Glycosaminoglycans (GAGs) and proteoglycans (PGs) are major components of the glycocalyx. The secreted GAG and CD44 ligand hyaluronic acid (HA), and the cell surface PG syndecan-1 (Sdc-1) modulate the expression and activity of cytokines, chemokines, growth factors, and adhesion molecules, acting as critical regulators of tumor cell behavior. Here, we studied the effect of Sdc-1 siRNA depletion and HA treatment on hallmark processes of cancer in breast cancer cell lines of different levels of aggressiveness. We analyzed HA synthesis, and parameters relevant to tumor progression, including the stem cell phenotype, Wnt signaling constituents, cell cycle progression and apoptosis, and angiogenic markers in luminal MCF-7 and triple-negative MDA-MB-231 cells. Sdc-1 knockdown enhanced HAS-2 synthesis and HA binding in MCF-7, but not in MDA-MB-231 cells. Sdc-1-depleted MDA-MB-231 cells showed a reduced CD24-/CD44+ population. Furthermore, Sdc-1 depletion was associated with survival signals in both cell lines, affecting cell cycle progression and apoptosis evasion. These changes were linked to the altered expression of KLF4, MSI2, and miR-10b and differential changes in Erk, Akt, and PTEN signaling. We conclude that Sdc-1 knockdown differentially affects HA metabolism in luminal and triple-negative breast cancer model cell lines and impacts the stem phenotype, cell survival, and angiogenic factors.

Endometriosis is an often painful disease in reproductive-aged women, in which endometrial-like tissue grows outside the uterine cavity. Since the limited current therapeutic alternatives fail in alleviating the symptoms and based on our previous research in in vitro models using the same compounds as the ones used in the present study, we aimed to evaluate the effects of urolithins A (UA) and B (UB) on the growth and survival of endometriotic-like lesions in a murine model of endometriosis. Female BALB/C mice were surgically induced with endometriosis and treated with 2.5 mg kg⁻¹ day⁻¹ intraperitoneal UA or UB. The mice were monitored daily and weighed and the estrous stage was determined. After 28 days of treatment, lesions were counted, measured, excised, and fixed. Both urolithins proved not to affect the estrous cycle or body weight of the mice. UA completely prevented endometriotic-like lesions, while UB diminished the implant volume (p < 0.05). Treatment also reduced epithelial and stromal cell proliferation within the implants (p < 0.001 and p < 0.01, respectively) and apoptosis was enhanced (p < 0.05 and p < 0.01, respectively). These results are promising and reveal that urolithins A and B, separately, have a beneficial effect on the overall endometriotic growth without affecting the body weight or estrous cycle.