Bovine microvascular endothelial cells of separate morphology differ in growth and response to the action of interferon-gamma

Mechanisms of angioregression of the corpus luteum

The corpus luteum is a transient ovarian endocrine gland that produces the progesterone necessary for the establishment and maintenance of pregnancy. The formation and function of this gland involves angiogenesis, establishing the tissue with a robust blood flow and vast microvasculature required to support production of progesterone. Every steroidogenic cell within the corpus luteum is in direct contact with a capillary, and disruption of angiogenesis impairs luteal development and function. At the end of a reproductive cycle, the corpus luteum ceases progesterone production and undergoes rapid structural regression into a nonfunctional corpus albicans in a process initiated and exacerbated by the luteolysin prostaglandin F2α (PGF2α). Structural regression is accompanied by complete regression of the luteal microvasculature in which endothelial cells die and are sloughed off into capillaries and lymphatic vessels. During luteal regression, changes in nitric oxide transiently increase blood flow, followed by a reduction in blood flow and progesterone secretion. Early luteal regression is marked by an increased production of cytokines and chemokines and influx of immune cells. Microvascular endothelial cells are sensitive to released factors during luteolysis, including thrombospondin, endothelin, and cytokines like tumor necrosis factor alpha (TNF) and transforming growth factor β 1 (TGFB1). Although PGF2α is known to be a vasoconstrictor, endothelial cells do not express receptors for PGF2α, therefore it is believed that the angioregression occurring during luteolysis is mediated by factors downstream of PGF2α signaling. Yet, the exact mechanisms responsible for angioregression in the corpus luteum remain unknown. This review describes the current knowledge on angioregression of the corpus luteum and the roles of vasoactive factors released during luteolysis on luteal vasculature and endothelial cells of the microvasculature.

Five different phenotypes of endothelial cell cultures from the bovine corpus luteum: present outcome and role of potential dendritic cells in luteolysis

Progress in understanding the background of structural luteolysis depends on insights into the physiological function of innate immunity (INIM), in particular the presence of dendritic cells (DCs) in the corpus luteum (CL). For this reason, the cultures of five endothelial cell-like phenotypes derived from the bovine CL and their long-lasting analysis (morphology, function, and origin) become important. Types 1 and 2 represent microvascular endothelial cells with cytokeratin (CK) expression, assumed to be danger-sensing cells. Types 3 and 4 express features of common endothelial cells. Type 5 indicates a steroidogenic cell type, which could be derived from steroidogenic CK(+) cells in the CL of development after loss of CK expression. Type 5 is a promising candidate to become a mature DC. It might act with the microvascular CK(+) cell/type 1 like a luteovascular unit, which connects INIM with adaptive/cell-mediated immunity (ADIM) in structural luteolysis.

Microvascular endothelial cells of the corpus luteum

The cyclic nature of the capillary bed in the corpus luteum offers a unique experimental model to examine the life cycle of endothelial cells, involving discrete physiologically regulated steps of angiogenesis, blood vessel maturation and blood vessel regression. The granulosa cells and theca cells of the developing antral follicle and the steroidogenic cells of the corpus luteum produce and respond to angiogenic factors and vasoactive peptides. Following ovulation the neovascularization during the early stages of corpus luteum development has been compared to the rapid angiogenesis observed during tumor formation. On the other end of the spectrum, the microvascular endothelial cells are the first cells to undergo apoptosis at the onset of corpus luteum regression. Important insights on the morphology and function of luteal endothelial cells have been gained from a combination of in vitro and in vivo studies on endothelial cells. Endothelial cells communicate with cells comprising the functional unit of the corpus luteum, i.e., other vascular cells, steroidogenic cells, and immune cells. This review is designed to provide an overview of the types of endothelial cells present in the corpus luteum and their involvement in corpus luteum development and regression. Available evidence indicates that microvascular endothelial cells of the corpus luteum are not alike, and may differ during the process of angiogenesis and angioregression. The contributions of vasoactive peptides generated by the luteal endothelin-1 and the renin-angiotensin systems are discussed in context with the function of endothelial cells during corpus luteum formation and regression. The ability of two cytokines, tumor necrosis factor alpha and interferon gamma, are evaluated as paracrine mediators of endothelial cell function during angioregression. Finally, chemokines are discussed as a vital endothelial cell secretory products that contribute to the recruitment of eosinophils and macrophages. The review highlights areas for future investigation of ovarian microvascular endothelial cells. The potential clinical applications of research directed on corpus luteum endothelial cells are intriguing considering reproductive processes in which vascular dysfunctions may play a role such as ovarian failure, polycystic ovary syndrome (PCOS), and ovarian hyperstimulation syndrome (OHSS).

