Branched-chain Α-keto Acid Research Articles

Whole-body metabolic fate of branched-chain amino acids.

Oxidation of branched-chain amino acids (BCAAs) is tightly regulated in mammals. We review here the distribution and regulation of whole-body BCAA oxidation. Phosphorylation and dephosphorylation of the rate-limiting enzyme, branched-chain α-ketoacid dehydrogenase complex directly regulates BCAA oxidation, and various other indirect mechanisms of regulation also exist. Most tissues throughout the body are capable of BCAA oxidation, and the flux of oxidative BCAA disposal in each tissue is influenced by three key factors: 1. tissue-specific preference for BCAA oxidation relative to other fuels, 2. the overall oxidative activity of mitochondria within a tissue, and 3. total tissue mass. Perturbations in BCAA oxidation have been implicated in many disease contexts, underscoring the importance of BCAA homeostasis in overall health.

Metabolomic analysis on blood of transgenic mice overexpressing PGC-1α in skeletal muscle.

PGC-1α expression increases in skeletal muscles during exercise and regulates the transcription of many target genes. In this study, we conducted a metabolomic analysis on the blood of transgenic mice overexpressing PGC-1α in its skeletal muscle (PGC-1α-Tg mice) using CE-TOFMS. The blood level of homovanillic acid (dopamine metabolite) and the gene expression of dopamine metabolic enzyme in the skeletal muscle of PGC-1α-Tg mice were high. The blood level of 5-methoxyindoleacetic acid was also high in PGC-1α-Tg mice. The blood levels of branched-chain α-keto acids and β-alanine were low in PGC-1α-Tg mice. These metabolites in the skeletal muscle were present in low concentration. The changes in these metabolites may reflect the skeletal muscle condition with increasing PGC-1α, such as exercise.

Dichloroacetate and Pyruvate Metabolism: Pyruvate Dehydrogenase Kinases as Targets Worth Investigating for Effective Therapy of Toxoplasmosis.

Toxoplasmosis, a protozoan infection caused by Toxoplasma gondii, is estimated to affect around 2.5 billion people worldwide. Nevertheless, the side effects of drugs combined with the long period of therapy usually result in discontinuation of the treatment. New therapies should be developed by exploring peculiarities of the parasite's metabolic pathways, similarly to what has been well described in cancer cell metabolism. An example is the switch in the metabolism of cancer that blocks the conversion of pyruvate into acetyl coenzyme A in mitochondria. In this context, dichloroacetate (DCA) is an anticancer drug that reverts the tumor proliferation by inhibiting the enzymes responsible for this switch: the pyruvate dehydrogenase kinases (PDKs). DCA has also been used in the treatment of certain symptoms of malaria; however, there is no evidence of how this drug affects apicomplexan species. In this paper, we studied the metabolism of T. gondii and demonstrate that DCA also inhibits T. gondii's in vitro infection with no toxic effects on host cells. DCA caused an increase in the activity of pyruvate dehydrogenase followed by an unbalanced mitochondrial activity. We also observed morphological alterations frequently in mitochondria and in a few apicoplasts, essential organelles for parasite survival. To date, the kinases that potentially regulate the activity of pyruvate metabolism in both organelles have never been described. Here, we confirmed the presence in the genome of two putative kinases (T. gondii PDK [TgPDK] and T. gondii branched-chain α-keto acid dehydrogenase kinase [TgBCKDK]), verified their cellular localization in the mitochondrion, and provided in silico data suggesting that they are potential targets of DCA.IMPORTANCE Currently, the drugs used for toxoplasmosis have severe toxicity to human cells, and the treatment still lacks effective and safer alternatives. The search for novel drug targets is timely. We report here that the treatment of T. gondii with an anticancer drug, dichloroacetate (DCA), was effective in decreasing in vitro infection without toxicity to human cells. It is known that PDK is the main target of DCA in mammals, and this inactivation increases the conversion of pyruvate into acetyl coenzyme A and reverts the proliferation of tumor cells. Moreover, we verified the mitochondrial localization of two kinases that possibly regulate the activity of pyruvate metabolism in T. gondii, which has never been studied. DCA increased pyruvate dehydrogenase (PDH) activity in T. gondii, followed by an unbalanced mitochondrial activity, in a manner similar to what was previously observed in cancer cells. Thus, we propose the conserved kinases as potential regulators of pyruvate metabolism and interesting targets for new therapies.

