Phoenixin-A Pleiotropic Gut-Brain Peptide

Examining the Potential Applicability of Orexigenic and Anorexigenic Peptides in Veterinary Medicine for the Management of Obesity in Companion Animals

This review article comprehensively explores the role of orexigenic and anorexigenic peptides in the management of obesity in companion animals, with a focus on clinical applications. Obesity in domestic animals, particularly dogs and cats, is prevalent, with significant implications for their health and well-being. Factors contributing to obesity include overfeeding, poor-quality diet, lack of physical activity, and genetic predispositions. Despite the seriousness of this condition, it is often underestimated, with societal perceptions sometimes reinforcing unhealthy behaviors. Understanding the regulation of food intake and identifying factors affecting the function of food intake-related proteins are crucial in combating obesity. Dysregulations in these proteins, whether due to genetic mutations, enzymatic dysfunctions, or receptor abnormalities, can have profound health consequences. Molecular biology techniques play a pivotal role in elucidating these mechanisms, offering insights into potential therapeutic interventions. The review categorizes food intake-related proteins into anorexigenic peptides (inhibitors of food intake) and orexigenic peptides (enhancers of food intake). It thoroughly examines current research on regulating energy balance in companion animals, emphasizing the clinical application of various peptides, including ghrelin, phoenixin (PNX), asprosin, glucagon-like peptide 1 (GLP-1), leptin, and nesfatin-1, in veterinary obesity management. This comprehensive review aims to provide valuable insights into the complex interplay between peptides, energy balance regulation, and obesity in companion animals. It underscores the importance of targeted interventions and highlights the potential of peptide-based therapies in improving the health outcomes of obese pets.

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.

Expression of Genes Encoding Selected Orexigenic and Anorexigenic Peptides and Their Receptors in the Organs of the Gastrointestinal Tract of Calves and Adult Domestic Cattle (Bos taurus taurus)

The regulation of food intake occurs at multiple levels, and two of the components of this process are orexigenic and anorexigenic peptides, which stimulate or inhibit appetite, respectively. The study of the function of these compounds in domestic cattle is essential for production efficiency, animal welfare, and health, as well as for economic benefits, environmental protection, and the contribution to a better understanding of physiological aspects that can be applied to other species. In this study, the real-time PCR method was utilized to determine the expression levels of GHRL, GHSR, SMIM20, GPR173, LEP, LEPR, and NUCB2 (which encode ghrelin, its receptor, phoenixin-14, its receptor, leptin, its receptor, and nesfatin-1, respectively) in the gastrointestinal tract (GIT) of Polish Holstein-Friesian breed cattle. In all analyzed GIT segments, mRNA for all the genes was present in both age groups, confirming their significance in these tissues. Gene expression levels varied distinctly across different GIT segments and between young and mature subjects. The differences between calves and adults were particularly pronounced in areas such as the forestomachs, ileum, and jejunum, indicating potential changes in peptides regulating food intake based on the developmental phase. In mature individuals, the forestomachs predominantly displayed an increase in GHRL expression, while the intestines had elevated levels of GHSR, GPR173, LEP, and NUCB2. In contrast, the forestomachs in calves showed upregulated expressions of LEP, LEPR, and NUCB2, highlighting the potential importance of peptides from these genes in bovine forestomach development.

Investigation of Serum Phoenixin-14 Concentration in Pregnant Women Diagnosed with Hyperemesis Gravidarum

OBJECTIVE

We aimed to investigate the relationship between the hyperemesis gravidarum (HG) and maternal serum phoenixin-14 (PNX-14) concentrations.

MATERIALS AND METHODS

This cross-sectional study was conducted with 88 pregnant women who applied to the Umraniye Training and Research Hospital Gynecology and Obstetrics Clinic between February 2022 and October 2022. The HG group consisted of 44 pregnant women diagnosed with HG between the 7th and 14th gestational weeks, and the control group consisted of 44 healthy pregnant women matched with the HG group in terms of age, BMI, and gestational week. Demographic characteristics, ultrasound findings, and laboratory outcomes were noted. The two groups were compared in terms of maternal serum PNX-14 concentrations.

