Reduced TRPC6 mRNA levels in the blood cells of patients with Alzheimer's disease and mild cognitive impairment

Ginsenosides Decrease β-Amyloid Production via Potentiating Capacitative Calcium Entry

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder characterized by extracellular amyloid plaques composed of amyloid β-peptide (Aβ). Studies have indicated that Ca2+ dysregulation is involved in AD pathology. It is reported that decreased capacitative Ca2+ entry (CCE), a refilling mechanism of intracellular Ca2+, resulting in increased Aβ production. In contrast, constitutive activation of CCE could decrease Aβ production. Panax ginseng Meyer is known to enhance memory and cognitive functions in healthy human subjects. We have previously reported that some ginsenosides decrease Aβ levels in cultured primary neurons and AD mouse model brains. However, mechanisms involved in the Aβ-lowering effect of ginsenosides remain unclear. In this study, we investigated the relationship between CCE and Aβ production by examining the effects of various ginsenosides on CCE levels. Aβ-lowering ginsenosides such as Rk1, Rg5, and Rg3 potentiated CCE. In contrast, ginsenosides without Aβ-lowering effects (Re and Rb2) failed to potentiate CCE. The potentiating effect of ginsenosides on CCE was inhibited by the presence of 2-aminoethoxydipherryl borate (2APB), an inhibitor of CCE. 2APB alone increased Aβ42 production. Furthermore, the presence of 2APB prevented the effects of ginsenosides on Aβ42 production. Our results indicate that ginsenosides decrease Aβ production via potentiating CCE levels, confirming a close relationship between CCE levels and Aβ production. Since CCE levels are closely related to Aβ production, modulating CCE could be a novel target for AD therapeutics.

Identification of common core ion channel genes in epilepsy and Alzheimer's disease

BACKGROUND

Although available literature indicates that the incidence of dementia in the epilepsy population and the risk of seizures in the Alzheimer's disease (AD) population are high, the specific genetic risk factors and the interaction mechanism are unclear, rendering rational genetic interpretation rather challenging.

AIMS

Our work aims to identify the common core ion channel genes in epilepsy and AD.

METHODS

In this study, we first integrated gene expression omnibus datasets (GSE48350 and GSE6834) on AD and epilepsy to identify differentially expressed genes (DEGs), performing Gene Ontology function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs. The related protein-protein interaction (PPI) network was constructed for DEGs, and the hub gene was evaluated.

RESULTS

A total of 2800 and 35 genes were identified in GSE48350 and GSE6834, and 12 DEGs were significantly differentially expressed between the datasets. KEGG pathway analysis showed that DEGs were primarily enriched in glutamatergic synapse and dopaminergic synapse pathways. SCN2A, GRIA1, and KCNJ9 were the hub genes with high connectivity.

CONCLUSIONS

The findings suggest that the three genes, SCN2A, GRIA1, and KCNJ9, may serve as potential targets for treating AD comorbid with epilepsy.

Role of Neuronal TRPC6 Channels in Synapse Development, Memory Formation and Animal Behavior

The transient receptor potential cation channel, subfamily C, member 6 (TRPC6), has been believed to adjust the formation of an excitatory synapse. The positive regulation of TRPC6 engenders synapse enlargement and improved learning and memory in animal models. TRPC6 is involved in different synaptoprotective signaling pathways, including antagonism of N-methyl-D-aspartate receptor (NMDAR), activation of brain-derived neurotrophic factor (BDNF) and postsynaptic store-operated calcium entry. Positive regulation of TRPC6 channels has been repeatedly shown to be good for memory formation and storage. TRPC6 is mainly expressed in the hippocampus, particularly in the dentate granule cells, cornu Ammonis 3 (CA3) pyramidal cells and gamma-aminobutyric acid (GABA)ergic interneurons. It has been observed that TRPC6 agonists have a great influence on animal behavior including memory formation and storage The purpose of this review is to collect the available information on the role of TRPC6 in memory formation in various parts of the brain to understand how TRPC6-specific pharmaceutical agents will affect memory in distinct parts of the central nervous system (CNS).

Plasma long non-coding RNAs ASMTL-AS1, AP001363.1, AC005730.3 and AL133415.1 as a potential biomarker for Alzheimer's disease

BACKGROUND

Long non-coding RNAs (lncRNAs) play critical role in the pathogenesis of neurodegenerative diseases. Human plasma contains lncRNAs that are present in the blood, and their disease-specific profile has been considered a potential biomarker in some diseases.

METHODS

This study reports screening of the plasma levels of lncRNAs between Alzheimer disease(AD) (n = 45) and matched healthy controls (n = 45). The plasma samples of 5 AD patients and 5 matched healthy controls were randomly selected for expression levels of lncRNAs using the TruSeq RNA Sample Prep Kit (Illumina). The receiver operating characteristic (ROC) curve and area under the curve (AUC) were used to study the potential of lncRNAs as biomarkers.

RESULTS

The differential expression profiles of plasma showed that 514 lncRNAs were upregulated, whereas 499 lncRNAs were downregulated.We found that the lncRNAs AL133415.1, AC020916.1, ENST00000654948, ASMTL-AS, AC005730.3, and AP001363.1 levels in the plasma of the AD patients were significantly lower compared to the control group (p1 = 0.0006, p2 < 0.001, p3 < 0.001, p4 = 0.039, p5 = 0.006, p6 < 0.001, respectively). ROC curve analysis revealed that the AUC of AL133415.1 was 0.635 (95% CI]: 0.507-0.763, p = 0.036), the AUC of ASMTL-AS1 was 0.658 (95% CI: 0.513-0.785, p = 0.015), the AUC of AC005730.3 was 0.627 (95%CI: 0.498-0.756, p = 0.049), and the AUC of AP001363.1 was 0.708 (95%CI: 0.595-0.822, p = 0.001).

CONCLUSION

This study indicated that the plasma levels of the lncRNAs ASMTL-AS1, AP001363.1, AC005730.3, and AL133415.1 might be considered potential biomarkers for AD in the Chinese Population.

Positive Allosteric Modulator of SERCA Pump NDC-1173 Exerts Beneficial Effects in Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is an irreversible neurodegenerative disease that affects millions of people worldwide. AD does not have a cure and most drug development efforts in the AD field have been focused on targeting the amyloid pathway based on the "amyloid cascade hypothesis". However, in addition to the amyloid pathway, substantial evidence also points to dysregulated neuronal calcium (Ca2+) signaling as one of the key pathogenic events in AD, and it has been proposed that pharmacological agents that stabilize neuronal Ca2+ signaling may act as disease-modifying agents in AD. In previous studies, we demonstrated that positive allosteric regulators (PAMs) of the Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) pump might act as such Ca2+ stabilizing agents. In the present study, we report the development of a novel SERCA PAM agent, compound NDC-1173. To test the effectiveness of this compound, we performed behavioral studies with the APP/PS1 transgenic AD mouse model. We also evaluated effects of this compound on expression of endoplasmic reticulum (ER) stress genes in the hippocampus of APP/PS1 mice. The results of this study support the hypothesis that the SERCA pump is a potential novel therapeutic drug target and that NDC-1173 is a promising lead molecule for developing disease-modifying agents in AD.

