Multiple target of hAmylin on rat primary hippocampal neurons

Inhibition of YIPF2 Improves the Vulnerability of Oligodendrocytes to Human Islet Amyloid Polypeptide

Excessive secretion of human islet amyloid polypeptide (hIAPP) is an important pathological basis of diabetic encephalopathy (DE). In this study, we aimed to investigate the potential implications of hIAPP in DE pathogenesis. Brain magnetic resonance imaging and cognitive scales were applied to evaluate white matter damage and cognitive function. We found that the concentration of serum hIAPP was positively correlated with white matter damage but negatively correlated with cognitive scores in patients with type 2 diabetes mellitus. In vitro assays revealed that oligodendrocytes, compared with neurons, were more prone to acidosis under exogenous hIAPP stimulation. Moreover, western blotting and co-immunoprecipitation indicated that hIAPP interfered with the binding process of monocarboxylate transporter (MCT)1 to its accessory protein CD147 but had no effect on the binding of MCT2 to its accessory protein gp70. Proteomic differential analysis of proteins co-immunoprecipitated with CD147 in oligodendrocytes revealed Yeast Rab GTPase-Interacting protein 2 (YIPF2, which modulates the transfer of CD147 to the cell membrane) as a significant target. Furthermore, YIPF2 inhibition significantly improved hIAPP-induced acidosis in oligodendrocytes and alleviated cognitive dysfunction in DE model mice. These findings suggest that increased CD147 translocation by inhibition of YIPF2 optimizes MCT1 and CD147 binding, potentially ameliorating hIAPP-induced acidosis and the consequent DE-related demyelination.

Lipid emulsion attenuates vasodilation by decreasing intracellular calcium and nitric oxide in vascular endothelial cells

Lipid emulsion (LE), a widely used parenteral nutrition, exhibits a well-documented ability to reverse the vasodilatory effects induced by acetylcholine in blood vessels. However, the specific mechanisms underlying this action are not yet fully understood. This study aimed to elucidate the mechanism by which LE reverses vasodilation in vitro through dose-response curve experiments, calcium imaging, and fluorescence assays. The results revealed a significant attenuation of acetylcholine (Ach)-induced vasodilation in rat thoracic aortic rings following LE exposure. In human aortic endothelial cells, pretreatment with LE significantly suppressed ATP-induced calcium elevation. This suppression persisted even after elimination of extracellular calcium with a calcium chelator. Moreover, LE pre-exposure reduced the intracellular calcium concentration ([Ca2+]i) elevation in endothelial cells following cyclopiazonic acid (CPA) treatment, suggesting enhanced endoplasmic reticulum (ER) calcium reuptake. Additionally, nitric oxide (NO) fluorescence assays showed a decrease in NO production upon ATP stimulation post-LE pretreatment of endothelial cells. Taken together, these results indicate that the reversal of vasodilation by LE may involve enhanced ER calcium uptake, leading to a reduction in intracellular calcium concentration and suppression of NO (key vasodilatory agent) synthesis.

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Jujuboside B inhibits febrile seizure by modulating AMPA receptor activity

ETHNOPHARMACOLOGICAL RELEVANCE

Febrile seizure is a common neurologic disorder with limited treatment occurring in infants and children under the age of five. Jujuboside B (JuB) is a main bioactive saponin component isolated from the Chinese anti-insomnia herbal medicine Ziziphi Spinosae Semen (ZSS), seed of Ziziphus jujuba Mill, which has been proved to exhibit neuroprotective effects recently.

AIM OF THE STUDY

In this study, we aimed at elucidating the effect of JuB on suppressing febrile seizure and the potential mechanisms.

METHODS

Electroencephalogram (EEG) recording was used to monitor the severity of febrile seizures. The JuB in the brain was identified by mass spectrometry. Neuronal excitability was investigated using patch clamp.

