Induction of pro-apoptotic calsenilin/DREAM/KChIP3 in Alzheimer's disease and cultured neurons after amyloid-beta exposure

The Alzheimer's Knowledge Base: A Knowledge Graph for Alzheimer Disease Research

BACKGROUND

As global populations age and become susceptible to neurodegenerative illnesses, new therapies for Alzheimer disease (AD) are urgently needed. Existing data resources for drug discovery and repurposing fail to capture relationships central to the disease's etiology and response to drugs.

OBJECTIVE

We designed the Alzheimer's Knowledge Base (AlzKB) to alleviate this need by providing a comprehensive knowledge representation of AD etiology and candidate therapeutics.

METHODS

We designed the AlzKB as a large, heterogeneous graph knowledge base assembled using 22 diverse external data sources describing biological and pharmaceutical entities at different levels of organization (eg, chemicals, genes, anatomy, and diseases). AlzKB uses a Web Ontology Language 2 ontology to enforce semantic consistency and allow for ontological inference. We provide a public version of AlzKB and allow users to run and modify local versions of the knowledge base.

RESULTS

AlzKB is freely available on the web and currently contains 118,902 entities with 1,309,527 relationships between those entities. To demonstrate its value, we used graph data science and machine learning to (1) propose new therapeutic targets based on similarities of AD to Parkinson disease and (2) repurpose existing drugs that may treat AD. For each use case, AlzKB recovers known therapeutic associations while proposing biologically plausible new ones.

CONCLUSIONS

AlzKB is a new, publicly available knowledge resource that enables researchers to discover complex translational associations for AD drug discovery. Through 2 use cases, we show that it is a valuable tool for proposing novel therapeutic hypotheses based on public biomedical knowledge.

Cellular plasticity and myeloid inflammation in the adult brain are independent of the transcriptional modulator DREAM

The downstream regulatory element antagonist modulator (DREAM) modulates ion channel function and gene transcription. Functionally, DREAM is implicated in physiological and pathological processes including cell proliferation, inflammation, and nociception. Despite its multiple functions and robust expression in forebrain tissue, neurons and glial cells, the role of DREAM in regard to cellular plasticity and tumor necrosis factor (TNF)-mediated inflammation is largely unexplored. Here, we demonstrate that adult hippocampal neurogenesis as well as the density and plasticity of glial cells in the hippocampus and thalamus are independent of the presence of DREAM. Further, DREAM deletion does not alter the regional myeloid response and inflammatory gene expression induced by chronic peripheral inflammation in mice overexpressing human TNF. Our data suggest that despite their highly dynamic regulation, neural cell plasticity and adult neurogenesis in the hippocampus do not depend on the multifunctional protein DREAM. Furthermore, TNF-mediated myeloid inflammation in the brain persists in the absence of DREAM.

Repaglinide Elicits a Neuroprotective Effect in Rotenone-Induced Parkinson's Disease in Rats: Emphasis on Targeting the DREAM-ER Stress BiP/ATF6/CHOP Trajectory and Activation of Mitophagy

Repaglinide, a meglitinide insulinotropic antidiabetic, was unraveled as a promising therapeutic agent for Huntington's disease by targeting the neuronal calcium sensor downstream regulatory element antagonist modulator (DREAM). However, its mechanistic profile in Parkinson's disease (PD) especially its impact on endoplasmic reticulum (ER) stress, mitophagy, and their interconnections is poorly elucidated. This study is the first to examine the neuroprotective potential of repaglinide in rotenone-induced PD in rats by exploring its effects on DREAM, BiP/ATF6/CHOP ER stress pathway, apoptosis, mitophagy/autophagy, oxidative stress, astrogliosis/microgliosis, and neuroinflammation. Male Wistar rats were randomly assigned to four groups: groups 1 and 2 received the vehicle or repaglinide (0.5 mg/kg/day p.o). Groups 3 and 4 received rotenone (1.5 mg/kg/48 h s.c) for 21 days; meanwhile, group 4 additionally received repaglinide (0.5 mg/kg/day p.o) for 15 days starting from day 11. Interestingly, repaglinide lessened striatal ER stress and apoptosis as evidenced by reduced BiP/ATF6/CHOP and caspase-3 levels; however, it augmented striatal DREAM mRNA expression. Repaglinide triggered the expression of the mitophagy marker PINK1 and the autophagy protein beclin1 and alleviated striatal oxidative stress through escalating catalase activity. In addition, repaglinide halted astrocyte/microglial activation and neuroinflammation in the striatum as expressed by reducing glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor protein 1 (Iba1) immunostaining and decreasing interleukin (IL)-6 and IL-1β levels. Repaglinide restored striatum morphological alterations, intact neuron count, and neurobehavioral motor performance in rats examined by an open field, grip strength, and footprint gait analysis. Conclusively, repaglinide modulates the DREAM-ER stress BiP/ATF6/CHOP cascade, increases mitophagy/autophagy, inhibits apoptosis, and lessens oxidative stress, astrocyte/microglial activation, and neuroinflammation in PD.