Role of Calcium Modulation in the Pathophysiology and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most frequent cause of progressive dementia in senior adults. It is characterized by memory loss and cognitive impairment secondary to cholinergic dysfunction and N-methyl-D-aspartate (NMDA)-mediated neurotoxicity. Intracellular neurofibrillary tangles, extracellular plaques composed of amyloid-β (Aβ), and selective neurodegeneration are the anatomopathological hallmarks of this disease. The dysregulation of calcium may be present in all the stages of AD, and it is associated with other pathophysiological mechanisms, such as mitochondrial failure, oxidative stress, and chronic neuroinflammation. Although the cytosolic calcium alterations in AD are not completely elucidated, some calcium-permeable channels, transporters, pumps, and receptors have been shown to be involved at the neuronal and glial levels. In particular, the relationship between glutamatergic NMDA receptor (NMDAR) activity and amyloidosis has been widely documented. Other pathophysiological mechanisms involved in calcium dyshomeostasis include the activation of L-type voltage-dependent calcium channels, transient receptor potential channels, and ryanodine receptors, among many others. This review aims to update the calcium-dysregulation mechanisms in AD and discuss targets and molecules with therapeutic potential based on their modulation.

Trpc6 knockout improves behavioral dysfunction and reduces Aβ production by inhibiting CN-NFAT1 signaling in T2DM mice

As the prevalence of diabetes and health awareness increase, type 2 diabetes mellitus -associated cognitive dysfunction is receiving increasing attention. However, the pathogenesis is not entirely understood. Transient receptor potential cation channel 6 (TRPC6) is highly correlated with intracellular Ca2+ concentrations, and neuronal calcium overload is an important cause of cognitive dysfunction. In the present study, we investigated the effect and mechanism of Trpc6 knockout in high-fat diet and streptozotocin-induced T2DM mice. The body weight and fasting blood glucose were recorded during the experiment. Behavioral dysfunction was detected using the open field test (OFT), elevated plus maze (EPM), hole-board test (HBT), Morris water maze (MWM) test and contextual fear conditioning (CFC) test. Nissl and H&E staining were used to examine neuronal damage. Western blot, quantitative real-time polymerase chain reaction (q-PCR), and immunofluorescence were performed to detect amyloid beta protein (Aβ) deposition and related indicators of neurological impairments in the cerebral cortex and hippocampus. The results indicated that Trpc6 knockout inhibited body weight loss and fasting blood glucose increase, improved spontaneous activity, learning and memory dysfunction, and alleviated neuroinflammation and neuronal damage in T2DM mice. The further results demonstrated that Trpc6 knockout decreased Aβ generation and deposition, and reduced the expressions of inflammasome-related proteins in T2DM mice. In addition, Trpc6 knockout inhibited intracellular calcium overload in diabetic mice and primary cultured hippocampal neurons, which in turn suppressed CN and NFAT1 expression. These data suggest that Trpc6 knockout may inhibit the CN-NFAT1 signaling pathway by decreasing intracellular calcium overload in the brain of T2DM mice, which consequently reduce Aβ deposition and neuroinflammation, and ultimately delay the development of T2DM-associated cognitive dysfunction.

Transient Receptor Potential Canonical 6 (TRPC6) Channel in the Pathogenesis of Diseases: A Jack of Many Trades

The mammalian Transient Receptor Potential Canonical (TRPC) subfamily comprises seven transmembrane proteins (TRPC1-7) forming cation channels in the plasma membrane of mammalian cells. TRPC channels mediate Ca²⁺ and Na⁺ influx into the cells. Amongst TRPCs, TRPC6 deficiency or increased activity due to gain-of-function mutations has been associated with a multitude of diseases, such as kidney disease, pulmonary disease, and neurological disease. Indeed, the TRPC6 protein is expressed in various organs and is involved in diverse signalling pathways. The last decade saw a surge in the investigative studies concerning the physiological roles of TRPC6 and describing the development of new pharmacological tools modulating TRPC6 activity. The current review summarizes the progress achieved in those investigations.

A blood mRNA panel that differentiates Alzheimer's disease from other dementia types

BACKGROUND

Messenger RNAs (mRNAs) have been reported to be associated with Alzheimer's disease (AD). In this study, we investigated whether plasma-based mRNAs could distinguish AD from cognitively normal controls and other types of dementia, including vascular dementia (VaD), Parkinson's disease dementia (PDD), behavioral variant frontotemporal dementia (bvFTD), and dementia with Lewy body (DLB).

METHODS

Plasma mRNA expression was measured in three independent datasets. Dataset 1 (n = 40; controls, 20; AD, 20) was used to identify the differentially expressed mRNAs. Dataset 2 (n = 122; controls: 60; AD: 62) was used to develop a diagnostic AD model using an mRNA panel. Furthermore, we applied the model to Dataset 3 (n = 334; control, 57; AD, 58; VaD, 55; PDD, 54; bvFTD, 55; DLB, 55) to verify its ability to identify AD and other types of dementia.

RESULTS

Dataset 1 showed 22 upregulated and 21 downregulated mRNAs. A panel of six mRNAs distinguished AD from the control group in Dataset 2. The panel was used to successfully differentiate AD from other types of dementia in Dataset 3.

CONCLUSIONS

An AD-specific panel of six mRNAs was created that can be used for AD diagnosis.

Usefulness of candidate mRNAs and miRNAs as biomarkers for mild cognitive impairment and Alzheimer's disease

OBJECTIVE

To explore potential molecular mechanisms and novel biomarkers of mild cognitive impairment (MCI) and Alzheimer's disease (AD).

METHODS

The mRNA expression datasets GSE63060 and GSE63061 and the miRNA expression dataset GSE120584 were obtained from the Gene Expression Omnibus database. The differentially expressed genes (DEGs) and miRNA (DEmiRs) were identified in the normal, MCI, and AD groups. Mfuzz clustering and weighted correlation network analyses (WGCNA) were conducted, followed by pathway and functional enrichment analyses and miRNA-mRNA network construction. Furthermore, phenotypic correlation analysis and experimental verification were performed on key DEGs and DEmiRs.

RESULTS

In total, 3,000 intersected DEGs from GSE63060/GSE63061 and 817 DEmiRs from GSE120584 were obtained. Mfuzz and WGCNA analyses revealed 106 DEGs including ribosomal protein L11 (RPL11) and 28 DEmiRs including miR-6764-5p. These DEGs and DEmiRs were mainly enriched in pathways like Ribosome. Moreover, 5 key DEGs including cytohesin 4 (CYTH4) and 6 crucial DEmiRs including miR-6734-3p were identified by miRNA-mRNA interaction network analysis. Phenotypic correlation analysis showed that CYTH4 and miR-6734-3p were correlated with patients' age. The results of quantitative polymerase chain reaction analysis confirmed that RPL11 expression was significantly downregulated in the MCI and AD groups compared to that in the normal group, while the expression of CYTH4, miR-6764-5p, and miR-6734-3p was remarkably upregulated in the MCI and AD groups.

CONCLUSIONS

miR-6764-5p might contribute to MCI and AD by targeting RPL11 in the ribosome pathway. Therefore, miR-6734-3p and its target mRNA CYTH4 might be used as novel biomarkers for MCI and AD.

New Positive TRPC6 Modulator Penetrates Blood–Brain Barrier, Eliminates Synaptic Deficiency and Restores Memory Deficit in 5xFAD Mice

Synapse loss in the brain of Alzheimer’s disease patients correlates with cognitive dysfunctions. Drugs that limit synaptic loss are promising pharmacological agents. The transient receptor potential cation channel, subfamily C, member 6 (TRPC6) regulates the formation of an excitatory synapse. Positive regulation of TRPC6 results in increased synapse formation and enhances learning and memory in animal models. The novel selective TRPC6 agonist, 3-(3-,4-Dihydro-6,7-dimethoxy-3,3-dimethyl-1-isoquinolinyl)-2H-1-benzopyran-2-one, has recently been identified. Here we present in silico, in vitro, ex vivo, pharmacokinetic and in vivo studies of this compound. We demonstrate that it binds to the extracellular agonist binding site of the human TRPC6, protects hippocampal mushroom spines from amyloid toxicity in vitro, efficiently recovers synaptic plasticity in 5xFAD brain slices, penetrates the blood–brain barrier and recovers cognitive deficits in 5xFAD mice. We suggest that C20 might be recognized as the novel TRPC6-selective drug suitable to treat synaptic deficiency in Alzheimer’s disease-affected hippocampal neurons.

