Mevalonate pathway: a review of clinical and therapeutical implications

Induction of cytoprotective pathways is central to the extension of lifespan conferred by multiple longevity pathways

Many genetic and physiological treatments that extend lifespan also confer resistance to a variety of stressors, suggesting that cytoprotective mechanisms underpin the regulation of longevity. It has not been established, however, whether the induction of cytoprotective pathways is essential for lifespan extension or merely correlated. Using a panel of GFP-fused stress response genes, we identified the suites of cytoprotective pathways upregulated by 160 gene inactivations known to increase Caenorhabditis elegans longevity, including the mitochondrial UPR (hsp-6, hsp-60), the ER UPR (hsp-4), ROS response (sod-3, gst-4), and xenobiotic detoxification (gst-4). We then screened for other gene inactivations that disrupt the induction of these responses by xenobiotic or genetic triggers, identifying 29 gene inactivations required for cytoprotective gene expression. If cytoprotective responses contribute directly to lifespan extension, inactivation of these genes would be expected to compromise the extension of lifespan conferred by decreased insulin/IGF-1 signaling, caloric restriction, or the inhibition of mitochondrial function. We find that inactivation of 25 of 29 cytoprotection-regulatory genes shortens the extension of longevity normally induced by decreased insulin/IGF-1 signaling, disruption of mitochondrial function, or caloric restriction, without disrupting normal longevity nearly as dramatically. These data demonstrate that induction of cytoprotective pathways is central to longevity extension and identify a large set of new genetic components of the pathways that detect cellular damage and couple that detection to downstream cytoprotective effectors.

Many mutations that increase animal lifespan also confer stress tolerance, suggesting that cytoprotective mechanisms underpin the regulation of longevity. It has not been established, however, whether the induction of individual cytoprotective pathways is essential for lifespan extension, or merely correlated. To establish whether the regulatory pathways for the induction of cytoprotective responses are key in the extension of lifespan, we performed an RNAi screen for gene inactivations that decouple the activation of cytoprotective pathways from xenobiotic stimuli that normally induce them. The screen identified 29 genes that constitute the regulatory cascades of the unfolded protein response, oxidative stress response, and detoxification. These upstream regulatory genes are critical to stress tolerance and the extension of lifespan conferred by decreased insulin/IGF-1 signaling, disruption of mitochondrial function, or caloric restriction, but have little effect on normal longevity.

Simvastatin evokes an unpredicted inhibition of β-adrenoceptor-mediated vasodilatation in porcine coronary artery

HMG-CoA reductase inhibitors, or statins, are widely used as cholesterol-lowering agents in the treatment of dyslipidemias. Statins have also been reported to have pleiotropic effects, independent of their effects on cholesterol synthesis, possibly through inhibition of the monomeric G proteins Ras and Rho, which are able to signal through ERK and Rho kinase activities, respectively. We have previously demonstrated that inhibition of ERK activation enhances β-adrenoceptor-mediated vasodilatation in the porcine isolated coronary artery. As statins can also inhibit ERK activation, the initial aim of this study was to determine whether statins have a similar influence on β-adrenoceptor-evoked vasodilatation. Segments of porcine distal coronary artery were mounted in a Mulvany wire myograph and bathed in Krebs-Henseleit buffer gassed with 95% O(2)/5% CO(2) and maintained at 37 °C. Tissues were pre-contracted with the thromboxane mimetic U46619 prior to cumulative concentration-response curves to the β-adrenoceptor agonist salbutamol in the absence or presence of simvastatin (1, 5 or 10 μM), pravastatin (10 μM), or lovastatin (10 μM). Simvastatin inhibited the salbutamol-induced relaxation of the coronary artery. Similar effects were seen with lovastatin, but not pravastatin or the sodium salt of simvastatin. Simvastatin, but not pravastatin also inhibited the relaxations to the Ca(2+)-activated K(+) channel opener NS1619 and the K(ATP) channel opener pinacidil. Unexpectedly, these data indicate that, rather than enhancing β-adrenoceptor-mediated vasodilatation, lipophilic statins impair these responses. This is likely to be due to effects on K(+) channels.

AlzPathway: a comprehensive map of signaling pathways of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the most common cause of dementia among the elderly. To clarify pathogenesis of AD, thousands of reports have been accumulating. However, knowledge of signaling pathways in the field of AD has not been compiled as a database before.

Description

Here, we have constructed a publicly available pathway map called “AlzPathway” that comprehensively catalogs signaling pathways in the field of AD. We have collected and manually curated over 100 review articles related to AD, and have built an AD pathway map using CellDesigner. AlzPathway is currently composed of 1347 molecules and 1070 reactions in neuron, brain blood barrier, presynaptic, postsynaptic, astrocyte, and microglial cells and their cellular localizations. AlzPathway is available as both the SBML (Systems Biology Markup Language) map for CellDesigner and the high resolution image map. AlzPathway is also available as a web service (online map) based on Payao system, a community-based, collaborative web service platform for pathway model curation, enabling continuous updates by AD researchers.

Conclusions

AlzPathway is the first comprehensive map of intra, inter and extra cellular AD signaling pathways which can enable mechanistic deciphering of AD pathogenesis. The AlzPathway map is accessible at http://alzpathway.org/.

Statins and cancer: current and future prospects

Statins are inhibitors of 3-hydroxy-methylglutaryl (HMG) CoA reductase. They exhibit effects beyond cholesterol reduction, including anticancer activity. This review presents the effects of statins in vitro and their possible molecular anticancer mechanisms and critically discusses the data regarding the role of statins in cancer prevention. Finally, this review focuses on the use of statins combined with other chemotherapeutics to increase the effectiveness of cancer treatments. Despite rare and inconclusive clinical data, the preclinical results strongly suggest that such combined treatment could be a promising new strategy for the treatment of certain tumor types.

Krüppel-like factors KLF2 and 6 and Ki-67 are direct targets of zoledronic acid in MCF-7 cells