RESULTS

JuB (30 mg/kg) significantly prolonged seizure latency and reduced the severity in hyperthermia-induced seizures model mice. Hippocampal neuronal excitability was significantly decreased by JuB. And JuB significantly reduced the excitatory synaptic transmission mediated by α-amino-3-hydroxy-5-methyl-4-iso-xazolepropionic acid receptor (AMPAR), including evoked excitatory postsynaptic currents (eEPSCs), and miniature EPSCs (mEPSCs) in hippocampal neurons. Furthermore, JuB also significantly inhibited recombinant GluA1 and GluA2 mediated AMPA current in HEK293 cell and decreased the upregulation of [Ca²⁺]_i induced by AMPA in primary cultured cortex neurons.

CONCLUSIONS

JuB suppressed the excitability of hippocampal neurons by inhibiting the activity of AMPAR and reducing the intracellular free calcium, thereby relieving febrile seizures.

Role of Receptors in Relation to Plaques and Tangles in Alzheimer's Disease Pathology

Despite the identification of Aβ plaques and NFTs as biomarkers for Alzheimer’s disease (AD) pathology, therapeutic interventions remain elusive, with neither an absolute prophylactic nor a curative medication available to impede the progression of AD presently available. Current approaches focus on symptomatic treatments to maintain AD patients’ mental stability and behavioral symptoms by decreasing neuronal degeneration; however, the complexity of AD pathology requires a wide range of therapeutic approaches for both preventive and curative treatments. In this regard, this review summarizes the role of receptors as a potential target for treating AD and focuses on the path of major receptors which are responsible for AD progression. This review gives an overall idea centering on major receptors, their agonist and antagonist and future prospects of viral mimicry in AD pathology. This article aims to provide researchers and developers a comprehensive idea about the different receptors involved in AD pathogenesis that may lead to finding a new therapeutic strategy to treat AD.

Insulin Resistance and Diabetes Mellitus in Alzheimer's Disease

Type 2 diabetes mellitus is a progressive disease that is characterized by the appearance of insulin resistance. The term insulin resistance is very wide and could affect different proteins involved in insulin signaling, as well as other mechanisms. In this review, we have analyzed the main molecular mechanisms that could be involved in the connection between type 2 diabetes and neurodegeneration, in general, and more specifically with the appearance of Alzheimer's disease. We have studied, in more detail, the different processes involved, such as inflammation, endoplasmic reticulum stress, autophagy, and mitochondrial dysfunction.

The Importance of Understanding Amylin Signaling Mechanisms for Therapeutic Development in the Treatment of Alzheimer's Disease

Type II Diabetes (T2D) is a major risk factor for Alzheimer's Disease (AD). These two diseases share several pathological features, including amyloid accumulation, inflammation, oxidative stress, cell death and cognitive decline. The metabolic hormone amylin and amyloid-beta are both amyloids known to self-aggregate in T2D and AD, respectively, and are thought to be the main pathogenic entities in their respective diseases. Furthermore, studies suggest amylin's ability to seed amyloid-beta aggregation, the activation of common signaling cascades in the pancreas and the brain, and the ability of amyloid beta to signal through amylin receptors (AMYR), at least in vitro. However, paradoxically, non-aggregating forms of amylin such as pramlintide are given to treat T2D and functional and neuroprotective benefits of amylin and pramlintide administration have been reported in AD transgenic mice. These paradoxical results beget a deeper study of the complex nature of amylin's signaling through the several AMYR subtypes and other receptors associated with amylin effects to be able to fully understand its potential role in mediating AD development and/or prevention. The goal of this review is to provide such critical insight to begin to elucidate how the complex nature of this hormone's signaling may explain its equally complex relationship with T2D and mechanisms of AD pathogenesis.

