The human DIMINUTO/DWARF1 homolog seladin-1 confers resistance to Alzheimer's disease-associated neurodegeneration and oxidative stress

Plant sterol metabolism. Δ(7)-Sterol-C5-desaturase (STE1/DWARF7), Δ(5,7)-sterol-Δ(7)-reductase (DWARF5) and Δ(24)-sterol-Δ(24)-reductase (DIMINUTO/DWARF1) show multiple subcellular localizations in Arabidopsis thaliana (Heynh) L

Sterols are crucial lipid components that regulate membrane permeability and fluidity and are the precursors of bioactive steroids. The plant sterols exist as three major forms, free sterols, steryl glycosides and steryl esters. The storage of steryl esters in lipid droplets has been shown to contribute to cellular sterol homeostasis. To further document cellular aspects of sterol biosynthesis in plants, we addressed the question of the subcellular localization of the enzymes implicated in the final steps of the post-squalene biosynthetic pathway. In order to create a clear localization map of steroidogenic enzymes in cells, the coding regions of Δ⁷-sterol-C₅-desaturase (STE1/DWARF7), Δ²⁴-sterol-Δ²⁴-reductase (DIMINUTO/DWARF1) and Δ^5,7-sterol-Δ⁷-reductase (DWARF5) were fused to the yellow fluorescent protein (YFP) and transformed into Arabidopsis thaliana mutant lines deficient in the corresponding enzymes. All fusion proteins were found to localize in the endoplasmic reticulum in functionally complemented plants. The results show that both Δ^5,7-sterol-Δ⁷-reductase and Δ²⁴-sterol-Δ²⁴-reductase are in addition localized to the plasma membrane, whereas Δ⁷-sterol-C₅-desaturase was clearly detected in lipid particles. These findings raise new challenging questions about the spatial and dynamic cellular organization of sterol biosynthesis in plants.

Crosstalk between thyroid hormone receptor and liver X receptor in the regulation of selective Alzheimer's disease indicator-1 gene expression

Selective Alzheimer’s disease (AD) indicator 1 (Seladin-1) has been identified as a gene down-regulated in the degenerated lesions of AD brain. Up-regulation of Seladin-1 reduces the accumulation of β-amyloid and neuronal death. Thyroid hormone (TH) exerts an important effect on the development and maintenance of central nervous systems. In the current study, we demonstrated that Seladin-1 gene and protein expression in the forebrain was increased in thyrotoxic mice compared with that of euthyroid mice. However, unexpectedly, no significant decrease in the gene and protein expression was observed in hypothyroid mice. Interestingly, an agonist of liver X receptor (LXR), TO901317 (TO) administration in vivo increased Seladin-1 gene and protein expression in the mouse forebrain only in a hypothyroid state and in the presence of mutant TR-β, suggesting that LXR-α would compensate for TR-β function to maintain Seladin-1 gene expression in hypothyroidism and resistance to TH. TH activated the mouse Seladin-1 gene promoter (−1936/+21 bp) and site 2 including canonical TH response element (TRE) half-site in the region between −159 and −154 bp is responsible for the positive regulation. RXR-α/TR-β heterodimerization was identified on site 2 by gel-shift assay, and chromatin immunoprecipitation assay revealed the recruitment of TR-β to site 2 and the recruitment was increased upon TH administration. On the other hand, LXR-α utilizes a distinct region from site 2 (−120 to −102 bp) to activate the mouse Seladin-1 gene promoter. Taking these findings together, we concluded that TH up-regulates Seladin-1 gene expression at the transcriptional level and LXR-α maintains the gene expression.

Promoter analysis of the DHCR24 (3β-hydroxysterol Δ(24)-reductase) gene: characterization of SREBP (sterol-regulatory-element-binding protein)-mediated activation

DHCR24 (3β-hydroxysterol Δ²⁴-reductase) catalyses the reduction of the C-24 double bond of sterol intermediates during cholesterol biosynthesis. DHCR24 has also been involved in cell growth, senescence and cellular response to oncogenic and oxidative stress. Despite its important roles, little is known about the transcriptional mechanisms controlling DHCR24 gene expression. We analysed the proximal promoter region and the cholesterol-mediated regulation of DHCR24. A putative SRE (sterol-regulatory element) at −98/−90 bp of the transcription start site was identified. Other putative regulatory elements commonly found in SREBP (SRE-binding protein)-targeted genes were also identified. Sterol responsiveness was analysed by luciferase reporter assays of approximately 1 kb 5′-flanking region of the human DHCR24 gene in HepG2 and SK-N-MC cells. EMSAs (electrophoretic mobility-shift assays) and ChIP (chromatin immunoprecipitation) assays demonstrated cholesterol-dependent recruitment and binding of SREBPs to the putative SRE. Given the presence of several CACCC-boxes in the DHCR24 proximal promoter, we assessed the role of KLF5 (Krüppel-like factor 5) in androgen-regulated DHCR24 expression. DHT (dihydrotestosterone) increased DHCR24 expression synergistically with lovastatin. However, DHT was unable to activate the DHCR24 proximal promoter, whereas KLF5 did, indicating that this mechanism is not involved in the androgen-induced stimulation of DHCR24 expression. The results of the present study allow the elucidation of the mechanism of regulation of the DHCR24 gene by cholesterol availability and identification of other putative cis-acting elements which may be relevant for the regulation of DHCR24 expression.

Role of oxidative stress in hepatocarcinogenesis induced by hepatitis C virus

Hepatitis C virus (HCV) easily establishes chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). During the progression of HCV infections, reactive oxygen species (ROS) are generated, and these ROS then induce significant DNA damage. The role of ROS in the pathogenesis of HCV infection is still not fully understood. Recently, we found that HCV induced the expression of 3β-hydroxysterol Δ24-reductase (DHCR24). We also found that a HCV responsive region is present in the 5′-flanking genomic promoter region of DHCR24 and the HCV responsive region was characterized as (−167/−140). Moreover, the transcription factor Sp1 was found to bind to this region in response to oxidative stress under the regulation of ataxia telangiectasia mutated (ATM) kinase. Overexpression of DHCR24 impaired p53 activity by suppression of acetylation and increased interaction with MDM2. This impairment of p53 suppressed the hydrogen peroxide-induced apoptotic response in hepatocytes. Thus, a target of oxidative stress in HCV infection is DHCR24 through Sp1, which suppresses apoptotic responses and increases tumorigenicity.

High-density lipoproteins inhibit vascular endothelial inflammation by increasing 3β-hydroxysteroid-Δ24 reductase expression and inducing heme oxygenase-1

RATIONALE

Lipid-free apolipoprotein (apo) A-I and discoidal reconstituted high-density lipoproteins (rHDL) containing apoA-I, (A-I)rHDL, inhibit vascular inflammation by increasing 3β-hydroxysteroid-Δ24 reductase (DHCR24) expression.

OBJECTIVE

To determine whether the lipid-free apoA-I-mediated and (A-I)rHDL-mediated increase in DHCR24 expression induces the cytoprotective and potentially cardioprotective enzyme, heme oxygenase-1 (HO-1).

METHODS AND RESULTS

In vivo: A single intravenous infusion of lipid-free apoA-I (8 mg/kg) administered 24 hours before inserting a nonocclusive periarterial carotid collar into New Zealand White rabbits decreased collar-induced endothelial vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 expression, reduced intima/media neutrophil infiltration, and increased DHCR24 and HO-1 mRNA levels. Knockdown of vascular DHCR24 and HO-1 and systemic administration of tin-protoporphyrin-IX, an HO inhibitor, abolished these anti-inflammatory effects. In vitro: Preincubation of human coronary artery endothelial cells with (A-I)rHDL before activation with tumor necrosis factor-α increased DHCR24 and HO-1 mRNA levels and inhibited cytokine-induced vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 expression. Transfection of the cells with DHCR24 and HO-1 small interfering RNA and tin-protoporphyrin-IX treatment abolished these effects. The (A-I)rHDL-mediated induction of HO-1 was reduced in human coronary artery endothelial cells transfected with DHCR24 small interfering RNA. Transfection of human coronary artery endothelial cells with HO-1 small interfering RNA and tin-protoporphyrin-IX treatment did not inhibit the (A-I)rHDL-mediated increase in DHCR24 expression. Inhibition of phosphatidylinositol 3-kinase/Akt reduced the (A-I)rHDL-mediated increase in HO-1, but not DHCR24 expression. The activation of phosphatidylinositol 3-kinase/Akt by (A-I)rHDL was decreased in human coronary artery endothelial cells that were transfected with DHCR24 small interfering RNA.