Lectin binding patterns in two cultured endothelial cell types derived from bovine corpus luteum

Epithelial cells of different phenotypes derived from bovine corpus luteum have been studied intensively in our laboratory. In this study, specific lectin binding was examined for cells of type 1 and 3, which were defined as endothelial cells. In order to confirm differences in their glycocalyx at the light microscopic level, five biotinylated lectins were applied to postconfluent cultures which had been fixed with buffered paraformaldehyde or glutaraldehyde. Cells were not permeabilized with any detergent. Lectin binding was localized with a streptavidin-peroxidase complex which was visualized with two different techniques. The DAB technique detected peroxidase histochemically, while the immunogold technique used an anti-peroxidase gold complex together with silver amplification. Neither cell type 1 nor cell type 3 bound a particular lectin selectively, yet each cell type expressed a particular lectin binding pattern. With the DAB technique, diverse lectin binding patterns were seen, probably indicating either "outside" binding, i.e., a diffuse pattern, a lateral-cell-side pattern and a microvillus-like pattern, or "inside" binding, i.e., a diffuse pattern, and a granule-like pattern. With the immunogold technique, only "outside" binding was observed. In addition, the patterns of single cilia or of single circles were detected, the latter roughly representing 3-micron-sized binding sites for concanavalin A. When localizing them at the ultrastructural level, single circles corresponded with micron-sized discontinuities of the plasma membrane. Shedding vesicles were detected whose outer membrane was labelled with concanavalin A. Our results confirm the diversity of the two cell types under study. The "inside" lectin binding may be caused by way of transient plasma membrane openings and related to shedding of right-side out vesicles ("ectocytosis").

Cytokeratin-positive and cytokeratin-negative cultured endothelial cells from bovine aorta and vena cava

The heterogeneous morphology of microvascular endothelial cells obtained from the bovine corpus luteum was recently attributed to the occurrence of cytokeratin (CK) positive and CK negative endothelial cells. The aim of the present study was to establish comparable differences for bovine macrovascular endothelial cells. For this reason, endothelial cells were scraped from the abdominal aorta as well as the inferior vena cava of cows. At the level of phase contrast microscopy, primary cultures originating from both large vessels could be classified as CK positive or CK negative endothelial cells. After seeding CK positive endothelial cells on Matrigel matrix, a two-dimensional meshwork of so called pseudotubules formed within 2 h. By using immunofluorescence localization CK positive cells were identified by a complex meshwork. It consisted of CK 8, 18 and 19 as displayed by Western blots. The CK negative group showed spindle-shaped or polygonal endothelial cells according to light microscopy. In postconfluent cultures, spindle-shaped cells developed a three-dimensional meshwork of tubules. After seeding spindle-shaped cells on Vitrogen 100 matrix, pseudotubules formed within 1 day. In considering the frequency of occurrence, primary harvests from the vena cava contained less than 1% CK positive cells. With respect to growth, the cell number was two to three times higher for the CK negative group than the CK positive group as judged on day 13 after cell seeding. It is concluded that subpopulations of endothelial cells are derived from large blood vessels.

Isolation of granulosa-like cells from the bovine secretory corpus luteum and their characterization in long-term culture

BACKGROUND

The isolation of cells termed type 5 from the bovine corpus luteum was recently reported. Since these cells were reminiscent of immature granulosa cells, their morphological and functional relationship requires further investigation in view of the novel concept of corpus luteum growth. It suggests that putative stem cells of unknown origin supply the pool of small luteal cells.

METHODS

Bovine corpora lutea were mechanically dispersed, cell suspensions separated over a Percoll density gradient, and type 5 cells purified by colony transfer. Granulosa cells were harvested from small-sized antral follicles. Observations were carried out at the light and electron microscopical level. 3 beta-Hydroxy-steroid-dehydrogenase was localized histochemically in addition to intracellular lipid droplets stained with nile red. Immunolocalization was used to study Factor VIII antigen presence, the architecture of the cytoskeleton, as well as the occurrence of neuronal cell adhesion molecules, and of neuronal cadherin-like molecules. The uptake of acetylated low density lipoprotein was examined. As for progesterone concentration, cells were seeded at low density on day zero. Cell numbers and progesterone levels of supernatants were determined on day 10 in culture.

RESULTS AND CONCLUSIONS

Type 5 cells behaved morphologically like immature granulosa cells, yet the total cell number and the progesterone concentration differed for type 5 cells compared to granulosa cells. The addition of LH had no influence on the progesterone concentration as seen for either type 5 cells or for granulosa cells. It is concluded that type 5 cells, which were originally mistaken for microvascular endothelial cells, display similarities with immature granulosa cells. Type 5 cells may play a role in renewal of luteal cells.