Malonyl-CoA: the regulator of fatty acid synthesis and oxidation

Endogenous ethanol production in health and disease

The gut microbiome exerts metabolic actions on distal tissues and organs outside the intestine, partly through microbial metabolites that diffuse into the circulation. The disruption of gut homeostasis results in changes to microbial metabolites, and more than half of the variance in the plasma metabolome can be explained by the gut microbiome. Ethanol is a major microbial metabolite that is produced in the intestine of nearly all individuals; however, elevated ethanol production is associated with pathological conditions such as metabolic dysfunction-associated steatotic liver disease and auto-brewery syndrome, in which the liver's capacity to metabolize ethanol is surpassed. In this Review, we describe the mechanisms underlying excessive ethanol production in the gut and the role of ethanol catabolism in mediating pathogenic effects of ethanol on the liver and host metabolism. We conclude by discussing approaches to target excessive ethanol production by gut bacteria.

Decreasing the burden of non-alcoholic fatty liver disease: From therapeutic targets to drug discovery opportunities

Non-alcoholic fatty liver disease (NAFLD) presents a pervasive global pandemic, affecting approximately 25 % of the world's population. This grave health issue not only demands urgent attention but also stands as a significant economic concern on a global scale. The genesis of NAFLD can be primarily attributed to unhealthy dietary habits and a sedentary lifestyle, albeit certain genetic factors have also been recorded to contribute to its occurrence. NAFLD is characterized by fat accumulation in more than 5 % of hepatocytes according to histological analysis, or >5.6 % of lipid volume fraction in total liver weight in patients. The pathophysiology of NAFLD/non-alcoholic steatohepatitis (NASH) is multifactorial and the mechanisms underlying the progression to advanced forms remain unclear, thereby representing a challenge to disease therapy. Despite the substantial efforts from the scientific community and the large number of pre-clinical and clinical trials performed so far, only one drug was approved by the Food and Drug Administration (FDA) to treat NAFLD/NASH specifically. This review provides an overview of available information concerning emerging molecular targets and drug candidates tested in clinical studies for the treatment of NAFLD/NASH. Improving our understanding of NAFLD pathophysiology and pharmacotherapy is crucial not only to explore new molecular targets, but also to potentiate drug discovery programs to develop new therapeutic strategies. This knowledge endeavours scientific efforts to reduce the time for achieving a specific and effective drug for NAFLD or NASH management and improve patients' quality of life.

Atf3-mediated metabolic reprogramming in hepatic macrophage orchestrates metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) is regulated by complex interplay between the macrophages and surrounding cells in the liver. Here, we show that Atf3 regulates glucose-fatty acid cycle in macrophages attenuates hepatocyte steatosis, and fibrogenesis in hepatic stellate cells (HSCs). Overexpression of Atf3 in macrophages protects against the development of MASH in Western diet-fed mice, whereas Atf3 ablation has the opposite effect. Mechanistically, Atf3 improves the reduction of fatty acid oxidation induced by glucose via forkhead box O1 (FoxO1) and Cd36. Atf3 inhibits FoxO1 activity via blocking Hdac1-mediated FoxO1 deacetylation at K242, K245, and K262 and increases Zdhhc4/5-mediated CD36 palmitoylation at C3, C7, C464, and C466; furthermore, macrophage Atf3 decreases hepatocytes lipogenesis and HSCs activation via retinol binding protein 4 (Rbp4). Anti-Rbp4 can prevent MASH progression that is induced by Atf3 deficiency in macrophages. This study identifies Atf3 as a regulator of glucose-fatty acid cycle. Targeting macrophage Atf3 or Rbp4 may be a plausible therapeutic strategy for MASH.

A multiomics approach reveals evidence for phenylbutyrate as a potential treatment for combined D,L-2- hydroxyglutaric aciduria

PURPOSE

To identify therapies for combined D, L-2-hydroxyglutaric aciduria (C-2HGA), a rare genetic disorder caused by recessive variants in the SLC25A1 gene.

METHODS

Patients C-2HGA were identified and diagnosed by whole exome sequencing and biochemical genetic testing. Patient derived fibroblasts were then treated with phenylbutyrate and the functional effects assessed by metabolomics and RNA-sequencing.

RESULTS

In this study, we demonstrated that C-2HGA patient derived fibroblasts exhibited impaired cellular bioenergetics. Moreover, Fibroblasts form one patient exhibited worsened cellular bioenergetics when supplemented with citrate. We hypothesized that treating patient cells with phenylbutyrate (PB), an FDA approved pharmaceutical drug that conjugates glutamine for renal excretion, would reduce mitochondrial 2-ketoglutarate, thereby leading to improved cellular bioenergetics. Metabolomic and RNA-seq analyses of PB-treated fibroblasts demonstrated a significant decrease in intracellular 2-ketoglutarate, 2-hydroxyglutarate, and in levels of mRNA coding for citrate synthase and isocitrate dehydrogenase. Consistent with the known action of PB, an increased level of phenylacetylglutamine in patient cells was consistent with the drug acting as 2-ketoglutarate sink.

CONCLUSION

Our pre-clinical studies suggest that citrate supplementation has the possibility exacerbating energy metabolism in this condition. However, improvement in cellular bioenergetics suggests phenylbutyrate might have interventional utility for this rare disease.

The key role of altered tubule cell lipid metabolism in kidney disease development

Kidney epithelial cells have very high energy requirements, which are largely met by fatty acid oxidation. Complex changes in lipid metabolism are observed in patients with kidney disease. Defects in fatty acid oxidation and increased lipid uptake, especially in the context of hyperlipidemia and proteinuria, contribute to this excess lipid build-up and exacerbate kidney disease development. Recent studies have also highlighted the role of increased de novo lipogenesis in kidney fibrosis. The defect in fatty acid oxidation causes energy starvation. Increased lipid uptake, synthesis, and lower fatty acid oxidation can cause toxic lipid build-up, reactive oxygen species generation, and mitochondrial damage. A better understanding of these metabolic processes may open new treatment avenues for kidney diseases by targeting lipid metabolism.

Replenishment of TCA cycle intermediates and long-noncoding RNAs regulation in breast cancer

The tricarboxylic acid (TCA) cycle is an essential interface that coordinates cellular metabolism and is as a primary route determining the fate of a variety of fuel sources, including glucose, fatty acid and glutamate. The crosstalk of nutrients replenished TCA cycle regulates breast cancer (BC) progression by changing substrate levels-induced epigenetic alterations, especially the methylation, acetylation, succinylation and lactylation. Long non-coding RNAs (lncRNA) have dual roles in inhibiting or promoting energy reprogramming, and so altering the metabolic flux of fuel sources to the TCA cycle, which may regulate epigenetic modifications at the cellular level of BC. This narrative review discussed the central role of the TCA cycle in interconnecting numerous fuels and the induced epigenetic modifications, and the underlying regulatory mechanisms of lncRNAs in BC.

Insights into the molecular mechanisms of malnutrition‐associated steatohepatitis: A review

Malnutrition is a public health epidemic mainly targeting poverty‐stricken people, young ones, older people, pregnant women, and individuals with metabolic disorders. Severe malnutrition is linked with several metabolic defects, such as hepatic dysfunction, hypertension, cardiovascular disease, and osteoarthritis. The proper functioning of the liver plays a crucial role in ensuring the supply of nutrients to the body. Consequently, inadequate nutrition can lead to severe periportal hepatic steatosis due to compromised mitochondrial and peroxisome functions. Reduced protein intake disrupts essential metabolic processes like the TCA cycle, oxidative phosphorylation, and β‐oxidation, ultimately affecting ATP production. Furthermore, this can trigger a cascade of events, including disturbances in amino acid metabolism, iron metabolism, and gut microbiota, which activate genes involved in de novo lipogenesis, leading to the accumulation of lipids in the liver. The condition, in prolonged cases, progresses to steatohepatitis and liver fibrosis. Limited therapeutic solutions are available; however, few dietary supplements and drugs have demonstrated positive effects on the growth and health of malnourished individuals. These supplements improve parameters such as inflammatory and oxidative status, reduce triglyceride accumulation, enhance insulin sensitivity, and downregulate gene expression in hepatic lipid metabolism. This review elucidates the various mechanisms involved in malnutrition‐associated steatohepatitis and provides an overview of the available approaches for treating this condition.

Exploring the impact of lipid droplets on the evolution and progress of hepatocarcinoma

Over the past 10 years, the biological role of lipid droplets (LDs) has gained significant attention in the context of both physiological and pathological conditions. Considerable progress has been made in elucidating key aspects of these organelles, yet much remains to be accomplished to fully comprehend the myriad functions they serve in the progression of hepatic tumors. Our current perception is that LDs are complex and active structures managed by a distinct set of cellular processes. This understanding represents a significant paradigm shift from earlier perspectives. In this review, we aim to recapitulate the function of LDs within the liver, highlighting their pivotal role in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) (Hsu and Loomba, 2024) and their contribution to the progression towards more advanced pathological stages up to hepatocellular carcinoma (HC) (Farese and Walther, 2009). We are aware of the molecular complexity and changes occurring in the neoplastic evolution of the liver. Our attempt, however, is to summarize the most important and recent roles of LDs across both healthy and all pathological liver states, up to hepatocarcinoma. For more detailed insights, we direct readers to some of the many excellent reviews already available in the literature (Gluchowski et al., 2017; Hu et al., 2020; Seebacher et al., 2020; Paul et al., 2022).

