ANP inhibits LPS-induced stimulation of rat microglial cells by suppressing NF-κB and AP-1 activations

Abstract

Atrial natriuretic peptide (ANP) contributes to the inhibition of such causes of inflammation as the lipopolysaccharide (LPS)-induced productions of nitric oxide (NO) and proinflammatory cytokines [including interleukin-1 (IL-1)] in macrophages. In the present study we used primary cultures of rat brain macrophage-like cells (i.e., microglial cells) to investigate whether ANP binding to its receptors inhibits LPS-induced microglial activation via effects on the activation of the proinflammatory transcription factors NF-kappaB and AP-1. The productions of NO and IL-1, as well as morphological changes, were examined to assess LPS-induced activation of microglial cells. Our RT-PCR study revealed that rat microglial cells express the mRNAs for ANP receptors (types A, B, and C) and that for the ANP molecule. LPS (100 ng/ml)-stimulated microglial cells showed increases in nitrite (a relatively stable metabolite of NO) and IL-1 concentrations, and in the expression of IL-1 mRNA, as well as a morphological change from an amoeboid shape to a multipolar (mostly bipolar, but sometimes tripolar) rod shape. These effects were all significantly inhibited by treatment with ANP (at 10(-6)M or less). The inhibition by ANP of the LPS-induced nitrite response was abrogated by a NP-receptor antagonist, HS-142-1 (100 ng/ml). NF-kappaB and AP-1 activities were enhanced in LPS-stimulated microglial cells, and these enhancements were significantly suppressed by ANP (10(-6)M). These results suggest that ANP inhibits LPS-stimulated activities in microglial cells through activation of microglial ANP receptors, leading to inhibitions of NF-kappaB and AP-1.

Probucol inhibits LPS-induced microglia activation and ameliorates brain ischemic injury in normal and hyperlipidemic mice

“…The MAPKs p38, ERK and JNK are known to be activated by LPS, and several studies have demonstrated the significance of MAPKs in the transcriptional regulation of the LPS-induced production of inflammatory mediators via the activation of transcription factor AP-1 [43] . In the present study, we demonstrated that treatment with probucol significantly inhibited LPS-stimulated phosphorylation of p38 and JNK (but not Erk1/2) and the activity of c-Jun, which is a major component of the AP-1 family that is responsible for the over-reactive inflammatory responses of BV2 cells.…”

Inhibition of IκB Kinase-β Protects Dopamine Neurons Against Lipopolysaccharide-Induced Neurotoxicity

“…Recently, increasing emphasis has been placed on the role of NF-B in the innate immune system. NF-B is the most important transcription factor in inflammatory responses by regulating the expression of various jpet.aspetjournals.org proinflammatory factors such as NO, TNF␣, and IL-1␤ (Jana et al, 2001;Lee et al, 2004;Moynagh, 2005;Moriyama et al, 2006). Nurr1, an orphan nuclear receptor, exerts anti-inflammatory effects by docking to NF-B-p65 on target inflammatory gene promoters, recruiting the CoREST corepressor complex, and subsequently resulting in clearance of NF-Bp65 and transcriptional repression in astrocytes and microglia.…”

“…For example, NF-B plays a critical role in the regulation of microglial production of several proinflammatory factors including tumor necrosis factor (TNF)-␣, interleukin (IL)-1␤, cyclooxygenase-2, and nitric oxide (NO) (Jana et al, 2001;Lee et al, 2004;Moriyama et al, 2006;Werner et al, 2008). NF-B activation is detected within the SN of PD patients and a PD animal model created by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (Hunot et al, 1997;Ghosh et al, 2007).…”

Regulation and Function of Cyclic GMP-Mediated Pathways in Glial Cells

“…In agreement with this, we have recently reported that ANP, and with less potency CNP, stimulate cGMP formation in ramified microglia co-cultured with astrocytes, as well as in isolated microglia [20]. Furthermore, expression of mRNA for all three NPRs as well as for ANP has been demonstrated in rat microglial cultures [54], suggesting that ANP may be an autocrine regulator in these cells.…”

“…As in macrophages [71], ANP is not able to induce NOS2 or TNF-a expression in microglia but significantly decreases the induction by LPS of these inflammatory genes [20]. Inhibition by ANP of nitrite accumulation and IL-1b expression has also been described in rat microglial cultures by Moriyama et al [54]. In contrast, enhanced basal and LPS-induced secretion of TNF-a and IL-1b and expression of NOS2 and MHC-II have been reported in rat microglial cells treated for 24 h with zaprinast, an inhibitor of cGMP-selective phosphodiesterases PDE5 and PDE9, or with a high concentration of dibutyryl cGMP (1 mM) [72], conditions that are expected to maintain cGMP levels elevated for longer periods of time than ANP.…”