Differential expression of prokineticin receptors by endothelial cells derived from different vascular beds: a physiological basis for distinct endothelial function

The regulation of the expression of prokineticin 1 and its receptors and its mechanism of action in the porcine corpus luteum

Prokineticin 1 (PROK1) is an important factor in pregnancy establishment in pigs, acting at the embryo-maternal interface and the corpus luteum (CL). Estradiol-17β (E2) is the primary pregnancy recognition signal in pigs, and its effects are augmented by luteotropic prostaglandin E2 (PGE2). On the contrary, prostaglandin F2α (PGF2α) exerts mainly a luteolytic effect. The present study aimed to elucidate whether E2, PGE2, and PGF2α regulate the expression of PROK1 and its receptors in the porcine CL and to determine the PROK1 effect on luteal endothelial cells and pathways that may be involved in this regulation. The effects of E2, PGE2, and PGF2α on the expressions of PROK1 and its receptors in the CL were studied using an in vitro model of ultrathin luteal tissue explants model. Additionally, the effects of E2 and PGE2 on the PROK1 system were determined using an in vivo approach, in which the hormones were administered into the uterine lumen to imitate their secretion by embryos. Endothelial cell proliferation was measured using the colorimetric method. E2 acting via estrogen receptors simulated the mRNA and protein expressions of PROK1 and PROKR1 in CL explants in vitro (p < 0.05). The simultaneous action of E2 with PGE2 enhanced the expression of luteal PROK1 mRNA in vitro (p < 0.05). Estradiol-17β acting alone significantly increased PROK1 mRNA levels in vivo, whereas E2 simultaneously administered with PGE2 significantly elevated the PROK1 mRNA expression and PROKR1 mRNA and protein contents in CLs adjacent to uterine horns receiving hormonal infusion compared with CLs adjacent to placebo-treated uterine horns (p < 0.01). The PROK1 protein expression was significantly higher in the CLs of pigs treated with E2, PGE2, and E2 together with PGE2 than in the control group. PGF2α increased the PROK1 mRNA content in CLs on days 12 and 14 of the estrous cycle (p < 0.05). The expression of PROKR2 at the mRNA and protein levels remained unchanged in response to in vitro and in vivo treatments. PROK1 stimulated the proliferation of luteal endothelial cells by activating the MAPK, AKT, and mTOR pathways (p < 0.05). In summary, the luteal expressions of PROK1 and PROKR1 in early pregnancy are regulated by E2 and PGE2. PROK1 stimulates luteal angiogenesis by activating the MAPK, AKT, and mTOR pathways. The regulation of luteal PROK1 expression by PGF2α indicates PROK1's putative role during luteolysis. We conclude that PROK1-PROKR1 signaling supports luteal function during CL rescue in pregnancy in pigs.

Prokineticin 1 is a novel factor regulating porcine corpus luteum function

Prokineticin 1 (PROK1) is a pleiotropic factor secreted by endocrine glands; however, its role has not been studied in the corpus luteum (CL) during pregnancy in any species. The present study aimed to investigate the contribution of PROK1 in regulating processes related to porcine CL function and regression: steroidogenesis, luteal cell apoptosis and viability, and angiogenesis. The luteal expression of PROK1 was greater on Days 12 and 14 of pregnancy compared to Day 9. PROK1 protein expression during pregnancy increased gradually and peaked on Day 14, when it was also significantly higher than that on Day 14 of the estrous cycle. Prokineticin receptor 1 (PROKR1) mRNA abundance increased on Days 12 and 14 of pregnancy, whereas PROKR2 elevated on Day 14 of the estrous cycle. PROK1, acting via PROKR1, stimulated the expression of genes involved in progesterone synthesis, as well as progesterone secretion by luteal tissue. PROK1-PROKR1 signaling reduced apoptosis and increased the viability of luteal cells. PROK1 acting through PROKR1 stimulated angiogenesis by increasing capillary-like structure formation by luteal endothelial cells and elevating angiogenin gene expression and VEGFA secretion by luteal tissue. Our results indicate that PROK1 regulates processes vital for maintaining luteal function during early pregnancy and the mid-luteal phase.

