Inhibition of the activation of hepatic stellate cells by arundic acid via the induction of cytoglobin

Transcriptomics of a cytoglobin knockout mouse: Insights from hepatic stellate cells and brain

The vertebrate respiratory protein cytoglobin (Cygb) is thought to exert multiple cellular functions. Here we studied the phenotypic effects of a Cygb knockout (KO) in mouse on the transcriptome level. RNA sequencing (RNA-Seq) was performed for the first time on sites of major endogenous Cygb expression, i.e. quiescent and activated hepatic stellate cells (HSCs) and two brain regions, hippocampus and hypothalamus. The data recapitulated the up-regulation of Cygb during HSC activation and its expression in the brain. Differential gene expression analyses suggested a role of Cygb in the response to inflammation in HSCs and its involvement in retinoid metabolism, retinoid X receptor (RXR) activation-induced xenobiotics metabolism, and RXR activation-induced lipid metabolism and signaling in activated cells. Unexpectedly, only minor effects of the Cygb KO were detected in the transcriptional profiles in hippocampus and hypothalamus, precluding any enrichment analyses. Furthermore, the transcriptome data pointed at a previously undescribed potential of the Cygb- knockout allele to produce cis-acting effects, necessitating future verification studies.

Structural and functional properties of Antarctic fish cytoglobins-1: Cold-reactivity in multi-ligand reactions

While the functions of the recently discovered cytoglobin, ubiquitously expressed in vertebrate tissues, remain uncertain, Antarctic fish provide unparalleled models to study novel protein traits that may arise from cold adaptation. We report here the spectral, ligand-binding and enzymatic properties (peroxynitrite isomerization, nitrite-reductase activity) of cytoglobin-1 from two Antarctic fish, Chaenocephalus aceratus and Dissostichus mawsoni, and present the crystal structure of D. mawsoni cytoglobin-1. The Antarctic cytoglobins-1 display high O₂ affinity, scarcely compatible with an O₂-supply role, a slow rate constant for nitrite-reductase activity, and do not catalyze peroxynitrite isomerization. Compared with mesophilic orthologues, the cold-adapted cytoglobins favor binding of exogenous ligands to the hexa-coordinated bis-histidyl species, a trait related to their higher rate constant for distal-His/heme-Fe dissociation relative to human cytoglobin. At the light of a remarkable 3D-structure conservation, the observed differences in ligand-binding kinetics may reflect Antarctic fish cytoglobin-1 specific features in the dynamics of the heme distal region and of protein matrix cavities, suggesting adaptation to functional requirements posed by the cold environment. Taken together, the biochemical and biophysical data presented suggest that in Antarctic fish, as in humans, cytoglobin-1 unlikely plays a role in O₂ transport, rather it may be involved in processes such as NO detoxification.

Adaptations to environmental change: Globin superfamily evolution in Antarctic fishes

The ancient origins and functional versatility of globins make them ideal subjects for studying physiological adaptation to environmental change. Our goals in this review are to describe the evolution of the vertebrate globin gene superfamily and to explore the structure/function relationships of hemoglobin, myoglobin, neuroglobin and cytoglobin in teleost fishes. We focus on the globins of Antarctic notothenioids, emphasizing their adaptive features as inferred from comparisons with human proteins. We dedicate this review to Guido di Prisco, our co-author, colleague, friend, and husband of C.V. Ever thoughtful, creative, and enthusiastic, Guido spearheaded study of the structure, function, and evolution of the hemoglobins of polar fishes - this review is testimony to his wide-ranging contributions. Throughout his career, Guido inspired younger scientists to embrace polar biological research, and he challenged researchers of all ages to explore evolutionary adaptation in the context of global climate change. Beyond his scientific contributions, we will miss his warmth, his culture, and his great intellect. Guido has left an outstanding legacy, one that will continue to inspire us and our research.

A modified method for isolating human quiescent pancreatic stellate cells

Background

This study explored a simple, high-yield method for isolating quiescent human pancreatic stellate cells (PSCs) to provide sufficient and reliable raw materials for PSC-related studies.

Materials and methods

Single-cell suspensions were prepared from normal human pancreatic tissue specimens using the gentleMACS^™ tissue processor, which enhanced the yield and viability of the suspensions. Percoll density gradient centrifugation was then performed to isolate quiescent normal PSCs (NPSCs). Cell viability was determined by trypan blue staining, and the states of the NPSCs were determined by autofluorescence and oil red O staining. The purity of human activated PSCs (APSCs) was determined by immunofluorescence assays.

Results

The yield of NPSCs was ~(2.75±0.65)×10⁶ cells/g. The maximum cell viability was 92%, whereas the maximum cell purity was 95%.

