Signaling and other functions of lipids in autophagy: a review

The process of autophagy is integral to cellular function. In this process, proteins, organelles, and metabolites are engulfed in a lipid vesicle and trafficked to a lysosome for degradation. Its central role in protein and organelle homeostasis has piqued interest for autophagy dysfunction as a driver of pathology for a number of diseases including cancer, muscular disorders, neurological disorders, and non-alcoholic fatty liver disease. For much of its history, the study of autophagy has centered around proteins, however, due to advances in mass spectrometry and refined methodologies, the role of lipids in this essential cellular process has become more apparent. This review discusses the diverse endogenous lipid compounds shown to mediate autophagy. Downstream lipid signaling pathways are also reviewed in the context of autophagy regulation. Specific focus is placed upon the Mammalian Target of Rapamycin (mTOR) and Peroxisome Proliferator-Activated Receptor (PPAR) signaling pathways as integration hubs for lipid regulation of autophagy.

The bright and the dark sides of L-carnitine supplementation: a systematic review

Background

L-carnitine (LC) is used as a supplement by recreationally-active, competitive and highly trained athletes. This systematic review aims to evaluate the effect of prolonged LC supplementation on metabolism and metabolic modifications.

Methods

A literature search was conducted in the MEDLINE (via PubMed) and Web of Science databases from the inception up February 2020. Eligibility criteria included studies on healthy human subjects, treated for at least 12 weeks with LC administered orally, with no drugs or any other multi-ingredient supplements co-ingestion.

Results

The initial search retrieved 1024 articles, and a total of 11 studies were finally included after applying inclusion and exclusion criteria. All the selected studies were conducted with healthy human subjects, with supplemented dose ranging from 1 g to 4 g per day for either 12 or 24 weeks. LC supplementation, in combination with carbohydrates (CHO) effectively elevated total carnitine content in skeletal muscle. Twenty-four-weeks of LC supplementation did not affect muscle strength in healthy aged women, but significantly increased muscle mass, improved physical effort tolerance and cognitive function in centenarians. LC supplementation was also noted to induce an increase of fasting plasma trimethylamine-N-oxide (TMAO) levels, which was not associated with modification of determined inflammatory nor oxidative stress markers.

Conclusion

Prolonged LC supplementation in specific conditions may affect physical performance. On the other hand, LC supplementation elevates fasting plasma TMAO, compound supposed to be pro-atherogenic. Therefore, additional studies focusing on long-term supplementation and its longitudinal effect on the cardiovascular system are needed.

Neutrophil extracellular traps promote corneal neovascularization-induced by alkali burn

OBJECTIVES

To investigate the effects of neutrophil extracellular traps (NETs) on angiogenesis in vitro and in vivo and the regulatory role of mammalian target of rapamycin (mTOR) activity in it.

METHODS

The regulatory role of mTOR in NETs formation was explored. In vitro, human neutrophils were pretreated with rapamycin. NETs formation was measured using immunofluorescence staining of NETs markers, SYTOX Green and PicoGreen after NaOH stimulation. In vivo, mice were treated with rapamycin, and NETs formation in cornea was measured using immunofluorescence staining 7 days after alkali burn. Then, the effects of NETs on angiogenesis were investigated. In vitro, human neutrophils were treated with DNase I or rapamycin. NETs were isolated after NaOH stimulation and the isolated NETs were co-culture with human umbilical vein endothelial cells (HUVECs). HUVECs migration, proliferation, and inflammatory activation were measured. In vivo, mice were injected subconjunctivally with supernatant containing NETs. Corneal neovascularization was visualized by immunofluorescence staining.

RESULTS

NETs structures can be observed in NaOH-stimulated neutrophils and alkali-burned mouse cornea compared with normal group. Treated with rapamycin enhanced NETs formation in response to NaOH management compared with DMSO control in vitro and in vivo. NETs increased the migration, proliferation and inflammatory activation of HUVECs, and subconjunctival injection of NETs promoted inflammatory and angiogenic response in corneal alkali burn model.

CONCLUSIONS

NETs formation can be triggered by NaOH stimulation. mTOR activity has a negative regulatory effect on NETs formation. NETs promoted angiogenic responses and inflammatory activation of HUVECs and increased corneal neovascularization and inflammatory response.

[Effect of electroacupuncture on expression of corticocerebral autophagy-related proteins in rats with traumatic brain injury]

OBJECTIVE

To observe the effect of electroacupuncture on the expression of phosphorylated adenosine 5'-monophosphate-activated protein kinase(p-AMPK), phosphorylated mammalian target of rapamycin(p-mTOR) and phosphorylated Ulk1(p-Ulk1) proteins in the cortex of traumatic brain injury (TBI) rats, so as to explore its mechanisms underlying treatment of TBI.

METHODS

Male SD rats were randomly divided into sham operation (sham), model, electroacupuncture Ⅰ (EA Ⅰ), electroacupuncture Ⅱ (EA Ⅱ) groups (n＝10 in each group). TBI model was established by using a free fall brain injury striking device after exposing the local cranial bone (to induce the left parietal cerebral contusion). Rats in EA Ⅰ group were treated by electroacupuncture at "Neiguan" (SP6) and "Zusanli" (ST36) combined with acupuncture at "Shuigou" (GV26) and "Baihui"(GV20) on the 7^thday after modeling, once a day for 7 consecutive days. Rats in EA Ⅱ group received the treatments as those in EA Ⅰ group on 24 h after modeling, once a day for 14 d. After the treatment, histopathological changes of the injured cerebral cortex were observed by HE staining and Nissl staining. Western blot was used to detect the expression of AMPK, p-AMPK, mTOR, p-mTOR, Ulk1, p-Ulk1 proteins in the injured cerebral cortex tissue.

