Class II HDAC inhibition hampers hepatic stellate cell activation by induction of microRNA-29

The interactive role of microRNA and other non-coding RNA in hepatitis B (HBV) associated fibrogenesis

One of the outstanding features of chronic hepatitis B infection (CHB) is its strong association with liver fibrosis. CHB induced inflammation and injury trigger multiple biochemical and physical changes that include the promotion of a wide range of cytokines, chemokines and growth factors that activate hepatic stellate cells (HSCs) CHB induced activation of hepatic stellate cells (HSCs) is regarded as a central event in fibrogenesis to directly promote the synthesis of myofibroblasts and the expression of a range of materials to repair injured liver tissue. Fibrogenesis is modulated by the mainstream epigenetic machinery, as well as by non-coding RNA (ncRNA) that are often referred to as an ancillary epigenetic response to fine tune gene expression. Although extensive research has explained the regulatory role of ncRNA in liver fibrogenesis, most of this research relates to non-CHB etiologies. This review paper outlines the complex interactive regulatory role of microRNA (miRNA) and their interaction with long non-coding RNA (lncRNA), circular RNA (circRNA) and the mainstream epigenetic machinery in CHB induced liver fibrosis. The paper also illustrates some of the difficulties involved in translating candidate ncRNA into approved drugs or diagnostic tools. In conclusion, the important regulatory role of ncRNA in CHB induced liver fibrosis warrants further investigation to exploit their undoubted potential as diagnostic and therapeutic agents.

Establishing validated RT-qPCR workflow for the analysis of oligodendrocyte gene expression in the developing murine brain

Myelination is essential for the proper conduction of impulses across neuronal networks. Mature, myelinating glia differentiate from progenitor cells through distinct stages that correspond to oligodendrocyte-specific gene expression markers. Reverse transcription quantiatative PCR (RT-qPCR) is a common technique used to quantify gene expression across cell development; however, a lack of standardization and transparency in methodology may lead to irreproducible data. Here, we have designed and validated RT-qPCR assays for oligodendrocyte genes and reference genes in the developing C57BL6/J mouse brain that align with the MIQE guidelines, including quality controls for primer specificity, temperature dependence, and efficiency. A panel of eight commonly used reference genes was ranked using a series of reference gene stability methods that consistently identified Gapdh, Sdha, Hmbs, Hprt1, and Pgk1 as the top candidates for normalization across brain regions. In the cerebrum, myelin genes peaked in expression at postnatal day 21, which corresponds to the peak of developmental myelination. The gene expression patterns from the brain homogenate were in agreement with previously reported RNA-seq and microarray profiles from oligodendrocyte lineage cells. The validated RT-qPCR assays begin to build a framework for future investigation into the molecular mechanisms that regulate myelination in mouse models of brain development, aging, and disease.

The Role of Zinc on Liver Fibrosis by Modulating ZIP14 Expression Throughout Epigenetic Regulatory Mechanisms

Zinc plays a pivotal role in tissue regeneration and maintenance being as a central cofactor in a plethora of enzymatic activities. Hypozincemia is commonly seen with chronic liver disease and is associated with an increased risk of liver fibrosis development and hepatocellular carcinoma. Previously favorable effects of zinc supplementation on liver fibrosis have been shown. However, the underlying mechanism of this effect is not elucidated. Liver fibrosis was induced in mice by using CCl4 injection, followed by treatment with zinc chloride (ZnCl2) both at fibrotic and sham groups, and their hepatocytes were isolated. Our results showed that the administration of ZnCl2 restored the depleted cytosolic zinc levels in the hepatocytes isolated from the fibrotic group. Also, alpha-smooth muscle actin (αSMA) expression in hepatocytes was decreased, indicating a reversal of the fibrotic process. Notably, ZIP14 expression significantly increased in the fibrotic group following ZnCl2 treatment, whereas in the sham group ZIP14 expression decreased. Chromatin immunoprecipitation (ChIP) experiments revealed an increased binding percentage of Metal-regulatory transcription factor 1 (MTF1) on ZIP14 promoter in the hepatocytes isolated from fibrotic mice compared to the sham group after ZnCl2 administration. In the same group, the binding percentage of the histone deacetylase HDAC4 on ZIP14 promoter decreased. Our results suggest that the ZnCl2 treatment ameliorates liver fibrosis by elevating intracellular zinc levels through MTF1-mediated regulation of ZIP14 expression and the reduction of ZIP14 deacetylation via HDAC4. The restoration of intracellular zinc concentrations and the modulation of ZIP14 expression by zinc orchestrated through MTF1 and HDAC4, appear to be essential determinants of the therapeutic response in hepatic fibrosis. These findings pave the way for potential novel interventions targeting zinc-related pathways for the treatment of liver fibrosis and associated conditions.

The landscape of histone modification in organ fibrosis

An increase in fibrous connective tissue and a decrease in parenchymal cells in organ tissues are the primary pathological alterations linked to organ fibrosis. If fibrosis is not treated, organ structure is destroyed, function can decline, or even fail, posing a serious risk to human life and health. Numerous organs develop fibrosis, and organ fibroproliferative illnesses account for almost 45% of patient deaths from various diseases in the industrialized world, as well as a major cause of disability and mortality in many other diseases. Recently, it has become evident that histone modification is an important way to regulate gene expression in organ fibrosis. Histone modifications alter the structure of chromatin, thereby affecting gene accessibility. Histone acetylation modifications relax chromatin, making it easier for gene transcription factors to access DNA, thereby promoting gene transcription. In addition, histone modifications recruit other proteins to interact with chromatin to form complexes that further regulate gene expression. Histone methylation modifications recruit methylation-reading proteins that recognize methylation marks and alter gene expression status. It not only affects the normal physiological function of cells, but also plays an important role in organ fibrosis. This article reviews the important role played by histone modifications in organ fibrosis and potential therapeutic approaches.

Histone deacetylases: potential therapeutic targets for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease of unknown origin and the most common interstitial lung disease. However, therapeutic options for IPF are limited, and novel therapies are urgently needed. Histone deacetylases (HDACs) are enzymes that participate in balancing histone acetylation activity for chromatin remodeling and gene transcription regulation. Increasing evidence suggests that the HDAC family is linked to the development and progression of chronic fibrotic diseases, including IPF. This review aims to summarize available information on HDACs and related inhibitors and their potential applications in treating IPF. In the future, HDACs may serve as novel targets, which can aid in understanding the etiology of PF, and selective inhibition of single HDACs or disruption of HDAC genes may serve as a strategy for treating PF.

Mechanistic insight into the hepatoprotective effect of Moringa oleifera Lam leaf extract and telmisartan against carbon tetrachloride-induced liver fibrosis: plausible roles of TGF-β1/SMAD3/SMAD7 and HDAC2/NF-κB/PPARγ pathways

The increasing prevalence and limited therapeutic options for liver fibrosis necessitates more medical attention. Our study aims to investigate the potential molecular targets by which Moringa oleifera Lam leaf extract (Mor) and/or telmisartan (Telm) alleviate carbon tetrachloride (CCl4)-induced liver fibrosis in rats. Liver fibrosis was induced in male Sprague-Dawley rats by intraperitoneal injection of 50% CCl4 (1 ml/kg) every 72 hours, for 8 weeks. Intoxicated rats with CCl4 were simultaneously orally administrated Mor (400 mg/kg/day for 8 weeks) and/or Telm (10 mg/kg/day for 8 weeks). Treatment of CCl4-intoxicated rats with Mor/Telm significantly reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities compared to CCl4 intoxicated group (P < 0.001). Additionally, Mor/Telm treatment significantly reduced the level of hepatic inflammatory, profibrotic, and apoptotic markers including; nuclear factor-kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), transforming growth factor-βeta1 (TGF-β1), and caspase-3. Interestingly, co-treatment of CCl4-intoxicated rats with Mor/Telm downregulated m-RNA expression of histone deacetylase 2 (HDAC2) (71.8%), and reduced protein expression of mothers against decapentaplegic homolog 3 (p-SMAD3) (70.6%) compared to untreated animals. Mor/Telm regimen also elevated p-SMAD7 protein expression as well as m-RNA expression of peroxisome proliferator-activated receptor γ (PPARγ) (3.6 and 3.1 fold, respectively p < 0.05) compared to CCl4 intoxicated group. Histopathological picture of the liver tissue intoxicated with CCl4 revealed marked improvement by Mor/Telm co-treatment. Conclusively, this study substantiated the hepatoprotective effect of Mor/Telm regimen against CCl4-induced liver fibrosis through suppression of TGF-β1/SMAD3, and HDAC2/NF-κB signaling pathways and up-regulation of SMAD7 and PPARγ expression.

