Seladin-1 transcription is linked to neuronal degeneration in Alzheimer's disease

Sex-associated microRNAs potentially implicated in sporadic Alzheimer's disease (sAD)

BACKGROUND

The onset and pathology of sporadic Alzheimer's disease (sAD) seem to be affected by both sex and genetic mechanisms. Evidence supports that the high prevalence of sAD in women, worldwide, may be attributed to an interplay among aging, sex, and lifestyle, influenced by genetics, metabolic changes, and hormones. Interestingly, epigenetic mechanisms such as microRNAs (miRNAs), known as master regulators of gene expression, may contribute to this observed sexual dimorphism in sAD.

OBJECTIVES

To investigate the potential impact of sex-associated miRNAs on processes manifesting sAD pathology, as described by the Tau-driven Adverse Outcome Pathway (AOP) leading to memory loss.

METHODS

Using publicly available human miRNA datasets, sex-biased miRNAs, defined as differentially expressed by sex in tissues possibly affected by sAD pathology, were collected. In addition, sex hormone-related miRNAs were also retrieved from the literature. The compiled sex-biased and sex hormone-related miRNAs were further plugged into the dysregulated processes of the Tau-driven AOP for memory loss.

RESULTS

Several miRNAs, previously identified as sex-associated, were implicated in dysregulated processes associated with the manifestation of sAD pathology. Importantly, the described pathology processes were not confined to a particular sex. A mechanistic-based approach utilizing miRNAs was adopted in order to elucidate the link between sex and biological processes potentially involved in the development of memory loss.

CONCLUSIONS

The identification of sex-associated miRNAs involved in the early processes manifesting memory loss may shed light to the complex molecular mechanisms underlying sAD pathogenesis in a sex-specific manner.

High fat diet induces brain injury and neuronal apoptosis via down-regulating 3-β hydroxycholesterol 24 reductase (DHCR24)

Hyperlipidemia (HLP) is one of the risk factors for memory impairment and cognitive impairment. However, its pathological molecular mechanism remained unclear. 3β-hydroxysterol Δ24- reductase (DHCR24) is a key enzyme in cholesterol synthesis and has been reported to decrease in the affected areas in the brain of neurodegenerative disorders. In this study, hyperlipidemic mouse model was established to study the effect of high blood lipid on brain. The data obtained from HPLC analysis demonstrated that the cholesterol level in the brain of mice with hyperlipidemia was significantly elevated compared to the control group. While the pathological damages were observed in both cerebral cortex and hippocampus in the brain of hyperlipidemic mice. Furthermore, the protein level of DHCR24 was downregulated accompanied by elevated ubiquitination level in the hyperlipidemic mice brain. The mouse neuroblastoma cells N2a were exposed to the excess cholesterol loading, the cells underwent apoptosis and the mRNA and protein of DHCR24 in cholesterol-loaded N2a cells were significantly reduced. In addition, the expression level of endoplasmic reticulum stress marker protein (Bip and Chop) was markedly increased in response to the cholesterol loading. More importantly, overexpression of DHCR24 in N2a reversed neuronal apoptosis induced by the cholesterol loading. Conclusively, these findings suggested that hyperlipidemia could cause brain tissue injuries via down-regulating DHCR24, and overexpression of DHCR24 may alleviate hyperlipidemia-induced neuronal cells damage by reversing the endoplasmic reticulum stress-mediated apoptosis.

DHCR24 reverses Alzheimer's disease-related pathology and cognitive impairment via increasing hippocampal cholesterol levels in 5xFAD mice

Accumulating evidences reveal that cellular cholesterol deficiency could trigger the onset of Alzheimer's disease (AD). As a key regulator, 24-dehydrocholesterol reductase (DHCR24) controls cellular cholesterol homeostasis, which was found to be downregulated in AD vulnerable regions and involved in AD-related pathological activities. However, DHCR24 as a potential therapeutic target for AD remains to be identified. In present study, we demonstrated the role of DHCR24 in AD by employing delivery of adeno-associated virus carrying DHCR24 gene into the hippocampus of 5xFAD mice. Here, we found that 5xFAD mice had lower levels of cholesterol and DHCR24 expression, and the cholesterol loss was alleviated by DHCR24 overexpression. Surprisingly, the cognitive impairment of 5xFAD mice was significantly reversed after DHCR24-based gene therapy. Moreover, we revealed that DHCR24 knock-in successfully prevented or reversed AD-related pathology in 5xFAD mice, including amyloid-β deposition, synaptic injuries, autophagy, reactive astrocytosis, microglial phagocytosis and apoptosis. In conclusion, our results firstly demonstrated that the potential value of DHCR24-mediated regulation of cellular cholesterol level as a promising treatment for AD.

DHCR24, a Key Enzyme of Cholesterol Synthesis, Serves as a Marker Gene of the Mouse Adrenal Gland Inner Cortex

Steroid hormones are synthesized through enzymatic reactions using cholesterol as the substrate. In steroidogenic cells, the required cholesterol for steroidogenesis can be obtained from blood circulation or synthesized de novo from acetate. One of the key enzymes that control cholesterol synthesis is 24-dehydrocholesterol reductase (encoded by DHCR24). In humans and rats, DHCR24 is highly expressed in the adrenal gland, especially in the zona fasciculata. We recently reported that DHCR24 was expressed in the mouse adrenal gland's inner cortex and also found that thyroid hormone treatment significantly upregulated the expression of Dhcr24 in the mouse adrenal gland. In the present study, we showed the cellular expression of DHCR24 in mouse adrenal glands in early postnatal stages. We found that the expression pattern of DHCR24 was similar to the X-zone marker gene 20αHSD in most developmental stages. This finding indicates that most steroidogenic adrenocortical cells in the mouse adrenal gland do not synthesize cholesterol locally. Unlike the 20αHSD-positive X-zone regresses during pregnancy, some DHCR24-positive cells remain present in parous females. Conditional knockout mice showed that the removal of Dhcr24 in steroidogenic cells did not affect the overall development of the adrenal gland or the secretion of corticosterone under acute stress. Whether DHCR24 plays a role in conditions where a continuous high amount of corticosterone production is needed requires further investigation.

