Bioenergetic mechanisms in astrocytes may contribute to amyloid plaque deposition and toxicity.

Alzheimer disease (AD) is characterized neuropathologically by synaptic disruption, neuronal loss, and deposition of amyloid ß (Aß) protein in brain structures that are critical for memory and cognition. There is increasing appreciation, however, that astrocytes, which are the major non-neuronal glial cells, may play an important role in AD pathogenesis. Unlike neurons, astrocytes are resistant to Aß cytotoxicity, which may, in part, be related to their greater reliance on glycolytic metabolism. Here we show that, in cultures of human fetal astrocytes, pharmacological inhibition or molecular down-regulation of a main enzymatic regulator of glycolysis, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB3), results in increased accumulation of Aß within and around astrocytes and greater vulnerability of these cells to Aß toxicity. We further investigated age-dependent changes in PFKFB3 and astrocytes in AD transgenic mice (TgCRND8) that overexpress human Aß. Using a combination of Western blotting and immunohistochemistry, we identified an increase in glial fibrillary acidic protein expression in astrocytes that paralleled the escalation of the Aß plaque burden in TgCRND8 mice in an age-dependent manner. Furthermore, PFKFB3 expression also demonstrated an increase in these mice, although at a later age (9 months) than GFAP and Aß. Immunohistochemical staining showed significant reactive astrogliosis surrounding Aß plaques with increased PFKFB3 activity in 12-month-old TgCRND8 mice, an age when AD pathology and behavioral deficits are fully manifested. These studies shed light on the unique bioenergetic mechanisms within astrocytes that may contribute to the development of AD pathology.

The prion protein modulates A-type K+ currents mediated by Kv4.2 complexes through dipeptidyl aminopeptidase-like protein 6.

Widely expressed in the adult central nervous system, the cellular prion protein (PrP(C)) is implicated in a variety of processes, including neuronal excitability. Dipeptidyl aminopeptidase-like protein 6 (DPP6) was first identified as a PrP(C) interactor using in vivo formaldehyde cross-linking of wild type (WT) mouse brain. This finding was confirmed in three cell lines and, because DPP6 directs the functional assembly of K(+) channels, we assessed the impact of WT and mutant PrP(C) upon Kv4.2-based cell surface macromolecular complexes. Whereas a Gerstmann-Sträussler-Scheinker disease version of PrP with eight extra octarepeats was a loss of function both for complex formation and for modulation of Kv4.2 channels, WT PrP(C), in a DPP6-dependent manner, modulated Kv4.2 channel properties, causing an increase in peak amplitude, a rightward shift of the voltage-dependent steady-state inactivation curve, a slower inactivation, and a faster recovery from steady-state inactivation. Thus, the net impact of wt PrP(C) was one of enhancement, which plays a critical role in the down-regulation of neuronal membrane excitability and is associated with a decreased susceptibility to seizures. Insofar as previous work has established a requirement for WT PrP(C) in the Aß-dependent modulation of excitability in cholinergic basal forebrain neurons, our findings implicate PrP(C) regulation of Kv4.2 channels as a mechanism contributing to the effects of oligomeric Aß upon neuronal excitability and viability.

Role of astrocytic glycolytic metabolism in Alzheimer's disease pathogenesis.

Alzheimer's disease (AD) has historically been considered to arise due to the specific dysfunction and pathology of neurons in brain areas related to cognition. Recent progress indicates that astrocytes play an important role in neurodegenerative processes underlying AD. In this review, we focus on the different glucose metabolism profiles between astrocytes and neurons. In AD, a variety of CNS insults, such as the presence of amyloid protein, trigger reactive astrogliosis, which disrupts normal glycolytic activity in these cells. The compromise of the astrocytic metabolism in turn weakens the integrity of astrocytic-neuronal partnership, damages the normal brain homeostasis, impairs clearance of amyloid, promotes cytokine release and other inflammatory mediators, and over time, leads to neurodegeneration.

Interaction between hypothalamic dorsomedial nucleus and the suprachiasmatic nucleus determines intensity of food anticipatory behavior.