CLN3, at the crossroads of endocytic trafficking

The CLN3 gene was identified over two decades ago, but the primary function of the CLN3 protein remains unknown. Recessive inheritance of loss of function mutations in CLN3 are responsible for juvenile neuronal ceroid lipofuscinosis (Batten disease, or CLN3 disease), a fatal childhood onset neurodegenerative disease causing vision loss, seizures, progressive dementia, motor function loss and premature death. CLN3 is a multipass transmembrane protein that primarily localizes to endosomes and lysosomes. Defects in endocytosis, autophagy, and lysosomal function are common findings in CLN3-deficiency model systems. However, the molecular mechanisms underlying these defects have not yet been fully elucidated. In this mini-review, we will summarize the current understanding of the CLN3 protein interaction network and discuss how this knowledge is starting to delineate the molecular pathogenesis of CLN3 disease. Accumulating evidence strongly points towards CLN3 playing a role in regulation of the cytoskeleton and cytoskeletal associated proteins to tether cellular membranes, regulation of membrane complexes such as channels/transporters, and modulating the function of small GTPases to effectively mediate vesicular movement and membrane dynamics.

Genome-wide Association Study Identifies a Regulatory Variant of RGMA Associated With Opioid Dependence in European Americans

BACKGROUND

Opioid dependence (OD) is at epidemic levels in the United States. Genetic studies can provide insight into its biology.

METHODS

We completed an OD genome-wide association study in 3058 opioid-exposed European Americans, 1290 of whom met criteria for a DSM-IV diagnosis of OD. Analysis used DSM-IV criterion count.

RESULTS

By meta-analysis of four cohorts, Yale-Penn 1 (n = 1388), Yale-Penn 2 (n = 996), Yale-Penn 3 (n = 98), and SAGE (Study of Addiction: Genetics and Environment) (n = 576), we identified a variant on chromosome 15, rs12442183, near RGMA, associated with OD (p = 1.3 × 10^-8). The association was also genome-wide significant in Yale-Penn 1 taken individually and nominally significant in two of the other three samples. The finding was further supported in a meta-analysis of all available opioid-exposed African Americans (n = 2014 [1106 meeting DSM-IV OD criteria]; p = 3.0 × 10^-3) from three cohorts; there was nominal significance in two of these samples. Thus, of seven subsamples examined in two populations, one was genome-wide significant, and four of six were nominally (or nearly) significant. RGMA encodes repulsive guidance molecule A, which is a central nervous system axon guidance protein. Risk allele rs12442183*T was correlated with higher expression of a specific RGMA transcript variant in frontal cortex (p = 2 × 10^-3). After chronic morphine injection, the homologous mouse gene (Rgma) was upregulated in C57BL/6J striatum. Coexpression analysis of 1301 brain samples revealed that RGMA messenger RNA expression was associated with that of four genes implicated in other psychiatric disorders, including GRIN1.

CONCLUSIONS

This is the first study to demonstrate an association of RGMA with OD. It provides a new lead into our understanding of OD pathophysiology.

Control of Neuronal Ryanodine Receptor-Mediated Calcium Signaling by Calsenilin

Calsenilin is a calcium ion (Ca²⁺)-binding protein involved in regulating the intracellular concentration of Ca²⁺, a second messenger that controls multiple cellular signaling pathways. The ryanodine receptor (RyR) amplifies Ca²⁺ signals entering the cytoplasm by releasing Ca²⁺ from endoplasmic reticulum (ER) stores, a process termed calcium-induced calcium release (CICR). Here, we describe a novel mechanism, in which calsenilin controls the activity of neuronal RyRs. We show calsenilin co-localized with RyR2 and 3 in the ER of mouse hippocampal and cortical neurons using immunocytochemistry. The underlying protein-protein interaction between calsenilin and the RyR was determined in mouse central nervous system (CNS) neurons using immunoprecipitation studies. The functional relevance of this interaction was assayed with single-channel electrophysiology. At low physiological Ca²⁺ concentrations, calsenilin binding to the cytoplasmic face of neuronal RyRs decreased the RyR's open probability, while calsenilin increased the open probability at high physiological Ca²⁺ concentrations. This novel molecular mechanism was studied further at the cellular level, where faster release kinetics of caffeine-induced Ca²⁺ release were measured in SH-SY5Y neuroblastoma cells overexpressing calsenilin. The interaction between calsenilin and neuronal RyRs reveals a new regulatory mechanism and possibly a novel pharmacological target for the control of Ca²⁺ release from intracellular stores.