RESULTS

After modeling and compared with the sham group, a large number of tissue necrosis, scattered arrangement of nerve fibers, vacuolar changes of cells, nuclear fragmentation, consolidation and hyperplastic scar tissue were found in the brain trauma area of rats in the model group. Nissl corpuscles were obviously absent. The ratio of p-AMPK/AMPK was up-regulated in the cortex of the wound region (P<0.01), and the ratio of p-mTOR/mTOR, p-Ulk1/Ulk1 were down-regulated (P<0.01). Compared with the model group, the pathological changes in brain injury area of rats in both EA groups were alleviated, the number of Nissl corpuscles increased, the ratio of p-AMPK/ AMPK was down-regulated in cortex of the injury area (P<0.01), and the ratios of p-mTOR/mTOR and p-Ulk1/Ulk1 were up-regulated (P<0.01). Compared with EA Ⅰ group, the pathological changes in the brain injury area in EA Ⅱ group showed obvious improvement, with down-regulation of p-AMPK/AMPK (P<0.05), and up-regulation of p-mTOR/mTOR and p-Ulk1/Ulk1 (P<0.05).

CONCLUSION

Electroacupuncture may inhibit the over-activation of autophagy of cranial neurons by regulating the activation of AMPK, mTOR and Ulk1, thus exerting brain protection effect on TBI rats, and early electroacupuncture intervention is more effective in acute phase of TBI.

Activation of ERK1/2-mTORC1-NOX4 mediates TGF-β1-induced epithelial-mesenchymal transition and fibrosis in retinal pigment epithelial cells

Transforming growth factor-β (TGF-β) plays a crucial role in the development of epithelial to mesenchymal transition (EMT) and fibrosis, particularly in an ocular disorder such as proliferative vitreoretinopathy (PVR). However, the key molecular mechanism underlying its pathogenesis remains unknown. In the present study, using cultured ARPE-19 cells, we determined that TGF-β initiates a signaling pathway through extracellular signal-regulated kinase (ERK)-mammalian target of rapamycin complex 1 (mTORC1) that stimulates trans-differentiation and fibrosis of retinal pigment epithelium. Blocking this pathway by a TGF-βRI, ERK or mTORC1 inhibitor protected cells from EMT and fibrotic protein expression. TGF-β1 treatment increased reactive oxygen species (ROS) via NOX4 upregulation, which acts downstream of ERK and mTORC1, as the ROS scavenger N-acetylcysteine and a pan-NADPH oxidase (NOX) inhibitor DPI dissipated excess ROS generation. TGF-β1-induced oxidative stress resulted in EMT and fibrotic changes, as NAC and DPI prevented α-SMA, Col4α3 expression and cell migration. All these inhibitors blocked the downstream pathway activation in addition to clearly preventing the activation of its upstream molecules, indicating the presence of a feedback loop system that may boost the upstream events. Furthermore, the FDA-approved drug trametinib (10 nM) blunted TGF-β1-induced mTORC1 activation and downstream pathogenic alterations through ERK1/2 inhibition, which opens a therapeutic avenue for the treatment of PVR in the future.

Cytotoxicity of nonylphenol on spermatogonial stem cells via phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin pathway

BACKGROUND

With continuous advancement of industrial society, environmental pollution has become more and more serious. There has been an increase in infertility caused by environmental factors. Nonylphenol (NP) is a stable degradation product widely used in daily life and production and has been proven to affect male fertility. However, the underlying mechanisms therein are unclear. Thus, it is necessary to study the effect and mechanism of NP on spermatogonial stem cells (SSCs).

AIM

To investigate the cytotoxic effect of NP on SSCs via the phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway.

METHODS

SSCs were treated with NP at 0, 10, 20 or 30 µmol. MTT assay was performed to evaluate the effect of NP on the proliferation of SSCs. Flow cytometry was conducted to measure SSC apoptosis. The expression of Bad, Bcl-2, cytochrome-c, pro-Caspase 9, SOX-2, OCT-4, Nanog, Nanos3, Stra8, Scp3, GFRα1, CD90, VASA, Nanos2, KIT, PLZF and PI3K/AKT/mTOR-related proteins was observed by western blot, and the mRNA expression of SOX-2, OCT-4 and Nanog was detected by quantitative reverse transcription polymerase chain reaction.

RESULTS

Compared with untreated cells (0 μmol NP), SSCs treated with NP at all concentrations showed a decrease in cell proliferation and expression of Bcl-2, Nanog, OCT-4, SOX-2, Nanos3, Stra8, Scp3, GFRα1, CD90, VASA, Nanos2, KIT, and PLZF (P < 0.05), whereas the expression of Bad, cytochrome-c, and pro-Caspase 9 increased significantly (P < 0.05). We further examined the PI3K/AKT/mTOR pathway and found that the phosphorylation of PI3K, AKT, mTORC1, and S6K was significantly decreased by NP at all concentrations compared to that in untreated SSCs (P < 0.05). NP exerted the greatest effect at 30 μmol among all NP concentrations.

CONCLUSION

NP attenuated the proliferation, differentiation and stemness maintenance of SSCs while promoting apoptosis and oxidative stress. The associated mechanism may be related to the PI3K/AKT/mTOR pathway.