MiR-34a-5p and miR-452-5p: The Novel Regulators of Pancreatic Endocrine Dysfunction in Diabetic Zucker Rats?

Objective: The pancreatic endocrinal system dominates the regulation of blood glucose levels in vivo, and the dysfunction of pancreatic endocrine β-cells is a major cause of the occurrence and development of Type 2 diabetes (T2D). Although microRNA (miRNA) have been found to be key regulators of pancreatic β-cells proliferation, differentiation and apoptosis, the underlying mechanism remains enigmatic. The aim of this study was to identify several novel miRNAs which might be involved in the etiopathogenesis of diabetic β-cells dysfunction.Methods: The miRNA expression profiles in the pancreas of high-fat diet (HFD) fed Zucker diabetic fatty (ZDF) rats and Zucker lean (ZL) rats feed with normal-fat diet (NFD) were detected by using miRNA microarray chip, and individually verified the most significant factors by quantitative real-time polymerase chain reaction (qRT-PCR) assay. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to predict the target genes related to each of the identified miRNAs and the functions of these target genes in different metabolic signaling pathways.Results: Compared with the ZL rats, a total of 24 differentially expressed miRNAs were detected in ZDF rats. Among which miR-34a-5p and miR-452-5p were the most significantly up-regulated and down-regulated respectively. These miRNAs have not been reported in rats' pancreas before. By GO and KEGG enrichment analyses, we found that miR-34a-5p could negatively regulate pancreatic β-cell proliferation through the involvement of Wnt signaling pathway. In addition, it was also found to regulate insulin secretion through the insulin signaling pathway to modulate blood glucose levels. At the same time, miR-452-5p was found to positively regulate the activity of the key rate-limiting enzyme branched-chain α-keto acid dehydrogenase-β (BCKDHB) in the catabolism of branched chain amino acids (BCAA), leading to mitochondrial dysfunction in pancreatic β-cells.Conclusions: miR-34a-5p and miR-452-5p were identified as the novel regulators of pancreatic endocrine dysfunction. These miRNAs might have the potential to be utilized as the new predictive biomarkers for the diagnosis of the occurrence and development of T2D, as well as the therapeutic targets for T2D treatment.

An induced pluripotent stem cell line (SDQLCHi033-A) derived from a patient with maple syrup urine disease type Ib carrying a homozygous mutation in BCKDHB gene.

Maple syrup urine disease (MSUD) type Ib is a subclass of MSUD (248600) which is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex. An induced pluripotent stem cell (iPSC) line was generated from an 11-day-old girl diagnosed with maple syrup urine disease type Ib and carrying a novel homozygous mutation of c.1097C>A (p.P366Q) in BCKDHB gene. This cell line demonstrates a normal karyotype and maintains a pluripotent state, displaying the capability to differentiate into the three germ layer lineages and the absence of exogenous pluripotency vector expression.

Response by Xu et al to Letter Regarding Article, “Branched-Chain Amino Acid Catabolism Promotes Thrombosis Risk by Enhancing Tropomodulin-3 Propionylation in Platelets”

