Structural basis of amine odorant perception by a mammal olfactory receptor.

Odorants are detected as smell in the nasal epithelium of mammals by two G-protein-coupled receptor families, the odorant receptors and the trace amine-associated receptors1,2 (TAARs). TAARs emerged following the divergence of jawed and jawless fish, and comprise a large monophyletic family of receptors that recognize volatile amine odorants to elicit both intraspecific and interspecific innate behaviours such as attraction and aversion3-5. Here we report cryo-electron microscopy structures of mouse TAAR9 (mTAAR9) and mTAAR9-Gs or mTAAR9-Golf trimers in complex with ß-phenylethylamine, N,N-dimethylcyclohexylamine or spermidine. The mTAAR9 structures contain a deep and tight ligand-binding pocket decorated with a conserved D3.32W6.48Y7.43 motif, which is essential for amine odorant recognition. In the mTAAR9 structure, a unique disulfide bond connecting the N terminus to ECL2 is required for agonist-induced receptor activation. We identify key structural motifs of TAAR family members for detecting monoamines and polyamines and the shared sequence of different TAAR members that are responsible for recognition of the same odour chemical. We elucidate the molecular basis of mTAAR9 coupling to Gs and Golf by structural characterization and mutational analysis. Collectively, our results provide a structural basis for odorant detection, receptor activation and Golf coupling of an amine olfactory receptor.

Moroidin, a Cyclopeptide from the Seeds of Celosia cristata That Induces Apoptosis in A549 Human Lung Cancer Cells.

Interference of microtubule dynamics with tubulin-targeted drugs is a validated approach for cancer chemotherapy. Moroidin (1) is an Urticaceae-type cyclopeptide having a potent inhibitory effect on purified tubulin polymerization. So far, moroidin has not been chemically synthesized, and its effect on cancer cells remains unknown. Herein, the cyclopeptide moroidin was isolated and identified from the seeds of Celosia cristata, and a revised assignment of its NMR data was presented. For the first time, moroidin (1) was demonstrated as having cytotoxic effects for several cancer cells, especially A549 lung cancer cells. The cellular evidence obtained showed that moroidin disrupts microtubule polymerization and decreases ß-tubulin protein levels, but is not as potent as colchicine. Molecular docking indicated that 1 has a high binding potential to the vinca alkaloid site on tubulin. Moreover, moroidin arrested A549 cells in the G2/M phase and induced cell apoptosis. The intrinsic mitochondrial pathway and AKT were involved in the moroidin-induced cell apoptosis. In addition, moroidin (1) inhibited the migration and invasion of A549 cells at sublethal concentrations.

Blended learning model via small private online course improves active learning and academic performance of embryology.

While blended learning has been growing in popularity in recent years, the effectiveness of this procedure remains controversial. In this report, we assess the effectiveness of blended learning of embryology within international medical students. The participants were international medical students taking embryology in the Bachelor of Medicine and Bachelor of Surgery program. The blended learning group (BLG) consisted of students (n = 43) in the 2018-2019 academic year, taught with blended learning model via a customized small private online course (SPOC). The control traditional teaching group (TTG) consisted students (n = 48) in the 2017-2018 academic year, taught with traditional teaching model. Academic performance, including mean scores and passing ratios on the final exam of two groups were compared and analyzed with a t-test. In addition, a questionnaire directed toward evaluating student's perceptions with the blended learning was administered to students in BLG. The majority of students in BLG actively participated in online self-study activities and discussion in face-to-face class sessions. The mean score and passing ratio were significantly greater than those of students in TTG (p < 0.01). Results from the questionnaire revealed that the majority of BLG students felt that this method was beneficial for their learning of human embryology. The blended learning model, that integrates SPOC with face-to-face class lectures proved a more effective means for the teaching of embryology than the traditional lecture-based teaching model. This blended learning method may serve as a feasible model that can be readily applied for use in other medical courses.

Myristica fragrans promotes ABCA1 expression and cholesterol efflux in THP-1-derived macrophages.

