Statins Reduce Amyloid-β Production through Inhibition of Protein Isoprenylation

Lipid rafts disruption by statins negatively impacts the interaction between SARS-CoV-2 S1 subunit and ACE2 in intestinal epithelial cells

The causative agent of the COVID-19 pandemic, SARS-CoV-2, is a virus that targets mainly the upper respiratory tract. However, it can affect other systems such as the gastrointestinal (GI) tract. Therapeutic strategies for this virus are still inconclusive and understanding its entry mechanism is important for finding effective treatments. Cholesterol is an important constituent in the structure of cellular membranes that plays a crucial role in a variety of cellular events. In addition, it is important for the infectivity and pathogenicity of several viruses. ACE2, the main receptor of SARS-CoV-2, is associated with lipid rafts which are microdomains composed of cholesterol and sphingolipids. In this study, we investigate the role of statins, lipid-lowering drugs, on the trafficking of ACE2 and the impact of cholesterol modulation on the interaction of this receptor with S1 in Caco-2 cells. The data show that fluvastatin and simvastatin reduce the expression of ACE2 to variable extents, impair its association with lipid rafts and sorting to the brush border membrane resulting in substantial reduction of its interaction with the S1 subunit of the spike protein. By virtue of the substantial effects of statins demonstrated in our study, these molecules, particularly fluvastatin, represent a promising therapeutic intervention that can be used off-label to treat SARS-CoV-2.

Association of Statin Use with Dementia Risk Among Older Adults in Japan: A Nested Case-Control Study Using the LIFE Study

Background

Previous studies have shown a possible association between statin use and a decreased risk of dementia, but the association has not been sufficiently established, especially in the super-aging society of Japan.

Objective

This study aimed to determine the association between statin use and the risk of dementia among Japanese participants aged> =65 years old.

Methods

Data from the Longevity Improvement and Fair Evidence (LIFE) Study were utilized, including medical and long-term care (LTC) claim data from 17 municipalities between April 2014 and December 2020. A nested case-control study was conducted with one case matched to five controls based on age, sex, municipality, and year of cohort entry. We used a conditional logistic regression model to calculate the odds ratios (ORs) and 95% confidence intervals (95% CIs).

Results

This study included 57,302 cases and 283,525 controls, with 59.7% of the participants being woman. After adjusting for potential confounders, statin use was associated with a lower risk of dementia (OR, 0.70; 95% CI: 0.68-0.73) and Alzheimer's disease (OR: 0.66; 95% CI: 0.63-0.69). Compared with non-users, the ORs of dementia were as follows: 1.42 (1.34-1.50) for 1-30 total standardized daily dose (TSDD), 0.91 (0.85-0.98) for 31-90 TSDD, 0.63 (0.58-0.69) for 91-180 TSDD, and 0.33 (0.31-0.36) for >180 TSDD in dose-analysis.

Conclusions

Statin use is associated with a reduced risk of dementia and Alzheimer's disease among older Japanese adults. A low cumulative statin dose is associated with an increased risk of dementia, whereas a high cumulative statin dose is a protective factor against dementia.

Atorvastatin rescues hyperhomocysteinemia-induced cognitive deficits and neuroinflammatory gene changes

BACKGROUND

Epidemiological data suggests statins could reduce the risk of dementia, and more specifically, Alzheimer's disease (AD). Pre-clinical data suggests statins reduce the risk of dementia through their pleiotropic effects rather than their cholesterol lowering effects. While AD is a leading cause of dementia, it is frequently found co-morbidly with cerebral small vessel disease and other vascular contributions to cognitive impairment and dementia (VCID), which are another leading cause of dementia. In this study, we determined if atorvastatin ameliorated hyperhomocysteinemia (HHcy)-induced VCID.

METHODS

Wild-type (C57Bl6/J) mice were placed on a diet to induce HHcy or a control diet each with or without atorvastatin for 14 weeks. Mice underwent novel object recognition testing before tissue collection. Plasma total cholesterol and total homocysteine as well as related metabolites were measured. Using qPCR and NanoString technology, we profiled glial cell-associated gene expression changes. Finally, microglial morphology, astrocyte end feet, and microhemorrhages were analyzed using histological methods.

RESULTS

Atorvastatin treatment of HHcy in mice led to no changes in total cholesterol but decreases in total homocysteine in plasma. While HHcy decreased expression of many glial genes, atorvastatin rescued these gene changes, which mostly occurred in oligodendrocytes and microglia. Microglia in HHcy mice with atorvastatin were trending towards fewer processes compared to control with atorvastatin, but there were no atorvastatin effects on astrocyte end feet. While atorvastatin treatment was trending towards increasing the area of microhemorrhages in HHcy mice in the frontal cortex, it only slightly (non-significantly) reduced the number of microhemorrhages. Finally, atorvastatin treatment in HHcy mice led to improved cognition on the novel object recognition task.

CONCLUSIONS

These data suggest that atorvastatin rescued cognitive changes induced by HHcy most likely through lowering plasma total homocysteine and rescuing gene expression changes rather than impacts on vascular integrity or microglial changes.

Crosstalk between the Rho and Rab family of small GTPases in neurodegenerative disorders

Neurodegeneration is associated with defects in cytoskeletal dynamics and dysfunctions of the vesicular trafficking and sorting systems. In the last few decades, studies have demonstrated that the key regulators of cytoskeletal dynamics are proteins from the Rho family GTPases, meanwhile, the central hub for vesicle sorting and transport between target membranes is the Rab family of GTPases. In this regard, the role of Rho and Rab GTPases in the induction and maintenance of distinct functional and morphological neuronal domains (such as dendrites and axons) has been extensively studied. Several members belonging to these two families of proteins have been associated with many neurodegenerative disorders ranging from dementia to motor neuron degeneration. In this analysis, we attempt to present a brief review of the potential crosstalk between the Rab and Rho family members in neurodegenerative pathologies such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington disease, and amyotrophic lateral sclerosis (ALS).

MOZART, a QSAR Multi-Target Web-Based Tool to Predict Multiple Drug-Enzyme Interactions

Developing models able to predict interactions between drugs and enzymes is a primary goal in computational biology since these models may be used for predicting both new active drugs and the interactions between known drugs on untested targets. With the compilation of a large dataset of drug-enzyme pairs (62,524), we recognized a unique opportunity to attempt to build a novel multi-target machine learning (MTML) quantitative structure-activity relationship (QSAR) model for probing interactions among different drugs and enzyme targets. To this end, this paper presents an MTML-QSAR model based on using the features of topological drugs together with the artificial neural network (ANN) multi-layer perceptron (MLP). Validation of the final best model found was carried out by internal cross-validation statistics and other relevant diagnostic statistical parameters. The overall accuracy of the derived model was found to be higher than 96%. Finally, to maximize the diffusion of this model, a public and accessible tool has been developed to allow users to perform their own predictions. The developed web-based tool is public accessible and can be downloaded as free open-source software.

Statins Use in Alzheimer Disease: Bane or Boon from Frantic Search and Narrative Review

Alzheimer’s disease (AD) was used to describe pre-senile dementia to differentiate it from senile dementia, which develops in the adult age group of more than 65 years. AD is characterized by the deposition of amyloid beta (Aβ) plaque and tau-neurofibrillary tangles (TNTs) in the brain. The neuropathological changes in AD are related to the deposition of amyloid plaques, neurofibrillary tangles, and progression of neuroinflammation, neuronal mitochondrial dysfunction, autophagy dysfunction, and cholinergic synaptic dysfunction. Statins are one of the main cornerstone drugs for the management of cardiovascular disorders regardless of dyslipidemia status. Increasing the use of statins, mainly in the elderly groups for primary and secondary prevention of cardiovascular diseases, may affect their cognitive functions. Extensive and prolonged use of statins may affect cognitive functions in healthy subjects and dementia patients. Statins-induced cognitive impairments in both patients and health providers had been reported according to the post-marketing survey. This survey depends mainly on sporadic cases, and no cognitive measures were used. Evidence from prospective and observational studies gives no robust conclusion regarding the beneficial or detrimental effects of statins on cognitive functions in AD patients. Therefore, this study is a narrative review aimed with evidences to the beneficial, detrimental, and neutral effects of statins on AD.

