Expression of hormonal receptors and Toll-like receptors in cultured canine uterine explants with pseudoplacentational endometrial hyperplasia and bacterial-elicited endometrial inflammation

Pseudoplacentational endometrial hyperplasia (PEH) is a common uterine lesion in dogs. A high frequency of pyometra has been associated with PEH in dogs, suggesting that PEH might be related to the pathogenesis of pyometra. This study aimed to assess transcription levels and expression of Toll like receptors (TLR) 1, 2 and 4; alpha estrogen receptors (ESR1), progesterone receptors (PR) and prolactin receptors (PRLR) in uteri with PEH. Furthermore, the inflammatory response of dog endometrium with PEH against ex vivo bacterial stimulus was also investigated. Uteri were classified as controls or with PEH. Uterine explants were cultured for 6 and 12 hours after in vitro stimulus with inactivated Escherichia coli. Transcription of receptors and proinflammatory cytokines, namely interleukin-6 (IL-6) and CXCL8 were evaluated. Expression of receptors was also evaluated in uterine explants and uteri from biopsy archives. CXCL8 concentration was measured in supernatants from all cultured explants. Transcription levels and expression of both PR and ESR1 were lower in uteri explants with PEH not stimulated and cultured for 6 hours. Expression of PRLR was higher in uteri with PEH from biopsy archives. Proinflammatory response by transcription levels of interleukin 6 demonstrated downregulation in uteri with PEH at 6 hours of stimulation followed by upregulation at 12 hours. However, no differences between groups were observed. Both control and uteri with PEH secreted similar concentrations of CXCL8 at 6 hours of bacterial stimulation. At 12 hours, no response to stimulation was observed in the PEH group and supernatant concentrations of CXCL8 were higher in the control group. The inflammatory response to bacterial stimulus in uteri with PEH had different pattern than the control group, with an inversion in IL-6 transcription levels between 6-12 hours of culture. Additionally, CXCL8 production ceased earlier in explants with PEH than in control.