Myristica fragrans is a traditional herbal medicine and has been shown to alleviate the development of atherosclerosis. However, the anti-atherogenic mechanisms of M. fragrans are still to be addressed. In this study, we explored the effect of M. fragrans on lipid metabolism and inflammation and its mechanisms in THP-1-derived macrophages. The quantitative polymerase chain reaction and western blot analysis results showed that M. fragrans promotes cholesterol efflux from THP-1-derived macrophages and reduces intracellular total cholesterol, cholesterol ester, and free cholesterol contents in a dose- and a time-dependent manner. Further study found that liver X receptor alpha (LXRα) antagonist GGPP significantly blocked the upregulation of ABCA1 expression with M. fragrans treatment. In addition, chromatin immunoprecipitation assay confirmed that GATA binding protein 3 (GATA3) can bind to the LXRα promoter, and inhibition of GATA3 led to the downregulation of LXRα and ATP-binding cassette subfamily A member 1 expression. Furthermore, M. fragrans reduced lipid accumulation, followed by decreasing tumor necrosis factor-α, interleukin (IL)-6, and IL-1ß and increasing IL-10 produced by THP-1-derived macrophages. Therefore, M. fragrans is identified as a valuable therapeutic medicine for atherosclerotic cardiovascular disease.

Melatonin Enhances Proliferation and Modulates Differentiation of Neural Stem Cells Via Autophagy in Hyperglycemia.

Dysfunction of neural stem cells (NSCs) has been linked to fetal neuropathy, one of the most devastating complications of gestational diabetes. Several studies have demonstrated that melatonin (Mel) exerted neuroprotective actions in various stresses. However, the role of autophagy and the involvement of Mel in NSCs in hyperglycemia (HG) have not yet been fully established. Here, we found that HG increased autophagy and autophagic flux of NSCs as evidenced by increasing LC3B II/I ratio, Beclin-1 expression, and autophagosomes. Moreover, Mel enhanced NSCs proliferation and self-renewal in HG with decreasing autophagy and activated mTOR signaling. Consistently, inhibition of autophagy by 3-Methyladenine (3-Ma) could assist Mel effects above, and induction of autophagy by Rapamycin (Rapa) could diminish Mel effects. Remarkably, HG induced premature differentiation of NSCs into neurons (Map2 positive cells) and astrocytes (GFAP positive cells). Furthermore, Mel diminished HG-induced premature differentiation and assisted NSCs in HG differentiation as that in normal condition. Coincidentally, inhibiting of NSCs autophagy by 3-Ma assisted Mel to modulate differentiation. However, increasing NSCs autophagy by Rapa disturbed the Mel effects and retarded NSCs differentiation. These findings suggested that Mel supplementation could contribute to mimicking normal NSCs proliferation and differentiation in fetal central nervous system by inhibiting autophagy in the context of gestational diabetes. Stem Cells 2019;37:504-515.

Pregnancy-Associated Plasma Protein-A Accelerates Atherosclerosis by Regulating Reverse Cholesterol Transport and Inflammation.

BACKGROUND: Recent studies have suggested that pregnancy-associated plasma protein-A (PAPP-A) is involved in the pathogenesis of atherosclerosis. This study aim is to investigate the role and mechanisms of PAPP-A in reverse cholesterol transport (RCT) and inflammation during the development of atherosclerosis. Methods and Results: PAPP-A was silenced in apolipoprotein E (apoE-/-) mice with administration of PAPP-A shRNA. Oil Red O staining of the whole aorta root revealed that PAPP-A knockdown reduced lipid accumulation in aortas. Oil Red O, hematoxylin and eosin (HE) and Masson staining of aortic sinus further showed that PAPP-A knockdown alleviated the formation of atherosclerotic lesions. It was found that PAPP-A knockdown reduced the insulin-like growth factor 1 (IGF-1) levels and repressed the PI3K/Akt pathway in both aorta and peritoneal macrophages. The expression levels of LXRα, ABCA1, ABCG1, and SR-B1 were increased in the aorta and peritoneal macrophages from apoE-/-mice administered with PAPP-A shRNA. Furthermore, PAPP-A knockdown promoted RCT from macrophages to plasma, the liver, and feces in apoE-/-mice. In addition, PAPP-A knockdown elevated the expression and secretion of monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), tumor necrosis factor-α, and interleukin-1ß through the nuclear factor kappa-B (NF-κB) pathway. CONCLUSIONS: The present study results suggest that PAPP-A promotes the development of atherosclerosis in apoE-/-mice through reducing RCT capacity and activating an inflammatory response.

