Abstract:
Endometriosis is characterized by presence of endometrial-like tissue outside the
uterine cavity. The TGF-β superfamily, consisting of TGF-βs, activins and inhibins, is
expressed in the endometrium and is putatively implicated in endometriosis.
Betaglycan (BG), a membrane-bound co-receptor and modulator of the TGF-β
superfamily ligands, especially of TGF-β2. BG undergoes proteolytic cleavage to release
soluble betaglycan (sBG) which often blocks TGF-βs in several physiological and
pathological processes. We investigated shedding of betaglycan and its role in TGF-β
family signaling in endometrial and endometriotic cell lines. Endometriotic epithelial
(12Z) and endometrial stromal (THESC) cells were treated with increasing
concentrations of TGF-β1/β2 (1-10 ng/ml), activin A (5-50 ng/ml) or inhibin A (5-50
ng/ml). The level of sBG was evaluated using ELISAs after 24, 48 and 72 hours of
stimulation. An ALK-4/5 inhibitor (LY364947, 10 μM) was used to study the signaling
pathways. Inhibition of BG shedding was analyzed using tissue inhibitors of
metalloproteinases3 (TIMP3, 2.5-10 nM) besides a pan-MMP inhibitor (GM6001, 10 μM).
TGF-β1/β2 along with activin A and inhibin A stimulation of 12Z and THESC cells
resulted in a significant time- and dose-dependent reduction in BG shedding. Moreover,
TGF-β1/2 and activin A-mediated reduction in BG shedding in 12Z cells was found to
be TGF-β type I receptor (ALK-5) and activin receptor type-1B (ALK-4)-dependent,
respectively. Shedding of BG was significantly attenuated by TIMP3 in a dose-
dependent manner and partially (~40%) by the pan-MMP inhibitor, signifying the
involvement of matrix metalloproteinases in BG shedding. Collectively, our data
suggest involvement of MMPs in shedding of BG and suggest potential involvement of
sBG in modulating TGF-β1/β2, activin A and inhibin A signaling in endometriotic and
endometrial cells. The signaling mechanisms involved and possible roles in
endometriosis merit further investigation.
