The Role of the Plasminogen Activator System in the Etiology of Ovarian Follicular Cysts in Dairy Cattle.

摘要

Cystic ovarian disease (COD) is an anovulatory condition in cattle that afflicts between 6-18% of all dairy cows in the US. Ovulation is dependent on the plasminogen activator (PA) family of proteases and protease inhibitor for proteolysis, culminating in follicular rupture. Failure of the follicle to ovulate suggests an aberration in proteolysis in cystic follicles. Polycystic ovarian disease in humans is phenotypically similar to COD is associated with elevated plasma PAI-1. PAI-1 regulates the proteolytic activity responsible for ovulation. Vitamin E supplementation reduces plasma PAI-1 and reduces the incidence of COD. Four experiments were conducted to elucidate the role of the plasminogen activator system in the etiology of COD and the ability of vitamin E supplementation to modulate the PA system in cattle. In experiment one, blood samples were collected from lactating dairy cows upon diagnosis of a follicular cyst at least 3.0 cm in diameter by a licensed veterinarian. Cows were classified based upon their history of follicular cysts. Tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) concentrations and activities were measured using commercially available ELISA and chromogenic reagents. No differences were detected between cystic and non-cystic dairy cows. In experiment two, six non-lactating beef cows were supplemented with 2750 IU of alpha-tocopherol every four days for 24 days. Blood samples were collected every two days and assayed for tPA and PAI-1 concentrations and activities. Supplementation with alpha-tocopherol decreased the ratio of PAI-1 to tPA activities adjusted to the Day 0 measurement (P=0.097). In experiment three, mRNA was isolated from follicular cysts and preovulatory follicles and relative quantitative RT-PCR was performed for tPA, urokinase-type plasminogen activator (uPA), urokinase-type plasminogen activator receptor (uPAR), PAI-1, and beta-actin. uPA expression was reduced (P0.1) and uPAR expression was greater (P0.1) in follicular cysts compared to preovulatory follicles. Lastly, in experiment four DNA was extracted from whole blood obtained from cystic and normal dairy cows and the promoter region of the PAI-1 gene was sequenced. More Jersey cows with COD possessed a four basepair deletion polymorphism than normal cows (P0.1) and more Jerseys possessed the deletion polymorphism than Holsteins (P0.01).