HomeCirculationVol. 142, No. 24Response by Xu et al to Letter Regarding Article, “Branched-Chain Amino Acid Catabolism Promotes Thrombosis Risk by Enhancing Tropomodulin-3 Propionylation in Platelets” Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyRedditDiggEmail Jump toFree AccessLetterPDF/EPUBResponse by Xu et al to Letter Regarding Article, “Branched-Chain Amino Acid Catabolism Promotes Thrombosis Risk by Enhancing Tropomodulin-3 Propionylation in Platelets” Yanyan Xu, PhD, Haojie Jiang, PhD and Junling Liu, PhD Yanyan XuYanyan Xu Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China (Y.X., H.J., J.L.). Search for more papers by this author , Haojie JiangHaojie Jiang Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China (Y.X., H.J., J.L.). Search for more papers by this author and Junling LiuJunling Liu Department of Biochemistry and Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China (Y.X., H.J., J.L.). The Cyrus Tang Hematology Center, Collaborative Innovation Center of Hematology, Soochow University, Suzhou, China (J.L.). Search for more papers by this author Originally published14 Dec 2020https://doi.org/10.1161/CIRCULATIONAHA.120.051367Circulation. 2020;142:e452–e453In Response:We thank Dr Liu and colleagues for their interest in our article, “Branched-Chain Amino Acid Catabolism Promotes Thrombosis Risk by Enhancing Tropomodulin-3 Propionylation in Platelets.”1We fully agree with Dr Liu that further exploration of the functions of leucine and mammalian target of rapamycin pathway will strengthen the understanding of the mechanism of branched-chain amino acid (BCAA)–induced platelet activation. In our previous study, we studied the individual functions of valine, isoleucine, leucine, and their catabolites on platelet activation. We found that valine/α-ketoisovaleric acid has the most significant promoting effect on platelet activation among BCAAs and branched-chain α-keto acids. Propionyl coenzyme A, as the end product of valine and isoleucine metabolism, promotes platelet aggregation and the TMOD3 (tropomodulin 3) propionylation. Leucine catabolism eventually leads to the formation of acetoacetyl coenzyme A and acetyl coenzyme A, but not propionyl coenzyme A. We found that leucine and its metabolite α-ketoisocaproic acid enhance agonist-induced platelet aggregation and P-selectin exposure. These suggested that there must be some other mechanisms between BCAAs and thrombosis formation. It has been reported that leucine participates in the mammalian target of rapamycin signaling pathway in T cells, macrophages, and other cells.2 It is necessary to further investigate the relationship between leucine and mammalian target of rapamycin in the process of platelet activation and thrombosis.We agree with Dr Liu that the age, medication, and diet of patients with type 2 diabetes mellitus should be taken into consideration to demonstrate the relationship between BCAA levels and platelet activation. In our study, the average age of inpatients with type 2 diabetes mellitus was 57.5±3.7 years and all patients had taken medication to control blood glucose level. Apparently, the number of patients in our study was not enough to perform the analysis of the correlation between the age, medication, diet, and the levels of BCAAs and platelet activation in patients. Larger scaled experiments are required to resolve this issue.As Dr Liu pointed out, BCAAs and branched-chain α-keto acids are supplied to patients who have chronic renal failure with other essential amino acids and their ketoanalogues to decrease protein intake as much as possible and maintain protein balance, which may increase the risk of thrombosis.3,4 Our unpublished data showed that P2Y12 inhibitor ticagrelor and thromboxane A2 production blocker aspirin significantly inhibited the enhancing effects of BCAAs on the aggregation of platelets in response to different agonists in vitro, which suggested that utilization of current antiplatelet drugs might reduce the risk of thrombosis in the therapy of patients with chronic renal failure. However, further basic and clinical studies must be performed before applying the findings to the supplement of BCAAs in patients.DisclosuresNone.

Growth and metabolic responses of grouper juveniles (Epinephelus coioides) fed diets containing varying levels of leucine