Effects of Simvastatin on Plasma Amyloid-β Transport in Patients with Hyperlipidemia: A 12-Week Randomized, Double-Blind, Placebo-Controlled Trial

Background: Abnormal blood lipids are associated with cognitive impairment and amyloid-β (Aβ) deposition in the brain. However, the effects of statins on Alzheimer’s disease (AD) have not been determined. Objective: Considering that plasma Aβ are related to Aβ deposition in the brain, we investigated the effects of simvastatin on plasma Aβ transport. Methods: This was a randomized, double-blind, placebo-controlled trial. One hundred and twenty patients with hyperlipidemia were randomly assigned to receive 40 mg of simvastatin per day or matching placebo for 12 weeks (sixty patients per group). Plasma Aβ, sLRP1, sRAGE, and lipid levels were measured at baseline and at the 6-week and 12-week visits. Results: The ITT database ultimately included 108 participants (placebo group: n = 53; simvastatin group: n = 55) and 64 (59.3%) were women, ranging in age from 45 to 75 years (mean 57.2±6.9 years). Multiple linear regression analysis showed that, after 12 weeks of follow-up, compared with the placebo group, ΔAβ 42 levels (the change of Aβ 42 levels from baseline at week 12) increased more and ΔsRAGE levels decreased more in the simvastatin group (Aβ 42: β= 5.823, p = 0.040; sRAGE: β= –72.012, p = 0.031), and a significant negative association was found between ΔAβ 42 and ΔsRAGE levels (β= –0.115, p = 0.045). In addition, generalized estimation equation analysis showed that triglycerides levels were negatively correlated with Aβ 40 (β= –16.79, p = 0.023), Aβ 42 (β= –6.10, p = 0.001), and sRAGE (β= –51.16, p = 0.003). Conclusion: Daily oral simvastatin (40 mg/day) in patients with hyperlipidemia for 12 weeks can significantly increase plasma Aβ 42 levels compared with placebo, which was associated with reduced triglycerides and sRAGE levels, indicating that statins may affect plasma Aβ transport.

Cholesterol as a key player in amyloid β-mediated toxicity in Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is one of the most devastating and widespread diseases worldwide, mainly affecting the aging population. One of the key factors contributing to AD-related neurotoxicity is the production and aggregation of amyloid β (Aβ). Many studies have shown the ability of Aβ to bind to the cell membrane and disrupt its structure, leading to cell death. Because amyloid damage affects different parts of the brain differently, it seems likely that not only Aβ but also the nature of the membrane interface with which the amyloid interacts, helps determine the final neurotoxic effect. Because cholesterol is the dominant component of the plasma membrane, it plays an important role in Aβ-induced toxicity. Elevated cholesterol levels and their regulation by statins have been shown to be important factors influencing the progression of neurodegeneration. However, data from many studies have shown that cholesterol has both neuroprotective and aggravating effects in relation to the development of AD. In this review, we attempt to summarize recent findings on the role of cholesterol in Aβ toxicity mediated by membrane binding in the pathogenesis of AD and to consider it in the broader context of the lipid composition of cell membranes.

RhoA Signaling in Neurodegenerative Diseases

Ras homolog gene family member A (RhoA) is a small GTPase of the Rho family involved in regulating multiple signal transduction pathways that influence a diverse range of cellular functions. RhoA and many of its downstream effector proteins are highly expressed in the nervous system, implying an important role for RhoA signaling in neurons and glial cells. Indeed, emerging evidence points toward a role of aberrant RhoA signaling in neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. In this review, we summarize the current knowledge of RhoA regulation and downstream cellular functions with an emphasis on the role of RhoA signaling in neurodegenerative diseases and the therapeutic potential of RhoA inhibition in neurodegeneration.

Exploring the Genetic Associations Between the Use of Statins and Alzheimer's Disease

Objective

Alzheimer's disease (AD) is the most common cause of dementia. The statins have shown beneficial effects on cognitive functions and reduced the risk of dementia development. However, the exact mechanisms of statin effects in AD are not yet fully understood. In this study, we aimed to explore the underlying mechanisms of statin on AD.

Methods

We downloaded AD blood dataset (GSE63060) and statin-related blood gene expression dataset (GSE86216). Then we performed gene expression analysis of each dataset and compared blood gene expressions between AD patients and statin-treated patients. Then, we downloaded mouse embryonic neural stem cell dataset (GSE111945) and performed gene expression analysis.

Results

From the human blood dataset, we identified upregulated/downregulated genes in AD patients and statin-treated patients. Some of the upregulated genes (AEN, MBTPS1, ABCG1) in the blood of AD patients are downregulated in statin-treated patients. Several downregulated genes (FGL2, HMGCS1, PSME2, SRSF3, and ATG3) are upregulated in statin-treated patients. Gene set enrichment analysis using mouse stem cell dataset revealed a significant relationship of Kyoto Encyclopedia of Genes and Genomes-defined pathway of AD in statin-treated neural stem cells compared to vehicle-treated neural stem cells (normalized enrichment score: −2.24 in male and −1.6 in female).

Conclusion

These gene expression analyses from human blood and mouse neural stem cell demonstrate the important clues on the molecular mechanisms of impacts of statin on AD disease. Further studies are needed to investigate the exact role of candidate genes and pathways suggested in our AD pathogenesis study.

An evidence-based review of neuronal cholesterol role in dementia and statins as a pharmacotherapy in reducing risk of dementia

INTRODUCTION

Dementia is a progressive neurodegenerative disorder impairing memory and cognition. Alzheimer's Disease, followed by vascular dementia - the most typical form. Risk factors for vascular dementia include diabetes, cardiovascular disease, hyperlipidemia. Lipids' levels are significantly associated with vascular changes in the brain.

AREAS COVERED

The present article reviews the cholesterol metabolism in the brain, which includes: the synthesis, transport, storage, and elimination process. Additionally, it reviews the role of cholesterol in the pathogenesis of dementia and statin as a therapeutic intervention in dementia. In addition to the above, it further reviews evidence in support of as well as against statin therapy in dementia, recent updates of statin pharmacology, and demerits of use of statin pharmacotherapy.

EXPERT OPINION

Amyloid-β peptides and intraneuronal neurofibrillary tangles are markers of Alzheimer's disease. Evidence shows cholesterol modulates the functioning of enzymes associated with Amyloid-β peptide processing and synthesis. Lowering cholesterol using statin may help prevent or delay the progression of dementia. This paper reviews the role of statin in dementia and recommends extensive future studies, including genetic research, to obtain a precise medication approach for patients with dementia.

Flavonoid-Based Nanomedicines in Alzheimer's Disease Therapeutics: Promises Made, a Long Way To Go

Alzheimer's disease (AD) is characterized by the continuous decline of the cognitive abilities manifested due to the accumulation of large aggregates of amyloid-beta 42 (Aβ42), the formation of neurofibrillary tangles of hyper-phosphorylated forms of microtubule-associated tau protein, which may lead to many alterations at the cellular and systemic level. The current therapeutic strategies primarily focus on alleviating pathological symptoms rather than providing a possible cure. AD is one of the highly studied but least understood neurological problems and remains an unresolved condition of human brain degeneration. Over the years, multiple naturally derived small molecules, including plant products, microbial isolates, and some metabolic byproducts, have been projected as supplements reducing the risk or possible treatment of the disease. However, unfortunately, none has met the expected success. One major challenge for most medications is their ability to cross the blood-brain barrier (BBB). In past decades, nanotechnology-based interventions have offered an alternative platform to address the problem of the successful delivery of the drugs to the specific targets. Interestingly, the exciting interface of natural products and nanomedicine is delivering promising results in AD treatment. The potential applications of flavonoids, the plant-derived compounds best known for their antioxidant activities, and their amalgamation with nanomedicinal approaches may lead to highly effective therapeutic strategies for treating well-known neurodegenerative diseases. In the present review, we explore the possibilities and recent developments on an exciting combination of flavonoids and nanoparticles in AD.

