The multifaceted role of mTORC1 in the control of lipid metabolism

Metabolic rewiring caused by mitochondrial dysfunction promotes mTORC1-dependent skeletal aging

Decline of mitochondrial respiratory chain (mtRC) capacity is a hallmark of mitochondrial diseases. Patients with mtRC dysfunction often present reduced skeletal growth as a sign of premature cartilage degeneration and aging, but how metabolic adaptations contribute to this phenotype is poorly understood. Here we show that, in mice with impaired mtRC in cartilage, reductive/reverse TCA cycle segments are activated to produce metabolite-derived amino acids and stimulate biosynthesis processes by mechanistic target of rapamycin complex 1 (mTORC1) activation during a period of massive skeletal growth and biomass production. However, chronic hyperactivation of mTORC1 suppresses autophagy-mediated organelle recycling and disturbs extracellular matrix secretion to trigger chondrocytes death, which is ameliorated by targeting the reductive metabolism. These findings explain how a primarily beneficial metabolic adaptation response required to counterbalance the loss of mtRC function, eventually translates into profound cell death and cartilage tissue degeneration. The knowledge of these dysregulated key nutrient signaling pathways can be used to target skeletal aging in mitochondrial disease.

Folliculin depletion results in liver cell damage and cholangiocarcinoma through MiT/TFE activation

Mutations in the tumor suppressor gene Folliculin (FLCN) are responsible for Birt-Hogg-Dube' (BHD) syndrome, a rare inherited condition that predisposes affected individuals to skin tumors, pulmonary cysts, and kidney tumors. FLCN regulates key cellular pathways, including TFEB, TFE3, and mTORC1, which are critical for maintaining cell homeostasis. Loss of FLCN leads to both hyperactivation of mTORC1 and constitutive activation of TFEB and TFE3, contributing to tumorigenesis. While previous studies showed that Flcn liver-specific conditional knockout (FlcnLiKO) mice are protected from developing liver fibrosis and damage upon high-fat diet exposure, the potential role of FLCN loss in liver carcinogenesis remained unexplored. Here, we demonstrate that hepatic loss of FLCN in mice results in cancer associated with inflammation and fibrosis with features of cholangiocarcinoma (CCA). This phenotype emerges in mice over 90-week-old, with a male predominance. Moreover, FlcnLiKO mice are more prone to develop diethylnitrosamine (DEN)- or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)- induced liver tumors with heterogenous histological features. Notably, depletion of TFE3, but not TFEB, in the liver of FlcnLiKO mice fully rescues the cancer phenotype and normalized mTORC1 signaling, highlighting TFE3 as the primary driver of liver cancer and mTORC1 hyperactivity in the absence of FLCN.

Dietary oleuropein supplementation affects lipolysis in broilers

Oleuropein, a phenolic compound derived from olives, was investigated for its effects on the adipose tissue physiology of broiler chickens during the initial 10 days post-hatch. We hypothesized that oleuropein could modulate the adipose tissue of the chicken due to its known bioactive properties. Sixty-eight day-of-hatch Cobb-Hubbard broilers were randomly divided into treatment groups receiving different amounts of oleuropein (0, 125, 250, or 500 mg/kg of commercial starter diet). Diets were fed ad-lib and on day 10 post-hatch, blood and adipose tissue samples (abdominal and subcutaneous) were collected from 12 broilers in each group. Plasma was collected to measure non-esterified fatty acids (NEFA) concentrations. The mRNA levels of key regulators of adipogenesis and lipolysis were assessed by real-time PCR. At day 10, body weights were lower in the 125 and 250-dose groups. In both adipose tissue depots, lipolytic enzyme adipose triglyceride lipase (ATGL) mRNA was higher in the 125-dose group compared to other groups. Diacylglycerol O-acyltransferase 2 (DGAT2) and peroxisome proliferator-activated receptor γ (PPARγ) were lower in the 125-dose group relative to other groups. Plasma NEFAs were greater in the 125-dose group than in the other groups. This suggests that oleuropein has pro-lipolytic and anti-adipogenic properties and may provide a means to reduce excessive adipose tissue accumulation in broilers.

Tools to Dissect Lipid Droplet Regulation, Players, and Mechanisms

Spurred by the authors' own recent discovery of reactive metabolite-regulated nexuses involving lipid droplets (LDs), this perspective discusses the latest knowledge and multifaceted approaches toward deconstructing the function of these dynamic organelles, LD-associated localized signaling networks, and protein players. Despite accumulating knowledge surrounding protein families and pathways of conserved importance for LD homeostasis surveillance and maintenance across taxa, much remains to be understood at the molecular level. In particular, metabolic stress-triggered contextual changes in LD-proteins' localized functions, crosstalk with other organelles, and feedback signaling loops and how these are specifically rewired in disease states remain to be illuminated with spatiotemporal precision. We hope this perspective promotes an increased interest in these essential organelles and innovations of new tools and strategies to better understand context-specific LD regulation critical for organismal health.

Proteomic profiling reveals alterations in metabolic and cellular pathways in severe obesity and following metabolic bariatric surgery

In this study, we investigated the impact of bariatric surgery on the adipose proteome to better understand the metabolic and cellular mechanisms underlying weight loss following the procedure. A total of 46 patients with severe obesity were included, with samples collected both before and after bariatric surgery. In addition, 15 healthy individuals without obesity who did not undergo surgery served as controls and were studied once. We utilized quantitative liquid chromatography-tandem mass spectrometry analysis to conduct a large-scale proteomic study on abdominal subcutaneous biopsies obtained from the study participants. Our proteomic profiling revealed that among the 2,254 compared proteins, 46 were upregulated and 34 were downregulated 6 months post surgery compared with baseline [false discovery rate (FDR) < 0.01]. We observed a downregulation of proteins associated with mitochondrial integrity, amino acid catabolism, and lipid metabolism in the patients with severe obesity compared with the controls. Bariatric surgery was associated with an upregulation in pathways related to mitochondrial function, protein synthesis, folding and trafficking, actin cytoskeleton regulation, and DNA binding and repair. These findings emphasize the significant changes in metabolic and cellular pathways following bariatric surgery, highlighting the potential mechanisms underlying the observed health improvements postbariatric surgery. The data provided alongside this paper will serve as a valuable resource for the development of targeted therapeutic strategies for obesity and related metabolic complications. ClinicalTrials.gov registration numbers: NCT00793143 (registered on 19 November 2008) (https://clinicaltrials.gov/ct2/show/NCT00793143) and NCT01373892 (registered on 15 June 2011) (https://clinicaltrials.gov/ct2/show/NCT01373892).NEW & NOTEWORTHY Our study investigates the effects of metabolic bariatric surgery on adipose tissue proteins, highlighting the mechanisms driving weight loss postsurgery. Through extensive proteomic analysis of adipose biopsies from patients with severe obesity pre- and postsurgery, alongside healthy subjects without obesity, we identified significant alterations in metabolic pathways. These findings provide insights into potential therapeutic targets for obesity-related complications.

Endogenous Ketone Bodies Are Associated with Metabolic Vulnerability and Disability in Multiple Sclerosis

Purpose: Ketone bodies could be useful biomarkers in multiple sclerosis (MS) because the pathophysiological processes underlying MS disease progression induce metabolic stress. The purpose was to assess the relationships of ketone bodies with biomarkers of metabolic, inflammatory, and oxidative stress in MS. Methods: Blood samples and neurological assessments were obtained from 153 healthy controls (HC), 187 relapsing-remitting (RRMS), and 91 progressive MS (PMS) patients. AcAc, BHB, and acetone were measured using proton nuclear magnetic resonance spectroscopy. Indices of inflammatory vulnerability (IVX), metabolic malnutrition (MMX), and metabolic vulnerability (MVX) were computed from the NMR profiles. Cholesterol, apolipoprotein, lipid peroxidation, and antioxidant profiles were obtained. Regression analysis adjusted for age, sex, body mass index, and HC, RRMS, or PMS disease status. Results: AcAc and BHB levels were greater in MS compared to HC. BHB and ketone bodies were positively associated with disability on the MS Severity Scale and ambulation time. BHB was positively associated with IVX, MMX, and MVX. AcAc was positively associated with MMX and negatively associated with IVX and MVX. Total ketone body concentration was positively associated with MMX and MVX. BHB and AcAc levels were negatively associated with the amino acids alanine, valine, and leucine. Conclusions: Ketone bodies are associated with inflammatory vulnerability, metabolic vulnerability, and ambulatory disability measures in MS.

