l-Leucine influx through Slc7a5 regulates inflammatory responses of human B cells via mammalian target of rapamycin complex 1 signaling

Maternal gut Bifidobacterium breve modifies fetal brain metabolism in germ-free mice

BACKGROUND

Recent advances have significantly expanded our understanding of the gut microbiome's influence on host physiology and metabolism. However, the specific role of certain microorganisms in gestational health and fetal development remains underexplored.

OBJECTIVE

This study investigates the impact of Bifidobacterium breve UCC2003 on fetal brain metabolism when colonized in the maternal gut during pregnancy.

METHODS

Germ-free pregnant mice were colonized with or without B. breve UCC2003 during pregnancy. The metabolic profiles of fetal brains were analyzed, focusing on the presence of key metabolites and the expression of critical metabolic and cellular pathways.

RESULTS

Maternal colonization with B. breve resulted in significant metabolic changes in the fetal brain. Specifically, ten metabolites, including citrate, 3-hydroxyisobutyrate, and carnitine, were reduced in the fetal brain. These alterations were accompanied by increased abundance of transporters involved in glucose and branched-chain amino acid uptake. Furthermore, supplementation with this bacterium was associated with elevated expression of critical metabolic pathways such as PI3K-AKT, AMPK, STAT5, and Wnt-β-catenin signaling, including its receptor Frizzled-7. Additionally, there was stabilization of HIF-2 protein and modifications in genes and proteins related to cellular growth, axogenesis, and mitochondrial function.

CONCLUSIONS

The presence of maternal B. breve during pregnancy plays a crucial role in modulating fetal brain metabolism and growth. These findings suggest that Bifidobacterium could modify fetal brain development, potentially offering new avenues for enhancing gestational health and fetal development through microbiota-targeted interventions.

The significant role of amino acid metabolic reprogramming in cancer

Amino acid metabolism plays a pivotal role in tumor microenvironment, influencing various aspects of cancer progression. The metabolic reprogramming of amino acids in tumor cells is intricately linked to protein synthesis, nucleotide synthesis, modulation of signaling pathways, regulation of tumor cell metabolism, maintenance of oxidative stress homeostasis, and epigenetic modifications. Furthermore, the dysregulation of amino acid metabolism also impacts tumor microenvironment and tumor immunity. Amino acids can act as signaling molecules that modulate immune cell function and immune tolerance within the tumor microenvironment, reshaping the anti-tumor immune response and promoting immune evasion by cancer cells. Moreover, amino acid metabolism can influence the behavior of stromal cells, such as cancer-associated fibroblasts, regulate ECM remodeling and promote angiogenesis, thereby facilitating tumor growth and metastasis. Understanding the intricate interplay between amino acid metabolism and the tumor microenvironment is of crucial significance. Expanding our knowledge of the multifaceted roles of amino acid metabolism in tumor microenvironment holds significant promise for the development of more effective cancer therapies aimed at disrupting the metabolic dependencies of cancer cells and modulating the tumor microenvironment to enhance anti-tumor immune responses and inhibit tumor progression.

Cellular metabolism and hypoxia interfacing with allergic diseases

Allergic diseases display significant heterogeneity in their pathogenesis. Understanding the influencing factors, pathogenesis, and advancing new treatments for allergic diseases is becoming more and more vital as currently, prevalence continues to rise, and mechanisms of allergic diseases are not fully understood. The upregulation of the hypoxia response is linked to an elevated infiltration of activated inflammatory cells, accompanied by elevated metabolic requirements. An enhanced hypoxia response may potentially contribute to inflammation, remodeling, and the onset of allergic diseases. It has become increasingly clear that the process underlying immune and stromal cell activation during allergic sensitization requires well-tuned and dynamic changes in cellular metabolism. The purpose of this review is to examine current perspectives regarding metabolic dysfunction in allergic diseases. In the past decade, new technological platforms such as "omic" techniques have been applied, allowing for the identification of different biomarkers in multiple models ranging from altered lipid species content, increased nutrient transporters, and altered serum amino acids in various allergic diseases. Better understanding, recognition, and integration of these alterations would increase our knowledge of pathogenesis and potentially actuate a novel repertoire of targeted treatment approaches that regulate immune metabolic pathways.

