The Troyer syndrome protein spartin mediates selective autophagy of lipid droplets.

Lipid droplets (LDs) are crucial organelles for energy storage and lipid homeostasis. Autophagy of LDs is an important pathway for their catabolism, but the molecular mechanisms mediating LD degradation by selective autophagy (lipophagy) are unknown. Here we identify spartin as a receptor localizing to LDs and interacting with core autophagy machinery, and we show that spartin is required to deliver LDs to lysosomes for triglyceride mobilization. Mutations in SPART (encoding spartin) lead to Troyer syndrome, a form of complex hereditary spastic paraplegia1. Interfering with spartin function in cultured human neurons or murine brain neurons leads to LD and triglyceride accumulation. Our identification of spartin as a lipophagy receptor, thus, suggests that impaired LD turnover contributes to Troyer syndrome development.

Chemogenetic regulation of the TARP-lipid interaction mimics LTP and reversibly modifies behavior.

Long-term potentiation (LTP), a well-characterized form of synaptic plasticity, is believed to underlie memory formation. Hebbian, postsynaptically expressed LTP requires TARPγ-8 phosphorylation for synaptic insertion of AMPA receptors (AMPARs). However, it is unknown whether TARP-mediated AMPAR insertion alone is sufficient to modify behavior. Here, we report the development of a chemogenetic tool, ExSYTE (Excitatory SYnaptic Transmission modulator by Engineered TARPγ-8), to mimic the cytoplasmic interaction of TARP with the plasma membrane in a doxycycline-dependent manner. We use this tool to examine the specific role of synaptic AMPAR potentiation in amygdala neurons that are activated by fear conditioning. Selective expression of active ExSYTE in these neurons potentiates AMPAR-mediated synaptic transmission in a doxycycline-dependent manner, occludes synaptically induced LTP, and mimics freezing triggered by cued fear conditioning. Thus, chemogenetic controlling of the TARP-membrane interaction is sufficient for LTP-like synaptic AMPAR insertion, which mimics fear conditioning.

NMDA receptor-targeted enrichment of CaMKIIα improves fear memory.

The establishment of effective molecular interventions to improve memory and alleviate memory deficits in disease remains a long-standing challenge despite growing molecular understanding of synaptic plasticity and memory formation. Capitalizing on the fact that long-term potentiation (LTP) requires N-methyl-D-aspartate receptors (NMDARs) and Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα), we develop an intrabody that targets NMDARs and show that intrabody-mediated postsynaptic enrichment of CaMKIIα in the hippocampus improves contextual fear memory. This molecular approach suggests a potential demand for effective targeting of postsynaptic molecules to enhance memory and provides insights into studying memory improvement in health and disease.

Protein phosphatase PPM1B inhibits DYRK1A kinase through dephosphorylation of pS258 and reduces toxic tau aggregation.

Down syndrome (DS) is mainly caused by an extra copy of chromosome 21 (trisomy 21), and patients display a variety of developmental symptoms, including characteristic facial features, physical growth delay, intellectual disability, and neurodegeneration (i.e., Alzheimer's disease; AD). One of the pathological hallmarks of AD is insoluble deposits of neurofibrillary tangles (NFTs) that consist of hyperphosphorylated tau. The human DYRK1A gene is mapped to chromosome 21, and the protein is associated with the formation of inclusion bodies in AD. For example, DYRK1A directly phosphorylates multiple serine and threonine residues of tau, including Thr212. However, the mechanism underpinning DYRK1A involvement in Trisomy 21-related pathological tau aggregation remains unknown. Here, we explored a novel regulatory mechanism of DYRK1A and subsequent tau pathology through a phosphatase. Using LC-MS/MS technology, we analyzed multiple DYRK1A-binding proteins, including PPM1B, a member of the PP2C family of Ser/Thr protein phosphatases, in HEK293 cells. We found that PPM1B dephosphorylates DYRK1A at Ser258, contributing to the inhibition of DYRK1A activity. Moreover, PPM1B-mediated dephosphorylation of DYRK1A reduced tau phosphorylation at Thr212, leading to inhibition of toxic tau oligomerization and aggregation. In conclusion, our study demonstrates that DYRK1A autophosphorylates Ser258, the dephosphorylation target of PPM1B, and PPM1B negatively regulates DYRK1A activity. This finding also suggests that PPM1B reduces the toxic formation of phospho-tau protein via DYRK1A modulation, possibly providing a novel cellular protective mechanism to regulate toxic tau-mediated neuropathology in AD of DS.

