Up-regulation of GPR139 in the medial septum ameliorates cognitive impairment in two mouse models of Alzheimer's disease.

G-protein coupled receptors (GPCRs) constitute the largest class of cell surface receptors and present prominent drug targets. GPR139 is an orphan GPCR detected in the septum of the brain. However, its roles in cognition are still unclear. Here we first established a mouse model of cognitive impairment by a single intracerebroventricular injection of aggregated amyloid-beta peptide 1-42 (Aß1-42). RNA-sequencing data analysis showed that Aß1-42 induced a significant decrease of GPR139 mRNA in the basal forebrain. Using GPR139 agonist JNJ-63533054 and behavioral tests, we found that GPR139 activation in the brain ameliorated Aß1-42-induced cognitive impairment. Using western blot, TUNEL apoptosis and Golgi staining assays, we showed that GPR139 activation alleviated Aß1-42-induced apoptosis and synaptotoxicity in the basal forebrain rather than prefrontal cortex and hippocampus. The further study identified that GPR139 was widely expressed in cholinergic neurons of the medial septum (MS). Using the overexpression virus and transgenic animal model, we showed that up-regulation of GPR139 in MS cholinergic neurons ameliorated cognitive impairment, apoptosis and synaptotoxicity in APP/PS1 transgenic mice. These findings reveal that GPR139 of MS cholinergic neurons could be a critical node in cognition and potentially provides insight into the pathogenesis of Alzheimer's disease.

Integration of Microfluidic Devices with Microelectrode Arrays to Functionally Assay Amyloid-ß-Induced Synaptotoxicity.

Alzheimer's disease (AD) is a neurodegenerative disease and the most frequent cause of dementia. It is characterized by the accumulation in the brain of two pathological protein aggregates: amyloid-ß peptides (Aß) and abnormally phosphorylated tau. The progressive cognitive decline observed in patients strongly correlates with the synaptic loss. Many lines of evidence suggest that soluble forms of Aß accumulate into the brain where they cause synapse degeneration. Stopping their spreading and/or targeting the pathophysiological mechanisms leading to synaptic loss would logically be beneficial for the patients. However, we are still far from understanding these processes. Our objective was therefore to develop a versatile model to assay and study Aß-induced synaptotoxicity. We integrated a microfluidic device that physically isolates synapses from presynaptic and postsynaptic neurons with a microelectrode array. We seeded mouse primary cortical cells in the presynaptic and postsynaptic chambers. After functional synapses have formed in the synaptic chamber, we exposed them to concentrated conditioned media from cell lines overexpressing the wild-type or mutated amyloid precursor protein and thus secreting different levels of Aß. We recorded the neuronal activity before and after exposition to Aß and quantified Aß's effects on the connectivity between presynaptic and postsynaptic neurons. We observed that the application of Aß on the synapses for 48 h strongly decreased the interchamber connectivity without significantly affecting the neuronal activity in the presynaptic or postsynaptic chambers. Thus, through this model, we are able to functionally assay the impact of Aß peptides (or other molecules) on synaptic connectivity and to use the latter as a proxy to study Aß-induced synaptotoxicity. Moreover, since the presynaptic, postsynaptic, and synaptic chambers can be individually targeted, our assay provides a powerful tool to evaluate the involvement of candidate genes in synaptic vulnerability and/or test therapeutic strategies for AD.

Manganese disrupts the maturation and degradation of axonal autophagosome leading to hippocampal synaptic toxicity in mice via the activation of LRRK2 on phosphorylation of Rab10.

