Central nervous system (CNS) astrocytes are glial cells performing crucial tasks encompassing energy metabolism, neurotransmission, ion and water stable levels, and immune defense and control local blood flow/oxygen levels. Arising from neural stem cells, astrocytes differentiate into subtypes that vary according to animal species. Human cerebral cortex astrocytes are sturdier and cytologically and functionally more complex, control wider domains, and spread calcium signals more quickly than their rodents’ counterparts. They actively partake in CNS homeostasis maintenance and functioning by teaming up with their client neurons, other glial cell types, and cerebrovascular cells. Alterations of astrocytes’ activities deeply impact on age-related chronic ailments like Alzheimer’s disease (AD), the commonest senile dementia; AD involves the growing accumulation of amyloid-β peptides (Aβs) and hyperphosphorylated Tau proteins the astrocytes, and neurons supply following the interaction of their calcium-sensing receptors (CaSRs) with exogenous Aβs. The activated Aβ∙CaSR signaling triggers a self-propagating mechanism that spreads the neuropathology among adjacent and far away astrocytes and their neuronal clients causing neurons’ death. CaSR antagonists or calcilytics suppress these noxious effects in vitro. Hence, calcilytics are potential therapeutics that could halt the spread of AD neuropathology and safeguard the patients’ neuronal viability, cognition, memory, and ultimately life.
- Alzheimer’s disease
- tau protein
- calcium-sensing receptor
Between the 16th and 18th week of intrauterine life, a pool of stem cells of the neural plate generates every neural cell type, excepting microglia, in humans. Once differentiated, the astrocytes undergo a complex maturing process through which they acquire their specific morpho-functional characteristics. When these processes achieve completion, human astrocytes account for up to 50%, if not more, of the entire CNS cell population. These cells are larger in size and endowed with more numerous branches than their much less abundant (<20% of all CNS cells) rodents’ counterparts . Being so plentiful, astrocytes have a relevant role in brain environment homeostasis maintenance [2, 3]. They metabolically sustain neurons, recycle neurotransmitters, affect synapse activity, control local blood flow, and partake in blood-brain barrier functional integrity (see for details [2, 3, 4] and below). Aging and CNS diseases, neurodegenerative ones included, can induce an activated or inflammatory or reactive condition in the astrocytes [5, 6].
2. Human astrocytes’ varieties
As their designation indicates, astrocytes have a typical star-shaped morphology as they emit different numbers of cytoplasmic branches according to their subtype. Astrocytes of several subtypes dwell in the human CNS. Some of them display locational predilections, e.g., fibrous astrocytes for the white matter and protoplasmic astrocytes for the gray matter. More recently, it has been realized that the classical protoplasmic and fibrous astrocytes can be differentiated into several subtypes, some of which proper only of the human cerebral cortex. Such subtypes share a specific marker, the glial fibrillary acidic protein (GFAP), which is an intermediate filaments’ constituent expressed by all the astrocytes cultured in vitro. However, in vivo only the fibrous astrocytes express GFAP in the white matter (see for Ref. ). Recent studies have singled out a novel marker expressed by both protoplasmic and fibrous astrocytes, the aldehyde dehydrogenase-1 family member L-1 (Aldh1L1) [1, 8, 9].
2.1. Radial astrocytes
Radial astrocytes are the first ones to appear in the course of embryogenesis. At that point in time, they aid neurons’ migration by acting as scaffolds . Later, they differentiate becoming
2.2. Fibrous astrocytes
These white-matter-located astrocytes present very long and thin processes which mostly do not emit branches. The processes’ terminal end-feet envelope the axonal nodes of Ranvier and also gets in touch with the walls of cerebral vessels. Most notably, fibrous astrocytes partake in the repair of injured brain tissue, especially at the spinal cord level .
2.3. Protoplasmic astrocytes
They are the most abundant astrocytic type. Their somata give out numerous (up to 200) long branches, which end up with leafy feet or end-feet in part touching the blood vessels’ walls and in part enwrapping several thousands of synapses [1, 8]. Near the pia mater’s inner surface, the astrocytes’ end-feet cluster together forms the CNS
It is worth recalling here that both Golgi silver staining and GFAP immunolabeling of brain tissue sections make the astrocytes appear as star-like cells. However, the astrocytes are the possessors of a certain number of cytoplasmic branches these methods do not stain. Therefore, such methods do not reveal the astrocytes’ true morphology as visible under the light and/or fluorescence microscope. Another concept of old is that during development the astrocytes’ branches form an interdigitated scaffold permitting the organization of the neurons. Recently, it has become clear that independent and distinct astrocytic domains develop with no connection with similar neighboring domains within the hippocampus . As abovementioned, the morpho-functional features of human protoplasmic and fibrous astrocytes differ from rodents’ ones. For instance, the diameters of gray matter-located human protoplasmic astrocytes are 2.6-fold longer, and their GFAP-positive processes are 10-fold more abundant. A single protoplasmic astrocyte can control from 270,000 to 2.0 million synapses placed inside its spatial domain. Most important, the branches of a single astrocyte touch, envelop, and regulate not only a huge number of synapses but also the capillary vessels controlling the blood flow going to those same synapses. This organized structure has been interpreted as the indication of a control of synaptic activity by the astrocytes independently of neuronal activity. Although unable to transmit neural impulses, human astrocytes propagate calcium ion [Ca2+] waves at speeds of up to 36 μm/s, i.e., 4–10-fold faster than rodents’ astrocytes do [15, 16, 17].
