ACLY as a modulator of liver cell functions and its role in Metabolic Dysfunction-Associated Steatohepatitis

BACKGROUND

Non-alcoholic Fatty Liver Disease (NAFLD), now better known as Metabolic (Dysfunction)-Associated Fatty Liver Disease (MAFLD) and its progression to Nonalcoholic Steatohepatitis (NASH), more recently referred to as Metabolic (Dysfunction)-Associated Steatohepatitis (MASH) are the most common causes of liver failure and chronic liver damage. The new names emphasize the metabolic involvement both in relation to liver function and pathological features with extrahepatic manifestations. This study aims to explore the role of the immunometabolic enzyme ATP citrate lyase (ACLY), with a critical function in lipogenesis, carbohydrate metabolism, gene expression and inflammation.

METHODS

ACLY function was investigated in TNFα-triggered human hepatocytes and in PBMC-derived macrophages from MASH patients. Evaluation of expression levels was carried out by western blotting and/or RT-qPCR. In the presence or absence of ACLY inhibitors, ROS, lipid peroxidation and GSSG oxidative stress biomarkers were quantified. Chromatin immunoprecipitation (ChIP), transient transfections, immunocytochemistry, histone acetylation quantitation were used to investigate ACLY function in gene expression reprogramming. IL-6 and IL-1β were quantified by Lumit immunoassays.

RESULTS

Mechanistically, ACLY inhibition reverted lipid accumulation and oxidative damage while reduced secretion of inflammatory cytokines in TNFα-triggered human hepatocytes. These effects impacted not only on lipid metabolism but also on other crucial features of liver function such as redox status and production of inflammatory mediators. Moreover, ACLY mRNA levels together with those of malic enzyme 1 (ME1) increased in human PBMC-derived macrophages from MASH patients when compared to age-matched healthy controls. Remarkably, a combination of hydroxycitrate (HCA), the natural ACLY inhibitor, with red wine powder (RWP) significantly lowered ACLY and ME1 mRNA amount as well as IL-6 and IL-1β production in macrophages from subjects with MASH.

CONCLUSION

Collectively, our findings for the first time highlight a broad spectrum of ACLY functions in liver as well as in the pathogenesis of MASH and its diagnostic and therapeutic potential value.

New Insights into NF-κB Signaling in Innate Immunity: Focus on Immunometabolic Crosstalks

The nuclear factor kappa B (NF-κB) is a family of transcription factors that, beyond their numberless functions in various cell processes, play a pivotal role in regulating immune cell activation. Two main pathways-canonical and non-canonical-are responsible for NF-κB activation and heterodimer translocation into the nucleus. A complex crosstalk between NF-κB signaling and metabolism is emerging in innate immunity. Metabolic enzymes and metabolites regulate NF-κB activity in many cases through post-translational modifications such as acetylation and phosphorylation. On the other hand, NF-κB affects immunometabolic pathways, including the citrate pathway, thereby building an intricate network. In this review, the emerging findings about NF-κB function in innate immunity and the interplay between NF-κB and immunometabolism have been discussed. These outcomes allow for a deeper comprehension of the molecular mechanisms underlying NF-κB function in innate immune cells. Moreover, the new insights are important in order to perceive NF-κB signaling as a potential therapeutic target for inflammatory/immune chronic diseases.

Immunometabolism Modulation by Extracts from Pistachio Stalks Formulated in Phospholipid Vesicles

Several studies have demonstrated the effectiveness of plant extracts against various diseases, especially skin disorders; namely, they exhibit overall protective effects. The Pistachio (Pistacia vera L.) is known for having bioactive compounds that can effectively contribute to a person's healthy status. However, these benefits may be limited by the toxicity and low bioavailability often inherent in bioactive compounds. To overcome these problems, delivery systems, such as phospholipid vesicles, can be employed. In this study, an essential oil and a hydrolate were produced from P. vera stalks, which are usually discarded as waste. The extracts were characterized by liquid and gas chromatography coupled with mass spectrometry and formulated in phospholipid vesicles intended for skin application. Liposomes and transfersomes showed small size (<100 nm), negative charge (approximately -15 mV), and a longer storage stability for the latter. The entrapment efficiency was determined via the quantification of the major compounds identified in the extracts and was >80%. The immune-modulating activity of the extracts was assayed in macrophage cell cultures. Most interestingly, the formulation in transfersomes abolished the cytotoxicity of the essential oil while increasing its ability to inhibit inflammatory mediators via the immunometabolic citrate pathway.