We conducted an 8-week feeding trial to evaluate the effects of dietary leucine on growth performance, body and muscle composition, hepatic and plasma components, gut morphology, and relative expression levels of genes in the mTOR pathway. Six isonitrogenous and isolipidic diets with increasing levels of Leu (1.88%, 2.84%, 3.51%, 4.45%, 5.27%, and 6.06%, respectively) were formulated. Each diet was fed to 4-replicate groups of 20 groupers (average initial body weight of 35.0 g/fish) twice daily, to apparent satiety. Weight gain and specific growth rates; feed intake; body protein, lipid, and muscle protein content; and liver GOT and branched chain α-keto acid dehydrogenase kinase activities showed positive linear and/or quadratic responses to dietary Leu levels. In contrast, body moisture and ash content, liver triglyceride and total-cholesterol content, and plasma GOT and GTP activity had negative linear and/or quadratic responses to different dietary Leu levels. There were no differences in the feed conversion ratio and hepatosomatic index, condition factor, plasma GOT activity, and plasma triglyceride and total-cholesterol content among treatments. The mucosal fold number in three gut segments (proximal intestine (PI), middle intestine (MI), and distal intestine (DI)) and mucosal fold length and muscle layer thickness in the DI showed positive quadratic responses to dietary Leu levels. In addition, mucosal fold length and number, and muscle layer thickness in the PI were greater that those observed for the MI and DI. The mRNA level of SLC3A2, SLC7A5, RagC/D, Ragulator, Raptor, mTOR, mLST8, and Tel2 in the muscle and/or gut showed positive quadratic responses to dietary Leu levels, whereas negative quadratic responses were observed for mRNA levels of RagA/B and V-ATPase in the muscle and/or gut, and SLC7A5 in the liver. The optimal amount of Leu required for this fish was estimated to be 8.88% of the dietary protein content, based on the regression analysis of percent weight gains against dietary Leu levels. The results indicate that appropriate dietary Leu levels (range 3.51%–4.45%) could help to improve growth performance and nutrient deposition, maintain gut structural integrity and positively regulate genes in the mTOR signaling pathway in the fish.

Branched-chain ketoacid overload inhibits insulin action in the muscle

Branched-chain α-keto acids (BCKAs) are catabolites of branched-chain amino acids (BCAAs). Intracellular BCKAs are cleared by branched-chain ketoacid dehydrogenase (BCKDH), which is sensitive to inhibitory phosphorylation by BCKD kinase (BCKDK). Accumulation of BCKAs is an indicator of defective BCAA catabolism and has been correlated with glucose intolerance and cardiac dysfunction. However, it is unclear whether BCKAs directly alter insulin signaling and function in the skeletal and cardiac muscle cell. Furthermore, the role of excess fatty acids (FAs) in perturbing BCAA catabolism and BCKA availability merits investigation. By using immunoblotting and ultra-performance liquid chromatography MS/MS to analyze the hearts of fasted mice, we observed decreased BCAA-catabolizing enzyme expression and increased circulating BCKAs, but not BCAAs. In mice subjected to diet-induced obesity (DIO), we observed similar increases in circulating BCKAs with concomitant changes in BCAA-catabolizing enzyme expression only in the skeletal muscle. Effects of DIO were recapitulated by simulating lipotoxicity in skeletal muscle cells treated with saturated FA, palmitate. Exposure of muscle cells to high concentrations of BCKAs resulted in inhibition of insulin-induced AKT phosphorylation, decreased glucose uptake, and mitochondrial oxygen consumption. Altering intracellular clearance of BCKAs by genetic modulation of BCKDK and BCKDHA expression showed similar effects on AKT phosphorylation. BCKAs increased protein translation and mTORC1 activation. Pretreating cells with mTORC1 inhibitor rapamycin restored BCKA's effect on insulin-induced AKT phosphorylation. This study provides evidence for FA-mediated regulation of BCAA-catabolizing enzymes and BCKA content and highlights the biological role of BCKAs in regulating muscle insulin signaling and function.