Food anticipatory behavior (FAA) is induced by limiting access to food for a few hours daily. Animals anticipate this scheduled meal event even without the suprachiasmatic nucleus (SCN), the biological clock. Consequently, a food-entrained oscillator has been proposed to be responsible for meal time estimation. Recent studies suggested the dorsomedial hypothalamus (DMH) as the site for this food-entrained oscillator, which has led to considerable controversy in the literature. Herein we demonstrate by means of c-Fos immunohistochemistry that the neuronal activity of the suprachiasmatic nucleus (SCN), which signals the rest phase in nocturnal animals, is reduced when animals anticipate the scheduled food and, simultaneously, neuronal activity within the DMH increases. Using retrograde tracing and confocal analysis, we show that inhibition of SCN neuronal activity is the consequence of activation of GABA-containing neurons in the DMH that project to the SCN. Next, we show that DMH lesions result in a loss or diminution of FAA, simultaneous with increased activity in the SCN. A subsequent lesion of the SCN restored FAA. We conclude that in intact animals, FAA may only occur when the DMH inhibits the activity of the SCN, thus permitting locomotor activity. As a result, FAA originates from a neuronal network comprising an interaction between the DMH and SCN. Moreover, this study shows that the DMH-SCN interaction may serve as an intrahypothalamic system to gate activity instead of rest overriding circadian predetermined temporal patterns.

Beta amyloid-induced depression of hippocampal long-term potentiation is mediated through the amylin receptor.

Alzheimer's disease (AD) is characterized by accumulation of amyloid-ß peptide (Aß) in the brain regions that subserve memory and cognition. The amylin receptor is a potential target receptor for expression of the deleterious actions of soluble oligomeric Aß species. We investigated whether the amylin receptor antagonist, AC253, neutralizes the depressant effects of Aß(1-42) and human amylin on hippocampal long-term potentiation (LTP). Furthermore, we examined whether depressed levels of LTP observed in transgenic mice, which overexpress amyloid precursor protein (TgCRND8), could be restored with AC253. In mouse hippocampal brain slices, field EPSPs were recorded from the stratum radiatum layer of the CA1 area (cornu ammonis 1 region of the hippocampus) in response to electrical stimulation of Schaeffer collateral afferents. LTP was induced by 3-theta burst stimulation protocols. Aß(1-42) (50 nM) and human amylin (50 nM), but not Aß(42-1) (50 nM), depressed LTP evoked using both stimulation protocols. Preapplication of AC253 (250 nM) blocked Aß- and human amylin-induced reduction of LTP without affecting baseline transmission or LTP on its own. In contrast to wild-type controls, where robust LTP is observed, 6- to 12-month-old TgCRND8 mice show blunted LTP that is significantly enhanced by application of AC253. Our data demonstrate that the effects of Aß(1-42) and human amylin on LTP are expressed via the amylin receptor, and moreover, blockade of this receptor increases LTP in transgenic mice that show increased brain amyloid burden. Amylin receptor antagonists could serve as potentially useful therapeutic agents in AD.

Amyloid ß (Aß) peptide directly activates amylin-3 receptor subtype by triggering multiple intracellular signaling pathways.

The two age-prevalent diseases Alzheimer disease and type 2 diabetes mellitus share many common features including the deposition of amyloidogenic proteins, amyloid ß protein (Aß) and amylin (islet amyloid polypeptide), respectively. Recent evidence suggests that both Aß and amylin may express their effects through the amylin receptor, although the precise mechanisms for this interaction at a cellular level are unknown. Here, we studied this by generating HEK293 cells with stable expression of an isoform of the amylin receptor family, amylin receptor-3 (AMY3). Aß1-42 and human amylin (hAmylin) increase cytosolic cAMP and Ca(2+), trigger multiple pathways involving the signal transduction mediators protein kinase A, MAPK, Akt, and cFos. Aß1-42 and hAmylin also induce cell death during exposure for 24-48 h at low micromolar concentrations. In the presence of hAmylin, Aß1-42 effects on HEK293-AMY3-expressing cells are occluded, suggesting a shared mechanism of action between the two peptides. Amylin receptor antagonist AC253 blocks increases in intracellular Ca(2+), activation of protein kinase A, MAPK, Akt, cFos, and cell death, which occur upon AMY3 activation with hAmylin, Aß1-42, or their co-application. Our data suggest that AMY3 plays an important role by serving as a receptor target for actions Aß and thus may represent a novel therapeutic target for development of compounds to treat neurodegenerative conditions such as Alzheimer disease.

