Recent Insight into the Role of Sphingosine-1-Phosphate Lyase in Neurodegeneration.

Sphingosine-1-phosphate lyase (SPL) is a pyridoxal 5'-phosphate-dependent enzyme involved in the irreversible degradation of sphingosine-1-phosphate (S1P)-a bioactive sphingolipid that modulates a broad range of biological processes (cell proliferation, migration, differentiation and survival; mitochondrial functioning; and gene expression). Although SPL activity leads to a decrease in the available pool of S1P in the cell, at the same time, hexadecenal and phosphoethanolamine, compounds with potential biological activity, are generated. The increased expression and/or activity of SPL, and hence the imbalance between S1P and the end products of its cleavage, were demonstrated in several pathological states. On the other hand, loss-of-function mutations in the SPL encoding gene are a cause of severe developmental impairments. Recently, special attention has been paid to neurodegenerative diseases as the most common pathologies of the nervous system. This review summarizes the current findings concerning the role of SPL in the nervous system with an emphasis on neurodegeneration. Moreover, it briefly discusses pharmacological compounds directed to inhibit its activity.

Alterations in the transcriptional profile of genes related to glutamatergic signalling in animal models of Alzheimer's disease. The effect of fingolimod.

Alzheimer's disease (AD) is a multi-factorial illness that leads to progressive cognitive impairment. A glutamatergic system dysfunction has been reported to be implicated in the pathomechanism of AD. Therefore, in the current study we characterized the transcriptional profile of glutamate-related genes in transgenic AbPP V717I (TgAD) and sporadic (SAD, streptozotocin-induced) models of AD. Genes encoding glutamate membrane-bound (GLAST, GLT1, EAAC1) and vesicular (VGLUT1-3) transporters as well as ionotropic (AMPA, NMDA) and metabotropic (mGluR3, mGluR5) receptors were analysed. Based on qPCR analysis, we observed a discrepancy between TgAD and SAD mice in the profile of targeted genes. We noticed age-dependent upregulation of genes encoding VGLUT1, NMDAR1 and mGluR3 in 12-month-old TgAD mice. In the SAD model upregulation of genes encoding AMPAR1 and NMDAR1 as well as downregulation of GLAST, VGLUT3 and mGluR5 were found. Next, the effect of fingolimod (FTY720) was indicated. In the TgAD model, the drug reversed altered transcription of the mGluR3 glutamate receptor to the control level, whereas in the SAD model it downregulated the genes encoding VGLUT1, AMPAR2 and mGluR3. Interestingly, FTY720 influenced mGluR3 mRNA in both examined models. Observed alterations of gene transcription and the effects of FTY720 may potentially constitute an interesting target for further pharmacological studies.

Age-Related Transcriptional Deregulation of Genes Coding Synaptic Proteins in Alzheimer's Disease Murine Model: Potential Neuroprotective Effect of Fingolimod.

Alzheimer's disease (AD) induces time-dependent changes in sphingolipid metabolism, which may affect transcription regulation and neuronal phenotype. We, therefore, analyzed the influence of age, amyloid ß precursor protein (AßPP), and the clinically approved, bioavailable sphingosine-1-phosphate receptor modulator fingolimod (FTY720) on the expression of synaptic proteins. RNA was isolated, reverse-transcribed, and subjected to real-time PCR. Expression of mutant (V717I) AßPP led to few changes at 3 months of age but reduced multiple mRNA coding for synaptic proteins in a 12-month-old mouse brain. Complexin 1 (Cplx1), SNAP25 (Snap25), syntaxin 1A (Stx1a), neurexin 1 (Nrxn1), neurofilament light (Nefl), and synaptotagmin 1 (Syt1) in the hippocampus, and VAMP1 (Vamp1) and neurexin 1 (Nrxn1) in the cortex were all significantly reduced in 12-month-old mice. Post mortem AD samples from the human hippocampus and cortex displayed lower expression of VAMP, synapsin, neurofilament light (NF-L) and synaptophysin. The potentially neuroprotective FTY720 reversed most AßPP-induced changes in gene expression (Cplx1, Stx1a, Snap25, and Nrxn1) in the 12-month-old hippocampus, which is thought to be most sensitive to early neurotoxic insults, but it only restored Vamp1 in the cortex and had no influence in 3-month-old brains. Further study may reveal the potential usefulness of FTY720 in the modulation of deregulated neuronal phenotype in AD brains.