TRPV4 mRNA is elevated in the caudate nucleus with NPH but not in Alzheimer's disease

Symptoms of normal pressure hydrocephalus (NPH) and Alzheimer's disease (AD) are somewhat similar, and it is common to misdiagnose these two conditions. Although there are fluid markers detectable in humans with NPH and AD, determining which biomarker is optimal in representing genetic characteristics consistent throughout species is poorly understood. Here, we hypothesize that NPH can be differentiated from AD with mRNA biomarkers of unvaried proximity to telomeres. We examined human caudate nucleus tissue samples for the expression of transient receptor potential cation channel subfamily V member 4 (TRPV4) and amyloid precursor protein (APP). Using the genome data viewer, we analyzed the mutability of TRPV4 and other genes in mice, rats, and humans through matching nucleotides of six genes of interest and one house keeping gene with two factors associated with high mutation rate: 1) proximity to telomeres or 2) high adenine and thymine (A + T) content. We found that TRPV4 and microtubule associated protein tau (MAPT) mRNA were elevated in NPH. In AD, mRNA expression of TRPV4 was unaltered unlike APP and other genes. In mice, rats, and humans, the nucleotide size of TRPV4 did not vary, while in other genes, the sizes were inconsistent. Proximity to telomeres in TRPV4 was <50 Mb across species. Our analyses reveal that TRPV4 gene size and mutability are conserved across three species, suggesting that TRPV4 can be a potential link in the pathophysiology of chronic hydrocephalus in aged humans (>65 years) and laboratory rodents at comparable ages.

Tetraspanin-29 activates Notch signaling by interacting with ADAM10 to enhance its activity in colorectal cancer

ADAM10 acts upstream of Notch signaling and plays oncogenic roles in various cancers. Tetraspanin family proteins regulate ADAM10 trafficking and activity. Here, we aimed to investigate whether and how tetraspanin-29 modulates ADAM10 in colorectal cancer (CRC). We found that ADAM10 expression was upregulated in CRC tissues and this was cross-validated in the TCGA COAD data set. The ADAM10 protein level and its α-secretase activity were enhanced in CRC cell lines compared with control cell lines. Co-immunoprecipitation showed ADAM10 interacted with tetraspanin-29 in the LoVo cell line. Tetraspanin-29 knockdown reduced the cell surface trafficking and α-secretase activity of ADAM10. In addition, tetraspanin-29 knockdown inhibited Notch activity in a luciferase reporter assay and reduced the levels of cleaved Notch1 and Notch target genes such as HES2, c-MYC, and cyclin D3. Consistently, tetraspanin-29 overexpression increased cleaved Notch1 and this effect was blocked by ADAM10 inhibitors. The TCGA COAD data set confirmed the positive correlations of tetraspanin-29 with HES2, c-MYC, and cyclin D3. Thus, the tetraspanin-29/ADAM10/Notch pathway plays an important role in CRC.

Neuroprotective Effects of Estrogen Through BDNF-Transient Receptor Potential Channels 6 Signaling Pathway in the Hippocampus in a Rat Model of Perimenopausal Depression

Estradiol (E₂) has been proven to be effective in treating perimenopausal depression (PD); however, the downstream signaling pathways have not been fully elucidated. Transient receptor potential channels 6 (TRPC6) plays a vital role in promoting neuronal development and the formation of excitatory synapses. At present, we found that the serum levels of E₂ and brain-derived neurotrophic factor (BDNF) declined significantly in the women with PD compared to perimenopausal women, which was accompanied by a clear reduction in TRPC6 levels. To further reveal the effects of TRPC6 on neuronal survival and excitability, the PD-like rat model was established by the total removal of left ovary and 80% removal of right ovary followed by 21 days of the chronic unpredictable mild stress. Intragastric administration of E₂ (2 mg/kg), intraperitoneal injection of BDNF/TrB signaling pathway inhibitor (K252a, 100 μg/kg) and TRPC6 agonist (OAG, 0.6 mg/kg), and intracerebroventricular infusion of anti-BDNF antibody for blocking BDNF (0.5 μg/24 μl/rat) daily for 21 days were conducted. The levels of BDNF and TRPC6 in rat serum were lower in PD rats compared to the control rats; the depression-like behavior was induced, the neuronal death rate in the hippocampus increased, and the thickness of postsynaptic density (PSD) and the number of asymmetric synapses decreased significantly in the PD group. E₂ treatment greatly upregulated the serum levels of BDNF and TRPC6, the neuronal excitability indicated by an elevation in the PSD thickness and the numbers of asymmetric synapses, and these actions were reversed by K252a; co-administration of TRPC6 agonist and K252a improved neuronal degeneration and increased the neuronal excitability induced in the E₂-treated PD rats. K252a or anti-BDNF antibody inhibited the increased neuronal BDNF and TRPC6 expression in E₂-treated PD rats; co-treatment of TRPC6 agonist and anti-BDNF antibody reduced neuronal death and increased the BDNF and TRPC6 expression in the hippocampal CA1 neurons in the E₂-treated PD rats. These results suggest that the neuroprotective role of E₂ in PD is closely related to enhance the activity of BDNF/TRPC6 pathway and is helpful to provide new prevention and strategies.

The China Alzheimer Report 2022

China’s population has rapidly aged over the recent decades of social and economic development as neurodegenerative disorders have proliferated, especially Alzheimer’s disease (AD) and related dementias (ADRD). AD’s incidence rate, morbidity, and mortality have steadily increased to make it presently the fifth leading cause of death among urban and rural residents in China and magnify the resulting financial burdens on individuals, families and society. The ‘Healthy China Action’ plan of 2019–2030 promotes the transition from disease treatment to health maintenance for this expanding population with ADRD. This report describes related epidemiological trends, evaluates the economic burden of the disease, outlines current clinical diagnosis and treatment status and delineates existing available public health resources. More specifically, it examines the public health impact of ADRD, including prevalence, mortality, costs, usage of care, and the overall effect on caregivers and society. In addition, this special report presents technical guidance and supports for the prevention and treatment of AD, provides expertise to guide relevant governmental healthcare policy development and suggests an information platform for international exchange and cooperation.

Ion Channel Dysfunction in Astrocytes in Neurodegenerative Diseases

Astrocytes play an important role in the central nervous system (CNS). Ion channels in these cells not only function in ion transport, and maintain water/ion metabolism homeostasis, but also participate in physiological processes of neurons and glial cells by regulating signaling pathways. Increasing evidence indicates the ion channel proteins of astrocytes, such as aquaporins (AQPs), transient receptor potential (TRP) channels, adenosine triphosphate (ATP)-sensitive potassium (K-ATP) channels, and P2X7 receptors (P2X7R), are strongly associated with oxidative stress, neuroinflammation and characteristic proteins in neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). Since ion channel protein dysfunction is a significant pathological feature of astrocytes in neurodegenerative diseases, we discuss these critical proteins and their signaling pathways in order to understand the underlying molecular mechanisms, which may yield new therapeutic targets for neurodegenerative disorders.

