Inhibition of interleukin‐1β production by extracellular acidification through the TDAG8/cAMP pathway in mouse microglia

Abstract

Interleukin-1b (IL-1b) is released from activated microglia and involved in the neurodegeneration of acute and chronic brain disorders, such as stroke and Alzheimer's disease, in which extracellular acidification has been shown to occur. Here, we examined the extracellular acidic pH regulation of IL-1b production, especially focusing on TDAG8, a major proton-sensing G-protein-coupled receptor, in mouse microglia. Extracellular acidification inhibited lipopolysaccharide -induced IL-1b production, which was associated with the inhibition of IL-1b cytoplasmic precursor and mRNA expression. The IL-1b mRNA and protein responses were significantly, though not completely, attenuated in microglia derived from TDAG8-deficient mice compared with those from wildtype mice. The acidic pH also stimulated cellular cAMP accumulation, which was completely inhibited by TDAG8 deficiency. Forskolin and a cAMP derivative, which specifically stimulates protein kinase A (PKA), mimicked the proton actions, and PKA inhibitors reversed the acidic pH-induced IL-1b mRNA expression. The acidic pH-induced inhibitory IL-1b responses were accompanied by the inhibition of extracellular signal-related kinase and c-Jun N-terminal kinase activities. The inhibitory enzyme activities in response to acidic pH were reversed by the PKA inhibitor and TDAG8 deficiency. We conclude that extracellular acidic pH inhibits lipopolysaccharide-induced IL-1b production, at least partly, through the TDAG8/cAMP/PKA pathway, by inhibiting extracellular signalrelated kinase and c-Jun N-terminal kinase activities, in mouse microglia. Keywords: acidification, cAMP, interleukin-1b, microglia, protein kinase A, TDAG8. Microglia fulfill a central role in the innate and adaptive immune system in brain. The activation of microglia and subsequent increase in the synthesis and release of proinflammatory cytokines, such as IL-1, have been shown to occur under acute, e.g., stroke and traumatic brain injury, and chronic conditions, e.g., Alzheimer's disease and Parkinson's disease (Yenari et al. 2010). IL-1 is known to have a causal role in their neurodegeneration, although the cytokine is also thought to be involved in the recovery of the neuronal functions ( -benzoyladenosine-3′,5′-cyclic monophosphate; NF-jB, nuclear factor-jB; p38 MAPK, p38 mitogen-activated protein kinase; PKA, cAMP-dependent protein kinase; proIL-1b cytoplasmic precursor of IL-1b; TLR, toll-like receptor.

Histamine H3 receptor in primary mouse microglia inhibits chemotaxis, phagocytosis, and cytokine secretion

“…Although cAMP level controls various cellular functions, the roles of cAMP in microglia remain to be elucidated. For example, the effects of cAMP increase on IL‐1β (Jin et al, ; Liu et al, ; Quan et al, ; Woo et al, ) and IL‐6 (Hashioka et al, ; Si et al, ) were different among studies. In contrast, almost all reports agreed that intracellular Ca 2+ concentration played a key role in cytokine production (Espinosa‐Parrilla et al, ; Sun et al, ).…”

Characterization of Imidazopyridine Compounds as Negative Allosteric Modulators of Proton-Sensing GPR4 in Extracellular Acidification-Induced Responses

“…Total RNA was prepared from HUVECs according to the manufacturer’s instructions for RNAiso Plus (Takara Bio Inc., Otsu, Japan). Quantitative real-time PCR (RT-qPCR) was performed by TaqMan technology, as described previously [30]. The expression level of the target mRNA was normalized to the relative ratio (x 10 3 ) of the expression of GAPDH mRNA.…”

Differential effects of lipopolysaccharide on energy metabolism in murine microglial N9 and cholinergicSN56 neuronal cells

“…; Jin et al . ). Therefore, neither cell line used here was subjected to any agent modifying their native phenotypes.…”

“…It is known that cAMP, retinoic acid, or NGF/BDNF (brain-derived neurotrophic factor) might interfere with LPS-linked signaling and energy metabolism pathways in microglial and neuronal cells, respectively (Szutowicz et al 1999(Szutowicz et al , 2004Schubert et al 2001;Jin et al 2014). Therefore, neither cell line used here was subjected to any agent (Szutowicz et al 2004(Szutowicz et al , 2013.…”