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The Binding of Different Substrate Molecules at the Docking Site and the Active Site of γ-Secretase Can Trigger Toxic Events in Sporadic and Familial Alzheimer's Disease. Int J Mol Sci 2023; 24:ijms24031835. [PMID: 36768156 PMCID: PMC9915333 DOI: 10.3390/ijms24031835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 01/09/2023] [Accepted: 01/11/2023] [Indexed: 01/19/2023] Open
Abstract
Pathogenic changes in γ-secretase activity, along with its response to different drugs, can be affected by changes in the saturation of γ-secretase with its substrate. We analyze the saturation of γ-secretase with its substrate using multiscale molecular dynamics studies. We found that an increase in the saturation of γ-secretase with its substrate could result in the parallel binding of different substrate molecules at the docking site and the active site. The C-terminal domain of the substrate bound at the docking site can interact with the most dynamic presenilin sites at the cytosolic end of the active site tunnel. Such interactions can inhibit the ongoing catalytic activity and increase the production of the longer, more hydrophobic, and more toxic Aβ proteins. Similar disruptions in dynamic presenilin structures can be observed with different drugs and disease-causing mutations. Both, C99-βCTF-APP substrate and its different Aβ products, can support the toxic aggregation. The aggregation depends on the substrate N-terminal domain. Thus, the C99-βCTF-APP substrate and β-secretase path can be more toxic than the C83-αCTF-APP substrate and α-secretase path. Nicastrin can control the toxic aggregation in the closed conformation. The binding of the C99-βCTF-APP substrate to γ-secretase can be controlled by substrate channeling between the nicastrin and β-secretase. We conclude that the presented two-substrate mechanism could explain the pathogenic changes in γ-secretase activity and Aβ metabolism in different sporadic and familial cases of Alzheimer's disease. Future drug-development efforts should target different cellular mechanisms that regulate the optimal balance between γ-secretase activity and amyloid metabolism.
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Svedružić ŽM, Vrbnjak K, Martinović M, Miletić V. Structural Analysis of the Simultaneous Activation and Inhibition of γ-Secretase Activity in the Development of Drugs for Alzheimer's Disease. Pharmaceutics 2021; 13:pharmaceutics13040514. [PMID: 33917979 PMCID: PMC8068388 DOI: 10.3390/pharmaceutics13040514] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 03/31/2021] [Accepted: 04/06/2021] [Indexed: 12/24/2022] Open
Abstract
Significance: The majority of the drugs which target membrane-embedded protease γ-secretase show an unusual biphasic activation–inhibition dose-response in cells, model animals, and humans. Semagacestat and avagacestat are two biphasic drugs that can facilitate cognitive decline in patients with Alzheimer’s disease. Initial mechanistic studies showed that the biphasic drugs, and pathogenic mutations, can produce the same type of changes in γ-secretase activity. Results: DAPT, semagacestat LY-411,575, and avagacestat are four drugs that show different binding constants, and a biphasic activation–inhibition dose-response for amyloid-β-40 products in SH-SY5 cells. Multiscale molecular dynamics studies have shown that all four drugs bind to the most mobile parts in the presenilin structure, at different ends of the 29 Å long active site tunnel. The biphasic dose-response assays are a result of the modulation of γ-secretase activity by the concurrent binding of multiple drug molecules at each end of the active site tunnel. The drugs activate γ-secretase by facilitating the opening of the active site tunnel, when the rate-limiting step is the tunnel opening, and the formation of the enzyme–substrate complex. The drugs inhibit γ-secretase as uncompetitive inhibitors by binding next to the substrate, to dynamic enzyme structures which regulate processive catalysis. The drugs can modulate the production of different amyloid-β catalytic intermediates by penetration into the active site tunnel, to different depths, with different flexibility and different binding affinity. Conclusions: Biphasic drugs and pathogenic mutations can affect the same dynamic protein structures that control processive catalysis. Successful drug-design strategies must incorporate transient changes in the γ-secretase structure in the development of specific modulators of its catalytic activity.
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Affiliation(s)
- Željko M. Svedružić
- Department of Biotechnology, University of Rijeka, 51000 Rijeka, Croatia; (K.V.); (M.M.)
- Laboratory for Medical Biochemistry, Psychiatric Hospital Rab, Kampor 224, 51280 Rab, Croatia
- Correspondence:
| | - Katarina Vrbnjak
- Department of Biotechnology, University of Rijeka, 51000 Rijeka, Croatia; (K.V.); (M.M.)
