Pathological Consequences of Hepatic mTORC1 Dysregulation

Hepatic-Metabolic Activity of α-Lipoic Acid-Its Influence on Sphingolipid Metabolism and PI3K/Akt/mTOR Pathway in a Rat Model of Metabolic Dysfunction-Associated Steatotic Liver Disease

Excessive lipid deposition affects hepatic homeostasis and contributes to the development of insulin resistance as a crucial factor for the deterioration of simple steatosis to steatohepatitis. So, it is essential to search for an effective agent for a new therapy for hepatic steatosis development before it progresses to the more advanced stages. Our study aimed to evaluate the potential protective effect of α-lipoic acid (α-LA) administration on the intrahepatic metabolism of sphingolipid and insulin signaling transduction in rats with metabolic dysfunction-associated steatotic liver disease (MASLD). The experiment was conducted on male Wistar rats subjected to a standard diet or a high-fat diet (HFD) and an intragastrically α-LA administration for eight weeks. High-performance liquid chromatography (HPLC) was used to determine sphingolipid content. Immunoblotting was used to measure the expression of selected proteins from sphingolipid and insulin signaling pathways. Multiplex assay kit was used to assess the level of the phosphorylated form of proteins from PI3K/Akt/mTOR transduction. The results revealed that α-LA decreased sphinganine, dihydroceramide, and sphingosine levels and increased ceramide level. We also observed an increased the concentration of phosphorylated forms of sphingosine and sphinganine. Changes in the expression of proteins from sphingolipid metabolism were consistent with changes in sphingolipid pools. Treatment with α-LA activated the PI3K/Akt/mTOR pathway, which enhanced the hepatic phosphorylation of Akt and mTOR. Based on these data, we concluded that α-lipoic acid may alleviate glucose intolerance and may have a protective influence on the sphingolipid metabolism under HFD; thus, this antioxidant appears to protect from MASLD development and steatosis deterioration.

Baitouweng decoction alleviates dextran sulfate sodium-induced ulcerative colitis by suppressing leucine-related mTORC1 signaling and reducing oxidative stress

ETHNOPHARMACOLOGICAL RELEVANCE

Baitouweng decoction (BTW) has been used for hundreds of years to treat ulcerative colitis (UC) in China and has produced remarkable clinical results. However, the knowledge in protective mechanism of BTW against UC is still unclear.

AIM OF THE STUDY

The present study was designed to investigate the anti-UC effects of BTW and the underlying mechanisms involved.

METHODS

3.5% dextran sulfate sodium (DSS)-induced experimental colitis was used to simulate human UC and the mice were treated with BTW (6.83 g/kg), leucine (200 mg/kg, Leu) or rapamycin (2 mg/kg, RAPA) as a positive control for 7 days. The clinical symptoms, serum myeloperoxidase (MPO) and malondialdehyde (MDA) levels were evaluated. Biological samples were collected to detect the effects of BTW on mechanistic target of rapamycin complex 1 (mTORC1) pathway and Leu metabolism.

RESULTS

In our study, BTW notably improved the clinical symptoms and histopathological tissue damage and reduced the release of proinflammatory cytokines, including IL-6, IL-1β and TNF-α in UC mice. BTW also alleviated oxidative stress by decreasing serum MPO and MDA levels. Additionally, BTW significantly suppressed mTORC1 activity in the colon tissues of UC mice. Serum metabolomics analysis revealed that the mice receiving BTW had lower Leu levels, which was in line with the decreased expression of branched-chain α-keto acid dehydrogenase kinase (BCKDK) in the colon tissues. Furthermore, oral administration of Leu aggravated DSS-induced acute colitis and enhanced mTORC1 activity in the colon.

CONCLUSION

These data strongly demonstrated that BTW could ameliorate DSS-induced UC by regulating the Leu-related mTORC1 pathway and reducing oxidative stress.

Adult mice offspring of obese mothers supplemented with melatonin show lessened liver steatosis, inflammation, oxidative stress, and endoplasmic reticulum stress

AIMS

To investigate, in the liver of adult offspring, the possible effects of melatonin supplementation in the obese mother during pregnancy and lactation.

MAIN METHODS

C57BL/6 females were fed with a control (C) or a high-fat (HF) diet and supplemented with melatonin (Mel) during the pregnancy and lactation, forming the groups: C, CMel, HF, and HFMel. After weaning until three months old, the offspring only received the C diet.

KEY FINDINGS

The HF mothers and their offspring showed higher body weight (BW) than the C mothers and offspring. However, at 3-mo-old, BW was reduced in HFMel vs. HF offspring. Also, plasmatic and liver lipid markers increased in HF vs. C offspring but were reduced in HFMel vs. HF offspring. Liver lipid content was lessened in HFMel vs. HF offspring by 50 %. Also, lipid metabolism, pro-inflammatory and endoplasmic reticulum (ER) stress genes were higher expressed in HF vs. C offspring but reduced in HFMel vs. HF offspring. Contrarily, beta-oxidation and antioxidant enzyme genes were less expressed in HF vs. C offspring but improved in HFMel vs. HF offspring. Finally, AMPK/mTOR pathway genes, initially dysregulated in the HF, were restored in the HFMel offspring.

