Oxidation of HDAC4 by Nox4-derived H2O2 maintains tube formation by endothelial cells

Redox regulation of chromatin remodelling in plants

Changes in the cellular redox balance that occur during plant responses to unfavourable environmental conditions significantly affect a myriad of redox-sensitive processes, including those that impact on the epigenetic state of the chromatin. Various epigenetic factors, like histone modifying enzymes, chromatin remodelers, and DNA methyltransferases can be targeted by oxidative posttranslational modifications. As their combined action affects the epigenetic regulation of gene expression, they form an integral part of plant responses to (a)biotic stress. Epigenetic changes triggered by unfavourable environmental conditions are intrinsically linked with primary metabolism that supplies intermediates and donors, such acetyl-CoA and S-adenosyl-methionine, that are critical for the epigenetic decoration of histones and DNA. Here, we review the recent advances in our understanding of redox regulation of chromatin remodelling, dynamics of epigenetic marks, and the interplay between epigenetic control of gene expression, redox signalling and primary metabolism within an (a)biotic stress context.

Zinc-Dependent Histone Deacetylases in Lung Endothelial Pathobiology

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and, as such, provides a semi-selective barrier between the blood and the interstitial space. Compromise of the lung EC barrier due to inflammatory or toxic events may result in pulmonary edema, which is a cardinal feature of acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS). The EC functions are controlled, at least in part, via epigenetic mechanisms mediated by histone deacetylases (HDACs). Zinc-dependent HDACs represent the largest group of HDACs and are activated by Zn2+. Members of this HDAC group are involved in epigenetic regulation primarily by modifying the structure of chromatin upon removal of acetyl groups from histones. In addition, they can deacetylate many non-histone histone proteins, including those located in extranuclear compartments. Recently, the therapeutic potential of inhibiting zinc-dependent HDACs for EC barrier preservation has gained momentum. However, the role of specific HDAC subtypes in EC barrier regulation remains largely unknown. This review aims to provide an update on the role of zinc-dependent HDACs in endothelial dysfunction and its related diseases. We will broadly focus on biological contributions, signaling pathways and transcriptional roles of HDACs in endothelial pathobiology associated mainly with lung diseases, and we will discuss the potential of their inhibitors for lung injury prevention.

Oxygen-consumption based quantification of chemogenetic H2O2 production in live human cells

Reactive Oxygen Species (ROS) in the form of H2O2 can act both as physiological signaling molecules as well as damaging agents, depending on their concentration and localization. The downstream biological effects of H2O2 were often studied making use of exogenously added H2O2, generally as a bolus and at supraphysiological levels. But this does not mimic the continuous, low levels of intracellular H2O2 production by for instance mitochondrial respiration. The enzyme d-Amino Acid Oxidase (DAAO) catalyzes H2O2 formation using d-amino acids, which are absent from culture media, as a substrate. Ectopic expression of DAAO has recently been used in several studies to produce inducible and titratable intracellular H2O2. However, a method to directly quantify the amount of H2O2 produced by DAAO has been lacking, making it difficult to assess whether observed phenotypes are the result of physiological or artificially high levels of H2O2. Here we describe a simple assay to directly quantify DAAO activity by measuring the oxygen consumed during H2O2 production. The oxygen consumption rate (OCR) of DAAO can directly be compared to the basal mitochondrial respiration in the same assay, to estimate whether the ensuing level of H2O2 production is within the range of physiological mitochondrial ROS production. In the tested monoclonal RPE1-hTERT cells, addition of 5 mM d-Ala to the culture media amounts to a DAAO-dependent OCR that surpasses ∼5% of the OCR that stems from basal mitochondrial respiration and hence produces supra-physiological levels of H2O2. We show that the assay can also be used to select clones that express differentially localized DAAO with the same absolute level of H2O2 production to be able to discriminate the effects of H2O2 production at different subcellular locations from differences in total oxidative burden. This method therefore greatly improves the interpretation and applicability of DAAO-based models, thereby moving the redox biology field forward.

(Pro)Renin Receptor Decoy Peptide PRO20 Protects against Oxidative Renal Damage Induced by Advanced Oxidation Protein Products

