Cholesterol and myelin biogenesis

FBXW7 regulates MYRF levels to control myelin capacity and homeostasis in the adult CNS

Myelin, along with the oligodendrocytes (OLs) that produce it, is essential for proper central nervous system (CNS) function in vertebrates. Although the accurate targeting of myelin to axons and its maintenance are critical for CNS performance, the molecular pathways that regulate these processes remain poorly understood. Through a combination of zebrafish genetics, mouse models, and primary OL cultures, we found FBXW7, a recognition subunit of an E3 ubiquitin ligase complex, is a regulator of adult myelination in the CNS. Loss of Fbxw7 in myelinating OLs resulted in increased myelin sheath lengths with no change in myelin thickness. As the animals aged, they developed progressive abnormalities including myelin outfolds, disrupted paranodal organization, and ectopic ensheathment of neuronal cell bodies with myelin. Through biochemical studies we found that FBXW7 directly binds and degrades the N-terminal of Myelin Regulatory Factor (N-MYRF), to control the balance between oligodendrocyte myelin growth and homeostasis.

The cytoplasmic tail of myelin protein zero induces morphological changes in lipid membranes

The major myelin protein expressed by the peripheral nervous system Schwann cells is protein zero (P0), which represents 50% of the total protein content in myelin. This 30-kDa integral membrane protein consists of an immunoglobulin (Ig)-like domain, a transmembrane helix, and a 69-residue C-terminal cytoplasmic tail (P0ct). The basic residues in P0ct contribute to the tight packing of myelin lipid bilayers, and alterations in the tail affect how P0 functions as an adhesion molecule necessary for the stability of compact myelin. Several neurodegenerative neuropathies are related to P0, including the more common Charcot-Marie-Tooth disease (CMT) and Dejerine-Sottas syndrome (DSS) as well as rare cases of motor and sensory polyneuropathy. We found that high P0ct concentrations affected the membrane properties of bicelles and induced a lamellar-to-inverted hexagonal phase transition, which caused bicelles to fuse into long, protein-containing filament-like structures. These structures likely reflect the formation of semicrystalline lipid domains with potential relevance for myelination. Not only is P0ct important for stacking lipid membranes, but time-lapse fluorescence microscopy also shows that it might affect membrane properties during myelination. We further describe recombinant production and low-resolution structural characterization of full-length human P0. Our findings shed light on P0ct effects on membrane properties, and with the successful purification of full-length P0, we have new tools to study the role of P0 in myelin formation and maintenance in vitro.

Schwann Cell Development and Myelination

Glial cells in the peripheral nervous system (PNS), which arise from the neural crest, include axon-associated Schwann cells (SCs) in nerves, synapse-associated SCs at the neuromuscular junction, enteric glia, perikaryon-associated satellite cells in ganglia, and boundary cap cells at the border between the central nervous system (CNS) and the PNS. Here, we focus on axon-associated SCs. These SCs progress through a series of formative stages, which culminate in the generation of myelinating SCs that wrap large-caliber axons and of nonmyelinating (Remak) SCs that enclose multiple, small-caliber axons. In this work, we describe SC development, extrinsic signals from the axon and extracellular matrix (ECM) and the intracellular signaling pathways they activate that regulate SC development, and the morphogenesis and organization of myelinating SCs and the myelin sheath. We review the impact of SCs on the biology and integrity of axons and their emerging role in regulating peripheral nerve architecture. Finally, we explain how transcription and epigenetic factors control and fine-tune SC development and myelination.

Exploring the Relationship Between Atorvastatin and Memory Loss: A Comprehensive Analysis Integrating Real-World Pharmacovigilance and Mendelian Randomization

BACKGROUND AND OBJECTIVE

Atorvastatin is a drug widely used to prevent cardiovascular and cerebrovascular diseases. Current observational studies suggest that atorvastatin may be associated with cognitive dysfunction (especially memory loss). However, some studies have suggested that dyslipidemia may be an important factor in cognitive dysfunction. The purpose of this study was to perform a pharmacovigilance analysis using real-world data from the US Food and Drug Administration's Adverse Event Reporting System (FAERS) to assess whether memory loss is an adverse effect of atorvastatin and to further clarify its causality through Mendelian randomization (MR).

METHODS

We extracted real-world data from the FAERS database (Quarter 1 2004 to Quarter 1 2023). Disproportionality analysis methods and measures of association such as the reporting odds ratio (OR), proportional reporting ratio, Bayesian confidence interval progressive neural network, and polynomial Gamma Poisson distribution reduction were used to assess whether memory loss was an adverse effect of atorvastatin. In addition, we used MR to evaluate causality in depth.

RESULTS

In the pharmacovigilance analysis of atorvastatin, we extracted four datasets of clinical symptoms associated with memory loss from the FAERS database [Amnesia (n = 1196), Memory impairment (n = 840), Transient global amnesia (n = 38), and Retrograde amnesia (n = 9)]. The reporting OR, proportional reporting ratio, Bayesian confidence interval progressive neural network, and Gamma Poisson distribution reduction all showed positive results for amnesia, transient global amnesia, and retrograde amnesia, while the reporting OR and Bayesian confidence interval progressive neural network also showed positive results for memory disorders. Thus, memory loss was a frequent side effect of atorvastatin. The MR analyses were used to further evaluate the association between statins and memory loss. The results of the MR analysis (statins and memory loss) are as follows: Ivw (mre) (β = 0.11 [OR = 1.11], P = 0.01 < 0.05) and the OR and β directions of MR-Egger and weighted mode were the same. The results of the MR analysis (statins and mitochondrial DNA copy number) are as follows: Ivw(mre) (β = -0.03 [OR = 0.96], P < 0.01) and the OR and β direction of MR-Egger and weighted mode are the same. The results of the MR analysis (DNA copy number and memory loss) are as follows: Ivw(β = - 0.06 [OR = 0.94], P = 0.04 < 0.05) and the OR and β direction of MR-Egger and weighted mode were the same. The pleiotropy test did not find horizontal diversity in our results.

CONCLUSIONS

This study suggests that memory loss is a notable adverse event associated with atorvastatin and provides evidence indicating a potential causal relationship between atorvastatin and memory loss. We also found that statins may further affect memory by affecting mitochondrial function. Therefore, in the clinical use of atorvastatin, it is important to carefully monitor the changes in cognitive function of patients. Second, a pharmacovigilance analysis combined with MR was used in this study to provide a new approach for the study of adverse drug reactions. This comprehensive analysis method helps to evaluate the safety of drugs and the risk of adverse reactions more comprehensively and provides doctors with a more accurate clinical decision-making basis.

Statin-related neurocognitive disorder: a real-world pharmacovigilance study based on the FDA adverse event reporting system

BACKGROUND

Concerns regarding statin-related neurocognitive disorders have emerged in recent years. However, previous studies have reported inconsistent results. We evaluated the association between statins and neurocognitive disorders using the FDA Adverse Event Reporting System (FAERS).

