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1.
Role of the mTOR-autophagy-ER stress pathway in high fructose-induced metabolic-associated fatty liver disease.
Wang, YL, Zhou, X, Li, DL, Ye, JM
Acta pharmacologica Sinica. 2022;(1):10-14
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Abstract
Metabolic-associated fatty liver disease (MAFLD) is the most common metabolic disease with a global prevalence of 25%. While MAFLD is serious and incurable at the later stage, it can be controlled or reversed at the early stage of hepatosteatosis originating from unhealthy diets. Recent laboratory evidence implicates a critical role of the mammalian target of rapamycin (mTOR)-autophagy signaling pathway in the pathogenesis of MAFLD induced by a high-fructose diet mimicking the overconsumption of sugar in humans. This review discusses the possible molecular mechanisms of mTOR-autophagy-endoplasmic reticulum (ER) stress in MAFLD. Based on careful analysis of recent studies, we suggest possible new therapeutic concepts or targets that can be explored for the discovery of new anti-MAFLD drugs.
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2.
Amino Acid-Induced Impairment of Insulin Signaling and Involvement of G-Protein Coupling Receptor.
Zakaria, NF, Hamid, M, Khayat, ME
Nutrients. 2021;(7)
Abstract
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.
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3.
The endolysosomal adaptor PLEKHM1 is a direct target for both mTOR and MAPK pathways.
Gubas, A, Karantanou, C, Popovic, D, Tascher, G, Hoffmann, ME, Platzek, A, Dawe, N, Dikic, I, Krause, DS, McEwan, DG
FEBS letters. 2021;(7):864-880
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Abstract
The lysosome is a cellular signalling hub at the point of convergence of endocytic and autophagic pathways, where the contents are degraded and recycled. Pleckstrin homology domain-containing family member 1 (PLEKHM1) acts as an adaptor to facilitate the fusion of endocytic and autophagic vesicles with the lysosome. However, it is unclear how PLEKHM1 function at the lysosome is controlled. Herein, we show that PLEKHM1 coprecipitates with, and is directly phosphorylated by, mTOR. Using a phosphospecific antibody against Ser432/S435 of PLEKHM1, we show that the same motif is a direct target for ERK2-mediated phosphorylation in a growth factor-dependent manner. This dual regulation of PLEKHM1 at a highly conserved region points to a convergence of both growth factor- and amino acid-sensing pathways, placing PLEKHM1 at a critical juncture of cellular metabolism.
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4.
Crosstalk between the mTOR and DNA Damage Response Pathways in Fission Yeast.
Alao, JP, Legon, L, Rallis, C
Cells. 2021;(2)
Abstract
Cells have developed response systems to constantly monitor environmental changes and accordingly adjust growth, differentiation, and cellular stress programs. The evolutionarily conserved, nutrient-responsive, mechanistic target of rapamycin signaling (mTOR) pathway coordinates basic anabolic and catabolic cellular processes such as gene transcription, protein translation, autophagy, and metabolism, and is directly implicated in cellular and organismal aging as well as age-related diseases. mTOR mediates these processes in response to a broad range of inputs such as oxygen, amino acids, hormones, and energy levels, as well as stresses, including DNA damage. Here, we briefly summarize data relating to the interplays of the mTOR pathway with DNA damage response pathways in fission yeast, a favorite model in cell biology, and how these interactions shape cell decisions, growth, and cell-cycle progression. We, especially, comment on the roles of caffeine-mediated DNA-damage override. Understanding the biology of nutrient response, DNA damage and related pharmacological treatments can lead to the design of interventions towards improved cellular and organismal fitness, health, and survival.
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5.
Unraveling the multifaceted nature of the nuclear function of mTOR.
Torres, AS, Holz, MK
Biochimica et biophysica acta. Molecular cell research. 2021;(2):118907
Abstract
Positioned at the axis between the cell and its environment, mTOR directs a wide range of cellular activity in response to nutrients, growth factors, and stress. Our understanding of the role of mTOR is evolving beyond the spatial confines of the cytosol, and its role in the nucleus becoming ever more apparent. In this review, we will address various studies that explore the role of nuclear mTOR (nmTOR) in specific cellular programs and how these pathways influence one another. To understand the emerging roles of nuclear mTOR, we discuss data and propose plausible mechanisms to offer novel ideas, hypotheses, and future research directions.
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L-Arginine Ameliorates Defective Autophagy in GM2 Gangliosidoses by mTOR Modulation.
Castejón-Vega, B, Rubio, A, Pérez-Pulido, AJ, Quiles, JL, Lane, JD, Fernández-Domínguez, B, Cachón-González, MB, Martín-Ruiz, C, Sanz, A, Cox, TM, et al
Cells. 2021;(11)
Abstract
AIMS: Tay-Sachs and Sandhoff diseases (GM2 gangliosidosis) are autosomal recessive disorders of lysosomal function that cause progressive neurodegeneration in infants and young children. Impaired hydrolysis catalysed by β-hexosaminidase A (HexA) leads to the accumulation of GM2 ganglioside in neuronal lysosomes. Despite the storage phenotype, the role of autophagy and its regulation by mTOR has yet to be explored in the neuropathogenesis. Accordingly, we investigated the effects on autophagy and lysosomal integrity using skin fibroblasts obtained from patients with Tay-Sachs and Sandhoff diseases. RESULTS Pathological autophagosomes with impaired autophagic flux, an abnormality confirmed by electron microscopy and biochemical studies revealing the accelerated release of mature cathepsins and HexA into the cytosol, indicating increased lysosomal permeability. GM2 fibroblasts showed diminished mTOR signalling with reduced basal mTOR activity. Accordingly, provision of a positive nutrient signal by L-arginine supplementation partially restored mTOR activity and ameliorated the cytopathological abnormalities. INNOVATION Our data provide a novel molecular mechanism underlying GM2 gangliosidosis. Impaired autophagy caused by insufficient lysosomal function might represent a new therapeutic target for these diseases. CONCLUSIONS We contend that the expression of autophagy/lysosome/mTOR-associated molecules may prove useful peripheral biomarkers for facile monitoring of treatment of GM2 gangliosidosis and neurodegenerative disorders that affect the lysosomal function and disrupt autophagy.