A selectively suppressing amino acid transporter: Sodium-coupled neutral amino acid transporter 2 inhibits cell growth and mammalian target of rapamycin complex 1 pathway in skeletal muscle cells

Sodium-coupled neutral amino acid transporter 2 (SNAT2), also known as solute carrier family 38 member 2 (SLC38A2), is expressed in the skeletal muscle. Our research previously indicated that SNAT2 mRNA expression level in the skeletal muscle was modulated by genotype and dietary protein. The aim of this study was to investigate the key role of the amino acid transporter SNAT2 in muscle cell growth, differentiation, and related signaling pathways via SNAT2 suppression using the inhibitor α-methylaminoisobutyric acid (MeAIB). The results showed that SNAT2 suppression down-regulated both the mRNA and protein expression levels of SNAT2 in C2C12 cells, inhibited cell viability and differentiation of the cell, and regulated the cell distribution in G0/G1 and S phases (P < 0.05). Meanwhile, most of the intercellular amino acid content of the cells after MeAIB co-culturing was significantly lower (P < 0.05). Furthermore, the mRNA expression levels of system L amino acid transporter 1 (LAT1), silent information regulator 1, and peroxisome proliferator-activated receptor-gamma co-activator 1 alpha, as well as the protein expression levels of amino acid transporters LAT1 and vacuolar protein sorting 34, were all down-regulated. The phosphorylated protein expression levels of mammalian target of rapamycin (mTOR), regulatory-associated protein of mTOR, 4E binding protein 1, and ribosomal protein S6 kinase 1 after MeAIB treatment were also significantly down-regulated (P < 0.05), which could contribute to the importance of SNAT2 in amino acid transportation and skeletal muscle cell sensing. In conclusion, SNAT2 suppression inhibited C2C12 cell growth and differentiation, as well as the availability of free amino acids. Although the mTOR complex 1 signaling pathway was found to be involved, its response to different nutrients requires further study.

Trehalose alleviates oxidative stress-mediated liver injury and Mallor-Denk body formation via activating autophagy in mice

Autophagy is a degradation pathway for long-lived cytoplasmic proteins or damaged organelles and also for many aggregate-prone and disease-causing proteins. Endoplasmic reticulum (ER) stress and oxidative stress are associated with the pathophysiology of various liver diseases. These stresses induce the accumulation of abnormal proteins, Mallory-Denk body (MDB) formation and apoptosis in hepatocytes. A disaccharide trehalose had been reported to induce autophagy and decrease aggregate-prone proteins and cytotoxicity in neurodegenerative disease models. But the effects of trehalose in hepatocytes have not been fully understood. We examined the effect of trehalose on autophagy, ER stress and oxidative stress-mediated cytotoxicity and MDB formation in hepatocytes using mice model with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) treatment for 3 months. We administered trehalose by intraperitoneal injection of water containing 10% trehalose (0.02 mg/g body weight) every other day for 3 months. Our results demonstrated that trehalose induced autophagy and reduced ER stress, oxidative stress, MDB formation and apoptosis in hepatocytes of DDC-fed mice by Western blotting and immunostaining analyses. Electron microscopy revealed that trehalose induced autolysosome formation, which located is close to the MDBs. Thus, our findings suggest that trehalose can become a therapeutic agent for oxidative stress-related liver diseases via activating autophagy.

A Hepatocellular Carcinoma Patient with TSC1 Mutations Benefits from Treatment with Everolimus: A Case Report

Hepatocellular carcinoma (HCC) has a high degree of malignancy and poor prognosis. Treatment options for patients with advanced HCC are limited. There is currently no evidence to approve the accumulation of targeted therapies for HCC to support the inhibition of the PI3K/Akt/mTOR signaling pathway as an effective therapeutic strategy. We report on a patient with advanced HCC carrying the TSC1 gene mutation who responded well to the mammalian target of rapamycin inhibitor everolimus. Computed tomography revealed tumor shrinkage and maintenance of partial remission after everolimus treatment for >12.3 months. To the best of our knowledge, this is the first clinical case report showing benefit from everolimus treatment in HCC patients with TSC1 gene mutations. Therefore, everolimus may be used as a potential targeted therapy for HCC with TSC1 gene mutation.

Pterostilbene induces Nrf2/HO-1 and potentially regulates NF-κB and JNK-Akt/mTOR signaling in ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury has a high occurrence rate of 1-4 per 1000 live births and is the leading cause of neurological disabilities. Despite the improvement in neonatal care, the effectiveness of current therapeutic strategies is limited, and thus, additional therapies with better results are of much needed. Pterostilbene is a stilbenoid possessing numerous preventive and therapeutic properties. The current study aimed to assess whether pterostilbene exerted protective effects in neonatal rats against experimentally induced ischemic brain injury. Pterostilbene was administered via oral gavage from postnatal day 3 to day 8. Rat pups that were seven-day-old were exposed to hypoxic-ischemic insult via ligation of the common carotid artery and hypoxic environment exposure. Pterostilbene treatment reduced neuronal loss and infarct volume. Pterostilbene administration regulated the NF-κB pathway, and the levels of inflammatory mediators (Nitric oxide, TNF-α, IL-1β, and IL-6) were reduced. HI-induced oxidative stress was significantly reduced by pterostilbene, as presented by decreased production of malondialdehyde and reactive oxygen species. Levels of glutathione were enhanced by pterostilbene. Pterostilbene regulated Nrf2/HO-1 and JNK expression and activated the PI3K/Akt-mTOR signals. These findings suggest that pterostilbene is a candidate compound for the treatment of neonatal HI.

[Effect of moxibustion on cardiac function and expression of autophagy-related proteins of cardiomyocytes in chronic heart failure rats]

OBJECTIVE

To observe the effect of moxibustion on cardiac function and expression of myocardial tumor suppressor protein p53, mammalian target of rapamycin (mTOR) and phosphorylated(p)-mTOR (excessive autophagy-associated proteins of cardiomyocytes) in rats with chronic heart failure (CHF), so as to explore its mechanisms underlying improvement of CHF.

