In vivo recording of suprachiasmatic nucleus dynamics reveals a dominant role of arginine vasopressin neurons in circadian pacesetting.

The central circadian clock of the suprachiasmatic nucleus (SCN) is a network consisting of various types of neurons and glial cells. Individual cells have the autonomous molecular machinery of a cellular clock, but their intrinsic periods vary considerably. Here, we show that arginine vasopressin (AVP) neurons set the ensemble period of the SCN network in vivo to control the circadian behavior rhythm. Artificial lengthening of cellular periods by deleting casein kinase 1 delta (CK1δ) in the whole SCN lengthened the free-running period of behavior rhythm to an extent similar to CK1δ deletion specific to AVP neurons. However, in SCN slices, PER2::LUC reporter rhythms of these mice only partially and transiently recapitulated the period lengthening, showing a dissociation between the SCN shell and core with a period instability in the shell. In contrast, in vivo calcium rhythms of both AVP and vasoactive intestinal peptide (VIP) neurons in the SCN of freely moving mice demonstrated stably lengthened periods similar to the behavioral rhythm upon AVP neuron-specific CK1δ deletion, without changing the phase relationships between each other. Furthermore, optogenetic activation of AVP neurons acutely induced calcium increase in VIP neurons in vivo. These results indicate that AVP neurons regulate other SCN neurons, such as VIP neurons, in vivo and thus act as a primary determinant of the SCN ensemble period.

A Farnesyltransferase Inhibitor Restores Cognitive Deficits in Tsc2+/- Mice through Inhibition of Rheb1.

Tuberous sclerosis complex (TSC) is caused by mutations in Tsc1 or Tsc2, whose gene products inhibit the small G-protein Rheb1. Rheb1 activates mTORC1, which may cause refractory epilepsy, intellectual disability, and autism. The mTORC1 inhibitors have been used for TSC patients with intractable epilepsy. However, its effectiveness for cognitive symptoms remains unclear. We found a new signaling pathway for synapse formation through Rheb1 activation, but not mTORC1. Here, we show that treatment with the farnesyltransferase inhibitor lonafarnib increased unfarnesylated (inactive) Rheb1 levels and restored synaptic abnormalities in cultured Tsc2+/- neurons, whereas rapamycin did not enhance spine synapse formation. Lonafarnib treatment also restored the plasticity-related Arc (activity-regulated cytoskeleton-associated protein) expression in cultured Tsc2+/- neurons. Lonafarnib action was partly dependent on the Rheb1 reduction with syntenin. Oral administration of lonafarnib increased unfarnesylated protein levels without affecting mTORC1 and MAP (mitogen-activated protein (MAP)) kinase signaling, and restored dendritic spine morphology in the hippocampi of male Tsc2+/- mice. In addition, lonafarnib treatment ameliorated contextual memory impairments and restored memory-related Arc expression in male Tsc2+/- mice in vivo Heterozygous Rheb1 knockout in male Tsc2+/- mice reproduced the results observed with pharmacological treatment. These results suggest that the Rheb1 activation may be responsible for synaptic abnormalities and memory impairments in Tsc2+/- mice, and its inhibition by lonafarnib could provide insight into potential treatment options for TSC-associated neuropsychiatric disorders.SIGNIFICANCE STATEMENT Tuberous sclerosis complex (TSC) is an autosomal-dominant disease that causes neuropsychiatric symptoms, including intractable epilepsy, intellectual disability (ID) and autism. No pharmacological treatment for ID has been reported so far. To develop a pharmacological treatment for ID, we investigated the mechanism of TSC and found that Rheb1 activation is responsible for synaptic abnormalities in TSC neurons. To inhibit Rheb1 function, we used the farnesyltransferase inhibitor lonafarnib, because farnesylation of Rheb1 is required for its activation. Lonafarnib treatment increased inactive Rheb1 and recovered proper synapse formation and plasticity-related Arc (activity-regulated cytoskeleton-associated protein) expression in TSC neurons. Furthermore, in vivo lonafarnib treatment restored contextual memory and Arc induction in TSC mice. Together, Rheb1 inhibition by lonafarnib could provide insight into potential treatments for TSC-associated ID.