CONCLUSIONS

Lipid-free apoA-I and (A-I)rHDL inhibit inflammation by increasing DHCR24 expression, which, in turn, activates phosphatidylinositol 3-kinase/Akt and induces HO-1.

Bepridil decreases Aβ and calcium levels in the thalamus after middle cerebral artery occlusion in rats

Alzheimer's disease (AD) and cerebral ischaemia share similar features in terms of altered amyloid precursor protein (APP) processing and β-amyloid (Aβ) accumulation. We have previously shown that Aβ and calcium deposition, and β-secretase activity, are robustly increased in the ipsilateral thalamus after transient middle cerebral artery occlusion (MCAO) in rats. Here, we investigated whether the non-selective calcium channel blocker bepridil, which also inhibits β-secretase cleavage of APP, affects thalamic accumulation of Aβ and calcium and in turn influences functional recovery in rats subjected to MCAO. A 27-day bepridil treatment (50 mg/kg, p.o.) initiated 2 days after MCAO significantly decreased the levels of soluble Aβ40, Aβ42 and calcium in the ipsilateral thalamus, as compared with vehicle-treated MCAO rats. Expression of seladin-1/DHCR24 protein, which is a potential protective factor against neuronal damage, was decreased at both mRNA and protein levels in the ipsilateral thalamus of MCAO rats. Conversely, bepridil treatment restored seladin-1/DHCR24 expression in the ipsilateral thalamus. Bepridil treatment did not significantly affect heme oxygenase-1- or NAD(P)H quinone oxidoreductase-1-mediated oxidative stress or inflammatory responses in the ipsilateral thalamus of MCAO rats. Finally, bepridil treatment mitigated MCAO-induced alterations in APP processing in the ipsilateral thalamus and improved contralateral forelimb use in MCAO rats. These findings suggest that bepridil is a plausible therapeutic candidate in AD or stroke owing to its multifunctional role in key cellular events that are relevant for the pathogenesis of these diseases.

Relationship between the neuroprotective effects of insulin-like growth factor-1 and 17β-oestradiol in human neuroblasts

Insulin-like growth factor-1 (IGF-1) and oestrogens interact with each other as neuroprotective factors. We have previously demonstrated that 17β-oestradiol protects against β-amyloid and oxidative stress toxicity and increases the amount of cell cholesterol in human foetal neuroblasts (FNC). The present study aimed: (i) to assess the protective effects of IGF-1 in FNC cells; (ii) to investigate the relationship between IGF-1 and 17β-oestradiol; and (iii) to determine whether cholesterol was a major mediator of the effects of IGF-1, similarly to 17β-oestradiol. We found that IGF-1 effectively exerts neuroprotective effects in FNC cells. We also demonstrated that the IGF-1 receptor (IGF-1R) pathway is needed to maintain oestrogen-mediated neuroprotection. Finally, we found that, opposite to 17β-oestradiol, IGF-1 did not cause a significant increase in cell cholesterol. These findings indicate that a cross-talk between IGF-1 and 17β-oestradiol occurs in FNC cells. In particular, the activation of the IGF-1R cascade appears to be fundamental to warrant 17β-oestradiol-mediated neuroprotection, even though cell cholesterol does not play a major role as an effector of this pathway.

Role of cholesterol in APP metabolism and its significance in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disorder believed to be initiated by accumulation of amyloid β (Aβ)-related peptides derived from proteolytic processing of amyloid precursor protein (APP). Research over the past two decades provided a mechanistic link between cholesterol and AD pathogenesis. Genetic polymorphisms in genes regulating the pivotal points in cholesterol metabolism have been suggested to enhance the risk of developing AD. Altered neuronal membrane cholesterol level and/or subcellular distribution have been implicated in aberrant formation, aggregation, toxicity, and degradation of Aβ-related peptides. However, the results are somewhat contradictory and we still do not have a complete understanding on how cholesterol can influence AD pathogenesis. In this review, we summarize our current understanding on the role of cholesterol in regulating the production/function of Aβ-related peptides and also examine the therapeutic potential of regulating cholesterol homeostasis in the treatment of AD pathology.

Brain aging and late-onset Alzheimer's disease: many open questions

Despite decades of research in the field of Alzheimer's disease (AD), a real understanding of its molecular pathophysiology and treatments relevant to the day-to-day lives of patients remain out of reach. Research has, with good reason, focused on certain key pathways and potential mechanisms, but sometimes this has been at the expense of work on other theories, which may be slowing down progress in this field. Interesting theories at present include oxidative stress and caloric restriction. Work on the Aβ cascade should continue but with a shift in focus to its intracellular effects and an awareness that additional pathogenetic factors and processes must be involved--most importantly, brain aging. Hyperphosphorylation of tau, for instance, provides another interesting pathway, with one old drug showing promise in this regard. Moreover, work in epigenetics and on protein homeostasis has produced interesting findings and both lines of investigation may reveal suitable targets for future intervention. Taken together, analysis of the biochemistry of aged neurons and the interplay with pathways of neurodegeneration may lead to a better understanding of AD and how to treat and prevent this condition.

Sterols regulate 3β-hydroxysterol Δ24-reductase (DHCR24) via dual sterol regulatory elements: cooperative induction of key enzymes in lipid synthesis by Sterol Regulatory Element Binding Proteins

3β-Hydroxysterol Δ24-reductase (DHCR24) catalyzes a final step in cholesterol synthesis, and has been ascribed diverse functions, such as being anti-apoptotic and anti-inflammatory. How this enzyme is regulated transcriptionally by sterols is currently unclear. Some studies have suggested that its expression is regulated by Sterol Regulatory Element Binding Proteins (SREBPs) while another suggests it is through the Liver X Receptor (LXR). However, these transcription factors have opposing effects on cellular sterol levels, so it is likely that one predominates. Here we establish that sterol regulation of DHCR24 occurs predominantly through SREBP-2, and identify the particular region of the DHCR24 promoter to which SREBP-2 binds. We demonstrate that sterol regulation is mediated by two sterol regulatory elements (SREs) in the promoter of the gene, assisted by two nearby NF-Y binding sites. Moreover, we present evidence that the dual SREs work cooperatively to regulate DHCR24 expression by comparison to two known SREBP target genes, the LDL receptor with one SRE, and farnesyl-diphosphate farnesyltransferase 1, with two SREs.

Hepatitis C virus promotes expression of the 3β-hydroxysterol δ24-reductase through Sp1

Hepatitis C virus (HCV) establishes chronic infection, which often causes hepatocellular carcinoma. Overexpression of 3β-hydroxysterol Δ24-reductase (DHCR24) by HCV has been shown to impair the p53-mediated cellular response, resulting in tumorigenesis. In the present study, the molecular mechanism by which HCV promotes the expression of DHCR24 was investigated. A significant increase in DHCR24 mRNA transcription was observed in a cell line expressing complete HCV genome, whereas no significant difference in the expression of DHCR24 was seen in cell lines expressing individual viral proteins. The 5'-flanking genomic region of DHCR24 was characterized to explore the genomic region and host factor(s) involved in the transcriptional regulation of DHCR24. As a result, the HCV response element (-167/-140) was identified, which contains AP-2α, MZF-1, and Sp1 binding motifs. The binding affinity of the host factor to this response element was increased in nuclear extracts from cells infected with HCV and corresponded with augmented affinity of Sp1. Both mithramycin A (Sp1 inhibitor) and small interfering RNA targeting Sp1 prevented the binding of host factors to the response element. Silencing of Sp1 also downregulated the increased expression of DHCR24. The binding affinity of Sp1 to the response element was augmented by oxidative stress, whereas upregulation of DHCR24 in cells expressing HCV was blocked significantly by a reactive oxygen species scavenger. Elevated phosphorylation of Sp1 in response to oxidative stress was mediated by the ATM kinase. Thus, activation of Sp1 by oxidative stress is involved in the promotion of expression of DHCR24 by HCV.

