Glial lipoproteins stimulate axon growth of central nervous system neurons in compartmented cultures

Lipid Droplets and Neurodegeneration

Energy metabolism in the brain has been considered one of the critical research areas of neuroscience for ages. One of the most vital parts of brain metabolism cascades is lipid metabolism, and fatty acid plays a crucial role in this process. The fatty acid breakdown process in mitochondria undergoes through a conserved pathway known as β-oxidation where acetyl-CoA and shorter fatty acid chains are produced along with a significant amount of energy molecule. Further, the complete breakdown of fatty acids occurs when they enter the mitochondrial oxidative phosphorylation. Cells store energy as neutral lipids in organelles known as Lipid Droplets (LDs) to prepare for variations in the availability of nutrients. Fatty acids are liberated by lipid droplets and are transported to various cellular compartments for membrane biogenesis or as an energy source. Current research shows that LDs are important in inflammation, metabolic illness, and cellular communication. Lipid droplet biology in peripheral organs like the liver and heart has been well investigated, while the brain's LDs have received less attention. Recently, there has been increased awareness of the existence and role of these dynamic organelles in the central nervous system, mainly connected to neurodegeneration. In this review, we discussed the role of beta-oxidation and lipid droplet formation in the oxidative phosphorylation process, which directly affects neurodegeneration through various pathways.

Cholesterol Metabolism in Neurodegenerative Diseases

SIGNIFICANCE

Cholesterol plays a crucial role in brain, where it is highly concentrated and tightly regulated to support normal brain functions. It serves as a vital component of cell membranes, ensuring their integrity, and acts as a key regulator of various brain processes. Dysregulation of cholesterol metabolism in the brain has been linked to impaired brain function and the onset of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD).

RECENT ADVANCES

A significant advancement has been the identification of astrocyte-derived ApoE as a key regulator of de novo cholesterol biosynthesis in neurons, providing insights into how extracellular signals influence neuronal cholesterol levels. Additionally, the development of antibody-based therapies, particularly for AD, presents promising opportunities for therapeutic interventions.

CRITICAL ISSUES

Despite significant research, the association between cholesterol and neurodegenerative diseases remains inconclusive. It is crucial to distinguish between plasma cholesterol and brain cholesterol, as these pools are relatively independent. This differentiation should be considered when evaluating statin-based treatment approaches. Assessing not only the total cholesterol content in the brain but also its distribution among different types of brain cells is essential.

FUTURE DIRECTION

Establishing a causal link between changes in brain/plasma cholesterol levels and the onset of brain dysfunction/neurodegenerative diseases remains a key objective. Additionally, conducting cell-specific analyses of cholesterol homeostasis in various types of brain cells under pathological conditions will enhance our understanding of cholesterol metabolism in neurodegenerative diseases. Manipulating cholesterol levels to restore homeostasis may represent a novel approach for alleviating neurological symptom.

Potential Use of the Cholesterol Transfer Inhibitor U18666A as a Potent Research Tool for the Study of Cholesterol Mechanisms in Neurodegenerative Disorders

Cholesterol is an essential component of mammalian cell membranes and a precursor for crucial signaling molecules. The brain contains the highest level of cholesterol in the body, and abnormal cholesterol metabolism links to many neurodegenerative disorders. The results indicate that faulty cholesterol metabolism is a common feature among people living with neurodegenerative conditions. The researchers suggest that restoring cholesterol levels may become a beneficial new strategy in treating certain neurodegenerative conditions. Several neurodegenerative disorders, such as Alzheimer's disease (AD), Niemann-Pick type C (NPC) disease, and Parkinson's disease (PD), have been connected to abnormalities in brain cholesterol metabolism. Consequently, using a lipid research tool is vital to study further and understand the effect of lipids in neurodegenerative disorders such as NPC, AD, PD, and Huntington's disease (HD). U18666A, also known as 3-(2-(diethylamino) ethoxy) androst-5-en-17-one, is a pharmaceutical drug that suppresses cholesterol trafficking and is a well-known class-2 amphiphile. U18666A has performed many functions, allowing for essential discoveries in lipid studies and shedding light on the pathophysiology of neurodegenerative disorders. Additionally, U18666A prevented the downregulation of low-density lipoprotein (LDL) receptors that are induced by LDL and led to the buildup of cholesterol in lysosomes. Numerous studies show that U18666A impacts the function of cholesterol trafficking to control the metabolism and transport of amyloid precursor proteins (APPs). Treating cortical neurons with U18666A may provide a new in vitro model system for studying the underlying molecular process of NPC, AD, HD, and PD. In this article, we review the mechanism and function of U18666A as a vital tool for studying cholesterol mechanisms in neurological diseases related to abnormal cholesterol metabolism, such as AD, NPC, HD, and PD.

Enhancing of cerebral Abeta clearance by modulation of ABC transporter expression: a review of experimental approaches

Clearance of amyloid-beta (Aβ) from the brain is impaired in both early-onset and late-onset Alzheimer's disease (AD). Mechanisms for clearing cerebral Aβ include proteolytic degradation, antibody-mediated clearance, blood brain barrier and blood cerebrospinal fluid barrier efflux, glymphatic drainage, and perivascular drainage. ATP-binding cassette (ABC) transporters are membrane efflux pumps driven by ATP hydrolysis. Their functions include maintenance of brain homeostasis by removing toxic peptides and compounds, and transport of bioactive molecules including cholesterol. Some ABC transporters contribute to lowering of cerebral Aβ. Mechanisms suggested for ABC transporter-mediated lowering of brain Aβ, in addition to exporting of Aβ across the blood brain and blood cerebrospinal fluid barriers, include apolipoprotein E lipidation, microglial activation, decreased amyloidogenic processing of amyloid precursor protein, and restricting the entrance of Aβ into the brain. The ABC transporter superfamily in humans includes 49 proteins, eight of which have been suggested to reduce cerebral Aβ levels. This review discusses experimental approaches for increasing the expression of these ABC transporters, clinical applications of these approaches, changes in the expression and/or activity of these transporters in AD and transgenic mouse models of AD, and findings in the few clinical trials which have examined the effects of these approaches in patients with AD or mild cognitive impairment. The possibility that therapeutic upregulation of ABC transporters which promote clearance of cerebral Aβ may slow the clinical progression of AD merits further consideration.

Lipoprotein Particles in Cerebrospinal Fluid

The brain is the most lipid-rich organ in the body, and the intricate interplay between lipid metabolism and pathologies associated with neurodegenerative disorders is being increasingly recognized. The brain is bathed in cerebrospinal fluid (CSF), which, like plasma, contains lipid-protein complexes called lipoproteins that are responsible for extracellular lipid transport. Multiple CSF lipoprotein populations exist, some of which are produced de novo in the central nervous system and others that appear to be generated from protein constituents that are produced in the periphery. These CSF lipoproteins are thought to play key roles in maintaining lipid homeostasis in the central nervous system, while little else is known due to their limited accessibility and their low abundance in CSF. Recent work has provided new insights into the compositional complexity of CSF lipoprotein families and their metabolism in cerebral circulation. The purpose of this review is to summarize our current state of knowledge on the composition, origin, and metabolism of CSF lipoproteins.