SIGNIFICANCE

The obese mother leads to liver alterations in the offspring. Current findings demonstrated the maternal melatonin supplementation during pregnancy and lactation in adult offspring's liver. Consequently, the effects were seen in mitigating the liver's AMPK/mTOR pathway genes, lipogenesis, beta-oxidation, inflammation, oxidative stress, and ER stress, preventing liver disease progression in the offspring.

Beyond controlling cell size: functional analyses of S6K in tumorigenesis

As a substrate and major effector of the mammalian target of rapamycin complex 1 (mTORC1), the biological functions of ribosomal protein S6 kinase (S6K) have been canonically assigned for cell size control by facilitating mRNA transcription, splicing, and protein synthesis. However, accumulating evidence implies that diverse stimuli and upstream regulators modulate S6K kinase activity, leading to the activation of a plethora of downstream substrates for distinct pathobiological functions. Beyond controlling cell size, S6K simultaneously plays crucial roles in directing cell apoptosis, metabolism, and feedback regulation of its upstream signals. Thus, we comprehensively summarize the emerging upstream regulators, downstream substrates, mouse models, clinical relevance, and candidate inhibitors for S6K and shed light on S6K as a potential therapeutic target for cancers.

The mTORC1/AMPK pathway plays a role in the beneficial effects of semaglutide (GLP-1 receptor agonist) on the liver of obese mice

PURPOSE

The liver regulates lipid metabolism. Decreasing mTOR (mechanistic target of rapamycin complex 1) and enhancing AMPK (AMP-activated protein kinase) help degrade hepatic diet-induced accumulated lipids. Therefore, the glucagon-like peptide type 1 receptor agonist (GLP-1) is indicated to treat obesity-related liver metabolic alterations. Then, we investigated the effects of semaglutide (recent GLP-1) by analyzing the liver mTORC1/AMPK pathway genes in obese mice.

BASIC PROCEDURES

C57BL/6 male mice were separated into two groups and submitted for 16 weeks of obesity induction. Then they were treated for an additional four weeks with semaglutide (subcutaneous, 40 μg/kg once every three days). The groups formed were: C, control group; CS, control group plus semaglutide; HF, high-fat group; HFS, high-fat group plus semaglutide. Next, the livers were dissected, and rapidly fragments of all lobes were kept and frozen at -80° C for analysis (RT-qPCR).

MAIN FINDINGS

Liver markers for the mTOR pathway associated with anabolism and lipogenesis de novo were increased in the HF group compared to the C group but comparatively attenuated by semaglutide. Also, liver markers for the AMPK pathway, which regulates chemical pathways involving the cell's primary energy source, were impaired in the HF group than in the C group but partly restored by semaglutide.

CONCLUSION

the mTOR pathway was attenuated, and the insulin signaling and the AMPK pathway were enhanced by semaglutide, ameliorating the liver gene expressions related to the metabolism of obese mice. These findings are promising in delaying the progression of nonalcoholic fatty liver disease.

Non-Alcoholic Fatty Liver Disease in HIV/HBV Patients - a Metabolic Imbalance Aggravated by Antiretroviral Therapy and Perpetuated by the Hepatokine/Adipokine Axis Breakdown

Non-alcoholic fatty liver disease (NAFLD) is strongly associated with the metabolic syndrome and is one of the most prevalent comorbidities in HIV and HBV infected patients. HIV plays an early and direct role in the development of metabolic syndrome by disrupting the mechanism of adipogenesis and synthesis of adipokines. Adipokines, molecules that regulate the lipid metabolism, also contribute to the progression of NAFLD either directly or via hepatic organokines (hepatokines). Most hepatokines play a direct role in lipid homeostasis and liver inflammation but their role in the evolution of NAFLD is not well defined. The role of HBV in the pathogenesis of NAFLD is controversial. HBV has been previously associated with a decreased level of triglycerides and with a protective role against the development of steatosis and metabolic syndrome. At the same time HBV displays a high fibrogenetic and oncogenetic potential. In the HIV/HBV co-infection, the metabolic changes are initiated by mitochondrial dysfunction as well as by the fatty overload of the liver, two interconnected mechanisms. The evolution of NAFLD is further perpetuated by the inflammatory response to these viral agents and by the variable toxicity of the antiretroviral therapy. The current article discusses the pathogenic changes and the contribution of the hepatokine/adipokine axis in the development of NAFLD as well as the implications of HIV and HBV infection in the breakdown of the hepatokine/adipokine axis and NAFLD progression.

