Cellular signaling of amino acids towards mTORC1 activation in impaired human leucine catabolism

Overexpression of the LAT1 in primary human trophoblast cells increases the uptake of essential amino acids and activates mTOR signaling

The System L amino acid transporter, particularly the isoform Large Neutral Amino Acid Transporter Small Subunit 1 (LAT1) encoded by SLC7A5, is believed to mediate the transfer of essential amino acids in the human placenta. Placental System L amino acid transporter expression and activity is decreased in pregnancies complicated by IUGR and increased in fetal overgrowth. However, it remains unknown if changes in the expression of LAT1 are mechanistically linked to System L amino acid transport activity. Here, we combined overexpression approaches with protein analysis and functional studies in cultured primary human trophoblast (PHT) cells to test the hypothesis that SLC7A5 overexpression increases the uptake of essential amino acids and activates mTOR signaling in PHT cells. Overexpression of SLC7A5 resulted in a marked increase in protein expression of LAT1 in the PHT cells microvillous plasma membrane and System L amino acid transporter activity. Moreover, mTOR signaling was activated, and System A amino acid transporter activity increased following SLC7A5 overexpression, suggesting coordination of trophoblast amino transporter expression and activity to ensure balanced nutrient flux to the fetus. This is the first report showing that overexpression of LAT1 is sufficient to increase the uptake of essential amino acids in PHT cells, which activates mTOR, a master regulator of placental function. The decreased placental System L activity in human IUGR and the increased placental activity of this transporter system in some cases of fetal overgrowth may directly contribute to changes in fetal amino acid availability and altered fetal growth in these pregnancy complications.

On-chip microfluidic dual detection of amino acid metabolism disorders using cell-free protein synthesis

Various metabolic diseases are associated with the accumulation of specific amino acids due to abnormal metabolic pathways, and thus can be diagnosed by measuring the level of amino acids in body fluids. However, present methods for amino acid analysis are not readily accessible because they require a complex experimental setup, expensive equipment, and a long processing time. Here, we present a dual sensing microfluidic device that enables fast, portable, and quantitative analysis of target amino acids, harnessing the biological mechanism of protein synthesis. In this device, the working principle of a finger-actuated pumping unit is applied, and the microchannels are designed to perform cell-free synthesis of a reporter protein in response to the target amino acids in the assay samples. Multiple steps required for the translational assay are controlled by the simple operation of two pushbuttons on the device. It is demonstrated that the developed microfluidic device provides precise quantification of two amino acids (methionine and phenylalanine) within 30 min at room temperature. We expect that the application of the presented device can be readily extended to the point-of-care testing of other metabolic compounds.

Peripheral tissular analysis of rapamycin's effect as a neuroprotective agent in vivo

Rapamycin is the best-characterized autophagy inducer, which is related to its antiaging and neuroprotective effects. Although rapamycin is an FDA-approved drug for human use in organ transplantation and cancer therapy, its administration as an antiaging and neuroprotective agent is still controversial because of its immunosuppressive and reported side effects. Therefore, it is critical to determine whether the dose that exerts a neuroprotective effect, 35 times lower than that used as an immunosuppressant agent, harms peripheral organs. We validated the rapamycin neuroprotective dosage in a Parkinson's disease (PD) model induced with paraquat. C57BL/6 J mice were treated with intraperitoneal (IP) rapamycin (1 mg/kg) three times per week, followed by paraquat (10 mg/kg) twice per week for 6 weeks, along with rapamycin on alternate days. Rapamycin significantly decreased dopaminergic neuronal loss induced by paraquat. Since rapamycin's neuroprotective effect in a PD model was observed at 7 weeks of treatment; we evaluated its effect on the liver, kidney, pancreas, and spleen. In addition, we prolonged treatment with rapamycin for 14 weeks. Tissue sections were subjected to histochemical, immunodetection, and morphometric analysis. Chronic rapamycin administration does not affect bodyweight, survival, and liver or kidney morphology. Although the pancreas tissular architecture and cellular distribution in Langerhans islets are modified, they may be reversible. The spleen B lymphocyte and macrophage populations were decreased. Notably, the lymphocyte T population was not affected. Therefore, chronic administration of a rapamycin neuroprotective dose does not produce significant tissular alterations. Our findings support the therapeutic potential of rapamycin as a neuroprotective agent.

