Levels of the neuropeptide phoenixin-14 and its receptor GRP173 in the hypothalamus, ovary and periovarian adipose tissue in rat model of polycystic ovary syndrome

Phoenixin-14 and its receptor GPR173 in the bovine endometrium: Expression and regulation during the estrous cycle and impact on secretory activity

The endometrium remodels during the estrous cycle due to many endogenous factors. Phoenixin (PNX)-14 is a relatively recently discovered neuropeptide with a pivotal role in reproduction, specifically in follicle development and the functioning of the corpus luteum and uterus. Our study aimed to determine (1) the expression of PNX-14 and G protein-coupled receptor 173 (GPR173) in the bovine endometrium during the estrous cycle, (2) the cellular localization of PNX-14 and GPR173, (3) the effect of luteotropic and luteolytic factors on PNX-14 and GPR173 expression in the endometrium, and (4) the impact of PNX-14 on the secretory activity of the endometrium. The ex vivo experiments used bovine uterine tissues collected from the four stages of the estrous cycle (days 2-5, 6-10, 11-16, and 17-20). The in vitro experiments used uteri collected from days 10-12 of the estrous cycle. The mRNA expression of small integral membrane protein 20 (SMIM20) and protein expression of PNX-14 was upregulated on days 6-10 of the estrous cycle. GRP173 protein expression was significantly higher on days 11-16. The concentration of PNX-14 in endometrial tissue homogenate was significantly lower on days 17-20 compared to all other days of the estrous cycle. In immunofluorescence analysis, luminal and glandular epithelium and endothelial cells of blood vessels were positive for PNX-14 and GPR173. Progesterone upregulated the mRNA expression of SMIM20 in the bovine endometrium, whereas progesterone and oxytocin upregulated GPR173 mRNA and protein expression. Treating endometrial slices with PNX-14 enhanced prostaglandin E2 secretion. In conclusion, these findings indicate that PNX-14 targets the bovine endometrium and should be considered a locally acting regulator of endometrium function in non-pregnant cows.

Serum Phoenixin Levels and Their Diagnostic Significance in Girls With Precocious Puberty

Context

Phoenixin (PNX), a recently identified neuropeptide, is recognized for its role in reproduction.

Objective

This study aims to explores serum phoenixin expression and its diagnostic value in girls with central precocious puberty (CPP).

Methods

Girls visiting the Pediatric Endocrinology Department of Lianyungang First People's Hospital (February 2023-February 2025) were included and divided into 3 groups: CPP (n = 48), premature thelarche (PT) (n = 58), and healthy controls (NCs, n = 50). Serum phoenixin levels were measured via enzyme-linked immunosorbent assay and compared among groups. Spearman correlation analysis assessed variable relationships, and receiver operating characteristic (ROC) curves evaluated phoenixin's diagnostic value for CPP.

Results

Serum PNX-14 levels of the CPP group (228.42 [193.29-277.22] pg/mL) were considerably higher relative to the PT group (192.58 [151.34-239.48] pg/mL) (P < .05), and higher serum PNX-14 levels were found in the PT group compared to the NC group (124.26 [88.78-167.49] pg/mL) (P < .05). No statistically significant differences in PNX-20 levels were found among the groups (P > .05). PNX-14 levels were positively correlated with height, weight, body mass index, bone age, uterine and ovarian volumes, and pituitary height, and negatively with sex hormone-binding globulin. ROC analysis showed an area under the curve of 0.695 for PNX-14 in identifying CPP, with a cutoff of 195.85 pg/mL (sensitivity: 75.0%; specificity: 69.0%).

Conclusion

Serum PNX-14 is associated with CPP and reflects growth and pubertal development. It may serve as a potential biomarker for adjunct diagnosis of CPP in girls.

Effect of phoenixin-14 on angiogenesis, cell proliferation, and apoptosis in porcine corpus luteum: Role of GPR173 and ERK1/2, AKT, and AMPK signal pathway

Our previous studies have identified phoenixin-14 (PNX-14) and its receptor GPR173 in the porcine corpus luteum (CL) during the estrous cycle and their role in the endocrine function. This study explored PNX-14's impact on luteal angiogenesis, proliferation, and apoptosis. Luteal cells were cultured with PNX-14 at doses 1-1000 nM for 24-72 h. Then, the transcript level and secretion of angiogenic factors (VEGFA, bFGF2, ANG-1) and protein expression of their receptors (VEGFR1, VEGFR2, FGFR1, FGFR2, TIE2) were analysed. Cell proliferation was assessed using the alamarBlue assay, whereas DNA fragmentation and caspase 3/7 activity through Cell Death Detection ELISA and CaspaseGlo 3/7 assay, respectively. We also examined mRNA and protein levels of proliferating cell nuclear antigen (PCNA), cyclins, and apoptotic factors. Using pharmacological inhibitors of extracellular signal-regulated kinases 1/2 (ERK1/2), protein kinase B (AKT), 5'AMP-activated protein kinase (AMPK), and silencing of GPR173 by siRNA we checked their involvement in PNX-14 action in CL. The results showed that PNX-14 increased levels of bFGF2 and ANG-1, and protein expression of VEGFR2, FGFR1, and TIE2, while it decreased FGFR2. It enhanced luteal cell proliferation and PCNA expression, with variable effects on transcript and protein levels of cyclins. Moreover, PNX-14 decreased DNA fragmentation and caspase 3/7 activity, expression of caspases 3, 8, 9, and BAX, and increased BCL2. Additionally, GPR173 receptor and ERK1/2, AKT, and AMPK are involved in PNX-14 action on luteal function. In conclusion, PNX-14 acts as a luteotropic factor in the porcine CL by promoting angiogenesis, proliferation, and protection against apoptosis.