TMEM163 Regulates ATP-Gated P2X Receptor and Behavior.

Fast purinergic signaling is mediated by ATP and ATP-gated ionotropic P2X receptors (P2XRs), and it is implicated in pain-related behaviors. The properties exhibited by P2XRs vary between those expressed in heterologous cells and in vivo. Several modulators of ligand-gated ion channels have recently been identified, suggesting that there are P2XR functional modulators in vivo. Here, we establish a genome-wide open reading frame (ORF) collection and perform functional screening to identify modulators of P2XR activity. We identify TMEM163, which specifically modulates the channel properties and pharmacology of P2XRs. We also find that TMEM163 is required for full function of the neuronal P2XR and a pain-related ATP-evoked behavior. These results establish TMEM163 as a critical modulator of P2XRs in vivo and a potential target for the discovery of drugs for treating pain.

Phosphorylation of the AMPAR-TARP Complex in Synaptic Plasticity.

Synaptic plasticity has been considered a key mechanism underlying many brain functions including learning, memory, and drug addiction. An increase or decrease in synaptic activity of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) complex mediates the phenomena as shown in the cellular models of synaptic plasticity, long-term potentiation (LTP), and depression (LTD). In particular, protein phosphorylation shares the spotlight in expressing the synaptic plasticity. This review summarizes the studies on phosphorylation of the AMPAR pore-forming subunits and auxiliary proteins including transmembrane AMPA receptor regulatory proteins (TARPs) and discusses its role in synaptic plasticity.

Validation of the Korean Version of the Clinical Assessment Interview for Negative Symptoms.

OBJECTIVE: Clinical Assessment Interview for Negative Symptoms (CAINS) has recently been developed to improve measurement of negative symptoms in schizophrenia. We performed a multi-center study to validate the Korean version of the CAINS (CAINS-K) and explore potential cultural variation. METHODS: One hundred eighty schizophrenia patients diverse in demographic and illness profile were recruited from four centers in Korea. Along with the CAINS-K, the Scale for the Assessment of Negative Symptoms (SANS), Brief Psychiatric Rating Scale (BPRS), Calgary Depression Scale for Schizophrenia (CDSS), a self-report measure of behavioral inhibition and activation (BIS/BAS) and neurocognitive tasks were administered to verify external validities. RESULTS: The CAINS-K showed high internal-consistency (0.92) and inter-rater reliability (0.77). Exploratory Factor Analysis replicated a two-factor structure of the original scale including motivation/pleasure and expression deficits dimensions. Korean patients tended to report lower pleasure compared to American patients in the prior study. The CAINS-K showed an adequate convergent validity with the SANS, negative symptoms of the BPRS, and BAS. A divergent validity was supported as the CAINS-K showed zero or only weak correlations with other symptoms of the BPRS, depression from the CDSS, and neurocognitive tasks. CONCLUSION: The CAINS-K demonstrated high internal consistency and adequate external validities, and is expected to promote studies on negative symptoms in Korean patients with schizophrenia.

CaMKII Phosphorylation of TARPγ-8 Is a Mediator of LTP and Learning and Memory.