Peroxisomal defects in microglial cells induce a disease-associated microglial signature

Microglial cells ensure essential roles in brain homeostasis. In pathological condition, microglia adopt a common signature, called disease-associated microglial (DAM) signature, characterized by the loss of homeostatic genes and the induction of disease-associated genes. In X-linked adrenoleukodystrophy (X-ALD), the most common peroxisomal disease, microglial defect has been shown to precede myelin degradation and may actively contribute to the neurodegenerative process. We previously established BV-2 microglial cell models bearing mutations in peroxisomal genes that recapitulate some of the hallmarks of the peroxisomal β-oxidation defects such as very long-chain fatty acid (VLCFA) accumulation. In these cell lines, we used RNA-sequencing and identified large-scale reprogramming for genes involved in lipid metabolism, immune response, cell signaling, lysosome and autophagy, as well as a DAM-like signature. We highlighted cholesterol accumulation in plasma membranes and observed autophagy patterns in the cell mutants. We confirmed the upregulation or downregulation at the protein level for a few selected genes that mostly corroborated our observations and clearly demonstrated increased expression and secretion of DAM proteins in the BV-2 mutant cells. In conclusion, the peroxisomal defects in microglial cells not only impact on VLCFA metabolism but also force microglial cells to adopt a pathological phenotype likely representing a key contributor to the pathogenesis of peroxisomal disorders.

DHCR24 Knockdown Induces Tau Hyperphosphorylation at Thr181, Ser199, Ser262, and Ser396 Sites via Activation of the Lipid Raft-Dependent Ras/MEK/ERK Signaling Pathway in C8D1A Astrocytes

The synthetase 3β-hydroxysterol-Δ24 reductase (DHCR24) is a key regulator involved in cholesterol synthesis and homeostasis. A growing body of evidence indicates that DHCR24 is downregulated in the brain of various models of Alzheimer’s disease (AD), such as astrocytes isolated from AD mice. For the past decades, astrocytic tau pathology has been found in AD patients, while the origin of phosphorylated tau in astrocytes remains unknown. A previous study suggests that downregulation of DHCR24 is associated with neuronal tau hyperphosphorylation. Herein, the present study is to explore whether DHCR24 deficiency can also affect tau phosphorylation in astrocytes. Here, we showed that DHCR24 knockdown could induce tau hyperphosphorylation at Thr181, Ser199, Thr231, Ser262, and Ser396 sites in C8D1A astrocytes. Meanwhile, we found that DHCR24-silencing cells had reduced the level of free cholesterol in the plasma membrane and intracellular organelles, as well as cholesterol esters. Furthermore, reduced cellular cholesterol level caused a decreased level of the caveolae-associated protein, cavin1, which disrupted lipid rafts/caveolae and activated rafts/caveolae-dependent Ras/MEK/ERK signaling pathway. In contrast, overexpression of DHCR24 prevented the overactivation of Ras/MEK/ERK signaling by increasing cellular cholesterol content, therefore decreasing tau hyperphosphorylation in C8D1A astrocytes. Herein, we firstly found that DHCR24 knockdown can lead to tau hyperphosphorylation in the astrocyte itself by activating lipid raft-dependent Ras/MEK/ERK signaling, which might contribute to the pathogenesis of AD and other degenerative tauopathies.

Clavulanic Acid: A Novel Potential Agent in Prevention and Treatment of Scopolamine-Induced Alzheimer's Disease

Background and Aim: Alzheimer's disease (AD) is the most common form of dementia in the elderly. It is characterized as a multifaced disorder with a greater genetic contribution. The contribution of many genes such as BDNF, Sirtuin 6, and Seladin 1 has been reported in the pathogenesis of AD. Current therapies include acetylcholinesterase inhibitors and N-methyl-d-aspartate receptor antagonists, which are only temporarily beneficial. Therefore, it seems that more studies should be conducted to determine the exact mechanisms of drugs to deal with the diseases' multifactorial features that we face. Methods: In this study, 42 adult rats were randomly divided into 7 groups and received drugs intraperitoneally and orally according to the protocol as follows: scopolamine group, clavulanic acid group, memantine group, scopolamine + memantine group, clavulanic acid pre- and post-treatment, and normal saline group. The Morris water maze method was performed to evaluate the spatial memory of animals, and the terminal deoxynucleotidyl transferase dUTP nick end labeling assay and real-time polymerase chain reaction were performed to study neuronal cell apoptosis and gene expression, respectively. Results: Significant differences were observed in the spatial memory of rats that received clavulanic acid prophylactically compared to the Alzheimer's model on the day of the test. Moreover, the results obtained during the training showed that both memantine and clavulanic acid improved spatial memory by increasing the time of rats present in the platform position and by reducing the swimming time in the scopolamine-induced Alzheimer's group. Besides, rats that received clavulanic acid and memantine had a greater percentage of healthy cells in comparison with the scopolamine-induced Alzheimer's group; however, the results were more significant for clavulanic acid. Furthermore, the expressions of BDNF, Seladin 1, and Sirtuin 6 as neuroprotective target genes were modified after clavulanic acid and memantine administrations; similarly, the results obtained from clavulanic acid were more significant. Conclusion: The results show that the administration of clavulanic acid before and after the use of scopolamine can reduce the percentage of apoptotic cells in the hippocampus and also improve the parameters related to learning and spatial memory; however, its effect in the prophylactic state was stronger. The results obtained from memantine revealed that it has neuroprotective potency against AD; however, clavulanic acid had a greater effect. Also, with increased expression of the neuroprotective genes, clavulanic acid could be considered as an option in the upcoming preclinical and clinical research about Alzheimer's disease.

The role of DHCR24 in the pathogenesis of AD: re-cognition of the relationship between cholesterol and AD pathogenesis

Previous studies show that 3β-hydroxysterol-Δ24 reductase (DHCR24) has a remarked decline in the brain of AD patients. In brain cholesterol synthetic metabolism, DHCR24 is known as the heavily key synthetase in cholesterol synthesis. Moreover, mutations of DHCR24 gene result in inhibition of the enzymatic activity of DHCR24, causing brain cholesterol deficiency and desmosterol accumulation. Furthermore, in vitro studies also demonstrated that DHCR24 knockdown lead to the inhibition of cholesterol synthesis, and the decrease of plasma membrane cholesterol and intracellular cholesterol level. Obviously, DHCR24 could play a crucial role in maintaining cholesterol homeostasis via the control of cholesterol synthesis. Over the past two decades, accumulating data suggests that DHCR24 activity is downregulated by major risk factors for AD, suggesting a potential link between DHCR24 downregulation and AD pathogenesis. Thus, the brain cholesterol loss seems to be induced by the major risk factors for AD, suggesting a possible causative link between brain cholesterol loss and AD. According to previous data and our study, we further found that the reduced cholesterol level in plasma membrane and intracellular compartments by the deficiency of DHCR24 activity obviously was involved in β-amyloid generation, tau hyperphosphorylation, apoptosis. Importantly, increasing evidences reveal that the brain cholesterol loss and lipid raft disorganization are obviously linked to neuropathological impairments which are associated with AD pathogenesis. Therefore, based on previous data and research on DHCR24, we suppose that the brain cholesterol deficiency/loss might be involved in the pathogenesis of AD.