Acetyl-CoA carboxylase obstructs CD8+ T cell lipid utilization in the tumor microenvironment

The solid tumor microenvironment (TME) imprints a compromised metabolic state in tumor-infiltrating T cells (TILs), hallmarked by the inability to maintain effective energy synthesis for antitumor function and survival. T cells in the TME must catabolize lipids via mitochondrial fatty acid oxidation (FAO) to supply energy in nutrient stress, and it is established that T cells enriched in FAO are adept at cancer control. However, endogenous TILs and unmodified cellular therapy products fail to sustain bioenergetics in tumors. We reveal that the solid TME imposes perpetual acetyl-coenzyme A (CoA) carboxylase (ACC) activity, invoking lipid biogenesis and storage in TILs that opposes FAO. Using metabolic, lipidomic, and confocal imaging strategies, we find that restricting ACC rewires T cell metabolism, enabling energy maintenance in TME stress. Limiting ACC activity potentiates a gene and phenotypic program indicative of T cell longevity, engendering T cells with increased survival and polyfunctionality, which sustains cancer control.

Leptin attenuates the osteogenic induction potential of BMP9 by increasing β-catenin malonylation modification via Sirt5 down-regulation

BMP9 has demonstrated significant osteogenic potential. In this study, we investigated the effect of Leptin on BMP9-induced osteogenic differentiation. Firstly, we found Leptin was decreased during BMP9-induced osteogenic differentiation and serum Leptin concentrations were increased in the ovariectomized (OVX) rats. Both in vitro and in vivo, exogenous expression of Leptin inhibited the process of osteogenic differentiation, whereas silencing Leptin enhanced. Exogenous Leptin could increase the malonylation of β-catenin. However, BMP9 could increase the level of Sirt5 and subsequently decrease the malonylation of β-catenin; the BMP9-induced osteogenic differentiation was inhibited by silencing Sirt5. These data suggested that Leptin can inhibit the BMP9-induced osteogenic differentiation, which may be mediated through reducing the activity of Wnt/β-catenin signalling via down-regulating Sirt5 to increase the malonylation level of β-catenin partly.

Characterization of palmitic acid toxicity induced insulin resistance in HepG2 cells

BACKGROUND

An etiology of palmitic acid (PA) induced insulin resistance (IR) is complex for which two mechanisms are proposed namely ROS induced JNK activation and lipid induced protein kinase-C (PKCε) activation. However, whether these mechanisms act alone or in consortium is not clear.

METHODS AND RESULTS

In this study, we have characterized PA induced IR in liver cells. These cells were treated with different concentrations of PA for either 8 or 16 h. Insulin responsiveness of cells treated with PA for 8 h was found to be same as that of control. However, cells treated with PA for 16 h, showed increased glucose output both in the presence and in absence of insulin only at higher concentrations, indicating development of IR. In these, both JNK and PKCε were activated in response to increased ROS and lipid accumulation, respectively. Activated JNK and PKCε phosphorylated IRS1 at Ser-307 resulting in inhibition of AKT which in turn inactivated GSK3β, leading to reduced glycogen synthase activity. Inhibition of AKT also reduced insulin suppression of hepatic gluconeogenesis by activating Forkhead box protein O1 (FOXO1) and increased expression of the gluconeogenic enzymes and their transcription factors.

CONCLUSION

Thus, our data clearly demonstrate that both these mechanisms work simultaneously and more importantly, identified a threshold of HepG2 cells, which when crossed led to the pathological state of IR in response to PA.

C-Terminal Binding Protein 2 Emerges as a Critical Player Linking Metabolic Imbalance to the Pathogenesis of Obesity

Metabolism is one of the vital functions of cells and living organisms, and the systems to sense and respond to the metabolic alterations play pivotal roles in a plethora of biological processes, including cell proliferative activities, immune cell functions, aging processes, and neuronal functions. Recently, we have reported that a transcriptional cofactor, C-terminal binding protein 2 (CtBP2), serves as a critical metabolite sensor in this context. CtBP2 has a structural pocket called Rossmann fold to accommodate metabolites, and it has been reported to be activated upon binding to NADH/NAD＋. Owing to its preferential binding affinity for NADH compared with NAD＋, increased glycolysis activates CtBP2 by regenerating NADH from NAD＋. Furthermore, we recently reported that fatty acyl-CoAs, metabolites accumulated under the condition of lipid overload, as represented by obesity, can inactivate CtBP2. These observations suggest that CtBP2 monitors not only redox state but also energy substrate preference in the maintenance of metabolic homeostasis. In line with these metabolite-sensing capabilities, CtBP2 is activated in healthy subjects to protect against metabolic disturbances, whereas inactivation of CtBP2 in obesity contributes to the pathogeneses of obesity.This metabolic system orchestrated by CtBP2 can provide a novel framework for understanding how cells maintain their homeostasis through coordination of metabolism, and CtBP2 incapacitation can be a critical point of the obesogenic cascade.

Yam Gruel alone and in combination with metformin regulates hepatic lipid metabolism disorders in a diabetic rat model by activating the AMPK/ACC/CPT-1 pathway

BACKGROUND

As independent and correctable risk factors, disturbances in lipid metabolism are significantly associated with type 2 diabetes mellitus (T2DM). This research investigated the mechanism underlying the lipid-regulating effects of Yam Gruel in diabetic rats.

METHODS

First, rats in the control group were given a normal diet, and a diabetic rat model was established via the consumption of a diet that was rich in both fat and sugar for six weeks followed by the intraperitoneal injection of streptozotocin (STZ). After the model was established, the rats were divided into five distinct groups: the control group, model group, Yam Gruel (SYZ) group, metformin (MET) group, and combined group; each treatment was administered for six weeks. The fasting blood glucose (FBG), body and liver weights as well as liver index of the rats were determined. Total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), aspartic acid transaminase (AST), alanine aminotransferase (ALT), and nonesterified fatty acid (NEFA) levels were measured. Oil Red O staining was used to assess hepatic steatosis. In addition, the levels of Phospho-acetyl-CoA carboxylase (p-ACC), acetyl coenzyme A carboxylase (ACC), AMP-activated protein kinase (AMPK), Phospho-AMPK (p-AMPK), carnitine palmitoyl transferase I (CPT-1), and Malonyl-CoA decarboxylase (MLYCD) in liver tissues were measured by real-time PCR (q-PCR) and western blotting.

RESULTS

After 6 weeks of treatment, Yam Gruel alone or in combination with metformin significantly reduced FBG level, liver weight and index. The concentrations of lipid indices (TG, TC, NEFA, and LDL-C), the levels of liver function indices (ALT and AST) and the degree of hepatic steatosis was improved in diabetic rats that were treated with Yam Gruel with or without metformin. Furthermore, Yam Gruel increased the protein levels of p-ACC/ACC, p-AMPK/AMPK, MLYCD, and CPT-1, which was consistent with the observed changes in gene expression. Additionally, the combination of these two agents was significantly more effective in upregulating the expression of AMPK pathway-related genes and proteins.

CONCLUSIONS

These results demonstrated that Yam Gruel may be a potential diet therapy for improving lipid metabolism in T2DM patients and that it may exert its effects via AMPK/ACC/CPT-1 pathway activation. In some respects, the combination of Yam Gruel and metformin exerted more benefits effects than Yam Gruel alone.

Fatty Acid Metabolism Signature Contributes to the Molecular Diagnosis of a Malignant Gastric Cancer Subtype with Poor Prognosis and Lower Mutation Burden

BACKGROUND

Gastric cancer (GC) is a common gastrointestinal tumor with high morbidity and mortality. Fatty acid metabolism (FAM) contributes to GC development. Patents have been issued for the use of compositions comprising fatty acid analogues for the treatment of many clinical conditions. However, its clinical significance and its relationship with tumor-related mutations have not been thoroughly discovered. This study was conducted to analyze and explore FAM-related genes' molecular characteristics, prognostic significance, and association with tumor- related mutations.

METHODS

The gastric adenocarcinoma's transcriptome, clinical data, and tumor mutation load (TMB) data were downloaded from TCGA and GEO databases. The differentially expressed FAM genes (FAM DEGs) between cancer and control samples were screened, and their correlation with TMB and survival was analyzed. A PPI network of FAM DEGs was constructed, and a downscaling clustering analysis was performed based on the expression of the FAM DEGs. Further immuno- infiltration and GO/KEGG enrichment analyses of the identified FAM clusters were performed to explore their heterogeneity in biological functions. The effects of FAM score and gastric cancer (STAD) on TMB, MSI, survival prognosis, and drug sensitivity were jointly analyzed, and finally, a single-gene analysis of the obtained core targets was performed.

