Analysis of gene and protein expression in the endometrium for validation of an ex vivo model of the equine uterus using PCR, digital and visual histopathology

In the past, most research in equine reproduction has been performed in vivo but the use of in vitro and ex vivo models has recently increased. This study aimed to evaluate the functional stability of an ex vivo hemoperfused model for equine uteri with molecular characterization of marker genes and their proteins. In addition, the study validated the respective protein expression and the aptness of the software QuPath for identifying and scoring immunohistochemically stained equine endometrium. After collection, uteri (n = 12) were flushed with preservation solution, transported to the laboratory on ice, and perfused with autologous blood for 6 h. Cycle stage was determined by examination of the ovaries for presence of Graafian follicles or corpora lutea and analysis of plasma progesterone concentration (estrus: n = 4; diestrus: n = 4; anestrus: n = 4). Samples were obtained directly after slaughter, after transportation, and during perfusion (240, 300, 360 min). mRNA expression levels of progesterone (PGR), estrogen (ESR1) and oxytocin (OXTR) receptor as well as of MKI67 (marker of cell growth) and CASP3 (marker of apoptosis) were analyzed by RT-qPCR, and correlation to protein abundance was validated by immunohistochemical staining. Endometrial samples were analyzed by visual and computer-assisted evaluation of stained antigens via QuPath. For PGR, effects of the perfusion and cycle stage on expression were found (P < 0.05), while ESR1 was affected only by cycle stage (P < 0.05) and OXTR was unaffected by perfusion and cycle stage. MKI67 was lower after 360 min of perfusion as compared to samples collected before perfusion (P < 0.05). For CASP3, differences in gene expression were found after transport and samples taken after 240 min (P < 0.05). Immunohistochemical staining revealed effects of perfusion on stromal and glandular cells for steroid hormone receptors, but not for Ki-67 and active Caspase 3. OXTR was visualized in all layers of the endometrium and was unaffected by perfusion. Comparison of QuPath and visual analysis resulted in similar results. For most cell types and stained antigens, the correlation coefficient was r > 0.5. In conclusion, the isolated hemoperfused model of the equine uterus was successfully validated at the molecular level, demonstrating stability of key marker gene expression. The utility of computer-assisted immunohistochemical analysis of equine endometrial samples was also confirmed.