Downstream Regulatory Element Antagonist Modulator (DREAM), a target for anti-thrombotic agents

Circulating platelets participate in the process of numerous diseases including thrombosis, inflammation, and cancer. Thus, it is of great importance to understand the underlying mechanisms mediating platelet activation under disease conditions. Emerging evidence indicates that despite the lack of a nucleus, platelets possess molecules that are involved in gene transcription in nucleated cells. This review will summarize downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, and highlight recent findings suggesting its novel non-transcriptional role in hemostasis and thrombosis.

DREAM plays an important role in platelet activation and thrombogenesis

Downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, is known to modulate pain responses. However, it is unknown whether DREAM is expressed in anucleate platelets and plays a role in thrombogenesis. By using intravital microscopy with DREAM-null mice and their bone marrow chimeras, we demonstrated that both hematopoietic and nonhematopoietic cell DREAMs are required for platelet thrombus formation following laser-induced arteriolar injury. In a FeCl₃-induced thrombosis model, we found that compared with wild-type (WT) control and nonhematopoietic DREAM knockout (KO) mice, DREAM KO control and hematopoietic DREAM KO mice showed a significant delay in time to occlusion. Tail bleeding time was prolonged in DREAM KO control mice, but not in WT or DREAM bone marrow chimeric mice. In vivo adoptive transfer experiments further indicated the importance of platelet DREAM in thrombogenesis. We found that DREAM deletion does not alter the ultrastructural features of platelets but significantly impairs platelet aggregation and adenosine triphosphate secretion induced by numerous agonists (collagen-related peptide, adenosine 5'-diphosphate, A23187, thrombin, or U46619). Biochemical studies revealed that platelet DREAM positively regulates phosphoinositide 3-kinase (PI3K) activity during platelet activation. Using DREAM-null platelets and PI3K isoform-specific inhibitors, we observed that platelet DREAM is important for α-granule secretion, Ca²⁺ mobilization, and aggregation through PI3K class Iβ (PI3K-Iβ). Genetic and pharmacological studies in human megakaryoblastic MEG-01 cells showed that DREAM is important for A23187-induced Ca²⁺ mobilization and its regulatory function requires Ca²⁺ binding and PI3K-Iβ activation. These results suggest that platelet DREAM regulates PI3K-Iβ activity and plays an important role during thrombus formation.

Failure of ubiquitin proteasome system: risk for neurodegenerative diseases

The ubiquitin proteasome system (UPS) is the primary proteolytic quality control system in cells and has an essential function in the nervous system. UPS dysfunction has been linked to neurodegenerative conditions, including Alzheimer's, Parkinson's and Huntington's diseases. The pathology of neurodegenerative diseases is characterized by the abnormal accumulation of insoluble protein aggregates or inclusion bodies within neurons. The failure or dysregulation of the UPS prevents the degradation of misfolded/aberrant proteins, leading to deficient synaptic function that eventually affects the nervous system. In this review, we discuss the UPS and its physiological roles in the nervous system, its influence on neuronal function, and how UPS dysfunction contributes to the development of neurodegenerative diseases.

Dipeptidyl peptidase 10 (DPP10(789)): a voltage gated potassium channel associated protein is abnormally expressed in Alzheimer's and other neurodegenerative diseases

The neuropathological features associated with Alzheimer's disease (AD) include the presence of extracellular amyloid-β peptide-containing plaques and intracellular tau positive neurofibrillary tangles and the loss of synapses and neurons in defined regions of the brain. Dipeptidyl peptidase 10 (DPP10) is a protein that facilitates Kv4 channel surface expression and neuronal excitability. This study aims to explore DPP10789 protein distribution in human brains and its contribution to the neurofibrillary pathology of AD and other tauopathies. Immunohistochemical analysis revealed predominant neuronal staining of DPP10789 in control brains, and the CA1 region of the hippocampus contained strong reactivity in the distal dendrites of the pyramidal cells. In AD brains, robust DPP10789 reactivity was detected in neurofibrillary tangles and plaque-associated dystrophic neurites, most of which colocalized with the doubly phosphorylated Ser-202/Thr-205 tau epitope. DPP10789 positive neurofibrillary tangles and plaque-associated dystrophic neurites also appeared in other neurodegenerative diseases such as frontotemporal lobar degeneration, diffuse Lewy body disease, and progressive supranuclear palsy. Occasional DPP10789 positive neurofibrillary tangles and neurites were seen in some aged control brains. Western blot analysis showed both full length and truncated DPP10789 fragments with the later increasing significantly in AD brains compared to control brains. Our results suggest that DPP10789 is involved in the pathology of AD and other neurodegenerative diseases.

