Requirement of hepatic pyruvate carboxylase during fasting, high fat, and ketogenic diet

Activating transcription factor 3 regulates hepatic apolipoprotein A4 upon metabolic stress

The liver plays essential roles in maintaining systemic glucolipid homeostasis under ever changing metabolic stressors. Metabolic dysregulation can lead to both adaptive and maladaptive changes that impact systemic physiology. Here, we examined disparate genetic and environmental metabolic stressors and identified apolipoprotein A4 (ApoA4) as a circulating protein upregulated in liver-specific KOs for carnitine palmitoyltransferase 2 and pyruvate carboxylase. We found this upregulation to be exacerbated by fasting and high-fat or ketogenic diets. Unique among these models was a concomitant increase in activating transcription factor 3 (Atf3). Liver-specific overexpression of Atf3 resulted in increased ApoA4 expression in a sex-dependent manner. To understand the requirement of Atf3 to metabolic stress, we generated liver-specific Atf3, Cpt2 double KO mice. These experiments demonstrated the requirement for Atf3 in the induction of ApoA4 mRNA, ApoA4 protein, and serum triglycerides that were also sex-dependent. These experiments reveal the roles of hepatic Atf3 and ApoA4 in response to metabolic stress in vivo.

EccDNA atlas in male mice reveals features protecting genes against transcription-induced eccDNA formation

eccDNA is a driver of many cancers and a potential intermediate in other age-related disorders. However, little is known about the mechanisms underlying eccDNA formation in healthy tissue and how aging affects these processes. Here, we present an atlas of eccDNA across seven tissues of male mice spanning four ages. EccDNA correlates with open chromatin characterized by signatures of H3K27ac and H3K4me1. Additionally, the mutational load of eccDNA on genes correlates with tissue-specific transcription and increases logarithmically as a function of transcript level. Still, a population of intron-dense genes with many splice forms remains sheltered from eccDNA formation. We also find that the total number of eccDNA molecules does not increase as mice age, unlike other types of mutations. Our data reveal a link between eccDNA formation and transcript level that may drive gene architecture in mammals.

Tissue specific roles of fatty acid oxidation

Mitochondrial long chain fatty acid β-oxidation is a critical central carbon catabolic process. The importance of fatty acid oxidation is made evident by the life-threatening disease associated with diverse inborn errors in the pathway. While inborn errors show multisystemic requirements for fatty acid oxidation, it is not clear from the clinical presentation of these enzyme deficiencies what the tissue specific roles of the pathway are compared to secondary systemic effects. To understand the cell or tissue specific contributions of fatty acid oxidation to systemic physiology, conditional knockouts in mice have been employed to determine the requirements of fatty acid oxidation in disparate cell types. This has produced a host of surprising results that sometimes run counter to the canonical view of this metabolic pathway. The rigor of conditional knockouts has also provided clarity over previous research utilizing cell lines in vitro or small molecule inhibitors with dubious specificity. Here we will summarize current research using mouse models of Carnitine Palmitoyltransferases to determine the tissue specific roles and requirements of long chain mitochondrial fatty acid β-oxidation.

Carnitine palmitoyltransferase 1 facilitates fatty acid oxidation in a non-cell-autonomous manner

Mitochondrial fatty acid oxidation is facilitated by the combined activities of carnitine palmitoyltransferase 1 (Cpt1) and Cpt2, which generate and utilize acylcarnitines, respectively. We compare the response of mice with liver-specific deficiencies in the liver-enriched Cpt1a or the ubiquitously expressed Cpt2 and discover that they display unique metabolic, physiological, and molecular phenotypes. The loss of Cpt1a or Cpt2 results in the induction of the muscle-enriched isoenzyme Cpt1b in hepatocytes in a Pparα-dependent manner. However, hepatic Cpt1b does not contribute substantively to hepatic fatty acid oxidation when Cpt1a is absent. Liver-specific double knockout of Cpt1a and Cpt1b or Cpt2 eliminates the mitochondrial oxidation of non-esterified fatty acids. However, Cpt1a/Cpt1b double knockout mice retain fatty acid oxidation by utilizing extracellular long-chain acylcarnitines that are dependent on Cpt2. These data demonstrate the non-cell-autonomous intercellular metabolism of fatty acids in hepatocytes.

