Neurofibrillary tangles mediated human neuronal tauopathies: insights from fly models

Spatial and planar profiling of Rac1/Cdc42 signaling in Alzheimer's disease brain

BACKGROUND

A neuropathogenic hallmark of Alzheimer's disease (AD) is loss of neuronal synapses in selective brain regions. Small GTPases Rac1 and Cdc42, critical modulators of synaptic architecture and remodeling, are dysregulated in AD brains and are potential AD therapeutic targets. However, the exact contribution of their signaling to AD is still not clear.

OBJECTIVE

We intend to investigate the hypothesis that Rac1/Cdc42 activity changes in a spatial and planar dependent manner in relation to AD.

METHODS

We applied anti-pRac/Cdc42 (Serine 71 phosphorylation), which recognizes an inactive form of Rac1/Cdc42, and anti-pPAK (Threonine 423 phosphorylation), which detects the active PAK, a positive downstream effector of Rac1/Cdc42 signaling. For this study, triple transgenic mouse model (3xTg-AD) brain and human AD brain samples were used.

RESULTS

pRac/Cdc42 expression was decreased in 3xTg-AD mouse cortex while pPAK expression increased compared to wild-type mouse cortex. Immunostaining of mouse brain serial sections revealed increased pRac/Cdc42 expression in the rostral region, decreased expression in the caudal region, and pPAK showed an overall opposite trend of pRac/Cdc42. There was also a brain plane specific nuclear to cytoplasmic redistribution of pRac/Cdc42. Human non-dementia and AD cortex and cerebellum showed differential expressions for pRac/Cdc42, Rac1, and Cdc42. Mouse whole transcriptome analysis demonstrated spatial dependent expression of Rac1/Cdc42 signaling-associated genes in neuronal and non-neuronal (astrocyte) populations of 3xTg-AD hippocampi.

CONCLUSIONS

Rac1/Cdc42 signaling is dysregulated in both 3xTg-AD mouse and AD human brain and Rac1/Cdc42 activity level changes along the spatial and planar dimensions.

A Systematic Review of Updated Mechanistic Insights Towards Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a degenerative neurological disorder that impairs memory, cognitive abilities, and the ability to do everyday activities. This neurodegenerative disease is growing increasingly common as the world's population ages. Here, we reviewed some of the key findings showing the function of Aβ peptide, oxidative stress, free radical damage Triggering Receptors Expressed cn Myeloid Cells 2 (TREM2), Nitric Oxide (NO) and gut microbiota in the aetiology of AD.

METHODS

The potentially relevant online medical databases, namely PubMed, Scopus, Google Scholar, Cochrane Library, and JSTOR, were exhaustively researched. In addition, the data reported in the present study were primarily intervened on the basis of the timeline selected from 1 January 2000 to 31 October 2021. The whole framework was designed substantially based on key terms and studies selected by virtue of their relevance to our investigations.

RESULTS

Findings suggested that channels of free radicals, such as transition metal accumulation and genetic factors, are mainly accountable for the redox imbalance that assist to understand better the pathogenesis of AD and incorporating new therapeutic approaches. Moreover, TREM2 might elicit a protective function for microglia in AD. NO causes an increase in oxidative stress and mitochondrial damage, compromising cellular integrity and viability. The study also explored that the gut and CNS communicate with one another and that regulating gut commensal flora might be a viable therapeutic for neurodegenerative illnesses like AD.

CONCLUSION

There are presently no viable therapies for Alzheimer's disease, but recent breakthroughs in our knowledge of the disease's pathophysiology may aid in the discovery of prospective therapeutic targets.

