Canine cystic endometrial hyperplasia and pyometra may downregulate neuropeptide phoenixin and GPR173 receptor expression

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.

The tissue distribution of nucleobindin-2/nesfatin-1 in the reproductive organs of bitches with regard to the animal's age and body weight

Introduction

Neuropeptide nesfatin-1, a nucleobindin-2 derivative, plays a role in regulating food intake, energy metabolism and body weight. It also interacts with the hypothalamic-pituitary-gonadal axis and has functions in the reproductive system. However, its impact on the canine reproductive tract has not been well documented. This study aimed to investigate the potential role of nesfatin-1 in canine ovarian activity and uterine function.

Material and Methods

Tissue and peripheral blood samples were collected from 60 bitches of various ages and body condition scores (BCS). Analyses included real-time PCR, immunofluorescence examinations and ELISA tests.

Results

Higher level of nucleobindin-2 mRNA were found in the ovarian tissue of both younger and elderly overweight dogs (BCS > 5/9). The elevated expression of nesfatin-1 was observed in the uterine tissues of overweight dogs (BCS > 5/9) compared to its expression in animals in optimal body condition (BCS = 4/9). This finding was consistent with higher nesfatin-1 levels in the peripheral blood of overweight dogs.

Conclusion

The distribution and expression of nesfatin-1 in canine reproductive organs vary depending on the animal's age and body weight. The role of nesfatin-1 in the reproductive system is influenced by the animal's body condition and the extent of surplus adipose tissue, which may have significant implications for reproductive functions.

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.

Predisposing Factors for Pseudoplacentational Endometrial Hyperplasia or Cystic Endometrial Hyperplasia in Dogs and Their Association with Pyometra

Pseudoplacentational endometrial hyperplasia (PEH) and cystic endometrial hyperplasia (CEH) are both hyperplastic conditions that may occur in the canine uterus during diestrus. CEH can impair fertility, and, although the consequences of PEH are poorly known, this condition is significantly associated with pyometra. The aim of this study was to investigate frequencies of both PEH and CEH in female dogs according to age, size, breed, and breed group. Uteri from 300 female dogs were sampled and processed for histopathologic analyses. Lesions were identified, and frequencies were statistically compared. PEH was significantly more frequent in dogs between 4 and 12 years of age and significantly less frequent in Yorkshires than Shih-tzus, as well as in the breed group that includes Brazilian Terriers and Yorkshires. CEH was significantly more frequent in dogs older than 12 years, but no breed predisposition was observed. The frequency of PEH was significantly higher than that of CEH. The frequency of pyometra in PEH cases was significantly higher than endometritis or uterus without inflammation. This study identified age, breed group, and size as predisposing factors for PEH and further demonstrated the association between this condition and pyometra in dogs.

Nesfatin-1 expression and blood plasma concentration in female dogs suffering from cystic endometrial hyperplasia and pyometra and its possible interaction with phoenixin-14

BACKGROUND

Nesfatin-1 is a neuropeptide that regulates the hypothalamic-pituitary-gonadal axis and may play a role in uterus function. It is co-expressed with other peptides, such as phoenixin, which can influence sex hormone secretion. Our previous research has confirmed that phoenixin-14 is involved in the development of cystic endometrial hyperplasia (CEH) and pyometra in dogs. Therefore, based on the similarities and interactions between these neuropeptides, we hypothesized that nesfatin-1 might also regulate the reproductive system in dogs. This study aimed to determine the expression of nesfatin-1 and its interaction with phoenixin-14 in dogs with CEH or pyometra compared to healthy females, and concerning animals' body condition score (BCS 4-5/9 vs. BCS > 5/9).

RESULTS

The analysis of nesfatin-1 in the uterus of bitches consisted of qPCR, western blot and immunofluorescence assays, and ELISAs. The results showed significantly higher nesfatin-1 encoding gene, nucleobindin-2 mRNA (Nucb2) and nesfatin-1 protein expression in overweight females and those suffering from CEH or pyometra compared to healthy animals. The immunoreactivity of nesfatin-1 was elevated in the uteri of bitches with higher BCS > 5/9. Moreover, nesfatin-1 blood concentrations increased in all examined overweight bitches. In the case of phoenixin signals, we found opposite results, regardless of the female body condition score.

CONCLUSION

The etiology of CEH and pyometra are not fully known, although we have expanded the level of knowledge with respect to the possible interaction of nesfatin-1 and phoenixin in female dogs' uteri. They interact oppositely. With increasing female body weight, the expression of nesfatin-1 in the uterus and its peripheral blood concentration increased. However, for female dogs affected by CEH and pyometra, a decreased level of phoenixin-14, irrespective of their body condition score is characteristic. This knowledge could be crucial in the development of biomarkers for these conditions, which may lead to earlier recognition.

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 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.

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.