Nicotine induces endothelial dysfunction and promotes atherosclerosis via GTPCH1.

Smoking is a major preventable risk factor for atherosclerosis. However, the causative link between cigarette smoke and atherosclerosis remains to be established. The objective of this study is to characterize the role of GTP cyclohydrolase 1 (GTPCH1), the rate-limiting enzyme for de novo tetrahydrobiopterin (BH4) synthesis, in the smoking-accelerated atherosclerosis and the mechanism involved. In vitro, human umbilical vein endothelial cells were treated with nicotine, a major component of cigarette smoke, which reduced the mRNA and protein levels of GTPCH1 and led to endothelial dysfunction. GTPCH1 overexpression or sepiapterin could attenuate nicotine-reduced nitric oxide and -increased reactive oxygen species levels. Mechanistically, human antigen R (HuR) bound with the adenylateuridylate-rich elements of the GTPCH1 3' untranslated region and increased its stability; nicotine inhibited HuR translocation from the nucleus to cytosol, which downregulated GTPCH1. In vivo, nicotine induced endothelial dysfunction and promoted atherosclerosis in ApoE-/- mice, which were attenuated by GTPCH1 overexpression or BH4 supplement. Our findings may provide a novel and promising approach to atherosclerosis treatment.

Heterotrimeric G Stimulatory Protein α Subunit Is Required for Intestinal Smooth Muscle Contraction in Mice.

BACKGROUND & AIMS: The α subunit of the heterotrimeric G stimulatory protein (Gsa), encoded by the guanine nucleotide binding protein, α-stimulating gene (Gnas, in mice), is expressed ubiquitously and mediates receptor-stimulated production of cyclic adenosine monophosphate and activation of the protein kinase A signaling pathway. We investigated the roles of Gsa in vivo in smooth muscle cells of mice. METHODS: We performed studies of mice with Cre recombinase-mediated disruption of Gnas in smooth muscle cells (GsaSMKO and SM22-CreERT2, induced in adult mice by tamoxifen). Intestinal tissues were collected for histologic, biochemical, molecular, cell biology, and physiology analyses. Intestinal function was assessed in mice using the whole-gut transit time test. We compared gene expression patterns of intestinal smooth muscle from mice with vs without disruption of Gnas. Biopsy specimens from ileum of patients with chronic intestinal pseudo-obstruction and age-matched control biopsies were analyzed by immunohistochemistry. RESULTS: Disruption of Gnas in smooth muscle of mice reduced intestinal motility and led to death within 4 weeks. Tamoxifen-induced disruption of Gnas in adult mice impaired contraction of intestinal smooth muscle and peristalsis. More than 80% of these died within 3 months of tamoxifen exposure, with features of intestinal pseudo-obstruction characterized by chronic intestinal dilation and dysmotility. Gsa deficiency reduced intestinal levels of cyclic adenosine monophosphate and transcriptional activity of the cyclic adenosine monophosphate response element binding protein 1 (CREB1); this resulted in decreased expression of the forkhead box F1 gene (Foxf1) and protein, and contractile proteins, such as myosin heavy chain 11; actin, α2, smooth muscle, aorta; calponin 1; and myosin light chain kinase. We found decreased levels of Gsa, FOXF1, CREB1, and phosphorylated CREB1 proteins in intestinal muscle layers of patients with chronic intestinal pseudo-obstruction, compared with tissues from controls. CONCLUSIONS: Gsa is required for intestinal smooth muscle contraction in mice, and its levels are reduced in ileum biopsies of patients with chronic intestinal pseudo-obstruction. Mice with disruption of Gnas might be used to study human chronic intestinal pseudo-obstruction.