Aß inhibition of ionic conductance in mouse basal forebrain neurons is dependent upon the cellular prion protein PrPC.

Current therapies for Alzheimer's disease (AD) address a loss of cholinergic neurons, while accumulation of neurotoxic amyloid ß (Aß) peptide assemblies is thought central to molecular pathogenesis. Overlaps may exist between prionopathies and AD wherein Aß oligomers bind to the cellular prion protein PrP(C) and inhibit synaptic plasticity in the hippocampus (Laurén et al., 2009). Here we applied oligomeric Aß to neurons with different PrP (Prnp) gene dosage. Whole-cell recordings were obtained from dissociated neurons of the diagonal band of Broca (DBB), a cholinergic basal forebrain nucleus. In wild-type (wt) mice, Aß1₋42 evoked a concentration-dependent reduction of whole-cell outward currents in a voltage range between -30 and +30 mV; reduction occurred through a combined modulation of a suite of potassium conductances including the delayed rectifier (I(K)), the transient outward (I(A)), and the iberiotoxin-sensitive (calcium-activated potassium, I(C)) currents. Inhibition was not seen with Aß42₋1 peptide, while Aß1₋42-induced responses were reduced by application of anti-PrP antibody, attenuated in cells from Prnp°/⁺ hemizygotes, and absent in Prnp°/° homozygotes. Similarly, amyloidogenic amylin peptide depressed DBB whole-cell currents in DBB cells from wt mice, but not Prnp°/° homozygotes. While prior studies give broad support for a neuroprotective function for PrP(C), our data define a latent pro-pathogenic role in the presence of amyloid assemblies.

ß-Amyloid protein (Aß) and human amylin regulation of apoptotic genes occurs through the amylin receptor.

Deposition of amyloid-beta (Aß) protein, a 39-43 amino acid peptide, in the brain is a major pathological feature of Alzheimer's disease (AD). We have previously provided evidence that in primary cultures of rat basal forebrain and human fetal neurons (HFNs), neurotoxic effects of oligomeric Aß are expressed through the amylin receptor. In this study, we utilized RT-PCR arrays to compare RNA expression levels of 84 markers for pro and anti- apoptotic signalling pathways following exposure of HFNs to either Aß(1-42) (20 µM) or human amylin (2 µM). Oligomeric Aß(1-42) or human amylin was applied to HFNs alone or after pre-treatment of cultures with the amylin receptor antagonist, AC253. Changes in RNA levels were then quantified and compared to each other in order to identify increases or decreases in gene expression of apoptotic markers. Applications of Aß(1-42) or human amylin, but not the inactive inverse sequence Aß(42-1) or rat amylin, resulted in a time-dependent marked increase in mediators of apoptosis including a 10- to 30-fold elevations in caspases 3, 6, 9, BID and XIAP levels. Amylin receptor antagonists, AC253 (10 µM) or AC187 (10 µM), significantly attenuated the induction of several pro-apoptotic mediators up-regulated following exposure to Aß(1-42) or human amylin and increased the expression of several anti-apoptotic markers. These data allow us to identify key elements in the Aß-induced apoptosis that are blocked by antagonism of the amylin receptor and further support the potential for amylin receptor blockade as a potential therapeutic avenue in AD.

Neuronal receptors as targets for the action of amyloid-beta protein (Aß) in the brain.