Recurrent moderate hypoglycemia accelerates the progression of cognitive deficits through impairment of TRPC6/GLUT3 pathway in diabetic APP/PS1 mice

Currently, the most effective strategy for dealing with Alzheimer’s disease (AD) is delaying the onset of dementia. Severe hypoglycemia is strongly associated with dementia; however, the effects of recurrent moderate hypoglycemia (RH) on the progression of cognitive deficits in patients with diabetes with genetic susceptibility to AD remain unclear. Here, we report that insulin-controlled hyperglycemia slightly aggravated AD-type pathologies and cognitive impairment; however, RH significantly increased neuronal hyperactivity and accelerated the progression of cognitive deficits in streptozotocin-induced (STZ-induced) diabetic APP/PS1 mice. Glucose transporter 3–mediated (GLUT3-mediated) neuronal glucose uptake was not significantly altered under hyperglycemia but was markedly reduced by RH, which induced excessive mitochondrial fission in the hippocampus. Overexpression of GLUT3, specifically in the dentate gyrus (DG) area of the hippocampus, enhanced mitochondrial function and improved cognitive deficits. Activation of the transient receptor potential channel 6 (TRPC6) increased GLUT3-mediated glucose uptake in the brain and alleviated RH-induced cognitive deficits, and inactivation of the Ca²⁺/AMPK pathway was responsible for TRPC6-induced GLUT3 inhibition. Taken together, RH impairs brain GLUT3-mediated glucose uptake and further provokes neuronal mitochondrial dysfunction by inhibiting TRPC6 expression, which then accelerates progression of cognitive deficits in diabetic APP/PS1 mice. Avoiding RH is essential for glycemic control in patients with diabetes, and TRPC6/GLUT3 represents potent targets for delaying the onset of dementia in patients with diabetes.

Na+/Ca2+ exchanger isoform 1 (NCX1) and canonical transient receptor potential channel 6 (TRPC6) are recruited by STIM1 to mediate Store-Operated Calcium Entry in primary cortical neurons

Excessive calcium (Ca²⁺) release from the endoplasmic reticulum (ER) represents an important hallmark of several neurodegenerative diseases. ER is recharged from Ca²⁺ through the so-called Store-Operated Calcium Entry (SOCE) thus providing Ca²⁺ signals to regulate critical cell functions. Single transmembrane-spanning domain protein stromal interacting molecule 1 (STIM1), mainly residing in the ER, and plasmalemmal channel Orai1 represent the SOCE key components at neuronal level. However, many other proteins participate to ER Ca²⁺ refilling including the Na⁺/Ca²⁺ exchanger isoform 1 (NCX1), whose regulation by ER remains unknown. In this study, we tested the possibility that neuronal NCX1 may take part to SOCE through the interaction with STIM1. In rat primary cortical neurons and in nerve growth factor (NGF)-differentiated PC12 cells NCX1 knocking down by siRNA strategy significantly prevented SOCE as well as SOCE pharmacological inhibition by SKF-96365 and 2-APB. A significant reduction of SOCE was recorded also in synaptosomes from ncx1^-/^- mice brain compared with ncx1⁺/⁺ mice. Double labeling confocal experiments showed a large co-localization between NCX1 and STIM1 in rat primary cortical neurons. Accordingly, NCX1 and STIM1 co-immunoprecipitated and functionally interacted each other during ischemic preconditioning, a phenomenon inducing ischemic tolerance. However, STIM1 knocking down reduced NCX1 activity recorded by either patch-clamp electrophysiology or Fura-2 single-cell microfluorimetry. Furthermore, canonical transient receptor potential channel 6 (TRPC6) was identified as the mechanism mediating local increase of sodium (Na⁺) useful to drive NCX1 reverse mode and, therefore, NCX1-mediated Ca²⁺ refilling. In fact, TRPC6 not only interacted with STIM1, as shown by the co-localization and co-immunoprecipitation with the ER Ca²⁺ sensor, but it also mediated 1,3-Benzenedicarboxylic acid, 4,4'-[1,4,10-trioxa-7,13-diazacyclopentadecane-7,13-diylbis(5-methoxy-6,12-benzofurandiyl)]bis-, tetrakis[(acetyloxy)methyl] ester (SBFI)-monitored Na⁺ increase elicited by thapsigargin in primary cortical neurons. Accordingly, efficient TRPC6 knockdown prevented thapsigargin-induced intracellular Na⁺ elevation and SOCE. Collectively, we identify NCX1 as a new partner of STIM1 in mediating SOCE, whose activation in the reverse mode may be facilitated by the local increase of Na⁺ concentration due to the interaction between STIM1 and TRPC6 in primary cortical neurons.

Mutations in trpγ, the homologue of TRPC6 autism candidate gene, causes autism-like behavioral deficits in Drosophila

Autism Spectrum Disorder (ASD) is characterized by impaired social communication, restricted interests, and repetitive and stereotyped behaviors. The TRPC6 (transient receptor potential channel 6) represents an ASD candidate gene under an oligogenic/multifactorial model based on the initial description and cellular characterization of an individual with ASD bearing a de novo heterozygous mutation disrupting TRPC6, together with the enrichment of disruptive TRPC6 variants in ASD cases as compared to controls. Here, we perform a clinical re-evaluation of the initial non-verbal patient, and also present eight newly reported individuals ascertained for ASD and bearing predicted loss-of-function mutations in TRPC6. In order to understand the consequences of mutations in TRPC6 on nervous system function, we used the fruit fly, Drosophila melanogaster, to show that null mutations in transient receptor gamma (trpγ; the fly gene most similar to TRPC6), cause a number of behavioral defects that mirror features seen in ASD patients, including deficits in social interactions (based on courtship behavior), impaired sleep homeostasis (without affecting the circadian control of sleep), hyperactivity in both young and old flies, and defects in learning and memory. Some defects, most notably in sleep, differed in severity between males and females and became normal with age. Interestingly, hyperforin, a TRPC6 agonist and the primary active component of the St. John's wort antidepressant, attenuated many of the deficits expressed by trpγ mutant flies. In summary, our results provide further evidence that the TRPC6 gene is a risk factor for ASD. In addition, they show that the behavioral defects caused by mutations in TRPC6 can be modeled in Drosophila, thereby establishing a paradigm to examine the impact of mutations in other candidate genes.

Analysis of hyperforin (St. John's wort) action at TRPC6 channel leads to the development of a new class of antidepressant drugs

St. John's wort is an herb, long used in folk medicine for the treatment of mild depression. Its antidepressant constituent, hyperforin, has properties such as chemical instability and induction of drug-drug interactions that preclude its use for individual pharmacotherapies. Here we identify the transient receptor potential canonical 6 channel (TRPC6) as a druggable target to control anxious and depressive behavior and as a requirement for hyperforin antidepressant action. We demonstrate that TRPC6 deficiency in mice not only results in anxious and depressive behavior, but also reduces excitability of hippocampal CA1 pyramidal neurons and dentate gyrus granule cells. Using electrophysiology and targeted mutagenesis, we show that hyperforin activates the channel via a specific binding motif at TRPC6. We performed an analysis of hyperforin action to develop a new antidepressant drug that uses the same TRPC6 target mechanism for its antidepressant action. We synthesized the hyperforin analog Hyp13, which shows similar binding to TRPC6 and recapitulates TRPC6-dependent anxiolytic and antidepressant effects in mice. Hyp13 does not activate pregnan-X-receptor (PXR) and thereby loses the potential to induce drug-drug interactions. This may provide a new approach to develop better treatments for depression, since depression remains one of the most treatment-resistant mental disorders, warranting the development of effective drugs based on naturally occurring compounds.