Role of APOE in glaucoma

Glaucoma is a chronic blinding eye disease caused by the progressive loss of retinal ganglion cells (RGCs). Currently, no clinically approved treatment can directly improve the survival rate of RGCs. The Apolipoprotein E (APOE) gene is closely related to the genetic risk of numerous neurodegenerative diseases and has become a hot topic in the field of neurodegenerative disease research in recent years. The optic nerve and retina are extensions of the brain's nervous system. The pathogenesis of retinal degenerative diseases is closely related to the degenerative diseases of the nerves in the brain. APOE consists of three alleles, ε4, ε3, and ε2, in a single locus. They have varying degrees of risk for glaucoma. APOE4 and the APOE gene deletion (APOE-/-) can reduce RGC loss. By contrast, APOE3 and the overall presence of APOE genes (APOE+/+) result in significant loss of RGC bodies and axons, increasing the risk of glaucoma RGCs death. Currently, there is no clear literature indicating that APOE2 is beneficial or harmful to glaucoma. This study summarises the mechanism of different APOE genes in glaucoma and speculates that APOE targeted intervention may be a promising method for protecting against RGCs loss in glaucoma.

miRNA-660-3p inhibits malignancy in glioblastoma via negative regulation of APOC1-TGFβ2 signaling pathway

Glioblastoma as the most common and aggressive central nervous system tumor in adults. Its prognosis and therapeutic outcome are poor due to the limited understanding of its molecular mechanism. Apolipoprotein C-1 (APOC1) as a member of the apolipoprotein family that acts as a tumor promoter in various cancers. MicroRNA (miRNA) can silence gene expression and suppress tumor progression. However, the role of APOC1 and its upstream miRNA has not been explored in glioblastoma. Two glioblastoma cell lines (U87 and U251) were used to explore the role of APOC1 and its upstream miRNA-660-3p in glioblastoma tumorigenesis in vitro. Cells with APOC1/miRNA-660-3p overexpression or knockdown were assessed for their proliferation, migration, and invasion in vitro, and tumorigenesis in vivo. Gene and protein expression was assessed by qRT-PCR and western blot, respectively. Cell proliferation was assessed by the MTT assay and the EdU and Ki67 staining. Cell migration and invasion were assessed by the transwell assay. Tumorigenesis in vivo was assessed in U87 cells with a xenograft mouse model. APOC1 was overexpressed in glioblastoma compared with normal peritumoral tissue and was inversely related to patient prognosis. APOC1 overexpression promotes cell proliferation, migration, and invasion in vitro. APOC1 inhibition reduced tumor growth in vivo. miRNA-660-3p inhibits tumorigenesis by directly targeting APOC1. Mechanistically, APOC1 drives the malignancy of glioblastoma by activating the TGFβ2 signaling pathway. miRNA-660-3p suppresses tumorigenesis by targeting APOC1. Therefore, miRNA-660-3p/APOC1 axis can serve as potential intervention targets in managing glioblastoma progression.

Brain cholesterol homeostasis and its association with neurodegenerative diseases

The brain is the most cholesterol-rich organ in mammals. However, cholesterol metabolism in the brain is completely independent of other tissues due to the presence of the blood-brain barrier (BBB). Neurons, astrocytes and oligodendrocytes are the main cells responsible for cholesterol synthesis in the brain. The cholesterol content in the brain is maintained at a relatively constant level under strict regulation of synthesis, transport, and turnover, that is, brain cholesterol homeostasis. Once this balance is disrupted, neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) ensue. This review summarizes the processes controlling cholesterol homeostasis with respect to the synthesis, transport and turnover of cholesterol in the brain. We further focus on how cholesterol imbalance contributes to neurodegenerative diseases to explore the possibilities to modulate the key steps involved, which will provide clues for the development of therapies for the treatment of central nervous system (CNS) diseases.

Cholesterol-dependent amyloid β production: space for multifarious interactions between amyloid precursor protein, secretases, and cholesterol

Amyloid β is considered a key player in the development and progression of Alzheimer's disease (AD). Many studies investigating the effect of statins on lowering cholesterol suggest that there may be a link between cholesterol levels and AD pathology. Since cholesterol is one of the most abundant lipid molecules, especially in brain tissue, it affects most membrane-related processes, including the formation of the most dangerous form of amyloid β, Aβ42. The entire Aβ production system, which includes the amyloid precursor protein (APP), β-secretase, and the complex of γ-secretase, is highly dependent on membrane cholesterol content. Moreover, cholesterol can affect amyloidogenesis in many ways. Cholesterol influences the stability and activity of secretases, but also dictates their partitioning into specific cellular compartments and cholesterol-enriched lipid rafts, where the amyloidogenic machinery is predominantly localized. The most complicated relationships have been found in the interaction between cholesterol and APP, where cholesterol affects not only APP localization but also the precise character of APP dimerization and APP processing by γ-secretase, which is important for the production of Aβ of different lengths. In this review, we describe the intricate web of interdependence between cellular cholesterol levels, cholesterol membrane distribution, and cholesterol-dependent production of Aβ, the major player in AD.

Astroglial exosome HepaCAM signaling and ApoE antagonization coordinates early postnatal cortical pyramidal neuronal axon growth and dendritic spine formation

Developing astroglia play important roles in regulating synaptogenesis through secreted and contact signals. Whether they regulate postnatal axon growth is unknown. By selectively isolating exosomes using size-exclusion chromatography (SEC) and employing cell-type specific exosome reporter mice, our current results define a secreted astroglial exosome pathway that can spread long-range in vivo and stimulate axon growth of cortical pyramidal neurons. Subsequent biochemical and genetic studies found that surface expression of glial HepaCAM protein essentially and sufficiently mediates the axon-stimulating effect of astroglial exosomes. Interestingly, apolipoprotein E (ApoE), a major astroglia-secreted cholesterol carrier to promote synaptogenesis, strongly inhibits the stimulatory effect of astroglial exosomes on axon growth. Developmental ApoE deficiency also significantly reduces spine density of cortical pyramidal neurons. Together, our study suggests a surface contact mechanism of astroglial exosomes in regulating axon growth and its antagonization by ApoE, which collectively coordinates early postnatal pyramidal neuronal axon growth and dendritic spine formation.

Advances in Nerve Injury Models on a Chip

Regeneration and functional recovery of the damaged nerve are challenging due to the need for effective therapeutic drugs, biomaterials, and approaches. The poor outcome of the treatment of nerve injury stems from the incomplete understanding of axonal biology and interactions between neurons and the surrounding environment, such as glial cells and extracellular matrix. Microfluidic devices, in combination with various injury techniques, have been applied to test biological hypotheses in nerve injury and nerve regeneration. The microfluidic devices provide multiple advantages over the in vitro cell culture on a petri dish and in vivo animal models because a specific part of the neuronal environment can be manipulated using physical and chemical interventions. In addition, single-cell behavior and interactions between neurons and glial cells can be visualized and quantified on microfluidic platforms. In this article, current in vitro nerve injury models on a chip that mimics in vivo axonal injuries and the regeneration process of axons are summarized. The microfluidic-based nerve injury models could enhance the understanding of the physiological and pathophysiological mechanisms of nerve tissues and simultaneously serve as powerful drug and biomaterial screening platforms.