Intergenerational genomic DNA methylation patterns in mouse hybrid strains

Background

DNA methylation is a contributing factor to both rare and common human diseases, and plays a major role in development and gene silencing. While the variation of DNA methylation among individuals has been partially characterized, the degree to which methylation patterns are preserved across generations is still poorly understood. To determine the extent of methylation differences between two generations of mice we examined DNA methylation patterns in the livers of eight parental and F1 mice from C57BL/6J and DBA/2J mouse strains using bisulfite sequencing.

Results

We find a large proportion of reproducible methylation differences between C57BL/6J and DBA/2J chromosomes in CpGs, which are highly heritable between parent and F1 mice. We also find sex differences in methylation levels in 396 genes, and 11% of these are differentially expressed between females and males. Using a recently developed approach to identify allelically methylated regions independently of genotypic differences, we identify 112 novel putative imprinted genes and microRNAs, and validate imprinting at the RNA level in 10 of these genes.

Conclusions

The majority of DNA methylation differences among individuals are associated with genetic differences, and a much smaller proportion of these epigenetic differences are due to sex, imprinting or stochastic intergenerational effects. Epigenetic differences can be a determining factor in heritable traits and should be considered in association studies for molecular and clinical traits, as we observed that methylation differences in the mouse model are highly heritable and can have functional consequences on molecular traits such as gene expression.

The regulation of apoptosis by the downstream regulatory element antagonist modulator/potassium channel interacting protein 3 (DREAM/KChIP3) through interactions with hexokinase I

The EF-hand protein, DREAM/KChIP3 (henceforth referred to as DREAM), regulates apoptosis by incompletely understood mechanisms. We demonstrate that in the presence of Ca2+, DREAM interacts with hexokinase I, a protein known to bind mitochondria and regulate apoptosis. A mutant DREAM protein construct incapable of binding Ca2+ does not associate with hexokinase I. The amino-terminal portion of DREAM is required for binding to hexokinase I, as a DREAM construct lacking the first 94 amino terminal residues fails to bind hexokinase I. Expression of DREAM in neuroblastoma cells enhances cisplatin mediated caspase-3 activity. Simultaneous expression of hexokinase I in such cells reduces DREAM-stimulated apoptosis. DREAM overexpression in neuroblastoma cells reduces hexokinase I localization on isolated mitochondria. The interaction of DREAM with hexokinase I may be important in the regulation of neuronal apoptosis.

E2F-1- and E2Ftr-mediated apoptosis: the role of DREAM and HRK

E2F-1-deleted mutant, ‘truncated E2F’ (E2Ftr, E2F-1[1–375]), lacking the carboxy-terminal transactivation domain, was shown to be more potent at inducing cancer cell apoptosis than wild-type E2F-1 (wtE2F-1; full-length E2F-1). Mechanisms by which wtE2F-1 and E2Ftr induce apoptosis, however, are not fully elucidated. Our study demonstrates molecular effects of pro-apoptotic BH3-only Bcl-2 family member Harakiri (Hrk) in wtE2F-1- and E2Ftr-induced melanoma cell apoptosis. We found that Hrk mRNA and Harakiri (HRK) protein expression was highly up-regulated in melanoma cells in response to wtE2F-1 and E2Ftr overexpression. HRK up-regulation did not require the E2F-1 transactivation domain. In addition, Hrk gene up-regulation and HRK protein expression did not require p53 in cancer cells. Hrk knockdown by Hrk siRNA was associated with significantly reduced wtE2F-1- and E2Ftr-induced apoptosis. We also found that an upstream factor, ‘downstream regulatory element antagonist modulator’ (DREAM), may be involved in HRK-mediated apoptosis in response to wtE2F-1 and E2Ftr overexpression. DREAM expression levels increased following wtE2F-1 and E2Ftr overexpression. Western blotting detected increased DREAM primarily in dimeric form. The homodimerization of DREAM resulting from wtE2F-1 and E2Ftr overexpression may contribute to the decreased binding activity of DREAM to the 3′-untranslated region of the Hrk gene as shown by electromobility shift assay. Results showed wtE2F-1- and E2Ftr-induced apoptosis is partially mediated by HRK. HRK function is regulated in response to DREAM. Our findings contribute to understanding the mechanisms that regulate wtE2F-1- and E2Ftr-induced apoptosis and provide insights into the further evaluation of how E2Ftr-induced apoptosis may be used for therapeutic gain.