Embryonic Thermal Programming and Dietary Baicalein Supplementation Post-Hatch: Effects on Broiler Adipose Tissue Deposition

Optimization of growth performance and fat metabolism in broilers are critical for meat quality and overall production efficiency. This experiment investigated the effects of dietary baicalein supplementation and embryonic heat conditioning (EHC) on the growth performance and adipose tissue metabolism of 10-day old broilers. Fertile eggs were divided into control and EHC groups, with EHC eggs exposed to intermittent heating (39.5 °C) from day 7 to day 16 of incubation. Hatched chicks were further divided into four groups: CC (control control), CT (control treatment with baicalein), EC (embryonic heat control), and ET (embryonic heat treatment with baicalein), and were fed ad libitum. On day 10 post-hatch, blood and adipose tissue samples were collected for analysis. C/EBPα mRNA was lower in the ET group compared to the EC group and higher in the CT group compared to the CC group. PPARγ and HSL mRNAs were elevated in both the ET and CT groups relative to their controls. Additionally, plasma non-esterified fatty acid (NEFA) levels were significantly higher in the CT group compared to the CC group. These results indicate that baicalein supplementation, particularly when combined with embryonic heat conditioning, can modulate fat metabolism and potentially improve the growth performance of broilers, thereby offering insights into strategies for enhancing poultry production.

10-Gingerol reduces cytoplasmic lipid droplets and induces lipolysis in 3T3-L1 adipocytes

Obesity is a globally prevalent metabolic disorder characterized by an increased number of adipose cells and excessive fat in adipocytes. Herbal medicines, such as ginger, have shown potential in treating obesity by inhibiting adipogenesis and reducing adipocyte hypertrophy. Ginger contains bioactive compounds, particularly gingerols, which have demonstrated anti-adipogenic and/or lipolytic effects. However, research on the effects of 10-gingerol on adipose tissue remains limited. This study aimed to evaluate the effect of 10-gingerol on lipid content, lipolysis markers, and the expression of genes related to lipid metabolism in 3T3-L1 adipocytes. Three groups were analyzed: a negative control (preadipocytes), a positive control (mature adipocytes), and a group treated with 10-gingerol (10-G). Results showed that 10-G reduced lipid accumulation by 42.16% in mature adipocytes compared to the control, without affecting cell viability. Additionally, 10-G increased glycerol release and downregulated lipogenic genes such as Pparγ, Acaca, Fabp4, and Mtor, while upregulating genes related to fatty acid oxidation, including Cebpα, Cpt1a, Lipe, and Prkaa1. In conclusion, 10-gingerol reduces lipid content in mature adipocytes by downregulating lipogenesis, increasing lipolysis, and enhancing fatty acid oxidation.

Evaluating SORT1 and SESN1 genes expression in peripheral blood mononuclear cells and oxidative stress status in patients with coronary artery disease

BACKGROUND

Coronary artery disease (CAD) significantly contributes to global fatalities. Recent studies have demonstrated the crucial roles of sortilin1 (SORT1) and sestrin1 (SESN1) in lipid metabolism, as well as their involvement in the development of CAD. The aberrant expression or activity of SORT1 can consequently lead to metabolic and vascular diseases. Sestrins, including SESN1, play a crucial role in helping cells survive by maintaining metabolic balance while also reducing oxidative stress (OS). OS contributes to the progression of atherosclerosis-related diseases, such as CAD. The study aimed to compare the gene expression of SORT1 and SESN1 in peripheral blood mononuclear cells (PBMCs), alongside serum OS markers, in CAD patients and controls.

MATERIALS

The case-control study included 49 CAD patients and 40 controls. The expression of the SORT1 and SESN1 genes was quantified using qRT-PCR, and the expression of the SORT1 protein was evaluated by western blotting. OS markers, including total oxidation status (TOS), total antioxidant capacity (TAC), and malondialdehyde (MDA), were measured using spectrophotometric and fluorometric methods.

RESULTS

SORT1 gene and protein expressions were similar between groups. CAD patients had a non-significant decrease in SESN1 gene expression. MDA levels were significantly higher in CAD patients, whereas TOS and TAC levels did not differ significantly.

CONCLUSION

For atherosclerosis-related disorders like CAD, MDA shows potential as a non-invasive, easy-to-use, affordable, and stable biomarker. Further research is needed to elucidate the precise roles of SORT1 and SESN1 in CAD pathogenesis.

The Combined Inhibition of SREBP and mTORC1 Signaling Synergistically Inhibits B-Cell Lymphoma

BACKGROUND

The sterol regulatory element-binding protein (SREBP) pathway is essential for maintaining sterol homeostasis during B cell activation and germinal center B cell proliferation. However, its potential as a therapeutic target to treat B-cell lymphoma remains unclear.

METHODS

We examined SREBP protein expression in human B-cell lymphoma samples using immunohistochemistry. Additionally, we conducted in vitro studies using SREBP signaling inhibitors in combination with rapamycin to assess their effects on cell proliferation and lipid metabolism in B-cell lymphoma cells.

RESULTS

Our analysis revealed high levels of SREBP2 protein expression in human B-cell lymphoma samples. Inhibiting SREBP signaling or its downstream target HMG-CoA reductase (HMGCR) with Fatostatin or Simvastatin effectively suppressed B-cell lymphoma cell proliferation. However, B-cell lymphoma cells responded to statin treatment by activating the mTORC1-pS6 pathway, suggesting a compensatory mechanism to overcome statin-induced cell cycle arrest. Combining low-dose statin treatment with the mTOR inhibitor rapamycin produced a synergistic effect, significantly inhibiting B-cell lymphoma proliferation, cell cycle progression, and lipid raft formation.

CONCLUSIONS

These results highlight the potential of a combined therapeutic approach targeting both SREBP and mTORC1 as a novel strategy for treating B-cell lymphoma.

NAFLD-associated hepatocellular carcinoma (HCC) - A compelling case for repositioning of existing mTORc1 inhibitors

The increasing prevalence of non-alcoholic fatty liver disease (NAFLD) is a growing concern for the high incidence rate of hepatocellular carcinoma (HCC) globally. The progression of NAFLD to HCC is heterogeneous and non-linear, involving intermediate stages of non-alcoholic steatohepatitis (NASH), liver fibrosis, and cirrhosis. There is a high unmet clinical need for appropriate diagnostic, prognostic, and therapeutic options to tackle this emerging epidemic. Unfortunately, at present, there is no validated marker to identify the risk of developing HCC in patients suffering from NAFLD or NASH. Additionally, the current treatment protocols for HCC don't differentiate between viral infection or NAFLD-specific etiology of the HCC and have a limited success rate. The mammalian target of rapamycin complex 1 (mTORc1) is an important protein involved in many vital cellular processes like lipid metabolism, glucose homeostasis, and inflammation. These cellular processes are highly implicated in NAFLD and its progression to severe liver manifestations. Additionally, hyperactivation of mTORc1 is known to promote cell proliferation, which can contribute to the genesis and progression of tumors. Many mTORc1 inhibitors are being evaluated for different types of cancers under various phases of clinical trials. This paper deliberates on the strong pathological implication of the mTORc1 signaling pathway in NAFLD and its progression to NASH and HCC and advocates for a systematic investigation of known mTORc1 inhibitors in suitable pre-clinical models of HCC having NAFLD/NASH-specific etiology.

Exploring the multifaceted role of ginkgolides and bilobalide from Ginkgo biloba in mitigating metabolic disorders

The ancient Ginkgo biloba tree grows across various regions, with distinctive leaves emitting a unique fragrance. Its extract contains flavonoids, organic acids, and terpenoids. Ginkgolide and bilobalide, which are G. biloba leaf extracts, offer diverse pharmaceutical benefits, including antioxidant, anti-inflammatory, and neuroprotective properties. The antioxidant and anti-inflammatory properties of these compounds are crucial for mitigating neurodegeneration, particularly in diseases such as Alzheimer's disease. Additionally, their effectiveness in countering oxidative stress and inflammation highlights their potential to prevent cardiovascular ailments. This study also suggests that these compounds have a promising impact on lipid metabolism, suggesting their significance in addressing obesity-related metabolic disorders. In conclusion, ginkgolides and bilobalide exhibit promising effects in sustaining the integrity of the nervous and endocrine systems, along with the modulation of lipid metabolism. The diverse health benefits suggest that these compounds could serve as promising therapeutic interventions for various conditions, including neurological, cardiovascular, and metabolic diseases.

Regulation of renal organic cation transporters

Transporters for organic cations (OCs) facilitate exchange of positively charged molecules through the plasma membrane. Substrates for these transporters encompass neurotransmitters, metabolic byproducts, drugs, and xenobiotics. Consequently, these transporters actively contribute to the regulation of neurotransmission, cellular penetration and elimination process for metabolic products, drugs, and xenobiotics. Therefore, these transporters have significant physiological, pharmacological, and toxicological implications. In cells of renal proximal tubules, the vectorial secretion pathways for OCs involve expression of organic cation transporters (OCTs) and multidrug and toxin extrusion proteins (MATEs) on basolateral and apical membrane domains, respectively. This review provides an overview of documented regulatory mechanisms governing OCTs and MATEs. Additionally, regulation of these transporters under various pathological conditions is summarized. The expression and functionality of OCTs and MATEs are subject to diverse pre- and post-translational modifications, providing insights into their regulation in various pathological conditions. Typically, in diseases, downregulation of transporter expression is observed, probably as a protective mechanism to prevent additional damage to kidney tissue. This regulation may be attributed to the intricate network of modifications these transporters undergo, shedding light on their dynamic responses in pathological contexts.