Bisphosphonates (BP) are used for the treatment of osteoporosis and bone metastases due to breast and prostate cancer. Recent clinical studies indicated a benefit in survival and tumor relapse with the supportive treatment of breast cancer using zoledronic acid (ZA), thus stimulating the debate about its putative anti-tumor activity in vivo. MCF-7 breast cancer cells were treated for 3 h (pulse treatment) and 72 h (permanent treatment) with ZA, and apoptosis rates and cell viability, defined as ATP content, were determined after 72 h. Permanent and pulse stimulation with ZA inhibited the viability of MCF-7 cells, which could partly be rescued by atorvastatin (Ator) pre-treatment but not by geranylgeranyl pyrophosphate (GGPP) co-treatment. Microarray analysis of ZA treated MCF-7 cells identified genes of the mevalonate pathway as significantly upregulated, which was verified by qPCR. Additionally the putative tumor suppressors krüppel-like factor 2 and 6 (KLF2 and KLF6) were markedly upregulated, while the classical proliferation marker Ki-67 was clearly downregulated. The expression of all three genes was confirmed by qPCR on mRNA level and by immunocytochemistry or Western blot staining. Expression of target genes were also analyzed in other breast (MDA-MB-231, BT-20, ZR75-1, T47D) and prostate (LNCaP, PC3) cancer cell lines by qPCR. ZA responsiveness of KLF2, KLF6 and Ki-67 could be verified in PC3 and T47D cells, KLF6 responsiveness in LNCaP and KLF2 responsiveness in MDA-MB-231 and BT-20 cells. Here we demonstrate in the apoptosis insensitive MCF-7 cell line a remarkable impact of ZA exposure on cell viability and on the regulation of putative tumor suppressors of the KLF family. The molecular mechanism involved might be the accumulation of isopentenyl pyrophosphate (IPP) and ApppI, since we could partly rescue the ZA effect by Ator pre-treatment and GGPP co-treatment. These data should stimulate further research into both the role of the mevalonate pathway and the accumulation of pyrophosphate compounds like ApppI in tumorigenesis and differentiation and their potential apart from the inhibition of mitochondrial ADP/ATP translocase and apoptosis, since such effects might well be responsible for the adjuvant ZA treatment benefit of patients suffering from breast cancer.

A novel EST-derived RNAi screen reveals a critical role for farnesyl diphosphate synthase in β2-adrenergic receptor internalization and down-regulation

The β2-adrenergic receptor (β2AR) plays important physiological roles in the heart and lung and is the primary target of β-agonists, the mainstay asthma drugs. Activation of β2AR by β-agonists is attenuated by receptor down-regulation, which ensures transient stimulation of the receptor but reduces the efficacy of β-agonists. Here we report the identification, through a functional genome-wide RNA interference (RNAi) screen, of new genes critically involved in β2AR down-regulation. We developed a lentivirus-based RNAi library consisting of 26-nt short-hairpin RNAs (shRNAs). The library was generated enzymatically from a large collection of expressed sequence tag (EST) DNAs corresponding to ∼20,000 human genes and contains on average ∼6 highly potent shRNAs (>75% knockdown efficiency) for each gene. Using this novel shRNA library, together with a robust cell model for β2AR expression, we performed fluorescence-activated cell sorting and isolated cells that, as a consequence of shRNA-mediated gene inactivation, exhibited defective agonist-induced down-regulation. The screen discovered several previously unrecognized β2AR regulators, including farnesyl diphosphate synthase (FDPS). We showed that inactivation of FDPS by shRNA, small interfering RNA, or the highly specific pharmaceutical inhibitor alendronate inhibited β2AR down-regulation. Notably, in human airway smooth muscle cells, the physiological target of β-agonists, alendronate treatment functionally reversed agonist-induced endogenous β2AR loss as indicated by an increase in cAMP production. FDPS inactivation interfered with β2AR internalization into endosomes through disrupting the membrane localization of the Rab5 small GTPase. Furthermore, Rab5 overexpression reversed the deficient receptor down-regulation induced by alendronate, suggesting that FDPS regulates receptor down-regulation in a Rab5-dependent manner. Together, our findings reveal a FDPS-dependent mechanism in the internalization and down-regulation of β2AR, identify FDPS as a potential target for improving the therapeutic efficacy of β-agonists, and demonstrate the utility of the unique EST-derived shRNA library for functional genetics studies.

Lipid metabolic pathways as lung cancer therapeutic targets: a computational study

Inhibitors of lipid metabolic pathways, particularly drugs targeting the mevalonate pathway, have been suggested to be valuable in enhancing the effectiveness of epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) and these compounds may also be effective in patients with inherent or acquired resistance to EGFR-TKIs. The present study examined gene expression profiles in lung adenocarcinoma to characterize the interaction between growth factor signals and lipid metabolic pathways at the transcriptional level. Gene expression correlation analysis showed that genes involved in the mevalonate pathway and unsaturated fatty acid synthesis were negatively correlated with the expression of EGFR, MET and other growth factor receptor genes, as well as with the expression of genes involved in cell migration and adhesion. On the other hand, the expression of genes related to cell cycle progression, DNA repair and DNA replication were positively correlated with the metabolic pathway genes mentioned above, and a significant number of such genes had promoter domains for nuclear factor Y (NFY). Genes whose expression showed a positive correlation with NFY expression and mevalonate pathway genes were found to exhibit protein-protein interactions with several 'hub' genes, including BRCA1, that have been associated with both lung cancer and cell division. These results support the idea that inhibition of lipid metabolic pathways may be valuable as an alternative therapeutic option for the treatment of lung adenocarcinoma, and suggest that NFY is a possible molecular target for such efforts.

Novel anti-cancer compounds for developing combinatorial therapies to target anoikis-resistant tumors

Anoikis, a cell death pathway induced by loss of normal cell-matrix attachment or upon adhesion to a non-native matrix, ensures the balance between proliferative potential of normal cells and maintenance of tissue integrity. Thereby, anoikis serves as a potential molecular barrier against oncogenic transformation of normal cells. Cancer cells acquire anoikis resistance for survival and distant metastatic progression. During the acquisition of anoikis resistance, tumors modulate multiple cell signaling parameters through changes in the expression of up-stream receptors and by dynamically calibrating the dependency on down-stream signaling cascades. Many compounds that target the tumor-acquired switches in integrins, tumor antigens, growth factors, metabolic pathways, oxidative and osmotic-stress signaling are in various phases of pre-clinical and clinical development. Combinatorial approaches maximize the therapeutic efficacy and minimize the activation of alternate signaling pathways, which will otherwise contribute to drug resistance. In this regard, an integrated analysis of the mechanisms of action of potential drugs and lead compounds that can target significant nodes of anoikis signaling networks will provide a rational frame-work for further development and clinical use of respective agents, by formulating more effective combinatorial therapies, in patients with distinct drug-sensitivity profiles.

Statin treatment depresses the fetal defence to acute hypoxia via increasing nitric oxide bioavailability

In addition to lowering cholesterol, statins increase nitric oxide (NO) bioavailability, improving endothelial function. In the fetus, enhanced NO during acute hypoxia opposes the fetal peripheral vasoconstrictor response, part of the brain-sparing defence. This study tested the hypothesis that treatment with statins depresses the fetal circulatory response to acute hypoxic stress via increasing NO bioavailability. Under anaesthesia, 12 fetal sheep at 118 ± 1 days of gestation (term ca 145 days) were instrumented with vascular catheters and a femoral artery Transonic flow probe for chronic recording. Five days later, all animals were subjected to 30 min of acute hypoxia (fetal arterial partial pressure of O(2) ( ) reduced by ca 50%) before and 24 h after fetal treatment with pravastatin (25 mg i.v.). In half of the fetuses (n = 6), responses to hypoxia post-pravastatin were evaluated during NO synthesis blockade. Fetal exposure to pravastatin did not affect fetal basal cardiovascular function. Fetal was similarly reduced in all acute hypoxia experiments from ca 21 to 10 mmHg. Fetal exposure to pravastatin markedly diminished the fetal femoral vasoconstrictor (5.1 ± 0.9 vs. 2.5 ± 0.5 mmHg (ml min(-1))(-1)) and lactic acidaemic (4.4 ± 0.5 vs. 3.0 ± 0.3 mm) responses to acute hypoxia (both P < 0.05), without affecting plasma catecholamine responses. Post-pravastatin, the circulatory (5.8 ± 1.5 mmHg (ml min(-1))(-1)) and metabolic (3.9 ± 0.3 mm) responses could be restored to control levels during fetal treatment with NO synthase blockade. Pravastatin depresses the fetal cardiovascular and metabolic defences to acute hypoxia via increasing NO bioavailability. The use of statins during pregnancy should be viewed with extreme caution.