RESEARCH DESIGN AND METHODS

Data from 2004 to 2022 were obtained from the FAERS database. After deduplication and standardization of drug names, we extracted neurocognitive disorder event (NCDE) cases reported with statins as the suspected drugs. The significant association between statins and NCDE was evaluated using the reporting odds ratio (ROR) and information component.

RESULTS

In total, 6,959 NCDE cases with statins as the primary suspected drugs were identified. Signals were detected in pravastatin (ROR, 1.49; 95% CI: 1.32-1.67), atorvastatin (ROR, 1.39; 95% CI: 1.34-1.44), and simvastatin (ROR, 1.31; 95% CI: 1.25-1.38). Age-stratified analysis showed that (1) in the population aged 65 years and older, signals were detected for atorvastatin, simvastatin, rosuvastatin, pravastatin, lovastatin, fluvastatin, and pitavastatin; and (2) in populations under 65 years of age, signals were detected for atorvastatin, simvastatin, rosuvastatin, pravastatin, and lovastatin.

CONCLUSIONS

This study suggests a significant association between the NCDE and statins, including atorvastatin, simvastatin, and pravastatin. The intensity of the association increased with age.

Novel insights into brain lipid metabolism in Alzheimer's disease: Oligodendrocytes and white matter abnormalities

Alzheimer's disease (AD) is the most common cause of dementia. A genome-wide association study has shown that several AD risk genes are involved in lipid metabolism. Additionally, epidemiological studies have indicated that the levels of several lipid species are altered in the AD brain. Therefore, lipid metabolism is likely changed in the AD brain, and these alterations might be associated with an exacerbation of AD pathology. Oligodendrocytes are glial cells that produce the myelin sheath, which is a lipid-rich insulator. Dysfunctions of the myelin sheath have been linked to white matter abnormalities observed in the AD brain. Here, we review the lipid composition and metabolism in the brain and myelin and the association between lipidic alterations and AD pathology. We also present the abnormalities in oligodendrocyte lineage cells and white matter observed in AD. Additionally, we discuss metabolic disorders, including obesity, as AD risk factors and the effects of obesity and dietary intake of lipids on the brain.

Detection and evaluation of different morphological forms of Mycoplasma hominis in human semen

Recently discovered microcolonial forms of Mycoplasma hominis ( M. hominis ) and their impact on human spermatogenesis are studied. The spermatozoa of 125 fertile men (sperm donors; from Reprobank [Reproductive Tissue Bank, Moscow, Russia]) and of 93 patients with fertility problems (from the Federal State Budgetary Institution "Research Centre for Medical Genetics [RCMG]", Moscow, Russia) were used. Classical colonies of M. hominis and microcolonies were detected by molecular biological methods, culture of bacteria, and transmission electron microscopy. The unique structure of microcolonial cells, in which the cytoplasmic cylinder is surrounded by concentric electron-dense and electron-light layers with a periodicity of 12-14 nm, and the ability of microcolonial cells to attach to spermatozoa are shown. In patients with lower sperm quality, microcolonies of M. hominis were detected 2.5 times more frequently than classical colonies. The detection of microcolonies in the ejaculate and the frequent isolation of microcolonies from sperm samples of patients with fertility problems suggest that microcolonial cells may be one cause of infertility.

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.

Myelin lipid metabolism and its role in myelination and myelin maintenance

Myelin is a specialized cell membrane indispensable for rapid nerve conduction. The high abundance of membrane lipids is one of myelin's salient features that contribute to its unique role as an insulator that electrically isolates nerve fibers across their myelinated surface. The most abundant lipids in myelin include cholesterol, glycosphingolipids, and plasmalogens, each playing critical roles in myelin development as well as function. This review serves to summarize the role of lipid metabolism in myelination and myelin maintenance, as well as the molecular determinants of myelin lipid homeostasis, with an emphasis on findings from genetic models. In addition, the implications of myelin lipid dysmetabolism in human diseases are highlighted in the context of hereditary leukodystrophies and neuropathies as well as acquired disorders such as Alzheimer's disease.

Statins in High Cardiovascular Risk Patients: Do Comorbidities and Characteristics Matter?

Atherosclerotic cardiovascular disease (ASCVD) morbidity and mortality are decreasing in high-income countries, but ASCVD remains the leading cause of morbidity and mortality in high-income countries. Over the past few decades, major risk factors for ASCVD, including LDL cholesterol (LDL-C), have been identified. Statins are the drug of choice for patients at increased risk of ASCVD and remain one of the most commonly used and effective drugs for reducing LDL cholesterol and the risk of mortality and coronary artery disease in high-risk groups. Unfortunately, doctors tend to under-prescribe or under-dose these drugs, mostly out of fear of side effects. The latest guidelines emphasize that treatment intensity should increase with increasing cardiovascular risk and that the decision to initiate intervention remains a matter of individual consideration and shared decision-making. The purpose of this review was to analyze the indications for initiation or continuation of statin therapy in different categories of patient with high cardiovascular risk, considering their complexity and comorbidities in order to personalize treatment.

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.

Connecting the Dots Between Hypercholesterolemia and Alzheimer’s Disease: A Potential Mechanism Based on 27-Hydroxycholesterol

Alzheimer’s disease (AD), the most common cause of dementia, is a complex and multifactorial disease involving genetic and environmental factors, with hypercholesterolemia considered as one of the risk factors. Numerous epidemiological studies have reported a positive association between AD and serum cholesterol levels, and experimental studies also provide evidence that elevated cholesterol levels accelerate AD pathology. However, the underlying mechanism of hypercholesterolemia accelerating AD pathogenesis is not clear. Here, we review the metabolism of cholesterol in the brain and focus on the role of oxysterols, aiming to reveal the link between hypercholesterolemia and AD. 27-hydroxycholesterol (27-OHC) is the major peripheral oxysterol that flows into the brain, and it affects β-amyloid (Aβ) production and elimination as well as influencing other pathogenic mechanisms of AD. Although the potential link between hypercholesterolemia and AD is well established, cholesterol-lowering drugs show mixed results in improving cognitive function. Nevertheless, drugs that target cholesterol exocytosis and conversion show benefits in improving AD pathology. Herbs and natural compounds with cholesterol-lowering properties also have a potential role in ameliorating cognition. Collectively, hypercholesterolemia is a causative risk factor for AD, and 27-OHC is likely a potential mechanism for hypercholesterolemia to promote AD pathology. Drugs that regulate cholesterol metabolism are probably beneficial for AD, but more research is needed to unravel the mechanisms involved in 27-OHC, which may lead to new therapeutic strategies for AD.