Chronic kidney disease (CKD) is associated with advanced oxidation protein products (AOPPs). A recent study has shown that AOPP-induced renal tubular injury is mediated by the (pro)renin receptor (PRR). However, it is unclear whether the PRR decoy inhibitor PRO20 can protect against renal damage related to AOPPs in vivo. In this study, we examined the role of the PRR in rats with AOPP-induced renal oxidative damage. Male SD rats were subjected to unilateral nephrectomy, and after a four-day recuperation period, they were randomly divided into four groups (n = 6/group) for four weeks: control (CTR), unmodified rat serum albumin (RSA, 50 mg/kg/day via tail-vein injection), AOPPs-RSA (50 mg/kg/day via tail-vein injection), and AOPPs-RSA + PRO20 (50 mg/kg/day via tail-vein injection + 500 μg/kg/day via subcutaneous injection) groups. PRO20 was administered 3 days before AOPPs-RSA injection. Renal histopathology evaluation was performed by periodic acid–Schiff (PAS) staining, and biochemical parameters related to renal injury and oxidative stress biomarkers were evaluated. The expression of related indicators was quantified by RT-qPCR and immunoblotting analysis. In the results, rats in the AOPPs-RSA group exhibited higher levels of albuminuria, inflammatory cell infiltration, and tubular dilation, along with upregulation of oxidative stress, profibrotic and proinflammatory factors, and elevation of AOPP levels. Meanwhile, in the PRO20 group, these were significantly reduced. Moreover, the levels of almost all components of the renin-angiotensin system (RAS) and Nox4-dependent H2O2 production in urine and the kidneys were elevated by AOPPs-RSA, while they were suppressed by PRO20. Furthermore, AOPPs-RSA rats showed elevated kidney expression of the PRR and soluble PRR (sPRR) and increased renal excretion of sPRR. In summary, these findings suggest that PRR inhibition may serve as a protective mechanism against AOPP-induced nephropathy by inhibiting the intrarenal RAS and Nox4-derived H2O2 mechanisms.

HDAC4 in cancer: A multitasking platform to drive not only epigenetic modifications

Controlling access to genomic information and maintaining its stability are key aspects of cell life. Histone acetylation is a reversible epigenetic modification that allows access to DNA and the assembly of protein complexes that regulate mainly transcription but also other activities. Enzymes known as histone deacetylases (HDACs) are involved in the removal of the acetyl-group or in some cases of small hydrophobic moieties from histones but also from the non-histone substrate. The main achievement of HDACs on histones is to repress transcription and promote the formation of more compact chromatin. There are 18 different HDACs encoded in the human genome. Here we will discuss HDAC4, a member of the class IIa family, and its possible contribution to cancer development.

The role of class IIa histone deacetylases in regulating endothelial function

Vascular endothelial cells (ECs) are monolayer cells located in the inner layer of the blood vessel. Endothelial function is crucial in maintaining local and systemic homeostasis and is precisely regulated by sophisticated signaling pathways and epigenetic regulation. Endothelial dysfunctions are the main factors for the pathophysiological process of cardiovascular and cerebrovascular diseases like atherosclerosis, hypertension, and stroke. In these pathologic processes, histone deacetylases (HDACs) involve in epigenetic regulation by removing acetyl groups from lysine residues of histones and regulating downstream gene expression. Among all HDACs, Class IIa HDACs (HDAC4, 5, 7, 9) contain only an N-terminal regulatory domain, exert limited HDAC activity, and present tissue-specific gene regulation. Here, we discuss and summarize the current understanding of this distinct subfamily of HDACs in endothelial cell functions (such as angiogenesis and immune response) with their molecular underpinnings. Furthermore, we also present new thoughts for further investigation of HDAC inhibitors as a potential treatment in several vascular diseases.

Peripheral vascular remodeling during ischemia

About 230 million people worldwide suffer from peripheral arterial disease (PAD), and the prevalence is increasing year by year. Multiple risk factors, including smoking, dyslipidemia, diabetes, and hypertension, can contribute to the development of PAD. PAD is typically characterized by intermittent claudication and resting pain, and there is a risk of severe limb ischemia, leading to major adverse limb events, such as amputation. Currently, a major progress in the research field of the pathogenesis of vascular remodeling, including atherosclerosis and neointima hyperplasia has been made. For example, the molecular mechanisms of endothelial dysfunction and smooth muscle phenotype switching have been described. Interestingly, a series of focused studies on fibroblasts of the vessel wall has demonstrated their impact on smooth muscle proliferation and even endothelial function via cell-cell communications. In this review, we aim to focus on the functional changes of peripheral arterial cells and the mechanisms of the pathogenesis of PAD. At the same time, we summarize the progress of the current clinical treatment and potential therapeutic methods for PAD and shine a light on future perspectives.

Nox4 promotes endothelial differentiation through chromatin remodeling

RATIONALE

Nox4 is a constitutively active NADPH oxidase that constantly produces low levels of H2O2. Thereby, Nox4 contributes to cell homeostasis and long-term processes, such as differentiation. The high expression of Nox4 seen in endothelial cells contrasts with the low abundance of Nox4 in stem cells, which are accordingly characterized by low levels of H2O2. We hypothesize that Nox4 is a major contributor to endothelial differentiation, is induced during the process of differentiation, and facilitates homeostasis of the resulting endothelial cells.

