BIM EL-mediated apoptosis in cumulus cells contributes to degenerative changes in aged porcine oocytes via a paracrine action

• Published in: Theriogenology Vol. 76; no. 8; pp. 1487 - 1495
• Main Authors: Wu, Yi, Wang, Xian-long, Liu, Jing-hao, Bao, Zhong-jian, Tang, Da-wei, Wu, Yue, Zeng, Shen-ming
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2011
• Subjects: Animals; Apoptosis; Apoptosis - physiology; Apoptosis Regulatory Proteins - genetics; Apoptosis Regulatory Proteins - metabolism; Bcl-2-Like Protein 11; BIM; Cumulus cell; Cumulus Cells - physiology; Gene Expression Regulation - physiology; Membrane Proteins - genetics; Membrane Proteins - metabolism; Oocyte aging; Oocytes - cytology; Oocytes - physiology; Paracrine Communication - physiology; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Spontaneous fragmentation; Swine; Time Factors; Oocyte aging; Spontaneous fragmentation; Cumulus cell; BIM; Apoptosis
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2011.06.016

Whether cumulus cells (CCs) contribute to oocyte aging remains controversial; in that regard, little is known about biochemical processes of gene expression in CCs surrounding aged oocytes. The objective was to elucidate contributions of CCs to porcine oocyte aging and degeneration, apoptosis and BIM expression in CCs during oocyte aging in vitro. When culture of cumulus oocyte complexes (COCs) was prolonged (68 h, which resulted in 24 h of aging), the rate of blastocyst formation following electro-activation was lower than that of oocytes aged without CCs (2.6 ± 0.1 vs 13.5 ± 1.3%, mean ± SEM; P < 0.05). In addition, the presence of CCs significantly accelerated spontaneous fragmentation of oocytes following prolonged (92 h) culture. Apoptotic CCs were present in COCs cultured for 68 h, and the abundance of Bim mRNA in CCs progressively increased after 56 h of culture (P < 0.05). Based on immunofluorescence, BIM protein expression was up-regulated in CCs surrounding aged oocytes; furthermore, quantification (Western blot) of BIM EL protein progressively increased after 56 h of culture. Lastly, in a series of experiments to elucidate the signal pathway, blocking gap junctions (with 1-octanol) during aging did not eliminate the effect of CCs on accelerating oocyte aging, but prolonged co-culture of denuded oocytes with COCs after in vitro maturation reduced blastocyst rate relative to culture of denuded oocytes aged alone (4.15 ± 0.1 vs 11.0 ± 0.7%, P < 0.05). We concluded that apoptotic CCs, in which BIM EL up-regulation was involved, accelerated oocyte aging and degeneration in vitro via a paracrine action.