RESULTS

Gestational age at blood sampling for PNX-14 was similar in both groups (p=1.000). While maternal serum PNX-14 concentration was 85.5 pg/ml in the HG group, it was 71.3 pg/ml in the control group (p=0.012). ROC analysis was performed to determine the value of maternal serum PNX-14 concentration in terms of predicting HG. AUC analysis of maternal serum PNX-14 for HG estimation was 0.656 (p=0.012, 95% CI=0.54-0.77). The optimal cutoff value for maternal serum PNX-14 concentration was determined as 79.81 pg/ml with 59% sensitivity and 59% specificity.

CONCLUSION

In this study, maternal serum PNX-14 concentration was found to be higher in pregnant women with HG, which indicates that high serum PNX-14 concentrations may have an anorexigenic effect on food intake in pregnancy. Concentrations of other PNX isoforms in HG and changes in PNX concentrations in pregnant women with HG who regained weight after treatment remain to be investigated.

Locked Out: Phoenixin-14 Does Not Cross a Stem-Cell-Derived Blood-Brain Barrier Model

Phoenixin-14 is a recently discovered peptide regulating appetite. Interestingly, it is expressed in the gastrointestinal tract; however, its supposed receptor, GPR173, is predominantly found in hypothalamic areas. To date, it is unknown how peripherally secreted phoenixin-14 is able to reach its centrally located receptor. To investigate whether phoenixin is able to pass the blood-brain barrier, we used an in vitro mono-culture blood-brain barrier (BBB) model consisting of brain capillary-like endothelial cells derived from human induced-pluripotent stem cells (hiPSC-BCECs). The passage of 1 nMol and 10 nMol of phoenixin-14 via the mono-culture was measured after 30, 60, 90, 120, 150, 180, 210, and 240 min using a commercial ELISA kit. The permeability coefficients (PC) of 1 nMol and 10 nMol phoenixin-14 were 0.021 ± 0.003 and 0.044 ± 0.013 µm/min, respectively. In comparison with the PC of solutes known to cross the BBB in vivo, those of phoenixin-14 in both concentrations are very low. Here, we show that phoenixin-14 alone is not able to cross the BBB, suggesting that the effects of peripherally secreted phoenixin-14 depend on a co-transport mechanism at the BBB in vivo. The mechanisms responsible for phoenixin-14's orexigenic property along the gut-brain axis warrant further research.

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.

Linking mitochondrial dynamics and fertility: promoting fertility by phoenixin through modulation of ovarian expression of GnRH receptor and mitochondrial dynamics proteins DRP-1 and Mfn-2

Obesity is linked to reproductive disorders. Novel neuropeptide phoenixin demonstrated many therapeutic actions. In this study, we aim to evaluate phoenixin’s potential effect in obesity-induced infertility through modulating mitochondrial dynamics. Ninety adult female rats were divided to 4 groups: (I), fed with normal pellet diet; (II), given phoenixin; (III), fed with high-fat diet. Rats that developed obesity and infertility were divided to 2 groups: (III-A), received no further treatment; (III-B), given phoenixin. Our results showed that phoenixin treatment in obese infertile rats significantly decreased serum levels of insulin and testosterone and ovarian levels of dynamin-related protein1(Drp1),reactive oxygen species ROS, TNF-α, MDA, and caspase-3. Phoenixin treatment also significantly increased serum estrogen progesterone, LH, and FSH together with ovarian levels of GnRH receptor (GnRHR), mitofusin2(Mfn2), mitochondrial transmembrane potential (ΔΨm), and electron transport chain (ETC) complex-I significantly when compared with obese group. Ovarian histopathological changes were similarly improved by phoenixin. Our data demonstrate phoenixin’s role in improving obesity-induced infertility.

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.

Central Phoenixin Protective Role on Pentylenetetrazol-Induced Seizures during Various Stages of the Estrous Cycle among Rats

