Regulation of the brain isoprenoids farnesyl- and geranylgeranylpyrophosphate is altered in male Alzheimer patients

Relationships of brain cholesterol and cholesterol biosynthetic enzymes to Alzheimer's pathology and dementia in the CFAS population-derived neuropathology cohort

Altered cholesterol metabolism is implicated in brain ageing and Alzheimer's disease. We examined whether key genes regulating cholesterol metabolism and levels of brain cholesterol are altered in dementia and Alzheimer's disease neuropathological change (ADNC). Temporal cortex (n = 99) was obtained from the Cognitive Function and Ageing Study. Expression of the cholesterol biosynthesis rate-limiting enzyme HMG-CoA reductase (HMGCR) and its regulator, SREBP2, were detected using immunohistochemistry. Expression of HMGCR, SREBP2, CYP46A1 and ABCA1 were quantified by qPCR in samples enriched for astrocyte and neuronal RNA following laser-capture microdissection. Total cortical cholesterol was measured using the Amplex Red assay. HMGCR and SREBP2 proteins were predominantly expressed in pyramidal neurones, and in glia. Neuronal HMGCR did not vary with ADNC, oxidative stress, neuroinflammation or dementia status. Expression of HMGCR neuronal mRNA decreased with ADNC (p = 0.022) and increased with neuronal DNA damage (p = 0.049), whilst SREBP2 increased with ADNC (p = 0.005). High or moderate tertiles for cholesterol levels were associated with increased dementia risk (OR 1.44, 1.58). APOE ε4 allele was not associated with cortical cholesterol levels. ADNC is associated with gene expression changes that may impair cholesterol biosynthesis in neurones but not astrocytes, whilst levels of cortical cholesterol show a weak relationship to dementia status.

Metabolite-derived damage-associated molecular patterns in immunological diseases

Damage-associated molecular patterns (DAMPs) are typically derived from the endogenous elements of necrosis cells and can trigger inflammatory responses by activating DAMPs-sensing receptors on immune cells. Failure to clear DAMPs may lead to persistent inflammation, thereby contributing to the pathogenesis of immunological diseases. This review focuses on a newly recognized class of DAMPs derived from lipid, glucose, nucleotide, and amino acid metabolic pathways, which are then termed as metabolite-derived DAMPs. This review summarizes the reported molecular mechanisms of these metabolite-derived DAMPs in exacerbating inflammation responses, which may attribute to the pathology of certain types of immunological diseases. Additionally, this review also highlights both direct and indirect clinical interventions that have been explored to mitigate the pathological effects of these DAMPs. By summarizing our current understanding of metabolite-derived DAMPs, this review aims to inspire future thoughts and endeavors on targeted medicinal interventions and the development of therapies for immunological diseases.

Geranylgeranyl diphosphate synthase: Role in human health, disease and potential therapeutic target

Geranylgeranyl diphosphate synthase (GGDPS), an enzyme in the isoprenoid biosynthesis pathway, is responsible for the production of geranylgeranyl pyrophosphate (GGPP). GGPP serves as a substrate for the post-translational modification (geranylgeranylation) of proteins, including those belonging to the Ras superfamily of small GTPases. These proteins play key roles in signalling pathways, cytoskeletal regulation and intracellular transport, and in the absence of the prenylation modification, cannot properly localise and function. Aberrant expression of GGDPS has been implicated in various human pathologies, including liver disease, type 2 diabetes, pulmonary disease and malignancy. Thus, this enzyme is of particular interest from a therapeutic perspective. Here, we review the physiological function of GGDPS as well as its role in pathophysiological processes. We discuss the current GGDPS inhibitors under development and the therapeutic implications of targeting this enzyme.

The mevalonate suppressor δ-tocotrienol increases AMPA receptor-mediated neurotransmission

Synaptic dysfunction is a hallmark of aging and is found in several neurological disorders such as Alzheimer's disease. A common mechanism related to synaptic dysfunction is dysregulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which mediate excitatory neurotransmission and synaptic plasticity. Accumulating evidence suggests that tocotrienols, vitamin E molecules that contain an isoprenoid side chain, may promote cognitive improvement in hippocampal-dependent learning tasks. Tocotrienols have also been shown to reduce the secretion of β-amyloid (Aβ) and cholesterol biosynthesis in part by downregulating 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme that controls flux of the mevalonate pathway and cholesterol biosynthesis. We hypothesized that tocotrienols might promote cognitive improvement by increasing AMPA receptor-mediated synaptic transmission. Here, we found that δ-tocotrienol increased surface levels of GluA1 but not the GluA2 AMPA receptor subunit in primary hippocampal neurons. Unexpectedly, δ-tocotrienol treatment caused a decrease in the phosphorylation of GluA1 at Serine 845 with no significant changes in GluA1 at Serine 831. Moreover, δ-tocotrienol increased spontaneous excitatory postsynaptic current (sEPSC) amplitude and reduced the secretion of Aβ₄₀ in primary hippocampal neurons. Taken together, our findings suggest that δ-tocotrienol increases AMPA receptor-mediated neurotransmission via noncanonical changes in GluA1 phosphorylation status. These findings suggest that δ-tocotrienol may be beneficial in ameliorating synaptic dysfunction found in aging and neurological disease.

