 inhibitors are now widely used for the treatment of type 2 diabetes. Experimental studies have suggested a renoprotective role of DPP-4 inhibitors in various models of diabetic kidney disease, which may be independent of lowering blood glucose levels. In the present study, we examined the effect of DPP-4 inhibitors in the rat Thy-1 glomerulonephritis model, a nondiabetic glomerular injury model. Rats were injected with OX-7 (1.2 mg/kg iv) and treated with the DPP-4 inhibitor alogliptin (20 mg·kg(-1)·day(-1)) or vehicle for 7 days orally by gavage. Alogliptin significantly reduced the number of CD68-positive inflammatory macrophages in the kidney, which was associated with a nonsignificant tendency to ameliorate glomerular injury and reduce proteinuria. Another DPP-4 inhibitor, anagliptin (300 mg·kg(-1)·day(-1) mixed with food) and a glucagon-like peptide-1 receptor agonist, exendin-4 (10 mg/kg sc), similarly reduced CD68-positive macrophage infiltration to the kidney. Furthermore, ex vivo transmigration assays using peritoneal macrophages revealed that exendin-4, but not alogliptin, dose dependently reduced monocyte chemotactic protein-1-stimulated macrophage infiltration. These data suggest that DPP-4 inhibitors reduced macrophage infiltration directly via glucagon-like peptide-1-dependent signaling in the rat Thy-1 nephritis model and indicate that the control of inflammation by DPP-4 inhibitors is useful for the treatment of nondiabetic kidney disease models.

Role of uremic toxins in erythropoiesis-stimulating agent resistance in chronic kidney disease and dialysis patients.

Patients with advanced chronic kidney disease are exposed to uremic toxins. In addition to causing uremic symptoms, uremic toxins accelerate the progression of renal failure. Indoxyl sulfate (IS) increases oxygen consumption in tubules, aggravating hypoxia of the kidney, and progression of the kidney disease. IS also induces endoplasmic reticulum stress and thereby contributes the progression of cellular damages in tubular epithelial cells. Hypoxia-inducible factor (HIF) is a master transcriptional regulator of adaptive responses against hypoxia and regulates expression of erythropoietin (EPO). IS suppresses EPO expression via HIF-dependent and HIF-independent manner. IS impedes the recruitment of transcriptional coactivators to HIF via upregulation of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 through a mechanism of posttranscriptional messenger RNA stabilization. Furthermore, IS induces activating transcription factor 4 via endoplasmic reticulum stress, decreasing EPO expression. Although erythropoiesis-stimulating agent (ESA) resistance is generally defined as lack of responses to exogenous ESA administration, suppression of endogenous production of EPO under uremic conditions may aggravate ESA resistance. Uremia is associated with increased formation of advanced glycation end products (AGE). Studies of transgenic rats overexpressing glyoxalse 1 (GLO1), which detoxifies precursors of advanced glycation end products, demonstrated that glycative stress causes renal senescence and vascular endothelial dysfunction. Glycative stress also suppresses HIF activation making the kidney susceptible to hypoxia as a final common pathway to end-stage kidney disease.

The potential for renoprotection with incretin-based drugs.

Incretin-based drugs, i.e., glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, are widely used for the treatment of type 2 diabetes. In addition to the primary role of incretins in stimulating insulin secretion from pancreatic ß-cells, they have extra pancreatic functions beyond glycemic control. Indeed, recent studies highlight the potential beneficial effects of incretin-based therapy in diabetic kidney disease (DKD). Experimental studies using various diabetic models suggest that incretins protect the vascular endothelium from injury by binding to GLP-1 receptors, thereby ameliorating oxidative stress and the local inflammatory response, which reduces albuminuria and inhibits glomerular sclerosis. In addition, there is some evidence that GLP-1 receptor agonists and DPP-4 inhibitors mediate sodium excretion and diuresis to lower blood pressure. The pleiotropic actions of DPP-4 inhibitors are ascribed primarily to their effects on GLP-1 signaling, but other substrates of DPP-4, such as brain natriuretic peptide and stromal-derived factor-1α, may have roles. In this review, we summarize recent studies of the roles of incretin-based therapy in ameliorating DKD and its complications.

Indoxyl sulfate signals for rapid mRNA stabilization of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) and suppresses the expression of hypoxia-inducible genes in experimental CKD and uremia.

