Plasma metabolomic profiling of patients with transient ischemic attack reveals positive role of neutrophils in ischemic tolerance

BACKGROUND

Transient ischemic attack (TIA) induces ischemic tolerance that can reduce the subsequent ischemic damage and improve prognosis of patients with stroke. However, the underlying mechanisms remain elusive. Recent advances in plasma metabolomics analysis have made it a powerful tool to investigate human pathophysiological phenotypes and mechanisms of diseases. In this study, we aimed to identify the bioactive metabolites from the plasma of patients with TIA for determination of their prophylactic and therapeutic effects on protection against cerebral ischemic stroke, and the mechanism of TIA-induced ischemic tolerance against subsequent stroke.

METHODS

Metabolomic profiling using liquid chromatography-mass spectrometry was performed to identify the TIA-induced differential bioactive metabolites in the plasma samples of 20 patients at day 1 (time for basal metabolites) and day 7 (time for established chronic ischemic tolerance-associated metabolites) after onset of TIA. Mouse middle cerebral artery occlusion (MCAO)-induced stroke model was used to verify their prophylactic and therapeutic potentials. Transcriptomics changes in circulating neutrophils of patients with TIA were determined by RNA-sequencing. Multivariate statistics and integrative analysis of metabolomics and transcriptomics were performed to elucidate the potential mechanism of TIA-induced ischemic tolerance.

FINDINGS

Plasma metabolomics analysis identified five differentially upregulated metabolites associated with potentially TIA-induced ischemic tolerance, namely all-trans 13,14 dihydroretinol (atDR), 20-carboxyleukotriene B4, prostaglandin B2, cortisol and 9-KODE. They were associated with the metabolic pathways of retinol, arachidonic acid, and neuroactive ligand-receptor interaction. Prophylactic treatment of MCAO mice with these five metabolites significantly improved neurological functions. Additionally, post-stroke treatment with atDR or 9-KODE significantly reduced the cerebral infarct size and enhanced sensorimotor functions, demonstrating the therapeutic potential of these bioactive metabolites. Mechanistically, we found in patients with TIA that these metabolites were positively correlated with circulating neutrophil counts. Integrative analysis of plasma metabolomics and neutrophil transcriptomics further revealed that TIA-induced metabolites are significantly correlated with specific gene expression in circulating neutrophils which showed prominent enrichment in FoxO signaling pathway and upregulation of the anti-inflammatory cytokine IL-10. Finally, we demonstrated that the protective effect of atDR-pretreatment on MCAO mice was abolished when circulating neutrophils were depleted.

INTERPRETATION

TIA-induced potential ischemic tolerance is associated with upregulation of plasma bioactive metabolites which can protect against cerebral ischemic damage and improve neurological functions through a positive role of circulating neutrophils.

FUNDING

National Natural Science Foundation of China (81974210), Science and Technology Planning Project of Guangdong Province, China (2020A0505100045), Natural Science Foundation of Guangdong Province (2019A1515010671), Science and Technology Program of Guangzhou, China (2023A03J0577), and Natural Science Foundation of Jiangxi, China（20224BAB216043).

Maf1 is an intrinsic suppressor against spontaneous neural repair and functional recovery after ischemic stroke

INTRODUCTION

Spontaneous recovery after CNS injury is often very limited and incomplete, leaving most stroke patients with permanent disability. Maf1 is known as a key growth suppressor in proliferating cells. However, its role in neuronal cells after stroke remains unclear.

OBJECTIVE

We aimed to investigate the mechanistic role of Maf1 in spontaneous neural repair and evaluated the therapeutic effect of targeting Maf1 on stroke recovery.

METHODS

We used mouse primary neurons to determine the signaling mechanism of Maf1, and the cleavage-under-targets-and-tagmentation-sequencing to map the whole-genome promoter binding sites of Maf1 in isolated mature cortical neurons. Photothrombotic stroke model was used to determine the therapeutic effect on neural repair and functional recovery by AAV-mediated Maf1 knockdown.

RESULTS

We found that Maf1 mediates mTOR signaling to regulate RNA polymerase III (Pol III)-dependent rRNA and tRNA transcription in mouse cortical neurons. mTOR regulates neuronal Maf1 phosphorylation and subcellular localization. Maf1 knockdown significantly increases Pol III transcription, neurite outgrowth and dendritic spine formation in neurons. Conversely, Maf1 overexpression suppresses such activities. In response to photothrombotic stroke in mice, Maf1 expression is increased and accumulates in the nucleus of neurons in the peripheral region of infarcted cortex, which is the key region for neural remodeling and repair during spontaneous recovery. Intriguingly, Maf1 knockdown in the peri-infarct cortex significantly enhances neural plasticity and functional recovery. Mechanistically, Maf1 not only interacts with the promoters and represses Pol III-transcribed genes, but also those of CREB-associated genes that are critical for promoting plasticity during neurodevelopment and neural repair.

CONCLUSION

These findings indicate Maf1 as an intrinsic neural repair suppressor against regenerative capability of mature CNS neurons, and suggest that Maf1 is a potential therapeutic target for enhancing functional recovery after ischemic stroke and other CNS injuries.

Spatial Proteomics Analysis of Soft and Stiff Regions in Human Acute Arterial Thrombus

BACKGROUND

The soft regions of a thrombus tend to be more susceptible to r-tPA (recombinant tissue-type plasminogen activator)-mediated thrombolysis and are more easily removed by mechanical thrombectomy than the stiff counterpart. This study aimed to understand the molecular pathological differences between the soft and stiff regions of human arterial thrombus.

METHODS

We developed a spatial proteomic workflow combining proteomics with laser-captured microdissection to analyze human arterial thrombi with Masson trichrome staining to identify stiff and soft regions from 2 independent cohorts of patients with acute myocardial or cerebral infarction. Dysregulated proteins in a C57BL6/J male mouse model of arterial thrombosis were identified by pathway enrichment and pairwise analyses from the common gene ontology enrichment and dysregulated proteins between carotid and coronary arterial thrombi, and validated by immunohistochemistry.

RESULTS

Spatial proteomics of the coronary arterial thrombi collected from 7 patients with myocardial infarct revealed 7 common dysregulated proteins in 2 cohorts of patients, and upregulation of TGF-β1 (transforming growth factor β1) was the most prominent fibrosis-related protein. Inhibition of TGF-β1 resulted in delayed arterial thrombosis and accelerated blood flow restoration in mouse model. We further expanded the spatial proteomic workflow to the carotid artery thrombi collected from 11 patients with cerebral infarction. Pairwise proteomic analysis of stiff and soft regions between carotid and coronary arterial thrombi further revealed 5 common gene ontology clusters including features of platelet activation, and a common dysregulated protein COL1A1 (collagen type 1 alpha 1) that was reported to be influenced by TGF-β1. We also verified the expression in human and mice carotid arterial thrombi.