Mevalonate governs interdependency of ergosterol and siderophore biosyntheses in the fungal pathogen Aspergillus fumigatus

Aspergillus fumigatus is the most common airborne fungal pathogen for humans. In this mold, iron starvation induces production of the siderophore triacetylfusarinine C (TAFC). Here we demonstrate a link between TAFC and ergosterol biosynthetic pathways, which are both critical for virulence and treatment of fungal infections. Consistent with mevalonate being a limiting prerequisite for TAFC biosynthesis, we observed increased expression of 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase (Hmg1) under iron starvation, reduced TAFC biosynthesis following lovastatin-mediated Hmg1 inhibition, and increased TAFC biosynthesis following Hmg1 overexpression. We identified enzymes, the acyl-CoA ligase SidI and the enoyl-CoA hydratase SidH, linking biosynthesis of mevalonate and TAFC, deficiency of which under iron starvation impaired TAFC biosynthesis, growth, oxidative stress resistance, and murine virulence. Moreover, inactivation of these enzymes alleviated TAFC-derived biosynthetic demand for mevalonate, as evidenced by increased resistance to lovastatin. Concordant with bilateral demand for mevalonate, iron starvation decreased the ergosterol content and composition, a phenotype that is mitigated in TAFC-lacking mutants.

Simvastatin protects auditory hair cells from gentamicin-induced toxicity and activates Akt signaling in vitro

Background

Inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, known as statins, are commonly used as cholesterol-lowering drugs. During the past decade, evidence has emerged that statins also have neuroprotective effects. Research in the retina has shown that simvastatin, a commonly used statin, increases Akt phosphorylation in vivo, indicating that the PI3K/Akt pathway contributes to the protective effects achieved. While research about neuroprotective effects have been conducted in several systems, the effects of statins on the inner ear are largely unknown.

Results

We evaluated whether the 3-hydroxy-3-methylglutaryl-coenzyme A reductase is present within the rat cochlea and whether simvastatin is able to protect auditory hair cells from gentamicin-induced apoptotic cell death in a in vitro mouse model. Furthermore, we evaluated whether simvastatin increases Akt phosphorylation in the organ of Corti. We detected 3-hydroxy-3-methylglutaryl-coenzyme A reductase mRNA in organ of Corti, spiral ganglion, and stria vascularis by reverse transcriptase-polymerase chain reaction (RT-PCR). Moreover, we observed a dose-dependent and significant reduction of hair cell loss in organs of Corti treated with simvastatin in addition to gentamicin, as compared to samples treated with gentamicin alone. The protective effect of simvastatin was reversed by addition of mevalonate, a downstream metabolite blocked by simvastatin, demonstrating the specificity of protection. Finally, Western blotting showed an increase in organ of Corti Akt phosphorylation after simvastatin treatment in vitro.

Conclusion

These results suggest a neuroprotective effect of statins in the inner ear, mediated by reduced 3-hydroxy-3-methylglutaryl-coenzyme A reductase metabolism and Akt activation.

Cholesterol depletion of hepatoma cells impairs hepatitis B virus envelopment by altering the topology of the large envelope protein

Previous reports have shown that cholesterol depletion of the membrane envelope of the hepatitis B virus (HBV) impairs viral infection of target cells. A potential function of this lipid in later steps of the viral life cycle remained controversial, with secretion of virions and subviral particles (SVP) being either inhibited or not affected, depending on the experimental approach employed to decrease the intracellular cholesterol level. This work addressed the role of host cell cholesterol on HBV replication, assembly, and secretion, using an alternative method to inhibition of the enzymes involved in the biosynthesis pathway. Growing HBV-producing cells with lipoprotein-depleted serum (LPDS) resulted in an important reduction of the amount of cholesterol within 24 h of treatment (about 40%). Cell exposure to chlorpromazine, an inhibitor of the clathrin-mediated pathway used by the low-density lipoprotein receptor for endocytosis, also impacted the cholesterol level; however, this level of inhibition was not achievable when the synthesis inhibitor lovastatin was used. HBV secretion was significantly inhibited in cholesterol-depleted cells (by ∼80%), while SVP release remained unaffected. The viral DNA genome accumulated in LPDS-treated cells in a time-dependent manner. Specific immunoprecipitation of nucleocapsids and mature virions revealed an increased amount of naked nucleocapsids, while synthesis of the envelope proteins occurred as normally. Following analysis of the large envelope protein conformation in purified microsomes, we concluded that cholesterol is important in maintaining the dual topology of this polypeptide, which is critical for viral envelopment.

Resveratrol inhibits the mevalonate pathway and potentiates the antiproliferative effects of simvastatin in rat theca-interstitial cells

OBJECTIVE

To examine the mechanisms of action of resveratrol and its interaction with simvastatin on growth and the mevalonate pathway in rat theca-interstitial cells.

DESIGN

In vitro study.

SETTING

Research laboratory.

ANIMAL(S)

Immature Sprague-Dawley female rats.

INTERVENTION(S)

Theca-interstitial cells were cultured in the absence or presence of resveratrol, simvastatin, mevalonic acid, farnesyl pyrophosphate, and/or geranylgeranyl pyrophosphate.

MAIN OUTCOME MEASURE(S)

DNA synthesis was assessed by thymidine incorporation assay; 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) expression and activity were evaluated with the use of quantitative real-time polymerase chain reaction, Western blot analysis, and HMGCR activity assay. Cholesterol synthesis was determined by the conversion of [(14)C]-acetate to [(14)C]-cholesterol.

RESULT(S)

Resveratrol potentiated the simvastatin-induced inhibition on cell proliferation in a concentration-dependent manner. Inhibitory effects of resveratrol were partly abrogated by the addition of mevalonic acid, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate. Resveratrol reduced HMGCR expression and activity, and decreased cholesterol synthesis. In contrast, simvastatin inhibited HMGCR activity with a compensatory increase in HMGCR expression. Resveratrol counteracted this effect of simvastatin on HMGCR expression but augmented the simvastatin-induced inhibition on HMGCR activity and cholesterol synthesis.