- Laboratory for Mechanisms of Cell Transformation (VIB-KU Leuven), ON IV Herestraat—Box 912, 3000 Leuven, Belgium
| | - Manuel Martinović
- Department of Biotechnology, University of Rijeka, 51000 Rijeka, Croatia; (K.V.); (M.M.)
| | - Vedran Miletić
- Department of Informatics, University of Rijeka, 51000 Rijeka, Croatia;
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Imbimbo BP, Lucca U, Watling M. Can Anti-β-amyloid Monoclonal Antibodies Work in Autosomal Dominant Alzheimer Disease? NEUROLOGY-GENETICS 2020; 7:e535. [PMID: 33575481 PMCID: PMC7862085 DOI: 10.1212/nxg.0000000000000535] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Accepted: 09/15/2020] [Indexed: 12/14/2022]
Abstract
The dominant theory of Alzheimer disease (AD) has been that amyloid-β (Aβ) accumulation in the brain is the initial cause of the degeneration leading to cognitive and functional deficits. Autosomal dominant Alzheimer disease (ADAD), in which pathologic mutations of the amyloid precursor protein (APP) or presenilins (PSENs) genes are known to cause abnormalities of Aβ metabolism, should thus offer perhaps the best opportunity to test anti-Aβ drugs. Two long-term preventive studies (Dominantly Inherited Alzheimer Network Trials Unit Adaptive Prevention Trial [DIAN-TU-APT] and Alzheimer Preventive Initiative-ADAD) were set up to evaluate the efficacy of monoclonal anti-Aβ antibodies (solanezumab, gantenerumab, and crenezumab) in carriers of ADAD, but the results of the DIAN-TU-APT study have shown that neither solanezumab nor gantenerumab slowed cognitive decline in 144 subjects with ADAD followed for 4 years, despite one of the drugs (gantenerumab) significantly affected biomarkers relevant to their intended mechanism of action. Surprisingly, solanezumab significantly accelerated cognitive decline of both asymptomatic and symptomatic subjects. These failures further undermine the Aβ hypothesis and could support the suggestion that ADAD is triggered by accumulation of other APP metabolites, rather than Aβ.
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Affiliation(s)
- Bruno P Imbimbo
- Department of Research & Development (B.P.I.), Chiesi Farmaceutici, Parma, Italy; Laboratory of Geriatric Neuropsychiatry (U.L.), Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milano, Italy; and CNS & Pain Department (M.W.), TranScrip Partners, Reading, United Kingdom
| | - Ugo Lucca
- Department of Research & Development (B.P.I.), Chiesi Farmaceutici, Parma, Italy; Laboratory of Geriatric Neuropsychiatry (U.L.), Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milano, Italy; and CNS & Pain Department (M.W.), TranScrip Partners, Reading, United Kingdom
| | - Mark Watling
- Department of Research & Development (B.P.I.), Chiesi Farmaceutici, Parma, Italy; Laboratory of Geriatric Neuropsychiatry (U.L.), Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milano, Italy; and CNS & Pain Department (M.W.), TranScrip Partners, Reading, United Kingdom
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Majdi A, Sadigh-Eteghad S, Rahigh Aghsan S, Farajdokht F, Vatandoust SM, Namvaran A, Mahmoudi J. Amyloid-β, tau, and the cholinergic system in Alzheimer's disease: seeking direction in a tangle of clues. Rev Neurosci 2020; 31:391-413. [PMID: 32017704 DOI: 10.1515/revneuro-2019-0089] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/22/2019] [Indexed: 12/14/2022]
Abstract
The link between histopathological hallmarks of Alzheimer's disease (AD), i.e. amyloid plaques, and neurofibrillary tangles, and AD-associated cognitive impairment, has long been established. However, the introduction of interactions between amyloid-beta (Aβ) as well as hyperphosphorylated tau, and the cholinergic system to the territory of descriptive neuropathology has drastically changed this field by adding the theory of synaptic neurotransmission to the toxic pas de deux in AD. Accumulating data show that a multitarget approach involving all amyloid, tau, and cholinergic hypotheses could better explain the evolution of events happening in AD. Various species of both Aβ and tau could be traced in cholinergic neurons of the basal forebrain system early in the course of the disease. These molecules induce degeneration in the neurons of this system. Reciprocally, aberrant cholinergic system modulation promotes changes in amyloid precursor protein (APP) metabolism and tau phosphorylation, resulting in neurotoxicity, neuroinflammation, and neuronal death. Altogether, these changes may better correlate with the clinical findings and cognitive impairment detected in AD patients. Failure of several of Aβ- and tau-related therapies further highlights the need for special attention to molecules that target all of these mentioned pathologic changes. Another noteworthy fact here is that none of the popular hypotheses of AD such as amyloidopathy or tauopathy seem to be responsible for the changes observed in AD alone. Thus, the main culprit should be sought higher in the stream somewhere in APP metabolism or Wnt signaling in the cholinergic system of the basal forebrain. Future studies should target these pathological events.