Adipokines level in plasma, hypothalamus, ovaries and adipose tissue of rats with polycystic ovary syndrome

RESEARCH QUESTION

Do the levels of adipokines (adiponectin, apelin, chemerin and vaspin) in plasma, hypothalamus, ovaries and periovarian adipose tissue differ during polycystic ovarian syndrome (PCOS)?

DESIGN

The PCOS was induced in rats by oral administration of non-steroidal aromatase inhibitor letrozole. To determine the plasma levels of adiponectin, apelin, chemerin and vaspin enzyme-linked immunosorbent assays were carried out. To assess the expression (gene and protein) and immunolocalization of these adipokines and their receptors, namely Adipor1 and Adipor2 for adiponectin, Aplnr for apelin, Ccrl2, Cmklr1 and Gpr1 for chemerin and Grp78 for vaspin in the hypothalamus, real-time polymerase chain reaction, and Western blot and immunohistochemistry were used to analyse ovaries and periovarian adipose tissue respectively.

RESULTS

In PCOS, the plasma level of adiponectin decreased (P = 0.0003), whereas apelin, chemerin and vaspin increased (P ≤ 0.0479). Moreover, PCOS modulates the expression of adipokines and their receptors in the hypothalamus, ovaries and periovarian adipose tissue compared with healthy rats (P ≤ 0.487).

CONCLUSIONS

A strong relationship was found between PCOS and adipokines, which suggests that adipokines may be a biomarker of PCOS.

Goldfish phoenixin: (I) structural characterization, tissue distribution, and novel function as a feedforward signal for feeding-induced food intake in fish model

Phoenixin (PNX) is a novel peptide with diverse functions mediated by the orphan receptor GPR173. It also plays a role in appetite control, but the effect is not consistent across species and the mechanisms involved are still unclear. Using goldfish as a model, the mechanisms underlying feeding regulation by PNX were examined. In our study, two isoforms of PNX, PNXa and PNXb, and one form of GPR173 were cloned in goldfish and found to be highly conserved compared to their counterparts in other species based on sequence alignment, phylogenetic analysis, and in silico protein modeling. Using RT-PCR, PNXa/b and GPR173 were confirmed to be ubiquitously expressed at the tissue level. In goldfish, transcript expression of PNXa/b and GPR173 in the liver and brain areas including the telencephalon, hypothalamus, and optic tectum, were elevated by food intake but suppressed by fasting. Intraperitoneal (IP) and intracerebroventricular (ICV) injections of PNX20a and PNX20b, the mature peptides for PNXa and PNXb respectively, were both effective in increasing foraging behavior, surface motility, and food intake. Furthermore, the expression of orexigenic factors (neuropeptide Y (NPY), agouti-related peptide, orexin, and apelin) was elevated with parallel drops in anorexigenic signals (cholecystokinin, pro-opiomelanocortin, corticotropin-releasing hormone, and melanin-concentrating hormone) in the telencephalon, hypothalamus, and/or optic tectum. In the same brain areas, receptor expression for anorexigenic factors (leptin and adiponectin) was attenuated with concurrent rises in receptor levels for orexigenic signals (NPY and ghrelin). In our study, after IP injection of PNX20a/b, downregulation of leptin, adiponectin, and other feeding inhibitors expressed in the liver was also noted. Our findings reveal that PNX20a/b can serve as an orexigenic factor in goldfish. PNX signals (both central and peripheral) can be induced by food intake and act within the brain to trigger foraging and food consumption via differential modulation of appetite-regulating factors and their receptors in different brain areas. The feeding responses observed may also involve a hepatic component with PNX repression of feeding inhibitors expressed in the liver. The PNX signals induced by feeding may form a feedforward loop to maintain/prolong food intake during a meal prior to the onset of satiation response in our fish model.

Spatial and quantitative gene expression analysis of SREB receptors in the gonads of green-spotted pufferfish (Dichotomyctere nigroviridis)

Super-conserved Receptors Expressed in Brain (SREB) are a highly conserved family of orphan G protein-coupled receptors that consist of three members in most vertebrates: SREB1 (GPR27), SREB2 (GPR85), and SREB3 (GPR173). Each receptor is associated with diverse physiological processes and expressed in both ovaries and testes, but reproductive functions are only beginning to be understood. In addition, some fishes gained a novel fourth gene, SREB3B, which may have unique functions. The purpose of this study was to conduct a spatial and quantitative analysis of SREBs in the gonads of pufferfish (Dichotomyctere nigroviridis), which expresses all four genes. Multiplex RNAscope and absolute qPCR were used to assess gene expression patterns in both ovaries and testes. Expression was detected in early ovaries and dominated by sreb1 (approximately 2500 copies/ng RNA vs. 300 or less for others), with notable expression of all receptors in primary oocytes, granulosa cells, and small numbers of extra-follicular cells. Within primary oocytes, sreb1 and sreb3b exhibited diffuse patterns that may indicate early functions, while sreb2 and sreb3a were granular and may reflect stored mRNA. Early testicular development was dominated by sreb1 and sreb2 (∼5000 copies/ng RNA) in spermatogonia. These patterns were somewhat reduced in late testes (∼1000-2600 copies/ng RNA), but sreb3b exhibited a novel spatial pattern (∼380 copies/ng RNA) within spermatogenic cysts. These results highlight diverse roles for the SREB family, and sreb3b is hypothesized to have unique roles in fish reproduction.

