Estetrol potentiates progesterone-driven growth restraint while blunting pro-angiogenic activation in murine endometriosis lesions.

BACKGROUND

Endometriosis is sustained by ectopic endometrial implants that remain proliferative and vascularized, making endocrine modulation a cornerstone of therapy. Estetrol (E4) an endogenous estrogen produced during pregnancy, with selective tissue activity, may modulate progesterone (P4) outputs in ectopic tissue and potentially shift lesion biology toward growth restraint without reinforcing vascular support.

OBJECTIVE

To test whether E4 modifies P4 effects on lesion proliferation, apoptosis-related signaling, and angiogenic/endothelial activation in vivo.

METHODS

Hormonally intact female mice bearing allografted endometriotic lesions received vehicle, E4 (3 mg/day), P4 (4.25 mg/day), or E4 + P4 once daily for 14 days. Lesions and eutopic endometrium were assessed by immunohistochemistry (Ki-67, cleaved caspase-3, BAX, VEGF, PECAM-1/CD31, Cyclin D1) with epithelial/stromal quantification, and endothelial angiogenic behavior was evaluated using a tube-formation assay.

RESULTS

Lesions exhibited higher proliferative activity than eutopic endometrium. P4 reduced lesion proliferation, and the E4 + P4 combination produced the strongest growth restraint. Apoptosis-related markers increased under endocrine treatments, with the combined regimen showing robust activation. Notably, P4 enhanced angiogenesis-related readouts (VEGF and PECAM/CD31), whereas E4 + P4 prevented these increases and reduced endothelial tube formation, consistent with attenuated endothelial activation under the combined regimen.

CONCLUSIONS

The E4-P4 combination supports a "balanced" endocrine profile-robust growth restraint without concurrent endothelial activation-thereby decoupling proliferation restraint from angiogenic activation.