Protein phosphorylation is an essential step for the expression of long-term potentiation (LTP), a long-lasting, activity-dependent strengthening of synaptic transmission widely regarded as a cellular mechanism underlying learning and memory. At the core of LTP is the synaptic insertion of AMPA receptors (AMPARs) triggered by the NMDA receptor-dependent activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII). However, the CaMKII substrate that increases AMPAR-mediated transmission during LTP remains elusive. Here, we identify the hippocampus-enriched TARPγ-8, but not TARPγ-2/3/4, as a critical CaMKII substrate for LTP. We found that LTP induction increases TARPγ-8 phosphorylation, and that CaMKII-dependent enhancement of AMPAR-mediated transmission requires CaMKII phosphorylation sites of TARPγ-8. Moreover, LTP and memory formation, but not basal transmission, are significantly impaired in mice lacking CaMKII phosphorylation sites of TARPγ-8. Together, these findings demonstrate that TARPγ-8 is a crucial mediator of CaMKII-dependent LTP and therefore a molecular target that controls synaptic plasticity and associated cognitive functions.

Measuring negative symptoms in patients with schizophrenia: reliability and validity of the Korean version of the Motivation and Pleasure Scale-Self-Report.

BACKGROUND: The Clinical Assessment Interview for Negative Symptoms (CAINS) is one of the validated interview measures of negative symptoms in psychotic disorders. The Motivation and Pleasure Scale-Self-Report (MPSR) is a self-report measure that assesses the motivation and pleasure domains of negative symptoms based on the CAINS. This study evaluated the reliability and validity of a Korean version of the MPSR. METHODS: A total of 139 patients with schizophrenia completed the MPSR, CAINS, Scale for the Assessment of Negative Symptoms (SANS), Brief Psychiatric Rating Scales, Calgary Depression Scale for Schizophrenia, and other measures of trait and cognitive function. RESULTS: The 15-item MPSR showed good internal consistency. In addition, it also had a good convergent validity with the Motivation and Pleasure subscale of the CAINS and the anhedonia/avolition subscale of the SANS. The scale was not associated with psychotic symptoms, agitation/mania, and depression/anxiety, and it showed good discriminant validity. MPSR scores were significantly correlated with Behavioral Activation System total score for trait measure. CONCLUSION: The Korean version of the MPSR is a notable self-report method for examining the severity of negative symptoms in schizophrenia.

New Perspectives of Dyrk1A Role in Neurogenesis and Neuropathologic Features of Down Syndrome.

Down syndrome (DS) is one of the most common genetic disorders accompanying with mental retardation, cognitive impairment, and deficits in learning and memory. The brains with DS also display many neuropathological features including alteration in neurogenesis and synaptogenesis and early onset of Alzheimer's disease (AD)-like symptoms. Triplication of all or a part of human chromosome 21, especially the 21q22.1~21q22.3 region called 'Down syndrome critical region (DSCR)', has been considered as the main cause of DS. One gene product of DSCR, dual-specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A), has been highlighted as a key contributor to the neural consequences of DS. This minireview summarizes accumulating recent reports about Dyrk1A involvement in the neuritogenesis, synaptogenesis, and AD-like neurofibrillary tangle formation, which is mainly focusing on Dyrk1A-mediated regulation of cytoskeletal proteins, such as tubulin, actin, and microtubule-associated protein tau. Understanding the molecular mechanisms of these phenomena may provide us a rational for new preventive and therapeutic treatment of DS.

Dyrk1A negatively regulates the actin cytoskeleton through threonine phosphorylation of N-WASP.