Neuroprotective Effects of the Amylin Analog, Pramlintide, on Alzheimer's Disease Are Associated with Oxidative Stress Regulation Mechanisms

Administration of the recombinant analog of the pancreatic amyloid amylin, Pramlintide, has shown therapeutic benefits in aging and Alzheimer's disease (AD) models, both on cognition and amyloid-β (Aβ) pathology. However, the neuroprotective mechanisms underlying the benefits of Pramlintide remain unclear. Given the early and critical role of oxidative stress in AD pathogenesis and the known reactive oxygen species (ROS) modulating function of amyloids, we sought to determine whether Pramlintide's neuroprotective effects involve regulation of oxidative stress mechanisms. To address this, we treated APP/PS1 transgenic mice with Pramlintide for 3 months, starting at 5.5 months prior to widespread AD pathology onset, and measured cognition (Morris Water Maze), AD pathology, and oxidative stress-related markers and enzymes in vivo. In vitro, we determined the ability of Pramlintide to modulate H2O2-induced oxidative stress levels. Our data show that Pramlintide improved cognitive function, altered amyloid-processing enzymes, reduced plaque burden in the hippocampus, and regulated endogenous antioxidant enzymes (MnSOD and GPx1) and the stress marker HO-1 in a location specific manner. In vitro, Pramlintide treatment in neuronal models reduced H2O2-induced endogenous ROS production and lipid peroxidation in a dose-dependent manner. Together, these results indicate that Pramlintide's benefits on cognitive function and pathology may involve antioxidant-like properties of this compound.

Compromised Lactate Efflux Renders Vulnerability of Oligodendrocyte Precursor Cells to Metabolic Stresses

Among the brain cells, oligodendrocyte progenitor cells (OPCs) are the most vulnerable in response to hypoxic and ischemic insults, of which the mechanism remains unknown. Brain cells are known to import or export lactate via differentially expressed monocarboxylate transporters (MCTs) to maintain energy metabolism and pH homeostasis. The present study aims to determine the role of MCT1 in the high vulnerability of OPCs. Here we show that a mild ischemic condition equivalent to ischemic preconditioning caused detectable loss of OPCs. MCT1, which is primarily expressed in oligodendrocyte lineage cells including OPCs, was up-regulated immediately under oxygen-glucose deprivation (OGD) conditions. However, persistent hypoxia, but not hypoglycemia, inhibited the function of MCT1, leading to an intracellular lactate accumulation and acidosis in OPCs. Neurons, which express primarily MCT2, were able to export lactate and maintain an intracellular pH homeostasis under similar conditions. The results support that compromised lactate efflux resulting from hypoxia-induced dysfunction of MCT1 contributes to the high vulnerability of OPCs.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

Channels that Cooperate with TRPV4 in the Brain

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective Ca²⁺-permeable cation channel that is a member of the TRP channel family. It is clear that TRPV4 channels are broadly expressed in the brain. As they are expressed on the plasma membrane, they interact with other channels and play a crucial role in nervous system activity. Under some pathological conditions, TRPV4 channels are upregulated and sensitized via cellular signaling pathways, and this can cause nervous system diseases. In this review, we focus on receptors that cooperate with TRPV4, including large-conductance Ca²⁺-activated K⁺(BKca) channels, N-methyl-D-aspartate receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors (AMPARs), inositol 1,4,5-trisphosphate receptors (IP3Rs), ryanodine receptors (RyRs), aquaporin 4 (AQP4), and other potential cooperative receptors in the brain. The data demonstrate how these channels work together to cause nervous system diseases under pathological conditions. The aim of this review was to discuss the receptors and signaling pathways related to TRPV4 based on recent data on the important physiological functions of TRPV4 channels to provide new clues for future studies and prospective therapeutic targets for related brain diseases.