Cholesterol synthesis inhibition or depletion in axon regeneration

Cholesterol is biosynthesized by all animal cells. Beyond its metabolic role in steroidogenesis, it is enriched in the plasma membrane where it has key structural and regulatory functions. Cholesterol is thus presumably important for post-injury axon regrowth, and this notion is supported by studies showing that impairment of local cholesterol reutilization impeded regeneration. However, several studies have also shown that statins, inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, are enhancers of axon regeneration, presumably acting through an attenuation of the mevalonate isoprenoid pathway and consequent reduction in protein prenylation. Several recent reports have now shown that cholesterol depletion, as well as inhibition of cholesterol synthesis per se, enhances axon regeneration. Here, I discussed these findings and propose some possible underlying mechanisms. The latter would include possible disruptions to axon growth inhibitor signaling by lipid raft-localized receptors, as well as other yet unclear neuronal survival signaling process enhanced by cholesterol lowering or depletion.

Metabolic Control of Sensory Neuron Survival by the p75 Neurotrophin Receptor in Schwann Cells

We report that the neurotrophin receptor p75 contributes to sensory neuron survival through the regulation of cholesterol metabolism in Schwann cells. Selective deletion of p75 in mouse Schwann cells of either sex resulted in a 30% loss of dorsal root ganglia (DRG) neurons and diminished thermal sensitivity. P75 regulates Schwann cell cholesterol biosynthesis in response to BDNF, forming a co-receptor complex with ErbB2 and activating ErbB2-mediated stimulation of sterol regulatory element binding protein 2 (SREBP2), a master regulator of cholesterol synthesis. Schwann cells lacking p75 exhibited decreased activation of SREBP2 and a reduction in 7-dehydrocholesterol (7-DHC) reductase (DHCR7) expression, resulting in accumulation of the neurotoxic intermediate, 7-dehyrocholesterol in the sciatic nerve. Restoration of DHCR7 in p75 null Schwann cells in mice significantly attenuated DRG neuron loss. Together, these results reveal a mechanism by which the disruption of lipid metabolism in glial cells negatively influences sensory neuron survival, which has implications for a wide range of peripheral neuropathies.SIGNIFICANCE STATEMENT Although expressed in Schwann cells, the role of p75 in myelination has remained unresolved in part because of its dual expression in sensory neurons that Schwann cells myelinate. When p75 was deleted selectively among Schwann cells, myelination was minimally affected, while sensory neuron survival was reduced by 30%. The phenotype is mainly due to dysregulation of cholesterol biosynthesis in p75-deficient Schwann cells, leading to an accumulation of neurotoxic cholesterol precursor, 7-dehydrocholesterol (7-DHC). Mechanism-wise, we discovered that in response to BDNF, p75 recruits and activates ErbB2 independently of ErbB3, thereby stimulating the master regulator, sterol regulatory element binding protein 2 (SREBP2). These results together highlight a novel role of p75 in Schwann cells in regulating DRG neuron survival by orchestrating proper cholesterol metabolism.

Lipids and peripheral neuropathy

PURPOSE OF REVIEW

Hyperlipidaemia is associated with the development of neuropathy. Indeed, a mechanistic link between altered lipid metabolism and peripheral nerve dysfunction has been demonstrated in a number of experimental and clinical studies. Furthermore, post hoc analyses of clinical trials of cholesterol and triglyceride-lowering pharmacotherapy have shown reduced rates of progression of diabetic neuropathy. Given, there are currently no FDA approved disease-modifying therapies for diabetic neuropathy, modulation of lipids may represent a key therapeutic target for the treatment of diabetic nerve damage. This review summarizes the current evidence base on the role of hyperlipidaemia and lipid lowering therapy on the development and progression of peripheral neuropathy.

RECENT FINDINGS

A body of literature supports a detrimental effect of dyslipidaemia on nerve fibres resulting in somatic and autonomic neuropathy. The case for an important modulating role of hypertriglyceridemia is stronger than for low-density lipoprotein cholesterol (LDL-C) in relation to peripheral neuropathy. This is reflected in the outcomes of clinical trials with the different therapeutic agents targeting hyperlipidaemia reporting beneficial or neutral effects with statins and fibrates. The potential concern with the association between proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor therapy and cognitive decline raised the possibility that extreme LDL-C lowering may result in neurodegeneration. However, studies in murine models and data from small observational studies indicate an association between increased circulating PCSK9 levels and small nerve fibre damage with a protective effect of PCSK9i therapy against small fibre neuropathy. Additionally, weight loss with bariatric surgery leads to an improvement in peripheral neuropathy and regeneration of small nerve fibres measured with corneal confocal microscopy in people with obesity with or without type 2 diabetes. These improvements correlate inversely with changes in triglyceride levels.

SUMMARY

Hyperlipidaemia, particularly hypertriglyceridemia, is associated with the development and progression of neuropathy. Lipid modifying agents may represent a potential therapeutic option for peripheral neuropathy. Post hoc analyses indicate that lipid-lowering therapies may halt the progression of neuropathy or even lead to regeneration of nerve fibres. Well designed randomized controlled trials are needed to establish if intensive targeted lipid lowering therapy as a part of holistic metabolic control leads to nerve fibre regeneration and improvement in neuropathy symptoms.

The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Axons in the adult mammalian nervous system can extend over formidable distances, up to one meter or more in humans. During development, axonal and dendritic growth requires continuous addition of new membrane. Of the three major kinds of membrane lipids, phospholipids are the most abundant in all cell membranes, including neurons. Not only immature axons, but also severed axons in the adult require large amounts of lipids for axon regeneration to occur. Lipids also serve as energy storage, signaling molecules and they contribute to tissue physiology, as demonstrated by a variety of metabolic disorders in which harmful amounts of lipids accumulate in various tissues through the body. Detrimental changes in lipid metabolism and excess accumulation of lipids contribute to a lack of axon regeneration, poor neurological outcome and complications after a variety of central nervous system (CNS) trauma including brain and spinal cord injury. Recent evidence indicates that rewiring lipid metabolism can be manipulated for therapeutic gain, as it favors conditions for axon regeneration and CNS repair. Here, we review the role of lipids, lipid metabolism and ectopic lipid accumulation in axon growth, regeneration and CNS repair. In addition, we outline molecular and pharmacological strategies to fine-tune lipid composition and energy metabolism in neurons and non-neuronal cells that can be exploited to improve neurological recovery after CNS trauma and disease.

Oligodendroglial Energy Metabolism and (re)Myelination

Central nervous system (CNS) myelin has a crucial role in accelerating the propagation of action potentials and providing trophic support to the axons. Defective myelination and lack of myelin regeneration following demyelination can both lead to axonal pathology and neurodegeneration. Energy deficit has been evoked as an important contributor to various CNS disorders, including multiple sclerosis (MS). Thus, dysregulation of energy homeostasis in oligodendroglia may be an important contributor to myelin dysfunction and lack of repair observed in the disease. This article will focus on energy metabolism pathways in oligodendroglial cells and highlight differences dependent on the maturation stage of the cell. In addition, it will emphasize that the use of alternative energy sources by oligodendroglia may be required to save glucose for functions that cannot be fulfilled by other metabolites, thus ensuring sufficient energy input for both myelin synthesis and trophic support to the axons. Finally, it will point out that neuropathological findings in a subtype of MS lesions likely reflect defective oligodendroglial energy homeostasis in the disease.

