Toll-like receptor 4 activation enhances Orai1-mediated calcium signal promoting cytokine production in spinal astrocytes. (July 2022)

• Record Type: Journal Article
• Authors: Birla, Hareram; Xia, Jingsheng; Gao, Xinghua; Zhao, Hui; Wang, Fengying; Patel, Shivam; Amponsah, Akwasi; Bekker, Alex; Tao, Yuan-Xiang; Hu, Huijuan
• Is Part Of: Cell calcium. Volume 105(2022)
• Publication Date: 2022-07
• Subjects: TLR4 -- Store-operated calcium channels -- Orai1 -- Astrocytes -- Cytokine -- Spinal cord; Calcium -- Metabolism -- Periodicals; Vertebrates -- Physiology -- Periodicals; Calcium -- Physiological effect -- Periodicals; Cell physiology -- Periodicals; Calcium in the body -- Periodicals; 572.516
• DOI: 10.1016/j.ceca.2022.102619
• Languages: English
• ISSNs: 0143-4160

Abstract

Highlights: Orai1 deficiency drastically decreases lipopolysaccharides (LPS)-induced TNF-α and IL-6 production in astrocytes. Inhibition of CRACs or deficiency of Orai1 does not alter LPS-induced MAPK activation. LPS exposure increases Orai1 protein expression vis NF-κB. LPS exposure enhances basal Ca 2+ level and SOCE. Orai1 deficiency almost eliminates Ca 2+ entry induced by elevating extracellular Ca 2+ concentration, suggesting that Orai1 functions as a leak Ca 2+ channel maintaining astrocytic Ca 2+ homeostasis. 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 Ca 2+ 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 Ca 2+ response and had no effect on thapsigargin (Ca 2+ -ATPase inhibitor)-induced store-dependent Ca 2+ 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 Ca 2+ level and SOCE after exposure to astrocytes. Moreover, elevating extracellular Ca 2+ concentration increased cytosolic Ca 2+ level, which was almost eliminated in Orai1 KO astrocytes. Our study reports novel findings that Orai1 acts as a Ca 2+ leak channel regulating the basal Ca 2+ 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. Graphical abstract: Image, graphical abstract