Negative modulation of NMDA receptor channel function by DREAM/calsenilin/KChIP3 provides neuroprotection?

N-methyl-D-aspartate receptors (NMDARs) are glutamate-gated ion channels highly permeable to calcium and essential to excitatory neurotransmission. The NMDARs have attracted much attention because of their role in synaptic plasticity and excitotoxicity. Evidence has recently accumulated that NMDARs are negatively regulated by intracellular calcium binding proteins. The calcium-dependent suppression of NMDAR function serves as a feedback mechanism capable of regulating subsequent Ca²⁺ entry into the postsynaptic cell, and may offer an alternative approach to treating NMDAR-mediated excitotoxic injury. This short review summarizes the recent progress made in understanding the negative modulation of NMDAR function by DREAM/calsenilin/KChIP3, a neuronal calcium sensor (NCS) protein.

The visinin-like proteins VILIP-1 and VILIP-3 in Alzheimer's disease-old wine in new bottles

The neuronal Ca²⁺-sensor (NCS) proteins VILIP-1 and VILIP-3 have been implicated in the etiology of Alzheimer's disease (AD). Genome-wide association studies (GWAS) show association of genetic variants of VILIP-1 (VSNL1) and VILIP-3 (HPCAL1) with AD+P (+psychosis) and late onset AD (LOAD), respectively. In AD brains the expression of VILIP-1 and VILIP-3 protein and mRNA is down-regulated in cortical and limbic areas. In the hippocampus, for instance, reduced VILIP-1 mRNA levels correlate with the content of neurofibrillary tangles (NFT) and amyloid plaques, the pathological characteristics of AD, and with the mini mental state exam (MMSE), a test for cognitive impairment. More recently, VILIP-1 was evaluated as a cerebrospinal fluid (CSF) biomarker and a prognostic marker for cognitive decline in AD. In CSF increased VILIP-1 levels correlate with levels of Aβ, tau, ApoE4, and reduced MMSE scores. These findings tie in with previous results showing that VILIP-1 is involved in pathological mechanisms of altered Ca²⁺-homeostasis leading to neuronal loss. In PC12 cells, depending on co-expression with the neuroprotective Ca²⁺-buffer calbindin D28K, VILIP-1 enhanced tau phosphorylation and cell death. On the other hand, VILIP-1 affects processes, such as cyclic nucleotide signaling and dendritic growth, as well as nicotinergic modulation of neuronal network activity, both of which regulate synaptic plasticity and cognition. Similar to VILIP-1, its interaction partner α4β2 nicotinic acetylcholine receptor (nAChR) is severely reduced in AD, causing severe cognitive deficits. Comparatively little is known about VILIP-3, but its interaction with cytochrome b5, which is part of an antioxidative system impaired in AD, hint toward a role in neuroprotection. A current hypothesis is that the reduced expression of visinin-like protein (VSNLs) in AD is caused by selective vulnerability of subpopulations of neurons, leading to the death of these VILIP-1-expressing neurons, explaining its increased CSF levels. While the Ca²⁺-sensor appears to be a good biomarker for the detrimental effects of Aβ in AD, its early, possibly Aβ-induced, down-regulation of expression may additionally attenuate neuronal signal pathways regulating the functions of dendrites and neuroplasticity, and as a consequence, this may contribute to cognitive decline in early AD.

Regulation of DREAM Expression by Group I mGluR

DREAM (downstream regulatory element antagonistic modulator) is a calcium-binding protein that regulates dynorphin expression, promotes potassium channel surface expression, and enhances presenilin processing in an expression level-dependent manner. However, no molecular mechanism has yet explained how protein levels of DREAM are regulated. Here we identified group I mGluR (mGluR1/5) as a positive regulator of DREAM protein expression. Overexpression of mGluR1/5 increased the cellular level of DREAM. Up-regulation of DREAM resulted in increased DREAM protein in both the nucleus and cytoplasm, where the protein acts as a transcriptional repressor and a modulator of its interacting proteins, respectively. DHPG (3,5-dihydroxyphenylglycine), a group I mGluR agonist, also up-regulated DREAM expression in cortical neurons. These results suggest that group I mGluR is the first identified receptor that may regulate DREAM activity in neurons.

