Impaired novelty acquisition and synaptic plasticity in congenital hyperammonemia caused by hepatic glutamine synthetase deficiency

Neuroprotective and cognitive enhancing effects of herbecetin against thioacetamide induced hepatic encephalopathy in rats via upregulation of AMPK and SIRT1 signaling pathways

Acute liver injury, there is a risky neurological condition known as hepatic encephalopathy (HE). Herbacetin is a glycosylated flavonoid with many pharmacological characteristics. The purpose of this study was to assess the ability of herbacetin to protect against the cognitive deficits associated with thioacetamide (TAA) rat model and delineate the underlying behavioral and pharmacological mechanisms. Rats were pretreated with herbacetin (20 and 40 mg/kg) for 30days. On 30th day, the rats were injected with TAA (i.p. 350 mg/kg) in a single dose. In addition to a histpathological studies, ultra-structural architecture of the brain, liver functions, oxidative stress biomarkers, and behavioral tests were evaluated. Compared to the TAA-intoxicated group, herbacetin improved the locomotor and cognitive deficits, serum hepatotoxicity indices and ammonia levels. Herbacetin reduced brain levels of malodialdeyde, glutamine synthetase (GS), tumor necrosis factor- alpha (TNF-α), interleukin 1 B (IL-1β), annexin v, and increased brain GSH, Sirtuin 1 (SIRT1), and AMP-activated kinase (AMPK) expression levels. Also, herbacetin improve the histopathological changes and ultra- structure of brain tissue via attenuating the number of inflammatory and apoptotic cells. Herbacetin treatment significantly reduced the toxicity caused by TAA. These findings suggest that herbacetin might be taken into account as a possible neuroprotective and cognitive enhancing agent due to its ability to reduce oxidative stress, inflammation and apoptosis associated with TAA.

Ashwagandha-loaded nanocapsules improved the behavioral alterations, and blocked MAPK and induced Nrf2 signaling pathways in a hepatic encephalopathy rat model

Ashwagandha (ASH), a vital herb in Ayurvedic medicine, demonstrated potent preclinical hepato- and neuroprotective effects. However, its efficacy is limited due to low oral bioavailability. Accordingly, we encapsulated ASH extract in chitosan-alginate bipolymeric nanocapsules (ASH-BPNCs) to enhance its physical stability and therapeutic effectiveness in the gastrointestinal tract. ASH-BPNC was prepared by emulsification followed by sonication. The NCs showed small particle size (< 220 nm), zeta-potential of 25.2 mV, relatively high entrapment efficiency (79%), physical stability at acidic and neutral pH, and in vitro release profile that extended over 48 h. ASH-BPNC was then investigated in a thioacetamide-induced hepatic encephalopathy (HE) rat model. Compared with free ASH, ASH-BPNC improved survival, neurological score, general motor activity, and cognitive task-performance. ASH-BPNC restored ALT, AST and ammonia serum levels, and maintained hepatic and brain architecture. ASH-BPNC also restored GSH, MDA, and glutathione synthetase levels, and Nrf2 and MAPK signaling pathways in liver and brain tissues. Moreover, ASH-BPNC downregulated hepatic NF-κB immunohistochemical expression. Moreover, the in vivo biodistribution studies demonstrated that most of the administered ASH-BPNC is accumulated in the brain and hepatic tissues. In conclusion, chitosan-alginate BPNCs enhanced the hepatoprotective and neuroprotective effects of ASH, thus providing a promising therapeutic approach for HE.

Transcriptome Profile in the Mouse Brain of Hepatic Encephalopathy and Alzheimer's Disease

Hepatic encephalopathy (HE) is a chronic metabolic disease accompanied by neuropathological and neuropsychiatric features, including memory deficits, psychomotor dysfunction, depression, and anxiety. Alzheimer's disease (AD), the most common neurodegenerative disease, is characterized by tau hyperphosphorylation, excessive amyloid beta (Aβ) accumulation, the formation of fibrillary tangles, hippocampus atrophy, and neuroinflammation. Recent studies have suggested a positive correlation between HE and AD. Some studies reported that an impaired cholesterol pathway, abnormal bile acid secretion, excessive ammonia level, impaired Aβ clearance, astrocytic dysfunction, and abnormal γ-aminobutyric acid GABAergic neuronal signaling in HE may also be involved in AD pathology. However, the mechanisms and related genes involved in AD-like pathology in the HE brain are unclear. Thus, we compared the cortical transcriptome profile between an HE mouse model, bile duct ligation (BDL), and an AD mouse model, the 5×FAD. Our study showed that the expression of many genes implicated in HE is associated with neuronal dysfunction in AD mice. We found changes in various protein-coding RNAs, implicated in synapses, neurogenesis, neuron projection, neuron differentiation, and neurite outgrowth, and non-coding RNAs possibly associated with neuropathology. Our data provide an important resource for further studies to elucidate AD-like pathophysiology in HE patients.