Lipids in regulating oligodendrocyte structure and function

Oligodendrocytes enwrap central nervous system axons with myelin, a lipid enriched highly organized multi-layer membrane structure that allows for fast long-distance saltatory conduction of neuronal impulses. Myelin has an extremely high lipid content (∼80 % of its dry weight) and a peculiar lipid composition, with a 2:2:1 cholesterol:phospholipid:glycolipid ratio. Inherited neurodegenerative diseases of the lipids (caused by mutations in lipogenic enzymes) often present oligodendrocyte and/or myelin defects which contribute to the overall disease pathophysiology. These phenomena triggered an increasing number of studies over the functions lipid exert to shape and maintain myelin, and brought to the finding that lipids are more than only structural building blocks. They act as signaling molecules to drive proliferation and differentiation of oligodendrocyte progenitor cells, as well as proliferation of premyelinating oligodendrocytes, and their maturation into myelinating ones. Here, we summarize key findings in these areas, while presenting the main related human diseases. Despite many advances in the field, various questions remain open which we briefly discuss. This article is part of a special issue entitled "Role of Lipids in CNS Cell Physiology and Pathology".

Myelin Fat Facts: An Overview of Lipids and Fatty Acid Metabolism

Myelin is critical for the proper function of the nervous system and one of the most complex cell–cell interactions of the body. Myelination allows for the rapid conduction of action potentials along axonal fibers and provides physical and trophic support to neurons. Myelin contains a high content of lipids, and the formation of the myelin sheath requires high levels of fatty acid and lipid synthesis, together with uptake of extracellular fatty acids. Recent studies have further advanced our understanding of the metabolism and functions of myelin fatty acids and lipids. In this review, we present an overview of the basic biology of myelin lipids and recent insights on the regulation of fatty acid metabolism and functions in myelinating cells. In addition, this review may serve to provide a foundation for future research characterizing the role of fatty acids and lipids in myelin biology and metabolic disorders affecting the central and peripheral nervous system.

Analysis of cholesterol in mouse brain by HPLC with UV detection

We describe a sensitive high performance liquid chromatography (HPLC)-based method for the determination of cholesterol in brain tissue. The method does not require the derivatization of the analyte and uses separation and quantification by reversed-phase HPLC coupled to UV detection. Lipids were methanol/chloroform extracted following the method of Bligh and Dyer, and separated using isopropanol/acetonitrile/water (60/30/10, v/v/v) as mobile phase. We observed lineal detection in a wide range of concentrations, from 62.5 to 2000 ng/μL, and were able to detect a significant increase in the brain cholesterol levels between postnatal days 2 and 10 in C57BL6 mice. Based on our validation parameters, we consider this analytical method a useful tool to assess free cholesterol in rodent brain samples and cell cultures.

Statins for Smith-Lemli-Opitz syndrome

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows: 1. To evaluate the efficacy of statin therapy in reducing the frequency or severity of the neurobehavioral abnormalities seen in people with SLOS (e.g. aggression, anxiety, irritability, self-mutilation, autistic behaviors, sleep disturbances, etc.) (Wassif 2017). 2. To evaluate the potential effects of statin therapy on survival.

Associations of cholesteryl ester transfer protein (CETP) gene variants with pituitary adenoma

AIM

The aim was to evaluate the association of CETP (rs5882 and rs708272) single nucleotide polymorphisms with the presence, invasiveness, hormonal activity and recurrence of pituitary adenoma (PA).

METHODS

The study group included 142 patients with PA and the control group, 753 healthy subjects. The genotyping of CETP (rs5882 and rs708272) was performed using a real-time PCR method.

RESULTS

After statistical analysis we found that CETP rs708272 genotype G/A under the over-dominant model was associated with the decreased odds of PA (OR=0.637; 95%CI: 0.443-0.917; P=0.015), active PA (OR=0.538; 95%CI: 0.335-0.865; P =0.01) and non-recurrent PA (OR=0.602; 95% CI: 0.402 - 0.902; P =0.014). When compared to controls, the rs708272 genotype G/A was less frequent in the active PA subgroup (37.5% vs 52.7%, P =0.009) and the non-recurrent PA subgroup (40.2% vs 52.7%, P=0.013), while the rs5882 genotype A/A was less frequent in the non-recurrent PA subgroup (37.5% vs 46.2%, P=0.015).

CONCLUSION

Our study showed that CETP rs708272 genotype G/A may be associated with a decreased risk of PA.

Role of Connexin-Based Gap Junction Channels in Communication of Myelin Sheath in Schwann Cells

Peripheral nerves have the capacity to conduct action potentials along great distances and quickly recover following damage which is mainly due to Schwann cells (SCs), the most abundant glial cells of the peripheral nervous system (PNS). SCs wrap around an axonal segment multiple times, forming a myelin sheath, allowing for a significant increase in action potential conduction by insulating the axons. Mature myelin consists of compact and non-compact (or cytoplasmic) myelin zones. Non-compact myelin is found in paranodal loops bordering the nodes of Ranvier, and in the inner and outermost cytoplasmic tongues and is the region in which Schmidt-Lanterman incisures (SLI; continuous spirals of overlapping cytoplasmic expansions within areas of compact myelin) are located. Using different technologies, it was shown that the layers of non-compact myelin could be connected to each other by gap junction channels (GJCs), formed by connexin 32 (Cx32), and their relative abundance allows for the transfer of ions and different small molecules. Likewise, Cx29 is expressed in the innermost layer of the myelin sheath. Here it does not form GJCs but colocalizes with K_v1, which implies that the SCs play an active role in the electrical condition in mammals. The critical role of GJCs in the functioning of myelinating SCs is evident in Charcot-Marie-Tooth disease (CMT), X-linked form 1 (CMTX1), which is caused by mutations in the gap junction protein beta 1 (GJB1) gene that codes for Cx32. Although the management of CMT symptoms is currently supportive, there is a recent method for targeted gene delivery to myelinating cells, which rescues the phenotype in KO-Cx32 mice, a model of CMTX1. In this mini-review article, we discuss the current knowledge on the role of Cxs in myelin-forming SCs and summarize recent discoveries that may become a real treatment possibility for patients with disorders such as CMT.

