Metalloproteinase activity has a role in equine chorionic girdle cell invasion

Chorionic girdle cells are a highly invasive subpopulation of trophoblast cells of the equine conceptus. By Day 35 (Day 0 = day of ovulation), cells of the chorionic girdle adhere to the uterine epithelium and begin to invade the endometrial wall. Invasive cells must attach to extracellular matrix proteins, secrete proteinases capable of degrading matrix, and migrate through the degraded matrix; invasion is largely dependent on the proteinase activity of the cells. The objective, therefore, was to develop an in vitro system to examine the mechanisms of equine chorionic girdle cell invasion through extracellular matrix. Day 34 chorionic girdle cell preparations were cultured on Matrigel Invasion Chambers. The cultured invasive cells were binucleate with prominent nucleoli and were often highly vacuolated, consistent with in vivo cup cell morphology. In addition, the cultured cells produced eCG. Additional Day 34 chorionic girdle cell preparations were cultured on Matrigel Invasion Chambers with or without proteinase inhibitors (aprotinin, bestatin, 1,10-phenanthroline) to determine the proteinase activity associated with girdle cell invasion. Only the metalloproteinase inhibitor, 1,10-phenanthroline, inhibited chorionic girdle cell invasion through Matrigel. Chorionic girdle cell supernatants were characterized by zymography, and the proteinases produced by these cells were confirmed to be metalloproteinases at approximate molecular masses of 72 and 95 kDa. The results indicated that equine chorionic girdle cells have matrix-degrading capabilities through metalloproteinase activity. Similar metalloproteinase activity has been reported to be necessary for mouse and human trophoblast invasion, suggesting a similar mechanism of implantation.