RESULTS

Through differential analysis, 68 FAM DEGs were obtained, and they were highly associated with STAD tumor mutation load. In addition, a high FAM DEGs CNV rate was observed. The PPI network showed a complex mutual correlation between the FAM DEGs. Consensus clustering classified the patients into three clusters based on the FAM DEGs, and the clusters presented different survival rates. The GSVA and immune infiltration analysis revealed that metabolism, apoptosis, and immune infiltration-related pathways were variated. In addition, FAM genes, STAD prognostic risk genes, and PCA scores were closely associated with the survival status of STAD patients. FAM score was closely correlated with STAD TMB, MSI, and immunotherapy, and the TMB values in the low FAM score group were significantly higher than those in the high FAM score group. Finally, combining the above results, it was found that the core gene PTGS1 performed best in predicting STAD survival prognosis and TMB/MSI/immunotherapy.

CONCLUSION

Fatty acid metabolism genes affect the development of gastric adenocarcinoma and can predict the survival prognosis, tumor mutational load characteristics, and drug therapy sensitivity of STAD patients, which can help explore more effective immunotherapy targets for GC.

Kinetic Modeling of Hepatic Metabolism and Simulation of Treatment Effects

Mathematical modeling is a promising strategy to fill the experimentally unapproachable knowledge gaps about the relative contribution of various molecular processes to cellular metabolic function. To this end, we developed detailed kinetic models of the central metabolism of different cell types, comprising multiple metabolic functionalities. We used the model to simulate metabolic changes in several cell types under different experimental settings in health and disease. In this way, we show that it is possible to decipher and characterize the relative influence of various metabolic pathways and enzymes to overall metabolic performance and phenotype.Quantitative Systems Metabolism (QSM™) allows quantitative assessment of metabolic functionality and metabolic profiling based on proteomic data. Here, we describe the technique, namely, molecular resolved kinetic modeling, underlying QSM™. We explain the necessary steps for the generation of cell-specific models to functionally interpret proteomic data and point out some unresolved challenges and open questions.

Metabolic Reprogramming in Gliocyte Post-cerebral Ischemia/ Reperfusion: From Pathophysiology to Therapeutic Potential

Ischemic stroke is a leading cause of disability and death worldwide. However, the clinical efficacy of recanalization therapy as a preferred option is significantly hindered by reperfusion injury. The transformation between different phenotypes of gliocytes is closely associated with cerebral ischemia/ reperfusion injury (CI/RI). Moreover, gliocyte polarization induces metabolic reprogramming, which refers to the shift in gliocyte phenotype and the overall transformation of the metabolic network to compensate for energy demand and building block requirements during CI/RI caused by hypoxia, energy deficiency, and oxidative stress. Within microglia, the pro-inflammatory phenotype exhibits upregulated glycolysis, pentose phosphate pathway, fatty acid synthesis, and glutamine synthesis, whereas the anti-inflammatory phenotype demonstrates enhanced mitochondrial oxidative phosphorylation and fatty acid oxidation. Reactive astrocytes display increased glycolysis but impaired glycogenolysis and reduced glutamate uptake after CI/RI. There is mounting evidence suggesting that manipulation of energy metabolism homeostasis can induce microglial cells and astrocytes to switch from neurotoxic to neuroprotective phenotypes. A comprehensive understanding of underlying mechanisms and manipulation strategies targeting metabolic pathways could potentially enable gliocytes to be reprogrammed toward beneficial functions while opening new therapeutic avenues for CI/RI treatment. This review provides an overview of current insights into metabolic reprogramming mechanisms in microglia and astrocytes within the pathophysiological context of CI/RI, along with potential pharmacological targets. Herein, we emphasize the potential of metabolic reprogramming of gliocytes as a therapeutic target for CI/RI and aim to offer a novel perspective in the treatment of CI/RI.

Isotope Labeling and Biochemical Assessment of Liver-Triacylglycerol in Patients with Different Levels of Histologically-Graded Liver Disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) prevalence is rapidly growing, and fatty liver has been found in a quarter of the US population. Increased liver lipids, particularly those derived from the pathway of de novo lipogenesis (DNL), have been identified as a hallmark feature in individuals with high liver fat. This has led to much activity in basic science and drug development in this area. No studies to date have investigated the contribution of DNL across a spectrum of disease, although it is clear that inhibition of DNL has been shown to reduce liver fat.

OBJECTIVES

The purpose of this study was to determine whether liver lipid synthesis increases across the continuum of liver injury.

METHODS

Individuals (n = 49) consumed deuterated water for 10 d before their scheduled bariatric surgeries to label DNL; blood and liver tissue samples were obtained on the day of the surgery. Liver lipid concentrations were quantitated, and levels of protein and gene expression assessed.

RESULTS

Increased liver DNL, measured isotopically, was significantly associated with liver fatty acid synthase protein content (R = 0.470, P = 0.003), total steatosis assessed by histology (R = 0.526, P = 0.0008), and the fraction of DNL fatty acids in plasma very low-density lipoprotein-triacylglycerol (R = 0.747, P < 0.001). Regression analysis revealed a parabolic relationship between fractional liver DNL (percent) and NAFLD activity score (R = 0.538, P = 0.0004).

CONCLUSION

These data demonstrate that higher DNL is associated with early to mid stages of liver disease, and this pathway may be an effective target for the treatment of NAFLD and nonalcoholic steatohepatitis. This study was registered at clinicaltrials.gov as NCT03683589.

Fatty Acid Oxidation Mediated by Malonyl-CoA Decarboxylase Represses Renal Cell Carcinoma Progression

Fatty acid metabolism reprogramming is a prominent feature of clear cell renal cell carcinoma (ccRCC). Increased lipid storage supports ccRCC progression, highlighting the importance of understanding the molecular mechanisms driving altered fatty acid synthesis in tumors. Here, we identified that malonyl-CoA decarboxylase (MLYCD), a key regulator of fatty acid anabolism, was downregulated in ccRCC, and low expression correlated with poor prognosis in patients. Restoring MLYCD expression in ccRCC cells decreased the content of malonyl CoA, which blocked de novo fatty acid synthesis and promoted fatty acid translocation into mitochondria for oxidation. Inhibition of lipid droplet accumulation induced by MLYCD-mediated fatty acid oxidation disrupted endoplasmic reticulum and mitochondrial homeostasis, increased reactive oxygen species levels, and induced ferroptosis. Moreover, overexpressing MLYCD reduced tumor growth and reversed resistance to sunitinib in vitro and in vivo. Mechanistically, HIF2α inhibited MLYCD translation by upregulating expression of eIF4G3 microexons. Together, this study demonstrates that fatty acid catabolism mediated by MLYCD disrupts lipid homeostasis to repress ccRCC progression. Activating MLYCD-mediated fatty acid metabolism could be a promising therapeutic strategy for treating ccRCC.

SIGNIFICANCE

MLYCD deficiency facilitates fatty acid synthesis and lipid droplet accumulation to drive progression of renal cell carcinoma, indicating inducing MYLCD as a potential approach to reprogram fatty acid metabolism in kidney cancer.

Impaired Autophagic Flux in Glucose-Deprived Cells: An Outcome of Lysosomal Acidification Failure Exacerbated by Mitophagy Dysfunction

Autophagy dysfunction is associated with human diseases and conditions including neurodegenerative diseases, metabolic issues, and chronic infections. Additionally, the decline in autophagic activity contributes to tissue and organ dysfunction and aging-related diseases. Several factors, such as down-regulation of autophagy components and activators, oxidative damage, microinflammation, and impaired autophagy flux, are linked to autophagy decline. An autophagy flux impairment (AFI) has been implicated in neurological disorders and in certain other pathological conditions. Here, to enhance our understanding of AFI, we conducted a comprehensive literature review of findings derived from two well-studied cellular stress models: glucose deprivation and replicative senescence. Glucose deprivation is a condition in which cells heavily rely on oxidative phosphorylation for ATP generation. Autophagy is activated, but its flux is hindered at the autolysis step, primarily due to an impairment of lysosomal acidity. Cells undergoing replicative senescence also experience AFI, which is also known to be caused by lysosomal acidity failure. Both glucose deprivation and replicative senescence elevate levels of reactive oxygen species (ROS), affecting lysosomal acidification. Mitochondrial alterations play a crucial role in elevating ROS generation and reducing lysosomal acidity, highlighting their association with autophagy dysfunction and disease conditions. This paper delves into the underlying molecular and cellular pathways of AFI in glucose-deprived cells, providing insights into potential strategies for managing AFI that is driven by lysosomal acidity failure. Furthermore, the investigation on the roles of mitochondrial dysfunction sheds light on the potential effectiveness of modulating mitochondrial function to overcome AFI, offering new possibilities for therapeutic interventions.