2.4. Additional astrocytes’ subtypes
Besides the above-described canonical kinds, several other astrocyte subtypes have been recognized. Emsley and Macklis  have used a combined approach consisting of S100β immunostaining, GFAP expression, and human GFAP promoter-prodded enhanced green fluorescent protein (eGFP) expression in transgenic mice, to identify within several subtypes of CNS astrocytes. The latter incorporate radial glia, protoplasmic astrocytes, fibrous astrocytes, ependymal glia, tanycytes, Bergmann glia, and velate glia. The cytoarchitectonics and functional requirements of their local placements mainly determine the morphological features, growth rates, and relative densities of these subtypes . NG2 cells are an additional CNS glial cell type likely possessed of stem cell features and hence capable of giving raise to astrocytes, neurons, and oligodendrocytes (OLGs) during both intra- and extrauterine life. NG2 glial cells functionally interact with neurons at the level of synapses. Studies are under way to clarify the heterogeneity of NG2 glia .
2.5. Human cortex-specific astrocytic subtypes
At variance with other mammalian species, humans have developed two novel cerebral cortical astroglia subtypes: the
3. Astrocytes’ physiology
In the past and still now, some scientists have been holding astrocytes as neuron-supporting and at the same time debris-scavenging cells protectively regulating the homeostasis of a microenvironment from which neurons derive the necessary nutrients [12, 19]. Astrocytes also control the workings of “tripartite synapses” by enveloping them with their branches, thus barring the diffusion of released neurotransmitters and preventing the firing activity of one neuron from altering that of adjacent neurons . In addition, astrocytes’ synaptic regulation does not influence only the tripartite synapses their branches envelop but also far away synapses via astrocytes’ signals, a process named
Since astrocytes cannot be electrically excited, their plasma membranes do not propagate action potentials as instead neurons do. The membrane potential of astrocytes at rest has very low values, ranging from −85 to −90 mV. This is due to their intense expression of TREK-1 and TWIK-1 potassium ion [K+] channels . As recent lines of evidence show, astrocytes residing in separate brain areas express dissimilar types and levels of ion channels and hence are equipped with distinctive electrophysiological characteristics. The huge group of ion channels implicated is also differently expressed during astrocytes’ developmental stages .
In addition, astrocytes express various kinds of metabotropic receptors, which are coupled to a number of intracellular second messenger systems. For example, astroglia are known to adjust neuronal excitability and synaptic transmission through the metabotropic glutamatergic receptor subtype 5 (mGluR5). The results of experiments using brain slices showed that in response to an assortment of neurotransmitters, comprising acetylcholine, adenosine, ATP, endocannabinoids, GABA, glutamate, norepinephrine, and prostaglandins, metabotropic receptors could raise the intracellular Ca2+ levels ([Ca2+]i) via phospholipase C (PLC)- and inositol (1,4,5)-triphosphate (IP3)-dependent activities .
4. Astrocytes and AD neuropathology
An aberrant reactivity of astrocytes is a telltale sign of chronic neurodegenerative ailments like AD and Parkinson’s disease [1, 3, 5]. While AD advances an
AD hits nearly 2% of the people of the Western world particularly after 60 years of age . AD’s clinical course can be dissected into (
In the healthy brain, neurons produce and release at their synapses tiny amounts of nontoxic Aβ42 monomers, the intra- and extracellular amounts of which remain at low (i.e., pM), physiological values owing to a set of removing mechanisms operated by several proteases, phagocytosis by microglia and astrocytes, and disposal into the blood circulation . In aged brains, the ability to clear the Aβs from the CNS increasingly plummets likely because of local microcirculation problems. Consequently, as the
Conversely, as the
Moreover, Aβ42-os and Aβ42 fibrillar aggregates bind various plasma membrane receptors, comprising the calcium-sensing receptors (CaSRs) and the receptors for advanced glycation end products (RAGEs) which can activate the astrocytes (see for further details [3, 11, 43, 44]). Such multiple receptor interactions with Aβs stir up astrocytes’ JAK2 and MEK1/MEK2/ERK-1/ERK-2 signaling pathways stimulate the direct binding of STAT1 and HIF-1α/HIF-1β complexes to the
5. The CaSR
A highly conserved gene, the
Notably, being positively charged, both soluble or fibrillar Aβs specifically form complexes with the plasma membrane CaSRs. Subsequently, the Aβs∙CaSR complexes coalesce into patches which are rapidly endocytosed and can be detected within EEA1-positive early endosomes in the cytoplasm (Figure 1) [54, 55]. However, it has not been ascertained whether Aβs’ binding site[s] is [are] of the orthosteric or allosteric kind or both [22, 44].