Recent Insights into the Interplay of Alpha-Synuclein and Sphingolipid Signaling in Parkinson's Disease.

Molecular studies have provided increasing evidence that Parkinson's disease (PD) is a protein conformational disease, where the spread of alpha-synuclein (ASN) pathology along the neuraxis correlates with clinical disease outcome. Pathogenic forms of ASN evoke oxidative stress (OS), neuroinflammation, and protein alterations in neighboring cells, thereby intensifying ASN toxicity, neurodegeneration, and neuronal death. A number of evidence suggest that homeostasis between bioactive sphingolipids with opposing function-e.g., sphingosine-1-phosphate (S1P) and ceramide-is essential in pro-survival signaling and cell defense against OS. In contrast, imbalance of the "sphingolipid biostat" favoring pro-oxidative/pro-apoptotic ceramide-mediated changes have been indicated in PD and other neurodegenerative disorders. Therefore, we focused on the role of sphingolipid alterations in ASN burden, as well as in a vast range of its neurotoxic effects. Sphingolipid homeostasis is principally directed by sphingosine kinases (SphKs), which synthesize S1P-a potent lipid mediator regulating cell fate and inflammatory response-making SphK/S1P signaling an essential pharmacological target. A growing number of studies have shown that S1P receptor modulators, and agonists are promising protectants in several neurological diseases. This review demonstrates the relationship between ASN toxicity and alteration of SphK-dependent S1P signaling in OS, neuroinflammation, and neuronal death. Moreover, we discuss the S1P receptor-mediated pathways as a novel promising therapeutic approach in PD.

Fingolimod Affects Transcription of Genes Encoding Enzymes of Ceramide Metabolism in Animal Model of Alzheimer's Disease.

The imbalance in sphingolipid signaling may be critically linked to the upstream events in the neurodegenerative cascade of Alzheimer's disease (AD). We analyzed the influence of mutant (V717I) amyloid ß precursor protein (AßPP) transgene on sphingolipid metabolism enzymes in mouse hippocampus. At 3 months of age AßPP/Aß presence upregulated enzymes of ceramide turnover on the salvage pathway: ceramide synthases (CERS2, CERS4, CERS6) and also ceramidase ACER3. At 6 months, only CERS6 was elevated, and no ceramide synthase was increased at 12 months. However, sphingomyelin synthases, which utilize ceramide on the sphingomyelinase pathway, were reduced (SGMS1 at 12 and SGMS2 at 6 months). mRNAs for sphingomyelin synthases SGMS1 and SGMS2 were also significantly downregulated in human AD hippocampus and neocortex when compared with age-matched controls. Our findings suggest early-phase deregulation of sphingolipid homeostasis in favor of ceramide signaling. Fingolimod (FTY720), a modulator of sphingosine-1-phosphate receptors countered the AßPP-dependent upregulation of hippocampal ceramide synthase CERS2 at 3 months. Moreover, at 12 months, FTY720 increased enzymes of ceramide-sphingosine turnover: CERS4, ASAH1, and ACER3. We also observed influence of fingolimod on the expression of the sphingomyelinase pathway enzymes. FTY720 counteracted the AßPP-linked reduction of sphingomyelin synthases SGMS1/2 (at 12 and 6 months, respectively) and led to elevation of sphingomyelinase SMPD2 (at 6 and 12 months). Therefore, our results demonstrate potentially beneficial, age-specific effects of fingolimod on transcription of sphingolipid metabolism enzymes in an animal model of AD.

