Protective effects of a small-molecule inhibitor DDQ against tau-induced toxicities in a transgenic tau mouse model of Alzheimer's disease

Unveiling the Role of Novel miRNA PC-5P-12969 in Alleviating Alzheimer's Disease

Background

The intricate and complex molecular mechanisms that underlie the progression of Alzheimer's disease (AD) have prompted a concerted and vigorous research endeavor aimed at uncovering potential avenues for therapeutic intervention.

Objective

This study aims to elucidate the role of miRNA PC-5P-12969 in the pathogenesis of AD.

Methods

We assessed the differential expression of miRNA PC-5P-12969 in postmortem AD brains, AD animal and cell models using real-time reverse-transcriptase RT-PCR, we also checked the gene and protein expression of GSK3α and APP.

Results

Our investigation revealed a notable upregulation of miRNA PC-5P-12969 in postmortem brains of AD patients, in transgenic mouse models of AD, and in mutant APP overexpressing-HT22 cells. Additionally, our findings indicate that overexpression of miRNA PC-5P-12969 exerts a protective effect on cell survival, while concurrently mitigating apoptotic cell death. Further-more, we established a robust and specific interaction between miRNA PC-5P-12969 and GSK3α. Our luciferase reporter assays provided confirmation of the binding between miRNA PC-5P-12969 and the 3'-UTR of the GSK3α gene. Manipulation of miRNA PC-5P-12969 levels in cellular models of AD yielded noteworthy alterations in the gene and protein expression levels of both GSK3α and APP. Remarkably, the manipulation of miRNA PC-5P-12969 levels yielded significant enhancements in mitochondrial respiration and ATP production, concurrently with a reduction in mitochondrial fragmentation, thus unveiling a potential regulatory role of miRNA PC-5P-12969 in these vital cellular processes.

Conclusions

In summary, this study sheds light on the crucial role of miRNA PC-5P-12969 and its direct interaction with GSK3α in the context of AD.

Regulation of retinoid mediated StAR transcription and steroidogenesis in hippocampal neuronal cells: Implications for StAR in protecting Alzheimer's disease

Retinoids (vitamin A and its derivatives) play pivotal roles in diverse processes, ranging from homeostasis to neurodegeneration, which are also influenced by steroid hormones. The rate-limiting step in steroid biosynthesis is mediated by the steroidogenic acute regulatory (StAR) protein. In the present study, we demonstrate that retinoids enhanced StAR expression and pregnenolone biosynthesis, and these parameters were markedly augmented by activation of the PKA pathway in mouse hippocampal neuronal HT22 cells. Deletion and mutational analyses of the 5'-flanking regions of the StAR gene revealed the importance of a retinoic acid receptor (RAR)/retinoid X receptor (RXR)-liver X receptor (LXR) heterodimeric motif at -200/-185 bp region in retinoid responsiveness. The RAR/RXR-LXR sequence motif can bind RARα and RXRα, and retinoid regulated transcription of the StAR gene was found to be influenced by the LXR pathway, representing signaling cross-talk in hippocampal neurosteroid biosynthesis. Steroidogenesis decreases during senescence due to declines in the central nervous system and the endocrine system, and results in hormone deficiencies, inferring the need for hormonal balance for healthy aging. Loss of neuronal cells, involving accumulation of amyloid beta (Aβ) and/or phosphorylated Tau within the brain, is the pathological hallmark of Alzheimer's disease (AD). HT22 cells overexpressing either mutant APP (mAPP) or mutant Tau (mTau), conditions mimetic to AD, enhanced toxicities, and resulted in attenuation of both basal and retinoid-responsive StAR and pregnenolone levels. Co-expression of StAR with either mAPP or mTau diminished cytotoxicity, and concomitantly elevated neurosteroid biosynthesis, pointing to a protective role of StAR in AD. These findings provide insights into the molecular events by which retinoid signaling upregulates StAR and steroid levels in hippocampal neuronal cells, and StAR, by rescuing mAPP and/or mTau-induced toxicities, modulates neurosteroidogenesis and restores hormonal balance, which may have important implications in protecting AD and age-related complications and diseases.