CONCLUSION(S)

Resveratrol inhibits the mevalonate pathway via distinctly different mechanisms than statins. These observations demonstrate a novel mechanism of action of resveratrol and underscore the potential translational/clinical relevance of resveratrol interactions with simvastatin.

Non-bisphosphonate inhibitors of isoprenoid biosynthesis identified via computer-aided drug design

The relaxed complex scheme, a virtual-screening methodology that accounts for protein receptor flexibility, was used to identify a low-micromolar, non-bisphosphonate inhibitor of farnesyl diphosphate synthase. Serendipitously, we also found that several predicted farnesyl diphosphate synthase inhibitors were low-micromolar inhibitors of undecaprenyl diphosphate synthase. These results are of interest because farnesyl diphosphate synthase inhibitors are being pursued as both anti-infective and anticancer agents, and undecaprenyl diphosphate synthase inhibitors are antibacterial drug leads.

The analytical determination of isoprenoid intermediates from the mevalonate pathway

In this article, assays on the analytical determination of farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP), two important isoprenoid intermediates at biochemically relevant branching points in the mevalonate pathway, are summarized and reviewed. There is considerable recent interest in the measurement of these two isoprenoids because of their direct involvement in several diseases, for example, statins lower cholesterol by inhibiting 3-hydroxy-3-methylglutaryl-CoA reductase but equally affect other metabolite biosyntheses. The isoprenoids FPP and GGPP are key intermediates due to their role as CaaX-specific substrates for posttranslational modification of proteins (protein prenylation). Disease pathologies and therapeutic efficacy of different treatments (e.g., cholesterol-lowering drugs) may lead to a reduction in isoprenoid levels and an accompanying reduction in prenylation of specific proteins. To understand the exact biochemical role of the isoprenoids FPP and GGPP, we need to know their levels. Several recent studies have shown exact levels of FPP and GGP in plasma and relevant tissues and their modulation following treatment. Furthermore, by directly measuring the extent of protein prenylation and identifying target proteins, further insight into the exact biochemical nature of the pathology and regulatory mechanisms will be possible. This short review aims to highlight the relevant literature on the analytical determination of the free isoprenoids FPP and GGPP in biological tissue as well as techniques for directly measuring prenylated proteins.

Perinatal onset mevalonate kinase deficiency

Defects in mevalonate kinase, a critical rate-limiting enzyme in cholesterol and isoprene metabolism, have been associated with 2 clinical phenotypes: mevalonic aciduria, which presents in infancy or early childhood with growth failure, dysmorphic features, and neurologic disease; and hyperimmunoglobulinemia D and periodic fever syndrome, which usually presents outside the neonatal period as an autoinflammatory periodic fever syndrome. This report describes a kindred with 2 siblings affected by severe mevalonate kinase deficiency (mevalonic aciduria) with perinatal onset. Dysmorphic and central nervous system abnormalities, anemia, and cholestasis were prominent features in 1 sibling. Both cases were fatal, 1 in the immediate neonatal period and 1 in utero. The small number of cases of mevalonate kinase deficiency presenting in the perinatal period have typically been severely affected, with signs and symptoms of a severe multisystem disorder. Predominant features of perinatal onset mevalonate kinase deficiency include intrauterine growth restriction, cerebral ventriculomegaly, dysmorphic features, skeletal abnormalities, dyserythropoietic anemia with extramedullary erythropoiesis, thrombocytopenia, cholestatic liver disease, persistent diarrhea, renal failure, recurrent sepsis-like episodes, and failure to thrive. Clinical findings may mimic severe intrauterine viral infection, a chromosomal abnormality, or an acute sepsis syndrome, potentially contributing to delays in diagnosis of this rare condition. Perinatal onset mevalonate kinase deficiency is associated with a very poor prognosis, with death in utero or in early infancy. Detailed autopsy findings in mevalonate kinase deficiency have rarely been reported.

High-throughput structural biology of metabolic enzymes and its impact on human diseases

The Structural Genomics Consortium (SGC) is a public-private partnership that aims to determine the three-dimensional structures of human proteins of medical relevance and place them into the public domain without restriction. To date, the Oxford Metabolic Enzyme Group at SGC has deposited the structures of more than 140 human metabolic enzymes from diverse protein families such as oxidoreductases, hydrolases, oxygenases and fatty acid transferases. A subset of our target proteins are involved in the inherited disorders of carbohydrate, fatty acid, amino acid and vitamin metabolism. This article will provide an overview of the structural data gathered from our high-throughput efforts and the lessons learnt in the structure-function relationship of these enzymes, small molecule development and the molecular basis of disease mutations.

Candidate genes involved in tanshinone biosynthesis in hairy roots of Salvia miltiorrhiza revealed by cDNA microarray

Salvia miltiorrhiza is a valuable Chinese herb (Danshen) that is widely used in traditional Chinese medicine. Diterpene quinones, known as tanshinones, are the main bioactive components of S. miltiorrhiza; however, there is only limited information regarding the molecular mechanisms underlying secondary metabolism in this plant. We used cDNA microarray analysis to identify changes in the gene expression profile at different stages of hairy root development in S. miltiorrhiza. A total of 203 genes were singled out from 4,354 cDNA clones on the microarray, and 114 unique differentially expressed cDNA clones were identified: six genes differentially expressed in 45-day hairy root compared with 30-day hairy root; 96 genes differentially expressed in 60-day hairy root compared with 30-day hairy root; and 12 genes unstably expressed at different stages. Among the 96 genes differentially expressed in 60-day hairy root compared with 30-day hairy root, a total of 57 genes were up-regulated, and 26 genes represent 29 metabolism-related enzymes. Copalyl diphosphate synthase, which catalyzes the conversion of the universal diterpenoid precursor (E,E,E)-geranylgeranyl diphosphate to copalyl diphosphate, was up-regulated 6.63 fold, and another six genes involved in tanshinone biosynthesis and eight candidate P450 genes were also differentially expressed. These data provide new insights for further identification of the enzymes involved in tanshinone biosynthesis.

Inhibition of human sterol Δ7-reductase and other postlanosterol enzymes by LK-980, a novel inhibitor of cholesterol synthesis

Novel potential inhibitors of the postsqualene portion of cholesterol synthesis were screened in HepG2 cells. 2-(4-Phenethylpiperazin-1-yl)-1-(pyridine-3-yl)ethanol (LK-980) was identified as a prospective compound and was characterized further in cultures of human primary hepatocytes from seven donors. In vitro kinetic measurements show that the half-life of LK-980 is at least 4.3 h. LK-980 does not induce CYP3A4 mRNA nor enzyme activity. Target prediction was performed by gas chromatography-mass spectrometry, allowing simultaneous separation and quantification of nine late cholesterol intermediates. Experiments indicated that human sterol Δ(7)-reductase (DHCR7) is the major target of LK-980 (34-fold increase of 7-dehydrocholesterol), whereas human sterol Δ(14)-reductase (DHCR14), human sterol Δ(24)-reductase (DHCR24), and human sterol C5-desaturase (SC5DL) represent minor targets. In the absence of purified enzymes, we used the mathematical model of cholesterol synthesis to evaluate whether indeed more than a single enzyme is inhibited. In silico inhibition of only DHCR7 modifies the flux of cholesterol intermediates, resulting in a sterol profile that does not support experimental data. Partial inhibition of the DHCR14, DHCR24, and SC5DL steps, in addition to DHCR7, supports the experimental sterol profile. In conclusion, we provide experimental and computational evidence that LK-980, a novel inhibitor from the late portion of cholesterol synthesis, inhibits primarily DHCR7 and to a lesser extent three other enzymes from this pathway.