Oligomer β-amyloid Induces Hyperactivation of Ras to Impede NMDA Receptor-Dependent Long-Term Potentiation in Hippocampal CA1 of Mice

The activity of Ras, a small GTPase protein, is increased in brains with Alzheimer’s disease. The objective of this study was to determine the influence of oligomeric Aβ_1-42 on the activation of Ras, and the involvement of the Ras hyperactivity in Aβ_1-42-induced deficits in spatial cognition and hippocampal synaptic plasticity. Herein, we show that intracerebroventricular injection of Aβ_1-42 in mice (Aβ-mice) enhanced hippocampal Ras activation and expression, while 60 min incubation of hippocampal slices in Aβ_1-42 (Aβ-slices) only elevated Ras activity. Aβ-mice showed deficits in spatial cognition and NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) in hippocampal CA1, but basal synaptic transmission was enhanced. The above effects of Aβ_1-42 were corrected by the Ras inhibitor farnesylthiosalicylic acid (FTS). ERK2 phosphorylation increased, and Src phosphorylation decreased in Aβ-mice and Aβ_1-42-slices. Both were corrected by FTS. In CA1 pyramidal cells of Aβ_1-42-slices, the response of AMPA receptor and phosphorylation of GluR1 were enhanced with dependence on Ras activation rather than ERK signaling. In contrast, NMDA receptor (NMDAR) function and GluN2A/2B phosphorylation were downregulated in Aβ_1-42-slices, which was recovered by application of FTS or the Src activator ouabain, and mimicked in control slices treated with the Src inhibitor PP2. The administration of PP2 impaired the spatial cognition and LTP induction in control mice and FTS-treated Aβ-mice. The treatment of Aβ-mice with ouabain rescued Aβ-impaired spatial cognition and LTP. Overall, the results indicate that the oligomeric Aβ_1-42 hyperactivates Ras and thereby causes the downregulation of Src which impedes NMDAR-dependent LTP induction resulting in cognitive deficits.

Cholesterol-lowering drugs reduce APP processing to Aβ by inducing APP dimerization

Amyloid beta (Aβ) is a major component of amyloid plaques, which are a key pathological hallmark found in the brains of Alzheimer’s disease (AD) patients. We show that statins are effective at reducing Aβ in human neurons from nondemented control subjects, as well as subjects with familial AD and sporadic AD. Aβ is derived from amyloid precursor protein (APP) through sequential proteolytic cleavage by BACE1 and γ-secretase. While previous studies have shown that cholesterol metabolism regulates APP processing to Aβ, the mechanism is not well understood. We used iPSC-derived neurons and bimolecular fluorescence complementation assays in transfected cells to elucidate how altering cholesterol metabolism influences APP processing. Altering cholesterol metabolism using statins decreased the generation of sAPPβ and increased levels of full-length APP (flAPP), indicative of reduced processing of APP by BACE1. We further show that statins decrease flAPP interaction with BACE1 and enhance APP dimerization. Additionally, statin-induced changes in APP dimerization and APP-BACE1 are dependent on cholesterol binding to APP. Our data indicate that statins reduce Aβ production by decreasing BACE1 interaction with flAPP and suggest that this process may be regulated through competition between APP dimerization and APP cholesterol binding.

Distinct dual roles of p-Tyr42 RhoA GTPase in tau phosphorylation and ATP citrate lyase activation upon different Aβ concentrations

Both the accumulation of Amyloid-β (Aβ) in plaques and phosphorylation of Tau protein (p-Tau) in neurofibrillary tangles have been identified as two major symptomatic features of Alzheimer's disease (AD). Despite of critical role of Aβ and p-Tau in AD progress, the interconnection of signalling pathways that Aβ induces p-Tau remains elusive. Herein, we observed that a popular AD model mouse (APP/PS1) and Aβ-injected mouse showed an increase in p-Tyr42 Rho in hippocampus of brain. Low concentrations of Aβ (1 μM) induced RhoA-mediated Ser422 phosphorylation of Tau protein (p-Ser422 Tau), but reduced the expression of ATP citrate lyase (ACL) in the HT22 hippocampal neuronal cell line. In contrast, high concentrations of Aβ (10 μM) along with high levels of superoxide production remarkably attenuated accumulation of p-Ser422 Tau, but augmented ACL expression and activated sterol regulatory element-binding protein 1 (SREBP1), leading to cellular senescence. Notably, a high concentration of Aβ (10 μM) induced nuclear localization of p-Tyr42 Rho, which positively regulated NAD kinase (NADK) expression by binding to the NADK promoter. Furthermore, severe AD patient brain showed high p-Tyr42 Rho levels. Collectively, our findings indicate that both high and low concentrations of Aβ are detrimental to neurons via distinct two p-Tyr42 RhoA-mediated signalling pathways in Ser422 phosphorylation of Tau and ACL expression.

Association of Statin Use and High Serum Cholesterol Levels With Risk of Primary Open-Angle Glaucoma

Importance

The use of statins (hydroxymethylglutaryl coenzyme A inhibitors) has been associated with a lower risk of primary open-angle glaucoma (POAG); however, results have been conflicting, and little is known about the association between high cholesterol levels and POAG.

Objective

To assess the association of elevated cholesterol levels and statin use with incident POAG.

Design, Setting, and Participants

This study used data collected biennially from participants aged 40 years or older who were free of glaucoma and reported eye examinations, within 3 population-based cohorts: the Nurses' Health Study (N = 50 710; followed up from 2000 to 2014), the Nurses' Health Study 2 (N = 62 992; 1999-2015), and the Health Professionals Follow-up Study (N = 23 080; 2000-2014). Incident cases of POAG were confirmed by medical record review. The analyses were performed in January 2019.

Exposures

Biennially updated self-reported information on elevated cholesterol level status, serum cholesterol levels, and duration of statin use.

Main Outcomes and Measures

Multivariable-adjusted relative risks (RRs) and 95% CIs were estimated using Cox proportional hazards regression models on pooled data, with stratification by cohort.

Results

Among the 136 782 participants in the 3 cohorts (113 702 women and 23 080 men), 886 incident cases of POAG were identified. Every 20-mg/dL increase in total serum cholesterol was associated with a 7% increase in risk of POAG (RR, 1.07 [95% CI, 1.02-1.11]; P = .004). Any self-reported history of elevated cholesterol was also associated with a higher risk of POAG (RR, 1.17 [95% CI, 1.00-1.37]). A history of any statin use was associated with a 15% lower risk of POAG (RR, 0.85 [95% CI, 0.73-0.99]). Use of statins for 5 or more years vs never use of statins was associated with a 21% lower risk of POAG (RR, 0.79 [95% CI, 0.65-0.97]; P = .02 for linear trend). The association between use of statins for 5 or more years vs never use of statins and risk of POAG was more inverse in those who were older (≥65 years: RR, 0.70 [95% CI, 0.56-0.87] vs <65 years: RR, 1.05 [95% CI, 0.68-1.63]; P = .01 for interaction).

Conclusions and Relevance

Among adults aged 40 years or older, higher serum cholesterol levels were associated with higher risk of POAG, while 5 or more years of statin use compared with never use of statins was associated with a lower risk of POAG.

