Age-related changes in neutral sphingomyelin-specific phospholipase C activity in striatum, hippocampus, and frontal cortex: Implication for sensitivity to stress and inflammation

The synaptic lipidome in health and disease

Adequate homeostasis of lipid, protein and carbohydrate metabolism is essential for cells to perform highly specific tasks in our organism, and the brain, with its uniquely high energetic requirements, posesses singular characteristics. Some of these are related to its extraordinary dotation of synapses, the specialized subcelluar structures where signal transmission between neurons occurs in the central nervous system. The post-synaptic compartment of excitatory synapses, the dendritic spine, harbors key molecules involved in neurotransmission tightly packed within a minute volume of a few femtoliters. The spine is further compartmentalized into nanodomains that facilitate the execution of temporo-spatially separate functions in the synapse. Lipids play important roles in this structural and functional compartmentalization and in mechanisms that impact on synaptic transmission. This review analyzes the structural and dynamic processes involving lipids at the synapse, highlighting the importance of their homeostatic balance for the physiology of this complex and highly specialized structure, and underscoring the pathologies associated with disbalances of lipid metabolism, particularly in the perinatal and late adulthood periods of life. Although small variations of the lipid profile in the brain take place throughout the adult lifespan, the pathophysiological consequences are clinically manifested mostly during late adulthood. Disturbances in lipid homeostasis in the perinatal period leads to alterations during nervous system development, while in late adulthood they favor the occurrence of neurodegenerative diseases.

Ceramide/Sphingosine 1-Phosphate Axis as a Key Target for Diagnosis and Treatment in Alzheimer’s Disease and Other Neurodegenerative Diseases

Alzheimer’s disease (AD) is considered the most prevalent neurodegenerative disease and the leading cause of dementia worldwide. Sphingolipids, such as ceramide or sphingosine 1-phosphate, are bioactive molecules implicated in structural and signaling functions. Metabolic dysfunction in the highly conserved pathways to produce sphingolipids may lead to or be a consequence of an underlying disease. Recent studies on transcriptomics and sphingolipidomics have observed alterations in sphingolipid metabolism of both enzymes and metabolites involved in their synthesis in several neurodegenerative diseases, including AD. In this review, we highlight the most relevant findings related to ceramide and neurodegeneration, with a special focus on AD.

Pharmacological inhibition of nSMase2 reduces brain exosome release and α-synuclein pathology in a Parkinson's disease model

Aim

We have previously reported that cambinol (DDL-112), a known inhibitor of neutral sphingomyelinase-2 (nSMase2), suppressed extracellular vesicle (EV)/exosome production in vitro in a cell model and reduced tau seed propagation. The enzyme nSMase2 is involved in the production of exosomes carrying proteopathic seeds and could contribute to cell-to-cell transmission of pathological protein aggregates implicated in neurodegenerative diseases such as Parkinson’s disease (PD). Here, we performed in vivo studies to determine if DDL-112 can reduce brain EV/exosome production and proteopathic alpha synuclein (αSyn) spread in a PD mouse model.

Methods

The acute effects of single-dose treatment with DDL-112 on interleukin-1β-induced extracellular vesicle (EV) release in brain tissue of Thy1-αSyn PD model mice and chronic effects of 5 week DDL-112 treatment on behavioral/motor function and proteinase K-resistant αSyn aggregates in the PD model were determined.

Results/discussion

In the acute study, pre-treatment with DDL-112 reduced EV/exosome biogenesis and in the chronic study, treatment with DDL-112 was associated with a reduction in αSyn aggregates in the substantia nigra and improvement in motor function. Inhibition of nSMase2 thus offers a new approach to therapeutic development for neurodegenerative diseases with the potential to reduce the spread of disease-specific proteopathic proteins.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13041-021-00776-9.

Brain lipid profiles in the spontaneously hypertensive rat after subchronic real-world exposure to ambient fine particulate matter