Alterations of Transcription of Genes Coding Anti-oxidative and Mitochondria-Related Proteins in Amyloid ß Toxicity: Relevance to Alzheimer's Disease.

A growing body of evidence indicates that pathological forms of amyloid beta (Aß) peptide contribute to neuronal degeneration and synaptic loss in Alzheimer's disease (AD). In this study, we investigated the impact of exogenous Aß1-42 oligomers (AßO) and endogenously liberated Aß peptides on transcription of genes for anti-oxidative and mitochondria-related proteins in cell lines (neuronal SH-SY5Y and microglial BV2) and in brain cortex of transgenic AD (Tg-AD) mice, respectively. Our results demonstrated significant AßO-evoked changes in transcription of genes in SH-SY5Y cells, where AßO enhanced expression of Sod1, Cat, mt-Nd1, Bcl2, and attenuated Sirt5, Sod2 and Sdha. In BV2 line, AßO increased the level of mRNA for Sod2, Dnm1l, Bcl2, and decreased for Gpx4, Sirt1, Sirt3, mt-Nd1, Sdha and Mfn2. Then, AßO enhanced free radicals level and impaired mitochondrial membrane potential only in SH-SY5Y cells, but reduced viability of both cell types. Inhibitor of poly(ADP-ribose)polymerase-1 and activator of sirtuin-1 more efficiently enhanced viability of SH-SY5Y than BV2 affected by AßO. Analysis of brain cortex of Tg-AD mice confirmed significant downregulation of Sirt1, Mfn1 and mt-Nd1 and upregulation of Dnm1l. In human AD brain, changes of microRNA pattern (miRNA-9, miRNA-34a, miRNA-146a and miRNA-155) seem to be responsible for decrease in Sirt1 expression. Overall, our results demonstrated a diverse response of neuronal and microglial cells to AßO toxicity. Alterations of genes encoding Sirt1, Mfn1 and Drp1 in an experimental model of AD suggest that modulation of mitochondria dynamics and Sirt1, including miRNA strategy, may be crucial for improvement of AD therapy.

The Role of Ceramide and Sphingosine-1-Phosphate in Alzheimer's Disease and Other Neurodegenerative Disorders.

Bioactive sphingolipids-ceramide, sphingosine, and their respective 1-phosphates (C1P and S1P)-are signaling molecules serving as intracellular second messengers. Moreover, S1P acts through G protein-coupled receptors in the plasma membrane. Accumulating evidence points to sphingolipids' engagement in brain aging and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. Metabolic alterations observed in the course of neurodegeneration favor ceramide-dependent pro-apoptotic signaling, while the levels of the neuroprotective S1P are reduced. These trends are observed early in the diseases' development, suggesting causal relationship. Mechanistic evidence has shown links between altered ceramide/S1P rheostat and the production, secretion, and aggregation of amyloid ß/α-synuclein as well as signaling pathways of critical importance for the pathomechanism of protein conformation diseases. Sphingolipids influence multiple aspects of Akt/protein kinase B signaling, a pathway that regulates metabolism, stress response, and Bcl-2 family proteins. The cross-talk between sphingolipids and transcription factors including NF-κB, FOXOs, and AP-1 may be also important for immune regulation and cell survival/death. Sphingolipids regulate exosomes and other secretion mechanisms that can contribute to either the spread of neurotoxic proteins between brain cells, or their clearance. Recent discoveries also suggest the importance of intracellular and exosomal pools of small regulatory RNAs in the creation of disturbed signaling environment in the diseased brain. The identified interactions of bioactive sphingolipids urge for their evaluation as potential therapeutic targets. Moreover, the early disturbances in sphingolipid metabolism may deliver easily accessible biomarkers of neurodegenerative disorders.

Modulatory Effects of Fingolimod (FTY720) on the Expression of Sphingolipid Metabolism-Related Genes in an Animal Model of Alzheimer's Disease.