Novel regulation of cardiac branched-chain amino acid metabolism through AMP deaminase: a possible therapeutic target for diabetic cardiomyopathy

Abstract Background Dysregulation of branched-chain amino acid (BCAA) metabolism has been shown to be associated with type 2 diabetes mellitus (T2DM) and heart failure. BCAA reportedly protects cells from fatty acid-induced mitochondrial injury via sequestration of fatty acids in intracellular lipid droplets from mitochondria. We previously reported that up-regulation of AMP deaminase 3 (AMPD3) impairs cardiac energetics in T2DM hearts, and AMPD3 was recently shown to participate in regulation of amino acid metabolism in skeletal muscle. Purpose We hypothesized that AMPD3 regulates cardiac amino acid metabolism by interaction with branched-chain α-ketoacid dehydrogenase (BCKDH) complex and that cardioprotective effect of sodium glucose cotransporter 2 inhibitors is mediated by modification of BCAA metabolism in diabetic cardiomyocytes. Methods and results Proteomic analyses of immunoprecipitates with an anti-AMPD3 antibody in rat hearts revealed that AMPD3 interacted with the E1α component of BCKDH complex. Whereas BCKDH has been reported to localize in mitochondria matrix as a rate-limiting enzyme for BCAA catabolism, immunoblotting using subcellular fractions revealed that BCKDH E1α is present in cytosol and endoplasmic reticulum as well. AMPD3-BCKDH E1α interaction was decreased by 68% in T2DM rats (OLETF) compared to that in control rats (LETO), and significant accumulation of BCAAs was observed in OLETF hearts (317±30 vs. 213±16 nmol/g). Survival rate at 48 hours after myocardial infarction (MI) was significantly lower in OLETF than in LETO (40% vs 84%). Empagliflozin treatment (10 mg/kg/day, 14 days) before MI improved the survival rate in OLETF to 70%, increased BCAAs as the top of 92 detected metabolites (791±187 nmol/g) and significantly preserved tissue ATP in the non-MI remote region. Electron microscopy showed a significantly higher prevalence of myocardium lipid droplets in OLETF, which was further increased by empagliflozin. Conclusions Results of the present analyses support the hypotheses that conversion of BCAA-derived branched-chain α-ketoacid to branched-chain acyl-CoA is suppressed by reduced AMPD3-BCKDH interaction in the myocardium of T2DM and that empagliflozin induces compensation of the dysregulated cardiac BCAA metabolism by augmentation of BCAA influx and promotion of fatty acid sequestration in intracellular lipid droplets. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Boehringer Ingelheim

Maple syrup urine disease in Brazilian patients: variants and clinical phenotype heterogeneity

BackgroundMaple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disease caused by deficient activity of the branched-chain α-keto acid dehydrogenase (BCKD) enzymatic complex. BCKD is a mitochondrial complex encoded by BCKDHA, BCKDHB, DBT, and DLD genes. MSUD is predominantly caused by Variants in BCKDHA, BCKDHB, and DBT genes encoding the E1α, E1β, and E2 subunits of BCKD complex, respectively. The aim of this study was to characterize the genetic basis of MSUD by identifying the point variants in BCKDHA, BCKDHB, and DBT genes in a cohort of Brazilian MSUD patients and to describe their phenotypic heterogeneity. It is a descriptive cross-sectional study with 21 MSUD patients involving molecular genotyping by Sanger sequencing.ResultsEight new variants predicted as pathogenic were found between 30 variants (damaging and non-damaging) identified in the 21 patients analyzed: one in the BCKDHA gene (p.Tyr120Ter); five in the BCKDHB gene (p.Gly131Val, p.Glu146Glnfs * 13, p.Phe149Cysfs * 9, p.Cys207Phe, and p.Lys211Asn); and two in the DBT gene (p.Glu148Ter and p.Glu417Val). Seventeen pathogenic variants were previously described and five variants showed no pathogenicity according to in silico analysis.ConclusionGiven that most of the patients received late diagnoses, the study results do not allow us to state that the molecular features of MSUD variant phenotypes are predictive of clinical severity.

Brain Branched-Chain Amino Acids in Maple Syrup Urine Disease: Implications for Neurological Disorders.