It is known that phoenixin-14 (PNX-14) has a mediatory role in reproduction; however, there is no report on the role of the PNX-14 on epilepsy. Therefore, this study aimed to investigate the antiepileptic effects of the PNX-14 on the pentylenetetrazol (PTZ)-induced epilepsy in the stages of the estrous cycle among rats. A total of 168 adult female Wistar rats were randomly divided into seven groups, including control (intracerebroventricular injection was performed with saline), PNX-14 (5 µg), PNX-14 (10 µg), bicuculline (competitive antagonist of GABA_A receptors; 5 nmol)+PNX-14 (5 µg), bicuculline (BIC) (5 nmol)+PNX-14 (10 µg), saclofen (competitive antagonist of GABA_B receptors; 2.5 µg)+PNX-14 (5 µg), and saclofen (2.5 µg)+PNX-14 (10 µg) in proestrus, estrus, metestrus, and diestrus. Afterward, the control and treatment groups were followed by intraperitoneal administration of 80 mg/kg PTZ. Initiation time of myoclonic seizures (ITMS), initiation time of tonic-clonic seizures (ITTS), seizure duration (SD), and mortality rate (MR) were monitored and recorded for 30 min. According to the results, PNX-14 alone significantly reduced the SD and seizure mortality in all phases of estrus (P<0.05). The injection of PNX-14 with BIC significantly reduced SD and seizure mortality in all estrus phases (P<0.05). PNX-14 alone increased both ITMS and ITTS in all phases of estrus (P<0.05). Furthermore, the injection of PNX-14 with BIC significantly reduced the effects of the PNX-14 on ITMS and ITTS in all estrus stages (P<0.05). These results showed that the antiepileptic activity of PNX-14 was probably mediated by GABA_A receptors, and this effect was more prominent during the luteal phase than the follicular phase.

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.

Protective Effects of Phoenixin-14 Peptide in the Indomethacin-Induced Duodenal Ulcer: An Experimental Study

Phoenixin-14‎ (PNX‎-14‎) is a newly identified neuropeptide with potential anti-inflammatory effects in the gastrointestinal tract. In this study, we evaluated the protective effect of PNX-14 against the formation of experimental indomethacin (IND)-induced duodenal ulcer. Thirty-two‎ male Sprague-Dawley rats were randomly assigned to the four following study groups: (1) negative control (2) IND (7.5 mg/kg subcutaneous IND), (3) famotidine (FA) (7.5 mg/kg subcutaneous IND followed by 40 mg/kg intraperitoneal‎ FA), and (4) PNX-14 (7.5 mg/kg subcutaneous IND followed by 50 µ/kg intraperitoneal‎ PNX-14). Outcome measures included macroscopic evaluation of duodenal lesion, serum levels of IL-1ß, TNF-α, IL-6, and IL-12, and tissue biochemical parameters of oxidative stress, including malondialdehyde (MDA)‎‏,‏‎ myeloperoxidase ‎‎(MPO) activity, superoxide dismutase (SOD) ‎activity, and catalase activity. Results The macroscopic grade of duodenal lesions were significantly smaller in the PNX-14 group than in the IND group (p < 0.001). Serum inflammatory cytokines were significantly increased in the IND group. PNX-14 treatment significantly decreased the serum levels of inflammatory cytokines (p < 0.0001). Oxidative contents (MDA and MPO activity) were significantly smaller in the PNX-14 group compared with the IND group (p < 0.0001), while anti-oxidative contents (SOD and catalase activity) were significantly more (p < 0.0001). PNX-14 was superior to FA in several anti-inflammatory properties, such as inhibiting the release of inflammatory cytokines and increasing the catalase activity. PNX-14 showed significant protective effects against the formation of IND-induced duodenal ulcers. These results suggest a promising therapeutic implication for PNX-14 in the treatment of gastrointestinal inflammatory disorders.

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.

Hormonal and neuroendocrine control of reproductive function in teleost fish

Reproduction is one of the important physiological events for the maintenance of the species. Hormonal and neuroendocrine regulation of teleost requires multiple and complex interactions along the hypothalamic-pituitary-gonad (HPG) axis. Within this axis, gonadotropin-releasing hormone (GnRH) regulates the synthesis and release of gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Steroidogenesis drives reproduction function in which the development and differentiation of gonads. In recent years, new neuropeptides have become the focus of reproductive physiology research as they are involved in the different regulatory mechanisms of these species' growth, metabolism, and reproduction. However, especially in fish, the role of these neuropeptides in the control of reproductive function is not well studied. The study of hormonal and neuroendocrine events that regulate reproduction is crucial for the development and success of aquaculture.

