TNF‐α/IFN‐γ‐induced iNOS expression increased by prostaglandin E₂ in rat primary astrocytes via EP2‐evoked cAMP/PKA and intracellular calcium signaling

Abstract

Astrocytes, the most abundant glia in the central nervous system (CNS), produce a large amount of prostaglandin E(2) (PGE(2)) in response to proinflammatory mediators after CNS injury. However, it is unclear whether PGE(2) has a regulatory role in astrocytic activity under the inflamed condition. In the present work, we showed that PGE(2) increased inducible nitric oxide synthase (iNOS) production by tumor necrosis factor-alpha and interferon-gamma (T/I) in astrocytes. Pharmacological and RNA interference approaches further indicated the involvement of the receptor EP2 in PGE(2)-induced iNOS upregulation in T/I-treated astrocytes. Quantitative real-time polymerase chain reaction and gel mobility shift assays also demonstrated that PGE(2) increased iNOS transcription through EP2-induced cAMP/protein kinase A (PKA)-dependent pathway. Consistently, the effect of EP2 was significantly attenuated by the PKA inhibitor KT-5720 and partially suppressed by the inhibitor (SB203580) of p38 mitogen-activated protein kinase (p38MAPK), which serves as one of the downstream components of the PKA-dependent pathway. Interestingly, EP2-mediated PKA signaling appeared to increase intracellular Ca(2+) release through inositol triphosphate (IP3) receptor activation, which might in turn stimulate protein kinase C (PKC) activation to promote iNOS production in T/I-primed astrocytes. By analyzing the expression of astrocytic glial fibrillary acidic protein (GFAP), we found that PGE(2) alone only triggered the EP2-induced cAMP/PKA/p38MAPK signaling pathway in astrocytes. Collectively, PGE(2) may enhance T/I-induced astrocytic activation by augmenting iNOS/NO production through EP2-mediated cross-talk between cAMP/PKA and IP3/Ca(2+) signaling pathways.

Inhibition of the prostaglandin receptor EP2 following status epilepticus reduces delayed mortality and brain inflammation

“…In the CNS, however, selective EP2 activation reduces microglial migration toward injured tissue (39), whereas ablation of the EP2 receptor limits lipopolysaccharideinduced, microglia-mediated inducible nitric oxide synthase (iNOS) production and neurotoxicity in mixed cortical cultures (40). As the resident forms of macrophages in the brain, microglia appear to play a pivotal role in seizure-induced immune responses because activated microglia are a major source of a host of proinflammatory and neurotoxic factors including cytokines, chemokines, free radicals, and prostanoids in injured neuronal tissues (41,42); activated astrocytes might also contribute to brain inflammation by producing iNOS in response to EP2 activation (43). Our work shows that an EP2 receptor antagonist significantly reduced the seizuremediated induction of seven cytokines and chemokines, among them IL-1β and IL-6, and also blunted the induction of activated glial markers (Fig.…”

Noradrenaline Induces Clock Gene Per1 mRNA Expression in C6 Glioma Cells Through β2-Adrenergic Receptor Coupled With Protein Kinase A – cAMP Response Element Binding Protein (PKA–CREB) and Src-Tyrosine Kinase – Glycogen Synthase Kinase-3β (Src–GSK-3β)

“…In addition, Moriya et al (39) have demonstrated that the expression of GFAP in SCN was dramatically changed under constant lighting conditions, while that was not constant under a light-dark cycle. Another study has suggested that alteration of GFAP expression might reflect activity of astrocytes (41), indicating the possibility that circadian rhythms of GFAP expression are correlated with those of astroglial functions. Glutamate transporter EAAT2 has also been proposed as a candidate for regulation by astrocyte circadian rhythms (4).…”

TGF-β1 reduces the heterogeneity of astrocytic cyclooxygenase-2 and nitric oxide synthase-2 gene expression in a stimulus-independent manner

“…In parallel, the induction of COX-2 itself can reduce surrounding NO levels through the ability of NO to act as a co-substrate for its peroxidase activity [73]. Further COX-2-derived products can also regulate (up or down) NOS-2 expression levels and activity depending on the cell-type and experimental paradigm studied [74][75][76]. Hence, the heterogeneity of NOS-2 and COX-2 astrocyte expression in brain, as well as their coordinate regulation, could contribute to the establishment and maintenance of a network of communication among neurons and glia under both physiological and pathophysiological conditions in ways we have yet to understand fully.…”