Hypercholesterolemia accelerates bone loss in postmenopausal women

OBJECTIVES

To clarify the effect of lipid profiles on postmenopausal bone loss using a longitudinal method and to determine whether cytokines are involved in bone loss.

METHODS

The subjects were Japanese residents participating in the Iwaki Health Promotion Projects. Women with one or more of the following factors were excluded: a history of surgical menopause, current or past users of bisphosphonates or current user of other drugs known to influence bone and lipid metabolism, and current medication for diabetes or hypertension. Consequently, 99 postmenopausal women (61.2 ± 7.7 years old) and 85 premenopausal women (41.2 ± 8.6 years old) were selected for this study. The osteo-sono-assessment index (OSI) of the left calcaneal bone was obtained twice at 1-year intervals and the annual percentage change in OSI was calculated. Serum total cholesterol, high and low density lipoprotein cholesterol, triglycerides, homocysteine and cytokines such as adipocytokines, interleukins and tumor necrosis factor-α were measured. Postmenopausal women were grouped into three groups according to their basal cholesterol level, and the relationship between basal cholesterol level and annual change in OSI was studied.

RESULTS

The annual percentage change in OSI in postmenopausal women with a serum total cholesterol level ≥240 mg/dl was significantly higher compared to those with a normal total cholesterol level, suggesting that hypercholesterolemia accelerates postmenopausal bone loss. No significant differences were seen in any of the cytokines that presumably cause bone resorption.

CONCLUSION

These results showed that hypercholesterolemia has an inverse effect on bone loss independent of cytokines presumed to mediate bone loss.

Interplay between cholesterol and drug metabolism

Cholesterol biosynthetic and metabolic pathways contain several branching points towards physiologically active molecules, such as coenzyme Q, vitamin D, glucocorticoid and steroid hormones, oxysterols, or bile acids. Sophisticated regulatory mechanisms are involved in maintenance of the homeostasis of not only cholesterol but also other cholesterogenic molecules. In addition to endogenous cues, cholesterol homeostasis needs to accommodate also to exogenous cues that are imported into the body, such as chemicals and medications. Steroid and nuclear receptors together with sterol regulatory element-binding protein (SREBP) mediate the fine tuning of biosynthetic and metabolic routes as well as transports of cholesterol and its derivatives. Similarly, drug/xenobiotic metabolism is the subject to the feedback regulation of cytochrome P450 enzymes and transporters. The regulatory mechanisms that maintain the homeostasis of cholesterogenic molecules and are involved in drug metabolism share similarities. Cholesterol and cholesterogenic compounds (bile acids, glucocorticoids, vitamin D, etc.) regulate the xenosensor signaling in drug-mediated induction of the major drug-metabolizing cytochrome P450 enzymes. The key cellular receptors, pregnane X receptor (PXR), constitutive androstane receptor (CAR), vitamin D receptor (VDR), and glucocorticoid receptor (GR) provide a functional cross-talk between the pathways maintaining cholesterol homeostasis and controlling the expression of drug-metabolizing enzymes. These receptors serve as metabolic sensors, resulting in a coordinate regulation of cholesterogenic compounds metabolism and of the defense against xenobiotic and endobiotic toxicity. Herein we present a comprehensive review of functional interactions between cholesterol homeostasis and drug metabolism involving the main nuclear and steroid receptors.

Modulation of cholesterol, farnesylpyrophosphate, and geranylgeranylpyrophosphate in neuroblastoma SH-SY5Y-APP695 cells: impact on amyloid beta-protein production

There is keen interest in the role of the isoprenoids farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) in protein prenylation and cell function in Alzheimer's disease (AD). We recently reported elevated FPP and GGPP brain levels and increased gene expression of FPP synthase (FPPS) and GGPP synthase (GGPPS) in the frontal cortex of AD patients. Cholesterol levels and gene expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase were similar in AD and control samples, suggesting that homeostasis of FPP and GGPP but not cholesterol is specifically targeted in brain tissue of AD patients (Neurobiol Dis 2009 35:251-257). In the present study, it was determined if cellular levels of FPP, GGPP, and cholesterol affect beta-amyloid (Abeta) abundance in SH-SY5Y cells, expressing human APP695. Cells were treated with different inhibitors of the mevalonate/isoprenoid/cholesterol pathway. FPP, GGPP, cholesterol, and Abeta(1-40) levels were determined, and activities of farnesyltransferase and geranylgeranyltransferase I were measured. Inhibitors of different branches of the mevalonate/isoprenoid/cholesterol pathway as expected reduced cholesterol and isoprenoid levels in neuroblastoma cells. Abeta(1-40) levels were selectively reduced by cholesterol synthesis inhibitors but not by inhibitors of protein isoprenylation, indicating that changes in cholesterol levels per se and not isoprenoid levels account for the observed modifications in Abeta production.

Probing ligand-binding pockets of the mevalonate pathway enzymes from Streptococcus pneumoniae

Diphosphomevalonate (Mev.pp) is the founding member of a new class of potential antibiotics targeting the Streptococcus pneumoniae mevalonate (Mev) pathway. We have synthesized a series of Mev.pp analogues designed to simultaneously block two steps in this pathway, through allosteric inhibition of mevalonate kinase (MK) and, for five of the analogues, by mechanism-based inactivation of diphosphomevalonate decarboxylase (DPM-DC). The analogue series expands the C(3)-methyl group of Mev.pp with hydrocarbons of varying size, shape, and chemical and physical properties. Previously, we established the feasibility of a prodrug strategy in which unphosphorylated Mev analogues could be enzymatically converted to the active Mev.pp forms by the endogenous MK and phosphomevalonate kinase. We now report the kinetic parameters for the turnover of non-, mono-, and diphosphorylated analogues as substrates and inhibitors of the three mevalonate pathway enzymes. The inhibition of MK by Mev.pp analogues revealed that the allosteric site is selective for compact, electron-rich C(3)-subsitutents. The lack of reactivity of analogues with DPM-DC provided evidence, counter to the existing model, for a decarboxylation transition state that is concerted rather than dissociative. The Mev pathway is composed of three structurally and functionally conserved enzymes that catalyze consecutive steps in a metabolic pathway. The current work reveals that these enzymes exhibit significant differences in specificity toward R-group substitution at C(3) and that these patterns are explained well by changes in the volume of the C(3) R-group-binding pockets of the enzymes.