A systematic scoping review of the multifaceted role of phoenixin in metabolism: insights from in vitro and in vivo studies

Phoenixin (PNX) is an emerging neuropeptide that plays a significant role in regulating metabolism and reproduction. This comprehensive review examines findings from human, in vivo, and in vitro studies to elucidate the functions of PNX in metabolic processes. PNX has been identified as a key player in essential metabolic pathways, including energy homeostasis, glucose, lipid and electrolyte metabolism, and mitochondrial dynamics. It modulates food and fluid intake, influences glucose and lipid profiles, and affects mitochondrial biogenesis and function. PNX is abundantly expressed in the hypothalamus, where it plays a crucial role in regulating reproductive hormone secretion and maintaining energy balance. Furthermore, PNX is also expressed in peripheral tissues such as the heart, spleen, and pancreas, indicating its involvement in the regulation of metabolism across central and peripheral systems. PNX is a therapeutic peptide that operates through the G protein-coupled receptor 173 (GPR173) at the molecular level. It activates signaling pathways such as cAMP-protein kinase A (PKA) and Epac-ERK, which are crucial for metabolic regulation. Research suggests that PNX may be effective in managing metabolic disorders like obesity and type 2 diabetes, as well as reproductive health issues like infertility. Since metabolic processes are closely linked to reproduction, further understanding of PNX's role in these areas is necessary to develop effective management/treatments. This review aims to highlight PNX's involvement in metabolism and identify gaps in current knowledge regarding its impact on human health. Understanding the mechanisms of PNX's action is crucial for the development of novel therapeutic strategies for the treatment of metabolic disorders and reproductive health issues, which are significant public health concerns globally.

Expression and in vitro effect of phoenixin-14 on the porcine ovarian granulosa cells

Phoenixin-14 (PNX-14) regulates energy metabolism via the G protein-coupled receptor 173 (GPR173); elevated plasma levels have been described in patients with polycystic ovary syndrome. The aims were to investigate the ovarian expression of PNX-14/GPR173 and the in vitro effect of PNX-14 on granulosa cells (Gc) function. Transcript and protein levels of PNX-14/GRP173 were analysed by real-time PCR, western blot and immunohistochemistry in the porcine ovarian follicles at days 2-3, 10-12 and 16-18 of the oestrous. For in vitro experiments, Gc were isolated from follicles at days 10-12 of the oestrous (4-6 mm) and PNX-14 at doses 1-1000 nM was added for 24-72 h to determine Gc proliferation. Cell cycle progression, E2 secretion, expression of proliferating cells nuclear antigen, cyclins, mitogen-activated kinase (MAP3/1; ERK1/2), protein kinase B (AKT) and signal transducer and activator of transcription 3 (STAT3) were studied. The involvement of these kinases in PNX-14 action on Gc proliferation was analysed using pharmacological inhibitors. Levels of GPR173 were increased in the ovarian follicles with oestrous progression, while only PNX-14 protein was the highest at days 10-12 of the oestrous. Immuno-signal of PNX-14 was detected in Gc and theca cells and oocyte, while GPR173 was mostly in theca. Interestingly, PNX-14 stimulated Gc proliferation, E2 secretion, cell cycle progression and cyclins expression and had a modulatory effect on MAP3/1, AKT and STAT3 activation. Our study suggests that PNX-14 could be an important factor for porcine reproduction by influencing ovarian follicle growth through direct action on Gc function.

Phoenixin-14 as a novel direct regulator of porcine luteal cell functions†

Phoenixin is a neuropeptide with a well-established role in the central regulation of reproductive processes; however, knowledge regarding its role in the ovary is limited. One of the main active phoenixin isoforms is phoenixin-14, which acts through G protein-coupled receptor 173. Our research hypothesis was that phoenixin-14 is expressed in porcine corpus luteum and exerts luteotropic action by affecting the endocrine function of luteal cells through G protein-coupled receptor 173 and protein kinase signaling. Luteal cells were cultured to investigate the effect of phoenixin-14 (1-1000 nM) on endocrine function. We showed that phoenixin-14 and G protein-coupled receptor 173 are produced locally in porcine corpus luteum and their levels change during the estrous cycle. We detected phoenixin-14 immunostaining in the cytoplasm and G protein-coupled receptor 173 in the cell membrane. Plasma phoenixin levels were highest during the early luteal phase. Interestingly, insulin, luteinizing hormone, progesterone, and prostaglandins decreased phoenixin-14 levels in luteal cells. Phoenixin-14 increased progesterone, estradiol, and prostaglandin E2 secretion, but decreased prostaglandin F2α, upregulated the expression of steroidogenic enzymes, and downregulated receptors for luteinizing hormone and prostaglandin. Also, phoenixin-14 increased the expression of G protein-coupled receptor 173 and the phosphorylation of extracellular signal-regulated kinase 1/2, protein kinase B, inhibited the phosphorylation of protein kinase A, and had mixed effect on AMP-activated protein kinase alpha and protein kinase C. G protein-coupled receptor 173 and extracellular signal-regulated kinase 1/2 mediated the effect of phoenixin-14 on endocrine function of luteal cells. Our results suggest that phoenixin is produced by porcine luteal cells and can be a new regulator of their function.

The Levels of Phoenixin-14 and Phoenixin-20 in Patients with Type 2 Diabetes Mellitus

BACKGROUND

New pathogenesis-related early detection markers are needed to prevent Type 2 Diabetes Mellitus (T2DM).

OBJECTIVE

We aimed to determine phoenixin (PNX)-14 and PNX-20 levels in T2DM patients and investigate their relationship with diabetes.

METHODS

36 T2DM patients and 36 healthy controls were included in the study, and PNX-14 and PNX-20 levels in blood samples taken from the groups were measured by ELISA method.

RESULTS

Patients' serum PNX-14 and PNX-20 levels were statistically significantly lower than in controls (p <0.001). A negative correlation was detected between PNX-14 and BMI, fasting blood sugar, HbA1c%, and HOMA-IR. A negative correlation was found between PNX-20 and BMI, fasting insulin and glucose, HbA1c%, and HO-MA-IR. A positive correlation was noticed between PNX-14 and PNX-20 levels. In ROC analyses, PNX-14 and PNX-20 performed almost equally in predicting T2DM. In predicting T2DM, the area under the ROC curve for PNX-14 was 0.874 (cutoff value 413.4 ng/L, sensitivity 89 %, specificity 72%), and for PNX-20 was 0.858 (cutoff value 228.7 ng/L, sensitivity 80 %, specificity 83 %).