Various species of G-proteins mediate CaSR’s intracellular signaling by (
CaSR’s expression occurs in every portion of the rat and human brain. By using the in situ hybridization method, Yano et al.  demonstrated that the CaSR is intensely expressed in several areas of the adult rat CNS. In relation to AD, we recall here that CaSR’s expression abounds in the hippocampus especially at the level of the somata and axon terminals of the pyramidal neurons, suggesting the functional modulation of such cells by CaSR’s signaling [47, 58]. Notably, the N-methyl-D-aspartate receptor (NMDAR) brain location is superimposable on the CaSR’s. Both NMDARs and CaSRs play crucial roles in the induction of long-term potentiation (LTP) . Typically, CaSR’s expression occurs not only in neurons but also in human primary astrocytes, astrocytoma cell lines, oligodendroglia, and microglial cells . Interestingly, total CaSR protein levels increase significantly though transiently in Aβ-exposed NAHAs . Furthermore, the intensity of CaSR’s immunoreactivity significantly increases with age in the hippocampus of 3xTg AD-model mice , particularly where Aβs and p-Taues also accumulate, a clear indication of the involvement of this receptor in AD pathophysiology in vivo (see also below).
The intracellular Ca2+ concentration ([Ca2+]i) can vary widely under both normal and pathological conditions. The Ca2+ influx into cultured astrocytes is linear and normally increases only up to 1.8 mM, suggesting that CaSR signaling controls it [61, 62]. In the past, aberrations of cell surface and intracellular Ca2+-controlling mechanisms were posited to happen in various neurodegenerative ailments, AD included [61, 62, 63, 64, 65]. Reportedly, exogenous Aβ42 and its well-established proxy, Aβ25–35, trigger [Ca2+]i surges and oscillations which persist for hours in the neurons and astrocytes too and concur with the loss of the inner mitochondrial membrane potential. This in turn promotes the release of reactive oxygen species (ROS) and oxidative stress in both neurons and astrocytes. Coculturing such reactive astrocytes with neurons caused the neurons’ death within 24 h unless the Aβ-elicited [Ca2+]i surges were forestalled .
Recent findings from our laboratory lend credence to the view that the CaSR, one of the receptors astrocytes express, drives the pathogenic mechanisms of AD [48, 66, 67, 68, 69].
6. Human cortical astrocytes, CaSRs, and AD promotion
It is time for us to zoom in on our preclinical model of cortical untransformed phenotypically stable, i.e.,
As we recalled above, CaSR’s expression takes place with dissimilar intensities, in every CNS cell type, astrocytes included [44, 57]. Recent studies have brought to light some of the physiological roles the CaSR plays in the human CNS, like modulation of neurons’ dendrites and axons growth and of OLGs development [57, 72]. Using the NAHAs as our experimental system, we first demonstrated that exogenous Aβ25–35—instigated CaSR signaling elicits the concurrent expression of nitric oxide synthase-2 (NOS-2) and of GTP cyclohydrolase-1 (GCH-1). GCH-1 makes the BH4 [tetrahydrobiopterin] cofactor that dimerizes and activates the NOS-2 moieties, thus allowing the synthesis of nitric oxide (NO) to occur [44, 73, 74]. Exogenous fibrillar Aβs also induce via direct CaSR signaling activation the cytoplasmic stabilization and nuclear translocation of the hypoxia-inducible HIF-1α•HIF-1β transcription complex in NAHAs. This elicits the vascular endothelial growth factor-A (
However, the most exciting discoveries were subsequently made possible by the advent of very sensitive ELISA kits assaying Aβs. In untreated NAHAs, the metabolic processing of amyloid precursor holoprotein (APP) takes place along the nonamyloidogenic pathway [NAP] being mediated by the activity of the α-secretases (mainly ADAM10) and extracellularly sheds all the soluble sAPPα it produces. Notably, sAPPα is a neurotrophic and neuroprotective compound positively affecting neurons’ functions and viability. Moreover, sAPPα synthesis precludes any Aβ40/42 production from APP as it is cut from the middle amino acid sequence of Aβ40/42. Therefore, NAP largely prevails over APP’s amyloidogenic processing [AP] in the untreated astrocytes, which secrete only very low basal Aβ40/42 amounts . Conversely, adding fibrillar Aβ25–35 by itself and hence stirring off Aβ25–35∙CaSR signaling remarkably reduces sAPPα’s extracellular shedding while driving an overproduction and oversecretion of neurotoxic Aβ42/Aβ42-os owing to concurrent raises in the sequential activities of BACE-1 and γ-secretase. The further addition of a microglial cytokine mixture only accelerates but not increases the total amount of Aβ42/Aβ42-os secretion by the NAHAs despite a concurring APP overexpression [44, 71]. Thus, these events could start of self-sustaining vicious cycle of Aβ42/Aβ42-os spreading within the brain [37, 44]. The same Aβ∙CaSR-induced signaling mechanism stimulates the secretion of neurotoxic Aβ42/Aβ42-os from human cortical postnatal HCN-1A neurons . Thereafter, the neurons start dying slowly like they do in vivo . Most important, we also gained preliminary evidence indicating that Tau and hyperphosphorylated (p)-Tau are both expressed by untreated NAHAs in culture and that their exposure to the usual Aβ42 proxy, Aβ25–35, significantly increases via Aβ∙CaSR-induced signaling the activity of GSK-3β , the main Tau protein kinase [84, 85]. The upshot is an increased production of p-Tau/p-Tau-os which both accumulate inside the cells and are extracellularly released inside exosomes . Novel lines of evidence suggest that extracellular vesicles, which comprise exosomes, play important physiological and pathological roles in the CNS . The above mechanism could promote the concurrent diffusion of both p-Tau/p-Tau-os and Aβ42-os, the two main AD drivers, within the brain, though the tauopathy’s noxious effects will take longer to manifest [37, 83].