Mechanismbased role of the intestinal microbiota in gestational diabetes mellitus: A systematic review and meta-analysis

Background

Metabolic disorders caused by intestinal microbial dysregulation are considered to be important causes of gestational diabetes mellitus (GDM). Increasing evidence suggests that the diversity and composition of gut microbes are altered in disease states, yet the critical microbes and mechanisms of disease regulation remain unidentified.

Methods

PubMed^® (National Library of Medicine, Bethesda, MD, USA), Embase^® (Elsevier, Amsterdam, the Netherlands), the Web of Science™ (Clarivate™, Philadelphia, PA, USA), and the Cochrane Library databases were searched to identify articles published between 7 July 2012 and 7 July 2022 reporting on case-control and controlled studies that analyzed differences in enterobacteria between patients with GDM and healthy individuals. Information on the relative abundance of enterobacteria was collected for comparative diversity comparison, and enterobacterial differences were analyzed using random effects to calculate standardized mean differences at a p-value of 5%.

Results

A total of 22 studies were included in this review, involving a total of 965 GDM patients and 1,508 healthy control participants. Alpha diversity did not differ between the participant groups, but beta diversity was significantly different. Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria were the dominant bacteria, but there was no significant difference between the two groups. Qualitative analysis showed differences between the groups in the Firmicutes/Bacteroidetes ratio, Blautia, and Collinsella, but these differences were not statistically different.

Conclusion

Enterobacterial profiles were significantly different between the GDM and non-GDM populations. Alpha diversity in patients with GDM is similar to that in healthy people, but beta diversity is significantly different. Firmicutes/Bacteroidetes ratios were significantly increased in GDM, and this, as well as changes in the abundance of species of Blautia and Collinsella, may be responsible for changes in microbiota diversity. Although the results of our meta-analysis are encouraging, more well-conducted studies are needed to clarify the role of the gut microbiome in GDM. The systematic review was registered with PROSPERO (https://www.crd.york.ac.uk/prospero/) as CRD42022357391.

Amino Acid-Induced Impairment of Insulin Signaling and Involvement of G-Protein Coupling Receptor

Amino acids are needed for general bodily function and well-being. Despite their importance, augmentation in their serum concentration is closely related to metabolic disorder, insulin resistance (IR), or worse, diabetes mellitus. Essential amino acids such as the branched-chain amino acids (BCAAs) have been heavily studied as a plausible biomarker or even a cause of IR. Although there is a long list of benefits, in subjects with abnormal amino acids profiles, some amino acids are correlated with a higher risk of IR. Metabolic dysfunction, upregulation of the mammalian target of the rapamycin (mTOR) pathway, the gut microbiome, 3-hydroxyisobutyrate, inflammation, and the collusion of G-protein coupled receptors (GPCRs) are among the indicators and causes of metabolic disorders generating from amino acids that contribute to IR and the onset of type 2 diabetes mellitus (T2DM). This review summarizes the current understanding of the true involvement of amino acids with IR. Additionally, the involvement of GPCRs in IR will be further discussed in this review.

Chronic everolimus treatment of high-fat diet mice leads to a reduction in obesity but impaired glucose tolerance

Everolimus, which inhibits mTOR kinase activity and is clinically used in graft rejection treatment, may have a two‐sided influence on metabolic syndrome; its role in obesity and hyperglycemic in animals and humans, however, has been explored insufficiently. This study further determined how continual everolimus treatment affects glucose homeostasis and body weight control in C57BL6/J mice with obesity. An obesity mouse model was developed by administering a high‐fat diet (HFD) to C57BL6/J mice over 12 weeks. The experimental group, while continuing their HFD consumption, were administered everolimus daily for 8 weeks. Metabolic parameters, glucose tolerance, fatty liver score, endocrine profile, insulin sensitivity index (ISI), insulin resistance (IR) index, and Akt phosphorylation, GLUT4, TNF‐α, and IL‐1 levels were measured in vivo. Compared with the control group, the everolimus group gained less body weight and had smaller adipocytes and lower fat pad weight; triglyceride (serum and hepatic), patatin‐like phospholipase domain‐containing 3, and fatty acid synthase levels; fatty liver scores; and glucose tolerance test values—all despite consuming more food. However, the everolimus group exhibited decreased ISI and muscle Akt phosphorylation and GLUT4 expression as well as impaired glucose tolerance and serum TNF‐α and IL‐1β levels—even when insulin levels were high. In conclusion, continual everolimus treatment may lead to diabetes with glucose intolerance and IR.