Amyloid pathway-based candidate gene analysis of [(11)C]PiB-PET in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort

Amyloid imaging with [(11)C]Pittsburgh Compound-B (PiB) provides in vivo data on plaque deposition in those with, or at risk for, Alzheimer's disease (AD). We performed a gene-based association analysis of 15 quality-controlled amyloid-pathway associated candidate genes in 103 Alzheimer's Disease Neuroimaging Initiative participants. The mean normalized PiB uptake value across four brain regions known to have amyloid deposition in AD was used as a quantitative phenotype. The minor allele of an intronic SNP within DHCR24 was identified and associated with a lower average PiB uptake. Further investigation at whole-brain voxel-wise level indicated that non-carriers of the minor allele had higher PiB uptake in frontal regions compared to carriers. DHCR24 has been previously shown to confer resistance against beta-amyloid and oxidative stress-induced apoptosis, thus our findings support a neuroprotective role. Pathway-based genetic analysis of targeted molecular imaging phenotypes appears promising to help elucidate disease pathophysiology and identify potential therapeutic targets.

Reciprocal regulation of cholesterol and beta amyloid at the subcellular level in Alzheimer's disease

Since the discovery that apolipoprotein E, a cholesterol transport protein, is a major risk factor for Alzheimer's disease (AD) development, there has been a remarkable interest in understanding the many facets of the relationship between cholesterol and AD. Several lines of evidence have demonstrated the importance of cholesterol in amyloid beta peptide (Aβ) production and metabolism, as well as the involvement of Aβ in cholesterol homeostasis. The emerging picture is complex and still incomplete. This review discusses findings that indicate that a reciprocal regulation exists between Aβ and cholesterol at the subcellular level. The pathological impact of such regulation is highlighted.

Hormonal modulation of cholesterol: experimental evidence and possible translational impact

Alzheimer's disease (AD) is still an incurable condition. There is in vitro evidence that estrogens exert neuroprotective effects; however, their role in the treatment of AD is still controversial. Approximately 10 years ago, a new gene, named seladin-1 (for selective AD indicator-1), was identified and found to be downregulated in brain regions affected by AD. Seladin-1 has neuroprotective properties, which have been associated, at least in part, with its anti-apoptotic activity. Estrogens stimulate the expression of the seladin-1 gene. Seladin-1 also has enzymatic activity (3-β-hydroxysterol Δ-24-reductase), which is involved in the synthesis of cholesterol from desmosterol. The amount of membrane cholesterol appears to play an important role in conferring protection to brain cells. This review focuses on the relationship between estrogens (and IGF-1, another hormone with neuroprotective properties), cholesterol and seladin-1.

Testosterone up-regulates seladin-1 expression by iAR and PI3-K/Akt signaling pathway in C6 cells

The previous study indicated that DHCR24/seladin-1 was an important neuroprotective effector. However, the molecular mechanisms that androgen modulates the expression of seladin-1 remain incompletely defined. In this paper, we showed that the expression of seladin-1 was significantly increased by testosterone at all concentrations tested at the protein and mRNA levels in C6 cells, the selective AR antagonist flutamide obviously inhibited the effect in a concentration-dependent manner. Furthermore, we found that testosterone significantly increased the phosphorylation level of V-akt murine thymoma viral oncogene (Akt), a key effector of the phosphoinositide 3-kinase (PI3-K)/Akt signaling pathway, while a specific PI3-K inhibitor LY294002 obviously prevented the activation of Akt phosphorylation. In addition, the PI3-K inhibitor LY294002 also markedly blocked the up-regulation expression of seladin-1 gene induced by testosterone at the protein and mRNA levels. Collectively, the above results suggested that testosterone regulated the expression of seladin-1 by the intracellular androgen receptor (iAR)-mediated genomic signaling pathway and the non-genomic PI3-K/Akt signaling pathway in C6 glial cells.

3β-Hydroxysterol-Delta24 reductase plays an important role in long bone growth by protecting chondrocytes from reactive oxygen species

Desmosterolosis is an autosomal recessive disease caused by mutations in the 3β-hydroxysterol-Delta24 reductase (DHCR24) gene, with severe developmental anomalies including short limbs. We utilized DHCR24 knockout (KO) mice to study the underlying bone pathology. Because the KO mice died within a few hours after birth, we cultured metatarsal bones from newborn mice. The growth of bones from KO mice was significantly retarded after 1 week of culture. Absence of proliferating chondrocytes in the growth plate and abnormal hypertrophy of prehypertrophic chondrocytes were observed in the bones from KO mice. Hypertrophic differentiation was evidenced by higher expression of Indian hedgehog, alkaline phosphatase, and matrix metalloproteinase 13. Since elevated levels of reactive oxygen species (ROS) during chondrogenesis are known to inhibit proliferation and to initiate chondrocyte hypertrophy in the growth plate, and since DHCR24 acts as a potent ROS scavenger, we hypothesized that the abnormal chondrocyte proliferation and differentiation in KO mice were due to decreased ROS scavenging activity. Treatment with an antioxidant, N-acetyl cysteine, could correct the abnormalities observed in the bones from KO mice. Treatment of bones from wild-type mice with U18666A, a chemical inhibitor of DHCR24, resulted in short broad bones with a disrupted proliferating zone. Treatment of ATDC cells with hydrogen peroxide (H(2)O(2)) induced hypertrophic changes as evidenced by the expression of the marker genes specific for hypertrophic chondrocyte differentiation. H(2)O(2)-induced hypertrophic change was prevented by adenoviral delivery of DHCR24. Induction of chondrocyte differentiation in ATDC cells by insulin was associated with increased ROS production that was markedly enhanced by treatment of ATDC5 cells with DHCR24 siRNA. This is the first demonstration that DHCR24 plays an important role in long bone growth by protecting chondrocytes from ROS.

Regulation of global gene expression in human Loa loa infection is a function of chronicity

Background

Human filarial infection is characterized by downregulated parasite-antigen specific T cell responses but distinct differences exist between patients with longstanding infection (endemics) and those who acquired infection through temporary residency or visits to filarial-endemic regions (expatriates).

Methods and Findings

To characterize mechanisms underlying differences in T cells, analysis of global gene expression using human spotted microarrays was conducted on CD4⁺ and CD8⁺ T cells from microfilaremic Loa loa-infected endemic and expatriate patients. Assessment of unstimulated cells showed overexpression of genes linked to inflammation and caspase-associated cell death, particularly in endemics, and enrichment of the Th1/Th2 canonical pathway in endemic CD4⁺ cells. However, pathways within CD8⁺ unstimulated cells were most significantly enriched in both patient groups. Antigen (Ag)-driven gene expression was assessed to microfilarial Ag (MfAg) and to the nonparasite Ag streptolysin O (SLO). For MfAg-driven cells, the number of genes differing significantly from unstimulated cells was greater in endemics compared to expatriates (p<0.0001). Functional analysis showed a differential increase in genes associated with NFkB (both groups) and caspase activation (endemics). While the expatriate response to MfAg was primarily a CD4⁺ pro-inflammatory one, the endemic response included CD4⁺ and CD8⁺ cells and was linked to insulin signaling, histone complexes, and ubiquitination. Unlike the enrichment of canonical pathways in CD8⁺ unstimulated cells, both groups showed pathway enrichment in CD4⁺ cells to MfAg. Contrasting with the divergent responses to MfAg seen between endemics and expatriates, the CD4⁺ response to SLO was similar; however, CD8⁺ cells differed strongly in the nature and numbers (156 [endemics] vs 36 [expatriates]) of genes with differential expression.