Manganese (Mn) overexposure induces hippocampal synaptotoxicity by the accumulation of dysfunctional synaptic vesicles (SVs). Leucine-rich repeat kinase 2 (LRRK2) kinase activity is involved in regulating axonal transport (autophagosomal maturation) and lysosomal function. Nevertheless, it remains unclear whether Mn-induced synaptotoxicity is associated with the LRRK2-mediated disruption of autophagosomal maturation in axonal transport and the impairment of lysosomes in hippocampal neurons. Here, we established models of manganism in C57BL/6 mice and hippocampal neuronal HT22 cells to verify the role of LRRK2-mediated Rab10 phosphorylation in the Mn-induced dysfunction of autophagy- lysosomal fusion. Our results proved that Mn-induced the disorder of axonal transport and that lysosome impairments were associated with the increased recruitment of phospho-Rab10 at the axon and lysosomes. Next, we established Lrrk2-KD and LRRK2 kinase- specific inhibitor (GNE-0877, GNE) pre-treated HT22 cells to inhibit Lrrk2 gene expression and kinase activity, respectively. In Mn-treated Lrrk2-KD or GNE-pretreated normal neurons, our results indicated that lysosomal pH and integrity and autophagic flow were restored, indicating by decreased levels of phospho-Rab10 on lysosomes and JNK-interacting proteins (JIP4). In addition, GNE pretreatment could provide protection against Mn-induced synaptotoxicity in vivo, which was evidenced by the partial recovery in synaptic plasticity and synaptic damage. Thus, the Mn-induced abnormal activation of LRRK2 affected lysosomes and the recruitment of phospho-Rab10 by JIP4, which disrupted autophagosomal maturation in proximal axons and resulted in the hippocampal synaptic toxicity of mice.

Amyloid ß-Oligomers Inhibit the Nuclear Ca2+ Signals and the Neuroprotective Gene Expression Induced by Gabazine in Hippocampal Neurons.

Hippocampal neuronal activity generates dendritic and somatic Ca2+ signals, which, depending on stimulus intensity, rapidly propagate to the nucleus and induce the expression of transcription factors and genes with crucial roles in cognitive functions. Soluble amyloid-beta oligomers (AßOs), the main synaptotoxins engaged in the pathogenesis of Alzheimer's disease, generate aberrant Ca2+ signals in primary hippocampal neurons, increase their oxidative tone and disrupt structural plasticity. Here, we explored the effects of sub-lethal AßOs concentrations on activity-generated nuclear Ca2+ signals and on the Ca2+-dependent expression of neuroprotective genes. To induce neuronal activity, neuron-enriched primary hippocampal cultures were treated with the GABAA receptor blocker gabazine (GBZ), and nuclear Ca2+ signals were measured in AßOs-treated or control neurons transfected with a genetically encoded nuclear Ca2+ sensor. Incubation (6 h) with AßOs significantly reduced the nuclear Ca2+ signals and the enhanced phosphorylation of cyclic AMP response element-binding protein (CREB) induced by GBZ. Likewise, incubation (6 h) with AßOs significantly reduced the GBZ-induced increases in the mRNA levels of neuronal Per-Arnt-Sim domain protein 4 (Npas4), brain-derived neurotrophic factor (BDNF), ryanodine receptor type-2 (RyR2), and the antioxidant enzyme NADPH-quinone oxidoreductase (Nqo1). Based on these findings we propose that AßOs, by inhibiting the generation of activity-induced nuclear Ca2+ signals, disrupt key neuroprotective gene expression pathways required for hippocampal-dependent learning and memory processes.

The reduction of astrocytic tau prevents amyloid-ß-induced synaptotoxicity.

Alzheimer's disease is a neurological disorder characterized by the overproduction and aggregation of amyloid-beta and the phosphorylation and intraneuronal accumulation of tau. These events promote synaptic dysfunction and loss, leading to neurodegeneration and cognitive deficits. Astrocytes are intimately associated with synapses and become activated under pathological conditions, becoming neurotoxic and detrimentally affecting synapses. Although it has been established that reducing neuronal tau expression prevents amyloid-beta-induced toxicity, the role of astrocytic tau in this setting remains understudied. Herein, we performed a series of astrocytic and neuronal primary cultures to evaluate the effects of decreasing astrocytic tau levels on astrocyte-mediated amyloid-beta-induced synaptic degeneration. Our results suggest that the downregulation of tau in astrocytes mitigates the loss of synapses triggered by their exposure to amyloid-beta. Additionally, the absence of tau from astrocytes promotes the upregulation of several synaptoprotective genes, followed by increased production of the neuroprotective factor Pentraxin 3. These results expand our understanding of the contribution of astrocytic tau to the neurodegenerative process induced by amyloid-beta-stimulation and how reducing astrocytic tau could improve astrocyte function by stimulating the expression of synaptoprotective factors. Reducing endogenous astrocytic tau expression could be a potential strategy to prevent synaptic damage in Alzheimer's disease and other neurological conditions.