CONCLUSION

This study shows that serum PNX measurement may have a high level of evidence in predicting T2DM. PNX, related to pathogenesis, may be useful in diagnosing T2DM and other information to support clinical decision-making.

Neuropeptide Network of Polycystic Ovary Syndrome - A Review

BACKGROUND

Polycystic Ovary Syndrome (PCOS), the ubiquitous reproductive disorder, has been documented as highly prevalent (6-9%) in India. 10% of women globally are predicted to have the disease. The highly mutable endocrinopathy, with differential clinical criteria for each diagnosis of PCOS, can mask the severity of the syndrome by influencing the incidence and occurrence of PCOS.

AREA COVERED

When there is a solid theoretical hypothesis between the neuroendocrine origin and ovarian origin of PCOS, recent evidence supports the neuroendocrine derivation of the pathology. It is considered of neuroendocrine basis - as it controls the ovarian axis and acts as a delicate target because it possesses receptors for various gonadal hormones, neurotransmitters & neuropeptides. Can these neuroendocrine alterations, variations in central brain circuits, and neuropeptide dysregulation be the tie that would link the pathophysiology of the disorder, the occurrence of all the 1˚ and 2˚ symptoms like polycystic ovaries, hyperandrogenism, obesity, insulin resistance, etc., in PCOS?

CONCLUSION

This review anticipates providing a comprehensive overview of how neuropeptides such as Kisspeptin, Neurokinin B, Dynorphin A, β-Endorphin, Nesfatin, Neuropeptide Y, Phoenixin, Leptin, Ghrelin, Orexin, and Neudesin influence PCOS, the understanding of which may help to establish potential drug candidates against precise targets in these central circuits.

[Neuroendocrine features of the pathogenesis of polycystic ovary syndrome (literature review)]

Polycystic ovary syndrome (PCOS) is one of the most pressing problems in endocrine gynecology. The main signs of the disease are hyperandrogenism, menstrual and/or ovulatory dysfunction, and polycystic ovarian structure according to ultrasound. Women with PCOS are at risk for developing metabolic syndrome, type 2 diabetes, cardiovascular disease, and endometrial cancer. In this connection, the pathogenetic mechanisms of the occurrence of this syndrome are continuously studied and new methods of treatment are being sought. PCOS is characterized by a wide range of various disorders of the neuroendocrine regulation of the reproductive system. The main focus of the review is aimed at summarizing information about the etiological role of neuropeptides and neurotransmitters, such as phoenixin, galanins, orexins, GABA, in the pathophysiology of PCOS and about the possibility of their use for diagnostic and therapeutic purposes. In recent decades, the interest of scientists has been focused on the study of KNDy neurons, because it is the kisspeptin synthesized by them that is one of the main regulators of the hypothalamic-pituitary-ovarian axis. This article discusses data on the significance of KNDy neurons in the pathogenesis of the syndrome. Information is provided on the effect of elevated levels of androgens and anti-Müllerian hormone on GnRH neurons. Also analyzed are studies on functional and structural disorders in the hypothalamus in PCOS. Literature search was carried out in national (eLibrary, CyberLeninka.ru) and international (PubMed, Cochrane Library) databases in Russian and English. The priority was free access to the full text of articles. The choice of sources was prioritized for the period from 2018 to 2023.However, taking into account the insufficient knowledge of the chosen topic, the choice of sources dates back to 1998.

Increased Serum Levels of Phoenixin-14, Nesfatin-1 and Dopamine Are Associated with Positive Pregnancy Rate after Ovarian Stimulation

BACKGROUND

We study the relationship between phoenixin (PNX-14), nesfatin-1 (NES-1), dopamine (DA) and oxytocin (OT) levels together with pregnancy rates in women after ovarian stimulation (OS).

METHODS

In a prospective case-control study, 56 infertile women were enrolled from the Department of Gynecological Endocrinology University Hospital. Infertile women age < 40 years old, with polycystic ovary syndrome (PCOS), confirmed tubal patency and suitable sperm quality were included. Blood samples were drawn twice-before the initiation of OS and before the human chorionic gonadotropin (hCG) administration. Assessments of PNX-14, NES-1, DA and OT serum levels were performed. Pregnancy rates after OS were observed.

RESULTS

Pregnant women showed higher baseline NES-1 and OT levels (+29.2% and +44%) but not PNX-14 and DA levels when compared to non-pregnant ones. In pregnant women, positive correlations between OT and prolactin, PRL (r = 0.47, p = 0.04), as well as between OT and NES-1 (r = 0.55, p = 0.02), were observed at baseline. At baseline, an OT level increase was associated with a positive pregnancy rate (per 100 pg/mL, OR = 1.39, 95% CI 1.04-1.74), while after OS, higher PNX-14 was a predictor of pregnancy (by 10 pg/mL, OR = 1.23, 95%CI 1.07-1.39). Post-stimulation PNX-14, NES-1 and DA concentrations were higher in pregnant women compared to non-pregnant ones (+17.4%, +26.1%, and +45.5%, respectively; all p < 0.05). In the pregnant group, OT levels were 2.7-times lower than in the remainder (p = 0.03). Moreover, in pregnant participants, a negative association between NES-1 and PNX (r = -0.53, p = 0.024) was observed.

CONCLUSION

Elevated PNX-14, NES-1 and DA along with decreased OT levels were observed in women who achieved pregnancy.

