Exploring the potential role of rab5 protein in endo-lysosomal impairment in Alzheimer's disease

Neurotoxic effects of coronavirus: Potential implications in Alzheimer's onset and progression

The COVID-19, caused by SARS-CoV-2, first affects the respiratory tract but evidence is emerging that the virus, reaching the central nervous system (CNS), can lead to severe neurological disorders. In particular, CoV infection could cause an acceleration of the neurodegenerative process. On the other hand, patients diagnosed with Alzheimer's disease (AD) develop more serious forms of COVID-19 with worse relapses. Therefore, understanding the connection between the two pathologies, AD and infection by coronavirus, could help in the development of new therapeutic approaches to counter them. We used the SH-SY5Y cell line differentiated into neurons, as widely used in studies of AD if supplemented with exogenous fibrillary β-amyloid (Aβ). As a glial counterpart, human microglia (HMC3) and astrocytic (D54MG) cell lines were used to create co-cultures with neurons via transwell systems. In these experimental models, we generated infection with the Human Coronavirus OC43 (HCoV-OC43), a low-risk model of SARS-CoV-2. Our results suggest that the infection by HCoV-OC43 leads to a neurotoxic effect not depending on an already present event of Aβ deposition. Indeed, unlike microglia, neurons and even more astrocytes are susceptible to CoV infection and, although the infection does not show a cytotoxic effect in the neurons in the first few days, significant alterations at a biochemical and morphological level have been observed, suggesting that the neurons are reacting to a stressful condition, including the prodromal and neurodegenerative features of AD. Interestingly, the interaction of infected astrocytes with the neurons resulted in the manifestation of signs of neurodegeneration, such as amyloid-beta deposition. By using exogenous fibrillary Aβ, as an AD in vitro model, our data suggest that there is an aggravating effect both on the infection itself and on the neurological disease progression. In conclusion, the results of this study suggest a causal interplay between HCoV-OC43 and neurological diseases and demonstrate that the co-presence of different CNS cell populations is the necessary condition to study the pathogenic effects in vitro as a whole.

An insight into structure-activity relationship of naturally derived biological macromolecules for the treatment of Alzheimer's disease: a review

Alzheimer's disease (AD) is a neurological disorder that affects millions of people worldwide. There are currently no cures for AD, although various drugs are used to manage the symptoms and reduce the disease's progression. AChE inhibitors such as rivastigmine, donepezil, galantamine, and the NMDA glutamate receptor antagonist memantine are currently FDA-approved drugs used in the treatment of AD. Recently, naturally derived biological macromolecules have shown promising results in the treatment of AD. Several biological macromolecules derived from natural sources are in various stages of preclinical and clinical trials. During the literature search, it was observed that there is a lack of a comprehensive review that particularly focuses on the role of naturally derived biological macromolecules (protein, carbohydrates, lipids, and nucleic acids) in the treatment of AD and the structure-activity relationship (SAR) approach for understanding the medicinal chemistry perspective. This review focuses on the SAR and probable mechanisms of action of biological macromolecules derived from natural sources for the treatment of AD, including peptides, proteins, enzymes, and polysaccharides. The paper further addresses the therapeutic possibilities of monoclonal antibodies, enzymes, and vaccines for the treatment of AD. Overall, the review provides insight into the SAR of naturally derived biological macromolecules in the treatment of AD. The ongoing research in this field holds great promise for the future development of AD treatment and provides hope for individuals affected by this devastating disease.Communicated by Ramaswamy H. Sarma.

CD2AP is Co-Expressed with Tropomyosin-Related Kinase A and Ras-Related Protein Rab-5A in Cholinergic Neurons of the Murine Basal Forebrain