G-CSF promotes autophagy and reduces neural tissue damage after spinal cord injury in mice.

Granulocyte colony-stimulating factor (G-CSF) was investigated for its capacity to induce autophagy and related neuroprotective mechanisms in an acute spinal cord injury model. To accomplish this goal, we established a mouse spinal cord hemisection model to test the effects of recombinant human G-CSF. The results showed that autophagy was activated after spinal cord injury and G-CSF appears to induce a more rapid activation of autophagy within injured spinal cords as compared with that of non-treated animals. Apoptosis as induced in mechanically injured neurons with G-CSF treatment was enhanced after inhibiting autophagy by 3-methyladenine (3-MA), which partially blocked the neuroprotective effect of autophagy as induced by G-CSF. In addition, G-CSF inhibited the activity of the NF-κB signal pathway in neurons after mechanical injury. We conclude that G-CSF promotes autophagy by inhibiting the NF-κB signal pathway and protects neuronal structure after spinal cord injury. We therefore suggest that G-CSF, which rapidly induces autophagy after spinal cord injury to inhibit neuronal apoptosis, may thus provide an effective auxiliary therapeutic intervention for spinal cord injury.

Melatonin prevents neural tube defects in the offspring of diabetic pregnancy.

Melatonin, an endogenous neurohormone secreted by the pineal gland, has a variety of physiological functions and neuroprotective effects. However, its protective role on the neural tube defects (NTDs) was not very clear. The aim of this study was to investigate the effects of melatonin on the incidence of NTDs (including anencephaly, encephalocele, and spina bifida) of offspring from diabetic pregnant mice as well as its underlying mechanisms. Pregnant mice were given 10 mg/kg melatonin by daily i.p. injection from embryonic day (E) 0.5 until being killed on E11.5. Here, we showed that melatonin decreased the NTDs (especially exencephaly) rate of embryos exposed to maternal diabetes. Melatonin stimulated proliferation of neural stem cells (NSCs) under hyperglycemic condition through the extracellular regulated protein kinases (ERK) pathway. Furthermore, as a direct free radical scavenger, melatonin decreased apoptosis of NSCs exposed to hyperglycemia. In the light of these findings, it suggests that melatonin supplementation may play an important role in the prevention of neural malformations in diabetic pregnancy.

Sox11 promotes endogenous neurogenesis and locomotor recovery in mice spinal cord injury.

We introduced a lentiviral vector containing the Sox11 gene into injured spinal cords of mice to evaluate the therapeutic potential of Sox11 in spinal cord injury. Sox11 markedly improved locomotor recovery after spinal cord injury and this recovery was accompanied by an up-regulation of Nestin/Doublecortin expression in the injured spinal cord. Sox11 was mainly located in endogenous neural stem cells lining the central canal and in newly-generated neurons in the spinal cord. In addition, Sox 11 significantly induced expressions of BDNF in the spinal cords of LV-Sox11-treated mice. We concluded that Sox11 induced activation of endogenous neural stem cells into neuronal determination and migration within the injured spinal cord. The resultant increase of BDNF at the injured site might form a distinct neurogenic niche which induces a final neuronal differentiation of these neural stem cells. Enhancing Sox11 expression to induce neurogenic differentiation of endogenous neural stem cells after injury may be a promising strategy in restorative therapy after SCI in mammals.

Granulocyte colony-stimulating factor improves neuron survival in experimental spinal cord injury by regulating nucleophosmin-1 expression.