CONCLUSIONS

This study demonstrates the spatially distinct composition of proteins in the stiff and soft regions of human arterial thrombi, and suggests that TGF-β1 is a key therapeutic target for promoting arterial thrombolysis.

Non-enzymatic role of SOD1 in intestinal stem cell growth

Superoxide dismutase 1 (SOD1) modulates intestinal barrier integrity and intestinal homeostasis as an antioxidant enzyme. Intestinal homeostasis is maintained by the intestinal stem cells (ISCs). However, whether and how SOD1 regulates ISCs is unknown. In this study, we established intestinal organoids from tamoxifen-inducible intestinal epithelial cell-specific Sod1 knockout (Sod1^f/f; Vil-creERT2) mice. We found that loss of Sod1 in organoids suppressed the proliferation and survival of cells and Lgr5 gene expression. SOD1 is known for nearly half a century for its canonical role as an antioxidant enzyme. We identified its enzyme-independent function in ISC: inhibition of SOD1 enzymatic activity had no impact on organoid growth, and enzymatically inactive Sod1 mutants could completely rescue the growth defects of Sod1 deficient organoids, suggesting that SOD1-mediated ISC growth is independent of its enzymatic activity. Moreover, Sod1 deficiency did not affect the ROS levels of the organoid, but induced the elevated WNT signaling and excessive Paneth cell differentiation, which mediates the occurrence of growth defects in Sod1 deficient organoids. In vivo, epithelial Sod1 loss induced a higher incidence of apoptosis in the stem cell regions and increased Paneth cell numbers, accompanied by enhanced expression of EGFR ligand Epiregulin (EREG) in the stromal tissue, which may compensate for Sod1 loss and maintain intestinal structure in vivo. Totally, our results show a novel enzyme-independent function of SOD1 in ISC growth under homeostasis.

Mediating bio-fate of polymeric cholecalciferol nanoparticles through rational size control

Whilst 10-200 nm polymeric nanoparticles hold enormous medical potential, successful clinical translation remains scarce. There is an inadequate understanding of how these nanoparticles could be fabricated with consistent particle architecture in this size range, as well as their corresponding biological performance. We seek to fill this important knowledge gap by employing Design of Experiment (DoE) to examine critical formulation and processing parameters of cholecalciferol (VitD3)-loaded nanoparticles by flash nanoprecipitation (FNP). Based on the regression analysis of the critical processing parameters, six VitD3 nanoparticle formulations with z-average particle sizes between 40 and 150 nm were successfully developed, possessing essentially the same particle shape and zeta potential. To evaluate the effect of particle size on the in vivo performance, not only VitD3 but also its active metabolites (25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3) were assayed in the biodistribution study. Results indicated that VitD3 nanoparticles with sizes ≤110 nm would achieve higher plasma retention. VitD3 nanoparticles with sizes of 40 nm and 150 nm were superior for lung deposition, while particle size had no major role in the brain uptake of VitD3 nanoparticles. The present study demonstrates the value of DoE for generating size-tunable nanoparticles with controlled particle properties in FNP and offers important insights into the particle size effect of nanoparticles <200 nm on their therapeutic potential.

Consensus clustering of gene expression profiles in peripheral blood of acute ischemic stroke patients

Acute ischemic stroke (AIS) is a primary cause of mortality and morbidity worldwide. Currently, no clinically approved immune intervention is available for AIS treatment, partly due to the lack of relevant patient classification based on the peripheral immunity status of patients with AIS. In this study, we adopted the consensus clustering approach to classify patients with AIS into molecular subgroups based on the transcriptomic profiles of peripheral blood, and we identified three distinct AIS molecular subgroups and 8 modules in each subgroup by the weighted gene co-expression network analysis. Remarkably, the pre-ranked gene set enrichment analysis revealed that the co-expression modules with subgroup I-specific signature genes significantly overlapped with the differentially expressed genes in AIS patients with hemorrhagic transformation (HT). With respect to subgroup II, exclusively male patients with decreased proteasome activity were identified. Intriguingly, the majority of subgroup III was composed of female patients who showed a comparatively lower level of AIS-induced immunosuppression (AIIS). In addition, we discovered a non-linear relationship between female age and subgroup-specific gene expression, suggesting a gender- and age-dependent alteration of peripheral immunity. Taken together, our novel AIS classification approach could facilitate immunomodulatory therapies, including the administration of gender-specific therapeutics, and attenuation of the risk of HT and AIIS after ischemic stroke.

Brain delivering RNA-based therapeutic strategies by targeting mTOR pathway for axon regeneration after central nervous system injury

Injuries to the central nervous system (CNS) such as stroke, brain, and spinal cord trauma often result in permanent disabilities because adult CNS neurons only exhibit limited axon regeneration. The brain has a surprising intrinsic capability of recovering itself after injury. However, the hostile extrinsic microenvironment significantly hinders axon regeneration. Recent advances have indicated that the inactivation of intrinsic regenerative pathways plays a pivotal role in the failure of most adult CNS neuronal regeneration. Particularly, substantial evidence has convincingly demonstrated that the mechanistic target of rapamycin (mTOR) signaling is one of the most crucial intrinsic regenerative pathways that drive axonal regeneration and sprouting in various CNS injuries. In this review, we will discuss the recent findings and highlight the critical roles of mTOR pathway in axon regeneration in different types of CNS injury. Importantly, we will demonstrate that the reactivation of this regenerative pathway can be achieved by blocking the key mTOR signaling components such as phosphatase and tensin homolog (PTEN). Given that multiple mTOR signaling components are endogenous inhibitory factors of this pathway, we will discuss the promising potential of RNA-based therapeutics which are particularly suitable for this purpose, and the fact that they have attracted substantial attention recently after the success of coronavirus disease 2019 vaccination. To specifically tackle the blood-brain barrier issue, we will review the current technology to deliver these RNA therapeutics into the brain with a focus on nanoparticle technology. We will propose the clinical application of these RNA-mediated therapies in combination with the brain-targeted drug delivery approach against mTOR signaling components as an effective and feasible therapeutic strategy aiming to enhance axonal regeneration for functional recovery after CNS injury.

Circular RNA circ-FoxO3 attenuates blood-brain barrier damage by inducing autophagy during ischemia/reperfusion

Blood-brain barrier (BBB) damage can be a result of central nervous system (CNS) diseases and may be a cause of CNS deterioration. However, there are still many unknowns regarding effective and targeted therapies for maintaining BBB integrity during ischemia/reperfusion (I/R) injury. In this study, we demonstrate that the circular RNA of FoxO3 (circ-FoxO3) promotes autophagy via mTORC1 inhibition to attenuate BBB collapse under I/R. Upregulation of circ-FoxO3 and autophagic flux were detected in brain microvessel endothelial cells in patients with hemorrhagic transformation and in mice models with middle cerebral artery occlusion/reperfusion. In vivo and in vitro studies indicated that circ-FoxO3 alleviated BBB damage principally by autophagy activation. Mechanistically, we found that circ-FoxO3 inhibited mTORC1 activity mainly by sequestering mTOR and E2F1, thus promoting autophagy to clear cytotoxic aggregates for improving BBB integrity. These results demonstrate that circ-FoxO3 plays a novel role in protecting against BBB damage, and that circ-FoxO3 may be a promising therapeutic target for neurological disorders associated with BBB damage.

