Effects of proinflammatory cytokines on anterior pituitary 5′-deiodinase type I and type II

Abstract

Cytokines are locally produced in the anterior pituitary and act through para-/autocrine mechanisms to modulate cell growth and hormone production. 5′-Deiodinases type I (D1) and type II (D2) are also expressed in the anterior pituitary and play an integrative role in the regulation of hormone production and pituitary feedback. D1 activity is known to be regulated by proinflammatory cytokines in liver and thyroid. Therefore, we examined the effects of IL-1β, IL-6 and TNFα on 5′-deiodinase activities in reaggregates of rat anterior pituitaries and rat somatomammotroph GH3 cells cultured alone, or in a bicameral culture system together with the murine folliculo-stellate (FS) cell line TtT/Gf. In reaggregate cultures of rat anterior pituitaries IL-1β stimulated D1 and D2 dose-dependency and D2 activity was increased by TNFα. When GH3 cells were cocultured with TtT/Gf cells, D2 activities were 2·3-fold lower than in GH3 cells cultured alone. TNFα (50 ng/ml) and IL-6 (100 U/ml) stimulated D2 in GH3 cells when the cells were cultured alone and treated with these cytokines for 24 h. When TtT/Gf cells in the coculture model were treated with IL-1β, TNFα and IL-6, no effect on D1 or D2 activities in GH3 cells was observed. In male, adult rats a single LPS injection (i.p.) stimulated D2 and D1 activities in the anterior pituitary, and decreased liver D1 activities and serum TSH levels. In vitro, LPS stimulation of the coculture model of GH3 and FS cells also increased D1 activity. Electrophoretic mobility shift assays (EMSAs) revealed that IL-1β and TNFα activate the transcription factor NFκB in reaggregates of rat anterior pituitaries and in TtT/Gf cells cultured alone or cocultured with GH3 cells. Taken together, these findings imply that in anterior pituitary cells 5′-deiodinase activities are stimulated by locally produced cytokines in a para-/autocrine manner but cell types other than FS cells seem to mediate some of the effects.