ADSCs-derived exosomes ameliorate hepatic fibrosis by suppressing stellate cell activation and remodeling hepatocellular glutamine synthetase-mediated glutamine and ammonia homeostasis

Background

Hepatic fibrosis is a common pathologic stage in chronic liver disease development, which might ultimately lead to liver cirrhosis. Accumulating evidence suggests that adipose-derived stromal cells (ADSCs)-based therapies show excellent therapeutic potential in liver injury disease owing to its superior properties, including tissue repair ability and immunomodulation effect. However, cell-based therapy still limits to several problems, such as engraftment efficiency and immunoreaction, which impede the ADSCs-based therapeutics development. So, ADSCs-derived extracellular vesicles (EVs), especially for exosomes (ADSC-EXO), emerge as a promise cell-free therapeutics to ameliorate liver fibrosis. The effect and underlying mechanisms of ADSC-EXO in liver fibrosis remains blurred.

Methods

Hepatic fibrosis murine model was established by intraperitoneal sequential injecting the diethylnitrosamine (DEN) for two weeks and then carbon tetrachloride (CCl₄) for six weeks. Subsequently, hepatic fibrosis mice were administrated with ADSC-EXO (10 μg/g) or PBS through tail vein infusion for three times in two weeks. To evaluate the anti-fibrotic capacity of ADSC-EXO, we detected liver morphology by histopathological examination, ECM deposition by serology test and Sirius Red staining, profibrogenic markers by qRT-PCR assay. LX-2 cells treated with TGF-β (10 ng/ml) for 12 h were conducted for evaluating ADSC-EXO effect on activated hepatic stellate cells (HSCs). RNA-seq was performed for further analysis of the underlying regulatory mechanisms of ADSC-EXO in liver fibrosis.

Results

In this study, we obtained isolated ADSCs, collected and separated ADSCs-derived exosomes. We found that ADSC-EXO treatment could efficiently ameliorate DEN/CCl₄-induced hepatic fibrosis by improving mice liver function and lessening hepatic ECM deposition. Moreover, ADSC-EXO intervention could reverse profibrogenic phenotypes both in vivo and in vitro, including HSCs activation depressed and profibrogenic markers inhibition. Additionally, RNA-seq analysis further determined that decreased glutamine synthetase (Glul) of perivenous hepatocytes in hepatic fibrosis mice could be dramatically up-regulated by ADSC-EXO treatment; meanwhile, glutamine and ammonia metabolism-associated key enzyme OAT was up-regulated and GLS2 was down-regulated by ADSC-EXO treatment in mice liver. In addition, glutamine synthetase inhibitor would erase ADSC-EXO therapeutic effect on hepatic fibrosis.

Conclusions

These findings demonstrated that ADSC-derived exosomes could efficiently alleviate hepatic fibrosis by suppressing HSCs activation and remodeling glutamine and ammonia metabolism mediated by hepatocellular glutamine synthetase, which might be a novel and promising anti-fibrotic therapeutics for hepatic fibrosis disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03049-x.

Muskelin regulates actin-dependent synaptic changes and intrinsic brain activity relevant to behavioral and cognitive processes

Muskelin (Mkln1) is implicated in neuronal function, regulating plasma membrane receptor trafficking. However, its influence on intrinsic brain activity and corresponding behavioral processes remains unclear. Here we show that murine Mkln1 knockout causes non-habituating locomotor activity, increased exploratory drive, and decreased locomotor response to amphetamine. Muskelin deficiency impairs social novelty detection while promoting the retention of spatial reference memory and fear extinction recall. This is strongly mirrored in either weaker or stronger resting-state functional connectivity between critical circuits mediating locomotor exploration and cognition. We show that Mkln1 deletion alters dendrite branching and spine structure, coinciding with enhanced AMPAR-mediated synaptic transmission but selective impairment in synaptic potentiation maintenance. We identify muskelin at excitatory synapses and highlight its role in regulating dendritic spine actin stability. Our findings point to aberrant spine actin modulation and changes in glutamatergic synaptic function as critical mechanisms that contribute to the neurobehavioral phenotype arising from Mkln1 ablation.

A murine muskelin knockout induces increased exploratory drive and alters cognition and functional connectivity. These effects correlate with actin-dependent changes in dendritic branching, spine structure, and AMPAR-mediated synaptic transmission.