Sepsis-induced changes in pyruvate metabolism: insights and potential therapeutic approaches

Sepsis is a heterogeneous syndrome resulting from a dysregulated host response to infection. It is considered as a global major health priority. Sepsis is characterized by significant metabolic perturbations, leading to increased circulating metabolites such as lactate. In mammals, pyruvate is the primary substrate for lactate production. It plays a critical role in metabolism by linking glycolysis, where it is produced, with the mitochondrial oxidative phosphorylation pathway, where it is oxidized. Here, we provide an overview of all cytosolic and mitochondrial enzymes involved in pyruvate metabolism and how their activities are disrupted in sepsis. Based on the available data, we also discuss potential therapeutic strategies targeting these pyruvate-related enzymes leading to enhanced survival.

Huppke-Brendel syndrome: Novel cases and a therapeutic trial with ketogenic diet and N-acetylcysteine

Huppke-Brendel syndrome (HBS) is an autosomal recessive disorder caused by SLC33A1 mutations, a gene coding for the acetyl-CoA transporter-1 (AT-1). So far it has been described in nine pediatric and one adult patient. Therapeutic trials with copper histidinate failed to achieve any clinical improvement. Here, we describe the clinical characteristics of two novel patients, one of them diagnosed by gene analysis and his sib postmortally based on clinical characteristics. We demonstrate a therapeutic trial with acetylation therapy, consisting of N-acetylcysteine and ketogenic diet, in one of them. We provide biochemical data on N-acetylated amino acids in cerebrospinal fluid (CSF) and plasma before and after starting this treatment regimen. Our results indicate that ketogenic diet and N-acetylcysteine do not seem to normalize the concentrations of N-acetylated amino acids in CSF or plasma. The overall metabolic pattern shows a trend toward lowered levels of N-acetylated amino acids in CSF and to a lesser extent in plasma. Although there are some assumptions, the function of AT-1 is still not clear and further studies are needed to better understand mechanisms underlying this complex disorder.

Transcriptome Analysis Reveals the Early Development in Subcutaneous Adipose Tissue of Laiwu Piglets

Adipose tissue plays an important role in pig production efficiency. Studies have shown that postnatal development has a vital impact on adipose tissue; however, the mechanisms behind pig adipose tissue early-life programming remain unknown. In this study, we analyzed the transcriptomes of the subcutaneous adipose tissue (SAT) of 1-day and 21-day old Laiwu piglets. The results showed that the SAT of Laiwu piglets significantly increased from 1-day to 21-day, and transcriptome analysis showed that there were 2352 and 2596 differentially expressed genes (DEGs) between 1-day and 21-day SAT in male and female piglets, respectively. Expression of genes in glycolysis, gluconeogenesis, and glycogen metabolism such as pyruvate kinase M1/2 (PKM), phosphoenolpyruvate carboxy kinase 1 (PCK1) and amylo-alpha-1, 6-glucosidase, 4-alpha-glucanotransferase (AGL) were significantly different between 1-day and 21-day SAT. Genes in lipid uptake, synthesis and lipolysis such as lipase E (LIPE), acetyl-CoA carboxylase alpha (ACACA), Stearoyl-CoA desaturase (SCD), and 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) were also differentially expressed. Functional analysis showed enrichment of DEGs in transcriptional regulation, protein metabolism and cellular signal transduction. The protein-protein interaction (PPI) networks of these DEGs were analyzed and potential hub genes in these pathways were identified, such as transcriptional factors forkhead box O4 (FOXO4), CCAAT enhancer binding protein beta (CEBPB) and CCAAT enhancer binding protein delta (CEBPD), signal kinases BUB1 mitotic checkpoint serine/threonine kinase (BUB1) and cyclin-dependent kinase 1 (CDK1), and proteostasis-related factors ubiquitin conjugating enzyme E2 C (UBE2C) and cathepsin D (CTSD). Moreover, we further analyzed the transcriptomes of SAT between genders and the results showed that there were 54 and 72 DEGs in 1-day and 21-day old SAT, respectively. Genes such as KDM5D and KDM6C showed gender-specific expression in 1-day and 21-day SAT. These results showed the significant changes in SAT between 1-day and 21-day in male and female Laiwu pigs, which would provide information to comprehensively understand the programming of adipose tissue early development and to regulate adipose tissue function.