Phoenixin-14 reduces the frequency of interictal-like events in mice brain slices

Phoenixin-14 (PNX-14) has a wide bioactivity in the central nervous system. Its role in the hypothalamus has been investigated, and it has been reported that it is involved in the regulation of excitability in hypothalamic neurons. However, its role in the regulation of excitability in entorhinal cortex and the hippocampus is unknown. In this study, we investigated whether i. PNX-14 induces any synchronous discharges or epileptiform activity and ii. PNX-14 has any effect on already initiated epileptiform discharges. We used 350 µm thick acute horizontal hippocampal-entorhinal cortex slices obtained from 30- to 35-day-old mice. Extracellular field potential recordings were evaluated in the entorhinal cortex and hippocampus CA1 region. Bath application of PNX-14 did not initiate any epileptiform activity or abnormal discharges. 4-Aminopyridine was applied to induce epileptiform activity in the slices. We found that 200 nM PNX-14 reduced the frequency of interictal-like events in both the entorhinal cortex and hippocampus CA1 region which was induced by 4-aminopyridine. Furthermore, PNX-14 led to a similar suppression in the total power of local field potentials of 1-120 Hz. The frequency or the duration of the ictal events was not affected. These results exhibited for the first time that PNX-14 has a modulatory effect on synchronized neuronal discharges which should be considered in future therapeutic approaches.

Mouse gastric mucosal endocrine cells are sources and sites of action of Phoenixin-20

Energy homeostasis is is determined by food intake and energy expenditure, which are partly regulated by the cross-talk between central and peripheral hormonal signals. Phoenixin (PNX) is a recently discovered pleiotropic neuropeptide with isoforms of 14 (PNX-14) and 20 (PNX-20) amino acids. It is a potent reproductive peptide in vertebrates, regulating the hypothalamo-pituitary-gonadal axis (HPG). It has been identified as a regulator of food intake during light phase when injected intracerebroventricularly in rats. In addition, plasma levels of PNX also increased after food intake in rats, suggesting that it might have possible roles in energy homeostasis. We hypothesized that gut is a source and site of action of PNX in mice. Immunoreactivity for PNX and its putative receptor, super-conserved receptor expressed in brain (SREB3; also known as the G-protein coupled receptor 173/GPR 173) was found in the stomach and intestine of male C57/BL6 J mice, and in MGN3-1 (mouse stomach endocrine) cells and STC-1 (mouse enteroendocrine) cells. In MGN3-1 cells, PNX-20 significantly upregulated ghrelin (10 nM) and ghrelin-O-acyl transferase (GOAT) mRNAs (1000 nM) at 6 h. In STC-1 cells, it significantly suppressed CCK (100 nM) at 2 h. No effects were found on other intestinal hormones tested (glucagon like peptide-1, glucose dependent insulinotropic polypeptide, and peptide YY). Together, these results indicate that PNX-20 is produced in the gut, and it could act directly on gut cells to regulate metabolic hormones.

Phoenixin-20 Prevents ox-LDL-Induced Attachment of Monocytes to Human Aortic Endothelial Cells (HAECs): A Protective Implication in Atherosclerosis

The exact cause of atherosclerosis is not known, and therefore, the current treatment options are limited. The activation of endothelial cells by oxidized low-density lipoprotein (ox-LDL) plays a key role in the initiation and progression of atherosclerosis. Phoenixin-20 is one of the newly identified neuropeptides with pleiotropic effects in the regulation of reproduction and other biological functions. G-protein receptor-coupled 173 (GPR173) is the putative receptor of Phoenixin-20. In the present study, we show that endothelial GPR173 is repressed upon ox-LDL stimulation in human aortic endothelial cells (HAECs). We further elaborate on the hypothesis that GPR173 could be involved in the pathogenesis of atherosclerosis through a series of experiments. Our results indicate that ox-LDL remarkably triggers the increase of ROS, NOX-4, pro-inflammatory cytokines IL-1β, IL-8, and MCP-1 expression, as well as adhesion molecules ICAM-1 and VCAM-1 release. However, the agonism of GPR173 using Phoenixin-20 significantly ameliorates all of these harmful effects from ox-LDL by suppressing the NF-κB pathway. Furthermore, we show that agonism of GPR173 by Phoenixin-20 prevents the attachment of monocytes THP-1 to endothelial cells, which is an important therapeutic approach to preventing atherogenesis. In conclusion, our study demonstrates that GPR173 agonism by Phoenixin-20 plays a protective role against ox-LDL-induced endothelial dysfunction, implying that Phoenixin-20 may have therapeutic implications in atherosclerosis.