Putative roles of SLC7A5 (LAT1) transporter in pain

Large amino acid transporter 1 (LAT1), also known as SLC7A5, is an essential amino acid transporter that forms a heterodimeric complex with the glycoprotein cell-surface antigen heavy chain (4F2hc (CD98, SLC3A2)). Within nociceptive pathways, LAT1 is expressed in the dorsal root ganglia and spinal cord. Although LAT1 expression is upregulated following spinal cord injury, little is known about LAT1 in neuropathic pain. To date, only circumstantial evidence supports LAT1/4F2hc's role in pain. Notably, LAT1's expression and regulation link it to key cell types and pathways implicated in pain. Transcriptional regulation of LAT1 expression occurs via the Wnt/frizzled/β-catenin signal transduction pathway, which has been shown to be involved in chronic pain. The LAT1/4F2hc complex may also be involved in pain pathways related to T- and B-cells. LAT1's expression induces activation of the mammalian target of rapamycin (mTOR) signaling axis, which is involved in inflammation and neuropathic pain. Similarly, hypoxia and cancer induce activation of hypoxia-inducible factor 2 alpha, promoting not only LAT1's expression but also mTORC1's activation. Perhaps the strongest evidence linking LAT1 to pain is its interactions with key voltage-gated ion channels connected to nociception, namely the voltage-gated potassium channels Kv1.1 and Kv1.2 and the voltage-gated sodium channel Nav1.7. Through functional regulation of these channels, LAT1 may play a role in governing the excitatory to inhibitory ratio which is altered in chronic neuropathic pain states. Remarkably, the most direct role for LAT1 in pain is to mediate the influx of gabapentin and pregabalin, two first-line neuropathic pain drugs, that indirectly inhibit high voltage-activated calcium channel auxiliary subunit α2δ-1. In this review, we discuss the expression, regulation, relevant signaling pathways, and protein interactions of LAT1 that may link it to the development and/or maintenance of pain. We hypothesize that LAT1 expressed in nociceptive pathways may be a viable new target in pain.

Targeting mTOR in Acute Lymphoblastic Leukemia

Acute Lymphoblastic Leukemia (ALL) is an aggressive hematologic disorder and constitutes approximately 25% of cancer diagnoses among children and teenagers. Pediatric patients have a favourable prognosis, with 5-years overall survival rates near 90%, while adult ALL still correlates with poorer survival. However, during the past few decades, the therapeutic outcome of adult ALL was significantly ameliorated, mainly due to intensive pediatric-based protocols of chemotherapy. Mammalian (or mechanistic) target of rapamycin (mTOR) is a conserved serine/threonine kinase belonging to the phosphatidylinositol 3-kinase (PI3K)-related kinase family (PIKK) and resides in two distinct signalling complexes named mTORC1, involved in mRNA translation and protein synthesis and mTORC2 that controls cell survival and migration. Moreover, both complexes are remarkably involved in metabolism regulation. Growing evidence reports that mTOR dysregulation is related to metastatic potential, cell proliferation and angiogenesis and given that PI3K/Akt/mTOR network activation is often associated with poor prognosis and chemoresistance in ALL, there is a constant need to discover novel inhibitors for ALL treatment. Here, the current knowledge of mTOR signalling and the development of anti-mTOR compounds are documented, reporting the most relevant results from both preclinical and clinical studies in ALL that have contributed significantly into their efficacy or failure.

Exosomes of pasteurized milk: potential pathogens of Western diseases

Milk consumption is a hallmark of western diet. According to common believes, milk consumption has beneficial effects for human health. Pasteurization of cow's milk protects thermolabile vitamins and other organic compounds including bioactive and bioavailable exosomes and extracellular vesicles in the range of 40-120 nm, which are pivotal mediators of cell communication via systemic transfer of specific micro-ribonucleic acids, mRNAs and regulatory proteins such as transforming growth factor-β. There is compelling evidence that human and bovine milk exosomes play a crucial role for adequate metabolic and immunological programming of the newborn infant at the beginning of extrauterine life. Milk exosomes assist in executing an anabolic, growth-promoting and immunological program confined to the postnatal period in all mammals. However, epidemiological and translational evidence presented in this review indicates that continuous exposure of humans to exosomes of pasteurized milk may confer a substantial risk for the development of chronic diseases of civilization including obesity, type 2 diabetes mellitus, osteoporosis, common cancers (prostate, breast, liver, B-cells) as well as Parkinson's disease. Exosomes of pasteurized milk may represent new pathogens that should not reach the human food chain.

