Expression and distribution of cytokeratin 8/18 intermediate filaments in bovine antral follicles and corpus luteum: an intrinsic mechanism of resistance to apoptosis?
Apoptosis is a mechanism of cell elimination during follicular atresia and luteal regression. Recent evidence suggests sensitivity to apoptosis in some cell types is partly dependent upon cytokeratin-containing intermediate filaments. Specifically, cytokeratin 8/18 (CK8/18) filaments are thought to impart resistance to apoptosis. Here, cytokeratin filament expression within bovine ovarian follicles and corpora lutea (CL) was characterized and the potential relationship between cell-specific CK8/18 expression and apoptosis explored. Immunoprecipitation and western blot analysis confirmed CK8 associates with CK18 to form CK8/18 heterodimeric filaments within bovine ovarian cells. Immunostaining revealed populations of CK18-positive (CK18+) cells in healthy growing follicles that increased in postovulatory follicles. Atretic follicles at all stages of atresia also contained some CK18+ cells. However, no CK18+ cells were detected in primordial or primary follicles. In CL, developing CL contained a higher proportion of CK18+ cells (approximately 35%, range 30-70%) than mature CL (approximately 16%) and regressing CL (approximately 5%; P<0.05, n = 3-5 CL/stage), suggesting CK8/18 filament expression diminishes over time, as luteal cells become more susceptible to apoptosis. Dual-fluorescence labeling for CK18 and a cell death marker (TUNEL labeling) confirmed this view, demonstrating less death of CK18+ than CK18- luteal cells throughout the estrous cycle (P<0.05). The results indicate differential expression of CK8/18 filaments occurs in cells of bovine ovarian follicles and CL throughout the estrous cycle. The prevalence and cell-specific pattern of cytokeratin expression in these structures is consistent with the concept these filaments might impart resistance to apoptosis in ovarian cells as is seen in other cell types.
Townson
David H
DH
University of New Hampshire, Department of Molecular, Cellular and Biomedical Sciences, Durham, NH 03824, USA. dave.townson@unh.edu
Putnam
Amanda N
AN
Sullivan
Brian T
BT
Guo
Lankai
L
Irving-Rodgers
Helen F
HF
D000818:Animals; D017209:Apoptosis; D002417:Cattle; D003338:Corpus Luteum / Q000378:metabolism*; D030762:Estrous Cycle; D005260:Female; D005496:Follicular Atresia / Q000502:physiology; D020287:In Situ Nick-End Labeling; D053538:Keratin-18 / Q000032:analysis / Q000378:metabolism; D007633:Keratins / Q000032:analysis / Q000378:metabolism; D008184:Luteal Cells; D006080:Ovarian Follicle / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D010053:Ovary / Q000378:metabolism
D053538:Keratin-18; D007633:Keratins