Alteration in the expression insulin-like growth factor-II (IGF-II) family members in bovine cystic ovarian disease

REY F; RODRÍGUEZ FM; SALVETTI NR; PALOMAR MM; BARBEITO CG; ORTEGA HH

Pittsburgh, Pennsylvania

Congreso; 42° Annual meeting of the Society for the Study of Reproduction; 2009

Society for the Study of Reproduction

Cystic ovarian disease (COD) is one of the most common reproductive disorders in cattle, and the mechanism leading to their development was proposed to be of multifactorial etiology. Although it is widely accepted that a neuroendocrinological dysfunction of the hypothalamic-pituitary-gonadal axis is an important etiological factor, several reports have discussed the association between COD and growth factors in different species. Our hypothesis states that variations in members of the IGF superfamily are involved in follicular cyst development. Based on our previous results about IGF-I expression, several members of IGF system were evaluated in the present study in order to test our hypothesis. Ovaries were collected at a local abattoir and dissected healthy follicles were classified into small (smaller than 5 mm), medium (5–10 mm), and large (larger than 10 mm) antral follicles. Follicular cysts were defined as follicles of more than 20 mm in diameter, without functional corpus luteum and were evaluated macroscopically, histologically and hormonally. In the follicular wall of cystic and healthy follicles we evaluated IGF-II and IGFBPs mRNA level by reverse transcription followed by PCR. Protein content of IGF-II was assessed in follicular fluid by an ELISA developed in our laboratory, and the synthesis in situ of IGF-II was determined by immunohistochemistry in granulosa and theca cells. The IGFBPs protein levels were evaluated as their binding activity by western ligand blots in cystic and healthy follicular fluids. Results obtained have shown that IGF-II mRNA detected in follicular wall was increased in cystic follicles relative to what was observed in healthy ones. Also observed at mRNA level, we detected a significant increase in IGF-II protein in granulosa and theca cells in cystic follicles evaluated by immunohistochemistry. On the other hand, both healthy and cystic follicles showed a lower expression of IGF-II in theca relative to granulosa cells. This result was in agreement with our previous finding of mRNA detection by in situ hybridization. In follicular fluid we detected, similar IGF-II content in different follicular structures, with a tendency to decrease in cysts. Total IGFBPs assessed by western ligand blots, were similar in different structures, however discriminating each IGFBP, we observed a tendency to decrease the IGFBP-2 levels in cystic follicles, that could be related with the higher levels of IGF-II observed. Additionally, the pattern of mRNA expression of IGFBPs was similar to those determined in IGFBP protein, also detecting a decreasing tendency in the IGFBP-2 mRNA. Results obtained in the present study showed alterations in the IGF system components analyzed in COD. Further studies should be done in order to evaluate IGF receptors as modulating factors of IGF response. Regardless, these finding support our hypothesis providing information that an alteration in IGF system could be related to COD in cattle. (Supported by APCyT grant PICT-2007-01202 BID 1728 OC/AR and UNL grant CAI+D Nº002).