Granulocyte colony-stimulating factor (G-CSF) and its related mechanisms were investigated to assess the potential for this factor to exert neuroprotective effects against spinal cord injury in mice. Recombinant human granulocyte colony-stimulating factor (rhG-CSF) was injected into mice spinal cord hemisection models. Locomotor activity was assessed by using the Basso-Bettie-Bresnahan scale. Neurons isolated from spinal cords were cultured in vitro and used in a neuronal mechanical injury model. Three treatment groups were compared with this model, 1) G-CSF, 2) G-CSF + NSC348884 (a nucleophosmin 1-specific inhibitor), and 3) NSC348884. Immunofluorescence staining and Western blotting were performed to analyze the expression of G-CSF and nucleophosmin 1 (Npm1). TUNEL staining was performed to analyze apoptosis after G-CSF treatment. We found that the G-CSF receptor (G-CSFR) and Npm1 were expressed in neurons and that Npm1 expression was induced after G-CSF treatment. G-CSF inhibited neuronal apoptosis. NSC348884 induced p53-dependent cell apoptosis and partially blocked the neuroprotective activity of G-CSF on neurons in vitro. G-CSF promoted locomotor recovery and demonstrated neuroprotective effects in an acute spinal cord injury model. The mechanism of G-CSF's neuroprotection may be related in part to attenuating neuronal apoptosis by NPM1.

Cyclopeptide moroidin inhibits vasculogenic mimicry formed by glioblastoma cells via regulating ß-catenin activation and EMT pathways.

Glioblastoma (GBM) is a highly vascularized malignant brain tumor with poor clinical outcomes. Vasculogenic mimicry (VM) formed by aggressive GBM cells is an alternative approach for tumor blood supply and contributes to the failure of anti-angiogenic therapy. To date, there is still a lack of effective drugs that target VM formation in GBM. In the present study, we evaluated the effects of the plant cyclopeptide moroidin on VM formed by GBM cells and investigated its underlying molecular mechanisms. Moroidin significantly suppressed cell migration, tube formation, and the expression levels of α-smooth muscle actin and matrix metalloproteinase-9 in human GBM cell lines at sublethal concentrations. The RNA sequencing data suggested the involvement of the epithelial-mesenchymal transition (EMT) pathway in the mechanism of moroidin. Exposure to moroidin led to a concentration-dependent decrease in the expression levels of the EMT markers N-cadherin and vimentin in GBM cells. Moreover, moroidin significantly reduced the level of phosphorylated extracellular signal-regulated protein kinase (p-ERK) and inhibited the activation of ß-catenin. Finally, we demonstrated that the plant cyclopeptide moroidin inhibited VM formation by GBM cells through inhibiting the ERK/ß-catenin-mediated EMT. Therefore, our study indicates a potential application of moroidin as an anti-VM agent in the treatment of GBM.

Rapid sequential clustering of NMDARs, CaMKII, and AMPARs upon activation of NMDARs at developing synapses.

Rapid, synapse-specific neurotransmission requires the precise alignment of presynaptic neurotransmitter release and postsynaptic receptors. How postsynaptic glutamate receptor accumulation is induced during maturation is not well understood. We find that in cultures of dissociated hippocampal neurons at 11 days in vitro (DIV) numerous synaptic contacts already exhibit pronounced accumulations of the pre- and postsynaptic markers synaptotagmin, synaptophysin, synapsin, bassoon, VGluT1, PSD-95, and Shank. The presence of an initial set of AMPARs and NMDARs is indicated by miniature excitatory postsynaptic currents (mEPSCs). However, AMPAR and NMDAR immunostainings reveal rather smooth distributions throughout dendrites and synaptic enrichment is not obvious. We found that brief periods of Ca2+ influx through NMDARs induced a surprisingly rapid accumulation of NMDARs within 1 min, followed by accumulation of CaMKII and then AMPARs within 2-5 min. Postsynaptic clustering of NMDARs and AMPARs was paralleled by an increase in their mEPSC amplitudes. A peptide that blocked the interaction of NMDAR subunits with PSD-95 prevented the NMDAR clustering. NMDAR clustering persisted for 3 days indicating that brief periods of elevated glutamate fosters permanent accumulation of NMDARs at postsynaptic sites in maturing synapses. These data support the model that strong glutamatergic stimulation of immature glutamatergic synapses results in a fast and substantial increase in postsynaptic NMDAR content that required NMDAR binding to PSD-95 or its homologues and is followed by recruitment of CaMKII and subsequently AMPARs.