Restraint stress affects circulating NUCB2/nesfatin-1 and phoenixin levels in male rats

The two peptides phoenixin and nesfatin-1 are colocalized in hypothalamic nuclei involved in the mediation of food intake and behavior. Phoenixin stimulates food intake and is anxiolytic, while nesfatin-1 is an anorexigenic peptide shown to increase anxiety and anhedonia. Interestingly, central activation of both peptides can be stimulated by restraint stress giving rise to a role in the mediation of stress. Thus, the aim of the study was to test whether also peripheral circulating levels of NUCB2/nesfatin-1 and phoenixin are altered by restraint stress. Male ad libitum fed Sprague Dawley rats equipped with a chronic intravenous catheter were subjected to restraint stress and plasma levels of NUCB2/nesfatin-1, phoenixin and cortisol were measured over a period of 240 min and compared to levels of freely moving rats. Peripheral cortisol levels were significantly increased in restrained rats at 30, 60, 120 and 240 min compared to controls (p < 0.05). In contrast, restraint stress decreased plasma phoenixin levels at 15 min compared to unstressed conditions (0.8-fold, p < 0.05). Circulating NUCB2/nesfatin-1 levels were increased only at 240 min in restrained rats compared to those in unstressed controls (1.3-fold, p < 0.05). In addition, circulating NUCB2/nesfatin-1 levels correlated positively with phoenixin levels (r = 0.378, p < 0.001), while neither phoenixin nor nesfatin-1 were associated with cortisol levels (r = 0.0275, and r=-0.143, p> 0.05). These data suggest that both peptides, NUCB2/nesfatin-1 and phoenixin, are affected by restraint stress, although less pronounced than circulating cortisol.

Nutrient regulation of somatic growth in teleost fish. The interaction between somatic growth, feeding and metabolism

This review covers the current knowledge on the regulation of the somatic growth axis and its interaction with metabolism and feeding regulation. The main endocrine and neuroendocrine factors regulating both the growth axis and feeding behavior will be briefly summarized. Recently discovered neuropeptides and peptide hormones will be mentioned in relation to feeding control as well as growth hormone regulation. In addition, the influence of nutrient and nutrient sensing mechanisms on growth axis will be highlighted. We expect that in this process gaps of knowledge will be exposed, stimulating future research in those areas.

GPR173 agonist phoenixin 20 promotes osteoblastic differentiation of MC3T3-E1 cells

Osteogenic differentiation is critical to bone homeostasis, and its imbalance plays a key role in the progression of osteoporosis. Osteoblast cells are responsible for synthesizing new bone tissue, and understanding how to control osteoblastic differentiation is vital to the treatment of osteoporosis. Herein, we show that GPR173 signaling is involved in the regulation of osteoblastic differentiation in MC3T3-E1 cells. Our data reveals that GPR173 is abundantly expressed in MC3T3-E1 cells, and its expression is inducible upon the introduction of osteogenic media. The activation of GPR173 by its selective agonist phoenixin 20 induces the expression of several osteoblast signature genes including collagen type 1 alpha 1 (Col-I), osteocalcin (OCN), alkaline phosphatase (ALP) as well as increased matrix mineralization and ALP activity, suggesting that the activation of GPR173 promotes osteoblastic differentiation. Moreover, we show that the effect of phoenixin 20 is mediated by its induction on the key regulator runt-Related Transcription Factor 2 (Runx2). Mechanistically, we display that the action of phoenixin 20 requires the activation of MAPK kinase p38, and deactivation of p38 by its inhibitor SB203580 weakens the phoenixin 20-mediated induction of RUNX-2, ALP, and matrix mineralization. Silencing of GPR173 attenuates phoenixin 20-mediated osteoblastic differentiation, indicating its dependence on the receptor. Collectively, our study reveals a new role of GPR173 and its agonist phoenixin 20 in osteoblastic differentiation.

Phoenixin 14 Inhibits High-Fat Diet-Induced Non-Alcoholic Fatty Liver Disease in Experimental Mice

Introduction

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases. The development of NAFLD is closely associated with hepatic lipotoxicity, inflammation, and oxidative stress. The new concept of NAFLD treatment is to seek molecular control of lipid metabolism and hepatic redox hemostasis. Phoenixin is a newly identified neuropeptide with pleiotropic effects. This study investigated the effects of phoenixin 14 against high-fat diet (HFD)-induced NAFLD in mice.