The Potential Therapeutic Application of Simvastatin for Brain Complications and Mechanisms of Action

Statins are common drugs that are clinically used to reduce elevated plasma cholesterol levels. Based on their solubility, statins are considered to be either hydrophilic or lipophilic. Amongst them, simvastatin has the highest lipophilicity to facilitate its ability to cross the blood-brain barrier. Recent studies have suggested that simvastatin could be a promising therapeutic option for different brain complications and diseases ranging from brain tumors (i.e., medulloblastoma and glioblastoma) to neurological disorders (i.e., Alzheimer's disease, Parkinson's disease, and Huntington's disease). Specific mechanisms of disease amelioration, however, are still unclear. Independent studies suggest that simvastatin may reduce the risk of developing certain neurodegenerative disorders. Meanwhile, other studies point towards inducing cell death in brain tumor cell lines. In this review, we outline the potential therapeutic effects of simvastatin on brain complications and review the clinically relevant molecular mechanisms in different cases.

Astroglial exosome HepaCAM signaling and ApoE antagonization coordinates early postnatal cortical pyramidal neuronal axon growth and dendritic spine formation

Developing astroglia play important roles in regulating synaptogenesis through secreted and contact signals. Whether they regulate postnatal axon growth is unknown. By selectively isolating exosomes using size-exclusion chromatography (SEC) and employing cell-type specific exosome reporter mice, our current results define a secreted astroglial exosome pathway that can spread long-range in vivo and stimulate axon growth of cortical pyramidal neurons. Subsequent biochemical and genetic studies found that surface expression of glial HepaCAM protein essentially and sufficiently mediates the axon-stimulating effect of astroglial exosomes. Interestingly, apolipoprotein E (ApoE), a major astroglia-secreted cholesterol carrier to promote synaptogenesis, strongly inhibits the stimulatory effect of astroglial exosomes on axon growth. Developmental ApoE deficiency also significantly reduces spine density of cortical pyramidal neurons. Together, our study suggests a surface contact mechanism of astroglial exosomes in regulating axon growth and its antagonization by ApoE, which collectively coordinates early postnatal pyramidal neuronal axon growth and dendritic spine formation.

Targeting Oncogenic Rewiring of Lipid Metabolism for Glioblastoma Treatment

Glioblastoma (GBM) is the most malignant primary brain tumor. Despite increasing research on GBM treatment, the overall survival rate has not significantly improved over the last two decades. Although recent studies have focused on aberrant metabolism in GBM, there have been few advances in clinical application. Thus, it is important to understand the systemic metabolism to eradicate GBM. Together with the Warburg effect, lipid metabolism has emerged as necessary for GBM progression. GBM cells utilize lipid metabolism to acquire energy, membrane components, and signaling molecules for proliferation, survival, and response to the tumor microenvironment. In this review, we discuss fundamental cholesterol, fatty acid, and sphingolipid metabolism in the brain and the distinct metabolic alterations in GBM. In addition, we summarize various studies on the regulation of factors involved in lipid metabolism in GBM therapy. Focusing on the rewiring of lipid metabolism will be an alternative and effective therapeutic strategy for GBM treatment.

Amyloid β, Lipid Metabolism, Basal Cholinergic System, and Therapeutics in Alzheimer’s Disease

The presence of insoluble aggregates of amyloid β (Aβ) in the form of neuritic plaques (NPs) is one of the main features that define Alzheimer’s disease. Studies have suggested that the accumulation of these peptides in the brain significantly contributes to extensive neuronal loss. Furthermore, the content and distribution of cholesterol in the membrane have been shown to have an important effect on the production and subsequent accumulation of Aβ peptides in the plasma membrane, contributing to dysfunction and neuronal death. The monomeric forms of these membrane-bound peptides undergo several conformational changes, ranging from oligomeric forms to beta-sheet structures, each presenting different levels of toxicity. Aβ peptides can be internalized by particular receptors and trigger changes from Tau phosphorylation to alterations in cognitive function, through dysfunction of the cholinergic system. The goal of this review is to summarize the current knowledge on the role of lipids in Alzheimer’s disease and their relationship with the basal cholinergic system, as well as potential disease-modifying therapies.

Cholesterol in Brain Development and Perinatal Brain Injury: More than a Building Block

The central nervous system (CNS) is enriched with important classes of lipids, in which cholesterol is known to make up a major portion of myelin sheaths, besides being a structural and functional unit of CNS cell membranes. Unlike in the adult brain, where the cholesterol pool is relatively stable, cholesterol is synthesized and accumulated at the highest rate in the developing brain to meet the needs of rapid brain growth at this stage, which is also a critical period for neuroplasticity. In addition to its biophysical role in membrane organization, cholesterol is crucial for brain development due to its involvement in brain patterning, myelination, neuronal differentiation, and synaptogenesis. Thus any injuries to the immature brain that affect cholesterol homeostasis may have long-term adverse neurological consequences. In this review, we describe the unique features of brain cholesterol biosynthesis and metabolism, cholesterol trafficking between different cell types, and highlight cholesterol-dependent biological processes during brain maturation. We also discuss the association of impaired cholesterol homeostasis with several forms of perinatal brain disorders in term and preterm newborns, including hypoxic-ischemic encephalopathy. Strategies targeting the cholesterol pathways may open new avenues for the diagnosis and treatment of developmental brain injury.

Intestine-enriched apolipoprotein b orthologs are required for stem cell progeny differentiation and regeneration in planarians

Lipid metabolism plays an instructive role in regulating stem cell state and differentiation. However, the roles of lipid mobilization and utilization in stem cell-driven regeneration are unclear. Planarian flatworms readily restore missing tissue due to injury-induced activation of pluripotent somatic stem cells called neoblasts. Here, we identify two intestine-enriched orthologs of apolipoprotein b, apob-1 and apob-2, which mediate transport of neutral lipid stores from the intestine to target tissues including neoblasts, and are required for tissue homeostasis and regeneration. Inhibition of apob function by RNAi causes head regression and lysis in uninjured animals, and delays body axis re-establishment and regeneration of multiple organs in amputated fragments. Furthermore, apob RNAi causes expansion of the population of differentiating neoblast progeny and dysregulates expression of genes enriched in differentiating and mature cells in eight major cell type lineages. We conclude that intestine-derived lipids serve as a source of metabolites required for neoblast progeny differentiation.