Conclusions

These data suggest several important pathways are responsible for the different outcomes seen among filarial-infected patients with varying levels of chronicity and imply an important role for CD8⁺ cells in some of the global changes seen with lifelong exposure.

Infection with the filarial parasite Loa loa causes a parasite-specific downregulation of T cell responses. However, differences exist (clinical and immunologic) between patients born and living in filarial endemic regions (endemics) and those who become infected during travel or short-term residency (expatriates). T cell responses are more depressed in endemics while expatriates have more clinical “allergic-type” symptoms. In this study, we showed that these differences reflect transcriptional differences within the T cell compartment. Using microarrays, we examined global gene expression in both CD4⁺ and CD8⁺ T cells of microfilaremic endemic and expatriate patients and found differences not only ex vivo, but also to parasite and, for CD8⁺ cells, to nonparasite antigens. Functional analysis showed that endemic patients expressed genes linked to inflammatory disease and caspase associated cell death at homeostasis while expatriates tended to have a more activation-induced gene profile at homeostasis and a CD4⁺ inflammatory response to parasite antigen. Patient groups were similar in their CD4⁺ response to nonparasite antigen but strongly differed in their CD8⁺ responses, demonstrating the potential global ramifications of chronic, longstanding infection. Our study describes potential transcriptional mechanisms for the variability seen in patients with different levels of exposure to and chronicity of filarial infection.

The membrane topological analysis of 3β-hydroxysteroid-Delta24 reductase (DHCR24) on endoplasmic reticulum

DHCR24 encodes 3β-hydroxysteroid-Δ24 reductase, catalyzing the conversion of desmosterol to cholesterol. Our previous study demonstrated that DHCR24 exerts an anti-apoptotic function as a reactive oxygen species (ROS) scavenger, for which it needs its FAD-binding domain. The membrane topology of DHCR24 on endoplasmic reticulum (ER) and the functional significance of its FAD-binding domain are not completely understood. Based on the structure predicted by bioinformatics, we studied the membrane topology of DHCR24 in murine neuroblastoma cells (N2A), using the fluorescent protease protection (FPP) technique. We showed that full-length DHCR24 is localized to the membrane of ER, whereas the predicted transmembrane (TM) domain-deleted DHCR24 mutation is localized to the cytoplasm. The change of DHCR24 localization suggests that the N-terminal TM domain is essential for the ER membrane targeting of DHCR24. The FPP assay demonstrated the membrane topology of DHCR24 with an N-terminal luminal/C-terminal cytoplasmic orientation. Measurement of intracellular ROS using H(2)DCFDA revealed that the ROS levels of cells infected by plasmids driving expression of full-length DHCR24 or the TM domain-deleted DHCR24 mutation after H(2)O(2) exposure were lower than those of control cells, suggesting that the ER membrane targeting of DHCR24 is not required for its enzymatic ROS scavenging activity. Confocal fluorescence microscopy revealed that the DHCR24-overexpressed cells were protected from apoptosis in response to oxidative stress, which was accompanied by a decrease in DHCR24 content on the ER and activation of caspase-3, suggesting that the anti-apoptotic function of DHCR24 is associated with its cleavage by caspase.

Neuroprotective effects of citrus flavonoids

Recent attention has been given to the influence of dietary factors on health and mental well-being. Oxidative stress is associated with many diseases including neurodegenerative disorders. Dietary flavonoids exert cardioprotective, chemopreventive, and neuroprotective effects. The biological activities of flavonoids have been attributed to their antioxidant, anti-inflammatory, and signaling properties. A clear understanding of the mechanisms of action, as either antioxidants or signaling molecules, is crucial for the application of flavonoids as interventions in neurodegeneration and as brain foods. Citrus flavonoids exert little adverse effect and have low or no cytotoxicity to healthy, normal cells. The main citrus flavonoids can also traverse the blood-brain barrier; hence, they are promising candidates for intervention in neurodegeneration and as constituents in brain foods. In this review, we discuss the bioactivity, multiple neuroprotection mechanisms, and antioxidant and signaling properties of citrus flavonoids. Receptor-mediated neuroprotective actions and parallel signaling pathways are also explored. Finally, the induction of cellular defense proteins against oxidative stress and neurotoxicity by hesperetin, a main and widespread citrus flavonoid, are also discussed. It is suggested that citrus fruits, which are rich in abundant sources of hesperetin and other flavonoids, are promising for the development of general food-based neuroprotection and brain foods.

Β-site APP-cleaving enzyme 1 trafficking and Alzheimer's disease pathogenesis

β-Site APP-cleaving enzyme (BACE1) cleaves the amyloid precursor protein (APP) at the β-secretase site to initiate the production of Aβ peptides. These accumulate to form toxic oligomers and the amyloid plaques associated with Alzheimer's disease (AD). An increase of BACE1 levels in the brain of AD patients has been mostly attributed to alterations of its intracellular trafficking. Golgi-associated adaptor proteins, GGA sort BACE1 for export to the endosomal compartment, which is the major cellular site of BACE1 activity. BACE1 undergoes recycling between endosome, trans-Golgi network (TGN), and the plasma membrane, from where it is endocytosed and either further recycled or retrieved to the endosome. Phosphorylation of Ser498 facilitates BACE1 recognition by GGA1 for retrieval to the endosome. Ubiquitination of BACE1 C-terminal Lys501 signals GGA3 for exporting BACE1 to the lysosome for degradation. In addition, the retromer mediates the retrograde transport of BACE1 from endosome to TGN. Decreased levels of GGA proteins and increased levels of retromer-associated sortilin have been associated with AD. Both would promote the co-localization of BACE1 and the amyloid precursor protein in the TGN and endosomes. Decreased levels of GGA3 also impair BACE1 degradation. Further understanding of BACE1 trafficking and its regulation may offer new therapeutic approaches for the treatment of Alzheimer's disease.

Mild cognitive impairment: pathology and mechanisms

Mild cognitive impairment (MCI) is rapidly becoming one of the most common clinical manifestations affecting the elderly. The pathologic and molecular substrate of people diagnosed with MCI is not well established. Since MCI is a human specific disorder and neither the clinical nor the neuropathological course appears to follow a direct linear path, it is imperative to characterize neuropathology changes in the brains of people who came to autopsy with a well-characterized clinical diagnosis of MCI. Herein, we discuss findings derived from clinical pathologic studies of autopsy cases who died with a clinical diagnosis of MCI. The heterogeneity of clinical MCI imparts significant challenges to any review of this subject. The pathologic substrate of MCI is equally complex and must take into account not only conventional plaque and tangle pathology but also a wide range of cellular, biochemical and molecular deficits, many of which relate to cognitive decline as well as compensatory responses to the progressive disease process. The multifaceted nature of the neuronal disconnection syndrome associated with MCI suggests that there is no single event which precipitates this prodromal stage of AD. In fact, it can be argued that neuronal degeneration initiated at different levels of the central nervous system drives cognitive decline as a final common pathway at this stage of the dementing disease process.