Role of Post-translational Modifications in Alzheimer's Disease

The global burden of Alzheimer's disease (AD) is growing. Valiant efforts to develop clinical candidates for treatment have continuously met with failure. Currently available palliative treatments are temporary and there is a constant need to search for reliable disease pathways, biomarkers and drug targets for developing diagnostic and therapeutic tools to address the unmet medical needs of AD. Challenges in drug-discovery efforts raise further questions about the strategies of current conventional diagnosis; drug design; and understanding of disease pathways, biomarkers and targets. In this context, post-translational modifications (PTMs) regulate protein trafficking, function and degradation, and their in-depth study plays a significant role in the identification of novel biomarkers and drug targets. Aberrant PTMs of disease-relevant proteins could trigger pathological pathways, leading to disease progression. Advancements in proteomics enable the generation of patterns or signatures of such modifications, and thus, provide a versatile platform to develop biomarkers based on PTMs. In addition, understanding and targeting the aberrant PTMs of various proteins provide viable avenues for addressing AD drug-discovery challenges. This review highlights numerous PTMs of proteins relevant to AD and provides an overview of their adverse effects on the protein structure, function and aggregation propensity that contribute to the disease pathology. A critical discussion offers suggestions of methods to develop PTM signatures and interfere with aberrant PTMs to develop viable diagnostic and therapeutic interventions in AD.

Regulation of Small GTPase Prenylation in the Nervous System

Mevalonate pathway inhibitors have been extensively studied for their roles in cholesterol depletion and for inhibiting the prenylation and activation of various proteins. Inhibition of protein prenylation has potential therapeutic uses against neurological disorders, like neural cancers, neurodegeneration, and neurotramatic lesions. Protection against neurodegeneration and promotion of neuronal regeneration is regulated in large part by Ras superfamily small guanosine triphosphatases (GTPases), particularly the Ras, Rho, and Rab subfamilies. These proteins are prenylated to target them to cellular membranes. Prenylation can be specifically inhibited through altering the function of enzymes of the mevalonate pathway necessary for isoprenoid production and attachment to target proteins to elicit a variety of effects on neural cells. However, this approach does not address how prenylation affects a specific protein. This review focuses on the regulation of small GTPase prenylation, the different techniques to inhibit prenylation, and how this inhibition has affected neural cell processes.

Natural substance rutin versus standard drug atorvastatin in a treatment of metabolic syndrome-like condition

BACKGROUND

Metabolic syndrome is a cluster of metabolic risk factors. The clear causes of its development are not known yet and there is no comprehensive treatment of this disease. There is a trend to use natural substances in the treatment of various diseases, but their effects need to be well explored. We decided to test effect of rutin compared to the effect of the standard drug atorvastatin.

METHODS

As a model of metabolic syndrome we used males of hypertriacylglycerolemic rats in combination with high-fat-high-fructose diet. Rutin (100 mg/kg) and atorvastatin (50 mg/kg) were administered orally daily for 5 weeks.

RESULTS

We determined biochemical parameters from blood: HDL-cholesterol, LDL-cholesterol, total cholesterol, triacylglycerols. Relaxation and contraction response of aorta was measured to determine vessel dysfunctions and possible predisposition to cardiovascular disease. The negative influence on cognitive functions could be associated with the development of metabolic cognitive syndrome. Therefore we aimed to monitor spatial memory by Morris water maze test. Both rutin and atorvastatin had a tendency to decrease levels of serum triacylglycerols, but only atorvastatin significantly reduced levels od LDL-cholesterol and increased HDL-cholesterol levels. Both compounds significantly reduced the phenylephrine-induced contractile response of the aorta and improved the relaxation response. Further, treated animals learned better compared to untreated rats in the Morris water maze.

CONCLUSION

Based on our results we can assume that atorvastatin and rutin had positive effect on spatial memory and vessel reactivity. Atorvastatin optimized lipid profile of blood serum.

Effect of pioglitazone and simvastatin in lipopolysaccharide-induced amyloidogenesis and cognitive impairment in mice: possible role of glutamatergic pathway and oxidative stress

Neuroinflammation and β-amyloid (Aβ) deposition in the brain are well known characteristics of neurodegeneration. Diabetes and hypercholesterolemia are the main risk factors leading to memory loss and cognitive impairment. Recently, it was found that statins and thiazolidinediones have promising anti-inflammatory and neuroprotective effects that could delay neurodegeneration and neuronal loss in diabetic and hypercholesterolemic patients. The aim of the present study was to investigate the protective effect of simvastatin, pioglitazone, and their combination in lipopolysaccharide (LPS)-induced neuroinflammation and amyloidogenesis. Mice were divided into five groups: group 1 received 0.9% saline, group 2 received LPS (0.8 mg/kg in saline), group 3 received LPS (0.8 mgl kg)+simvastatin (5 mg/kg in saline), group 4 received LPS (0.8 mg/kg)+pioglitazone (20 mg/kg in saline), group 5 receiving LPS (0.8 mg/kg)+simvastatin (5 mg/kg)+pioglitazone (20 mg/kg). Y-maze and novel object recognition were used to assess the spatial and nonspatial behavioral changes. Nitric oxide levels and glutamate levels were measured to elucidate the anti-glutamatergic and anti-inflammatory effects of the tested drugs. Immunohistochemistry was performed to detect the presence of Aβ1-42 in the mice brain. LPS impaired memory, and increased Aβ deposition, nitric oxide, and glutamate brain levels. Both drugs produced a significant improvement in all parameters. We conclude that simvastatin and pioglitazone may have a protective effect against cognitive impairment induced by LPS, through targeting the glutamatergic and inflammatory pathways, especially in patients having hypercholesterolemia and diabetes.

Preliminary Study on Clusterin Protein (sCLU) Expression in PC-12 Cells Overexpressing Wild-Type and Mutated (Swedish) AβPP genes Affected by Non-Steroid Isoprenoids and Water-Soluble Cholesterol

In this study we attempted to verify the hypothesis that the mevalonate pathway affects amyloid beta precursor protein (AβPP) processing and regulates clusterin protein levels. AβPP expression was monitored by green fluorescence (FL) and Western blot (WB). WB showed soluble amyloid protein precursor alpha (sAβPPα) presence in AβPP-wt cells and Aβ expression in AβPP-sw cells. Nerve growth factor (NGF)-differentiated rat neuronal pheochromocytoma PC-12 cells were untreated/treated with statins alone or together with non-sterol isoprenoids. Co-treatment with mevalonate, dolichol, ubiquinol, farnesol, geranylgeraniol, or water-soluble cholesterol demonstrated statin-dependent neurotoxicity resulted from the attenuated activity of mevalonate pathway rather than lower cholesterol level. Atorvastatin (50 μM) or simvastatin (50 μM) as well as cholesterol chelator methyl-β-cyclodextrin (0.2 mM) diminished cell viability (p < 0.05) and clusterin levels. Interestingly, co-treatment with mevalonate, dolichol, ubiquinol, farnesol, geranylgeraniol, or water-soluble cholesterol stimulated (p < 0.05) clusterin expression. Effects of non-sterol isoprenoids, but not water soluble cholesterol (Chol-PEG), were the most significant in mock-transfected cells. Geranylgeraniol (GGOH) overcame atorvastatin (ATR)-dependent cytotoxicity. This effect does not seem to be dependent on clusterin, as its level became lower after GGOH. The novelty of these findings is that they show that the mevalonate (MEV) pathway rather than cholesterol itself plays an important role in clusterin expression levels. In mock-transfected, rather than in AβPP-overexpressing cells, GGOH/farnesol (FOH) exerted a protective effect. Thus, protein prenylation with GGOH/FOH might play substantial role in neuronal cell survival.

Statins and the Brain: More than Lipid Lowering Agents?