Platycodin D inhibits autophagy and increases glioblastoma cell death via LDLR upregulation

Targeting autophagy is a promising therapeutic approach in cancer therapy. Here, we screened 30 traditional herbal medicines to identify novel autophagy regulators and found that Platycodon grandiflorus (PG) and platycodin D (PD), a triterpenoid saponin from PG, inhibited autophagy in glioblastoma multiforme (GBM) cells. Mechanistically, PD prevented lysosomal degradation and the fusion between autophagosomes and lysosomes by inducing sequestration of free cholesterol in lysosomes. The autophagy inhibitory effect of PD was mimicked by both genetic and pharmacological inhibition of Niemann-Pick C1 (NPC1), which exports low-density lipoprotein (LDL)-derived cholesterol from lysosomes. Moreover, PD promoted the uptake of exogenous LDL cholesterol via upregulation of LDL receptor (LDLR), leading to further accumulation of cholesterol within lysosomes and GBM cell death. Importantly, these phenomena were more pronounced in LDLR-overexpressing GBM cells than in normal astrocytes. Finally, blockade of cholesterol uptake by LDLR knockdown reversed the PD-induced inhibition of autophagy and GBM cell growth. Our study proposes that PD could be a potent anti-GBM drug by disrupting cholesterol trafficking and autophagy.

Lipid droplets in the nervous system

Lipid droplets are dynamic intracellular lipid storage organelles that respond to the physiological state of cells. In addition to controlling cell metabolism, they play a protective role for many cellular stressors, including oxidative stress. Despite prior descriptions of lipid droplets appearing in the brain as early as a century ago, only recently has the role of lipid droplets in cells found in the brain begun to be understood. Lipid droplet functions have now been described for cells of the nervous system in the context of development, aging, and an increasing number of neuropathologies. Here, we review the basic mechanisms of lipid droplet formation, turnover, and function and discuss how these mechanisms enable lipid droplets to function in different cell types of the nervous system under healthy and pathological conditions.

Phytosterols: Targeting Neuroinflammation in Neurodegeneration

Plant-derived sterols, phytosterols, are well known for their cholesterol-lowering activity in serum and their anti-inflammatory activities. Recently, phytosterols have received considerable attention due to their beneficial effects on various non-communicable diseases, and recommended use as daily dietary components. The signaling pathways mediated in the brain by phytosterols have been evaluated, but little is known about their effects on neuroinflammation, and no clinical studies have been undertaken on phytosterols of interest. In this review, we discuss the beneficial roles of phytosterols, including their attenuating effects on inflammation, blood cholesterol levels, and hallmarks of the disease, and their regulatory effects on neuroinflammatory disease pathways. Despite recent advancements made in phytosterol pharmacology, some critical questions remain unanswered. Therefore, we have tried to highlight the potential of phytosterols as viable therapeutics against neuroinflammation and to direct future research with respect to clinical applications.

Circulating lipids and glioma risk: results from the UK Biobank, Nurses' Health Study, and Health Professionals Follow-Up Study

PURPOSE

Evidence is mixed on whether cholesterol plays a role in the pathogenesis of glioma. We explored the associations between circulating lipids and glioma risk in three prospective cohorts.

METHODS

Using prospective data from the UK Biobank, we examined the associations of total cholesterol (TC), high- and low-density lipoprotein cholesterol (HDL-C, LDL-C), and triglycerides (TG) with glioma risk in multivariable (MV)-adjusted Cox proportional hazards models. Within the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS), we carried out a matched, nested case-control study to examine these same associations.

RESULTS

In the UK Biobank, 490 gliomas accrued over 2,358,964 person-years. TC was not significantly associated with glioma risk (MV HR = 1.20, 95% CI 0.89-1.61 for highest quartile vs. lowest, p-trend = 0.24). In 4-year lagged analyses (n = 229), higher TC was associated with significantly higher risk of glioma in men (MV HR = 2.26, 95% CI 1.32-3.89, p-trend = 0.002) but not women (MV HR = 1.28, 95% CI 0.61-2.68, p-trend = 0.72); similar findings emerged for HDL-C and, to a lesser extent, LDL-C. In the NHS/HPFS, no significant associations were found between cholesterol and glioma risk. No significant associations were identified for TG.

CONCLUSION

In the UK Biobank, higher prediagnostic TC and HDL-C levels were associated with higher risk of glioma in 4-year lagged analyses, but not in non-lagged analyses, in men only. These findings merit further investigation, given that there are few risk factors and no reliable biomarkers of risk identified for glioma.

Maturation of the Olfactory Sensory Neuron and Its Cilia

Olfactory sensory neurons (OSNs) are bipolar neurons, unusual because they turn over continuously and have a multiciliated dendrite. The extensive changes in gene expression accompanying OSN differentiation in mice are largely known, especially the transcriptional regulators responsible for altering gene expression, revealing much about how differentiation proceeds. Basal progenitor cells of the olfactory epithelium transition into nascent OSNs marked by Cxcr4 expression and the initial extension of basal and apical neurites. Nascent OSNs become immature OSNs within 24-48 h. Immature OSN differentiation requires about a week and at least 2 stages. Early-stage immature OSNs initiate expression of genes encoding key transcriptional regulators and structural proteins necessary for further neuritogenesis. Late-stage immature OSNs begin expressing genes encoding proteins important for energy production and neuronal homeostasis that carry over into mature OSNs. The transition to maturity depends on massive expression of one allele of one odorant receptor gene, and this results in expression of the last 8% of genes expressed by mature OSNs. Many of these genes encode proteins necessary for mature function of axons and synapses or for completing the elaboration of non-motile cilia, which began extending from the newly formed dendritic knobs of immature OSNs. The cilia from adjoining OSNs form a meshwork in the olfactory mucus and are the site of olfactory transduction. Immature OSNs also have a primary cilium, but its role is unknown, unlike the critical role in proliferation and differentiation played by the primary cilium of the olfactory epithelium's horizontal basal cell.

Dysregulated Brain Cholesterol Metabolism Is Linked to Neuroinflammation in Huntington's Disease

Huntington's disease is an autosomal-dominant, neurodegenerative disorder caused by a CAG repeat expansion in exon-1 of the huntingtin gene. Alterations in cholesterol metabolism and distribution have been reported in Huntington's disease, including abnormal interactions between mutant huntingtin and sterol regulatory element-binding proteins, decreased levels of apolipoprotein E/cholesterol/low-density lipoprotein receptor complexes, and alterations in the synthesis of ATP-binding cassette transporter A1. Plasma levels of 24S-hydroxycholestrol, a key intermediary in cholesterol metabolism and a possible marker in neurodegenerative diseases, decreased proportionally to the degree of caudate nucleus atrophy. The interaction of mutant huntingtin with sterol regulatory element-binding proteins is of particular interest given that sterol regulatory element-binding proteins play a dual role: They take part in lipid and cholesterol metabolism, but also in the inflammatory response that induces immune cell migration as well as toxic effects, particularly in astrocytes. This work summarizes current evidence on the metabolic and immune implications of sterol regulatory element-binding protein dysregulation in Huntington's disease, highlighting the potential use of drugs that modulate these alterations. © 2020 International Parkinson and Movement Disorder Society.