Estrogenic hormones receptors in Alzheimer's disease

Estrogens are hormones that play a critical role during development and growth for the adequate functioning of the reproductive system of women, as well as for maintaining bones, metabolism, and cognition. During menopause, the levels of estrogens are decreased, altering their signaling mediated by their intracellular receptors such as estrogen receptor alpha and beta (ERα and ERβ), and G protein-coupled estrogen receptor (GPER). In the brain, the reduction of molecular pathways mediated by estrogenic receptors seems to favor the progression of Alzheimer's disease (AD) in postmenopausal women. In this review, we investigate the participation of estrogen receptors in AD in women during aging.

Exploring ER stress response in cellular aging and neuroinflammation in Alzheimer's disease

One evident hallmark of Alzheimer's disease (AD) is the irregular accumulation of proteins due to changes in proteostasis involving endoplasmic reticulum (ER) stress. To alleviate ER stress and reinstate proteostasis, cells undergo an integrated signaling cascade called the unfolded protein response (UPR) that reduces the number of misfolded proteins and inhibits abnormal protein accumulation. Aging is associated with changes in the expression of ER chaperones and folding enzymes, leading to the impairment of proteostasis, and accumulation of misfolded proteins. The disrupted initiation of UPR prevents the elimination of unfolded proteins, leading to ER stress. In AD, the accumulation of misfolded proteins caused by sustained cellular stress leads to neurodegeneration and neuronal death. Current research has revealed that ER stress can trigger an inflammatory response through diverse transducers of UPR. Although the involvement of a neuroinflammatory component in AD has been documented for decades, whether it is a contributing factor or part of the neurodegenerative events is so far unknown. Besides, a feedback loop occurs between neuroinflammation and ER stress, which is strongly associated with neurodegenerative processes in AD. In this review, we focus on the current research on ER stress and UPR in cellular aging and neuroinflammatory processes, leading to memory impairment and synapse dysfunction in AD.

DHCR24 Knock-Down Induced Tau Hyperphosphorylation at Thr181, Ser199, Thr231, Ser262, Ser396 Epitopes and Inhibition of Autophagy by Overactivation of GSK3β/mTOR Signaling

Accumulating evidences supported that knock-down of DHCR24 is linked to the pathological risk factors of AD, suggesting a potential role of DHCR24 in AD pathogenesis. However, the molecular mechanism link between DHCR24 and tauopathy remains unknown. Here, in order to elucidate the relationship between DHCR24 and tauopathy, we will focus on the effect of DHCR24 on the tau hyperphosphorylation at some toxic sites. In present study, we found that DHCR24 knock-down significantly lead to the hyperphosphorylation of tau sites at Thr181, Ser199, Thr231, Ser262, Ser396. Moreover, DHCR24 knock-down also increase the accumulation of p62 protein, simultaneously decreased the ratio of LC3-II/LC3-I and the number of autophagosome compared to the control groups, suggesting the inhibition of autophagy activity. In contrast, DHCR24 knock-in obviously abolished the effect of DHCR24 knock-down on tau hyperphosphrylation and autophagy. In addition, to elucidate the association between DHCR24 and tauopathy, we further showed that the level of plasma membrane cholesterol, lipid raft-anchored protein caveolin-1, and concomitantly total I class PI3-K (p110α), phospho-Akt (Thr308 and Ser473) were significantly decreased, resulting in the disruption of lipid raft/caveola and inhibition of PI3-K/Akt signaling in silencing DHCR24 SH-SY5Y cells compared to control groups. At the same time, DHCR24 knock-down simultaneously decreased the level of phosphorylated GSK3β at Ser9 (inactive form) and increased the level of phosphorylated mTOR at Ser2448 (active form), leading to overactivation of GSK3β and mTOR signaling. On the contrary, DHCR24 knock-in largely increased the level of membrane cholesterol and caveolin-1, suggesting the enhancement of lipid raft/caveola. And synchronously DHCR24 knock-in also abolished the effect of DHCR24 knock-down on the inhibition of PI3-K/Akt signaling as well as the overactivation of GSK3β and mTOR signaling. Collectively, our data strongly supported DHCR24 knock-down lead to tau hyperphosphorylation and the inhibition of autophagy by a lipid raft-dependent PI3-K/Akt-mediated GSK3β and mTOR signaling. Taking together, our results firstly demonstrated that the decrease of plasma membrane cholesterol mediated by DHCR24 deficiency might contribute to the tauopathy in AD and other tauopathies.

DHCR24 Knockdown Lead to Hyperphosphorylation of Tau at Thr181, Thr231, Ser262, Ser396, and Ser422 Sites by Membrane Lipid-Raft Dependent PP2A Signaling in SH-SY5Y Cells