Aspects of Newborn Screening in Isovaleric Acidemia

Isovaleric acidemia (IVA), an inborn error of leucine catabolism, is caused by mutations in the isovaleryl-CoA dehydrogenase (IVD) gene, resulting in the accumulation of derivatives of isovaleryl-CoA including isovaleryl (C5)-carnitine, the marker metabolite used for newborn screening (NBS). The inclusion of IVA in NBS programs in many countries has broadened knowledge of the variability of the condition, whereas prior to NBS, two distinct clinical phenotypes were known, an "acute neonatal" and a "chronic intermittent" form. An additional biochemically mild and potentially asymptomatic form of IVA and its association with a common missense mutation, c.932C>T (p.A282V), was discovered in subjects identified through NBS. Deficiency of short/branched chain specific acyl-CoA dehydrogenase (2-methylbutyryl-CoA dehydrogenase), a defect of isoleucine degradation whose clinical significance remains unclear, also results in elevated C5-carnitine, and may therefore be detected by NBS for IVA. Treatment strategies for the long-term management of symptomatic IVA comprise the prevention of catabolism, dietary restriction of natural protein or leucine intake, and supplementation with l-carnitine and/or l-glycine. Recommendations on how to counsel and manage individuals with the mild phenotype detected by NBS are required.

Effect of light-load resistance exercise on postprandial amino acid transporter expression in elderly men

An impaired amino acid sensing is associated with age‐related loss of skeletal muscle mass. We tested whether light‐load resistance exercise (LL‐RE) affects postprandial amino acid transporter (AAT) expression in aging skeletal muscle. Untrained, healthy men (age: +65 years) were subjected to 13 h of supine rest. After 2 1/2 h of rest, unilateral LL‐RE was conducted (leg extensions, 10 sets of 36 repetitions) at 16% 1RM. Thereafter, the subjects were randomized into groups that orally ingested 40 g of whey protein either as hourly drinks (4 g per drink) (PULSE, N = 10) or two boluses (28 g at 0 h and 12 g at 7 h) (BOLUS, N = 10), or hourly isocaloric maltodextrin drinks (placebo, N = 10). Quadriceps muscle biopsies were taken at 0, 3, 7, and 10 h postexercise from both the resting and exercised leg, from which the membrane protein and mRNA expression of select AATs were analyzed by Western Blot and RT‐PCR, respectively. LAT1 and PAT1 protein expression increased in response to LL‐RE in the PULSE group, and SNAT2 and PAT1 protein expression increased in the BOLUS group when plasma BCAA concentration was low. In all three groups, LL‐RE increased LAT1 mRNA expression, whereas a time course decrease in SNAT2 mRNA expression was observed. LL‐RE increased membrane‐associated AAT protein expression and mRNA expression. Altered AAT protein expression was only seen in groups that ingested whey protein, with the greatest effect observed after hourly feeding. This points toward an importance of AATs in the anabolic response following LL‐RE and protein intake.

Roles of Mitogen-Activating Protein Kinase Kinase Kinase Kinase-3 (MAP4K3) in Preterm Skeletal Muscle Satellite Cell Myogenesis and Mammalian Target of Rapamycin Complex 1 (mTORC1) Activation Regulation

Background

Preterm skeletal muscle genesis is a paradigm for myogenesis. The role of mitogen-activating protein kinase kinase kinase kinase-3 (MAP4K3) in preterm skeletal muscle satellite cells myogenesis or its relationship to mammalian target of rapamycin complex 1 (mTORC1) activity have not been previously elaborated.

Material/Methods

Small interfering RNA (siRNA) interference technology was used to inhibit MAP4K3 expression. Leucine stimulation experiments were performed following MAP4K3-siRNA interference. The differentiation of primary preterm skeletal muscle satellite cells was observed after siRNA-MAP4K3 interference. Western blot analysis was used to determine the expression of MAP4K3, MyHC, MyoD, myogenin, p-mTOR, and p-S6K1. The immunofluorescence fusion index of MyHC and myogenin were detected. MAP4K3 effects on preterm rat satellite cells differentiation and its relationship to mTORC1 activity are reported.