The deubiquitinase cofactor UAF1 interacts with USP1 and plays an essential role in spermiogenesis.

Spermiogenesis defines the final phase of male germ cell differentiation. While multiple deubiquitinating enzymes have been linked to spermiogenesis, the impacts of deubiquitination on spermiogenesis remain poorly characterized. Here, we investigated the function of UAF1 in mouse spermiogenesis. We selectively deleted Uaf1 in premeiotic germ cells using the Stra8-Cre knock-in mouse strain (Uaf1 sKO), and found that Uaf1 is essential for spermiogenesis and male fertility. Further, UAF1 interacts and colocalizes with USP1 in the testes. Conditional knockout of Uaf1 in testes results in disturbed protein levels and localization of USP1, suggesting that UAF1 regulates spermiogenesis through the function of the deubiquitinating enzyme USP1. Using tandem mass tag-based proteomics, we identified that conditional knockout of Uaf1 in the testes results in reduced levels of proteins that are essential for spermiogenesis. Thus, we conclude that the UAF1/USP1 deubiquitinase complex is essential for normal spermiogenesis by regulating the levels of spermiogenesis-related proteins.

Melatonin antagonizes hypoxia-mediated glioblastoma cell migration and invasion via inhibition of HIF-1α.

Hypoxia is a crucial factor in tumor aggressiveness and resistance to therapy, especially in glioblastoma. Our previous results have shown that melatonin exerts antimigratory and anti-invasive action in glioblastoma cells under normoxia. However, the effect of melatonin on migration and invasion of glioblastoma cells under hypoxic condition remains poorly understood. Here, we show that melatonin strongly reduced hypoxia-mediated invasion and migration of U251 and U87 glioblastoma cells. In addition, we found that melatonin significantly blocked HIF-1α protein expression and suppressed the expression of downstream target genes, matrix metalloproteinase 2 (MMP-2) and vascular endothelial growth factor (VEGF). Furthermore, melatonin destabilized hypoxia-induced HIF-1α protein via its antioxidant activity against ROS produced by glioblastoma cells in response to hypoxia. Along with this, HIF-1α silencing by small interfering RNA markedly inhibited glioblastoma cell migration and invasion, and this appeared to be associated with MMP-2 and VEGF under hypoxia. Taken together, our findings suggest that melatonin suppresses hypoxia-induced glioblastoma cell migration and invasion via inhibition of HIF-1α. Considering the fact that overexpression of the HIF-1α protein is often detected in glioblastoma multiforme, melatonin may prove to be a potent therapeutic agent for this tumor.

Deficiency of the Tmem232 Gene Causes Male Infertility with Morphological Abnormalities of the Sperm Flagellum in Mice.

The axoneme and accessory structures of flagella are critical for sperm motility and male fertilization. Sperm production needs precise and highly ordered gene expression to initiate and sustain the many cellular processes that result in mature spermatozoa. Here, we identified a testis enriched gene transmembrane protein 232 (Tmem232), which is essential for the structural integrity of the spermatozoa flagella axoneme. Tmem232 knockout mice were generated for in vivo analyses of its functions in spermatogenesis. Phenotypic analysis showed that deletion of Tmem232 in mice causes male-specific infertility. Transmission electron microscopy together with scanning electron microscopy were applied to analyze the spermatozoa flagella and it was observed that the lack of TMEM232 caused failure of the cytoplasm removal and the absence of the 7th outer microtubule doublet with its corresponding outer dense fiber (ODF). Co-IP assays further identified that TMEM232 interacts with ODF family protein ODF1, which is essential to maintain sperm motility. In conclusion, our findings indicate that TMEM232 is a critical protein for male fertility and sperm motility by regulating sperm cytoplasm removal and maintaining axoneme integrity.

The Slingshot phosphatase 2 is required for acrosome biogenesis during spermatogenesis in mice.