In Vivo Prenylomic Profiling in the Brain of a Transgenic Mouse Model of Alzheimer's Disease Reveals Increased Prenylation of a Key Set of Proteins

Dysregulation of protein prenylation has been implicated in many diseases, including Alzheimer's disease (AD). Prenylomic analysis, the combination of metabolic incorporation of an isoprenoid analogue (C15AlkOPP) into prenylated proteins with a bottom-up proteomic analysis, has allowed the identification of prenylated proteins in various cellular models. Here, transgenic AD mice were administered with C15AlkOPP through intracerebroventricular (ICV) infusion over 13 days. Using prenylomic analysis, 36 prenylated proteins were enriched in the brains of AD mice. Importantly, the prenylated forms of 15 proteins were consistently upregulated in AD mice compared to nontransgenic wild-type controls. These results highlight the power of this in vivo metabolic labeling approach to identify multiple post-translationally modified proteins that may serve as potential therapeutic targets for a disease that has proved refractory to treatment thus far. Moreover, this method should be applicable to many other types of protein modifications, significantly broadening its scope.

Prenylation Defects and Oxidative Stress Trigger the Main Consequences of Neuroinflammation Linked to Mevalonate Pathway Deregulation

The cholesterol biosynthesis represents a crucial metabolic pathway for cellular homeostasis. The end products of this pathway are sterols, such as cholesterol, which are essential components of cell membranes, precursors of steroid hormones, bile acids, and other molecules such as ubiquinone. Furthermore, some intermediates of this metabolic system perform biological activity in specific cellular compartments, such as isoprenoid molecules that can modulate different signal proteins through the prenylation process. The defects of prenylation represent one of the main causes that promote the activation of inflammation. In particular, this mechanism, in association with oxidative stress, induces a dysfunction of the mitochondrial activity. The purpose of this review is to describe the pleiotropic role of prenylation in neuroinflammation and to highlight the consequence of the defects of prenylation.

Targeting of Mevalonate-Isoprenoid Pathway in Acute Myeloid Leukemia Cells by Bisphosphonate Drugs

Metabolic reprogramming represents a hallmark of tumorigenesis to sustain survival in harsh conditions, rapid growth and metastasis in order to resist to cancer therapies. These metabolic alterations involve glucose metabolism, known as the Warburg effect, increased glutaminolysis and enhanced amino acid and lipid metabolism, especially the cholesterol biosynthesis pathway known as the mevalonate pathway and these are upregulated in several cancer types, including acute myeloid leukemia (AML). In particular, it was demonstrated that the mevalonate pathway has a pivotal role in cellular transformation. Therefore, targeting this biochemical process with drugs such as statins represents a promising therapeutic strategy to be combined with other anticancer treatments. In the last decade, several studies have revealed that amino-bisphosphonates (BP), primarily used for bone fragility disorders, also exhibit potential anti-cancer activity in leukemic cells, as well as in patients with symptomatic multiple myeloma. Indeed, these compounds inhibit the farnesyl pyrophosphate synthase, a key enzyme in the mevalonate pathway, reducing isoprenoid formation of farnesyl pyrophosphate and geranylgeranyl pyrophosphate. This, in turn, inhibits the prenylation of small Guanosine Triphosphate-binding proteins, such as Ras, Rho, Rac, Rab, which are essential for regulating cell survival membrane ruffling and trafficking, interfering with cancer key signaling events involved in clonal expansion and maturation block of progenitor cells in myeloid hematological malignancies. Thus, in this review, we discuss the recent advancements about bisphosphonates’ effects, especially zoledronate, analyzing the biochemical mechanisms and anti-tumor effects on AML model systems. Future studies will be oriented to investigate the clinical relevance and significance of BP treatment in AML, representing an attractive therapeutic strategy that could be integrated into chemotherapy.

Plasma High Density Lipoprotein Small Subclass is Reduced in Alzheimer's Disease Patients and Correlates with Cognitive Performance

Background:

The link between cholesterol and Alzheimer’s disease (AD) has received much attention, as evidence suggests high levels of cholesterol might be an AD risk factor. The carriage of cholesterol and lipids through the body is mediated via lipoproteins, some of which, particularly apolipoprotein E (ApoE), are intimately linked with AD. In humans, high density lipoprotein (HDL) is regarded as a “good” lipid complex due to its ability to enable clearance of excess cholesterol via ‘cholesterol reverse transport’, although its activities in the pathogenesis of AD are poorly understood. There are several subclasses of HDL; these range from the newly formed small HDL, to much larger HDL.

Objective:

We examined the major subclasses of HDL in healthy controls, mild cognitively impaired, and AD patients who were not taking statins to determine whether there were HDL profile differences between the groups, and whether HDL subclass levels correlated with plasma amyloid-β (Aβ) levels or brain Aβ deposition.

Methods:

Samples from AIBL cohort were used in this study. HDL subclass levels were assessed by Lipoprint while Aβ_1–42 levels were assessed by ELISA. Brain Aβ deposition was assessed by PET scan. Statistical analysis was performed using parametric and non-parametric tests.

Results:

We found that small HDL subclass is reduced in AD patients and it correlates with cognitive performance while plasma Aβ concentrations do not correlate with lipid profile or HDL subfraction levels.

Conclusion:

Our data indicate that AD patients exhibit altered plasma HDL profile and that HDL subclasses correlate with cognitive performances.