Dicarboxylic acylcarnitine biomarkers in peroxisome biogenesis disorders

The peroxisome is an essential eukaryotic organelle with diverse metabolic functions. Inherited peroxisomal disorders are associated with a wide spectrum of clinical outcomes and are broadly divided into two classes, those impacting peroxisome biogenesis (PBD) and those impacting specific peroxisomal factors. Prior studies have indicated a role for acylcarnitine testing in the diagnosis of some peroxisomal diseases through the detection of long chain dicarboxylic acylcarnitine abnormalities (C16-DC and C18-DC). However, there remains limited independent corroboration of these initial findings and acylcarnitine testing for peroxisomal diseases has not been widely adopted in clinical laboratories. To explore the utility of acylcarnitine testing in the diagnosis of peroxisomal disorders we applied a LC-MS/MS acylcarnitine method to study a heterogenous clinical sample set (n = 598) that included residual plasma specimens from nineteen patients with PBD caused by PEX1 or PEX6 deficiency, ranging in severity from lethal neonatal onset to mild late onset forms. Multiple dicarboxylic acylcarnitines were significantly elevated in PBD patients including medium to long chain (C8-DC to C18-DC) species as well as previously undescribed elevations of malonylcarnitine (C3-DC) and very long chain dicarboxylic acylcarnitines (C20-DC and C22-DC). The best performing plasma acylcarnitine biomarkers, C20-DC and C22-DC, were detected at elevated levels in 100% and 68% of PBD patients but were rarely elevated in patients that did not have a PBD. We extended our analysis to residual newborn screening blood spot cards and were able to detect dicarboxylic acylcarnitine abnormalities in a newborn with a PBD caused by PEX6 deficiency. Similar to prior studies, we failed to detect substantial dicarboxylic acylcarnitine abnormalities in blood spot cards from patients with x-linked adrenoleukodystrophy (x-ald) indicating that these biomarkers may have utility in quickly narrowing the differential diagnosis in patients with a positive newborn screen for x-ald. Overall, our study identifies widespread dicarboxylic acylcarnitine abnormalities in patients with PBD and highlights key acylcarnitine biomarkers for the detection of this class of inherited metabolic disease.

Changes in Plasma Pyruvate and TCA Cycle Metabolites upon Increased Hepatic Fatty Acid Oxidation and Ketogenesis in Male Wistar Rats

Altered hepatic mitochondrial fatty acid β-oxidation and associated tricarboxylic acid (TCA) cycle activity contributes to lifestyle-related diseases, and circulating biomarkers reflecting these changes could have disease prognostic value. This study aimed to determine hepatic and systemic changes in TCA-cycle-related metabolites upon the selective pharmacologic enhancement of mitochondrial fatty acid β-oxidation in the liver, and to elucidate the mechanisms and potential markers of hepatic mitochondrial activity. Male Wistar rats were treated with 3-thia fatty acids (e.g., tetradecylthioacetic acid (TTA)), which target mitochondrial biogenesis, mitochondrial fatty acid β-oxidation, and ketogenesis predominantly in the liver. Hepatic and plasma concentrations of TCA cycle intermediates and anaplerotic substrates (LC-MS/MS), plasma ketones (colorimetric assay), and acylcarnitines (HPLC-MS/MS), along with associated TCA-cycle-related gene expression (qPCR) and enzyme activities, were determined. TTA-induced hepatic fatty acid β-oxidation resulted in an increased ratio of plasma ketone bodies/nonesterified fatty acid (NEFA), lower plasma malonyl-CoA levels, and a higher ratio of plasma acetylcarnitine/palmitoylcarnitine (C2/C16). These changes were associated with decreased hepatic and increased plasma pyruvate concentrations, and increased plasma concentrations of succinate, malate, and 2-hydroxyglutarate. Expression of several genes encoding TCA cycle enzymes and the malate-oxoglutarate carrier (Slc25a11), glutamate dehydrogenase (Gdh), and malic enzyme (Mdh1 and Mdh2) were significantly increased. In conclusion, the induction of hepatic mitochondrial fatty acid β-oxidation by 3-thia fatty acids lowered hepatic pyruvate while increasing plasma pyruvate, as well as succinate, malate, and 2-hydroxyglutarate.

A subpopulation of lipogenic brown adipocytes drives thermogenic memory

Sustained responses to transient environmental stimuli are important for survival. The mechanisms underlying long-term adaptations to temporary shifts in abiotic factors remain incompletely understood. Here, we find that transient cold exposure leads to sustained transcriptional and metabolic adaptations in brown adipose tissue, which improve thermogenic responses to secondary cold encounter. Primary thermogenic challenge triggers the delayed induction of a lipid biosynthesis programme even after cessation of the original stimulus, which protects from subsequent exposures. Single-nucleus RNA sequencing and spatial transcriptomics reveal that this response is driven by a lipogenic subpopulation of brown adipocytes localized along the perimeter of Ucp1hi adipocytes. This lipogenic programme is associated with the production of acylcarnitines, and supplementation of acylcarnitines is sufficient to recapitulate improved secondary cold responses. Overall, our data highlight the importance of heterogenous brown adipocyte populations for 'thermogenic memory', which may have therapeutic implications for leveraging short-term thermogenesis to counteract obesity.

Medium-chain fatty acid oxidation is independent of l-carnitine in liver and kidney but not in heart and skeletal muscle

Medium-chain fatty acid (MCFA) consumption confers a wide range of health benefits that are highly distinct from long-chain fatty acids (LCFAs). A major difference between the metabolism of LCFAs compared with MCFAs is that mitochondrial LCFA oxidation depends on the carnitine shuttle, whereas MCFA mitochondrial oxidation is not. Although MCFAs are said to range from 6 to 14 carbons long based on physicochemical properties in vitro, the biological cut-off length of acyl chains that can bypass the carnitine shuttle in different mammalian tissues is unknown. To define the range of acyl chain length that can be oxidized in the mitochondria independent of carnitine, we determined the oxidative metabolism of free fatty acids (FFAs) from 6 to 18 carbons long in the liver, kidney, heart, and skeletal muscle. The liver oxidized FFAs 6 to 14 carbons long, whereas the kidney oxidized FFAs from 6 to 10 carbons in length. Heart and skeletal muscle were unable to oxidize FFAs of any chain length. These data show that while the liver and kidney can oxidize MCFAs in the free form, the heart and skeletal muscle require carnitine for the oxidative metabolism of MCFAs. Together these data demonstrate that MCFA oxidation independent of carnitine is tissue-specific.NEW & NOTEWORTHY This work demonstrates that the traditional concept of mitochondrial medium-chain fatty acid oxidation as unregulated and independent of carnitine applies only to liver metabolism, and to kidney to a lesser extent, but not the heart or skeletal muscle. Thus, the benefits of dietary medium-chain fatty acids are set by liver metabolic activity and peripheral tissues are unlikely to receive direct benefits from medium-chain fatty acid metabolism, but rather metabolic byproducts of liver's medium-chain oxidative metabolism.

Effects of Heated Drinking Water during the Cold Season on Serum Biochemistry, Ruminal Fermentation, Bacterial Community, and Metabolome of Beef Cattle

This study explored the effects of drinking heated water in the cold seasons on the serum metabolism, rumen microbial fermentation, and metabolome of beef cattle. Twelve fattening cattle (642 ± 14.6 kg) aged 21 to 22 months were randomly and equally divided into two groups based on body weight: one receiving room-temperature water (RTW; average 4.39 ± 2.55 °C) and the other heated water (HW; average 26.3 ± 1.70 °C). The HW group displayed a significant decrease in serum glucose (p < 0.01) and non-esterified fatty acid (p < 0.01), but increases in insulin (p = 0.04) and high-density lipoprotein (p = 0.03). The rumen fermentation parameters of the HW group showed substantial elevations in acetate (p = 0.04), propionate (p < 0.01), isobutyrate (p = 0.02), and total volatile fatty acids (p < 0.01). Distinct bacterial composition differences were found between RTW and HW at the operational taxonomic unit (OTU) level (R = 0.20, p = 0.01). Compared to RTW, the HW mainly had a higher relative abundance of Firmicutes (p = 0.07) at the phylum level and had a lower abundance of Prevotella (p < 0.01), norank_f_p-215-o5 (p = 0.03), and a higher abundance of NK4A214_group (p = 0.01) and Lachnospiraceae_NK3A20_group (p = 0.05) at the genus level. In addition, NK4A214_group and Lachnospiraceae_NK3A20_group were significantly positively correlated with the rumen propionate and isovalerate (r > 0.63, p < 0.05). Prevotella was negatively correlated with rumen propionate and total volatile fatty acids (r = -0.61, p < 0.05). In terms of the main differential metabolites, compared to the RTW group, the expression of Cynaroside A, N-acetyl-L-glutamic acid, N-acetyl-L-glutamate-5-semialdehyde, and Pantothenic acid was significantly upregulated in HW. The differentially regulated metabolic pathways were primarily enriched in nitrogen metabolism, arginine biosynthesis, and linoleic acid metabolism. Prevotella was significantly positively correlated with suberic acid and [6]-Gingerdiol 3,5-diacetate (r > 0.59, p < 0.05) and was negatively correlated with Pantothenic acid and isoleucyl-aspartate (r < -0.65, p < 0.05). NK4A214_group was positively correlated with L-Methionine and glycylproline (r > 0.57, p < 0.05). Overall, our research demonstrates the important relationship between drinking water temperature and metabolic and physiological responses in beef cattle. Heating drinking water during cold seasons plays a pivotal role in modulating internal energy processes. These findings underscore the potential benefits of using heated water as a strategic approach to optimize energy utilization in beef cattle during the cold seasons.