Mitochondrial Role in Intrinsic Apoptosis Induced by a New Synthesized Chalcone in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is the most common type of liver cancer and the fourth cause of cancer-related deaths worldwide. Presently, a few drugs are available for HCC treatment and prevention, including both natural and synthetic compounds. In this study, a new chalcone, (E)-1-(2,4,6-triethoxyphenyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (ETTC), was synthesized and its effects and mechanisms of action over human hepatoma cells were investigated. Cytotoxic activity was revealed in HCC cells, while no effects were observed in normal hepatocytes. In HCC cells, ETTC caused subG1 cell cycle arrest and apoptosis, characterized by nuclear fragmentation. The activation of caspases 3/7 and 9, the increase in pro-apoptotic BAX, and the decrease in anti-apoptotic BCL-2 suggest the activation of the intrinsic pathway of apoptosis. ETTC mitochondrial targeting is confirmed by the reduction in mitochondrial membrane potential and Complex I activity together with levels of superoxide anion increasing. Our outcomes prove the potential mitochondria-mediated antitumor effect of newly synthesized chalcone ETTC in HCC.

Liposome-Mediated Inhibition of Inflammation by Hydroxycitrate

Hydroxycitrate (HCA), a main organic acid component of the fruit rind of Garcinia cambogia, is a natural citrate analog that can inhibit the ATP citrate lyase (ACLY) enzyme with a consequent reduction of inflammatory mediators (i.e., nitric oxide (NO), reactive oxygen species (ROS), and prostaglandin E₂ (PGE₂)) levels. Therefore, HCA has been proposed as a novel means to prevent, treat, and ameliorate conditions involving inflammation. However, HCA presents a low membrane permeability, and a large quantity is required to have a biological effect. To overcome this problem, HCA was formulated in liposomes in this work, and the enhancement of HCA cell availability along with the reduction in the amount required to downregulate NO, ROS, and PGE₂ in macrophages were assessed. The liposomes were small in size (~60 nm), monodispersed, negatively charged (−50 mV), and stable on storage. The in vitro results showed that the liposomal encapsulation increased by approximately 4 times the intracellular accumulation of HCA in macrophages, and reduced by 10 times the amount of HCA required to abolish LPS-induced NO, ROS, and PGE₂ increase. This suggests that liposomal HCA can be exploited to target the citrate pathway involved in inflammatory processes.

New synthesized polyoxygenated diarylheptanoids suppress lipopolysaccharide-induced neuroinflammation

In neurodegenerative diseases, such as Alzheimer's disease, Huntington's disease, Parkinson's disease and multiple sclerosis, neuroinflammation induced by the microglial activation plays a crucial role. In effort to develop effective anti-neuroinflammatory compounds, different new linear polyoxygenated diarylheptanoids were synthesized. In LPS-triggered BV-2 microglial cells their ability to reduce the concentration of IL-6 and TNF-α pro-inflammatory cytokines was evaluated. Moreover, their effect on NF-κB and ATP citrate lyase (ACLY), a recently emerged target of metabolic reprogramming in inflammation, was assessed. Finally, we turned our attention to inflammatory mediators derived from the cleavage of citrate catalyzed by ACLY: prostaglandin E₂, nitric oxide and reactive oxygen species. All compounds showed null or minimal cytotoxicity; most of them had a great anti-neuroinflammatory activity. Diarylheptanoids 6b and 6c, bearing a halide atom and benzyl ether protective groups, exhibited the best effect since they blocked the secretion of all inflammatory mediators analyzed and reduced NF-κB and ACLY protein levels.

Cystic Hygroma: A Preliminary Genetic Study and a Short Review from the Literature

BACKGROUND

The objective of this study is to examine the hypothesis that cystic hygroma (CH) with normal karyotype can manifest as a Mendelian inherited trait, and that a genetic similitude with hereditary lymphedema exists. To reach this goal, we investigated the prevalence of genetic variants in angiogenesis and lymphangiogenesis genes in a cohort of euploid fetuses with CH that almost resolved before delivery. A short review of cases from literature is also reported.

METHODS AND RESULTS

Five fetuses were screened using a next-generation sequencing approach by targeting 33 genes known to be associated with vascular and lymphatic malformations. The genetic evaluation revealed two novel variants in KDR and KRIT1 genes.