Basic Science Review: Statin Therapy-Part I: The Pleiotropic Effects of Statins in Cardiovascular Disease

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA-reductase) inhibitors, otherwise known as statins, are currently the medical treatment of choice for hypercholesterolemia. Hypercholesterolemia is a known risk factor for cardiovascular disease, and statin therapy has led to a significant reduction in morbidity and mortality from adverse cardiac events, stroke, and peripheral arterial disease. In addition to achieving a therapeutic decrease in serum cholesterol levels, statin therapy appears to promote other effects that are independent of changes in serum cholesterol. These ‘‘pleiotropic’’ effects include attenuation of vascular inflammation, improved endothelial cell function, stabilization of atherosclerotic plaque, decreased vascular smooth muscle cell migration and proliferation, and inhibition of platelet aggregation. This article is part I of a 2-part review, and it focuses on the pleiotropic effects of statins at the cellular level.

Isoprenoids, small GTPases and Alzheimer's disease

The mevalonate pathway is a crucial metabolic pathway for most eukaryotic cells. Cholesterol is a highly recognized product of this pathway but growing interest is being given to the synthesis and functions of isoprenoids. Isoprenoids are a complex class of biologically active lipids including for example, dolichol, ubiquinone, farnesylpyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Early work had shown that the long-chain isoprenoid dolichol is decreased but that dolichyl phosphate and ubiquinone are elevated in brains of Alzheimer's disease (AD) patients. Until recently, levels of their biological active precursors FPP and GGPP were unknown. These short-chain isoprenoids are critical in the post-translational modification of certain proteins which function as molecular switches in numerous signaling pathways. The major protein families belong to the superfamily of small GTPases, consisting of roughly 150 members. Recent experimental evidence indicated that members of the small GTPases are involved in AD pathogenesis and stimulated interest in the role of FPP and GGPP in protein prenylation and cell function. A straightforward prediction derived from those studies was that FPP and GGPP levels would be elevated in AD brains as compared with normal neurological controls. For the first time, recent evidence shows significantly elevated levels of FPP and GGPP in human AD brain tissue. Cholesterol levels did not differ between AD and control samples. One obvious conclusion is that homeostasis of FPP and GGPP but not of cholesterol is specifically targeted in AD. Since prenylation of small GTPases by FPP or GGPP is indispensable for their proper function we are proposing that these two isoprenoids are up-regulated in AD resulting in an over abundance of certain prenylated proteins which contributes to neuronal dysfunction.

Quantitative proteomics analysis of inborn errors of cholesterol synthesis: identification of altered metabolic pathways in DHCR7 and SC5D deficiency

Smith-Lemli-Opitz syndrome (SLOS) and lathosterolosis are malformation syndromes with cognitive deficits caused by mutations of 7-dehydrocholesterol reductase (DHCR7) and lathosterol 5-desaturase (SC5D), respectively. DHCR7 encodes the last enzyme in the Kandutsch-Russel cholesterol biosynthetic pathway, and impaired DHCR7 activity leads to a deficiency of cholesterol and an accumulation of 7-dehydrocholesterol. SC5D catalyzes the synthesis of 7-dehydrocholesterol from lathosterol. Impaired SC5D activity leads to a similar deficiency of cholesterol but an accumulation of lathosterol. Although the genetic and biochemical causes underlying both syndromes are known, the pathophysiological processes leading to the developmental defects remain unclear. To study the pathophysiological mechanisms underlying SLOS and lathosterolosis neurological symptoms, we performed quantitative proteomics analysis of SLOS and lathosterolosis mouse brain tissue and identified multiple biological pathways affected in Dhcr7(Delta3-5/Delta3-5) and Sc5d(-/-) E18.5 embryos. These include alterations in mevalonate metabolism, apoptosis, glycolysis, oxidative stress, protein biosynthesis, intracellular trafficking, and cytoskeleton. Comparison of proteome alterations in both Dhcr7(Delta3-5/Delta3-5) and Sc5d(-/-) brain tissues helps elucidate whether perturbed protein expression was due to decreased cholesterol or a toxic effect of sterol precursors. Validation of the proteomics results confirmed increased expression of isoprenoid and cholesterol synthetic enzymes. This alteration of isoprenoid synthesis may underlie the altered posttranslational modification of Rab7, a small GTPase that is functionally dependent on prenylation with geranylgeranyl, that we identified and validated in this study. These data suggested that although cholesterol synthesis is impaired in both Dhcr7(Delta3-5/Delta3-5) and Sc5d(-/-) embryonic brain tissues the synthesis of nonsterol isoprenoids may be increased and thus contribute to SLOS and lathosterolosis pathology. This proteomics study has provided insight into the pathophysiological mechanisms of SLOS and lathosterolosis, and understanding these pathophysiological changes will help guide clinical therapy for SLOS and lathosterolosis.

Synthesis of 4-diphosphocytidyl-2-C-methyl-D-erythritol 2-phosphate and kinetic studies of Mycobacterium tuberculosis IspF

Many pathogenic bacteria utilize the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for the biosynthesis of isopentenyl diphosphate and dimethylallyl diphosphate, two major building blocks of isoprenoid compounds. The fifth enzyme in the MEP pathway, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate (ME-CPP) synthase (IspF), catalyzes the conversion of 4-diphosphocytidyl-2-C-methyl-D-erythritol 2-phosphate (CDP-ME2P) to ME-CPP with a corresponding release of cytidine 5-monophosphate (CMP). Because there is no ortholog of IspF in human cells, IspF is of interest as a potential drug target. However, study of IspF has been hindered by a lack of enantiopure CDP-ME2P. Herein, we report the first, to our knowledge, synthesis of enantiomerically pure CDP-ME2P from commercially available D-arabinose. Cloned, expressed, and purified M. tuberculosis IspF was able to utilize the synthetic CDP-ME2P as a substrate, a result confirmed by mass spectrometry. A convenient, sensitive, in vitro IspF assay was developed by coupling the CMP released during production of ME-CPP to mononucleotide kinase, which can be used for high throughput screening.

Antiangiogenic mechanisms of simvastatin in retinal endothelial cells

BACKGROUND

While statins have an anti-angiogenic property, their underlying mechanisms are not fully understood. We investigated intracellular mechanisms of simvastatin-mediated reduction in VEGF-induced signalings.

METHODS

The effects of simvastatin on cell proliferation and viability were evaluated by [(3)H]-thymidine incorporation in retinal endothelial cells (RECs) and cell counting. The impact of simvastatin on VEGF-induced phosphorylation of p44/42 mitogen-activated protein (MAP) kinase, myosin light chain (MLC), and VEGF-receptor (VEGFR) 2 were examined by Western blotting. Involvement of the mevalonate pathway in VEGF-induced signaling was also examined.