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Affiliation(s)
- Alireza Majdi
- Neurosciences Research Center (NSRC), Tabriz University of Medical Sciences, Tabriz 51368, Iran
| | - Saeed Sadigh-Eteghad
- Neurosciences Research Center (NSRC), Tabriz University of Medical Sciences, Tabriz 51368, Iran
| | - Sepideh Rahigh Aghsan
- Department of Clinical Pharmacy, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz 51368, Iran
| | - Fereshteh Farajdokht
- Neurosciences Research Center (NSRC), Tabriz University of Medical Sciences, Tabriz 51368, Iran
| | - Seyed Mehdi Vatandoust
- Neurosciences Research Center (NSRC), Tabriz University of Medical Sciences, Tabriz 51368, Iran
| | - Ali Namvaran
- Immunology Research Center, Tabriz University of Medical Sciences, Tabriz 51368, Iran
| | - Javad Mahmoudi
- Neurosciences Research Center (NSRC), Tabriz University of Medical Sciences, Tabriz 51368, Iran
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Blanco JA, Alonso A, Blanco J, Rojo E, Tellería JJ, Torres MA, Uribe F. Novel presenilin 1 mutation (p.Thr-Pro116-117Ser-Thr) in a Spanish family with early-onset Alzheimer's disease. Neurobiol Aging 2019; 84:238.e19-238.e24. [PMID: 31204041 DOI: 10.1016/j.neurobiolaging.2019.05.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2019] [Revised: 05/15/2019] [Accepted: 05/16/2019] [Indexed: 11/26/2022]
Abstract
Presenilin 1 (PSEN1) is a γ-secretase component, which is in charge of the amyloid precursor protein (APP) cleavage. APP is believed to play a central role in the pathogenesis of Alzheimer's disease (AD). PSEN1 mutations are the most important causes of familial AD, being related to the earlier onset and rapid progression of the disease. Presenilins and APP mutations represent an extraordinary opportunity to study the pathophysiology of AD. We describe the clinical and genetic study of a 37-year-old male patient with a novel mutation in PSEN1 (p.Thr-Pro116-117Ser-Thr). We have studied the pedigree of his family with a further 9 members affected, all of them with onset in their 30s. We have also described the clinical data and results of brain biopsies in 2 of them. DNA sequencing of a tissue sample from an uncle of the patient, who died of AD in the 80s, showed the same mutation as in the patient. These data and predictive analysis indicate the pathogenicity of the mutation.
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Affiliation(s)
- Jose Antonio Blanco
- Psychiatry Service, Clinical University Hospital of Valladolid, Valladolid, Spain; School of Medicine, University of Valladolid, Valladolid, Spain.
| | - Adrian Alonso
- Psychiatry Service, Clinical University Hospital of Valladolid, Valladolid, Spain
| | - Jorge Blanco
- Psychiatry Service, Basurto Hospital of Bilbao, Bilbao, Spain
| | - Esther Rojo
- Neurology Service, Clinical University Hospital of Valladolid, Valladolid, Spain
| | | | - Maria Angeles Torres
- Histopathology Service, Rio Hortega University Hospital of Valladolid, Valladolid, Spain
| | - Fernando Uribe
- Psychiatry Service, Clinical University Hospital of Valladolid, Valladolid, Spain
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Presenilins as Drug Targets for Alzheimer's Disease-Recent Insights from Cell Biology and Electrophysiology as Novel Opportunities in Drug Development. Int J Mol Sci 2018; 19:ijms19061621. [PMID: 29857474 PMCID: PMC6032171 DOI: 10.3390/ijms19061621] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2018] [Revised: 05/26/2018] [Accepted: 05/28/2018] [Indexed: 01/24/2023] Open
Abstract
A major cause underlying familial Alzheimer's disease (AD) are mutations in presenilin proteins, presenilin 1 (PS1) and presenilin 2 (PS2). Presenilins are components of the γ-secretase complex which, when mutated, can affect amyloid precursor protein (APP) processing to toxic forms of amyloid beta (Aβ). Consequently, presenilins have been the target of numerous and varied research efforts to develop therapeutic strategies for AD. The presenilin 1 gene harbors the largest number of AD-causing mutations resulting in the late onset familial form of AD. As a result, the majority of efforts for drug development focused on PS1 and Aβ. Soon after the discovery of the major involvement of PS1 and PS2 in γ-secretase activity, it became clear that neuronal signaling, particularly calcium ion (Ca2+) signaling, is regulated by presenilins and impacted by mutations in presenilin genes. Intracellular Ca2+ signaling not only controls the activity of neurons, but also gene expression patterns, structural functionality of the cytoskeleton, synaptic connectivity and viability. Here, we will briefly review the role of presenilins in γ-secretase activity, then focus on the regulation of Ca2+ signaling, oxidative stress, and cellular viability by presenilins within the context of AD and discuss the relevance of presenilins in AD drug development efforts.
