Phoenixin-14 stimulates proliferation and insulin secretion in insulin producing INS-1E cells

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.

Characterizing the SREB G protein-coupled receptor family in fish: Brain gene expression and genomic differences in upstream transcription factor binding sites

The SREB (Super-conserved Receptors Expressed in Brain) family of orphan G protein-coupled receptors is highly conserved in vertebrates and consists of three members: SREB1 (orphan designation GPR27), SREB2 (GPR85), and SREB3 (GPR173). SREBs are associated with processes ranging from neuronal plasticity to reproductive control. Relatively little is known about similarities across the entire family, or how mammalian gene expression patterns compare to non-mammalian vertebrates. In fish, this system may be particularly complex, as some species have gained a fourth member (SREB3B) while others have lost genes. To better understand the system, the present study aimed to: 1) use qPCR to characterize sreb and related gene expression patterns in the brains of three fish species with different systems, and 2) identify possible differences in transcriptional regulation among the receptors, using upstream transcription factor binding sites across 70 ray-finned fish genomes. Overall, regional patterns of sreb expression were abundant in forebrain-related areas. However, some species-specific patterns were detected, such as abundant expression of receptors in zebrafish (Danio rerio) hypothalamic-containing sections, and divergence between sreb3a and sreb3b in pufferfish (Dichotomyctere nigroviridis). In addition, a gene possibly related to the system (dkk3a) was spatially correlated with the receptors in all three species. Genomic regions upstream of sreb2 and sreb3b, but largely not sreb1 or sreb3a, contained many highly conserved transcription factor binding sites. These results provide novel information about expression differences and transcriptional regulation across fish that may inform future research to better understand these receptors.

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.

Current state of phoenixin-the implications of the pleiotropic peptide in stress and its potential as a therapeutic target

Phoenixin is a pleiotropic peptide, whose known functions have broadened significantly over the last decade. Initially first described as a reproductive peptide in 2013, phoenixin is now recognized as being implicated in hypertension, neuroinflammation, pruritus, food intake, anxiety as well as stress. Due to its wide field of involvement, an interaction with physiological as well as psychological control loops has been speculated. It has shown to be both able to actively reduce anxiety as well as being influenced by external stressors. Initial rodent models have shown that central administration of phoenixin alters the behavior of the subjects when confronted with stress-inducing situations, proposing an interaction with the perception and processing of stress and anxiety. Although the research on phoenixin is still in its infancy, there are several promising insights into its functionality, which might prove to be of value in the pharmacological treatment of several psychiatric and psychosomatic illnesses such as anorexia nervosa, post-traumatic stress disorder as well as the increasingly prevalent stress-related illnesses of burnout and depression. In this review, we aim to provide an overview of the current state of knowledge of phoenixin, its interactions with physiological processes as well as focus on the recent developments in stress response and the possible novel treatment options this might entail.

Phoenixin 14 ameloriates pancreatic injury in streptozotocin-induced diabetic rats by alleviating oxidative burden

Phoenixin-14 (PNX) is a neuropeptide that has been shown to prevent oxidative damage and stimulates insulin secretion. We investigated the effects of PNX on pancreatic injury induced by streptozotocin (STZ), and nicotinamide (NAD). Male Sprague-Dawley rats, in control (C) and diabetic (STZ) groups, were treated with either saline, or PNX (0.45 nmol/kg, or 45 nmol/kg) daily for 3 days 1 week after STZ injection. Fasting blood glucose (FBG) and gastric emptying rate (GER) were measured. Tissue and blood samples were collected. PNX treatments prevented pancreatic damage and β cell loss. Increased luminol and lucigenin levels in the pancreas, ileum and liver tissues of STZ groups were alleviated by PNX treatment in pancreatic and ileal tissues. PNX0.45 decreased FBG without any change in insulin blood level and pancreatic mRNA. GER increased in all diabetic rats while PNX0.45 delayed GER only in the C group. PNX diminishes pancreatic damage and lowers FBG by reducing oxidative load.

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.

Investigation of serum phoenixin levels in patients with hypertension

OBJECTIVE:

Hypertension is a major modifiable risk factor for cardiovascular disease and premature death worldwide. Phoenixin is a newly identified neuropeptide with multiple bioactivity. However, there was no published data about phoenixin levels in hypertension. The aim of this study was to evaluate the relationship between phoenixin and hypertension.

