What is new on the physiopathology of endometrosis in the mare?

Abstract

The mare endometrium is a highly regenerative tissue that undergoes remodelling events during physiological events like endometrial regeneration, uterine involution, and parturition. In addition, the equine endometrium presents the particularity of developing fibrosis (collagen deposition) in the stroma, leading to endometrosis, responsible for early embryo loss. Endometrosis pathogenesis is not fully understood. Since reservoirs of somatic stem cells SSC are present in adult tissues capable of constant mature cell production or post injury regeneration, we evaluated the presence of cells positive for undifferentiated markers (Oct-4, Sox-2) in mare endometria. Both markers were expressed in differentiated glandular epithelial cells and stroma cells, in the presence or absence of endometrosis, in the different phases of the estrous cycle. The ability of equine neutrophils PMN to form neutrophils extracellular traps (NETs) might be a mechanism to kill some bacteria responsible for mare endometritis. Nevertheless, NETs proteins myeloperoxidase, elastase, and cathepsin G might also contribute for fibrosis establishment in the mare endometrium. Besides, NETs components and cytokine CTGF are involved in TGFbl and TIMP-1 production and up regulate the transcription of genes related with pathological collagen proteins deposition characteristic of fibrosis and likely related with TGFbl fibrogenic action. Understanding the complexity of cytokines, NETs and SSC driven mechanisms of fibrosis in mare endometrium is important to unravel endometrosis pathogenesis.