Local low dose curcumin treatment improves functional recovery and remyelination in a rat model of sciatic nerve crush through inhibition of oxidative stress

Traumatic injuries to peripheral nerves are frequent, however, specific pharmacological treatments are currently lacking. Curcumin has antioxidant, anti-inflammatory and neuroprotective properties but high oral doses are required for therapeutic use, particularly due to its low bioavailability. The aim of the present study was to investigate the effects of local and continuous treatment using low curcumin doses on functional recovery and nerve regeneration after rat sciatic nerve crush (SNC). Curcumin was administered by osmotic pumps with a catheter delivering the drug at the injury site (0.2 mg/day for 4 weeks). Functionally, early improvements in mechanical sensitivity, finger spacing of the injured paw, skilful walking and grip strength were observed in curcumin-treated animals. The curcumin treatment increased expression of compact myelin proteins (MPZ and PMP22), myelin sheath thickness and, correspondingly, increased motor and sensitive nerve conduction velocity. Microscopic analysis of gastrocnemius muscle indicated a curcumin-induced decrease in neurogenic lesions. Curcumin treatment reduced the production of reactive oxygen species (ROS) (which were notably produced by macrophages), lipid peroxidation and increased expression of transcription factor Nrf2. In silico analyses indicated that curcumin combines all the characteristics required to be an efficient lipid peroxidation inhibitor at the heart of biological membranes, hence protecting their degradation due to ROS. This antioxidant capacity is likely to contribute to the beneficial effects of curcumin after SNC injury. These results demonstrate that, when administrated locally, low doses of curcumin represent a promising therapy for peripheral nerve regeneration.

Association between altered lipid profiles and attention deficit hyperactivity disorder in boys

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder, which is multifactorial, complex, and seen most commonly in childhood.

AIMS

The aim of this study was to examine the hypothesis that altered serum lipid profiles are associated with ADHD.

METHODS

The study inluded 32 boys diagnosed with ADHD according to DSM-IV-R criteria and a control group of 29 healthy subjects. All patients were assessed with The Kiddie Schedule for Affective Disorders and Schizophrenia Present and Lifetime Version, the Turgay DSM-IV-based Disruptive Behavior Disorders Child and Adolescent Rating and Screening Scale, the Conners Parent Rating Scale-Revised Long Form, and the Conners Teacher Rating Scale. Measurements were taken of fasting plasma total cholesterol (T-Chol), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and 1-day food intake levels, and the groups were compared.

RESULTS

The mean TC, LDL, and HDL levels were significantly lower in the ADHD group than the control group (p = .005, p < .001, p = .002, respectively). There was no significant difference between the groups' TG levels (p = .295). No significant differences were determined between the combined-type ADHD patients and the predominantly inattentive subtype of ADHD in respect to the lipid profile.

CONCLUSION

The results of this study add to the growing body of evidence indicating an association between serum cholesterol and ADHD in boys. Further genetic and molecular studies are required to elucidate the biochemical mechanisms underlying this relationship.

Structure and dynamics of a human myelin protein P2 portal region mutant indicate opening of the β barrel in fatty acid binding proteins

Background

Myelin is a multilayered proteolipid sheath wrapped around selected axons in the nervous system. Its constituent proteins play major roles in forming of the highly regular membrane structure. P2 is a myelin-specific protein of the fatty acid binding protein (FABP) superfamily, which is able to stack lipid bilayers together, and it is a target for mutations in the human inherited neuropathy Charcot-Marie-Tooth disease. A conserved residue that has been proposed to participate in membrane and fatty acid binding and conformational changes in FABPs is Phe57. This residue is thought to be a gatekeeper for the opening of the portal region upon ligand entry and egress.

Results

We performed a structural characterization of the F57A mutant of human P2. The mutant protein was crystallized in three crystal forms, all of which showed changes in the portal region and helix α2. In addition, the behaviour of the mutant protein upon lipid bilayer binding suggested more unfolding than previously observed for wild-type P2. On the other hand, membrane binding rendered F57A heat-stable, similarly to wild-type P2. Atomistic molecular dynamics simulations showed opening of the side of the discontinuous β barrel, giving important indications on the mechanism of portal region opening and ligand entry into FABPs. The results suggest a central role for Phe57 in regulating the opening of the portal region in human P2 and other FABPs, and the F57A mutation disturbs dynamic cross-correlation networks in the portal region of P2.

Conclusions

Overall, the F57A variant presents similar properties to the P2 patient mutations recently linked to Charcot-Marie-Tooth disease. Our results identify Phe57 as a residue regulating conformational changes that may accompany membrane surface binding and ligand exchange in P2 and other FABPs.

Electronic supplementary material

The online version of this article (10.1186/s12900-018-0087-2) contains supplementary material, which is available to authorized users.

Does Sirt2 Regulate Cholesterol Biosynthesis During Oligodendroglial Differentiation In Vitro and In Vivo?

Sirtuin2 (SIRT2) is a deacetylase enzyme predominantly expressed in myelinating glia of the central nervous system (CNS). We have previously demonstrated that Sirt2 expression enhances oligodendrocyte (OL) differentiation and arborization in vitro, but the molecular targets of SIRT2 in OLs remain speculative. SIRT2 has been implicated in cholesterol biosynthesis by promoting the nuclear translocation of sterol regulatory element binding protein (SREBP)-2. We investigated this further in CNS myelination by examining the role of Sirt2 in cholesterol biosynthesis in vivo and in vitro employing Sirt2 -/- mice, primary OL cells and CG4-OL cells. Our results demonstrate that expression of cholesterol biosynthetic genes in the CNS white matter or cholesterol content in purified myelin fractions did not differ between Sirt2 -/- and age-matched wild-type mice. Cholesterol biosynthetic gene expression profiles and total cholesterol content were not altered in primary OLs from Sirt2 -/- mice and in CG4-OLs when Sirt2 was either down-regulated with RNAi or overexpressed. In addition, Sirt2 knockdown or overexpression in CG4-OLs had no effect on SREBP-2 nuclear translocation. Our results indicate that Sirt2 does not impact the expression of genes encoding enzymes involved in cholesterol biosynthesis, total cholesterol content, or nuclear translocation of SREBP-2 during OL differentiation and myelination.

Disturbance of Plasma Lipid Metabolic Profile in Guillain-Barre Syndrome

Guillain-Barre Syndrome (GBS) is an inflammatory disease of the peripheral nervous system. Given that plasma metabolic profiles in GBS patients have never been explored, plasma samples of 38 GBS patients, 22 multiple sclerosis (MS) patients, and 40 healthy controls were analyzed by using untargeted and targeted metabolomics analysis. The untargeted analysis showed that levels of a set of plasma lipid metabolites were significantly decreased in GBS patients compared to the controls. Furthermore, the targeted analysis demonstrated that levels of 41 metabolites in GBS patients were significantly changed compared to either the controls or MS patients. A further metabolic analysis showed that 12 of 41 metabolites were significantly lower in classical GBS patients compared to Miller-Fisher syndrome. Among them, each of PCae C34:0, PCae C42:2, PCae C42:3, and SM C24:0 was inversely correlated with Hughes functional grading scale of GBS patients at both nadir and discharge. Receiver operating characteristic curve analysis of combination of three metabolites (PCaa C42:2, PCae C36:0 and SM C24:0) showed a good discrimination between the GBS and the controls (area under curve = 0.86). This study has demonstrated disruption of lipid metabolites in GBS may be potential biomarkers to indicate disease severity and prognosis of GBS.