Recent studies have illustrated an association between ambient fine particulate matter (PM_2.5) exposure and neuronal toxicity in epidemiological studies and animal models. However, the possible molecular effects on brains under real-world exposure to PM_2.5 remain unclear. In this pilot study, male spontaneously hypertensive rats were whole-bodily exposed to ambient air from the outdoor environment of Taipei City for 3 months, while the control rats inhaled HEPA-filtered air. The PM_2.5-induced phosphatidylcholine and sphingomyelin profiles in the hippocampus, cortex, medulla, cerebellum, and olfactory bulb were assessed by mass spectrometry (MS)-based lipidomics. Partial least squares discriminant analysis (PLS-DA) and the Wilcoxon rank sum test were used to examine the lipid changes between the exposed and control groups. The PLS-DA models showed that phosphatidylcholine and sphingomyelin profiles of the PM_2.5 exposure group were different from those of the control group in each brain region except the cortex. More lipid changes were found in the hippocampus, while fewer lipid changes were observed in the olfactory bulb. The lipid alteration in the hippocampus may strengthen membrane integrity, modulate signaling pathways, and avoid accumulation of lipofuscin to counter the PM_2.5-induced stress. The lipid changes in the cortex and medulla may respond to PM_2.5-induced injury and inflammation; while the lipid changes in the cerebellum were associated with neuron protection. This study suggests that the MS-based lipidomics is a powerful approach to discriminate the brain lipid profiles even at the environmental level of ambient PM_2.5 and has the potential to suggest possible adverse health effects in long-term PM_2.5 exposure studies.

The Cross-Talk Between Sphingolipids and Insulin-Like Growth Factor Signaling: Significance for Aging and Neurodegeneration

Bioactive sphingolipids: sphingosine, sphingosine-1-phosphate (S1P), ceramide, and ceramide-1-phosphate (C1P) are increasingly implicated in cell survival, proliferation, differentiation, and in multiple aspects of stress response in the nervous system. The opposite roles of closely related sphingolipid species in cell survival/death signaling is reflected in the concept of tightly controlled sphingolipid rheostat. Aging has a complex influence on sphingolipid metabolism, disturbing signaling pathways and the properties of lipid membranes. A metabolic signature of stress resistance-associated sphingolipids correlates with longevity in humans. Moreover, accumulating evidence suggests extensive links between sphingolipid signaling and the insulin-like growth factor I (IGF-I)-Akt-mTOR pathway (IIS), which is involved in the modulation of aging process and longevity. IIS integrates a wide array of metabolic signals, cross-talks with p53, nuclear factor κB (NF-κB), or reactive oxygen species (ROS) and influences gene expression to shape the cellular metabolic profile and stress resistance. The multiple connections between sphingolipids and IIS signaling suggest possible engagement of these compounds in the aging process itself, which creates a vulnerable background for the majority of neurodegenerative disorders.

Protective effects of Aporosa octandra bark extract against D-galactose induced cognitive impairment and oxidative stress in mice

Aporosa octandra (Buch.-Ham. ex D.Don) Vickery is a native species of India. Different parts of the plant are used for the medicinal purpose by the tribal peoples of south-eastern part of India. However, the biological properties of A. octandra have not been studied well. The extracts obtained from the bark of A. octandra were evaluated to determine their protective effect on cognitive impairment and oxidative stress in mice induced by D-galactose using the standard protocol. Different dosages of extract AOE-4 (100, 200, and 300 mg/kg, p.o.) were administered to mice, which were previously treated for six weeks with D-galactose (100 mg/kg s.c.). The D-galactose-induced mice showed significantly impaired cognitive behavior, i.e., oxidative defense, compared to the sham group. Six weeks of treatment with A. octandra extract AOE-4 (100, 200 and 300 mg/kg, p.o.) considerably improved the cognitive behavior and oxidative impairment of mice compared to the control alone (D-galactose). For the phytochemical investigation, the bark of A. octandra was successively extracted with dichloromethane and methanol. The chemical constituents of A. octandra were isolated by multiple column chromatography and characterized by different spectral analyses. (R)-Coclaurine (AO-5), an alkaloid, was isolated along with two other compounds from the AOE-4 extract; three more compounds were also isolated from the AOE-1 extract of the bark of A. octandra. All the compounds were isolated for the first time from the bark of A. octandra, and their structures were established by detailed spectral studies. The structure of compound AO-5 was also investigated and confirmed by X-ray diffraction and DFT studies. This study highlights the protective effect of A. octandra bark extract against D-galactose-induced biochemically dysfunction in mice. (R)-Coclaurine (AO-5) was isolated as one of the major components of A. octandra bark from AOE-4 extract; this compound could be further evaluated for the development of new potential drug candidates.