Protein farnesylation is upregulated in Alzheimer's human brains and neuron-specific suppression of farnesyltransferase mitigates pathogenic processes in Alzheimer's model mice

The pathogenic mechanisms underlying the development of Alzheimer's disease (AD) remain elusive and to date there are no effective prevention or treatment for AD. Farnesyltransferase (FT) catalyzes a key posttranslational modification process called farnesylation, in which the isoprenoid farnesyl pyrophosphate is attached to target proteins, facilitating their membrane localization and their interactions with downstream effectors. Farnesylated proteins, including the Ras superfamily of small GTPases, are involved in regulating diverse physiological and pathological processes. Emerging evidence suggests that isoprenoids and farnesylated proteins may play an important role in the pathogenesis of AD. However, the dynamics of FT and protein farnesylation in human brains and the specific role of neuronal FT in the pathogenic progression of AD are not known. Here, using postmortem brain tissue from individuals with no cognitive impairment (NCI), mild cognitive impairment (MCI), or Alzheimer's dementia, we found that the levels of FT and membrane-associated H-Ras, an exclusively farnesylated protein, and its downstream effector ERK were markedly increased in AD and MCI compared with NCI. To elucidate the specific role of neuronal FT in AD pathogenesis, we generated the transgenic AD model APP/PS1 mice with forebrain neuron-specific FT knockout, followed by a battery of behavioral assessments, biochemical assays, and unbiased transcriptomic analysis. Our results showed that the neuronal FT deletion mitigates memory impairment and amyloid neuropathology in APP/PS1 mice through suppressing amyloid generation and reversing the pathogenic hyperactivation of mTORC1 signaling. These findings suggest that aberrant upregulation of protein farnesylation is an early driving force in the pathogenic cascade of AD and that targeting FT or its downstream signaling pathways presents a viable therapeutic strategy against AD.

Effects of simvastatin on white matter integrity in healthy middle-aged adults

Background

The brain is the most cholesterol‐rich organ and myelin contains 70% of total brain cholesterol. Statins are potent cholesterol‐lowing medications used by millions of adults for prevention of vascular disease, yet the effect of statins on cholesterol‐rich brain white matter (WM) is largely unknown.

Methods

We used longitudinal neuroimaging data acquired from 73 healthy, cognitively unimpaired, statin‐naïve, middle‐aged adults during an 18‐month randomized controlled trial of simvastatin 40 mg daily (n = 35) or matching placebo (n = 38). ANCOVA models (covariates: age, sex, APOE‐ɛ4) tested the effect of treatment group on percent change in WM, gray matter (GM), and WM hyperintensity (WMH) neuroimaging measures at each study visit. Mediation analysis tested the indirect effects of simvastatin on WM microstructure through change in serum total cholesterol levels.

Results

At 18 months, the simvastatin group showed a significant preservation in global WM fractional anisotropy (β = 0.88%, 95% CI 0.27 to 1.50, P = 0.005), radial diffusivity (β = −1.10%, 95% CI −2.13 to −0.06, P = 0.039), and WM volume (β = 0.72%, 95% CI 0.13 to 1.32, P = 0.018) relative to the placebo group. There was no significant effect of simvastatin on GM or WMH volume. Change in serum total cholesterol mediated approximately 30% of the effect of simvastatin on WM microstructure.

Conclusions

Simvastatin treatment in healthy, middle‐aged adults resulted in preserved WM microstructure and volume at 18 months. The partial mediation by serum cholesterol reduction suggests both peripheral and central mechanisms. Future studies are needed to determine whether these effects persist and translate to cognitive outcomes.

Trial Registration

NCT00939822 (ClinicalTrials.gov).

Abnormal brain cholesterol homeostasis in Alzheimer's disease-a targeted metabolomic and transcriptomic study

The role of brain cholesterol metabolism in Alzheimer's disease (AD) remains unclear. Peripheral and brain cholesterol levels are largely independent due to the impermeability of the blood brain barrier (BBB), highlighting the importance of studying the role of brain cholesterol homeostasis in AD. We first tested whether metabolite markers of brain cholesterol biosynthesis and catabolism were altered in AD and associated with AD pathology using linear mixed-effects models in two brain autopsy samples from the Baltimore Longitudinal Study of Aging (BLSA) and the Religious Orders Study (ROS). We next tested whether genetic regulators of brain cholesterol biosynthesis and catabolism were altered in AD using the ANOVA test in publicly available brain tissue transcriptomic datasets. Finally, using regional brain transcriptomic data, we performed genome-scale metabolic network modeling to assess alterations in cholesterol biosynthesis and catabolism reactions in AD. We show that AD is associated with pervasive abnormalities in cholesterol biosynthesis and catabolism. Using transcriptomic data from Parkinson's disease (PD) brain tissue samples, we found that gene expression alterations identified in AD were not observed in PD, suggesting that these changes may be specific to AD. Our results suggest that reduced de novo cholesterol biosynthesis may occur in response to impaired enzymatic cholesterol catabolism and efflux to maintain brain cholesterol levels in AD. This is accompanied by the accumulation of nonenzymatically generated cytotoxic oxysterols. Our results set the stage for experimental studies to address whether abnormalities in cholesterol metabolism are plausible therapeutic targets in AD.

