Role of Betaglycan in TGF-β Signaling and Wound Healing in Human Endometriotic Epithelial Cells and in Endometriosis

SIMPLE SUMMARY: Endometriosis is a benign female disorder presumably caused by dislocation of endometrial tissue during menstruation most often into the pelvis and is mainly resulting in pain and infertility. Up to date the pathogenesis of endometriosis is still unclear and a non-invasive biomarker not available. One of the cytokines suggested to be involved in the pathogenesis are the transforming growth factor-betas 1-3, which signal via two high-affinity receptors and in the case of transforming growth factor-beta2 also via the co-receptor betaglycan. In this study, we have analyzed the involvement of betaglycan into transforming growth factor-beta signaling and the contribution to biological functions such as wound healing with an in vitro model. We demonstrated an interesting interaction of betaglycan with the transforming growth factor-betas 1-3 and vice versa. Remarkably, the co-receptor betaglycan in its soluble form reduced wound healing as well as secretion of transforming growth factor-betas. Although we found some hints that endocervical mucus levels are different between healthy subjects and cases with endometriosis it was not sufficient for a reliable non-invasive diagnosis of the disease. Taken together, our findings suggest a novel role for betaglycan in the pathogenesis of endometriosis. ABSTRACT: Endometriosis is characterized by the presence of ectopic endometrium most often in the pelvis. The transforming growth factor-beta (TGF-β) superfamily is also involved in the pathogenesis; however, betaglycan (BG, syn. TGF-β type III receptor) as an important co-receptor was not studied. We analyzed mainly BG ectodomain shedding because released soluble BG (sBG) often antagonizes TGF-β signaling. Furthermore, we studied the role of TGF-βs and BG in wound healing and evaluated the suitability of BG measurements in serum and endocervical mucus for non-invasive diagnosis of endometriosis. Evaluation of the BG shedding and signaling pathways involved as well as wound healing was performed with enzyme-linked immune assays (ELISAs), reverse transcription-quantitative polymerase chain reaction (RT-qPCR), small interfering RNA (siRNA) knockdown, and scratch assays with human endometriotic epithelial cells. TGF-β1/2 stimulation resulted in a significant dose-dependent reduction in BG shedding in endometriotic cells, which was TGF-β/activin receptor-like kinase-5 (ALK-5)/mother against decapentaplegic homolog3 (SMAD3)- but not SMAD2-dependent. Inhibition of matrix metalloproteinases (MMPs) using the pan-MMP inhibitor GM6001 and tissue inhibitor of MMPs (TIMP3) equally attenuated BG shedding, signifying the involvement of MMPs in shedding. Likewise, recombinant BG moderately reduced the secretion of TGF-β1/2 and wound healing of endometriotic cells. TGF-β1 significantly enhanced the secretion of MMP2 and MMP3 and moderately promoted wound healing. In order to evaluate the role of BG in endometriosis, serum (n = 238) and mucus samples (n = 182) were analyzed. Intriguingly, a significant reduction in the levels of sBG in endocervical mucus but not in the serum of endometriosis patients compared to controls was observed. Collectively, these observations support a novel role for BG in the pathophysiology of endometriosis.