Influence of human amylin on the membrane stability of rat primary hippocampal neurons

The two most common aging-related diseases, Alzheimer's disease and type 2 diabetes mellitus, are associated with accumulation of amyloid proteins (β-amyloid and amylin, respectively). This amylin aggregation is reportedly cytotoxic to neurons. We found that aggregation of human amylin (hAmylin) induced neuronal apoptosis without obvious microglial infiltration in vivo. High concentrations of hAmylin irreversibly aggregated on the surface of the neuronal plasma membrane. Long-term incubation with hAmylin induced morphological changes in neurons. Moreover, hAmylin permeabilized the neuronal membrane within 1 min in a manner similar to Triton X-100, allowing impermeable fluorescent antibodies to enter the neurons and stain intracellular antigens. hAmylin also permeabilized the cell membrane of astrocytes, though more slowly. Under scanning electron microscopy, we observed that hAmylin destroyed the integrity of the cell membranes of both neurons and astrocytes. Additionally, it increased intracellular reactive oxygen species generation and reduced the mitochondrial membrane potential. Thus, by aggregating on the surface of neurons, hAmylin impaired the cell membrane integrity, induced reactive oxygen species production, reduced the mitochondrial membrane potential, and ultimately induced neuronal apoptosis.

Selective Susceptibility of Oligodendrocytes to Carbon Monoxide Poisoning: Implication for Delayed Neurologic Sequelae (DNS)

Delayed neurologic sequelae (DNS) are recurrent-transient neuropsychiatric consequences of carbon monoxide (CO) intoxication. Pathologically DNS features damages to the brain white matter. Here we test a hypothesis that direct cytotoxicity of CO to oligodendrocytes plays a role in the development of DNS. In an in vitro model of CO poisoning with the carbon monoxide releasing molecule-2 (CORM-2) as a CO donor, we show that CORM-2 at concentrations higher than 200 µM significantly inhibited viability and caused significant death of PC12 cells. Similar minimum toxicity concentration was observed on primary brain cells including neurons, astrocytes, and microglia. Interestingly, oligodendrocytes showed cytotoxicity to CORM-2 at a much lower concentration (100 µM). We further found that CORM-2 at 100 µM inhibited proteolipid protein (PLP) production and reduced myelin coverage on axons in an in vitro model of myelination. Our results show that direct cytotoxicity is a mechanism of CO poisoning and DNS may result from a high susceptibility of oligodendrocytes to CO poisoning.

Neuroprotective Effects of Amylin Analogues on Alzheimer's Disease Pathogenesis and Cognition

Type II diabetes (T2D) has been identified as a major risk factor for the development of Alzheimer's disease (AD). Interestingly, both AD and T2D have similar characteristics including amyloid peptide aggregation, decreased metabolism, and increased oxidative stress and inflammation. Despite their prevalence, therapies for these diseases are limited. To date, most therapies for AD have targeted amyloid-β or tau. Unfortunately, most of these clinical trials have been largely unsuccessful, creating a crucial need for novel therapies. A number of studies have shown that metabolic hormone therapies are effective at ameliorating high blood glucose levels in diabetics as well as improving cognitive function in AD and mild cognitive impairment patients. Pramlintide, a synthetic analogue of the pancreatic hormone amylin, has been developed and used for years now as a treatment for both type I diabetes and T2D due to the loss of β-islet cells responsible for producing amylin. Importantly, recent data demonstrates its potential therapeutic role for AD as well. This review aims at addressing parallels between T2D and AD at a pathological and functional level, focusing on amylin signaling as a key, overlapping mediator in both diseases. The potential therapeutic use of this hormone to treat AD will also be explored from a mechanistic viewpoint.

Association of Plasma Amylin Concentration With Alzheimer Disease and Brain Structure in Older Adults

IMPORTANCE

Preclinical studies suggest that amylin has a U-shaped dose-response association with risk of Alzheimer disease (AD). The association of plasma amylin with AD in humans is unknown.