Conclusion

The method employed in this study to isolate PSCs is a simple, high-yield and stable method that is worth popularizing.

Autophagy activation by Jiang Zhi Granule protects against metabolic stress-induced hepatocyte injury

AIM

To elucidate the potential role of autophagy and the protective effects of Jiang Zhi Granule (JZG) in metabolic stress-induced hepatocyte injury.

METHODS

An in vitro and in vivo approach was used in this study. HepG2 cells were incubated in culture medium containing palmitate (PA; 0, 0.1, 0.2, 0.3, 0.4 or 0.5 mmol/L) and treated with or without JZG (100 μg/mL) for 24 h or 48 h, and the progression of autophagy was visualized by stable fluorescence-expressing cell lines LC3 and p62. Western blot analyses were performed to examine the expression of LC3-II/LC3-I, p62, mTOR and PI3K, while mitochondrial integrity and oxidative stress were observed by fluorescence staining of JC-1 and reactive oxygen species. C57BL/6 mice were divided into three groups: control group (n = 10), high fat (HF) group (n = 13) and JZG group (n = 13); and, histological staining was carried out to detect inflammation and lipid content in the liver.

RESULTS

The cell trauma induced by PA was aggravated in a dose- and time-dependent manner, and hepatic function was improved by JZG. PA had dual effects on autophagy by activating autophagy induction and blocking autophagic flux. The PI3K-AKT-mTOR signaling pathway and the fusion of isolated hepatic autophagosomes and lysosomes were critically involved in this process. JZG activated autophagy progression by either induction of autophagosomes or co-localization of autophagosomes and lysosomes as well as degradation of autolysosomes to protect against PA-induced hepatocyte injury, and protected mitochondrial integrity against oxidative stress in PA-induced mitochondrial dysfunction. In addition, JZG ameliorated lipid droplets and inflammation induced by HF diet in vivo, leading to improved metabolic disorder and associated liver injury in a mouse model of non-alcoholic fatty liver disease (NAFLD).

CONCLUSION

Metabolic stress-induced hepatocyte injury exhibited dual effects on autophagy and JZG activated the entire process, resulting in beneficial effects in NAFLD.

Antarctic fish versus human cytoglobins - The same but yet so different

The cytoglobins of the Antarctic fish Chaenocephalus aceratus and Dissostichus mawsoni have many features in common with human cytoglobin. These cytoglobins are heme proteins in which the ferric and ferrous forms have a characteristic hexacoordination of the heme iron, i.e. axial ligation of two endogenous histidine residues, as confirmed by electron paramagnetic resonance, resonance Raman and optical absorption spectroscopy. The combined spectroscopic analysis revealed only small variations in the heme-pocket structure, in line with the small variations observed for the redox potential. Nevertheless, some striking differences were also discovered. Resonance Raman spectroscopy showed that the stabilization of an exogenous heme ligand, such as CO, occurs differently in human cytoglobin in comparison with Antarctic fish cytoglobins. Furthermore, while it has been extensively reported that human cytoglobin is essentially monomeric and can form an intramolecular disulfide bridge that can influence the ligand binding kinetics, 3D modeling of the Antarctic fish cytoglobins indicates that the cysteine residues are too far apart to form such an intramolecular bridge. Moreover, gel filtration and mass spectrometry reveal the occurrence of non-covalent multimers (up to pentamers) in the Antarctic fish cytoglobins that are formed at low concentrations. Stabilization of these oligomers by disulfide-bridge formation is possible, but not essential. If intermolecular disulfide bridges are formed, they influence the heme-pocket structure, as is shown by EPR measurements.

Arundic Acid Prevents Developmental Upregulation of S100B Expression and Inhibits Enteric Glial Development

S100B is expressed in various types of glial cells and is involved in regulating many aspects of their function. However, little is known about its role during nervous system development. In this study, we investigated the effect of inhibiting the onset of S100B synthesis in the development of the enteric nervous system, a network of neurons and glia located in the wall of the gut that is vital for control of gastrointestinal function. Intact gut explants were taken from embryonic day (E)13.5 mice, the day before the first immunohistochemical detection of S100B, and cultured in the presence of arundic acid, an inhibitor of S100B synthesis, for 48 h. The effects on Sox10-immunoreactive enteric neural crest progenitors and Hu-immunoreactive enteric neurons were then analyzed. Culture in arundic acid reduced the proportion of Sox10+ cells and decreased cell proliferation. There was no change in the density of Hu+ enteric neurons, however, a small population of cells exhibited atypical co-expression of both Sox10 and Hu, which was not observed in control cultures. Addition of exogenous S100B to the cultures did not change Sox10+ cell numbers. Overall, our data suggest that cell-intrinsic intracellular S100B is important for maintaining Sox10 and proliferation of the developing enteric glial lineage.

