Functional Metabolic Mapping Reveals Highly Active Branched-Chain Amino Acid Metabolism in Human Astrocytes, Which Is Impaired in iPSC-Derived Astrocytes in Alzheimer's Disease

The branched-chain amino acids (BCAAs) leucine, isoleucine, and valine are important nitrogen donors for synthesis of glutamate, the main excitatory neurotransmitter in the brain. The glutamate carbon skeleton originates from the tricarboxylic acid (TCA) cycle intermediate α-ketoglutarate, while the amino group is derived from nitrogen donors such as the BCAAs. Disturbances in neurotransmitter homeostasis, mainly of glutamate, are strongly implicated in the pathophysiology of Alzheimer's disease (AD). The divergent BCAA metabolism in different cell types of the human brain is poorly understood, and so is the involvement of astrocytic and neuronal BCAA metabolism in AD. The goal of this study is to provide the first functional characterization of BCAA metabolism in human brain tissue and to investigate BCAA metabolism in AD pathophysiology using astrocytes and neurons derived from human-induced pluripotent stem cells (hiPSCs). Mapping of BCAA metabolism was performed using mass spectrometry and enriched [15N] and [13C] isotopes of leucine, isoleucine, and valine in acutely isolated slices of surgically resected cerebral cortical tissue from human brain and in hiPSC-derived brain cells carrying mutations in either amyloid precursor protein (APP) or presenilin-1 (PSEN-1). We revealed that both human astrocytes of acutely isolated cerebral cortical slices and hiPSC-derived astrocytes were capable of oxidatively metabolizing the carbon skeleton of BCAAs, particularly to support glutamine synthesis. Interestingly, hiPSC-derived astrocytes with APP and PSEN-1 mutations exhibited decreased amino acid synthesis of glutamate, glutamine, and aspartate derived from leucine metabolism. These results clearly demonstrate that there is an active BCAA metabolism in human astrocytes, and that leucine metabolism is selectively impaired in astrocytes derived from the hiPSC models of AD. This impairment in astrocytic BCAA metabolism may contribute to neurotransmitter and energetic imbalances in the AD brain.

1232Relationship between leucine metabolism and executive function development: the GUSTO cohort

Background Molecular biomarkers for cognitive function have also been widely investigated. However, few investigated early development of executive function (EF) comprehensively, which is a higher-level of cognitive function responsible for coordinating other cognitive ability. Methods We investigated the metabolomic biomarkers for EF in a multi-ethnicity birth cohort in Singapore. Circulating level of 165 metabolites were quantified using a nuclear magnetic resonance (NMR)-based metabolomics platform in 457 and 524 children at age 6 and 8 years. EF was assessed in 495 children (∼7 years) using parent-reported Behavior Rating Inventory of Executive Function, Second Edition. We incorporated genetic data and performed mediation analysis to investigate the role of rs1260326 (GCKR) in the relationship between leucine metabolism and EF. Results Higher circulating level of leucine was consistently associated with poorer EFs (Initiate, Working Memory, Plan/Organize, Task-Monitor, and Organization of Materials) after adjusting for age, sex, maternal ethnicity, maternal educational level, household income at recruitment, and child body-mass index (BMI). Comparing to CT genotype, CC genotype in rs1260326 is potentially associated with poorer EFs. But these associations were not mediated via circulating leucine level or BMI. Higher circulating leucine exerts effect on EFs and part of the effect may be via impact on BMI. Leucine-BMI interaction may exist in CT subgroup. Conclusions Our analysis suggested that leucine exerts harmful effect on EF, but at a lower level, leucine-BMI interaction may counteract with the effect of leucine. Key messages Higher level of circulating leucine was associated with poorer EF. Leucine-BMI interaction influences the leucine-EF association.

MCCC2 promotes HCC development by supporting leucine oncogenic function

Background The role of methylcrotonoyl-CoA carboxylase 2 (MCCC2) in the development of tumors is well-established, and the involvement of leucine in the liver is well-known. However, the role of MCCC2 and the correlation between MCCC2 and leucine in the progression of hepatocellular carcinoma (HCC) have not yet been reported. Methods In this study, the Gepia database was used to evaluate the prognostic value of MCCC2 in HCC. The expression and localization of MCCC2 in HCC cells were determined by western blot and immunofluorescence assays. Flow cytometry and CCK-8 and transwell assays were carried out to explore the effect of MCCC2 on cell proliferation, migration, and invasion. In addition, mass spectrometry analysis was used to predict the potential cell function of MCCC2 in HCC. Results We found that the expression of MCCC2 increased in HCC tissues and that high expression of MCCC2 could predict poor outcomes in HCC patients. Knockdown expression of MCCC2 in HCC cells could reduce cell proliferation, migration, and invasion ability in vitro and could inhibit HCC cell proliferation in vivo. Interestingly, we found that HCC cells transfected with MCCC2-sgRNA failed to respond to leucine deprivation. Meanwhile, leucine deprivation inhibited cell proliferation, migration, and invasion in HCC cells where MCCC2 was present rather than in cells where MCCC2 was absent. In addition, knockdown of MCCC2 significantly reduced the glycolysis markers, glucose consumption, lactate secretion, and acetyl-CoA level, which is a product of leucine metabolism. Furthermore, we found that MCCC2 promotes the activation of ERK. Profiling the MCCC2 binding proteins revealed that MCCC2-associated proteins are enriched in biological processes, such as protein metabolism, energy pathway, and metabolism in HCC cells. Conclusions Our findings revealed that MCCC2 plays a critical role in the development of HCC, and the leucine metabolism pathway might be a novel target in HCC treatment.

Leucine Metabolism

Leucine, an essential branched amino acid, has anti-obesity effects on glucose tolerance, lipid metabolism, and insulin sensitivity. The catabolism of Leucine is a conserved regulator of physiological aging, participating in diverse physiological and pathological processes. This topic review offers an up-to-date report on the decomposition and metabolites of leucine in mammals, as α-ketoisocaproate (KIC) and β-hydroxy-β-methylbutyrate (HMB).