Sphingolipid signaling disturbances correlate with Alzheimer's disease (AD) progression. We examined the influence of FTY720/fingolimod, a sphingosine analog and sphingosine-1-phosphate (S1P) receptor modulator, on the expression of sphingolipid metabolism and signaling genes in a mouse transgenic AD model. Our results demonstrated that AßPP (V717I) transgene led with age to reduced mRNA expression of S1P receptors (S1PRs), sphingosine kinase SPHK2, ceramide kinase CERK, and the anti-apoptotic Bcl2 in the cerebral cortex and hippocampus, suggesting a pro-apoptotic shift in 12-month old mice. These changes largely emulated alterations we observed in the human sporadic AD hippocampus: reduced SPHK1, SPHK2, CERK, S1PR1, and BCL2. We observed that the responses to FTY720 treatment were modified by age and notably differed between control (APP-) and AD transgenic (APP+) animals. AßPP (V717I)-expressing 12-month-old animals reacted to fingolimod with wide changes in the gene expression program in cortex and hippocampus, including increased pro-survival SPHKs and CERK. Moreover, BCL2 was elevated by FTY720 in the cortex at all ages (3, 6, 12 months) while in hippocampus this increase was observed at 12 months only. In APP- mice, fingolimod did not induce any significant mRNA changes at 12 months. Our results indicate significant effect of FTY720 on the age-dependent transcription of genes involved in sphingolipid metabolism and pro-survival signaling, suggesting its neuroprotective role in AD animal model.

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.

The role of ceramide and SEW 2871 in the transcription of enzymes involved in amyloid b precursor protein metabolism in an experimental model of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by alterations of amyloid precursor protein (APP) metabolism, accumulation of amyloid  peptides (A), hyperphosphorylation of Tau proteins and also by sphingolipids disturbances. These changes lead to oxidative stress, mitochondria dysfunction, synaptic loss and neuro-inflammation. It is known that A may promote ceramides formation and reversely, ceramides could stimulate A peptides release. However, the effect of ceramide and sphingosine-1-phosphate (S1P) on APP metabolism has not been fully elucidated. In this study we investigated the role of ceramide and S1P on APP metabolism. Moreover, the effect of ceramide and SEW 2871 (agonist for S1P receptor-1) on Sirt1 (NAD+-dependent nuclear enzyme responsible for stress response) gene expression under A toxicity was analyzed. Experiments were carried out using pheochromocytoma cells (PC-12) transfected with: an empty vector (used as a control), human wild-type APP gene (APPwt) and Swedish mutated (K670M/N671L) APP gene (APPsw). Our results indicated that C2-ceramide significantly decreased the viability of the APPwt, APPsw as well as empty vector-transfected PC12 cells. It was observed that C2-ceramide had no significant effect on the mRNA level of - and -secretase in APPwt and APPsw cells. However, it significantly decreased transcription of -secretase in control cells. Results also showed a significant increase in Psen1 (crucial subunit of -secretase) gene expression in APPsw cells after incubation with C2-ceramide. We observed that SEW 2871 significantly upregulated the mRNA level of -secretase in control-empty vector-transfected cells subjected to C2-ceramide toxicity. The same tendency, though insignificant, was observed in APPwt and APPsw cells. Moreover, SEW 2871 enhanced the mRNA level of -secretase and Psen1 in APPsw cells after C2-ceramide treatment. Additionally, SEW 2871 significantly upregulated a gene expression of Sirt1 in APPwt and also APPsw cells subjected to C2-ceramide toxicity. Furthermore, it was observed that SEW 2871 significantly enhanced the viability of all investigated cells' lines probably through its positive influence on Sirt1.

Opportunities for the repurposing of PARP inhibitors for the therapy of non-oncological diseases.