Early and brain region-specific decrease of de novo cholesterol biosynthesis in Huntington's disease: A cross-validation study in Q175 knock-in mice

Cholesterol precursors and cholesterol levels are reduced in brain regions of Huntington's disease (HD) mice. Here we quantified the rate of in vivo de novo cholesterol biosynthesis in the HD brain. Samples from different brain regions and blood of the heterozygous knock-in mouse model carrying 175 CAG repeats (Q175) at different phenotypic stages were processed independently by two research units to quantify cholesterol synthesis rate by ²H₂O labeling and measure the concentrations of lathosterol, cholesterol and its brain-specific cholesterol catabolite 24-hydroxy-cholesterol (24OHC) by isotope dilution mass spectrometry. The daily synthesis rate of cholesterol and the corresponding concentration of lathosterol were significantly reduced in the striatum of heterozygous Q175 mice early in the disease course. We also report that the decrease in lathosterol was inversely correlated with CAG-size at symptomatic stage, as observed in striatal samples from an allelic series of HD mice. There was also a significant correlation between the fractional synthesis rates of total cholesterol and 24OHC in brain of wild-type (WT) and Q175 mice, supporting the evidence that plasma 24OHC may reflect cholesterol synthesis in the adult brain. This comprehensive analysis demonstrates consistent cholesterol biosynthesis defects in HD mouse models and suggests that plasma 24OHC may serve as a biomarker of brain cholesterol metabolism.

Statins are underused in recent-onset Parkinson's disease with increased vascular risk: findings from the UK Tracking Parkinson's and Oxford Parkinson's Disease Centre (OPDC) discovery cohorts

BACKGROUND

Cardiovascular disease (CVD) influences phenotypic variation in Parkinson's disease (PD), and is usually an indication for statin therapy. It is less clear whether cardiovascular risk factors influence PD phenotype, and if statins are prescribed appropriately.

OBJECTIVES

To quantify vascular risk and statin use in recent-onset PD, and examine the relationship between vascular risk, PD severity and phenotype.

METHODS

Cardiovascular risk was quantified using the QRISK2 calculator (high ≥20%, medium ≥10 and <20%, low risk <10%). Motor severity and phenotype were assessed using the Movement Disorder Society Unified PD Rating Scale (UPDRS) and cognition by the Montreal cognitive assessment.

RESULTS

In 2909 individuals with recent-onset PD, the mean age was 67.5 years (SD 9.3), 63.5% were men and the mean disease duration was 1.3 years (SD 0.9). 33.8% of cases had high vascular risk, 28.7% medium risk, and 22.3% low risk, while 15.2% of cases had established CVD. Increasing vascular risk and CVD were associated with older age (p<0.001), worse motor score (p<0.001), more cognitive impairment (p<0.001) and worse motor phenotype (p=0.021). Statins were prescribed in 37.2% with high vascular risk, 15.1% with medium vascular risk and 6.5% with low vascular risk, which compared with statin usage in 75.3% of those with CVD.

CONCLUSIONS

Over 60% of recent-onset PD patients have high or medium cardiovascular risk (meriting statin usage), which is associated with a worse motor and cognitive phenotype. Statins are underused in these patients, compared with those with vascular disease, which is a missed opportunity for preventive treatment.

TRIAL REGISTRATION NUMBER

GN11NE062, NCT02881099.

Simulated microgravity enhances oligodendrocyte mitochondrial function and lipid metabolism

The primary energy sources of mammalian cells are proteins, fats, and sugars that are processed by well-known biochemical mechanisms that have been discovered and studied in 1G (terrestrial gravity). Here we sought to determine how simulated microgravity (sim-µG) impacts both energy and lipid metabolism in oligodendrocytes (OLs), the myelin-forming cells in the central nervous system. We report increased mitochondrial respiration and increased glycolysis 24 hr after exposure to sim-µG. Moreover, examination of the secretome after 3 days' exposure of OLs to sim-µG increased the Krebs cycle (Krebs and Weitzman, ) flux in sim-µG. The secretome study also revealed a significant increase in the synthesis of fatty acids and complex lipids such as 1,2-dipalmitoyl-GPC (5.67); lysolipids like 1-oleoyl-GPE (4.48) were also increased by microgravity. Although longer-chain lipids were not observed in this study, it is possible that at longer time points OLs would have continued moving forward toward the synthesis of lipids that constitute myelin. For centuries, basic developmental biology research has been the pillar of an array of discoveries that have led to clinical applications; we believe that studies using microgravity will open new avenues to our understanding of the brain in health and disease-in particular, to the discovery of new molecules and mechanisms impossible to unveil while in 1G. © 2016 Wiley Periodicals, Inc.

Transcriptional Fingerprint of Hypomyelination in Zfp191null and Shiverer (Mbpshi) Mice

The transcriptional program that controls oligodendrocyte maturation and central nervous system (CNS) myelination has not been fully characterized. In this study, we use high-throughput RNA sequencing to analyze how the loss of a key transcription factor, zinc finger protein 191 (ZFP191), results in oligodendrocyte development abnormalities and CNS hypomyelination. Using a previously described mutant mouse that is deficient in ZFP191 protein expression (Zfp191^null), we demonstrate that key transcripts are reduced in the whole brain as well as within oligodendrocyte lineage cells cultured in vitro. To determine whether the loss of myelin seen in Zfp191^null mice contributes indirectly to these perturbations, we also examined the transcriptome of a well-characterized mouse model of hypomyelination, in which the myelin structural protein myelin basic protein (MBP) is deficient. Interestingly, Mbp^shi (shiverer) mice had far fewer transcripts perturbed with the loss of myelin alone. This study demonstrates that the loss of ZFP191 disrupts expression of genes involved in oligodendrocyte maturation and myelination, largely independent from the loss of myelin. Nevertheless, hypomyelination in both mouse mutants results in the perturbation of lipid synthesis pathways, suggesting that oligodendrocytes have a feedback system that allows them to regulate myelin lipid synthesis depending on their myelinating state. The data presented are of potential clinical relevance as the human orthologs of the Zfp191 and MBP genes reside on a region of Chromosome 18 that is deleted in childhood leukodystrophies.

Oligodendroglial membrane dynamics in relation to myelin biogenesis

In the central nervous system, oligodendrocytes synthesize a specialized membrane, the myelin membrane, which enwraps the axons in a multilamellar fashion to provide fast action potential conduction and to ensure axonal integrity. When compared to other membranes, the composition of myelin membranes is unique with its relatively high lipid to protein ratio. Their biogenesis is quite complex and requires a tight regulation of sequential events, which are deregulated in demyelinating diseases such as multiple sclerosis. To devise strategies for remedying such defects, it is crucial to understand molecular mechanisms that underlie myelin assembly and dynamics, including the ability of specific lipids to organize proteins and/or mediate protein-protein interactions in healthy versus diseased myelin membranes. The tight regulation of myelin membrane formation has been widely investigated with classical biochemical and cell biological techniques, both in vitro and in vivo. However, our knowledge about myelin membrane dynamics, such as membrane fluidity in conjunction with the movement/diffusion of proteins and lipids in the membrane and the specificity and role of distinct lipid-protein and protein-protein interactions, is limited. Here, we provide an overview of recent findings about the myelin structure in terms of myelin lipids, proteins and membrane microdomains. To give insight into myelin membrane dynamics, we will particularly highlight the application of model membranes and advanced biophysical techniques, i.e., approaches which clearly provide an added value to insight obtained by classical biochemical techniques.