CircOGDH Is a Penumbra Biomarker and Therapeutic Target in Acute Ischemic Stroke

BACKGROUND

Acute ischemic stroke (AIS) is a leading cause of disability and mortality worldwide. Prediction of penumbra existence after AIS is crucial for making decision on reperfusion therapy. Yet a fast, inexpensive, simple, and noninvasive predictive biomarker for the poststroke penumbra with clinical translational potential is still lacking. We aim to investigate whether the CircOGDH (circular RNA derived from oxoglutarate dehydrogenase) is a potential biomarker for penumbra in patients with AIS and its role in ischemic neuronal damage.

METHODS

CircOGDH was screened from penumbra of middle cerebral artery occlusion mice and was assessed in plasma of patients with AIS by quantitative polymerase chain reaction. Magnetic resonance imaging was used to examine the penumbra volumes. CircOGDH interacted with miR-5112 in primary cortical neurons was detected by fluorescence in situ hybridization, RNA immunoprecipitation, and luciferase reporter assay. ADV-mediated CircOGDH knockdown ameliorated neuronal apoptosis induced by COL4A4 (Gallus collagen, type VI, alpha VI) overexpression. Transmission electron microscope, nanoparticle tracking analysis, and Western blot were performed to confirm exosomes.

RESULTS

CircOGDH expression was dramatically and selectively upregulated in the penumbra tissue of middle cerebral artery occlusion mice and in the plasma of 45 patients with AIS showing a 54-fold enhancement versus noncerebrovascular disease controls. Partial regression analysis revealed that CircOGDH expression was positively correlated with the size of penumbra in patients with AIS. Sequestering of miR-5112 by CircOGDH enhanced COL4A4 expression to elevate neuron damage. Additionally, knockdown of CircOGDH significantly enhanced neuronal cell viability under ischemic conditions. Furthermore, the expression of CircOGDH in brain tissue was closely related to that in the serum of middle cerebral artery occlusion mice. Finally, we found that CircOGDH was highly expressed in plasma exosomes of patients with AIS compared with those in noncerebrovascular disease individuals.

CONCLUSIONS

These results demonstrate that CircOGDH is a potential therapeutic target for regulating ischemia neuronal viability, and is enriched in neuron-derived exosomes in the peripheral blood, exhibiting a predictive biomarker of penumbra in patients with AIS.

Pharmacological preconditioning by TERT inhibitor BIBR1532 confers neuronal ischemic tolerance through TERT-mediated transcriptional reprogramming

After a sublethal ischemic preconditioning (IPC) stimulus, the brain has a remarkable capability of acquiring tolerance to subsequent ischemic insult by establishing precautionary self-protective mechanism. Understanding this endogenous mechanism would reveal novel and effective neuroprotective targets for ischemic brain injury. Our previous study has implied that telomerase reverse transcriptase (TERT) is associated with IPC-induced tolerance. Here, we investigated the mechanism of TERT-mediated ischemic tolerance. Preconditioning was modeled by oxygen-glucose deprivation (OGD) and by TERT inhibitor BIBR1532 in primary neurons. We found that ischemic tolerance was conferred by BIBR1532 preconditioning. We used the Cleavage-Under-Targets-And-Tagmentation approach, a recently developed method with superior signal-to-noise ratio, to comprehensively map the genomic binding sites of TERT in primary neurons, and showed that more than 50% of TERT-binding sites were located at the promoter regions. Mechanistically, we demonstrated that under normal conditions TERT physically bound to many previously unknown genomic loci in neurons, whereas BIBR1532 preconditioning significantly altered TERT-chromatin-binding profile. Intriguingly, we found that BIBR1532-preconditioned neurons showed significant up-regulation of promoter binding of TERT to the mitochondrial anti-oxidant genes, which were correlated with their elevated expression. Functional analysis further indicated that BIBR1532-preconditioning significantly reduced ROS levels and enhanced tolerance to severe ischemia-induced mitochondrial oxidative stress in neurons in a TERT-dependent manner. Together, these results demonstrate that BIBR1532 confers neuronal ischemic tolerance through TERT-mediated transcriptional reprogramming for up-regulation of mitochondrial anti-oxidation gene expression, suggesting the translational potential of BIBR1532 as a therapeutic agent for the treatment of cerebral ischemic injury and oxidative stress-induced neurological disorders.

Rifampicin Suppresses Amyloid-β Accumulation Through Enhancing Autophagy in the Hippocampus of a Lipopolysaccharide-Induced Mouse Model of Cognitive Decline

BACKGROUND

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) deposition. The metabolism of Aβ is critically affected by autophagy. Although rifampicin is known to mediate neuroinflammation, the underlying mechanism by which rifampicin regulates the cognitive sequelae remains unknown.

OBJECTIVE

Based on our previous findings that rifampicin possesses neuroprotective effects on improving cognitive function after neuroinflammation, we aimed to examine in this study whether rifampicin can inhibit Aβ accumulation by enhancing autophagy in a mouse model of lipopolysaccharide (LPS)-induced cognitive impairment.

METHODS

Adult C57BL/6 mice were intraperitoneally injected with rifampicin, chloroquine, and/or LPS every day for 7 days. Pathological and biochemical assays and behavioral tests were performed to determine the therapeutic effect and mechanism of rifampicin on the hippocampus of LPS-induced mice.

RESULTS

We found that rifampicin ameliorated cognitive impairments in the LPS-induced mice. In addition, rifampicin attenuated the inhibition of autophagosome formation, suppressed the accumulation of Aβ1-42, and protected the hippocampal neurons against LPS-induced damage. Our results further demonstrated that rifampicin improved the neurological function by promoting autophagy through the inhibition of Akt/mTOR/p70S6K signaling pathway in the hippocampus of LPS-induced mice.

CONCLUSION

Rifampicin ameliorates cognitive impairment by suppression of Aβ1-42 accumulation through inhibition of Akt/mTOR/p70S6K signaling and enhancement of autophagy in the hippocampus of LPS-induced mice.