Effect of Vitamin D3 on Chemerin and Adiponectin Levels in Uterus of Polycystic Ovary Syndrome Rats

BACKGROUND

Polycystic ovary syndrome (PCOS) is an endocrine disorder with disrupted uterus structure and function. A positive effect of vitamin D3 (VD3) in female reproduction was observed. Chemerin (RARRES2) and adiponectin (ADIPOQ) are the main adipokines whose levels are altered in PCOS patients. Therefore, the aim of this study was to investigate the impact of VD3 supplementation on RARRES2 and ADIPOQ levels in the uterus of PCOS rats.

METHODS

We analyzed the plasma levels and uterine transcript and protein expression of RARRES2 and ADIPOQ and their receptors (CCRL2, CMKLR1, GPR1, and ADIPOR1 and ADIPOR2, respectively) in rats with letrozole-induced PCOS.

RESULTS

In control animals, VD3 did not change plasma levels of both adipokines, while in PCOS rats supplemented with VD3, they returned to control levels. The expression of RARRES2 and all investigated receptors increased in the uterus of VD3-treated rats; however, the levels of Rarres2 and Gpr1 genes remained unchanged. VD3 supplementation decreased RARRES2, CMKLR1, and GPR1 but increased CCRL2 level to the control value. In the uterus of VD3-treated rats, the transcript and protein levels of ADIPOQ and both receptors ADIPOR1 increased. At the same time, VD3 supplementation induced an increase in Adipoq, Adipor1, and Adipor2 gene expression and restored protein levels to control level values.

CONCLUSIONS

our findings indicate a new mechanism of VD3 action in the uterine physiology of PCOS rats.

Expression and localization of the neuropeptide phoenixin-14 and its receptor GRP173 in the canine reproductive organs and periovarian adipose tissue

Phoenixin-14 (PNX-14) is a regulatory neuropeptide encoded by the SMIM20 gene, which has been implicated in the reproductive cycle by modulating the hypothalamic-pituitary-gonadal (HPG) axis. Recently, we showed that PNX-14 is downregulated in bitches with cystic endometrial hyperplasia and pyometra. The objective of this study was to determine the expression of Smim20, PNX-14, and its putative receptor GRP173 in the canine ovary (both healthy and those with ovarian cysts), periovarian adipose tissue (PAT) and in the endometrium during the oestrous cycle. The expression was analysed by RT-qPCR and Western blot. In tissue sections, peptides were localised by immunofluorescent assays, and blood plasma concentrations of PNX-14 were detected by EIA. The results demonstrated increased levels of PNX in bitches in the anestrus groups compared to diestrus animals. The expression of GPR173 increased in PAT during the diestrus phase and endometrial tissue in late diestrus bitches. In the ovary, strong signals of PNX-14 and GPR173 were detected in the luteal and follicular cells. Furthermore, bitches with cystic ovaries were characterised by elevated circulating PNX levels and a significantly higher expression of PNX and GPR173 in gonadal tissues, when compared with healthy animals. Moreover, a positive correlation between PNX and progesterone in the blood of healthy bitches was noted, which changed to a negative correlation in females affected by cystic ovaries. These studies expand the knowledge regarding the expression and localization of the PNX/GRP173 system in canine reproductive organs during physiological and pathological conditions.

PNX14 but not PNX20 as a novel regulator of preadipocyte differentiation via activating Epac-ERK signaling pathway in Gallus gallus

Small integral membrane protein 20 (SMIM20) could generate two main peptides, PNX14 and PNX20, which participate in multiple biological roles such as reproduction, inflammation and energy metabolism in mammals. However, little is known about their physiological functions in non-mammalian vertebrates. Using chicken (c-) as an animal model, we found cSMIM20 was moderately expressed in adipose tissues, and its expression was gradually increased during the differentiation of chicken preadipocytes, suggesting that it may play an important role in chicken adipogenesis. Further research showed cPNX14 could facilitate the differentiation of chicken preadipocytes into mature adipocytes by enhancing expression of adipogenic genes including PPARγ, CEBPα and FABP4, and promoting the formation of lipid droplets. This pro-adipogenic effect of cPNX14 was completely attenuated by Epac-specific and ERK inhibitor. Interestingly, cPNX20 failed to regulate the adipogenic genes and lipid droplet content. Collectively, our findings reveal that cPNX14 but not cPNX20 can serve as a novel adipogenesis mediator by activating the Epac-ERK signaling pathway in chickens.

Expression of phoenixin-14 and nesfatin-1 in the hypothalamo-pituitary-gonadal axis in the phases of the estrous cycle

Phoenixin-14 (PNX-14) and nucleobindin 2 (NUCB2)/nesfatin-1 are regulatory neuropeptides expressed in the hypothalamus. These neuropeptides can be effective in hormonal regulation of the hypothalamo-pituitary-gonadal (HPG) axis and reproductive functions. In the present study, the distribution of PNX-14 and NUCB2/nesfatin-1 in the hypothalamus, pituitary, ovary, and uterus tissues during the phases of the estrous cycle in female rats was investigated. Eighteen Wistar Albino rats determined among animals showing regular estrous cycle by vaginal smear method were divided into three groups: proestrus (Group I), estrus (Group II) and diestrus (Group III). Serum gonadotropin-releasing hormone (GnRH), plasma PNX-14, and NUCB2/nesfatin-1 concentrations were the highest, moderate, and lowest in estrus, diestrus, and proestrus phases, respectively. PNX-14 immunoreactivity in the supraoptic and arcuate nuclei of the hypothalamus and NUCB2/nesfatin-1 immunoreactivity in the paraventricular nuclei were particularly evident in the estrus phase. These neuropeptide immunoreactivities were decreased in different cells of anterior pituitary during proestrus compared with those during estrus and diestrus. PNX-14 immunoreactivity in the ovary, especially during the estrus phase, was diffuse and intense in the granulosa and luteal cells and oocytes, and it was few and weak in theca cells. In addition, NUCB2/nesfatin-1 immunoreactivity was abundant and strong in granulosa and luteal cells, theca and interstitial cells, and oocytes during estrus. In the estrus phase, PNX-14 immunoreactivity was strong in the glandular epithelial cells and stromal cells of the endometrium, also NUCB2/nesfatin-1 immunoreactivity was strong in the epithelial and glandular epithelial cells. As a result, when the estrous cycle was evaluated, it was concluded that the changes in the distribution of PNX-14 and NUCB2/nesfatin-1 at all phases were related to GnRH and that these neuropeptides showed the highest immunoreactivity especially in the HPG axis and uterus tissues of estrus rats.