Neural Wiskott-Aldrich syndrome protein (N-WASP) is involved in tight regulation of actin polymerization and dynamics. N-WASP activity is regulated by intramolecular interaction, binding to small GTPases and tyrosine phosphorylation. Here, we report on a novel regulatory mechanism; we demonstrate that N-WASP interacts with dual-specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A). In vitro kinase assays indicate that Dyrk1A directly phosphorylates the GTPase-binding domain (GBD) of N-WASP at three sites (Thr196, Thr202 and Thr259). Phosphorylation of the GBD by Dyrk1A promotes the intramolecular interaction of the GBD and verprolin, cofilin and acidic (VCA) domains of N-WASP, and subsequently inhibits Arp2/3-complex-mediated actin polymerization. Overexpression of either Dyrk1A or a phospho-mimetic N-WASP mutant inhibits filopodia formation in COS-7 cells. By contrast, the knockdown of Dyrk1A expression or overexpression of a phospho-deficient N-WASP mutant promotes filopodia formation. Furthermore, the overexpression of a phospho-mimetic N-WASP mutant significantly inhibits dendritic spine formation in primary hippocampal neurons. These findings suggest that Dyrk1A negatively regulates actin filament assembly by phosphorylating N-WASP, which ultimately promotes the intramolecular interaction of its GBD and VCA domains. These results provide insight on the mechanisms contributing to diverse actin-based cellular processes such as cell migration, endocytosis and neuronal differentiation.

ASK1 negatively regulates the 26 S proteasome.

The 26 S proteasome, composed of the 20 S core and 19 S regulatory particle, plays a central role in ubiquitin-dependent proteolysis. Disruption of this process contributes to the pathogenesis of the various diseases; however, the mechanisms underlying the regulation of 26 S proteasome activity remain elusive. Here, cell culture experiments and in vitro assays demonstrated that apoptosis signal-regulating kinase 1 (ASK1), a member of the MAPK kinase kinase family, negatively regulated 26 S proteasome activity. Immunoprecipitation/Western blot analyses revealed that ASK1 did not interact with 20 S catalytic core but did interact with ATPases making up the 19 S particle, which is responsible for recognizing polyubiquitinated proteins, unfolding them, and translocating them into the 20 S catalytic core in an ATP-dependent process. Importantly, ASK1 phosphorylated Rpt5, an AAA ATPase of the 19 S proteasome, and inhibited its ATPase activity, an effect that may underlie the ability of ASK1 to inhibit 26 S proteasome activity. The current findings point to a novel role for ASK1 in the regulation of 26 S proteasome and offer new strategies for treating human diseases caused by proteasome malfunction.

Dyrk1A phosphorylates p53 and inhibits proliferation of embryonic neuronal cells.

Down syndrome (DS) is associated with many neural defects, including reduced brain size and impaired neuronal proliferation, highly contributing to the mental retardation. Those typical characteristics of DS are closely associated with a specific gene group "Down syndrome critical region" (DSCR) on human chromosome 21. Here we investigated the molecular mechanisms underlying impaired neuronal proliferation in DS and, more specifically, a regulatory role for dual-specificity tyrosine-(Y) phosphorylation-regulated kinase 1A (Dyrk1A), a DSCR gene product, in embryonic neuronal cell proliferation. We found that Dyrk1A phosphorylates p53 at Ser-15 in vitro and in immortalized rat embryonic hippocampal progenitor H19-7 cells. In addition, Dyrk1A-induced p53 phosphorylation at Ser-15 led to a robust induction of p53 target genes (e.g. p21(CIP1)) and impaired G(1)/G(0)-S phase transition, resulting in attenuated proliferation of H19-7 cells and human embryonic stem cell-derived neural precursor cells. Moreover, the point mutation of p53-Ser-15 to alanine rescued the inhibitory effect of Dyrk1A on neuronal proliferation. Accordingly, brains from embryonic DYRK1A transgenic mice exhibited elevated levels of Dyrk1A, Ser-15 (mouse Ser-18)-phosphorylated p53, and p21(CIP1) as well as impaired neuronal proliferation. These findings suggest that up-regulation of Dyrk1A contributes to altered neuronal proliferation in DS through specific phosphorylation of p53 at Ser-15 and subsequent p21(CIP1) induction.

Function and regulation of Dyrk1A: towards understanding Down syndrome.