Inhibition of PDE1-B by Vinpocetine Regulates Microglial Exosomes and Polarization Through Enhancing Autophagic Flux for Neuroprotection Against Ischemic Stroke

Exosomes contribute to cell–cell communications. Emerging evidence has shown that microglial exosomes may play crucial role in regulation of neuronal functions under ischemic conditions. However, the underlying mechanisms of microglia-derived exosome biosynthesis are largely unknown. Herein, we reported that the microglial PDE1-B expression was progressively elevated in the peri-infarct region after focal middle cerebral artery occlusion. By an oxygen-glucose-deprivation (OGD) ischemic model in cells, we found that inhibition of PDE1-B by vinpocetine in the microglial cells promoted M2 and inhibited M1 phenotype. In addition, knockdown or inhibition of PDE1-B significantly enhanced the autophagic flux in BV2 cells, and vinpocetine-mediated suppression of M1 phenotype was dependent on autophagy in ischemic conditions. Co-culture of BV2 cells and neurons revealed that vinpocetine-treated BV2 cells alleviated OGD-induced neuronal damage, and treatment of BV2 cells with 3-MA abolished the observed effects of vinpocetine. We further demonstrated that ischemia and vinpocetine treatment significantly altered microglial exosome biogenesis and release, which could be taken up by recipient neurons and regulated neuronal damage. Finally, we showed that the isolated exosome per se from conditioned BV2 cells is sufficient to regulate cortical neuronal survival in vivo. Taken together, these results revealed a novel microglia-neuron interaction mediated by microglia-derived exosomes under ischemic conditions. Our findings further suggest that PDE1-B regulates autophagic flux and exosome biogenesis in microglia which plays a crucial role in neuronal survival under cerebral ischemic conditions.

USP8 protects against lipopolysaccharide-induced cognitive and motor deficits by modulating microglia phenotypes through TLR4/MyD88/NF-κB signaling pathway in mice

Ubiquitin-specific protease 8 (USP8) regulates inflammation in vitro; however, the mechanisms by which USP8 inhibits neuroinflammation and its pathophysiological functions are not completely understood. In this study, we aimed to determine whether USP8 exerts neuroprotective effects in a mouse model of lipopolysaccharide (LPS)-induced cognitive and motor impairment. We commenced intracerebroventricular USP8 administration 7 days prior to i.p. injection of LPS (750 μg/kg). All treatments and behavioral experiments were performed once per day for 7 consecutive days. Behavioral tests and pathological/biochemical assays were performed to evaluate LPS-induced hippocampal damage. USP8 attenuated LPS-induced cognitive and motor impairments in mice. Moreover, USP8 downregulated several pro-inflammatory cytokines [nitric oxide (NO), tumor necrosis factor α (TNF-α), prostaglandin E₂ (PGE₂), and interleukin-1β (IL-1β)] in the serum and brain, and the relevant protein factors [inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2)] in the brain. Furthermore, USP8 upregulated the anti-inflammatory mediators interleukin (IL)-4 and IL-10 in the serum and brain, and promoted a shift from pro-inflammatory to anti-inflammatory microglial phenotypes. The LPS-induced microglial pro-inflammatory phenotype was abolished by TLR4 inhibitor and in TLR4^-/- mice; these effects were similar to those of USP8 treatment. Mechanistically, we found that USP8 increased the expression of neuregulin receptor degradation protein-1 (Nrdp1), potently downregulated the expression of TLR4 and myeloid differentiation primary response protein 88 (MyD88) protein, and inhibited the phosphorylation of IκB kinase (IKK) β and kappa B-alpha (IκBα), thereby reducing nuclear translocation of p65 by inhibiting the activation of the nuclear factor-kappaB (NF-κB) signaling pathway in LPS-induced mice. Our results demonstrated that USP8 exerts protective effects against LPS-induced cognitive and motor deficits in mice by modulating microglial phenotypes via TLR4/MyD88/NF-κB signaling.

Identification of Blood Circular RNAs as Potential Biomarkers for Acute Ischemic Stroke

Many hospitals lack facilities for accurate diagnosis of acute ischemic stroke (AIS). Circular RNA (circRNA) is highly expressed in the brain and is closely associated with stroke. In this study, we examined whether the blood-borne circRNAs could be promising candidates as adjunctive diagnostic biomarkers and their pathophysiological roles after stroke. We profiled the blood circRNA expression in mice subjected to experimental focal cerebral ischemia and validated the selected circRNAs in AIS patients. We demonstrated that 128, 198, and 789 circRNAs were significantly altered at 5 min, 3 h, and 24 h after ischemic stroke, respectively. Our bioinformatics analysis revealed that the circRNA-targeted genes were associated with the Hippo signaling pathway, extracellular matrix-receptor interaction, and fatty acid metabolism at 5 min, 3 h and 24 h after ischemic stroke, respectively. We verified that many of these circRNAs existed in the mouse brain. Furthermore, we found that most of the predicted circRNA-miRNA interactions apparently exhibited functional roles in terms of regulation of their target gene expression in the brain. We also verified that many of these mouse circRNAs were conserved in human. Finally, we found that circBBS2 and circPHKA2 were differentially expressed in the blood of AIS patients. These results demonstrate that blood circRNAs may serve as potential biomarkers for AIS diagnosis and reveal the pathophysiological responses in the brain after ischemic stroke.

Prostaglandin E1 Alleviates Cognitive Dysfunction in Chronic Cerebral Hypoperfusion Rats by Improving Hemodynamics

Compensatory vascular mechanisms can restore cerebral blood flow (CBF) but fail to protect against chronic cerebral hypoperfusion (CCH)-mediated neuronal damage and cognitive impairment. Prostaglandin E1 (PGE1) is known as a vasodilator to protect against ischemic injury in animal models, but its protective role in CCH remains unclear. To determine the effect of PGE1 on cerebral hemodynamics and cognitive functions in CCH, bilateral common carotid artery occlusion (BCCAO) was used to mimic CCH in rats, which were subsequently intravenously injected with PGE1 daily for 2 weeks. Magnetic resonance imaging, immunofluorescence staining and Morris water maze (MWM) were used to evaluate CBF, angiogenesis, and cognitive functions, respectively. We found that PGE1 treatment significantly restored CBF by enhancing vertebral artery dilation. In addition, PGE1 treatment increased the number of microvascular endothelial cells and neuronal cells in the hippocampus, and decreased the numbers of astrocyte and apoptotic cells. In the MWM test, we further showed that the escape latency of CCH rats was significantly reduced after PGE1 treatment. Our results suggest that PGE1 ameliorates cognitive dysfunction in CCH rats by enhancing CBF recovery, sustaining angiogenesis, and reducing astrocyte activation and neuronal loss.

A balancing act: mTOR integrates nutrient signals to regulate redox-dependent growth and survival through SOD1

Maintaining cellular redox is critical for growth, metabolism and survival in response to changing environments. How nutrients regulate this process is a long-standing fundamental question in cell biology. Our recent study revealed a conserved mechanism by which eukaryotes, particularly cancer cells, couple nutrient signaling to dynamically regulate redox homeostasis. Abbreviations: ATP: adenosine triphosphate; Ala: alanine; C₆H₁₂O₆: glucose; OH^-: hydroxyl radical; Glu: glutamate; mRNA: messenger RNA; mTOR: mechanistic/mammalian target of rapamycin; OXYPHOS: oxidative phosphorylation; Ser: serine; ROS: reactive oxygen species; O₂ ^-: superoxide; SOD1: superoxide dismutase 1; Thr: threonine.