OBJECTIVE

To determine the role of No×4 in differentiation of murine inducible pluripotent stem cells (miPSC) into endothelial cells (ECs).

METHODS AND RESULTS

miPSC, generated from mouse embryonic wildtype (WT) and Nox4-/- fibroblasts, were differentiated into endothelial cells (miPSC-EC) by stimulation with BMP4 and VEGF. During this process, Nox4 expression increased and knockout of Nox4 prolonged the abundance of pluripotency markers, while expression of endothelial markers was delayed in differentiating Nox4-depleted iPSCs. Eventually, angiogenic capacity of iPSC-ECs is reduced in Nox4 deficient cells, indicating that an absence of Nox4 diminishes stability of the reached phenotype. As an underlying mechanism, we identified JmjD3 as a redox target of Nox4. iPSC-ECs lacking Nox4 display a lower nuclear abundance of the histone demethylase JmjD3, resulting in an increased triple methylation of histone 3 (H3K27me3), which serves as a repressive mark for several genes involved in differentiation.

CONCLUSIONS

Nox4 promotes differentiation of miPSCs into ECs by oxidation of JmjD3 and subsequent demethylation of H3K27me3, which forced endothelial differentiation and stability.

HDAC4 promotes the growth and metastasis of gastric cancer via autophagic degradation of MEKK3

Background

Histone deacetylases (HDACs) have been shown to be involved in tumorigenesis, but their precise role and molecular mechanisms in gastric cancer (GC) have not yet been fully elucidated.

Methods

Bioinformatics screening analysis, qRT-PCR, and immunohistochemistry (IHC) were used to identify the expression of HDAC4 in GC. In vitro and in vivo functional assays illustrated the biological function of HDAC4. RNA-seq, GSEA pathway analysis, and western blot revealed that HDAC4 activated p38 MAPK signalling. Immunofluorescence, western blot, and IHC verified the effect of HDAC4 on autophagy. ChIP and dual-luciferase reporter assays demonstrated that the transcriptional regulation mechanism of HDAC4 and ATG4B.

Results

HDAC4 is upregulated in GC and correlates with poor prognosis. In vitro and in vivo assays showed that HDAC4 contributes to the malignant phenotype of GC cells. HDAC4 inhibited the MEF2A-driven transcription of ATG4B and prevented MEKK3 from p62-dependent autophagic degradation, thus activating p38 MAPK signalling. Reciprocally, the downstream transcription factor USF1 enhanced HDAC4 expression by regulating HDAC4 promoter activity, forming a positive feedback loop and continuously stimulating HDAC4 expression and p38 MAPK signalling activation.

Conclusion

HDAC4 plays an oncogenic role in GC, and HDAC4-based targeted therapy would represent a novel strategy for GC treatment.

HDAC6/FOXP3/HNF4α axis promotes bile acids induced gastric intestinal metaplasia

Bile reflux is one of the main causes of gastric intestinal metaplasia (IM) which is an important precancerous lesion. Our previous study has shown that ectopic expression of Histone deacetylase 6 (HDAC6) promotes the activation of intestinal markers in bile acids (BA) induced gastric IM cells; however, the mechanism underlying how HDAC6-mediated epigenetic modifications regulate intestinal markers is not clear. In this study, we aimed to investigate the downstream targets of HDAC6 and the underlying mechanism in the process of BA induced gastric IM. We demonstrated that deoxycholic acid (DCA) upregulated HDAC6 in gastric cells, which further inhibited the transcription of Forkhead box protein 3 (FOXP3). Then, FOXP3 transcriptionally inhibited Hepatocyte nuclear factor 4α (HNF4α), which further inhibits the expression of downstream intestinal markers. These molecules have been shown to be clinically relevant, as FOXP3 levels were negatively correlated with HDAC6 and HNF4α in IM tissues. Transgenic mice experiments confirmed that HNF4α overexpression combined with DCA treatment induced gastric mucosa to secrete intestinal mucus and caused an abnormal mucosal structure. Our findings suggest that HDAC6 reduces FOXP3 through epigenetic modification, thus forming a closed loop HDAC6/FOXP3/HNF4α to promote gastric IM. Inhibition of HDAC6 may be a potential approach to prevent gastric IM in patients with bile reflux.

Hydrogen peroxide-induced stress acclimation in plants

Among all reactive oxygen species (ROS), hydrogen peroxide (H2O2) takes a central role in regulating plant development and responses to the environment. The diverse role of H2O2 is achieved through its compartmentalized synthesis, temporal control exerted by the antioxidant machinery, and ability to oxidize specific residues of target proteins. Here, we examine the role of H2O2 in stress acclimation beyond the well-studied transcriptional reprogramming, modulation of plant hormonal networks and long-distance signalling waves by highlighting its global impact on the transcriptional regulation and translational machinery.