CONCLUSION

A review of the literature to date revealed that an association exists between CH and hereditary lymphedema and, similar to lymphedema, CH can be inherited in autosomal recessive and autosomal dominant manner, with the latter most likely associated with a better prognosis. About KDR and KRIT1 genes, no other similar associations are reported in the literature and caution is needed in their interpretation. In conclusion, we thought that a genetic test for the outcome of familial CH could be of enormous prognostic value.

TNFR1 -383 A˃C polymorphism and ankylosing spondylitis in a Russian Caucasian population: a preliminary study

The aim of this study was to assess the association between the TNFR1 rs2234649 polymorphism and ankylosing spondylitis susceptibility in a Russian Caucasian population. A total of 41 ankylosing spondylitis patients and 43 healthy controls, matched according to age and sex, were enrolled, and polymerase chain reaction-restriction fragment length polymorphism analysis was used to genotype the rs2234649 variant. We evaluated genotype distributions in the patient and control groups with the chi-square test, and assessed the relationship between genotypes and ankylosing spondylitis using the odds ratio. Our analysis showed that the rs2234649 polymorphism does not increase ankylosing spondylitis risk. In conclusion, the TNFR1 gene polymorphism tested does not appear to be useful for assessing predisposition to this disease or for its diagnosis or prognosis.

Mitochondrial carriers in inflammation induced by bacterial endotoxin and cytokines

Significant metabolic changes occur in the shift from resting to activated cellular status in inflammation. Thus, changes in expression of a large number of genes and extensive metabolic reprogramming gives rise to acquisition of new functions (e.g. production of cytokines, intermediates for biosynthesis, lipid mediators, PGE, ROS and NO). In this context, mitochondrial carriers, which catalyse the transport of solute across mitochondrial membrane, change their expression to transport mitochondrially produced molecules, among which citrate and succinate, to be used as intracellular signalling molecules in inflammation. This review summarises the mitochondrial carriers studied so far that are, directly or indirectly, involved in inflammation.

The contribution of the citrate pathway to oxidative stress in Down syndrome

Inflammatory conditions and oxidative stress have a crucial role in Down syndrome (DS). Emerging studies have also reported an altered lipid profile in the early stages of DS. Our previous works demonstrate that citrate pathway activation is required for oxygen radical production during inflammation. Here, we find up-regulation of the citrate pathway and down-regulation of carnitine/acylcarnitine carrier and carnitine palmitoyl-transferase 1 genes in cells from children with DS. Interestingly, when the citrate pathway is inhibited, we observe a reduction in oxygen radicals as well as in lipid peroxidation levels. Our preliminary findings provide evidence for a citrate pathway dysregulation, which could be related to some phenotypic traits of people with DS.

Sudemycin E influences alternative splicing and changes chromatin modifications

Sudemycin E is an analog of the pre-messenger RNA splicing modulator FR901464 and its derivative spliceostatin A. Sudemycin E causes the death of cancer cells through an unknown mechanism. We found that similar to spliceostatin A, sudemycin E binds to the U2 small nuclear ribonucleoprotein (snRNP) component SF3B1. Native chromatin immunoprecipitations showed that U2 snRNPs physically interact with nucleosomes. Sudemycin E induces a dissociation of the U2 snRNPs and decreases their interaction with nucleosomes. To determine the effect on gene expression, we performed genome-wide array analysis. Sudemycin E first causes a rapid change in alternative pre-messenger RNA splicing, which is later followed by changes in overall gene expression and arrest in the G2 phase of the cell cycle. The changes in alternative exon usage correlate with a loss of the H3K36me3 modification in chromatin encoding these exons. We propose that sudemycin E interferes with the ability of U2 snRNP to maintain an H3K36me3 modification in actively transcribed genes. Thus, in addition to the reversible changes in alternative splicing, sudemycin E causes changes in chromatin modifications that result in chromatin condensation, which is a likely contributing factor to cancer cell death.

Valproic acid causes proteasomal degradation of DICER and influences miRNA expression

Valproic acid (VPA) is a commonly used drug to treat epilepsy and bipolar disorders. Known properties of VPA are inhibitions of histone deacetylases and activation of extracellular signal regulated kinases (ERK), which cannot fully explain VPA's clinical features. We found that VPA induces the proteasomal degradation of DICER, a key protein in the generation of micro RNAs. Unexpectedly, the concentration of several micro RNAs increases after VPA treatment, which is caused by the upregulation of their hosting genes prior to DICER degradation. The data suggest that a loss of DICER protein and changes in micro RNA concentration contributes to the clinical properties of VPA. VPA can be used experimentally to down regulate DICER protein levels, which likely reflects a natural regulation of DICER.