METHODS:

This study was performed in 36 patients with hypertension and 36 healthy controls. Serum phoenixin-14 and phoenixin-20 levels were determined by Enzyme-Linked ImmunoSorbent Assay method.

RESULTS:

Serum phoenixin-14 and phoenixin-20 values were significantly lower in hypertension patients compared with the control group (p<0.001). The levels of phoenixin-14 were negatively correlated with weight (r=-0.376; p<0.005), body mass index (r=-0.407; p<0.001), systolic blood pressure (r=-0.586; p<0.001), and diastolic blood pressure (r=-0.319; p<0.01). There was a negative correlation between serum phoenixin-20 and weight (r=-0.378; p<0.005), body mass index (r=-0.383; p<0.005), systolic blood pressure (r=-0.551; p<0.001), and diastolic blood pressure (r=-0.306; p<0.01). We used receiver operating characteristic curve analyses to compare the diagnosis value of Phoenixin-14 and Phoenixin-20 levels in hypertensive patients. We found that Phoenixin-14 value is an area under the curve of 0.87 (cutoff value 404.7 ng/L, sensitivity 92%, specificity 72%) and Phoenixin-20 value is an area under the curve of 0.83 (cutoff value 209.9 ng/L, sensitivity 86%, specificity 75%). Phoenixin-14 did nearly show equally compared to phoenixin-20 in predicting hypertension.

CONCLUSION:

Serum phoenixin-14 and phoenixin-20 may be related to the pathogenesis of hypertension. Our findings indicated that serum phoenixin-14 and phoenixin-20 may serve as a novel biomarker for the diagnosis of hypertension.

Blood and aqueous humor phoenixin, endocan and spexin in patients with diabetes mellitus and cataract with and without diabetic retinopathy

Peptide phoenixin (PNX), endocan (EDC), and spexin (SPX) are associated with diabetes. Therefore, the purpose of this study was to investigate the levels of PNX, EDC and SPX in the blood and aqueous humor (AH) of patient with type 2 diabetes with and without DRP and cataract. 30 type 2 diabetes patients with cataract (DM + C), 30 DRP patient with cataract (DRP + C), 30 non-diabetic patient with only cataract and 30 control participants were enrolled into this study. PNX, EDC, and SPX were measured in blood and AH by ELISA. In patients with DRP + C, the levels of PNX and EDC were significantly higher in both AH and blood samples compared with the group of patients without DRP + C (<0.05). Also, in patients with DM + C, the levels of PNX and EDC were higher in both AH and blood samples compared with the group of patients without DM + C. However, in patients with DRP + C, the levels of SPX were significantly lower in both AH and blood samples compared with the group of patients without DRP + C (<0.05). Also, in patients with DM + C, the levels of SPX were also lower in both AH and blood samples compared with the group of patients without DM + C. These findings suggest that increased PNX, EDC, and decreased SPX amounts in blood and AH of DM + C and DRP + C groups when compared with control and cataract groups show that they might have a role in the pathophysiology of DM + C, especially in the DRP + C.

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.

Neuropeptide B/W receptor 1 peptidomimetic agonists: Structure-activity relationships and plasma stability

Neuropeptides B and W (NPB and NPW) are endogenous ligands of the Neuropeptide B/W Receptor 1 (NPBWR1) which has been implicated in a wide range of functions including regulation of pain and energy homeostasis. There is currently little information on the structure-activity relationships (SAR) of these two neuropeptides. In a quest to develop stable and potent NPBWR1 peptidomimetic agonists, we performed systematic SAR by truncation, Alanine/Glycine and d-amino acid scans, and replacement with unnatural amino acids. Evaluation in the NPBWR1 calcium assay revealed that the C-terminal GRAAGLL and N-terminal WYK regions constitute the two-epitope pharmacophore for NPBWR1 agonism. Replacement of the N-terminal Trp with its desaminoTrp residue resulted in compound 30 which exhibited nanomolar potency comparable to the endogenous NPB at NPBWR1 (Calcium assay: EC₅₀ = 8 nM vs. 13 nM, cAMP assay: 2.7 nM vs 3.5 nM) and enhanced metabolic stability against rat plasma (39.1 min vs. 11.9 min).