SOD1 Phosphorylation by mTORC1 Couples Nutrient Sensing and Redox Regulation

Nutrients are not only organic compounds fueling bioenergetics and biosynthesis, but also key chemical signals controlling growth and metabolism. Nutrients enormously impact the production of reactive oxygen species (ROS), which play essential roles in normal physiology and diseases. How nutrient signaling is integrated with redox regulation is an interesting, but not fully understood, question. Herein, we report that superoxide dismutase 1 (SOD1) is a conserved component of the mechanistic target of rapamycin complex 1 (mTORC1) nutrient signaling. mTORC1 regulates SOD1 activity through reversible phosphorylation at S39 in yeast and T40 in humans in response to nutrients, which moderates ROS level and prevents oxidative DNA damage. We further show that SOD1 activation enhances cancer cell survival and tumor formation in the ischemic tumor microenvironment and protects against the chemotherapeutic agent cisplatin. Collectively, these findings identify a conserved mechanism by which eukaryotes dynamically regulate redox homeostasis in response to changing nutrient conditions.

Neuroprotective Mechanisms of Lycium barbarum Polysaccharides Against Ischemic Insults by Regulating NR2B and NR2A Containing NMDA Receptor Signaling Pathways

Glutamate excitotoxicity plays an important role in neuronal death after ischemia. However, all clinical trials using glutamate receptor inhibitors have failed. This may be related to the evidence that activation of different subunit of NMDA receptor will induce different effects. Many studies have shown that activation of the intrasynaptic NR2A subunit will stimulate survival signaling pathways, whereas upregulation of extrasynaptic NR2B will trigger apoptotic pathways. A Lycium barbarum polysaccharide (LBP) is a mixed compound extracted from Lycium barbarum fruit. Recent studies have shown that LBP protects neurons against ischemic injury by anti-oxidative effects. Here we first reported that the effect of LBP against ischemic injury can be achieved by regulating NR2B and NR2A signaling pathways. By in vivo study, we found LBP substantially reduced CA1 neurons from death after transient global ischemia and ameliorated memory deficit in ischemic rats. By in vitro study, we further confirmed that LBP increased the viability of primary cultured cortical neurons when exposed to oxygen-glucose deprivation (OGD) for 4 h. Importantly, we found that LBP antagonized increase in expression of major proteins in the NR2B signal pathway including NR2B, nNOS, Bcl-2-associated death promoter (BAD), cytochrome C (cytC) and cleaved caspase-3, and also reduced ROS level, calcium influx and mitochondrial permeability after 4 h OGD. In addition, LBP prevented the downregulation in the expression of NR2A, pAkt and pCREB, which are important cell survival pathway components. Furthermore, LBP attenuated the effects of a NR2B co-agonist and NR2A inhibitor on cell mortality under OGD conditions. Taken together, our results demonstrated that LBP is neuroprotective against ischemic injury by its dual roles in activation of NR2A and inhibition of NR2B signaling pathways, which suggests that LBP may be a superior therapeutic candidate for targeting glutamate excitotoxicity for the treatment of ischemic stroke.

Dl-3-n-Butylphthalide Treatment Enhances Hemodynamics and Ameliorates Memory Deficits in Rats with Chronic Cerebral Hypoperfusion

Our previous study has revealed that chronic cerebral hypoperfusion (CCH) activates a compensatory vascular mechanism attempting to maintain an optimal cerebral blood flow (CBF). However, this compensation fails to prevent neuronal death and cognitive impairment because neurons die prior to the restoration of normal CBF. Therefore, pharmacological invention may be critical to enhance the CBF for reducing neurodegeneration and memory deficit. Dl-3-n-butylphthalide (NBP) is a compound isolated from the seeds of Chinese celery and has been proven to be able to prevent neuronal loss, reduce inflammation and ameliorate memory deficits in acute ischemic animal models and stroke patients. In the present study, we used magnetic resonance imaging (MRI) techniques, immunohistochemistry and Morris water maze (MWM) to investigate whether NBP can accelerate CBF recovery, reduce neuronal death and improve cognitive deficits in CCH rats after permanent bilateral common carotid artery occlusion (BCCAO). Rats were intravenously injected with NBP (5 mg/kg) daily for 14 days beginning the first day after BCCAO. The results showed that NBP shortened recovery time of CBF to pre-occlusion levels at 2 weeks following BCCAO, compared to 4 weeks in the vehicle group, and enhanced hemodynamic compensation through dilation of the vertebral arteries (VAs) and increase in angiogenesis. NBP treatment also markedly reduced reactive astrogliosis and cell apoptosis and protected hippocampal neurons against ischemic injury. The escape latency of CCH rats in the MWM was also reduced in response to NBP treatment. These findings demonstrate that NBP can accelerate the recovery of CBF and improve cognitive function in a rat model of CCH, suggesting that NBP is a promising therapy for CCH patients or vascular dementia.

SOX9 is targeted for proteasomal degradation by the E3 ligase FBW7 in response to DNA damage

SOX9 encodes a transcription factor that governs cell fate specification throughout development and tissue homeostasis. Elevated SOX9 is implicated in the genesis and progression of human tumors by increasing cell proliferation and epithelial-mesenchymal transition. We found that in response to UV irradiation or genotoxic chemotherapeutics, SOX9 is actively degraded in various cancer types and in normal epithelial cells, through a pathway independent of p53, ATM, ATR and DNA-PK. SOX9 is phosphorylated by GSK3β, facilitating the binding of SOX9 to the F-box protein FBW7α, an E3 ligase that functions in the DNA damage response pathway. The binding of FBW7α to the SOX9 K2 domain at T236-T240 targets SOX9 for subsequent ubiquitination and proteasomal destruction. Exogenous overexpression of SOX9 after genotoxic stress increases cell survival. Our findings reveal a novel regulatory mechanism for SOX9 stability and uncover a unique function of SOX9 in the cellular response to DNA damage. This new mechanism underlying a FBW7-SOX9 axis in cancer could have implications in therapy resistance.

MAF1 suppresses AKT-mTOR signaling and liver cancer through activation of PTEN transcription

The phosphatidylinositol 3-kinase/phosphatidylinositol 3,4,5-trisphosphate 3-phosphatase/protein kinase B/mammalian target of rapamycin (PI3K-PTEN-AKT-mTOR) pathway is a central controller of cell growth and a key driver for human cancer. MAF1 is an mTOR downstream effector and transcriptional repressor of ribosomal and transfer RNA genes. MAF1 expression is markedly reduced in hepatocellular carcinomas, which is correlated with disease progression and poor prognosis. Consistently, MAF1 displays tumor-suppressor activity toward in vitro and in vivo cancer models. Surprisingly, blocking the synthesis of ribosomal and transfer RNAs is insufficient to account for MAF1's tumor-suppressor function. Instead, MAF1 down-regulation paradoxically leads to activation of AKT-mTOR signaling, which is mediated by decreased PTEN expression. MAF1 binds to the PTEN promoter, enhancing PTEN promoter acetylation and activity.