Neuronal voltage-gated K+ (Kv) channels function in macromolecular complexes

Considerable evidence indicates that native neuronal voltage-gated K+ (Kv) currents reflect the functioning of macromolecular Kv channel complexes, composed of pore-forming (α)-subunits, cytosolic and transmembrane accessory subunits, together with regulatory and scaffolding proteins. The individual components of these macromolecular complexes appear to influence the stability, the trafficking, the localization and/or the biophysical properties of the channels. Recent studies suggest that Kv channel accessory subunits subserve multiple roles in the generation of native neuronal Kv channels. Additional recent findings suggest that Kv channel accessory subunits can respond to changes in intracellular Ca(2+) or metabolism and thereby integrate signaling pathways to regulate Kv channel expression and properties. Although studies in heterologous cells have provided important insights into the effects of accessory subunits on Kv channel expression/properties, it has become increasingly clear that experiments in neurons are required to define the physiological roles of Kv channel accessory and associated proteins. A number of technological and experimental hurdles remain that must be overcome in the design, execution and interpretation of experiments aimed at detailing the functional roles of accessory subunits and associated proteins in the generation of native neuronal Kv channels. With the increasing association of altered Kv channel functioning with neurological disorders, the potential impact of these efforts is clear.

Neurocalcin protein labeling reveals a dimorphism within the developing zebra finch brain

The exact mechanism(s) responsible for sexual differentiation of the zebra finch song system remains unknown but likely involve a combination of hormonal and genetic factors. One product that may play a role is the calcium binding protein, neurocalcin. A previous study indicated that neurocalcin mRNA was widely distributed throughout the zebra finch telencephalon, overlapping with song control regions. Because it was not clear how much of that expression was functionally relevant, we labeled tissue with a specific antibody. At the three age ranges that were examined, there were region-specific fluctuations in the number of neurocalcin immunoreactive cells. During post-hatching developmental ages (P) 18-23, quantitative analyses indicated that females had significantly more neurons containing neurocalcin protein in HVC and RA than males. This difference was not detected at P10 or in adults. Labeling in LMAN did not reveal a sex difference at any of the ages. In other areas of the brain, semi-quantitative analyses of the relative number of cells immunopositive for neurocalcin varied across specific regions, but with the possible exception of the lateral striatum, no obvious sex differences were apparent. Taken together, these data are consistent with the idea that neurocalcin may be important for regulating sexual dimorphisms within the neural song system at a specific developmental period. In addition, because of variations in events related to post-transcriptional modification, a thorough study of a gene's role in development and/or behavior should include investigations of its transcription as well as translation.

BACE and gamma-secretase characterization and their sorting as therapeutic targets to reduce amyloidogenesis

Secretases are named for enzymes processing amyloid precursor protein (APP), a prototypic type-1 membrane protein. This led directly to discovery of novel Aspartyl proteases (beta-secretases or BACE), a tetramer complex gamma-secretase (gamma-SC) containing presenilins, nicastrin, aph-1 and pen-2, and a new role for metalloprotease(s) of the ADAM family as a alpha-secretases. Recent advances in defining pathways that mediate endosomal-lysosomal-autophagic-exosomal trafficking now provide targets for new drugs to attenuate abnormal production of fibril forming products characteristic of AD. A key to success includes not only characterization of relevant secretases but mechanisms for sorting and transport of key metabolites to abnormal vesicles or sites for assembly of fibrils. New developments we highlight include an important role for an 'early recycling endosome' coated in retromer complex containing lipoprotein receptor LRP-II (SorLA) for switching APP to a non-amyloidogenic pathway for alpha-secretases processing, or to shuttle APP to a 'late endosome compartment' to form Abeta or AICD. LRP11 (SorLA) is of particular importance since it decreases in sporadic AD whose etiology otherwise is unknown.

Fenton chemistry and oxidative stress mediate the toxicity of the beta-amyloid peptide in a Drosophila model of Alzheimer's disease

The mechanism by which aggregates of the β-amyloid peptide (Aβ) mediate their toxicity is uncertain. We show here that the expression of the 42-amino-acid isoform of Aβ (Aβ_1–42) changes the expression of genes involved in oxidative stress in a Drosophila model of Alzheimer’s disease. A subsequent genetic screen confirmed the importance of oxidative stress and a molecular dissection of the steps in the cellular metabolism of reactive oxygen species revealed that the iron-binding protein ferritin and the H₂O₂ scavenger catalase are the most potent suppressors of the toxicity of wild-type and Arctic (E22G) Aβ_1–42. Likewise, treatment with the iron-binding compound clioquinol increased the lifespan of flies expressing Arctic Aβ_1–42. The effect of iron appears to be mediated by oxidative stress as ferritin heavy chain co-expression reduced carbonyl levels in Aβ_1–42 flies by 65% and restored the survival and locomotion function to normal. This was achieved despite the presence of elevated levels of the Aβ_1–42. Taken together, our data show that oxidative stress, probably mediated by the hydroxyl radical and generated by the Fenton reaction, is essential for Aβ_1–42 toxicity in vivo and provide strong support for Alzheimer’s disease therapies based on metal chelation.