The recent clinical availability of the PARP inhibitor olaparib (Lynparza) opens the door for potential therapeutic repurposing for non-oncological indications. Considering (a) the preclinical efficacy data with PARP inhibitors in non-oncological diseases and (b) the risk-benefit ratio of treating patients with a compound that inhibits an enzyme that has physiological roles in the regulation of DNA repair, we have selected indications, where (a) the severity of the disease is high, (b) the available therapeutic options are limited, and (c) the duration of PARP inhibitor administration could be short, to provide first-line options for therapeutic repurposing. These indications are as follows: acute ischaemic stroke; traumatic brain injury; septic shock; acute pancreatitis; and severe asthma and severe acute lung injury. In addition, chronic, devastating diseases, where alternative therapeutic options cannot halt disease development (e.g. Parkinson's disease, progressive multiple sclerosis or severe fibrotic diseases), should also be considered. We present a preclinical and clinical action plan for the repurposing of PARP inhibitors. LINKED ARTICLES: This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Inhibition of poly(ADP-ribose) polymerase-1 alters expression of mitochondria-related genes in PC12 cells: relevance to mitochondrial homeostasis in neurodegenerative disorders.

Alzheimer's disease (AD) is characterized by the release of amyloid beta peptides (Aß) in the form of monomers/oligomers which may lead to oxidative stress, mitochondria dysfunction, synaptic loss, neuroinflammation and, in consequence, to overactivation of poly(ADP-ribose) polymerase-1 (PARP-1). However, Aß peptides are also released in the brain ischemia, traumatic injury and in inflammatory response. PARP-1 is suggested to be a promising target in therapy of neurodegenerative disorders. We investigated the impact of PARP-1 inhibition on transcription of mitochondria-related genes in PC12 cells. Moreover, the effect of PARP-1 inhibitor (PJ34) on cells subjected to Aß oligomers (AßO) - evoked stress was analyzed. Our data demonstrated that inhibition of PARP-1 in PC12 cells enhanced the transcription of genes for antioxidative enzymes (Sod1, Gpx1, Gpx4), activated genes regulating mitochondrial fission/fusion (Mfn1, Mfn2, Dnm1l, Opa1, Fis1), subunits of ETC complexes (mt-Nd1, Sdha, mt-Cytb) and modulated expression of several TFs, enhanced Foxo1 and decreased Nrf1, Stat6, Nfkb1. AßO elevated free radicals concentration, decreased mitochondria membrane potential (MMP) and cell viability after 24h. Gene transcription was not affected by AßO after 24h, but was significantly downregulated after 96h. In AßO stress, PJ34 exerted stimulatory effect on expression of several genes (Gpx1, Gpx4, Opa1, Mfn2, Fis1 and Sdha), decreased transcription of numerous TFs (Nrf1, Tfam, Stat3, Stat6, Trp53, Nfkb1) and prevented oxidative stress. Our results indicated that PARP-1 inhibition significantly enhanced transcription of genes involved in antioxidative defense and in regulation of mitochondria function, but was not able to ameliorate cells viability affected by Aß.

Inhibition of Poly(ADP-ribose) Polymerase-1 Enhances Gene Expression of Selected Sirtuins and APP Cleaving Enzymes in Amyloid Beta Cytotoxicity.

Poly(ADP-ribose) polymerases (PARPs) and sirtuins (SIRTs) are involved in the regulation of cell metabolism, transcription, and DNA repair. Alterations of these enzymes may play a crucial role in Alzheimer's disease (AD). Our previous results indicated that amyloid beta (Aß) peptides and inflammation led to activation of PARP1 and cell death. This study focused on a role of PARP1 in the regulation of gene expression for SIRTs and beta-amyloid precursor protein (ßAPP) cleaving enzymes under Aß42 oligomers (AßO) toxicity in pheochromocytoma cells (PC12) in culture. Moreover, the effect of endogenously liberated Aß peptides in PC12 cells stably transfected with human gene for APP wild-type (APPwt) was analyzed. Our results demonstrated that AßO enhanced transcription of presenilins (Psen1 and Psen2), the crucial subunits of γ-secretase. Aß peptides in APPwt cells activated expression of ß-secretase (Bace1), Psen1, Psen2, and Parp1. The inhibitor of PARP1, PJ-34 in the presence of AßO upregulated transcription of α-secretase (Adam10), Psen1, and Psen2, but also Bace1. Concomitantly, PJ-34 enhanced mRNA level of nuclear Sirt1, Sirt6, mitochondrial Sirt4, and Parp3 in PC12 cells subjected to AßOs toxicity. Our data indicated that Aß peptides through modulation of APP secretases may lead to a vicious metabolic circle, which could be responsible for maintaining Aß at high level. PARP1 inhibition, besides activation of nuclear SIRTs and mitochondrial Sirt4 expression, enhanced transcription of enzyme(s) involved in ßAPP metabolism, and this effect should be considered in its application against Aß peptide toxicity.