Results

MAP4K3 siRNA knockdown inhibited myotube formation and both MyoD and myogenin expression in primary preterm rat skeletal muscle satellite cells, but MAP4K3 siRNA had no effect on the activity of mTORC1. In primary preterm rat skeletal muscle satellite cells, MAP4K3 knockdown resulted in significantly weaker, but not entirely blunted, leucine-induced mTORC1 signaling.

Conclusions

MAP4K3 positively regulates preterm skeletal muscle satellite cell myogenesis, but may not regulate mTORC1 activity. MAP4K3 may play a role in mTORC1 full activation in response to leucine.

Recurrent background mutations in WHI2 impair proteostasis and degradation of misfolded cytosolic proteins in Saccharomyces cerevisiae

Proteostasis promotes viability at both the cellular and organism levels by maintaining a functional proteome. This requires an intricate protein quality control (PQC) network that mediates protein folding by molecular chaperones and removes terminally misfolded proteins via the ubiquitin proteasome system and autophagy. How changes within the PQC network can perturb proteostasis and shift the balance between protein folding and proteolysis remain poorly understood. However, given that proteostasis is altered in a number of conditions such as cancer and ageing, it is critical that we identify the factors that mediate PQC and understand the interplay between members of the proteostatic network. In this study, we investigated the degradation of a thermally unstable cytosolic model substrate and identified a surprisingly high number of strains in the yeast knockout collection that displayed impaired turnover of the misfolded substrate. We found that this phenotype was caused by frequent background mutations in the general stress response gene WHI2. We linked this proteostatic defect to the lack of activity of the stress response transcription factor Msn2, potentially under conditions where the TOR pathway is active. Our results underscore how changes to the elaborate PQC network can perturb proteostasis and impair degradation of misfolded cytosolic proteins.

Analysis of Sub-Lethal Toxicity of Perfluorooctane Sulfonate (PFOS) to Daphnia magna Using ¹H Nuclear Magnetic Resonance-Based Metabolomics

¹H nuclear magnetic resonance (NMR)-based metabolomics was used to characterize the response of Daphnia magna after sub-lethal exposure to perfluorooctane sulfonate (PFOS), a commonly found environmental pollutant in freshwater ecosystems. Principal component analysis (PCA) scores plots showed significant separation in the exposed samples relative to the controls. Partial least squares (PLS) regression analysis revealed a strong linear correlation between the overall metabolic response and PFOS exposure concentration. More detailed analysis showed that the toxic mode of action is metabolite-specific with some metabolites exhibiting a non-monotonic response with higher PFOS exposure concentrations. Our study indicates that PFOS exposure disrupts various energy metabolism pathways and also enhances protein degradation. Overall, we identified several metabolites that are sensitive to PFOS exposure and may be used as bioindicators of D. magna health. In addition, this study also highlights the important utility of environmental metabolomic methods when attempting to elucidate acute and sub-lethal pollutant stressors on keystone organisms such as D. magna.

Leucine alleviates dexamethasone-induced suppression of muscle protein synthesis via synergy involvement of mTOR and AMPK pathways

Both mTOR and AMPK pathways are involved in the DEX-induced suppression of protein synthesis in muscle cells. Leucine supplementation relieves DEX-induced inhibition on protein synthesis by evoking mTOR and suppressing AMPK pathway.

Glucocorticoids (GCs) are negative muscle protein regulators that contribute to the whole-body catabolic state during stress. Mammalian target of rapamycin (mTOR)-signalling pathway, which acts as a central regulator of protein metabolism, can be activated by branched-chain amino acids (BCAA). In the present study, the effect of leucine on the suppression of protein synthesis induced by GCs and the pathway involved were investigated. In vitro experiments were conducted using cultured C2C12 myoblasts to study the effect of GCs on protein synthesis, and the involvement of mTOR pathway was investigated as well. After exposure to dexamethasone (DEX, 100 μmol/l) for 24 h, protein synthesis in muscle cells was significantly suppressed (P<0.05), the phosphorylations of mTOR, ribosomal protein S6 protein kinase 1 (p70s6k1) and eukaryotic initiation factor 4E binding protein 1 (4EBP1) were significantly reduced (P<0.05). Leucine supplementation (5 mmol/l, 10 mmol/l and 15 mmol/l) for 1 h alleviated the suppression of protein synthesis induced by DEX (P<0.05) and was accompanied with the increased phosphorylation of mTOR and decreased phosphorylation of AMPK (P<0.05). Branched-chain amino transferase 2 (BCAT2) mRNA level was not influenced by DEX (P>0.05) but was increased by leucine supplementation at a dose of 5 mmol/l (P<0.05).

