mTOR signalling: jack-of-all-trades 1

Tongguan capsule for treating myocardial ischemia-reperfusion injury: integrating network pharmacology and mechanism study

CONTEXT

Although Tongguan capsule (TGC) is used in the treatment of coronary atherosclerotic disease, the exact mechanism remains unclear.

OBJECTIVE

Network pharmacology and experimental validation were applied to examine the mechanism of TGC for treating myocardial ischemia-reperfusion injury (MIRI).

MATERIALS AND METHODS

The components and candidate targets were searched based on various databases such as TCMSP, TCMID, BATMAN-TCM. The binding ability was determined by molecular docking. The ischemia-reperfusion (I/R) model was constructed by ligating the left anterior descending (LAD) coronary artery. APOE^-/- mice were divided into three groups (n = 6): Sham group, I/R group, and TGC group (1 g/kg/d). To further verification, HCAEC cells were subjected to hypoxia-reoxygenation (H/R) to establish in vitro model.

RESULTS

The compounds, such as quercetin, luteolin, tanshinone IIA, kaempferol and bifendate, were obtained after screening. The affinity values of the components with GSK-3β, mTOR, Beclin-1, and LC3 were all <-5 kcal/mol. In vivo, TGC improved LVEF and FS, reducing infarct size. In vitro, Hoechst 33258 staining result showed TGC inhibited apoptosis. Compare with the H/R model, TGC treatment increased the levels of GSK-3β, LC3, and Beclin1, while decreasing the expression of mTOR and p62 (p < 0.05).

DISCUSSION AND CONCLUSION

The findings revealed that TGC exerted a cardioprotective effect by up regulating autophagy-related proteins through the mTOR pathway, which may be a therapeutic option for MIRI. However, there are still some limitations in this research. It is necessary to search more databases to obtain information and further demonstrated through randomized controlled trials for generalization.

Bcl-3 regulates T cell function through energy metabolism

BACKGROUND

Bcl-3 is a member of the IκB protein family and an essential modulator of NF-κB activity. It is well established that Bcl-3 is critical for the normal development, survival and differentiation of adaptive immune cells, especially T cells. However, the regulation of immune cell function by Bcl-3 through metabolic pathways has rarely been studied.

RESULTS

In this study, we explored the role of Bcl-3 in the metabolism and function of T cells via the mTOR pathway. We verified that the proliferation of Bcl-3-deficient Jurkat T cells was inhibited, but their activation was promoted, and Bcl-3 depletion regulated cellular energy metabolism by reducing intracellular ATP and ROS production levels and mitochondrial membrane potential. Bcl-3 also regulates cellular energy metabolism in naive CD4+ T cells. In addition, the knockout of Bcl-3 altered the expression of mTOR, Akt, and Raptor, which are metabolism-related genes, in Jurkat cells.

CONCLUSIONS

This finding indicates that Bcl-3 may mediate the energy metabolism of T cells through the mTOR pathway, thereby affecting their function. Overall, we provide novel insights into the regulatory role of Bcl-3 in T-cell energy metabolism for the prevention and treatment of immune diseases.

The Role of Retinal Pigment Epithelial Cells in Age-Related Macular Degeneration: Phagocytosis and Autophagy

Age-related macular degeneration (AMD) causes vision loss in the elderly population. Dry AMD leads to the formation of Drusen, while wet AMD is characterized by cell proliferation and choroidal angiogenesis. The retinal pigment epithelium (RPE) plays a key role in AMD pathogenesis. In particular, helioreceptor renewal depends on outer segment phagocytosis of RPE cells, while RPE autophagy can protect cells from oxidative stress damage. However, when the oxidative stress burden is too high and homeostasis is disturbed, the phagocytosis and autophagy functions of RPE become damaged, leading to AMD development and progression. Hence, characterizing the roles of RPE cell phagocytosis and autophagy in the pathogenesis of AMD can inform the development of potential therapeutic targets to prevent irreversible RPE and photoreceptor cell death, thus protecting against AMD.