Regulation and physiological functions of phoenixin

Phoenixin is a newly discovered neuropeptide generated from small integral membrane protein 20. Phoenixin is a ligand for the G protein-coupled receptor 173 (GPR173) and has been detected in central and peripheral tissues of human, rats, mice, bovine, and zebrafish. It was initially involved in regulating reproductive function by stimulating the luteinizing hormone release from pituitary cells by increasing the level of gonadotropin-releasing hormone. Recently, many functions of phoenixin have been generalized, including regulation of food intake, memory, Alzheimer’s disease, anxiety, inflammation, neuronal and microglial activity, energy metabolism and body fluid balance, cardiovascular function, and endocrine activity. In addition, the interaction between phoenixin and nesfatin-1 have been revealed. The present article summarized the latest research progress on physiological function of phoenixin, suggesting that it is a potential target for novel drug development and clinical application.

Phoenixin-14 alters transcriptome and steroid profiles in female green-spotted puffer (Dichotomyctere nigroviridis)

Phoenixin (PNX) is a highly conserved, novel hormone with diverse functions, including hypothalamic control of reproduction, appetite modulation, and regulation of energy metabolism and inflammation. While some functions appear conserved across vertebrates, additional research is required to fully characterize these complex pleiotropic effects. For instance, very little is known about transcriptome level changes associated with PNX exposure, including responses in the hypothalamic-pituitary-gonadal (HPG) axis, which is critical in vertebrate reproduction. In addition, the PNX system may be especially complex in fish, where an additional receptor is likely present in some species. The purpose of this study was to assess hypothalamic and ovarian transcriptomes after PNX-14 administration in female vitellogenic green-spotted puffer (Dichotomyctere nigroviridis). Steroid-related changes were also assessed in the liver and blood plasma. Hypothalamic responses included pro-inflammatory signals such as interleukin 1β, possibly related to gut-brain axis functions, as well as suppression of cell proliferation. Ovarian responses were more widely downregulated across all identified pathways, which may reflect progression to a less transcriptionally active state in oocytes. Both organs shared regulation in transforming growth factor-β and extracellular matrix remodeling (periostin) pathways. Reproductive processes were in general downregulated, but both inhibiting (bone morphogenetic protein 15 and follistatin) and promoting (17-hydroxyprogesterone) factors for oocyte maturation were identified. Select genes involved in reproduction (vitellogenins, estrogen receptors) in the liver were unresponsive to PNX-14 and higher doses may be needed to induce reproductive effects in D. nigroviridis. These results reinforce the complexity of PNX actions in diverse tissues and highlight important roles for this hormone in regulating the immune response, energy metabolism, and cell growth.

Super-conserved receptors expressed in the brain: biology and medicinal chemistry efforts

The super-conserved receptors expressed in the brain (SREB) constitute a family of orphan G protein-coupled receptors that include GPR27 (SREB1), GPR85 (SREB2) and GPR173 (SREB3). Their sequences are highly conserved in vertebrates, and they are almost exclusively expressed in the central nervous system. This family of receptors has attracted much attention due to their putative physiological functions and their potential as novel drug targets. The SREB family has been postulated to play important roles in a wide range of different diseases, including pancreatic β-cell insulin secretion and regulation, schizophrenia, autism and atherosclerosis. This review intends to provide a comprehensive overview of the SREB family and its recent advances in biology and medicinal chemistry.

Phoenixin-14 Ameliorates Cellular Senescence Against Morphine in M17 Neuronal Cells

Drug dependence on morphine is commonly accompanied by neurodegenerative disorders. A previous study showed that prolonged exposure to morphine induces cellular senescence in neuronal cells by reducing telomere length. Phoenixin-14 is a newly discovered brain peptide with pleiotropic roles. However, it is unknown whether phoenixin-14 possesses a beneficial property against morphine-induced cellular senescence. Our results show that morphine reduced the expression of G protein-coupled receptor 173 (GPR173) in M17 neuronal cells. Therefore, we speculated that phoenixin-14, as a ligand for GPR173, may be involved in the morphine-mediated response in M17 cells. Further, we found that phoenixin-14 mitigated morphine-induced oxidative stress by reducing the reactive oxygen species (ROS) production and increasing superoxide dismutase (SOD) activity in M17 neuronal cells. The morphine-induced cellular senescence in M17 neuronal cells was prevented by phoenixin-14. Phoenixin-14 resolved the morphine-caused cell cycle arrest with significant changes in the expression levels of p21, cyclin-dependent kinases 6 (CDK6), and p-Rb. It also elevated the telomerase activity and restored the expressions of human telomerase reverse transcriptase (hTERT) and TERF2 in morphine-induced M17 neuronal cells. Furthermore, phoenixin-14 restored the yes-associated protein (YAP) expression against morphine in M17 neuronal cells. Knockdown of YAP abolished the beneficial effects of phoenixin-14 on cellular senescence against morphine induction. Taken together, these aggregate data demonstrate that phoenixin-14 prevented cellular senescence against morphine induction in M17 neuronal cells via regulating YAP expression.