A Combination Therapy of Urolithin A+EGCG Has Stronger Protective Effects Than Single Drug Urolithin A in a Humanized Amyloid Beta Knockin Mice for Late-Onset Alzheimer’s Disease

In the current study, for the first time, we study mitophagy enhancer urolithin A and a combination of urolithin A+green tea extract EGCG against human Aβ peptide-induced mitochondrial and synaptic, dendritic, inflammatory toxicities and behavioral changes in humanized homozygous amyloid beta knockin (hAbKI) mice of late-onset Alzheimer’s disease (AD). Our findings reveal significantly increased positive effects of urolithin A and a combination treatment of urolithin A+EGCG in hAbKI mice for phenotypic behavioral changes including motor coordination, locomotion/exploratory activity, spatial learning and working memory. mRNA and protein levels of mitochondrial fusion, synaptic, mitophagy and autophagy genes were upregulated, and mitochondrial fission genes are downregulated in urolithin A and combine treatment in hAbKI mice; however, the effect is stronger in combined treatment. Immunofluorescence analysis of hippocampal brain sections shows similar findings of mRNA and protein levels. Mitochondrial dysfunction is significantly reduced in both treatment groups, but a stronger reduction is observed in combined treatment. Dendritic spines and lengths are significantly increased in both treatment groups, but the effect is stronger in combined treatment. The fragmented number of mitochondria is reduced, and mitochondrial length is increased, and mitophagosomal formations are increased in both the groups, but the effect is stronger in the combined treatment. The levels of amyloid beta (Aβ) 40 and Aβ42 are reduced in both treatments, however, the reduction is higher for combined treatment. These observations suggest that urolithin A is protective against human Aβ peptide-induced toxicities; however, combined treatment of urolithin A+EGCG is effective and stronger, indicating that combined therapy is promising to treat late-onset AD patients.

Reduced VDAC1, Maintained Mitochondrial Dynamics and Enhanced Mitochondrial Biogenesis in a Transgenic Tau Mouse Model of Alzheimer’s Disease

Alzheimer’s disease (AD) is one of the most common forms of neurodegeneration, defined by reduced cognitive function, which is caused by the gradual death of neurons in the brain. Recent studies have shown an age-dependent rise in the levels of voltage-dependent anion channel 1 (VDAC1) in AD. In addition, we discovered an aberrant interaction between VDAC1 and P-TAU in the brains of AD patients, which led to abnormalities in the structural and functional integrity of the mitochondria. The purpose of our study is to understand the protective effects of reduced VDAC1 against impaired mitochondrial dynamics and defective mitochondrial biogenesis in transgenic TAU mice. Recently, we crossed heterozygote VDAC1 knockout (VDAC1^+/−) mice with transgenic TAU mice to obtain double-mutant VDAC1^+/−/TAU mice. Our goal was to evaluate whether a partial decrease in VDAC1 lessens the amount of mitochondrial toxicity in transgenic Tau (P301L) mice. We found that mitochondrial fission proteins were significantly reduced, and mitochondrial fusion and biogenesis proteins were increased in double-mutant mice compared to TAU mice. On the basis of these discoveries, the current work may have significance for the development of reduced-VDAC1-based treatments for individuals suffering from AD as well as other tauopathies.

A partial reduction of VDAC1 enhances mitophagy, autophagy, synaptic activities in a transgenic Tau mouse model

Alzheimer's disease (AD) is the most common cause of mental dementia in the aged population. AD is characterized by the progressive decline of memory and multiple cognitive functions, and changes in behavior and personality. Recent research has revealed age-dependent increased levels of VDAC1 in postmortem AD brains and cerebral cortices of APP, APPxPS1, and 3xAD.Tg mice. Further, we found abnormal interaction between VDAC1 and P-Tau in the AD brains, leading to mitochondrial structural and functional defects. Our current study aimed to understand the impact of a partial reduction of voltage-dependent anion channel 1 (VDAC1) protein on mitophagy/autophagy, mitochondrial and synaptic activities, and behavior changes in transgenic TAU mice in Alzheimer's disease. To determine if a partial reduction of VDAC1 reduces mitochondrial and synaptic toxicities in transgenic Tau (P301L) mice, we crossed heterozygote VDAC1 knockout (VDAC1^+/- ) mice with TAU mice and generated double mutant (VDAC1^+/- /TAU) mice. We assessed phenotypic behavior, protein levels of mitophagy, autophagy, synaptic, other key proteins, mitochondrial morphology, and dendritic spines in TAU mice relative to double mutant mice. Partial reduction of VDAC1 rescued the TAU-induced behavioral impairments such as motor coordination and exploratory behavioral changes, and learning and spatial memory impairments in VDAC1^+/- /TAU mice. Protein levels of mitophagy, autophagy, and synaptic proteins were significantly increased in double mutant mice compared with TAU mice. In addition, dendritic spines were significantly increased; the mitochondrial number was significantly reduced, and mitochondrial length was increased in double mutant mice. Based on these observations, we conclude that reduced VDAC1 is beneficial in symptomatic-transgenic TAU mice.