Metabolic ripple effects - deciphering how lipid metabolism in cancer interfaces with the tumor microenvironment

Cancer cells require a constant supply of lipids. Lipids are a diverse class of hydrophobic molecules that are essential for cellular homeostasis, growth and survival, and energy production. How tumors acquire lipids is under intensive investigation, as these mechanisms could provide attractive therapeutic targets for cancer. Cellular lipid metabolism is tightly regulated and responsive to environmental stimuli. Thus, lipid metabolism in cancer is heavily influenced by the tumor microenvironment. In this Review, we outline the mechanisms by which the tumor microenvironment determines the metabolic pathways used by tumors to acquire lipids. We also discuss emerging literature that reveals that lipid availability in the tumor microenvironment influences many metabolic pathways in cancers, including those not traditionally associated with lipid biology. Thus, metabolic changes instigated by the tumor microenvironment have 'ripple' effects throughout the densely interconnected metabolic network of cancer cells. Given the interconnectedness of tumor metabolism, we also discuss new tools and approaches to identify the lipid metabolic requirements of cancer cells in the tumor microenvironment and characterize how these requirements influence other aspects of tumor metabolism.

Identification of key genes and pathways in duck fatty liver syndrome using gene set enrichment analysis

High-laying ducks are often fed high-energy, nutritious feeds to maintain high productivity, which predisposes them to lipid metabolism disorders and the development of fatty liver syndrome (FLS), which seriously affects production performance and has a substantial economic impact on the poultry industry. Therefore, it is necessary to elucidate the mechanisms underlying the development of fatty liver syndrome. In this study, seven Shan Partridge ducks, each with fatty liver syndrome and normal laying ducks, were selected, and Hematoxylin Eosin staining (HE staining), Masson staining, and transcriptome sequencing were performed on liver tissue. In addition to exploring key genes and pathways using conventional analysis methods, we constructed the first Kyoto Encyclopedia of Genes and Genomes (KEGG) database-based predefined gene set containing 12,764 pathways and 16,836 genes and further performed gene set enrichment analysis (GSEA) on the liver transcriptome data. Finally, key nodes and biological processes were identified via the protein-protein interaction (PPI) network. The results showed that the liver in the FL group exhibited steatosis and fibrosis, and a total of 3,663 genes with upregulated expression versus 2,296 downregulated genes were screened by conventional analysis. GSEA analysis and PPI network analysis revealed that the liver in the FL group exhibited disruption of the mitochondrial electron transport chain, leading to decreased oxidative phosphorylation and the secretion of excessive proinflammatory factors amid the continuous accumulation of lipids. Under continuous chronic inflammation, cell cycle arrest triggers apoptosis, while fibrosis becomes more severe, and procarcinogenic genes are activated, leading to the continuous development and deterioration of the liver. In conclusion, the predefined gene set constructed in this study can be used for GSEA, and the identified hub genes provide useful reference data and a solid foundation for the study of the genetic regulatory mechanism of fatty liver syndrome in ducks.

Genotype-First Approach Identifies an Association between rs28374544/FOG2S657G and Liver Disease through Alterations in mTORC1 Signaling

Metabolic dysfunction-associated Fatty Liver Disease (MAFLD) has emerged as one of the leading cardiometabolic diseases. Friend of GATA2 (FOG2) is a transcriptional co-regulator that has been shown to regulate hepatic lipid metabolism and accumulation. Using meta-analysis from several different biobank datasets, we identified a coding variant of FOG2 (rs28374544, A1969G, S657G) predominantly found in individuals of African ancestry (minor allele frequency~20%), which is associated with liver failure/cirrhosis phenotype and liver injury. To gain insight into potential pathways associated with this variant, we interrogated a previously published genomics dataset of 38 human induced pluripotent stem cell (iPSCs) lines differentiated into hepatocytes (iHeps). Using Differential Gene Expression Analysis and Gene Set Enrichment Analysis, we identified the mTORC1 pathway as differentially regulated between iHeps from individuals with and without the variant. Transient lipid-based transfections were performed on the human hepatoma cell line (Huh7) using wild-type FOG2 and FOG2S657G and demonstrated that FOG2S657G increased mTORC1 signaling, de novo lipogenesis, and cellular triglyceride synthesis and mass. In addition, we observed a significant downregulation of oxidative phosphorylation in FOG2S657G cells in fatty acid-loaded cells but not untreated cells, suggesting that FOG2S657G may also reduce fatty acid to promote lipid accumulation. Taken together, our multi-pronged approach suggests a model whereby the FOG2S657G may promote MAFLD through mTORC1 activation, increased de novo lipogenesis, and lipid accumulation. Our results provide insights into the molecular mechanisms by which FOG2S657G may affect the complex molecular landscape underlying MAFLD.

Risk of Fat Mass- and Obesity-Associated Gene-Dependent Obesogenic Programming by Formula Feeding Compared to Breastfeeding

It is the purpose of this review to compare differences in postnatal epigenetic programming at the level of DNA and RNA methylation and later obesity risk between infants receiving artificial formula feeding (FF) in contrast to natural breastfeeding (BF). FF bears the risk of aberrant epigenetic programming at the level of DNA methylation and enhances the expression of the RNA demethylase fat mass- and obesity-associated gene (FTO), pointing to further deviations in the RNA methylome. Based on a literature search through Web of Science, Google Scholar, and PubMed databases concerning the dietary and epigenetic factors influencing FTO gene and FTO protein expression and FTO activity, FTO's impact on postnatal adipogenic programming was investigated. Accumulated translational evidence underscores that total protein intake as well as tryptophan, kynurenine, branched-chain amino acids, milk exosomal miRNAs, NADP, and NADPH are crucial regulators modifying FTO gene expression and FTO activity. Increased FTO-mTORC1-S6K1 signaling may epigenetically suppress the WNT/β-catenin pathway, enhancing adipocyte precursor cell proliferation and adipogenesis. Formula-induced FTO-dependent alterations of the N6-methyladenosine (m6A) RNA methylome may represent novel unfavorable molecular events in the postnatal development of adipogenesis and obesity, necessitating further investigations. BF provides physiological epigenetic DNA and RNA regulation, a compelling reason to rely on BF.

Roles of lipid droplets and related proteins in metabolic diseases

Lipid droplets (LDs), which are active organelles, derive from the monolayer membrane of the endoplasmic reticulum and encapsulate neutral lipids internally. LD-associated proteins like RAB, those in the PLIN family, and those in the CIDE family participate in LD formation and development, and they are active players in various diseases, organelles, and metabolic processes (i.e., obesity, non-alcoholic fatty liver disease, and autophagy). Our synthesis on existing research includes insights from the formation of LDs to their mechanisms of action, to provide an overview needed for advancing research into metabolic diseases and lipid metabolism.

Leucine-Mediated SLC7A5 Promotes Milk Protein and Milk Fat Synthesis through mTOR Signaling Pathway in Goat Mammary Epithelial Cells

The SLC7A5 gene encodes a Na+ and pH-independent transporter protein that regulates cell growth by regulating the uptake of AA. This study, utilizing RNA-seq, aimed to explore the effect of SLC7A5 on the synthesis of milk proteins and fats in goat mammary epithelial cells (GMECs) through gene interference and overexpression techniques. The results demonstrated that the overexpression of SLC7A5 resulted in a significant increase in the expression of CSN1S1, SCD, CEBPB, ACACA, αS1-casein, p-S6K, and p-S6. The levels of p-S6K and p-S6 gradually increased as the AA/Leu stimulation time lengthened. The overexpression of SLC7A5 rescued the role of Torin1 in GMECs. In conclusion, SLC7A5 plays a crucial role in promoting the synthesis of milk proteins and milk fats through the mTOR signaling pathway in GMECs, providing a theoretical foundation for improving the quality of goat milk.

Construction of oxidative phosphorylation-related prognostic risk score model in uveal melanoma

BACKGROUND

Uveal melanoma (UVM) is a malignant intraocular tumor in adults. Targeting genes related to oxidative phosphorylation (OXPHOS) may play a role in anti-tumor therapy. However, the clinical significance of oxidative phosphorylation in UVM is unclear.

METHOD

The 134 OXPHOS-related genes were obtained from the KEGG pathway, the TCGA UVM dataset contained 80 samples, served as the training set, while GSE22138 and GSE39717 was used as the validation set. LASSO regression was carried out to identify OXPHOS-related prognostic genes. The coefficients obtained from Cox multivariate regression analysis were used to calculate a risk score, which facilitated the construction of a prognostic model. Kaplan-Meier survival analysis, logrank test and ROC curve using the time "timeROC" package were conducted. The immune cell frequency in low- and high-risk group was analyzed through Cibersort tool. The specific genomic alterations were analyzed by "maftools" R package. The differential expressed genes between low- or high-risk group were analyzed and performed Gene Ontology (GO) and GSEA. Finally, we verified the function of CYC1 in UVM by gene silencing in vitro.