Materials and Methods

For this study, we used HFD-induced NAFLD mice models to analyze the effect of phonenixin14. The mice were fed on HFD and normal diet and also given phoenixin 14 (100 ng/g body weight) by gastrogavage for 10 weeks. The peripheral blood samples were collected for biochemical assays. The liver tissues were examined for HFD-induced tissue fibrosis, lipid deposition and oxidative activity including SOD, GSH, and MDA. The liver tissues were analyzed for the inflammatory cytokines and oxidative stress pathway genes.

Results

The results indicate that phoenixin 14 significantly ameliorated HFD-induced obesity and fatty liver. The biochemical analysis of blood samples revealed that phoenixin 14 ameliorated HFD-induced elevated circulating alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol, and triglyceride levels, suggesting that phoenixin 14 has a protective role in liver function and lipid metabolism. Hematoxylin-eosin (HE) and Oil Red O staining of the liver showed that phoenixin 14 alleviated HFD-induced tissue damage and lipid deposition in the liver. Furthermore, the mice administered with phoenixin 14 had increased hepatic SOD activity, increased production of GSH and reduced MDA activity, as well as reduced production of TNF-α and IL-6 suggesting that phoenixin 14 exerts beneficial effects against inflammation and ROS. The findings suggest an explanation of how mechanistically phoenixin 14 ameliorated HFD-induced reduced activation of the SIRT1/AMPK and NRF2/HO-1 pathways.

Conclusion

Collectively, this study revealed that phoenixin 14 exerts a protective effect in experimental NAFLD mice. Phoenixin could be of the interest in preventive modulation of NAFLD.

Effect of the neuropeptide phoenixin and its receptor GPR173 during folliculogenesis

Folliculogenesis is a complex process, defined by the growth and development of follicles from the primordial population. Granulosa cells (GCs) play a vital role in every stage of follicular growth through proliferation, acquisition of gonadotropic responsiveness, steroidogenesis and production of autocrine/paracrine factors. A recently discovered hypothalamic neuropeptide phoenixin is involved in the regulation of the reproductive system. Phoenixin acts through its receptor, G protein-coupled receptor 173 (GPR173), to activate the cAMP/PKA pathway leading to the phosphorylation of CREB (pCREB). Here, we demonstrated the expression patterns of phoenixin and GPR173 in human ovary and explored its role in folliculogenesis. Phoenixin and GPR173 were both expressed in the human ovarian follicle, with increased expression in GCs as the follicle grows. Phoenixin treatment at 100 nM for 24 h induced the proliferation of human non-luteinized granulosa cell line, HGrC1 and significantly increased the expression levels of CYP19A1, FSHR, LHR and KITL, but decreased NPPC expression levels. These effects were suppressed by GPR173 siRNA. The expression level of CREB1, pCREB and estradiol (E2) production in the culture medium was significantly enhanced by phoenixin treatment in a concentration-dependent manner. Phoenixin also significantly increased the follicular area in a murine ovarian tissue culture model, leading to an increased number of ovulated oocytes with a higher level of maturation. Taken together, our data demonstrate that phoenixin is an intraovarian factor that promotes follicular growth through its receptor GPR173 by accelerating proliferation of GCs, inducing E2 production and increasing the expression of genes related to follicle development.

Phoenixin 14 inhibits ischemia/reperfusion-induced cytotoxicity in microglia

The process of ischemia/reperfusion (IR) in ischemic stroke often leads to significant cell death and permanent neuronal damage. Safe and effective treatments are urgently needed to mitigate the damage caused by IR injury. The naturally occurring pleiotropic peptide phoenixin 14 (PNX-14) has recently come to light as a potential treatment for IR injury. In the present study, we examined the effects of PNX-14 on several key processes involved in ischemic injury, such as pro-inflammatory cytokine expression, oxidative stress, and the related cascade mediated through the toll-like receptor 4 (TLR4) pathway, using BV2 microglia exposed to oxygen-glucose deprivation and reoxygenation (OGD/R). Our results demonstrate an acute ability of PNX-14 to regulate the expression levels of proinflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). PNX-14 also prevented oxidative stress by reducing the generation of reactive oxygen species (ROS) and increasing the level of the antioxidant glutathione (GSH). Importantly, PNX-14 inhibited high-mobility group box 1 (HMGB1)/TLR4/myeloid differentiation primary response 88 (MyD88)/nuclear factor-κB (NF-κB) signaling pathway, by inhibiting the activation of TLR4 and preventing the nuclear translocation of p65 protein. We further confirmed the cerebroprotective effects of PNX-14 in an MCAO rat model, which resulted in reduced infarct volume and decreased microglia activation. Together, the results of this study implicate a possible protective role of PNX-14 against various aspects of IR injury in vitro.

