Objectives: To investigate the presence and functionality of estrogen receptor alpha (ERα) in IL-1β-treated rabbit articular chondrocytes in culture. To determine the mechanisms of 17β estradiol (E2) effects on IL-1β-induced iNOS expression.
Methods: The presence and functionality of ER& [alpha] were investigated by immunocytochemistry and transient expression of an E2-responsive reporter construct. iNOS expression and production were determined by transient expression of a chimeric iNOS promoter-luciferase construct and protein immunoblotting. NO production was determined by the Griess reaction. DNA binding activities of NF-kB and AP- 1 were determined by EMSA-Elisa assays. Nuclear translocation of p65 was studied by immunocytochemistry.
Results: ERα was identified in the nucleus of chondrocytes. ERα efficiently transactivated a transiently expressed E2-responsive construct. Upon IL-1& [beta] treatment, ERα partially diffused from its nuclear localisation into the cytoplasm and its transactivation ability was impaired. Nevertheless, E2, Tamoxifen and Raloxifene efficiently inhibited IL-1& [beta] induced NO production (- 34%, - 31% and - 36% respectively). E2 decreased IL-1β induced iNOS protein expression (- 40%). Transient expression of an iNOS promoter construct strongly suggested that iNOS expression was inhibited at the transcriptional level and EMSA-ELISA assays showed that E2 reduced (- 60%) the IL-1β induced p65 DNA binding capacity. Finally, the p65 nuclear translocation induced by IL-1β was also strongly decreased by E2.
Conclusions: Our data support a reciprocal antagonism between estrogens and IL-1β ultimately resulting in the decrease of cytokine-dependent NO production through transcriptional inhibition of iNOS expression. This effect was associated with selective inhibition of p65 DNA binding and nuclear translocation.
- selective estrogen receptor modulators
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The name of Mourad Benallaoua is misspelled : "Benallaloua" appears instead of "Benallaoua", both in the authors list and in the authors affiliations list.