Spine morphogenesis and synapse formation in tubular sclerosis complex models.

Tuberous sclerosis complex (TSC) is caused by mutations in the Tsc1 or Tsc2 genes, whose products form a complex and inactivate the small G-protein Rheb1. The activation of Rheb1 may cause refractory epilepsy, intellectual disability, and autism, which are the major neuropsychiatric manifestations of TSC. Abnormalities in dendritic spines and altered synaptic structure are hallmarks of epilepsy, intellectual disability, and autism. In addition, spine dysmorphology and aberrant synapse formation are observed in TSC animal models. Therefore, it is important to investigate the molecular mechanism underlying the regulation of spine morphology and synapse formation in neurons to identify therapeutic targets for TSC. In this review, we focus on the representative proteins regulated by Rheb1 activity, mTORC1 and syntenin, which are pivotal downstream factors of Rheb1 in the alteration of spine formation and synapse function in TSC neurons.

Tuberous Sclerosis Complex (TSC) Inactivation Increases Neuronal Network Activity by Enhancing Ca2+ Influx via L-Type Ca2+ Channels.

Tuberous sclerosis complex (TSC) is a multisystem developmental disorder characterized by hamartomas in various organs, such as the brain, lungs, and kidneys. Epilepsy, along with autism and intellectual disability, is one of the neurologic impairments associated with TSC that has an intimate relationship with developmental outcomes and quality of life. Sustained activation of the mammalian target of rapamycin (mTOR) via TSC1 or TSC2 mutations is known to be involved in the onset of epilepsy in TSC. However, the mechanism by which mTOR causes seizures remains unknown. In this study, we showed that, human induced pluripotent stem cell-derived TSC2-deficient (TSC2-/-) neurons exhibited elevated neuronal activity with highly synchronized Ca2+ spikes. Notably, TSC2-/- neurons presented enhanced Ca2+ influx via L-type Ca2+ channels (LTCCs), which contributed to the abnormal neurite extension and sustained activation of cAMP response element binding protein (CREB), a critical mediator of synaptic plasticity. Expression of Cav1.3, a subtype of LTCCs, was increased in TSC2-/- neurons, but long-term rapamycin treatment suppressed this increase and reversed the altered neuronal activity and neurite extensions. Thus, we identified Cav1.3 LTCC as a critical downstream component of TSC-mTOR signaling that would trigger enhanced neuronal network activity of TSC2-/- neurons. We suggest that LTCCs could be potential novel targets for the treatment of epilepsy in TSC.SIGNIFICANCE STATEMENT There is a close relationship between elevated mammalian target of rapamycin (mTOR) activity and epilepsy in tuberous sclerosis complex (TSC). However, the underlying mechanism by which mTOR causes epilepsy remains unknown. In this study, using human TSC2-/- neurons, we identified elevated Ca2+ influx via L-type Ca2+ channels as a critical downstream component of TSC-mTOR signaling and a potential cause of both elevated neuronal activity and neurite extension in TSC2-/- neurons. Our findings demonstrate a previously unrecognized connection between sustained mTOR activation and elevated Ca2+ signaling via L-type Ca2+ channels in human TSC neurons, which could cause epilepsy in TSC.

Dendritic Spine Density is Increased in Arcadlin-deleted Mouse Hippocampus.