Protection of cardiomyocytes from ischemic/hypoxic cell death via Drbp1 and pMe2GlyDH in cardio-specific ARC transgenic mice

The ischemic death of cardiomyocytes is associated in heart disease and heart failure. However, the molecular mechanism underlying ischemic cell death is not well defined. To examine the function of apoptosis repressor with a caspase recruitment domain (ARC) in the ischemic/hypoxic damage of cardiomyocytes, we generated cardio-specific ARC transgenic mice using a mouse alpha-myosin heavy chain promoter. Compared with the control, the hearts of ARC transgenic mice showed a 3-fold overexpression of ARC. Langendoff preparation showed that the hearts isolated from ARC transgenic mice exhibited improved recovery of contractile performance during reperfusion. The cardiomyocytes cultured from neonatal ARC transgenic mice were significantly resistant to hypoxic cell death. Furthermore, the ARC C-terminal calcium-binding domain was as potent to protect cardiomyocytes from hypoxic cell death as ARC. Genome-wide RNA expression profiling uncovered a list of genes whose expression was changed (>2-fold) in ARC transgenic mice. Among them, expressional regulation of developmentally regulated RNA-binding protein 1 (Drbp1) or the dimethylglycine dehydrogenase precursor (pMe(2)GlyDH) affected hypoxic death of cardiomyocytes. These results suggest that ARC may protect cardiomyocytes from hypoxic cell death by regulating its downstream, Drbp1 and pMe(2)GlyDH, shedding new insights into the protection of heart from hypoxic damages.

Solution structure and calcium-binding properties of EF-hands 3 and 4 of calsenilin

Calsenilin is a member of the recoverin branch of the EF-hand superfamily that is reported to interact with presenilins, regulate prodynorphin gene expression, modulate voltage-gated Kv4 potassium channel function, and bind to neurotoxins. Calsenilin is a Ca+2-binding protein and plays an important role in calcium signaling. Despite its importance in numerous neurological functions, the structure of this protein has not been reported. In the absence of Ca+2, the protein has limited spectral resolution that increases upon the addition of Ca+2. Here, we describe the three-dimensional solution structure of EF-hands 3 and 4 of calsenilin in the Ca+2-bound form. The Ca+2-bound structure consists of five alpha-helices and one two-stranded antiparallel beta-sheet. The long loop that connects EF hands 3 and 4 is highly disordered in solution. In addition to its structural effects, Ca+2 binding also increases the protein's propensity to dimerize. These changes in structure and oligomerization state induced upon Ca+2 binding may play important roles in molecular recognition during calcium signaling.

Neurosecretases provide strategies to treat sporadic and familial Alzheimer disorders

Recent discoveries on neurosecretases and their trafficking to release fibril-forming neuropeptides or other products, are of interest to pathology, cell signaling and drug discovery. Nomenclature arose from the use of amyloid precursor protein (APP) as a prototypic type-1 substrate leading to the isolation of beta-secretase (BACE), multimeric complexes (gamma-secretase, gamma-SC) for intramembranal cleavage, and attributing a new function to well-characterized metalloproteases of the ADAM family (alpha-secretase) for normal APP turnover. While purified alpha/beta-secretases facilitate drug discovery, gamma-SC presents greater challenges for characterization and mechanisms of catalysis. The review comments on links between mutation or polymorphisms in relation to enzyme mechanisms and disease. The association between lipoprotein receptor LRP11 variants and sporadic Alzheimer's disease (SAD) offers scope to integrate components of pre- and post-Golgi membranes, or brain clathrin-coated vesicles within pathways for trafficking as targets for intervention. The presence of APP and metabolites in brain clathrin-coated vesicles as significant cargo with lipoproteins and adaptors focuses attention as targets for therapeutic intervention. This overview emphasizes the importance to develop new therapies targeting neurosecretases to treat a major neurological disorder that has vast economic and social implications.