BACKGROUND

Statins represent a class of medications widely prescribed to efficiently treat dyslipidemia. These drugs inhibit 3-βhydroxy 3β-methylglutaryl Coenzyme A reductase (HMGR), the rate-limiting enzyme of mevalonate (MVA) pathway. Besides cholesterol, MVA pathway leads to the production of several other compounds, which are essential in the regulation of a plethora of biological activities, including in the central nervous system. For these reasons, statins are able to induce pleiotropic actions, and acquire increased interest as potential and novel modulators in brain processes, especially during pathological conditions.

OBJECTIVE

The purpose of this review is to summarize and examine the current knowledge about pharmacokinetic and pharmacodynamic properties of statins in the brain. In addition, effects of statin on brain diseases are discussed providing the most up-to-date information.

METHODS

Relevant scientific information was identified from PubMed database using the following keywords: statins and brain, central nervous system, neurological diseases, neurodegeneration, brain tumors, mood, stroke.

RESULTS

315 scientific articles were selected and analyzed for the writing of this review article. Several papers highlighted that statin treatment is effective in preventing or ameliorating the symptomatology of a number of brain pathologies. However, other studies failed to demonstrate a neuroprotective effect.

CONCLUSION

Even though considerable research studies suggest pivotal functional outcomes induced by statin therapy, additional investigation is required to better determine the pharmacological effectiveness of statins in the brain, and support their clinical use in the management of different neuropathologies.

Connecting the brain cholesterol and renin-angiotensin systems: potential role of statins and RAS-modifying medications in dementia

Millions of people worldwide receive agents targeting the renin-angiotensin system (RAS) to treat hypertension or statins to lower cholesterol. The RAS and cholesterol metabolic pathways in the brain are autonomous from their systemic counterparts and are interrelated through the cholesterol metabolite 27-hydroxycholesterol (27-OHC). These systems contribute to memory and dementia pathogenesis through interference in the amyloid-beta cascade, vascular mechanisms, glucose metabolism, apoptosis, neuroinflammation and oxidative stress. Previous studies examining the relationship between these treatments and cognition and dementia risk have produced inconsistent results. Defining the blood-brain barrier penetration of these medications has been challenging, and the mechanisms of action on cognition are not clearly established. Potential biases are apparent in epidemiological and clinical studies, such as reverse epidemiology, indication bias, problems defining medication exposure, uncertain and changing doses, and inappropriate grouping of outcomes and medications. This review summarizes current knowledge of the brain cholesterol and RAS metabolism and the mechanisms by which these pathways affect neurodegeneration. The putative mechanisms of action of statins and medications inhibiting the RAS will be examined, together with prior clinical and animal studies on their effects on cognition. We review prior epidemiological studies, analysing their strengths and biases, and identify areas for future research. Understanding the pathophysiology of the brain cholesterol system and RAS and their links to neurodegeneration has enormous potential. In future, well-designed epidemiological studies could identify potential treatments for Alzheimer's disease (AD) amongst medications that are already in use for other indications.

Isoprenoids and protein prenylation: implications in the pathogenesis and therapeutic intervention of Alzheimer's disease

The mevalonate-isoprenoid-cholesterol biosynthesis pathway plays a key role in human health and disease. The importance of this pathway is underscored by the discovery that two major isoprenoids, farnesyl and geranylgeranyl pyrophosphate, are required to modify an array of proteins through a process known as protein prenylation, catalyzed by prenyltransferases. The lipophilic prenyl group facilitates the anchoring of proteins in cell membranes, mediating protein-protein interactions and signal transduction. Numerous essential intracellular proteins undergo prenylation, including most members of the small GTPase superfamily as well as heterotrimeric G proteins and nuclear lamins, and are involved in regulating a plethora of cellular processes and functions. Dysregulation of isoprenoids and protein prenylation is implicated in various disorders, including cardiovascular and cerebrovascular diseases, cancers, bone diseases, infectious diseases, progeria, and neurodegenerative diseases including Alzheimer's disease (AD). Therefore, isoprenoids and/or prenyltransferases have emerged as attractive targets for developing therapeutic agents. Here, we provide a general overview of isoprenoid synthesis, the process of protein prenylation and the complexity of prenylated proteins, and pharmacological agents that regulate isoprenoids and protein prenylation. Recent findings that connect isoprenoids/protein prenylation with AD are summarized and potential applications of new prenylomic technologies for uncovering the role of prenylated proteins in the pathogenesis of AD are discussed.

Ras inhibitor S-trans, trans-farnesylthiosalicylic acid enhances spatial memory and hippocampal long-term potentiation via up-regulation of NMDA receptor

Statins by reducing farnesyl-pyrophosphate or farnesyl transferase inhibitors have been demonstrated to enhance spatial memory and long-term potentiation (LTP). The objective of this study was to investigate effects of the synthetic Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS) on spatial cognitive function in adult mice, synaptic plasticity in hippocampal CA1 regions, and NMDA receptor (NMDAr) activity of pyramidal cells. Here, we show that administering FTS (5 mg/kg, i.p.) enhanced spatial cognitive performance, as assessed via Morris water maze and Y-maze tests. Treating hippocampal slices with FTS (5 μM) for 2 h enhanced selectively NMDAr-dependent LTP without changing the synaptic properties. In comparison with the controls, the FTS-treated slices showed increases in the amplitude of NMDA-evoked currents (I_NMDA) and the phosphorylation of NMDAr GluN2A/GluN2B subunits and Src. The Src inhibitor PP2 blocked the enhancing effects of FTS on the activity and phosphorylation of NMDAr. In FTS-treated slices, basal levels of CaMKII, ERK2 and CREB phosphorylation did not differ significantly from those of controls; however, high-frequency stimulation-induced increases in CaMKII, ERK2 and CREB phosphorylation were more significant than in the controls, which were sensitive to PP2 and NMDAr antagonist MK801. Furthermore, the phosphorylation of AMPA receptor GluR1 during LTP was higher in FTS-treated slices compared with the control, which depended on Src and ERK1/2 signaling. The results indicate that the Ras inhibition by FTS can enhance NMDAr-dependent LTP by increasing Src activity to promote NMDAr GluN2A/GluN2B phosphorylation, which then leads to spatial memory potentiation.

The role of statins in both cognitive impairment and protection against dementia: a tale of two mechanisms

Nearly 30% of adults 40 years and older in the United States are on a statin. Their widespread use heightens the importance of careful consideration of their varied effects on the body. Although randomized controlled trials have not confirmed cognitive impairing effects with statins, continuing evidence suggests statins have the ability to cause reversible cognitive impairment in some patients. Paradoxically, statins have also been shown to decrease the risk of dementia, Alzheimer's disease, and improve cognitive impairment in some cases. However, randomized controlled trials have similarly failed to find the beneficial effect. Supporting evidence for both claims is compelling whereas known limitations of the clinical trials may explain the lack of findings. This narrative review aims to explain why there is still controversy and how both effects can, and may, be possible. The mechanisms that have been hypothesized for each effect are seemingly independent from one another and may explain the contradicting results. Being mindful of the complex effects of statins, health care providers need to be able to identify patients who are at risk for or already experiencing cognitive impairment from statin use while also identifying those who could potentially decrease their risk of dementia with statins.

Isoprenoids and tau pathology in sporadic Alzheimer's disease

The mevalonate pathway has been described to play a key role in Alzheimer's disease (AD) physiopathology. Farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are nonsterol isoprenoids derived from mevalonate, which serve as precursors to numerous human metabolites. They facilitate protein prenylation; hFPP and hGGPP synthases act as gateway enzymes to the prenylation of the small guanosine triphosphate (GTP)ase proteins such as RhoA and cdc42 that have been shown to facilitate phospho-tau (p-Tau, i.e., protein tau phosphorylated) production in the brain. In this study, a significant positive correlation was observed between the synthases mRNA prevalence and disease status (FPPS, p < 0.001, n = 123; GGPPS, p < 0.001, n = 122). The levels of mRNA for hFPPS and hGGPPS were found to significantly correlate with the amount of p-Tau protein levels (p < 0.05, n = 34) and neurofibrillary tangle density (p < 0.05, n = 39) in the frontal cortex. Interestingly, high levels of hFPPS and hGGPPS mRNA prevalence are associated with earlier age of onset in AD (p < 0.05, n = 58). Together, these results suggest that accumulation of p-Tau in the AD brain is related, at least in part, to increased levels of neuronal isoprenoids.