The neural network undergoes remodeling in response to neural activity and interventions, such as antidepressants. Cell adhesion molecules that link pre- and post-synaptic membranes are responsible not only for the establishment of the neural circuitry, but also for the modulation of the strength of each synaptic connection. Among the various classes of synaptic cell adhesion molecules, a non-clustered protocadherin, Arcadlin/Paraxial protocadherin/Protocadherin-8 (Acad), is unique in that it is induced quickly in response to neural activity. Although the primary structure of Arcadlin implies its cell adhesion activity, it weakens the adhesion of N-cadherin. Furthermore, Arcadlin reduces the dendritic spine density in cultured hippocampal neurons. In order to gain an insight into the function of Arcadlin in the brain, we examined the dendritic morphologies of the hippocampal neurons in Acad-/- mice. Acad-/- mice showed a higher spine density than wild-type mice. Following an electroconvulsive seizure (ECS), which strongly induces Arcadlin in the hippocampus, the spine density gradually decreased for 8 h. ECS did not reduce the spine density of CA1 apical dendrites in Acad-/- mice. Daily intraperitoneal injection of the antidepressant fluoxetine (25 mg/kg/day) for 18 days resulted in the induction of Arcadlin in the hippocampus. This treatment reduced spine density in the dentate gyrus and CA1. Chronic fluoxetine treatment did not suppress spine density in Acad-/- mice, suggesting that fluoxetine-induced decrease in spine density is largely due to Arcadlin. The present findings confirm the spine-repulsing activity of Arcadlin and its involvement in the remodeling of hippocampal neurons in response to antidepressants.

Serotonin induces Arcadlin in hippocampal neurons.

The monoamine hypothesis does not fully explain the delayed onset of recovery after antidepressant treatment or the mechanisms of recovery after electroconvulsive therapy (ECT). The common mechanism that operates both in ECT and monoaminergic treatment presumably involves molecules induced in both of these conditions. A spine density modulator, Arcadlin (Acad), the rat orthologue of human Protocadherin-8 (PCDH8) and of Xenopus and zebrafish Paraxial protocadherin (PAPC), is induced by both electroconvulsive seizure (ECS) and antidepressants; however, its cellular mechanism remains elusive. Here we confirm induction of Arcadlin upon stimulation of an N-methyl-d-aspartate (NMDA) receptor in cultured hippocampal neurons. Stimulation of an NMDA receptor also induced acute (20 min) and delayed (2 h) phosphorylation of the p38 mitogen-activated protein (MAP) kinase; the delayed phosphorylation was not obvious in Acad-/- neurons, suggesting that it depends on Arcadlin induction. Exposure of highly mature cultured hippocampal neurons to 1-10 µM serotonin for 4 h resulted in Arcadlin induction and p38 MAP kinase phosphorylation. Co-application of the NMDA receptor antagonist d-(-)-2-amino-5-phosphonopentanoic acid (APV) completely blocked Arcadlin induction and p38 MAP kinase phosphorylation. Finally, administration of antidepressant fluoxetine in mice for 16 days induced Arcadlin expression in the hippocampus. Our data indicate that the Arcadlin-p38 MAP kinase pathway is a candidate neural network modulator that is activated in hippocampal neurons under the dual regulation of serotonin and glutamate and, hence, may play a role in antidepressant therapies.

Syntenin: PDZ Protein Regulating Signaling Pathways and Cellular Functions.

Syntenin is an adaptor-like molecule that has two adjacent tandem postsynaptic density protein 95/Discs large protein/Zonula occludens 1 (PDZ) domains. The PDZ domains of syntenin recognize multiple peptide motifs with low to moderate affinity. Many reports have indicated interactions between syntenin and a plethora of proteins. Through interactions with various proteins, syntenin regulates the architecture of the cell membrane. As a result, increases in syntenin levels induce the metastasis of tumor cells, protrusion along the neurite in neuronal cells, and exosome biogenesis in various cell types. Here, we review the updated data that support various roles for syntenin in the regulation of neuronal synapses, tumor cell invasion, and exosome control.

Role of neuritin in retinal ganglion cell death in adult mice following optic nerve injury.