RESULTS

Simvastatin (1 and 10 microM) suppressed VEGF-induced RECs proliferation in a concentration-dependent manner, without affecting cell viability. Simvastatin significantly inhibited VEGF-induced phosphorylation of VEGFR2 and its downstream mediators, p44/42 MAP kinase and MLC. Mevalonate completely reversed VEGF-induced VEGFR2 phosphorylation, but only partially reversed the phosphorylation of p44/42 MAP kinase and MLC.

CONCLUSION

These data indicate that simvastatin exerts its anti-angiogenic effects through the reduction of VEGFR2 phosphorylation in RECs at least in part. However, there seems to be both mevalonate-dependent and independent pathway in simvastatin's anti-angiogenic property.

Serum lipids and bone metabolism in Spanish men: the Camargo cohort study

There is growing evidence of a link between lipid and bone metabolism, although data on this association in European men are scarce. This cross-sectional study from a community-based prospective cohort aims to explore the association of serum lipids with different aspects of bone metabolism in Spanish men. Demographic and anthropometric measurements, biochemical parameters including serum lipids, bone remodelling markers and calciotropic hormones, bone mineral density (BMD) assessed by dual X-ray absorptiometry and heel quantitative ultrasound, and prevalent vertebral and non-vertebral fractures, were evaluated in 289 men. Calciotropic hormones or bone markers were not associated with serum lipids. Serum total (TC) and LDL cholesterol, as well as LDL/HDL ratio were positively correlated to BMD at lumbar spine and hip. No significant correlation was noted for triglycerides or HDL. We observed a positive association between triglycerides, LDL/HDL ratio and BUA, and between TC/HDL ratio and both, QUI and BUA. BMD at the femoral neck and total hip was significantly higher in men with hypercholesterolemia after controlling for all the covariates (p=0.007). We did not observe any association between serum lipids and prevalent vertebral fractures. However, we found that TC (p=0.03) and LDL (p=0.04) were lower in subjects with non-vertebral fractures. In conclusion, we have found that a more unfavorable lipid profile (mainly higher LDL-C levels) is associated with higher BMD at lumbar spine and hip in Spanish men. Moreover, we did not observe any association between hypercholesterolemia and prevalent vertebral fractures, but we found lower serum TC and LDL-C levels in men with prevalent non-vertebral fractures.

Application of GC/MS-based metabonomic profiling in studying the lipid-regulating effects of Ginkgo biloba extract on diet-induced hyperlipidemia in rats

AIM

To evaluate the lipid-regulating effects of extract from Ginkgo biloba leaves (EGB) using pharmacological methods and metabonomic profiling in a rat model of diet-induced hyperlipidemia.

METHODS

EGB was orally administered at a dose level of 40 mg/kg in both the EGB-prevention and -treatment groups. All rat samples obtained were examined for known and potential biomarkers and enzyme activity using commercial assay kits and GC/MS-based metabonomic profiling coupled with principal component analysis (PCA).

RESULTS

The data obtained from the assay kits indicated that EGB reduced total cholesterol and low density lipoprotein cholesterol levels and increased high density lipoprotein cholesterol levels in rat plasma obtained from both the EGB-prevention and -treatment groups compared with those of the diet-induced hyperlipidemia group. EGB also increased the activities of lipoprotein lipase and hepatic lipase and excretion of fecal bile acid in rats from the EGB-prevention and-treatment groups. Using GC/MS-based metabonomic analysis, more than 40 endogenous metabolites were identified in rat plasma. PCA of rat plasma samples obtained using GC/MS produced a distinctive separation of the four treatment groups and sampling points within each group. Metabolic changes during hyperlipidemia formation and improvement resulting from EGB treatment were definitively monitored with PCA score plots. Furthermore, elevated levels of sorbitol, tyrosine, glutamine and glucose, and decreased levels of citric acid, galactose, palmitic acid, arachidonic acid, acetic acid, cholesterol, butyrate, creatinine, linoleate, ornithine and proline, were observed in the plasma of rats treated with EGB.

CONCLUSION

EGB exerts multi-directional lipid-lowering effects on the rat metabonome, including limitation of the absorption of cholesterol, inactivation of HMGCoA and favorable regulation of profiles of essential polyunsaturated fatty acid (EFA). Further experiments are warranted to explore the mechanisms of action underlying the lipid-regulating effects of EGB against hyperlipidemia.

Mevalonate pathway intermediates downregulate zoledronic acid-induced isopentenyl pyrophosphate and ATP analog formation in human breast cancer cells

Increasing evidence is accumulating that zoledronic acid (ZOL), a nitrogen-containing bisphosphonate (N-BP), is able to affect tumor cells by inhibiting the enzyme farnesyl pyrophosphate synthase (FPPS) in the mevalonate pathway (MVP). The consequent accumulation of unprenylated proteins is believed to largely account for the cytotoxic effects of ZOL. FPPS inhibition leads also to the accumulation of isopentenyl pyrophosphate (IPP) and the apoptotic ATP analog, ApppI, but the role of this mechanism in the cytotoxic action of bisphosphonates is less clear. Since treatment with MVP intermediates has been shown to overcome N-BP-induced apoptosis via rescuing protein prenylation, our aim here was to determine their mechanism of action on ZOL-induced IPP/ApppI accumulation. Interestingly, the results revealed that ZOL-induced IPP/ApppI accumulation in MCF-7 cells were decreased by farnesol, and almost completely blocked by geranylgeraniol and geranylpyrophosphate. The functionality of the regulatory enzymes of IPP and ApppI, IPP isomerase and aminoacyl-tRNA-synthase, respectively, or protein levels of FPPS were not affected by the treatments. However, the protein levels of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) and unprenylated Rap1A were observed to be strongly downregulated by geranylgeraniol and geranylpyrophosphate. This study represents a novel insight into the mechanism of action of MVP intermediates on the regulation of MVP after FPPS inhibition. The data implies that in addition to the previously reported effects on rescuing protein prenylation, MVP intermediates can preserve cell activity by inhibiting the accumulation of IPP/ApppI via HMGR downregulation. This supports the hypothesis that IPP/ApppI formation is a significant mechanism in the anticancer action of ZOL.

Identified biosynthetic pathway of aspergiolide A and a novel strategy to increase its production in a marine-derived fungus Aspergillus glaucus by feeding of biosynthetic precursors and inhibitors simultaneously

Aspergiolide A is a novel anti-tumor anthraquinone derivant produced by marine-derived fungus Aspergillus glaucus. To identify its biosynthetic pathway and further improve the production, the effects of biosynthetic pathway specific inhibitors and precursors were investigated. Cerulenin and iodoacetamide, the specific inhibitors of polyketide pathway, could completely inhibit the aspergiolide A accumulation. Putative precursors of polyketide pathway could increase aspergiolide A production greatly, such as 6 mM acetate increased production by 135%. Simvastatin and citrate, the inhibitors of mevalonate pathway, stimulated the production by 63% and 179%, respectively. Considering that acetyl-CoA is the common starter unit in both polyketide and mevalonate pathway, a novel strategy was designed to stimulate the aspergiolide A accumulation. Combinations of 12 mM acetate with 0.3 mM simvastatin could increase the production by 151%, while the supplementation with 12 mM acetate and 12 mM citrate brought a 262% increase of aspergiolide A production. The strategy might be very useful to enhance the production of other secondary metabolites derived from polyketide pathway.