Given the relevance of the roles that the several upshots of the Aβ∙CaSR-elicited signaling could have on the promotion of AD, we were enticed to test whether an allosteric highly specific CaSR antagonist [short-termed as
We wish to stress that these results could be gained by using untransformed human cortical adult astrocytes and postnatal neurons,
7. Conclusions and future perspectives
Mounting lines of evidence lend credence to the view that the human astrocytes—the characteristics of which remarkably differ from those of their rodent counterparts—play manifold roles in the molecular mechanisms associated with AD’s pathophysiology. A growing accumulation of Aβs, p-Taues, NO, and VEGF-A hinges upon the signaling of Aβs∙CaSR complexes. This initiates a self-spreading cascade of events which culminate in neuronal synaptic disconnection, dysfunction, and death coupled with the oligodendrocyte dysfunction, axonal myelin sheaths damage and death, the activation of the microglia, the alteration of BBB permeability, and the expression of all the other neuropathological hallmarks of AD. The upshot is a concurrent degeneration of the gray and white matters. Thus, the CNS will keep shrinking; AD clinical symptoms will emerge and increase in intensity until the patients having lost their memories and cognitive abilities die. It is obvious that given their mounting numbers, the care of LOAD patients does heavily impact on their relatives and, for the huge costs of their assistance, on their National Health Services. In this disheartening scenario, the repurposing of highly specific CaSR antagonists or calcilytics as anti-AD therapeutics has the potential for shining a ray of hope.
|aMCI||amnestic minor cognitive impairment|
|APP||Aβ precursor protein|
|BOLD||blood oxygen level-dependent|
|CNS||central nervous system|
|fMRI||functional magnetic resonance imaging|
|GSK-3β||glycogen synthase kinase-3β|
|NAHAs||normal (untransformed) adult human astrocytes|
|p-Tau||hyperphosphorylated Tau protein|
|VEGF||vascular endothelial growth factor|
Khakh BS, Sofroniew MW. Diversity of astrocyte functions and phenotypes in neural circuits. Nature Neuroscience. 2015; 18:942-552. DOI: 10.1038/nn.4043
Avila-Muñoz E, Arias C. When astrocytes become harmful: Functional and inflammatory responses that contribute to Alzheimer's disease. Ageing Research Reviews. 2014; 18:29-40. DOI: 10.1016/j.arr.2014.07.004
Filous AR, Silver J. Targeting astrocytes in CNS injury and disease: A translational research approach. Progress in Neurobiology. 2016; 144:173-187. DOI: 10.1016/j.pneurobio.2016.03.009
Eroglu C, Barres BA. Regulation of synaptic connectivity by glia. Nature. 2010; 468( 7321):223-231. DOI: 10.1038/nature09612
Pekny M, Wilhelmsson U, Pekna M. The dual role of astrocyte activation and reactive gliosis. Neuroscience Letters. 2014; 565:30-38. DOI: 10.1016/j.neulet.2013.12.071
Ferrer I. Diversity of astroglial responses across human neurodegenerative disorders and brain aging. Brain Pathology. 2017; 27:645-674. DOI: 10.1111/bpa.12538
Middeldorp J, Hol EM. GFAP in health and disease. Progress in Neurobiology. 2011; 93:421-443. DOI: 10.1016/j.pneurobio.2011.01.005
Bushong EA, Martone ME, Jones YZ, Ellisman MH. Protoplasmic astrocytes in CA1 stratum radiatum occupy separate anatomical domains. The Journal of Neuroscience. 2002; 22:183-192
Boesmans W, Rocha NP, Reis HJ, Holt M, Vanden Berghe P. The astrocyte marker Aldh1L1 does not reliably label enteric glial cells. Neuroscience Letters. 2014; 566:102-105. DOI: 10.1016/j.neulet.2014.02.042
Ge WP, Jia GM. Local production of astrocytes in the cerebral cortex. Neuroscience. 2016; 323:3-9. DOI: 10.1016/j.neuroscience.2015.08.057.
Hamby ME, Sofroniew MV. Reactive astrocytes as therapeutic targets for CNS disorders. Neurotherapeutics. 2010; 7:494-506. DOI: 10.1016/j.nurt.2010.07.003
Lliff JJ, Wang M, Liao Y, Plogg BA, Peng W, Gundersen GA, Benveniste H, Vates GE, Deane R,Goldman SA, Nagelhus EA, Nedergaard M. A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid β. Science Translational Medicine. 2012; 4:147ra111. DOI: 10.1126/scitranslmed.3003748
Cheslow L, Alvarez JI. Glial-endothelial crosstalk regulates blood-brain barrier function. Current Opinion in Pharmacology. 2015; 26:39-46. DOI: 10.1016/j.coph.2015.09.010.
Xu G, Wang W, Zhou M. Spatial organization of NG2 glial cells and astrocytes in rat hippocampal CA1 region. Hippocampus. 2014; 24:383-395. DOI: 10.1002/hipo.22232
Oberheim NA, Takano T, Han X, He W, Lin JH, Wang F, Xu Q, Wyatt JD, Pilcher W, Ojemann JG, Ransom BR, Goldman SA, Nedergaard M. Uniquely hominid features of adult human astrocytes, The Journal of Neuroscience 2009; 29.3276-3287. DOI: 10.1523/JNEUROSCI.4707-08.2009.