New Aspects of Corpus Luteum Regulation in Physiological and Pathological Conditions: Involvement of Adipokines and Neuropeptides

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones-adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

Neuroendocrine Determinants of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women and a major cause of anovulatory infertility. A diagnosis of PCOS is established based the presence of two out of three clinical symptoms, which are criteria accepted by the ESHRE/ASRM (European Society of Human Reproduction and Embryology/American Society for Reproductive Medicine). Gonadotropin-releasing hormone (GnRH) is responsible for the release of luteinizing hormone, and follicle stimulating hormone from the pituitary and contributes a leading role in controlling reproductive function in humans. The goal of this review is to present the current knowledge on neuroendocrine determinations of PCOS. The role of such neurohormones as GnRH, and neuropeptides kisspeptin, neurokinin B, phoenixin-14, and galanin is discussed in this aspect. Additionally, different neurotransmitters (gamma-aminobutyric acid (GABA), glutamate, serotonin, dopamine, and acetylcholine) can also be involved in neuroendocrine etiopathogenesis of PCOS. Studies have shown a persistent rapid GnRH pulse frequency in women with PCOS present during the whole ovulatory cycle. Other studies have proved that patients with PCOS are characterized by higher serum kisspeptin levels. The observations of elevated serum kisspeptin levels in PCOS correspond with the hypothesis that overactivity in the kisspeptin system is responsible for hypothalamic-pituitary-gonadal axis overactivity. In turn, this causes menstrual disorders, hyperandrogenemia and hyperandrogenism. Moreover, abnormal regulation of Neurokinin B (NKB) is also suspected of contributing to PCOS development, while NKB antagonists are used in the treatment of PCOS leading to reduction in Luteinizing hormone (LH) concentration and total testosterone concentration. GnRH secretion is regulated not only by kisspeptin and neurokinin B, but also by other neurohormones, such as phoenixin-14, galanin, and Glucagon-like peptide-1 (GLP-1), that have favorable effects in counteracting the progress of PCOS. A similar process is associated with the neurotransmitters such as GABA, glutamate, serotonin, dopamine, and acetylcholine, as well as the opioid system, which may interfere with secretion of GnRH, and therefore, influence the development and severity of symptoms in PCOS patients. Additional studies are required to explain entire, real mechanisms responsible for PCOS neuroendocrine background.

Mediatory role of the central NPY, melanocortine and corticotrophin systems on phoenixin-14 induced hyperphagia in neonatal chicken

Animal research indicates the neuropeptide Y (NPY), corticotrophin and melanocortin systems have a mediatory role in reward, however, how these substances interact with phenytoin-14 (PNX-14) induced food intake in birds remains to be identified. Accordingly, in this research eight tests were carried out to investigate the potential interactions of the NPY, melanocortin, as well as corticotrophin systems with PNX-14 on food consumption in neonatal chickens. In the first experiment, chickens were intracerebroventricular (ICV) injected with phosphate-buffered saline (PBS) and PNX-14 (0.8, 0.16, and 3.2 nmol). In second experiment, PBS, the antagonist of CRF₁/CRF₂ receptors (astressin-B, 30 μg) and PNX-14 + astressin-B were injected. In the rest of the experiments chicken received astressin2-B (CRF₂ receptor antagonist; 30 µg), SHU9119 (MCR₃/MCR₄ receptor antagonist, 0.5nomol), MCL0020 (MCR₄ receptor agonist, 0.5 nmol), B5063 (NPY₁ receptor antagonist, 1.25 μg), SF22 (NPY₂ receptor antagonist, 1.25 μg) and SML0891 (NPY₅ receptor antagonist, 1.25 μg) rather than astressin-B. Then, cumulative intake of food was recorded for 2 h. Based on the findings, PNX-14 (0.16 and 3.2 nmol) led to increment in food consumption compared with the control (P < 0.05). Co-administration of the PNX-14 and astressin-B promoted PNX-14-induced hyperphagia (P < 0.05). Co-injection of the PNX-14 + astressin2-B potentiated hyperphagia PNX-14 (P < 0.05). Co-injection of PNX-14 + B5063 inhibited the effects of the PNX-14 (P < 0.05). The co-administration of the PNX-14 and SML0891 potentiated hypophagic effects of the PNX-14 (P < 0.05). The results showed that PNX-14-induced hyperphagia mediates via NPY₁, NPY_5, and CRF₁/CRF₂ receptors in neonatal chickens.

The Regulation of Phoenixin: A Fascinating Multidimensional Peptide

The phoenixin (PNX) peptide is linked to the control of reproduction, food intake, stress, and inflammation. However, little is known about what regulates its gene and protein expression, information that is critical to understand the physiological role of PNX. In this review, we summarize what is known about the transcriptional control of Pnx and its receptor Gpr173. A main function of PNX is as a positive regulator of the hypothalamic-pituitary-gonadal axis, but there is a lack of research on its control by reproductive hormones and peptides. PNX is also associated with food intake, and its expression is linked to feeding status, fatty acids, and glucose. It is influenced by environmental and hormonal-induced stress. The regulation of Pnx in most contexts remains an enigma, in part due to conflicting and negative results. An extensive analysis of the response of the Pnx gene to factors related to reproduction, metabolism, stress, and inflammation is required. Analysis of the Pnx promoter and epigenetic regulation must be considered to understand how this level of control contributes to its pleiotropic effects. PNX is now linked to a broad range of functions, but more research on its gene regulation is required to understand its place in overall physiology and therapeutic potential.