Cyanidin-3-O-β-glucoside combined with its metabolite protocatechuic acid attenuated the activation of mice hepatic stellate cells

Cyanidin-3-O-β-glucoside with the aid of its metabolite protocatechuic acid attenuated the activation of mice hepatic stellate cells.

Cytoglobin as a Marker of Hepatic Stellate Cell-derived Myofibroblasts

Myofibroblasts play important roles in inflammation, fibrosis and tumorigenesis in chronically inflamed liver. Liver myofibroblasts originate from hepatic stellate cells, portal fibroblasts or mesothelial cells, and they are localized in and around fibrotic septum and portal tracts. Liver myofibroblasts are the source of extracellular matrix materials, including type I collagen and multiple fibrogenic growth factors, such as transforming growth factor-β and vascular endothelial growth factor. Although a detailed characterization of the function of individual myofibroblasts has not been conducted, owing to the lack of appropriate cell markers, recent lineage-tracing technology has revealed the limited contribution of myofibroblasts that are derived from portal fibroblasts to various types of liver fibrosis, as compared with the contribution of hepatic stellate cells. In addition, cytoglobin, which is the fourth globin in mammals and function as a local gas sensor, provides a new perspective on the involvement of stellate cells in fibrosis and carcinogenesis, possibly through its anti-oxidative properties and is a promising new marker that discriminates between myofibroblasts derived from stellate cells and those from portal fibroblasts.

Cytoglobin expression in the hepatic stellate cell line HSC-T6 is regulated by extracellular matrix proteins dependent on FAK-signalling

BACKGROUND

Fibrosis is a physiological response to cellular injury in the liver and is mediated by the activation of hepatic stellate cells resulting in the replacement of hepatocytes with extracellular matrix comprised principally of collagen 1 to form a hepatic scar. Although the novel hexaco-ordinated globin cytoglobin was identified in activated hepatic stellate cells more than 10 years ago, its role in stellate cell biology and liver fibrosis remains enigmatic.

RESULTS

In the current study, we investigated the role of different extracellular matrix proteins in stellate cell proliferation, activation (alpha smooth muscle actin expression and retinoic acid uptake) and cytoglobin expression. Our results demonstrate that cytoglobin expression is correlated with a more quiescent phenotype of stellate cells in culture and that cytoglobin is regulated by the extracellular matrix through integrin signalling dependent on activation of focal adhesion kinase.

CONCLUSIONS

Although further studies are required, we provide evidence that cytoglobin is a negative regulator of stellate cell activation and therefore may represent a novel target for anti-fibrotic treatments in the future.

Cytoglobin as a Biomarker in Cancer: Potential Perspective for Diagnosis and Management

The search for biomarkers to detect the earliest glimpse of cancer has been one of the primary objectives of cancer research initiatives. These endeavours, in spite of constant clinical challenges, are now more focused as early cancer detection provides increased opportunities for different interventions and therapies, with higher potential for improving patient survival and quality of life. With the progress of the omics technologies, proteomics and metabolomics are currently being used for identification of biomarkers. In this line, cytoglobin (Cygb), a ubiquitously found protein, has been actively reviewed for its functional role. Cytoglobin is dynamically responsive to a number of insults, namely, fibrosis, oxidative stress, and hypoxia. Recently, it has been reported that Cygb is downregulated in a number of malignancies and that an induced overexpression reduces the proliferative characteristics of cancer cells. Thus, the upregulation of cytoglobin can be indicative of a tumour suppressor ability. Nevertheless, without a comprehensive outlook of the molecular and functional role of the globin, it will be most unlikely to consider cytoglobin as a biomarker for early detection of cancer or as a therapeutic option. This review provides an overview of the proposed role of cytoglobin and explores its potential functional role as a biomarker for cancer and other diseases.