Prokineticins and their G protein-coupled receptors in health and disease

Prokineticins are two conserved small proteins (~8kDa), prokineticin 1 (PROK1; also called EG-VEGF) and prokineticin 2 (PROK2; also called Bv8), with an N-terminal AVITGA sequence and 10 cysteines forming 5 disulfide bridges. PROK1 and PROK2 bind to two highly related G protein-coupled receptors (GPCRs), prokineticin receptor 1 (PROKR1) and prokineticin receptor 2 (PROKR2). Prokineticins and their receptors are widely expressed. PROK1 is predominantly expressed in peripheral tissues, especially steroidogenic organs, whereas PROK2 is mainly expressed in the central nervous system and nonsteroidogenic cells of the testes. Prokineticins signaling has been implicated in several important physiological functions, including gastrointestinal smooth muscle contraction, circadian rhythm regulation, neurogenesis, angiogenesis, pain perception, mood regulation, and reproduction. Dysregulation of prokineticins signaling has been observed in a variety of diseases, such as cancer, ischemia, and neurodegeneration, in which prokineticins signaling seems to be a promising therapeutic target. Based on the phenotypes of knockout mice, PROKR2 and PROK2 have recently been identified as causative genes for idiopathic hypogonadotropic hypogonadism, a developmental disorder characterized by impaired development of gonadotropin-releasing hormone neurons and infertility. In vitro functional studies with these disease-associated PROKR2 mutations uncovered some novel features for this receptor, such as biased signaling, which may be used to understand GPCR signaling regulation in general.

Can prokineticin prevent obesity and insulin resistance?

PURPOSE OF REVIEW

Because of its increasing prevalence and morbi-mortality, obesity is a major health problem. Obesity etiology includes a combination of excess dietary calories and decreased physical activity, coupled with either predisposing genetic factors or metabolic disorders such as insulin resistance. Adipose tissue secretes several metabolically important proteins known as 'adipokines' that play a major role in obesity and insulin resistance. High levels of a newly identified group of adipokines, called prokineticins, have been found in obese adipose tissues. Prokineticins are peptide hormones released principally from macrophages and reproductive organs. They act on the G protein-coupled receptors PKR1 and PKR2. This review aims to provide an overview of current knowledge of the role of prokineticins and their receptors in the development of obesity and insulin resistance.

RECENT FINDINGS

The principal biological effect of prokineticins in the central nervous system is the control of food intake. Nevertheless, peripheral biological effects of prokineticin are associated with increasing insulin sensitivity and suppressing the adipose tissue expansion.

SUMMARY

We outline the biological significance of the central and peripheral effects of prokineticins, and the potential of their receptors as targets for the treatment of obesity and insulin resistance.

The role of hypoxia-induced genes in ovarian angiogenesis

The hypoxic microenvironment that occurs in fast-growing tissue such as the corpus luteum (CL) is a major contributor to its ability to survive via the induction of an intricate vascular network. Cellular responses to hypoxia are mediated by hypoxia-inducible factor-1 (HIF-1), an oxygen-regulated transcriptional activator. HIF-1, a heterodimer consisting of a constitutively-expressed β subunit and an oxygen-regulated α subunit, binds to the hypoxia responsive element (HRE) present in the promoter regions of responsive genes. This review summarises evidence for the involvement of hypoxia and HIF-1α in CL development and function. Special emphasis is given to hypoxia-induced, luteal cell-specific expression of multiple genes (vascular endothelial growth factor A (VEGFA), fibroblast growth factor 2 (FGF-2), prokineticin receptor 2 (PK-R2), stanniocalcin 1 (STC-1) and endothelin 2 (EDN-2) that participate in the angiogenic process during CL formation.