Computer-Based Drug Design of Positive Modulators of Store-Operated Calcium Channels to Prevent Synaptic Dysfunction in Alzheimer's Disease

Store-operated calcium entry (SOCE) constitutes a fine-tuning mechanism responsible for the replenishment of intracellular stores. Hippocampal SOCE is regulated by store-operated channels (SOC) organized in tripartite complex TRPC6/ORAI2/STIM2. It is suggested that in neurons, SOCE maintains intracellular homeostatic Ca2+ concentration at resting conditions and is needed to support the structure of dendritic spines. Recent evidence suggests that positive modulators of SOC are prospective drug candidates to treat Alzheimer’s disease (AD) at early stages. Although STIM2 and ORAI2 are definitely involved in the regulation of nSOC amplitude and a play major role in AD pathogenesis, growing evidence suggest that it is not easy to target these proteins pharmacologically. Existing positive modulators of TRPC6 are unsuitable for drug development due to either bad pharmacokinetics or side effects. Thus, we concentrate the review on perspectives to develop specific nSOC modulators based on available 3D structures of TRPC6, ORAI2, and STIM2. We shortly describe the structural features of existing models and the methods used to prepare them. We provide commonly used steps applied for drug design based on 3D structures of target proteins that might be used to develop novel AD preventing therapy.

Abnormal amyloid beta metabolism in systemic abnormalities and Alzheimer's pathology: Insights and therapeutic approaches from periphery

Alzheimer's disease (AD) is an age-associated, multifactorial neurodegenerative disorder that is incurable. Despite recent success in treatments that partially improve symptomatic relief, they have failed in most clinical trials. Re-holding AD for accurate diagnosis and treatment is widely known as a challenging task. Lack of knowledge of basic molecular pathogenesis might be a possible reason for ineffective AD treatment. Historically, a majority of therapy-based studies have investigated the role of amyloid-β (Aβ peptide) in the central nervous system (CNS), whereas less is known about Aβ peptide in the periphery in AD. In this review, we provide a comprehensive summary of the current understanding of Aβ peptide metabolism (anabolism and catabolism) in the brain and periphery. We show that the abnormal metabolism of Aβ peptide is significantly linked with central-brain and peripheral abnormalities; the interaction between peripheral Aβ peptide metabolism and peripheral abnormalities affects central-brain Aβ peptide metabolism, suggesting the existence of significant communication between these two pathways of Aβ peptide metabolism. This close interaction between the central brain and periphery in abnormal Aβ peptide metabolism plays a key role in the development and progression of AD. In conclusion, we need to obtain a full understanding of the dynamic roles of Aβ peptide at the molecular level in both the brain and periphery in relation to the pathology of AD. This will not only provide new information regarding the complex disease pathology, but also offer potential new clues to improve therapeutic strategies and diagnostic biomarkers for the successful treatment of AD.

Bilobalide inhibits inflammation and promotes the expression of Aβ degrading enzymes in astrocytes to rescue neuronal deficiency in AD models

The pathogenesis of Alzheimer's disease (AD) involves multiple cell types including endothelial cells, glia, and neurons. It suggests that therapy against single target in single cell type may not be sufficient to treat AD and therapies with protective effects in multiple cell types may be more effective. Here, we comprehensively investigated the effects of bilobalide on neuroinflammation and Aβ degrading enzymes in AD cell model and mouse model. We find that bilobalide inhibits Aβ-induced and STAT3-dependent expression of TNF-α, IL-1β, and IL-6 in primary astrocyte culture. Bilobalide also induces robust expression of Aβ degrading enzymes like NEP, IDE, and MMP2 to facilitate astrocyte-mediated Aβ clearance. Moreover, bilobalide treatment of astrocyte rescues neuronal deficiency in co-cultured APP/PS1 neurons. Most importantly, bilobalide reduces amyloid and inflammation in AD mouse brain. Taken together, the protective effects of bilobalide in in vitro cultures were fully recapitulated in in vivo AD mouse model. Our study supports that bilobalide has therapeutic potential for AD treatment.

Selected transient receptor potential channel genes' expression in peripheral blood mononuclear cells of multiple sclerosis

Transient receptor potential channels have responsibilities in many cellular processes such as cytokine production, cell differentiation, and cytotoxicity by affecting intracellular cation levels or intracellular signal pathways. Multiple sclerosis is a chronic autoimmune central nervous system (CNS) disease caused by environmental and genetic factors. In this study, we aim to investigate TRPV1-TRPV4, TRPM2, TRPM4, TRPM7, TRPC6, and TRPA1 mRNA expression levels, which are associated with the inflammatory process, in the peripheral blood mononuclear cells (PBMCs) of relapsing-remitting multiple sclerosis (RRMS) patients. Thirty-five healthy controls and age-gender matched thirty patients with RRMS were involved in the study. TRPC6, TRPA1, TRPM2, TRPM4, TRPM7, TRPV1, TRPV2, TRPV3, and TRPV4 PBMCs mRNA expression levels were determined by qPCR. In the present study, the TRPC6, TRPM7, TRPV1, TRPV3, and TRPV4 mRNA expressions of RRMS patients in PBMCs decreased at a significant level compared to the healthy control group (p = .000, p = .000, p = .044, p = .000, p = .004, respectively). The decreased expression of TRPC6, TRPM7, TRPV1, TRPV3, and TRPV4 in PBMCs may be associated with the pathogenesis of MS. Further studies are required to understand the mechanism of the relation between these TRP channels and MS and other autoimmune diseases.

Hypoxia, Oxidative Stress, and Inflammation: Three Faces of Neurodegenerative Diseases

The cerebral hypoxia-ischemia can induce a wide spectrum of biologic responses that include depolarization, excitotoxicity, oxidative stress, inflammation, and apoptosis, and result in neurodegeneration. Several adaptive and survival endogenous mechanisms can also be activated giving an opportunity for the affected cells to remain alive, waiting for helper signals that avoid apoptosis. These signals appear to help cells, depending on intensity, chronicity, and proximity to the central hypoxic area of the affected tissue. These mechanisms are present not only in a large list of brain pathologies affecting commonly older individuals, but also in other pathologies such as refractory epilepsies, encephalopathies, or brain trauma, where neurodegenerative features such as cognitive and/or motor deficits sequelae can be developed. The hypoxia inducible factor 1α (HIF-1α) is a master transcription factor driving a wide spectrum cellular response. HIF-1α may induce erythropoietin (EPO) receptor overexpression, which provides the therapeutic opportunity to administer pharmacological doses of EPO to rescue and/or repair affected brain tissue. Intranasal administration of EPO combined with other antioxidant and anti-inflammatory compounds could become an effective therapeutic alternative, to avoid and/or slow down neurodegenerative deterioration without producing adverse peripheral effects.

AAV Delivery of shRNA Against TRPC6 in Mouse Hippocampus Impairs Cognitive Function

Transient Receptor Potential Canonical 6 (TRPC6) has been suggested to be involved in synapse function and contribute to hippocampal-dependent cognitive processes. Gene silencing of TRPC6 was performed by injecting adeno-associated virus (AAV) expressing TRPC6-specific shRNA (shRNA-TRPC6) into the hippocampal dentate gyrus (DG). Spatial learning, working memory and social recognition memory were impaired in the shRNA-TRPC6 treated mice compared to control mice after 4 weeks. In addition, gene ontology (GO) analysis of RNA-sequencing revealed that viral intervention of TRPC6 expression in DG resulted in the enrichment of the process of synaptic transmission and cellular compartment of synaptic structure. KEGG analysis showed PI3K-Akt signaling pathway were significantly down-regulated. Furthermore, the shRNA-TRPC6 treatment reduced dendritic spines of DG granule neurons, in terms of spine loss, the thin and mushroom types predominated. Accompanying the spine loss, the levels of PSD95, pAkt and CREB in the hippocampus were decreased in the shRNA-TRPC6 treated animals. Taken together, our results suggest that knocking down TRPC6 in the DG have a disadvantageous effect on cognitive processes.