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The Role of the PI3K/AKT/mTOR Signalling Pathway in Male Reproduction.
Deng, CY, Lv, M, Luo, BH, Zhao, SZ, Mo, ZC, Xie, YJ
Current molecular medicine. 2021;(7):539-548
Abstract
Male fertility is closely related to the normal function of the hypothalamicpituitary- testicular axis. The testis is an important male reproductive organ that secretes androgen and produces sperm through spermatogenesis. Spermatogenesis refers to the process by which spermatogonial stem cells (SSCs) produce highly differentiated spermatozoa and is divided into three stages: mitosis, meiosis and spermiogenesis. Spermatogenesis requires SSCs to strike a proper balance between self-renewal and differentiation and the commitment of spermatocytes to meiosis, which involves many molecules and signalling pathways. Abnormal gene expression or signal transduction in the hypothalamus and pituitary, but particularly in the testis, may lead to spermatogenic disorders and male infertility. The phosphoinositol-3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signalling pathway is involved in many stages of male reproduction, including the regulation of the hypothalamus-pituitarygonad (HPG) axis during spermatogenesis, the proliferation and differentiation of spermatogonia and somatic cells, and the regulation of sperm autophagy and testicular endocrine function in the presence of environmental pollutants, particularly endocrinedisrupting chemicals (EDCs). In the PI3K/AKT/mTOR signalling pathway, mTOR is considered the central integrator of several signals, regulating metabolism, cell growth and proliferation. In particular, mTOR plays an important role in the maintenance and differentiation of SSCs, as well as in regulating the redox balance and metabolic activity of Sertoli cells, which play an important role in nutritional support during spermatogenesis.
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Auxin and Target of Rapamycin Spatiotemporally Regulate Root Organogenesis.
Xie, X, Wang, Y, Datla, R, Ren, M
International journal of molecular sciences. 2021;(21)
Abstract
The programs associated with embryonic roots (ERs), primary roots (PRs), lateral roots (LRs), and adventitious roots (ARs) play crucial roles in the growth and development of roots in plants. The root functions are involved in diverse processes such as water and nutrient absorption and their utilization, the storage of photosynthetic products, and stress tolerance. Hormones and signaling pathways play regulatory roles during root development. Among these, auxin is the most important hormone regulating root development. The target of rapamycin (TOR) signaling pathway has also been shown to play a key role in root developmental programs. In this article, the milestones and influential progress of studying crosstalk between auxin and TOR during the development of ERs, PRs, LRs and ARs, as well as their functional implications in root morphogenesis, development, and architecture, are systematically summarized and discussed.
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Delineating the Smith-Kingsmore syndrome phenotype: Investigation of 16 patients with the MTOR c.5395G > A p.(Glu1799Lys) missense variant.
Poole, RL, Curry, PDK, Marcinkute, R, Brewer, C, Coman, D, Hobson, E, Johnson, D, Lynch, SA, Saggar, A, Searle, C, et al
American journal of medical genetics. Part A. 2021;(8):2445-2454
Abstract
Smith-Kingsmore Syndrome (SKS) is a rare genetic syndrome associated with megalencephaly, a variable intellectual disability, autism spectrum disorder, and MTOR gain of function variants. Only 30 patients with MTOR missense variants are published, including 14 (47%) with the MTOR c.5395G>A p.(Glu1799Lys) variant. Limited phenotypic data impacts the quality of information delivered to families and the robustness of interpretation of novel MTOR missense variation. This study aims to improve our understanding of the SKS phenotype through the investigation of 16 further patients with the MTOR c.5395G>A p.(Glu1799Lys) variant. Through the careful phenotypic evaluation of these 16 patients and integration with data from 14 previously reported patients, we have defined major (100% patients) and frequent (>15%) SKS clinical characteristics and, using these data, proposed guidance for evidence-based management. In addition, in the absence of functional studies, we suggest that the combination of the SKS major clinical features of megalencephaly (where the head circumference is at least 3SD) and an intellectual disability with a de novo MTOR missense variant (absent from population databases) should be considered diagnostic for SKS.
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10.
Protein Phosphorylation Signaling Cascades in Autism: The Role of mTOR Pathway.
Boksha, IS, Prokhorova, TA, Tereshkina, EB, Savushkina, OK, Burbaeva, GS
Biochemistry. Biokhimiia. 2021;(5):577-596
Abstract
The mammalian target of rapamycin (mTOR) signaling pathway is a central regulator of cell metabolism, growth, and survival in response to hormones, growth factors, nutrients, and stress-induced signals. In this review, we analyzed the studies on the molecular abnormalities of the mTOR-associated signaling cascades in autism spectrum disorders (ASDs) and outlined the prospects for the pathogenicity-targeting pharmacotherapeutic approaches to ASDs, in particular syndromic ASDs. Based on available experimental and clinical data, we suggest that very early detection of molecular abnormalities in the ASD risk groups can be facilitated by using peripheral blood platelets. Also, identification of the time window of critical dysregulations in the described pathways in the ASD risk groups might suggest further research directions leading to more efficacious pharmacotherapeutic interventions in ASDs.