CONCLUSION

In contrast to its canonical function as a transcriptional repressor, MAF1 can also act as a transcriptional activator for PTEN, which is important for MAF1's tumor-suppressor function. These results have implications in disease staging, prognostic prediction, and AKT-mTOR-targeted therapy in liver cancer. (Hepatology 2016;63:1928-1942).

Superoxide dismutase 1 acts as a nuclear transcription factor to regulate oxidative stress resistance

Superoxide dismutase 1 (Sod1) has been known for nearly half a century for catalysis of superoxide to hydrogen peroxide. Here we report a new Sod1 function in oxidative signalling: in response to elevated endogenous and exogenous reactive oxygen species (ROS), Sod1 rapidly relocates into the nucleus, which is important for maintaining genomic stability. Interestingly, H2O2 is sufficient to promote Sod1 nuclear localization, indicating that it is responding to general ROS rather than Sod1 substrate superoxide. ROS signalling is mediated by Mec1/ATM and its effector Dun1/Cds1 kinase, through Dun1 interaction with Sod1 and regulation of Sod1 by phosphorylation at S60, 99. In the nucleus, Sod1 binds to promoters and regulates the expression of oxidative resistance and repair genes. Altogether, our study unravels an unorthodox function of Sod1 as a transcription factor and elucidates the regulatory mechanism for its localization.

Fabrication of nano-scale Cu bond pads with seal design in 3D integration applications

A method to fabricate nano-scale Cu bond pads for improving bonding quality in 3D integration applications is reported. The effect of Cu bonding quality on inter-level via structural reliability for 3D integration applications is investigated. We developed a Cu nano-scale-height bond pad structure and fabrication process for improved bonding quality by recessing oxides using a combination of SiO2 CMP process and dilute HF wet etching. In addition, in order to achieve improved wafer-level bonding, we introduced a seal design concept that prevents corrosion and provides extra mechanical support. Demonstrations of these concepts and processes provide the feasibility of reliable nano-scale 3D integration applications.

Acrylamide in Asian foods in Hong Kong

About 400 food samples, mainly Asian foods available in Hong Kong, were tested for acrylamide by an LC-MS/MS method using [1, 2, 3-(13)C(3)]-acrylamide as surrogate. The acrylamide levels in the more commonly consumed food items in the food groups such as rice and rice products, noodles, bakery and batter-based products, were generally less than 60 microg kg(-1). Higher levels were found in the food groups such as biscuit-related products and crisps. The highest levels were detected in potato crisps (1500-1700 microg kg(-1)). Lower levels were found in rye flour-based crisps (440 microg kg(-1)), followed by corn-based (65 to 230 microg kg(-1)) and wheat flour-based crisps (61-200 microg kg(-1)), and then rice flour-based crisps (15-42 microg kg(-1)). The acrylamide formation during deep frying of a wheat flour-based product, Chinese fried fritter, was studied. Deep-frying at 170 degrees C resulted in gentle but steady rise in acrylamide content. A steep rise for frying at 210 degrees C was recorded. The moisture content of the product decreased with frying time, but the fat content increased. It is proposed that the reaction for the formation of acrylamide was initiated on the surface and then penetrated into the interior of the food matrix by heat transfer via radiation/conduction and diffusion of hot oil.

mTOR binds to the promoters of RNA polymerase I- and III-transcribed genes

Target of rapamycin (TOR) is a conserved regulator of gene expression from yeast to humans. In budding yeast, TOR is associated with ribosomal DNA (rDNA) promoter, which is critical for ribosome biogenesis and transfer RNA (tRNA) synthesis. Whether mTOR behaves similarly in mammalian cells is unknown. Here, we report that mTOR is detected at several different promoters in human and murine cells, including that of rDNA and tRNA genes. The association of mTOR with these promoters is regulated by growth signals and sensitive to rapamycin. Together, our observations suggest that mTOR is closely involved in gene regulation at the promoters, which is a conserved mechanism to control RNA polymerase I- and III-dependent genes that are critical for protein synthesis and cell growth.

Mechanisms of regulation of RNA polymerase III-dependent transcription by TORC1

We have found earlier that Tor1 binds to 5S rDNA chromatin but the functional significance has not been established. Here, we show that association with 5S rDNA chromatin is necessary for TOR complex 1 (TORC1) to regulate the synthesis of 5S ribosomal RNA and transfer RNAs (tRNAs) by RNA polymerase (Pol) III, as well as the phosphorylation and binding to Pol III-transcribed genes of the Pol III repressor Maf1. Interestingly, TORC1 does not bind to tRNA genes, suggesting that TORC1 modulates tRNA synthesis indirectly through Maf1 phosphorylation at the rDNA loci. We also find that Maf1 cytoplasmic localization is dependent on the SSD1-v allele. In W303 cells that carry the SSD1-d allele, Maf1 is constitutively nuclear but its nucleolar localization is inhibited by TORC1, indicating that TORC1 regulates nucleoplasm-to-nucleolus transport of Maf1. Finally, we show that TORC1 interacts with Maf1 in vivo and phosphorylates Maf1 in vitro, and regulates Maf1 nucleoplasm-to-nucleolus translocation. Together, these observations provide new insights into the chromatin-dependent mechanism by which TORC1 controls transcription by Pol III.

Opposing role of condensin and radiation-sensitive gene RAD52 in ribosomal DNA stability regulation

Blocking target of rapamycin signaling by starvation or rapamycin inhibits ribosomal DNA (rDNA) transcription and causes condensin-mediated rDNA condensation and nucleolar contraction. In the absence of condensin, however, repression of rDNA transcription leads to rDNA instability and elevated level of extrachromosomal rDNA circles and nucleolar fragmentation. Here, we show that mutations in the Rad52 homologous recombination machinery block rDNA instability. Rad52 is normally excluded from the nucleolus. In the absence of condensin, however, repression of rDNA transcription results in Rad52 localization to the nucleolus, association with rDNA and subsequent formation of extrachromosomal rDNA circles, and reduced cell survival. In contrast, deletion of RAD52 restores cell viability under the same conditions. These results reveal an opposing role of condensin and Rad52 in the control of rDNA stability under nutrient starvation conditions.

Compacting DNA during the interphase: condensin maintains rDNA integrity

During mitosis, condensin is responsible for folding chromatin fibers into highly compact chromosomes, ensuring the faithful segregation of replicated chromosomes into daughter cells after each cell division. Our laboratory has unexpectedly found that condensin is capable of condensing DNA during the interphase: upon nutrient starvation, condensin is loaded to the rDNA array, leading to DNA condensation in this region. This subchromosomal DNA condensation appears to protect the integrity of the rDNA array. These observations provide the first microscopic evidence of DNA compaction by condensin outside mitosis. In addition, they show that condensin is also highly regulated outside mitosis.