RESULTS

A total of 9 OXPHOS-related prognostic genes were identified, including NDUFB1, NDUFB8, ATP12A, NDUFA3, CYC1, COX6B1, ATP6V1G2, ATP4B and NDUFB4. The UVM prognostic risk model was constructed based on the 9 OXPHOS-related prognostic genes. The prognosis of patients in the high-risk group was poorer than low-risk group. Besides, the ROC curve demonstrated that the area under the curve of the model for predicting the 1 to 5-year survival rate of UVM patients were all more than 0.88. External validation in GSE22138 and GSE39717 dataset revealed that these 9 genes could also be utilized to evaluate and predict the overall survival of patients with UVM. The risk score levels related to immune cell frequency and specific genomic alterations. The DEGs between the low- and high- risk group were enriched in tumor OXPHOS and immune related pathway. In vitro experiments, CYC1 silencing significantly inhibited UVM cell proliferation and invasion, induced cell apoptosis.

CONCLUSION

In sum, a prognostic risk score model based on oxidative phosphorylation-related genes in UVM was developed to enhance understanding of the disease. This prognostic risk score model may help to find potential therapeutic targets for UVM patients. CYC1 acts as an oncogene role in UVM.

Sexual dimorphism and the multi-omic response to exercise training in rat subcutaneous white adipose tissue

Subcutaneous white adipose tissue (scWAT) is a dynamic storage and secretory organ that regulates systemic homeostasis, yet the impact of endurance exercise training (ExT) and sex on its molecular landscape is not fully established. Utilizing an integrative multi-omics approach, and leveraging data generated by the Molecular Transducers of Physical Activity Consortium (MoTrPAC), we show profound sexual dimorphism in the scWAT of sedentary rats and in the dynamic response of this tissue to ExT. Specifically, the scWAT of sedentary females displays -omic signatures related to insulin signaling and adipogenesis, whereas the scWAT of sedentary males is enriched in terms related to aerobic metabolism. These sex-specific -omic signatures are preserved or amplified with ExT. Integration of multi-omic analyses with phenotypic measures identifies molecular hubs predicted to drive sexually distinct responses to training. Overall, this study underscores the powerful impact of sex on adipose tissue biology and provides a rich resource to investigate the scWAT response to ExT.

The causal effect of mTORC1-dependent circulating protein levels on nonalcoholic fatty liver disease: A Mendelian randomization study

BACKGROUND

The mechanistic target of rapamycin (mTOR) signal pathway plays a crucial role in the development of nonalcoholic fatty liver disease (NAFLD). However, the causal effect of mTOR downstream proteins on NAFLD remains unknown.

AIMS

We conducted a two-sample Mendelian randomization (MR) study to investigate whether the mTOR-dependent circulating proteins, including Eukaryotic Initiation Factor 4E Binding Proteins (eIF4EBPs), Ribosomal Protein S6K kinase 1 (RP-S6K), Eukaryotic Initiation Factor 4E (eIF4E), Eukaryotic Initiation Factor 4A (eIF4A) and Eukaryotic Initiation Factor 4 G (eIF4G), have causal effects on the risk of NAFLD.

METHODS

The causal estimate was evaluated with the inverse-variance weighted (IVW) method in discovery stage and validation stage. The single-nucleotide polymorphisms (SNPs) were selected to genetically predict exposures from Genome-Wide Association Studies (GWAS). Exposures with statistically significant effects in the discovery dataset would be further validated in the validation dataset.

RESULTS

MR study revealed that eIF4E had a causal effect on NAFLD in both discovery stage (OR = 1.339, P = 0.037) and validation stage (OR = 1.0007, P = 0.022). Sensitivity analyses confirmed robustness of the results.

CONCLUSION

The genetically predicted higher level of mTOR-dependent eIF4E in plasma might have a causal effect on the occurrence of NAFLD.

Metabolic Disorders in Liver Transplant Recipients: The State of the Art

Liver transplantation represents a chief therapeutic approach for acute liver failure, end-stage liver disease and hepatocellular carcinoma. Despite witnessing advancements in short- and medium-term survival over recent decades, attributed to refinements in surgical techniques and immunosuppressive protocols, long-term mortality remains impervious to modification. Notably, cardiovascular disease emerges as a predominant cause of mortality among liver transplant recipients. This trend is accentuated by the increasing prominence of non-alcoholic steatohepatitis-related cirrhosis as an indication for liver transplantation. Moreover, the administration of immunosuppressive agents is intricately linked to the degradation of the metabolic profile in liver transplant recipients, thereby contributing to the initiation or exacerbation of cardiovascular risk factors, such as hypertension, diabetes, and dyslipidaemia. In addition, the post-liver transplantation period is marked by a decline in lifestyle quality and a failure to acknowledge the psychological distress experienced by patients throughout the transplant process. These factors can precipitate a deterioration in the patient's metabolic profile, exacerbated by suboptimal therapeutic compliance. This narrative review aims to comprehensively address the principal metabolic disorders intricately associated with liver transplantation.

The obesity-autophagy-cancer axis: Mechanistic insights and therapeutic perspectives

Autophagy, a self-degradative process vital for cellular homeostasis, plays a significant role in adipose tissue metabolism and tumorigenesis. This review aims to elucidate the complex interplay between autophagy, obesity, and cancer development, with a specific emphasis on how obesity-driven changes affect the regulation of autophagy and subsequent implications for cancer risk. The burgeoning epidemic of obesity underscores the relevance of this research, particularly given the established links between obesity, autophagy, and various cancers. Our exploration delves into hormonal influence, notably INS (insulin) and LEP (leptin), on obesity and autophagy interactions. Further, we draw attention to the latest findings on molecular factors linking obesity to cancer, including hormonal changes, altered metabolism, and secretory autophagy. We posit that targeting autophagy modulation may offer a potent therapeutic approach for obesity-associated cancer, pointing to promising advancements in nanocarrier-based targeted therapies for autophagy modulation. However, we also recognize the challenges inherent to these approaches, particularly concerning their precision, control, and the dual roles autophagy can play in cancer. Future research directions include identifying novel biomarkers, refining targeted therapies, and harmonizing these approaches with precision medicine principles, thereby contributing to a more personalized, effective treatment paradigm for obesity-mediated cancer.

Protein Kinases in Obesity, and the Kinase-Targeted Therapy

The action of protein kinases and protein phosphatases is essential for multiple physiological responses. Each protein kinase displays its own unique substrate specificity and a regulatory mechanism that may be modulated by association with other proteins. Protein kinases are classified as dual-specificity kinases and dual-specificity phosphatases. Dual-specificity phosphatases are important signal transduction enzymes that regulate various cellular processes in coordination with protein kinases and play an important role in obesity. Impairment of insulin signaling in obesity is largely mediated by the activation of the inhibitor of kappa B-kinase beta and the c-Jun N-terminal kinase (JNK). Oxidative stress and endoplasmic reticulum (ER) stress activate the JNK pathway which suppresses insulin biosynthesis. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) are important for proper regulation of glucose metabolism in mammals at both the hormonal and cellular levels. Additionally, obesity-activated calcium/calmodulin dependent-protein kinase II/p38 suppresses insulin-induced protein kinase B phosphorylation by activating the ER stress effector, activating transcription factor-4. To alleviate lipotoxicity and insulin resistance, promising targets are pharmacologically inhibited. Nifedipine, calcium channel blocker, stimulates lipogenesis and adipogenesis by downregulating AMPK and upregulating mTOR, which thereby enhances lipid storage. Contrary to the nifedipine, metformin activates AMPK, increases fatty acid oxidation, suppresses fatty acid synthesis and deposition, and thus alleviates lipotoxicity. Obese adults with vascular endothelial dysfunction have greater endothelial cells activation of unfolded protein response stress sensors, RNA-dependent protein kinase-like ER eukaryotic initiation factor-2 alpha kinase (PERK), and activating transcription factor-6. The transcriptional regulation of adipogenesis in obesity is influenced by AGC (protein kinase A (PKA), PKG, PKC) family signaling kinases. Obesity may induce systemic oxidative stress and increase reactive oxygen species in adipocytes. An increase in intracellular oxidative stress can promote PKC-β activation. Activated PKC-β induces growth factor adapter Shc phosphorylation. Shc-generated peroxides reduce mitochondrial oxygen consumption and enhance triglyceride accumulation and lipotoxicity. Liraglutide attenuates mitochondrial dysfunction and reactive oxygen species generation. Co-treatment of antiobesity and antidiabetic herbal compound, berberine with antipsychotic drug olanzapine decreases the accumulation of triglyceride. While low-dose rapamycin, metformin, amlexanox, thiazolidinediones, and saroglitazar protect against insulin resistance, glucagon-like peptide-1 analog liraglutide inhibits palmitate-induced inflammation by suppressing mTOR complex 1 (mTORC1) activity and protects against lipotoxicity.