Identification of key transcriptome biomarkers based on a vital gene module associated with pathological changes in Alzheimer's disease

Dysregulation of transcriptome expression has been reported to play an increasingly significant role in AD. In this study, we firstly identified a vital gene module associated with the accumulation of β-amyloid (Aβ) and phosphorylated tau (p-tau) using the WGCNA method. The vital module, named target module, was then employed for the identification of key transcriptome biomarkers. For coding RNA, GNA13 and GJA1 were identified as key biomarkers based on ROC analysis. As for non-coding RNA, MEG3, miR-106a-3p, and miR-24-3p were determined as key biomarkers based on analysis of a ceRNA network and ROC analysis. Experimental analyses firstly confirmed that GNA13, GJA1, and ROCK2, a downstream effector of GNA13, were all increased in 5XFAD mice, compared to littermate mice. Moreover, their expression was increased with aging in 5XFAD mice, as Aβ and p-tau pathology developed. Besides, the expression of key ncRNA biomarkers was verified to be decreased in 5XFAD mice. GSEA results indicated that GNA13 and GJA1 were respectively involved in ribosome and spliceosome dysfunction. MEG3, miR-106a-3p, and miR-24-3p were identified to be involved in MAPK pathway and PI3K-Akt pathway based on enrichment analysis. In summary, we identified several key transcriptome biomarkers, which promoted the prediction and diagnosis of AD.

Alpha 1-antichymotrypsin may be a biomarker for the progression of amnestic mild cognitive impairment

Alpha 1-antichymotrypsin (ACT), an acute-phase protein, has been reported to be increased in the brain and blood of Alzheimer's disease (AD) patients. However, few previous studies have focused on amnestic mild cognitive impairment (aMCI) patients. The aim of our study was to investigate the changing trend in ACT concentrations during the progression of aMCI. Hence, we measured the cerebrospinal fluid (CSF) and serum levels of ACT in aMCI subjects and normal controls (NC) at 2-year follow-up assessments using ELISA and Western blot. Forty-four NCs, 28 stable aMCI (sMCI) patients, and 20 progressive aMCI (pMCI) patients finished the follow-up assessments, and their data were used for analysis. We found that CSF and serum ACT levels of both sMCI and pMCI patients increased over time, while those of NCs remained stable; CSF and serum ACT levels were significantly higher in both sMCI and pMCI patients than in NCs, except for baseline serum ACT. In pMCI patients prior to developing AD, CSF and serum ACT levels were already significantly higher than those in sMCI patients. The ROC curve results demonstrated that combining CSF and serum ACT levels can distinguish aMCI patients from NCs with high specificity and sensitivity. Our data suggest that ACT may be a biomarker for diagnosing aMCI.

Functional Importance of Transient Receptor Potential (TRP) Channels in Neurological Disorders

Transient receptor potential (TRP) channels are transmembrane protein complexes that play important roles in the physiology and pathophysiology of both the central nervous system (CNS) and the peripheral nerve system (PNS). TRP channels function as non-selective cation channels that are activated by several chemical, mechanical, and thermal stimuli as well as by pH, osmolarity, and several endogenous or exogenous ligands, second messengers, and signaling molecules. On the pathophysiological side, these channels have been shown to play essential roles in the reproductive system, kidney, pancreas, lung, bone, intestine, as well as in neuropathic pain in both the CNS and PNS. In this context, TRP channels have been implicated in several neurological disorders, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and epilepsy. Herein, we focus on the latest involvement of TRP channels, with a special emphasis on the recently identified functional roles of TRP channels in neurological disorders related to the disruption in calcium ion homeostasis.

Contribution of TRPC Channels in Neuronal Excitotoxicity Associated With Neurodegenerative Disease and Ischemic Stroke

The seven canonical members of transient receptor potential (TRPC) proteins form cation channels that evoke membrane depolarization and intracellular calcium concentration ([Ca²⁺] _i ) rise, which are not only important for regulating cell function but their deregulation can also lead to cell damage. Recent studies have implicated complex roles of TRPC channels in neurodegenerative diseases including ischemic stroke. Brain ischemia reduces oxygen and glucose supply to neurons, i.e., Oxygen and Glucose Deprivation (OGD), resulting in [Ca²⁺] _i elevation, ion dyshomeostasis, and excitotoxicity, which are also common in many forms of neurodegenerative diseases. Although ionotropic glutamate receptors, e.g., N-methyl-D-aspartate receptors, are well established to play roles in excitotoxicity, the contribution of metabotropic glutamate receptors and their downstream effectors, i.e., TRPC channels, should not be neglected. Here, we summarize the current findings about contributions of TRPC channels in neurodegenerative diseases, with a focus on OGD-induced neuronal death and rodent models of cerebral ischemia/reperfusion. TRPC channels play both detrimental and protective roles to neurodegeneration depending on the TRPC subtype and specific pathological conditions involved. When illustrated the mechanisms by which TRPC channels are involved in neuronal survival or death seem differ greatly, implicating diverse and complex regulation. We provide our own data showing that TRPC1/C4/C5, especially TRPC4, may be generally detrimental in OGD and cerebral ischemia/reperfusion. We propose that although TRPC channels significantly contribute to ischemic neuronal death, detailed mechanisms and specific roles of TRPC subtypes in brain injury at different stages of ischemia/reperfusion and in different brain regions need to be carefully and systematically investigated.

Low-glucose-sensitive TRPC6 dysfunction drives hypoglycemia-induced cognitive impairment in diabetes

Background

Recurrent moderate hypoglycemia (RH), a major adverse effect of hypoglycemic therapy in diabetic patients, is one of the main risk factors for cognitive impairment and dementia. Transient receptor potential canonical channel 6 (TRPC6) is a potential therapeutic target for Alzheimer's disease (AD) and its expression is highly regulated by glucose concentration.

Objective

To investigate whether RH regulates the expression of TRPC6 in brain and whether TRPC6 dysfunction can drive hypoglycemia‐associated cognitive impairment in diabetes, and reveal the underlying mechanism.

Methods

Histological staining, in vivo two‐photon Ca²⁺ imaging, and behavioral tests were used to measure neuronal death, brain network activity, and cognitive function in mice, respectively. High‐resolution respirometry and transmission electron microscope were used to assess mitochondrial structure and function. Intracellular calcium measurement and molecular biology techniques were conducted to uncover the underlying mechanism.

Results

Here, we report that the expression of TRPC6 in hippocampus was specifically repressed by RH in streptozocin‐induced type 1 diabetic mice, but not in nondiabetic mice. TRPC6 knockout directly leads to neuron loss, neuronal activity, and cognitive function impairment under diabetic condition, the degree of which is similar to that of RH. Activation of TRPC6 with hyperforin substantially improved RH‐induced cognitive impairment. Mechanistically, TRPC6 inhibited mitochondrial fission in the hippocampus of diabetic mice undergoing RH episodes by activating adenosine 5‘‐monophosphate‐activated protein kinase, and TRPC6‐mediated cytosolic calcium influx was required for this process. Clinically, dysfunction of TRPC6 was closely associated with cognitive impairment in type 2 diabetic patients with RH.

Conclusions

Our results indicate that TRPC6 is a critical sensitive cation channel to hypoglycemia and is a promising target to prevent RH‐induced cognitive impairment by properly orchestrating the mitochondrial dynamics in diabetic patients.

