Induction of an angiogenic phenotype in endometriotic stromal cell cultures by interleukin-1β

Activated peritoneal macrophages are associated with endometriosis and may play a central role in its aetiology by releasing interleukin-1 beta (IL-1 beta) in response to refluxed endometrium. Pari passu with the establishment of endometriotic implants is the development of a vascular supply. In this study we investigated the angiogenic properties of two endometrial proteins, vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6), and assessed their production in response to IL-1 beta stimulation in human stromal cells isolated from normal endometrium (NE) and endometriotic lesions (EI), Proliferation of bovine brain capillary endothelial cells (BBCE) with a [H-3]-thymidine incorporation assay was observed when VEGF (2.1 +/- 0.2-fold; P < 0.05) or VEGF and IL-6 (1.8 +/- 0.1-fold; P < 0.05) were added in vitro, relative to saline-treated control cultures. Northern blot analysis showed induction of VEGF mRNA (2.6-fold; P < 0.05) and IL-6 mRNA (6.3-fold; P < 0.05) transcripts in EI cells, but not NE cells, exposed to IL-1 beta. A similar induction was seen with VEGF and IL-6 protein secretion in the responsive EI cells. Reverse transcription-polymerase chain reaction (RT-PCR) for the IL-1 receptor type I (IL-1 RI) indicated that the differential effects of IL-1 beta on NE and EI cells was associated with 2.4 +/- 0.1-fold more receptor mRNA in EI versus NE cells. We propose that the ability of IL-1 beta to activate an angiogenic phenotype in EI stromal cells but not in NE cells, is mediated by the IL-1 RI.