Long-chain dicarboxylic acids play a critical role in inducing peroxisomal β-oxidation and hepatic triacylglycerol accumulation

Recent studies provide evidence that peroxisomal β-oxidation negatively regulates mitochondrial fatty acid oxidation, and induction of peroxisomal β-oxidation causes hepatic lipid accumulation. However, whether there exists a triggering mechanism inducing peroxisomal β-oxidation is not clear. Long-chain dicarboxylic acids (LCDAs) are the product of mono fatty acids subjected to ω-oxidation, and both fatty acid ω-oxidation and peroxisomal β-oxidation are induced under ketogenic conditions, indicating there might be a crosstalk between. Here, we revealed that administration of LCDAs strongly induces peroxisomal fatty acid β-oxidation and causes hepatic steatosis in mice through the metabolites acetyl-CoA and hydrogen peroxide. Under ketogenic conditions, upregulation of fatty acid ω-oxidation resulted in increased generation of LCDAs and induction of peroxisomal β-oxidation, which causes hepatic accumulation of lipid droplets in animals. Inhibition of fatty acid ω-oxidation reduced LCDA formation and significantly lowered peroxisomal β-oxidation and improved hepatic steatosis. Our results suggest that endogenous LCDAs act as triggering molecules inducing peroxisomal β-oxidation and hepatic triacylglycerol deposition. Targeting fatty acid ω-oxidation might be an effective pathway in treating fatty liver and related metabolic diseases through regulating peroxisomal β-oxidation.

Flaxseed Reduces Cancer Risk by Altering Bioenergetic Pathways in Liver: Connecting SAM Biosynthesis to Cellular Energy

This article illustrates how dietary flaxseed can be used to reduce cancer risk, specifically by attenuating obesity, type 2 diabetes, and non-alcoholic fatty liver disease (NAFLD). We utilize a targeted metabolomics dataset in combination with a reanalysis of past work to investigate the "metabo-bioenergetic" adaptations that occur in White Leghorn laying hens while consuming dietary flaxseed. Recently, we revealed how the anti-vitamin B6 effects of flaxseed augment one-carbon metabolism in a manner that accelerates S-adenosylmethionine (SAM) biosynthesis. Researchers recently showed that accelerated SAM biosynthesis activates the cell's master energy sensor, AMP-activated protein kinase (AMPK). Our paper provides evidence that flaxseed upregulates mitochondrial fatty acid oxidation and glycolysis in liver, concomitant with the attenuation of lipogenesis and polyamine biosynthesis. Defatted flaxseed likely functions as a metformin homologue by upregulating hepatic glucose uptake and pyruvate flux through the pyruvate dehydrogenase complex (PDC) in laying hens. In contrast, whole flaxseed appears to attenuate liver steatosis and body mass by modifying mitochondrial fatty acid oxidation and lipogenesis. Several acylcarnitine moieties indicate Randle cycle adaptations that protect mitochondria from metabolic overload when hens consume flaxseed. We also discuss a paradoxical finding whereby flaxseed induces the highest glycated hemoglobin percentage (HbA1c%) ever recorded in birds, and we suspect that hyperglycemia is not the cause. In conclusion, flaxseed modifies bioenergetic pathways to attenuate the risk of obesity, type 2 diabetes, and NAFLD, possibly downstream of SAM biosynthesis. These findings, if reproducible in humans, can be used to lower cancer risk within the general population.

Lipid oxidation dysregulation: an emerging player in the pathophysiology of sepsis

Sepsis is a life-threatening organ dysfunction caused by abnormal host response to infection. Millions of people are affected annually worldwide. Derangement of the inflammatory response is crucial in sepsis pathogenesis. However, metabolic, coagulation, and thermoregulatory alterations also occur in patients with sepsis. Fatty acid mobilization and oxidation changes may assume the role of a protagonist in sepsis pathogenesis. Lipid oxidation and free fatty acids (FFAs) are potentially valuable markers for sepsis diagnosis and prognosis. Herein, we discuss inflammatory and metabolic dysfunction during sepsis, focusing on fatty acid oxidation (FAO) alterations in the liver and muscle (skeletal and cardiac) and their implications in sepsis development.

Integrated metabolic and epigenetic mechanisms in cardiomyocyte proliferation

Heart disease continues to be the leading cause of mortality worldwide, primarily attributed to the restricted regenerative potential of the adult human heart following injury. In contrast to their adult counterparts, many neonatal mammals can spontaneously regenerate their myocardium in the first few days of life via extensive proliferation of the pre-existing cardiomyocytes. Reasons for the decline in regenerative capacity during postnatal development, and how to control it, remain largely unexplored. Accumulated evidence suggests that the preservation of regenerative potential depends on a conducive metabolic state in the embryonic and neonatal heart. Along with the postnatal increase in oxygenation and workload, the mammalian heart undergoes a metabolic transition, shifting its primary metabolic substrate from glucose to fatty acids shortly after birth for energy advantage. This metabolic switch causes cardiomyocyte cell-cycle arrest, which is widely regarded as a key mechanism for the loss of regenerative capacity. Beyond energy provision, emerging studies have suggested a link between this intracellular metabolism dynamics and postnatal epigenetic remodeling of the mammalian heart that reshapes the expression of many genes important for cardiomyocyte proliferation and cardiac regeneration, since many epigenetic enzymes utilize kinds of metabolites as obligate cofactors or substrates. This review summarizes the current state of knowledge of metabolism and metabolite-mediated epigenetic modifications in cardiomyocyte proliferation, with a particular focus on highlighting the potential therapeutic targets that hold promise to treat human heart failure via metabolic and epigenetic regulations.

Expression of HMGCS2 in intestinal epithelial cells is downregulated in inflammatory bowel disease associated with endoplasmic reticulum stress

Introduction

The Unfolded Protein Response, a mechanism triggered by the cell in response to Endoplasmic reticulum stress, is linked to inflammatory responses. Our aim was to identify novel Unfolded Protein Response-mechanisms that might be involved in triggering or perpetuating the inflammatory response carried out by the Intestinal Epithelial Cells in the context of Inflammatory Bowel Disease.

Methods

We analyzed the transcriptional profile of human Intestinal Epithelial Cell lines treated with an Endoplasmic Reticulum stress inducer (thapsigargin) and/or proinflammatory stimuli. Several genes were further analyzed in colonic biopsies from Ulcerative Colitis patients and healthy controls. Lastly, we generated Caco-2 cells lacking HMGCS2 by CRISPR Cas-9 and analyzed the functional implications of its absence in Intestinal Epithelial Cells.

Results

Exposure to a TLR ligand after thapsigargin treatment resulted in a powerful synergistic modulation of gene expression, which led us to identify new genes and pathways that could be involved in inflammatory responses linked to the Unfolded Protein Response. Key differentially expressed genes in the array also exhibited transcriptional alterations in colonic biopsies from active Ulcerative Colitis patients, including NKG2D ligands and the enzyme HMGCS2. Moreover, functional studies showed altered metabolic responses and epithelial barrier integrity in HMGCS2 deficient cell lines.

Conclusion

We have identified new genes and pathways that are regulated by the Unfolded Protein Response in the context of Inflammatory Bowel Disease including HMGCS2, a gene involved in the metabolism of Short Chain Fatty Acids that may have an important role in intestinal inflammation linked to Endoplasmic Reticulum stress and the resolution of the epithelial damage.

Gallstone and Gallbladder Disease: Biliary Tract and Cholangiopathies

Cholestatic liver diseases are named primarily due to the blockage of bile flow and buildup of bile acids in the liver. Cholestasis can occur in cholangiopathies, fatty liver diseases, and during COVID-19 infection. Most literature evaluates damage occurring to the intrahepatic biliary tree during cholestasis; however, there may be associations between liver damage and gallbladder damage. Gallbladder damage can manifest as acute or chronic inflammation, perforation, polyps, cancer, and most commonly gallstones. Considering the gallbladder is an extension of the intrahepatic biliary network, and both tissues are lined by biliary epithelial cells that share common mechanisms and properties, it is worth further evaluation to understand the association between bile duct and gallbladder damage. In this comprehensive article, we discuss background information of the biliary tree and gallbladder, from function, damage, and therapeutic approaches. We then discuss published findings that identify gallbladder disorders in various liver diseases. Lastly, we provide the clinical aspect of gallbladder disorders in liver diseases and ways to enhance diagnostic and therapeutic approaches for congruent diagnosis. © 2023 American Physiological Society. Compr Physiol 13:4909-4943, 2023.

The lactate dehydrogenase gene is involved in the growth and metabolism of Lacticaseibacillus paracasei and the production of fermented milk flavor substances

Objective

Lactate dehydrogenase (ldh) in lactic acid bacteria is an important enzyme that is involved in the process of milk fermentation. This study aimed to explore the changes and effects of fermented milk metabolites in mutant strains after knocking out the ldh gene of Lacticaseibacillus paracasei.