METHODS

SD rats were divided into blank control (n＝11), model(n＝8), autophagy activator (n＝8), autophagy inhibitor (n＝9) and moxibustion(n＝9) groups. The CHF model was established by i．p. injection of Doxorubicin Hydrochloride (DOX, 1 mg/mL, 1-4 mg/kg) every other day. Moxibustion was applied to bilateral "Feishu" (BL13) and "Xinshu" (BL15) for 20 min, 5 times a week for 3 weeks. Rats of the autophagy activator group received gavage of Rapamycin (RAPA, 2 mg/kg) and those of the autophagy inhibitor group received i．p. injection of Methyladenine (3-MA, 15 mg/kg) 5 times a week for 3 weeks after successful modeling. The heart weight and body weight were measured to calculate heart mass index (HW/BW＝heart weight ÷ body weight). Cardiac output (CO) and heart rate (HR) were measured by using a cardiac function meter. Serum N-terminal pro-brain natriuretic peptide (NT-pro BNP) content was assayed by using ELISA, and the expression of myocardial p53, p-mTOR and mTOR proteins was examined by Western blot.

RESULTS

(1) Compared with the blank control group, the HR, HW/BW, NT-pro BNP content and p53 expression levels were significantly increased (P<0.01), and the CO and ratio of p-mTOR/mTOR were significantly decreased in the model group (P<0.01). (2) Compared with the model group, the HR, HW/BW and NT-pro BNP content of the autophagy inhibitor and moxibustion groups were significantly decreased (P<0.01, P<0.05), and CO and p-mTOR/mTOR ratio were significantly increased in both autophagy inhibitor and moxibustion groups (P<0.01). (3) Compared with the autophagy activator group, the levels of HR, HW/BW, NT-pro BNP and p53 in the autophagy inhibitor and moxibustion groups were significantly lower (P<0.01), and those of CO and p-mTOR/mTOR levels were significantly higher (P<0.01).

CONCLUSION

Moxibustion, similar to the autophagy inhibitor, has a protective action on myocardium in CHF rats, which is possible by preventing over expression of myocardial autophagy-associated proteins during CHF.

Identification of 3',4',5'-trihydroxyflavone as an mammalian target of rapamycin inhibitor and its suppressive effects on dextran sulfate sodium-induced ulcerative colitis

Flavone derivatives have been shown to possess anti-inflammatory properties in various inflammation model systems; however, their underlying molecular mechanisms remain elusive. In this study, a flavone derivative 3',4',5'-trihydroxyflavone (THF; NJK16003) was synthesized, and its anti-inflammatory effects and molecular targets were investigated using in vitro systems and an in vivo colitis model. NJK16003 showed potent anti-inflammatory activities in cell-based assays using macrophages. In vitro enzyme activity assays using various inflammation-related kinases revealed the mammalian target of rapamycin (mTOR) as a possible molecular target. Treatment of RAW264.7 cells with NJK16003 resulted in an increase in light chain 3B protein lipidation and a decrease in p62 protein levels and ribosomal S6 kinase phosphorylation, indicating that NJK16003 induces autophagy through mTOR inhibition. NJK16003 treatment resulted in significant induction of autophagy and suppression of inflammatory responses in intestinal epithelial cells. Autophagy induction has been shown to alleviate colitis by suppressing inflammatory responses and apoptotic cell death of intestinal epithelial cells. Indeed, inflammatory responses and intestinal epithelial cell death in our DSS-induced colitis mouse model were significantly suppressed by NJK16003 treatment. Our results indicate that NJK16003 could suppress inflammation by inducing autophagy through its mTOR inhibitory activity. These results suggest that NJK16003 could be a possible therapeutic agent for the treatment of inflammatory bowel diseases including colitis.

The Effects of Evening Primrose/Hemp Seed Oil Compared to Rapamycin on the Gene Expression of Immunological Parameters in Experimental Autoimmune Encephalomyelitis Splenocytes

Mouse model of multiple sclerosis (MS) is used for the inflammatory demyelinating disease. Rapamycin (RAPA) may contribute to the reduction of inflammatory responses to experimental autoimmune encephalomyelitis (EAE). Due to its adverse side effects, identifying new therapeutic agents is important. We investigated the transcriptional effects of evening primrose/hemp seed oil (EP/HS oil) compared to RAPA on the expression of immunological factors genes in spleen cells of EAE mouse models. We firstly induced EAE mice by injection of myelin oligodendrocyte glycoprotein (MOG). Then, the EAE mice treated and untreated with EP/HS oil were evaluated and compared with naïve mice. The spinal cords were examined histologically. The immunological factors including genes expression of the regulatory-associated protein of mammalian target of rapamycin (RAPTOR), regulatory-associated companion of mammalian target of rapamycin (RICTOR), interferon (IFN)-γ, interleukin (IL)-10, signal transducer and activator of transcription factors (STAT3), forkhead box P3 (FOXP3), and IL-17 of splenocytes were evaluated by real time-polymerase chain reaction (RT-PCR). The data showed that EP/HS oil was able to reduce the severity of EAE and inhibited the development of the disease. EP/HS oil treatment significantly inhibited the expression of RAPTOR, IFN-γ, IL-17, and STAT3 genes and promoted the expression of RICTOR, IL-10, and FOXP3 genes. In conclusion, the EP/HS oil is likely to be involved in transcription of factors in favor of EAE improvement as well as participating in remyelination in the EAE spinal cord and that it suggests to be effective in therapeutic approaches for MS.

mTOR pathway activation in focal cortical dysplasia

BACKGROUND

Focal cortical dysplasia (FCD) is a localized cortical malformation and considerable morphological overlap exists between FCD IIB and neurological lesions associated with Tuberous sclerosis complex (TSC). Abnormal mTOR pathway secondary to somatic mTOR mutation and TSC gene mutation linked to PI3K/AKT/mTOR pathway have supported the hypothesis of common pathogenesis involved. Role of converging pathway, viz. Wnt/β-Catenin and mTOR is unknown in FCD. We aimed to analyse FCD IIB for TSC1/TSC2 mutations, immunoreactivity of hamartin, tuberin, mTOR and Wnt signalling cascades, and stem cell markers.