Levels of selected pro- and anti-inflammatory cytokines in cerebrospinal fluid in patients with hydrocephalus.

Cytokines are widely known mediators of inflammation accompanying many neurodegenerative disorders including normal pressure hydrocephalus (NPH). NPH is caused by impaired cerebrospinal fluid (CSF) absorption and treated by surgical shunt insertion. The early diagnosis of NPH is difficult because of various manifestations of the disease. One of the most promising research directions is biochemical CSF analysis. The aim of this study was to determine the CSF levels of cytokines. The levels of various cytokines (IL-6, IL-8, IL-12, IL-10 and TNF-α) were measured in patients with idiopathic active normal pressure hydrocephalus, arrested hydrocephalus and hydrocephalus with brain atrophy compared to controls. Our study showed that the concentrations of IL-6 and IL-8 were significantly elevated in the group with idiopathic active hydrocephalus compared to control patients. Moreover, we observed that the levels of IL-6 and IL-8 in the group with idiopathic active hydrocephalus were significantly higher compared to patients with arrested hydrocephalus and hydrocephalus with brain atrophy..

Sirtuins and Their Roles in Brain Aging and Neurodegenerative Disorders.

Sirtuins (SIRT1-SIRT7) are unique histone deacetylases (HDACs) whose activity depends on NAD+ levels and thus on the cellular metabolic status. SIRTs regulate energy metabolism and mitochondrial function. They orchestrate the stress response and damage repair. Through these functions sirtuins modulate the course of aging and affect neurodegenerative diseases. SIRTSs interact with multiple signaling proteins, transcription factors (TFs) and poly(ADP-ribose) polymerases (PARPs) another class of NAD+-dependent post-translational protein modifiers. The cross-talk between SIRTs TFs and PARPs is a highly promising research target in a number of brain pathologies. This review describes updated results on sirtuins in brain aging/neurodegeneration. It focuses on SIRT1 but also on the roles of mitochondrial SIRTs (SIRT3, 4, 5) and on SIRT6 and SIRT2 localized in the nucleus and in cytosol, respectively. The involvement of SIRTs in regulation of insulin-like growth factor signaling in the brain during aging and in Alzheimer's disease was also focused. Moreover, we analyze the mechanism(s) and potential significance of interactions between SIRTs and several TFs in the regulation of cell survival and death. A critical view is given on the application of SIRT activators/modulators in therapy of neurodegenerative diseases.

The Lipoxygenases: Their Regulation and Implication in Alzheimer's Disease.