Chronic hypoxia in the tubulointerstitium serves as a final common pathway in progressive renal disease. Circumstantial evidence suggests that hypoxia-inducible factor (HIF)-1 in the ischemic tubules may be functionally inhibited in a chronic kidney disease (CKD) milieu. In this study, we hypothesized that indoxyl sulfate (IS), a uremic toxin, impairs the cellular hypoxic response. In human kidney (HK-2) proximal tubular cells, IS reduced the hypoxic induction of HIF-1 target genes. This effect was not associated with quantitative changes in the HIF-1α protein, but with functional impairment of the HIF-1α C-terminal transactivation domain (CTAD). Among factors that impeded the recruitment of transcriptional coactivators to the HIF-1αCTAD, IS markedly up-regulated Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) through a mechanism of post-transcriptional mRNA stabilization involving the extracellular signal-regulated kinase (ERK) 1/2 pathway. In vivo, disproportionate expression of HIF target genes was demonstrated in several CKD models, which was offset by an oral adsorbent, AST-120. Furthermore, administration of indole reduced the induction of angiogenic, hypoxia-inducible genes in rats with experimental heart failure. Results of these studies reveal a novel role of IS in modulating the transcriptional response of HIF-1 and provide insight into molecular mechanisms underlying progressive nephropathies as well as cardiovascular complications.

Excretion of urinary exosomal AQP2 in rats is regulated by vasopressin and urinary pH.

Urinary exosomes are small vesicles secreted into urine from all renal epithelial cell types and known to contain proteins that are involved in renal secretion and reabsorption. Among these proteins, urinary exosomal aquaporin-2 (AQP2) has been suggested to be useful for diagnosis of renal disease. However, the mechanisms underlying the excretion of urinary exosomal AQP2 are largely unknown. In this study, we examined the mechanisms of urinary exosomal AQP2 excretion in vivo, using diuretics including furosemide (FS), an inhibitor of the sodium-potassium-chloride symporter; acetazolamide (ACTZ), an inhibitor of carbonic anhydrase; OPC-31260 (OPC), a vasopressin type 2 receptor antagonist; and NaHCO3, a urinary alkalizing agent. Samples of urine from rats were collected for 2 h just after treatment with each diuretic, and urinary exosomes were isolated by ultracentrifugation. Urinary exosomal AQP2 excretion was dramatically increased by treatment with FS accompanied by urine acidification or with ACTZ accompanied by urine alkalization. Immunohistochemistry showed that apical localization of AQP2 was clearly evident and the plasma vasopressin level was increased after each treatment. Although treatment with OPC alone had no significant effect, coadministration of OPC completely inhibited the FS-induced and partially reduced the ACTZ-induced responses, respectively. Treatment with NaHCO3 increased the excretion of urinary exosomal AQP2 accompanied by urine alkalization. This increased response was partially inhibited by coadministration of OPC. These data suggest that an increased plasma level of vasopressin promoted the excretion of urinary exosomal AQP2 and that urine alkalinization also increased it independently of vasopressin.

Acetylation of histone H2B marks active enhancers and predicts CBP/p300 target genes.

Chromatin features are widely used for genome-scale mapping of enhancers. However, discriminating active enhancers from other cis-regulatory elements, predicting enhancer strength and identifying their target genes is challenging. Here we establish histone H2B N-terminus multisite lysine acetylation (H2BNTac) as a signature of active enhancers. H2BNTac prominently marks candidate active enhancers and a subset of promoters and discriminates them from ubiquitously active promoters. Two mechanisms underlie the distinct H2BNTac specificity: (1) unlike H3K27ac, H2BNTac is specifically catalyzed by CBP/p300; (2) H2A-H2B, but not H3-H4, are rapidly exchanged through transcription-induced nucleosome remodeling. H2BNTac-positive candidate enhancers show a high validation rate in orthogonal enhancer activity assays and a vast majority of endogenously active enhancers are marked by H2BNTac and H3K27ac. Notably, H2BNTac intensity predicts enhancer strength and outperforms current state-of-the-art models in predicting CBP/p300 target genes. These findings have broad implications for generating fine-grained enhancer maps and modeling CBP/p300-dependent gene regulation.

Potential roles of super enhancers in inflammatory gene transcription.

Acute and chronic inflammation is a basic pathological event that contributes to atherosclerosis, cancer, infectious diseases, and immune disorders. Inflammation is an adaptive process to both external and internal stimuli experienced by the human body. Although the mechanism of gene transcription is highly complicated and orchestrated in a timely and spatial manner, recent developments in next-generation sequencing, genome-editing, cryo-electron microscopy, and single cell-based technologies could provide us with insights into the roles of super enhancers (SEs). Initially, SEs were implicated in determining cell fate; subsequent studies have clarified that SEs are associated with various pathological conditions, including cancer and inflammatory diseases. Recent technological advances have unveiled the molecular mechanisms of SEs, which involve epigenetic histone modifications, chromatin three-dimensional structures, and phase-separated condensates. In this review, we discuss the relationship between inflammation and SEs and the therapeutic potential of SEs for inflammatory diseases.

Bivalent-histone-marked immediate-early gene regulation is vital for VEGF-responsive angiogenesis.