Obesity under the moonlight of c-MYC

The moonlighting protein c-Myc is a master regulator of multiple biological processes including cell proliferation, differentiation, angiogenesis, apoptosis and metabolism. It is constitutively and aberrantly expressed in more than 70% of human cancers. Overwhelming evidence suggests that c-Myc dysregulation is involved in several inflammatory, autoimmune, metabolic and other non-cancerous diseases. In this review, we addressed the role of c-Myc in obesity. Obesity is a systemic disease, accompanied by multi-organ dysfunction apart from white adipose tissue (WAT), such as the liver, the pancreas, and the intestine. c-Myc plays a big diversity of functions regulating cellular proliferation, the maturation of progenitor cells, fatty acids (FAs) metabolism, and extracellular matrix (ECM) remodeling. Moreover, c-Myc drives the expression of a wide range of metabolic genes, modulates the inflammatory response, induces insulin resistance (IR), and contributes to the regulation of intestinal dysbiosis. Altogether, c-Myc is an interesting diagnostic tool and/or therapeutic target in order to mitigate obesity and its consequences.

10‑Gingerol, a novel ginger compound, exhibits antiadipogenic effects without compromising cell viability in 3T3‑L1 cells

Obesity is defined as excessive fat accumulation that can be detrimental to health and currently affects a large part of the global population. Obesity arises from excessive energy intake along with a sedentary lifestyle and leads to adipocytes with aggravated hypertrophy. Strategies have been designed to prevent and treat obesity. Nutrigenomics may serve a role in prevention of obesity using bioactive compounds present in certain foods with anti-obesogenic effects. Ginger (Zingiber officinale Roscoe) contains gingerols, key bioactive compounds that inhibit hypertrophy and hyperplasia of adipocytes. The present study aimed to evaluate the antiadipogenic activity of 10-gingerol (10-G) in the 3T3-L1 cell line. Three study groups were formed: Negative (3T3-L1 preadipocytes) and positive control (mature 3T3-L1 adipocytes) and 10-G (3T3-L1 preadipocytes stimulated with 10-G during adipogenic differentiation). Cell viability and lipid content were evaluated by MTT assay and Oil Red O staining, respectively. mRNA expression of CCAAT enhancer-binding protein α (C/ebpα), peroxisome proliferator-activated receptor γ (Pparγ), mechanistic target of rapamycin complex (Mtor), sterol regulatory element binding transcription factor 1 (Srebf1), acetyl-coenzyme A carboxylase (Acaca), fatty acid binding protein 4 (Fabp4), and 18S rRNA (Rn18s), was quantified by quantitative PCR. The protein expression of C/EPBα was analyzed by western blot. In the 10-G group, lipid content was decreased by 28.83% (P<0.0001) compared with the positive control; notably, cell viability was not affected (P=0.336). The mRNA expression in the 10-G group was higher for C/ebpα (P<0.001) and lower for Acaca (P<0.001), Fabp4 (P<0.001), Mtor (P<0.0001) and Srebf1 (P<0.0001) compared with the positive control group, while gene expression of Pparγ did not present significant changes. The presence of 10-G notably decreased C/EBPα protein levels in 3T3-L1 adipocytes. In summary, the antiadipogenic effect of 10-G during the differentiation of 3T3-L1 cells into adipocytes may be explained by mRNA downregulation of adipogenic transcriptional factors and lipid metabolism-associated genes.

Phytochemicals Target Multiple Metabolic Pathways in Cancer

Cancer metabolic reprogramming is a complex process that provides malignant cells with selective advantages to grow and propagate in the hostile environment created by the immune surveillance of the human organism. This process underpins cancer proliferation, invasion, antioxidant defense, and resistance to anticancer immunity and therapeutics. Perhaps not surprisingly, metabolic rewiring is considered to be one of the "Hallmarks of cancer". Notably, this process often comprises various complementary and overlapping pathways. Today, it is well known that highly selective inhibition of only one of the pathways in a tumor cell often leads to a limited response and, subsequently, to the emergence of resistance. Therefore, to increase the overall effectiveness of antitumor drugs, it is advisable to use multitarget agents that can simultaneously suppress several key processes in the tumor cell. This review is focused on a group of plant-derived natural compounds that simultaneously target different pathways of cancer-associated metabolism, including aerobic glycolysis, respiration, glutaminolysis, one-carbon metabolism, de novo lipogenesis, and β-oxidation of fatty acids. We discuss only those compounds that display inhibitory activity against several metabolic pathways as well as a number of important signaling pathways in cancer. Information about their pharmacokinetics in animals and humans is also presented. Taken together, a number of known plant-derived compounds may target multiple metabolic and signaling pathways in various malignancies, something that bears great potential for the further improvement of antineoplastic therapy.

Hepatocyte TIPE2 is a fasting-induced Raf-1 inactivator that drives hepatic gluconeogenesis to maintain glucose homeostasis

BACKGROUND

The liver regulates metabolic balance during fasting-feeding cycle. Hepatic adaptation to fasting is precisely modulated on multiple levels. Tumor necrosis factor-α-induced protein 8-like 2 (TIPE2) is a negative regulator of immunity that reduces several liver pathologies, but its physiological roles in hepatic metabolism are largely unknown.

METHODS

TIPE2 expression was examined in mouse liver during fasting-feeding cycle. TIPE2-knockout mice, liver-specific TIPE2-knockout mice, liver-specific TIPE2-overexpressed mice were examined for fasting blood glucose and pyruvate tolerance test. Primary hepatocytes or liver tissues from these mice were evaluated for glucose production, lipid accumulation, gene expression and regulatory pathways. TIPE2 interaction with Raf-1 and TIPE2 transcription regulated by PPAR-α were examined using gene overexpression or knockdown, co-immunoprecipitation, western blot, luciferase reporter assay and DNA-protein binding assay.

RESULTS

TIPE2 expression was upregulated in fasted mouse liver and starved hepatocytes, which was positively correlated with gluconeogenic genes. Liver-specific TIPE2 deficiency impaired blood glucose homeostasis and gluconeogenic capacity in mice upon fasting, while liver-specific TIPE2 overexpression elevated fasting blood glucose and hepatic gluconeogenesis in mice. In primary hepatocytes upon starvation, TIPE2 interacted with Raf-1 to accelerate its ubiquitination and degradation, resulting in ERK deactivation and FOXO1 maintenance to sustain gluconeogenesis. During prolonged fasting, hepatic TIPE2 deficiency caused aberrant activation of ERK-mTORC1 axis that increased hepatic lipid accumulation via lipogenesis. In hepatocytes upon starvation, PPAR-α bound with TIPE2 promoter and triggered its transcriptional expression.

CONCLUSIONS

Hepatocyte TIPE2 is a PPAR-α-induced Raf-1 inactivator that sustains hepatic gluconeogenesis and prevents excessive hepatic lipid accumulation, playing beneficial roles in hepatocyte adaptation to fasting.

The murine retinal pigment epithelium requires peroxisomal β-oxidation to maintain lysosomal function and prevent dedifferentiation

Retinal pigment epithelium (RPE) cells have to phagocytose shed photoreceptor outer segments (POS) on a daily basis over the lifetime of an organism, but the mechanisms involved in the digestion and recycling of POS lipids are poorly understood. Although it was frequently assumed that peroxisomes may play an essential role, this was never investigated. Here, we show that global as well as RPE-selective loss of peroxisomal β-oxidation in multifunctional protein 2 (MFP2) knockout mice impairs the digestive function of lysosomes in the RPE at a very early age, followed by RPE degeneration. This was accompanied by prolonged mammalian target of rapamycin activation, lipid deregulation, and mitochondrial structural anomalies without, however, causing oxidative stress or energy shortage. The RPE degeneration caused secondary photoreceptor death. Notably, the deterioration of the RPE did not occur in an Mfp2/rd1 mutant mouse line, characterized by absent POS shedding. Our findings prove that peroxisomal β-oxidation in the RPE is essential for handling the polyunsaturated fatty acids present in ingested POS and shed light on retinopathy in patients with peroxisomal disorders. Our data also have implications for gene therapy development as they highlight the importance of targeting the RPE in addition to the photoreceptor cells.

Host nutrient sensing is mediated by mTOR signaling in cnidarian-dinoflagellate symbiosis

To survive in the nutrient-poor waters of the tropics, reef-building corals rely on intracellular, photosynthetic dinoflagellate symbionts. Photosynthates produced by the symbiont are translocated to the host, and this enables corals to form the structural foundation of the most biodiverse of all marine ecosystems. Although the regulation of nutrient exchange between partners is critical for ecosystem stability and health, the mechanisms governing how nutrients are sensed, transferred, and integrated into host cell processes are largely unknown. Ubiquitous among eukaryotes, the mechanistic target of the rapamycin (mTOR) signaling pathway integrates intracellular and extracellular stimuli to influence cell growth and cell-cycle progression and to balance metabolic processes. A functional role of mTOR in the integration of host and symbiont was demonstrated in various nutritional symbioses, and a similar role of mTOR was proposed for coral-algal symbioses. Using the endosymbiosis model Aiptasia, we examined the role of mTOR signaling in both larvae and adult polyps across various stages of symbiosis. We found that symbiosis enhances cell proliferation, and using an Aiptasia-specific antibody, we localized mTOR to symbiosome membranes. We found that mTOR signaling is activated by symbiosis, while inhibition of mTOR signaling disrupts intracellular niche establishment and symbiosis altogether. Additionally, we observed that dysbiosis was a conserved response to mTOR inhibition in the larvae of a reef-building coral species. Our data confim that mTOR signaling plays a pivotal role in integrating symbiont-derived nutrients into host metabolism and symbiosis stability, ultimately allowing symbiotic cnidarians to thrive in challenging environments.