Combined gas chromatographic/mass spectrometric analysis of cholesterol precursors and plant sterols in cultured cells

We developed a powerful gas chromatographic/mass spectrometric method allowing quantitative analysis of 11 structurally similar cholesterol precursors and plant sterols (squalene, desmosterol, 7-dehydrocholesterol, lathosterol, zymosterol, dihydro-lanosterol, lanosterol, FF-MAS, T-MAS, campesterol, sitosterol) from cultured human hepatocytes in a single chromatographic run. Deuterium labelled cholesterol, sitosterol and lathosterol were used as internal standards. Care was taken to select ions for the detection that gave the most appropriate discrimination in the assay. Replicate analyses gave a coefficient of variation less than 6%. Recovery experiments were satisfactory for 7-dehydrocholesterol, campesterol, desmosterol, lathosterol, zymosterol and cholesterol with less than 7% difference between expected and found levels. For other sterols, the difference between expected and found levels varied between 10 and 16%. It is concluded that this method is suitable for studies on the effect of different inhibitors and stimulators of cholesterol synthesis in cultured cells. Additionally, the method is relevant also for clinical applications since abnormally increased late cholesterol intermediates in patients are representations of the inherited disorders linked to different enzyme defects in the post-squalene cholesterol biosynthesis.

Role of cholesterol pathways in norovirus replication

Norwalk virus (NV) is a prototype strain of the noroviruses (family Caliciviridae) that have emerged as major causes of acute gastroenteritis worldwide. I have developed NV replicon systems using reporter proteins such as a neomycin-resistant protein (NV replicon-bearing cells) and a green fluorescent protein (pNV-GFP) and demonstrated that these systems were excellent tools to study virus replication in cell culture. In the present study, I first performed DNA microarray analysis of the replicon-bearing cells to identify cellular factors associated with NV replication. The analysis demonstrated that genes in lipid (cholesterol) or carbohydrate metabolic pathways were significantly (P < 0.001) changed by the gene ontology analysis. Among genes in the cholesterol pathways, I found that mRNA levels of hydroxymethylglutaryl-coenzyme A (HMG-CoA) synthase, squalene epoxidase, and acyl-CoA:cholesterol acyltransferase (ACAT), ACAT2, small heterodimer partner, and low-density lipoprotein receptor (LDLR)-related proteins were significantly changed in the cells. I also found that the inhibition of cholesterol biosynthesis using statins (an HMG-CoA reductase inhibitor) significantly increased the levels of NV proteins and RNA, whereas inhibitors of ACAT significantly reduced the replication of NV in replicon-bearing cells. Up- or downregulation of virus replication with these agents significantly correlated with the mRNA level of LDLR in replicon-bearing cells. Finally, I found that the expression of LDLR promoted NV replication in trans by transfection study with pNV-GFP. I conclude that the cholesterol pathways such as LDLR expression and ACAT activity may be crucial in the replication of noroviruses in cells, which may provide potential therapeutic targets for viral infection.

Update on statin-mediated anti-inflammatory activities in atherosclerosis

Anti-inflammatory activities of statins in atherosclerosis have been well documented by both basic research and clinical studies. Statins have been introduced in the 1980s as 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors to block cholesterol synthesis and lower cholesterol serum levels. In the last three decades, statins have been shown to possess several anti-inflammatory and antioxidant activities resulting in the beneficial reduction of atherosclerotic processes and cardiovascular risk in both humans and animal models. Inflammatory intracellular pathways involving kinase phosphorylation and protein prenylation are modulated by statins. The same intracellular mechanisms might also cause statin-induced myotoxicity. In the present review, we will update evidence on statin-mediated regulation of inflammatory pathways in atherogenesis.

Statins impair CD1d-mediated antigen presentation through the inhibition of prenylation

Statins are widely used as cholesterol-lowering agents that also decrease inflammation and target enzymes essential for prenylation, an important process in the activation and intracellular transport of proteins vital for a wide variety of cellular functions. Here, we report that statins impair a critical component of the innate immune response, CD1d-mediated Ag presentation. The addition of specific intermediates in the isoprenylation pathway reversed this effect, whereas specific targeting of enzymes responsible for prenylation mimicked the inhibitory effects of statins on Ag presentation by CD1d as well as MHC class II molecules. This study demonstrates the importance of isoprenylation in the regulation of Ag presentation and suggests a mechanism by which statins reduce inflammatory responses.

Dynamical modeling of the cholesterol regulatory pathway with Boolean networks

BACKGROUND

Qualitative dynamics of small gene regulatory networks have been studied in quite some details both with synchronous and asynchronous analysis. However, both methods have their drawbacks: synchronous analysis leads to spurious attractors and asynchronous analysis lacks computational efficiency, which is a problem to simulate large networks. We addressed this question through the analysis of a major biosynthesis pathway. Indeed the cholesterol synthesis pathway plays a pivotal role in dislypidemia and, ultimately, in cancer through intermediates such as mevalonate, farnesyl pyrophosphate and geranyl geranyl pyrophosphate, but no dynamic model of this pathway has been proposed until now.

RESULTS

We set up a computational framework to dynamically analyze large biological networks. This framework associates a classical and computationally efficient synchronous Boolean analysis with a newly introduced method based on Markov chains, which identifies spurious cycles among the results of the synchronous simulation. Based on this method, we present here the results of the analysis of the cholesterol biosynthesis pathway and its physiological regulation by the Sterol Response Element Binding Proteins (SREBPs), as well as the modeling of the action of statins, inhibitor drugs, on this pathway. The in silico experiments show the blockade of the cholesterol endogenous synthesis by statins and its regulation by SREPBs, in full agreement with the known biochemical features of the pathway.

CONCLUSION

We believe that the method described here to identify spurious cycles opens new routes to compute large and biologically relevant models, thanks to the computational efficiency of synchronous simulation. Furthermore, to the best of our knowledge, we present here the first dynamic systems biology model of the human cholesterol pathway and several of its key regulatory control elements, hoping it would provide a good basis to perform in silico experiments and confront the resulting properties with published and experimental data. The model of the cholesterol pathway and its regulation, along with Boolean formulae used for simulation are available on our web site http://Bioinformaticsu613.free.fr. Graphical results of the simulation are also shown online. The SBML model is available in the BioModels database http://www.ebi.ac.uk/biomodels/ with submission ID: MODEL0568648427.