Metalloproteinase-dependent shedding of LRP-1 ectodomain decreases endocytic clearance of endometrial matrix metalloproteinases-2 and -9 at menstruation.

Selvais, Charlotte [UCL] Courtoy, Pierre J. [UCL] Gaide Chevronnay, Héloïse P. [UCL] Lemoine, Pascale [UCL] Dedieu, Stéphane Henriet, Patrick [UCL] Marbaix, Etienne [UCL] Emonard, Hervé [UCL]

Cyclic elimination of endometrium functional layer through menstrual bleeding results from intense tissue breakdown by proteolytic enzymes, mainly members of the matrix metalloproteinase (MMP) family. In contrast to menstrual-restricted MMPs, e.g. interstitial collagenase (MMP-1), gelatinases A (MMP-2) and B (MMP-9) mRNAs are abundant throughout the cycle without detectable tissue degradation at proliferative and secretory phases, implying a tight post-translational control of both gelatinases. This paper addresses the role of low-density lipoprotein receptor-related protein (LRP)-1 in the endocytic clearance of endometrial gelatinases. LRP-1 mRNA and protein were studied using RT-PCR, Western blotting and immunolabeling. Post-translational control of LRP-1 was analyzed in explant culture. The receptor-associated protein (RAP), used as LRP antagonist, strongly increased (pro)gelatinases accumulation in medium conditioned by endometrial explants, suggesting a role for LRP-1 in their clearance. Although LRP-1 mRNA remained constant throughout the cycle, the protein ectodomain vanished at menses. LRP-1 immunolabeling selectively disappeared in areas of extracellular matrix breakdown in menstrual samples. It also disappeared from explants cultured without estrogen and progesterone (EP) due to ectodomain shedding in the medium. The shedding was inhibited by metalloproteinase inhibitors, including a disintegrin and metalloproteinase (ADAM) inhibitor, and by tissue inhibitors of MMPs (TIMP)-3 and -2, but barely by TIMP-1, pointing to ADAM-12 as the putative sheddase. In good agreement, ADAM-12 mRNA expression was repressed by EP. In conclusion, the efficient LRP-1-mediated clearance of gelatinases activity in non-bleeding endometrium is abrogated upon EP withdrawal, due to shedding of LRP-1 ectodomain by a metalloproteinase, presumably ADAM-12, itself regulated by EP.