Neuritin is a small extracellular protein that plays important roles in the process of neural development, synaptic plasticity, and neural cell survival. Here we investigated the function of neuritin in a mouse model of optic nerve injury (ONI). ONI induced upregulation of neuritin mRNA in the retina of WT mice. The retinal structure and the number of retinal ganglion cells (RGCs) were normal in adult neuritin knockout (KO) mice. In vivo retinal imaging and histopathological analyses demonstrated that RGC death and inner retinal degeneration following ONI were more severe in neuritin KO mice. Immunoblot analyses revealed that ONI-induced phosphorylation of Akt and ERK were suppressed in neuritin KO mice. Our findings suggest that neuritin has neuroprotective effects following ONI and may be useful for treatment of posttraumatic complication.

Pentylenetetrazole-Induced Kindling Mouse Model.

Pentylenetetrazole (PTZ) is a GABA-A receptor antagonist. An intraperitoneal injection of PTZ into an animal induces an acute, severe seizure at a high dose, whereas sequential injections of a subconvulsive dose have been used for the development of chemical kindling, an epilepsy model. A single low-dose injection of PTZ induces a mild seizure without convulsion. However, repetitive low-dose injections of PTZ decrease the threshold to evoke a convulsive seizure. Finally, continuous low-dose administration of PTZ induces a severe tonic-clonic seizure. This method is simple and widely applicable to investigate the pathophysiology of epilepsy, which is defined as a chronic disease that involves repetitive seizures. This chemical kindling protocol causes repetitive seizures in animals. With this method, vulnerability to PTZ-mediated seizures or the degree of aggravation of epileptic seizures was estimated. These advantages have led to the use of this method for screening anti-epileptic drugs and epilepsy-related genes. In addition, this method has been used to investigate neuronal damage after epileptic seizures because the histological changes observed in the brains of epileptic patients also appear in the brains of chemical-kindled animals. Thus, this protocol is useful for conveniently producing animal models of epilepsy.

Brain Interleukin-1 Facilitates Learning of a Water Maze Spatial Memory Task in Young Mice.

The proinflammatory cytokine interleukin-1 (IL-1) is produced by many types of cells, including immune cells in the periphery and glia and neurons in the brain. The type I IL-1 receptor (IL-1r1) is primarily responsible for transmitting the inflammatory effects of IL-1 and mediates several biological functions by binding to either IL-1α or IL-1ß. IL-1ß activation is associated with hippocampus-dependent memory tasks. Although IL-1ß impairs spatial memory under certain pathophysiological conditions, IL-1ß may be required for the normal physiological regulation of hippocampal plasticity and memory. In addition, brain IL-1ß levels are thought to change in the hippocampus in an age-dependent manner. These findings suggest that IL-1ß may have a beneficial, temporary effect on learning and memory in young mice, but the matter remains unclear. Therefore, we hypothesized that hippocampal IL-1ß has a beneficial effect on spatial learning and memory in young mice via IL-1r1, which is diminished in adults. We investigated the performance of young (3-month-old) and adult (6-month-old) wild-type mice, IL-1ß knockout mice (IL-1ßko) and IL-1r1 knockout mice (IL-1r1ko) in learning a spatial memory task with a fixed platform in a water maze (WM) and measured the levels of IL-1ß and IL-1α in the hippocampus and cortex of adult and young mice by using homogeneous time-resolved fluorescence (HTRF). Learning was significantly impaired in the training trials of the WM spatial memory task in young IL-1ßko and IL-1r1ko mice but not in adult IL-1ßko and IL-1r1ko mice. Moreover, young IL-1r1ko mice but not IL-1ßko mice showed an impairment in long-term memory extinction, suggesting that IL-1α might facilitate memory extinction. In this study, the cytokine assay using HTRF did not indicate a higher expression of hippocampal IL-1 in young mice but cortical IL-1ß and IL-1α were significantly increased in adult mice. We need to investigate the role of cortical IL-1 and the local IL-1 expression in the hippocampal neurons in the future.

Neuritin Mediates Activity-Dependent Axonal Branch Formation in Part via FGF Signaling.