OBJECTIVES

To measure amylin concentration in plasma by using enzyme-linked immunosorbent assay and to study the association between plasma amylin, incidence of AD, and brain structure in humans.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used data from the Framingham Heart Study offspring cohort from 1998 to 2015. Using a Monte Carlo approach, participants were divided into 3 plasma amylin concentration groups: (1) low (<75 pmol/L), (2) high (75-2800 pmol/L), and (3) extremely high (≥2800 pmol/L). Data analyses were conducted October 5, 2017, to December 18, 2018.

EXPOSURES

Baseline plasma amylin concentrations at examination 7.

MAIN OUTCOMES AND MEASURES

Incidence of dementia or AD and brain volumetric measures from structural magnetic resonance imaging data.

RESULTS

From the Framingham Heart Study offspring cohort, 3061 participants (mean [SD] age at baseline, 61.0 [9.5] years; 1653 [54.0%] women) who had plasma amylin measurements, dementia incidence, and brain volume measurements on record were included in this study. The distribution of plasma amylin concentrations was highly skewed (median [interquartile range], 7.5 [4.6-18.9] pmol/L; mean [SD], 302.3 [1941.0] pmol/L; range, 0.03-44 623.7 pmol/L). Compared with the low plasma amylin concentration group, the high plasma amylin concentration group had a lower rate of AD incidence (2.3% vs 5.6%; P = .04), but the extremely high plasma amylin concentration group had a higher rate of AD incidence (14.3%; P < .001). After adjusting for age, sex, education, body mass index, diabetes, cardiovascular disease, high-density lipoprotein level, and APOE4, high plasma amylin was not associated with decreased AD risk (hazard ratio, 0.42 [95% CI, 0.16-1.14]; P = .09) but was positively associated with volume of gray matter in the temporal lobe (β = 0.17 [SE, 0.05]; P < .001). In contrast, extremely high plasma amylin concentration was associated with a higher AD risk (hazard ratio, 2.51 [95% CI, 1.38-4.57]; P = .003) but not associated with temporal lobe volume (β = 0.02 [SE, 0.07]; P = .82).

CONCLUSIONS AND RELEVANCE

This study found that plasma amylin concentration was associated with AD incidence and brain structure with a U-shaped pattern. These findings are consistent with preclinical findings that suggest amylin is a neuropeptide that is physiological; however, at extremely high concentrations, it may lead to amylin aggregation and therefore may be a risk factor for AD.

L-type voltage-gated calcium channels in stem cells and tissue engineering

L-type voltage-gated calcium ion channels (L-VGCCs) have been demonstrated to be the mediator of several significant intracellular activities in excitable cells, such as neurons, chromaffin cells and myocytes. Recently, an increasing number of studies have investigated the function of L-VGCCs in non-excitable cells, particularly stem cells. However, there appear to be no systematic reviews of the relationship between L-VGCCs and stem cells, and filling this gap is prescient considering the contribution of L-VGCCs to the proliferation and differentiation of several types of stem cells. This review will discuss the possible involvement of L-VGCCs in stem cells, mainly focusing on osteogenesis mediated by mesenchymal stem cells (MSCs) from different tissues and neurogenesis mediated by neural stem/progenitor cells (NSCs). Additionally, advanced applications that use these channels as the target for tissue engineering, which may offer the hope of tissue regeneration in the future, will also be explored.

Amylin Signaling in Diabetes and Alzheimer's Disease: Therapy or Pathology?

Growing evidence highlights the intimate relationship between type II diabetes (T2D) and Alzheimer's disease (AD). Importantly, these two diseases share a number of pathological similarities, including amyloid accumulation, oxidative stress, inflammation, and cell death. To date, drug therapies for AD and T2D are lacking and there is a crucial need for the discovery and development of novel therapeutics for these diseases. A number of human and rodent studies have given evidence that metabolic hormone supplementation is highly valuable for improving cognitive function and overall metabolic health in both T2D and AD. The pancreatic hormone amylin has arisen as a crucial component of the disease etiology of both T2D and AD, though the exact role that amylin plays in these diseases is not yet well understood. Here, we critically review the current literature that utilizes human amylin or its synthetic analogue, pramlintide, as well as amylin receptor antagonists for the treatment of AD.