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Kametani F, Hasegawa M. Reconsideration of Amyloid Hypothesis and Tau Hypothesis in Alzheimer's Disease. Front Neurosci 2018; 12:25. [PMID: 29440986 PMCID: PMC5797629 DOI: 10.3389/fnins.2018.00025] [Citation(s) in RCA: 493] [Impact Index Per Article: 82.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 01/12/2018] [Indexed: 12/20/2022] Open
Abstract
The so-called amyloid hypothesis, that the accumulation and deposition of oligomeric or fibrillar amyloid β (Aβ) peptide is the primary cause of Alzheimer's disease (AD), has been the mainstream concept underlying AD research for over 20 years. However, all attempts to develop Aβ-targeting drugs to treat AD have ended in failure. Here, we review recent findings indicating that the main factor underlying the development and progression of AD is tau, not Aβ, and we describe the deficiencies of the amyloid hypothesis that have supported the emergence of this idea.
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Affiliation(s)
- Fuyuki Kametani
- Department of Dementia and Higher Brain Function, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Masato Hasegawa
- Department of Dementia and Higher Brain Function, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
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Dias RA, Gonçalves BP, da Rocha JF, da Cruz E Silva OAB, da Silva AMF, Vieira SI. NeuronRead, an open source semi-automated tool for morphometric analysis of phase contrast and fluorescence neuronal images. Mol Cell Neurosci 2017; 85:57-69. [PMID: 28847569 DOI: 10.1016/j.mcn.2017.08.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Revised: 07/07/2017] [Accepted: 08/10/2017] [Indexed: 11/30/2022] Open
Abstract
Neurons are specialized cells of the Central Nervous System whose function is intricately related to the neuritic network they develop to transmit information. Morphological evaluation of this network and other neuronal structures is required to establish relationships between neuronal morphology and function, and may allow monitoring physiological and pathophysiologic alterations. Fluorescence-based microphotographs are the most widely used in cellular bioimaging, but phase contrast (PhC) microphotographs are easier to obtain, more affordable, and do not require invasive, complicated and disruptive techniques. Despite the various freeware tools available for fluorescence-based images analysis, few exist that can tackle the more elusive and harder-to-analyze PhC images. To surpass this, an interactive semi-automated image processing workflow was developed to easily extract relevant information (e.g. total neuritic length, average cell body area) from both PhC and fluorescence neuronal images. This workflow, named 'NeuronRead', was developed in the form of an ImageJ macro. Its robustness and adaptability were tested and validated on rat cortical primary neurons under control and differentiation inhibitory conditions. Validation included a comparison to manual determinations and to a golden standard freeware tool for fluorescence image analysis. NeuronRead was subsequently applied to PhC images of neurons at distinct differentiation days and exposed or not to DAPT, a pharmacological inhibitor of the γ-secretase enzyme, which cleaves the well-known Alzheimer's amyloid precursor protein (APP) and the Notch receptor. Data obtained confirms a neuritogenic regulatory role for γ-secretase products and validates NeuronRead as a time- and cost-effective useful monitoring tool.
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Affiliation(s)
- Roberto A Dias
- Cell Differentiation and Regeneration group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal; Neurosciences and Signalling group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal
| | - Bruno P Gonçalves
- Cell Differentiation and Regeneration group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal; Neurosciences and Signalling group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal
| | - Joana F da Rocha
- Cell Differentiation and Regeneration group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal; Neurosciences and Signalling group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal
| | - Odete A B da Cruz E Silva
- Neurosciences and Signalling group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal
| | - Augusto M F da Silva
- Instituto de Engenharia Electrónica e Telemática (IEETA), Departamento de Electrónica e Telecomunicações (DETI), Universidade de Aveiro, Aveiro, Portugal
| | - Sandra I Vieira
- Cell Differentiation and Regeneration group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal; Neurosciences and Signalling group, Institute of Biomedicine (iBiMED), Department of Medical Sciences, Universidade de Aveiro, Aveiro, Portugal.
