Uterine cysts in female mice deficient for caveolin-1 and insulin-like 3 receptor RXFP2

Caveolin-1 Regulation and Function in Mouse Uterus during Early Pregnancy and under Human In Vitro Decidualization

Decidualization is essential to rodent and primate pregnancy. Senescence is increased during decidualization. Failure of senescence clearance during decidualization will cause pregnancy abnormality. Caveolin-1 is located in plasmalemmal caveolae and involved in senescence. However, whether caveolin-1 is involved in decidualization remains undefined. In this study, we examined the expression, regulation and function of Caveolin-1 during mouse early pregnancy and under mouse and human in vitro decidualization. From days 1 to 8 of pregnancy, Caveolin-1 signals are mainly located in endothelium and myometrium. Estrogen stimulates Caveolin-1 expression in endothelium. Deficiency of estrogen receptor α significantly promotes Caveolin-1 level in uterine stromal cells. Progesterone upregulates Caveolin-1 expression in luminal epithelium. During mouse in vitro decidualization, Caveolin-1 is significantly increased. However, Caveolin-1 is obviously decreased during human in vitro decidualization. Caveolin-1 overexpression and siRNA suppress and upregulate IGFBP1 expression under in vitro decidualization, respectively. Blastocysts-derived tumor necrosis factor α (TNFα) and human Chorionic Gonadotropin (hCG) regulate Caveolin-1 in mouse and human decidual cells, respectively. Caveolin-1 levels are also regulated by high glucose and insulin. In conclusion, a low level of Caveolin-1 should be beneficial for human decidualization.

Insulin-like peptide 3 in domestic animals with normal and abnormal reproductive functions, in comparison to rodents and humans

Background

Insulin-like peptide 3 (INSL3) is a circulating hormone secreted from only testis and ovaries in mammals. Findings on INSL3 have been gathered from subjects with normal and abnormal reproductive statuses, especially rodents and humans. However, little to no review articles focusing on INSL3 in domestic animals exist.

Methods

The author reviewed the past and recent literature regarding the structure, expression, roles of INSL3 in the reproductive organs, and its circulation under normal and aberrant reproductive conditions in domestic animals in comparison with rodents and humans.

Main findings

As with humans and rodents, blood INSL3 concentrations rise around puberty in normal male domestic animals and are associated with testicular size. INSL3 levels are acutely upregulated by luteinizing hormone (LH), and the increase is smaller than that of testosterone in male ruminants, whereas the acute regulation of INSL3 by LH does not occur in human men. Dogs with cryptorchidism and bulls with abnormal semen have lowered INSL3 levels.

Conclusion

The findings regarding INSL3 secretions in male domestic animals with normal and aberrant reproductive functions illustrate similar or dissimilar points to humans and rodents. Data on blood INSL3 levels in normal and abnormal female domestic species are still limited and require further investigation.

Evidence for existence of insulin-like factor 3 (INSL3) hormone-receptor system in the ovarian corpus luteum and extra-ovarian reproductive organs during pregnancy in goats

Insulin-like factor 3 (INSL3), initially described as a male hormone, is expressed in female reproductive organs during the estrous cycle and pregnancy but its function has not yet been established. This study explores the function of INSL3 in pregnant Saanen goats by characterizing the expression dynamics of INSL3 and its receptor, relaxin family peptide receptor 2 (RXFP2) and by demonstrating specific INSL3 binding in reproductive organs, using molecular and immunological approaches and ligand-receptor interaction assays. We demonstrate that the corpus luteum (CL) acts as both a source and target of INSL3 in pregnant goats, while extra-ovarian reproductive organs serve as additional INSL3 targets. The expression of INSL3 and RXFP2 in the CL reached maximum levels in middle pregnancy, followed by a decrease in late pregnancy; in contrast, RXFP2 expression levels in extra-ovarian reproductive organs were higher in the mammary glands but lower in the uterus, cervix and placenta and did not significantly change during pregnancy. The functional RXFP2 enabling INSL3 to bind was identified as an ~ 85 kDa protein in both the CL and mammary glands and localized in large and small luteal cells in the CL and in tubuloalveolar and ductal epithelial cells in the mammary glands. Additionally, INSL3 also bound to multiple cell types expressing RXFP2 in the uterus, cervix and placenta in a hormone-specific and saturable manner. These results provide evidence that an active intra- and extra-ovarian INSL3 hormone-receptor system operates during pregnancy in goats.