Insight into mechanism of in vitro insulin secretion increase induced by antipsychotic clozapine: role of FOXA1 and mitochondrial citrate carrier

The use of clozapine and other antipsychotic drugs is known to be associated with a number of adverse metabolic side effects, including diabetes mellitus. These side effects could be, at least in part, the result of impaired islet cell function and abnormal insulin secretion, although the underlying mechanisms are unknown. The aim of this study is the identification of targets for clozapine related to the abnormal insulin secretion. We identify a specific activation of the transcriptional factor FOXA1, but not FOXA2 and FOXA3, by clozapine in HepG2 cells. Clozapine enhances FOXA1 DNA-binding and its transcriptional activity, increasing mitochondrial citrate carrier gene expression, which contains a FOXA1 site in its promoter. Haloperidol, a conventional antipsychotic drug, does not determine any increase of FOXA1 gene expression. We also demonstrate that clozapine upregulates FOXA1 and CIC gene expression in INS-1 cells only at basal glucose concentration. In addition, we find that abnormal insulin secretion in basal glucose conditions could be completely abolished by FOXA1 silencing in INS-1 cells treated with clozapine. The identification of FOXA1 as a novel target for clozapine may shed more light to understand molecular mechanism of abnormal insulin secretion during clozapine treatment.

Genome wide array analysis indicates that an amyotrophic lateral sclerosis mutation of FUS causes an early increase of CAMK2N2 in vitro

Mutations in the RNA binding protein FUS (fused in sarcoma) have been linked to a subset of familial amyotrophic lateral sclerosis (ALS) cases. The mutations are clustered in the C-terminal nuclear localization sequence (NLS). Various FUS mutants accumulate in the cytoplasm whereas wild-type (WT) FUS is mainly nuclear. Here we investigate the effect of one ALS causing mutant (FUS-ΔNLS, also known as R495X) on pre-mRNA splicing and RNA expression using genome wide exon-junction arrays. Using a non-neuronal stable cell line with inducible FUS expression, we detected early changes in RNA composition. In particular, mutant FUS-ΔNLS increased calcium/calmodulin-dependent protein kinase II inhibitor 2 (CAMK2N2) at both mRNA and protein levels, whereas WT-FUS had no effect. Chromatin immunoprecipitation experiments showed that FUS-ΔNLS accumulated at the CAMK2N2 promoter region, whereas promoter occupation by WT-FUS remained constant. Given the loss of FUS-ΔNLS in the nucleus through the mutation-induced translocation, this increase of promoter occupancy is surprising. It indicates that, despite the obvious cytoplasmic accumulation, FUS-ΔNLS can act through a nuclear gain of function mechanism.

Function of alternative splicing

Almost all polymerase II transcripts undergo alternative pre-mRNA splicing. Here, we review the functions of alternative splicing events that have been experimentally determined. The overall function of alternative splicing is to increase the diversity of mRNAs expressed from the genome. Alternative splicing changes proteins encoded by mRNAs, which has profound functional effects. Experimental analysis of these protein isoforms showed that alternative splicing regulates binding between proteins, between proteins and nucleic acids as well as between proteins and membranes. Alternative splicing regulates the localization of proteins, their enzymatic properties and their interaction with ligands. In most cases, changes caused by individual splicing isoforms are small. However, cells typically coordinate numerous changes in 'splicing programs', which can have strong effects on cell proliferation, cell survival and properties of the nervous system. Due to its widespread usage and molecular versatility, alternative splicing emerges as a central element in gene regulation that interferes with almost every biological function analyzed.

Identification of a novel Sp1 splice variant as a strong transcriptional activator

The transcription factor Sp1 regulates expression of numerous genes involved in many cellular processes. Different post-transcriptional modifications can influence the transcriptional control activity and stability of Sp1. In addition to these modifications, alternative splicing isoforms may also be the basis of its distinct functional activities. In this study, we identified a novel alternative splice isoform of Sp1 named Sp1c. This variant is generated by exclusion of a short domain, which we designate α, through alternative splice acceptor site usage in the exon 3. The existence of this new isoform was confirmed in vivo by Western blotting analysis. Although at very low levels, Sp1c is ubiquitously expressed, as seen in its full-length Sp1. A preliminary characterization of Sp1c shows that: (a) Sp1c works as stronger activator of transcription than full-length Sp1; (b) percentage of HEK293 Sp1c-overexpressing cells is higher in G1 phase and lower in S phase than percentage of HEK293 Sp1-overexpressing cells.