Aberrant branch formation of granule cell axons (mossy fiber sprouting) is observed in the dentate gyrus of many patients with temporal lobe epilepsy and in animal models of epilepsy. However, the mechanisms underlying mossy fiber sprouting remain elusive. Based on the hypothesis that seizure-mediated gene expression induces abnormal mossy fiber growth, we screened activity-regulated genes in the hippocampus and found that neuritin, an extracellular protein anchored to the cell surface, was rapidly upregulated after electroconvulsive seizures. Overexpression of neuritin in the cultured rat granule cells promoted their axonal branching. Also, kainic acid-dependent axonal branching was abolished in the cultured granule cells fromneuritinknock-out mice, suggesting that neuritin may be involved in activity-dependent axonal branching. Moreover,neuritinknock-out mice showed less-severe seizures in chemical kindling probably by reduced mossy fiber sprouting and/or increased seizure resistance. We found that inhibition of the fibroblast growth factor (FGF) receptor attenuated the neuritin-dependent axonal branching. FGF administration also increased branching in granule neurons, whereasneuritinknock-out mice did not show FGF-dependent axonal branching. In addition, FGF and neuritin treatment enhanced the recruitment of FGF receptors to the cell surface. These findings suggest that neuritin and FGF cooperate in inducing mossy fiber sprouting through FGF signaling. Together, these results suggest that FGF and neuritin-mediated axonal branch induction are involved in the aggravation of epilepsy. SIGNIFICANCE STATEMENT: This study reveals the molecular mechanism underlying mossy fiber sprouting. Mossy fiber sprouting is the aberrant axonal branching of granule neurons in the hippocampus, which is observed in patients with epilepsy. Excess amounts of neuritin, a protein upregulated by neural activity, promoted axonal branching in granule neurons. A deficiency of neuritin suppressed mossy fiber sprouting and resulted in mitigation of seizure severity. Neuritin and fibroblast growth factor (FGF) cooperated in stimulating FGF signaling and enhancing axonal branching. Neuritin is necessary for FGF-mediated recruitment of FGF receptors to the cell surface. The recruitment of FGF receptors would promote axonal branching. The discovery of this new mechanism should contribute to the development of novel antiepileptic drugs to inhibit axonal branching via neuritin-FGF signaling.

Glucose-dependent acetylation of Rictor promotes targeted cancer therapy resistance.

Cancer cells adapt their signaling in response to nutrient availability. To uncover the mechanisms regulating this process and its functional consequences, we interrogated cell lines, mouse tumor models, and clinical samples of glioblastoma (GBM), the highly lethal brain cancer. We discovered that glucose or acetate is required for epidermal growth factor receptor vIII (EGFRvIII), the most common growth factor receptor mutation in GBM, to activate mechanistic target of rapamycin complex 2 (mTORC2) and promote tumor growth. Glucose or acetate promoted growth factor receptor signaling through acetyl-CoA-dependent acetylation of Rictor, a core component of the mTORC2 signaling complex. Remarkably, in the presence of elevated glucose levels, Rictor acetylation is maintained to form an autoactivation loop of mTORC2 even when the upstream components of the growth factor receptor signaling pathway are no longer active, thus rendering GBMs resistant to EGFR-, PI3K (phosphoinositide 3-kinase)-, or AKT (v-akt murine thymoma viral oncogene homolog)-targeted therapies. These results demonstrate that elevated nutrient levels can drive resistance to targeted cancer treatments and nominate mTORC2 as a central node for integrating growth factor signaling with nutrient availability in GBM.

Rheb activation disrupts spine synapse formation through accumulation of syntenin in tuberous sclerosis complex.