Role of sphingolipids in senescence: implication in aging and age-related diseases

Aging is defined as the progressive deterioration of physiological function with age. Incidence of many pathologies increases with age, including neurological and cardiovascular diseases and cancer. Aging tissues become less adaptable and renewable, and cells undergo senescence, a process by which they "irreversibly" stop dividing. Senescence has been shown to serve as a tumor suppression mechanism with clear desirable effects. However, senescence also has deleterious consequences, especially for cardiovascular, metabolic, and immune systems. Sphingolipids are a major class of lipids that regulate cell biology, owing to their structural and bioactive properties and diversity. Their involvement in the regulation of aging and senescence has been demonstrated and studied in multiple organisms and cell types, especially that of ceramide and sphingosine-1-phosphate; ceramide induces cellular senescence and sphingosine-1-phosphate delays it. These discoveries could be very useful in the future to understand aging mechanisms and improve therapeutic interventions.

Regulation of sphingomyelin metabolism

Sphingolipids (SFs) represent a large class of lipids playing diverse functions in a vast number of physiological and pathological processes. Sphingomyelin (SM) is the most abundant SF in the cell, with ubiquitous distribution within mammalian tissues, and particularly high levels in the Central Nervous System (CNS). SM is an essential element of plasma membrane (PM) and its levels are crucial for the cell function. SM content in a cell is strictly regulated by the enzymes of SM metabolic pathways, which activities create a balance between SM synthesis and degradation. The de novo synthesis via SM synthases (SMSs) in the last step of the multi-stage process is the most important pathway of SM formation in a cell. The SM hydrolysis by sphingomyelinases (SMases) increases the concentration of ceramide (Cer), a bioactive molecule, which is involved in cellular proliferation, growth and apoptosis. By controlling the levels of SM and Cer, SMSs and SMases maintain cellular homeostasis. Enzymes of SM cycle exhibit unique properties and diverse tissue distribution. Disturbances in their activities were observed in many CNS pathologies. This review characterizes the physiological roles of SM and enzymes controlling SM levels as well as their involvement in selected pathologies of the Central Nervous System, such as ischemia/hypoxia, Alzheimer disease (AD), Parkinson disease (PD), depression, schizophrenia and Niemann Pick disease (NPD).

Increased oligomerization and phosphorylation of α-synuclein are associated with decreased activity of glucocerebrosidase and protein phosphatase 2A in aging monkey brains

Aging is associated with an increased risk for Parkinson's disease and dementia with Lewy bodies, in which α-synuclein (α-syn) oligomerization plays key pathogenic roles. Here, we show that oligomeric α-syn levels increase with age in the brain of cynomolgus monkeys and are accompanied by a decrease in the expression and activity of glucocerebrosidase (GCase), a lysosomal enzyme whose dysfunction is linked to accumulation of oligomeric α-syn. Besides, levels of α-syn phosphorylated at serine 129 (pS129 α-syn), a modification that promotes α-syn oligomerization also increase with age in the brain and is associated with a reduction in the activity of protein phosphatase 2A (PP2A), an enzyme that facilitates α-syn dephosphorylation. The inverse relationship between levels of oligomeric α-syn and pS129 α-syn and activity of GCase and PP2A was more evident in brain regions susceptible to neurodegeneration (i.e., the striatum and hippocampus) than those that are less vulnerable (i.e., cerebellum and occipital cortex). In vitro experiments showed that GCase activity was more potently inhibited by oligomeric than by monomeric α-syn in the lysosome-enriched fractions isolated from brain tissues and cultured neuronal cells. Inhibition of GCase activity induced an elevation of oligomeric α-syn levels, which was shown to increase pS129 α-syn levels and reduce PP2A activity in cultured neuronal cells. The alterations in oligomeric and pS129 α-syns and their association with GCase and PP2A in aging brains may explain the vulnerability of certain brain regions to neurodegeneration in Parkinson's disease and dementia with Lewy bodies.

Ceramides in Alzheimer's Disease: Key Mediators of Neuronal Apoptosis Induced by Oxidative Stress and Aβ Accumulation

Alzheimer's disease (AD), the most common chronic and progressive neurodegenerative disorder, is characterized by extracellular deposits of amyloid β-peptides (Aβ) and intracellular deposits of hyperphosphorylated tau (phospho-tau) protein. Ceramides, the major molecules of sphingolipid metabolism and lipid second messengers, have been associated with AD progression and pathology via Aβ generation. Enhanced levels of ceramides directly increase Aβ through stabilization of β-secretase, the key enzyme in the amyloidogenic processing of Aβ precursor protein (APP). As a positive feedback loop, the generated oligomeric and fibrillar Aβ induces a further increase in ceramide levels by activating sphingomyelinases that catalyze the catabolic breakdown of sphingomyelin to ceramide. Evidence also supports important role of ceramides in neuronal apoptosis. Ceramides may initiate a cascade of biochemical alterations, which ultimately leads to neuronal death by diverse mechanisms, including depolarization and permeabilization of mitochondria, increased production of reactive oxygen species (ROS), cytochrome c release, Bcl-2 depletion, and caspase-3 activation, mainly by modulating intracellular signalling, particularly along the pathways related to Akt/PKB kinase and mitogen-activated protein kinases (MAPKs). This review summarizes recent findings related to the role of ceramides in oxidative stress-driven neuronal apoptosis and interplay with Aβ in the cascade of events ending in neuronal degeneration.