Insulin and the sebaceous gland function

Insulin affects metabolic processes in different organs, including the skin. The sebaceous gland (SG) is an important appendage in the skin, which responds to insulin-mediated signals, either directly or through the insulin growth factor 1 (IGF-1) axis. Insulin cues are differently translated into the activation of metabolic processes depending on several factors, including glucose levels, receptor sensitivity, and sebocyte differentiation. The effects of diet on both the physiological function and pathological conditions of the SG have been linked to pathways activated by insulin and IGF-1. Experimental evidence and theoretical speculations support the association of insulin resistance with acne vulgaris, which is a major disorder of the SG. In this review, we examined the effects of insulin on the SG function and their implications in the pathogenesis of acne.

Malonyl-CoA is a conserved endogenous ATP-competitive mTORC1 inhibitor

Cell growth is regulated by the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which functions both as a nutrient sensor and a master controller of virtually all biosynthetic pathways. This ensures that cells are metabolically active only when conditions are optimal for growth. Notably, although mTORC1 is known to regulate fatty acid biosynthesis, how and whether the cellular lipid biosynthetic capacity signals back to fine-tune mTORC1 activity remains poorly understood. Here we show that mTORC1 senses the capacity of a cell to synthesise fatty acids by detecting the levels of malonyl-CoA, an intermediate of this biosynthetic pathway. We find that, in both yeast and mammalian cells, this regulation is direct, with malonyl-CoA binding to the mTOR catalytic pocket and acting as a specific ATP-competitive inhibitor. When fatty acid synthase (FASN) is downregulated/inhibited, elevated malonyl-CoA levels are channelled to proximal mTOR molecules that form direct protein-protein interactions with acetyl-CoA carboxylase 1 (ACC1) and FASN. Our findings represent a conserved and unique homeostatic mechanism whereby impaired fatty acid biogenesis leads to reduced mTORC1 activity to coordinately link this metabolic pathway to the overall cellular biosynthetic output. Moreover, they reveal the existence of a physiological metabolite that directly inhibits the activity of a signalling kinase in mammalian cells by competing with ATP for binding.

The outcome of boosting mitochondrial activity in alcohol-associated liver disease is organ-dependent

BACKGROUND AND AIMS

Alcohol-associated liver disease (ALD) accounts for 70% of liver-related deaths in Europe, with no effective approved therapies. Although mitochondrial dysfunction is one of the earliest manifestations of alcohol-induced injury, restoring mitochondrial activity remains a problematic strategy due to oxidative stress. Here, we identify methylation-controlled J protein (MCJ) as a mediator for ALD progression and hypothesize that targeting MCJ may help in recovering mitochondrial fitness without collateral oxidative damage.

APPROACH AND RESULTS

C57BL/6 mice [wild-type (Wt)] Mcj knockout and Mcj liver-specific silencing (MCJ-LSS) underwent the NIAAA dietary protocol (Lieber-DeCarli diet containing 5% (vol/vol) ethanol for 10 days, plus a single binge ethanol feeding at day 11). To evaluate the impact of a restored mitochondrial activity in ALD, the liver, gut, and pancreas were characterized, focusing on lipid metabolism, glucose homeostasis, intestinal permeability, and microbiota composition. MCJ, a protein acting as an endogenous negative regulator of mitochondrial respiration, is downregulated in the early stages of ALD and increases with the severity of the disease. Whole-body deficiency of MCJ is detrimental during ALD because it exacerbates the systemic effects of alcohol abuse through altered intestinal permeability, increased endotoxemia, and dysregulation of pancreatic function, which overall worsens liver injury. On the other hand, liver-specific Mcj silencing prevents main ALD hallmarks, that is, mitochondrial dysfunction, steatosis, inflammation, and oxidative stress, as it restores the NAD + /NADH ratio and SIRT1 function, hence preventing de novo lipogenesis and improving lipid oxidation.

CONCLUSIONS

Improving mitochondrial respiration by liver-specific Mcj silencing might become a novel therapeutic approach for treating ALD.

The stress-responsive protein REDD1 and its pathophysiological functions

Regulated in development and DNA damage-response 1 (REDD1) is a stress-induced protein that controls various cellular functions, including metabolism, oxidative stress, autophagy, and cell fate, and contributes to the pathogenesis of metabolic and inflammatory disorders, neurodegeneration, and cancer. REDD1 usually exerts deleterious effects, including tumorigenesis, metabolic inflammation, neurodegeneration, and muscle dystrophy; however, it also exhibits protective functions by regulating multiple intrinsic cell activities through either an mTORC1-dependent or -independent mechanism. REDD1 typically regulates mTORC1 signaling, NF-κB activation, and cellular pro-oxidant or antioxidant activity by interacting with 14-3-3 proteins, IκBα, and thioredoxin-interacting protein or 75 kDa glucose-regulated protein, respectively. The diverse functions of REDD1 depend on cell type, cellular context, interaction partners, and cellular localization (e.g., mitochondria, endomembrane, or cytosol). Therefore, comprehensively understanding the molecular mechanisms and biological roles of REDD1 under pathophysiological conditions is of utmost importance. In this review, based on the published literature, we highlight and discuss the molecular mechanisms underlying the REDD1 expression and its actions, biological functions, and pathophysiological roles.

NK Cells from Human Cytomegalovirus-Seropositive Individuals Have a Distinct Metabolic Profile That Correlates with Elevated mTOR Signaling

CMV can elicit adaptive immune features in both mouse and human NK cells. Mouse Ly49H+ NK cells expand 100- to 1000-fold in response to mouse CMV infection and persist for months after exposure. Human NKG2C+ NK cells also expand after human CMV (HCMV) infection and persist for months. The clonal expansion of adaptive NK cells is likely an energy-intensive process, and the metabolic requirements that support adaptive NK cell expansion and persistence remain largely uncharacterized. We previously reported that NK cells from HCMV-seropositive donors had increased maximum capacity for both glycolysis and mitochondrial oxidative phosphorylation relative to NK cells from HCMV-seronegative donors. In this article, we report an extension of this work in which we analyzed the metabolomes of NK cells from HCMV-seropositive donors with NKG2C+ expansions and NK cells from HCMV seronegative donors without such expansions. NK cells from HCMV+ donors exhibited striking elevations in purine and pyrimidine deoxyribonucleotides, along with moderate increases in plasma membrane components. Mechanistic target of rapamycin (mTOR) is a serine/threonine protein kinase that, as a part of mTOR complex 1 (mTORC1), bridges nutrient signaling to metabolic processes necessary for cell growth. Signaling through mTORC1 induces both nucleotide and lipid synthesis. We observed elevated mTORC1 signaling on activation in both NKG2C- and NKG2C+ NK cells from HCMV+ donors relative to those from HCMV- donors, demonstrating a correlation between higher mTORC1 activity and synthesis of key metabolites for cell growth and division.

Acteoside improves adipocyte browning by CDK6-mediated mTORC1-TFEB pathway

Adipocyte browning increases energy expenditure by thermogenesis, which has been considered a potential strategy against obesity and its related metabolic diseases. Phytochemicals derived from natural products with the ability to improve adipocyte thermogenesis have aroused extensive attention. Acteoside (Act), a phenylethanoid glycoside, exists in various medicinal or edible plants and has been shown to regulate metabolic disorders. Here, the browning effect of Act was evaluated by stimulating beige cell differentiation from the stromal vascular fraction (SVF) in the inguinal white adipose tissue (iWAT) and 3 T3-L1 preadipocytes, and by converting the iWAT-SVF derived mature white adipocytes. Act improves adipocyte browning by differentiation of the stem/progenitors into beige cells and by direct conversion of mature white adipocytes into beige cells. Mechanistically, Act inhibited CDK6 and mTOR, and consequently relieved phosphorylation of the transcription factor EB (TFEB) and increased its nuclear retention, leading to induction of PGC-1α, a driver of mitochondrial biogenesis, and UCP1-dependent browning. These data thus unveil a CDK6-mTORC1-TFEB pathway that regulates Act-induced adipocyte browning.

Mitochondrial reprogramming in peripheral blood mononuclear cells of patients with glycogen storage disease type Ia

BACKGROUND

Glycogen storage disease type Ia (GSDIa) is an inborn metabolic disorder caused by the deficiency of glucose-6-phospatase-α (G6Pase-α) leading to mitochondrial dysfunction. It remains unclear whether mitochondrial dysfunction is present in patients' peripheral blood mononuclear cells (PBMC) and whether dietary treatment can play a role. The aim of this study was to investigate mitochondrial function in PBMC of GSDIa patients.

METHODS

Ten GSDIa patients and 10 age-, sex- and fasting-time matched controls were enrolled. Expression of genes involved in mitochondrial function and activity of key fatty acid oxidation (FAO) and Krebs cycle proteins were assessed in PBMC. Targeted metabolomics and assessment of metabolic control markers were also performed.