Rheb is a small GTP-binding protein and its GTPase activity is activated by the complex of Tsc1 and Tsc2 whose mutations cause tuberous sclerosis complex (TSC). We previously reported that cultured TSC neurons showed impaired spine synapse morphogenesis in an mTORC1-independent manner. Here we show that the PDZ protein syntenin preferentially binds to the GDP-bound form of Rheb. The levels of syntenin are significantly higher in TSC neurons than in wild-type neurons because the Rheb-GDP-syntenin complex is prone to proteasomal degradation. Accumulated syntenin in TSC neurons disrupts spine synapse formation through inhibition of the association between syndecan-2 and calcium/calmodulin-dependent serine protein kinase. Instead, syntenin enhances excitatory shaft synapse formation on dendrites by interacting with ephrinB3. Downregulation of syntenin in TSC neurons restores both spine and shaft synapse densities. These findings suggest that Rheb-syntenin signalling may be a novel therapeutic target for abnormalities in spine and shaft synapses in TSC neurons.

Prostaglandin transporter in the rat brain: its localization and induction by lipopolysaccharide.

Prostaglandin E2 (PGE2) is produced in the brain during infectious/inflammatory diseases, and it mediates acute-phase responses including fever. In the recovery phase of such diseases, PGE2 disappears from the brain through yet unidentified mechanisms. Rat prostaglandin transporter (PGT), which facilitates transmembrane transport of PGE2, might be involved in the clearance of PGE2 from the brain. Here, we examined the cellular localization of PGT mRNA and its protein in the brains of untreated rats and those injected intraperitoneally with a pyrogen lipopolysaccharide (LPS) or saline. PGT mRNA was weakly expressed in the arachnoid membrane of untreated rats and saline-injected ones, but was induced in blood vessels of the subarachnoidal space and choroid plexus and in arachnoid membrane at 5 h and 12 h after LPS injection. In the same type of cells, PGT-like immunoreactivity was found in the cytosol and cell membrane even under nonstimulated conditions, and its level was also elevated after LPS injection. PGT-positive cells in blood vessels were identified as endothelial cells. In most cases, PGT was not colocalized with cyclooxygenase-2, a marker of prostaglandin-producing cells. The PGE2 level in the cerebrospinal fluid reached its peak at 3 h after LPS, and then dropped over 50% by 5 h, which time point coincides with the maximum PGT mRNA expression and enhanced level of PGT protein. These results suggest that PGT is involved in the clearance of PGE2 from the brain during the recovery phase of LPS-induced acute-phase responses.

Role of inflammatory mediators in the pathogenesis of epilepsy.

Epilepsy is one of the most common chronic brain disorders worldwide, affecting 1% of people across different ages and backgrounds. Epilepsy is defined as the sporadic occurrence of spontaneous recurrent seizures. Accumulating preclinical and clinical evidence suggest that there is a positive feedback cycle between epileptogenesis and brain inflammation. Epileptic seizures increase key inflammatory mediators, which in turn cause secondary damage to the brain and increase the likelihood of recurrent seizures. Cytokines and prostaglandins are well-known inflammatory mediators in the brain, and their biosynthesis is enhanced following seizures. Such inflammatory mediators could be therapeutic targets for the development of new antiepileptic drugs. In this review, we discuss the roles of inflammatory mediators in epileptogenesis.

Activation of Rheb, but not of mTORC1, impairs spine synapse morphogenesis in tuberous sclerosis complex.

Mutations in the Tsc1 or Tsc2 genes cause tuberous sclerosis complex (TSC). Tsc1 and Tsc2 proteins form a complex that inhibits mammalian target of rapamycin complex 1 (mTORC1) signalling through Rheb-GTPase. We found that Tsc2(+/-) neurons showed impaired spine synapse formation, which was resistant to an mTORC1 inhibitor. Knockdown of mTOR also failed to restore these abnormalities, suggesting mTORC may not participate in impaired spinogenesis in Tsc2(+/-) neurons. To address whether Rheb activation impairs spine synapse formation, we expressed active and inactive forms of Rheb in WT and Tsc2(+/-) neurons, respectively. Expression of active Rheb abolished dendritic spine formation in WT neurons, whereas inactive Rheb restored spine synapse formation in Tsc2(+/-) neurons. Moreover, inactivation of Rheb with farnesyl transferase inhibitors recovered spine synapse morphogenesis in Tsc2(+/-) neurons. In conclusion, dendritic spine abnormalities in TSC neurons may be caused through activation of Rheb, but not through of mTORC1.