Accumulating data suggest that the downregulation of DHCR24 is linked to the pathological risk factors of AD, denoting a potential role of DHCR24 in AD pathogenesis. However, it remains unclear whether the downregulation of DHCR24 affects the abnormal heper-phosphorylation of tau protein, which is involved in tauopathy. In present papers, immunofluorescence and Filipin III fluorescence results showed that DHCR24 knockdown significantly lowered the level of plasma membrane cholesterol and expression level of membrane lipid-raft structural protein caveolin-1; and overexpression of DHCR24 could increase the plasma membrane cholesterol levels and facilitating caveolae structure through increase the expression of caveolin-1. PP2A is the key phosphatase involving in tau phosphorylation, which is localized in cholesterol-dependent caveola/raft lipid domains. Here, the PP2A activity was detected by western blot assay. Interestingly, the level of p-PP2Ac at Y307 (inactive) and p-GSK3β at Y216 (active) in the downstream of the PP2A signal pathway were both significantly increased in silencing DHCR24 SH-SY5Y cells, which denoted an inhibition of the PP2A and activation of GSK3β signaling. Conversely, overexpression of DHCR24 blunted the inhibition effect of PP2A and activation of GSK3β. Besides, in the SH-SY5Y cell lines we demonstrated that DHCR24 knockdown obviously induced hyperphosphorylation of tau at Thr181, Thr231, Ser262, Ser396, and Ser422 Sites. In contrast, DHCR24 overexpression protects neuronal SH-SY5Y cells against the hyperphosphorylation of tau at Thr181, Thr231, Ser262, Ser396, and Ser422 Sites. Furthermore, PP2A activator D-erythro-Sphingosine (DES) also obviously inhibited the hyperphosphorylation of tau induced by DHCR24 knockdown. Collectively, our findings firstly confirmed that DHCR24 knockdown obviously induced abnormal hyperphosphorylation of tau by a novel lipid raft-dependent PP2A signaling. We propose that DHCR24 downregulation led to altered cholesterol synthesis as a potential mechanism in the progression of tau hyperphosphorylation involving in AD and other tauopathies.

Serum seladin-1 levels in diabetes mellitus and Alzheimer's disease patients

BACKGROUND

Diabetes mellitus (DM) has been shown to increase the risk of Alzheimer's disease (AD). Downregulation of selective Alzheimer's disease indicator-1 (seladin-1) occurs in the cerebral regions affected by AD. However, inconsistent results have been reported for the relationship between seladin-1 levels and AD. The effect of DM on serum seladin-1 levels in AD is unknown. The present study is aimed to investigate serum seladin-1 levels in diabetic and non-diabetic patients with AD.

METHODS

Forty-six patients with AD and 25 healthy volunteers over 65 years of age were included in this study. The patients were divided into three groups-those with AD only, those with DM and AD, and control groups. Demographic characteristics and serum seladin-1 levels were compared among the groups.

RESULTS

There was no statistically significant difference in seladin-1 levels in the AD only group compared to the control group (p = 0.376). However, seladin-1 levels were significantly lower in the DM and AD group compared to the AD only and control groups (p = 0.002, p = 0.001; respectively). Negative correlations were present between seladin-1 and fasting glucose, postprandial glucose, HbA1c, and insulin (p < 0.05; all).

CONCLUSION

Decreased serum seladin-1 values in the presence of DM and inverse correlations with diabetic parameters in patients with AD, together with a non-significant difference from the control group, suggests that seladin-1 may be altered only in the presence of DM in patients with AD. Lower serum seladin-1 levels may also play a role in the pathogenesis of AD in patients with DM.

Regulation of ABCG4 transporter expression by sterols and LXR ligands

BACKGROUND

Oxysterols, which are derivatives of cholesterol produced by enzymic or non-enzymic pathways, are potent regulators of cellular lipid homeostasis. Sterol homeostasis in the brain is an important area of interest with regards to neurodegenerative conditions like Alzheimer's disease (AD). Brain cells including neurons and astrocytes express sterol transporters belonging to the ABC transporter family of proteins, including ABCA1, ABCG1 and ABCG4, and these transporters are considered of interest as therapeutic targets. Although regulation of ABCA1 and ABCG1 is well established, regulation of ABCG4 is still controversial, in particular whether the transporter is an Liver X receptor (LXR) target. ABCG4 is thought to transport cholesterol, oxysterols and cholesterol synthesis intermediates, and was recently found on the blood brain barrier (BBB), implicated in amyloid-beta export. In this study, we investigate the regulation of ABCG4 by oxysterols, cholesterol-synthesis intermediates and cholesterol itself.

METHODS

ABC transporter expression was measured in neuroblastoma and gliablastoma cell lines and cells overexpressing ABCG4 in response to synthetic LXR ligands, oxysterols and cholesterol-synthesis intermediates.

RESULTS

In contrast to previous reports, ABCG4 expression was induced by a synthetic LXR ligand in U87-MG astrocytes but not in neuroblastoma and BBB endothelial cell lines. In addition, ABCG4 protein was stabilized by cholesterol as was previously shown for ABCG1. ABCG4 protein was furthermore stabilized by cholesterol-synthesis intermediates, desmosterol, lathosterol and lanosterol.

CONCLUSIONS

These results identify new aspects of the post-translational control of ABCG4 that warrant further exploration into the role of this transporter in the maintenance of sterol homeostasis in the brain.

DHCR24 overexpression modulates microglia polarization and inflammatory response via Akt/GSK3β signaling in Aβ25-35 treated BV-2 cells

Microglial phenotypic polarization, divided into pro-inflammatory "M1" phenotype and anti-inflammatory "M2" phenotype, played a crucial role in the pathogenesis of Alzheimer's disease (AD). Facilitating microglial polarization from M1 to M2 phenotype was shown to alleviate AD-associate pathologic damage, and modulator of the microglial phenotype has become a promising therapeutic approach for the treatment of AD. Previous little evidence showed that DHCR24 (3-β-hydroxysteroid-Δ-24-reductase), also known as seladin-1 (selective Alzheimer's disease indicator-1), exerted potential anti-inflammatory property, however, the link between DHCR24 and microglial polarization has never been reported. Thus, the role of DHCR24 in microglial polarization in amyloid-beta 25-35 (Aβ_25-35) treated BV-2 cells was evaluated in this study. Our results demonstrated that Aβ_25-35 aggravated inflammatory response and facilitated the transition of microglia phenotype from M2 to M1 in BV-2 cells, by upregulating M1 marker (i-NOS, IL-1β and TNF-α) and downregulating M2 marker (arginase-1, IL-4 and TGF-β). DHCR24 overexpression by lentivirus transfection could significantly reverse these effects, meanwhile, activated Akt/GSK3β signaling pathway via increasing the protein expression of P-Akt and P-GSK3β. Furthermore, when co-treated with Akt inhibitor MK2206, the effect of DHCR24 was obviously reversed. The study exhibited the neuroprotective function of DHCR24 in AD-related inflammatory injury and provided a novel therapeutic target for AD in the future.