Protein expression of the amino acid transporter SLC7A5 in tumor tissue is prognostic in early-stage colorectal cancer

Proteins overexpressed in early-stage cancers may serve as early diagnosis and prognosis markers as well as targets for cancer therapies. In this study, we examined the expression of an essential amino acid carrier SLC7A5 (LAT1, CD98, or 4F2 light chain) in cancer tissue from two well-annotated cohorts of 575 cases of early-stage and 106 cases of late-stage colorectal cancer patients. Immunohistochemistry showed SLC7A5 overexpression in 72.0% of early-stage and 56.6% of late-stage cases. SLC7A5 expression was not influenced by patient gender, age, location, or mismatch repair status, although it appeared to be slightly less prevalent in tumors of mucinous differentiation or with lymphovascular invasion. Statistical analyses revealed a positive correlation between SLC7A5 overexpression and both overall survival and disease-free survival in early-stage but not late-stage cancers. Co-expression analyses of the TCGA and CPTAC colorectal cancer cohorts identified a network of gene transcripts positively related to SLC7A5, with its heterodimer partner SLC3A2 having the highest co-expression score. Network analysis uncovered the SLC7A network to be significantly associated with ncRNA such as tRNA processing and the mitotic cell cycle. Since SLC7A5 is also a marker of activated lymphocytes such as NK, T, and B lymphocytes, SLC7A5 overexpression in early colorectal cancers might trigger a strong anti-tumor immune response which could results in better clinical outcome. Overall, our study provides clear evidence of differential SLC7A5 expression and its prognostic value for early-stage colorectal cancer, although the understanding of its functions in colorectal tumorigenesis and cancer immunity is currently rather limited and awaits further characterization.

The human LAT1-4F2hc (SLC7A5-SLC3A2) transporter complex: Physiological and pathophysiological implications

LAT1 and 4F2hc form a heterodimeric membrane protein complex, which functions as one of the best characterized amino acid transporters. Since LAT1-4F2hc is required for the efficient uptake of essential amino acids and hormones, it promotes cellular growth, in part, by stimulating mTORC1 (mechanistic target of rapamycin complex 1) signalling and by repressing the integrated stress response (ISR). Gain or loss of LAT1-4F2hc function is associated with cancer, diabetes, and immunological and neurological diseases. Hence, LAT1-4F2hc represents an attractive drug target for disease treatment. Specific targeting of LAT1-4F2hc will be facilitated by the increasingly detailed understanding of its molecular architecture, which provides important concepts for its function and regulation. Here, we summarize (i) structural insights that help to explain how LAT1 and 4F2hc assemble to transport amino acids across membranes, (ii) the role of LAT1-4F2hc in key metabolic signalling pathways, and (iii) how derailing these processes could contribute to diseases.

Amino acid metabolism in immune cells: essential regulators of the effector functions, and promising opportunities to enhance cancer immunotherapy

Amino acids are basic nutrients for immune cells during organ development, tissue homeostasis, and the immune response. Regarding metabolic reprogramming in the tumor microenvironment, dysregulation of amino acid consumption in immune cells is an important underlying mechanism leading to impaired anti-tumor immunity. Emerging studies have revealed that altered amino acid metabolism is tightly linked to tumor outgrowth, metastasis, and therapeutic resistance through governing the fate of various immune cells. During these processes, the concentration of free amino acids, their membrane bound transporters, key metabolic enzymes, and sensors such as mTOR and GCN2 play critical roles in controlling immune cell differentiation and function. As such, anti-cancer immune responses could be enhanced by supplement of specific essential amino acids, or targeting the metabolic enzymes or their sensors, thereby developing novel adjuvant immune therapeutic modalities. To further dissect metabolic regulation of anti-tumor immunity, this review summarizes the regulatory mechanisms governing reprogramming of amino acid metabolism and their effects on the phenotypes and functions of tumor-infiltrating immune cells to propose novel approaches that could be exploited to rewire amino acid metabolism and enhance cancer immunotherapy.

Zonated leucine sensing by Sestrin-mTORC1 in the liver controls the response to dietary leucine

The mechanistic target of rapamycin complex 1 (mTORC1) kinase controls growth in response to nutrients, including the amino acid leucine. In cultured cells, mTORC1 senses leucine through the leucine-binding Sestrin proteins, but the physiological functions and distribution of Sestrin-mediated leucine sensing in mammals are unknown. We find that mice lacking Sestrin1 and Sestrin2 cannot inhibit mTORC1 upon dietary leucine deprivation and suffer a rapid loss of white adipose tissue (WAT) and muscle. The WAT loss is driven by aberrant mTORC1 activity and fibroblast growth factor 21 (FGF21) production in the liver. Sestrin expression in the liver lobule is zonated, accounting for zone-specific regulation of mTORC1 activity and FGF21 induction by leucine. These results establish the mammalian Sestrins as physiological leucine sensors and reveal a spatial organization to nutrient sensing by the mTORC1 pathway.