Methods

The ldh mutant ΔAF91_07315 was obtained from L. paracasei using clustered regularly interspaced short palindromic repeats technology, and we determined fermented milk pH, titratable acidity, viable count, and differential metabolites in the different stages of milk fermentation that were identified using metabolomic analysis.

Results

The results showed that the growth rate and acidification ability of the mutant strain were lower than those of the wild-type strain before the end of fermentation, and analysis of the differential metabolites showed that lactate, L-cysteine, proline, and intermediate metabolites of phenylalanine, tryptophan, and methionine were downregulated (P < 0.05), which affected the growth initiation rate and acidification ability of the strain. At the end of fermentation (pH 4.5), the fermentation time of the mutant strain was prolonged and all differential metabolites were upregulated (P < 0.05), including amino acids and precursors, acetyl coenzyme A, and other metabolites involved in amino acid and fatty acid synthesis, which are associated with the regulation of fermented milk flavors. In addition, riboflavin was upregulated to promote the growth of the strain and compensate for the growth defects caused by the mutation.

Conclusion

Our data established a link between the AF91_07315 gene and strain growth and metabolism and provided a target for the regulation of fermented milk flavor substances.

Obesity-induced metabolic imbalance allosterically modulates CtBP2 to inhibit PPAR-alpha transcriptional activity

Maintenance of metabolic homeostasis is secured by metabolite-sensing systems, which can be overwhelmed by constant macronutrient surplus in obesity. Not only the uptake processes but also the consumption of energy substrates determine the cellular metabolic burden. We herein describe a novel transcriptional system in this context comprised of peroxisome proliferator-activated receptor alpha (PPARα), a master regulator for fatty acid oxidation, and C-terminal binding protein 2 (CtBP2), a metabolite-sensing transcriptional co-repressor. CtBP2 interacts with PPARα to repress its activity, and the interaction is enhanced upon binding to malonyl-CoA, a metabolic intermediate increased in tissues in obesity and reported to suppress fatty acid oxidation through inhibition of carnitine palmitoyltransferase 1 (CPT1). In line with our preceding observations that CtBP2 adopts a monomeric configuration upon binding to acyl-CoAs, we determined that mutations in CtBP2 that shift the conformational equilibrium toward monomers increase the interaction between CtBP2 and PPARα. In contrast, metabolic manipulations that reduce malonyl-CoA decreased the formation of the CtBP2/PPARα complex. Consistent with these in vitro findings, we found that the CtBP2/PPARα interaction is accelerated in obese livers while genetic deletion of CtBP2 in the liver causes derepression of PPARα target genes. These findings support our model where CtBP2 exists primarily as a monomer in the metabolic milieu of obesity to repress PPARα, representing a liability in metabolic diseases that can be exploited to develop therapeutic approaches.

Fatty acid elongases 1-3 have distinct roles in mitochondrial function, growth, and lipid homeostasis in Trypanosoma cruzi

Trypanosomatids are a diverse group of uniflagellate protozoan parasites that include globally relevant pathogens such as Trypanosoma cruzi, the causative agent of Chagas disease. Trypanosomes lack the fatty acid synthase system typically used for de novo fatty acid (FA) synthesis in other eukaryotes. Instead, these microbes have evolved a modular FA elongase (ELO) system comprised of individual ELO enzymes (ELO1-4) that can operate processively to generate long chain- and very long chain-FAs. The importance of ELO's for maintaining lipid homeostasis in trypanosomatids is currently unclear, given their ability to take up and utilize exogenous FAs for lipid synthesis. To assess ELO function in T. cruzi, we generated individual KO lines, Δelo1, Δelo2, and Δelo3, in which the genes encoding ELO1-3 were functionally disrupted in the parasite insect stage (epimastigote). Using unbiased lipidomic and metabolomic analyses, in combination with metabolic tracing and biochemical approaches, we demonstrate that ELO2 and ELO3 are required for global lipid homeostasis, whereas ELO1 is dispensable for this function. Instead, ELO1 activity is needed to sustain mitochondrial activity and normal growth in T. cruzi epimastigotes. The cross-talk between microsomal ELO1 and the mitochondrion is a novel finding that, we propose, merits further examination of the trypanosomatid ELO pathway as critical for central metabolism.

The Role of Pyruvate Metabolism in Mitochondrial Quality Control and Inflammation

Pyruvate metabolism, a key pathway in glycolysis and oxidative phosphorylation, is crucial for energy homeostasis and mitochondrial quality control (MQC), including fusion/fission dynamics and mitophagy. Alterations in pyruvate flux and MQC are associated with reactive oxygen species accumulation and Ca2+ flux into the mitochondria, which can induce mitochondrial ultrastructural changes, mitochondrial dysfunction and metabolic dysregulation. Perturbations in MQC are emerging as a central mechanism for the pathogenesis of various metabolic diseases, such as neurodegenerative diseases, diabetes and insulin resistance-related diseases. Mitochondrial Ca2+ regulates the pyruvate dehydrogenase complex (PDC), which is central to pyruvate metabolism, by promoting its dephosphorylation. Increase of pyruvate dehydrogenase kinase (PDK) is associated with perturbation of mitochondria-associated membranes (MAMs) function and Ca2+ flux. Pyruvate metabolism also plays an important role in immune cell activation and function, dysregulation of which also leads to insulin resistance and inflammatory disease. Pyruvate metabolism affects macrophage polarization, mitochondrial dynamics and MAM formation, which are critical in determining macrophage function and immune response. MAMs and MQCs have also been intensively studied in macrophage and T cell immunity. Metabolic reprogramming connected with pyruvate metabolism, mitochondrial dynamics and MAM formation are important to macrophages polarization (M1/M2) and function. T cell differentiation is also directly linked to pyruvate metabolism, with inhibition of pyruvate oxidation by PDKs promoting proinflammatory T cell polarization. This article provides a brief review on the emerging role of pyruvate metabolism in MQC and MAM function, and how dysfunction in these processes leads to metabolic and inflammatory diseases.

Acetyl-CoA carboxylase 1 is a suppressor of the adipocyte thermogenic program

Disruption of adipocyte de novo lipogenesis (DNL) by deletion of fatty acid synthase (FASN) in mice induces browning in inguinal white adipose tissue (iWAT). However, adipocyte FASN knockout (KO) increases acetyl-coenzyme A (CoA) and malonyl-CoA in addition to depletion of palmitate. We explore which of these metabolite changes triggers adipose browning by generating eight adipose-selective KO mouse models with loss of ATP-citrate lyase (ACLY), acetyl-CoA carboxylase 1 (ACC1), ACC2, malonyl-CoA decarboxylase (MCD) or FASN, or dual KOs ACLY/FASN, ACC1/FASN, and ACC2/FASN. Preventing elevation of acetyl-CoA and malonyl-CoA by depletion of adipocyte ACLY or ACC1 in combination with FASN KO does not block the browning of iWAT. Conversely, elevating malonyl-CoA levels in MCD KO mice does not induce browning. Strikingly, adipose ACC1 KO induces a strong iWAT thermogenic response similar to FASN KO while also blocking malonyl-CoA and palmitate synthesis. Thus, ACC1 and FASN are strong suppressors of adipocyte thermogenesis through promoting lipid synthesis rather than modulating the DNL intermediates acetyl-CoA or malonyl-CoA.

Extracting functionally accurate context-specific models of Atlantic salmon metabolism

Constraint-based models (CBMs) are used to study metabolic network structure and function in organisms ranging from microbes to multicellular eukaryotes. Published CBMs are usually generic rather than context-specific, meaning that they do not capture differences in reaction activities, which, in turn, determine metabolic capabilities, between cell types, tissues, environments, or other conditions. Only a subset of a CBM's metabolic reactions and capabilities are likely to be active in any given context, and several methods have therefore been developed to extract context-specific models from generic CBMs through integration of omics data. We tested the ability of six model extraction methods (MEMs) to create functionally accurate context-specific models of Atlantic salmon using a generic CBM (SALARECON) and liver transcriptomics data from contexts differing in water salinity (life stage) and dietary lipids. Three MEMs (iMAT, INIT, and GIMME) outperformed the others in terms of functional accuracy, which we defined as the extracted models' ability to perform context-specific metabolic tasks inferred directly from the data, and one MEM (GIMME) was faster than the others. Context-specific versions of SALARECON consistently outperformed the generic version, showing that context-specific modeling better captures salmon metabolism. Thus, we demonstrate that results from human studies also hold for a non-mammalian animal and major livestock species.

Mitochondria in cell senescence: A Friend or Foe?