Alpha-Secretase ADAM10 Regulation: Insights into Alzheimer's Disease Treatment

ADAM (a disintegrin and metalloproteinase) is a family of widely expressed, transmembrane and secreted proteins of approximately 750 amino acids in length with functions in cell adhesion and proteolytic processing of the ectodomains of diverse cell-surface receptors and signaling molecules. ADAM10 is the main α-secretase that cleaves APP (amyloid precursor protein) in the non-amyloidogenic pathway inhibiting the formation of β-amyloid peptide, whose accumulation and aggregation leads to neuronal degeneration in Alzheimer’s disease (AD). ADAM10 is a membrane-anchored metalloprotease that sheds, besides APP, the ectodomain of a large variety of cell-surface proteins including cytokines, adhesion molecules and notch. APP cleavage by ADAM10 results in the production of an APP-derived fragment, sAPPα, which is neuroprotective. As increased ADAM10 activity protects the brain from β-amyloid deposition in AD, this strategy has been proved to be effective in treating neurodegenerative diseases, including AD. Here, we describe the physiological mechanisms regulating ADAM10 expression at different levels, aiming to propose strategies for AD treatment. We report in this review on the physiological regulation of ADAM10 at the transcriptional level, by epigenetic factors, miRNAs and/or translational and post-translational levels. In addition, we describe the conditions that can change ADAM10 expression in vitro and in vivo, and discuss how this knowledge may help in AD treatment. Regulation of ADAM10 is achieved by multiple mechanisms that include transcriptional, translational and post-translational strategies, which we will summarize in this review.

Inhibition of the RhoA/Rho-associated, coiled-coil-containing protein kinase-1 pathway is involved in the therapeutic effects of simvastatin on pulmonary arterial hypertension

BACKGROUND

Recent research has shown that statins improve pulmonary arterial hypertension (PAH), but their mechanisms of action are not fully understood. This study aimed to investigate the role of RhoA/ROCK1 regulation in the therapeutic effects of simvastatin on PAH.

METHODS

For in vivo experiments, rats (N = 40) were randomly assigned to four groups: control, simvastatin, monocrotaline (MCT), and MCT + simvastatin. The MCT group and MCT + simvastatin groups received proline dithiocarbamate (50 mg/kg, i.p.) on the first day of the study. The MCT + simvastatin group received simvastatin (2 mg/kg) daily for 4 weeks, after which pulmonary arterial pressure was measured by right heart catheterization. The protein and mRNA levels of Rho and ROCK1 were measured by immunohistochemistry, Western blot, and PCR. For in vitro experiments, human pulmonary endothelial cells were divided into seven groups: control, simvastatin, monocrotaline pyrrole (MCTP), MCTP + simvastatin, MCTP + simvastatin + mevalonate, MCTP + simvastatin + farnesyl pyrophosphate (FPP), and MCTP + simvastatin + FPP + geranylgeranyl pyrophosphate (GGPP). After 72 h exposed to the drugs, the protein and mRNA levels of RhoA and ROCK1 were measured by Western blot and PCR.

RESULTS

The MCT group showed increased mean pulmonary arterial pressure, marked vascular remodeling, and increased protein and mRNA levels of RhoA and ROCK1 compared to the other groups (P < 0.05). In vitro, the MCTP group showed a marked proliferation of vascular endothelial cells, as well as increased protein and mRNA levels of RhoA and ROCK1 compared to the MCTP + simvastatin group. The MCTP + simvastatin + mevalonate group, MCTP + simvastatin+ FPP group, and MCTP + simvastatin + FPP + GGPP group showed increased mRNA levels of RhoA and ROCK1, as well as increased protein levels of RhoA, compared to the MCTP + simvastatin group.

CONCLUSIONS

Simvastatin improved vascular remodeling and inhibited the development of PAH. The effects of simvastatin were mediated by inhibition of RhoA/ROCK1. Simvastatin decreased RhoA/ROCK1 overexpression by inhibition of mevalonate, FPP, and GGPP synthesis.

Neuroprotective effects of statins against amyloid β-induced neurotoxicity

A growing body of evidence suggests that disruption of the homeostasis of lipid metabolism affects the pathogenesis of Alzheimer's disease (AD). In particular, dysregulation of cholesterol homeostasis in the brain has been reported to considerably increase the risk of developing AD. Thus, dysregulation of lipid homeostasis may increase the amyloid β (Aβ) levels by affecting amyloid precursor protein (APP) cleavage, which is the most important risk factor involved in the pathogenesis of AD. Previous research demonstrated that Aβ can trigger neuronal insulin resistance, which plays an important role in response to Aβ-induced neurotoxicity in AD. Epidemiological studies also suggested that statin use is associated with a decreased incidence of AD. Therefore, statins are believed to be a good candidate for conferring neuroprotective effects against AD. Statins may play a beneficial role in reducing Aβ-induced neurotoxicity. Their effect involves a putative mechanism beyond its cholesterol-lowering effects in preventing Aβ-induced neurotoxicity. However, the underlying molecular mechanisms of the protective effect of statins have not been clearly determined in Aβ-induced neurotoxicity. Given that statins may provide benefits beyond the inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, these drugs may also improve the brain. Thus, statins may have beneficial effects on impaired insulin signaling by activating AMP-activated protein kinase (AMPK) in neuronal cells. They play a potential therapeutic role in targeting Aβ-mediated neurotoxicity.

Aβ inhibits SREBP-2 activation through Akt inhibition

We previously demonstrated that oligomeric amyloid β₄₂ (oAβ₄₂) inhibits the mevalonate pathway impairing cholesterol synthesis and protein prenylation. Enzymes of the mevalonate pathway are regulated by the transcription factor SREBP-2. Here, we show that in several neuronal types challenged with oAβ₄₂, SREBP-2 activation is reduced. Moreover, SREBP-2 activation is also decreased in the brain cortex of the Alzheimer's disease (AD) mouse model, TgCRND8, suggesting that SREBP-2 may be affected in vivo early in the disease. We demonstrate that oAβ₄₂ does not affect enzymatic cleavage of SREBP-2 per se, but may impair SREBP-2 transport from the endoplasmic reticulum (ER) to the Golgi. Trafficking of SREBP-2 from the ER to the Golgi requires protein kinase B (Akt) activation. oAβ₄₂ significantly reduces Akt phosphorylation and this decrease is responsible for the decline in SREBP-2 activation. Overexpression of constitutively active Akt prevents the effect of oAβ₄₂ on SREBP-2 and the downstream inhibition of cholesterol synthesis and protein prenylation. Our work provides a novel mechanistic link between Aβ and the mevalonate pathway, which will impact the views on issues related to cholesterol, isoprenoids, and statins in AD. We also identify SREBP-2 as an indirect target of Akt in neurons, which may play a role in the cross-talk between AD and diabetes.

