Platelet-activating factor acetylhydrolase gene polymorphism and its activity in Japanese patients with multiple sclerosis

New Insights Into the Pathologic Roles of the Platelet-Activating Factor System

Described almost 50 years ago, the glycerophosphocholine lipid mediator Platelet-activating factor (PAF) has been implicated in many pathologic processes. Indeed, elevated levels of PAF can be measured in response to almost every type of pathology involving inflammation and cell damage/death. In this review, we provide evidence for PAF involvement in pathologic processes, with focus on cancer, the nervous system, and in photobiology. Importantly, recent insights into how PAF can generate and travel via bioactive extracellular vesicles such as microvesicle particles (MVP) are presented. What appears to be emerging from diverse pathologies in different organ systems is a common theme where pro-oxidative stressors generate oxidized glycerophosphocholines with PAF agonistic effects, which then trigger more enzymatic PAF synthesis via the PAF receptor. A downstream consequence of PAF receptor activation is the generation and release of MVP which provide a mechanism to transmit PAF as well as other bioactive agents. The knowledge gaps which when addressed could result in novel therapeutic strategies are also discussed. Taken together, an enhanced understanding of the PAF family of lipid mediators is essential in our improved comprehension of the relationship amongst the diverse cutaneous, cancerous, neurologic and systemic pathologic processes.

Platelet-activating factor acetylhydrolases: An overview and update

Platelet-activating factor acetylhydrolases (PAF-AHs) are unique members of the phospholipase A₂ family that can hydrolyze the acetyl group of PAF, a signaling phospholipid that has roles in diverse (patho)physiological processes. Three types of PAF-AH have been identified in mammals, one plasma type and two intracellular types [PAF-AH (I) and PAF-AH (II)]. Plasma PAF-AH and PAF-AH (II) are monomeric enzymes that are structurally similar, while PAF-AH (I) is a multimeric enzyme with no homology to other PAF-AHs. PAF-AH (I) shows a strong preference for an acetyl group, whereas plasma PAF-AH and PAF-AH (II) also hydrolyze phospholipids with oxidatively modified fatty acids. Plasma PAF-AH has been implicated in several diseases including cardiovascular disease. PAF-AH (I) is required for spermatogenesis and is increasingly recognized as an oncogenic factor. PAF-AH (II) was recently shown to act as a bioactive lipid-producing enzyme in mast cells and thus could be a drug target for allergic diseases. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Naturally Occurring Missense Mutation in Plasma PAF-AH Among the Japanese Population

A single nucleotide polymorphism in the plasma PAF-AH enzyme, i.e., G994T, which causes the substitution of Val at amino acid 279 with Phe (V279F), has been found in the Japanese population. This enzyme preferentially degrades oxidatively modulated or truncated phospholipids; therefore, it has been suggested that this enzyme may prevent the accumulation of proinflammatory and proatherogenic oxidized phospholipids. This hypothesis is supported by the higher prevalence of the V279F mutation in patients with asthmatic and atherosclerotic diseases, as compared with healthy controls. This mutation is rare in the Caucasian population. The plasma PAF-AH mass and enzyme activity are distributed over a wide range in the plasma and they are positively correlated with low-density lipoprotein (LDL) cholesterol. However, several clinical studies in the Caucasian population have suggested that this enzyme has the opposite role. This enzyme plays an active role in the development and progression of atherosclerosis via proinflammatory and proatherogenic lysophosphatidylcholine and oxidized fatty acids produced through the oxidation of LDL by this enzyme. Thus, plasma PAF-AH is a unique enzyme with dual roles in human inflammatory diseases. In this chapter, on the basis of recent findings we describe the association between a naturally occurring missense mutation in plasma PAF-AH and human diseases especially including atherosclerosis and asthma.

IL2RA Allele Increases Risk of Neuromyelitis Optica in Southern Han Chinese

Background:

Neuromyelitis optica (NMO) and multiple sclerosis (MS) are chronic neuro-inflammatory diseases believed to arise from complex interactions between environmental and genetic factors. Recently, single nucleotide polymorphisms (SNPs) in interleukin (IL)-2 and -7 receptor alpha genes have been identified as novel susceptibility alleles for MS in genome-wide association studies. However, similar research on NMO is limited. We aimed to investigate the association of IL2RA SNPs rs2104286 and rs12722489 and IL7RA SNP rs6897932 with Southern Han Chinese NMO and MS patients.

Methods:

Frequencies of the three SNPs were examined in Southern Han Chinese mS cases (n=78), NMS cases (n=67) and controls (n=133) using sequencing-based typing.

Results:

The rs2104286G frequency in the IL2RA gene was significantly higher in NMO patients than in controls (puncorr=0.013, pcorr=0.026, OR:1.942, 95%CI:1.146-3.291).

Conclusion:

The rs2104286 G allele in IL2RA is present at higher frequencies in NMO patients than in healthy controls within a Southern Han Chinese population.

Role of platelets in neuroinflammation: a wide-angle perspective

OBJECTIVES

This review summarizes recent developments in platelet biology relevant to neuroinflammatory disorders. Multiple sclerosis (MS) is taken as the "Poster Child" of these disorders but the implications are wide. The role of platelets in inflammation is well appreciated in the cardiovascular and cancer research communities but appears to be relatively neglected in neurological research.