Diabetes as a risk factor for Alzheimer's disease in the Middle East and its shared pathological mediators

The incidence of Alzheimer's disease (AD) has risen exponentially worldwide over the past decade. A growing body of research indicates that AD is linked to diabetes mellitus (DM) and suggests that impaired insulin signaling acts as a crucial risk factor in determining the progression of this devastating disease. Many studies suggest people with diabetes, especially type 2 diabetes, are at higher risk of eventually developing Alzheimer's dementia or other dementias. Despite nationwide efforts to increase awareness, the prevalence of Diabetes Mellitus (DM) has risen significantly in the Middle East and North African (MENA) region which might be due to rapid urbanization, lifestyle changes, lack of physical activity and rise in obesity. Growing body of evidence indicates that DM and AD are linked because both conditions involve impaired glucose homeostasis and altered brain function. Current theories and hypothesis clearly implicate that defective insulin signaling in the brain contributes to synaptic dysfunction and cognitive deficits in AD. In the periphery, low-grade chronic inflammation leads to insulin resistance followed by tissue deterioration. Thus insulin resistance acts as a bridge between DM and AD. There is pressing need to understand on how DM increases the risk of AD as well as the underlying mechanisms, due to the projected increase in age related disorders. Here we aim to review the incidence of AD and DM in the Middle East and the possible link between insulin signaling and ApoE carrier status on Aβ aggregation, tau hyperphosphorylation, inflammation, oxidative stress and mitochondrial dysfunction in AD. We also critically reviewed mutation studies in Arab population which might influence DM induced AD. In addition, recent clinical trials and animal studies conducted to evaluate the efficiency of anti-diabetic drugs have been reviewed.

Targeting cholesterol metabolism in glioblastoma: a new therapeutic approach in cancer therapy

Glioblastoma multiforme (GBM) is the most aggressive malignant brain tumor known with a poor survival rate despite current advances in the field of cancer. Additional research into the pathophysiology of GBM is urgently needed given the devastating nature of this disease. Recent studies have revealed the unique cellular physiology of GBM cells as compared with healthy astrocytes. Intriguingly, GBM cells are incapable of de novo cholesterol synthesis via the mevalonate pathway. Thus, the survival of GBM cells depends on cholesterol uptake via low-density lipoprotein receptors (LDLRs) in the form of apolipoprotein-E-containing lipoproteins and ATP-binding cassette transporter A1 (ABCA1) that efflux surplus cholesterol out of cells. Liver X receptors regulate intracellular cholesterol levels in neurons and healthy astrocytes through changes in the expression of LDLR and ABCA1 in response to cholesterol and its derivatives. In GBM cells, due to the dysregulation of this surveillance pathway, there is an accumulation of intracellular cholesterol. Furthermore, intracellular cholesterol regulates temozolomide-induced cell death in glioblastoma cells via accumulation and activation of death receptor 5 in plasma membrane lipid rafts. The mevalonate pathway and autophagy flux are also fundamentally related with implications for cell health and death. Thus, via cholesterol metabolism, the mevalonate pathway may be a crucial player in the pathogenesis and treatment of GBM where our current understanding is still lacking. Targeting cholesterol metabolism in GBM may hold promise as a novel adjunctive clinical therapy for this devastating cancer.

Cholesterol Metabolism: A Potential Therapeutic Target in Glioblastoma

Glioblastoma is a highly lethal adult brain tumor with no effective treatments. In this review, we discuss the potential to target cholesterol metabolism as a new strategy for treating glioblastomas. Twenty percent of cholesterol in the body is in the brain, yet the brain is unique among organs in that it has no access to dietary cholesterol and must synthesize it de novo. This suggests that therapies targeting cholesterol synthesis in brain tumors might render their effects without compromising cell viability in other organs. We will describe cholesterol synthesis and homeostatic feedback pathways in normal brain and brain tumors, as well as various strategies for targeting these pathways for therapeutic intervention.

Role of cholesterol and sphingolipids in brain development and neurological diseases

Brain is a vital organ of the human body which performs very important functions such as analysis, processing, coordination, and execution of electrical signals. For this purpose, it depends on a complex network of nerves which are ensheathed in lipids tailored myelin; an abundant source of lipids in the body. The nervous system is enriched with important classes of lipids; sphingolipids and cholesterol which compose the major portion of the brain particularly in the form of myelin. Both cholesterol and sphingolipids are embedded in the microdomains of membrane rafts and are functional units of the neuronal cell membrane. These molecules serve as the signaling molecules; hold important roles in the neuronal differentiation, synaptogenesis, and many others. Thus, their adequate provision and active metabolism are of crucial importance in the maintenance of physiological functions of brain and body of an individual. In the present review, we have highlighted the physiological roles of cholesterol and sphingolipids in the development of the nervous system as well as the association of their altered metabolism to neurological and neurodegenerative diseases.

Cytocidal effects of arenobufagin and hellebrigenin, two active bufadienolide compounds, against human glioblastoma cell line U-87

Glioblastoma is the most common and lethal intracranial tumor type, characterized by high angiogenic and infiltrative capacities. To provide a novel insight into therapeutic strategies against glioblastoma, the cytotoxicity of arenobufagin and hellebrigenin was investigated in the human glioblastoma cell line, U-87. Similar dose-dependent cytotoxicity was observed in the cells, whereas no detectable toxicity was confirmed in mouse primary astrocytes. Treatment with each drug downregulated the expression levels of Cdc25C, Cyclin B1 and survivin, which occurred in parallel with G₂/M phase arrest. Necrotic-like cell death was only observed in the cells treated with a relatively high concentration (>100 ng/ml). These results indicate that the two drugs exhibited distinct cytotoxicity against cancerous glial cells with high potency and selectivity, suggesting that growth inhibition associated with G₂/M phase arrest and/or necrosis were attributed to their toxicities. Activation of the p38 mitogen activated protein kinase (MAPK) signaling pathway was also observed in treated cells. Notably, a specific inhibitor of p38 MAPK, SB203580, itself caused a significant decrease in cell viability, and further enhanced the cytotoxicity of the two drugs, suggesting an important pro-survival role for p38 MAPK. Given that p38 MAPK serves an essential role in promoting glioblastoma cell survival, developing a novel combination regimen of arenobufagin/hellebrigenin plus a p38 MAPK inhibitor may improve the efficacy of the two drugs, and may provide more therapeutic benefits to patients with glioblastoma. The qualitative assessment demonstrated the existence of arenobufagin in the cerebrospinal fluid of arenobufagin-treated rats, supporting its clinical application.

Involvement of Intracellular Cholesterol in Temozolomide-Induced Glioblastoma Cell Death

Glioblastoma (GBM) still carries a poor prognosis due to the refractoriness against antitumor drugs. Temozolomide (TMZ), one of the few standard therapy drugs against GBM worldwide, has only limited effect due to acquired TMZ resistance of GBM. Therefore, development of novel therapeutic methods to overcome the TMZ resistance of GBM is urgent. The brain is the most cholesterol-rich organ in the human body, so modulation of cholesterol in tumor cells originating from the brain including GBM may be a tumor-specific therapeutic strategy including enhancement of TMZ effects. The unique lipid metabolism of glioma has recently been reported, but the involvement of intracellular cholesterol in TMZ therapy is yet to be fully elucidated. This review summarizes the effect of modulation of intracellular cholesterol level on cancer therapy including GBM treatment and the implications for TMZ therapy. Our recent findings about the involvement of intracellular cholesterol in TMZ-induced GBM cell death are described.