Involvement of hepatic stellate cell cytoglobin in acute hepatocyte damage through the regulation of CYP2E1-mediated xenobiotic metabolism

Oxygen (O2) is required for cytochrome P450 (CYP)-dependent drug metabolism. Cytoglobin (CYGB) is a unique globin expressed exclusively in hepatic stellate cells (HSCs). However, its role in O2-dependent metabolism in neighboring hepatocytes remains unknown. This study provides evidence that CYGB in HSCs is involved in acetaminophen (N-acetyl-p-aminophenol; APAP)-induced hepatotoxicity. Serum alanine aminotransferase levels were higher in wild-type mice than in Cygb-null mice. Wild-type mice exhibited more severe hepatocyte necrosis around the central vein area compared with Cygb-null mice, thus indicating that CYGB deficiency protects against APAP-induced liver damage. Although no difference in the hepatic expression of CYP2E1, a key enzyme involved in APAP toxicity, was observed between wild-type and Cygb-null mice, the serum levels of the APAP metabolites cysteinyl-APAP and N-acetyl-cysteinyl-APAP were decreased in Cygb-null mice, suggesting reduced APAP metabolism in the livers of Cygb-null mice. In primary cultures, APAP-induced hepatocyte damage was increased by co-culturing with wild-type HSCs but not with Cygb-null HSCs. In addition, cell damage was markedly alleviated under low O2 condition (5% O2), suggesting the requirement of O2 for APAP toxicity. Carbon tetrachloride-induced liver injury (CYP2E1-dependent), but not lipopolysaccharide/D-galactosamine-induced injury (CYP2E1-independent), was similarly alleviated in Cygb-null mice. Considering the function of CYGB as O2 carrier, these results strongly support the hypothesis that HSCs are involved in the CYP2E1-mediated xenobiotic activation by augmenting O2 supply to hepatocytes. In conclusion, CYGB in HSCs contributes to the CYP-mediated metabolism of xenobiotics in hepatocytes by supplying O2 for enzymatic oxidation.

Inhibition of LXRα/SREBP-1c-Mediated Hepatic Steatosis by Jiang-Zhi Granule

Nonalcoholic fatty liver (NAFL) is increasingly recognized as one of the most common causes of chronic liver disease worldwide. Traditional Chinese medicine (TCM), as the alternative and complementary medicine, may provide some profound health benefit. “Jiang-Zhi” Granule (JZG) was composed based on TCM pathogenesis of NAFL: the retention of inner dampness, heat and blood stasis. This study investigated effects of JZG on liver X receptor-α (LXRα)/sterol regulatory element binding protein-1c (SREBP-1c) pathway in high-fat-diet-(HFD-)induced hepatic steatosis, as well as in free-fatty-acid-(FFA-)and T0901317-treated HepG2 cells. The results showed that JZG had an antisteatotic effect on HFD-fed rats. JZG decreased the activation of SREBP-1c through inhibiting LXRα-mediated SREBP-1c transcription, as well as through inhibiting the maturation of SREBP-1c independent of LXRα. These findings may provide molecular evidence for the use of JZG as a promising therapeutic option for NAFL and support us to continue JZG treatment in NAFL. For JZG treatment to be widely accepted, a randomized, double-blind, multicenter, placebo-controlled, phase III trial is ongoing.

Non-covalent and covalent modifications modulate the reactivity of monomeric mammalian globins

Multimeric globins (e.g., hemoglobin) are considered to be the prototypes of allosteric enzymes, whereas monomeric globins (e.g., myoglobin; Mb) usually are assumed to be non-allosteric. However, the modulation of the functional properties of monomeric globins by non-covalent (or allosteric) and covalent modifications casts doubts on this general assumption. Here, we report examples referable to these two extreme mechanisms modulating the reactivity of three mammalian monomeric globins. Sperm whale Mb, which acts as a reserve supply of O2 and facilitates the O2 flux within a myocyte, displays the allosteric modulation of the O2 affinity on lactate, an obligatory product of glycolysis under anaerobic conditions, thus facilitating O2 diffusion to the mitochondria in supporting oxidative phosphorylation. Human neuroglobin (NGB), which appears to protect neurons from hypoxia in vitro and in vivo, undergoes hypoxia-dependent phosphorylation (i.e., covalent modulation) affecting the coordination equilibrium of the heme-Fe atom and, in turn, the heme-protein reactivity. This facilitates heme-Fe-ligand binding and enhances the rate of anaerobic nitrite reduction to form NO, thus contributing to cellular adaptation to hypoxia. The reactivity of human cytoglobin (CYGB), which has been postulated to protect cells against oxidative stress, depends on both non-covalent and covalent mechanisms. In fact, the heme reactivity of CYGB depends on the lipid, such as oleate, binding which stabilizes the penta-coordination geometry of the heme-Fe atom. Lastly, the reactivity of NGB and CYGB is modulated by the redox state of the intramolecular CysCD7/CysD5 and CysB2/CysE9 residue pairs, respectively, affecting the heme-Fe atom coordination state. In conclusion, the modulation of monomeric globins reactivity by non-covalent and covalent modifications appears a very widespread phenomenon, opening new perspectives in cell survival and protection. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.