Accumulation of neurotoxic soluble amyloid-beta protein (Aß) oligomers in the brains of patients with Alzheimer disease (AD) and their role in AD pathogenesis have emerged as topics of considerable interest in recent years. Soluble Aß oligomers impair synaptic and neuronal function, leading to neurodegeneration that is clinically manifested by memory and cognitive dysfunction. The precise mechanisms whereby Aß oligomers cause neurotoxicity remain unknown. Emerging insights into the mechanistic link between neuronal receptors and soluble Aß oligomers highlight the potential role of these receptors in Aß-mediated neurotoxicity in AD. The current review focuses on studies describing interactions between soluble Aß oligomers and neuronal receptors, and their role in AD pathogenesis. Furthermore, these studies provide insight into potential therapies for AD using compounds directed at putative target receptors for the action of Aß in the central nervous system. We focus on interactions of Aß with subtypes of acetylcholine and glutamatergic receptors. Additionally, neuronal receptors such as insulin, amylin and receptor for advanced glycation end products could be potential targets for soluble Aß-oligomer-mediated neurotoxicity. Aß interactions with other receptors such as the p75 neurotrophin receptors, which are highly expressed on cholinergic basal forebrain neurons lost in AD, are also highlighted.

Actions of ß-amyloid protein on human neurons are expressed through the amylin receptor.

Disruption of neurotoxic effects of amyloid ß protein (Aß) is one of the major, but as yet elusive, goals in the treatment of Alzheimer's disease (AD). The amylin receptor, activated by a pancreatic polypeptide isolated from diabetic patients, is a putative target for the actions of Aß in the brain. Here we show that in primary cultures of human fetal neurons (HFNs), AC253, an amylin receptor antagonist, blocks electrophysiological effects of Aß. Pharmacological blockade of the amylin receptor or its down-regulation using siRNA in HFNs confers neuroprotection against oligomeric Aß-induced caspase-dependent and caspase-independent apoptotic cell death. In transgenic mice (TgCRND8) that overexpress amyloid precursor protein, amylin receptor is up-regulated in specific brain regions that also demonstrate an elevated amyloid burden. The expression of Aß actions through the amylin receptor in human neurons and temporospatial interrelationship of Aß and the amylin receptor in an in vivo model of AD together provide a persuasive rationale for this receptor as a novel therapeutic target in the treatment of AD.

Bridging Integrator 1 (BIN1, rs6733839) and Sex Are Moderators of Vascular Health Predictions of Memory Aging Trajectories.

BACKGROUND: A promising risk loci for sporadic Alzheimer's disease (AD), Bridging Integrator 1 (BIN1), is thought to operate through the tau pathology pathway. OBJECTIVE: We examine BIN1 risk for a moderating role with vascular health (pulse pressure; PP) and sex in predictions of episodic memory trajectories in asymptomatic aging adults. METHODS: The sample included 623 participants (Baseline Mean age = 70.1; 66.8% female) covering a 44-year longitudinal band (53-97 years). With an established memory latent variable arrayed as individualized trajectories, we applied Mplus 8.5 to determine the best fitting longitudinal growth model. Main analyses were conducted in three sequential phases to investigate: 1) memory trajectory prediction by PP, 2) moderation by BIN1 genetic risk, and 3) stratification by sex. RESULTS: We first confirmed that good vascular health (lower PP) was associated with higher memory level and shallower decline and males were more severely affected by worsening PP in both memory performance and longitudinal decline. Second, the PP prediction of memory trajectories was significant for BIN1 C/C and C/T carriers but not for persons with the highest AD risk (T/T homozygotes). Third, when further stratified by sex, the BIN1 moderation of memory prediction by PP was selective for females. CONCLUSION: We observed a novel interaction whereby BIN1 (linked with tauopathy in AD) and sex sequentially moderated a benchmark PP prediction of differential memory decline in asymptomatic aging. This multi-modal biomarker interaction approach, disaggregated by sex, can be an effective method for enhancing precision of AD genetic risk assessment.

Genetic Depletion of Amylin/Calcitonin Receptors Improves Memory and Learning in Transgenic Alzheimer's Disease Mouse Models.

Based upon its interactions with amyloid ß peptide (Aß), the amylin receptor, a class B G protein-coupled receptor (GPCR), is a potential modulator of Alzheimer's disease (AD) pathogenesis. However, past pharmacological approaches have failed to resolve whether activation or blockade of this receptor would have greater therapeutic benefit. To address this issue, we generated compound mice expressing a human amyloid precursor protein gene with familial AD mutations in combination with deficiency of amylin receptors produced by hemizygosity for the critical calcitonin receptor subunit of this heterodimeric GPCR. These compound transgenic AD mice demonstrated attenuated responses to human amylin- and Aß-induced depression of hippocampal long-term potentiation (LTP) in keeping with the genetic depletion of amylin receptors. Both the LTP responses and spatial memory (as measured with Morris water maze) in these mice were improved compared to AD mouse controls and, importantly, a reduction in both the amyloid plaque burden and markers of neuroinflammation was observed. Our data support the notion of further development of antagonists of the amylin receptor as AD-modifying therapies.

