Toll-like receptor 4 activation enhances Orai1-mediated calcium signal promoting cytokine production in spinal astrocytes.

ABSTRACT: Toll-like receptor 4 (TLR4) has been implicated in pathological conditions including chronic pain. Activation of astrocytic TLRs leads to the synthesis of pro-inflammatory cytokines like interleukin 6 (IL-6) and tumor necrosis factor-ɑ (TNF-α), which can cause pathological inflammation and tissue damage in the central nervous system. However, the mechanisms of TLR4-mediated cytokine releases from astrocytes are incomplete understood. Our previous study has shown that Orai1, a key component of calcium release activated calcium channels (CRACs), mediates Ca²⁺ entry in astrocytes. How Orai1 contributes to TLR4 signaling remains unclear. Here we show that Orai1 deficiency drastically attenuated lipopolysaccharides (LPS)-induced TNF-α and IL-6 production in astrocytes. Acute LPS treatment did not induce Ca²⁺ response and had no effect on thapsigargin (Ca²⁺-ATPase inhibitor)-induced store-dependent Ca²⁺ entry. Inhibition or knockdown of Orai1 showed no reduction in LPS-induced p-ERK1/2, p-c-Jun N-terminal kinase, or p-p38 MAPK activation. Interestingly, Orai1 protein level was significantly increased after LPS exposure, which was blocked by inhibition of NF-κB activity. LPS significantly increased basal Ca²⁺ level and SOCE after exposure to astrocytes. Moreover, elevating extracellular Ca²⁺ concentration increased cytosolic Ca²⁺ level, which was almost eliminated in Orai1 KO astrocytes. Our study reports novel findings that Orai1 acts as a Ca²⁺ leak channel regulating the basal Ca²⁺ level and enhancing cytokine production in astrocytes under the inflammatory condition. These findings highlight an important role of Orai1 in astrocytic TRL4 function and may suggest that Orai1 could be a potential therapeutic target for neuroinflammatory disorders including chronic pain.

SUBMITTER: Birla H 

PROVIDER: S-EPMC9928533 | biostudies-literature | 2022 Jul

REPOSITORIES: biostudies-literature