Notch Signaling Controls Sprouting Angiogenesis of Endometriotic Lesions

Angiogenesis is essential for the engraftment and growth of endometriotic lesions. In this study, we analyzed whether this process is regulated by Notch signaling. Endometriotic lesions were induced by endometrial tissue transplantation into dorsal skinfold chambers of C57BL/6 mice, which were treated with the γ-secretase inhibitor DAPT or vehicle. Vascularization, morphology, and proliferation of the newly developing lesions were analyzed using intravital fluorescence microscopy, histology, and immunohistochemistry over 14 days. Inhibition of Notch signaling by DAPT significantly increased the number of angiogenic sprouts within the endometrial grafts during the first days after transplantation when compared to vehicle-treated controls. This was associated with an accelerated vascularization, as indicated by a higher functional microvessel density of DAPT-treated lesions on day 6. However, inhibition of Notch signaling did not affect the morphology and proliferating activity of the lesions, as previously described for tumors. Both DAPT- and vehicle-treated lesions finally consisted of cyst-like dilated glands, which were surrounded by a well-vascularized stroma and contained comparable numbers of proliferating cell nuclear antigen-positive cells. These findings demonstrate that sprouting angiogenesis in endometriotic lesions is controlled by Notch signaling. However, inhibition of Notch signaling does not have beneficial therapeutic effects on lesion development.