LP340, a novel histone deacetylase inhibitor, decreases liver injury and fibrosis in mice: role of oxidative stress and microRNA-23a

Effective therapy for liver fibrosis is lacking. Here, we examined whether LP340, the lead candidate of a new-generation of hydrazide-based HDAC1,2,3 inhibitors (HDACi), decreases liver fibrosis. Liver fibrosis was induced by CCl4 treatment and bile duct ligation (BDL) in mice. At 6 weeks after CCl4, serum alanine aminotransferase increased, and necrotic cell death and leukocyte infiltration occurred in the liver. Tumor necrosis factor-α and myeloperoxidase markedly increased, indicating inflammation. After 6 weeks, α-smooth muscle actin (αSMA) and collagen-1 expression increased by 80% and 575%, respectively, indicating hepatic stellate cell (HSC) activation and fibrogenesis. Fibrosis detected by trichrome and Sirius-red staining occurred primarily in pericentral regions with some bridging fibrosis in liver sections. 4-Hydroxynonenal adducts (indicator of oxidative stress), profibrotic cytokine transforming growth factor-β (TGFβ), and TGFβ downstream signaling molecules phospho-Smad2/3 also markedly increased. LP340 attenuated indices of liver injury, inflammation, and fibrosis markedly. Moreover, Ski-related novel protein-N (SnoN), an endogenous inhibitor of TGFβ signaling, decreased, whereas SnoN expression suppressor microRNA-23a (miR23a) increased markedly. LP340 (0.05 mg/kg, ig., daily during the last 2 weeks of CCl4 treatment) decreased 4-hydroxynonenal adducts and miR23a production, blunted SnoN decreases, and inhibited the TGFβ/Smad signaling. By contrast, LP340 had no effect on matrix metalloproteinase-9 expression. LP340 increased histone-3 acetylation but not tubulin acetylation, indicating that LP340 inhibited Class-I but not Class-II HDAC in vivo. After BDL, focal necrosis, inflammation, ductular reactions, and portal and bridging fibrosis occurred at 2 weeks, and αSMA and collagen-1 expression increased by 256% and 560%, respectively. LP340 attenuated liver injury, ductular reactions, inflammation, and liver fibrosis. LP340 also decreased 4-hydroxynonenal adducts and miR23a production, prevented SnoN decreases, and inhibited the TGFβ/Smad signaling after BDL. In vitro, LP340 inhibited immortal human hepatic stellate cells (hTERT-HSC) activation in culture (αSMA and collagen-1 expression) as well as miR23a production, demonstrating its direct inhibitory effects on HSC. In conclusions, LP340 is a promising therapy for both portal and pericentral liver fibrosis, and it works by inhibiting oxidative stress and decreasing miR23a.

Epigenetic modification in liver fibrosis: Promising therapeutic direction with significant challenges ahead

Liver fibrosis, characterized by scar tissue formation, can ultimately result in liver failure. It's a major cause of morbidity and mortality globally, often associated with chronic liver diseases like hepatitis or alcoholic and non-alcoholic fatty liver diseases. However, current treatment options are limited, highlighting the urgent need for the development of new therapies. As a reversible regulatory mechanism, epigenetic modification is implicated in many biological processes, including liver fibrosis. Exploring the epigenetic mechanisms involved in liver fibrosis could provide valuable insights into developing new treatments for chronic liver diseases, although the current evidence is still controversial. This review provides a comprehensive summary of the regulatory mechanisms and critical targets of epigenetic modifications, including DNA methylation, histone modification, and RNA modification, in liver fibrotic diseases. The potential cooperation of different epigenetic modifications in promoting fibrogenesis was also highlighted. Finally, available agonists or inhibitors regulating these epigenetic mechanisms and their potential application in preventing liver fibrosis were discussed. In summary, elucidating specific druggable epigenetic targets and developing more selective and specific candidate medicines may represent a promising approach with bright prospects for the treatment of chronic liver diseases.

HDAC9 as a Privileged Target: Reviewing its Role in Different Diseases and Structure-activity Relationships (SARs) of its Inhibitors

HDAC9 is a histone deacetylase enzyme belonging to the class IIa of HDACs which catalyses histone deacetylation. HDAC9 inhibit cell proliferation by repairing DNA, arresting the cell cycle, inducing apoptosis, and altering genetic expression. HDAC9 plays a significant part in human physiological system and are involved in various type of diseases like cancer, diabetes, atherosclerosis and CVD, autoimmune response, inflammatory disease, osteoporosis and liver fibrosis. This review discusses the role of HDAC9 in different diseases and structure-activity relationships (SARs) of various hydroxamate and non-hydroxamate-based inhibitors. SAR of compounds containing several scaffolds have been discussed in detail. Moreover, structural requirements regarding the various components of HDAC9 inhibitor (cap group, linker and zinc-binding group) has been highlighted in this review. Though, HDAC9 is a promising target for the treatment of a number of diseases including cancer, a very few research are available. Thus, this review may provide useful information for designing novel HDAC9 inhibitors to fight against different diseases in the future.

MiR-22-3p and miR-29a-3p synergistically inhibit hepatic stellate cell activation by targeting AKT3

Hepatic fibrosis (HF) is a worldwide health problem for which there is no medically effective drug treatment at present, and which is characterized by activation of hepatic stellate cells (HSCs) and excessive extracellular matrix (ECM) deposition. The HF model in cholestatic rats by ligating the common bile duct was induced and the differentially expressed miRNAs in the liver tissues were analyzed by microarray, which showed that miR-22-3p and miR-29a-3p were significantly downregulated in bile-duct ligation (BDL) rat liver compared with the sham control. The synergistic anti-HF activity and molecular mechanism of miR-22-3p and miR-29a-3p by targeting AKT serine/threonine kinase 3 (AKT3) in HSCs were explored. The expression levels of miR-22-3p and miR-29a-3p were downregulated in activated LX-2 and human primary normal hepatic fibroblasts (NFs), whereas AKT3 was found to be upregulated in BDL rat liver and activated LX-2 cells. The proliferation, colony-forming, and migration ability of LX-2 were inhibited synergistically by miR-22-3p and miR-29a-3p. In addition, cellular senescence was induced and the expressions of the LX-2 fibrosis markers COL1A1 and α-SMA were inhibited by miR-22-3p and miR-29a-3p synergistically. Subsequently, these two miRNAs binding to the 3'UTR of AKT3 mRNA was predicted and evidenced by the luciferase reporter assay. Furthermore, the proliferation, migration, colony-forming ability, and the expression levels of COL1A1 and α-SMA were promoted and cellular senescence was inhibited by AKT3 in LX-2 cells. Thus, miR-22-3p/miR-29a-3p/AKT3 regulates the activation of HSCs, providing a new avenue in the study and treatment of HF.