An integrative approach to assessing effects of a short-term Western diet on gene expression in rat liver

Consumption of a diet rich in saturated fatty acids and carbohydrates contributes to the accumulation of fat in the liver and development of non-alcoholic steatohepatitis (NASH). Herein we investigated the hypothesis that short-term consumption of a high fat/sucrose Western diet (WD) alters the genomic and translatomic profile of the liver in association with changes in signaling through the protein kinase mTORC1, and that such alterations contribute to development of NAFLD. The results identify a plethora of mRNAs that exhibit altered expression and/or translation in the liver of rats consuming a WD compared to a CD. In particular, consumption of a WD altered the abundance and ribosome association of mRNAs involved in lipid and fatty acid metabolism, as well as those involved in glucose metabolism and insulin signaling. Hepatic mTORC1 signaling was enhanced when rats were fasted overnight and then refed in the morning; however, this effect was blunted in rats fed a WD as compared to a CD. Despite similar plasma insulin concentrations, fatty acid content was elevated in the liver of rats fed a WD as compared to a CD. We found that feeding had a significant positive effect on ribosome occupancy of 49 mRNAs associated with hepatic steatosis (e.g., LIPE, LPL), but this effect was blunted in the liver of rats fed a WD. In many cases, changes in ribosome association were independent of alterations in mRNA abundance, suggesting a critical role for diet-induced changes in mRNA translation in the expression of proteins encoded by those mRNAs. Overall, the findings demonstrate that short-term consumption of a WD impacts hepatic gene expression by altering the abundance of many mRNAs, but also causes wide-spread variation in mRNA translation that potentially contribute to development of hepatic steatosis.

Depdc5 deficiency exacerbates alcohol-induced hepatic steatosis via suppression of PPARα pathway

Alcohol-related liver disease (ALD), a condition caused by alcohol overconsumption, occurs in three stages of liver injury including steatosis, hepatitis, and cirrhosis. DEP domain-containing protein 5 (DEPDC5), a component of GAP activities towards Rags 1 (GATOR1) complex, is a repressor of amino acid-sensing branch of the mammalian target of rapamycin complex 1 (mTORC1) pathway. In the current study, we found that aberrant activation of mTORC1 was likely attributed to the reduction of DEPDC5 in the livers of ethanol-fed mice or ALD patients. To further define the in vivo role of DEPDC5 in ALD development, we generated Depdc5 hepatocyte-specific knockout mouse model (Depdc5-LKO) in which mTORC1 pathway was constitutively activated through loss of the inhibitory effect of GATOR1. Hepatic Depdc5 ablation leads to mild hepatomegaly and liver injury and protects against diet-induced liver steatosis. In contrast, ethanol-fed Depdc5-LKO mice developed severe hepatic steatosis and inflammation. Pharmacological intervention with Torin 1 suppressed mTORC1 activity and remarkably ameliorated ethanol-induced hepatic steatosis and inflammation in both control and Depdc5-LKO mice. The pathological effect of sustained mTORC1 activity in ALD may be attributed to the suppression of peroxisome proliferator activated receptor α (PPARα), the master regulator of fatty acid oxidation in hepatocytes, because fenofibrate (PPARα agonist) treatment reverses ethanol-induced liver steatosis and inflammation in Depdc5-LKO mice. These findings provide novel insights into the in vivo role of hepatic DEPDC5 in the development of ALD.

Vitamin E and Lactobacillus Provide Protective Effects Against Liver Injury Induced by HgCl2: Role of CHOP, GPR87, and mTOR Proteins

BACKGROUND AND OBJECTIVE

Mercury is one of the most harmful heavy metals and its toxicity causes severe multi-organ dysfunction. This study was designed to explore novel molecular pathways involved in the hepatoprotective effect of vitamin E (Vit-E) and Lactobacillius plantarum (Lac-B) against mercury toxicity.

METHOD

Acute hepatotoxicity was induced by administration of high dose of mercuric chloride (HgCl2) in male rats, Vit-E or/and Lac-B were given along with HgCl2 for 2 weeks. The effects of those antioxidants were studied focusing on their anti-apoptotic, anti-oxidative stress and anti-inflammatory eficacies. Histopathological examinations were also conducted.

RESULTS

The administration of HgCl2 induced liver injury which manifested by elevation in serum ALT and AST. Liver MDA, caspase-3 and TNF-α levels were markedly increased; whereas, GSH level and SOD activity were declined. HgCl2 significantly elevated the expressions of hepatic CHOP, GPR87, NF-κB and mTOR. Histopathological examination revealed massive hepatocyte degeneration following HgCl2 administration. Treatment with Vit-E or/and Lac-B restored the normal levels of the previously mentioned parameters, as well as improved hepatic architecture.

CONCLUSION

Vit-E and Lac-B provided protective effect against HgCl2-induced hepatotoxicity via reduction of oxidative stress and inflammation, and downregulation of CHOP, GPR87, NF-κB and mTOR proteins' expressions.