Behavioral Evidence for a Tau and HIV-gp120 Interaction

Despite successful virologic control with combination antiretroviral therapy (cART), about half of people living with the human immunodeficiency virus-1 (HIV) develop an HIV-associated neurocognitive disorder (HAND). It is estimated that 50% of individuals who are HIV-positive in the United States are aged 50 years or older. Therefore, a new challenge looms as individuals living with HIV increase in age. There is concern that Alzheimer’s disease (AD) may become prevalent with an earlier onset of cognitive decline in people living with HIV (PLWH). Clinical data studies reported the presence of AD biomarkers in PLWH. However, the functional significance of the interaction between HIV or HIV viral proteins and AD biomarkers is still not well studied. The main goal of the present study is to address this knowledge gap by determining if the HIV envelope glycoprotein 120 (HIV-gp120) can affect the cognitive functions in the Tau mouse AD model. Male Tau and age-matched, wild-type (WT) control mice were treated intracerebroventricularly (ICV) with HIV-gp120. The animals were evaluated for cognitive function using a Y-maze. We found that HIV-gp120 altered cognitive function in Tau mice. Notably, HIV-gp120 was able to promote a cognitive decline in transgenic Tau (P301L) mice compared to the control (HIV-gp120 and WT). We provide the first in vivo evidence of a cognitive interaction between an HIV viral protein and Tau mice.

Early Cellular, Molecular, Morphological and Behavioral Changes in the Humanized Amyloid-Beta-Knock-In Mouse Model of Late-Onset Alzheimer's Disease

The purpose of our study is to investigate early cellular, molecular, morphological and behavioral changes in humanized amyloid-beta-knock-in (hAbKI) mice. Using seven-month-old homozygous hAbKI mice, we studied behavioral phenotype parameters, including spatial learning and memory (Morris Water Maze), locomotor activity (open field), working memory (Y-maze) and motor coordination (rotarod); mRNA abundance, protein levels, soluble amyloid-beta 40 and 42 levels and regional immunoreactivities of key markers of mitochondrial dynamics, mitochondrial biogenesis, synaptic health, mitophagy and autophagy; mitochondrial function and using transmission electron microscopy & Golgi–Cox staining, we assessed mitochondrial morphology and dendritic spines. Our extensive behavioral analysis revealed that seven-month-old hAbKI mice showed impairments in motor coordination, reduced locomotor and exploration activities, impairments in working memory and spatial learning and memory. Our mRNA and protein analyses revealed the increased expression of mitochondrial-fission genes and reduced expression of mitochondrial-fusion, mitochondrial-biogenesis, synaptic, autophagy and mitophagy genes in seven-month-old hAbKI mice. An immunofluorescence analysis revealed altered immunoreactivities and agreed with the immunoblot results. Transmission-electron-microscopy data revealed increased mitochondrial fragmentation and reduced mitochondrial length in both hippocampal and cortical tissues of seven-month-old hAbKI mice and mitochondrial function defective. A Golgi–Cox-staining analysis revealed reduced dendritic spines in both cerebral cortices and hippocampi of hAbKI mice. Soluble amyloid-beta (1–40 and 1–42) were detected in three-month-old hAbKI mice and progressively increased in seven-month-old mice. These observations suggest that the human amyloid-beta peptide is sufficient to cause behavioral, mitochondrial, synaptic and ultrastructural changes in seven-month-old hAbKI mice. Our study findings also suggest that hAbKI mice might serve as a model for preclinical studies of preventive therapies.

Sirtuins at the Crossroads between Mitochondrial Quality Control and Neurodegenerative Diseases: Structure, Regulation, Modifications, and Modulators

Sirtuins (SIRT1-SIRT7), a family of nicotinamide adenine dinucleotide (NAD⁺)-dependent enzymes, are key regulators of life span and metabolism. In addition to acting as deacetylates, some sirtuins have the properties of deacylase, decrotonylase, adenosine diphosphate (ADP)-ribosyltransferase, lipoamidase, desuccinylase, demalonylase, deglutarylase, and demyristolyase. Mitochondrial dysfunction occurs early on and acts causally in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Sirtuins are implicated in the regulation of mitochondrial quality control, which is highly associated with the pathogenesis of neurodegenerative diseases. There is growing evidence indicating that sirtuins are promising and well-documented molecular targets for the treatment of mitochondrial dysfunction and neurodegenerative disorders by regulating mitochondrial quality control, including mitochondrial biogenesis, mitophagy, mitochondrial fission/fusion dynamics, and mitochondrial unfolded protein responses (mtUPR). Therefore, elucidation of the molecular etiology of sirtuin-mediated mitochondrial quality control points to new prospects for the treatment of neurodegenerative diseases. However, the mechanisms underlying sirtuin-mediated mitochondrial quality control remain obscure. In this review, we update and summarize the current understanding of the structure, function, and regulation of sirtuins with an emphasis on the cumulative and putative effects of sirtuins on mitochondrial biology and neurodegenerative diseases, particularly their roles in mitochondrial quality control. In addition, we outline the potential therapeutic applications for neurodegenerative diseases of targeting sirtuin-mediated mitochondrial quality control through exercise training, calorie restriction, and sirtuin modulators in neurodegenerative diseases.