LAT1, a novel pharmacological target for the treatment of glioblastoma

The L-Type Amino Acid transporter, LAT1 (SLC7A5), has a crucial role in mediating amino acid uptake into the cells, thus modulating cell growth and proliferation as well as other intracellular functions. Different studies have reported a central role of LAT1 in glioblastoma development and progression, suggesting that the modulation of its activity could be a novel therapeutic strategy. LAT1 also has an important role in the peripheral immune system, by regulating the activation status of several immune cells through modulation of the mechanistic target of rapamycin kinase. In glioblastoma (GBM), the blood-brain barrier is disrupted, which allows the recruitment of peripheral immune cells to the tumour site. These cells, together with resident microglia, contribute to cancer growth and progression. Currently, little is known about the function of LAT1 in the reprogramming of the immune component of the tumour microenvironment in the context of GBM. In this article, we review the available data on the role of LAT1 in the regulation of GBM biology, including its potential role in the tumour microenvironment, particularly in infiltrating-peripheral immune cells and resident microglial cells. In addition, we review the available data on the main pharmacological inhibitors of LAT1, aiming to evaluate their possible role as novel therapeutics for GBM.

Neuronal allodynic mechanisms of Slc7a5 (LAT1) in the spared nerve injury rodent model of neuropathic pain

High-impact chronic pain is suffered by 1 in 5 patients in the USA and globally. Effective, non-addictive, non-opioid therapeutics are urgently needed for the treatment of chronic pain. Slc7a5 (Lat1), also known as system L-neutral amino acid transporter, is involved in a number of physiological processes related to inflammation. Transcriptomics studies have shown that Slc7a5 and its binding partner Slc3a2 are expressed in neurons of the dorsal root ganglia (DRG) and spinal dorsal horn, which are critical to the initiation and maintenance of nociception and pathophysiology of chronic pain. In addition, Slc7a5 is a transporter for the first-line anti-allodynic gabapentinoid drugs and binds to ion channels implicated in nociception and chronic pain including the voltage-gated sodium channel Nav1.7 and the voltage-gated potassium channels Kv1.1 and Kv1.2. We found that blocking Slc7a5 with intrathecal administration of the drug JPH203 alleviated allodynia in the spared nerve injury (SNI) rodent model of neuropathic pain. Western blot and immunohistochemistry studies revealed an increase in Slc7a5 protein levels in the spinal cord and DRGs of SNI mice compared to control mice. Using whole-cell current-clamp electrophysiology, we observed that JPH203 treatment reduced excitability of small-diameter (< 30 µm) DRG neurons from SNI mice, in agreement with its behavioral effects. Voltage-clamp recordings from JPH203-treated naïve rat DRGs identified an effect on tetrodotoxin-resistant (TTX-R) sodium currents. Altogether, these results demonstrate that Slc7a5 is dysregulated in chronic neuropathic pain and can be targeted to provide relief of hypersensitivity.

Contribution of LAT1-4F2hc in Urological Cancers via Toll-like Receptor and Other Vital Pathways

Simple Summary

LAT1-4F2hc complex is an important amino acid transporter. It mainly transports specific amino acids through the cell membrane, provides nutrition for cells, and participates in a variety of metabolic pathways. LAT1 plays a role in transporting essential amino acids including leucine, which regulates the mTOR signaling pathway. However, the importance of SLCs is still not well known in the field of urological cancer. Therefore, the purpose of this review is to report the role of the LAT1-4F2hc complex in urological cancers, as well as their clinical significance and application. Moreover, the inhibitor of LAT1-4F2hc complex is a promising direction as a targeted therapy to improve the treatment and prognosis of urological cancers.

Abstract

Tumor cells are known for their ability to proliferate. Nutrients are essential for rapidly growing tumor cells. In particular, essential amino acids are essential for tumor cell growth. Tumor cell growth nutrition requires the regulation of membrane transport proteins. Nutritional processes require amino acid uptake across the cell membrane. Leucine, one of the essential amino acids, has recently been found to be closely associated with cancer, which activate mTOR signaling pathway. The transport of leucine into cells requires an L-type amino acid transporter protein 1, LAT1 (SLC7A5), which requires the 4F2 cell surface antigen heavy chain (4F2hc, SLC3A2) to form a heterodimeric amino acid transporter protein complex. Recent evidence identified 4F2hc as a specific downstream target of the androgen receptor splice variant 7 (AR-V7). We stressed the importance of the LAT1-4F2hc complex as a diagnostic and therapeutic target in urological cancers in this review, which covered the recent achievements in research on the involvement of the LAT1-4F2hc complex in urinary system tumors. In addition, JPH203, which is a selective LAT1 inhibitor, has shown excellent inhibitory effects on the proliferation in a variety of tumor cells. The current phase I clinical trials of JPH203 in patients with biliary tract cancer have also achieved good results, which is the future research direction for LAT1 targeted therapy drugs.