A calcium-sensitive antibody isolates soluble amyloid-ß aggregates and fibrils from Alzheimer's disease brain.

Aqueously soluble oligomers of amyloid-ß peptide may be the principal neurotoxic forms of amyloid-ß in Alzheimer's disease, initiating downstream events that include tau hyperphosphorylation, neuritic/synaptic injury, microgliosis and neuron loss. Synthetic oligomeric amyloid-ß has been studied extensively, but little is known about the biochemistry of natural oligomeric amyloid-ß in human brain, even though it is more potent than simple synthetic peptides and comprises truncated and modified amyloid-ß monomers. We hypothesized that monoclonal antibodies specific to neurotoxic oligomeric amyloid-ß could be used to isolate it for further study. Here we report a unique human monoclonal antibody (B24) raised against synthetic oligomeric amyloid-ß that potently prevents Alzheimer's disease brain oligomeric amyloid-ß-induced impairment of hippocampal long-term potentiation. B24 binds natural and synthetic oligomeric amyloid-ß and a subset of amyloid plaques, but only in the presence of Ca2+. The amyloid-ß N terminus is required for B24 binding. Hydroxyapatite chromatography revealed that natural oligomeric amyloid-ß is highly avid for Ca2+. We took advantage of the reversible Ca2+-dependence of B24 binding to perform non-denaturing immunoaffinity isolation of oligomeric amyloid-ß from Alzheimer's disease brain-soluble extracts. Unexpectedly, the immunopurified material contained amyloid fibrils visualized by electron microscopy and amenable to further structural characterization. B24-purified human oligomeric amyloid-ß inhibited mouse hippocampal long-term potentiation. These findings identify a calcium-dependent method for purifying bioactive brain oligomeric amyloid-ß, at least some of which appears fibrillar.

Mechanisms of organophosphate neurotoxicity.

The canonical mechanism of organophosphate (OP) neurotoxicity is the inhibition of acetylcholinesterase (AChE). However, multiple lines of evidence suggest that mechanisms in addition to or other than AChE inhibition contribute to the neurotoxic effects associated with acute and chronic OP exposures. Characterizing the role(s) of AChE inhibition versus noncholinergic mechanisms in OP neurotoxicity remains an active area of research with significant diagnostic and therapeutic implications. Here, we review recently published studies that provide mechanistic insights regarding (1) OP-induced status epilepticus, (2) long-term neurologic consequences of acute OP exposures, and (3) neurotoxic effects associated with repeated low-level OP exposures. Key data gaps and challenges are also discussed.

Reactive Astrocytes Contribute to Alzheimer's Disease-Related Neurotoxicity and Synaptotoxicity in a Neuron-Astrocyte Co-culture Assay.

Pathological hallmarks of Alzheimer's disease (AD) include deposition and accumulation of amyloid- ß (Aß), neurofibrillary tangle formation, and neuronal loss. Pathogenesis of presymptomatic disease stages remains elusive, although studies suggest that the early structural and functional alterations likely occur at neuronal dendritic spines. Presymptomatic alterations may also affect different CNS cell types. However, specific contributions of these cell types as cause or consequence of pathology are difficult to study in vivo. There is a shortage of relatively simple, well-defined, and validated in vitro models that allow a straightforward interpretation of results and recapitulate aspects of pathophysiology. For instance, dissecting the AD-related processes (e.g., neurotoxicity vs. synaptotoxicity) may be difficult with the common cell-based systems such as neuronal cell lines or primary neurons. To investigate and characterize the impact of reactive astrocytes on neuronal morphology in the context of AD-related cues, we modified an in vitro co-culture assay of primary mouse neurons and primary mouse astrocytes based on the so-called Banker "sandwich" co-culture assay. Here, we provide a simple and modular assay with fully differentiated primary mouse neurons to study the paracrine interactions between the neurons and the astrocytes in the co-culture setting. Readouts were obtained from both cell types in our assay. Astrocyte feeder cells were pre-exposed to neuroinflammatory conditions by means of Aß42, Aß40, or lipopolysaccharide (LPS). Non-cell autonomous toxic effects of reactive astrocytes on neurons were assessed using the Sholl analysis to evaluate the dendritic complexity, whereas synaptic puncta served as a readout of synaptotoxicity. Here, we show that astrocytes actively contribute to the phenotype of the primary neurons in an AD-specific context, emphasizing the role of different cell types in AD pathology. The cytokine expression pattern was significantly altered in the treated astrocytes. Of note, the impact of reactive astrocytes on neurons was highly dependent on the defined cell ratios. Our co-culture system is modular, of low cost, and allows us to probe aspects of neurodegeneration and neuroinflammation between the two major CNS cell types, neurons, and astrocytes, under well-defined experimental conditions. Our easy-to-follow protocol, including work-flow figures, may also provide a methodological outline to study the interactions of astrocytes and neurons in the context of other diseases in the future.