Targeting Histone Deacetylases in Idiopathic Pulmonary Fibrosis: A Future Therapeutic Option

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited therapeutic options, and there is a huge unmet need for new therapies. A growing body of evidence suggests that the histone deacetylase (HDAC) family of transcriptional corepressors has emerged as crucial mediators of IPF pathogenesis. HDACs deacetylate histones and result in chromatin condensation and epigenetic repression of gene transcription. HDACs also catalyse the deacetylation of many non-histone proteins, including transcription factors, thus also leading to changes in the transcriptome and cellular signalling. Increased HDAC expression is associated with cell proliferation, cell growth and anti-apoptosis and is, thus, a salient feature of many cancers. In IPF, induction and abnormal upregulation of Class I and Class II HDAC enzymes in myofibroblast foci, as well as aberrant bronchiolar epithelium, is an eminent observation, whereas type-II alveolar epithelial cells (AECII) of IPF lungs indicate a significant depletion of many HDACs. We thus suggest that the significant imbalance of HDAC activity in IPF lungs, with a "cancer-like" increase in fibroblastic and bronchial cells versus a lack in AECII, promotes and perpetuates fibrosis. This review focuses on the mechanisms by which Class I and Class II HDACs mediate fibrogenesis and on the mechanisms by which various HDAC inhibitors reverse the deregulated epigenetic responses in IPF, supporting HDAC inhibition as promising IPF therapy.

Autophagy-Related Activation of Hepatic Stellate Cells Reduces Cellular miR-29a by Promoting Its Vesicular Secretion

BACKGROUND & AIMS

Liver fibrosis arises from long-term chronic liver injury, accompanied by an accelerated wound healing response with interstitial accumulation of extracellular matrix (ECM). Activated hepatic stellate cells (HSC) are the main source for ECM production. MicroRNA29a (miR-29a) is a crucial antifibrotic miRNA that is repressed during fibrosis, resulting in up-regulation of collagen synthesis.

METHODS

Intracellular and extracellular miRNA levels of primary and immortalized myofibroblastic HSC in response to profibrogenic stimulation by transforming growth factor β (TGFβ) or platelet-derived growth factor-BB (PDGF-BB) or upon inhibition of vesicular transport and autophagy processes were determined by quantitative polymerase chain reaction. Autophagy flux was studied by electron microscopy, flow cytometry, immunoblotting, and immunocytochemistry. Hepatic and serum miR-29a levels were quantified by using both liver tissue and serum samples from a cohort of chronic hepatitis C virus patients and a murine CCl4 induced liver fibrosis model.

RESULTS

In our study, we show that TGFβ and PDGF-BB resulted in decrease of intracellular miR-29a and a pronounced increase of vesicular miR-29a release into the supernatant. Strikingly, miR-29a vesicular release was accompanied by enhanced autophagic activity and up-regulation of the autophagy marker protein LC3. Moreover, autophagy inhibition strongly prevented miR-29a secretion and repressed its targets' expression such as Col1A1. Consistently, hepatic miR-29a loss and increased LC3 expression in myofibroblastic HSC were associated with increased serum miR-29a levels in CCl4-treated murine liver fibrosis and specimens of hepatitis C virus patients with chronic liver disease.

CONCLUSIONS

We provide evidence that activation-associated autophagy in HSC induces release of miR-29a, whereas inhibition of autophagy represses fibrogenic gene expression in part through attenuated miR-29a secretion.

Backstage players of fibrosis: NOX4, mTOR, HDAC, and S1P; companions of TGF-β

The fibrotic process could be easily defined as a pathological excess of extracellular matrix deposition, leading to disruption of tissue architecture and eventually loss of function; however, this process involves a complex network of several signal transduction pathways. Virtually almost all organs could be affected by fibrosis, the most affected are the liver, lung, skin, kidney, heart, and eyes; in all of them, the transforming growth factor-beta (TGF-β) has a central role. The canonical and non-canonical signal pathways of TGF-β impact the fibrotic process at the cellular and molecular levels, inducing the epithelial-mesenchymal transition (EMT) and the induction of profibrotic gene expression with the consequent increase in proteins such as alpha-smooth actin (α-SMA), fibronectin, collagen, and other extracellular matrix proteins. Recently, it has been reported that some molecules that have not been typically associated with the fibrotic process, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4), mammalian target of rapamycin (mTOR), histone deacetylases (HDAC), and sphingosine-1 phosphate (S1P); are critical in its development. In this review, we describe and discuss the role of these new players of fibrosis and the convergence with TGF-β signaling pathways, unveiling new insights into the panorama of fibrosis that could be useful for future therapeutic targets.

Histone deacetylase‑2: A potential regulator and therapeutic target in liver disease (Review)

Histone acetyltransferases are responsible for histone acetylation, while histone deacetylases (HDACs) counteract histone acetylation. An unbalanced dynamic between histone acetylation and deacetylation may lead to aberrant chromatin landscape and chromosomal function. HDAC2, a member of class I HDAC family, serves a crucial role in the modulation of cell signaling, immune response and gene expression. HDAC2 has emerged as a promising therapeutic target for liver disease by regulating gene transcription, chromatin remodeling, signal transduction and nuclear reprogramming, thus receiving attention from researchers and clinicians. The present review introduces biological information of HDAC2 and its physiological and biochemical functions. Secondly, the functional roles of HDAC2 in liver disease are discussed in terms of hepatocyte apoptosis and proliferation, liver regeneration, hepatocellular carcinoma, liver fibrosis and non-alcoholic steatohepatitis. Moreover, abnormal expression of HDAC2 may be involved in the pathogenesis of liver disease, and its expression levels and pharmacological activity may represent potential biomarkers of liver disease. Finally, research on selective HDAC2 inhibitors and non-coding RNAs relevant to HDAC2 expression in liver disease is also reviewed. The aim of the present review was to improve understanding of the multifunctional role and potential regulatory mechanism of HDAC2 in liver disease.

Tumor-Associated Macrophages-Implications for Molecular Oncology and Imaging

Tumor-associated macrophages (TAMs) represent the largest group of leukocytes within the tumor microenvironment (TME) of solid tumors and orchestrate the composition of anti- as well as pro-tumorigenic factors. This makes TAMs an excellent target for novel cancer therapies. The plasticity of TAMs resulting in varying membrane receptors and expression of intracellular proteins allow the specific characterization of different subsets of TAMs. Those markers similarly allow tracking of TAMs by different means of molecular imaging. This review aims to provides an overview of the origin of tumor-associated macrophages, their polarization in different subtypes, and how characteristic markers of the subtypes can be used as targets for molecular imaging and theranostic approaches.

The Epigenetic Regulation of Microenvironment in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a highly lethal and complex malignancy strongly influenced by the surrounding tumor microenvironment. The HCC microenvironment comprises hepatic stellate cells (HSCs), tumor-associated macrophages (TAMs), stromal and endothelial cells, and the underlying extracellular matrix (ECM). Emerging evidence demonstrates that epigenetic regulation plays a crucial role in altering numerous components of the HCC tumor microenvironment. In this review, we summarize the current understanding of the mechanisms of epigenetic regulation of the microenvironment in HCC. We review recent studies demonstrating how specific epigenetic mechanisms (DNA methylation, histone regulation, and non-coding RNAs mediated regulation) in HSCs, TAMs, and ECM, and how they contribute to HCC development, so as to gain new insights into the treatment of HCC via regulating epigenetic regulation in the tumor microenvironment.

Role of long non‑coding RNAs and related epigenetic mechanisms in liver fibrosis (Review)

Liver fibrosis is one of the major liver pathologies affecting patients worldwide. It results from an improper tissue repair process following liver injury or inflammation. If left untreated, it ultimately leads to liver cirrhosis and liver failure. Long non‑coding RNAs (lncRNAs) have been implicated in a wide variety of diseases. They can regulate gene expression and modulate signaling. Some of the lncRNAs promote, while others inhibit liver fibrosis. Similarly, other epigenetic processes, such as methylation and acetylation regulate gene transcription and can modulate gene expression. Notably, there are several regulatory associations of lncRNAs with other epigenetic processes. A major mechanism of action of long non‑coding RNAs is to competitively bind to their target microRNAs (miRNAs or miRs), which in turn affects miRNA availability and bioactivity. In the present review, the role of lncRNAs and related epigenetic processes contributing to liver fibrosis is discussed. Finally, various potential therapeutic approaches targeting lncRNAs and related epigenetic processes, which are being considered as possible future treatment targets for liver fibrosis are identified.