Downregulation of cholesterol biosynthesis genes in the forebrain of ERCC1-deficient mice

Several genetic defects of the nucleotide excision repair (NER) pathway, including deficiency of the Excision Repair Cross-Complementing rodent repair deficiency, complementation group 1 (ERCC1), result in pre-mature aging, impaired growth, microcephaly and delayed development of the cerebellum. These phenotypes are recapitulated in Ercc1-knockout mice, which survive for up to 4 weeks after birth. Therefore, we analyzed cerebellar and hippocampal transcriptomes of these animals at 3 weeks of age to identify the candidate mechanisms underlying central nervous system abnormalities caused by inherited defects in NER. In the cerebellum, the most prominent change was the upregulation of genes associated with gliosis. Although Purkinje cell degeneration has been reported in some mouse strains with NER impairment, the transcripts whose downregulation is associated with Purkinje cell loss were mostly unaffected by the knockout of Ercc1. In the hippocampus, there was extensive downregulation of genes related to cholesterol biosynthesis. Reduced expression of these genes was also present in the neocortex of adult mice with reduced expression of ERCC1. These changes were accompanied by reduced mRNA expression of the transcription factor Sterol Regulatory Element Binding Transcription Factor-2 (SREBF2) which is a master regulator of cholesterol biosynthesis. The downregulation of forebrain cholesterol biosynthesis genes is a newly identified consequence of ERCC1 deficiency. Reduced cholesterol biosynthesis may contribute to the neurodevelopmental disruption that is associated with ERCC1 defects and several other NER deficiencies including Cockayne syndrome. In addition, this reduction may negatively affect the function of mature synapses.

The endogenous regulator 24(S),25-epoxycholesterol inhibits cholesterol synthesis at DHCR24 (Seladin-1)

The oxysterol 24(S),25-epoxycholesterol (24,25EC) can affect cholesterol metabolism at multiple points. Previously, we proposed that 24,25EC has an especially significant role in fine-tuning cholesterol synthesis, since it parallels cholesterol production, and without it, acute cholesterol synthesis is exaggerated. 24,25EC is structurally similar to desmosterol, a substrate for the enzyme 3β-hydroxysterol ∆(24)-reductase (DHCR24, also called Seladin-1) which catalyzes a final step in cholesterol synthesis. In this study, we reveal a novel mode by which 24,25EC can regulate cholesterol synthesis, by interfering with DHCR24, resulting in the rapid accumulation of the substrate desmosterol, at the expense of cholesterol. This effect was independent of DHCR24 protein levels, and was observed in multiple mammalian cell-lines, including those of hepatic and neuronal origin. Conversely, overexpression of DHCR24 blunted the inhibition by 24,25EC. We also determined that the specificity of this effect was restricted to certain side-chain oxysterols, notably those oxygenated at C-25. Importantly, endogenous levels of 24,25EC, manipulated by genetic and pharmacological methods, were sufficient to reduce DHCR24 activity. Together, our work introduces a novel role for 24,25EC in cholesterol homeostasis, through its rapid inhibition of cholesterol synthesis at DHCR24. Also, our work provides new insights into a little studied area, the post-transcriptional regulation of DHCR24, an important enzyme in human health and disease.

Constitutive androstane receptor transactivates the hepatic expression of mouse Dhcr24 and human DHCR24 encoding a cholesterogenic enzyme 24-dehydrocholesterol reductase

Phenobarbital treatment has long been known to influence serum and hepatic cholesterol levels in rodents and humans. Constitutive androstane receptor (CAR), a member of the nuclear receptor superfamily, mediates various biological actions of phenobarbital. We have thus investigated whether CAR transactivates cholesterogenic genes in livers. Activation of CAR in mouse livers and cultured human hepatocytes increased mRNA levels of mouse Dhcr24 and human DHCR24, both of which encode 24-dehydrocholesterol reductase (DHCR24) catalyzing the last step of cholesterol biosynthesis. CAR transactivated the expression of these genes in reporter assays with cultured hepatoma cells. Furthermore, we have identified a DR4 (direct repeat separated by 4 nucleotides) motif in the human DHCR24 distal promoter as a binding site of CAR/retinoid X receptor α (RXRα) heterodimer. We have also demonstrated that the heterodimer of pregnane X receptor (PXR)/ RXRα binds to the DR4 motif and that human DHCR24 reporter gene is transactivated by the ligand-activated PXR. These results suggest a role of xenobiotic-responsive nuclear receptor CAR, and also possibly PXR, in cholesterol biosynthesis in the liver of mice and humans.

Inhibition of neuronal cholesterol biosynthesis with lovastatin leads to impaired synaptic vesicle release even in the presence of lipoproteins or geranylgeraniol

Cholesterol is highly enriched in the brain, and plays a key role in synapse formation and function. The brain does not derive cholesterol from the circulation; instead, the majority of cholesterol is made in glia and secreted in form of lipoproteins. Neurons can synthesize cholesterol, but the extent of neuronal cholesterol biosynthesis in the adult brain is unknown. Cholesterol biosynthesis inhibitors of the statin family are widely used to lower circulating cholesterol and cardiovascular risk. Lipophilic statins can cross the blood brain barrier and inhibit brain cholesterol biosynthesis with possible consequences for synaptic cholesterol homeostasis. We have investigated the effects of lovastatin on synapse maturation and synaptic vesicle release. Treatment of primary hippocampal neurons with low levels of lovastatin for one week reduced synapse density and impaired synaptic vesicle release. Neither lipoproteins nor geranylgeraniol fully counteracted the lovastatin-induced decrease of synaptic vesicle exocytosis, even when cholesterol depletion was prevented. In contrast, restoration of neuronal cholesterol synthesis with mevalonate prevented defects in vesicle exocytosis without fully normalizing neuronal cholesterol content. These results raise the possibility that chronic exposure of neurons to lipophilic statins may affect synaptic transmission, and indicate that hippocampal neurons need a certain level of endogenous cholesterol biosynthesis.

Augmentation of DHCR24 expression by hepatitis C virus infection facilitates viral replication in hepatocytes

BACKGROUND & AIMS

We characterized the role of 24-dehydrocholesterol reductase (DHCR24) in hepatitis C virus infection (HCV). DHCR24 is a cholesterol biosynthetic enzyme and cholesterol is a major component of lipid rafts, which is reported to play an important role in HCV replication. Therefore, we examined the potential of DHCR24 as a target for novel HCV therapeutic agents.

METHODS

We examined DHCR24 expression in human hepatocytes in both the livers of HCV-infected patients and those of chimeric mice with human hepatocytes. We targeted DHCR24 with siRNA and U18666A which is an inhibitor of both DHCR24 and cholesterol synthesis. We measured the level of HCV replication in these HCV replicon cell lines and HCV infected cells. U18666A was administrated into chimeric mice with humanized liver, and anti-viral effects were assessed.

RESULTS

Expression of DHCR24 was induced by HCV infection in human hepatocytes in vitro, and in human hepatocytes of chimeric mouse liver. Silencing of DHCR24 by siRNA decreased HCV replication in replicon cell lines and HCV JFH-1 strain-infected cells. Treatment with U18666A suppressed HCV replication in the replicon cell lines. Moreover, to evaluate the anti-viral effect of U18666A in vivo, we administrated U18666A with or without pegylated interferon to chimeric mice and observed an inhibitory effect of U18666A on HCV infection and a synergistic effect with interferon.

CONCLUSIONS

DHCR24 is an essential host factor which augmented its expression by HCV infection, and plays a significant role in HCV replication. DHCR24 may serve as a novel anti-HCV drug target.

Characterisation of a desmosterol reductase involved in phytosterol dealkylation in the silkworm, Bombyx mori

Most species of invertebrate animals cannot synthesise sterols de novo and many that feed on plants dealkylate phytosterols (mostly C₂₉ and C₂₈) yielding cholesterol (C₂₇). The final step of this dealkylation pathway involves desmosterol reductase (DHCR24)-catalysed reduction of desmosterol to cholesterol. We now report the molecular characterisation in the silkworm, Bombyx mori, of such a desmosterol reductase involved in production of cholesterol from phytosterol, rather than in de novo synthesis of cholesterol. Phylogenomic analysis of putative desmosterol reductases revealed the occurrence of various clades that allowed for the identification of a strong reductase candidate gene in Bombyx mori (BGIBMGA 005735). Following PCR-based cloning of the cDNA (1.6 kb) and its heterologous expression in Saccharomyces cerevisae, the recombinant protein catalysed reduction of desmosterol to cholesterol in an NADH- and FAD- dependent reaction.