Endothelial cells (ECs) are phenotypically heterogeneous, mainly due to their dynamic response to the tissue microenvironment. Vascular endothelial cell growth factor (VEGF), the best-known angiogenic factor, activates calcium-nuclear factor of activated T cells (NFAT) signaling following acute angiogenic gene transcription. Here, we evaluate the global mapping of VEGF-mediated dynamic transcriptional events, focusing on major histone-code profiles using chromatin immunoprecipitation sequencing (ChIP-seq). Remarkably, the gene loci of immediate-early angiogenic transcription factors (TFs) exclusively acquire bivalent H3K4me3-H3K27me3 double-positive histone marks after the VEGF stimulus. Moreover, NFAT-associated Pax transactivation domain-interacting protein (PTIP) directs bivalently marked TF genes transcription through a limited polymerase II running. The non-canonical polycomb1 variant PRC1.3 specifically binds to and allows the transactivation of PRC2-enriched bivalent angiogenic TFs until conventional PRC1-mediated gene silencing is achieved. Knockdown of these genes abrogates post-natal aberrant neovessel formation via the selective inhibition of indispensable bivalent angiogenic TF gene transcription. Collectively, the reported dynamic histone mark landscape may uncover the importance of immediate-early genes and the development of advanced anti-angiogenic strategies.

PERK inhibition attenuates vascular remodeling in pulmonary arterial hypertension caused by BMPR2 mutation.

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by excessive pulmonary vascular remodeling. However, despite advances in therapeutic strategies, patients with PAH bearing mutations in the bone morphogenetic protein receptor type 2 (BMPR2)-encoding gene present severe phenotypes and outcomes. We sought to investigate the effect of PER-like kinase (PERK), which participates in one of three major pathways associated with the unfolded protein response (UPR), on PAH pathophysiology in BMPR2 heterozygous mice. BMPR2 heterozygosity in pulmonary artery smooth muscle cells (PASMCs) decreased the abundance of the antiapoptotic microRNA miR124-3p through the arm of the UPR mediated by PERK. Hypoxia promoted the accumulation of unfolded proteins in BMPR2 heterozygous PASMCs, resulting in increased PERK signaling, cell viability, cellular proliferation, and glycolysis. Proteomic analyses revealed that PERK ablation suppressed PDGFRß-STAT1 signaling and glycolysis in hypoxic BMPR2 heterozygous PASMCs. Furthermore, PERK ablation or PERK inhibition ameliorated pulmonary vascular remodeling in the Sugen/chronic hypoxia model of PAH, irrespective of BMPR2 status. Hence, these findings suggest that PERK inhibition is a promising therapeutic strategy for patients with PAH with or without BMPR2 mutation.

Inhibition of cardiac PERK signaling promotes peripartum cardiac dysfunction.

Peripartum cardiomyopathy (PPCM) is a life-threatening heart failure occurring in the peripartum period. Although mal-angiogenesis, induced by the 16-kDa N-terminal prolactin fragment (16 K PRL), is involved in the pathogenesis, the effect of full-length prolactin (23 K PRL) is poorly understood. We transfected neonate rat cardiomyocytes with plasmids containing 23 K PRL or 16 K PRL in vitro and found that 23 K PRL, but not 16 K PRL, upregulated protein kinase RNA-like endoplasmic reticulum kinase (PERK) signaling, and hypoxia promoted this effect. During the perinatal period, cardiomyocyte-specific PERK homogenous knockout (CM-KO) mice showed PPCM phenotypes after consecutive deliveries. Downregulation of PERK or JAK/STAT signaling and upregulation of apoptosis were observed in CM-KO mouse hearts. Moreover, in bromocriptine-treated CM-KO mice, cardiac function did not improve and cardiomyocyte apoptosis was not suppressed during the peripartum period. These results demonstrate that interaction between 23 K PRL and PERK signaling is cardioprotective during the peripartum term.

PERK-Mediated Suppression of microRNAs by Sildenafil Improves Mitochondrial Dysfunction in Heart Failure.

Oxidative/nitrosative stress is a major trigger of cardiac dysfunction, involving the unfolded protein response and mitochondrial dysfunction. Activation of nitric oxide-cyclic guanosine monophosphate-protein kinase G signaling by sildenafil improves cardiac mal-remodeling during pressure-overload-induced heart failure. Transcriptome analysis was conducted in failing hearts with or without sildenafil treatment. Protein kinase R-like endoplasmic reticulum (ER) kinase (PERK) downstream signaling pathways, EIF2 and NRF2, were significantly altered. Although EIF2 signaling was suppressed, NRF2 signaling was upregulated, inhibiting the maturation of miR 24-3p through EGFR-mediated Ago2 phosphorylation. To study the effect of sildenafil on these pathways, we generated cardiac-specific PERK knockout mice. In these mice, sildenafil could not inhibit the maturations, the nuclear translocation of NRF2 was suppressed, and mitochondrial dysfunction advanced. Altogether, these results show that PERK-mediated suppression of miRNAs by sildenafil is vital for maintaining mitochondrial homeostasis through NRF2-mediated oxidative stress response.