Modulatory effect of methylsulfonylmethane against BPA/γ-radiation induced neurodegenerative alterations in rats: Influence of TREM-2/DAP-12/Syk pathway

AIMS

Methylsulfonylmethane (MSM), is an organosulfur compound, has many health benefits. Bisphenol-A (BPA) and γ-radiation (R) are two risky environmental contaminants that human beings are exposed to in everyday life. This work aims at unveiling the modulatory role of MSM in combating BPA and R co-exposure induced neurodegenerative disorder (Alzheimer's (AD)-mimic neurotoxicity).

MAIN METHODS

Female rats were randomly divided into five groups. One group was normal control and the other four groups were subjected to subacute BPA intoxication and/or exposed to fractionated weekly doses of R for 4 weeks and either untreated or treated with MSM concomitantly.

KEY FINDINGS

BPA and R co-exposure induced typical hallmarks of neurodegenerative disorders as revealed by tremendously elevated oxidative stress, extensive neuroinflammation (tumor necrosis factor -α and interleukin-1β), elevated AD markers (amyloid-beta (Aβ₄₂), acetylcholinesterase (AchE) activity and tau-phosphorylation) in cortex and hippocampus as well as up-regulation of microglial pro-inflammatory triggering receptor expressed on myeloid cell-2(TREM-2)/DNAX-activating protein of 12 kDa (DAP-12)/spleen-tyrosine kinase (Syk) pathway and its downstream targets (PLC-γ/DAG/p38-MAPK) in hippocampus. Also, neurodegenerative lesions were revealed in histopathological examination of cortex and hippocampus coupled with marked Aβ deposition in hippocampus. Whereas, MSM treatment improved histopathological insults and ameliorated level of oxidative stress, neuroinflammation and AD markers as well as modulated TREM-2/DAP-12/Syk pathway.

SIGNIFICANCE

Our data suggest that MSM afforded neuroprotection against BPA and R; supporting its potential application in the associated neurodegenerative disorders.

Interactions of Aromatase and Seladin-1: A Neurosteroidogenic and Gender Perspective

Aromatase and seladin-1 are enzymes that have major roles in estrogen synthesis and are important in both brain physiology and pathology. Aromatase is the key enzyme that catalyzes estrogen biosynthesis from androgen precursors and regulates the brain’s neurosteroidogenic activity. Seladin-1 is the enzyme that catalyzes the last step in the biosynthesis of cholesterol, the precursor of all hormones, from desmosterol. Studies indicated that seladin-1 is a downstream mediator of the neuroprotective activity of estrogen. Recently, we also showed that there is an interaction between aromatase and seladin-1 in the brain. Therefore, the expression of local brain aromatase and seladin-1 is important, as they produce neuroactive steroids in the brain for the protection of neuronal damage. Increasing steroid biosynthesis specifically in the central nervous system (CNS) without affecting peripheral hormone levels may be possible by manipulating brain-specific promoters of steroidogenic enzymes. This review emphasizes that local estrogen, rather than plasma estrogen, may be responsible for estrogens’ protective effects in the brain. Therefore, the roles of aromatase and seladin-1 and their interactions in neurodegenerative events such as Alzheimer’s disease (AD), ischemia/reperfusion injury (stroke), and epilepsy are also discussed in this review.

Upregulation of seladin-1 and nestin expression in bone marrow mesenchymal stem cell transplantation via the ERK1/2 and PI3K/Akt signaling pathways in an Alzheimer's disease model

The aim of the present study was to determine the roles of bone marrow mesenchymal stem cell (BM-MSC) transplantation in a model of Alzheimer's disease (AD) and determine the underlying mechanism. The expression of selective Alzheimer's disease indicator-1 (Seladin-1) and nestin was detected using reverse transcription-quantitative polymerase chain reaction and western blot analysis. The phosphoinositide 3-kinase (PI3K) and extracellular signal-regulated kinase (ERK)1/2 inhibitors, LY294002 and PD98059, were employed to evaluate the molecular mechanism. The results indicated that the mRNA and protein expression of Seladin-1 and nestin was lower in the AD group when compared with the control group. BM-MSC transplantation reversed this decrease in expression, potentially by increasing the protein expression of phosphorylated (p)-protein kinase B (Akt) and p-ERK1/2. In addition, LY294002 (the PI3K inhibitor) and/or PD98059 (the ERK1/2 inhibitor) blocked the enhancement of BM-MSC transplantation on the expression of Seladin-1 and nestin in the hippocampus. These results indicated that BM-MSC transplantation enhanced Seladin-1 and nestin expression potentially via a mechanism associated with the activation of the PI3K/Akt and ERK1/2 signaling pathways. The present study offers preliminary evidence that treatment with BM-MSCs may represent a potential therapeutic approach against brain lesions in AD.

DHCR24 exerts neuroprotection upon inflammation-induced neuronal death

BACKGROUND

DHCR24, involved in the de novo synthesis of cholesterol and protection of neuronal cells against different stress conditions, has been shown to be selectively downregulated in neurons of the affected brain areas in Alzheimer's disease.

METHODS

Here, we investigated whether the overexpression of DHCR24 protects neurons against inflammation-induced neuronal death using co-cultures of mouse embryonic primary cortical neurons and BV2 microglial cells upon acute neuroinflammation. Moreover, the effects of DHCR24 overexpression on dendritic spine density and morphology in cultured mature mouse hippocampal neurons and on the outcome measures of ischemia-induced brain damage in vivo in mice were assessed.

RESULTS

Overexpression of DHCR24 reduced the loss of neurons under inflammation elicited by LPS and IFN-γ treatment in co-cultures of mouse neurons and BV2 microglial cells but did not affect the production of neuroinflammatory mediators, total cellular cholesterol levels, or the activity of proteins linked with neuroprotective signaling. Conversely, the levels of post-synaptic cell adhesion protein neuroligin-1 were significantly increased upon the overexpression of DHCR24 in basal growth conditions. Augmentation of DHCR24 also increased the total number of dendritic spines and the proportion of mushroom spines in mature mouse hippocampal neurons. In vivo, overexpression of DHCR24 in striatum reduced the lesion size measured by MRI in a mouse model of transient focal ischemia.

CONCLUSIONS

These results suggest that the augmentation of DHCR24 levels provides neuroprotection in acute stress conditions, which lead to neuronal loss in vitro and in vivo.