Conceptual translation of the cDNA, that encodes a 58.9 kDa protein, and database searching, revealed that the enzyme belongs to an FAD-dependent oxidoreductase family. Western blotting revealed reductase protein expression exclusively in the microsomal subcellular fraction and primarily in the gut. The protein is peripherally associated with microsomal membranes. 2D-native gel and PAGE analysis revealed that the reductase is part of a large complex with molecular weight approximately 250kDa. The protein occurs in midgut microsomes at a fairly constant level throughout development in the last two instars, but is drastically reduced during the wandering stage in preparation for metamorphosis. Putative Broad Complex transcription factor-binding sites detectable upstream of the DHCR24 gene may play a role in this down-regulation.

Effect of hesperetin against oxidative stress via ER- and TrkA-mediated actions in PC12 cells

Hesperetin is known to activate estrogen receptors (ERs). Estrogen-mediated neuroprotection could be via both ER and tyrosine kinase receptor (Trk) signaling. This study tested whether hesperetin protected PC12 cells from hydrogen peroxide induced oxidative damage via ER- and/or TrkA-mediated actions. Hesperetin (0.1, 1, and 50 μM) inhibited cell viability decreases and reactive oxygen species, intracellular calcium level, and caspase-3 activity increases in H(2)O(2)-induced PC12 cells. Such actions were significantly (p < 0.05) suppressed by ICI 182,780 (an ER antagonist) or K252a (a TrkA antagonist) at low concentrations (0.1 or 1 μM) only. Hesperetin also stimulated the activation of Akt, ERK, and CREB as well as induced brain-derived neurotrophic factor, PPARγ coactivator 1α (PGC-1α), and seladin-1 (selective Alzheimer's disease indicator-1) via both ER and TrkA in the cells. This study demonstrates that the neuroprotective effects of hesperetin, at low concentrations, are attributed to its stimulation on receptor signaling. Moreover, ER and TrkA are known to be expressed in most Alzheimer's disease (AD) vulnerable brain regions. This study thus suggests that hesperetin might have potential for intervention in neurodegenerative disorders, particularly for AD.

Hepatitis C virus-induced oxidative stress and mitochondrial dysfunction: a focus on recent advances in proteomics

The natural history of chronic hepatitis C virus (HCV) infection presents two major aspects. On one side, the illness is by itself benign, whereas, on the other side, epidemiological evidence clearly identifies chronic HCV infection as the principal cause of cirrhosis, hepatocellular carcinoma, and extrahepatic diseases, such as autoimmune type II mixed cryoglobulinemia and some B cell non-Hodgkin's lymphomas. The mechanisms responsible for the progression of liver disease to severe liver injury are still poorly understood. Nonetheless, considerable biological data and studies from animal models suggest that oxidative stress contributes to steatohepatitis and that the increased generation of reactive oxygen and nitrogen species, together with the decreased antioxidant defense, promotes the development of hepatic and extrahepatic complications of HCV infection. The principal mechanisms causing oxidative stress in HCV-positive subjects have only been partially elucidated and have identified chronic inflammation, iron overload, ER stress, and a direct activity of HCV proteins in increasing mitochondrial ROS production, as key events. This review summarizes current knowledge regarding mechanisms of HCV-induced oxidative stress with its long-term effects in the context of HCV-related diseases, and includes a discussion of recent contributions from proteomics studies.

Gonadotropin-releasing hormone modulates cholesterol synthesis and steroidogenesis in SH-SY5Y cells

Neurosteroids are involved in Central Nervous System development, brain functionality and neuroprotection but little is known about regulators of their biosynthesis. Recently gonadotropins, Gonadotropin-releasing Hormone (GnRH) and their receptors have been localized in different brain regions, such as hippocampus and cortex. Using human neuronal-like cells we found that GnRH up-regulates the expression of key genes of cholesterol and steroid synthesis when used in a narrow range around 1.0 nM. The expression of Hydroxysterol D24-reductase (seladin-1/DHCR24), that catalyzes the last step of cholesterol biosynthesis, is increased by 50% after 90 min of incubation with GnRH. StAR protein and P450 side chain cleavage (P450scc) are up-regulated by 3.3 times after 90 min and by 3.5 times after 3 h, respectively. GnRH action is mediated by LH and 1.0 nM GnRH enhances the expression of LHβ as well. A two fold increase of cell cholesterol is induced after 90 min of GnRH incubation and 17β-estradiol (E2) production is increased after 24, 48 and 72 h. These data indicate for the first time that GnRH regulates both cholesterol and steroid biosynthesis in human neuronal-like cells and suggest a new physiological role for GnRH in the brain.

Membrane cholesterol as a mediator of the neuroprotective effects of estrogens

Alzheimer's disease (AD), the most common neurodegenerative disease associated with aging, is still an incurable condition. Although in vitro evidence strongly indicates that estrogens exert neurotrophic and neuroprotective effects, the role of this class of hormones in the treatment of AD is still a debated issue. In 2000 a new gene, named seladin-1 (for SELective Alzheimer's Disease INdicator-1), was identified and found to be down regulated in vulnerable brain regions in AD. Seladin-1 was considered a novel neuroprotective factor, because of its anti-apoptotic activity. Subsequently, it was demonstrated that seladin-1 has also enzymatic activity [3-β-hydroxysterol delta-24-reductase, (DHCR24)], which catalyzes the synthesis of cholesterol from desmosterol. The amount of membrane cholesterol may play an important role both in protecting neuronal cells against toxic insults and in inhibiting the production of β-amyloid. We demonstrated that seladin-1 overexpression increases the amount of membrane cholesterol and induces resistance against β-amyloid aggregates in neuroblastoma cells, whereas a specific inhibitor of DHCR24 increased cell vulnerability. We also hypothesized that seladin-1 might be a mediator of the neuroprotective effects of estrogens. We first demonstrated that, in human fetal neuroepithelial cells (FNC), 17β-estradiol, raloxifene, and tamoxifen exert protective effects against β-amyloid toxicity and oxidative stress. In addition, these molecules significantly increased the expression of seladin-1 and the amount of cell cholesterol. Then, we showed that, upon seladin-1 silencing, the protective effects of estrogens were abolished, thus indicating this factor as a fundamental mediator of estrogen-mediated neuroprotection, at least in FNC cells. Furthermore, we detected the presence of functionally active half-palindromic estrogen responsive elements upstream the coding region of the seladin-1 gene. Overall, our results indicate that seladin-1 may be viewed as a multi-faceted protein, which conjugates both the neuroprotective properties of estrogens and the important functions of cholesterol in maintaining brain homeostasis. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

Identification and analysis of the promoter region of the human DHCR24 gene: involvement of DNA methylation and histone acetylation

Mutations in the DHCR24 gene, which encodes the cholesterol biosynthesis enzyme 3ß-hydroxysterol-∆24 reductase, result in an autosomal recessive disease called desmosterolosis. Further, reduced expression of DHCR24 is found in the temporal cortex of Alzheimer's disease patients. This suggests that variability in the regulatory regions of DHCR24 may contribute to the development of this neurodegenerative disease. In this work, we functionally characterised the proximal fragment of the human DHCR24 gene, for the first time. We show that the transcription of DHCR24 is initiated from a single CpG-rich promoter that is regulated by DNA methylation in some cell types. An activator sequence was also uncovered in the -1203/-665 bp region by reporter gene assays. Furthermore, sodium butyrate (a well-known HDAC inhibitor) increased DHCR24 expression in SH-SY5Y cells by recruiting acetylated core histones H3 and H4 to the enhancer region, as demonstrated by transient transfection and chromatin immunoprecipitation assays. Understanding the regulation of the DHCR24 gene may lead to alternative therapeutic strategies in at least some Alzheimer's patients.