Oxysterols present in Alzheimer's disease brain induce synaptotoxicity by activating astrocytes: A major role for lipocalin-2.

Among Alzheimer's disease (AD) brain hallmarks, the presence of reactive astrocytes was demonstrated to correlate with neuronal loss and cognitive deficits. Evidence indeed supports the role of reactive astrocytes as mediators of changes in neurons, including synapses. However, the complexity and the outcomes of astrocyte reactivity are far from being completely elucidated. Another key role in AD pathogenesis is played by alterations in brain cholesterol metabolism. Oxysterols (cholesterol oxidation products) are crucial for brain cholesterol homeostasis, and we previously demonstrated that changes in the brain levels of various oxysterols correlate with AD progression. Moreover, oxysterols have been shown to contribute to various pathological mechanisms involved in AD pathogenesis. In order to deepen the role of oxysterols in AD, we investigated whether they could contribute to astrocyte reactivity, and consequently impact on neuronal health. Results showed that oxysterols present in mild or severe AD brains induce a clear morphological change in mouse primary astrocytes, accompanied by the upregulation of some reactive astrocyte markers, including lipocalin-2 (Lcn2). Moreover, astrocyte conditioned media analysis revealed a significant increase in the release of Lcn2, cytokines, and chemokines in response to oxysterols. A significant reduction of postsynaptic density protein 95 (PSD95) and a concurrent increase in cleaved caspase-3 protein levels have been demonstrated in neurons co-cultured with oxysterol-treated astrocytes, pointing out that mediators released by astrocytes have an impact on neurons. Among these mediators, Lcn2 has been demonstrated to play a major role on synapses, affecting neurite morphology and decreasing dendritic spine density. These data demonstrated that oxysterols present in the AD brain promote astrocyte reactivity, determining the release of several mediators that affect neuronal health and synapses. Lcn2 has been shown to exert a key role in mediating the synaptotoxic effect of oxysterol-treated astrocytes.

Vascular amyloid accumulation alters the gabaergic synapse and induces hyperactivity in a model of cerebral amyloid angiopathy.

Cerebral amyloid angiopathy (CAA) is typified by the cerebrovascular deposition of amyloid. The mechanisms underlying the contribution of CAA to neurodegeneration are not currently understood. Although CAA is highly associated with the accumulation of ß-amyloid (Aß), other amyloids are known to associate with the vasculature. Alzheimer's disease (AD) is characterized by parenchymal Aß deposition and intracellular accumulation of tau as neurofibrillary tangles (NFTs), affecting synapses directly, leading to behavioral and physical impairment. CAA increases with age and is present in 70%-97% of individuals with AD. Studies have overwhelmingly focused on the connection between parenchymal amyloid accumulation and synaptotoxicity; thus, the contribution of vascular amyloid is mostly understudied. Here, synaptic alterations induced by vascular amyloid accumulation and their behavioral consequences were characterized using a mouse model of Familial Danish dementia (FDD), a neurodegenerative disease characterized by the accumulation of Danish amyloid (ADan) in the vasculature. The mouse model (Tg-FDD) displays a hyperactive phenotype that potentially arises from impairment in the GABAergic synapses, as determined by electrophysiological analysis. We demonstrated that the disruption of GABAergic synapse organization causes this impairment and provided evidence that GABAergic synapses are impaired in patients with CAA pathology. Understanding the mechanism that CAA contributes to synaptic dysfunction in AD-related dementias is of critical importance for developing future therapeutic interventions.

