Does IL-6 release ACTH by exerting a direct effect in the rat anterior pituitary

Interleukin-1α leads to growth hormone deficiency in adamantinomatous craniopharyngioma by targeting pericytes: implication in pituitary fibrosis

BACKGROUND

The incidence of growth hormone deficiency (GHD) in adamantinomatous craniopharyngioma (aCP) is significantly higher than in other sellar region tumors, but the possible mechanism is still elusive. A high level of inflammatory responses is another feature of aCP. We investigated the internal connection between interleukin-1α (IL-1α) and GHD, while focusing on its biological activities in pituitary fibrosis.

MATERIALS AND METHODS

To diagnosis of GHD, the Body Mass Index (BMI), Insulin Like Growth Factor-1(IGF-1) and peak growth hormone (GH) values after insulin stimulation test of 15 aCP patients were recorded. Histological staining was performed on the aCP samples. Levels of 9 proinflammatory cytokines in tumor tissue and cell supernatant were detected using Millipore bead arrays. The effect of IL-1α on GH secretion was evaluated in vivo and in vitro. Western blot, qRT-PCR and cell functional assays were used to explore the potential mechanism through which IL-1α acts on GH secretion. The stereotactic ALZET osmotic pump technique was used to simulate aCP secretion of proinflammatory cytokines in rats. Recombinant IL-1α (rrIL-1α) and conditioned media (CM) prepared from the supernatant of aCP cells was infused directly into the intra-sellar at a rate of 1 μl/h over 28 days, and then the effects of IL-1α treatment on pathological changes of pituitary gland and GH secretion were measured. To further confirm whether IL-1α affects GH secretion through IL-1R1, an IL-1R1 blocker (IL-1R1a, 10 mg/kg body weight, once daily) was administered subcutaneously from the first day until day 28.

RESULTS

There was a significant positive correlation between pituitary fibrosis and GHD (rS = 0.756, P = 0.001). A number of cytokines, in particular IL-1α, interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1), were elevated in tumor tissue and cell supernatant. Only IL-1α showed a significant difference between the GHD group and the No-GHD group (P < 0.001, F = 6.251 in tumor tissue; P = 0.003, F = 1.529 in cell supernatant). IL-1α significantly reduced GH secretion in coculture of GH3 and pericytes. The activation of pericytes induced by IL-1α was mediated by the IL-1R1 signaling pathway. In vivo, IL-1α induces pituitary fibrosis, further leading to a decreased level of GH. This pathological change was antagonized by IL-1R1a.

CONCLUSION

This study found that the cross talk between aCP cells and stroma cells in the pituitary, i.e. pericytes, is an essential factor in the formation of GHD, and we propose that neutralization of IL-1α signaling might be a potential therapy for GHD in aCP.