Inhibition of DHCR24/seladin-1 impairs cellular homeostasis in prostate cancer

BACKGROUND

Seladin-1 belongs to a subgroup of androgen-dependent genes associated with anti-proliferative, pro-differentiation, and pro-apoptotic functions and plays a protective role against oncogenic stress. The present study aims to investigate the localization and expression of Seladin-1 protein in normal and tumoral human prostatic tissues as well as to explore its role in proliferation and steroid secretion in androgen-dependent (LnCaP) and androgen-independent (DU145) cell lines and in human prostate primary cell culture.

METHODS

Seladin-1 protein localization and expression were assessed on whole tissue sections by tissue array/immunohistochemistry and following immunofluorescence and Western blotting. Proliferation (Ki67 fluorescence labeling and cell counts) and steroid secretion (ELISA) were assessed in cell lines and primary epithelial cell cultures.

RESULTS

In human prostatic tissue and cells, Seladin-1 was mostly localized within epithelial and rarely within stromal cells and primarily present in secretory luminal cells of normal and tumoral prostate cells. Its expression was increased in low-risk prostate cancer but reduced in advanced prostate cancers when compared to normal tissues. Seladin-1 was highly expressed in LnCaP, whereas its expression level was lower in DU145 cells. Seladin-1 inhibition by treatment with its specific inhibitor, U18666A (75 nM), increased proliferation in LnCaP and primary cell culture, as well as testosterone and dihydrotestosterone levels in both LnCaP and DU145 cell lines.

CONCLUSIONS

Seladin-1 involvement in proliferation and secretion suggests that its downregulation may be a major mechanism causing prostate cancer evolution. Seladin-1 may thus potentially decrease cell growth and steroid dependency in low-grade prostate cancer.

Seladin-1 is a novel lipopolysaccharide (LPS)-responsive gene and inhibits the tumour necrosis factor-alpha production and osteoclast formation in response to LPS

Selective Alzheimer disease indicator-1 (seladin-1) is a broadly expressed oxidoreductase and is related to Alzheimer disease, cholesterol metabolism and carcinogenesis. The effect of lipopolysaccharide (LPS) on the expression of seladin-1 was examined using RAW 264.7 macrophage-like cells and murine peritoneal macrophages. Lipopolysaccharide induced the expression of seladin-1 protein and messenger RNA in those macrophages. The seladin-1 expression was also augmented by a series of Toll-like receptor ligands. The LPS augmented the expression of seladin-1 via reactive oxygen species generation and p38 activation. Seladin-1 inhibited LPS-induced activation of p38 but not nuclear factor-kappaB and inhibited the production of tumour necrosis factor-alpha in response to LPS. Moreover, seladin-1 inhibited LPS-induced osteoclast formation and enhanced LPS-induced alkaline phosphatase activity. Therefore, it was suggested that seladin-1 might be an LPS-responsible gene product and regulate the LPS-induced inflammatory response negatively.

The liver X receptor: control of cellular lipid homeostasis and beyond Implications for drug design

Liver X receptor (LXR) α and β are nuclear receptors that control cellular metabolism. LXRs modulate the expression of genes involved in cholesterol and lipid metabolism in response to changes in cellular cholesterol status. Because of their involvement in cholesterol homeostasis, LXRs have emerged as promising drug targets for anti-atherosclerotic therapies. In rodents, synthetic LXR agonists promote cellular cholesterol efflux, transport and excretion. As a result, the progression of atherosclerosis is halted. However, pharmacological LXR activation also induces hepatic steatosis and promotes the secretion of atherogenic triacylglycerol-rich VLDL particles by the liver, complicating the clinical application of LXR agonists. The more recently emerged roles of LXRs in fat tissue, pituitary and brain may have implications for treatment of obesity and Alzheimer disease. In addition to the improvements in atherosclerosis, LXR activation exerts beneficial effects on glucose control in mouse models of type 2 diabetes. Future therapeutic strategies aiming to exert beneficial effects on cholesterol and glucose homeostasis, while circumventing the undesired effects on hepatic lipid metabolism, should target specific LXR-mediated processes. Therefore, tissue and/or isotype-specific effects of LXR action need to be established. The consequences of combinatorial drug approaches and the identification of the co-regulatory networks involved in the LXR-mediated control of particular genes may contribute to development of novel LXR agonists. Finally, pathway analyses of LXR actions provide tools to evaluate and optimize the effectiveness of novel therapeutic strategies to prevent and/or treat metabolic diseases.

Seladin-1 and testicular germ cell tumours: new insights into cisplatin responsiveness

The molecular basis for the exquisite sensitivity of testicular germ cell tumours of adolescents and adults (TGCTs), ie seminomas and non-seminomatous germ cell tumours, to chemo/radiotherapy has not been fully clarified so far. It has been suggested that it may be dependent on factors involved in the regulation of apoptosis. Seladin-1 is a multi-functional protein involved in various biological processes, including apoptosis. The aim of our study was to assess the expression of seladin-1 in different histological types of TGCTs, known to have varying treatment sensitivity, in order to establish whether this protein may influence cisplatin responsiveness in vitro. Seladin-1 expression levels, both at the mRNA and at the protein level, were higher in the adjacent normal parenchyma than in the pathological counterparts. In tumoural tissues, the level of expression differed among TGCT histological types. The highest tumour-expression level was found in teratoma, whereas the lowest was detected in seminoma, corresponding to the different chemo/and radiosensitivities of these tumour types. In common with other cancers, in TGCT-derived cell lines seladin-1 showed anti-apoptotic properties through inhibition of caspase-3 activation. We confirmed our results using a non-seminomatous cell line model (NT2) before and after differentiation with retinoic acid. Significantly higher seladin-1 expression was observed in the differentiated derivatives (teratoma) and an inverse relationship was found between seladin-1 expression and the amount of cleaved caspase-3. Seladin-1 silencing or overexpression in this cell line supports involvement of seladin-1 in cisplatin responsiveness. Seladin-1 silencing was associated with greater cisplatin responsiveness demonstrated by decreased cell viability and increased expression of apoptotic markers. In contrast, overexpression of seladin-1 was associated with a higher survival rate and a clear anti-apoptotic effect. In conclusion, we have demonstrated for the first time an important role for seladin-1 in the biology of TGCTs and provided new insights into cisplatin responsiveness of these tumours.

Interactions of estradiol and insulin-like growth factor-I signalling in the nervous system: new advances

Estradiol and insulin-like growth factor-I (IGF-I) interact in the brain to regulate a variety of developmental and neuroplastic events. Some of these interactions are involved in the control of hormonal homeostasis and reproduction. However, the interactions may also potentially impact on affection and cognition by the regulation of adult neurogenesis in the hippocampus and by promoting neuroprotection under neurodegenerative conditions. Recent studies suggest that the interaction of estradiol and IGF-I is also relevant for the control of cholesterol homeostasis in neural cells. The molecular mechanisms involved in the interaction of estradiol and IGF-I include the cross-regulation of the expression of estrogen and IGF-I receptors, the regulation of estrogen receptor-mediated transcription by IGF-I and the regulation of IGF-I receptor signalling by estradiol. Current investigations are evidencing the role exerted by key signalling molecules, such as glycogen synthase kinase 3 and beta-catenin, in the cross-talk of estrogen receptors and IGF-I receptors in neural cells.

Cholesterol in Alzheimer's disease and other amyloidogenic disorders

The complex association of cholesterol metabolism and Alzheimer's disease is presented in depth, including the possible benefits to be gained from cholesterol-lowering statin therapy. Then follows a survey of the role of neuronal membrane cholesterol in Abeta pore formation and Abeta fibrillogenesis, together with the link with membrane raft domains and gangliosides. The contribution of structural studies to Abeta fibrillogenesis, using TEM and AFM, is given some emphasis. The role of apolipoprotein E and its isoforms, in particular ApoE4, in cholesterol and Abeta binding is presented, in relation to genetic risk factors for Alzheimer's disease. Increasing evidence suggests that cholesterol oxidation products are of importance in generation of Alzheimer's disease, possibly induced by Abeta-produced hydrogen peroxide. The body of evidence for a link between cholesterol in atherosclerosis and Alzheimer's disease is increasing, along with an associated inflammatory response. The possible role of cholesterol in tau fibrillization, tauopathies and in some other non-Abeta amyloidogenic disorders is surveyed.