Swainsonine-induced vacuolar degeneration is regulated by mTOR-mediated autophagy in HT22 cells

The indolizidine alkaloid, swainsonine (SW), is the main toxic component of locoweed, which can cause locoism in animals with characteristic neurological dysfunction. Pathological manifestations at cellular level include extensive vacuolar degeneration. Studies have shown that SW can induces autophagy, but the role and mechanism of autophagy in SW-induced vacuolar degeneration is unclear. In this study, we analyzed the role of autophagy in SW-induced cell injury in mouse hippocampal neurons cell line (HT22) using western blotting, qRT-PCR, transmission electron microscopy and immunofluorescence microscopy. The results showed that the expressions of LC3-II, ATG5, Beclin1 and p62 proteins and their mRNAs in HT22 cells were induced by SW treatment. The SW treatment increased the number of autophagosomes with enhanced fluorescence intensity of monodansylcadaverine (MDC) and LC3-II in a time-dose dependent manner. The results of lysosome staining showed that SW could increase the number of lysosomes, increase the intraluminal pH. Transmission electron microscopy results indicate that SW induced autophagosomes, and Baf A1 could effectively alleviate SW-induced vacuolar degeneration. At the molecular level, SW treatment inhibited the expression of p-PI3K, p-AKT, p-ERK, p-AMPK, p-mTOR, p-p70S6K and p-4EBP1 and promoted the expression of p53. Our results collectively suggest, PI3K/AKT/mTOR, ERK/mTOR and p53/mTOR signaling pathways are involved in the regulation of SW-induced autophagy in HT22 cells, while the AMPK/mTOR signaling pathway is not involved in this regulation. Inhibition of autophagic degradation can effectively alleviate SW-induced vacuolar degeneration.

Effective-compounds of Jinshui Huanxian formula ameliorates fibroblast activation in pulmonary fibrosis by inhibiting the activation of mTOR signaling

BACKGROUND

Jinshui Huanxian formula (JHF) ameliorates idiopathic pulmonary fibrosis patients. Active compounds, including icariin, isoliquiritigenin, nobiletin, peimine, and paeoniflorin, deriving from JHF were combined as effective-component compatibility ECC of JHF II (ECC-JHF II), which is an effective therapeutic strategy for pulmonary fibrosis (PF) induced by bleomycin (BLM) in rats.

PURPOSE

This study aimed to explore the underlying mechanism of ECC-JHF II on pulmonary fibrosis.

METHODS

A model of PF in rats was established through intratracheal instillation of BLM. Pulmonary function, pathological changes, and collagen deposition were examined. The gene and protein expressions in fibroblast activation were detected by quantitative real-time PCR and western blotting respectively.

RESULTS

ECC-JHF II significantly improved BLM-induced PF in rats, manifested as decreased collagen deposition, reduced pathological damage and improved pulmonary function. Furthermore, ECC-JHF II inhibited fibroblast activation by reducing the expression of α-smooth muscle actin (α-SMA) and fibronectin. We analyzed the targets of ECC-JHF II and differentially expressed genes (DEGs) of fibroblast activation induced by transforming growth factor-β1 (TGF-β1) and found that ECC-JHF II might regulate fibroblast activation by EGFR, PI3K-Akt or mTOR signaling pathway. In vitro experiments, we also found that ECC-JHF II suppressed the mTOR pathway, such as downregulating the phosphorylation levels of p70S6K in fibroblast activation induced by TGF-β1. After activating mTOR signaling, the inhibition of ECC-JHF II on fibroblast activation was blocked. These results suggested that ECC-JHF II potently ameliorated pulmonary fibrosis in rats and effectively suppressed fibroblast activation by interfering with mTOR signaling.

CONCLUSION

We combined transcriptomics with the network analysis to predict the mechanism underlying ECC-JHF II suppression of fibroblast activation. In summary, ECC-JHF II improved BLM-induced pulmonary fibrosis, which might be associated with the suppression of fibroblast activation by inhibiting the mTOR signaling.