New evidence of the relative protective effects of neurodegenerative diseases and cancer against each other

BACKGROUND

Cancer and degenerative diseases share some pathogenic mechanisms which act in opposition to one another to produce either uncontrolled cell proliferation or cell death. According to several studies, patients with Alzheimer disease have a lower risk of neoplasia, and vice versa. This study describes the prevalence of tumours (active or successfully treated) in a series of patients with and without a dementing degenerative disease treated at a cognitive neurology unit.

PATIENTS AND METHOD

We analysed the frequency and topography of tumours and the presence or absence of a neurodegenerative disease in a group of 1,164 patients. Neurodegenerative diseases were classified in 4 groups: Alzheimer disease, synucleinopathies, Pick complex, and polyglutamine complex. We subsequently compared tumour frequency in patients with and without a degenerative disease, and prevalence of neurodegenerative diseases in patients with and without tumours.

RESULTS

Tumours were detected in 12.1% of the patients with a neurodegenerative disease and in 17.3% of the remaining patients. Around 14.8% of the patients with a history of neoplasia and 20.8% of the patients with no history of neoplasia were diagnosed with a neurodegenerative disease. Except for these differences and the differences between subgroups (type of degenerative disease and tumour location) were not statistically significant, except when comparing neurodegenerative diseases to central nervous system tumours, and synucleinopathies to neoplasms.

CONCLUSION

Dementing degenerative diseases and neoplastic disorders are not mutually exclusive. Nevertheless, the rate of co-occurrence is lower than would be expected given the prevalence rate for each group.

Lack of insulin results in reduced seladin-1 expression in primary cultured neurons and in cerebral cortex of STZ-induced diabetic rats

Several studies demonstrated that Diabetes mellitus (DM) enhances the risk for Alzheimer's disease (AD). Although hyperglycemia and perturbed function of insulin signaling have been proposed to contribute to AD pathogenesis, the molecular mechanisms behind this association is not clear yet. Seladin-1 is an enzyme catalyzing the last step in cholesterol biosynthesis converting desmosterol to cholesterol. The neuroprotective function of seladin-1 has gained interest in AD research recently. Seladin-1 has anti-apoptotic properties and regulates the expression of β-secretase (BACE-1). Here we measured seladin-1 mRNA and protein expressions in rat primary cultured neurons under diabetic conditions and also in the brains of rats with streptozotocine (STZ)-induced diabetes. We show that constant lack of insulin for 5days decreased seladin-1 levels in cultured rat primary neurons. Similarly, a decrease in seladin-1 was found in the brains of rats with STZ-induced diabetes. However, if the lack of insulin and/or high glucose treatment was intermittent, neuronal seladin-1 levels were not affected in vitro. On the other hand, treatment of neurons with metformin resulted in a significant increase in seladin-1. Constant lack of insulin for 5days, as well as high glucose treatment, increased the neuronal expression of BACE-1 in vitro, but not in the in vivo model. Our study defines insulin as a regulator of seladin-1 expression for the first time. The relevance of these findings for the association of DM with AD is discussed.

Seladin-1/DHCR24 Is Neuroprotective by Associating EAAT2 Glutamate Transporter to Lipid Rafts in Experimental Stroke

Background and Purpose—

3β-Hydroxysteroid-Δ24 reductase (DHCR24) or selective alzheimer disease indicator 1 (seladin-1), an enzyme of cholesterol biosynthetic pathway, has been implicated in neuroprotection, oxidative stress, and inflammation. However, its role in ischemic stroke remains unexplored. The aim of this study was to characterize the effect of seladin-1/DHCR24 using an experimental stroke model in mice.

Methods—

Dhcr24 +/− and wild-type (WT) mice were subjected to permanent middle cerebral artery occlusion. In another set of experiments, WT mice were treated intraperitoneally either with vehicle or U18666A (seladin-1/DHCR24 inhibitor, 10 mg/kg) 30 minutes after middle cerebral artery occlusion. Brains were removed 48 h after middle cerebral artery occlusion for infarct volume determination. For protein expression determination, peri-infarct region was obtained 24 h after ischemia, and Western blot or cytometric bead array was performed.

Results—

Dhcr24 +/ − mice displayed larger infarct volumes after middle cerebral artery occlusion than their WT littermates. Treatment of WT mice with the seladin-1/DHCR24 inhibitor U18666A also increased ischemic lesion. Inflammation-related mediators were increased after ischemia in Dhcr24 +/ − mice compared with WT counterparts. Consistent with a role of cholesterol in proper function of glutamate transporter EAAT2 in membrane lipid rafts, we found a decreased association of EAAT2 with lipid rafts after ischemia when DHCR24 is genetically deleted or pharmacologically inhibited. Accordingly, treatment with U18666A decreases [ 3 H]-glutamate uptake in cultured astrocytes.

Conclusions—

These results support the idea that lipid raft integrity, ensured by seladin-1/DHCR24, plays a crucial protective role in the ischemic brain by guaranteeing EAAT2-mediated uptake of glutamate excess.

Investigation into the effects of antioxidant-rich extract of Tamarindus indica leaf on antioxidant enzyme activities, oxidative stress and gene expression profiles in HepG2 cells

The leaf extract of Tamarindus indica L. (T. indica) had been reported to possess high phenolic content and showed high antioxidant activities. In this study, the effects of the antioxidant-rich leaf extract of the T. indica on lipid peroxidation, antioxidant enzyme activities, H₂O₂-induced ROS production and gene expression patterns were investigated in liver HepG2 cells. Lipid peroxidation and ROS production were inhibited and the activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase was enhanced when the cells were treated with the antioxidant-rich leaf extract. cDNA microarray analysis revealed that 207 genes were significantly regulated by at least 1.5-fold (p < 0.05) in cells treated with the antioxidant-rich leaf extract. The expression of KNG1, SERPINC1, SERPIND1, SERPINE1, FGG, FGA, MVK, DHCR24, CYP24A1, ALDH6A1, EPHX1 and LEAP2 were amongst the highly regulated. When the significantly regulated genes were analyzed using Ingenuity Pathway Analysis software, “Lipid Metabolism, Small Molecule Biochemistry, Hematological Disease” was the top biological network affected by the leaf extract, with a score of 36. The top predicted canonical pathway affected by the leaf extract was the coagulation system (P < 2.80 × 10⁻⁶) followed by the superpathway of cholesterol biosynthesis (P < 2.17 × 10⁻⁴), intrinsic prothrombin pathway (P < 2.92 × 10⁻⁴), Immune Protection/Antimicrobial Response (P < 2.28 × 10⁻³) and xenobiotic metabolism signaling (P < 2.41 × 10⁻³). The antioxidant-rich leaf extract of T. indica also altered the expression of proteins that are involved in the Coagulation System and the Intrinsic Prothrombin Activation Pathway (KNG1, SERPINE1, FGG), Superpathway of Cholesterol Biosynthesis (MVK), Immune protection/antimicrobial response (IFNGR1, LEAP2, ANXA3 and MX1) and Xenobiotic Metabolism Signaling (ALDH6A1, ADH6). In conclusion, the antioxidant-rich leaf extract of T. indica inhibited lipid peroxidation and ROS production, enhanced antioxidant enzyme activities and significantly regulated the expression of genes and proteins involved with consequential impact on the coagulation system, cholesterol biosynthesis, xenobiotic metabolism signaling and antimicrobial response.

