Secretory role for human uterodomes (pinopods): secretion of LIF

The differentiation of human endometrial epithelium is a dynamic event, which occurs throughout the menstrual cycle in preparation for pregnancy. The appearance of uterodomes (pinopods) in this regard was first introduced in rodents with an established pinocytotic function, whereas little evidence was available in humans in this context. This study was undertaken to identify the potential physiological roles of uterodomes in the implantation process. To address this, endometrial biopsies from early, mid- and late luteal phases of the menstrual cycle of 23 fertile female patients with regular menses were used. Scanning and transmission electron microscopies (SEM and TEM) as well as immunofluorescence and immunogold TEM were performed to study the morphological changes and the expression pattern of leukaemia inhibitory factor (LIF) at uterodomes. Our results illustrated a high level of LIF expression in the human uterodomes, which was colocalized with the well-known biochemical markers of exocytosis, including syntaxin-1, 25-kDa synaptosomal protein (SNAP-25) and vesicle-associated membrane protein-2 (VAMP-2). Our morphological and immunocytochemical findings illustrated a secretory function for human uterodomes for the first time. In conclusion, this novel function for uterodomes provides an important clue in detection of their physiological function(s) during the process of the plasma membrane transformation.