Post-translational modifications talk and crosstalk to class IIa histone deacetylases

Epigenetic modifications, such as histone or DNA modifications are key regulators of gene transcription and changes are often associated with maladaptive processes underlying cardiovascular disease. Epigenetic regulators therefore likely play a crucial role in cardiomyocyte homeostasis and facilitate the cellular adaption to various internal and external stimuli, responding to different intercellular and extracellular cues. Class IIa histone deacetylases are a class of epigenetic regulators that possess a myriad of post-transcriptional modification sites that modulate their activity in response to oxidative stress, altered catecholamine signalling or changes in the cellular metabolism. This review summaries the known reversible, post-translational modifications (PTMs) of class IIa histone deacetylases (HDACs) that ultimately drive transcriptional changes in homeostasis and disease. We also highlight the idea of a crosstalk of various PTMs on class IIa HDACs potentially leading to compensatory or synergistic effects on the class IIa HDAC-regulated cell behavior.

Physiological interrelationships between NADPH oxidases and chromatin remodelling

The epigenetic landscape describes the chromatin structure of the eukaryotic genome and is therefore the major determinant of gene transcription and hence cellular phenotype. The molecular processes which act to shape the epigenetic landscape through cellular differentiation are thus central to cellular determination and specification. In addition, cellular adaptation to (patho)-physiological stress requires dynamic and reversible chromatin remodelling. It is becoming clear that redox-dependent molecular mechanisms are important determinants of this epigenetic regulation. NADPH oxidases generate reactive oxygen species (ROS) to activate redox-dependent signalling pathways in response to extracellular and intracellular environmental cues. This mini review aims to summarise the current knowledge of the role of NADPH oxidases in redox-dependent chromatin remodelling, and how epigenetic changes might feedback and impact upon the transcriptional expression of these ROS-producing enzymes themselves. The potential physiological significance of this relationship in the control of cellular differentiation and homeostasis by Nox4, specifically, is discussed.

NOX4 Mediates Pseudomonas aeruginosa-Induced Nuclear Reactive Oxygen Species Generation and Chromatin Remodeling in Lung Epithelium

Pseudomonas aeruginosa (PA) infection increases reactive oxygen species (ROS), and earlier, we have shown a role for NADPH oxidase-derived ROS in PA-mediated lung inflammation and injury. Here, we show a role for the lung epithelial cell (LEpC) NOX4 in PA-mediated chromatin remodeling and lung inflammation. Intratracheal administration of PA to Nox4flox/flox mice for 24 h caused lung inflammatory injury; however, epithelial cell-deleted Nox4 mice exhibited reduced lung inflammatory injury, oxidative stress, secretion of pro-inflammatory cytokines, and decreased histone acetylation. In LEpCs, NOX4 was localized both in the cytoplasmic and nuclear fractions, and PA stimulation increased the nuclear NOX4 expression and ROS production. Downregulation or inhibition of NOX4 and PKC δ attenuated the PA-induced nuclear ROS. PA-induced histone acetylation was attenuated by Nox4-specific siRNA, unlike Nox2. PA stimulation increased HDAC1/2 oxidation and reduced HDAC1/2 activity. The PA-induced oxidation of HDAC2 was attenuated by N-acetyl-L-cysteine and siRNA specific for Pkc δ, Sphk2, and Nox4. PA stimulated RAC1 activation in the nucleus and enhanced the association between HDAC2 and RAC1, p-PKC δ, and NOX4 in LEpCs. Our results revealed a critical role for the alveolar epithelial NOX4 in mediating PA-induced lung inflammatory injury via nuclear ROS generation, HDAC1/2 oxidation, and chromatin remodeling.

The Relationship Between Reactive Oxygen Species and Endothelial Cell Metabolism

Cardiovascular disease (CVD) has been the leading cause of death for many decades, highlighting the importance of new research and treatments in the field. The role of hypoxia and subsequent free radical production [reactive oxygen species (ROS)] have become an area of particular interest in CVD. Interestingly, our laboratory and other laboratories have recently reported positive roles of subcellular ROS in modulating endothelial cell (EC) metabolism, proliferation, and angiogenesis. This bidirectional relationship between ROS and EC metabolism, as well as functional changes, continues to be an area of active research. Interestingly, ECs have been shown to rely on anaerobic processes for ATP generation, despite their direct access to oxygen. This paradox has proven to be beneficial as the major reliance on glycolysis produces ATP faster, preserves oxygen, and results in reduced ROS levels in contrast to oxidative phosphorylation. This review will address the relationship between ROS and carbohydrate, lipid, and nitrogen metabolism in ECs, and their effects on EC phenotype such as sprouting angiogenesis.