The beneficial effects of HMG-CoA reductase inhibitors in the processes of neurodegeneration

Statins, cholesterol lowering drugs, have been demonstrated to exert beneficial effects in other conditions such as primary and progressing neurodegenerative diseases beyond their original role. Observation that statins ameliorate the neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), multiple sclerosis (MS) and cerebral ischemic stroke, the neuroprotective effects of these drugs are thought to be linked to their anti-inflammatory, anti-oxidative, and anti-excitotoxic properties. Despite the voluminous literature on the clinical advantages of 3-hydroxy-3-methylglutaryl Co-enzyme A reductase (HMGCR) inhibitors (statins) in cardiovascular system, the neuroprotective effects and the underlying mechanisms are little understood. Hence, the present review tries to provide a critical overview on the statin-induced neuroprotection, which are presumed to be associated with the ability to reduce cholesterol, Amyloid-β and apolipoprotein E (ApoE) levels, decrease reactive oxygen and nitrogen species (ROS and RNS) formation, inhibit excitotoxicity, modulate matrix metalloproteinases (MMPs), stimulate endothelial nitric oxide synthase (eNOS), and increase cerebral blood perfusion. This review is also aimed to illustrate that statins protect neurons against the neuro-inflammatory processes through balancing pro-inflammatory/anti-inflammatory cytokines. Ultimately, the beneficial role of statins in ameliorating the development of PD, AD, MS and cerebral ischemic stroke has been separately reviewed.

Exploring the biochemistry of the prenylome and its role in disease through proteomics: progress and potential

INTRODUCTION

Protein prenylation is a ubiquitous covalent post-translational modification characterized by the addition of farnesyl or geranylgeranyl isoprenoid groups to a cysteine residue located near the carboxyl terminal of a protein. It is essential for the proper localization and cellular activity of numerous proteins, including Ras family GTPases and G-proteins. In addition to its roles in cellular physiology, the prenylation process has important implications in human diseases and in the recent years, it has become attractive target of inhibitors with therapeutic potential. Areas covered: This review attempts to summarize the basic aspects of prenylation integrating them with biological functions in diseases and giving an account of the current status of prenylation inhibitors as potential therapeutics. We also summarize the methodologies for the characterization of this modification. Expert commentary: The growing body of evidence suggesting an important role of prenylation in diseases and the subsequent development of inhibitors of the enzymes responsible for this modification lead to the urgent need to identify the full spectrum of prenylated proteins that are altered in the disease or affected by drugs. Proteomic tools to analyze prenylated proteins are recently emerging, thanks to the advancement in the field of mass spectrometry coupled to enrichment strategies.

Inhibition of Cholesterol Biosynthesis Reduces γ-Secretase Activity and Amyloid-β Generation

Amyloid-β (Aβ) is one of major molecules contributing to the pathogenesis of Alzheimer's disease (AD). Aβ is derived from amyloid-β protein precursor (AβPP) through sequential cleavages by β- and γ-secretases. Regulation of these components is thought to be an important factor in Aβ generation during the pathogenesis of AD. AβPP, β-secretase, and γ-secretase reside in lipid rafts, where cholesterol regulates the integrity and flexibility of membrane proteins and Aβ is generated. However, the relationship between cholesterol and Aβ generation is controversial. In this study, we aimed to elucidate the direct effects of cholesterol depletion on AβPP processing using AY9944, which blocks the last step of cholesterol biosynthesis and thus minimizes the unknown side effects of upstream inhibitors, such as HMG-CoA reductase inhibitors. Treatment with AY9944 decreased γ-secretase activity and Aβ generation. These results suggested that changes in membrane composition by lowering cholesterol with AY9944 affected γ-secretase activity and Aβ generation, which is associated with AD pathogenesis.

Aβ-Induced Insulin Resistance and the Effects of Insulin on the Cholesterol Synthesis Pathway and Aβ Secretion in Neural Cells

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) toxicity, tau pathology, insulin resistance, neuroinflammation, and dysregulation of cholesterol homeostasis, all of which play roles in neurodegeneration. Insulin has polytrophic effects on neurons and may be at the center of these pathophysiological changes. In this study, we investigated possible relationships among insulin signaling and cholesterol biosynthesis, along with the effects of Aβ42 on these pathways in vitro. We found that neuroblastoma 2a (N2a) cells transfected with the human gene encoding amyloid-β protein precursor (AβPP) (N2a-AβPP) produced Aβ and exhibited insulin resistance by reduced p-Akt and a suppressed cholesterol-synthesis pathway following insulin treatment, and by increased phosphorylation of insulin receptor subunit-1 at serine 612 (p-IRS-S612) as compared to parental N2a cells. Treatment of human neuroblastoma SH-SY5Y cells with Aβ42 also increased p-IRS-S612, suggesting that Aβ42 is responsible for insulin resistance. The insulin resistance was alleviated when N2a-AβPP cells were treated with higher insulin concentrations. Insulin increased Aβ release from N2a-AβPP cells, by which it may promote Aβ clearance. Insulin increased cholesterol-synthesis gene expression in SH-SY5Y and N2a cells, including 24-dehydrocholesterol reductase (DHCR24) and 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR) through sterol-regulatory element-binding protein-2 (SREBP2). While Aβ42-treated SH-SY5Y cells exhibited increased HMGCR expression and c-Jun phosphorylation as pro-inflammatory responses, they also showed down-regulation of neuro-protective/anti-inflammatory DHCR24. These results suggest that Aβ42 may cause insulin resistance, activate JNK for c-Jun phosphorylation, and lead to dysregulation of cholesterol homeostasis, and that enhancing insulin signaling may relieve the insulin-resistant phenotype and the dysregulated cholesterol-synthesis pathway to promote Aβ release for clearance from neural cells.

Simvastatin inhibits protein isoprenylation in the brain

Evidence suggests that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, may reduce the risk of Alzheimer's disease (AD). Statin action in patients with AD, as in those with heart disease, is likely to be at least partly independent of the effects of statins on cholesterol. Statins can alter cellular signaling and protein trafficking through inhibition of isoprenylation of Rho, Cdc42, and Rab family GTPases. The effects of statins on protein isoprenylation in vivo, particularly in the central nervous system, are poorly studied. We utilized two-dimensional gel electrophoresis approaches to directly monitor the levels of isoprenylated and non-isoprenylated forms of Rho and Rab family GTPases. We report that simvastatin significantly inhibits RhoA and Rab4, and Rab6 isoprenylation at doses as low as 50nM in vitro. We also provide the first in vivo evidence that statins inhibit the isoprenylation of RhoA in the brains of rats and RhoA, Cdc42, and H-Ras in the brains of mice treated with clinically relevant doses of simvastatin.

Simvastatin enhances NMDA receptor GluN2B expression and phosphorylation of GluN2B and GluN2A through increased histone acetylation and Src signaling in hippocampal CA1 neurons

Simvastatin (SV) can improve cognitive deficits in Alzheimer's disease patients and mice. Herein, we report that the administration of SV (20 mg/kg) for 5 days in mice (SV-mice) or the treatment of slices with SV (10 μM) for 4 h (SV-slices) could increase the density of NMDA-evoked inward currents (INMDA) in hippocampal CA1 pyramidal cells, which were blocked by farnesol (FOH) that converts farnesyl pyrophosphate (FPP), but not geranylgeraniol (GGOH) that increases geranylgeranylpyrophosphate (GGPP). Sensitivity of INMDA to ifenprodil in SV-mice or SV-slices was significantly increased. The levels of hippocampal GluN2B and GluN2A or Src phosphorylation in SV-mice or SV-slices were higher than controls, which were sensitive to FOH. The Src inhibitor PP2 could inhibit the SV-enhanced phosphorylation of GluN2B and GluN2A and SV-augmented INMDA, but PI3K inhibitor LY294002 did not. The levels of GluN2B mRNA and protein were elevated in SV-mice, which was abolished by FOH, but not by GGOH or PP2. Furthermore, the histone H3K9 and H3K27 acetylation of GluN2B promoter was increased in SV-mice, which was suppressed by FOH rather than GGOH or PP2. In control mice and slices, the reduction of FPP by farnesyl transferase inhibitor could increase the levels of GluN2B expression, the histone H3K9 and H3K27 acetylation and enhance the phosphorylation of GluN2B, GluN2A and Src. The findings indicate that the administration of SV can enhance GluN2B expression and GluN2B and GluN2A phosphorylation leading to augmentation of NMDAR activity through reducing FPP to increase histone acetylation of GluN2B and Src signaling.