Geranylgeranyl pyrophosphate-mediated protein geranylgeranylation regulates endothelial cell proliferation and apoptosis during vasculogenesis in mouse embryo

Vascular development is essential for the establishment of the circulatory system during embryonic development and requires the proliferation of endothelial cells. However, the underpinning regulatory mechanisms are not well understood. Here, we report that geranylgeranyl pyrophosphate (GGPP), a metabolite involved in protein geranylgeranylation, plays an indispensable role in embryonic vascular development. GGPP is synthesized by geranylgeranyl pyrophosphate synthase (GGPPS) in the mevalonate pathway. The selective knockout of Ggpps in endothelial cells led to aberrant vascular development and embryonic lethality, resulting from the decreased proliferation and enhanced apoptosis of endothelial cells during vasculogenesis. The defect in protein geranylgeranylation induced by GGPP depletion inhibited the membrane localization of RhoA and enhanced yes-associated protein (YAP) phosphorylation, thereby prohibiting the entry of YAP into the nucleus and the expression of YAP target genes related to cell proliferation and the antiapoptosis process. Moreover, inhibition of the mevalonate pathway by simvastatin induced endothelial cell proliferation defects and apoptosis, which were ameliorated by GGPP. Geranylgeraniol (GGOH), a precursor of GGPP, ameliorated the harmful effects of simvastatin on vascular development of developing fetuses in pregnant mice. These results indicate that GGPP-mediated protein geranylgeranylation is essential for endothelial cell proliferation and the antiapoptosis process during embryonic vascular development.

Farnesyl pyrophosphate is a new danger signal inducing acute cell death

Cell death is a vital event in life. Infections and injuries cause lytic cell death, which gives rise to danger signals that can further induce cell death, inflammation, and tissue damage. The mevalonate (MVA) pathway is an essential, highly conserved and dynamic metabolic pathway. Here, we discover that farnesyl pyrophosphate (FPP), a metabolic intermediate of the MVA pathway, functions as a newly identified danger signal to trigger acute cell death leading to neuron loss in stroke. Harboring both a hydrophobic 15-carbon isoprenyl chain and a heavily charged pyrophosphate head, FPP leads to acute cell death independent of its downstream metabolic pathways. Mechanistically, extracellular calcium influx and the cation channel transient receptor potential melastatin 2 (TRPM2) exhibit essential roles in FPP-induced cell death. FPP activates TRPM2 opening for ion influx. Furthermore, in terms of a mouse model constructing by middle cerebral artery occlusion (MCAO), FPP accumulates in the brain, which indicates the function of the FPP and TRPM2 danger signal axis in ischemic injury. Overall, our data have revealed a novel function of the MVA pathway intermediate metabolite FPP as a danger signal via transient receptor potential cation channels.

Serotonin transporter regulation by cholesterol-independent lipid signaling

Serotonin neurotransmission is largely governed by the regulation of the serotonin transporter (SERT). SERT is modulated in part by cholesterol, but the role of cholesterol and lipid signaling intermediates in regulating SERT are unknown. Serotonergic neurons were treated with statins to decrease cholesterol and lipid signaling intermediates. Contrary to reported decreases in 5-HT uptake after cholesterol depletion, biochemical and imaging methods both showed that statins increased 5-HT uptake in a fluoxetine-dependent manner. Simvastatin lowered the Km without changing Vmax for 5-HT or SERT distribution to the plasma membrane. Cholesterol repletion did not block enhanced 5-HT uptake by simvastatin but the enhanced uptake was blocked by lipid isoprenylation intermediates farnesyl pyrophosphate and geranylgeranyl pyrophosphate. Blockade of geranylgeranylation alone without statins also enhanced 5-HT uptake. Overall, this study revealed a specific neuronal effect of statin drugs and identified lipid signaling through geranylgeranylation within the isoprenylation pathway regulates SERT in a cholesterol-independent manner.

Prenylation of Axonally Translated Rac1 Controls NGF-Dependent Axon Growth

Compartmentalized signaling is critical for cellular organization and specificity of functional outcomes in neurons. Here, we report that post-translational lipidation of newly synthesized proteins in axonal compartments allows for short-term and autonomous responses to extrinsic cues. Using conditional mutant mice, we found that protein prenylation is essential for sympathetic axon innervation of target organs. We identify a localized requirement for prenylation in sympathetic axons to promote axonal growth in response to the neurotrophin, nerve growth factor (NGF). NGF triggers prenylation of proteins including the Rac1 GTPase in axons, counter to the canonical view of prenylation as constitutive, and strikingly, in a manner dependent on axonal protein synthesis. Newly prenylated proteins localize to TrkA-harboring endosomes in axons and promote receptor trafficking necessary for axonal growth. Thus, coupling of prenylation to local protein synthesis presents a mechanism for spatially segregated cellular functions during neuronal development.

Neuroprotective role of alendronate against APP processing and neuroinflammation in mice fed a high fat diet

Obesity and consumption of diet rich in fat are known to contribute to the development of Alzheimer's disease (AD) which is a complex and multifactorial neurodegenerative disease and a leading cause of mortality with unmet medical needs. Hypercholesterolemia was discovered to increase neuropathological changes along with cognitive decline in AD mouse models but still the underlying mechanism is elusive. Furthermore, isoprenoids, the crucial products of Mevalonate-pathway produced by the action of farnesyl pyrophosphate synthase (FPPS) enzyme, are also demonstrated to play a key role in AD. Nevertheless, bisphosphonates target this enzyme in order to treat osteoporosis and also found to alleviate dementia in such patients. As per the cited inhibitory action of alendronate, against acetylcholinesterase and cholesterol level, we hypothesized to explore the potential of alendronate against high fat diet (HFD) induced neuropathologies and cognitive disabilities in AD mouse model. Here we noticed that in mice provided with HFD for 14 weeks, spatial memory was compromised as interpreted in different behavioral paradigms. Together with cognitive depletion, there was observed a provoking effect on amyloid precursor protein (APP)-processing via amyloidogenic pathway due to enhanced β-site APP cleaving enzyme-1 (BACE-1) level which in turn leads to augmented release of amyloid beta (Aβ) in hippocampus of HFD mice. Relevant to these, significant elevation in hippocampal level of neuroinflammatory cytokines, oxidative stress markers and isoprenoids and serum cholesterol were also found after HFD exposure. Marked reversal of cognitive impairment, enhanced APP-processing, neuroinflammation along with other neuropathological alterations in hippocampus was demonstrated following oral administration of alendronate (1.76 mg/kg) for 15 days despite of HFD treatment. These changes were noted to be due to modulation of isoprenoids and cholesterol level by alendronate. Supporting these, histopathological analysis done by congo red revealed the reduced Aβ deposition in hippocampus of drug treated HFD mice The current outcomes provide important implications for the contribution of Mevalonate-pathway and HFD for the onset of AD and also support alendronate as a prominent intervention for amelioration of AD-like pathologies.