Down syndrome (DS) is associated with a variety of symptoms, such as incapacitating mental retardation and neurodegeneration (i.e., Alzheimer's disease), that prevent patients from leading fully independent lives. These phenotypes are a direct consequence of the overexpression of chromosome 21 genes, which are present in duplicate due to non-disjunction of chromosome 21. Accumulating data suggest that the chromosome 21 gene product, dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (Dyrk1A), participates in the pathogenic mechanisms underlying the mental and other physical symptoms of DS. In this review, we summarize the evidence supporting a role for Dyrk1A in DS, especially DS pathogenesis. Recently, several natural and synthetic compounds have been identified as Dyrk1A inhibitors. Understanding the function and regulation of Dyrk1A may lead to the development of novel therapeutic agents aimed at treating DS.

Two key genes closely implicated with the neuropathological characteristics in Down syndrome: DYRK1A and RCAN1.

The most common genetic disorder Down syndrome (DS) displays various developmental defects including mental retardation, learning and memory deficit, the early onset of Alzheimer's disease (AD), congenital heart disease, and craniofacial abnormalities. Those characteristics result from the extra-genes located in the specific region called nDown syndrome critical region (DSCR)' in human chromosome 21. In this review, we summarized the recent findings of the DYRK1A and RCAN1 genes, which are located on DSCR and thought to be closely associated with the typical features of DS patients, and their implication to the pathogenesis of neural defects in DS. DYRK1A phosphorylates several transcriptional factors, such as CREB and NFAT, endocytic complex proteins, and AD-linked gene products. Meanwhile, RCAN1 is an endogenous inhibitor of calcineurin A, and its unbalanced activity is thought to cause major neuronal and/or non-neuronal malfunction in DS and AD. Interestingly, they both contribute to the learning and memory deficit, altered synaptic plasticity, impaired cell cycle regulation, and AD-like neuropathology in DS. By understanding their biochemical, functional and physiological roles, we hope to get important molecular basis of DS pathology, which would consequently lead to the basis to develop the possible therapeutic tools for the neural defects in DS. [BMB reports 2009; 42(1): 6-15].

Down syndrome critical region 2 protein inhibits the transcriptional activity of peroxisome proliferator-activated receptor beta in HEK293 cells.

Down syndrome is mainly caused by a trisomy of chromosome 21. The Down syndrome critical region 2 (DSCR2) gene is located within a part of chromosome 21, the Down syndrome critical region (DSCR). To investigate the function of DSCR2, we sought to identify DSCR2-interacting proteins using yeast two-hybrid assays. A human fetal brain cDNA library was screened, and DSCR2 was found to interact with a member of the nuclear receptor superfamily, peroxisome proliferator-activated receptor beta, (PPARbeta). A co-immunoprecipitation assay demonstrated that DSCR2 physically interacts with PPARbeta in mammalian HEK293 cells. DSCR2 also inhibited the ligand-induced transcriptional activity of PPARbeta. Furthermore, PPARbeta also decreased the solubility of DSCR2, which increased levels of insoluble DSCR2.

NF-kappaB-inducing kinase phosphorylates and blocks the degradation of Down syndrome candidate region 1.

Down syndrome, the most frequent genetic disorder, is characterized by an extra copy of all or part of chromosome 21. Down syndrome candidate region 1 (DSCR1) gene, which is located on chromosome 21, is highly expressed in the brain of Down syndrome patients. Although its cellular function remains unknown, DSCR1 expression is linked to inflammation, angiogenesis, and cardiac development. To explore the functional role of DSCR1 and the regulation of its expression, we searched for novel DSCR1-interacting proteins using a yeast two-hybrid assay. Using a human fetal brain library, we found that DSCR1 interacts with NF-kappaB-inducing kinase (NIK). Furthermore, we demonstrate that NIK specifically interacts with and phosphorylates the C-terminal region of DSCR1 in immortalized hippocampal cells as well as in primary cortical neurons. This NIK-mediated phosphorylation of DSCR1 increases its protein stability and blocks its proteasomal degradation, the effects of which lead to an increase in soluble and insoluble DSCR1 levels. We show that an increase in insoluble DSCR1 levels results in the formation of cytosolic aggregates. Interestingly, we found that whereas the formation of these inclusions does not significantly alter the viability of neuronal cells, the overexpression of DSCR1 without the formation of aggregates is cytotoxic.