Dual Pharmacological Targeting of HDACs and PDE5 Inhibits Liver Disease Progression in a Mouse Model of Biliary Inflammation and Fibrosis

Simple Summary

Chronic liver injury and inflammation leads to excessive deposition of extracellular matrix, known as liver fibrosis, and the distortion of the hepatic parenchyma. Liver fibrosis may progress to cirrhosis, a condition in which hepatic function is impaired and most cases of liver tumors occur. Currently, there are no effective therapies to inhibit and reverse the progression of liver fibrosis, and therefore, chronic liver disease remains a global health problem. In this study we have tested the efficacy of a new class of molecules that simultaneously target two molecular pathways known to be involved in the pathogenesis of hepatic fibrosis. In a clinically relevant mouse model of liver injury and inflammation we show that the combined inhibition of histones deacetylases and the cyclic guanosine monophosphate (cGMP) phosphodiesterase phosphodiesterase 5 (PDE5) results in potent anti-inflammatory and anti-fibrotic effects. Our findings open new avenues for the treatment of liver fibrosis and therefore, the prevention of hepatic carcinogenesis.

Abstract

Liver fibrosis, a common hallmark of chronic liver disease (CLD), is characterized by the accumulation of extracellular matrix secreted by activated hepatic fibroblasts and stellate cells (HSC). Fibrogenesis involves multiple cellular and molecular processes and is intimately linked to chronic hepatic inflammation. Importantly, it has been shown to promote the loss of liver function and liver carcinogenesis. No effective therapies for liver fibrosis are currently available. We examined the anti-fibrogenic potential of a new drug (CM414) that simultaneously inhibits histone deacetylases (HDACs), more precisely HDAC1, 2, and 3 (Class I) and HDAC6 (Class II) and stimulates the cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) pathway activity through phosphodiesterase 5 (PDE5) inhibition, two mechanisms independently involved in liver fibrosis. To this end, we treated Mdr2-KO mice, a clinically relevant model of liver inflammation and fibrosis, with our dual HDAC/PDE5 inhibitor CM414. We observed a decrease in the expression of fibrogenic markers and collagen deposition, together with a marked reduction in inflammation. No signs of hepatic or systemic toxicity were recorded. Mechanistic studies in cultured human HSC and cholangiocytes (LX2 and H69 cell lines, respectively) demonstrated that CM414 inhibited pro-fibrogenic and inflammatory responses, including those triggered by transforming growth factor β (TGFβ). Our study supports the notion that simultaneous targeting of pro-inflammatory and fibrogenic mechanisms controlled by HDACs and PDE5 with a single molecule, such as CM414, can be a new disease-modifying strategy.

Epigenetics in Liver Fibrosis: Could HDACs be a Therapeutic Target?

Chronic liver diseases (CLD) represent a worldwide health problem. While CLDs may have diverse etiologies, a common pathogenic denominator is the presence of liver fibrosis. Cirrhosis, the end-stage of CLD, is characterized by extensive fibrosis and is markedly associated with the development of hepatocellular carcinoma. The most important event in hepatic fibrogenesis is the activation of hepatic stellate cells (HSC) following liver injury. Activated HSCs acquire a myofibroblast-like phenotype becoming proliferative, fibrogenic, and contractile cells. While transient activation of HSCs is part of the physiological mechanisms of tissue repair, protracted activation of a wound healing reaction leads to organ fibrosis. The phenotypic changes of activated HSCs involve epigenetic mechanisms mediated by non-coding RNAs (ncRNA) as well as by changes in DNA methylation and histone modifications. During CLD these epigenetic mechanisms become deregulated, with alterations in the expression and activity of epigenetic modulators. Here we provide an overview of the epigenetic alterations involved in fibrogenic HSCs transdifferentiation with particular focus on histones acetylation changes. We also discuss recent studies supporting the promising therapeutic potential of histone deacetylase inhibitors in liver fibrosis.

Can Prohibitin 1 be a Safeguard against liver disease?

Prohibitin (PHB) 1 is involved in multiple regulatory pathways in liver disease to protect hepatocytes, and its function is associated with subcellular localization. PHB1 located in the nucleus, cytoplasm and the mitochondrial inner membrane has anti-oxidative stress and anti-inflammatory effects in hepatitis and cirrhosis, which can protect liver cells from damage caused by inflammatory factors and reactive oxygen species (ROS) stimulation. The low expression of PHB1 located in the nucleus of liver cancer cells inhibits the proliferation and metastasis of liver cancer; thus, PHB1 exhibits the function of a tumor suppressor gene. Understanding the mechanisms of PHB1 in liver diseases may be useful for further research on the disease and may provide new ideas for the development of targeted therapeutic drugs in the future. Therefore, this review puts forward an overview of the role of PHB1 and its protective mechanism in liver diseases.

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and ranges from steatosis to steatohepatitis and to liver fibrosis. Lipotoxicity in hepatocytes, elevated oxidative stress and the activation of proinflammatory mediators of Kupffer cells, and fibrogenic pathways of activated hepatic stellate cells can contribute to the development of NAFLD. MicroRNAs (miRs) play a crucial role in the dysregulated metabolism and inflammatory signaling connected with NAFLD and its progression towards more severe stages. Of note, the protective effect of non-coding miR-29a on liver damage and its versatile action on epigenetic activity, mitochondrial homeostasis and immunomodulation may improve our perception of the pathogenesis of NAFLD. Herein, we review the biological functions of critical miRs in NAFLD, as well as highlight the emerging role of miR-29a in therapeutic application and the recent advances in molecular mechanisms underlying its liver protective effect.

miR-29b attenuates histone deacetylase-4 mediated podocyte dysfunction and renal fibrosis in diabetic nephropathy

Purpose

As epigenetic modifications like chromatin histone modifications have been suggested to play a role in the pathophysiology of Diabetic Nephropathy (DN) and are also found to be regulated by microRNAs. Our main purpose was to explore the role of microRNA in histone modulations associated with DN. There is downregulation of miR-29b due to advanced glycation end products in diabetes. Histone Deacetylase-4 (HDAC4) is amongst the histone modulators which promotes podocytes' impairment and upregulates transforming growth factor-1 (TGF-β1) leading to renal fibrosis. Moreover, macrophage infiltration causes podocytes' apoptosis and IL-6 mediated inflammation. As miR-29b is downregulated in diabetes and HDAC4, TGF-β1 and IL-6 could be the possible therapeutic targets in DN, our study was focussed on unveiling the role of miR-29b in modulation of HDAC4 and hence, in podocyte dysfunction and renal fibrosis in DN.

Methods

In silico analysis and luciferase assay were done to study the interaction between miR-29b and HDAC4. In-vitro DN model was developed in podocytes and miR-29b mimics were transfected. Also, podocytes were co-cultured with macrophage and miR-29b mimics were transfected. At the end, in-vivo DN model was generated in C57BL/6 J male mice and the effect of miR-29b mimics was reconfirmed.

Results

It was found that miR-29b targets the 3' untranslated region of HDAC4. In both in-vitro and in-vivo DN model, downregulation of miR-29b and subsequent increase in HDAC4 expression was observed. The miR-29b mimics suppressed podocytes' inflammation mediated through macrophages and attenuated HDAC4 expression, glomerular damage and renal fibrosis.

Conclusion

This study concludes that miR-29b regulates the expression of HDAC4 which plays a role in controlling renal fibrosis and podocytes' impairment in DN.

Epigenetic Mechanisms in Hepatic Stellate Cell Activation During Liver Fibrosis and Carcinogenesis

Liver fibrosis is an essential component of chronic liver disease (CLD) and hepatocarcinogenesis. The fibrotic stroma is a consequence of sustained liver damage combined with exacerbated extracellular matrix (ECM) accumulation. In this context, activation of hepatic stellate cells (HSCs) plays a key role in both initiation and perpetuation of fibrogenesis. These cells suffer profound remodeling of gene expression in this process. This review is focused on the epigenetic alterations participating in the transdifferentiation of HSCs from the quiescent to activated state. Recent advances in the field of DNA methylation and post-translational modifications (PTM) of histones (acetylation and methylation) patterns are discussed here, together with altered expression and activity of epigenetic remodelers. We also consider recent advances in translational approaches, including the use of epigenetic marks as biomarkers and the promising antifibrotic properties of epigenetic drugs that are currently being used in patients.