Diverse functions of insulin-like 3 peptide

Insulin-like 3 peptide (INSL3) is a member of the insulin-like peptide superfamily and is the only known physiological ligand of relaxin family peptide receptor 2 (RXFP2), a G protein-coupled receptor (GPCR). In mammals, INSL3 is primarily produced both in testicular Leydig cells and in ovarian theca cells, but circulating levels of the hormone are much higher in males than in females. The INSL3/RXFP2 system has an essential role in the development of the gubernaculum for the initial transabdominal descent of the testis and in maintaining proper reproductive health in men. Although its function in female physiology has been less well-characterized, it was reported that INSL3 deletion affects antral follicle development during the follicular phase of the menstrual cycle and uterus function. Since the discovery of its role in the reproductive system, the study of INSL3/RXFP2 has expanded to others organs, such as skeletal muscle, bone, kidney, thyroid, brain, and eye. This review aims to summarize the various advances in understanding the physiological function of this ligand-receptor pair since its first discovery and elucidate its future therapeutic potential in the management of various diseases.

Targeting the relaxin/insulin-like family peptide receptor 1 and 2 with small molecule compounds

The peptide hormone relaxin has beneficial roles in several organs through its action on its cognate G protein-coupled receptor, RXFP1. Relaxin administration is limited to intravenous, subcutaneous, intramuscular, or spinal injection. Another drawback of peptide-based therapy is the short half-life, which requires continuous delivery of the drug to achieve efficient concentration in target organs. The discovery of a non-peptide small molecule agonist of RXFP1, ML290, provides an alternative to the natural ligand. This review summarizes the development of ML290 and its potential future therapeutic applications in various diseases, including liver fibrosis and cardiovascular diseases. We also discuss the development of small molecule agonists targeting the insulin-like 3 receptor, RXFP2, and propose the potential use of these small molecules in the context of bone and muscle remodeling.

The physiological expression of scavenger receptor SR-B1 in canine endometrial and placental epithelial cells and its potential involvement in pathogenesis of pyometra

Pyometra, the purulent inflammation of the uterus, is a common uterine disease of bitches that has potentially life-threatening consequences. The opportunistic bacterial infection of the uterus often progresses into the serious systemic inflammatory response syndrome. In a previous study, we characterized epithelial foam cells in the canine endometrial surface occurring in metestrus, and we regularly observed pronounced epithelial foam-cell formations in pyometra-affected uteri. Therefore, it was assumed that the mechanism behind lipid droplet accumulation in surface epithelial cells might even increase bacterial binding capacity and promote pyometra development. Lipid droplet accumulation in epithelial cells is accomplished via specialized lipid receptors called scavenger receptors (SR). Scavenger receptor class B type 1 (SR-B1) is an important receptor for lipid accumulation in diverse cell types, but it is also a strong binding partner for bacteria, and thereby enhances bacterial adhesion and clinical signs of systemic inflammatory response syndrome. In the present study, after the isolation of metestrous surface epithelial cells from canine uteri by laser capture microdissection, SR-B1 was identified at the messenger RNA (mRNA) level by quantitative real time polymerase chain reaction and also at the protein level by means of immunohistochemistry. In pyometra-affected uteri, SR-B1 mRNA expression was higher than that in the healthy control samples, and SR-B1 protein was expressed in the surface and crypt epithelial cells. Furthermore, to understand the physiological role of SR-B1 expression in the metestrus surface epithelial cells, we investigated its expression in the epithelial cells of the glandular chambers of canine placenta in different stages of gestation because these cells are also characterized by lipid droplet accumulation. SR-B1 was present in the placental epithelial cells of the glandular chambers from 25 to 30 and 45 to 50 days of gestation, where basal and basal and/or apical expression patterns were observed. The physiological expression of SR-B1 in metestrous endometrial surface epithelia might be related to the implantation process and embryo development, as SR-B1 was also identified in the epithelial cells of the canine placental chambers. The increased levels of SR-B1 in pyometra-affected uteri indicate a potential role for this scavenger receptor in endometrial bacterial adhesion.