Comprehensive Analysis of lncRNAs, miRNAs and mRNAs in Mouse Hippocampus With Hepatic Encephalopathy

Hepatic encephalopathy (HE) often presents with varying degrees of cognitive impairment. However, the molecular mechanism of its cognitive impairment has not been fully elucidated. Whole transcriptome analysis of hippocampus between normal and HE mice was performed by using RNA sequencing. 229 lncRNAs, 49 miRNAs and 363 mRNAs were differentially expressed in HE mice. The lncRNA-miRNA-mRNA interaction networks were established, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed. Dysregulated RNAs in interaction networks were mainly involved in synaptic plasticity and the regulation of learning and memory. In NH4Cl-treated hippocampal neurons, the dendritic spine density and maturity decreased significantly, the amplitude and frequency of mIPSC increased, while the amplitude and frequency of mEPSC decreased. These manifestations can be reversed by silencing SIX3OS1. Further research on these no-coding RNAs may lead to new therapies for the treatment and management of brain dysfunction caused by HE.

Hepatic Encephalopathy: From Metabolic to Neurodegenerative

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of both acute and chronic liver disease. As a metabolic disorder, HE is considered to be reversible and therefore is expected to resolve following the replacement of the diseased liver with a healthy liver. However, persisting neurological complications are observed in up to 47% of transplanted patients. Several retrospective studies have shown that patients with a history of HE, particularly overt-HE, had persistent neurological complications even after liver transplantation (LT). These enduring neurological conditions significantly affect patient's quality of life and continue to add to the economic burden of chronic liver disease on health care systems. This review discusses the journey of the brain through the progression of liver disease, entering the invasive surgical procedure of LT and the conditions associated with the post-transplant period. In particular, it will discuss the vulnerability of the HE brain to peri-operative factors and post-LT conditions which may explain non-resolved neurological impairment following LT. In addition, the review will provide evidence; (i) supporting overt-HE impacts on neurological complications post-LT; (ii) that overt-HE leads to permanent neuronal injury and (iii) the pathophysiological role of ammonia toxicity on astrocyte and neuronal injury/damage. Together, these findings will provide new insights on the underlying mechanisms leading to neurological complications post-LT.

Cognition-tracking-based strategies for diagnosis and treatment of minimal hepatic encephalopathy

Minimal hepatic encephalopathy (MHE), which shows mild cognitive impairment, is a subtle complication of cirrhosis that has been shown to affect daily functioning and quality of life. However, until 2014, relevant guidelines do not give much attention to the diagnosis and treatment of MHE, resulting in patients being ignored and denied the benefits of treatment. In this review, we summarize recent cognition-based research about (1) alteration of nerve cells, including astrocytes, microglial cells and neurons, in mild cognitive impairment in MHE; (2) comparison of methods in detecting cognitive impairment in MHE; and (3) comparison of methods for therapy of cognitive impairment in MHE. We hope to provide information about diagnosis and treatment of cognitive impairment in patients with MHE.

Instant activation of TRP channels by NH4 + promotes neuronal bursting and glutamate spikes in CA1 neurons

Ammonia ( NH 4 + ) is a by-product of cell metabolism and may elicit subcellular effects with specific physiological responses. Chronic effects have been implicated in several neurological diseases and attributed to persistent elevation in blood ammonia levels transferred to the brain. In previous studies the activities of neurons and astrocytes have been examined at ammonia concentrations an order of magnitude higher than measured in the blood. The effects developed within several minutes. Here we focused upon acute responses of neurons to ammonia and whether they may occur at much lower doses. To this end, we combined patch-clamp in CA1 neurons with glutamate imaging in hippocampal slices. Particular attention was paid to the Rett syndrome that has been originally attributed to hyperammonemia. We compared the responses in the wild-type (WT) and model Rett mice (MECP2-null, RTT) to ammonia doses from 0.3 mM on. In both preparations NH 4 + promptly depolarized neurons and increased the ambient glutamate. The bursting activity emerged in WT and it was augmented in RTT. Searching for subcellular mechanisms we examined possible modulation of ion channels by ammonia. We did not find any changes in HCN- and Ca²⁺ currents, which substantially contribute to the bursting activity. The non-selective cation channels were markedly potentiated by ammonia. ASIC channels had a major contribution to the augmentation of neuronal activity by ammonia. Interestingly, their general blocker amiloride (100 μM) moderately excited CA1 cells akin to NH 4 + . In its presence subsequent ammonia effects were markedly compromised. Blockade of TRPC1 channels partially occluded NH 4 + effects. ASIC and TRPC1 blockers decreased the amplitude of excitatory postsynaptic currents (EPSC) and neuronal bursts, congruent with a postsynaptic location of the channels. Inhibition of TRPV1 channels potentiated the responses to NH 4 + . EPSC amplitudes did not change, but the frequency decreased, indicating presynaptic effects. All extracellular NH 4 + actions were observed at concentrations as low as 0.3 mM and the neurons reacted immediately after ammonia arrived the slice. We propose that a brief augmentation of neuronal activity by NH 4 + may occur either spontaneously during arousal or induced by inhalation of smelling salts.