RESULTS

Adult GSDIa patients showed increased CPT1A, SDHB, TFAM, mTOR expression (p < 0.05) and increased VLCAD, CPT2 and citrate synthase activity in PBMC (p < 0.05). VLCAD activity directly correlated with WC (p < 0.01), BMI (p < 0.05), serum malonycarnitine levels (p < 0.05). CPT2 activity directly correlated with BMI (p < 0.05).

CONCLUSION

Mitochondrial reprogramming is detectable in PBMC of GSDIa patients. This feature may develop as an adaptation to the liver enzyme defect and may be triggered by dietary (over)treatment in the frame of G6Pase-α deficiency. PBMC can represent an adequate mean to assess (diet-induced) metabolic disturbances in GSDIa.

Deregulation of mTORC1-TFEB axis in human iPSC model of GBA1-associated Parkinson's disease

Mutations in the GBA1 gene are the single most frequent genetic risk factor for Parkinson's disease (PD). Neurodegenerative changes in GBA1-associated PD have been linked to the defective lysosomal clearance of autophagic substrates and aggregate-prone proteins. To elucidate novel mechanisms contributing to proteinopathy in PD, we investigated the effect of GBA1 mutations on the transcription factor EB (TFEB), the master regulator of the autophagy-lysosomal pathway (ALP). Using PD patients' induced-pluripotent stem cells (iPSCs), we examined TFEB activity and regulation of the ALP in dopaminergic neuronal cultures generated from iPSC lines harboring heterozygous GBA1 mutations and the CRISPR/Cas9-corrected isogenic controls. Our data showed a significant decrease in TFEB transcriptional activity and attenuated expression of many genes in the CLEAR network in GBA1 mutant neurons, but not in the isogenic gene-corrected cells. In PD neurons, we also detected increased activity of the mammalian target of rapamycin complex1 (mTORC1), the main upstream negative regulator of TFEB. Increased mTORC1 activity resulted in excess TFEB phosphorylation and decreased nuclear translocation. Pharmacological mTOR inhibition restored TFEB activity, decreased ER stress and reduced α-synuclein accumulation, indicating improvement of neuronal protiostasis. Moreover, treatment with the lipid substrate reducing compound Genz-123346, decreased mTORC1 activity and increased TFEB expression in the mutant neurons, suggesting that mTORC1-TFEB alterations are linked to the lipid substrate accumulation. Our study unveils a new mechanism contributing to PD susceptibility by GBA1 mutations in which deregulation of the mTORC1-TFEB axis mediates ALP dysfunction and subsequent proteinopathy. It also indicates that pharmacological restoration of TFEB activity could be a promising therapeutic approach in GBA1-associated neurodegeneration.

Metformin-induced TTP mediates communication between Kupffer cells and hepatocytes to alleviate hepatic steatosis by regulating lipophagy and necroptosis

OBJECTIVE

Emerging evidence suggests that crosstalk between Kupffer cells (KCs) and hepatocytes protects against non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanisms that lead to the reduction of steatosis in NAFLD remain obscure.

METHODS

Ttp^+/+ and Ttp^-/- mice were fed with a high-fat diet. Hepatic steatosis was analyzed by Nile Red staining and measurement of inflammatory cytokines. Lipid accumulation and cell death were evaluated in co-culture systems with primary hepatocytes and KCs derived from either Ttp^+/+ or Ttp^-/- mice.

RESULTS

Tristetraprolin (TTP), an mRNA binding protein, was essential for the protective effects of metformin in NAFLD. Metformin activated TTP via the AMPK-Sirt1 pathway in hepatocytes and KCs. TTP inhibited TNF-α production in KCs, which in turn decreased hepatocyte necroptosis. Downregulation of Rheb expression by TTP promoted hepatocyte lipophagy via mTORC1 inhibition and increased nuclear translocation of transcription factor-EB (TFEB). Consistently, TTP-deficient NAFLD mice failed to respond to metformin with respect to alleviation of hepatic steatosis, protection of hepatocyte necroptosis, or induction of lipophagy.

CONCLUSIONS

TTP, which is essential for the protective effects of metformin, may represent a novel primary therapeutic target in NAFLD.

mTORC1 syndrome (TorS): unified paradigm for diabetes/metabolic syndrome

'Glucolipotoxicity' and 'insulin resistance' are claimed to drive type 2 diabetes (T2D) and the non-glycemic diseases of the metabolic syndrome (MetS) (obesity, dyslipidemia, hypertension). In line with that, glycemic and/or insulin control are considered to be primary goal in treating T2D/MetS. However, recent standard-of-care (SOC) treatments of T2D, initially designed to control T2D hyperglycemia, appear now to alleviate the cardio-renal and non-glycemic diseases of T2D/MetS independently of glucose lowering and insulin resistance, and in non-T2D patients altogether, calling for an alternative unifying pathophysiology/treatment paradigm for T2D/MetS. This opinion article proposes to replace the current 'glucolipotoxic/insulin-resistance' paradigm of T2D/MetS with an 'mammalian target of rapamycin complex 1 (mTORC1) syndrome' (TorS) paradigm, implying an exhaustive cohesive disease entity driven by an upstream hyperactive mTORC1, and which includes diabetic hyperglycemia, diabetic dyslipidemia, hypertension, diabetic macrovascular and microvascular disease, non-alcoholic fatty liver disease, some cancers, neurodegeneration, polycystic ovary syndrome (PCOS), psoriasis, and others. The TorS paradigm may account for the insulin-resistant glycemic context of TorS, combined with response to insulin of the non-glycemic diseases of TorS. The TorS paradigm may account for the efficacy of current antidiabetic SOC treatments in diabetic and nondiabetic patients. Most importantly, the TorS paradigm may generate novel treatments for TorS.

Circular RNA- and microRNA-Mediated Post-Transcriptional Regulation of Preadipocyte Differentiation in Adipogenesis: From Expression Profiling to Signaling Pathway

Adipogenesis is an indispensable cellular process that involves preadipocyte differentiation into mature adipocyte. Dysregulated adipogenesis contributes to obesity, diabetes, vascular conditions and cancer-associated cachexia. This review aims to elucidate the mechanistic details on how circular RNA (circRNA) and microRNA (miRNA) modulate post-transcriptional expression of targeted mRNA and the impacted downstream signaling and biochemical pathways in adipogenesis. Twelve adipocyte circRNA profiling and comparative datasets from seven species are analyzed using bioinformatics tools and interrogations of public circRNA databases. Twenty-three circRNAs are identified in the literature that are common to two or more of the adipose tissue datasets in different species; these are novel circRNAs that have not been reported in the literature in relation to adipogenesis. Four complete circRNA-miRNA-mediated modulatory pathways are constructed via integration of experimentally validated circRNA-miRNA-mRNA interactions and the downstream signaling and biochemical pathways involved in preadipocyte differentiation via the PPARγ/C/EBPα gateway. Despite the diverse mode of modulation, bioinformatics analysis shows that the circRNA-miRNA-mRNA interacting seed sequences are conserved across species, supporting mandatory regulatory functions in adipogenesis. Understanding the diverse modes of post-transcriptional regulation of adipogenesis may contribute to the development of novel diagnostic and therapeutic strategies for adipogenesis-associated diseases and in improving meat quality in the livestock industries.

Maternal prenatal cholesterol levels predict offspring weight trajectories during childhood in the Norwegian Mother, Father and Child Cohort Study

BACKGROUND

Numerous intrauterine factors may affect the offspring's growth during childhood. We aimed to explore if maternal and paternal prenatal lipid, apolipoprotein (apo)B and apoA1 levels are associated with offspring weight, length, and body mass index from 6 weeks to eight years of age. This has previously been studied to a limited extent.

METHODS

This parental negative control study is based on the Norwegian Mother, Father and Child Cohort Study and uses data from the Medical Birth Registry of Norway. We included 713 mothers and fathers with or without self-reported hypercholesterolemia and their offspring. Seven parental metabolites were measured by nuclear magnetic resonance spectroscopy, and offspring weight and length were measured at 12 time points. Data were analyzed by linear spline mixed models, and the results are presented as the interaction between parental metabolite levels and offspring spline (age).

RESULTS

Higher maternal total cholesterol (TC) level was associated with a larger increase in offspring body weight up to 8 years of age (0.03 ≤ P_interaction ≤ 0.04). Paternal TC level was not associated with change in offspring body weight (0.17 ≤ P_interaction ≤ 0.25). Higher maternal high-density lipoprotein cholesterol (HDL-C) and apoA1 levels were associated with a lower increase in offspring body weight up to 8 years of age (0.001 ≤ P_interaction ≤ 0.005). Higher paternal HDL-C and apoA1 levels were associated with a lower increase in offspring body weight up to 5 years of age but a larger increase in offspring body weight from 5 to 8 years of age (0.01 ≤ P_interaction ≤ 0.03). Parental metabolites were not associated with change in offspring height or body mass index up to 8 years of age (0.07 ≤ P_interaction ≤ 0.99).

