Relaxin increases secretion of matrix metalloproteinase-2 and matrix metalloproteinase-9 during uterine and cervical growth and remodeling in the pig

Matrix metalloproteinases are proteolytic enzymes that degrade the extracellular matrix and are essential for tissue remodeling. Uterine and cervical growth require remodeling of structural barriers to cell invasion and matrix metalloproteinase-2 and -9 degrade type IV collagen, the major component of basement membranes. Relaxin stimulates uterine and cervical growth and remodeling, which includes remodeling of support elements such as basement membranes. The objective of this study was to determine whether relaxin alters the production and/or activity of matrix metalloproteinase-2 and -9 in the uterus or cervix of the pig. The growth-promoting effects of relaxin were elicited by administering relaxin to prepubertal gilts every 6 h for 54 h. The expression of matrix metalloproteinase-2 and matrix metalloproteinase-9 was characterized by gel zymography, and proteins were quantified by immunoblotting. Total enzyme activity was measured using matrix metalloproteinase-specific fluorescent substrate assays. In both uterine and cervical tissues, immunoreactive matrix metalloproteinase-2 and matrix metalloproteinase-9 protein expression was similar in relaxin-treated and control animals. However, tissue-associated gelatinase activity was attenuated by relaxin (P < 0.05). In contrast, relaxin significantly increased the secretion of active matrix metalloproteinase-2 and -9 protein into uterine fluid (P < 0.05). Given the importance of matrix metalloproteinases in extracellular matrix degradation, the observation that relaxin promotes uterine secretion of matrix metalloproteinase-2 and -9 supports the concept that relaxin facilitates the growth and remodeling of reproductive tissues by increasing extracellular proteolysis in the pig reproductive tract.