Metabolomics in rheumatic diseases: desperately seeking biomarkers

Metabolomics enables the profiling of large numbers of small molecules in cells, tissues and biological fluids. These molecules, which include amino acids, carbohydrates, lipids, nucleotides and their metabolites, can be detected quantitatively. Metabolomic methods, often focused on the information-rich analytical techniques of NMR spectroscopy and mass spectrometry, have potential for early diagnosis, monitoring therapy and defining disease pathogenesis in many therapeutic areas, including rheumatic diseases. By performing global metabolite profiling, also known as untargeted metabolomics, new discoveries linking cellular pathways to biological mechanisms are being revealed and are shaping our understanding of cell biology, physiology and medicine. These pathways can potentially be targeted to diagnose and treat patients with immune-mediated diseases.

mTORC1 is involved in the regulation of branched-chain amino acid catabolism in mouse heart

The branched‐chain α‐ketoacid dehydrogenase (BCKDH) complex regulates branched‐chain amino acid (BCAA) catabolism by controlling the second step of this catabolic pathway. In the present study, we examined the in vivo effects of treatment with an mTORC1 inhibitor, rapamycin, on cardiac BCKDH complex activity in mice. Oral administration of leucine in control mice significantly activated the cardiac BCKDH complex with an increase in cardiac concentrations of leucine and α‐ketoisocaproate. However, rapamycin treatment significantly suppressed the leucine‐induced activation of the complex despite similar increases in cardiac leucine and α‐ketoisocaproate levels. Rapamycin treatment fully inhibited mTORC1 activity, measured by the phosphorylation state of ribosomal protein S6 kinase 1. These results suggest that mTORC1 is involved in the regulation of cardiac BCAA catabolism.

Regulation of autophagy by amino acids and MTOR-dependent signal transduction

Amino acids not only participate in intermediary metabolism but also stimulate insulin-mechanistic target of rapamycin (MTOR)-mediated signal transduction which controls the major metabolic pathways. Among these is the pathway of autophagy which takes care of the degradation of long-lived proteins and of the elimination of damaged or functionally redundant organelles. Proper functioning of this process is essential for cell survival. Dysregulation of autophagy has been implicated in the etiology of several pathologies. The history of the studies on the interrelationship between amino acids, MTOR signaling and autophagy is the subject of this review. The mechanisms responsible for the stimulation of MTOR-mediated signaling, and the inhibition of autophagy, by amino acids have been studied intensively in the past but are still not completely clarified. Recent developments in this field are discussed.

Milk--A Nutrient System of Mammalian Evolution Promoting mTORC1-Dependent Translation

Based on own translational research of the biochemical and hormonal effects of cow's milk consumption in humans, this review presents milk as a signaling system of mammalian evolution that activates the nutrient-sensitive kinase mechanistic target of rapamycin complex 1 (mTORC1), the pivotal regulator of translation. Milk, a mammary gland-derived secretory product, is required for species-specific gene-nutrient interactions that promote appropriate growth and development of the newborn mammal. This signaling system is highly conserved and tightly controlled by the lactation genome. Milk is sufficient to activate mTORC1, the crucial regulator of protein, lipid, and nucleotide synthesis orchestrating anabolism, cell growth and proliferation. To fulfill its mTORC1-activating function, milk delivers four key metabolic messengers: (1) essential branched-chain amino acids (BCAAs); (2) glutamine; (3) palmitic acid; and (4) bioactive exosomal microRNAs, which in a synergistical fashion promote mTORC1-dependent translation. In all mammals except Neolithic humans, postnatal activation of mTORC1 by milk intake is restricted to the postnatal lactation period. It is of critical concern that persistent hyperactivation of mTORC1 is associated with aging and the development of age-related disorders such as obesity, type 2 diabetes mellitus, cancer, and neurodegenerative diseases. Persistent mTORC1 activation promotes endoplasmic reticulum (ER) stress and drives an aimless quasi-program, which promotes aging and age-related diseases.

Elevated Serum MicroRNA Let-7c in Moyamoya Disease

BACKGROUND

Few studies have examined the relationship between mircroRNAs and moyamoya disease (MMD). We performed a study of the significance of let-7c expression in the serum of MMD patients.