Cell senescence denotes cell growth arrest in response to continuous replication or stresses damaging DNA or mitochondria. Mounting research suggests that cell senescence attributes to aging-associated failing organ function and diseases. Conversely, it participates in embryonic tissue maturation, wound healing, tissue regeneration, and tumor suppression. The acute or chronic properties and microenvironment may explain the double faces of senescence. Senescent cells display unique characteristics. In particular, its mitochondria become elongated with altered metabolomes and dynamics. Accordingly, mitochondria reform their function to produce more reactive oxygen species at the cost of low ATP production. Meanwhile, destructed mitochondrial unfolded protein responses further break the delicate proteostasis fostering mitochondrial dysfunction. Additionally, the release of mitochondrial damage-associated molecular patterns, mitochondrial Ca²⁺ overload, and altered NAD⁺ level intertwine other cellular organelle strengthening senescence. These findings further intrigue researchers to develop anti-senescence interventions. Applying mitochondrial-targeted antioxidants reduces cell senescence and mitigates aging by restoring mitochondrial function and attenuating oxidative stress. Metformin and caloric restriction also manifest senescent rescuing effects by increasing mitochondria efficiency and alleviating oxidative damage. On the other hand, Bcl2 family protein inhibitors eradicate senescent cells by inducing apoptosis to facilitate cancer chemotherapy. This review describes the different aspects of mitochondrial changes in senescence and highlights the recent progress of some anti-senescence strategies.

Lipid metabolism in Th17 cell function

Among the subset of T helper cells, Th17 cells are known to play a crucial role in the pathogenesis of various autoimmune disorders, such as psoriasis, rheumatoid arthritis, inflammatory bowel disease, steroid-resistant asthma, and multiple sclerosis. The master transcription factor retinoid-related orphan receptor gamma t (RORγt), a nuclear hormone receptor, plays a vital role in inducing Th17-cell differentiation. Recent findings suggest that metabolic control is critical for Th17-cell differentiation, particularly through the engagement of de novo lipid biosynthesis. Inhibition of lipid biosynthesis, either through the use of pharmacological inhibitors or by the deficiency of related enzymes in CD4⁺ T cells, results in significant suppression of Th17-cell differentiation. Mechanistic studies indicate that metabolic fluxes through both the fatty acid and cholesterol biosynthetic pathways are essential for controlling RORγt activity through the generation of a lipid ligand of RORγt. This review highlights recent findings that underscore the significant role of lipid metabolism in the differentiation and function of Th17 cells, as well as elucidating the distinctive molecular pathways that drive the activation of RORγt by cellular lipid metabolism. We further elaborate on a pioneering therapeutic approach for ameliorating autoimmune disorders via the inhibition of RORγt.

The Key Role of Mitochondrial Function in Health and Disease

The role of mitochondrial function in health and disease has become increasingly recognized, particularly in the last two decades. Mitochondrial dysfunction as well as disruptions of cellular bioenergetics have been shown to be ubiquitous in some of the most prevalent diseases in our society, such as type 2 diabetes, cardiovascular disease, metabolic syndrome, cancer, and Alzheimer's disease. However, the etiology and pathogenesis of mitochondrial dysfunction in multiple diseases have yet to be elucidated, making it one of the most significant medical challenges in our history. However, the rapid advances in our knowledge of cellular metabolism coupled with the novel understanding at the molecular and genetic levels show tremendous promise to one day elucidate the mysteries of this ancient organelle in order to treat it therapeutically when needed. Mitochondrial DNA mutations, infections, aging, and a lack of physical activity have been identified to be major players in mitochondrial dysfunction in multiple diseases. This review examines the complexities of mitochondrial function, whose ancient incorporation into eukaryotic cells for energy purposes was key for the survival and creation of new species. Among these complexities, the tightly intertwined bioenergetics derived from the combustion of alimentary substrates and oxygen are necessary for cellular homeostasis, including the production of reactive oxygen species. This review discusses different etiological mechanisms by which mitochondria could become dysregulated, determining the fate of multiple tissues and organs and being a protagonist in the pathogenesis of many non-communicable diseases. Finally, physical activity is a canonical evolutionary characteristic of humans that remains embedded in our genes. The normalization of a lack of physical activity in our modern society has led to the perception that exercise is an "intervention". However, physical activity remains the modus vivendi engrained in our genes and being sedentary has been the real intervention and collateral effect of modern societies. It is well known that a lack of physical activity leads to mitochondrial dysfunction and, hence, it probably becomes a major etiological factor of many non-communicable diseases affecting modern societies. Since physical activity remains the only stimulus we know that can improve and maintain mitochondrial function, a significant emphasis on exercise promotion should be imperative in order to prevent multiple diseases. Finally, in populations with chronic diseases where mitochondrial dysfunction is involved, an individualized exercise prescription should be crucial for the "metabolic rehabilitation" of many patients. From lessons learned from elite athletes (the perfect human machines), it is possible to translate and apply multiple concepts to the betterment of populations with chronic diseases.

Metabolic sensing and control in mitochondria

Mitochondria are membrane-enclosed organelles with endosymbiotic origins, harboring independent genomes and a unique biochemical reaction network. To perform their critical functions, mitochondria must maintain a distinct biochemical environment and coordinate with the cytosolic metabolic networks of the host cell. This coordination requires them to sense and control metabolites and respond to metabolic stresses. Indeed, mitochondria adopt feedback or feedforward control strategies to restrain metabolic toxicity, enable metabolic conservation, ensure stable levels of key metabolites, allow metabolic plasticity, and prevent futile cycles. A diverse panel of metabolic sensors mediates these regulatory circuits whose malfunctioning leads to inborn errors of metabolism with mild to severe clinical manifestations. In this review, we discuss the logic and molecular basis of metabolic sensing and control in mitochondria. The past research outlined recurring patterns in mitochondrial metabolic sensing and control and highlighted key knowledge gaps in this organelle that are potentially addressable with emerging technological breakthroughs.

Decreased β-hydroxybutyrate and ketogenic amino acid levels in depressed human adults

β-hydroxybutyrate (BHB) is a major ketone body synthesized mainly in the liver mitochondria and is associated with stress and severity of depression in humans. It is known to alleviate depressive-like behaviors in mouse models of depression. In this study, plasma BHB, ketogenic and glucogenic amino acids selected from the Tohoku Medical Megabank Project Community-Based Cohort Study were analysed and measured using nuclear magnetic resonance spectroscopy. The Center for Epidemiologic Studies Depression Scale (CES-D) was utilized to select adult participants with depressive symptoms (CES-D ≥ 16; n = 5722) and control participants (CES-D < 16; n = 18,150). We observed significantly reduced plasma BHB, leucine, and tryptophan levels in participants with depressive symptoms. Using social defeat stress (SDS) mice models, we found that BHB levels in mice sera increased after acute SDS, but showed no change after chronic SDS, which differed from human plasma results. Furthermore, acute SDS increased mitochondrial BHB levels in the prefrontal cortex at 6 h. In contrast, chronic SDS significantly increased the amount of food intake but reduced hepatic mitochondrial BHB levels in mice. Moreover, gene transcriptions of voltage-dependent anion-selective channel 1 (Vdac1) and monocarboxylic acid transporter 1 (Mct1), major molecules relevant to mitochondrial biogenesis and BHB transporter, significantly decreased in the liver and PFC after chronic SDS exposure. These results provide evidence that hepatic and prefrontal mitochondrial biogenesis plays an important role in BHB synthesis under chronic stress and in humans with depressive symptoms.

Cancer Metabolism: Fasting Reset, the Keto-Paradox and Drugs for Undoing

In tumor cells, ketolysis "via" succinyl-CoA: 3-oxoacid-CoAtransferase (SCOT) and acetyl-CoA acetyltransferase 1 (ACAT1) is a major source of mitochondrial acetyl-CoA. Active ACAT1 tetramers stabilize by tyrosine phosphorylation, which facilitates the SCOT reaction and ketolysis. Tyrosine phosphorylation of pyruvate kinase PK M2 has the opposite effect, stabilizing inactive dimers, while pyruvate dehydrogenase (PDH), which is already inhibited by phosphorylation, is acetylated by ACAT1 and is doubly locked. This closes the glycolytic supply of acetyl-CoA. In addition, since tumor cells must synthesize fatty acids to create new membranes, they automatically turn off the degradation of fatty acids into acetyl-CoA ("via" the malonyl-CoA brake for the fatty acid carnityl transporter). Thus, inhibiting SCOT the specific ketolytic enzyme and ACAT1 should hold back tumor progression. However, tumor cells are still able to take up external acetate and convert it into acetyl-CoA in their cytosol "via" an acetyl-CoA synthetase, which feeds the lipogenic pathway; additionally, inhibiting this enzyme would make it difficult for tumor cells to form new lipid membrane and survive.