Hepatitis C virus impairs p53 via persistent overexpression of 3beta-hydroxysterol Delta24-reductase

Persistent infection with hepatitis C virus (HCV) induces tumorigenicity in hepatocytes. To gain insight into the mechanisms underlying this process, we generated monoclonal antibodies on a genome-wide scale against an HCV-expressing human hepatoblastoma-derived cell line, RzM6-LC, showing augmented tumorigenicity. We identified 3beta-hydroxysterol Delta24-reductase (DHCR24) from this screen and showed that its expression reflected tumorigenicity. HCV induced the DHCR24 overexpression in human hepatocytes. Ectopic or HCV-induced DHCR24 overexpression resulted in resistance to oxidative stress-induced apoptosis and suppressed p53 activity. DHCR24 overexpression in these cells paralleled the increased interaction between p53 and MDM2 (also known as HDM2), a p53-specific E3 ubiquitin ligase, in the cytoplasm. Persistent DHCR24 overexpression did not alter the phosphorylation status of p53 but resulted in decreased acetylation of p53 at lysine residues 373 and 382 in the nucleus after treatment with hydrogen peroxide. Taken together, these results suggest that DHCR24 is elevated in response to HCV infection and inhibits the p53 stress response by stimulating the accumulation of the MDM2-p53 complex in the cytoplasm and by inhibiting the acetylation of p53 in the nucleus.

Polybrominated diphenyl ethers cause oxidative stress in human umbilical vein endothelial cells

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants to prevent combustion in consumer products, such as electronics, construction materials, and textiles and, therefore, have become important commercial substances. PBDEs were also detected in maternal blood, breast milk, umbilical cord blood, and cord tissue, thereby indicating that fetuses were also exposed to PBDEs. The purpose of this study is to identify the effect of PBDEs on human umbilical vein endothelial cells (HUVECs). Cultured HUVECs were exposed to a commercial mixture of penta-BDE (DE71), octa-BDE (DE79), and deca-BDE (DE83). Each gene expression that was altered in DNA microarray was confirmed by real-time reverse transcription-polymerase chain reaction and Western blotting analysis. The results indicated that gene expressions concerning antioxidant system, i.e., thioredoxin family, 24-dehydrocholesterol reductase (DHCR24), and tumor suppressor protein p53, were altered by PBDEs exposure in HUVECs. Moreover, it was demonstrated that thioredoxin-interacting protein (TXNIP) was a target gene in exposure to DE71 and DE79 in HUVECs, by drastically decreasing time-dependent TXNIP expression in HUVECs.

Down-regulation of seladin-1 increases BACE1 levels and activity through enhanced GGA3 depletion during apoptosis

Seladin-1 is a neuroprotective protein selectively down-regulated in brain regions affected in Alzheimer disease (AD). Seladin-1 protects cells against beta-amyloid (Abeta) peptide 42- and oxidative stress-induced apoptosis activated by caspase-3, a key mediator of apoptosis. Here, we have employed RNA interference to assess the molecular effects of seladin-1 down-regulation on the beta-secretase (BACE1) function and beta-amyloid precursor protein (APP) processing in SH-SY5Y human neuroblastoma cells in both normal and apoptotic conditions. Our results show that approximately 60% reduction in seladin-1 protein levels, resembling the decrease observed in AD brain, did not significantly affect APP processing or Abeta secretion in normal growth conditions. However, under apoptosis, seladin-1 small interfering RNA (siRNA)-transfected cells showed increased caspase-3 activity on average by 2-fold when compared with control siRNA-transfected cells. Increased caspase-3 activity coincided with a significant depletion of the BACE1-sorting protein, GGA3 (Golgi-localized gamma-ear-containing ADP-ribosylation factor-binding protein), and subsequently augmented BACE1 protein levels and activity. Augmented BACE1 activity in turn correlated with the enhanced beta-amyloidogenic processing of APP and ultimately increased Abeta production. These adverse changes associated with decreased cell viability in seladin-1 siRNA-transfected cells under apoptosis. No changes in GGA3 or BACE1 levels were found after seladin-1 knockdown in normal growth conditions. Collectively, our results suggest that under stress conditions, reduced seladin-1 expression results in enhanced GGA3 depletion, which further leads to augmented post-translational stabilization of BACE1 and increased beta-amyloidogenic processing of APP. These mechanistic findings related to seladin-1 down-regulation are important in the context of AD as the oxidative stress-induced apoptosis plays a key role in the disease pathogenesis.

24-dehydrocholesterol reductase/seladin-1: a key protein differentially involved in adrenocorticotropin effects observed in human and rat adrenal cortex

DHCR24 (24-dehydrocholesterol reductase), or seladin-1, is one of the most expressed genes in the adrenal gland. Because the rat and human adult adrenal cortex differ in their respective functional properties, the aim of the present study was to verify whether seladin-1 may be differentially involved in basal and ACTH-stimulated steroidogenesis and oxidative stress management. Seladin-1 expression was predominantly observed in both human and rat zona fasciculata, with a predominant cytoplasmic localization in human cells and a nucleo-cytoplasmic distribution in rat cells. In human fasciculata cells, localization of the protein was primarily associated with the endoplasmic reticulum. Although its expression was increased by ACTH, its intracellular localization was not altered by ACTH treatment (10 nm) or by the seladin-1 inhibitor U18666A (75 nm). Preincubation with U18666A did not modify the ACTH-induced increase in cortisol secretion but abolished the ACTH-induced increase in dehydroepiandrosterone secretion. In rat fasciculata cells, ACTH induced a massive redistribution of seladin-1 from the cytoplasm (cis-Golgi apparatus) to the nucleus, which was inhibited by preincubation with U18666A. Preincubation with U18666A also decreased ACTH-induced seladin-1 and 11beta-hydroxylase protein expression as well as corticosterone production, increased ACTH-induced ROS production but decreased ACTH-induced expression of the detoxifying protein aldo-ketoreductase 1b7. Thus, protection against acutely elevated ACTH-induced oxidative stress in rat fasciculata cells is correlated with nuclear relocalization of seladin-1 and its effects on cellular detoxifying machinery. Altogether, these results indicate that seladin-1 expression and intracellular localization are correlated with both the intensity and nature of ACTH-induced steroidogenesis and resultant oxidative stress.

New insights on the neuroprotective role of sterols and sex steroids: the seladin-1/DHCR24 paradigm

In 2000 a new gene, i.e. seladin-1 (for selective Alzheimer's disease indicator-1) was identified and found to be down regulated in vulnerable brain regions in Alzheimer's disease. Seladin-1 was considered a novel neuroprotective factor, because of its anti-apoptotic properties. Subsequently, it has been demonstrated that seladin-1 corresponds to the gene that encodes 3-beta-hydroxysterol delta-24-reductase (DHCR24), that catalyzes the synthesis of cholesterol from desmosterol. There is evidence that cholesterol plays a fundamental role in maintaining brain homeostasis. Because of its enzymatic activity, seladin-1/DHCR24 has been considered the human homolog of the plant protein DIMINUTO/DWARF1, that is involved in the synthesis of sterol plant hormones. We have recently demonstrated that seladin-1/DHCR24 is a fundamental mediator of the protective effects of estrogens in the brain. This review describes how this protein interacts with cholesterol and estrogens, thus generating a neuroprotective network, that might open new possibilities in the prevention/treatment of neurodegenerative diseases.