Amyloid-ß oligomers synaptotoxicity: The emerging role of EphA4/c-Abl signaling in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by progressive memory loss and dementia. The strong correlation between cognitive decline and the loss of synapses supports the idea that synaptic damage is a relevant pathogenic mechanism underlying AD progression. It has been shown that amyloid beta oligomers (AßOs) induce synaptotoxicity ultimately leading to the reduction of dendritic spine density, which underlies cognitive damage. However, the signaling pathways connecting AßOs to synaptic dysfunction have not been completely elucidated. In this review, we have gathered evidence on AßOs receptors and the signaling pathways involved in synaptic damage. We make special emphasis on a new AßOs induced axis that involves the tyrosine kinase ephrin receptor A4 (EphA4) and c-Abl tyrosine kinase activation. EphA4 is a key player in homeostatic plasticity, mediating dendritic spine remodeling and retraction. AßOs aberrantly activate EphA4 leading to dendritic spine elimination. c-Abl is activated in AßOs exposed neurons and in AD patient's brain, and the inhibition of activated c-Abl ameliorates cognitive deficits in AD mouse model. The EphA4 receptor activates c-Abl intracellular signaling. Therefore EphA4 is an emerging AßOs receptor and the activation of the EphA4/c-Abl axis would explain the synaptic spine alterations found in AD.

Molecular Mechanisms of Synaptotoxicity and Neuroinflammation in Alzheimer's Disease.

Alzheimer's disease (AD) is the most common neurodegenerative disorder, which is clinically associated with a global cognitive decline and progressive loss of memory and reasoning. According to the prevailing amyloid cascade hypothesis of AD, increased soluble amyloid-ß (Aß) oligomer levels impair the synaptic functions and augment calcium dyshomeostasis, neuroinflammation, oxidative stress as well as the formation of neurofibrillary tangles at specific brain regions. Emerging new findings related to synaptic dysfunction and initial steps of neuroinflammation in AD have been able to delineate the underlying molecular mechanisms, thus reinforcing the development of new treatment strategies and biomarkers for AD beyond the conventional Aß- and tau-targeted approaches. Particularly, the identification and further characterization of disease-associated microglia and their RNA signatures, AD-associated novel risk genes, neurotoxic astrocytes, and in the involvement of complement-dependent pathway in synaptic pruning and loss in AD have set the outstanding basis for further preclinical and clinical studies. Here, we discuss the recent development and the key findings related to the novel molecular mechanisms and targets underlying the synaptotoxicity and neuroinflammation in AD.

Neuronal Adenosine A2A Receptors Are Critical Mediators of Neurodegeneration Triggered by Convulsions.

Neurodegeneration is a process transversal to neuropsychiatric diseases and the understanding of its mechanisms should allow devising strategies to prevent this irreversible step in brain diseases. Neurodegeneration caused by seizures is a critical step in the aggravation of temporal lobe epilepsy, but its mechanisms remain undetermined. Convulsions trigger an elevation of extracellular adenosine and upregulate adenosine A2A receptors (A2AR), which have been associated with the control of neurodegenerative diseases. Using the rat and mouse kainate model of temporal lobe epilepsy, we now tested whether A2AR control convulsions-induced hippocampal neurodegeneration. The pharmacological or genetic blockade of A2AR did not affect kainate-induced convulsions but dampened the subsequent neurotoxicity. This neurotoxicity began with a rapid A2AR upregulation within glutamatergic synapses (within 2 h), through local translation of synaptic A2AR mRNA. This bolstered A2AR-mediated facilitation of glutamate release and of long-term potentiation (LTP) in CA1 synapses (4 h), triggered a subsequent synaptotoxicity, heralded by decreased synaptic plasticity and loss of synaptic markers coupled to calpain activation (12 h), that predated overt neuronal loss (24 h). All modifications were prevented by the deletion of A2AR selectively in forebrain neurons. This shows that synaptic A2AR critically control synaptic excitotoxicity, which underlies the development of convulsions-induced neurodegeneration.