ORGANIZATION

After a brief introduction to platelets, topics covered include the matrix metalloproteinases, platelet chemokines, cytokines and growth factors, the recent finding of platelet PPAR receptors and Toll-like receptors, complement, bioactive lipids, and other agents/functions likely to be relevant in neuroinflammatory diseases. Each section cites literature linking the topic to areas of active research in MS or other disorders, including especially Alzheimer's disease.

CONCLUSION

The final section summarizes evidence of platelet involvement in MS. The general conclusion is that platelets may be key players in MS and related disorders, and warrant more attention in neurological research.

Functional Consequences of Mutations and Polymorphisms in the Coding Region of the PAF Acetylhydrolase (PAF-AH) Gene

In the past several years a number of alterations in the PAF-AH/PLA₂G7/LpPLA₂ gene have been described. These include inactivating mutations, polymorphisms in the coding region, and other genetic changes located in promoter and intronic regions of the gene. The consequences associated with these genetic variations have been evaluated from different perspectives, including in vitro biochemical and molecular studies and clinical analyses in human subjects. This review highlights the current state of the field and suggests new approaches that can be used to evaluate functional consequences associated with mutations and polymorphisms in the PAF-AH gene.

Neuromyelitis optica and asian phenotype of multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS), whereas neuromyelitis optica (NMO) is an inflammatory disease of the CNS selectively affecting the optic nerves and spinal cord. The pathological hallmark in MS is sharply demarcated demyelinating plaque with axons relatively preserved, whereas in NMO both axons and myelin are involved, resulting in necrotic cavitation. The nosological position of NMO has long been a matter of debate. In Asians, MS is rare; however, when it appears, the selective but severe involvement of the optic nerves and spinal cord is characteristic. This form, termed opticospinal MS (OSMS), has similar features to those of the relapsing form of NMO in Western populations. Recent discovery of a specific immunoglobulin G (IgG) against NMO, designated NMO-IgG, suggests that NMO is a distinct disease entity with a fundamentally different etiology from that of MS. Because NMO-IgG has been reported to be present in about 50%-60% of OSMS patients with longitudinally extensive spinal cord lesions (LESCLs), OSMS in Asians has been suggested to be the same entity as NMO. About half of the patients with the anti-aquaporin 4 (AQP4) antibody demonstrate brain lesions fulfilling the Barkhof criteria, whereas OSMS patients without the anti-AQP4 antibody show significantly fewer brain lesions. These findings indicate that the mechanism of LESCLs in Asians is heterogeneous, both related and unrelated to anti-AQP4 antibody, and that the disease condition with anti-AQP4 antibody does not completely overlap OSMS in Asians. This review discusses possible mechanisms for OSMS and anti-AQP4 autoimmune syndrome of the CNS.

Anterior periventricular linear lesions in optic-spinal multiple sclerosis: a combined neuroimaging and neuropathological study

There are two distinct subtypes of multiple sclerosis (MS) in Asians, optic-spinal (OSMS) and conventional (CMS). In OSMS, severe spinal cord lesions are characteristic while brain lesions are scant. We sought to clarify atypical brain lesions in OSMS by neuroimaging and pathological studies. For brain MRI, 124 consecutive Japanese patients with clinically definite MS based on Poser criteria were enrolled, 57 with OSMS and 67 with CMS. Ten autopsied cases (seven OSMS and three CMS) were studied pathologically. Although the frequency of brain lesions fulfilling Barkhof criteria was significantly higher in CMS than in OSMS, periventricular linear lesions along with the anterior portion of the corpus callosum and the lateral ventricles were significantly more common in OSMS than in CMS. Pathologically, periventricular lesions in CMS extended deeply into the white matter, while those in OSMS were confined to periventricular areas. T cell infiltration in lesions was prominent in CMS but not in OSMS. Although severe axonal loss and cavity formation were commonly seen in periventricular and spinal cord lesions in OSMS, lymphocytic infiltrates and vessel wall thickening were observed only in the latter. Thus, we suggested that anterior periventricular linear lesions without ovoid ones are characteristic of OSMS.

Recent advances in genetic analysis of multiple sclerosis: genetic associations and therapeutic implications

Epidemiological studies have confirmed that genetic factors are a key component in the pathogenesis of multiple sclerosis (MS) and that those determining MS susceptibility have been extensively studied. Many papers have been published regarding the heritable differences useful in genetic studies; these include variations in DNA, such as single-nucleotide polymorphisms, microsatellites and insertion/deletion polymorphisms. However, to date, among other regions, HLA is the only region confirmed to possess genes that determine MS susceptibility. In this article, we review the progress during the last 5 years in the studies on the susceptibility genes and the pharmacogenetics of MS. Newer techniques and methods of analysis will hopefully result in better screening of individuals who are at highest risk and novel treatments.

Post-translational modifications in the rat lumbar spinal cord in experimental autoimmune encephalomyelitis

Changes in protein methylation, citrullination, and phosphorylation during experimental autoimmune encephalomyelitis, a rodent model of multiple sclerosis, were evaluated using isobaric tags for relative and absolute quantification analysis of peptides produced from normal and diseased rat lumbar spinal cords. We observed alterations in the post-translational modification of key proteins regulating signal transduction and axonal integrity. Dephosphorylation of discrete serine residues within the neurofilament heavy subunit C-terminus was observed. We report for the first time elevated citrullination of Arg27 in glial fibrillary acidic protein, which may contribute to the pathophysiology of astrocytes.