Histamine-induced plasticity and gene expression in corticostriatal pathway under hyperammonemia

Aims

Histamine H3 receptor (H3R) antagonists/inverse agonists increase vigilance. We studied brain histaminergic pathways under hyperammonemia and the transcriptome of receptors and their signaling cascades to provide a rationale for wake‐promoting therapies.

Methods

We analyzed histamine‐induced long‐lasting depression of corticostriatal synaptic transmission (LLDhist). As the expression of dopamine 1 receptors (D1R) is upregulated in LGS‐KO striatum where D1R‐H3R dimers may exist, we investigated actions of H3R and D1R agonists and antagonists. We analyzed transcription of selected genes in cortex and dorsal striatum in a mouse model of inborn hyperammonemia (liver‐specific glutamine synthetase knockout: LGS‐KO) and compared it with human hepatic encephalopathy.

Results

LGS‐KO mice showed significant reduction of the direct depression (DD) but not the long‐lasting depression (LLD) by histamine. Neither pharmacological activation nor inhibition of D1R significantly affected DDhist and LLDhist in WT striatum, while in LGS‐KO mice D1R activation suppressed LLDhist. Histaminergic signaling was found unchanged at the transcriptional level except for the H2R. A study of cAMP‐regulated genes indicated a significant reduction in the molecular signature of wakefulness in the diseased cortex.

Conclusions

Our findings provide a rationale for the development of aminergic wake‐promoting therapeutics in hyperammonemic disorders.

Taurine transporter (TauT) deficiency impairs ammonia detoxification in mouse liver

Hepatic ammonia handling was analyzed in taurine transporter (TauT) KO mice. Surprisingly, hyperammonemia was present at an age of 3 and 12 months despite normal tissue integrity. This was accompanied by cerebral RNA oxidation. As shown in liver perfusion experiments, glutamine production from ammonia was diminished in TauT KO mice, whereas urea production was not affected. In livers from 3-month-old TauT KO mice protein expression and activity of glutamine synthetase (GS) were unaffected, whereas the ammonia-transporting RhBG protein was down-regulated by about 50%. Double reciprocal plot analysis of glutamine synthesis versus perivenous ammonia concentration revealed that TauT KO had no effect on the capacity of glutamine formation in 3-month-old mice, but doubled the ammonia concentration required for half-maximal glutamine synthesis. Since hepatic RhBG expression is restricted to GS-expressing hepatocytes, the findings suggest that an impaired ammonia transport into these cells impairs glutamine synthesis. In livers from 12-, but not 3-month-old TauT KO mice, RhBG expression was not affected, surrogate markers for oxidative stress were strongly up-regulated, and GS activity was decreased by 40% due to an inactivating tyrosine nitration. This was also reflected by kinetic analyses in perfused liver, which showed a decreased glutamine synthesizing capacity by 43% and a largely unaffected ammonia concentration dependence. It is concluded that TauT deficiency triggers hyperammonemia through impaired hepatic glutamine synthesis due to an impaired ammonia transport via RhBG at 3 months and a tyrosine nitration-dependent inactivation of GS in 12-month-old TauT KO mice.

General Pathophysiology of Astroglia

Astroglial cells are involved in most if not in all pathologies of the brain. These cells can change the morpho-functional properties in response to pathology or innate changes of these cells can lead to pathologies. Overall pathological changes in astroglia are complex and diverse and often vary with different disease stages. We classify astrogliopathologies into reactive astrogliosis, astrodegeneration with astroglial atrophy and loss of function, and pathological remodelling of astrocytes. Such changes can occur in neurological, neurodevelopmental, metabolic and psychiatric disorders as well as in infection and toxic insults. Mutation in astrocyte-specific genes leads to specific pathologies, such as Alexander disease, which is a leukodystrophy. We discuss changes in astroglia in the pathological context and identify some molecular entities underlying pathology. These entities within astroglia may repent targets for novel therapeutic intervention in the management of brain pathologies.