A multiomics approach to understanding pathology of Combined D,L-2- Hydroxyglutaric Aciduria and phenylbutyrate as potential treatment

Combined D, L-2-Hydroxyglutaric Aciduria (D,L-2HGA) is a rare genetic disorder caused by recessive mutations in the SLC25A1 gene that encodes the mitochondrial citrate carrier protein (CIC). SLC25A1 deficiency leads to a secondary increase in mitochondrial 2-ketoglutarate that, in turn, is reduced to neurotoxic 2-hydroxyglutarate. Clinical symptoms of Combined D,L-2HGA include neonatal encephalopathy, respiratory insufficiency and often with death in infancy. No current therapies exist, although replenishing cytosolic stores by citrate supplementation to replenish cytosolic stores has been proposed. In this study, we demonstrated that patient derived fibroblasts exhibited impaired cellular bioenergetics that were worsened with citrate supplementation. We hypothesized treating patient cells with phenylbutyrate, an FDA approved pharmaceutical drug, would reduce mitochondrial 2-ketoglutarate, leading to improved cellular bioenergetics including oxygen consumption and fatty acid oxidation. Metabolomic and RNA-seq analyses demonstrated a significant decrease in intracellular 2-ketoglutarate, 2-hydroxyglutarate, and in levels of mRNA coding for citrate synthase and isocitrate dehydrogenase. Consistent with the known action of phenylbutyrate, detected levels of phenylacetylglutamine was consistent with the drug acting as 2-ketoglutarate sink in patient cells. Our pre-clinical studies suggest citrate supplementation is unlikely to be an effective treatment of the disorder. However, cellular bioenergetics suggests phenylbutyrate may have interventional utility for this rare disease.

Metformin suppresses SARS-CoV-2 in cell culture

Comorbidities such as diabetes worsen COVID-19 severity and recovery. Metformin, a first-line medication for type 2 diabetes, has antiviral properties and certain studies have also indicated its prognostic potential in COVID-19. Here, we report that metformin significantly inhibits SARS-CoV-2 growth in cell culture models. First, a steady increase in AMPK phosphorylation was detected as infection progressed, suggesting its important role during viral infection. Activation of AMPK in Calu3 and Caco2 cell lines using metformin revealed that metformin suppresses SARS-CoV-2 infectious titers up to 99%, in both naïve as well as infected cells. IC50 values from dose-variation studies in infected cells were found to be 0.4 and 1.43 mM in Calu3 and Caco2 cells, respectively. Role of AMPK in metformin's antiviral suppression was further confirmed using other pharmacological compounds, AICAR and Compound C. Collectively, our study demonstrates that metformin is effective in limiting the replication of SARS-CoV-2 in cell culture and thus possibly could offer double benefits as diabetic COVID-19 patients by lowering both blood glucose levels and viral load.

Macrophage-derived exosome promotes regulatory T cell differentiation in malignant pleural effusion

Introduction

Tumor-associated macrophages are one of the key components of the tumor microenvironment. The immunomodulatory activity and function of macrophages in malignant pleural effusion (MPE), a special tumor metastasis microenvironment, have not been clearly defined.

Methods

MPE-based single-cell RNA sequencing data was used to characterize macrophages. Subsequently, the regulatory effect of macrophages and their secreted exosomes on T cells was verified by experiments. Next, miRNA microarray was used to analyze differentially expressed miRNAs in MPE and benign pleural effusion, and data from The Cancer Genome Atlas (TCGA) was used to evaluate the correlation between miRNAs and patient survival.

Results

Single-cell RNA sequencing data showed macrophages were mainly M2 polarized in MPE and had higher exosome secretion function compared with those in blood. We found that exosomes released from macrophages could promote the differentiation of naïve T cells into Treg cells in MPE. We detected differential expression miRNAs in macrophage-derived exosomes between MPE and benign pleural effusion by miRNA microarray and found that miR-4443 was significantly overexpressed in MPE exosomes. Gene functional enrichment analysis showed that the target genes of miR-4443 were involved in the regulation of protein kinase B signaling and lipid biosynthetic process.

Conclusions

Taken together, these results reveal that exosomes mediate the intercellular communication between macrophages and T cells, yielding an immunosuppressive environment for MPE. miR-4443 expressed by macrophages, but not total miR-4443, might serve as a prognostic marker in patients with metastatic lung cancer.

The multiple facets of acetyl-CoA metabolism: Energetics, biosynthesis, regulation, acylation and inborn errors

Acetyl-coenzyme A (Ac-CoA) is a core metabolite with essential roles throughout cell physiology. These functions can be classified into energetics, biosynthesis, regulation and acetylation of large and small molecules. Ac-CoA is essential for oxidative metabolism of glucose, fatty acids, most amino acids, ethanol, and of free acetate generated by endogenous metabolism or by gut bacteria. Ac-CoA cannot cross lipid bilayers, but acetyl groups from Ac-CoA can shuttle across membranes as part of carrier molecules like citrate or acetylcarnitine, or as free acetate or ketone bodies. Ac-CoA is the basic unit of lipid biosynthesis, providing essentially all of the carbon for the synthesis of fatty acids and of isoprenoid-derived compounds including cholesterol, coenzyme Q and dolichols. High levels of Ac-CoA in hepatocytes stimulate lipid biosynthesis, ketone body production and the diversion of pyruvate metabolism towards gluconeogenesis and away from oxidation; low levels exert opposite effects. Acetylation changes the properties of molecules. Acetylation is necessary for the synthesis of acetylcholine, acetylglutamate, acetylaspartate and N-acetyl amino sugars, and to metabolize/eliminate some xenobiotics. Acetylation is a major post-translational modification of proteins. Different types of protein acetylation occur. The most-studied form occurs at the epsilon nitrogen of lysine residues. In histones, lysine acetylation can alter gene transcription. Acetylation of other proteins has diverse, often incompletely-documented effects. Inborn errors related to Ac-CoA feature a broad spectrum of metabolic, neurological and other features. To date, a small number of studies of animals with inborn errors of CoA thioesters has included direct measurement of acyl-CoAs. These studies have shown that low levels of tissue Ac-CoA correlate with the development of clinical signs, hinting that shortage of Ac-CoA may be a recurrent theme in these conditions. Low levels of Ac-CoA could potentially disrupt any of its roles.

Targeting peroxisomal fatty acid oxidation improves hepatic steatosis and insulin resistance in obese mice

Obesity and diabetes normally cause mitochondrial dysfunction and hepatic lipid accumulation, while fatty acid synthesis is suppressed and malonyl-CoA is depleted in the liver of severe obese or diabetic animals. Therefore, a negative regulatory mechanism might work for the control of mitochondrial fatty acid metabolism that is independent of malonyl-CoA in the diabetic animals. As mitochondrial β-oxidation is controlled by the acetyl-CoA/CoA ratio, and the acetyl-CoA generated in peroxisomal β-oxidation could be transported into mitochondria via carnitine shuttles, we hypothesize that peroxisomal β-oxidation might play a role in regulating mitochondrial fatty acid oxidation and inducing hepatic steatosis under the condition of obesity or diabetes. This study reveals a novel mechanism by which peroxisomal β-oxidation controls mitochondrial fatty acid oxidation in diabetic animals. We determined that excessive oxidation of fatty acids by peroxisomes generates considerable acetyl-carnitine in the liver of diabetic mice, which significantly elevates the mitochondrial acetyl-CoA/CoA ratio and causes feedback suppression of mitochondrial β-oxidation. Additionally, we found that specific suppression of peroxisomal β-oxidation enhances mitochondrial fatty acid oxidation by reducing acetyl-carnitine formation in the liver of obese mice. In conclusion, we suggest that induction of peroxisomal fatty acid oxidation serves as a mechanism for diabetes-induced hepatic lipid accumulation. Targeting peroxisomal β-oxidation might be a promising pathway in improving hepatic steatosis and insulin resistance as induced by obesity or diabetes.

Hepatic transcriptome profiling reveals early signatures associated with disease transition from non-alcoholic steatosis to steatohepatitis

Background and aim

Non-alcoholic fatty liver disease (NAFLD) is becoming a leading cause of chronic liver disease worldwide. The molecular events that influence disease progression from non-alcoholic fatty liver (NAFL) to aggressive non-alcoholic steatohepatitis (NASH) remain incompletely understood, leading to lack of mechanism-based targeted treatment options for NASH. This study aims to identify early signatures associated with disease progression from NAFL to NASH in mice and humans.

Materials and methods

Male C57BL/6J mice were fed a high-fat, -cholesterol, and - fructose (HFCF) diet for up to 9 months. The extent of steatosis, inflammation, and fibrosis was evaluated in liver tissues. Total RNA sequencing (RNA-seq) was conducted to determine liver transcriptomic changes.

Results

After being fed the HFCF diet, mice sequentially developed steatosis, early steatohepatitis, steatohepatitis with fibrosis, and eventually spontaneous liver tumor. Hepatic RNA-seq revealed that the key signatures during steatosis progression to early steatohepatitis were pathways related to extracellular matrix organization and immune responses such as T cell migration, arginine biosynthesis, C-type lectin receptor signaling, and cytokine-cytokine receptor interaction. Genes regulated by transcription factors forkhead box M1 (FOXM1) and negative elongation factor complex member E (NELFE) were significantly altered during disease progression. This phenomenon was also observed in patients with NASH.

Conclusions

In summary, we identified early signatures associated with disease progression from NAFL to early NASH in a mouse model that recapitulated key metabolic, histologic, and transcriptomic changes seen in humans. The findings from our study may shed light on the development of novel preventative, diagnostic, and therapeutic strategies for NASH.