Enteric Glial Dysfunction Evoked by Apolipoprotein E Deficiency Contributes to Delayed Gastric Emptying

BACKGROUND AND AIM

Diabetes is the main cause of gastroparesis accompanying decreased neuronal nitric oxide synthase (nNOS) in myenteric ganglia of the stomach. Decreased nNOS expression in the stomach also results from defects in apolipoprotein E (ApoE), which is secreted by astrocytes and has neuroprotective effects on the central nervous system. However, the roles of ApoE and enteric glial cells on gastric motility are uncertain. In this study, ApoE and enteric glial cell alterations in gastroparesis were investigated.

METHODS

Type 2 diabetic (db/db) mice and ApoE-knockout mice were analyzed. Gastric emptying was measured using the ¹³C acetic acid breath test. Expression levels of the pan-neuronal marker, protein gene product 9.5 (PGP 9.5), and glial marker, glial fibrillary acidic protein (GFAP) were examined by immunohistochemistry. Neural stem cells (NSCs) were injected into the gastric antral wall of ApoE-knockout mice.

RESULTS

Delayed gastric emptying was observed in 27% of db/db mice with significant decreases in serum ApoE levels and GFAP expression in the gastric antrum. Gastric emptying was also delayed in ApoE-knockout mice, with a significant decrease in GFAP expression, but no change in PGP 9.5 expression. Transplantation of NSCs improved gastric emptying in ApoE-knockout mice through supplementation of GFAP-positive cells.

CONCLUSIONS

Our results suggest that decreased enteric glial cells in ApoE-knockout mice are crucial for development of delayed gastric emptying, and NSC transplantation is effective in restoring myenteric ganglia and gastric motility.

Cholesterol as a modifying agent of the neurovascular unit structure and function under physiological and pathological conditions

The brain, demanding constant level of cholesterol, precisely controls its synthesis and homeostasis. The brain cholesterol pool is almost completely separated from the rest of the body by the functional blood-brain barrier (BBB). Only a part of cholesterol pool can be exchanged with the blood circulation in the form of the oxysterol metabolites such, as 27-hydroxycholesterol (27-OHC) and 24S-hydroxycholesterol (24S-OHC). Not only neurons but also blood vessels and neuroglia, constituting neurovascular unit (NVU), are crucial for the brain cholesterol metabolism and undergo precise regulation by numerous modulators, metabolites and signal molecules. In physiological conditions maintaining the optimal cholesterol concentration is important for the energetic metabolism, composition of cell membranes and myelination. However, a growing body of evidence indicates the consequences of the cholesterol homeostasis dysregulation in several pathophysiological processes. There is a causal relationship between hypercholesterolemia and 1) development of type 2 diabetes due to long-term high-fat diet consumption, 2) significance of the oxidative stress consequences for cerebral amyloid angiopathy and neurodegenerative diseases, 3) insulin resistance on progression of the neurodegenerative brain diseases. In this review, we summarize the current state of knowledge concerning the cholesterol influence upon functioning of the NVU under physiological and pathological conditions.

Nuclear Localization of Apolipoprotein E4: A New Trick for an Old Protein

One of the most important genetic risk factors for late-onset Alzheimer's Disease (AD) is harboring the ApoE4 allele. Much is known regarding the functions of the ApoE4 protein including cholesterol transport in the CNS and a critical role in clearing beta-amyloid deposits in the AD brain. However, recent studies demonstrating the nuclear localization suggest a novel function beyond the classical known actions of ApoE4. The purpose of the current review is to examine how this secreted protein traffics to the nucleus and to discuss possible outcomes of nuclear localization in the CNS. It is suggested that proteolytic fragmentation of ApoE4 is a key step leading to nuclear localization and the outcome of this event is to initiate transcription of various genes involved in inflammation and cell death. Therefore, the nuclear localization and induction of gene expression may provide a link between harboring the ApoE4 allele and enhanced dementia risk observed in AD.

Internalization of scavenger receptor ligands by cortical neurons

Scavenger receptors (SRs) are a family of receptors displaying affinity for a wide variety of ligands including modified lipoproteins. SRs may play a range of physiological functions including intracellular transport, lipid transport and pathogen clearance. The role of SRs has been documented in pathologies such as atherosclerosis and Alzheimer's disease. Although most studies on SRs have focused on macrophages, they are also present in other cells like endothelium, smooth muscles and brain tissue. Within brain, due to its functional similarity, SRs have been studied mostly in microglia. However, in situ images from Allen's brain atlas suggest SRs are abundant in neurons. In this study we have used two fluorophore labeled well characterized SR ligand, maleylated-BSA (MBSA) and polyguanylic acid (poloyG) to probe acute cortical slices. Our data indicate that within cortex, neurons avidly endocytose both ligands. Thus in cerebral cortex neurons may have higher number of functional SRs on the surface than other cell-types.

Role of LRP1 in the pathogenesis of Alzheimer's disease: evidence from clinical and preclinical studies

Among the LDL receptor (LDLR) family members, the roles of LDLR-related protein (LRP)1 in the pathogenesis of Alzheimer's disease (AD), especially late-onset AD, have been the most studied by genetic, neuropathological, and biomarker analyses (clinical studies) or cellular and animal model systems (preclinical studies) over the last 25 years. Although there are some conflicting reports, accumulating evidence from preclinical studies indicates that LRP1 not only regulates the metabolism of amyloid-β peptides (Aβs) in the brain and periphery, but also maintains brain homeostasis, impairment of which likely contributes to AD development in Aβ-independent manners. Several preclinical studies have also demonstrated an involvement of LRP1 in regulating the pathogenic role of apoE, whose gene is the strongest genetic risk factor for AD. Nonetheless, evidence from clinical studies is not sufficient to conclude how LRP1 contributes to AD development. Thus, despite very promising results from preclinical studies, the role of LRP1 in AD pathogenesis remains to be further clarified. In this review, we discuss the potential mechanisms underlying how LRP1 affects AD pathogenesis through Aβ-dependent and -independent pathways by reviewing both clinical and preclinical studies. We also discuss potential therapeutic strategies for AD by targeting LRP1.