Basal forebrain cholinergic neurons project to the hippocampus and cortex, are critical for learning and memory, and are central to the pathogenesis of Alzheimer's disease (AD). GWAS have consistently shown that genomic variants at the CD2AP gene locus are associated with significant increased risk of AD. GWAS studies have also shown that genetic variants in endocytosis genes, including RAB5A , significantly increase susceptibility to AD. Previous work in our lab has shown that CD2AP functions as a docking-scaffold/adaptor protein as a coordinator of nerve growth factor (NGF) and trophic signaling in neurons. We have also demonstrated that CD2AP positively regulates Rab5-mediated mechanisms of endocytosis in primary sensory neurons. The purpose of this study was to perform an in vivo characterization of CD2AP expression in cholinergic neurons of the brain regions most relevant to AD pathogenesis and to investigate the colocalization of CD2AP and Rab5 in cholinergic neurons of the murine basal forebrain. Brain tissue was perfused, harvested from ChAT BAC -eGFP transgenic mice (N=4 male, N=4 female; aged 10 mo), where cholinergic neurons (co-) express green fluorescence protein (GFP) in central and peripheral neurons that express choline acetyltransferase (ChAT). Frozen tissue sections were used to assess the specificity of the reporter in mouse brain along with localization of both CD2AP and Rab5 (co-) expression using immunofluorescence (IF) analysis of ChAT-GFP+ neurons and primary antibodies against ChAT, CD2AP and Rab5. Image J software was used to develop and optimize a colocalization assay for CD2AP and Rab5 puncta. Experiments were repeated in a follow-up cohort of aged-adult mice (N=2 male, N=2 female; aged 18 mo). IF expression of CD2AP was quantified in the basal forebrain, diagonal band of Broca (vDB), and striatal regions and compared to results from the cortical regions of the adult mouse brain. Colocalization of CD2AP was observed in the cell bodies of ChAT-GFP+ neurons of the striatum, vDB and basal forebrain regions, where CD2AP expression intensity as well as the number of cell bodies with positive signal increased incrementally. Colocalization analyses revealed near-complete overlap of CD2AP and Rab5 expression in ChAT-GFP+ cholinergic neurons of the basal forebrain region. We conclude that cholinergic neurons express CD2AP in healthy adult and aged-adult mouse brains. These data provide the first evidence of quantifiable CD2AP protein expression of cholinergic neurons specific to the diagonal band of Broca (vDB) and basal forebrain. Together with previous research from our lab, these data support a role for CD2AP in the pathogenesis of AD through orchestration of endocytosis and retrograde signaling. Ongoing studies are underway to verify these findings in a novel AD mouse model that incorporates the humanized variant of CD2AP , created by MODEL-AD, where we aim to further investigate how CD2AP variants may affect mechanistic components of Rab5 endocytosis as well as subsequent survival of cholinergic neurons in the context of known amyloid beta and Tau pathologies.

Increasing the Survival of a Neuronal Model of Alzheimer's Disease Using Docosahexaenoic Acid, Restoring Endolysosomal Functioning by Modifying the Interactions between the Membrane Proteins C99 and Rab5

Docosahexaenoic acid (DHA, C22:6 ω3) may be involved in various neuroprotective mechanisms that could prevent Alzheimer's disease (AD). Its influence has still been little explored regarding the dysfunction of the endolysosomal pathway, known as an early key event in the physiopathological continuum triggering AD. This dysfunction could result from the accumulation of degradation products of the precursor protein of AD, in particular the C99 fragment, capable of interacting with endosomal proteins and thus contributing to altering this pathway from the early stages of AD. This study aims to evaluate whether neuroprotection mediated by DHA can also preserve the endolysosomal function. AD-typical endolysosomal abnormalities were recorded in differentiated human SH-SY5Y neuroblastoma cells expressing the Swedish form of human amyloid precursor protein. This altered phenotype included endosome enlargement, the reduced secretion of exosomes, and a higher level of apoptosis, which confirmed the relevance of the cellular model chosen for studying the associated deleterious mechanisms. Second, neuroprotection mediated by DHA was associated with a reduced interaction of C99 with the Rab5 GTPase, lower endosome size, restored exosome production, and reduced neuronal apoptosis. Our data reveal that DHA may influence protein localization and interactions in the neuronal membrane environment, thereby correcting the dysfunction of endocytosis and vesicular trafficking associated with AD.