Ionic mechanisms of action of prion protein fragment PrP(106-126) in rat basal forebrain neurons.

Prion diseases are neurodegenerative disorders that are characterized by the presence of the misfolded prion protein (PrP). Neurotoxicity in these diseases may result from prion-induced modulation of ion channel function, changes in neuronal excitability, and consequent disruption of cellular homeostasis. We therefore examined PrP effects on a suite of potassium (K(+)) conductances that govern excitability of basal forebrain neurons. Our study examined the effects of a PrP fragment [PrP(106-126), 50 nM] on rat neurons using the patch clamp technique. In this paradigm, PrP(106-126) peptide, but not the "scrambled" sequence of PrP(106-126), evoked a reduction of whole-cell outward currents in a voltage range between -30 and +30 mV. Reduction of whole-cell outward currents was significantly attenuated in Ca(2+)-free external media and also in the presence of iberiotoxin, a blocker of calcium-activated potassium conductance. PrP(106-126) application also evoked a depression of the delayed rectifier (I(K)) and transient outward (I(A)) potassium currents. By using single cell RT-PCR, we identified the presence of two neuronal chemical phenotypes, GABAergic and cholinergic, in cells from which we recorded. Furthermore, cholinergic and GABAergic neurons were shown to express K(v)4.2 channels. Our data establish that the central region of PrP, defined by the PrP(106-126) peptide used at nanomolar concentrations, induces a reduction of specific K(+) channel conductances in basal forebrain neurons. These findings suggest novel links between PrP signalling partners inferred from genetic experiments, K(+) channels, and PrP-mediated neurotoxicity.

Brain energy rescue: an emerging therapeutic concept for neurodegenerative disorders of ageing.

The brain requires a continuous supply of energy in the form of ATP, most of which is produced from glucose by oxidative phosphorylation in mitochondria, complemented by aerobic glycolysis in the cytoplasm. When glucose levels are limited, ketone bodies generated in the liver and lactate derived from exercising skeletal muscle can also become important energy substrates for the brain. In neurodegenerative disorders of ageing, brain glucose metabolism deteriorates in a progressive, region-specific and disease-specific manner - a problem that is best characterized in Alzheimer disease, where it begins presymptomatically. This Review discusses the status and prospects of therapeutic strategies for countering neurodegenerative disorders of ageing by improving, preserving or rescuing brain energetics. The approaches described include restoring oxidative phosphorylation and glycolysis, increasing insulin sensitivity, correcting mitochondrial dysfunction, ketone-based interventions, acting via hormones that modulate cerebral energetics, RNA therapeutics and complementary multimodal lifestyle changes.

Prolactin-releasing peptide effects in the rat brain are mediated through the Neuropeptide FF receptor.

Prolactin-releasing peptide (PrRP), an RF amide peptide present in the brain, generates a wide variety of centrally generated autonomic responses, including increases in arterial blood pressure and heart rate. The identity of the receptor mediating the effects of PrRP is unknown. In addition to GPR10, which is its putative endogenous receptor, PrRP demonstrates a high binding affinity for Neuropeptide FF (NPFF) receptors, specifically the NPFF2 receptor. In the present study, we examined whether the central cardiovascular effects of PrRP in the intact animal and its cellular effects on parvocellular paraventricular nucleus (PVN) neurons are mediated via NPFF receptors. In conscious rats, intracerebroventricular (i.c.v.) PrRP caused an increase in arterial blood pressure and heart rate, which was blocked with RF9, a specific NPFF receptor antagonist. These PrRP-evoked cardiovascular effects were preserved in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat strain, in which the GRP10 receptor gene was mutated. In rat brain slices, whole-cell patch clamp recordings of parvocellular paraventricular nucleus neurons show PrRP caused a decrease in evoked and miniature GABAergic inhibitory postsynaptic currents (IPSCs), effects that were antagonized by RF9, but not neuropeptide Y, a putative GPR10 receptor antagonist. The effects of PrRP on IPSCs in OLETF rats were similar to those in wild-type rats. Both in vivo and in vitro data strongly suggest that certain PrRP effects in the brain are expressed via NPFF receptors, probably NPFF2, rather than the GPR10 receptor. These observations may assume clinical relevance as RF amide peptides such NPFF and PrRP become therapeutic targets for a variety of autonomically related disorders.