The role of the mTOR pathway in diabetic retinopathy

The retina, the part of the eye, translates the light signal into an electric current that can be sent to the brain as visual information. To achieve this, the retina requires fine-tuned vascularization for its energy supply. Diabetic retinopathy (DR) causes alterations in the eye vascularization that reduce the oxygen supply with consequent retinal neurodegeneration. During DR, the mammalian target of rapamycin (mTOR) pathway seems to coordinate retinal neurodegeneration with multiple anabolic and catabolic processes, such as autophagy, oxidative stress, cell death, and the release of pro-inflammatory cytokines, which are closely related to chronic hyperglycemia. This review outlines the normal anatomy of the retina and how hyperglycemia can be involved in the neurodegeneration underlying this disease through over activation or inhibition of the mTOR pathway.

Emerging role and therapeutic implication of mTOR signalling in intervertebral disc degeneration

Intervertebral disc degeneration (IDD), an important cause of chronic low back pain (LBP), is considered the pathological basis for various spinal degenerative diseases. A series of factors, including inflammatory response, oxidative stress, autophagy, abnormal mechanical stress, nutritional deficiency, and genetics, lead to reduced extracellular matrix (ECM) synthesis by intervertebral disc (IVD) cells and accelerate IDD progression. Mammalian target of rapamycin (mTOR) is an evolutionarily conserved serine/threonine kinase that plays a vital role in diverse degenerative diseases. Recent studies have shown that mTOR signalling is involved in the regulation of autophagy, oxidative stress, inflammatory responses, ECM homeostasis, cellular senescence, and apoptosis in IVD cells. Accordingly, we reviewed the mechanism of mTOR signalling in the pathogenesis of IDD to provide innovative ideas for future research and IDD treatment.

TM4SF5-Mediated Regulation of Hepatocyte Transporters during Metabolic Liver Diseases

Nonalcoholic fatty liver disease (NAFLD) is found in up to 30% of the world’s population and can lead to hepatocellular carcinoma (HCC), which has a poor 5-year relative survival rate of less than 40%. Clinical therapeutic strategies are not very successful. The co-occurrence of metabolic disorders and inflammatory environments during the development of steatohepatitis thus needs to be more specifically diagnosed and treated to prevent fatal HCC development. To improve diagnostic and therapeutic strategies, the identification of molecules and/or pathways responsible for the initiation and progression of chronic liver disease has been explored in many studies, but further study is still required. Transmembrane 4 L six family member 5 (TM4SF5) has been observed to play roles in the regulation of metabolic functions and activities in hepatocytes using in vitro cell and in vivo animal models without or with TM4SF5 expression in addition to clinical liver tissue samples. TM4SF5 is present on the membranes of different organelles or vesicles and cooperates with transporters for fatty acids, amino acids, and monocarbohydrates, thus regulating nutrient uptake into hepatocytes and metabolism and leading to phenotypes of chronic liver diseases. In addition, TM4SF5 can remodel the immune environment by interacting with immune cells during TM4SF5-mediated chronic liver diseases. Because TM4SF5 may act as an NAFLD biomarker, this review summarizes crosstalk between TM4SF5 and nutrient transporters in hepatocytes, which is related to chronic liver diseases.

Phosphomimicry on STAU1 Serine 20 Impairs STAU1 Posttranscriptional Functions and Induces Apoptosis in Human Transformed Cells

Staufen 1 (STAU1) is an RNA-binding protein that is essential in untransformed cells. In cancer cells, it is rather STAU1 overexpression that impairs cell proliferation. In this paper, we show that a modest increase in STAU1 expression in cancer cells triggers apoptosis as early as 12 h post-transfection and impairs proliferation in non-apoptotic cells for several days. Interestingly, a mutation that mimics the phosphorylation of STAU1 serine 20 is sufficient to cause these phenotypes, indicating that serine 20 is at the heart of the molecular mechanism leading to apoptosis. Mechanistically, phosphomimicry on serine 20 alters the ability of STAU1 to regulate translation and the decay of STAU1-bound mRNAs, indicating that the posttranscriptional regulation of mRNAs by STAU1 controls the balance between proliferation and apoptosis. Unexpectedly, the expression of RBD2S20D, the N-terminal 88 amino acids with no RNA-binding activity, is sufficient to induce apoptosis via alteration, in trans, of the posttranscriptional functions of endogenous STAU1. These results suggest that STAU1 is a sensor that controls the balance between cell proliferation and apoptosis, and, therefore, may be considered as a novel therapeutic target against cancer.

