Store-Operated Calcium Entry Upregulated IL6 Expression in Glomerular Mesangial Cells through NF-κB Pathway

Abstract

Background: IL6 is a pleotropic cytokine and functions as a pro‐ as well as anti‐inflammatory mechanism depending on the cell type or the specific pathological environment. It is unclear if a particular signaling pathway confers IL6 with this property. Immunological and inflammatory mechanisms play a significant role in the development of diabetic nephropathy (DN). Locally produced cytokines/chemokines contributes to the early changes and histological impairment in DN. Glomerular mesangial cell (MC) is a major cell type in glomerulus to produce cytokines/chemokines in response to diabetes and a major contributor to mesangial expansion in DN. We have previously demonstrated that the Orai‐1 mediated store‐operated calcium entry (SOCE) suppressed ECM protein production by MCs. The aim of this study was to determine whether and how SOCE in MCs regulated IL6 production by MCs. Methods: Orai1, the channel protein mediating SOCE in MCs was knocked down using the targeted nanoparticle‐siRNA delivery system in wild type C57BLKS/J mice at the age of 16 weeks. Immunohistochemistry was performed on the paraffin embedded kidney sections to examine glomerular IL6 expression. In cultured human MCs, the expression of IL6 was examined in culture media and whole cell lysates using ELISA and Western blot analysis, respectively in the presence of normal glucose (5 mM D‐glucose + 20 mM L‐glucose) with/without an activator (thapsigargin at 1 μM) or inhibitor (GSK‐7975A 10 μM) of SOCE for 15 hrs. To determine the role of NF‐κB in SOCE effects on IL6 production, human MCs were treated with an inhibitor of NF‐κB, helenaline or siRNA against p65 subunit of NF‐κB. Furthermore, the effect of SOCE on the nuclear translocation of p65 was examined by assessing abundance of nuclear p65 protein in response to activation and inhibition of SOCE. Results: The IL6 expression level was reduced in the glomeruli of the mice treated with nanoparticle/Orai1 siRNA for 2 weeks compared to that in the control mice. In cultured human MCs, thapsigargin significantly increased IL‐6 level in supernatant media and in whole cell lysates of MCs, and this effect was attenuated by GSK 7975‐A, a selective inhibitor of SOCE. However, tunicamycin, an ER stress inducer did not alter the amount of IL6 as thapsigargin did. Treatment with helenaline, an inhibitor of NF‐κB pathway, or knockdown of p65, a subunit of NF‐κB significantly blunted the thapsigargin‐induced increase in IL6 protein abundance. Moreover, thapsigargin stimulated the nuclear translocation of p65 in human MCs. Conclusion: Orai1‐mediated SOCE positively regulates IL6 production by MCs through activation of NF‐κB pathway.

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