Amyloid ß synaptotoxicity is Wnt-PCP dependent and blocked by fasudil.

INTRODUCTION: Synapse loss is the structural correlate of the cognitive decline indicative of dementia. In the brains of Alzheimer's disease sufferers, amyloid ß (Aß) peptides aggregate to form senile plaques but as soluble peptides are toxic to synapses. We previously demonstrated that Aß induces Dickkopf-1 (Dkk1), which in turn activates the Wnt-planar cell polarity (Wnt-PCP) pathway to drive tau pathology and neuronal death. METHODS: We compared the effects of Aß and of Dkk1 on synapse morphology and memory impairment while inhibiting or silencing key elements of the Wnt-PCP pathway. RESULTS: We demonstrate that Aß synaptotoxicity is also Dkk1 and Wnt-PCP dependent, mediated by the arm of Wnt-PCP regulating actin cytoskeletal dynamics via Daam1, RhoA and ROCK, and can be blocked by the drug fasudil. DISCUSSION: Our data add to the importance of aberrant Wnt signaling in Alzheimer's disease neuropathology and indicate that fasudil could be repurposed as a treatment for the disease.

Astrocytic GluN2A and GluN2B Oppose the Synaptotoxic Effects of Amyloid-ß1-40 in Hippocampal Cells.

Early-stage Alzheimer's disease (AD) is characterized by synaptic dysfunction, a phenomenon in which soluble oligomers of amyloid-beta (Aß) and N-methyl-D-aspartate receptor (NMDAR) are implicated. Here, we demonstrated that astrocytes express NMDARs and therefore have the potential to modulate the synaptotoxic actions of Aß. We found that specific pharmacological antagonism of two of the major NMDAR subunits, GluN2A and GluN2B, exacerbates Aß-induced synaptotoxicity suggesting, for the first time, that astrocytic GluN2A and GluN2B mediate synaptoprotection. From the perspective of the pathogenic mechanisms of Alzheimer's disease, in which Aß and NMDAR play significant roles, these observations are striking since neuronal GluN2A and GluN2B are well known modulators of neurodegeneration. We did initial studies to understand the basis for the differential effects of astrocytic and neuronal GluN2A and GluN2B in the promotion of synapse survival, and identified a neurotrophin produced by astrocytes, nerve growth factor ß (ß-NGF), as a likely mediator of the synaptoprotective effects of astrocytic GluN2A and GluN2B activation. The results presented suggest that astrocytes may be suitable druggable targets for the prevention and/or delay of the synaptic loss that occurs during early stages of AD.

How does adenosine control neuronal dysfunction and neurodegeneration?

The adenosine modulation system mostly operates through inhibitory A1 (A1 R) and facilitatory A2A receptors (A2A R) in the brain. The activity-dependent release of adenosine acts as a brake of excitatory transmission through A1 R, which are enriched in glutamatergic terminals. Adenosine sharpens salience of information encoding in neuronal circuits: high-frequency stimulation triggers ATP release in the 'activated' synapse, which is locally converted by ecto-nucleotidases into adenosine to selectively activate A2A R; A2A R switch off A1 R and CB1 receptors, bolster glutamate release and NMDA receptors to assist increasing synaptic plasticity in the 'activated' synapse; the parallel engagement of the astrocytic syncytium releases adenosine further inhibiting neighboring synapses, thus sharpening the encoded plastic change. Brain insults trigger a large outflow of adenosine and ATP, as a danger signal. A1 R are a hurdle for damage initiation, but they desensitize upon prolonged activation. However, if the insult is near-threshold and/or of short-duration, A1 R trigger preconditioning, which may limit the spread of damage. Brain insults also up-regulate A2A R, probably to bolster adaptive changes, but this heightens brain damage since A2A R blockade affords neuroprotection in models of epilepsy, depression, Alzheimer's, or Parkinson's disease. This initially involves a control of synaptotoxicity by neuronal A2A R, whereas astrocytic and microglia A2A R might control the spread of damage. The A2A R signaling mechanisms are largely unknown since A2A R are pleiotropic, coupling to different G proteins and non-canonical pathways to control the viability of glutamatergic synapses, neuroinflammation, mitochondria function, and cytoskeleton dynamics. Thus, simultaneously bolstering A1 R preconditioning and preventing excessive A2A R function might afford maximal neuroprotection. The main physiological role of the adenosine modulation system is to sharp the salience of information encoding through a combined action of adenosine A2A receptors (A2A R) in the synapse undergoing an alteration of synaptic efficiency with an increased inhibitory action of A1 R in all surrounding synapses. Brain insults trigger an up-regulation of A2A R in an attempt to bolster adaptive plasticity together with adenosine release and A1 R desensitization; this favors synaptotocity (increased A2A R) and decreases the hurdle to undergo degeneration (decreased A1 R). Maximal neuroprotection is expected to result from a combined A2A R blockade and increased A1 R activation. This article is part of a mini review series: "Synaptic Function and Dysfunction in Brain Diseases".