The acrosome is a membranous organelle positioned in the anterior portion of the sperm head and is essential for male fertility. Acrosome biogenesis requires the dynamic cytoskeletal shuttling of vesicles toward nascent acrosome which is regulated by a series of accessory proteins. However, much remains unknown about the molecular basis underlying this process. Here, we generated Ssh2 knockout (KO) mice and HA-tagged Ssh2 knock-in (KI) mice to define the functions of Slingshot phosphatase 2 (SSH2) in spermatogenesis and demonstrated that as a regulator of actin remodeling, SSH2 is essential for acrosome biogenesis and male fertility. In Ssh2 KO males, spermatogenesis was arrested at the early spermatid stage with increased apoptotic index and the impaired acrosome biogenesis was characterized by defective transport/fusion of proacrosomal vesicles. Moreover, disorganized F-actin structures accompanied by excessive phosphorylation of COFILIN were observed in the testes of Ssh2 KO mice. Collectively, our data reveal a modulatory role for SSH2 in acrosome biogenesis through COFILIN-mediated actin remodeling and the indispensability of this phosphatase in male fertility in mice.

Saturated fatty acids activate microglia via Toll-like receptor 4/NF-κB signalling.

Diets rich in SFA have been implicated in Alzheimer's disease (AD). There is strong evidence to suggest that microglial activation augments the progression of AD. However, it remains uncertain whether SFA can initiate microglial activation and whether this response can cause neuronal death. Using the BV-2 microglial cell line and primary microglial culture, we showed that palmitic acid (PA) and stearic acid (SA) could activate microglia, as assessed by reactive morphological changes and significantly increased secretion of pro-inflammatory cytokines, NO and reactive oxygen species, which trigger primary neuronal death. In addition, the mRNA level of these pro-inflammatory mediators determined by RT-PCR was also increased by PA and SA. We further investigated the intracellular signalling mechanism underlying the release of pro-inflammatory mediators from PA-activated microglial cells. The present results showed that PA activated the phosphorylation and nuclear translocation of the p65 subunit of NF-κB. Furthermore, pyrrolidine dithiocarbamate, a NF-κB inhibitor, attenuated the production of pro-inflammatory mediators except for IL-6 in PA-stimulated microglia. Administration of anti-Toll-like receptor (TLR)4-neutralising antibody repressed PA-induced NF-κB activation and pro-inflammatory mediator production. In conclusion, the present in vitro study demonstrates that SFA could activate microglia and stimulate the TLR4/NF-κB pathway to trigger the production of pro-inflammatory mediators, which may contribute to neuronal death.

Cytoprotective effects of melatonin on astroglial cells subjected to palmitic acid treatment in vitro.

Melatonin, an endogenously produced neurohormone secreted mainly by the pineal gland, has a variety of physiological functions and neuroprotective effects. Saturated fatty acids (SFAs) have been known to induce neurotoxicity and oxidative stress in central nervous system injuries and neurodegenerative pathologies. However, the effect of melatonin on SFAs-induced cytotoxicity in astroglial cells, if any, has remained to be explored. This study reports that in primary cultured astroglial cells, melatonin significantly attenuated palmitic acid (PA)-induced cytotoxicity in a concentration- and time-dependent manner. Additionally, melatonin effectively suppressed PA-induced reactive oxygen species generation and prevented PA-induced apoptosis whereby the rise in Bax/Bcl-2 ratio and caspase-3 activation in astroglial cells was inhibited. However, it did not appear to exert an obvious effect on PA-induced intracellular calcium overload. Luzindole, a nonselective melatonin receptor antagonist, attenuated melatonin's promotion effect of cell survival and Stat3 phosphorylation, indicating that melatonin exerts its protective property in astroglial cells, at least in part, through the activation of membrane receptors and then Stat3 signaling pathway. Finally, melatonin had an inhibitory effect on the pro-inflammatory cytokine gene expression. The results suggest that melatonin may be an effective cytoprotective agent against PA-based cytotoxicity through modulating cell survival and inflammatory response in astroglial cells.