Imbalance of expression of bFGF and PK1 is associated with defective maturation and antenatal placental insufficiency

OBJECTIVE

Defective placental maturation is associated with restricted functional capacity and adverse perinatal fetal outcomes. The aim of the study was a comparative analysis of the role of mRNA expression of various angiogenic factors in placental maturation defects.

STUDY DESIGN

We examined the mRNA expression patterns of prokineticin 1 (PK1), its receptors (PKRs), basic-fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) in tissue from third-trimester placentae that exhibited delayed or accelerated villous maturation.

RESULTS

The expression of PK1 and PKR2 was elevated in placental tissue exhibiting accelerated maturation and a predominant differentiation of terminal villi. The opposite was found in tissue exhibiting delayed maturation and deficiency of the terminal villi. In addition, low expression of bFGF correlated with the predominant differentiation of terminal villi, whereas the opposite was observed when terminal villi were deficient. The expression of VEGF, PIGF, and PKR1 showed no significant differences between the groups.

CONCLUSION

Defective placental maturation is associated with an imbalance of expression of bFGF and PK1. Our results demonstrate an involvement of the PK1/PKR2-signalling pathway in the regulation of the functional adequate capillarization in late pregnancy. We propose the bFGF/PK1-ratio as a monitor of placental function and a possible indicator of latent clinical problems, such as placental dysfunction leading to fetal hypoxia.

Endothelial microparticles increase in mitral valve disease and impair mitral valve endothelial function

Mitral valve endothelial cells are important for maintaining lifelong mitral valve integrity and function. Plasma endothelial microparticles (EMPs) increased in various pathological conditions related to activation of endothelial cells. However, whether EMPs will increase in mitral valve disease and their relationship remains unclear. Here, 81 patients with mitral valve disease and 45 healthy subjects were analyzed for the generation of EMPs by flow cytometry. Human mitral valve endothelial cells (HMVECs) were treated with EMPs. The phosphorylation of Akt and endothelial nitric oxide synthase (eNOS), the association of eNOS and heat shock protein 90 (HSP90), and the generation of nitric oxide (NO) and superoxide anion (O(2)(∙-)) were measured. EMPs were increased significantly in patients with mitral valve disease compared with those in healthy subjects. EMPs were negatively correlated with mitral valve area in patients with isolated mitral stenosis. EMPs were significantly higher in the group with severe mitral regurgitation than those in the group with mild and moderate mitral regurgitation. Furthermore, EMPs were decreased dramatically in both Akt and eNOS phosphorylation and the association of HSP90 with eNOS in HMVECs. EMPs decreased NO production but increased O(2)(∙-) generation in HMVECs. Our data demonstrated that EMPs were significantly increased in patients with mitral valve disease. The increase of EMPs can in turn impair HMVEC function by inhibiting the Akt/eNOS-HSP90 signaling pathway. These findings suggest that EMPs may be a therapeutic target for mitral valve disease.

Revisiting the role of hCG: new regulation of the angiogenic factor EG-VEGF and its receptors

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF) is an angiogenic factor reported to be specific for endocrine tissues, including the placenta. Its biological activity is mediated via two G protein-coupled receptors, prokineticin receptor 1 (PROKR1) and prokineticin receptor 2 (PROKR2). We have recently shown that (i) EG-VEGF expression peaks between the 8th and 11th weeks of gestation, (ii) its mRNA and protein levels are up-regulated by hypoxia, (iii) EG-VEGF is a negative regulator of trophoblast invasion and (iv) its circulating levels are increased in preeclampsia (PE), the most threatening pathology of pregnancy. Here, we investigated the regulation of the expression of EG-VEGF and its receptors by hCG, a key pregnancy hormone that is also deregulated in PE. During the first trimester of pregnancy, hCG and EG-VEGF exhibit the same pattern of expression, suggesting that EG-VEGF is potentially regulated by hCG. Both placental explants (PEX) and primary cultures of trophoblasts from the first trimester of pregnancy were used to investigate this hypothesis. Our results show that (i) LHCGR, the hCG receptor, is expressed both in cyto- and syncytiotrophoblasts, (ii) hCG increases EG-VEGF, PROKR1 and PROKR2 mRNA and protein expression in a dose- and time-dependent manner, (iii) hCG increases the release of EG-VEGF from PEX conditioned media, (iv) hCG effects are transcriptional and post-transcriptional and (v) the hCG effects are mediated by cAMP via cAMP response elements present in the EG-VEGF promoter region. Altogether, these results demonstrate a new role for hCG in the regulation of EG-VEGF and its receptors, an emerging regulatory system in placental development.