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.

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.

Sterol regulatory element binding protein 1 couples mechanical cues and lipid metabolism

Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate lipid biosynthesis and adipogenesis by controlling the expression of several enzymes required for cholesterol, fatty acid, triacylglycerol and phospholipid synthesis. In vertebrates, SREBP activation is mainly controlled by a complex and well-characterized feedback mechanism mediated by cholesterol, a crucial bio-product of the SREBP-activated mevalonate pathway. In this work, we identified acto-myosin contractility and mechanical forces imposed by the extracellular matrix (ECM) as SREBP1 regulators. SREBP1 control by mechanical cues depends on geranylgeranyl pyrophosphate, another key bio-product of the mevalonate pathway, and impacts on stem cell fate in mouse and on fat storage in Drosophila. Mechanistically, we show that activation of AMP-activated protein kinase (AMPK) by ECM stiffening and geranylgeranylated RhoA-dependent acto-myosin contraction inhibits SREBP1 activation. Our results unveil an unpredicted and evolutionary conserved role of SREBP1 in rewiring cell metabolism in response to mechanical cues.

Fluvastatin inhibits Rab5-mediated IKs internalization caused by chronic Ca2+-dependent PKC activation

Statins, in addition to their cholesterol lowering effects, can prevent isoprenylation of Rab GTPase proteins, a key protein family for the regulation of protein trafficking. Rab-GTPases have been shown to be involved in the control of membrane expression level of ion channels, including one of the major cardiac repolarizing channels, IKs. Decreased IKs function has been observed in a number of disease states and associated with increased propensity for arrhythmias, but the mechanism underlying IKs decrease remains elusive. Ca²⁺-dependent PKC isoforms (cPKC) are chronically activated in variety of human diseases and have been suggested to acutely regulate IKs function. We hypothesize that chronic cPKC stimulation leads to Rab-mediated decrease in IKs membrane expression, and that can be prevented by statins. In this study we show that chronic cPKC stimulation caused a dramatic Rab5 GTPase-dependent decrease in plasma membrane localization of the IKs pore forming subunit KCNQ1, reducing IKs function. Our data indicates fluvastatin inhibition of Rab5 restores channel localization and function after cPKC-mediated channel internalization. Our results indicate a novel statin anti-arrhythmic effect that would be expected to inhibit pathological electrical remodeling in a number of disease states associated with high cPKC activation. Because Rab-GTPases are important regulators of membrane trafficking they may underlie other statin pleiotropic effects.

Synthesis and NMR Characterization of the Prenylated Peptide, a-Factor

Protein and peptide prenylation is an essential biological process involved in many signal transduction pathways. Hence, it plays a critical role in establishing many major human ailments, including Alzheimer's disease, amyotrophic lateral sclerosis (ALS), malaria, and Ras-related cancers. Yeast mating pheromone a-factor is a small dodecameric peptide that undergoes prenylation and subsequent processing in a manner identical to larger proteins. Due to its small size in addition to its well-characterized behavior in yeast, a-factor is an attractive model system to study the prenylation pathway. Traditionally, chemical synthesis and characterization of a-factor have been challenging, which has limited its use in prenylation studies. In this chapter, a robust method for the synthesis of a-factor is presented along with a description of the characterization of the peptide using MALDI and NMR. Finally, complete assignments of resonances from the isoprenoid moiety and a-factor from COSY, TOCSY, HSQC, and long-range HMBC NMR spectra are presented. This methodology should be useful for the synthesis and characterization of other mature prenylated peptides and proteins.

Simultaneous Quantitation of Isoprenoid Pyrophosphates in Plasma and Cancer Cells Using LC-MS/MS

Isoprenoids (IsoP) are an important class of molecules involved in many different cellular processes including cholesterol synthesis. We have developed a sensitive and specific LC-MS/MS method for the quantitation of three key IsoPs in bio-matrices, geranyl pyrophosphate (GPP), farnesyl pyrophosphate (FPP), and geranylgeranyl pyrophosphate (GGPP). LC-MS/MS analysis was performed using a Nexera UPLC System connected to a LCMS-8060 (Shimadzu Scientific Instruments, Columbia, MD) with a dual ion source. The electrospray ionization source was operated in the negative MRM mode. The chromatographic separation and detection of analytes was achieved on a reversed phase ACCQ-TAG Ultra C18 (1.7 µm, 100 mm × 2.1 mm I.D.) column. The mobile phase consisted of (1) a 10 mM ammonium carbonate with 0.1% ammonium hydroxide in water, and (2) a 0.1% ammonium hydroxide in acetonitrile/methanol (75/25). The flow rate was set to 0.25 mL/min in a gradient condition. The limit of quantification was 0.04 ng/mL for all analytes with a correlation coefficient (r2) of 0.998 or better and a total run time of 12 min. The inter- and intra-day accuracy (85–115%) precision (<15%), and recovery (40–90%) values met the acceptance criteria. The validated method was successfully applied to quantitate basal concentrations of GPP, FPP and GGPP in human plasma and in cultured cancer cell lines. Our LC-MS/MS method may be used for IsoP quantification in different bio-fluids and to further investigate the role of these compounds in various physiological processes.