TOR-in(g) the nucleus

Target of rapamycin (TOR) is a central component of the eukaryotic growth regulatory network. TOR controls the expression of diverse genes by all three RNA polymerases, including ribosome biogenesis, utilization and transport of nutrients, and stress-related genes. Until recently, TOR was thought to be a classical signaling kinase that regulates transcription factors in the cytoplasm. However, our recent study shows that in yeast, TOR dynamically shuttles between the cytoplasm and nucleus, and binds to 35S ribosomal DNA (rDNA) promoter. Importantly, nuclear localization and promoter-binding is crucial for TOR to control RNA polymerase (Pol) I-dependent 35S rDNA transcription. In contrast, either cytoplasmic or nuclear TOR is sufficient to regulate Pol II-dependent transcription. These observations suggest that TOR in the nucleus plays an important role in gene regulation, and that TOR takes a multifaceted approach to control expression of different genes.

Nutrient starvation promotes condensin loading to maintain rDNA stability

Nutrient starvation or rapamycin treatment, through inhibition of target of rapamycin, causes condensation of ribosomal DNA (rDNA) array and nucleolar contraction in budding yeast. Here we report that under such conditions, condensin is rapidly relocated into the nucleolus and loaded to rDNA tandem repeats, which is required for rDNA condensation. Rpd3-dependent histone deacetylation is necessary and sufficient for condensin's relocalization and loading to rDNA array, suggesting that histone modification plays a regulatory role for condensin targeting. Rapamycin independently, yet coordinately, inhibits rDNA transcription and promotes condensin loading to rDNA array. Unexpectedly, we found that inhibition of rDNA transcription in the absence of condensin loading leads to rDNA instability. Our data suggest that enrichment of condensin prevents rDNA instability during nutrient starvation. Together, these observations unravel a novel role for condensin in the maintenance of regional genomic stability.

Targeting mammalian target of rapamycin (mTOR) for health and diseases

The macrolide rapamycin is used clinically to treat graft rejection and restenosis. Mammalian target of rapamycin (mTOR) is a central controller of cellular and organism growth that integrates nutrient and hormonal signals, and regulates diverse cellular processes. New studies have linked mTOR to several human diseases including cancer, diabetes, obesity, cardiovascular diseases and neurological disorders. Recent data have also revealed that mTOR is involved in the regulation of lifespan and in age-related diseases. These findings demonstrate the importance of growth control in the pathology of major diseases and overall human health, and underscore the therapeutic potential of the mTOR pathway.

Nutrient regulates Tor1 nuclear localization and association with rDNA promoter

TOR is the target of the immunosuppressant rapamycin and a key regulator of cell growth. It modulates diverse cellular processes in the cytoplasm and nucleus, including the expression of amino acid transporters, ribosomal RNAs and ribosomal proteins. Despite considerable recent progress, little is known about the spatial and temporal regulation of TOR signalling, particularly that leading into the nucleus. Here we show that Tor1 is dynamically distributed in the cytoplasm and nucleus in yeast. Tor1 nuclear localization is nutrient dependent and rapamycin sensitive: starvation or treatment with rapamycin causes Tor1 to exit from the nucleus. Tor1 nuclear localization is critical for 35S rRNA synthesis, but not for the expression of amino acid transporters and ribosomal protein genes. We show further that Tor1 is associated with 35S ribosomal DNA (rDNA) promoter chromatin in a rapamycin- and starvation-sensitive manner; this association is necessary for 35S rRNA synthesis and cell growth. These results indicate that the spatial regulation of TOR complex 1 (TORC1) might be involved in differential control of its target genes. TOR is known as a classic cytoplasmic kinase that mediates the cytoplasm-to-nucleus signalling by controlling the localization of transcription factors. Our data indicate that TOR might be more intimately involved in gene regulation than previously thought.

Sargachromenol, a novel nerve growth factor-potentiating substance isolated from Sargassum macrocarpum, promotes neurite outgrowth and survival via distinct signaling pathways in PC12D cells

We previously found that the methanol extract of a marine brown alga, Sargassum macrocarpum showed marked nerve growth factor (NGF)-dependent neurite outgrowth promoting activity to PC12D cells. The active substance purified was elucidated to be sargachromenol. The median effective dose (ED50) was 9 microM against PC12D cells in the presence of 10 ng/ml NGF, although it showed no neurotrophic effect on its own. Pretreatment of cells with protein kinase A (PKA) inhibitor or U0126 substantially suppressed the sargachromenol-enhanced neurite outgrowth from PC12D cells, suggesting that the activation of cyclic AMP-mediated protein kinase and mitogen-activated protein (MAP) kinase 1/2 was apparently required for the action of sargachromenol. On the other hand, sargachromenol significantly promoted the survival of neuronal PC12D cells at 0-50 ng/ml NGF in serum-free medium. Neither PKA inhibitor nor U0126 could inhibit the survival supporting effect of sargachromenol, whereas wortmannin significantly blocked the sargachromenol-induced survival supporting effect on neuronal PC12D cells, suggesting that sargachromenol rescued neuronal PC12D cells by activating phosphatidylinositol-3 kinase. These results demonstrate that sargachromenol promotes neuronal differentiation of PC12D cells and supports the survival of neuronal PC12D cells via two distinct signaling pathways.

Sargaquinoic acid supports the survival of neuronal PC12D cells in a nerve growth factor-independent manner

Sargaquinoic acid (designated previously as MC14) was isolated from a marine brown alga Sargassum macrocarpum, and has been found to possess a novel nerve growth factor (NGF)-dependent neurite outgrowth promoting activity in PC12D cells. In this study, we explored the neuroprotective effects of MC14 in terms of its survival supporting, antioxidant and neurite-regenerating activities under NGF deficient or deprived conditions. Intriguingly, MC14 did not only promote the NGF-induced survival support on neuronal PC12D cells, but also significantly abated neuronal PC12D cell death even in the absence of NGF. The pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K) by wortmannin significantly suppressed the survival supporting activity of MC14, whereas the NGF receptor (tyrosine kinase A or TrkA) inhibitor K252a showed no detectable effect on MC14 activity. These results demonstrate that MC14 supports survival of neuronal PC12D cells in an NGF-independent manner, and that PI3K may be required for the neuroprotective activity of MC14. In addition, we have shown that MC14 markedly enhanced neurite-regeneration and protected PC12D cells from hydrogen peroxide (H(2)O(2))-induced oxidative stress. These pharmacological features suggest that MC14 may be a potentially important neuroprotective agent.

Chromatin-mediated regulation of nucleolar structure and RNA Pol I localization by TOR

The target of rapamycin (TOR) protein is a conserved regulator of ribosome biogenesis, an important process for cell growth and proliferation. However, how TOR is involved remains poorly understood. In this study, we find that rapamycin and nutrient starvation, conditions inhibiting TOR, lead to significant nucleolar size reduction in both yeast and mammalian cells. In yeast, this morphological change is accompanied by release of RNA polymerase I (Pol I) from the nucleolus and inhibition of ribosomal DNA (rDNA) transcription. We also present evidence that TOR regulates association of Rpd3-Sin3 histone deacetylase (HDAC) with rDNA chromatin, leading to site-specific deacetylation of histone H4. Moreover, histone H4 hypoacetylation mutations cause nucleolar size reduction and Pol I delocalization, while rpd3Delta and histone H4 hyperacetylation mutations block the nucleolar changes as a result of TOR inhibition. Taken together, our results suggest a chromatin-mediated mechanism by which TOR modulates nucleolar structure, RNA Pol I localization and rRNA gene expression in response to nutrient availability.

