Complex Modulation of IL-6 Signaling by Apelin and Elabela in HTR-8/SVneo Cells Under Cobalt Chloride-Induced Chemical Hypoxia
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Preeclampsia is a pregnancy complication characterized by hypertension, proteinuria, and end-organ dysfunction. Abnormal placentation leading to reduced placental perfusion may contribute to its development. Previous studies demonstrated that the activation of the apelin receptor (APJ) system has hypotensive, renoprotective, and antioxidant effects in preeclamptic rat models. Apelin and elabela (ELA) can stimulate the proliferation of trophoblast cells, suggesting a role in embryonic development. However, the mechanisms underlying the actions of apelin or ELA in trophoblast cells are not well understood, particularly in hypoxic settings. The immortalized HTR-8/SVneo trophoblastic cells were treated with cobalt chloride (CoCl 2 ) at 0.2 mM for 24 hours to mimic hypoxic conditions. RT-qPCR, ELISA or Western blotting was used to measure mRNA or protein levels of apelin, elabela, and the components of IL-6 signaling in cell lysates or conditioned media. The exposure to CoCl 2 increased total apelin and elabela content approximately 2-fold in the conditioned media but did not affect APJ levels. CoCl 2 upregulated proinflammatory cytokine concentrations: soluble fms-like tyrosine kinase 1 (sFlt-1), soluble gp130 (sgp130), interleukin-6 (IL-6), and sIL-6 receptor (IL-s6R). Both apelin and elabela downregulated IL-6 mRNA but had no effect on sFlt-1 mRNA. Apelin attenuated sgp130, while ELA decreased the membrane form of IL- s6R. Apelin also decreased the pSTAT3/STAT3 ratio. CoCl 2 -induced hypoxia upregulated the pro- inflammatory milieu in HTR-8/SVneo cells. Local activation of this peptidergic system may be a compensatory response of the trophoblast cells to hypoxia as exogenous apelin and elabela treatment ameliorated the hypoxia-induced pro-inflammatory milieu.
Highlights
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ur data confirmed that both membrane and soluble forms of IL-6R, and the components of IL-6 trans-signaling such as soluble and membrane-bound gp130 are present in HTR-8/SVneo trophoblastic cells.
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CoCl 2 exposure upregulated apelin and elabela but not apelin receptor APJ in HTR-8/SVneo cells.
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IL-6 and soluble gp130 were upregulated by CoCl 2 exposure which was reversed by apelin or elabela. Elabela also downregulated membrane-bound IL-6R in CoCl 2 -exposed HTR-8/SVneo cells.
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IL-6 signaling through its soluble receptor primarily drives inflammation, whereas signaling via the membrane-bound receptor tends to support cell survival and anti-inflammatory effects, our data suggest that apelin or elabela could be involved in the complex regulation of the hypoxic environment in trophoblast cells relevant for preeclampsia.
Schematic of proposed interactions between IL-6 signaling and apelin and elabela in HTR-8/SVneo trophoblastic cells under CoCl₂-mimicked hypoxia. We hypothesize that apelin/elabela/APJ axis regulates IL-6 signaling via its actions on various components of the IL-6 classical and trans-signaling pathway.