Inflammatory processes and alterations of lipid metabolism play a crucial role in Alzheimer's disease (AD) and other neurodegenerative disorders. Polyunsaturated fatty acids (PUFA) metabolism impaired by cyclooxygenases (COX-1, COX-2), which are responsible for formation of several eicosanoids, and by lipoxygenases (LOXs) that catalyze the addition of oxygen to linolenic, arachidonic (AA), and docosahexaenoic acids (DHA) and other PUFA leading to formation of bioactive lipids, significantly affects the course of neurodegenerative diseases. Among several isoforms, 5-LOX and 12/15-LOX are especially important in neuroinflammation/neurodegeneration. These two LOXs are regulated by substrate concentration and availability, and by phosphorylation/dephosphorylation through protein kinases PKA, PKC and MAP-kinases, including ERK1/ERK2 and p38. The protein/protein interaction also is involved in the mechanism of 5-LOX regulation through FLAP protein and coactosin-like protein. Moreover, non-heme iron and calcium ions are potent regulators of LOXs. The enzyme activity significantly depends on the cell redox state and is differently regulated by various signaling pathways. 5-LOX and 12/15-LOX convert linolenic acid, AA, and DHA into several bioactive compounds e.g. hydroperoxyeicosatetraenoic acids (5-HPETE, 12S-HPETE, 15S-HPETE), which are reduced to corresponding HETE compounds. These enzymes synthesize several bioactive lipids, e.g. leucotrienes, lipoxins, hepoxilins and docosahexaenoids. 15-LOX is responsible for DHA metabolism into neuroprotectin D1 (NPD1) with significant antiapoptotic properties which is down-regulated in AD. In this review, the regulation and impact of 5-LOX and 12/15-LOX in the pathomechanism of AD is discussed. Moreover, we describe the role of several products of LOXs, which may have significant pro- or anti-inflammatory activity in AD, and the cytoprotective effects of LOX inhibitors.

Sphingosine-1-phosphate and its effect on glucose deprivation/glucose reload stress: from gene expression to neuronal survival.

Sphingosine kinase-1 (Sphk1-1, EC 2.7.1.91) is a regulator of pro-survival signalling, and its alterations have been observed in Alzheimer's disease, brain ischemia and other neurological disorders. In this study we addressed the question whether Sphk1 and its product, sphingosine-1-phosphate (S1P), play a significant role in glucose deprivation (GD)/glucose reload (GR) stress in hippocampal neuronal cells (HT22). It was found that GD (6 h) followed by 24 h of GR evoked enhancement of the free radical level and neuronal HT22 cell death. Moreover, the significantly stronger gene expression for the pro-apoptotic Bax protein and down-regulation of the anti-apoptotic Bcl-2 and Bcl-XL proteins were observed. Concomitantly, this stress up-regulated: gene expression, protein level and activity of Sphk1. Exogenous S1P at 1 µM concentration and the other agonists of the S1P1 receptor (SEW 2871 and P-FTY720) enhanced HT22 cell viability affected by GD/GR stress. This mechanism is mediated by S1P receptor(s) signalling and by the activation of gene expression for Bcl-2 and Bcl-XL. Summarising, our data suggest that sphingolipid metabolism may play an important role in the early events that take place in neuronal cell survival/death under GD/GR stress. Our data demonstrate that exogenous S1P, through the activation of specific receptors S1P1 and S1P3 signalling pathways, regulates the gene expression for anti-apoptotic proteins and enhances neuronal cell survival affected by GD/GR stress.

Sphingosine kinases modulate the secretion of amyloid ß precursor protein from SH-SY5Y neuroblastoma cells: the role of α-synuclein.

Sphingosine kinases (SphK 1&2) are involved in the regulation of cell survival, differentiation and neurotransmitter secretion. Current data suggest potential links between sphingolipid signalling, α-synuclein (ASN) and Alzheimer's disease (AD). Our aim was to investigate the possible role of SphKs and ASN in the regulation of the production and secretion of the amyloid ß precursor protein (APP). We have previously shown that ASN intensified the secretion and toxicity of amyloid ß (Aß) to the point where it caused cell death. Our current results show that APP, the precursor protein for Aß, is also influenced by ASN. The stable overexpression of wtASN in SH-SY5Y cells caused a three-fold, significant increase of the cellular APP level. This suggests that the influence of ASN on Aß metabolism may actually occur at the level of APP protein rather than only through the changes of its cleavage into Aß. To elucidate the mechanisms of APP modulation the cells were exposed to S1P and an SphK inhibitor (SKI). 72 h S1P treatment at 5 µM caused a nearly 50% reduction of the cellular APP signal. S1P also caused a tendency towards higher APP secretion, though the results were insignificant. The inhibition of SphKs decreased medium APP levels in a dose-dependent manner, reaching significance at 5 µM SKI with a correspondingly elevated intracellular level. Thus, it is reasonable to expect that in fact the influence of SphK activity on APP might be pro-secretory. This would also be in agreement with numerous articles on SphK-dependent secretion in the literature. The chronic nature of AD further suggests that subtle alterations in APP metabolism could have the potential to drive important changes in brain condition.