Lysophosphatidylcholine export by human ABCA7

The ATP-binding cassette transporter A7 (ABCA7), which is highly expressed in the brain, is associated with the pathogenesis of Alzheimer's disease (AD). However, the physiological function of ABCA7 and its transport substrates remain unclear. Immunohistochemical analyses of human brain sections from AD and non-AD subjects revealed that ABCA7 is expressed in neuron and microglia cells in the cerebral cortex. The transport substrates and acceptors were identified in BHK/ABCA7 cells and compared with those of ABCA1. Like ABCA1, ABCA7 exported choline phospholipids in the presence of apoA-I and apoE; however, unlike ABCA1, cholesterol efflux was marginal. Lipid efflux by ABCA7 was saturated by 5μg/ml apoA-I and was not dependent on apoE isoforms, whereas efflux by ABCA1 was dependent on apoA-I up to 20μg/ml and apoE isoforms. Liquid chromatography-tandem mass spectrometry analyses revealed that the two proteins had different preferences for phospholipid export: ABCA7 preferred phosphatidylcholine (PC)≥lysoPC>sphingomyelin (SM)=phosphatidylethanolamine (PE), whereas ABCA1 preferred PC>>SM>PE=lysoPC. The major difference in the pattern of lipid peaks between ABCA7 and ABCA1 was the high lysoPC/PC ratio of ABCA7. These results suggest that lysoPC is one of the major transport substrates for ABCA7 and that lysoPC export may be a physiologically important function of ABCA7 in the brain.

Pathological vascular and inflammatory biomarkers of acute- and chronic-phase traumatic brain injury

Given the demand for developing objective methods for characterizing traumatic brain injury (TBI), research dedicated to evaluating putative biomarkers has burgeoned over the past decade. Since it is critical to elucidate the underlying pathological processes that underlie the higher diverse outcomes that follow neurotrauma, considerable efforts have been aimed at identifying biomarkers of both the acute- and chronic-phase TBI. Such information is not only critical for helping to elucidate the pathological changes that lead to poor long-term outcomes following TBI but it may also assist in the identification of possible prevention and interventions for individuals who sustain head trauma. In the current review, we discuss the potential role of vascular dysfunction and chronic inflammation in both acute- and chronic-phase TBI, and we also highlight existing studies that have investigated inflammation biomarkers associated with poorer injury outcome.

Biochemical effects of venlafaxine on astrocytes as revealed by 1H NMR-based metabolic profiling

As a serotonin–norepinephrine reuptake inhibitor [SNRI], venlafaxine is one of the most commonly prescribed clinical antidepressants, with a broad range of antidepressant effects.

ABCA1/ApoE/HDL Pathway Mediates GW3965-Induced Neurorestoration After Stroke

BACKGROUND AND PURPOSE

ATP-binding cassette transporter A1 (ABCA1) is a major reverse cholesterol transporter and plays critical role in the formation of brain high-density lipoprotein (HDL) cholesterol. Apolipoprotein E (ApoE) is the most abundant apolipoprotein and transports cholesterol into cells in brain. ABCA1 and ApoE are upregulated by liver-X receptors. Activation of liver-X receptors has neurorestorative benefit for stroke. The current study investigates whether ABCA1/ApoE/HDL pathway mediates GW3965, a synthetic dual liver-X receptor agonist, induced neurorestoration after stroke.

METHODS

Middle-aged male specific brain ABCA1-deficient (ABCA1^-B/-B) and floxed-control (ABCA1^fl/fl) mice were subjected to distal middle-cerebral artery occlusion (dMCAo) and gavaged with saline or GW3965 (10 mg/kg) or intracerebral infusion of artificial cerebrospinal fluid or human plasma HDL3 in ABCA1^-B/-B stroke mice, starting 24 hours after dMCAo and daily until euthanization 14 days after dMCAo.

RESULTS

No differences in the blood level of total cholesterol and triglyceride and lesion volume were found among the groups. Compared with ABCA1^fl/fl ischemic mice, ABCA1^-B/-B ischemic mice exhibited impairment functional outcome and decreased ABCA1/ApoE expression and decreased gray/white matter densities in the ischemic boundary zone 14 days after dMCAo. GW3965 treatment of ABCA1^fl/fl ischemic mice led to increased brain ABCA1/ApoE expression, concomitantly to increased blood HDL, gray/white matter densities and oligodendrocyte progenitor cell numbers in the ischemic boundary zone, as well as improved functional outcome 14 days after dMCAo. GW3965 treatment had negligible beneficial effects in ABCA1^-B/-B ischemic mice. However, intracerebral infusion of human plasma HDL3 significantly attenuated ABCA1^-B/-B-induced deficits. In vitro, GW3965 treatment (5 μM) increased ABCA1/synaptophysin level and neurite/axonal outgrowth in primary cortical neurons derived from ABCA1^fl/fl embryos, but not in neurons derived from ABCA1^-B/-B embryos. HDL treatment (80 μg/mL) attenuated the reduction of neurite/axonal outgrowth in neurons derived from ABCA1^-B/-B embryos.

CONCLUSIONS

ABCA1/ApoE/HDL pathway, at least partially, contributes to GW3965-induced neurorestoration after stroke.

An LXR-Cholesterol Axis Creates a Metabolic Co-Dependency for Brain Cancers

Small-molecule inhibitors targeting growth factor receptors have failed to show efficacy for brain cancers, potentially due to their inability to achieve sufficient drug levels in the CNS. Targeting non-oncogene tumor co-dependencies provides an alternative approach, particularly if drugs with high brain penetration can be identified. Here we demonstrate that the highly lethal brain cancer glioblastoma (GBM) is remarkably dependent on cholesterol for survival, rendering these tumors sensitive to Liver X receptor (LXR) agonist-dependent cell death. We show that LXR-623, a clinically viable, highly brain-penetrant LXRα-partial/LXRβ-full agonist selectively kills GBM cells in an LXRβ- and cholesterol-dependent fashion, causing tumor regression and prolonged survival in mouse models. Thus, a metabolic co-dependency provides a pharmacological means to kill growth factor-activated cancers in the CNS.

Astrocyte arachidonate and palmitate uptake and metabolism is differentially modulated by dibutyryl-cAMP treatment

Astrocytes play a vital role in brain lipid metabolism; however the impact of the phenotypic shift in astrocytes to a reactive state on arachidonic acid metabolism is unknown. Therefore, we determined the impact of dibutyryl-cAMP (dBcAMP) treatment on radiolabeled arachidonic acid ([1-(14)C]20:4n-6) and palmitic acid ([1-(14)C]16:0) uptake and metabolism in primary cultured murine cortical astrocytes. In dBcAMP treated astrocytes, total [1-(14)C]20:4n-6 uptake was increased 1.9-fold compared to control, while total [1-(14)C]16:0 uptake was unaffected. Gene expression of long-chain acyl-CoA synthetases (Acsl), acyl-CoA hydrolase (Acot7), fatty acid binding protein(s) (Fabp) and alpha-synuclein (Snca) were determined using qRT-PCR. dBcAMP treatment increased expression of Acsl3 (4.8-fold) and Acsl4 (1.3-fold), which preferentially use [1-(14)C]20:4n-6 and are highly expressed in astrocytes, consistent with the increase in [1-(14)C]20:4n-6 uptake. However, expression of Fabp5 and Fabp7 were significantly reduced by 25% and 45%, respectively. Acot7 (20%) was also reduced, suggesting dBcAMP treatment favors acyl-CoA formation. dBcAMP treatment enhanced [1-(14)C]20:4n-6 (2.2-fold) and [1-(14)C]16:0 (1.6-fold) esterification into total phospholipids, but the greater esterification of [1-(14)C]20:4n-6 is consistent with the observed uptake through increased Acsl, but not Fabp expression. Although total [1-(14)C]16:0 uptake was not affected, there was a dramatic decrease in [1-(14)C]16:0 in the free fatty acid pool as esterification into the phospholipid pool was increased, which is consistent with the increase in Acsl3 and Acsl4 expression. In summary, our data demonstrates that dBcAMP treatment increases [1-(14)C]20:4n-6 uptake in astrocytes and this increase appears to be due to increased expression of Acsl3 and Acsl4 coupled with a reduction in Acot7 expression.