Exploring the role of the multiple sclerosis susceptibility gene CLEC16A in T cells

C-type lectin-like domain family 16 member A (CLEC16A) is associated with autoimmune disorders, including multiple sclerosis (MS), but its functional relevance is not completely understood. CLEC16A is expressed in several immune cells, where it affects autophagic processes and receptor expression. Recently, we reported that the risk genotype of an MS-associated single nucleotide polymorphism in CLEC16A intron 19 is associated with higher expression of CLEC16A in CD4⁺ T cells. Here, we show that CLEC16A expression is induced in CD4⁺ T cells upon T cell activation. By the use of imaging flow cytometry and confocal microscopy, we demonstrate that CLEC16A is located in Rab4a-positive recycling endosomes in Jurkat TAg T cells. CLEC16A knock-down in Jurkat cells resulted in lower cell surface expression of the T cell receptor, however, this did not have a major impact on T cell activation response in vitro in Jurkat nor in human, primary CD4⁺ T cells.

Type 2 diabetes - unmet need, unresolved pathogenesis, mTORC1-centric paradigm

The current paradigm of type 2 diabetes (T2D) is gluco-centric, being exclusively categorized by glycemic characteristics. The gluco-centric paradigm views hyperglycemia as the primary target, being driven by resistance to insulin combined with progressive beta cells failure, and considers glycemic control its ultimate treatment goal. Most importantly, the gluco-centric paradigm considers the non-glycemic diseases associated with T2D, e.g., obesity, dyslipidemia, hypertension, macrovascular disease, microvascular disease and fatty liver as 'risk factors' and/or 'outcomes' and/or 'comorbidities', rather than primary inherent disease aspects of T2D. That is in spite of their high prevalence (60-90%) and major role in profiling T2D morbidity and mortality. Moreover, the gluco-centric paradigm fails to realize that the non-glycemic diseases of T2D are driven by insulin and, except for glycemic control, response to insulin in T2D is essentially the rule rather than the exception. Failure of the gluco-centric paradigm to offer an exhaustive unifying view of the glycemic and non-glycemic diseases of T2D may have contributed to T2D being still an unmet need. An mTORC1-centric paradigm maintains that hyperactive mTORC1 drives the glycemic and non-glycemic disease aspects of T2D. Hyperactive mTORC1 is proposed to act as double-edged agent, namely, to interfere with glycemic control by disrupting the insulin receptor-Akt transduction pathway, while concomitantly driving the non-glycemic diseases of T2D. The mTORC1-centric paradigm may offer a novel perspective for T2D in terms of pathogenesis, clinical focus and treatment strategy.

Amino Acids in Health and Endocrine Function

Dietary amino acids play an important role in maintaining health. Branched chain amino acids can adversely increase blood pressure whereas arginine and citrulline can reduce it. D-amino acids play important roles in several cell types including testis, the nervous system and adrenal glands. Several amino acids also can have dramatic effects on diabetes; branched chain amino acids, phenylalanine and tyrosine have been implicated while others, namely arginine and citrulline can improve outcomes. Leucine has been shown to play important roles in muscle primarily through the mTOR pathway though this effect does not translate across every population. Glutamine, arginine and D-aspartate also exert their muscle effects through mTOR. Relationships between amino acids and endocrine function include that of glucocorticoids, thyroid function, glucagon-like peptide 1 (GLP-1), ghrelin, insulin-like growth factor-1 (IGF-1) and leptin. Leucine, for example, can alleviate the effect of dexamethasone on muscle protein accretion. Interestingly, amino acid transporters play an important role in thyroid function. Several amino acids have been shown to increase GLP-1 levels in non-diabetics when administered orally. Similarly, several amino acids increase ghrelin levels in different species while cysteine can decrease it in mice. There is evidence to suggest that the arginine/NO pathway may be involved in modulating some of the effects of ghrelin on cells. In regard to IGF-1, branched chain amino acids can increase levels in adults while tryptophan and phenylalanine have been shown to increase levels in infants. Finally, leptin levels can be elevated by branched chain amino acids while restricting leucine in high fat diets can increase leptin sensitivity.