Applications of Immunomagnetic Reduction Technology as a Biosensor in Therapeutic Evaluation of Chinese Herbal Medicine in Tauopathy Alleviation of an AD Drosophila Model

Alzheimer's disease (AD) is the most common form of dementia. The most convincing biomarkers in the blood for AD are currently β-amyloid (Aβ) and Tau protein because amyloid plaques and neurofibrillary tangles are pathological hallmarks in the brains of patients with AD. The development of assay technologies in diagnosing early-stage AD is very important. The study of human AD subjects is hindered by ethical and technical limitations. Thus, many studies have therefore turned to AD animal models, such as Drosophila melanogaster, to explore AD pathology. However, AD biomarkers such as Aβ and p-Tau protein in Drosophilamelanogaster occur at extremely low levels and are difficult to detect precisely. In this study, we applied the immunomagnetic reduction (IMR) technology of nanoparticles for the detection of p-Tau expressions in hTauR406W flies, an AD Drosophila model. Furthermore, we used IMR technology as a biosensor in the therapeutic evaluation of Chinese herbal medicines in hTauR406W flies with Tau-induced toxicity. To uncover the pathogenic pathway and identify therapeutic interventions of Chinese herbal medicines in Tau-induced toxicity, we modeled tauopathy in the notum of hTauR406W flies. Our IMR data showed that the selected Chinese herbal medicines can significantly reduce p-Tau expressions in hTauR406W flies. Using evidence of notal bristle quantification and Western blotting analysis, we confirmed the validity of the IMR data. Thus, we suggest that IMR can serve as a new tool for measuring tauopathy and therapeutic evaluation of Chinese herbal medicine in an AD Drosophila model.

UBE4B, a microRNA-9 target gene, promotes autophagy-mediated Tau degradation

The formation of hyperphosphorylated intracellular Tau tangles in the brain is a hallmark of Alzheimer's disease (AD). Tau hyperphosphorylation destabilizes microtubules, promoting neurodegeneration in AD patients. To identify suppressors of tau-mediated AD, we perform a screen using a microRNA (miR) library in Drosophila and identify the miR-9 family as suppressors of human tau overexpression phenotypes. CG11070, a miR-9a target gene, and its mammalian orthologue UBE4B, an E3/E4 ubiquitin ligase, alleviate eye neurodegeneration, synaptic bouton defects, and crawling phenotypes in Drosophila human tau overexpression models. Total and phosphorylated Tau levels also decrease upon CG11070 or UBE4B overexpression. In mammalian neuroblastoma cells, overexpression of UBE4B and STUB1, which encodes the E3 ligase CHIP, increases the ubiquitination and degradation of Tau. In the Tau-BiFC mouse model, UBE4B and STUB1 overexpression also increase oligomeric Tau degradation. Inhibitor assays of the autophagy and proteasome systems reveal that the autophagy-lysosome system is the major pathway for Tau degradation in this context. These results demonstrate that UBE4B, a miR-9 target gene, promotes autophagy-mediated Tau degradation together with STUB1, and is thus an innovative therapeutic approach for AD.

Sunset yellow degradation product, as an efficient water-soluble inducer, accelerates 1N4R Tau amyloid oligomerization: In vitro preliminary evidence against the food colorant safety in terms of "Triggered Amyloid Aggregation"

Today, Alzheimer's disease (AD) as the most prevalent type of dementia turns into one of the most severe health problems. Neurofibrillary tangle (NFT), mostly comprised of fibrils formed by Tau, is a hallmark of a class of neurodegenerative diseases. Tau protein promotes assembly and makes stable microtubules that play a role in the appropriate function of neurons. Polyanionic cofactors such as heparin, and azo dyes, can induce aggregation of tau protein in vitro. Sunset Yellow is a food colorant used widely in food industries. In the current work, we introduced degradation product (DP) of Sunset Yellow as an effective inducer of Tau aggregation. Two Tau aggregation inducers were produced, and then the aggregation kinetics and the structure of 1N4R Tau amyloid fibrils were characterized using ThT fluorescence spectroscopy, X-Ray Diffraction (XRD), circular dichroism (CD) and atomic force microscopy (AFM). Also, the toxic effects of the induced aggregates on RBCs and SH-SY5Y cells were demonstrated by hemolysis and LDH assays, respectively. Both inducers efficiently accelerated the formation of the amyloid fibril. Along with the confirmation of the β-sheets structure in Tau aggregates by Far-UV CD spectra, X-ray diffractions revealed the typical cross-β diffraction pattern. The oligomer formation in the presence of DPs was also confirmed by AFM. The possible in vivo effect of artificial azo dyes on Tau aggregation should be considered seriously as a newly opened dimension in food safety and human health.