Clathrin mediated endocytosis in Alzheimer's disease: cell type specific involvement in amyloid beta pathology

This review provides a comprehensive examination of the role of clathrin-mediated endocytosis (CME) in Alzheimer's disease (AD) pathogenesis, emphasizing its impact across various cellular contexts beyond neuronal dysfunction. In neurons, dysregulated CME contributes to synaptic dysfunction, amyloid beta (Aβ) processing, and Tau pathology, highlighting its involvement in early AD pathogenesis. Furthermore, CME alterations extend to non-neuronal cell types, including astrocytes and microglia, which play crucial roles in Aβ clearance and neuroinflammation. Dysregulated CME in these cells underscores its broader implications in AD pathophysiology. Despite significant progress, further research is needed to elucidate the precise mechanisms underlying CME dysregulation in AD and its therapeutic implications. Overall, understanding the complex interplay between CME and AD across diverse cell types holds promise for identifying novel therapeutic targets and interventions.

FoxG1 as a Potential Therapeutic Target for Alzheimer's Disease: Modulating NLRP3 Inflammasome via AMPK/mTOR Autophagy Pathway

An increasing body of research suggests that promoting microglial autophagy hinders the neuroinflammation initiated though the NLRP3 inflammasome activation in Alzheimer's disease (AD). The function of FoxG1, a crucial transcription factor involved in cell survival by regulating mitochondrial function, remains unknown during the AD process and neuroinflammation occurs. In the present study, we firstly found that Aβ peptides induced AD-like neuroinflammation upregulation and downregulated the level of autophagy. Following low-dose Aβ25-35 stimulation, FoxG1 expression and autophagy exhibited a gradual increase. Nevertheless, with high-concentration Aβ25-35 treatment, progressive decrease in FoxG1 expression and autophagy levels as the concentration of Aβ25-35 escalated. In addition, FoxG1 has a positive effect on cell viability and autophagy in the nervous system. In parallel with the Aβ25-35 stimulation, we employed siRNA to decrease the expression of FoxG1 in N2A cells. A substantial reduction in autophagy level (Beclin1, LC3II, SQSTM1/P62) and a notable growth in inflammatory response (NLRP3, TNF-α, and IL-6) were observed. In addition, we found FoxG1 overexpression owned the effect on the activation of AMPK/mTOR autophagy pathway and siRNA-FoxG1 successfully abolished this effect. Lastly, FoxG1 suppressed the NLRP3 inflammasome and enhanced the cognitive function in AD-like mouse model induced by Aβ25-35. Confirmed by cellular and animal experiments, FoxG1 suppressed NLRP3-mediated neuroinflammation, which was strongly linked to autophagy regulated by AMPK/mTOR. Taken together, FoxG1 may be a critical node in the pathologic progression of AD and has the potential to serve as therapeutic target.

Comparative interactome mapping of Tau-protein in classical and rapidly progressive Alzheimer's disease identifies subtype-specific pathways

AIMS

Tau is a key player in Alzheimer's disease (AD) and other Tauopathies. Tau pathology in the brain directly correlates with neurodegeneration in AD. The recent identification of a rapid variant of AD demands an urgent need to uncover underlying mechanisms leading to differential progression in AD. Accordingly, we aimed to dissect the underlying differential mechanisms of toxicity associated with the Tau protein in AD subtypes and to find out subtype-dependent biomarkers and therapeutic targets.

METHODS

To identify and characterise subtype-specific Tau-associated mechanisms of pathology, we performed comparative interactome mapping of Tau protein in classical AD (cAD) and rapidly progressive AD (rpAD) cases using co-immunoprecipitation coupled with quantitative mass spectrometry. The mass spectrometry data were extensively analysed using several bioinformatics approaches.

RESULTS

The comparative interactome mapping of Tau protein revealed distinct and unique interactors (DPYSL4, ARHGEF2, TUBA4A and UQCRC2) in subtypes of AD. Interestingly, an analysis of the Tau-interacting proteins indicated enrichment of mitochondrial organisation processes, including negative regulation of mitochondrion organisation, mitochondrial outer membrane permeabilisation involved in programmed cell death, regulation of autophagy of mitochondrion and necroptotic processes, specifically in the rpAD interactome. While, in cAD, the top enriched processes were related to oxidation-reduction process, transport and monocarboxylic acid metabolism.