Current approaches in CRISPR-Cas system for metabolic disorder

A new era in genomic medicine has been brought by the development of CRISPR-Cas technology, which presents hitherto unheard-of possibilities for the treatment of metabolic illnesses. The treatment approaches used in CRISPR/Cas9-mediated gene therapy, emphasize distribution techniques such as viral vectors and their use in preclinical models of metabolic diseases like hypercholesterolemia, glycogen storage diseases, and phenylketonuria. The relevance of high-throughput CRISPR screens for target identification in discovering new genes and pathways associated with metabolic dysfunctions is an important aspect of the discovery of new approaches. With cutting-edge options for genetic correction and cellular regeneration, the combination of CRISPR-Cas technology with stem cell therapy has opened new avenues for the treatment of metabolic illnesses. The integration of stem cell therapy and CRISPR-Cas technology is an important advance in the treatment of metabolic diseases, which are difficult to treat because of their intricate genetic foundations. This chapter addresses the most recent developments in the application of stem cell therapy and CRISPR-Cas systems to treat a variety of metabolic disorders, providing fresh hope for effective and maybe curative therapies. This chapter examines techniques and developments that have been made recently to address a variety of metabolic disorders using CRISPR-Cas systems. Our chapter focuses on the foundational workings of CRISPR-Cas technology and its potential uses in gene editing, gene knockout, and activation/repression-based gene modification.

Causal Relationship between Mitochondrial Biological Function and Periodontitis: Evidence from a Mendelian Randomization Study

A growing number of studies indicate that mitochondrial dysfunction serves as a pathological mechanism for periodontitis. Therefore, this two-sample Mendelian randomization (MR) study was carried out to explore the causal associations between mitochondrial biological function and periodontitis, because the specific nature of this causal relationship remains inconclusive in existing MR studies. Inverse variance weighting, Mendelian randomization-Egger, weighted mode, simple mode, and weighted median analyses were performed to assess the causal relationships between the exposure factors and periodontitis. The results of the present study revealed a causal association between periodontitis and medium-chain specific acyl-CoA dehydrogenase (MCAD), malonyl-CoA decarboxylase (MLYCD), glutaredoxin 2 (Grx2), oligoribonuclease (ORN), and pyruvate carboxylase (PC). Notably, MCAD and MLYCD are causally linked to periodontitis, and serve as protective factors. However, Grx2, ORN, and PC function as risk factors for periodontitis. Our study established a causal relationship between mitochondrial biological function and periodontitis, and such insights may provide a promising approach for treating periodontitis via mitochondrial regulation.

Hepatic malonyl-CoA synthesis restrains gluconeogenesis by suppressing fat oxidation, pyruvate carboxylation, and amino acid availability

Acetyl-CoA carboxylase (ACC) promotes prandial liver metabolism by producing malonyl-CoA, a substrate for de novo lipogenesis and an inhibitor of CPT-1-mediated fat oxidation. We report that inhibition of ACC also produces unexpected secondary effects on metabolism. Liver-specific double ACC1/2 knockout (LDKO) or pharmacologic inhibition of ACC increased anaplerosis, tricarboxylic acid (TCA) cycle intermediates, and gluconeogenesis by activating hepatic CPT-1 and pyruvate carboxylase flux in the fed state. Fasting should have marginalized the role of ACC, but LDKO mice maintained elevated TCA cycle intermediates and preserved glycemia during fasting. These effects were accompanied by a compensatory induction of proteolysis and increased amino acid supply for gluconeogenesis, which was offset by increased protein synthesis during feeding. Such adaptations may be related to Nrf2 activity, which was induced by ACC inhibition and correlated with fasting amino acids. The findings reveal unexpected roles for malonyl-CoA synthesis in liver and provide insight into the broader effects of pharmacologic ACC inhibition.

Nuclear receptor corepressors non-canonically drive glucocorticoid receptor-dependent activation of hepatic gluconeogenesis

Nuclear receptor corepressors (NCoRs) function in multiprotein complexes containing histone deacetylase 3 (HDAC3) to alter transcriptional output primarily through repressive chromatin remodelling at target loci1-5. In the liver, loss of HDAC3 causes a marked hepatosteatosis largely because of de-repression of genes involved in lipid metabolism6,7; however, the individual roles and contribution of other complex members to hepatic and systemic metabolic regulation are unclear. Here we show that adult loss of both NCoR1 and NCoR2 (double knockout (KO)) in hepatocytes phenocopied the hepatomegalic fatty liver phenotype of HDAC3 KO. In addition, double KO livers exhibited a dramatic reduction in glycogen storage and gluconeogenic gene expression that was not observed with hepatic KO of individual NCoRs or HDAC3, resulting in profound fasting hypoglycaemia. This surprising HDAC3-independent activation function of NCoR1 and NCoR2 is due to an unexpected loss of chromatin accessibility on deletion of NCoRs that prevented glucocorticoid receptor binding and stimulatory effect on gluconeogenic genes. These studies reveal an unanticipated, non-canonical activation function of NCoRs that is required for metabolic health.

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.