Evidence for altered cholesterol metabolism in Huntington's disease post mortem brain tissue

AIMS

Cholesterol plays an essential role in membrane structure and function, being especially important in the brain. Alteration of brain cholesterol synthesis and metabolism has been demonstrated in several Huntington's disease (HD) mouse and cell models; however, less is known about these alterations in human tissue. This study aimed to identify alterations to cholesterol synthetic and metabolic pathways in human HD brain tissue.

METHODS

A broad range of cholesterol synthetic precursors, metabolites and oxidation products were measured by gas chromatography-tandem mass spectrometry in five regions of human post mortem HD brain and compared with age- and sex-matched control tissues. The level of enzymes that regulate cholesterol homeostasis, cholesterol 24-hydroxylase and delta(24)-sterol reductase were investigated by Western blotting and qPCR in putamen.

RESULTS

The most significant changes were localized to the putamen, where a 60% decrease in 24(S)-hydroxycholesterol, 30% increase in cholesterol and 100-200% increase in synthetic precursors (lathosterol, zymosterol and desmosterol) was detected. The enzymes cholesterol 24-hydroxylase and delta(24)-sterol reductase were also significantly decreased in HD putamen as compared with control tissues. Free radical-generated cholesterol oxidation products 7-keto cholesterol and 7β-hydroxycholesterol were also increased by 50-70% in HD putamen.

CONCLUSION

Human HD brain has significantly decreased cholesterol metabolism and disrupted cholesterol homeostasis. Our data also indicate that lipid oxidative stress accompanies HD pathology.

Apolipoprotein E polymorphism is associated with susceptibility to schizophrenia among Saudis

INTRODUCTION

Apolipoprotein E (APOE) genotypes influence the phenotype of several neurodegenerative disorders including Alzheimer's and Parkinson disease and may affect schizophrenia pathogenesis. This study was undertaken to determine the association between APOE gene polymorphisms and schizophrenia in the Saudi population.

MATERIAL AND METHODS

APOE allele and genotype frequencies were studied in 380 Saudi subjects including schizophrenia patients and matched controls using polymerase chain reaction (PCR) and reverse-hybridization techniques.

RESULTS

The frequencies of the APOE allele ε2 and genotypes ε2/ε3 and ε2/ε4 were significantly higher in the schizophrenia patients as compared to controls, suggesting that the ε2 allele and its heterozygous genotypes may increase the susceptibility to schizophrenia. In contrast, the frequencies of the ε3 allele and ε3/ε3 genotype were lower in patients as compared to controls, suggesting a protective effect of APOE ε3 for schizophrenia. This study indicated that APOE ε4 was differentially associated with schizophrenia depending on the symptoms as the frequency of the ε4 allele was significantly higher in schizophrenia patients with positive symptoms. By contrast, no significant association between APOE ε4 and schizophrenia patients with negative symptoms was observed. Genotypes ε2/ε2 and ε4/ε4 were absent in patients and controls. Moreover, the age of onset was significantly lower in patients with the APOE ε2/ε3 genotype. There was no significant difference in the frequencies of APOE alleles and genotypes between male and female schizophrenia patients.

CONCLUSIONS

The results of this study clearly show that APOE alleles and genotypes are associated with risk of developing schizophrenia and early age of onset in Saudis.

Neurite outgrowth stimulation by n-3 and n-6 PUFAs of phospholipids in apoE-containing lipoproteins secreted from glial cells

PUFAs, which account for 25-30% of the total fatty acids in the human brain, are important for normal brain development and cognitive function. However, it remains unclear how PUFAs are delivered to neurons and exert their effects. In this study, we demonstrated that n-3 and n-6 PUFAs added to the medium are incorporated into membrane phospholipids of primary glial cells from rat cortices, and then secreted as the fatty acid moiety of phospholipids in apoE-containing lipoproteins (LpEs). Tandem mass spectrometry analysis further showed that LpEs secreted from glial cells contain a variety of metabolites of PUFAs produced in glial cells by elongation and unsaturation. LpEs are absorbed by endocytosis into neurons via LDL receptor-related protein 1. LpE-containing n-3 and n-6 PUFAs exhibit a strong effect on neurite outgrowth of hippocampal neurons by increasing the number of branches. This study sheds light on the novel role of LpEs in the central nervous system and also a novel pathway in which PUFAs act on neurons.

Disorders of cholesterol metabolism and their unanticipated convergent mechanisms of disease

Cholesterol plays a key role in many cellular processes, and is generated by cells through de novo biosynthesis or acquired from exogenous sources through the uptake of low-density lipoproteins. Cholesterol biosynthesis is a complex, multienzyme-catalyzed pathway involving a series of sequentially acting enzymes. Inherited defects in genes encoding cholesterol biosynthetic enzymes or other regulators of cholesterol homeostasis result in severe metabolic diseases, many of which are rare in the general population and currently without effective therapy. Historically, these diseases have been viewed as discrete disorders, each with its own genetic cause and distinct pathogenic cascades that lead to its specific clinical features. However, studies have recently shown that three of these diseases have an unanticipated mechanistic convergence. This surprising finding is not only shedding light on details of cellular cholesterol homeostasis but also suggesting novel approaches to therapy.

1H NMR-based metabolic profiling reveals the effects of fluoxetine on lipid and amino acid metabolism in astrocytes

Fluoxetine, a selective serotonin reuptake inhibitor (SSRI), is a prescribed and effective antidepressant and generally used for the treatment of depression. Previous studies have revealed that the antidepressant mechanism of fluoxetine was related to astrocytes. However, the therapeutic mechanism underlying its mode of action in astrocytes remains largely unclear. In this study, primary astrocytes were exposed to 10 µM fluoxetine; 24 h post-treatment, a high-resolution proton nuclear magnetic resonance (¹H NMR)-based metabolomic approach coupled with multivariate statistical analysis was used to characterize the metabolic variations of intracellular metabolites. The orthogonal partial least-squares discriminant analysis (OPLS-DA) score plots of the spectra demonstrated that the fluoxetine-treated astrocytes were significantly distinguished from the untreated controls. In total, 17 differential metabolites were identified to discriminate the two groups. These key metabolites were mainly involved in lipids, lipid metabolism-related molecules and amino acids. This is the first study to indicate that fluoxetine may exert antidepressant action by regulating the astrocyte’s lipid and amino acid metabolism. These findings should aid our understanding of the biological mechanisms underlying fluoxetine therapy.