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.

Simvastatin Enhances Activity and Trafficking of α7 Nicotinic Acetylcholine Receptor in Hippocampal Neurons Through PKC and CaMKII Signaling Pathways

Simvastatin (SV) enhances glutamate release and synaptic plasticity in hippocampal CA1 region upon activation of α7 nicotinic acetylcholine receptor (α7nAChR). In this study, we examined the effects of SV on the functional activity of α7nAChR on CA1 pyramidal cells using patch-clamp recording and explored the underlying mechanisms. We found that the treatment of hippocampal slices with SV for 2 h induced a dose-dependent increase in the amplitude of ACh-evoked inward currents (I_ACh) and the level of α7nAChR protein on the cell membrane without change in the level of α7nAChR phosphorylation. These SV-induced phenotypes were suppressed by addition of farnesol (FOH) that converts farnesyl pyrophosphate, but not geranylgeraniol. Similarly, the farnesyl transferase inhibitor FTI277 was able to increase the amplitude of I_ACh and enhance the trafficking of α7nAChR. The treatment with SV enhanced phosphorylation of CaMKII and PKC. The SV-enhanced phosphorylation of CaMKII rather than PKC was blocked by FOH, Src inhibitor PP2 or NMDA receptor antagonist MK801 and mimicked by FTI. The SV-enhanced phosphorylation of PKC was sensitive to the IP3R antagonist 2-APB. The SV-increased amplitude of I_ACh was suppressed by PKC inhibitor GF109203X and Go6983, or CaMKII inhibitor KN93. The SV- and FTI-enhanced trafficking of α7nAChR was sensitive to KN93, but not GF109203X or Go6983. The PKC activator PMA increased α7nAChR activity, but had no effect on trafficking of α7nAChR. Collectively, these results indicate that acute treatment with SV enhances the activity and trafficking of α7nAChR by increasing PKC phosphorylation and reducing farnesyl-pyrophosphate to trigger NMDA receptor-mediated CaMKII activation.

Bisphosphonates: Future perspective for neurological disorders

Neurodegenerative disorders and osteoporosis share some common underlying pathological features including calcium overload, accumulation of toxic chemicals, inflammation and impaired protein prenylation by isoprenoids (farnesyl pyrophosphate and geranylgeranyl pyrophosphate) appear later stage of life. Substantial number of pre-clinical and clinical reports as well as in vitro data univocally acknowledged the negative impact of altered post-translational modification (prenylation) of proteins like small GTPases (Rffhes, Rho, Rac etc.) and cholesterol levels in both serum and brain on CNS integrity. Bisphosphonates (BPs), referred to as gold standard for osteoporosis treatment, have well established role in attenuation of bone resorption and osteoclast apoptosis by inhibition of farnesyl pyrophosphate synthase enzyme (FPPS) in mevalonate pathway. BPs mainly nitrogen containing BPs (NBPs) have potential to offer new therapeutic targets for neurological disorders and received increasing attention in recent years. A year back clinical and pre-clinical studies revealed that NBPs have the potential to alleviate the symptoms of neurological disorders like brain calcification, Alzheimer's disease and Huntington's disease by targeting mevalonate pathway. Though these drugs have well developed role in inhibition of isoprenoids synthesis, these were demonstrated to inhibit acetyl cholinesterase enzyme and cholesterol synthesis in brain that are considered as the critical factors for impairment of cognitive functions which is the hallmark of several neurological disorders. Still the current understanding of BPs' effect in CNS is limited due to lack of studies focusing the molecular and cellular mechanism. The present review aims to reveal the updated discussion on the mechanism contributing BPs' effect in CNS disorders.

Loss-of-Function PCSK9 Mutations Are Not Associated With Alzheimer Disease

BACKGROUND

Hypercholesterolemia is a major risk factor for the late-onset form of Alzheimer disease (AD). Loss-of-function (LOF) mutations of PCSK9 and PCSK9 inhibitors lower low-density lipoprotein cholesterol (LDL-C) and have been associated with a reduced risk of cardiovascular disease. The aim of this study was to examine the effect of PCSK9 LOF variants on risk and age of onset of AD.

METHODS

A total of 878 participants (410 controls and 468 AD cases) from the Quebec Founder Population were included in the study.

RESULTS

Fifty-four (6.2%) participants carried the R46L mutation, whereas 226 (26.2%) participants carried the InsLEU mutation. There was no protective or no deleterious effect of carrying PCSK9 LOF mutations on AD prevalence nor on age of onset, even when stratified by apolipoprotein E epsilon 4 genotype or by gender.

CONCLUSION

Our data indicate that carrying PCSK9 LOF mutations has a neutral effect on neurocognitive health and the prevalence of AD.

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.

