Embryo implantation has been defined as the “black box” of human reproduction. Most of the knowledge on mechanisms underlining this process derives from animal models, but they cannot always be translated to humans. Therefore, the development of an in vitro/ex vivo model recapitulating as closely and precisely as possible the fundamental functional features of the human endometrial tissue is very much desirable. Here, we have validated endometrial organoids as a suitable 3D-model to studying epithelial endometrial interface for embryo implantation. Transmission and scanning electron microscopy analyses showed that organoids preserve the glandular organization and cell ultrastructural characteristics. They also retain the responsiveness to hormonal treatment specific to the corresponding phase of the menstrual cycle, mimicking the in vivo glandular-like aspect and functions. Noteworthy, organoids mirroring the early secretive phase show the development of pinopodes, large cytoplasmic apical protrusions of the epithelial cells, traditionally considered as reliable key features of the implantation window. Moreover, organoids express glycodelin A (GdA), a cycle-dependent marker of the endometrial receptivity, with its quantitative and qualitative features accounting well for the profile detected in the endometrium in vivo. Accordingly, organoids deriving from the eutopic endometrium of women with endometriosis show a GdA glycosylation pattern significantly different from healthy organoids, confirming our prior data on endometrial tissues. The present results strongly support the idea that organoids may closely recapitulate the molecular and functional characteristics of their cells/tissue of origin.

Taste receptors (TASRs) are expressed not only in the oral cavity but also throughout the body, thus suggesting that they may play different roles in organ systems beyond the tongue. Recent studies showed the expression of several TASRs in mammalian testis and sperm, indicating an involvement of these receptors in male gametogenesis and fertility. This notion is supported by an impaired reproductive phenotype of mouse carrying targeted deletion of taste receptor genes, as well as by a significant correlation between human semen parameters and specific polymorphisms of taste receptor genes. To better understand the biological and thus clinical significance of these receptors for human reproduction, we analyzed the expression of several members of the TAS2Rs family of bitter receptors in human testis and in ejaculated sperm before and after in vitro selection and capacitation. Our results provide evidence for the expression of TAS2R genes, with TAS2R14 being the most expressed bitter receptor subtype in both testis tissue and sperm cells, respectively. In addition, it was observed that in vitro capacitation significantly affects both the expression and the subcellular localization of these receptors in isolated spermatozoa. Interestingly, α-gustducin and α-transducin, two Gα subunits expressed in taste buds on the tongue, are also expressed in human spermatozoa; moreover, a subcellular redistribution of both G protein α-subunits to different sub-compartments of sperm was registered upon in vitro capacitation. Finally, we shed light on the possible downstream transduction pathway initiated upon taste receptor activation in the male reproductive system. Performing ultrasensitive droplets digital PCR assays to quantify RNA copy numbers of a distinct gene, we found a significant correlation between the expression of TAS2Rs and TRPM5 (r = 0.87), the cation channel involved in bitter but also sweet and umami taste transduction in taste buds on the tongue. Even if further studies are needed to clarify the precise functional role of taste receptors for successful reproduction, the presented findings significantly extend our knowledge of the biological role of TAS2Rs for human male fertility.