Amyloid beta protein modulates glutamate-mediated neurotransmission in the rat basal forebrain: involvement of presynaptic neuronal nicotinic acetylcholine and metabotropic glutamate receptors.

Amyloid beta (Abeta) protein, a 39-43 amino acid peptide deposited in brains of individuals with Alzheimer's disease (AD), has been shown to interact directly with a number of receptor targets including neuronal nicotinic acetylcholine receptors (nAChRs) and glutamate receptors. In this study, we investigated the synaptic effects of Abeta(1-42) on glutamate-mediated neurotransmission in the diagonal band of Broca (DBB), a cholinergic basal forebrain nucleus. Glutamatergic miniature EPSCs (mEPSCs) were recorded using whole-cell patch-clamp recordings from identified cholinergic DBB neurons in rat forebrain slices. In 54% of DBB neurons, bath application of Abeta(1-42) (100 nM), but not Abeta(42-1) (inverse fragment), significantly increased the frequency of mEPSCs without affecting amplitude or kinetic parameters (rise or decay time). In 32% of DBB neurons, bath application of Abeta(1-42) significantly decreased only the frequency but not amplitude of mEPSCs. Application of dihydro-beta-erythroidine (DHbetaE) (an antagonist for the alpha4beta2 subtype of nAChRs) but not alpha-bungarotoxin (an antagonist for the alpha7 subtype of nAChRs) blocked Abeta(1-42)-mediated increases in mEPSC frequency. The Abeta(1-42)-mediated increase in glutamatergic transmission is thus presynaptic and mediated via non-alpha7 AChRs. In contrast, Abeta(1-42)-mediated decreases in mEPSC frequency could not be antagonized by either DHbetaE or alpha-bungarotoxin. However, the Abeta(1-42)-evoked depression in mEPSC frequency was antagonized by (RS)-alpha-methyl-4-carboxyphenyglycine, a nonselective group I/II metabotropic glutamate receptor antagonist. These observations provide further insight into the mechanisms whereby Abeta affects synaptic function in the brain and may be relevant in the context of synaptic failure observed in AD.

Neuropeptide FF2 receptor distribution in the human brain. An immunohistochemical study.

Human neuropeptide FF2 (hFF2) receptor has been postulated to mediate central autonomic regulation by virtue of its ability to bind with high affinity to many amidated neuropeptides. In the present immunohistochemical study, we identified hFF2 positive neurons in the forebrain and medulla oblongata of individuals, who died suddenly of mechanical trauma or hypothermia. Morphologically, these neurons demonstrated features identified with both projection neurons and interneurons. In the forebrain, the highest density of hFF2 expressing neurons was observed in the anterior amygdaloid area and dorsomedial hypothalamic nucleus, especially in its caudal part. A lesser density of hFF2 neurons was identified in the ventromedial hypothalamic nucleus, lateral and posterior hypothalamic areas whereas few cells were visualized in the paraventricular hypothalamic nucleus, perifornical nucleus, horizontal limb of the diagonal band, ventral division of the bed nucleus of the stria terminalis, nucleus basalis of Meynert and ventral tegmental area. In the medulla, significant numbers of hFF2 neurons were observed in the dorsal motor nucleus of vagus and to a lesser extent in the area of catecholaminergic cell groups, A1/C1. These data provide first immunohistochemical evidence of hFF2 localization in the human brain, which is consistent with that reported for tissue distribution of FF2 mRNA and FF2 binding sites within the brain of a variety of mammalian species. The distribution of hFF2 may help in identifying the role of amidated neuropeptides in the human brain within the context of central autonomic and neuroendocrine regulation.