Phoenixin as a New Target in the Development of Strategies for Endometriosis Diagnosis and Treatment

Small integral membrane protein 20/phoenixin (SMIM20/PNX) and its receptor GPR173 (G Protein-Coupled Receptor 173) play a role in the regulation of the hypothalamic-pituitary-gonadal axis (HPG). The aim of the study was to determine PNX, FSH, LH, and 17β-estradiol association in women with endometriosis, and the expression of SMIM20/PNX signaling via GPR173. Serum PNX, FSH, LH, and 17β-estradiol concentrations were measured by enzyme and electrochemiluminescence immunoassay. SMIM20/PNX and GPR173 expression in the eutopic and ectopic endometrium was assessed by qPCR and immunohistochemistry. Reduced PNX level, increased LH/FSH ratio and elevated 17β-estradiol concentration were found in patients with endometriosis. No differences in SMIM20 expression were observed between the studied endometria. GPR173 expression was lower in ectopic than in eutopic endometria. SMIM20 expression was mainly restricted to stroma. GPR173 was detected in some eutopic and ectopic stromal cells and in eutopic glandular epithelial cells. Discriminant analysis indicates the diagnostic relevance of PNX and LH/FSH ratio in patients with endometriosis. In women with endometriosis, reduced PNX levels and GPR173 expression may be responsible for HPG axis dysregulation. These new insights may contribute to a better understanding of the pathophysiology of endometriosis and provide the basis for a new strategy for diagnosis and treatment of endometriosis.

Recent updates on animal models for understanding the etiopathogenesis of polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is the primary cause of female infertility affecting several women worldwide. Changes in hormonal functions such as hyperandrogenism are considered a significant factor in developing PCOS in women. In addition, many molecular pathways are involved in the pathogenesis of PCOS in women. To have better insights about PCOS, it is data from clinical studies carried on women suffering from PCOS should be collected. However, this approach has several implications, including ethical considerations, cost involved and availability of subject. Moreover, during the early drug development process, it is always advisable to use non-human models mimicking human physiology as they are less expensive, readily available, have a shorter gestation period and less risk involved. Many animal models have been reported that resemble the PCOS pathways in human subjects. However, the models developed on rats and mice are more preferred over other rodent/non-rodent models due to their closer resemblance with human PCOS development mechanism. The most extensively reported PCOS models for rats and mice include those induced by using testosterone, letrozole and estradiol valerate. As the pathophysiology of PCOS is complex, none of the explored models completely surrogates the PCOS related conditions occurring in women. Hence, there is a need to develop an animal model that can resemble the pathophysiology of PCOS in women. The review focuses on various animal models explored to understand the pathophysiology of PCOS. The article also highlights some environmental and food-related models that have been used to induce PCOS.

The Role of Peptide Hormones Discovered in the 21st Century in the Regulation of Adipose Tissue Functions

Peptide hormones play a prominent role in controlling energy homeostasis and metabolism. They have been implicated in controlling appetite, the function of the gastrointestinal and cardiovascular systems, energy expenditure, and reproduction. Furthermore, there is growing evidence indicating that peptide hormones and their receptors contribute to energy homeostasis regulation by interacting with white and brown adipose tissue. In this article, we review and discuss the literature addressing the role of selected peptide hormones discovered in the 21st century (adropin, apelin, elabela, irisin, kisspeptin, MOTS-c, phoenixin, spexin, and neuropeptides B and W) in controlling white and brown adipogenesis. Furthermore, we elaborate how these hormones control adipose tissue functions in vitro and in vivo.

Phoenixin: More than Reproductive Peptide

Phoenixin (PNX) neuropeptide is a cleaved product of the Smim20 protein. Its most common isoforms are the 14- and 20-amino acid peptides. The biological functions of PNX are mediated via the activation of the GPR173 receptor. PNX plays an important role in the central nervous system (CNS) and in the female reproductive system where it potentiates LH secretion and controls the estrus cycle. Moreover, it stimulates oocyte maturation and increases the number of ovulated oocytes. Nevertheless, PNX not only regulates the reproduction system but also exerts anxiolytic, anti-inflammatory, and cell-protective effects. Furthermore, it is involved in behavior, food intake, sensory perception, memory, and energy metabolism. Outside the CNS, PNX exerts its effects on the heart, ovaries, adipose tissue, and pancreatic islets. This review presents all the currently available studies demonstrating the pleiotropic effects of PNX.

Altered vitamin D3 metabolism in the ovary and periovarian adipose tissue of rats with letrozole-induced PCOS

Vitamin D₃ (VD₃) plays an important role in the ovary and its deficiency is associated with ovarian pathologies, including polycystic ovary syndrome (PCOS). However, there is no data related to VD₃ metabolism in the ovary during PCOS. Herein, we investigated differences in the expression of VD₃ receptor (VDR) and key VD₃ metabolic enzymes, 1α-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24A1), in the ovary and periovarian adipose tissue (POAT) of control (proestrus and diestrus) and PCOS induced by letrozole rats. Vdr, Cyp27b1 and Cyp24a1 mRNA expression was determined, their protein abundance was examined and immunolocalized. Furthermore, VD₃ metabolite concentrations in plasma (25OHD) and tissues (ovary and POAT; 1,25(OH)₂D₃), and plasma calcium level were determined. 25OHD concentration decreased markedly in letrozole-treated rats in comparison with controls, whereas calcium concentration did not vary among the examined groups. The amount of 1,25(OH)₂D₃ decreased in both ovary and POAT of PCOS rats. In the ovary, we found decreased Cyp27b1 and increased Vdr mRNA expression in letrozole-treated and diestrus control group. Corresponding protein abundances were down-regulated and up-regulated, respectively but only following letrozole treatment. In POAT, only Cyp27b1 transcript level and CYP27B1 protein abundance were decreased in letrozole-treated rats. VDR was immunolocalized in healthy and cystic follicles, while CYP27B1 and CYP24A1 were found exclusively in healthy ones. Concluding, our results provide the first evidence of disrupted VD₃ metabolism in the ovary and POAT of PCOS rats. The reduced 1,25(OH)₂D₃ concentration in those tissues suggests their contribution to VD₃ deficiency observed in PCOS and might implicate in PCOS pathogenesis.