Effects of Amylin Against Amyloid-β-Induced Tauopathy and Synapse Loss in Primary Neurons

Recent studies demonstrate that peripheral amylin treatment reduces pathology in mouse models of Alzheimer's disease (AD). However, soluble and aggregated amylin are distinct species; while amylin is a physiological neuropeptide, amylin aggregation is a pathological factor for diabetes. We thus hypothesized that because of their similarity in secondary structures, amylin antagonizes amyloid-β peptide (Aβ)-induced AD pathology in neurons with a dose-dependent pattern. To test the hypothesis, we conducted both in vitro and in vivo experiments with different doses of amylin and with its analog, pramlintide. Here we report that a high concentration of either Aβ or amylin alone induced tau phosphorylation (pTau) in primary neurons. Interestingly, with a low concentration, amylin had direct effects to reverse the Aβ-induced pTau, as well as damaged neuronal synapses and neurite disorganization. However, when the concentration was high (10.24 μM), amylin lost the effects against the Aβ-induced cellular AD pathology and, together with Aβ, worsened tauopathy in neurons. In the 5XFAD AD mouse model, daily peripheral amylin treatment with a low dose (200 μg/kg) more effectively reduced amyloid burden, and increased synapse, but with a high dose (800 μg/kg), it more effectively reduced tauopathy. Correspondingly, amylin treatment improved learning and memory in these mice. It demonstrates that amylin has a dose-dependent U-shape effect against AD pathogenesis. Within a physiological range, amylin is a neuroprotective hormone against AD in neurons; but when both Aβ and amylin concentrations are elevated, imbalance of Aβ and amylin may contribute to brain AD pathogenesis.

14,15-epoxyeicosatrienoic acid produced by cytochrome P450s enhances neurite outgrowth of PC12 and rat hippocampal neuronal cells

Polyunsaturated fatty acids, such as arachidonic acid, are accumulated in brain and induce neuronal differentiation. Arachidonic acid is metabolized to epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids (HETEs) by cytochrome P450s. In this study, we found that 14,15-EET and 20-HETE-enhanced NGF-induced rat pheochromocytoma PC12 cell neurite outgrowth even at the concentration of 100 nmol L-1. LC-MS analysis revealed that 14,15-EET was effectively produced from arachidonic acid by rat CYP2C11, 2C13, and 2C23, and these P450s were expressed in PC12 cells. An inhibitor of these P450s, ketoconazole, inhibited neurite outgrowth, whereas inhibition of soluble epoxide hydrolase, which hydrolyzes EETs to their corresponding diols enhanced neurite outgrowth. To determine the mechanism of neurite formation enhancement by arachidonic acid metabolites, we focused on transient receptor potential (TRP) channels expressed in PC12 cells. The TRPV4 inhibitor HC067047, but not the TRPV1 inhibitor capsazepine, inhibited the effects of 14,15-EET on neurite outgrowth of PC12. Furthermore, 14,15-EET increased the cytosolic calcium ion concentration and this increase was inhibited by HC067047. 14,15-EET also enhanced neurite outgrowth of primary cultured neuron from rat hippocampus. This study suggests that arachidonic acid metabolites produced by P450 contribute to neurite outgrowth through calcium influx.

Amylin in Alzheimer's disease: Pathological peptide or potential treatment?