HDAC Inhibitors: Therapeutic Potential in Fibrosis-Associated Human Diseases

Fibrosis is characterized by excessive deposition of the extracellular matrix and develops because of fibroblast differentiation during the process of inflammation. Various cytokines stimulate resident fibroblasts, which differentiate into myofibroblasts. Myofibroblasts actively synthesize an excessive amount of extracellular matrix, which indicates pathologic fibrosis. Although initial fibrosis is a physiologic response, the accumulated fibrous material causes failure of normal organ function. Cardiac fibrosis interferes with proper diastole, whereas pulmonary fibrosis results in chronic hypoxia; liver cirrhosis induces portal hypertension, and overgrowth of fibroblasts in the conjunctiva is a major cause of glaucoma surgical failure. Recently, several reports have clearly demonstrated the functional relevance of certain types of histone deacetylases (HDACs) in various kinds of fibrosis and the successful alleviation of the condition in animal models using HDAC inhibitors. In this review, we discuss the therapeutic potential of HDAC inhibitors in fibrosis-associated human diseases using results obtained from animal models.

microRNA-146a is involved in rSjP40-inhibited activation of LX-2 cells by targeting Smad4 expression

Previous studies have demonstrated that the recombinant Schistosoma japonicum protein P40 (rSjP40) could inhibit activation of hepatic stellate cells (HSCs) through the TGF-β1/Smads signaling pathway. Since multiple microRNAs could play essential roles in HSC activation and in the process of hepatic fibrosis through targeting Smads, we attempted to seek the potential microRNAs that could be involved in rSjP40-induced inhibition of HSC activation. Using the method of quantitative real-time PCR, we found that rSjP40 could induce miR-146a expression in LX-2 cells. The down-regulated expression levels of Smad4 and α-SMA in LX-2 cells induced by rSjP40 were partially restored by an miR-146a inhibitor. miR-146a can be involved in rSjP40-induced inhibition of HSC activation through targeting Smad4. These findings provide us a new idea to explore the potential mechanisms by which rSjP40 could regulate the process of hepatic fibrosis.

HDAC4 stimulates MRTF-A expression and drives fibrogenesis in hepatic stellate cells by targeting miR-206

Activation of hepatic stellate cells (HSCs) is a hallmark event during liver fibrogenesis. We have previously shown that the transcriptional modulator MRTF-A contributes to liver fibrosis by programming epigenetic activation of HSCs. In the present study we investigated the mechanism whereby MRTF-A expression is regulated in this process. We report here that MRTF-A protein levels, but not mRNA levels, were up-regulated in vivo in the livers of mice induced to develop hepatic fibrosis. Pro-fibrogenic stimuli (TGF-β and PDGF-BB) also activated MRTF-A expression post-transcriptionally in vitro in cultured HSCs. miR-206 bound to the 3′-UTR of MRTF-A presumably to inhibit translation. miR-206 levels were down-regulated in response to pro-fibrogenic stimuli in vivo and in vitro allowing MRTF-A proteins to accumulate. Mechanistically, histone deacetylase 4 (HDAC4) was induced by pro-fibrogenic stimuli and recruited to the miR-206 promoter to repress miR-206 transcription. HDAC4 stimulated MRTF-A expression and drove fibrogenesis in HSCs in a miR-206 dependent manner. Therefore, our data reveal an HDAC4-miR-206-MRTF-A axis that can play a potentially important role in HSC activation and liver fibrosis.

MiR-185/AKT and miR-29a/collagen 1a pathways are activated in IPF BAL cells

MicroRNA signatures of BAL cells and alveolar macrophages are currently lacking in IPF. Here we sought to investigate the expression of fibrosis-related microRNAs in the cellular component of the BAL in IPF. We thus focused on microRNAs previously associated with fibrosis (miR-29a, miR-29b, miR-29c, let-7d, and miR-21) and rapid IPF progression (miR-185, miR-210, miR-302c-3p miR-376c and miR-423-5p). Among the tested microRNAs miR-29a and miR-185 were found significantly downregulated in IPF while miR-302c-3p and miR-376c were not expressed by BAL cells. Importantly, the downregulation of miR-29a inversely correlated with the significantly increased levels of COL1A1 mRNA in IPF BAL cells. Collagen 1 a was found mainly overexpressed in alveolar macrophages and not other cell types of the BAL by immunofluorescence. In view of the downregulation of miR-185, we tested the response of THP-1 macrophages to profibrotic cytokine TGFb and observed the downregulation of miR-185. Conversely, proinflammatory stimulation lead to miR-185 upregulation. Upon examination of the mRNA levels of known miR-185 targets AKT1, DNMT1 and HMGA2, no significant correlations were observed in the BAL cells. However, increased levels of total AKT and AKTser473 phosphorylation were observed in the IPF BAL cells. Furthermore, miR-185 inhibition in THP-1 macrophages resulted in significant increase of AKTser473 phosphorylation. Our study highlights the importance of BAL microRNA signatures in IPF and identifies significant differences in miR-185/AKT and miR-29a/collagen axes in the BAL cells of IPF patients.

Prior alcohol use enhances vulnerability to compulsive cocaine self-administration by promoting degradation of HDAC4 and HDAC5

Addiction to cocaine is commonly preceded by experiences with legal or decriminalized drugs, such as alcohol, nicotine, and marijuana. The biological mechanisms by which these gateway drugs contribute to cocaine addiction are only beginning to be understood. We report that in the rat, prior alcohol consumption results in enhanced addiction-like behavior to cocaine, including continued cocaine use despite aversive consequences. Conversely, prior cocaine use has no effect on alcohol preference. Long-term, but not short-term, alcohol consumption promotes proteasome-mediated degradation of the nuclear histone deacetylases HDAC4 and HDAC5 in the nucleus accumbens, a brain region critical for reward-based memory. Decreased nuclear HDAC activity results in global H3 acetylation, creating a permissive environment for cocaine-induced gene expression. We also find that selective degradation of HDAC4 and HDAC5, facilitated by the class II-specific HDAC inhibitor MC1568, enhances compulsive cocaine self-administration. These results parallel our previously reported findings that the gateway drug nicotine enhances the behavioral effects of cocaine via HDAC inhibition. Together, our findings suggest a shared mechanism of action for the gateway drugs alcohol and nicotine, and reveal a novel mechanism by which environmental factors may alter the epigenetic landscape of the reward system to increase vulnerability to cocaine addiction.

The roles of microRNA families in hepatic fibrosis

When hepatocytes are damaged severely, a variety of signaling pathways will be triggered by inflammatory factors and cytokines involving in the process of hepatic fibrosis. The microRNA (miRNA) family consists of several miRNAs which have the potential for synergistic regulation of these signaling pathways. However, it is poor to understand the roles of miRNA family as a whole in hepatic fibrosis. Increasing studies have suggested several miRNA families are related with activation of hepatic stellate cells and hepatic fibrosis through cooperatively regulating certain signaling pathways. During the process of hepatic fibrosis, miR-29 family primarily induces cell apoptosis by modulating phosphatidylinositol 3-kinase/AKT signaling pathway and regulates extracellular matrix accumulation. miR-34 family promotes the progression of hepatic fibrosis by inducing activation of hepatic stellate cells, while miR-378 family suppresses the process in Glis dependent manner. miR-15 family mainly promotes cell proliferation and induces apoptosis. The miR-199 family and miR-200 family are responsible for extracellular matrix deposition and the release of pro-fibrotic cytokines. These miRNA family members play pro-fibrotic or anti-fibrotic roles by targeting genes collectively or respectively which involve in hepatic fibrosis related signaling pathways and hepatic stellate cell activation. Thus, good understandings of molecular mechanisms which are based on miRNA families may provide new ideas for the molecular targeted therapy of hepatic fibrosis in the future.