MATERIALS AND METHODS

Sixteen FCD IIB cases were retrieved along with 16 FCD IIA cases for comparison. Immunohistochemistry was performed for tuberin, hamartin, mTOR pathway markers, markers of stem cell phenotype, and Wnt pathway markers. Mutation analysis for TSC1 and TSC2 was performed by sequencing in 9 FCD cases.

RESULTS

All FCD cases showed preserved hamartin and tuberin immunoreactivity. Aberrant immunoreactivity of phospho-P70S6 kinase, S6 ribosomal, phospho-S6 ribosomal and Stat3 was noted in FCD IIB, with variable phospho-4E-BP1 (45%) and absent phospho-Stat3 expression. Immunoreactivity for phospho-P70S6 kinase (100%), S6 ribosomal protein (100%) and Stat3 (100%) was noted in FCD IIA, but not for phospho-S6 ribosomal, phospho-4E-BP1 and phospho-Stat3. c-Myc immunoreactivity was noted in all FCD cases. Nestin (81%) and Sox 2 (88%) stained balloon cells in FCD IIB (44%), while in FCD IIA cases were negative. All FCD cases were immunopositive for Wnt, but were negative for β-Catenin and cyclin-D1. TSC mutations were detected in two cases of FCD IIB.

CONCLUSION

Abnormal mTOR pathway activation exists in FCD IIB and IIA, however, shows differential immunoreactivity profile, indicating varying degrees of dysregulation. Labelling of neuronal stem cell markers in balloon cells suggests they are phenotypically immature. TSC1/2 mutation play role in the pathogenesis of FCD. Deep targeted sequencing is preferred diagnostic technique since conventional sanger sequencing often fails to detect low-allele frequency variants involved in mTOR/TSC pathway genes, commonly found in FCD.

Amino acids regulate energy utilization through mammalian target of rapamycin complex 1 and adenosine monophosphate activated protein kinase pathway in porcine enterocytes

As major fuels for the small intestinal mucosa, dietary amino acids (AA) are catabolized in the mitochondria and serve as sources of energy production. The present study was conducted to investigate AA metabolism that supply cell energy and the underlying signaling pathways in porcine enterocytes. Intestinal porcine epithelial cells (IPEC-J2) were treated with different concentrations of AA, inhibitor, or agonist of mammalian target of rapamycin complex 1 (mTORC1) and adenosine monophosphate activated protein kinase (AMPK), and mitochondrial respiration was monitored. The results showed that AA treatments resulted in enhanced mitochondrial respiration, increased intracellular content of pyruvic acid and lactic acid, and increased hormone-sensitive lipase mRNA expression. Meanwhile, decreased citrate synthase, isocitrate dehydrogenase alpha, and carnitine palmitoyltransferase 1 mRNA expression were also observed. We found that AA treatments increased the protein levels of phosphorylated mammalian target of rapamycin (p-mTOR), phosphorylated-p70 ribosomal protein S6 kinase, and phosphorylated-4E-binding protein 1. What is more, the protein levels of phosphorylated AMPK α (p-AMPKα) and nicotinamide adenine dinucleotide (NAD)-dependent protein deacetylase sirtuin-1 (SIRT1) were decreased by AA treatments in a time depending manner. Mitochondrial bioenergetics and the production of tricarboxylic acid cycle intermediates were decreased upon inhibition of mTORC1 or AMPK. Moreover, AMPK activation could up-regulate the mRNA expressions of inhibitor of nuclear factor kappa-B kinase subunit beta (Ikbkβ), integrin-linked protein kinase (ILK), unconventional myosin-Ic (Myo1c), ribosomal protein S6 kinase beta-2 (RPS6Kβ2), and vascular endothelial growth factor (VEGF)-β, which are downstream effectors of mammalian target of rapamycin (mTOR). The mRNA expressions of phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit delta isoform (PIK3CD) and 5′-AMP-activated protein kinase subunit gamma-1 (PRKAG1), which are upstream regulators of mTOR, were also up-regulated by AMPK activation. On the other hand, AMPK activation also down-regulated FK506-binding protein 1A (FKBP1A), serine/threonine-protein phosphatase 2A 55 kDa regulatory subunit B beta isoform, phosphatase and tensin homolog (PTEN), and unc-51 like autophagy activating kinase 1 (Ulk1), which are up-stream regulators of mTORC1. Taken together, these data indicated that AA regulated cellular energy metabolism through mTOR and AMPK pathway in porcine enterocytes. These results demonstrated interactions of AMPK and mTORC1 pathways in AA catabolism and energy metabolism in intestinal mucosa cells of piglets, and also provided reference for using AA to remedy human intestinal diseases.

SCD1 activity promotes cell migration via a PLD-mTOR pathway in the MDA-MB-231 triple-negative breast cancer cell line

BACKGROUND

Breast cancer is the most common cancer in women. Despite high survival rates in Western countries, treatments are less effective in metastatic cases and triple-negative breast cancer (TNBC) patient survival is the shortest across breast cancer subtypes. High expression levels of stearoyl-CoA desaturase-1 (SCD1) have been reported in breast cancer. The SCD1 enzyme catalyzes the formation of oleic acid (OA), a lipid stimulating the migration of metastatic breast cancer cells. Phospholipase activity is also implicated in breast cancer metastasis, notably phospholipase D (PLD).