Glutamine promotes the generation of B10+ cells via the mTOR/GSK3 pathway

Alterations in cell metabolism can shift the differentiation of immune cells towards a regulatory or inflammatory phenotype, thus opening up new therapeutic opportunities for immune-related diseases. Indeed, growing knowledge on T cell metabolism has revealed differences in the metabolic programs of suppressive regulatory T cells (Tregs) as compared to inflammatory Th1 and Th17 cells. In addition to Tregs, IL-10-producing regulatory B cells are crucial for maintaining tolerance, inhibiting inflammation and autoimmunity. Yet, the metabolic networks regulating diverse B lymphocyte responses are not well known. Here, we show that glutaminase blockade decreased downstream mTOR activation and attenuated IL-10 secretion. Direct suppression of mTOR activity by rapamycin selectively impaired IL-10 production by B cells whereas secretion was restored upon GSK3 inhibition. Mechanistically, we found mTORC1 activation leads to GSK3 inhibition, identifying a key signalling pathway regulating IL-10 secretion by B lymphocytes. Thus, our results identify glutaminolysis and the mTOR/GSK3 signalling axis, as critical regulators of the generation of IL-10 producing B cells with regulatory functions. This article is protected by copyright. All rights reserved.

L-type amino acid transporter 1 as a target for inflammatory disease and cancer immunotherapy

Ingestion of amino acids is fundamental for cellular activity. Amino acids are important components for protein synthesis but are also crucial for intracellular metabolic reactions and signal transduction. Following activation, immune cells induce metabolic reprogramming to generate adequate energy and constitutive substances. Hence, the delivery of amino acids by transporters is necessary for the progression of metabolic rewiring. In this review, we discuss how amino acids and their transporters regulate immune cell functions, with emphasis on LAT1, a transporter of large neutral amino acids. Furthermore, we explore the possibility of targeting amino acid transporters to improve immune disorders and cancer immune therapies.

Baicalein Delays H2O2-Induced Astrocytic Senescence through Inhibition of Senescence-Associated Secretory Phenotype (SASP), Suppression of JAK2/STAT1/NF-κB Pathway, and Regulation of Leucine Metabolism

Baicalein is an active ingredient extracted from the dried roots of the Scutellaria baicalensis Georgi. It has been demonstrated to improve memory impairment in multiple animal models; however, the underlying mechanisms remain ambiguous. The accumulation of senescent astrocytes and senescence-associated secretory phenotype (SASP) secreted by senescent astrocytes has been deemed as potential contributors to neurodegenerative diseases. Therefore, this study explored the protective effects of baicalein against astrocyte senescence and investigated the molecular mechanisms and metabolic mechanisms of baicalein against astrocyte senescence. Our results demonstrated that treatment with baicalein protects T98G cells from H₂O₂-induced damage, delays cell senescence, inhibits the secretion of SASP (IL-6, IL-8, TNF-α, CXCL1, and MMP-1), and inhibits SASP-related pathways NF-κB and JAK2/STAT1. ¹H NMR metabolomics analysis and correlation analysis revealed that leucine was significantly correlated with SASP factors. Further study demonstrated that supplement with leucine could restrain SASP secretion, and baicalein could significantly increase leucine level through down-regulation of BCAT1 and up-regulation of SLC7A5 expression. The above results revealed that baicalein exerted protective and antisenescence effects in H₂O₂-induced T98G cells possibly through inhibition of SASP, suppression of JAK2/STAT1/NF-κB pathway, and regulation of leucine metabolism. Consistent results were obtained in primary astrocytes of newborn SD rats, which suggests that baicalein significantly increases viabilities, delays senescence, inhibits IL-6 secretion, and increases leucine level in H₂O₂-induced primary astrocytes.