Oberheim NA, Wang GS, Nedergaard M. Astrocytic complexity distinguishes the human brain. Trends in Neurosciences. 2006; 29:547-553
Emsley JG, Macklis JD. Astroglial heterogeneity closely reflects the neuronal-defined anatomy of the adult murine CNS. Neuron Glia Biology. 2006; 2:175-186
Viganò F, Dimou L. The heterogeneous nature of NG2-glia. Brain Research. 2016; 1638([PtB]):129-137. DOI: 10.1016/j.brainres.2015.09.012
Zhang H, YJ S, Zhou WW, Wang SW, PX X, XL Y, Liu RT. Activated scavenger receptor a promotes glial internalization of Aβ. PLoS One. 2014; 9:e94197. DOI: 10.1371/journal.pone.0094197
Pérez-Alvarez A, Araque A. Astrocyte-neuron interaction at tripartite synapses. Current Drug Targets. 2013; 14:1220-1224
Covelo A, Araque A. Lateral regulation of synaptic transmission by astrocytes. Neuroscience. 2016; 323:62-66. DOI: 10.1016/j.neuroscience.2015. 02.036
Dal Prà I, Chiarini A, Pacchiana R, Gardenal E, Chakravarthy B, Whitfield JF, Armato U. Calcium-sensing receptors of human astrocyte-neuron teams: Amyloid-β-driven mediators and therapeutic targets of Alzheimer's disease. Current Neuropharmacology. 2014; 12:353-364. DOI: 10.2174/ 1570159X12666140828214701
Harada K, Kamiya T, Tsuboi T. Gliotransmitter release from astrocytes: Functional, developmental, and pathological implications in the brain. Frontiers in Neuroscience. 2016; 9:499. DOI: 10.3389/fnins.2015.00499. eCollection 2015.
Newman EA. Glial cell regulation of neuronal activity and blood flow in the retina by release of gliotransmitters. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 2015; 370:pii:20140195. DOI: 10.1098/rstb.2014.0195.
Zhou M, Xu G, Xie M, Zhang X, Schools GP, Ma L, Kimelberg HK, Chen H. TWIK-1 and TREK-1 are potassium channels contributing significantly to astrocyte passive conductance in rat hippocampal slices. The Journal of Neuroscience. 2009; 29:8551-8564. DOI: 10.1523/JNEUROSCI.5784-08.2009
Olsen ML, Khakh BS, Skatchkov SN, Zhou M, Lee CJ, Rouach N. New insights on astrocyte ion channels: Critical for homeostasis and neuron-glia Signaling. The Journal of Neuroscience. 2015; 35:13827-13835. DOI: 10.1523/JNEUROSCI.2603-15.2015
Panatier A, Robitaille R. Astrocytic mGluR5 and the tripartite synapse. Neuroscience. 2016; 323:29-34. DOI: 10.1016/j.neuroscience.2015.03.063
Zamanian JL, Xu L, Foo LC, Nouri N, Zhou L, Giffard RG, Barres BA. Genomic analysis of reactive astrogliosis. The Journal of Neuroscience. 2012; 32:6391-6410. DOI: 10.1523/JNEUROSCI.6221-11.2012
Garwood CJ, Pooler AM, Atherton J, Hanger DP, Noble W. Astrocytes are important mediators of Aβ-induced neurotoxicity and tau phosphorylation in primary culture. Cell Death & Disease. 2011; 2:e167. DOI: 10.1038/cddis.2011.50
Alzheimer’s Association. Alzheimer’s disease facts and figures. Alzheimer's & Dementia. 2008; 4:110-133
Querfurth HW, LaFerla FM. Alzheimer’s disease. The New England Journal of Medicine. 2010; 362:329-344
Gallagher M, Koh MT. Episodic memory on the path to Alzheimer's disease. Current Opinion in Neurobiology. 2011; 21:929-934. DOI: 10.1016/j.conb.2011.10.021
Armato U, Chakravarthy B, Pacchiana R, Whitfield JF. Alzheimer's disease: An update of the roles of receptors, astrocytes and primary cilia. International Journal of Molecular Medicine. 2013; 31:3-10. DOI: 10.3892/ijmm.2012.1162
Khan UA, Liu L, Provenzano FA, Berman DE, Profaci CP, Sloan R, Mayeux R, Duff KE, Small SA. Molecular drivers and cortical spread of lateral entorhinal cortex dysfunction in preclinical Alzheimer's disease. Nature Neuroscience. 2014; 17:304-311. DOI: 10.1038/nn.3606
Sehlin D, Englund H, Simu B, Karlsson M, Ingelsson M, Nikolajeff F, Lannfelt L, Pettersson FE. Large aggregates are the major soluble Aβ species in AD brain fractionated with density gradient ultracentrifugation. PLoS One. 2012; 7:e32014. DOI: 10.1371/journal.pone.0032014
Selkoe DJ. Soluble oligomers of the amyloid beta-protein impair synaptic plasticity and behavior. Behavioural Brain Research. 2008; 192:106-113. DOI: 10.1016/j.bbr.2008.02.016
Dal Prà I, Chiarini A, Gui L, Chakravarthy B, Pacchiana R, Gardenal E, Whitfield JF, Armato U. Do astrocytes collaborate with neurons in spreading the “infectious” aβ and tau drivers of Alzheimer's disease? The Neuroscientist. 2015; 21:9-29. DOI: 10.1177/1073858414529828