Regulation of angiogenesis-related prostaglandin f2alpha-induced genes in the bovine corpus luteum

We recently compared prostaglandin F2alpha (PG)-induced global gene expression profiles in PG-refractory, bovine corpus luteum (CL) collected on Day 4 of the estrous cycle, versus PG-responsive, Day 11 CL. Transcriptome analyses led us to study the regulation of angiogenesis-related genes by PG and their functions in luteal endothelial cells (ECs). We found that PG regulated angiogenesis-modulating factors in a luteal stage-dependent way. A robust increase in FGF2 expression (mRNA and protein) occurred in the PG-refractory Day 4 CL promoting CL survival and function. Inhibitors of FGF2 action, thrombospondin 1 and 2, their receptor (CD36), and PTX3 were upregulated by PG specifically in Day 11 CL undergoing luteolysis. VEGF mRNA decreased 4 h post-PG in both Day 4 and Day 11 CL. The resulting destabilization of blood vessels in Day 11 CL is expected to weaken the gland and reduce its hormonal output. These genes were expressed in dispersed luteal ECs and steroidogenic cells; however, thrombospondin 1 and FGF2 were more abundant in luteal ECs. Expression of such genes and their ability to modulate FGF2 actions were investigated. Similar to its in vivo effect, PG, in vitro, stimulated the expression of thrombospondins and PTX3 genes in several luteal cell models. Importantly, these factors influenced the angiogenic properties of luteal ECs. FGF2 dose-dependently enhanced cell migration and proliferation, whereas thrombospondin 1 and PTX3 inhibited FGF2 actions in luteal ECs. Collectively, the data presented here suggest that, by tilting the balance between pro- and antiangiogenic factors, PG can potentially control the ability of the CL to resist or advance toward luteolysis.

The role of the prokineticin 2 pathway in human reproduction: evidence from the study of human and murine gene mutations

A widely dispersed network of hypothalamic GnRH neurons controls the reproductive axis in mammals. Genetic investigation of the human disease model of isolated GnRH deficiency has revealed several key genes crucial for GnRH neuronal ontogeny and GnRH secretion. Among these genes, prokineticin 2 (PROK2), and PROK2 receptor (PROKR2) have recently emerged as critical regulators of reproduction in both mice and humans. Both prok2- and prokr2-deficient mice recapitulate the human Kallmann syndrome phenotype. Additionally, PROK2 and PROKR2 mutations are seen in humans with Kallmann syndrome, thus implicating this pathway in GnRH neuronal migration. However, PROK2/PROKR2 mutations are also seen in normosmic GnRH deficiency, suggesting a role for the prokineticin signaling system in GnRH biology that is beyond neuronal migration. This observation is particularly surprising because mature GnRH neurons do not express PROKR2. Moreover, mutations in both PROK2 and PROKR2 are predominantly detected in the heterozygous state with incomplete penetrance or variable expressivity frequently seen within and across pedigrees. In some of these pedigrees, a "second hit" or oligogenicity has been documented. Besides reproduction, a pleiotropic physiological role for PROK2 is now recognized, including regulation of pain perception, circadian rhythms, hematopoiesis, and immune response. Therefore, further detailed clinical studies of patients with PROK2/PROKR2 mutations will help to map the broader biological role of the PROK2/PROKR2 pathway and identify other interacting genes/proteins that mediate its molecular effects in humans.