Single transmembrane domain insulin-like growth factor-II/mannose-6-phosphate receptor regulates central cholinergic function by activating a G-protein-sensitive, protein kinase C-dependent pathway.

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor is a single-pass transmembrane glycoprotein that plays an important role in the intracellular trafficking of lysosomal enzymes and endocytosis-mediated degradation of IGF-II. However, its role in signal transduction after IGF-II binding remains unclear. In the present study, we report that IGF-II/M6P receptor in the rat brain is coupled to a G-protein and that its activation by Leu27IGF-II, an analog that binds rather selectively to the IGF-II/M6P receptor, potentiates endogenous acetylcholine release from the rat hippocampal formation. This effect is mediated by a pertussis toxin (PTX)-sensitive GTP-binding protein and is dependent on protein kinase Calpha (PKCalpha)-induced phosphorylation of downstream substrates, myristoylated alanine-rich C kinase substrate, and growth associated protein-43. Additionally, treatment with Leu27IGF-II causes a reduction in whole-cell currents and depolarization of cholinergic basal forebrain neurons. This effect, which is blocked by an antibody against the IGF-II/M6P receptor, is also sensitive to PTX and is mediated via activation of a PKC-dependent pathway. These results together revealed for the first time that the single transmembrane domain IGF-II/M6P receptor expressed in the brain is G-protein coupled and is involved in the regulation of central cholinergic function via the activation of specific intracellular signaling cascades.

Pramlintide Antagonizes Beta Amyloid (Aß)- and Human Amylin-Induced Depression of Hippocampal Long-Term Potentiation.

Accumulation of amyloid-ß peptide (Aß) is a pathological hallmark of Alzheimer's disease (AD). We have previously demonstrated that electrophysiological and neurotoxic effects of Aß and human amylin are expressed via the amylin receptor. Recently, pramlintide, a synthetic analog of amylin, has been reported to improve cognitive function in transgenic AD mouse models. In this study, we examined the effects of pramlintide on Aß1-42 and human amylin-evoked depression of long-term potentiation (LTP) at Schaeffer collateral-CA1 hippocampal synapses. In mouse hippocampal brain slices, field excitatory postsynaptic potentials (fEPSPs) were recorded from the stratum radiatum layer of the CA1 area in response to electrical stimulation of Schaeffer collateral afferents and LTP induced by 3-theta-burst stimulation (TBS) protocol. Aß1-42 (50 nM) and human amylin (50 nM), but not Aß42-1 (50 nM), depressed LTP. Pre-application of pramlintide (250 nM) blocked Aß- and human amylin-induced reduction of LTP without affecting baseline transmission or LTP. We also examined the effects of pramlintide on LTP in transgenic mice (TgCRND8) that over-express amyloid precursor protein. In contrast to wild-type controls, where robust LTP was observed, 10- to 12-month-old TgCRND8 mice show blunted LTP. In TgCRND8 mice, basal LTP is enhanced by application of pramlintide. Our data indicate that pramlintide acts as a functional amylin receptor antagonist to reverse the effects of Aß1-42 and human amylin on LTP and also increases LTP in transgenic mice that demonstrate increased ambient brain amyloid levels. Amylin receptor antagonists may thus serve as potentially useful therapeutic agents in treatment of AD.

Amylin Receptor: A Potential Therapeutic Target for Alzheimer's Disease.

Alzheimer'sdisease (AD) is a progressive neurodegenerative disorder, characterized by senile plaques constituting extracellular deposits of ß-amyloid (Aß) fibrils. Since Aß accumulation in the brain is considered an early event preceding, by decades, cognitive dysfunction, disease-modifying treatments are aimed at facilitating clearance of this protein from the brain or ameliorating its toxic effects. Recent studies have identified the amylin receptor as a capable mediator of the deleterious actions of Aß and furthermore, administration of amylin receptor-based peptides has been shown to improve spatial memory and learning in transgenic mouse models of AD. Here, by discussing available evidence, we posit that the amylin receptor could be considered a potential therapeutic target for AD, and present the rationale for using amylin receptor antagonists to treat this debilitating condition.