Pioglitazone alleviates the mitochondrial apoptotic pathway and mito-oxidative damage in the d-galactose-induced mouse model

Chronic injection of d-galactose can cause gradual deterioration in learning and memory capacity, and activates oxidative stress, mitochondrial dysfunction and apoptotic cell death in the brain of mice. Thus, it serves as an animal model of ageing. Recent evidence has shown that mild cognitive impairment in humans might be alleviated by treatment with piogliatzone (peroxisome proliferator-activated receptor gamma (PPARγ) agonists). To continue exploring the effects of piogliatzone in this model, we focused on behavioural alteration, oxidative damage, mitochondrial dysfunction and apoptosis in d-galactose-induced mice. The ageing model was established by administration of d-galactose (100 mg/kg) for 6 weeks. Pioglitazone (10 and 30 mg/kg) and bisphenol A diglycidyl ether (15 mg/kg) were given daily to d-galactose-induced senescent mice. The cognitive behaviour of mice was monitored using the Morris water maze. The anti-oxidant status and apoptotic activity in the ageing mice was measured by determining mito-oxidative parameters and caspase-3 activity in brain tissue. Systemic administration of d-galactose significantly increased behavioural alterations, biochemical parameters, mitochondrial enzymes, and activations of caspase-3 and acetylcholinesterase enzyme activity as compared with the control group. Piogliatzone treatment significantly improved behavioural abnormalities, biochemical, cellular alterations, and attenuated the caspase-3 and acetylcholinesterase enzyme activity as compared with the control. Furthermore, pretreatment of BADGE (PPARγ antagonist) with pioglitazone reversed the protective effect of pioglitazone in d-galactose-induced mice. The present study highlights the protective effects of pioglitzone against d-galactose-induced memory dysfunction, mito-oxidative damage and apoptosis through activation of PPARγ receptors. These findings suggest that pioglitazone might be helpful for the prevention or alleviation of ageing.

Exosome reduction in vivo is associated with lower amyloid plaque load in the 5XFAD mouse model of Alzheimer's disease

We present evidence here that exosomes stimulate aggregation of amyloid beta (Aβ)1-42 in vitro and in vivo and interfere with uptake of Aβ by primary cultured astrocytes and microglia in vitro. Exosome secretion is prevented by the inhibition of neutral sphingomyelinase 2 (nSMase2), a key regulatory enzyme generating ceramide from sphingomyelin, with GW4869. Using the 5XFAD mouse, we show that intraperitoneal injection of GW4869 reduces the levels of brain and serum exosomes, brain ceramide, and Aβ1-42 plaque load. Reduction of total Aβ1-42 as well as number of plaques in brain sections was significantly greater (40% reduction) in male than female mice. Our results suggest that GW4869 reduces amyloid plaque formation in vivo by preventing exosome secretion and identifies nSMase2 as a potential drug target in AD by interfering with exosome secretion.

Vitamin E prevents the age-dependent and palmitate-induced disturbances of sphingolipid turnover in liver cells

Sphingolipid turnover has been shown to be activated at old age and in response to various stress stimuli including oxidative stress. Reduction of vitamin E content in the liver under the pro-oxidant action is associated with enhanced sphingolipid turnover and ceramide accumulation in hepatocytes. In the present paper, the correction of sphingolipid metabolism in the liver cells of old rats and in the palmitate-treated young hepatocytes using α-tocopherol has been investigated. 3- and 24-month-old rats, [(14) C]palmitic acid, [methyl-(14) C-choline]sphingomyelin (SM), and [(14) C]serine were used. α-Tocopherol administration to old rats or addition to the culture medium of old liver slices or hepatocytes prevented age-dependent increase of ceramide synthesis and lipid accumulation, and increased SM content in liver tissue and cells. α-Tocopherol treatment of old cells decreased the neutral and acid sphingomyelinase (SMase) activities in hepatocytes and serine palmitoyl transferase activity in the liver cell microsomes. Effect of α- or γ-tocopherol, but not of δ-tocopherol, on the newly synthesized ceramide content in old cells was correlated with the action of inhibitor of serine palmitoyl transferase (SPT) activity (myriocin) and SMase inhibitors (glutathione, imipramine). Addition of α-tocopherol as well as myriocin to the culture medium of young hepatocytes, treated by palmitate, abolished ceramide accumulation and synthesis. The data obtained demonstrate that α-tocopherol normalized elevated ceramide content in the old liver cells via inhibition of acid and neutral SMase activities and lipid synthesis de novo. α-Tocopherol, reducing ceramide synthesis, prevented palmitate-induced aging-like ceramide accumulation in young liver cells.