Nicotine induces dendritic spine remodeling in cultured hippocampal neurons.

Cholinergic neurons in the CNS are involved in synaptic plasticity and cognition. Both muscarinic and nicotinic acetylcholine receptors (nAChRs) influence plasticity and cognitive function. The mechanism underlying nAChR-induced plasticity, however, has remained elusive. Here, we demonstrate morphological changes in dendritic spines following activation of α4ß2* nAChRs, which are expressed on glutamatergic pre-synaptic termini of cultured hippocampal neurons. Exposure of the neurons to nicotine resulted in a lateral enlargement of spine heads. This was abolished by dihydro-ß-erythroidine, an antagonist of α4ß2* nAChRs, but not by α-bungarotoxin, an antagonist of α7 nAChRs. Tetanus toxin or a mixture of 2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione, antagonists of NMDA- and AMPA-type glutamate receptors, blocked the nicotine-induced spine remodeling. In addition, nicotine exerted full spine-enlarging response in the post-synaptic neuron whose ß2 nAChR expression was knocked down. Finally, pre-treatment with nicotine enhanced the Ca(2+)-response of the neurons to glutamate. These data suggest that nicotine influences the activity of glutamatergic neurotransmission through the activation of pre-synaptic α4ß2 nAChRs, resulting in the modulation of spinal architecture and responsiveness. The present findings may represent one of the cellular mechanisms underlying cholinergic tuning of brain function. Activation of nicotinic acetylcholine receptors (nAChRs) in brain influences plasticity and cognition. Here, activation of α4ß2* nAChRs, which are expressed on glutamatergic presynaptic termini, results in the enlargement of dendritic spines through the modulation of the glutamatergic neurotransmission. The remodeled spinal architecture might be responsible for the change in responsiveness of neural circuitry, leading to cholinergic tuning of brain function.

Neuroprotective function of 14-3-3 proteins in neurodegeneration.

14-3-3 proteins are abundantly expressed adaptor proteins that interact with a vast number of binding partners to regulate their cellular localization and function. They regulate substrate function in a number of ways including protection from dephosphorylation, regulation of enzyme activity, formation of ternary complexes and sequestration. The diversity of 14-3-3 interacting partners thus enables 14-3-3 proteins to impact a wide variety of cellular and physiological processes. 14-3-3 proteins are broadly expressed in the brain, and clinical and experimental studies have implicated 14-3-3 proteins in neurodegenerative disease. A recurring theme is that 14-3-3 proteins play important roles in pathogenesis through regulating the subcellular localization of target proteins. Here, we review the evidence that 14-3-3 proteins regulate aspects of neurodegenerative disease with a focus on their protective roles against neurodegeneration.

Intercellular signaling pathway among Endothelia, astrocytes and neurons in excitatory neuronal damage.

Neurons interact closely with astrocytes via glutamate; this neuron-glia circuit may play a pivotal role in synaptic transmission. On the other hand, astrocytes contact vascular endothelial cells with their end-feet. It is becoming obvious that non-neuronal cells play a critical role in regulating the neuronal activity in the brain. We find that kainic acid (KA) administration induces the expression of microsomal prostaglandin E synthase-1 (mPGES-1) in venous endothelial cells and the prostaglandin E2 (PGE2) receptor prostaglandin E receptor (EP)-3 on astrocytes. Endothelial mPGES-1 exacerbates KA-induced neuronal damage in in vivo experiments. In in vitro experiments, mPGES-1 produces PGE2, which enhances astrocytic Ca2+ levels via the EP3 receptor and increases Ca2+-dependent glutamate release, thus aggravating neuronal injury. This novel endothelium-astrocyte-neuron signaling pathway may be crucial for driving neuronal damage after repetitive seizures and could be a new therapeutic target for epilepsy and other brain disorders.