Probing the therapeutic potential of TRPC6 for Alzheimer's disease in live neurons from patient-specific iPSCs

The induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to model and study Alzheimer's disease (AD) under patient-specific genetic background. The lower expression of transient receptor potential canonical 6 (TRPC6) was associated with AD patients, which might be involved in AD pathogenesis. However, the role of TRPC6 that played in AD process still needs more investigation in patient-relevant neurons. In this study, the iPSCs were generated from peripheral blood cells of sporadic AD patients and efficiently differentiated into mature cortical neurons. These sporadic AD-bearing neurons displayed higher levels of AD pathological markers Aβ and phospho-tau, but lower levels of TRPC6, than those of control neurons. Treatment of AD neurons with TRPC6 protein fragment or agonist inhibited the elevation of Aβ and phospho-tau. Our results in live AD neurons manifest that the compromised expression of TRPC6 substantially contributed to Aβ pathology of sporadic AD, suggesting that targeting TRPC6 could help to develop novel therapeutic strategies for the treatments of AD.

The top 100 most-cited articles citing human brain banking from 1970 to 2020: a bibliometric analysis

Many articles involving human brain banks have been published. Bibliometric analysis can determine the history of the development of research and future research trends in a specific field. Three independent researchers retrieved and reviewed articles from the Web of Science database using the following strategy: "TS = (((brain OR cerebral) AND (bank* OR biobank*)) OR brainbank*)." The top 100 most-cited articles were identified and listed in descending order by total citations. Web of Science was used to identify ten recent articles describing bank construction. GeenMedical ( https://www.geenmedical.com/ ) was used to identify ten recent articles from journals with an impact factor (IF) > 20. The top 100 most-cited articles citing human brain banks were published between 1991 and 2017. Fifty-two percent of the articles focused on a specific type of neurodegenerative disease, and 16% discussed the construction and development of human brain banks. Articles using brain tissue had more total and annual citations than those on bank construction. Ten articles with high IFs were published from 2017 to 2019, and they were primarily studies using novel research techniques such RNA sequencing and genome-wide association studies. Most studies were published in journals specializing in neurology or neuroscience such as Movement Disorders (10%), and had been conducted in the United States (52%) by neurologists (62%). The top 100 most-cited articles and recent publications citing human brain banks and their bibliometric characteristics were identified and analyzed, which may serve as a useful reference and pave the way for further research.

Circular RNAs regulate its parental genes transcription in the AD mouse model using two methods of library construction

Circular RNA (circRNA) is an important class of noncoding RNA. Current, protocols to detected circRNAs have utilized nonpolyadenylated RNAs, ribosomal RNA-depleted RNA samples (rRNA- library), and rRNA-depleted RNA that has been treated with RNase R to digest linear RNA (rRNA- RNase R+ library). Accumulating evidence suggests the participation of circRNAs in Alzheimer's disease (AD)-associated pathophysiology, but the details remain largely unknown. Here, we elucidated the brain circRNAs profiles of AD-model and WT mice using two methods of library construction (rRNA- RNase R+ libraries and rRNA- libraries). We focused on the construction of libraries that best allow the identification of circRNAs from next-generation RNA sequencing data. We obtained a significantly higher abundance of circRNAs in the rRNA- RNase R+ libraries than in the rRNA- libraries. Additionally, the rRNA- RNase R+ libraries more clearly revealed differentially expressed circRNAs. We performed a correlation analysis between differentially expressed circRNAs and their parental genes and performed KEGG analysis of the parental genes to explore the role of circRNA in AD. Our results identified significantly dysregulated circRNAs and KEGG analysis revealed that the identified circRNAs are involved in regulating AD development from distinct origins, including cAMP signaling, MAPK signaling, insulin secretion, Axon guidance, Long-term potentiation, dopaminergic synapse, and ErBb signaling pathways. Following rigorous selection, we identified several important circRNAs and mRNAs and propose the circRNAs regulate parental gene transcription or affect variable splicing, which were discovered to be mainly involved in Aβ production and cognitive performance (TRPC6) and neuronal differentiation and development (NME7). These newly identified circRNAs should serve as a valuable resource for the future development of potential biomarkers and therapeutic targets for AD.

TRP Channels as Emerging Therapeutic Targets for Neurodegenerative Diseases

The development of treatment for neurodegenerative diseases (NDs) such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis is facing medical challenges due to the increasingly aging population. However, some pharmaceutical companies have ceased the development of therapeutics for NDs, and no new treatments for NDs have been established during the last decade. The relationship between ND pathogenesis and risk factors has not been completely elucidated. Herein, we review the potential involvement of transient receptor potential (TRP) channels in NDs, where oxidative stress and disrupted Ca²⁺ homeostasis consequently lead to neuronal apoptosis. Reactive oxygen species (ROS) -sensitive TRP channels can be key risk factors as polymodal sensors, since progressive late onset with secondary pathological damage after initial toxic insult is one of the typical characteristics of NDs. Recent evidence indicates that the dysregulation of TRP channels is a missing link between disruption of Ca²⁺ homeostasis and neuronal loss in NDs. In this review, we discuss the latest findings regarding TRP channels to provide insights into the research and quests for alternative therapeutic candidates for NDs. As the structures of TRP channels have recently been revealed by cryo-electron microscopy, it is necessary to develop new TRP channel antagonists and reevaluate existing drugs.

Reversal of Calcium Dysregulation as Potential Approach for Treating Alzheimer's Disease

Despite decades of research and effort, there is still no effective disease-modifying treatment for Alzheimer's Disease (AD). Most of the recent AD clinical trials were targeting amyloid pathway, but all these trials failed. Although amyloid pathology is a hallmark and defining feature of AD, targeting the amyloid pathway has been very challenging due to low efficacy and serious side effects. Alternative approaches or mechanisms for our understanding of the major cause of memory loss in AD need to be considered as potential therapeutic targets. Increasing studies suggest that Ca2+ dysregulation in AD plays an important role in AD pathology and is associated with other AD abnormalities, such as excessive inflammation, increased ROS, impaired autophagy, neurodegeneration, synapse, and cognitive dysfunction. Ca2+ dysregulation in cytosolic space, Endoplasmic Reticulum (ER) and mitochondria have been reported in the context of various AD models. Drugs or strategies, to correct the Ca2+ dysregulation in AD, have been demonstrated to be promising as an approach for the treatment of AD in preclinical models. This review will discuss the mechanisms of Ca2+ dysregulation in AD and associated pathology and discuss potential approaches or strategies to develop novel drugs for the treatment of AD by targeting Ca2+ dysregulation.

Early detection of Alzheimer's disease by peptides from phage display screening

Alzheimer's disease (AD) is the most common neurodegenerative disorder without effective treatment so far. As clinical trials show that early-stage patients are more likely to respond to potential interventions, various technologies have been used to search blood biomarkers for the early diagnosis of AD. Phage display could be used to select specific peptides against desired target and here, we established a peptide binding assay based on phage display peptide library to detect early-stage AD patients. We first selected peptides from phage display library against plasmas from AD patients (n = 10) and normal healthy controls (n = 10), respectively, in the discovery set. Then, we further characterized one AD-specific peptide (AD#1 peptide) and one control-specific peptide (Con#1 peptide), and evaluated their diagnostic performance in independent validation set (35 AD patients, 45 MCI, 45 controls and 20 PD patients). Our results show that both AD#1 peptide and Con#1 peptide could distinguish AD/MCI patients from controls and combination of these two peptides could greatly improve the diagnostic performance (AUC is above 0.80 in ROC curve analysis). In addition, we found that AD#1 peptide stained Aβ-treated primary astrocyte and bound to recombinant human YKL-40 protein in in-vitro assay. It supports that AD#1 peptide detects AD inflammation related cytokine. Thus, the detection assay based on phage-derived peptides may offer a novel blood biomarker test for the early diagnosis of AD.