Alzheimer's disease (AD) is a neurodegenerative disease for which we currently lack effective treatments or a cure. The pancreatic peptide hormone amylin has recently garnered interest as a potential pharmacological target for the treatment of AD. A number of studies have demonstrated that amylin and amylin analogs like the FDA-approved diabetes drug pramlintide can reduce amyloid burden in the brain and improve cognitive symptoms of AD. However, other data suggest that amylin may have pathological effects in AD due to its propensity to misfold and aggregate under certain conditions. Here, the literature supporting a beneficial versus harmful role of amylin in AD is reviewed. Additionally, several critical gaps in the literature are discussed, such as our limited understanding of the amylin system during aging and in disease states, as well as complexities of amylin receptor signaling and of changing pathophysiology during AD progression that might underlie the seemingly conflicting or contradictory results in the amylin/AD literature. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Molecular studies of CGRP and the CGRP family of peptides in the central nervous system

BACKGROUND

Calcitonin gene-related peptide is an important target for migraine and other painful neurovascular conditions. Understanding the normal biological functions of calcitonin gene-related peptide is critical to understand the mechanisms of calcitonin gene-related peptide-blocking therapies as well as engineering improvements to these medications. Calcitonin gene-related peptide is closely related to other peptides in the calcitonin gene-related peptide family of peptides, including amylin. Relatedness in peptide sequence and in receptor biology makes it difficult to tease apart the contributions that each peptide and receptor makes to physiological processes and to disorders.

SUMMARY

The focus of this review is the expression of calcitonin gene-related peptide, related peptides and their receptors in the central nervous system. Calcitonin gene-related peptide is expressed throughout the nervous system, whereas amylin and adrenomedullin have only limited expression at discrete sites in the brain. The components of two receptors that respond to calcitonin gene-related peptide, the calcitonin gene-related peptide receptor (calcitonin receptor-like receptor with receptor activity-modifying protein 1) and the AMY₁ receptor (calcitonin receptor with receptor activity-modifying protein 1), are expressed throughout the nervous system. Understanding expression of the peptides and their receptors lays the foundation for more deeply understanding their physiology, pathophysiology and therapeutic use.

The release and transmission of amyloid precursor protein via exosomes

Amyloid precursor protein (APP) processing is central in Alzheimer's disease (AD) pathogenesis. The healthy unaffected neurons suffer the transmission of amyloid protein from pathologically affected neurons, which may play an important role in the anatomical spread of the disease. Exosomes are appropriate candidates for transmission of amyloid species, because of their potential role as "intercellular transportation". To address a role of secreted exosomes in neuronal homeostasis in AD, we harvested exosomes from the conditioned medium of HEK293-APP Swe/Ind cells. We have demonstrated that these exosomes contained APP and were capable of efficiently transferring APP to normal primary neurons. Moreover, these exosomes had dose-dependent detrimental effect on cultured neurons. Our results suggest a key mechanism underlying the spread of amyloid protein in the brain and the acceleration of pathology in AD; exosomes secretion serves to amplify and propagate Alzheimer's disease related pathology.

Computational modeling of amylin-induced calcium dysregulation in rat ventricular cardiomyocytes

Hyperamylinemia is a condition that accompanies obesity and precedes type II diabetes, and it is characterized by above-normal blood levels of amylin, the pancreas-derived peptide. Human amylin oligomerizes easily and can deposit in the pancreas [1], brain [2], and heart [3], where they have been associated with calcium dysregulation. In the heart, accumulating evidence suggests that human amylin oligomers form moderately cation-selective [4,5] channels that embed in the cell sarcolemma (SL). The oligomers increase membrane conductance in a concentration-dependent manner [5], which is correlated with elevated cytosolic Ca²⁺. These findings motivate our core hypothesis that non-selective inward Ca²⁺ conduction afforded by human amylin oligomers increase cytosolic and sarcoplasmic reticulum (SR) Ca²⁺ load, which thereby magnifies intracellular Ca²⁺ transients. Questions remain however regarding the mechanism of amylin-induced Ca²⁺ dysregulation, including whether enhanced SL Ca²⁺ influx is sufficient to elevate cytosolic Ca²⁺ load [6], and if so, how might amplified Ca²⁺ transients perturb Ca²⁺-dependent cardiac pathways. To investigate these questions, we modified a computational model of cardiomyocytes Ca²⁺ signaling to reflect experimentally-measured changes in SL membrane permeation and decreased sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) function stemming from acute and transgenic human amylin peptide exposure. With this model, we confirmed the hypothesis that increasing SL permeation alone was sufficient to enhance Ca²⁺ transient amplitudes. Our model indicated that amplified cytosolic transients are driven by increased Ca²⁺ loading of the SR and that greater fractional release may contribute to the Ca²⁺-dependent activation of calmodulin, which could prime the activation of myocyte remodeling pathways. Importantly, elevated Ca²⁺ in the SR and dyadic space collectively drive greater fractional SR Ca²⁺ release for human amylin expressing rats (HIP) and acute amylin-exposed rats (+Amylin) mice, which contributes to the inotropic rise in cytosolic Ca²⁺ transients. These findings suggest that increased membrane permeation induced by oligomeratization of amylin peptide in cell sarcolemma contributes to Ca²⁺ dysregulation in pre-diabetes.