Maple syrup urine disease (MSUD) is an autosomal recessive disorder caused by decreased activity of the branched-chain α-ketoacid dehydrogenase complex (BCKDC), which catalyzes the irreversible catabolism of branched-chain amino acids (BCAAs). Current management of this BCAA dyshomeostasis consists of dietary restriction of BCAAs and liver transplantation, which aims to partially restore functional BCKDC activity in the periphery. These treatments improve the circulating levels of BCAAs and significantly increase survival rates in MSUD patients. However, significant cognitive and psychiatric morbidities remain. Specifically, patients are at a higher lifetime risk for cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorder. Recent literature suggests that the neurological sequelae may be due to the brain-specific roles of BCAAs. This review will focus on the derangements of BCAAs observed in the brain of MSUD patients and will explore the potential mechanisms driving neurologic dysfunction. Finally, we will discuss recent evidence that implicates the relevance of BCAA metabolism in other neurological disorders. An understanding of the role of BCAAs in the central nervous system may facilitate future identification of novel therapeutic approaches in MSUD and a broad range of neurological disorders.

The metabolic effect of α-ketoisocaproic acid: in vivo and in vitro studies.

Maple syrup urine disease (MSUD) is characterized by a deficiency in the mitochondrial branched-chain α-keto acid dehydrogenase complex activity and, consequently, accumulation of the branched-chain amino acids and their respective branched-chain α-keto acids in fluids and the tissue. MSUD clinical symptoms include neurological alterations. KIC is considered one of the significant neurotoxic metabolites since its increased plasma concentrations are associated with neurological symptoms. We evaluated the effect of KIC intracerebroventricular (ICV) injection in hippocampal mitochondria function in rats. We also investigated the impact of KIC in cells' metabolic activity (using MTT assay) and reactive species (RS) production in HT-22 cells. For this, thirty-day-old male rats were bilaterally ICV injected with KIC or aCSF. Thus, 1 hour after the administration, animals were euthanized, and the hippocampus was harvested for measured the activities of mitochondrial respiratory chain enzymes and RS production. Furthermore, HT-22 cells were incubated with KIC (1-10mM) in 6, 12, and 24h. Mitochondrial complexes activities were reduced, and the formation of RS was increased in the hippocampus of rats after KIC administration. Moreover, KIC reduced the cells' metabolic ability to reduce MTT and increased RS production in hippocampal neurons. Impairment in hippocampal mitochondrial function seems to be involved in the neurotoxicity induced by KIC.

Short communication: Colostrum versus formula: Effects on mRNA expression of genes related to branched-chain amino acid metabolism in neonatal dairy calves

The objective of the current study was to elucidate the effect of feeding colostrum or milk-based formula on the tissue mRNA abundance of the most relevant branched-chain amino acids (BCAA) transporters and catabolizing enzymes in newborn calves. German Holstein calves were fed either colostrum (COL; n = 7) or milk-based formula (FOR; n = 7) with comparable nutrient composition but lower contents of free BCAA, insulin, and insulin-like growth factor-I in the formula than in the respective colostrum for up to 4 d of life. Tissue samples from liver, kidney fat, 3 different muscles [M. longissimus dorsi (MLD), M. semitendinosus (MST), and M. masseter (MM)], as well as duodenum, jejunum, and ileum were collected following euthanasia on d 4 at 2 h after feeding. The plasma-free BCAA were analyzed, and the tissue abundance of solute carrier family 1 member 5 (SLC1A5), SLC7A5, and SLC38A2 as well as mitochondrial isoform of branched-chain aminotransferase (BCATm), branched-chain α-keto acid dehydrogenase E1α (BCKDHA), and branched-chain α-keto acid dehydrogenase E1β (BCKDHB) were assessed. The preprandial plasma concentrations of free BCAA were affected by time but did not differ between groups. The plasma concentrations of free BCAA decreased in COL, whereas they increased in FOR after feeding, resulting in higher postprandial plasma total BCAA concentrations in FOR than in COL. The mRNA abundances of BCATm, BCKDHA, BCKDHB, as well as BCAA transporters in the liver, were not affected by the diet. In kidney fat, the mRNA abundance of BCAA catabolizing enzymes did not differ between groups, but that of SLC1A5 was lower in FOR than in COL. The mRNA abundance of BCAA catabolizing enzymes in different sections of the small intestine was not affected by the diet, whereas that of SLC7A5 was or tended to be lower in the duodenum, proximal jejunum, and mid jejunum of the COL calves compared with the FOR calves. The mRNA abundance of BCKDHA was lower in MLD and MM but greater in MS for the FOR calves compared with the COL calves. The mRNA abundance of SLC7A5 in MST was lower in FOR than in COL, whereas it was unaffected by the diet in MLD and MM. The differential effect of feeding colostrum on the mRNA abundance of BCKDHA in 3 different muscle tissues might point to a muscle type-specific response. The results also indicate that the colostral BCAA might be favorably used for anabolic metabolism in the small intestine of neonatal calves. Such effects are speculated to be due to the stimulatory effects of growth factors and hormones present in colostrum.