Inhibition of Rab prenylation by statins induces cellular glycosphingolipid remodeling

Statins, which specifically inhibit HMG Co-A reductase, the rate-limiting step of cholesterol biosynthesis, are widely prescribed to reduce serum cholesterol and cardiac risk, but many other effects are seen. We now show an effect of these drugs to induce profound changes in the step-wise synthesis of glycosphingolipids (GSLs) in the Golgi. Glucosylceramide (GlcCer) was increased several-fold in all cell lines tested, demonstrating a widespread effect. Additionally, de novo or elevated lactotriaosylceramide (Lc3Cer; GlcNAcβ1-3Galβ1-4GlcCer) synthesis was observed in 70%. Western blot showed that GlcCer synthase (GCS) was elevated by statins, and GCS and Lc3Cer synthase (Lc3S) activities were increased; however, transcript was elevated for Lc3S only. Supplementation with the isoprenoid precursor, geranylgeranyl pyrophosphate (GGPP), a downstream product of HMG Co-A reductase, reversed statin-induced glycosyltransferase and GSL elevation. The Rab geranylgeranyl transferase inhibitor 3-PEHPC, but not specific inhibitors of farnesyl transferase, or geranylgeranyl transferase I, was sufficient to replicate statin-induced GlcCer and Lc3Cer synthesis, supporting a Rab prenylation-dependent mechanism. While total cholesterol was unaffected, the trans-Golgi network (TGN) cholesterol pool was dissipated and medial Golgi GCS partially relocated by statins. GSL-dependent vesicular retrograde transport of Verotoxin and cholera toxin to the Golgi/endoplasmic reticulum were blocked after statin or 3-PEHPC treatment, suggesting aberrant, prenylation-dependent vesicular traffic as a basis of glycosyltransferase increase and GSL remodeling. These in vitro studies indicate a previously unreported link between Rab prenylation and regulation of GCS activity and GlcCer metabolism.

Pharmacological modulation of dietary lipid-induced cerebral capillary dysfunction: Considerations for reducing risk for Alzheimer's disease

An increasing body of evidence suggests that cerebrovascular dysfunction and microvessel disease precede the evolution of hallmark pathological features that characterise Alzheimer's disease (AD), consistent with a causal association for onset or progression. Recent studies, principally in genetically unmanipulated animal models, suggest that chronic ingestion of diets enriched in saturated fats and cholesterol may compromise blood-brain barrier (BBB) integrity resulting in inappropriate blood-to-brain extravasation of plasma proteins, including lipid macromolecules that may be enriched in amyloid-β (Aβ). Brain parenchymal retention of blood proteins and lipoprotein bound Aβ is associated with heightened neurovascular inflammation, altered redox homeostasis and nitric oxide (NO) metabolism. Therefore, it is a reasonable proposition that lipid-lowering agents may positively modulate BBB integrity and by extension attenuate risk or progression of AD. In addition to their robust lipid lowering properties, reported beneficial effects of lipid-lowering agents were attributed to their pleiotropic properties via modulation of inflammation, oxidative stress, NO and Aβ metabolism. The review is a contemporary consideration of a complex body of literature intended to synthesise focussed consideration of mechanisms central to regulation of BBB function and integrity. Emphasis is given to dietary fat driven significant epidemiological evidence consistent with heightened risk amongst populations consuming greater amounts of saturated fats and cholesterol. In addition, potential neurovascular benefits associated with the use of hypolipidemic statins, probucol and fenofibrate are also presented in the context of lipid-lowering and pleiotropic properties.

Overnutrition Determines LPS Regulation of Mycotoxin Induced Neurotoxicity in Neurodegenerative Diseases

Chronic neurodegenerative diseases are now associated with obesity and diabetes and linked to the developing and developed world. Interests in healthy diets have escalated that may prevent neurodegenerative diseases such as Parkinson's and Alzheimer's disease. The global metabolic syndrome involves lipoprotein abnormalities and insulin resistance and is the major disorder for induction of neurological disease. The effects of bacterial lipopolysaccharides (LPS) on dyslipidemia and NAFLD indicate that the clearance and metabolism of fungal mycotoxins are linked to hypercholesterolemia and amyloid beta oligomers. LPS and mycotoxins are associated with membrane lipid disturbances with effects on cholesterol interacting proteins, lipoprotein metabolism, and membrane apo E/amyloid beta interactions relevant to hypercholesterolemia with close connections to neurological diseases. The influence of diet on mycotoxin metabolism has accelerated with the close association between mycotoxin contamination from agricultural products such as apple juice, grains, alcohol, and coffee. Cholesterol efflux in lipoproteins and membrane cholesterol are determined by LPS with involvement of mycotoxin on amyloid beta metabolism. Nutritional interventions such as diets low in fat/carbohydrate/cholesterol have become of interest with relevance to low absorption of lipophilic LPS and mycotoxin into lipoproteins with rapid metabolism of mycotoxin to the liver with the prevention of neurodegeneration.

Mevalonate Pathway Regulates Cell Size Homeostasis and Proteostasis through Autophagy

Balance between cell growth and proliferation determines cell size homeostasis, but little is known about how metabolic pathways are involved in the maintenance of this balance. Here, we perform a screen with a library of clinically used drug molecules for their effects on cell size. We find that statins, inhibitors of the mevalonate pathway, reduce cell proliferation and increase cell size and cellular protein density in various cell types, including primary human cells. Mevalonate pathway effects on cell size and protein density are mediated through geranylgeranylation of the small GTPase RAB11, which is required for basal autophagic flux. Our results identify the mevalonate pathway as a metabolic regulator of autophagy and expose a paradox in the regulation of cell size and proteostasis, where inhibition of an anabolic pathway can cause an increase in cell size and cellular protein density.

•

Mevalonate pathway regulates cell size, proliferation, and cellular protein density

•

Geranylgeranylation of RAB11 links mevalonate pathway to autophagy

•

Mevalonate pathway is required for basal autophagic flux

•

Cell size and protein density effects are dependent on RAB11 and autophagy

Potential of tocotrienols in the prevention and therapy of Alzheimer's disease

Currently there is no cure for Alzheimer's disease (AD); clinical trials are underway to reduce amyloid generation and deposition, a neuropathological hallmark in brains of AD patients. While genetic factors and neuroinflammation contribute significantly to AD pathogenesis, whether increased cholesterol level is a causative factor or a result of AD is equivocal. Prenylation of proteins regulating neuronal functions requires mevalonate-derived farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). The observation that the levels of FPP and GGPP, but not that of cholesterol, are elevated in AD patients is consistent with the finding that statins, competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, reduce FPP and GGPP levels and amyloid β protein production in preclinical studies. Retrospective studies show inverse correlations between incidence of AD and the intake and serum levels of the HMG CoA reductase-suppressive tocotrienols; tocopherols show mixed results. Tocotrienols, but not tocopherols, block the processing and nuclear localization of sterol regulatory element binding protein-2, the transcriptional factor for HMG CoA reductase and FPP synthase, and enhance the degradation of HMG CoA reductase. Consequently, tocotrienols deplete the pool of FPP and GGPP and potentially blunt prenylation-dependent AD pathogenesis. The antiinflammatory activity of tocotrienols further contributes to their protection against AD. The mevalonate- and inflammation-suppressive activities of tocotrienols may represent those of an estimated 23,000 mevalonate-derived plant secondary metabolites called isoprenoids, many of which are neuroprotective. Tocotrienol-containing plant foods and tocotrienol derivatives and formulations with enhanced bioavailability may offer a novel approach in AD prevention and treatment.