Systemic or Forebrain Neuron-Specific Deficiency of Geranylgeranyltransferase-1 Impairs Synaptic Plasticity and Reduces Dendritic Spine Density

Isoprenoids and prenylated proteins regulate a variety of cellular functions, including neurite growth and synaptic plasticity. Importantly, they are implicated in the pathogenesis of several diseases, including Alzheimer's disease (AD). Recently, we have shown that two protein prenyltransferases, farnesyltransferase (FT) and geranylgeranyltransferase-1 (GGT), have differential effects in a mouse model of AD. Haplodeficiency of either FT or GGT attenuates amyloid-β deposition and neuroinflammation but only reduction in FT rescues cognitive function. The current study aimed to elucidate the potential mechanisms that may account for the lack of cognitive benefit in GGT-haplodeficient mice, despite attenuated neuropathology. The results showed that the magnitude of long-term potentiation (LTP) was markedly suppressed in hippocampal slices from GGT-haplodeficient mice. Consistent with the synaptic dysfunction, there was a significant decrease in cortical spine density and cognitive function in GGT-haplodeficient mice. To further study the neuron-specific effects of GGT deficiency, we generated conditional forebrain neuron-specific GGT-knockout (GGT^f/fCre+) mice using a Cre/LoxP system under the CAMKIIα promoter. We found that both the magnitude of hippocampal LTP and the dendritic spine density of cortical neurons were decreased in GGT^f/fCre+ mice compared with GGT^f/fCre- mice. Immunoblot analyses of cerebral lysate showed a significant reduction in cell membrane-associated (geranylgeranylated) Rac1 and RhoA but not (farnesylated) H-Ras, in GGT^f/fCre+ mice, suggesting that insufficient geranylgeranylation of the Rho family of small GTPases may underlie the detrimental effects of GGT deficiency. These findings reinforce the critical role of GGT in maintaining spine structure and synaptic/cognitive function in development and in the mature brain.

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.

Bioanalysis of farnesyl pyrophosphate in human plasma by high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry and hybrid quadrupole Orbitrap high-resolution mass spectrometry

The isoprenoids farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are pivotal intermediates for cholesterol homeostasis and cell signaling in the mevalonate pathway. We developed a sensitive and selective high-performance liquid chromatography tandem triple quadrupole mass spectrometry (LC-QQQ-MS) method for FPP in human plasma without the need for a derivatization process. We optimized the sample preparation procedure to extract FPP and ¹³C₅-FPP (as internal standard) from sample fluids using methanol. Phosphate-buffered saline was used as the surrogate matrix for the preparation of calibration curves and quality control samples. Using an XBridge C18 column (3.5 μm, 2.1 × 100-mm ID) with gradient elution composed of 10 mmol/L ammonium carbonate/ammonium hydroxide (1000:5, v/v) and acetonitrile/ammonium hydroxide (1000:5, v/v) provided the sharp peaks of FPP and ¹³C₅-FPP in human plasma. The calibration curve ranged from 0.2 to 20 ng/mL in human plasma with acceptable intra-day and inter-day precision and accuracy. The sensitivity of this bioanalytical method was sufficient for clinical analysis. The endogenous FPP plasma concentrations in 40 human healthy volunteers ascertained by LC-QQQ-MS and high-performance liquid chromatography tandem hybrid quadrupole Orbitrap high-resolution mass spectrometry (LC-Q-Orbi-MS) were comparable. Furthermore, the endogenous GGPP in human plasma was selectively detected for the first time by LC-Q-Orbi-MS. In conclusion, a sensitive bioanalytical method for FPP in human plasma by means of LC-QQQ-MS and LC-Q-Orbi-MS was developed in this study. Taking into account the versatility of LC-Q-Orbi-MS, the simultaneous detection of FPP and GGPP may be feasible in clinical practice.

Pharmacophore Mapping of Thienopyrimidine-Based Monophosphonate (ThP-MP) Inhibitors of the Human Farnesyl Pyrophosphate Synthase

The human farnesyl pyrophosphate synthase (hFPPS), a key regulatory enzyme in the mevalonate pathway, catalyzes the biosynthesis of the C-15 isoprenoid farnesyl pyrophosphate (FPP). FPP plays a crucial role in the post-translational prenylation of small GTPases that perform a plethora of cellular functions. Although hFPPS is a well-established therapeutic target for lytic bone diseases, the currently available bisphosphonate drugs exhibit poor cellular uptake and distribution into nonskeletal tissues. Recent drug discovery efforts have focused primarily on allosteric inhibition of hFPPS and the discovery of non-bisphosphonate drugs for potentially treating nonskeletal diseases. Hit-to-lead optimization of a new series of thienopyrimidine-based monosphosphonates (ThP-MPs) led to the identification of analogs with nanomolar potency in inhibiting hFPPS. Their interactions with the allosteric pocket of the enzyme were characterized by crystallography, and the results provide further insight into the pharmacophore requirements for allosteric inhibition.

Metabolic Labeling with an Alkyne-modified Isoprenoid Analog Facilitates Imaging and Quantification of the Prenylome in Cells

Protein prenylation is a post-translational modification that is responsible for membrane association and protein-protein interactions. The oncogenic protein Ras, which is prenylated, has been the subject of intense study in the past 20 years as a therapeutic target. Several studies have shown a correlation between neurodegenerative diseases including Alzheimer's disease and Parkinson's disease and protein prenylation. Here, a method for imaging and quantification of the prenylome using microscopy and flow cytometry is described. We show that metabolically incorporating an alkyne isoprenoid into mammalian cells, followed by a Cu(I)-catalyzed alkyne azide cycloaddition reaction to a fluorophore, allows for detection of prenylated proteins in several cell lines and that different cell types vary significantly in their levels of prenylated proteins. The addition of a prenyltransferase inhibitor or the precursors to the native isoprenoid substrates lowers the levels of labeled prenylated proteins. Finally, we demonstrate that there is a significantly higher (22%) level of prenylated proteins in a cellular model of compromised autophagy as compared to normal cells, supporting the hypothesis of a potential involvement of protein prenylation in abrogated autophagy. These results highlight the utility of total prenylome labeling for studies on the role of protein prenylation in various diseases including aging-related disorders.