Genotype-phenotype correlation of 33 patients with maple syrup urine disease.

Maple syrup urine disease (MSUD) is a rare autosomal recessive inherited disorder due to defects in the branched-chain α-ketoacid dehydrogenase complex (BCKDC). MSUD varies in severity and its clinical spectrum is quite broad, ranging from mild to severe phenotypes. Thirty-three MSUD patients were recruited into this study for molecular genetic variant profiling and genotype-phenotype correlation. Except for one patient, all other patients presented with the classic neonatal form of the disease. Seventeen different variants were detected where nine were novel. The detected variants spanned across the entire BCKDHA, BCKDHB and DBT genes. All variants were in homozygous forms. The commonest alterations were nonsense and frameshift variants, followed by missense variants. For the prediction of variant's pathogenicity, we used molecular modeling and several in silico tools including SIFT, Polyphen2, Condel, and Provean. In addition, six other tools were used for the prediction of the conservation of the variants' sites including Eigen-PC, GERP++, SiPhy, PhastCons vertebrates and primates, and PhyloP100 rank scores. Herein, we presented a comprehensive characterization of a large cohort of patients with MSUD. The clinical severity of the variants' phenotypes was well correlated with the genotypes. The study underscores the importance of the use of in silico analysis of MSUD genotypes for the prediction of the clinical outcomes in patients with MSUD.

First person – Hui-Ying Tsai and Shih-Cheng Wu

ABSTRACTFirst Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping early-career researchers promote themselves alongside their papers. Hui-Ying Tsai and Shih-Cheng Wu are co-first authors on ‘Loss of the Drosophila branched-chain α-ketoacid dehydrogenase complex results in neuronal dysfunction’, published in DMM. Hui-Ying is a research assistant in the lab of Chun-Hong Chen at National Health Research Institutes, Zhunan, Taiwan. Her research interest is modeling the human neurological disease maple syrup urine disease in Drosophila, assessing behavior as well as brain damage. Shih-Cheng is a postdoc in the same lab, with interests in modeling human disease and immunometabolism.

Vitamin B1 Supports the Differentiation of T Cells through TGF-β Superfamily Production in Thymic Stromal Cells.

SummaryHomeostatic generation of T cells, which occurs in the thymus, is controlled at least in part by endogenous cytokines and ligands. In addition, nutritional factors are other key regulators for the homeostasis of host immunity, but whether and how nutrition affects the homeostatic generation of thymocytes remains to be established. Here, we showed that vitamin B1 deficiency resulted in a bias toward the maturation of γδ thymocytes accompanied by decreased differentiation into double-positive thymocytes during thymic involution. These events were mediated through the increased production of TGF-β superfamily members due to the accumulation of branched-chain α-keto acids in thymic stromal cells. These findings revealed essential roles of vitamin B1 in the appropriate differentiation of T cells through the metabolism of thymic stromal cells.

BDK Deficiency in Cerebral Cortex Neurons Causes Neurological Abnormalities and Affects Endurance Capacity.

