Temporal relationship between proliferating and apoptotic hormone-producing and endothelial cells in the equine corpus luteum

Abstract

The temporal relationship between endothelial cell death, vascular regression and the death of hormone-producing cells in the mare has not been established. To determine the dynamics of cell proliferation and death throughout the luteal phase, corpora lutea were studied at the early, mid-and late luteal phase, and after treatment with cloprostenol in the mid-luteal phase to induce premature luteolysis. Changes in cell proliferation and apoptosis were investigated utilising specific markers (phosphorylated histone-3 and activated caspase-3 respectively). Histone-3 positive cells were most abundant during the early luteal phase, and were mainly present in endothelial cells. Histone-3 activity significantly increased in hormone-producing cells 36 h after cloprostenol treatment. Frequency of activated caspase-3 staining peaked on day 14, and was induced by 36 h after cloprostenol administration in mid-luteal phase. However, cell death occurred simultaneously in the endothelial and hormone-producing cells. These results show that a subset of hormone-producing cells enter the early stages of cell division around luteolysis, while the majority of cells are undergoing cell death. Natural and induced functional and structural luteal regression in the mare can be at least partially attributed to simultaneous apoptosis of endothelial and hormone-producing cells. However, there is no evidence that endothelial cell death is the trigger for naturally occurring luteolysis.

Administration of vascular endothelial growth factor Trap during the ‘post-angiogenic’ period of the luteal phase causes rapid functional luteolysis and selective endothelial cell death in the marmoset

“…In addition, death of hormone-producing and endothelial cells was consistently observed to occur contemporaneously. Similarly, in humans, the peak level of cell death in the corpus luteum is apparent during the peri-menstrual period, with no evidence of this being preceded by preferential endothelial cell loss (Gaytan et al 1998, Morales et al 2000, while in the regressing equine corpus luteum, we have found that activated caspase-3 staining appears simultaneously in the hormone-producing and the endothelial cells (Aguilar et al 2006). These and other observations (Funayama et al 1996) indicate that structural luteolysis normally follows functional luteolysis in the primate, and there is as yet no convincing evidence to show that during this process, endothelial cells die before hormone-producing cells.…”

Cytokines and Angiogenesis in the Corpus Luteum

“…Active caspase-3 was also identified in large luteal cells and endothelial cells [74, 78]. In both steroidogenic and endothelial cells, the increase in caspase-3 expression was on day 14 of the luteal phase or 36 h after PGF2 α administration [89]. Another important finding is the relationship between the onset of caspase-3 expression in endothelial cells on day 14 of luteal phase (or after luteolysis induction) and the decrease in mRNA and protein expression of VEGF in steroidogenic cells [81].…”

Endothelial cells and angiogenesis in the horse in health and disease—A review

“…The complex development of a vascular network from a primitive endothelial sprout involves apoptotic death of endothelial cells during lumen formation and vascular remodelling (Lienau et al., 2005; Watson, Grant, & Coultas, 2017). Analysis of equine endothelial apoptosis can be successfully done via TUNEL test detecting DNA fragmentation (Al‐zi'abi, Fraser, & Watson, 2002) or via activated caspase‐3, another marker for apoptosis (Aguilar et al., 2006).…”

“…Angiogenic activity was monitored by different methods. Measurements of vascular perfusion (Abdelnaby & El‐Maaty, 2017), capillary density (Ferreira‐Dias, Bravo, Mateus, Redmer, & Medeiros, 2006; Ferreira‐Dias & Mateus, 2003; Watson & Ai‐zi'abi, 2002), proliferation and apoptosis in situ (Aguilar et al., 2006) as well as evaluation of angiogenesis assays in vitro (Ferreira‐Dias, Costa, et al, 2006) show an increase in angiogenesis before ovulation and in the early and mid‐luteal phase in the equine ovary.…”