Senescent endothelial dysfunction is attributed to the up-regulation of sphingosine-1-phosphate receptor-2 in aged rats

Sphingosine-1-phosphate (S1P) regulates an array of biological activities in various cell types. Many S1P-regulated functions are mediated by S1P receptor subtypes. Previous studies have shown that the S1P receptor-2 (S1P(2) receptor) is involved in senescence of endothelial cells in vitro. However, the functional outcomes of S1P(2) receptor-mediated signaling pathways in a physiological environment are currently unknown. The main aim of this study was to explore the underlying mechanisms of senescent-associated impairments in pulmonary microvascular endothelial cells (PMECs) isolated from young and aged rats in vivo. The expression of S1P receptor subtypes in PMECs was detected using RT-PCR and Western blot analyses. The chemotaxis of PMECs was measured using the transwell migration assay. The endothelial morphogenesis assay was performed in three-dimensional Matrigel. The wound-healing assay was performed using a scratch wound model on primary PMEC monolayers. We observed that the S1P(2) receptor was markedly increased and S1P-regulated responses were significantly inhibited in PMECs isolated from aged rats. Furthermore, the senescent-associated impairments were revoked by the down-regulation of the S1P(2) receptor in senescent PMECs. These results indicate that the impaired functions (such as chemotactic, wound healing, and morphogenetic responses) in senescent PMECs in vivo are mediated by the S1P(2) receptor.

Centella asiatica Attenuates D-Galactose-Induced Cognitive Impairment, Oxidative and Mitochondrial Dysfunction in Mice

D-galactose induced neurotoxicity is well known model for studying aging and related oxidative damage and memory impairment. Aging is a biological process, characterized by the gradual loss of physiological functions by unknown mechanism. Centella asiatica, Indian pennywort has been documented in the treatment of various neurological disorders including aging. Therefore, present study has been conducted in order to explore the possible role of Centella asiatica against D-galactose induced cognitive impairment, oxidative and mitochondrial dysfunction in mice. Chronic administration of D-galactose (100 mg/kg s.c.) for a period of six weeks significantly impaired cognitive task (both in both Morris water maze and elevated plus maze) and oxidative defense (Increased lipid peroxidation, nitrite concentration and decreased activity of superoxide dismutase, catalase and non-protein thiols) and impaired mitochondrial complex (I, II and III) enzymes activities as compared to sham group. Six weeks Centella asiatica (150 and 300 mg/kg, p.o) treatment significantly improved behavioral alterations, oxidative damage and mitochondrial enzyme complex activities as compared to contro l (D-galactose). Centella asiatica also attenuated enhanced acetylcholine esterase enzyme level in D-galactose senescence mice. Present study highlights the protective effect of Centella asiatica against D-galactose induced behavioral, biochemical and mitochondrial dysfunction in mice.

Effect of age on proliferation-regulating factors in human adult neurogenic regions

Neurogenesis, the birth of new neurons, continues throughout adulthood in the human subventricular zone (SVZ) and hippocampus. It is not known how levels of putative proliferation-regulating factors change with age in human adult neurogenic areas. The current project employed ELISAs to investigate changes in levels of putative proliferation-regulating factors in the healthy human SVZ and dentate gyrus throughout the adult lifespan (18-104 years). Levels of brain-derived neurotrophic factor, basic fibroblast growth factor and interleukin (IL)-1β were significantly higher in the hippocampus than in the SVZ and levels of glial-derived neurotrophic factor and transforming growth factor-α were significantly higher in the SVZ (p < 0.005), suggesting that factors with predominant influences on neurogenesis differ between the two human adult neurogenic areas. Hippocampal levels of transforming growth factor-β1 strongly increased with age (n = 9, p < 0.01), whereas hippocampal and SVZ levels of brain-derived neurotrophic factor, epidermal growth factor, basic fibroblast growth factor, glial-derived neurotrophic factor, heparin-binding epidermal growth factor, insulin-like growth factor-1, IL-1β, IL-6 and transforming growth factor-α did not change significantly with age in the SVZ or hippocampus. These findings suggest regulation of the adult neurogenic environment in the human brain may differ over time from that in other species.