A systemic view of Alzheimer disease - insights from amyloid-β metabolism beyond the brain

Alzheimer disease (AD) is the most common type of dementia, and is currently incurable; existing treatments for AD produce only a modest amelioration of symptoms. Research into this disease has conventionally focused on the CNS. However, several peripheral and systemic abnormalities are now understood to be linked to AD, and our understanding of how these alterations contribute to AD is becoming more clearly defined. This Review focuses on amyloid-β (Aβ), a major hallmark of AD. We review emerging findings of associations between systemic abnormalities and Aβ metabolism, and describe how these associations might interact with or reflect on the central pathways of Aβ production and clearance. On the basis of these findings, we propose that these abnormal systemic changes might not only develop secondary to brain dysfunction but might also affect AD progression, suggesting that the interactions between the brain and the periphery have a crucial role in the development and progression of AD. Such a systemic view of the molecular pathogenesis of AD could provide a novel perspective for understanding this disease and present new opportunities for its early diagnosis and treatment.

TRPC6 mRNA levels in peripheral leucocytes of patients with Alzheimer's disease and mild cognitive impairment: A case-control study

BACKGROUND

Transient receptor potential canonical (TRPC) 6 inhibits Aβ in Alzheimer's disease (AD) mouse brain and improves the behavioral performance.

AIMS

To evaluate the association of TRPC6 expression in peripheral leucocytes from AD and mild cognitive impairment (MCI) patients and to explore its potential value in early diagnosis of AD.

METHODS

TRPC6 mRNA levels in peripheral leucocytes were detected by quantitative real-time PCR. The Spearman correlation test was used to ascertain the associations between TRPC6 and the scores of MMSE, ADL, CSDD, CDR. The Receiver Operating Characteristic (ROC) curve was drawn to evaluate the diagnostic potential of TRPC6 for AD and MCI.

RESULTS

There were 108 CE, 136 MCI, 164 Con and 60 PD in the study. The expression of TRPC6 mRNA level in peripheral leucocytes was significantly lower: 1) in patients with AD and MCI compared to Con; 2) in AD compared to MCI; 3) in hospitalized AD compared to AD from communities. There was a significantly positive correlation between TRPC6 mRNA and MMSE score (p = .001, R = 0.327). Significantly inverse correlations were found between TRPC6 and CDR score (p < 0.001, R = -0.303) as well as between TRPC6 and ADL score (p = .001, R = -0.342) for all AD. The area under curve of ROC was 0.881 for the classification of AD, and 0.706 for the classification of MCI, respectively.

CONCLUSION

TRPC6 expression is inversely correlated with cognitive performance of AD. TRPC6 in peripheral leucocytes may be a potential biomarker for the diagnosis of AD.

Neurotrophin Receptor p75 mRNA Level in Peripheral Blood Cells of Patients with Alzheimer's Disease

The neurotrophin receptor p75 (p75NTR) plays important roles in regulating amyloid-beta (Aβ) metabolism in the brain. The expression of p75NTR is altered in the brain of patients with Alzheimer's disease (AD). In this study, we aimed to evaluate whether p75NTR mRNA level in the peripheral blood cells is changed among AD patients and its potential to be a biomarker for AD. The study subjects included 26 patients with AD (PiB-PET positive) and 28 cognitively normal controls (PiB-PET negative). RNA was extracted from peripheral blood cells of fast blood. p75NTR mRNA was measured using quantitative real-time PCR assay. p75NTR mRNA levels in blood cells were comparable between AD patients and controls. p75NTR mRNA levels in blood cells were not correlated with MMSE scores, ApoE genotypes, gender, and age. p75NTR mRNA expression in blood cells is not changed in AD patients and is unlikely to be a biomarker for AD.

Circular HDAC9/microRNA-138/Sirtuin-1 Pathway Mediates Synaptic and Amyloid Precursor Protein Processing Deficits in Alzheimer's Disease

Synaptic dysfunction and abnormal processing of amyloid precursor protein (APP) are early pathological features in Alzheimer's disease (AD). Recently, non-coding RNAs such as microRNAs (miRNAs) and circular RNAs (circRNAs) have been reported to contribute to the pathogenesis of AD. We found an age-dependent elevation of miR-138 in APP/PS1 (presenilin-1) mice. MiR-138 inhibited the expression of ADAM10 [a disintegrin and metalloproteinase domain-containing protein 10], promoted amyloid beta (Aβ) production, and induced synaptic and learning/memory deficits in APP/PS1 mice, while its suppression alleviated the AD-like phenotype in these mice. Overexpression of sirtuin 1 (Sirt1), a target of miR-138, ameliorated the miR-138-induced inhibition of ADAM10 and elevation of Aβ in vitro. The circRNA HDAC9 (circHDAC9) was predicted to contain a miR-138 binding site in several databases. Its expression was inversely correlated with miR-138 in both Aβ-oligomer-treated N2a cells and APP/PS1 mice, and it co-localized with miR-138 in the cytoplasm of N2a cells. CircHDAC9 acted as a miR-138 sponge, decreasing miR-138 expression, and reversing the Sirt1 suppression and excessive Aβ production induced by miR-138 in vitro. Moreover, circHDAC9 was decreased in the serum of both AD patients and individuals with mild cognitive impairment. These results suggest that the circHDAC9/miR-138/Sirt1 pathway mediates synaptic function and APP processing in AD, providing a potential therapeutic target for its treatment.

Derivatives of Piperazines as Potential Therapeutic Agents for Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is the major cause of dementia in the elderly. There is no cure against AD. We have recently discovered a novel transient receptor potential canonical 6 (TRPC6)-mediated intracellular signaling pathway that regulates the stability of dendritic spines and plays a role in memory formation. We have previously shown that TRPC6 agonists exert beneficial effects in models of AD and may serve as lead compounds for development of AD therapeutic agents. In the current study, we used the Clarivate Analytics Integrity database to search for additional TRPC6 agonists. We selected four compounds to study as potential neuroprotective agents. We applied bioinformatics analyses to test the basic pharmacological properties of the selected compounds. We performed in vitro screening of these compounds to validate their ability to protect mushroom spines from amyloid toxicity and determined that two of these compounds exert neuroprotective effects in the nanomolar concentration range. We have chosen one of these compounds [piperazine (PPZ)] for further testing. In agreement with previously published data, we have shown that PPZ potentiates TRPC6 channels. We demonstrated that the neuroprotective mechanism of the investigated PPZ is based on activation of neuronal store-operated calcium entry in spines. We have shown that PPZ restores long-term potentiation induction in 6-month-old 5xFAD mouse hippocampal slices. The obtained results suggest that PPZ and its derivatives are potential lead molecules for development of AD therapeutic agents.

TRPC6 expression in neurons is differentially regulated by NR2A- and NR2B-containing NMDA receptors

The expression of transient receptor potential canonical 6 (TRPC6) in central nervous system (CNS) is important for neuronal functions and certain neural disorders. However, the regulatory mechanism of TRPC6 expression in neurons is still obscure. In this study, we show that TRPC6 expression in the primary cultured cortical neurons is bidirectionally regulated by glutamate. Activation of NR2A-containing NMDARs induces TRPC6 transcription through a calcineurin-dependent pathway. In contrast, activation of NR2B-containing NMDARs causes TRPC6 degradation through calpain. Thus, TRPC6 expression in neurons is regulated by glutamate in a bidirectional manner that is dependent on NR2A and NR2B.