METHODS

Kaplan-Meier survival plots generated from gene expression databases were used to analyze the involvement of SCD1 and PLD in several cancer subtypes. SCD1 enzymatic activity was modulated with a pharmaceutical inhibitor or by OA treatment (to mimic SCD1 over-activity) in three breast cancer cell lines: TNBC-derived MDA-MB-231 cells as well as non-TNBC MCF-7 and T47D cells. Cell morphology and migration properties were characterized by various complementary methods.

RESULTS

Our survival analyses suggest that SCD1 and PLD2 expression in the primary tumor are both associated to metastasis-related morbid outcomes in breast cancer patients. We show that modulation of SCD1 activity is associated with the modification of TNBC cell migration properties, including changes in speed, direction and cell morphology. Cell migration properties are regulated by SCD1 activity through a PLD-mTOR/p70S6K signaling pathway. These effects are not observed in non-TNBC cell lines.

CONCLUSION

Our results establish a key role for the lipid desaturase SCD1 and delineate an OA-PLD-mTOR/p70S6K signaling pathway in TNBC-derived MDA-MB-231 cell migration.

Immunohistochemical Analysis of mTOR Pathway-Related Proteins in Kaposiform Hemangioendothelioma

BACKGROUND

Mammalian target of rapamycin (mTOR) inhibitors have been shown to have excellent effects in the management of kaposiform hemangioendothelioma (KHE); however, the mechanism of action is unclear. This study identified the expressions of mTOR pathway-related proteins in different vascular tumors to provide insight into the pathogenesis of KHE.

METHODS

We retrospectively reviewed the pathologic specimens of 30 patients (KHE, 15; tufted angioma [TA], 5; infantile hemangioma [IH], 5; and lymphatic malformation [LM], 5). The immunohistochemical expression of mTOR-related proteins tuberous sclerosis complex 2 (TSC2), phosphatase and tensin homologue (PTEN), phosphorylated eukaryotic translation initiation factor 4E binding protein 1 (p-4EBP1), phosphorylated mTOR (p-mTOR), and phosphorylated ribosomal protein S6 kinase B1 (p-P70S6K) were analyzed using Image-Pro Plus software. KHE had the following pattern of expression in the spindle vascular endothelial cells: TSC2 (-); PTEN (-); p-4EBP1 (+); p-mTOR (+); and p-P70S6K (+).

RESULTS

All 3 patients treated with sirolimus had good responses. The TA results were similar to KHE with no significant differences (p-4EBP1: p = 0.0687; p-mTOR: p = 0.0832). The expressions of TSC2, PTEN, p-4EBP1, p-mTOR, and p-P70S6K were negative or weakly positive in IH with a statistically significant difference compared to KHE (p-4EBP1: p < 0.001; p-mTOR: p < 0.001; p-P70S6K: p < 0.001). LM had no significant differences when compared to KHE.

CONCLUSIONS

The absence of TSC2 and PTEN caused abnormal activation of the mTOR signaling pathway and may be involved in the pathogenesis of KHE. The expression of mTOR-related proteins in TA and LM was similar to KHE, unlike IH. The KHE pattern of expression [PTEN (-), TSC2 (-), p-mTOR (+), p-P70S6K (+), and p-4EBP1 (+)] suggested that sirolimus may be a good therapeutic choice.

mTORC1 is involved in DGKβ-induced neurite outgrowth and spinogenesis

Diacylglycerol kinase β (DGKβ) is an enzyme converting DG to phosphatidic acid (PA) and is specifically expressed in neurons, especially those in the cerebral cortex, hippocampus and striatum. We previously reported that DGKβ induces neurite outgrowth and spinogenesis, contributing to higher brain function including emotion and memory, and plasma membrane localization of DGKβ via the C1 domain and a cluster of basic amino acids at the C-terminus is necessary for its function. To clarify the mechanisms involved in neuronal development by DGKβ, we investigated whether DGKβ activity induces neurite outgrowth using human neuroblastoma SH-SY5Y cells. DGKβ induced neurite outgrowth by activation of mammalian target of rapamycin complex 1 (mTORC1) through a kinase-dependent pathway. In addition, in primary cultured cortical and hippocampal neurons, inhibition of mTORC1 abolished DGKβ induced-neurite outgrowth, branching and spinogenesis. These results indicated that DGKβ induces neurite outgrowth and spinogenesis by activating mTORC1 in a kinase-dependent pathway.

Mammalian target of rapamycin and p70S6K mediate thrombin-induced nuclear factor-κB activation and IL-8/CXCL8 release in human lung epithelial cells