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.

Statins and the brain: New perspective for old drugs

Statins are one of the most popular lipid-lowering drugs (LLDs). Upon oral administration, these drugs are well absorbed by the intestine and effectively used for the treatment of dyslipidemias. Recently, statins are becoming also well-known for their cholesterol-independent effects and their potential use in brain diseases and different types of cancers. While still controversial, recent research has suggested that statin's cholesterol-independent activities work possibly through alterations on isoprenoid levels. This reduction of isoprenoids in the central nervous system might result in effective biochemical and behavioral improvements on certain neurological disorders. This manuscript aims to highlight current research describing the use of statin therapy in the brain and discuss whether statins might affect neuronal dynamics and function independently of their cholesterol regulatory role.

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.

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.

Statins and brain integrity in older adults: secondary analysis of the Health ABC study

INTRODUCTION

We examined whether statins are associated with better cerebral white (WM) and gray matter (GM) indices in community-dwelling elders.

METHODS

In 295 older adults, we compared white matter hyperintensities (WMH) on brain magnetic resonance imaging and, total WM fractional anisotropy (FA) and GM mean diffusivity (MD) on diffusion tensor imaging, of Alzheimer's disease (AD) relevant regions in statin-exposed and statin-unexposed participants stratified by Modified Mini-Mental Status Examination (3MS) score.

RESULTS

There was no overall effect of statin exposure on cerebral structural indices. The interaction between statin exposure and 3MS was significant for total-WMH and WM FA (both P < .05) but not GM MD. In the lowest 3MS tertile (mean: 86), statin-exposed individuals had lower total-WMH and higher WM FA (P = .005 and P = .044) and FA of tracts linked to clinical AD (P-value range= .005-.04) despite statistical adjustments. These differences were not significant in the two higher 3MS tertiles.

DISCUSSION

Statins may benefit WM in older adults vulnerable to dementia.

Lentiviral-mediated silencing of farnesyl pyrophosphate synthase through RNA interference in mice

Farnesyl pyrophosphate synthase (FPPS) plays a vital role in the mevalonate pathway and has been shown to be involved in hypertrophy and cardiovascular diseases. Lentivirus-mediated RNA interference (RNAi) to knock down a gene of interest has become a promising new tool for the establishment of transgenic animals. The interfering fragment, named pLVT202, was chosen from cardiomyocytes tested in vitro and was microinjected into the perivitelline space of zygotes from C57BL/6J mice via a lentivirus vehicle; 20 were identified as carrying copies of the transgene using the polymerase chain reaction (PCR). Real-time PCR and western blotting analysis showed that FPPS was downregulated in multiple tissues in the transgenic mice. The transgenic mouse model provides a novel means of studying the gene function of FPPS.

Inhibiting geranylgeranyltransferase I activity decreases spine density in central nervous system

Geranylgeranyltransferase I (GGT), a protein prenyltransferase, is responsible for the posttranslational lipidation of Rho GTPases, such as Rac, Rho and Cdc42, all of which play an important role in neuronal synaptogenesis. We previously demonstrated that GGT promotes dendritic morphogenesis in cultured hippocampal neurons and cerebellar slices. We report here that inhibiting GGT activity decreases basal- and activity-dependent changes in spine density as well as in learning and memory ability of mice in vivo. We found that KCl- or bicuculline-induced dendritic spine density increases was abolished by specific GGT inhibitor GGTi-2147 treatment in cultured hippocampal neurons. GGTi-2147 lateral ventricular injection reduced GGT activity and membrane association of Rac and decreased the density of dendritic spines in the mouse hippocampus, frontal cortex and cerebellum. GGTi-2147 administration also impaired learning and memory ability of mice. More importantly, mice exposed to environmental enrichment (EE) showed increased spine density and learning and memory ability, which were significantly reversed by GGTi-2147 administration. These data demonstrate that inhibiting GGT activity prevents both basal- and activity-dependent changes in spine density in central nervous system both in vitro and in vivo. Manipulating GGT activity may be a promising strategy for the therapies of neurodevelopmental disorders, such as autism, depression, and schizophrenia.

Molecular mechanisms underlying the effects of statins in the central nervous system

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, commonly referred to as statins, are widely used in the treatment of dyslipidaemia, in addition to providing primary and secondary prevention against cardiovascular disease and stroke. Statins’ effects on the central nervous system (CNS), particularly on cognition and neurological disorders such as stroke and multiple sclerosis, have received increasing attention in recent years, both within the scientific community and in the media. Current understanding of statins’ effects is limited by a lack of mechanism-based studies, as well as the assumption that all statins have the same pharmacological effect in the central nervous system. This review aims to provide an updated discussion on the molecular mechanisms contributing to statins’ possible effects on cognitive function, neurodegenerative disease, and various neurological disorders such as stroke, epilepsy, depression and CNS cancers. Additionally, the pharmacokinetic differences between statins and how these may result in statin-specific neurological effects are also discussed.