Braak H, Thal DR, Ghebremedhin E, Del Tredici K. Stages of the pathologic process in Alzheimer disease: Age categories from 1 to 100 years. Journal of Neuropathology and Experimental Neurology. 2011; 70:960-969. DOI: 10.1097/NEN.0b013e318232a379
Braak H, Del Tredici K. The preclinical phase of the pathological process underlying sporadic Alzheimer's disease. Brain. 2015; 138(Pt 10):2814-2833. DOI: 10.1093/brain/awv236
Gerson JE, Kayed R. Formation and propagation of tau oligomeric seeds. Frontiers in Neurology. 2013; 4:93. DOI: 10.3389/fneur.2013.00093. eCollection 2013
Jin M, Shepardson N, Yang T, Chen G, Walsh D, Selkoe DJ. Soluble amyloid beta-protein dimers isolated from Alzheimer cortex directly induce tau hyperphosphorylation and neuritic degeneration. Proceedings of the National Academy of Sciences of the United States of America. 2011; 108:5819-5824. DOI: 10.1073/pnas.1017033108
Wakabayashi K, Mori F, Hasegawa M, Kusumi T, Yoshimura I, Takahashi H, Kaneko S. Co-localization of beta-peptide and phosphorylated tau in astrocytes in a patient with corticobasal degeneration. Neuropathology. 2006; 26:66-71
Chiarini A, Armato U, Liu D, Dal Prà I. Calcium-sensing receptors of human neural cells play crucial roles in Alzheimer's disease. Frontiers in Physiology. 2016; 7:134. DOI: 10.3389/fphys.2016.00134. eCollection 2016
Armato U, Chiarini A, Chakravarthy B, Chioffi F, Pacchiana R, Colarusso E, Whitfield JF, Dal Prà I. Calcium-sensing receptor antagonist [calcilytic] NPS 2143 specifically block the increased secretion of endogenous Ab42 prompted by exogenous fibrillary or soluble Ab25-35 in human cortical astrocytes and neurons—Therapeutic relevance to Alzheimer’s disease. Biochimica et Biophysica Acta (BBA): Molecular Basis of Disease. 2013; 1832:1634-1652. DOI: 10.1016/j.bbadis.2013.04.020
Gold M, El Khoury J. β-amyloid, microglia, and the inflammasome in Alzheimer's disease. Seminars in Immunopathology. 2015; 37:607-611. DOI: 10.1007/s00281-015-0518-0
Blasko I, Veerhuis R, Stampfer-Kountchev M, Saurwein-Teissl M, Eikelenboom P, Grubeck-Loebenstein B. Costimulatory effects of interferon-gamma and interleukin-1beta or tumor necrosis factor alpha on the synthesis of Abeta1-40 and Abeta1-42 by human astrocytes. Neurobiology of Disease. 2000; 7[6PtB]:682-689.
Brown EM, Gamba G, Riccardi D, Lombardi M, Butters R, Kifor O, Sun A, Hediger MA, Lytton J, Hebert SC. Cloning and characterization of an extracellular Ca2+-sensing receptor from bovine parathyroid. Nature. 1993; 366(6455):575-580
Armato U, Bonafini C, Chakravarthy B, Pacchiana R, Chiarini A, Withfiled JF, Dal Prà I. The calcium-sensing receptor: A novel Alzheimer’s disease crucial target? Journal of the Neurological Sciences. 2012; 322:137-140
Pidasheva S, Grant M, Canaff L, Ercan O, Kumar U, Hendy GN. Calcium-sensing receptor dimerizes in the endoplasmic reticulum: Biochemical and biophysical characterization of CASR mutants retained intracellularly. Human Molecular Genetics. 2006; 15:2200-2209
Geng Y, Mosyak L, Kurinov I, Zuo H, Sturchler E, Cheng TC, Subramanyam P, Brown AP, Brennan SC, Mun HC, Bush M, Chen Y, Nguyen TX, Cao B, Chang DD, Quick M, Conigrave AD, Colecraft HM, McDonald P, Fan QR. Structural mechanism of ligand activation in human calcium-sensing receptor. Elife. 2016; 5:pii: e13662. DOI: 10.7554/eLife.13662
Dal Prà I, Chiarini A, Nemeth EF, Armato U, Whitfield JF. Roles of Ca2+ and the Ca2+-sensing receptor [CASR] in the expression of inducible NOS [nitric oxide synthase]-2 and its BH4 [tetrahydrobiopterin]-dependent activation in cytokine-stimulated adult human astrocytes. Journal of Cellular Biochemistry. 2005; 96:428-438
Pacchiana R, Abbate M, Armato U, Dal Prà I, Chiarini A. Combining immunofluorescence with in situ proximity ligation assay: A novel imaging approach to monitor protein-protein interactions in relation to subcellular localization. Histochemistry and Cell Biology. 2014; 142:593-600. DOI: 10.1007/s00418-014-1244-8