The polyunsaturated fatty acids, EPA and DPA exert a protective effect in the hippocampus of the aged rat

Age is characterized by deficits in synaptic function identified by decreased performance of aged animals in spatial learning tasks and reduced ability of animals to sustain long term potentiation (LTP). Several cellular and molecular events are correlated with these deficits, many of which are indicative of age-related neuroinflammatory and oxidative cell stress. It is significant that agents which decrease microglial activation are commonly associated with restoration of function. We set out to examine whether the n-3 polyunsaturated fatty acid docosapentaenoic acid (DPA), which is a metabolite of eicosapentaenoic acid (EPA), could modulate the age-related increase in microglial activation and the associated increase in oxidative changes and therefore impact on synaptic function in aged rats. We demonstrate that docosapentaenoic acid possesses neurorestorative effects and is capable of downregulating microglial activation. The data show that it also decreases the coupled activation of sphingomyelinase and caspase 3, probably because of its ability to decrease age-related oxidative changes, and consequently attenuates the age-related decrease in spatial learning and long-term potentiation.

Effect of prolonged phenytoin administration on rat brain gene expression assessed by DNA microarrays

Preliminary clinical trials have recently shown that phenytoin, an antiepileptic drug, may also be beneficial for treatment of bipolar disorder. To examine molecular mechanisms of action of phenytoin as a potential mood stabilizer, DNA microarrays were used to study the effect of phenytoin on gene expression in the hippocampus and frontal cortex of Sprague-Dawley rats. While our particular interest is in bipolar disorder, this is the first DNA microarray study on the effect of phenytoin in brain tissue, in general. As compared with control rats, treated rats had 508 differentially expressed genes in the hippocampus and 62 in the frontal cortex. Phenytoin modulated the expression of genes which may affect neurotransmission, e.g. glutamate decarboxylase 1 (Gad1) and gamma-aminobutyric acid A receptor, alpha 5 (Gabra5). Phenytoin also exerted an effect on neuroprotection-related genes, namely the survival-promoting and antioxidant genes v-akt murine thymoma viral oncogene homolog 1 (Akt1), FK506 binding protein 12-rapamycin associated protein 1 (Frap1), glutathione reductase (Gsr) and glutamate cysteine ligase catalytic subunit (Gclc). The expression of genes potentially associated with mechanisms of mood regulation such as adenylate cyclase-associated protein 1 (Cap1), Glial Fibrillary Acidic Protein (Gfap) and prodynorphin (Pdyn) was also altered. Some of the above genes are regarded as targets of classical mood stabilizers and their modulation supports the clinical observation that phenytoin may have mood-stabilizing effects. The results may provide new insights regarding the mechanism of action of phenytoin and genes found differentially expressed following phenytoin administration may play a role in the pathophysiology of either bipolar disorder or epilepsy.

Age- and brain region-specific effects of dietary vitamin K on myelin sulfatides

Dysregulation of myelin sulfatides is a risk factor for cognitive decline with age. Vitamin K is present in high concentrations in the brain and has been implicated in the regulation of sulfatide metabolism. Our objective was to investigate the age-related interrelation between dietary vitamin K and sulfatides in myelin fractions isolated from the brain regions of Fischer 344 male rats fed one of two dietary forms of vitamin K: phylloquinone or its hydrogenated form, 2',3'-dihydrophylloquinone (dK), for 28 days. Both dietary forms of vitamin K were converted to menaquinone-4 (MK-4) in the brain. The efficiency of dietary dK conversion to MK-4 compared to dietary phylloquinone was lower in the striatum and cortex, and was similar to that in the hippocampus. There were significant positive correlations between sulfatides and MK-4 in the hippocampus (phylloquinone-supplemented diet, 12 and 24 months; dK-supplemented diet, 12 months) and cortex (phylloquinone-supplemented diet, 12 and 24 months). No significant correlations were observed in the striatum. Furthermore, sulfatides in the hippocampus were significantly positively correlated with MK-4 in serum. This is the first attempt to establish and characterize a novel animal model that exploits the inability of dietary dK to convert to brain MK-4 to study the dietary effects of vitamin K on brain sulfatide in brain regions controlling motor and cognitive functions. Our findings suggest that this animal model may be useful for investigation of the effect of the dietary vitamin K on sulfatide metabolism, myelin structure and behavior functions.