Ceramide in the molecular mechanisms of neuronal cell death. The role of sphingosine-1-phosphate.

Ceramide and sphingosine-1-phosphate (S1P), two important bioactive sphingolipids, have been suggested as being key players in the pathology of Alzheimer's disease in inflammation and cancer. However, their role in the molecular mechanisms of neuronal death has not been fully elucidated. Our study indicated that ceramide significantly enhanced the level of free radicals and decreased the viability of the human neuroblastoma cell line (SH-SY5Y) through inhibition of the prosurvival PI3-K/Akt pathway. Ceramide also decreased anti-apoptotic (Bcl-2) and increased pro-apoptotic (Bax, Hrk) mRNA/protein levels. Concomitantly, our study indicated that ceramide induced poly(ADP-ribose) polymerase-1 (PARP-1) activation and accumulation of poly(ADP-ribose) PAR, a signalling molecule involved in mitochondria-nucleus cross-talk and mitochondria integrity. Ceramide treatment significantly decreased the level of apoptosis-inducing factor (AIF) in the mitochondria. The PARP-1 inhibitor (PJ-34) prevented AIF release from the mitochondria. In addition, our data showed that exogenously added S1P increased the viability of SH-SY5Y through the S1P (1,3) receptor-dependent mechanism. It was also revealed that the S1P and PARP-1 inhibitor (PJ-34) decreased oxidative stress, gene expression of the pro-apoptotic Hrk protein and up-regulated the anti-apoptotic Bcl-2 protein. Our data demonstrate that neuronal cell death evoked by ceramide is regulated by PARP/PAR/AIF and by S1P receptor signalling. In summary, our results suggest that PARP-1 inhibitor(s) and modulators of sphingosine-1-phosphate receptor(s) should be considered in potential therapeutic strategies directed at neurodegenerative diseases.

Expression and activity of PARP family members in the hippocampus during systemic inflammation: their role in the regulation of prooxidative genes.

Poly(ADP-ribose)polymerase-1 (PARP-1) plays an important role in DNA repair processes during oxidative/genotoxic stress, in regulation of transcription factors and in cell death mechanisms. However, little is known about the physiopathological role of other PARP family members. In this study we analyzed, for the first time, expression of PARP family genes in the hippocampus of mice subjected to lipopolysaccharide (LPS)-evoked systemic inflammatory response (SIR). Moreover, the effect of SIR on PARP activity and on its role in gene expression was evaluated. Our data indicated that SIR enhances PARP-1, -3, -9, -12 and -14 gene expressions in mouse hippocampus. PARP activity in the hippocampus was also considerably elevated during SIR with a maximum value at 12h after LPS administration, indicating significant formation and accumulation of poly(ADP-ribose) (PAR) - this reaction's product. Concomitantly, higher expression of genes for inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), TNF-α and NADPH oxidase subunits occurred in the hippocampus during the first hours of SIR. The inhibitor of PARP, i.e. 3-aminobenzamide (3-AB; 30mg/kg b.w.), protected the hippocampal cells against PAR formation and expression of the gene for iNOS. However, PARP activity had no effect on the mRNA level of COX-2, TNF-α and NADPH oxidase in the hippocampus. Bioinformatic analysis predicted that interaction between PARP/PAR and 41 transcription factors may be important for regulation of expression of 139 genes from the group of 262 that changed expression in the hippocampus during SIR. Summarizing, enhancement of gene expression and activity of PARP family members by SIR could lead, through modification of the protein poly(ADP-ribosylation) process, to changes in the proteins' activity. A higher level of PAR and PARP/PAR protein interaction may affect the functioning of several transcription factors. PARP activity plays a role in regulation of expression of iNOS, the main enzyme responsible for oxidative/nitrosative stress in SIR.