Dyrk1A overexpression in immortalized hippocampal cells produces the neuropathological features of Down syndrome.

Down syndrome (DS) is the most common genetic disorder, characterized by mental retardation, congenital heart abnormalities, and susceptibility to Alzheimer's disease (AD). Brain development of DS patients is associated with elevated apoptosis and abnormal neuronal differentiation. Those key features are closely associated with many genes mapped within Down syndrome critical region (DSCR) on human chromosome 21. Proline-directed serine/threonine kinase, Dyrk1A, is mapped within DSCR, and involved in the control of cell growth and postembryonic neurogenesis. Despite the potential involvement of Dyrk1A in neurodegeneration, its links to AD susceptibility and the neuropathology of DS patients are not yet clearly understood. Here, we report evidence supporting the correlation between Dyrk1A and neuropathology of DS. Our results show that Dyrk1A interacts with and directly phosphorylates tau and amyloid precursor protein in immortalized hippocampal progenitor H19-7 cells. In addition, the formation of tau inclusion and the enhanced generation of beta-amyloid fragment were detected in H19-7 cells that overexpressed Dyrk1A. Furthermore, these cells show a marked increase in apoptotic cell death under conditions of serum deprivation and also exhibit defects in neuronal differentiation. These results suggest that up-regulation of Dyrk1A may cause AD-like pathogenesis and abnormal neurobiological features in DS patients.

Alpha-synuclein overexpression reduces gap junctional intercellular communication in dopaminergic neuroblastoma cells.

Alpha-synuclein has been implicated in the pathology of certain neurodegenerative diseases, including Parkinson disease (PD) and dementia with Lewy bodies (LBs). Overexpression of human alpha-synuclein in neuronal cells reduces cell viability, but the precise cellular and molecular mechanisms remain poorly understood. Gap junctional intercellular communication (GJIC) is thought to be essential for maintaining cellular homeostasis and growth control. In the present study, the effect of alpha-synuclein overexpression on GJIC in human dopaminergic neuroblastoma SH-SY5Y cells was investigated. Cells overexpressing wild-type alpha-synuclein were more vulnerable to hydrogen peroxide and 6-hydroxydopamine. GJIC was decreased in cells overexpressing alpha-synuclein. In addition, alpha-synuclein binds directly to connexin-32 (Cx32). As such, the post-translational modification of Cx32 was enhanced in cells overexpressing alpha-synuclein. These findings suggest that alpha-synuclein can modulate GJIC in a dopaminergic neuronal cell line through specific binding to Cx32.

Quantitative EEG and low resolution electromagnetic tomography (LORETA) imaging of patients with persistent auditory hallucinations.

Electrophysiological studies have demonstrated gamma and beta frequency oscillations in response to auditory stimuli. The purpose of this study was to test whether auditory hallucinations (AH) in schizophrenia patients reflect abnormalities in gamma and beta frequency oscillations and to investigate source generators of these abnormalities. This theory was tested using quantitative electroencephalography (qEEG) and low-resolution electromagnetic tomography (LORETA) source imaging. Twenty-five schizophrenia patients with treatment refractory AH, lasting for at least 2 years, and 23 schizophrenia patients with non-AH (N-AH) in the past 2 years were recruited for the study. Spectral analysis of the qEEG and source imaging of frequency bands of artifact-free 30 s epochs were examined during rest. AH patients showed significantly increased beta 1 and beta 2 frequency amplitude compared with N-AH patients. Gamma and beta (2 and 3) frequencies were significantly correlated in AH but not in N-AH patients. Source imaging revealed significantly increased beta (1 and 2) activity in the left inferior parietal lobule and the left medial frontal gyrus in AH versus N-AH patients. These results imply that AH is reflecting increased beta frequency oscillations with neural generators localized in speech-related areas.