Sphingolipids and gangliosides of the nervous system in membrane function and dysfunction

Simple sphingolipids such as ceramide and sphingomyelin (SM) as well as more complex glycosphingolipids play very important roles in cell function under physiological conditions and during disease development and progression. Sphingolipids are particularly abundant in the nervous system. Due to their amphiphilic nature they localize to cellular membranes and many of their roles in health and disease result from membrane reorganization and from lipid interaction with proteins within cellular membranes. In this review we discuss some of the functions of sphingolipids in processes that entail cellular membranes and their role in neurodegenerative diseases, with an emphasis on SM, ceramide and gangliosides.

Cognitive impairment in folate-deficient rats corresponds to depleted brain phosphatidylcholine and is prevented by dietary methionine without lowering plasma homocysteine

Poor folate status is associated with cognitive decline and dementia in older adults. Although impaired brain methylation activity and homocysteine toxicity are widely thought to account for this association, how folate deficiency impairs cognition is uncertain. To better define the role of folate deficiency in cognitive dysfunction, we fed rats folate-deficient diets (0 mg FA/kg diet) with or without supplemental L-methionine for 10 wk, followed by cognitive testing and tissue collection for hematological and biochemical analysis. Folate deficiency with normal methionine impaired spatial memory and learning; however, this impairment was prevented when the folate-deficient diet was supplemented with methionine. Under conditions of folate deficiency, brain membrane content of the methylated phospholipid phosphatidylcholine was significantly depleted, which was reversed with supplemental methionine. In contrast, neither elevated plasma homocysteine nor brain S-adenosylmethionine and S-adenosylhomocysteine concentrations predicted cognitive impairment and its prevention by methionine. The correspondence of cognitive outcomes to changes in brain membrane phosphatidylcholine content suggests that altered phosphatidylcholine and possibly choline metabolism might contribute to the manifestation of folate deficiency-related cognitive dysfunction.

Up-regulating sphingosine 1-phosphate receptor-2 signaling impairs chemotactic, wound-healing, and morphogenetic responses in senescent endothelial cells

Vascular endothelial cells (ECs) have a finite lifespan when cultured in vitro and eventually enter an irreversible growth arrest state called "cellular senescence." It has been shown that sphingolipids may be involved in senescence; however, the molecular links involved are poorly understood. In this study, we investigated the signaling and functions of sphingosine 1-phosphate (S1P), a serum-borne bioactive sphingolipid, in ECs of different in vitro ages. We observed that S1P-regulated responses are significantly inhibited and the S1P(1-3) receptor subtypes are markedly increased in senescent ECs. Increased expression of S1P(1) and S1P(2) was also observed in the lesion regions of atherosclerotic endothelium, where senescent ECs have been identified in vivo. S1P-induced Akt and ERK1/2 activation were comparable between ECs of different in vitro ages; however, PTEN (phosphatase and tensin homolog deleted on chromosome 10) activity was significantly elevated and Rac activation was inhibited in senescent ECs. Rac activation and senescent-associated impairments were restored in senescent ECs by the expression of dominant-negative PTEN and by knocking down S1P(2) receptors. Furthermore, the senescent-associated impairments were induced in young ECs by the expression of S1P(2) to a level similar to that of in vitro senescence. These results indicate that the impairment of function in senescent ECs in culture is mediated by an increase in S1P signaling through S1P(2)-mediated activation of the lipid phosphatase PTEN.

Ceramide is responsible for the failure of compensatory nerve sprouting in apolipoprotein E knock-out mice

Apolipoprotein E (apoE) is a key transporter of the cholesterol and phospholipids required for membrane synthesis and nerve growth. We now report a virtual absence in apoE knock-out (KO) mice of normal nerve growth factor (NGF)-driven compensatory sprouting of undamaged cutaneous nociceptive nerves. In contrast, NGF-independent regeneration of crushed axons was unaffected. Essentially similar results came from aged wild-type mice. In apoE KO mice, the endogenous sprouting stimulus was suspect, because NGF administration induced normal sprouting; nevertheless, NGF increased normally in denervated skin, transported normally in the axons, and led to phosphorylation of trkA, erk1, and erk2. However, sprouting was restored in apoE KO mice (although not in aged mice) by fumonisin B1, an inhibitor of ceramide synthesis. A shotgun analysis revealed a wide array of changes in individual ceramide species in DRG neurons of apoE KO mice, and the changes for ceramide species OH_N15:0 made it a candidate inhibitor of sprouting (increased in apoE KO mice and normalized by fumonisin B1). Nevertheless, the unknown effects of individual ceramide species on sprouting, as well as the variability of their changed levels in apoE KO mice and how these were affected by fumonisin B1, support a different conclusion. We suggest that absence of apoE expression alters the balance among ceramide species to one that collectively inhibits compensatory sprouting, whereas fumonisin B1 establishes a new balance that allows sprouting. Nontoxic ceramide modulators might usefully promote sprouting and circuitry repair in neurodegenerative disorders in which ceramide species are perturbed, adding to the benefits of reducing ceramide-induced neuronal apoptosis.

