Molecular and functional characterization of polymorphisms in the secreted phospholipase A2 group X gene: relevance to coronary artery disease

Among secreted phospholipases A2 (sPLA2s), human group X sPLA2 (hGX sPLA2) is emerging as a novel attractive therapeutic target due to its implication in inflammatory diseases. To elucidate whether hGX sPLA2 plays a causative role in coronary artery disease (CAD), we screened the human PLA2G10 gene to identify polymorphisms and possible associations with CAD end-points in a prospective study, AtheroGene. We identified eight polymorphisms, among which, one non-synonymous polymorphism R38C in the propeptide region of the sPLA2. The T-512C polymorphism located in the 5′ untranslated region was associated with a decreased risk of recurrent cardiovascular events during follow-up. The functional analysis of the R38C polymorphism showed that it leads to a profound change in expression and activity of hGX sPLA2, although there was no detectable impact on CAD risk. Due to the potential role of hGX sPLA2 in inflammatory processes, these polymorphisms should be investigated in other inflammatory diseases

A Common Carcinogen Benzo[a]pyrene Causes Neuronal Death in Mouse via Microglial Activation

BACKGROUND: Benzo[a]pyrene (B[a]P) belongs to a class of polycyclic aromatic hydrocarbons that serve as micropollutants in the environment. B[a]P has been reported as a probable carcinogen in humans. Exposure to B[a]P can take place by ingestion of contaminated (especially grilled, roasted or smoked) food or water, or inhalation of polluted air. There are reports available that also suggests neurotoxicity as a result of B[a]P exposure, but the exact mechanism of action is unknown. METHODOLOGY/PRINCIPAL FINDINGS: Using neuroblastoma cell line and primary cortical neuron culture, we demonstrated that B[a]P has no direct neurotoxic effect. We utilized both in vivo and in vitro systems to demonstrate that B[a]P causes microglial activation. Using microglial cell line and primary microglial culture, we showed for the first time that B[a]P administration results in elevation of reactive oxygen species within the microglia thereby causing depression of antioxidant protein levels; enhanced expression of inducible nitric oxide synthase, that results in increased production of NO from the cells. Synthesis and secretion of proinflammatory cytokines were also elevated within the microglia, possibly via the p38MAP kinase pathway. All these factors contributed to bystander death of neurons, in vitro. When administered to animals, B[a]P was found to cause microglial activation and astrogliosis in the brain with subsequent increase in proinflammatory cytokine levels. CONCLUSIONS/SIGNIFICANCE: Contrary to earlier published reports we found that B[a]P has no direct neurotoxic activity. However, it kills neurons in a bystander mechanism by activating the immune cells of the brain viz the microglia. For the first time, we have provided conclusive evidence regarding the mechanism by which the micropollutant B[a]P may actually cause damage to the central nervous system. In today's perspective, where rising pollution levels globally are a matter of grave concern, our study throws light on other health hazards that such pollutants may exert

Real-Time Imaging Reveals the Dynamics of Leukocyte Behaviour during Experimental Cerebral Malaria Pathogenesis

During experimental cerebral malaria (ECM) mice develop a lethal neuropathological syndrome associated with microcirculatory dysfunction and intravascular leukocyte sequestration. The precise spatio-temporal context in which the intravascular immune response unfolds is incompletely understood. We developed a 2-photon intravital microscopy (2P-IVM)-based brain-imaging model to monitor the real-time behaviour of leukocytes directly within the brain vasculature during ECM. Ly6Chi monocytes, but not neutrophils, started to accumulate in the blood vessels of Plasmodium berghei ANKA (PbA)-infected MacGreen mice, in which myeloid cells express GFP, one to two days prior to the onset of the neurological signs (NS). A decrease in the rolling speed of monocytes, a measure of endothelial cell activation, was associated with progressive worsening of clinical symptoms. Adoptive transfer experiments with defined immune cell subsets in recombinase activating gene (RAG)-1-deficient mice showed that these changes were mediated by Plasmodium-specific CD8+ T lymphocytes. A critical number of CD8+ T effectors was required to induce disease and monocyte adherence to the vasculature. Depletion of monocytes at the onset of disease symptoms resulted in decreased lymphocyte accumulation, suggesting reciprocal effects of monocytes and T cells on their recruitment within the brain. Together, our studies define the real-time kinetics of leukocyte behaviour in the central nervous system during ECM, and reveal a significant role for Plasmodium-specific CD8+ T lymphocytes in regulating vascular pathology in this disease. © 2014 Pai et al

Macrophage secretory phospholipase A2 group X enhances anti-inflammatory responses, promotes lipid accumulation, and contributes to aberrant lung pathology.

Secreted phospholipase A2 group X (sPLA(2)-X) is one of the most potent enzymes of the phospholipase A(2) lipolytic enzyme superfamily. Its high catalytic activity toward phosphatidylcholine (PC), the major phospholipid of cell membranes and low-density lipoproteins (LDL), has implicated sPLA(2)-X in chronic inflammatory conditions such as atherogenesis. We studied the role of sPLA(2)-X enzyme activity in vitro and in vivo, by generating sPLA(2)-X-overexpressing macrophages and transgenic macrophage-specific sPLA(2)-X mice. Our results show that sPLA(2)-X expression inhibits macrophage activation and inflammatory responses upon stimulation, characterized by reduced cell adhesion and nitric oxide production, a decrease in tumor necrosis factor (TNF), and an increase in interleukin (IL)-10. These effects were mediated by an increase in IL-6, and enhanced production of prostaglandin E(2) (PGE(2)) and 15-deoxy-Delta12,14-prostaglandin J(2) (PGJ(2)). Moreover, we found that overexpression of active sPLA(2)-X in macrophages strongly increases foam cell formation upon incubation with native LDL but also oxidized LDL (oxLDL), which is mediated by enhanced expression of scavenger receptor CD36. Transgenic sPLA(2)-X mice died neonatally because of severe lung pathology characterized by interstitial pneumonia with massive granulocyte and surfactant-laden macrophage infiltration. We conclude that overexpression of the active sPLA(2)-X enzyme results in enhanced foam cell formation but reduced activation and inflammatory responses in macrophages in vitro. Interestingly, enhanced sPLA(2)-X activity in macrophages in vivo leads to fatal pulmonary defects, suggesting a crucial role for sPLA(2)-X in inflammatory lung disease

Helicobacter pylori

Helicobacter pylori infection plays an important role in the pathogenesis of peptic ulcer disease (PUD). Several factors have been proposed as possible H. pylori virulence determinants; for example, bacterial adhesins and gastric inflammation factors are associated with an increased risk of PUD. However, differences in bacterial virulence factors alone cannot explain the opposite ends of the PUD disease spectrum, i.e., duodenal and gastric ulcers; presumably, both bacterial and host factors contribute to the differential response. Carriers of the high-producer alleles of the pro-inflammatory cytokines interleukin (IL)-1B, IL-6, IL-8, IL-10, and tumor necrosis factor-α who also carry low-producer allele carriers of anti-inflammatory cytokines have severe gastric mucosal inflammation, whereas carriers of the alternative alleles have mild inflammation. Recent reports have suggested that the PSCA and CYP2C19 ultra-rapid metabolizer genotypes are also associated with PUD