Söderberg O, Gullberg M, Jarvius M, Ridderstråle K, Leuchowius KJ, Jarvius J, Wester K, Hydbring P, Bahram F, Larsson LG, Landegren U. Direct observation of individual endogenous protein complexes in situ by proximity ligation. Nature Methods. 2006; 3:995-1000
Voltan AR, Sardi Jde C, Soares CP, Pelajo Machado M, Fusco Almeida AM, Mendes-Giannini MJ. Early endosome antigen 1 [EEA1] decreases in macrophages infected with Paracoccidioides brasiliensis. Medical Mycology. 2013; 51:759-764. DOI: 10.3109/13693786.2013.777859
Dal Prà I, Armato U, Chioffi F, Pacchiana R, Whitfield JF, Chakravarthy B, Gui L, Chiarini A. The Aβ peptides-activated calcium-sensing receptor stimulates the production and secretion of vascular endothelial growth factor-A by normoxic adult human cortical astrocytes. Neuromolecular Medicine. 2014; 16:645-657. DOI: 10.1007/s12017-014-8315-9
Chakravarty B, Chattopadhyay N, Brown EM. Signaling through the extracellular calcium-sensing receptor [CaSR]. Advances in Experimental Medicine and Biology. 2012; 740:103-142. DOI: 10.1007/978-94-007-2888-2_5
Yano S, Brown EM, Chattopadhyay N. Calcium-sensing receptor in the brain. Cell Calcium. 2004; 35:257-264. DOI: 10.1016/j.ceca.2003.10.008
Chen W, Bergsman JB, Wang X, Gilkey G, Pierpoint CR, Daniel EA, Awumey EM, Dauban P, Dodd RH, Ruat M, Smith SM. Presynaptic external calcium signaling involves the calcium-sensing receptor in neocortical nerve terminals. PLoS One. 2010; 5:e8563. DOI: 10.1371/journal.pone.0008563
Chattopadhyay N, Legradi G, Bai M, Kifor O, Ye C, Vassilev PM, Brown EM, Lechan RM. Calcium-sensing receptor in the rat hippocampus: A developmental study. Brain Research. Developmental Brain Research. 1997; 100:13-21
Gardenal E, Chiarini A, Armato U, Dal Prà I, Verkhratsky A, Rodríguez JJ. Increased calcium-sensing receptor immunoreactivity in the hippocampus of a triple transgenic mouse model of Alzheimer's disease. Frontiers in Neuroscience. 2017; 11:81. DOI: 10.3389/fnins.2017.00081. eCollection 2017
Mattson MP, Cheng B, Davis D, Bryant K, Lieberburg I, Rydel RE. beta-Amyloid peptides destabilize calcium homeostasis and render human cortical neurons vulnerable to excitotoxicity. The Journal of Neuroscience. 1992; 12:376-389
Mattson MP. Calcium and neurodegeneration. Aging Cell. 2007; 6:337-350
Khakh BS, McCarthy KD. Astrocyte calcium signaling: From observations to functions and the challenges therein. Cold Spring Harbor Perspectives in Biology. 2015; 7:a020404. DOI: 10.1101/cshperspect.a020404
Fairless R, Williams SK, Diem R. Dysfunction of neuronal calcium signalling in neuroinflammation and neurodegeneration. Cell and Tissue Research. 2014; 357:455-462
Berridge MJ. Calcium regulation of neural rhythms, memory and Alzheimer's disease. The Journal of Physiology. 2014; 592:281-293. DOI: 10.1113/jphysiol.2013.257527
Chiarini A, Dal Prà I, Marconi M, Chakravarthy B, Whitfield JF, Armato U. Calcium-sensing receptor [CaSR] in human brain's pathophysiology: Roles in late-onset Alzheimer's disease [LOAD]. Current Pharmaceutical Biotechnology. 2009; 10:317-326
Ye C, Ho-Pao CL, Kanazirska M, Quinn S, Rogers K, Seidman CE, Seidman JG, Brown EM, Vassilev PM. Amyloid-beta proteins activate Ca2+-permeable channels through calcium-sensing receptors. Journal of Neuroscience Research. 1997; 47:547-554
Dal Prà I, Chiarini A, Armato U. Antagonizing amyloid-β/calcium-sensing receptor signaling in human astrocytes and neurons: A key to halt Alzheimer's disease progression? Neural Regeneration Research. 2015; 10:213-218. DOI: 10.4103/1673-5374.152373
Conley YP, Mukherjee A, Kammerer C, DeKosky ST, Kamboh MI, Finegold DN, Ferrell RE. Evidence supporting a role for the calcium-sensing receptor in Alzheimer disease. American Journal of Medical Genetics. Part B, Neuropsychiatric Genetics. 2009; 150B:703-709. DOI: 10.1002/ajmg.b.30896
Chiarini A, Whitfield J, Bonafini C, Chakravarthy B, Armato U, Dal Prà I. Amyloid-β[25-35], an amyloid-β[1-42] surrogate, and proinflammatory cytokines stimulate VEGF-A secretion by cultured, early passage, normoxic adult human cerebral astrocytes. Journal of Alzheimer's Disease. 2010; 21:915-926. DOI: 10.3233/JAD-2010-100471