Sargaquinoic acid promotes neurite outgrowth via protein kinase A and MAP kinases-mediated signaling pathways in PC12D cells

We previously isolated a nerve growth factor (NGF)-dependent neurite outgrowth promoting substance MC14 (sargaquinoic acid) from a marine brown alga, Sargassum macrocarpum. In the present study, the NGF-potentiating activity of MC14 to neural differentiation of PC12D cells was investigated in detail. The treatment of cells with 3 microg/ml MC14 in the presence of 1.25-100 ng/ml NGF markedly enhanced the proportion of neurite-bearing cells compared with the NGF-only controls. In addition, MC14 significantly elevated the NGF-induced specific acetylcholinesterase (AchE) activity in PC12D cells, suggesting that MC14 could morphologically and biochemically promote the differentiation of PC12D cells. The mechanism of action of MC14 was further investigated by pharmacological inhibition of several intracellular signaling molecules. Results indicated that the neurite outgrowth promoting activity of MC14 was almost completely blocked by 10 microM PD98059, suggesting that a TrkA-dependent MAP kinases-mediated signaling pathway may play a crucial role in modulating the effect of MC14. Besides, the MC14-enhanced neurite outgrowth was substantially suppressed by the pretreatment with 10 ng/ml protein kinase A (PKA) inhibitor, demonstrating that the adenylate cyclase-PKA signaling cascade was also involved in the action of MC14. In contrast, a PKC inhibitor chelerythrine chloride did not inhibit the neurite outgrowth promoting activity of MC14. Altogether, these results demonstrate that MC14 enhances the neurite outgrowth by cooperating at least two separated signaling pathways, a TrkA-MAP kinases pathway and an adenylate cyclase-PKA pathway, in PC12D cells.

Regulation of subtelomeric silencing during stress response

Sir proteins play a critical role in silent chromatin domains. While mutations can cause derepression of heterochromatin, it remains unclear whether silencing is actively involved in transcriptional control under changing environmental conditions. We find that TOR inhibits Sir3 phosphorylation. Rapamycin or stress induced by chlorpromazine leads to activation of MAP kinase Mpk1/Slt2, which phosphorylates Sir3. Sir3 hyperphosphorylation is correlated with reduced subtelomeric silencing, increased subtelomeric cell wall gene expression, and stress resistance to chlorpromazine, but does not affect the silent HML and rDNA loci. Based on these observations, we propose that regulation of silencing may be used to control gene expression at specific silent chromatin domains in response to stress and possibly other environmental changes.

Novel effect of vitamin K(1) (phylloquinone) and vitamin K(2) (menaquinone) on promoting nerve growth factor-mediated neurite outgrowth from PC12D cells

The nerve growth factor (NGF)-potentiating effect of K vitamins on PC12D cells was investigated. Treatment of PC12D cells with vitamin K(1) or K(2) in the presence of NGF significantly enhanced the proportion of neurite-bearing cells and acetylcholinesterase activity compared with NGF treatment alone. The K vitamins-enhanced neurite outgrowth on PC12D cells was completely blocked by a protein kinase A (PKA) inhibitor or mitogen-activated protein kinase (MAPK) kinase inhibitor PD98059, whereas a protein kinase C inhibitor chelerythrine chloride did not significantly inhibit the enhancing effect of the K vitamins. These results suggest that the K vitamins enhance neurite outgrowth via the activation of PKA and MAPK-mediated signaling pathways in PC12D cells.

A YRBS survey of youth risk behaviors at alternative high schools and mainstream high schools in Hong Kong

In Hong Kong, prevocational schools serve as an alternative to mainstream schools to provide education with more emphasis on practical and technical subjects. In this paper, health-risk behaviors of prevocational school (PVS) students were identified, and comparisons of health-risk behaviors with or without adjusting the demographic factors from prevocational schools and mainstream schools were made. The PVS students were at higher risk for most categories of health-risk behaviors such as unintentional and intentional injuries, smoking, alcohol drinking, glue sniffing, inadequate physical activity, insufficient consumption of fresh fruits and vegetables, and early sexual activity with multiple partners. Female students of PVS reported higher prevalence of emotional problems and substance abuse. Findings suggest that the school environment is an influential factor on the lifestyle behavior of students. Comprehensive health education and intervention programs are needed for youth in Hong Kong prevocational schools.

Older school children are not necessarily healthier: analysis of medical consultation pattern of school children from a territory-wide School Health Surveillance

It is important to maintain the health of our school children as health is a major factor affecting learning. In developed countries, we assume that school children, especially in higher grades, are healthy because they are relatively free of diseases. However, many of the health problems encountered by school children are not reported in routine health data as they seek help in primary care or by self-medication. In this paper, the medical consultation pattern of school children in Hong Kong was analyzed. It was revealed that school children had a high rate of consultation and self-medication, and the health status of older school children is not better. They were not offered adequate preventive advice. The piecemeal approach to focus on curative medicine will only lead to a high rate of episodic consultation and self-medication without empowering the young people with the skills of self-care and self-help, and positive health behavior. The concept of a health-promoting school with emphasis on more extra-curricular health promotion activities, improved communication between health and education sectors, active involvement by pupils and parents, and changing policies and practices would help to make the co-ordinated school health program a greater success.

Biodegradation capacity of tributyltin by two Chlorella species

Two microalgal species, Chlorella vulgaris and Chlorella sp., which showed high tributyltin (TBT) tolerant ability were investigated for their capabilities in degrading TBT at sublethal concentration. The distribution of TBT and its degraded products dibutyltin (DBT) and monobutyltin (MBT) in the incubation medium, extracellular surface and intracellular fraction were monitored during an exposure period of 14 days. Results showed that biosorption of TBT by the algal cell wall was the major mechanism in reducing 40% of the initial TBT from the medium in the first 2 days. The half-life of TBT incubated with C. vulgaris was 60 h while that of Chlorella sp. was 80 h. The occurrence of DBT at Day 1 in the culture medium provided direct evidence to the biodegradation of TBT by both Chlorella species. At the end of the experimental period, 27 and 41% of the original TBT were recovered as DBT and MBT in cultures of C. vulgaris, respectively. In contrast, DBT appeared to be the only degradation product of Chlorella sp. and only 26% of the original TBT was transformed to DBT. Despite the same genus, TBT was debutylated to a greater extent to MBT by C. vulgaris, while DBT was the end degradation product by Chlorella sp. The capability of such debutylating process therefore accounted for the higher tolerant ability of C. vulgaris than Chlorella sp.