Thrombin plays a crucial role in lung inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Thrombin induces the release of interleukin-8 (IL-8)/CXCL8 by lung epithelial cells, and this phenomenon plays a vital role in lung inflammation. Our previous studies have indicated that thrombin stimulates IL-8/CXCL8 expression through PI3K/Akt/IκB kinase (IKK)α/β/nuclear factor-κB (NF-κB) and p300 pathways in human lung epithelial cells. In the present study, we explored the roles of mammalian target of rapamycin (mTOR) and p70S6 kinase (p70S6K) in thrombin-induced NF-κB activation and IL-8/CXCL8 release in human lung epithelial cells. In this study, we found that rapamycin (an mTOR inhibitor) and p70S6K siRNA diminished thrombin-induced IL-8/CXCL8 release. Thrombin induced mTOR Ser2448 phosphorylation and p70S6K Thr389 phosphorylation in a time-dependent manner. Moreover, rapamycin attenuated thrombin-stimulated p70S6K phosphorylation. We also found that transfection of cells with the dominant negative mutant of Akt (Akt DN) reduced the thrombin-induced increase in mTOR phosphorylation and p70S6K phosphorylation. Moreover, thrombin-stimulated p300 phosphorylation was attenuated by Akt DN, rapamycin, and p70S6K siRNA. Thrombin triggered p70S6K translocation from the cytosol to the nucleus in a time-dependent manner. Thrombin induced the complex formation of p70S6K, p300, and p65; acetylation of p65 Lys310, and recruitment of p70S6K, p300, and p65 to the κB-binding site of the IL-8/CXCL8 promoter region. In conclusion, these results indicate that thrombin initiates the Akt-dependent mTOR/p70S6K signaling pathway to promote p300 phosphorylation and NF-κB activation and finally induces IL-8/CXCL8 release in human lung epithelial cells.

1,25-Dihydroxyvitamin D3 induces human myeloid cell differentiation via the mTOR signaling pathway

1,25-Dihydroxyvitamin D₃ or 1,25(OH)₂D₃ is known to play an important role in the differentiation of human myeloid cells. However, the molecular mechanism underlying the 1,25(OH)₂D₃-mediated differentiation of human myeloid cells is incompletely understood. Here, we report that 1,25(OH)₂D₃ induces differentiation of human myeloid cell lines such as U937 and THP-1 cells via the mammalian target of rapamycin (mTOR) signaling pathway. Both the expression of the differentiation marker CD14 and activation of the mTOR signaling pathway were induced by 1,25(OH)₂D₃ in phorbol 12-myristate 13-acetate (PMA)-differentiated U937 and THP-1 cells. The 1,25(OH)₂D₃-induced expression of CD14 in PMA-differentiated U937 and THP-1 cells was prevented by mTOR inhibitors, PP242 and Torin1. The 1,25(OH)₂D₃-induced morphological changes as characteristics of differentiated myeloid cells were also reversed after PP242 and Torin1 treatment. Silencing of either regulatory-associated protein of mTOR (Raptor) or rapamycin-insensitive companion of mTOR (Rictor) in PMA-differentiated THP-1 cells with small-interfering RNA resulted in the inhibition of CD14 expression and morphological changes induced by 1,25(OH)₂D₃, indicating that both mTORC1 and mTORC2 were important for the differentiation of myeloid THP-1 cells. Previous studies have shown that phosphatidic acid (PA) maintains the stability of the mTOR complex. Here we found that the attenuation of PA production with 1-butanol or a PLD inhibitor prevented the 1,25(OH)₂D₃-induced upregulation of CD14. Taken together, our results show that 1,25(OH)₂D₃ enhances the differentiation of human myeloid cells through the mTOR signaling pathway.

mTOR-coordinated Post-Transcriptional Gene Regulations: from Fundamental to Pathogenic Insights

Post-transcriptional regulations of mRNA transcripts such as alternative splicing and alternative polyadenylation can affect the expression of genes without changing the transcript levels. Recent studies have demonstrated that these post-transcriptional events can have significant physiological impacts on various biological systems and play important roles in the pathogenesis of a number of diseases, including cancers. Nevertheless, how cellular signaling pathways control these post-transcriptional processes in cells are not very well explored in the field yet. The mammalian target of rapamycin complex 1 (mTORC1) pathway plays a key role in sensing cellular nutrient and energy status and regulating the proliferation and growth of cells by controlling various anabolic and catabolic processes. Dysregulation of mTORC1 pathway can tip the metabolic balance of cells and is associated with a number of pathological conditions, including various types of cancers, diabetes, and cardiovascular diseases. Numerous reports have shown that mTORC1 controls its downstream pathways through translational and/or transcriptional regulation of the expression of key downstream effectors. And, recent studies have also shown that mTORC1 can control downstream pathways via post-transcriptional regulations. In this review, we will discuss the roles of post-transcriptional processes in gene expression regulations and how mTORC1-mediated post-transcriptional regulations contribute to cellular physiological changes. We highlight post-transcriptional regulation as an additional layer of gene expression control by mTORC1 to steer cellular biology. These emphasize the importance of studying post-transcriptional events in transcriptome datasets for gaining a fuller understanding of gene expression regulations in the biological systems of interest.

Rapid antidepressant actions of imipramine potentiated by zinc through PKA-dependented regulation of mTOR and CREB signaling

The slow onset of traditional antidepressants has become an urgent clinical issue, researchers are constantly exploring new antidepressants with prompt action. Previous studies have found that zinc levels were decreased in serum and brain of depressed patients or animal models. Zinc treatment can improve depressive symptoms and enhance the antidepressant effects of monoamine antidepressants. However, its mechanism of action is still unclear. This present study aims to investigate whether the zinc can enhance the rapid action of traditional antidepressant imipramine and to explore the potential mechanisms of action through the rapid antidepressant targets CREB (cAMP-response element binding protein) and mTOR (mammalian target of the rapamycin). Drug treatment included intraperitoneal injection of imipramine or zinc alone and imipramine plus zinc. Zinc had a rapid enhanced antidepressive effect on the imipramine and achieved a rapid antidepressant effect similar to ketamine. Combination of zinc with imipramine rapidly enhanced the phosphorylation of mTOR Ser2448 and CREB Ser133, and increased the expression of mTOR and CREB, which were dependent on the activation of PKA. In conclusion, combination therapy with zinc and monoamine antidepressants may overcome the problem of slow-onset action of traditional antidepressants in clinical uses.