Amino Acid Transporters Are a Vital Focal Point in the Control of mTORC1 Signaling and Cancer

The mechanistic target of rapamycin complex 1 (mTORC1) integrates signals from growth factors and nutrients to control biosynthetic processes, including protein, lipid, and nucleic acid synthesis. Dysregulation in the mTORC1 network underlies a wide array of pathological states, including metabolic diseases, neurological disorders, and cancer. Tumor cells are characterized by uncontrolled growth and proliferation due to a reduced dependency on exogenous growth factors. The genetic events underlying this property, such as mutations in the PI3K-Akt and Ras-Erk signaling networks, lead to constitutive activation of mTORC1 in nearly all human cancer lineages. Aberrant activation of mTORC1 has been shown to play a key role for both anabolic tumor growth and resistance to targeted therapeutics. While displaying a growth factor-independent mTORC1 activity and proliferation, tumors cells remain dependent on exogenous nutrients such as amino acids (AAs). AAs are an essential class of nutrients that are obligatory for the survival of any cell. Known as the building blocks of proteins, AAs also act as essential metabolites for numerous biosynthetic processes such as fatty acids, membrane lipids and nucleotides synthesis, as well as for maintaining redox homeostasis. In most tumor types, mTORC1 activity is particularly sensitive to intracellular AA levels. This dependency, therefore, creates a targetable vulnerability point as cancer cells become dependent on AA transporters to sustain their homeostasis. The following review will discuss the role of AA transporters for mTORC1 signaling in cancer cells and their potential as therapeutic drug targets.

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.

Metabolic Pathways That Control Skin Homeostasis and Inflammation

Keratinocytes and skin immune cells are actively metabolizing nutrients present in their microenvironment. This is particularly important in common chronic inflammatory skin diseases such as psoriasis and atopic dermatitis, characterized by hyperproliferation of keratinocytes and expansion of inflammatory cells, thus suggesting increased cell nutritional requirements. Proliferating inflammatory cells and keratinocytes express high levels of glucose transporter (GLUT)1, l-type amino acid transporter (LAT)1, and cationic amino acid transporters (CATs). Main metabolic regulators such as hypoxia-inducible factor (HIF)-1α, MYC, and mechanistic target of rapamycin (mTOR) control immune cell activation, proliferation, and cytokine release. Here, we provide an updated perspective regarding the potential role of nutrient transporters and metabolic pathways that could be common to immune cells and keratinocytes, to control psoriasis and atopic dermatitis.

Quinolinate as a Marker for Kynurenine Metabolite Formation and the Unresolved Question of NAD+ Synthesis During Inflammation and Infection

Quinolinate (Quin) is a classic example of a biochemical double-edged sword, acting as both essential metabolite and potent neurotoxin. Quin is an important metabolite in the kynurenine pathway of tryptophan catabolism leading to the de novo synthesis of nicotinamide adenine dinucleotide (NAD+). As a precursor for NAD+, Quin can direct a portion of tryptophan catabolism toward replenishing cellular NAD+ levels in response to inflammation and infection. Intracellular Quin levels increase dramatically in response to immune stimulation [e.g., lipopolysaccharide (LPS) or pokeweed mitogen (PWM)] in macrophages, microglia, dendritic cells, and other cells of the immune system. NAD+ serves numerous functions including energy production, the poly ADP ribose polymerization (PARP) reaction involved in DNA repair, and the activity of various enzymes such as the NAD+-dependent deacetylases known as sirtuins. We used highly specific antibodies to protein-coupled Quin to delineate cells that accumulate Quin as a key aspect of the response to immune stimulation and infection. Here, we describe Quin staining in the brain, spleen, and liver after LPS administration to the brain or systemic PWM administration. Quin expression was strong in immune cells in the periphery after both treatments, whereas very limited Quin expression was observed in the brain even after direct LPS injection. Immunoreactive cells exhibited diverse morphology ranging from foam cells to cells with membrane extensions related to cell motility. We also examined protein expression changes in the spleen after kynurenine administration. Acute (8 h) and prolonged (48 h) kynurenine administration led to significant changes in protein expression in the spleen, including multiple changes involved with cytoskeletal rearrangements associated with cell motility. Kynurenine administration resulted in several expression level changes in proteins associated with heat shock protein 90 (HSP90), a chaperone for the aryl-hydrocarbon receptor (AHR), which is the primary kynurenine metabolite receptor. We propose that cells with high levels of Quin are those that are currently releasing kynurenine pathway metabolites as well as accumulating Quin for sustained NAD+ synthesis from tryptophan. Further, we propose that the kynurenine pathway may be linked to the regulation of cell motility in immune and cancer cells.