Cathepsin H-Mediated Degradation of HDAC4 for Matrix Metalloproteinase Expression in Hepatic Stellate Cells: Implications of Epigenetic Suppression of Matrix Metalloproteinases in Fibrosis through Stabilization of Class IIa Histone Deacetylases

In three-dimensional extracellular matrix, mesenchymal cells including hepatic stellate cells (HSCs) gain the ability to express matrix metalloproteinases (MMPs) on injury signals. In contrast, in myofibroblastic HSCs in fibrotic liver, many MMP genes are silenced into an epigenetically nonpermissive state. The mechanism by which the three-dimensional extracellular matrix confers the MMP genes into an epigenetically permissive state has not been well characterized. In continuation of previous work, we show here that the up-regulation of MMP genes is mediated through degradation of class IIa histone deacetylases (HDACs) by certain cysteine cathepsins (Cts). In three-dimensional extracellular matrix culture, CtsH, among other cysteine cathepsins, was up-regulated and localized as puncta in the nuclear and cytoplasmic compartments in a complex with HDAC4 for its degradation. Conversely, along with HSC trans-differentiation, CtsH and CtsL were progressively down-regulated, whereas HDAC4 was concurrently stabilized. The inhibition of cysteine cathepsins by specific proteinase inhibitors or chloroquine, which raises cellular pH, restored HDAC4. Recombinant CtsH could break down HDAC4 in the transfected cells and in vitro at acidic pH. In human cirrhotic liver, activated HSCs express high levels of class IIa HDACs but little CtsH. We propose that cysteine cathepsin-mediated degradation of class IIa HDACs plays a key role in the modulation of MMP expression/suppression and HSC functions in tissue injury and fibrosis.

Epigenetic regulation of hepatic stellate cell activation and liver fibrosis

Chronic liver injury to hepatocytes or cholangiocytes, when left unmanaged, leads to the development of liver fibrosis, a condition characterized by the excessive intrahepatic deposition of extracellular matrix proteins. Activated hepatic stellate cells constitute the predominant source of extracellular matrix in fibrotic livers and their transition from a quiescent state during fibrogenesis is associated with important alterations in their transcriptional and epigenetic landscape. Areas covered: We briefly describe the processes involved in hepatic stellate cell activation and discuss our current understanding of alterations in the epigenetic landscape, i.e DNA methylation, histone modifications and the functional role of non-coding RNAs that accompany this key event in the development of chronic liver disease. Expert commentary: Although great progress has been made, our understanding of the epigenetic regulation of hepatic stellate cell activation is limited and, thus far, insufficient to allow the development of epigenetic drugs that can selectively interrupt liver fibrosis.

Histone deacetylase 9 plays a role in the antifibrogenic effect of astaxanthin in hepatic stellate cells

Activation of hepatic stellate cells (HSCs) is critical for liver fibrosis development. Previously, we showed that astaxanthin (ASTX), a xanthophyll carotenoid, has antifibrogenic effects in LX-2 cells, a human HSC cell line. We sought to determine the effect of ASTX on HSC activation, and to identify molecular mediators that are critically involved in the processes. ASTX prevented the activation of mouse primary HSCs, as evidenced by attenuated induction of procollagen type I α1. In human primary HSCs, ASTX also inhibited transforming growth factor β1 (TGFβ1)-induced fibrogenic gene expression. Among 11 classical histone deacetylases (HDACs), difference in HDAC9 mRNA levels between quiescent and activated HSCs was most evident while ASTX significantly decreased the expression of HDAC9 and its transcriptional regulator myocyte enhancer factor 2 (MEF2). ASTX decreased HDAC9 protein as well. In the activated HSCs, ASTX significantly reduced mRNA of HDAC9 and MEF2. Human primary biliary cirrhosis livers showed significantly higher HDAC9 mRNA and protein levels than normal livers, and other liver pathologies also exhibited induced HDAC9 expression. HDAC9 knockdown in LX-2 cells decreased TGFβ1-induced fibrogenic gene expression. In conclusion, ASTX inhibits HSC activation and facilitates HSC inactivation, which is attributable to its inhibitory action on HDAC9 expression.

MC1568 inhibits HDAC6/8 activity and influenza A virus replication in lung epithelial cells: role of Hsp90 acetylation

AIM

Histone deacetylases (HDACs) regulate the life cycle of several viruses. We investigated the ability of different HDAC inhibitors, to interfere with influenza virus A/Puerto Rico/8/34/H1N1 (PR8 virus) replication in Madin-Darby canine kidney and NCI cells.

RESULTS

3-(5-(3-Fluorophenyl)-3-oxoprop-1-en-1-yl)-1-methyl-1H-pyrrol-2-yl)-N-hydroxyacrylamide (MC1568) inhibited HDAC6/8 activity and PR8 virus replication, with decreased expression of viral proteins and their mRNAs. Such an effect may be related to a decrease in intranuclear content of viral polymerases and, in turn, to an early acetylation of Hsp90, a major player in their nuclear import. Later, the virus itself induced Hsp90 acetylation, suggesting a differential and time-dependent role of acetylated proteins in virus replication.

CONCLUSION

The inhibition of HDAC6/8 activity during early steps of PR8 virus replication could lead to novel anti-influenza strategy.

Interleukin-6 secreted by bipotential murine oval liver stem cells induces apoptosis of activated hepatic stellate cells by activating NF-κB-inducible nitric oxide synthase signaling

Liver fibrosis is now well recognized as the causative factor for increased mortality from complications associated with liver pathologies. Activated hepatic stellate cells (HSCs) play a critical role in the progression of liver fibrosis. Therefore, targeting these activated HSCs to prevent and (or) treat liver disease is a worthwhile approach to explore. In the present in vitro study, we investigated the use of bipotential murine oval liver cells (BMOL) in regulating the functions of activated HSCs to prevent progression of liver fibrosis. We used a conditioned medium-based approach to study the effect of BMOL cells on activated HSC survival and function. Our data showed that BMOL cells block the contraction of activated HSCs by inducing apoptosis of these cells. We demonstrated that BMOL cells secrete soluble factors, such as interleukin-6 (IL-6), which induced apoptosis of activated HSCs. Using both pharmacological and molecular inhibitor approaches, we further identified that IL-6-mediated activation of NF-κB-iNOS-NO-ROS signaling in activated HSCs plays a critical role in BMOL-cell-mediated apoptosis of activated HSCs. Thus, the present study provides an alternative cell-based therapeutic approach to treat liver fibrosis.

FXR agonist obeticholic acid reduces hepatic inflammation and fibrosis in a rat model of toxic cirrhosis

Hepatic inflammation drives hepatic stellate cells (HSC), resulting in liver fibrosis. The Farnesoid-X receptor (FXR) antagonizes inflammation through NF-κB inhibition. We investigated preventive and therapeutic effects of FXR agonist obeticholic acid (OCA) on hepatic inflammation and fibrosis in toxic cirrhotic rats. Cirrhosis was induced by thioacetamide (TAA) intoxication. OCA was given during or after intoxication with vehicle-treated rats as controls. At sacrifice, fibrosis, hemodynamic and biochemical parameters were assessed. HSC activation, cell turn-over, hepatic NF-κB activation, pro-inflammatory and pro-fibrotic cytokines were determined. The effect of OCA was further evaluated in isolated HSC, Kupffer cells, hepatocytes and liver sinusoidal endothelial cells (LSEC). OCA decreased hepatic inflammation and fibrogenesis during TAA-administration and reversed fibrosis in established cirrhosis. Portal pressure decreased through reduced intrahepatic vascular resistance. This was paralleled by decreased expression of pro-fibrotic cytokines (transforming growth-factor β, connective tissue growth factor, platelet-derived growth factor β-receptor) as well as markers of hepatic cell turn-over, by blunting effects of pro-inflammatory cytokines (e.g. monocyte chemo-attractant protein-1). In vitro, OCA inhibited both LSEC and Kupffer cell activation; while HSC remained unaffected. This related to NF-κB inhibition via up-regulated IκBα. In conclusion, OCA inhibits hepatic inflammation in toxic cirrhotic rats resulting in decreased HSC activation and fibrosis.