Phoenixin 20 promotes neuronal mitochondrial biogenesis via CREB-PGC-1α pathway

Neurodegenerative disorders are dreadful diseases that affect millions of people worldwide. Mitochondrial dysfunction is closely associated with the development of neurodegenerative disorders. Phoenixin 20 is a newly discovered neuropeptide with a pleiotropic effect. This study showed that the presence of Phoenixin 20 promoted neuronal mitochondrial biogenesis in vitro. In cultured neuronal M17 cells, Phoenixin 20 increased the expression of mitochondrial regulators PGC-1α, NRF-1, and TFAM at both mRNA and protein levels. The treatment of Phoenixin 20 increased the ratio of mitochondrial vs nuclear DNA (mtDNA/nDNA) and the multiple mitochondrial gene expression as revealed by increasing mRNA expression of Tomm22, Timm50, Atp5d, Ndufs3, and protein expression of NDUFB8. At a cellular level, Phoenixin 20 promoted mitochondrial respiratory rate and cellular ATP production. Mechanistically, we found that Phoenixin 20 induced the phosphorylation of CREB, which suggests that Phoenixin 20 promoted the activation of the CREB pathway. The blockage of CREB by its selective inhibitor H89 prevented the effect of Phoenixin 20 on mitochondrial regulators and biogenesis. Moreover, the study showed that Phoenixin 20 induced the expression of its tentative receptor GPR173 at the mRNA and protein level, and the silence of GPR173 in neuronal cells ablated all its effect on mitochondrial regulation. Collectively, we showed that Phoenixin 20 promoted neuronal mitochondrial biogenesis via the regulation of CREB-PGC-1α pathway. This study revealed a new role and underlying mechanism of Phoenixin 20 in neuronal cells, suggesting it influences the therapeutic implication of neurodegenerative diseases.

Contingent role of phoenixin and nesfatin-1 on secretions of the male reproductive hormones

Phoenixin (PNX) and nesfatin-1 are localised in the hypothalamus and the pituitary gland. Moreover, the most of the PNX-expressing neurons in the hypothalamus also co-express nesfatin-1. These outcomes may suggest that there is an interaction between PNX and nesfatin-1, at least in terms of neuroendocrine-mediated regulations. Hence, the study was planned to find out the effects of centrally delivered PNX and nesfatin-1 on male sex hormones or to show the interactive association of intracerebroventricularly (ICV) injected PNX+nesfatin-1 combination on the release of male hormones. PNX and nesfatin-1, single or together, were delivered ICV to different male Wistar Albino rat groups. Both PNX and nesfatin-1 induced a significant enhancement in plasma FSH, LH and testosterone without inducing any alteration in plasma GnRH in the rats. The central combinatorial treatment of both the neuropeptides produced a more potent rise in male plasma hormone levels than treating with single neuropeptide. In summary, our preliminary data show that centrally delivered PNX and nesfatin-1 can affect plasma male hormone levels. Moreover, that the combinatorial treatment with both the neuropeptides in male rats leading to a more potent effect on the plasma male hormone levels might suggest that both these neuropeptides act synergistically in terms of regulation of male HPGA.

The role of phoenixin in behavior and food intake

The recently discovered peptide phoenixin was initially implicated in reproduction as a regulator of gonadotropin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release from the pituitary. Subsequently, various functions of phoenixin have been demonstrated including mediation of itching sensation, stimulation of vasopressin secretion, stimulation of white adipogenesis and hypothalamic nutrient sensing. Subsequently, additional actions of phoenixin have been described, namely effects on behavior. A systematic search of four data bases was performed and original articles selected accordingly. The present systematic review will present the current knowledge on the effects of phoenixin on different behaviors such as anxiety and food intake as well as cognition. Lastly, gaps in knowledge will be mentioned to stimulate further research.