Interactions of PACAP and ceramides in the control of granule cell apoptosis during cerebellar development

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that belongs to the secretin/glucagon/vasoactive intestinal polypeptide superfamily. The PACAPergic system is actively expressed in the developing cerebellum of mammals. In particular, PACAP receptors are expressed by granule cell precursors suggesting a role of the peptide in neurogenesis of this cell type. Consistent with this hypothesis, several studies reported antiapoptotic effects of PACAP in the developing cerebellum. On the other hand, the sphingomyelin metabolites ceramides are recognized as important signaling molecules that play pivotal roles during neuronal development. Ceramides, which production can be induced by death factors such as FasL or TNFalpha, are involved in the control of cell survival during brain development through activation of caspase-dependent mechanisms. The present review focuses on the interactions between PACAP and ceramides in the control of granule cell survival and on the transduction mechanisms associated with the anti- and proapoptotic effects of PACAP and ceramides, respectively.

Influence of age or circadian time on bcl-2 and bax mRNA expression in the rat hippocampus after corticosterone exposure

A rapid elevation in the level of endogenous corticosterone (CORT) functions in the stress response associated with the hypothalamus-pituitary-adrenal axis, and it has been well documented that high levels of CORT play neurotoxic roles in the hippocampus. Both aging and the circadian rhythm possibly affect the sensitivity to CORT, although their endogenous modifications in the CORT-mediated events remain unclear. To explore the influence of age or circadian time on hippocampal vulnerability to excess CORT, we examined the relative mRNA expression of bcl-2 and bax in the dentate gyrus (DG) and the CA1 subfield, compared with the CA3 as an internal standard, after acute CORT administration using in situ RT-PCR. Male rats aged 10 weeks (young) or 6 months (adult) were treated with CORT at 0800 or 2000 h. The bcl-2 to bax mRNA ratio in the dentate gyrus (DG) was significantly decreased 2h after CORT exposure in the young rats treated at 0800 or 2000 h. In the adult rats, the treatment with CORT at 0800 h significantly decreased the bcl-2 to bax ratio, whereas the treatment at 2000 h was ineffective; the discrepancy between the treatment time points was apparent in adult rats, but not in young rats. Our results emphasize the importance of circadian time as well as age as a factor influencing the stress paradigm.

Inflammatory cytokines, behaviour and age as determinants of self-rated health in women

Self-rated health is a powerful and independent predictor of long-term health, but its biological basis is unknown. We have shown previously that self-rated health is associated with increased levels of circulating cytokines in women. The main aim of the present study was to increase the understanding of the association between markers of wellbeing, such as self-rated health, and cytokines and to investigate the impact of age on these associations. In 174 female consecutive primary health care patients divided into three age groups, we examined subjective ratings of health and aspects of wellbeing and circulating levels of IL (interleukin)-1beta, IL-1ra (IL-1 receptor antagonist), IL-6 and TNF-alpha (tumour necrosis factor-alpha). Poor self-rated health was significantly associated with higher levels of TNF-alpha in all of the age groups. For IL-1beta and IL-1ra, the correlations with self-rated health were significant only in the oldest age group. Lower ratings of other measurements of health and wellbeing were related to higher levels of cytokines, most pronounced for TNF-alpha and IL-1beta, and in the middle and olderst age groups. More symptoms resembling a sickness response induced by inflammation were implicated to be associated with lower self-rated health. The strength of the association between inflammatory cytokines and poor health perception increased with advanced age, indicating an increased vulnerability for inflammatory activity during aging. It is suggested that higher levels of TNF-alpha are connected to a sickness response that, in turn, is connected to self-rated health. The results provide a possible psychobiological basis to understand better diffuse subjective symptoms and poor subjective health in women.