Calsenilin interacts with transcriptional co-repressor C-terminal binding protein(s)

Calsenilin/potassium channel-interacting protein (KChIP)3/ downstream regulatory element sequence antagonist modulator (DREAM) is a neuronal calcium-binding protein that has been shown to have multiple functions in the cell, including the regulation of presenilin processing, repression of transcription and modulation of A-type potassium channels. To gain a better understanding of the precise role of calsenilin in specific cellular compartments, an interactor hunt for proteins that bind to the N-terminal domain of calsenilin was carried out. Using a yeast two-hybrid system and co-immunoprecipitation studies, we have identified the transcriptional co-repressor C-terminal binding protein (CtBP)2 as an interactor for calsenilin and have shown that the two proteins can interact in vivo. In co-immunoprecipitation studies, calsenilin also interacted with CtBP1, a CtBP2 homolog. Our data also showed a calsenilin-dependent increase in c-fos protein levels in CtBP knockout fibroblasts, suggesting that CtBP may modulate the transcriptional repression of c-fos by calsenilin. Furthermore, the finding that histone deacetylase protein and activity were associated with the calsenilin-CtBP immunocomplex suggests a mechanism by which calsenilin-CtBP may act to repress transcription. Finally, we demonstrated that calsenilin and CtBP are present in synaptic vesicles and can interact in vivo.

Enhanced caffeine-induced Ca2+ release in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia among the elderly and is a complex disorder that involves altered proteolysis, oxidative stress and disruption of ion homeostasis. Animal models have proven useful in studying the impact of mutant AD-related genes on other cellular signaling pathways, such as Ca2+ signaling. Along these lines, disturbances of intracellular Ca2+ ([Ca2+]i) homeostasis are an early event in the pathogenesis of AD. Here, we have employed microfluorimetric measurements of [Ca2+]i to investigate disturbances in Ca2+ homeostasis in primary cortical neurons from a triple transgenic mouse model of Alzheimer's disease (3xTg-AD). Application of caffeine to mutant presenilin-1 knock-in neurons (PS1KI) and 3xTg-AD neurons evoked a peak rise of [Ca2+]i that was significantly greater than those observed in non-transgenic neurons, although all groups had similar decay rates of their Ca2+ transient. This finding suggests that Ca2+ stores are greater in both PS1KI and 3xTg-AD neurons as calculated by the integral of the caffeine-induced Ca2+ transient signal. Western blot analysis failed to identify changes in the levels of several Ca2+ binding proteins (SERCA-2B, calbindin, calsenilin and calreticulin) implicated in the pathogenesis of AD. However, ryanodine receptor expression in both PS1KI and 3xTg-AD cortex was significantly increased. Our results suggest that the enhanced Ca2+ response to caffeine observed in both PS1KI and 3xTg-AD neurons may not be attributable to an alteration of endoplasmic reticulum store size, but to the increased steady-state levels of the ryanodine receptor.

Differential regulation of Abeta42-induced neuronal C1q synthesis and microglial activation

Expression of C1q, an early component of the classical complement pathway, has been shown to be induced in neurons in hippocampal slices, following accumulation of exogenous Aβ42. Microglial activation was also detected by surface marker expression and cytokine production. To determine whether C1q induction was correlated with intraneuronal Aβ and/or microglial activation, D-(-)-2-amino-5-phosphonovaleric acid (APV, an NMDA receptor antagonist) and glycine-arginine-glycine-aspartic acid-serine-proline peptide (RGD, an integrin receptor antagonist), which blocks and enhances Aβ42 uptake, respectively, were assessed for their effect on neuronal C1q synthesis and microglial activation. APV inhibited, and RGD enhanced, microglial activation and neuronal C1q expression. However, addition of Aβ10–20 to slice cultures significantly reduced Aβ42 uptake and microglial activation, but did not alter the Aβ42-induced neuronal C1q expression. Furthermore, Aβ10–20 alone triggered C1q production in neurons, demonstrating that neither neuronal Aβ42 accumulation, nor microglial activation is required for neuronal C1q upregulation. These data are compatible with the hypothesis that multiple receptors are involved in Aβ injury and signaling in neurons. Some lead to neuronal C1q induction, whereas other(s) lead to intraneuronal accumulation of Aβ and/or stimulation of microglia.

The neuronal calcium-sensor proteins

Changes in intracellular free Ca(2+) concentration ([Ca(2+)](i)) affect many different aspects of neuronal function ranging from millisecond regulation of ion channels to long term changes in gene expression. These effects of Ca(2+) are transduced by Ca(2+)-binding proteins that act as Ca(2+) sensors by binding Ca(2+), undergoing a conformational change and then modifying the function of additional target proteins. Mammalian species express 14 members of the neuronal calcium sensor (NCS) family of EF hand-containing Ca(2+)-binding proteins which are expressed mainly in photoreceptor cells or neurons. Many of the NCS proteins are membrane targeted through their N-terminal myristoylation either constitutively or following exposure of the myristoyl group after Ca(2+) binding (the Ca(2+)/myristoyl switch). The NCS proteins have been implicated in a wide range of functional roles in neuronal regulation, several of which have been confirmed though molecular genetic analyses.