Neuronal differentiation of rat hair follicle stem cells: the involvement of the neuroprotective factor Seladin-1 (DHCR24)

Background: The seladin-1 (selective Alzheimer disease indicator-1), also known as DHCR24, is a gene found to be down-regulated in brain region affected by Alzheimer disease (AD). Whereas, hair follicle stem cells (HFSC), which are affected in with neurogenic potential, it might to hypothesize that this multipotent cell compartment is the predominant source of seladin-1. Our aim was to evaluate seladin-1 gene expression in hair follicle stem cells. Methods: In this study, bulge area of male Wistar rat HFSC were cultured and then characterized with Seladin-1 immunocytochemistry and flow cytometry on days 8 to 14. Next, 9-11-day cells were evaluated for seladin-1 gene expression by real-time PCR. Results: Our results indicated that expression of the seladin-1 gene (DHCR24) on days 9, 10, and 11 may contribute to the development of HFSC. However, the expression of this gene on day 11 was more than day 10 and on 10^th day was more than day 9. Also, we assessed HFSC on day 14 and demonstrated these cells were positive for β-ш tubulin, and seladin-1 was not expressed in this day. Conclusion: HFSC express seladin-1 and this result demonstrates that these cells might be used to cell therapy for AD in future.

Desmosterol in brain is elevated because DHCR24 needs REST for Robust Expression but REST is poorly expressed

Cholesterol synthesis in the fetal brain is inhibited because activity of DHCR24 (24-dehydrocholesterol reductase) is insufficient, causing concentrations of the precursor desmosterol to increase temporarily to 15-25% of total sterols at birth. We demonstrate that failure of DHCR24 to be adequately upregulated during periods of elevated cholesterol synthesis in the brain results from the presence in its promoter of the repressor element 1 (RE1) nucleotide sequence that binds the RE1-silencing transcription factor (REST) and that REST, generally reduced in neural tissues, uncharacteristically but not without precedent, enhances DHCR24 transcription. DHCR24 and REST mRNA levels are reduced 3- to 4-fold in fetal mouse brain compared to liver (p < 0.001). Chromatin immunoprecipitation assays suggested that REST binds to the human DHCR24 promoter in the vicinity of the predicted human RE1 sequence. Luminescent emission from a human DHCR24 promoter construct with a mutated RE1 sequence was reduced 2-fold compared to output from a reporter with wild-type RE1 (p < 0.005). Silencing REST in HeLa cells resulted in significant reductions of DHCR24 mRNA (2-fold) and DHCR24 protein (4-fold). As expected, relative concentrations of Δ(24)-cholesterol precursor sterols increased 3- to 4-fold, reflecting the inhibition of DHCR24 enzyme activity. In contrast, mRNA levels of DHCR7 (sterol 7-dehydrocholesterol reductase), a gene essential for cholesterol synthesis lacking an RE1 sequence, and concentrations of HMGR (3-hydroxy-3-methyl-glutaryl-CoA reductase) enzyme protein were both unaffected. Surprisingly, a dominant negative fragment of REST consisting of just the DNA binding domain (about 20% of the protein) and full-length REST enhanced DHCR24 expression equally well. Furthermore, RE1 and the sterol response element (SRE), the respective binding sites for REST and the SRE binding protein (SREBP), are contiguous. These observations led us to hypothesize that REST acts because it is bound in close proximity to SREBP, thus amplifying its ability to upregulate DHCR24. It is likely that modulation of DHCR24 expression by REST persisted in the mammalian genome either because it does no harm or because suppressing metabolically active DHCR24 while providing abundant quantities of the multifunctional sterol desmosterol during neural development proved useful.

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.

Desmosterol and DHCR24: unexpected new directions for a terminal step in cholesterol synthesis

3β-Hydroxysterol Δ(24)-reductase (DHCR24) catalyzes the conversion of desmosterol to cholesterol. This ultimate step of cholesterol biosynthesis appears to be remarkable in its diverse functions and the number of diseases it is implicated in from vascular disease to Hepatitis C virus (HCV) infection to cancer to Alzheimer's disease. This review summarizes the present knowledge on the DHCR24 gene, sterol Δ(24)-reductase protein and the regulation of both. In addition, the functions of desmosterol, DHCR24 and their roles in human diseases are discussed. It is apparent that DHCR24 exerts more complex effects than what would be expected based on the enzymatic activity of sterol Δ(24)-reduction alone, such as its influence in modulating oxidative stress. Increasing information about DHCR24 membrane association, processing, enzymatic regulation and interaction partners will provide further fundamental insights into DHCR24 and its many and varied biological roles.

Alzheimer's disease: brain desmosterol levels

Desmosterol is a C27 sterol intermediate in cholesterol synthesis generated during the metabolic pathway that transforms lanosterol into cholesterol. It has become of particular interest in the pathogenesis of Alzheimer's disease (AD) because of the report that the activity of the gene coding for the enzyme DHCR24, which metabolizes desmosterol to cholesterol, is selectively reduced in the affected areas of the brain. Any change in the pattern of C27 sterol intermediates in cholesterol synthesis merits investigation with respect to the pathogenesis of AD, since neurosteroids such as progesterone can modulate the tissue levels. We therefore analyzed the C27 sterol composition using a metabolomics approach that preserves the proportion of the different sterol intermediates. In AD, the proportion of desmosterol was found to be less than that of age-matched controls. The findings do not directly support the focus on Seladin-1, although they could reflect different stages of a slowly progressive disease.

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.