Activation of mTOR Signaling Pathway in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer and occurs mainly in patients with liver cirrhosis. The mammalian target of rapamycin (mTOR) signaling pathway is involved in many hallmarks of cancer including cell growth, metabolism re-programming, proliferation and inhibition of apoptosis. The mTOR pathway is upregulated in HCC tissue samples as compared with the surrounding liver cirrhotic tissue. In addition, the activation of mTOR is more intense in the tumor edge, thus reinforcing its role in HCC proliferation and spreading. The inhibition of the mTOR pathway by currently available pharmacological compounds (i.e., sirolimus or everolimus) is able to hamper tumor progression both in vitro and in animal models. The use of mTOR inhibitors alone or in combination with other therapies is a very attractive approach, which has been extensively investigated in humans. However, results are contradictory and there is no solid evidence suggesting a true benefit in clinical practice. As a result, neither sirolimus nor everolimus are currently approved to treat HCC or to prevent tumor recurrence after curative surgery. In the present comprehensive review, we analyzed the most recent scientific evidence while providing some insights to understand the gap between experimental and clinical studies.

Transmembrane 4 L Six Family Member 5 Senses Arginine for mTORC1 Signaling

The mechanistic target of rapamycin complex (mTORC1) is a signaling hub on the lysosome surface, responding to lysosomal amino acids. Although arginine is metabolically important, the physiological arginine sensor that activates mTOR remains unclear. Here, we show that transmembrane 4 L six family member 5 (TM4SF5) translocates from plasma membrane to lysosome upon arginine sufficiency and senses arginine, culminating in mTORC1/S6K1 activation. TM4SF5 bound active mTOR upon arginine sufficiency and constitutively bound amino acid transporter SLC38A9. TM4SF5 binding to the cytosolic arginine sensor Castor1 decreased upon arginine sufficiency, thus allowing TM4SF5-mediated sensing of metabolic amino acids. TM4SF5 directly bound free L-arginine via its extracellular loop possibly for the efflux, being supported by mutant study and homology and molecular docking modeling. Therefore, we propose that lysosomal TM4SF5 senses and enables arginine efflux for mTORC1/S6K1 activation, and arginine-auxotroph in hepatocellular carcinoma may be targeted by blocking the arginine sensing using anti-TM4SF5 reagents.

Novel therapeutic roles of MC-4 in combination with everolimus against advanced renal cell carcinoma by dual targeting of Akt/pyruvate kinase muscle isozyme M2 and mechanistic target of rapamycin complex 1 pathways

Current clinical trials of new anticancer therapies against metastatic renal cell carcinoma (RCC), including molecular-targeted therapies, have not shown promise. The purpose of this study was to preclinically assess the antitumor effects of MC-4, a partially purified material of Artemisia annua L., as a monotherapy or in combination with the known mechanistic target of rapamycin complex 1 (mTORC1) inhibitor, everolimus, against Caki-1 (Von Hippel-Lindau (VHL)+/+) and 786-O (VHL-/-) human RCC cells. MC-4 monotherapy significantly increased tumor growth inhibition and autophagic cell death in RCC cells in vitro and in vivo. Everolimus led to compensatory Akt activation by inhibiting only mTORC1 signaling pathway. In contrast to everolimus, MC-4 enhanced phosphatase and tensin homolog expression and reduced its downstream effector, Akt/pyruvate kinase muscle isozyme M2 (PKM2), leading to decreased expression of glucose transporter 1, which is associated with cancer cell metabolism. The synergistic antitumor and anti-metastatic effects induced by co-administration of MC-4 and everolimus involve cell growth inhibition and autophagic cell death via dual targeting of phosphatidylinositol 3-kinase (PI3K)/Akt/PKM2 and mTORC1. These findings suggest that MC-4 is a novel Akt/PKM2 inhibitor that can overcome the limitation of existing mTOR inhibitors and can be considered a novel strategy to treat patients with rapidly progressing advanced RCC.