Comparative proteomic analysis of follicular fluids from normal and cystic follicles in sows

Follicular fluid (FF) includes various biologically active proteins which can affect follicular growth and maturation. Certain proteins could reflect the physiological and pathological status of follicles. The aim of the present study was to explore the key proteins associated with pathogenesis of follicular cysts, some of which may be candidate biomarkers for the condition. We analysed the proteomes of FF from small, medium, large and cystic follicles by two-dimensional electrophoresis (2-DE) combined with mass spectrometry (MS). The protein components in FF were found to be significantly different among groups; about 300 proteins spots in each group were examined, and 32 differentially expressed proteins were identified from different groups. To further reveal the source of identified proteins, transcripts encoding two of these, transferrin and RBP-4, were detected in granulosa cells (GCs) by RT-PCR, as well as the proteins were detected in 24 h culture media of GCs by ELISA. High levels of RBP-4 were examined in FF of cystic follicles by 2-DE analysis, which were significantly different to those in large follicles (p < 0.05). In conclusion, the study enriches our understanding of the proteins of FF; RBP-4 and transferrin originate from passive transfer and follicular synthesized secretion, and RBP-4 might be a candidate biomarker for porcine follicular cysts. Combined with histological studies, these results further suggest that changes of the type and quantity of proteins in FF might be attributed to an abnormal metabolism of follicular cells and structure of follicular wall in cystic follicles. Our findings will contribute to further insight into the pathogenesis of follicular cysts.