MT5-MMP is a new pro-amyloidogenic proteinase that promotes amyloid pathology and cognitive decline in a transgenic mouse model of Alzheimer's disease.

Membrane-type 5-matrix metalloproteinase (MT5-MMP) is a proteinase mainly expressed in the nervous system with emerging roles in brain pathophysiology. The implication of MT5-MMP in Alzheimer's disease (AD), notably its interplay with the amyloidogenic process, remains elusive. Accordingly, we crossed the genetically engineered 5xFAD mouse model of AD with MT5-MMP-deficient mice and examined the impact of MT5-MMP deficiency in bigenic 5xFAD/MT5-MMP(-/-) mice. At early stages (4 months) of the pathology, the levels of amyloid beta peptide (Aß) and its amyloid precursor protein (APP) C-terminal fragment C99 were largely reduced in the cortex and hippocampus of 5xFAD/MT5-MMP(-/-), compared to 5xFAD mice. Reduced amyloidosis in bigenic mice was concomitant with decreased glial reactivity and interleukin-1ß (IL-1ß) levels, and the preservation of long-term potentiation (LTP) and spatial learning, without changes in the activity of α-, ß- and γ-secretases. The positive impact of MT5-MMP deficiency was still noticeable at 16 months of age, as illustrated by reduced amyloid burden and gliosis, and a better preservation of the cortical neuronal network and synaptophysin levels in bigenic mice. MT5-MMP expressed in HEKswe cells colocalized and co-immunoprecipitated with APP and significantly increased the levels of Aß and C99. MT5-MMP also promoted the release of a soluble APP fragment of 95 kDa (sAPP95) in HEKswe cells. sAPP95 levels were significantly reduced in brain homogenates of 5xFAD/MT5-MMP(-/-) mice, supporting altogether the idea that MT5-MMP influences APP processing. MT5-MMP emerges as a new pro-amyloidogenic regulator of APP metabolism, whose deficiency alleviates amyloid pathology, neuroinflammation and cognitive decline.

Beneficial Effect of Astragaloside on Alzheimer's Disease Condition Using Cultured Primary Cortical Cells Under ß-amyloid Exposure.

ß-amyloid (Aß)-mediated neuronal apoptosis contributes to the pathogenesis of Alzheimer's disease (AD). This study aimed to investigate whether astragalosides (AST) could inhibit Aß-induced apoptosis in vivo and in vitro and to explore the underlying mechanisms. Amyloid ß-protein fragment 25-35 (Aß25-35) was administered to cerebral lateral ventricle of rats to make the AD models in vivo. AST was able to attenuate both cortical cell degeneration and memory deficits in the AD rats. AST also inhibited Aß25-35-induced cytotoxicity (e.g., decreased cell viability); apoptosis (e.g., increased caspase-3 expression, increased DNA fragmentation, and Tau hyperphosphorylation); synaptotoxicity (e.g., increased loss of both a dendritic marker, microtubule-associated protein 2 (MAP-2) and synaptic proteins, synaptophysins); and mitochondrial dysfunction (e.g., increased mitochondrial membrane potential) in cultured primary rat cortical cells. The beneficial effect of AST in reducing Aß-induced cytotoxicity, apoptosis, and mitochondrial dysfunction in cortical cells were blocked by inhibition of phosphoinositide 3-kinase (PI3K)-dependent protein kinase B (PKB, as known as AKT) activation with LY294002. In addition, inhibition of extracellular protein kinase (ERK) with U0126 shared with the AST the same beneficial effects in reducing Aß-induced apoptosis. Our data suggest that the cortical PI3K/AKT and MAPK (or ERK) pathways as appealing therapeutic targets in treating AD, and AST may have a positive impact on AD treatment via modulation of both PI3K/AKT and ERK pathways.