Use of mammalian target of rapamycin inhibitors in patient with autosomal dominant polycystic kidney disease: an updated meta-analysis

PURPOSE

Mammalian target of rapamycin (mTOR) inhibitors were previously considered a potential therapy for autosomal dominant polycystic kidney disease (ADPKD), but prior studies remained controversial about their efficacy. We performed an updated meta-analysis regarding the therapeutic and adverse effects of mTOR inhibitors in patients with ADPKD.

METHODS

We systematically searched Cochrane Library, PubMed, EMBASE, and Medline for randomized controlled trials (RCTs) comparing mTOR inhibitors to placebo in ADPKD patients up to August 2019. We calculated weighted mean differences (WMDs) for total kidney volume (TKV), estimated glomerular filtration rates (eGFRs), and weighted odds ratios (ORs) for treatment-related complications between the treatment and the placebo groups, using the random effects model.

RESULTS

We retrieved a total of 9 RCTs enrolling 784 ADPKD patients receiving rapamycin, sirolimus, or everolimus between 2009 and 2016. The WMDs of TKV and eGFR from baseline to the last measurement were - 31.54 mL (95% confidence interval [CI] - 76.79 to 13.71 mL) and 2.81 mL/min/1.73 m² (95% CI - 1.85 to 7.46 mL/min/1.73 m²), respectively. Patients receiving mTOR inhibitors had a significantly increased risk of any adverse effects (OR 5.92, 95% CI 3.53-9.94), with the most common ones being aphthous stomatitis (OR 15.45, 95% CI 9.68-24.66) and peripheral edema (OR 3.49, 95% CI 1.31-9.27) compared to placebo users.

CONCLUSIONS

mTOR inhibitors did not significantly influence renal progression in patients with ADPKD, but were associated with a higher risk of complications. Whether mTOR inhibitors can be an add-on option or second-line agents remain undetermined.

Vitamin D increases glucocorticoid efficacy via inhibition of mTORC1 in experimental models of multiple sclerosis

The limited efficacy of glucocorticoids (GCs) during therapy of acute relapses in multiple sclerosis (MS) leads to long-term disability. We investigated the potential of vitamin D (VD) to enhance GC efficacy and the mechanisms underlying this VD/GC interaction. In vitro, GC receptor (GR) expression levels were quantified by ELISA and induction of T cell apoptosis served as a functional readout to assess synergistic 1,25(OH)₂D₃ (1,25D)/GC effects. Experimental autoimmune encephalomyelitis (MOG_35-55 EAE) was induced in mice with T cell-specific GR or mTORc1 deficiency. 25(OH)D (25D) levels were determined in two independent cohorts of MS patients with stable disease or relapses either responsive or resistant to GC treatment (initial cohort: n = 110; validation cohort: n = 85). Gene expression of human CD8⁺ T cells was analyzed by microarray (n = 112) and correlated with 25D serum levels. In vitro, 1,25D upregulated GR protein levels, leading to increased GC-induced T cell apoptosis. 1,25D/GC combination therapy ameliorated clinical EAE course more efficiently than respective monotherapies, which was dependent on GR expression in T cells. In MS patients from two independent cohorts, 25D deficiency was associated with GC-resistant relapses. Mechanistic studies revealed that synergistic 1,25D/GC effects on apoptosis induction were mediated by the mTOR but not JNK pathway. In line, 1,25D inhibited mTORc1 activity in murine T cells, and low 25D levels in humans were associated with a reduced expression of mTORc1 inhibiting tuberous sclerosis complex 1 in CD8⁺ T cells. GR upregulation by 1,25D and 1,25D/GC synergism in vitro and therapeutic efficacy in vivo were abolished in animals with a T cell-specific mTORc1 deficiency. Specific inhibition of mTORc1 by everolimus increased the efficacy of GC in EAE. 1,25D augments GC-mediated effects in vitro and in vivo in a T cell-specific, GR-dependent manner via mTORc1 inhibition. These data may have implications for improvement of anti-inflammatory GC therapy.

Effects of electroacupuncture at Taichong (LR 3) and Baihui (DU 20) on cardiac hypertrophy in rats with spontaneous hypertension

OBJECTIVE

To investigate the effects of electroacupuncture (EA) at Taichong (LR 3) and Baihui (DU 20) on myocardial hypertrophy in spontaneously hypertensive rats (SHRs).

METHODS

Thirty-six SHRs were randomly assigned to model, EA, and Losartan groups, with twelve rats per group. Twelve Wistar Kyoto rats were selected as the normal control group. Systolic blood pressure (SBP) and cardiac function were measured in all rats. Expression levels of factors associated with the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway were evaluated by Western blotting and real-time PCR. Pathological changes of the heart tissue were observed by hematoxylin-eosin staining.

RESULTS

After treatment, enhanced SBP was significantly decreased in the EA and Losartan groups compared with the model group (P < 0.01). Echocardiographic and morphological analyses revealed that enhanced end-diastolic interventricular septal thickness and left ventricular posterior wall thickness, as well as ratio of left ventricular weight to body weight were markedly diminished in the EA and Losartan groups (P < 0.01 or P < 0.05), while reduced left ventricular end-diastolic dimension and left ventricular ejection fraction were significantly ameliorated (P < 0.01). Real-time PCR and western blotting analyses showed that the expression levels of PI3K, Akt, and mTOR in SHRs were significantly up-regulated by EA and Losartan (P < 0.01), while the expression levels of PTEN and ANP were down-regulated (P < 0.01).

CONCLUSION

EA at Taichong (LR 3) and Baihui (DU 20) inhibited the development of cardiac hypertrophy and improved the cardiac function in SHRs, possibly through regulation of the PI3K/Akt/mTOR signalling pathway.