Role of histone deacetylases(HDACs) in progression and reversal of liver fibrosis

Liver fibrosis refers to a reversible wound healing process response to chronic liver injuries. Activation of hepatic stellate cells (HSCs) is closely correlated with the development of liver fibrosis. Histone deacetylases(HDACs) determine the acetylation levels of core histones to modulate expression of genes. To demonstrate the link between HDACs and liver fibrosis, CCl4-induced mouse liver fibrosis model and its spontaneous reversal model were established. Results of the current study demonstrated that deregulation of liver HDACs may involved in the development of liver fibrosis. Among 11 HDACs tested in our study (Class I, II, and IV HDACs), expression of HDAC2 was maximally increased in CCl4-induced fibrotic livers but decreased after spontaneous recovery. Moreover, expression of HDAC2 was elevated in human liver fibrotic tissues. In this regard, the potential role of HDAC2 in liver fibrosis was further evaluated. Our results showed that administration of HSC-T6 cells with transforming growth factor-beta1 (TGF-β1) resulted in an increase of HDAC2 protein expression in dose- and time-dependent manners. Moreover, HDAC2 deficiency inhibited HSC-T6 cell proliferation and activation induced by TGF-β1. More importantly, the present study showed HDAC2 may regulate HSCs activation by suppressing expression of Smad7, which is a negative modulator in HSCs activation and liver fibrosis. Collectively, these observations revealed that HDAC2 may play a pivotal role in HSCs activation and liver fibrosis while deregulation of HDACs may serve as a novel mechanism underlying liver fibrosis.

Evolving Insights on Metabolism, Autophagy, and Epigenetics in Liver Myofibroblasts

Liver myofibroblasts (MFB) are crucial mediators of extracellular matrix (ECM) deposition in liver fibrosis. They arise mainly from hepatic stellate cells (HSCs) upon a process termed “activation.” To a lesser extent, and depending on the cause of liver damage, portal fibroblasts, mesothelial cells, and fibrocytes may also contribute to the MFB population. Targeting MFB to reduce liver fibrosis is currently an area of intense research. Unfortunately, a clog in the wheel of antifibrotic therapies is the fact that although MFB are known to mediate scar formation, and participate in liver inflammatory response, many of their molecular portraits are currently unknown. In this review, we discuss recent understanding of MFB in health and diseases, focusing specifically on three evolving research fields: metabolism, autophagy, and epigenetics. We have emphasized on therapeutic prospects where applicable and mentioned techniques for use in MFB studies. Subsequently, we highlighted uncharted territories in MFB research to help direct future efforts aimed at bridging gaps in current knowledge.

Class IIa histone deacetylases affect neuronal remodeling and functional outcome after stroke

We have previously demonstrated that stroke induces nuclear shuttling of class IIa histone deacetylase 4 (HDAC4). Stroke-induced nuclear shuttling of HDAC4 is positively and significantly correlated with improved indices of neuronal remodeling in the peri-infarct cortex. In this study, using a rat model for middle cerebral artery occlusion (MCAO), we tested the effects of selective inhibition of class IIa HDACs on functional recovery and neuronal remodeling when administered 24hr after stroke. Adult male Wistar rats (n = 15-17/group) were subjected to 2 h MCAO and orally gavaged with MC1568 (a selective class IIa HDAC inhibitor), SAHA (a non-selective HDAC inhibitor), or vehicle-control for 7 days starting 24 h after MCAO. A battery of behavioral tests was performed. Lesion volume measurement and immunohistochemistry were performed 28 days after MCAO. We found that stroke increased total HDAC activity in the ipsilateral hemisphere compared to the contralateral hemisphere. Stroke-increased HDAC activity was significantly decreased by the administration of SAHA as well as by MC1568. However, SAHA significantly improved functional outcome compared to vehicle control, whereas selective class IIa inhibition with MC1568 increased mortality and lesion volume and did not improve functional outcome. In addition, MC1568 decreased microtubule associated protein 2 (MAP2, dendrites), phosphorylated neurofilament heavy chain (pNFH, axons) and myelin basic protein (MBP, myelination) immunoreactivity in the peri-infarct cortex. Quantitative RT-PCR of cortical neurons isolated by laser capture microdissection revealed that MC1568, but not SAHA, downregulated CREB and c-fos expression. Additionally, MC1568 decreased the expression of phosphorylated CREB (active) in neurons. Taken together, these findings demonstrate that selective inhibition of class IIa HDACs impairs neuronal remodeling and neurological outcome. Inactivation of CREB and c-fos by MC1568 likely contributes to this detrimental effect.

Hepatic Stellate Cells and microRNAs in Pathogenesis of Liver Fibrosis

microRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by either blocking translation or inducing degradation of target mRNA. miRNAs play essential roles in diverse biological and pathological processes, including development of hepatic fibrosis. Hepatic stellate cells (HSCs) play a central role in development of hepatic fibrosis and there are intricate regulatory effects of miRNAs on their activation, proliferation, collagen production, migration, and apoptosis. There are multiple differentially expressed miRNAs in activated HSCs, and in this review we aim to summarize current data on miRNAs that participate in the development of hepatic fibrosis. Based on this review, miRNAs may serve as biomarkers for diagnosis of liver disease, as well as markers of disease progression. Most importantly, dysregulated miRNAs may potentially be targeted by novel therapies to treat and reverse progression of hepatic fibrosis.

Pathologic Regulation of Collagen I by an Aberrant Protein Phosphatase 2A/Histone Deacetylase C4/MicroRNA-29 Signal Axis in Idiopathic Pulmonary Fibrosis Fibroblasts

Idiopathic pulmonary fibrosis (IPF) is characterized by the relentless expansion of fibroblasts depositing type I collagen within the alveolar wall and obliterating the alveolar airspace. MicroRNA (miR)-29 is a potent regulator of collagen expression. In IPF, miR-29 levels are low, whereas type I collagen expression is high. However, the mechanism for suppression of miR-29 and increased type I collagen expression in IPF remains unclear. Here we show that when IPF fibroblasts are seeded on polymerized type I collagen, miR-29c levels are suppressed and type I collagen expression is high. In contrast, miR-29c is high and type I collagen expression is low in control fibroblasts. We demonstrate that the mechanism for suppression of miR-29 during IPF fibroblast interaction with polymerized collagen involves inappropriately low protein phosphatase (PP) 2A function, leading to histone deacetylase (HDA) C4 phosphorylation and decreased nuclear translocation of HDAC4. We demonstrate that overexpression of HDAC4 in IPF fibroblasts restored miR-29c levels and decreased type I collagen expression, whereas knocking down HDAC4 in control fibroblasts suppressed miR-29c levels and increased type I collagen expression. Our data indicate that IPF fibroblast interaction with polymerized type I collagen results in an aberrant PP2A/HDAC4 axis, which suppresses miR-29, causing a pathologic increase in type I collagen expression.

Histone deacetylase 4 promotes cholestatic liver injury in the absence of prohibitin-1

Prohibitin-1 (PHB1) is an evolutionarily conserved pleiotropic protein that participates in diverse processes depending on its subcellular localization and interactome. Recent data have indicated a diverse role for PHB1 in the pathogenesis of obesity, cancer, and inflammatory bowel disease, among others. Data presented here suggest that PHB1 is also linked to cholestatic liver disease. Expression of PHB1 is markedly reduced in patients with primary biliary cirrhosis and biliary atresia or with Alagille syndrome, two major pediatric cholestatic conditions. In the experimental model of bile duct ligation, silencing of PHB1 induced liver fibrosis, reduced animal survival, and induced bile duct proliferation. Importantly, the modulatory effect of PHB1 is not dependent on its known mitochondrial function. Also, PHB1 interacts with histone deacetylase 4 (HDAC4) in the presence of bile acids. Hence, PHB1 depletion leads to increased nuclear HDAC4 content and its associated epigenetic changes. Remarkably, HDAC4 silencing and the administration of the HDAC inhibitor parthenolide during obstructive cholestasis in vivo promote genomic reprogramming, leading to regression of the fibrotic phenotype in liver-specific Phb1 knockout mice.