Comorbidities in Neurology: Is adenosine the common link?

Comorbidities in Neurology represent a major conceptual and therapeutic challenge. For example, temporal lobe epilepsy (TLE) is a syndrome comprised of epileptic seizures and comorbid symptoms including memory and psychiatric impairment, depression, and sleep dysfunction. Similarly, Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic Lateral Sclerosis (ALS) are accompanied by various degrees of memory dysfunction. Patients with AD have an increased likelihood for seizures, whereas all four conditions share certain aspects of psychosis, depression, and sleep dysfunction. This remarkable overlap suggests common pathophysiological mechanisms, which include synaptic dysfunction and synaptotoxicity, as well as glial activation and astrogliosis. Astrogliosis is linked to synapse function via the tripartite synapse, but astrocytes also control the availability of gliotransmitters and adenosine. Here we will specifically focus on the 'adenosine hypothesis of comorbidities' implying that astrocyte activation, via overexpression of adenosine kinase (ADK), induces a deficiency in the homeostatic tone of adenosine. We present evidence from patient-derived samples showing astrogliosis and overexpression of ADK as common pathological hallmark of epilepsy, AD, PD, and ALS. We discuss a transgenic 'comorbidity model', in which brain-wide overexpression of ADK and resulting adenosine deficiency produces a comorbid spectrum of seizures, altered dopaminergic function, attentional impairment, and deficits in cognitive domains and sleep regulation. We conclude that dysfunction of adenosine signaling is common in neurological conditions, that adenosine dysfunction can explain co-morbid phenotypes, and that therapeutic adenosine augmentation might be effective for the treatment of comorbid symptoms in multiple neurological conditions.

MRZ-99030 - A novel modulator of Aß aggregation: II - Reversal of Aß oligomer-induced deficits in long-term potentiation (LTP) and cognitive performance in rats and mice.

ß-amyloid1-42 (Aß1-42) is a major endogenous pathogen underlying the aetiology of Alzheimer's disease (AD). Recent evidence indicates that soluble Aß oligomers, rather than plaques, are the major cause of synaptic dysfunction and neurodegeneration. Small molecules that suppress Aß aggregation, reduce oligomer stability or promote off-pathway non-toxic oligomerization represent a promising alternative strategy for neuroprotection in AD. MRZ-99030 was recently identified as a dipeptide that modulates Aß1-42 aggregation by triggering a non-amyloidogenic aggregation pathway, thereby reducing the amount of intermediate toxic soluble oligomeric Aß species. The present study evaluated the relevance of these promising results with MRZ-99030 under pathophysiological conditions i.e. against the synaptotoxic effects of Aß oligomers on hippocampal long term potentiation (LTP) and two different memory tasks. Aß1-42 interferes with the glutamatergic system and with neuronal Ca(2+) signalling and abolishes the induction of LTP. Here we demonstrate that MRZ-99030 (100-500 nM) at a 10:1 stoichiometric excess to Aß clearly reversed the synaptotoxic effects of Aß1-42 oligomers on CA1-LTP in murine hippocampal slices. Co-application of MRZ-99030 also prevented the two-fold increase in resting Ca(2+) levels in pyramidal neuron dendrites and spines triggered by Aß1-42 oligomers. In anaesthetized rats, pre-administration of MRZ-99030 (50 mg/kg s.c.) protected against deficits in hippocampal LTP following i.c.v. injection of oligomeric Aß1-42. Furthermore, similar treatment significantly ameliorated cognitive deficits in an object recognition task and under an alternating lever cyclic ratio schedule after the i.c.v. application of Aß1-42 and 7PA2 conditioned medium, respectively. Altogether, these results demonstrate the potential therapeutic benefit of MRZ-99030 in AD.