CONCLUSIONS

Maternal compared to paternal TC, HDL-C, and apoA1 levels were more strongly and consistently associated with offspring body weight during childhood, supporting a direct intrauterine effect.

Hypolipidemic Effects of Beetroot Juice in SHR-CRP and HHTg Rat Models of Metabolic Syndrome: Analysis of Hepatic Proteome

Recently, red beetroot has attracted attention as a health-promoting functional food. Studies have shown that beetroot administration can reduce blood pressure and ameliorate parameters of glucose and lipid metabolism; however, mechanisms underlying these beneficial effects of beetroot are not yet fully understood. In the current study, we analysed the effects of beetroot on parameters of glucose and lipid metabolism in two models of metabolic syndrome: (i) transgenic spontaneously hypertensive rats expressing human C-reactive protein (SHR-CRP rats), and (ii) hereditary hypertriglyceridemic (HHTg) rats. Treatment with beetroot juice for 4 weeks was, in both models, associated with amelioration of oxidative stress, reduced circulating lipids, smaller visceral fat depots, and lower ectopic fat accumulation in the liver compared to the respective untreated controls. On the other hand, beetroot treatment had no significant effects on the sensitivity of the muscle and adipose tissue to insulin action in either model. Analyses of hepatic proteome revealed significantly deregulated proteins involved in glycerophospholipid metabolism, mTOR signalling, inflammation, and cytoskeleton rearrangement.

Aerobic exercise ameliorates insulin resistance in C57BL/6 J mice via activating Sestrin3

Skeletal muscle insulin resistance (IR) is closely linked to hyperglycemia and metabolic disorders. Regular exercise enhances insulin sensitivity in skeletal muscle, but its underlying mechanisms remain unknown. Sestrin3 (SESN3) is a stress-inducible protein that protects against obesity-induced hepatic steatosis and insulin resistance. Regular exercise training is known to increase SESN3 expression in skeletal muscle. The purpose of this study was to explore whether SESN3 mediates the metabolic effects of exercise in the mouse model of high-fat diet (HFD)-induced IR. SESN3^-/- mice exhibited severer body weight gain, ectopic lipid accumulation, and dysregulation of glucose metabolism after long-term HFD feeding compared with the wild-type (WT) mice. Moreover, we found that SESN3 deficiency weakened the effects of exercise on reducing serum insulin levels and improving glucose tolerance in mice. Exercise training increased pAKT-S473 and GLUT4 expression, accompanied by enhanced pmTOR-S2481 (an indicator of mTORC2 activity) in WT quadriceps that were less pronounced in SESN3^-/- mice. SESN3 overexpression in C2C12 myotubes further confirmed that SESN3 played an important role in skeletal muscle glucose metabolism. SESN3 overexpression increased the binding of Rictor to mTOR and pmTOR-S2481 in C2C12 myotubes. Moreover, SESN3 overexpression resulted in an elevation of glucose uptake and a concomitant increase of pAKT-S473 in C2C12 myotubes, whereas these effects were diminished by downregulation of mTORC2 activity. Taken together, SESN3 is a crucial protein in amplifying the beneficial effects of exercise on insulin sensitivity in skeletal muscle and systemic glucose levels. SESN3/mTORC2/AKT pathway mediated the effects of exercise on skeletal muscle insulin sensitivity.

MC-LR Aggravates Liver Lipid Metabolism Disorders in Obese Mice Fed a High-Fat Diet via PI3K/AKT/mTOR/SREBP1 Signaling Pathway

Obesity, a metabolic disease caused by excessive fat accumulation in the body, has attracted worldwide attention. Microcystin-LR (MC-LR) is a hepatotoxic cyanotoxin which has been reportedly to cause lipid metabolism disorder. In this study, C57BL/6J mice were fed a high-fat diet (HFD) for eight weeks to build obese an animal model, and subsequently, the obese mice were fed MC-LR for another eight weeks, and we aimed to determine how MC-LR exposure affects the liver lipid metabolism in high-fat-diet-induced obese mice. The results show that MC-LR increased the obese mice serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT), indicating damaged liver function. The lipid parameters include serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), and liver TG, which were all increased, whilst the high-density lipoprotein cholesterol (HDL-c) was decreased. Furthermore, after MC-LR treatment, histopathological observation revealed that the number of red lipid droplets increased, and that steatosis was more severe in the obese mice. In addition, the lipid synthesis-related genes were increased and the fatty acid β-oxidation-related genes were decreased in the obese mice after MC-LR exposure. Meanwhile, the protein expression levels of phosphorylation phosphatidylinositol 3-kinase (p-PI3K), phosphorylation protein kinase B (p-AKT), phosphorylation mammalian target of rapamycin (p-mTOR), and sterol regulatory element binding protein 1c (SREBP1-c) were increased; similarly, the p-PI3K/PI3K, p-AKT/AKT, p-mTOR/mTOR, and SREBP1/β-actin were significantly up-regulated in obese mice after being exposed to MC-LR, and the activated PI3K/AKT/mTOR/SREBP1 signaling pathway. In addition, MC-LR exposure reduced the activity of superoxide dismutase (SOD) and increased the level of malondialdehyde (MDA) in the obese mice's serum. In summary, the MC-LR could aggravate the HFD-induced obese mice liver lipid metabolism disorder by activating the PI3K/AKT/mTOR/SREBP1 signaling pathway to hepatocytes, increasing the SREBP1-c-regulated key enzymes for lipid synthesis, and blocking fatty acid β-oxidation.

The regulation of adipocyte growth in white adipose tissue

Adipocytes can increase in volume up to a thousand-fold, storing excess calories as triacylglycerol in large lipid droplets. The dramatic morphological changes required of adipocytes demands extensive cytoskeletal remodeling, including lipid droplet and plasma membrane expansion. Cell growth-related signalling pathways are activated, stimulating the production of sufficient amino acids, functional lipids and nucleotides to meet the increasing cellular needs of lipid storage, metabolic activity and adipokine secretion. Continued expansion gives rise to enlarged (hypertrophic) adipocytes. This can result in a failure to maintain growth-related homeostasis and an inability to cope with excess nutrition or respond to stimuli efficiently, ultimately leading to metabolic dysfunction. We summarize recent studies which investigate the functional and cellular structure remodeling of hypertrophic adipocytes. How adipocytes adapt to an enlarged cell size and how this relates to cellular dysfunction are discussed. Understanding the healthy and pathological processes involved in adipocyte hypertrophy may shed light on new strategies for promoting healthy adipose tissue expansion.

Loss of RUBCN/rubicon in adipocytes mediates the upregulation of autophagy to promote the fasting response

Upon fasting, adipocytes release their lipids that accumulate in the liver, thus promoting hepatic steatosis and ketone body production. However, the mechanisms underlying this process are not fully understood. In this study, we found that fasting caused a substantial decrease in the adipose levels of RUBCN/rubicon, a negative regulator of macroautophagy/autophagy, along with an increase in autophagy. Adipose-specific rubcn-knockout mice exhibited systemic fat loss that was not accelerated by fasting. Genetic inhibition of autophagy in adipocytes in fasted mice led to a reduction in fat loss, hepatic steatosis, and ketonemia. In terms of mechanism, autophagy decreased the levels of its substrates NCOA1/SRC-1 and NCOA2/TIF2, which are also coactivators of PPARG/PPARγ, leading to a fasting-induced reduction in the mRNA levels of adipogenic genes in adipocytes. Furthermore, RUBCN in adipocytes was degraded through the autophagy pathway, suggesting that autophagic degradation of RUBCN serves as a feedforward system for autophagy induction during fasting. Collectively, we propose that loss of adipose RUBCN promotes a metabolic response to fasting via increasing autophagic activity.

The uniformity and stability of cellular mass density in mammalian cell culture

Cell dry mass is principally determined by the sum of biosynthesis and degradation. Measurable change in dry mass occurs on a time scale of hours. By contrast, cell volume can change in minutes by altering the osmotic conditions. How changes in dry mass and volume are coupled is a fundamental question in cell size control. If cell volume were proportional to cell dry mass during growth, the cell would always maintain the same cellular mass density, defined as cell dry mass dividing by cell volume. The accuracy and stability against perturbation of this proportionality has never been stringently tested. Normalized Raman Imaging (NoRI), can measure both protein and lipid dry mass density directly. Using this new technique, we have been able to investigate the stability of mass density in response to pharmaceutical and physiological perturbations in three cultured mammalian cell lines. We find a remarkably narrow mass density distribution within cells, that is, significantly tighter than the variability of mass or volume distribution. The measured mass density is independent of the cell cycle. We find that mass density can be modulated directly by extracellular osmolytes or by disruptions of the cytoskeleton. Yet, mass density is surprisingly resistant to pharmacological perturbations of protein synthesis or protein degradation, suggesting there must be some form of feedback control to maintain the homeostasis of mass density when mass is altered. By contrast, physiological perturbations such as starvation or senescence induce significant shifts in mass density. We have begun to shed light on how and why cell mass density remains fixed against some perturbations and yet is sensitive during transitions in physiological state.