METHODS

The experimental group includes 49 MMD patients, and the control group consists of 30 normal people, 20 cerebral hemorrhage patients, 20 massive cerebral infarction patients, 20 nonmassive cerebral infarction patients, and 20 neurological autoimmune disease patients. Let-7 family levels were determined by polymerase chain reaction. A dual luciferase assay was used to test whether let-7c recognized the 3'UTR of RNF213.

RESULTS

The expression level of let-7c in MMD patients is higher than that observed in the control groups (P < .001). The luciferase assay results indicated that hsa-let-7c could diminish luciferase activity from a reporter vector containing the 3'-UTR of RNF213 (P < .05). The suppression of luciferase activity is not found in mutRNF213 (P > .05).

CONCLUSIONS

Increased expression of let-7c in MMD patients may contribute to MMD pathogenesis by targeting RNF213. Thus, let-7c may be a potential biomarker for the diagnosis of MMD.

Environmental and metabolic sensors that control T cell biology

The T lymphocyte response to pathogens is shaped by the microenvironment. Environmental sensors in T cells include the nutrient-sensing serine/threonine kinases, adenosine monophosphate-activated protein kinase and mammalian target of rapamycin complex 1. Other environmental sensors are transcription factors such as hypoxia-inducible factor-1 and the aryl hydrocarbon receptor. The present review explores the molecular basis for the impact of environmental signals on the differentiation of conventional T cell receptor αβ T cells and how the T cell response to immune stimuli can coordinate the T cell response to environmental cues.

A bifunctional protein regulates mitochondrial protein synthesis

Mitochondrial gene expression is predominantly regulated at the post-transcriptional level and mitochondrial ribonucleic acid (RNA)-binding proteins play a key role in RNA metabolism and protein synthesis. The AU-binding homolog of enoyl-coenzyme A (CoA) hydratase (AUH) is a bifunctional protein with RNA-binding activity and a role in leucine catabolism. AUH has a mitochondrial targeting sequence, however, its role in mitochondrial function has not been investigated. Here, we found that AUH localizes to the inner mitochondrial membrane and matrix where it associates with mitochondrial ribosomes and regulates protein synthesis. Decrease or overexpression of the AUH protein in cells causes defects in mitochondrial translation that lead to changes in mitochondrial morphology, decreased mitochondrial RNA stability, biogenesis and respiratory function. Because of its role in leucine metabolism, we investigated the importance of the catalytic activity of AUH and found that it affects the regulation of mitochondrial translation and biogenesis in response to leucine.

The catalytic subunit of the system L1 amino acid transporter (slc7a5) facilitates nutrient signalling in mouse skeletal muscle

The System L1-type amino acid transporter mediates transport of large neutral amino acids (LNAA) in many mammalian cell-types. LNAA such as leucine are required for full activation of the mTOR-S6K signalling pathway promoting protein synthesis and cell growth. The SLC7A5 (LAT1) catalytic subunit of high-affinity System L1 functions as a glycoprotein-associated heterodimer with the multifunctional protein SLC3A2 (CD98). We generated a floxed Slc7a5 mouse strain which, when crossed with mice expressing Cre driven by a global promoter, produced Slc7a5 heterozygous knockout (Slc7a5+/−) animals with no overt phenotype, although homozygous global knockout of Slc7a5 was embryonically lethal. Muscle-specific (MCK Cre-mediated) Slc7a5 knockout (MS-Slc7a5-KO) mice were used to study the role of intracellular LNAA delivery by the SLC7A5 transporter for mTOR-S6K pathway activation in skeletal muscle. Activation of muscle mTOR-S6K (Thr389 phosphorylation) in vivo by intraperitoneal leucine injection was blunted in homozygous MS-Slc7a5-KO mice relative to wild-type animals. Dietary intake and growth rate were similar for MS-Slc7a5-KO mice and wild-type littermates fed for 10 weeks (to age 120 days) with diets containing 10%, 20% or 30% of protein. In MS-Slc7a5-KO mice, Leu and Ile concentrations in gastrocnemius muscle were reduced by ∼40% as dietary protein content was reduced from 30 to 10%. These changes were associated with >50% decrease in S6K Thr389 phosphorylation in muscles from MS-Slc7a5-KO mice, indicating reduced mTOR-S6K pathway activation, despite no significant differences in lean tissue mass between groups on the same diet. MS-Slc7a5-KO mice on 30% protein diet exhibited mild insulin resistance (e.g. reduced glucose clearance, larger gonadal adipose depots) relative to control animals. Thus, SLC7A5 modulates LNAA-dependent muscle mTOR-S6K signalling in mice, although it appears non-essential (or is sufficiently compensated by e.g. SLC7A8 (LAT2)) for maintenance of normal muscle mass.