Oligomeric amyloid-β peptide affects the expression of genes involved in steroid and lipid metabolism in primary neurons

Amyloid-β peptide (Aβ) is the principal component of plaques in the brains of patients with Alzheimer's disease (AD), and the most toxic form of Aβ may be as soluble oligomers. We report here the results of a microarray study of gene expression profiles in primary mouse cortical neurons in response to oligomeric Aβ(1-42). A major and unexpected finding was the down-regulation of genes involved in the biosynthesis of cholesterol and other steroids and lipids (such as Fdft1, Fdps, Idi1, Ldr, Mvd, Mvk, Nsdhl, Sc4mol), the expression of which was verified by quantitative real-time RT-PCR (qPCR). The ATP-binding cassette gene Abca1, which has a major role in cholesterol transport in brain and other tissues and has been genetically linked to AD, was notably up-regulated. The possible involvement of cholesterol and other lipids in Aβ synthesis and action in Alzheimer's disease has been studied and debated extensively but remains unresolved. These new data suggest that Aβ may influence steroid and lipid metabolism in neurons via multiple gene-expression changes.

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.

Discovering context-specific relationships from biological literature by using multi-level context terms

Background

The Swanson's ABC model is powerful to infer hidden relationships buried in biological literature. However, the model is inadequate to infer relations with context information. In addition, the model generates a very large amount of candidates from biological text, and it is a semi-automatic, labor-intensive technique requiring human expert's manual input. To tackle these problems, we incorporate context terms to infer relations between AB interactions and BC interactions.

Methods

We propose 3 steps to discover meaningful hidden relationships between drugs and diseases: 1) multi-level (gene, drug, disease, symptom) entity recognition, 2) interaction extraction (drug-gene, gene-disease) from literature, 3) context vector based similarity score calculation. Subsequently, we evaluate our hypothesis with the datasets of the "Alzheimer's disease" related 77,711 PubMed abstracts. As golden standards, PharmGKB and CTD databases are used. Evaluation is conducted in 2 ways: first, comparing precision of the proposed method and the previous method and second, analysing top 10 ranked results to examine whether highly ranked interactions are truly meaningful or not.

Results

The results indicate that context-based relation inference achieved better precision than the previous ABC model approach. The literature analysis also shows that interactions inferred by the context-based approach are more meaningful than interactions by the previous ABC model.

Conclusions

We propose a novel interaction inference technique that incorporates context term vectors into the ABC model to discover meaningful hidden relationships. By utilizing multi-level context terms, our model shows better performance than the previous ABC model.

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.

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.

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.

Seladin-1 expression is regulated by promoter methylation in adrenal cancer

BACKGROUND

Seladin-1 overexpression exerts a protective mechanism against apoptosis. Seladin-1 mRNA is variably expressed in normal human tissues. Adrenal glands show the highest levels of seladin-1 expression, which are significantly reduced in adrenal carcinomas (ACC). Since up to now seladin-1 mutations were not described, we investigated whether promoter methylation could account for the down-regulation of seladin-1 expression in ACC.

METHODS

A methylation sensitive site was identified in the seladin-1 gene. We treated DNA extracted from two ACC cell lines (H295R and SW13) with the demethylating agent 5-Aza-2-deoxycytidine (5-Aza). Furthermore, to evaluate the presence of an epigenetic regulation also 'in vivo', seladin-1 methylation and its mRNA expression were measured in 9 ACC and in 5 normal adrenal glands.

RESULTS

The treatment of cell lines with 5-Aza induced a significant increase of seladin-1 mRNA expression in H295R (fold increase, F.I. = 1.8; p = 0.02) and SW13 (F.I. = 2.9; p = 0.03). In ACC, methylation density of seladin-1 promoter was higher (2682 +/- 686) than in normal adrenal glands (362 +/- 97; p = 0.02). Seladin-1 mRNA expression in ACC (1452 +/- 196) was significantly lower than in normal adrenal glands (3614 +/- 949; p = 0.01).

CONCLUSION

On this basis, methylation could be involved in the altered pattern of seladin-1 gene expression in ACC.

Transcritpional effects of S100B on neuroblastoma cells: perturbation of cholesterol homeostasis and interference on the cell cycle

S100B is a Ca2+ binding protein mainly secreted by astrocytes in the vertebrate brain that is considered a multifunctional cytokine and/or a damage-associated molecular pattern (DAMP) protein and a marker of brain injury and neurodegeneration when measured in different body fluids. It has been widely shown that this protein can exert diverse effects in neural cultures depending on its concentration, having detrimental effects at micromolar concentrations. The molecular mechanisms underlying this effect are still largely unknown. This study attempts to delineate the genome-wide gene expression analysis of the events associated with exposure to micromolar concentration of S100B in a human neuroblastoma cell line. In this experimental condition cells undergo a severe perturbation of lipid homeostasis along with cell cycle arrest. These mechanisms might reasonably mediate some aspects of the S100B-related detrimental effects of S100B, although obvious differences between mature neurons and neuroblastoma cells have to be considered.

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.

ER stress in Alzheimer's disease: a novel neuronal trigger for inflammation and Alzheimer's pathology

The endoplasmic reticulum (ER) is involved in several crucial cellular functions, e.g. protein folding and quality control, maintenance of Ca²⁺ balance, and cholesterol synthesis. Many genetic and environmental insults can disturb the function of ER and induce ER stress. ER contains three branches of stress sensors, i.e. IRE1, PERK and ATF6 transducers, which recognize the misfolding of proteins in ER and activate a complex signaling network to generate the unfolded protein response (UPR). Alzheimer's disease (AD) is a progressive neurodegenerative disorder involving misfolding and aggregation of proteins in conjunction with prolonged cellular stress, e.g. in redox regulation and Ca²⁺ homeostasis. Emerging evidence indicates that the UPR is activated in neurons but not in glial cells in AD brains. Neurons display pPERK, peIF2α and pIRE1α immunostaining along with abundant diffuse staining of phosphorylated tau protein. Recent studies have demonstrated that ER stress can also induce an inflammatory response via different UPR transducers. The most potent pathways are IRE1-TRAF2, PERK-eIF2α, PERK-GSK-3, ATF6-CREBH, as well as inflammatory caspase-induced signaling pathways. We will describe the mechanisms which could link the ER stress of neurons to the activation of the inflammatory response and the evolution of pathological changes in AD.