CONCLUSION

PHB1 is an important mediator of cholestatic liver injury that regulates the activity of HDAC4, which controls specific epigenetic markers; these results identify potential novel strategies to treat liver injury and fibrosis, particularly as a consequence of chronic cholestasis.

Activation of Mir-29a in Activated Hepatic Stellate Cells Modulates Its Profibrogenic Phenotype through Inhibition of Histone Deacetylases 4

Background

Recent studies have shown that microRNA-29 (miR-29) is significantly decreased in liver fibrosis and that its downregulation influences the activation of hepatic stellate cells (HSCs). In addition, inhibition of the activity of histone deacetylases 4 (HDAC4) has been shown to strongly reduce HSC activation in the context of liver fibrosis.

Objectives

In this study, we examined whether miR-29a was involved in the regulation of HDAC4 and modulation of the profibrogenic phenotype in HSCs.

Methods

We employed miR-29a transgenic mice (miR-29aTg mice) and wild-type littermates to clarify the role of miR-29a in cholestatic liver fibrosis, using the bile duct-ligation (BDL) mouse model. Primary HSCs from both mice were treated with a miR-29a mimic and antisense inhibitor in order to analyze changes in profibrogenic gene expression and HSC activation using real-time quantitative RT-PCR, immunofluorescence staining, western blotting, and cell proliferation and migration assays.

Results

After BDL, overexpression of miR-29a decreased collagen-1α1, HDAC4 and activated HSC markers of glial fibrillary acidic protein expression in miR-29aTg mice compared to wild-type littermates. Overexpression of miR-29a and HDAC4 RNA-interference decreased the expression of fibrotic genes, HDAC4 signaling, and HSC migration and proliferation. In contrast, knockdown of miR-29a with an antisense inhibitor increased HDAC4 function, restored HSC migration, and accelerated HSC proliferation.

Conclusions

Our results indicate that miR-29a ameliorates cholestatic liver fibrosis after BDL, at least partially, by modulating the profibrogenic phenotype of HSCs through inhibition of HDAC4 function.

Epigenetic modifications by histone deacetylases: Biological implications and therapeutic potential in liver fibrosis

Liver fibrosis is an important pathological repair process in reaction to liver injury characterized by progressive accumulation of extracellular matrix (ECM) components. Mechanism that orchestrates this fibrotic disorder is the activation of hepatic stellate cell (HSC) that requires extensive alterations in gene expression. Reversible deacetylation of histone proteins is one of the most abundant epigenetic modifications and is crucial in modulating gene expression. Recent evidence has highlighted a pathological imbalance between the acetylation and deacetylation of histone proteins regulated by histone deacetylases (HDACs). In the past several years, the role of HDACs in liver fibrosis initiation and progression, as well as the therapeutic effects of HDAC inhibitors, has been well studied. Here, the innovative aspects of histone deacetylation will be presented, with respect to the roles of HDACs in liver fibrosis, the affected genes and signal pathways involved in HSCs activation, as well as significant data emerging from the field in support of HDAC inhibitors as potential therapeutic targets for the treatment of liver fibrosis.

Intestinal fibrosis in Crohn's disease: role of microRNAs as fibrogenic modulators, serum biomarkers, and therapeutic targets

Inflammation often precedes fibrosis and stricture formation in patients with Crohn's disease. Established medical therapies reduce inflammation, but there are currently no specific therapies to prevent fibrosis or treat established fibrosis. Our understanding of the pathogenic processes underpinning fibrogenesis is limited compared with our knowledge of the events initiating and propagating inflammation. There are several biomarkers for intestinal inflammation, but there are none that reflect the development of fibrosis. MicroRNAs (miRNAs) are regulators of cellular activities including inflammation and fibrosis and may serve as biomarkers of disease processes. Differential serum and mucosal miRNA expression profiles have been identified between patients with inflammatory bowel disease with active and inactive inflammatory disease. In contrast, studies in patients with fibrotic phenotypes are comparatively few, although specific miRNAs have defined roles in the development of fibrosis in other organ systems. Here, we discuss the most recent research on miRNA and fibrogenesis with a particular emphasis on Crohn's disease. We also anticipate the potential of miRNAs in fulfilling current unmet translational needs in this patient group by focusing on the role of miRNAs as modulators of fibrogenesis and on their potential value as serum biomarkers and therapeutic targets in the management of fibrosis.

Promiscuous actions of small molecule inhibitors of the protein kinase D-class IIa HDAC axis in striated muscle

PKD-mediated phosphorylation of class IIa HDACs frees the MEF2 transcription factor to activate genes that govern muscle differentiation and growth. Studies of the regulation and function of this signaling axis have involved MC1568 and Gö-6976, which are small molecule inhibitors of class IIa HDAC and PKD catalytic activity, respectively. We describe unanticipated effects of these compounds. MC1568 failed to inhibit class IIa HDAC catalytic activity in vitro, and exerted divergent effects on skeletal muscle differentiation compared to a bona fide inhibitor of these HDACs. In cardiomyocytes, Gö-6976 triggered calcium signaling and activated stress-inducible kinases. Based on these findings, caution is warranted when employing MC1568 and Gö-6976 as pharmacological tool compounds to assess functions of class IIa HDACs and PKD.

MicroRNAs: new players in IBD

MicroRNAs (miRNAs) are small non-coding RNAs, 18-23 nucleotides long, which act as post-transcriptional regulators of gene expression. miRNAs are strongly implicated in the pathogenesis of many common diseases, including IBDs. This review aims to outline the history, biogenesis and regulation of miRNAs. The role of miRNAs in the development and regulation of the innate and adaptive immune system is discussed, with a particular focus on mechanisms pertinent to IBD and the potential translational applications.

microRNAs in the tumor microenvironment: solving the riddle for a better diagnostics

miRNAs are small noncoding RNAs with gene regulatory functions, frequently dysregulated in human cancers. Specific signatures of differentially expressed miRNAs can be used in the diagnosis of cancer and in some cases harbor prognostic implications. The biology of cancer is dictated not only by cancer cells but also by the surrounding tumor microenvironment. In particular, the role of miRNAs within the tumor microenvironment is emerging as of paramount importance. This review will focus on the current knowledge of the role of miRNAs and both cellular and stromal components of the tumor microenvironment. We will also discuss more recent findings, showing that miRNAs can be found inside of exosomes and mediate the cross-talk between cancer cells and surrounding cells, leading to the discovery of new fascinating molecular mechanisms leading to a better understanding of the cancer 'niche' and how these noncoding RNAs can become very promising diagnostic molecules.

Assessment of Liver Fibrotic Insults In Vitro

In vitro systems are required to evaluate potential liver fibrogenic effects of drugs and compounds during drug development and toxicity screening, respectively. Upon liver injury or toxicity, hepatic stellate cells are activated, thereby acquiring a myofibroblastic phenotype and participating in extracellular matrix deposition and liver fibrosis. The most widely used in vitro models to investigate liver fibrogenesis are primary cultures of hepatic stellate cells, which can be isolated from healthy human livers. Currently, there are no effective methods to maintain hepatic stellate cells in vitro in a quiescent phenotype. Therefore, when cells are plated, they spontaneously become activated in few days. Most in vitro studies in this area have been performed with monocultures of hepatic stellate cells in order to assess the direct effects of a given factor on hepatic stellate cell activation or the induction of inflammatory and fibrogenic responses. In this chapter, focus is put on basic protocols to isolate hepatic stellate cells from human tissue and to maintain them in culture as well as on common in vitro assays to evaluate their response to profibrogenic factors.