Statins and Cognitive Side Effects: What Cardiologists Need to Know

Statins are widely used in secondary and primary prevention of atherosclerotic cardiovascular disease. They reduce cardiovascular events and mortality, and have an excellent safety record. Recent case reports suggest a possible association between statins and adverse effects on cognition. This article reviews recent literature related to statins and cognition and provides recommendations to clinicians. Cognitive considerations should not play a role in decision making for most patients for whom statins are indicated. Future trials of statin, or any novel antilipemic agent should include systematic assessment of cognition.

Analytical challenges for measuring steroid responses to stress, neurodegeneration and injury in the central nervous system

Levels of steroids in the adult central nervous system (CNS) show marked changes in response to stress, degenerative disorders and injury. However, their analysis in complex matrices such as fatty brain and spinal cord tissues, and even in plasma, requires accurate and precise analytical methods. Radioimmunoassays (RIA) and enzyme-linked immunosorbent assays, even with prepurification steps, do not provide sufficient specificity, and they are at the origin of many inconsistent results in the literature. The analysis of steroids by mass spectrometric methods has become the gold standard for accurate and sensitive steroid analysis. However, these technologies involve multiple purification steps prone to errors, and they only provide accurate reference values when combined with careful sample workup. In addition, the interpretation of changes in CNS steroid levels is not an easy task because of their multiple sources: the endocrine glands and the local synthesis by neural cells. In the CNS, decreased steroid levels may reflect alterations of their biosynthesis, as observed in the case of chronic stress, post-traumatic stress disorders or depressive episodes. In such cases, return to normalization by administering exogenous hormones or by stimulating their endogenous production may have beneficial effects. On the other hand, increases in CNS steroids in response to acute stress, degenerative processes or injury may be part of endogenous protective or rescue programs, contributing to the resistance of neural cells to stress and insults. The aim of this review is to encourage a more critical reading of the literature reporting steroid measures, and to draw attention to the absolute need for well-validated methods. We discuss reported findings concerning changing steroid levels in the nervous system by insisting on methodological issues. An important message is that even recent mass spectrometric methods have their limits, and they only become reliable tools if combined with careful sample preparation.

Specific white matter tissue microstructure changes associated with obesity

Obesity-related structural brain alterations point to a consistent reduction in gray matter with increasing body mass index (BMI) but changes in white matter have proven to be more complex and less conclusive. Hence, more recently diffusion tensor imaging (DTI) has been employed to investigate microstructural changes in white matter structure. Altogether, these studies have mostly shown a loss of white matter integrity with obesity-related factors in several brain regions. However, the variety of these obesity-related factors, including inflammation and dyslipidemia, resulted in competing influences on the DTI indices. To increase the specificity of DTI results, we explored specific brain tissue properties by combining DTI with quantitative multi-parameter mapping in lean, overweight and obese young adults. By means of multi-parameter mapping, white matter structures showed differences in MRI parameters consistent with reduced myelin, increased water and altered iron content with increasing BMI in the superior longitudinal fasciculus, anterior thalamic radiation, internal capsule and corpus callosum. BMI-related changes in DTI parameters revealed mainly alterations in mean and axial diffusivity with increasing BMI in the corticospinal tract, anterior thalamic radiation and superior longitudinal fasciculus. These alterations, including mainly fiber tracts linking limbic structures with prefrontal regions, could potentially promote accelerated aging in obese individuals leading to an increased risk for cognitive decline.

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We combined DTI with quantitative multi-parametric mapping (qMPM).

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Obesity was associated with a reduction in myelin displayed by decreased R1.

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Obesity was associated with increased water content (decreased R1 and increased PD*).

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DTI revealed mainly alterations in mean and axial diffusivity with obesity.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

Statins may benefit WM in older adults vulnerable to dementia.

Central Nervous System Demyelination and Remyelination is Independent from Systemic Cholesterol Level in Theiler's Murine Encephalomyelitis

High dietary fat and/or cholesterol intake is a risk factor for multiple diseases and has been debated for multiple sclerosis. However, cholesterol biosynthesis is a key pathway during myelination and disturbances are described in demyelinating diseases. To address the possible interaction of dyslipidemia and demyelination, cholesterol biosynthesis gene expression, composition of the body's major lipid repositories and Paigen diet-induced, systemic hypercholesterolemia were examined in Theiler's murine encephalomyelitis (TME) using histology, immunohistochemistry, serum clinical chemistry, microarrays and high-performance thin layer chromatography. TME-virus (TMEV)-infected mice showed progressive loss of motor performance and demyelinating leukomyelitis. Gene expression associated with cholesterol biosynthesis was overall down-regulated in the spinal cord of TMEV-infected animals. Spinal cord levels of galactocerebroside and sphingomyelin were reduced on day 196 post TMEV infection. Paigen diet induced serum hypercholesterolemia and hepatic lipidosis. However, high dietary fat and cholesterol intake led to no significant differences in clinical course, inflammatory response, astrocytosis, and the amount of demyelination and remyelination in the spinal cord of TMEV-infected animals. The results suggest that down-regulation of cholesterol biosynthesis is a transcriptional marker for demyelination, quantitative loss of myelin-specific lipids, but not cholesterol occurs late in chronic demyelination, and serum hypercholesterolemia exhibited no significant effect on TMEV infection.

Schwann cell myelination

Myelinated nerve fibers are essential for the rapid propagation of action potentials by saltatory conduction. They form as the result of reciprocal interactions between axons and Schwann cells. Extrinsic signals from the axon, and the extracellular matrix, drive Schwann cells to adopt a myelinating fate, whereas myelination reorganizes the axon for its role in conduction and is essential for its integrity. Here, we review our current understanding of the development, molecular organization, and function of myelinating Schwann cells. Recent findings into the extrinsic signals that drive Schwann cell myelination, their cognate receptors, and the downstream intracellular signaling pathways they activate will be described. Together, these studies provide important new insights into how these pathways converge to activate the transcriptional cascade of myelination and remodel the actin cytoskeleton that is critical for morphogenesis of the myelin sheath.

Statins and memory loss: An Australian experience

BACKGROUND

Statins are a first-line drug treatment for hypercholesterolaemia. Recently there has been general public and media interest surrounding uses and side effects of statins, including memory loss.