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.

Role of the Novel Peptide Phoenixin in Stress Response and Possible Interactions with Nesfatin-1

The novel peptide phoenixin was shown to be involved in several physiological processes ranging from reproduction to food intake. Interest in this protein has steadily increased over the last few years and its known implications have become much broader, playing a role in glucose homeostasis, anxiety, nociception, and pruritus. Phoenixin is expressed in a multitude of organs such as the small intestine, pancreas, and in the hypothalamus, as well as several other brain nuclei influencing numerous physiological functions. Its highly conserved amino-acid sequence amongst species leads to the assumption, that phoenixin might be involved in essential physiological functions. Its co-expression and opposing functionality to the extensively studied peptide nesfatin-1 has given rise to the idea of a possible counterbalancing role. Several recent publications focused on phoenixin’s role in stress reactions, namely restraint stress and lipopolysaccharide-induced inflammation response, in which also nesfatin-1 is known to be altered. This review provides an overview on the phoenixins and nesfatin-1 properties and putative effects, and especially highlights the recent developments on their role and interaction in the response to response.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese. We have also considered the likely outcomes on islet function that the altered GPCR expression status confers and the possible impact that adipokines, secreted from expanded fat depots, could have at those GPCRs showing altered expression in obesity.

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.

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 (PNX) is a newly discovered peptide produced by proteolytic cleavage of a small integral membrane protein 20 (Smim20), which acts as an important regulator of energy homeostasis and reproduction. Since dysfunction of reproduction is characteristic in polycystic ovarian syndrome (PCOS), the role of PNX in pathogenesis of PCOS needs further investigation. The objective of this study was to determine expression of Smim20, PNX-14 and its receptor GRP173 in the hypothalamus, ovary and periovarian adipose tissue (PAT) of letrozole induced PCOS rats. Phosphorylation of extracellular signal-regulated kinase (ERK1/2), protein kinases A (PKA) and B (Akt) were also estimated. We observed that PCOS rats had high weight gain and a number of ovarian cyst, high levels of testosterone, luteinizing hormone and PNX-14, while low estradiol. Smim20 mRNA expression was higher in the ovary and PAT, while PNX-14 peptide production was higher only in the ovary of PCOS rat. Moreover, in PCOS rats Gpr173 level was lower in PAT but at the protein level increased only in the ovary. Depending on the tissues, kinases phosphorylation were significantly differ in PCOS rats. Our results showed higher levels of PNX-14 in PCOS rats and indicated some novel findings regarding the mechanisms of PCOS pathophysiology.

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 suppresses food intake, modulates glucoregulatory enzymes, and enhances glycolysis in zebrafish

Phoenixin is a 20-amino acid peptide (PNX-20) cleaved from the small integral membrane protein 20 (SMIM20), with multiple biological roles in mammals. However, its role in nonmammalian vertebrates is poorly understood. This research aimed to determine whether PNX-20 influences feeding and metabolism in zebrafish. The mRNAs encoding SMIM20 and its putative receptor, super conserved receptor expressed in brain 3 (SREB3), are present in both central and peripheral tissues of zebrafish. Immunohistochemical analysis confirmed the presence of PNX-like immunoreactivity in the gut and in zebrafish liver (ZFL) cell line. We also found that short-term fasting (7 days) significantly decreased smim20 mRNA expression in the brain, gut, liver, gonads, and muscle, which suggests a role for PNX-20 in food intake regulation. Indeed, single intraperitoneal injection of 1,000 ng/g body wt PNX-20 reduced feeding in both male and female zebrafish, likely in part by enhancing hypothalamic cart and reducing hypothalamic/gut preproghrelin mRNAs. Furthermore, the present results demonstrated that PNX-20 modulates the expression of genes involved in glucose transport and metabolism in ZFL cells. In general terms, such PNX-induced modulation of gene expression was characterized by the upregulation of glycolytic genes and the downregulation of gluconeogenic genes. A kinetic study of the ATP production rate from both glycolytic and mitochondrial pathways demonstrated that PNX-20-treated ZFL cells exhibited significantly higher ATP production rate associated with glycolysis than control cells. This confirms a positive role for PNX-20 on glycolysis. Together, these results indicate that PNX-20 is an anorexigen with important metabolic roles in zebrafish.