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 β-amyloid (Aβ) fibrils. Since Aβ 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 Aβ 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.

Amylin and its G-protein-coupled receptor: A probable pathological process and drug target for Alzheimer's disease

G-protein-coupled receptors (GPCRs) are shown to be involved in Alzheimer's disease (AD) pathogenesis. However, because GPCRs include a large family of membrane receptors, it is unclear which specific GPCR or pathway with rational ligands can become effective therapeutic targets for AD. Amylin receptor (AmR) is a GPCR that mediates several activities, such as improving glucose metabolism, relaxing cerebrovascular structure, modulating inflammatory reactions and potentially enhancing neural regeneration. Recent studies show that peripheral treatments with amylin or its clinical analog, pramlintide, reduced several components of AD pathology, including amyloid plaques, tauopathy, neuroinflammation and other components in the brain, corresponding with improved learning and memory in AD mouse models. Because amylin shares a similar secondary structure with amyloid-β peptide (Aβ), I propose that the AmR/GPCR pathway is disturbed by a large amount of Aβ in the AD brain, leading to tau phosphorylation, neuroinflammation and neuronal death in the pathological cascade. Amylin-type peptides, readily crossing the blood-brain barrier (BBB), are the rational ligands to enhance this GPCR pathway and may exhibit utility as novel therapeutic agents for treating AD.

Amylin receptor ligands reduce the pathological cascade of Alzheimer's disease

Amylin is an important gut-brain axis hormone. Since amylin and amyloid-β peptide (Aβ) share similar β sheet secondary structure despite not having the same primary sequences, we hypothesized that the accumulation of Aβ in the brains of subjects with Alzheimer's disease (AD) might compete with amylin for binding to the amylin receptor (AmR). If true, adding exogenous amylin type peptides would compete with Aβ and reduce the AD pathological cascade, improving cognition. Here we report that a 10-week course of peripheral treatment with human amylin significantly reduced multiple different markers associated with AD pathology, including reducing levels of phospho-tau, insoluble tau, two inflammatory markers (Iba1 and CD68), as well as cerebral Aβ. Amylin treatment also led to improvements in learning and memory in two AD mouse models. Mechanistic studies showed that an amylin receptor antagonist successfully antagonized some protective effects of amylin in vivo, suggesting that the protective effects of amylin require interaction with its cognate receptor. Comparison of signaling cascades emanating from AmR suggest that amylin electively suppresses activation of the CDK5 pathway by Aβ. Treatment with amylin significantly reduced CDK5 signaling in a receptor dependent manner, dramatically decreasing the levels of p25, the active form of CDK5 with a corresponding reduction in tau phosphorylation. This is the first report documenting the ability of amylin treatment to reduce tauopathy and inflammation in animal models of AD. The data suggest that the clinical analog of amylin, pramlintide, might exhibit utility as a therapeutic agent for AD and other neurodegenerative diseases.