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In silico design of the first DNA-independent mechanism-based inhibitor of mammalian DNA methyltransferase Dnmt1. PLoS One 2017; 12:e0174410. [PMID: 28399172 PMCID: PMC5388339 DOI: 10.1371/journal.pone.0174410] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2016] [Accepted: 03/08/2017] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND We use our earlier experimental studies of the catalytic mechanism of DNA methyltransferases to prepare in silico a family of novel mechanism-based inhibitors of human Dnmt1. Highly specific inhibitors of DNA methylation can be used for analysis of human epigenome and for the creation of iPS cells. RESULTS We describe a set of adenosyl-1-methyl-pyrimidin-2-one derivatives as novel mechanism-based inhibitors of mammalian DNA methyltransferase Dnmt1. The inhibitors have been designed to bind simultaneously in the active site and the cofactor site and thus act as transition-state analogues. Molecular dynamics studies showed that the lead compound can form between 6 to 9 binding interactions with Dnmt1. QM/MM analysis showed that the upon binding to Dnmt1 the inhibitor can form a covalent adduct with active site Cys1226 and thus act as a mechanism-based suicide-inhibitor. The inhibitor can target DNA-bond and DNA-free form of Dnmt1, however the suicide-inhibition step is more likely to happen when DNA is bound to Dnmt1. The validity of presented analysis is described in detail using 69 modifications in the lead compound structure. In total 18 of the presented 69 modifications can be used to prepare a family of highly specific inhibitors that can differentiate even between closely related enzymes such as Dnmt1 and Dnmt3a DNA methyltransferases. CONCLUSIONS Presented results can be used for preparation of some highly specific and potent inhibitors of mammalian DNA methylation with specific pharmacological properties.
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Strain-Specific Altered Regulatory Response of Rab7a and Tau in Creutzfeldt-Jakob Disease and Alzheimer's Disease. Mol Neurobiol 2016; 54:697-709. [PMID: 26768426 DOI: 10.1007/s12035-016-9694-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 01/05/2016] [Indexed: 09/29/2022]
Abstract
There is an increasing demand for the understanding of pathophysiology on neurodegeneration diseases at early stages. Changes in endocytic machinery and the cytoskeleton-associated response are the first alterations observed in Creutzfeldt-Jakob disease (CJD) and Alzheimer's disease AD brain. In this study, we performed a targeted search for endocytic pathway proteins in the different regions of the brain. We found late endosome marker Rab7a which was significantly upregulated in the frontal cortex region in the rapid progressive CJD form (MM1) and rapid progressive AD (rpAD) forms. However, Rab9 expression was significantly downregulated only in CJD-MM1 brain frontal cortex region. In the cerebellum, Rab7a expression showed significant upregulation in both subtype MM1 and VV2 CJD forms, in contrast to Rab9 which showed significant downregulation in both subtype MM1 and VV2 CJD forms at terminal stage of the disease. To check regulatory response at pre-symptomatic stage of the disease, we checked the regulatory interactive response of Rab7a, Rab9, and known biomarkers PrPC and tau forms in frontal cortex at pre-symptomatic stage of the disease in tg340 mice expressing about fourfold of human PrP-M129 with PrP-null background that had been inoculated with human sCJD MM1 brain tissue homogenates (sCJD MM1 mice). In addition, we analyzed 5XFAD mice, exhibiting five mutations in the APP and presenilin genes related to familial Alzheimer's disease (FAD), to validate specific regulatory response of Rab7a, Rab9, tau, and phosphorylated form of tau by immunostaining 5XFAD mice in comparison with the wild-type age-matched mice brain. The cortical region of 5XFAD mice brain showed accumulated form of Rab7a in puncta that co-label for p-Tau, indicating colocalization by using confocal laser-scanning microscopy and was confirmed by using reverse co-immunoprecipitation. Furthermore, synthetic RNA (siRNA) against the Rab7a gene decreased expression of Rab7a protein, in cortical primary neuronal cultures of PrPC wild type. This depleted expression of Rab7a led to the increased accumulation of PrPC in Rab9-positive endosomal compartments and consequently an increased co-localization between PrPC/Rab9; however, total tau level decreased. Interestingly, siRNA against tau gene in cortical primary neuronal cultures of PrPC wild-type mice showed enhanced Rab7a and Rab9 expression and increase formation of dendritic spines. The work described highlighted the selective involvement of late endosomal compartment marker Rab7a in CJD, slow and rapid progressive forms of AD pathogenesis.
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