Differential expression of caveolin-1 in human myometrial and uterine leiomyoma smooth muscle

OBJECTIVE

Uterine leiomyomas, the most common neoplasms of the female genital tract, are benign tumors of the uterus arising from the smooth muscle cells (SMCs) of the myometrium with an involvement of estrogen. Caveolin-1 (Cav-1), a major protein component in caveolae membrane lipid rafts, is down-regulated in several estrogen-related cancer cells, and overexpression of Cav-1 inhibits proliferation of cancer cells and vascular SMCs as well. Therefore, we hypothesize that Cav-1 is down-regulated in human uterine leiomyoma.

RESULTS

Western blot using tissues from clinical patients showed that Cav-1 expression was significantly lower or undetectable in uterine leiomyoma compared with their matched myometrium (P < .001). This finding was confirmed by immunohistochemistry and confocal microscopy. The cav-1 mRNA level in uterine leiomyomas was also significantly lower as detected by reverse transcription-quantitative polymerase chain reaction analysis (P = .001). To further study the underlying mechanism, we performed primary cell culture, and found that the expression of Cav-1 remained low in cultured leiomyoma SMCs (P = .009). Serum withdrawal did not change Cav-1 expression in leiomyoma SMCs, but increased expression in myometrial SMCs (P = .006). 17-β estradiol inhibited the expression of Cav-1 protein (P = .047) and mRNA (P = .007) in leiomyoma SMCs, whereas it stimulated expression in myometrial SMCs (P = .043). 17-β estradiol, although activating the mitogen-activated protein kinase pathway in both SMCs, did not stimulate their proliferation.

CONCLUSION

We conclude that human uterine leiomyomas in vitro express low levels of Cav-1, which may result from estrogen inhibition. This effect of estrogen may contribute to the pathogenesis of uterine leiomyoma. Further studies in vivo are needed to verify these results.

RELAXIN enhances differentiation and matrix mineralization through Relaxin/insulin-like family peptide receptor 2 (Rxfp2) in MC3T3-E1 cells in vitro

RELAXIN (RLN) is a polypeptide hormone of the insulin-like hormone family; it facilitates birth by softening and widening the pubic symphysis and cervix in many mammals, including humans. The role of RLN in bone metabolism was recently suggested by its ability to induce osteoclastogenesis and activate osteoclast function. RLN binds to RELAXIN/INSULIN-LIKE FAMILY PEPTIDE 1 (RXFP1) and 2 (RXFP2), with varying species-specific affinities. Young men with mutated RXFP2 are at high risk for osteoporosis, as RXFP2 influences osteoblast metabolism by binding to INSULIN-LIKE PEPTIDE 3 (INSL3). However, there have been no reports on RLN function in osteoblast differentiation and mineralization or on the functionally dominant receptors for RLN in osteoblasts. We previously described Rxfp1 and 2 expression patterns in developing mouse oral components, including the maxillary and mandibular bones, Meckel's cartilage, tongue, and tooth primordia. We hypothesized that Rln/Rxfp signaling is a key mediator of skeletal development and metabolism. Here, we present the gene expression patterns of Rxfp1 and 2 in developing mouse calvarial frontal bones as determined by in situ hybridization. In addition, RLN enhanced osteoblastic differentiation and caused abnormal mineralization and extracellular matrix metabolism through Rxfp2, which was predominant over Rxfp1 in MC3T3-E1 mouse calvarial osteoblasts. Our data suggest a novel role for Rln in craniofacial skeletal development and metabolism through Rxfp2.