Role of amino acid transporters in amino acid sensing

Amino acid (AA) transporters may act as sensors, as well as carriers, of tissue nutrient supplies. This review considers recent advances in our understanding of the AA-sensing functions of AA transporters in both epithelial and nonepithelial cells. These transporters mediate AA exchanges between extracellular and intracellular fluid compartments, delivering substrates to intracellular AA sensors. AA transporters on endosomal (eg, lysosomal) membranes may themselves function as intracellular AA sensors. AA transporters at the cell surface, particularly those for large neutral AAs such as leucine, interact functionally with intracellular nutrient-signaling pathways that regulate metabolism: for example, the mammalian target of rapamycin complex 1 (mTORC1) pathway, which promotes cell growth, and the general control non-derepressible (GCN) pathway, which is activated by AA starvation. Under some circumstances, upregulation of AA transporter expression [notably a leucine transporter, solute carrier 7A5 (SLC7A5)] is required to initiate AA-dependent activation of the mTORC1 pathway. Certain AA transporters may have dual receptor-transporter functions, operating as "transceptors" to sense extracellular (or intracellular) AA availability upstream of intracellular signaling pathways. New opportunities for nutritional therapy may include targeting of AA transporters (or mechanisms that upregulate their expression) to promote protein-anabolic signals for retention or recovery of lean tissue mass.

Control of amino-acid transport by antigen receptors coordinates the metabolic reprogramming essential for T cell differentiation

T lymphocytes must regulate nutrient uptake to meet the metabolic demands of an immune response. Here we show that the intracellular supply of large neutral amino acids (LNAAs) in T cells was regulated by pathogens and the T cell antigen receptor (TCR). T cells responded to antigen by upregulating expression of many amino-acid transporters, but a single System L ('leucine-preferring system') transporter, Slc7a5, mediated uptake of LNAAs in activated T cells. Slc7a5-null T cells were unable to metabolically reprogram in response to antigen and did not undergo clonal expansion or effector differentiation. The metabolic catastrophe caused by loss of Slc7a5 reflected the requirement for sustained uptake of the LNAA leucine for activation of the serine-threonine kinase complex mTORC1 and for expression of the transcription factor c-Myc. Control of expression of the System L transporter by pathogens is thus a critical metabolic checkpoint for T cells.

Effects of a leucine and pyridoxine-containing nutraceutical on body weight and composition in obese subjects

BACKGROUND

We recently demonstrated leucine to modulate energy partitioning between adipose tissue and muscle. Further, leucine exhibits a synergy with B6, resulting in reduced adipocyte lipid storage coupled with increased muscle fat oxidation. Accordingly, a nutraceutical (NuShape™) containing 2.25 g leucine and 30 mg B6 increased fat oxidation by >30 g/day in a 28-day randomized controlled trial. The present study evaluated the long-term efficacy of this combination in modulating body weight and composition.

METHODS

Two 24-week, placebo-controlled, randomized trials, one with weight maintenance (n = 20) and one hypocaloric (-500 kcal/day; n = 24), were conducted using the nutraceutical Nushape in obese subjects.

RESULTS

The supplement resulted in fat loss in the maintenance study (-1.12 ± 0.36 and -1.82 ± 0.70 kg at 12 and 24 weeks, P < 0.01 versus placebo) while no change was found in the placebo group. In the hypocaloric study, the supplement group lost up to twice as much weight (6.18 ± 1.02 versus 3.40 ± 0.81 kg at 12 weeks and 8.15 ± 1.33 versus 5.25 ± 1.13 kg at 24 weeks, P < 0.01) and fat (4.96 ± 0.61 versus 2.31 ± 0.53 kg at 12 weeks and 7.00 ± 0.95 versus 4.22 ± 0.74 kg at 24 weeks, P < 0.01) than the placebo group.

CONCLUSION

This nutraceutical combination results in significant fat loss in the absence of caloric restriction and markedly enhances weight and fat loss by 50%-80% over a 24-week period.