CONCLUSIONS

Overall, our results provide a comprehensive map of Tau-interacting protein networks in a subtype-dependent manner and shed light on differential functions/pathways in AD subtypes. This comprehensive map of the Tau-interactome has provided subsets of disease-related proteins that can serve as novel biomarkers/biomarker panels and new drug targets.

Upregulation of endocytic protein expression in the Alzheimer's disease male human brain

Amyloid-beta (Aβ) is produced from amyloid precursor protein (APP) primarily after APP is internalised by endocytosis and clathrin-mediated endocytic processes are altered in Alzheimer's disease (AD). There is also evidence that cholesterol and flotillin affect APP endocytosis. We hypothesised that endocytic protein expression would be altered in the brains of people with AD compared to non-diseased subjects which could be linked to increased Aβ generation. We compared protein expression in frontal cortex samples from men with AD compared to age-matched, non-diseased controls. Soluble and insoluble Aβ40 and Aβ42, the soluble Aβ42/Aβ40 ratio, βCTF, BACE1, presenilin-1 and the ratio of phosphorylated:total GSK3β were significantly increased while the insoluble Aβ42:Aβ40 ratio was significantly decreased in AD brains. Total and phosphorylated tau were markedly increased in AD brains. Significant increases in clathrin, AP2, PICALM isoform 4, Rab-5 and caveolin-1 and 2 were seen in AD brains but BIN1 was decreased. However, using immunohistochemistry, caveolin-1 and 2 were decreased. The results obtained here suggest an overall increase in endocytosis in the AD brain, explaining, at least in part, the increased production of Aβ during AD.

Atg4b Overexpression Extends Lifespan and Healthspan in Drosophila melanogaster

Autophagy plays important but complex roles in aging, affecting health and longevity. We found that, in the general population, the levels of ATG4B and ATG4D decreased during aging, yet they are upregulated in centenarians, suggesting that overexpression of ATG4 members could be positive for healthspan and lifespan. We therefore analyzed the effect of overexpressing Atg4b (a homolog of human ATG4D) in Drosophila, and found that, indeed, Atg4b overexpression increased resistance to oxidative stress, desiccation stress and fitness as measured by climbing ability. The overexpression induced since mid-life increased lifespan. Transcriptome analysis of Drosophila subjected to desiccation stress revealed that Atg4b overexpression increased stress response pathways. In addition, overexpression of ATG4B delayed cellular senescence, and improved cell proliferation. These results suggest that ATG4B have contributed to a slowdown in cellular senescence, and in Drosophila, Atg4b overexpression may have led to improved healthspan and lifespan by promoting a stronger stress response. Overall, our study suggests that ATG4D and ATG4B have the potential to become targets for health and lifespan interventions.

The Pursuit of the "Inside" of the Amyloid Hypothesis-Is C99 a Promising Therapeutic Target for Alzheimer's Disease?

Aducanumab, co-developed by Eisai (Japan) and Biogen (U.S.), has received Food and Drug Administration approval for treating Alzheimer's disease (AD). In addition, its successor antibody, lecanemab, has been approved. These antibodies target the aggregated form of the small peptide, amyloid-β (Aβ), which accumulates in the patient brain. The "amyloid hypothesis" based therapy that places the aggregation and toxicity of Aβ at the center of the etiology is about to be realized. However, the effects of immunotherapy are still limited, suggesting the need to reconsider this hypothesis. Aβ is produced from a type-I transmembrane protein, Aβ precursor protein (APP). One of the APP metabolites, the 99-amino acids C-terminal fragment (C99, also called βCTF), is a direct precursor of Aβ and accumulates in the AD patient's brain to demonstrate toxicity independent of Aβ. Conventional drug discovery strategies have focused on Aβ toxicity on the "outside" of the neuron, but C99 accumulation might explain the toxicity on the "inside" of the neuron, which was overlooked in the hypothesis. Furthermore, the common region of C99 and Aβ is a promising target for multifunctional AD drugs. This review aimed to outline the nature, metabolism, and impact of C99 on AD pathogenesis and discuss whether it could be a therapeutic target complementing the amyloid hypothesis.