Branched-chain amino acid (BCAA) catabolism is regulated by its rate-limiting enzyme, branched-chain α-keto acid dehydrogenase (BCKDH), which is negatively regulated by BCKDH kinase (BDK). Loss of BDK function in mice and humans leads to dysregulated BCAA catabolism accompanied by neurological symptoms such as autism; however, which tissues or cell types are responsible for the phenotype has not been determined. Since BDK is highly expressed in neurons compared to astrocytes, we hypothesized that neurons are the cell type responsible for determining the neurological features of BDK deficiency. To test this hypothesis, we generated mice in which BDK deletion is restricted to neurons of the cerebral cortex (BDKEmx1-KO mice). Although BDKEmx1-KO mice were born and grew up normally, they showed clasped hind limbs when held by the tail and lower brain BCAA concentrations compared to control mice. Furthermore, these mice showed a marked increase in endurance capacity after training compared to control mice. We conclude that BDK in neurons of the cerebral cortex is essential for maintaining normal neurological functions in mice, and that accelerated BCAA catabolism in that region may enhance performance in running endurance following training.

Tumour-reprogrammed stromal BCAT1 fuels branched-chain ketoacid dependency in stromal-rich PDAC tumours.

SUMMARYBranched chain amino acids (BCAAs) supply both carbon and nitrogen in pancreatic cancers, and their increased levels have been associated with increased risk of pancreatic ductal adenocarcinomas (PDACs). It remains unclear, however, how stromal cells regulate BCAA metabolism in PDAC cells and how mutualistic determinants control BCAA metabolism in the tumor milieu. Here we show distinct catabolic, oxidative, and protein turnover fluxes between cancer-associated fibroblasts (CAFs) and cancer cells and a marked branched chain ketoacid (BCKA)-reliance in PDAC cells in stroma-rich tumors. We report that cancer-induced stromal reprogramming fuels this BCKA demand. The TGF-β/SMAD5 axis directly targets BCAT1 in CAFs and dictates internalization of the extracellular matrix from the tumor microenvironment to supply amino acid precursors for BCKA secretion by CAFs. The in vitro results were corroborated with human patient-derived circulating tumor cells (CTCs) and PDAC tissue slices. Our findings reveal therapeutically actionable targets in pancreatic stromal and cancer cells.

Give and take: competition for BCAAs in the tumour microenvironment.

Pancreatic adenocarcinoma (PDAC) is often characterized by substantial amounts of fibrosis, and how these stromal components affect metabolite availability is not fully understood. Zhu et al. now show that cancer-associated fibroblasts consume branched-chain amino acids (BCAAs) at high levels but release corresponding branched-chain α-ketoacids that support PDAC cell growth.

Ibuprofen during gestation prevents some changes in physical and reflex development in offspring in a model of hyperleucinemia and maternal inflammation.

Maple Syrup Urine Disease (MSUD) is caused by a severe deficiency in the branched-chain ketoacid dehydrogenase complex activity. Patients MSUD accumulate the branched-chain amino acids leucine (Leu), isoleucine, valine in blood, and other tissues. Leu and/or their branched-chain α-keto acids are linked to neurological damage in MSUD. When immediately diagnosed and treated, patients develop normally. Inflammation in MSUD can elicit a metabolic decompensation crisis. There are few cases of pregnancy in MSUD women, and little is known about the effect of maternal hyperleucinemia on the neurodevelopment of their babies. During pregnancy, some intercurrences like maternal infection or inflammation may affect fetal development and are linked to neurologic diseases. Lipopolysaccharide is widely accepted as a model of maternal inflammation. We analyzed the effects of maternal hyperleucinemia and inflammation and the possible positive impact the use of ibuprofen in Wistar rats on a battery of physics (ear unfolding, hair growing, incisors eruption, eye-opening, and auditive channel opening) and neurological reflexes (palmar grasp, surface righting, negative geotaxis, air-righting, and auditory-startle response) maturation parameters in the offspring. Maternal hyperleucinemia and inflammation delayed some physical parameters and neurological reflexes, indicating that both situations may be harmful to fetuses, and ibuprofen reversed some settings.