Chiarini A, Armato U, Liu D, Dal Prà I. Calcium-sensing receptor antagonist NPS 2143 restores amyloid precursor protein physiological non-Amyloidogenic processing in Aβ-exposed adult human astrocytes. Scientific Reports. 2017; 7:1277. DOI: 10.1038/s41598-017-01215-3
Ferry S, Traiffort E, Stinnakre J, Ruat M. Developmental and adult expression of rat calcium-sensing receptor transcripts in neurons and oligodendrocytes. The European Journal of Neuroscience. 2000; 12:872-884
Chiarini A, Dal Prà I, Gottardo R, Bortolotti F, Whitfield JF, Armato U. BH [tetrahydrobiopterin]-dependent activation, but not the expression, of inducible NOS [nitric oxide synthase]-2 in proinflammatory cytokine-stimulated, cultured normal human astrocytes is mediated by MEK-ERK kinases. Journal of Cellular Biochemistry. 2005; 94:731-743
Chiarini A, Armato U, Pacchiana R, Dal Pra I. Proteomic analysis of GTP cyclohydrolase 1 multiprotein complexes in cultured normal adult human astrocytes under both basal and cytokine-activated conditions. Proteomics. 2009; 9:1850-1860. DOI: 10.1002/pmic.200800561
Sanchez A, Tripathy D, Luo J, Yin X, Martinez J, Grammas P. Neurovascular unit and the effects of dosage in VEGF toxicity: Role for oxidative stress and thrombin. Journal of Alzheimer's Disease. 2013; 34:281-291. DOI: 10.3233/JAD-121636
Ruhrberg C, Bautch VL. Neurovascular development and links to disease. Cellular and Molecular Life Sciences. 2013; 70:1675-1684. DOI: 10.1007/s00018-013-1277-5
Carmeliet P, Ruiz de Almodovar CVEGF. Ligands and receptors: Implications in neurodevelopment and neurodegeneration. Cellular and Molecular Life Sciences. 2013; 70:1763-1778. DOI: 10.1007/s00018-013-1283-7. Erratum in: Cell Mol Life Sci. 2013; 70:2221. Carmen, Ruiz de Almodovar [corrected to Ruiz de Almodovar, Carmen].
Tang H, Mao X, Xie L, Greenberg DA, Jin K. Expression level of vascular endothelial growth factor in hippocampus is associated with cognitive impairment in patients with Alzheimer's disease. Neurobiology of Aging. 2013; 34:1412-1415. DOI: 10.1016/j.neurobiolaging.2012.10.029
Chiarini A, Armato U, Whitfield JF, Dal Prà I. Targeting human astrocytes' calcium-sensing receptors for treatment of Alzheimer's disease. Current Pharmaceutical Design. 2017 Jul 10. DOI: 10.2174/1381612823666170710162509
Dickerson BC, Salat DH, Greve DN, Chua EF, Rand-Giovannetti E, Rentz DM, Bertram L, Mullin K, Tanzi RE, Blacker D, Albert MS, Sperling RA. Increased hippocampal activation in mild cognitive impairment compared to normal aging and AD. Neurology. 2005; 65:404-411
Yassa MA, Stark SM, Bakker A, Albert MS, Gallagher M, Stark CE. High-resolution structural and functional MRI of hippocampal CA3 and dentate gyrus in patients with amnestic mild cognitive impairment. NeuroImage. 2010; 51:1242-1252. DOI: 10.1016/j.neuroimage.2010.03.040
Yassa MA. Ground zero in Alzheimer's disease. Nature Neuroscience. 2014; 17:146-147. DOI: 10.1038/nn.3631
Chiarini A, Armato U, Gardenal E, Gui L, Dal Prà I. Amyloid β-exposed human astrocytes overproduce phospho-tau and overrelease it within exosomes, effects suppressed by calcilytic NPS 2143-further implications for Alzheimer's therapy. Frontiers in Neuroscience. 2017; 11:217. DOI: 10.3389/fnins.2017.00217. eCollection 2017
Buée L, Bussière T, Buée-Scherrer V, Delacourte A, Hof PR. Tau protein isoforms, phosphorylation and role in neurodegenerative disorders. Brain Research. Brain Research Reviews. 2000; 33:95-130
Schraen-Maschke S, Sergeant N, Dhaenens CM, Bombois S, Deramecourt V, Caillet-Boudin ML, Pasquier F, Maurage CA, Sablonnière B, Vanmechelen E, Buée L. Tau as a biomarker of neurodegenerative diseases. Biomarkers in Medicine. 2008; 2:363-384. DOI: 10.2217/17520318.104.22.1683
Rajendran L, Bali J, Barr MM, Court FA, Krämer-Albers EM, Picou F, Raposo G, van der Vos KE, van Niel G, Wang J, Breakefield XO. Emerging roles of extracellular vesicles in the nervous system. The Journal of Neuroscience. 2014; 34:15482-11549. DOI: 10.1523/JNEUROSCI.3258-14.2014
Nemeth EF. Pharmacological regulation of parathyroid hormone secretion. Current Pharmaceutical Design. 2002; 8:2077-2087
Nemeth EF. The search for calcium receptor antagonists [calcilytics]. Journal of Molecular Endocrinology. 2002; 29:15-21