Endometriosis is a condition defined as presence of endometrium outside of the uterine cavity. These endometrial cells are able to attach and invade the peritoneum or ovary, thus forming respectively the deep infiltrating endometriosis (DIE) and the ovarian endometrioma (OMA), the ectopic lesions feature of this pathology. Endometriotic cells display high invasiveness and share some features of malignancy with cancer cells. Indeed, the tissue remodeling underlining lesion formation is achieved by matrix metalloproteinases (MMPs) and their inhibitors. Therefore, these molecules are believed to play a key role in development and pathogenesis of endometriosis. This study investigated the molecular profile of metalloproteinases and their inhibitors in healthy (n = 15) and eutopic endometrium (n = 19) in OMA (n = 10) and DIE (n = 9); moreover, we firstly validated the most reliable housekeeping genes allowing accurate gene expression analysis in these tissues. Gene expression, Western blot, and immunofluorescence analysis of MMP2, MMP3, and MMP10 and their tissue inhibitors TIMP1 and TIMP2 demonstrated that these enzymes are finely tuned in these tissues. In OMA lesions, all the investigated MMPs and their inhibitors were significantly increased, while DIE expressed high levels of MMP3. Finally, in vitro TNFα treatment induced a significant upregulation of MMP3, MMP10, and TIMP2 in both healthy and eutopic endometrial stromal cells. This study, shedding light on MMP and TIMP expression in endometriosis, confirms that these molecules are altered both in eutopic endometrium and endometriotic lesions. Although further studies are needed, these data may help in understanding the molecular mechanisms involved in the extracellular matrix remodeling, a crucial process for the endometrial physiology.

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STUDY QUESTION Are selective markers for the neuronal differentiation such as microtubule-associated protein 2 (MAP-2) and synaptophysin (SYP) as well as the nerve growth factor (NGF) expressed by fibroids, myometrium and eutopic endometrium? SUMMARY ANSWER Neuronal markers NGF, MAP-2 and SYP are highly expressed in fibroids compared with matched myometrium, and this neurogenic pathway is upregulated by tumor necrosis factor (TNF) alpha in cultured smooth muscle cells (SMCs). WHAT IS KNOWN ALREADY Uterine fibroids or leiomyomas are the most common benign tumors, accounting for approximately one-third of hysterectomies. The present trend is to improve the medical treatment avoiding surgery, also for fertility sparing; hence, the pathogenic mechanisms are investigated, aiming to develop new therapeutic strategy. STUDY DESIGN, SIZE, DURATION This laboratory-based case–control study is focused on fibroids and myometrial specimens obtained between 2015 and 2017 from 15 women of reproductive age at the proliferative phase of the menstrual cycle. Leiomyomas, matched myometrium and endometrium from each woman were analyzed. Control endometrium was obtained from women undergoing surgery for ovarian cyst (n = 15). PARTICIPANTS/MATERIALS, SETTING, METHODS qRT-PCR, western blotting and immunostaining were applied to evaluate the expression of neurogenic markers; the effects of TNF on NGF, MAP-2 and SYP expression in cultured SMCs from leiomyomas and matched myometrium were analyzed. MAIN RESULTS AND THE ROLE OF CHANCE qRT-PCR analyses using tissues from clinical patients showed that the levels of NGF, MAP-2 and SYP mRNA were significantly higher in uterine leiomyomas compared with their matched myometrium (P < 0.05), whereas only NGF was significantly increased in eutopic endometrium compared with healthy endometrium. In primary SMCs, isolated from fibroids or from the adjacent myometrium, NGF, MAP-2 and SYP mRNA expression were significantly increased by TNF treatment (P < 0.05). Finally, human endometrial stromal cells prepared from the endometrium of patients affected by uterine fibroids display higher TNF expression (P < 0.001). LIMITATIONS, REASONS FOR CAUTION qRT-PCR analysis and immunofluorescence validation are robust methods demonstrating a clear upregulation of neurogenic factors in leiomyomas, even though additional studies are needed to establish a correlation between increased neuronal gene expression and degree of pain, as well as the involvement of inflammation mediators in the development of the neurogenic unhinge. Therefore, more in vivo studies are needed to confirm the results achieved from primary cultured SMCs. WIDER IMPLICATIONS OF THE FINDINGS The increased expression of neurogenic factors in uterine fibroids and endometrium may contribute to explain the painful stimuli. Accordingly, these neurogenic pathways may represent potential therapeutic avenues to treat the fibroid-related disorders. STUDY FUNDING/COMPETING INTEREST(S) This study was supported by research grants from the University of Siena. The authors declare no conflict of interest. TRIAL REGISTRATION NUMBER N/A.