AIMS

We analysed an Australian experience in statin usage in an attempt to improve understanding of the relationship between statins and memory-related adverse events.

METHODS

Total adverse events (TAE) and adverse events with single suspected medicines (SSM) for memory loss and other memory-related adverse events were searched for statin compounds from January 1992 to May 2013, using the Medicare Australia and Pharmaceutical Benefits Scheme (PBS) websites and Therapeutic Goods Administration (TGA) adverse events data. TAE and SSM were compared to the number of prescriptions by item number searched using the PBS. The process was repeated for non-statin cholesterol-lowering drugs.

RESULTS

The most common adverse event was amnesia (167 events for statins and six for non-statins). There were 239 TAE (incidence rate=0.88) listed for statins and 10 for non-statins (incidence rate=0.53). There were 217 SSM events listed for the statins (incidence rate = 0.08) and eight for the alternatives (incident rate=0.04). The differences between TAE and SSM incidence rates between statins and non-statins drugs were not significant (both p values >0.05).

CONCLUSION

We found that there were no differences in memory-related adverse events between statins and other cholesterol-lowering medications using Australian PBS and TGA adverse events data.

Metabolism and functions of lipids in myelin

Rapid conduction of nerve impulses requires coating of axons by myelin sheaths, which are lipid-rich and multilamellar membrane stacks. The lipid composition of myelin varies significantly from other biological membranes. Studies in mutant mice targeting various lipid biosynthesis pathways have shown that myelinating glia have a remarkable capacity to compensate the lack of individual lipids. However, compensation fails when it comes to maintaining long-term stability of myelin. Here, we summarize how lipids function in myelin biogenesis, axon-glia communication and in supporting long-term maintenance of myelin. We postulate that change in myelin lipid composition might be relevant for our understanding of aging and demyelinating diseases. This article is part of a Special Issue titled Brain Lipids.

Increasing membrane cholesterol of neurons in culture recapitulates Alzheimer's disease early phenotypes

BACKGROUND

It is suspected that excess of brain cholesterol plays a role in Alzheimer's disease (AD). Membrane-associated cholesterol was shown to be increased in the brain of individuals with sporadic AD and to correlate with the severity of the disease. We hypothesized that an increase of membrane cholesterol could trigger sporadic AD early phenotypes.

RESULTS

We thus acutely loaded the plasma membrane of cultured neurons with cholesterol to reach the 30% increase observed in AD brains. We found changes in gene expression profiles that are reminiscent of early AD stages. We also observed early AD cellular phenotypes. Indeed we found enlarged and aggregated early endosomes using confocal and electron microscopy after immunocytochemistry. In addition amyloid precursor protein vesicular transport was inhibited in neuronal processes, as seen by live-imaging. Finally transient membrane cholesterol loading lead to significantly increased amyloid-β42 secretion.

CONCLUSIONS

Membrane cholesterol increase in cultured neurons reproduces most early AD changes and could thus be a relevant model for deciphering AD mechanisms and identifying new therapeutic targets.

Balanced mTORC1 activity in oligodendrocytes is required for accurate CNS myelination

The mammalian target of rapamycin (mTOR) pathway integrates multiple signals and regulates crucial cell functions via the molecular complexes mTORC1 and mTORC2. These complexes are functionally dependent on their raptor (mTORC1) or rictor (mTORC2) subunits. mTOR has been associated with oligodendrocyte differentiation and myelination downstream of the PI3K/Akt pathway, but the functional contributions of individual complexes are largely unknown. We show, by oligodendrocyte-specific genetic deletion of Rptor and/or Rictor in the mouse, that CNS myelination is mainly dependent on mTORC1 function, with minor mTORC2 contributions. Myelin-associated lipogenesis and protein gene regulation are strongly reliant on mTORC1. We found that also oligodendrocyte-specific overactivation of mTORC1, via ablation of tuberous sclerosis complex 1 (TSC1), causes hypomyelination characterized by downregulation of Akt signaling and lipogenic pathways. Our data demonstrate that a delicately balanced regulation of mTORC1 activation and action in oligodendrocytes is essential for CNS myelination, which has practical overtones for understanding CNS myelin disorders.

MicroRNAs: a connection between cholesterol metabolism and neurodegeneration

Dysregulation of cholesterol metabolism in the brain has been associated with many neurodegenerative disorders such as Alzheimer's disease, Niemann-Pick type C disease, Smith-Lemli-Opitz syndrome, Hungtington's disease and Parkinson's disease. Specifically, genes involved in cholesterol biosynthesis (24-dehydrocholesterol reductase, DHCR24) and cholesterol efflux (ATP-binding cassete transporter, ABCA1, and apolipoprotein E, APOE) have been associated with developing Alzheimer's disease. Indeed, APOE was the first gene variation found to increase the risk of Alzheimer's disease and remains the risk gene with the greatest known impact. Mutations in another cholesterol biosynthetic gene, 7-dehydrocholesterol reductase (DHCR7), cause Smith-Lemli-Opitz syndrome and impairment in cellular cholesterol trafficking caused by mutations in the NPC1 protein results in Niemann-Pick type C disease. Taken together, these findings provide strong evidence that cholesterol metabolism needs to be controlled at very tight levels in the brain. Recent studies have implicated microRNAs (miRNAs) as novel regulators of cholesterol metabolism in several tissues. These small non-coding RNAs regulate gene expression at the post-transcriptional level by either suppressing translation or inducing mRNA degradation. This review article focuses on how cholesterol homeostasis is regulated by miRNAs and their potential implication in several neurodegenerative disorders, such as Alzheimer's disease. Finally, we also discuss how antagonizing miRNA expression could be a potential therapy for treating cholesterol related diseases.

Serum cholesterol and variant in cholesterol-related gene CETP predict white matter microstructure

Several common genetic variants influence cholesterol levels, which play a key role in overall health. Myelin synthesis and maintenance are highly sensitive to cholesterol concentrations, and abnormal cholesterol levels increase the risk for various brain diseases, including Alzheimer's disease. We report significant associations between higher serum cholesterol (CHOL) and high-density lipoprotein levels and higher fractional anisotropy in 403 young adults (23.8 ± 2.4 years) scanned with diffusion imaging and anatomic magnetic resonance imaging at 4 Tesla. By fitting a multi-locus genetic model within white matter areas associated with CHOL, we found that a set of 18 cholesterol-related, single-nucleotide polymorphisms implicated in Alzheimer's disease risk predicted fractional anisotropy. We focused on the single-nucleotide polymorphism with the largest individual effects, CETP (rs5882), and found that increased G-allele dosage was associated with higher fractional anisotropy and lower radial and mean diffusivities in voxel-wise analyses of the whole brain. A follow-up analysis detected white matter associations with rs5882 in the opposite direction in 78 older individuals (74.3 ± 7.3 years). Cholesterol levels may influence white matter integrity, and cholesterol-related genes may exert age-dependent effects on the brain.