Cyanobacterial Microcystis aeruginosa Lipopolysaccharide Elicits Release of Superoxide Anion, Thromboxane B2, Cytokines, Chemokines, and Matrix Metalloproteinase-9 by Rat Microglia

Abstract

Microcystis aeruginosa (M. aeruginosa) is a cosmopolitan Gram-negative cyanobacterium that may contaminate freshwater by releasing toxins, such as lipopolysaccharide (LPS) during aquatic blooms, affecting environmental and human health. The putative toxic effects of cyanobacterial LPS on brain microglia, a glial cell type that constitutes the main leukocyte-dependent source of reactive oxygen species in the central nervous system, are presently unknown. We tested the hypothesis that in vitro concentration- and time-dependent exposure to M. aeruginosa LPS strain UTCC 299 would activate rat microglia and the concomitant generation of superoxide anion (O₂⁻). After a 17-h exposure of microglia to M.aeruginosa LPS, the following concentration-dependent responses were observed: 0.1-100 ng/ml M. aeruginosa LPS enhanced O₂⁻ generation, with limited inflammatory mediator generation; 1000-10,000 ng/ml M. aeruginosa LPS caused thromboxane B₂ (TXB₂), matrix metalloproteinase-9 (MMP-9), and macrophage inflammatory protein-2 (MIP-2/CXCL2) release, concurrent with maximal O₂⁻ generation; 100,000 ng/mL M. aeruginosa LPS deactivated O₂⁻ production but maintained elevated levels of TXB₂, MMP-9, tumor necrosis factor-α (TNF-α), interleukin 1-α (IL-1α), and interleukin-6 (IL-6), macrophage inflammatory protein 1α (MIP-1α/CCL3), and MIP-2/CXCL2, with concomitant lactic dehydrogenase release. Although M. aeruginosa LPS was consistently less potent than Escherichia coli LPS, with the exception of O₂⁻, TXB₂, and MCP-1/CCL2 generation, it was more efficacious because higher levels of MMP-9, TNF-α, IL-1α, IL-6, MIP-1α/CCL3, and MIP-2/CXCL2 were produced. Our in vitro studies suggest that one or more of the inflammatory mediators released during M. aeruginosa LPS stimulation of microglia may play a critical role in the subsequent ability of microglia to generate O₂⁻. To our knowledge, this is the first experimental evidence that LPS isolated from a M. aeruginosa strain, can activate brain microglia in vitro, as well as the release of O₂⁻, and other inflammatory mediators hypothesized to be involved in neuroinflammation and neurodegeneration.

Anti-inflammatory effects of thymoquinone in activated BV-2 microglial cells

“…These findings are somewhat in alignment with previous reports investigating LPS activation in microglial cells, in particular for elevation of MIP-2, TNF-alpha, IL-1a, IL-6, MIP-1a, MCP-1 and GCSF, NO, inducible nitric oxide synthase (iNOS) (Soliman et al, 2013) where others report elevation of additional pro-inflammatory markers such as free radicals, osteopontin (Hasegawa-Ishii, Takei, 2011, Mayer et al, 2011), IL-1beta (Ye et al, 2013), PGE2 (Kim et al, 2013b) and increased the levels of cyclooxygenase (Cox) 1 and 2 (Soliman, et al 2013). In general pro-inflammatory processes associated with activated BV-2 microglial cells involved a number of signaling pathways that involve Src-MEK1/2-ERK1/2 (Manivannan et al, 2013, Yeh et al, 2013) p38MAPK phosphorylation (Kim et al, 2013a), phosphorylation of c-Jun N-terminal kinase and the nuclear translocation of NF-kappaB p65 (Jung et al, 2013, More et al, 2013) /activation of NFkappaB-signaling pathway (Yeh, Yang, 2013) or down-regulation of HO-1 / and PKA-mediated CREB phosphorylation.…”

Role of neuroinflammation in ischemic stroke

“…Neuroinflammation is regulated by the production of reactive oxygen species (ROS), cytokines and chemokines. [31] Once neuroinflammation happens, it enhances the release of several cytokines in the brain. [32,33] It also involves the reaction of innate immune cells (i.e.…”

Vibrio vulnificus MO6-24/O Lipopolysaccharide Stimulates Superoxide Anion, Thromboxane B2, Matrix Metalloproteinase-9, Cytokine and Chemokine Release by Rat Brain Microglia in Vitro

“…We have repeatedly observed that E. coli LPS pre-treatment primes rat microglia for agonist-stimulated O 2 − generation in vitro [27,38]. As shown in Figure 1, untreated microglia release low levels of O 2 − after phorbol 12-myristate 13-acetate (PMA) stimulation.…”