Divergent roles of prokineticin receptors in the endothelial cells: angiogenesis and fenestration

Prokineticins are secreted peptides that activate two G protein-coupled receptors: PKR1 and PKR2. Prokineticins induce angiogenesis and fenestration, but the cognate receptors involved in these functions are unknown. We hypothesized a role for prokineticin receptor signaling pathways and expression profiles in determining the selective effects of prokineticins on coronary endothelial cells (H5V). Activation of the PKR1/MAPK/Akt signaling pathway stimulates proliferation, migration, and angiogenesis in H5V cells, in which PKR1 predominates over PKR2. PKR1 was colocalized with Gα11 and was internalized following the stimulation of these cells with prokineticin-2. Knock down of PKR1 or Gα11 expression in H5V cells effectively inhibited prokineticin-2-induced vessel formation and MAPK/Akt activation, indicating a role for PKR1/Gα11 in this process. However, in conditions in which PKR2 predominated over PKR1, these cells displayed a fenestrated endothelial cell phenotype. H5V cells overexpressing PKR2 displayed large numbers of multivesicular bodies and caveolar clusters and a disruption of the distribution of zonula occluden-1 tight junction protein. Prokineticin-2 induced the colocalization of PKR2 with Gα12, and activated Gα12, which bound to zonula occluden-1 to trigger the degradation of this protein in these cells. Prokineticin-2 induced the formation of vessel-like structures by human aortic endothelial cells expressing only PKR1, and disorganized the tight junctions in human hepatic sinusoidal endothelial cells expressing only PKR2, confirming the divergent roles of these receptors. Our findings show the functional characteristics of coronary endothelial cells depend on the expression of PKR1 and PKR2 levels and the divergent signaling pathways used by these receptors.

Prokineticin receptors in cardiovascular function: foe or friend?

Prokineticins are small secreted bioactive peptides, comprising two classes: prokineticin-1 and prokineticin-2. They exert their biological activity by binding to two G-protein-coupled receptors: prokineticin receptor (PKR) 1 and 2. Recent data have demonstrated that PKR1 induces postnatal neovasculogenesis by activating adult epicardial-derived progenitor cell differentiation, whereas myocardial PRK2 signaling confers detrimental actions on cardiomyocytes, leading to dilated cardiomyopathy and release of an unknown paracrine factor to induce capillary fenestration and vascular leakage. The knowledge gained from these studies leads to a model in which PKR1 and PKR2 signaling exert opposing actions in heart physiology and pathophysiology and facilitate the discovery of specific agonists and antagonists targeting PKR1 and PKR2 for possible use in treatment of cardiovascular diseases.

Induction of heparanase in bovine granulosa cells by luteinizing hormone: possible role during the ovulatory process

Follicular development, follicular rupture, and corpus luteum (CL) formation are accompanied by extensive tissue remodeling. We examined whether heparanase (HPSE), which cleaves heparan sulfate glycosaminoglycans, is induced during these processes. Prostaglandin F2alpha injection, which initiated luteolysis and the development of a preovulatory follicle, moderately increased HPSE mRNA in bovine granulosa cells (GCs). GnRH, used to induce gonadotropin surge, markedly augmented HPSE mRNA levels 12 h after its injection. The temporal pattern of HPSE gene expression in follicular-luteal transition was further examined in follicles collected before, and 4, 10, 20, 25, and 60 h after GnRH injection. HPSE mRNA increased transiently 10-20 h after GnRH injection to levels 10-fold higher than in untreated heifers. HPSE protein levels were similarly elevated 20 h after GnRH injection in GCs, but not in the theca layer. Cyclooxygenase-2 (PTGS2) mRNA peaked before ovulation when HPSE levels returned to baseline levels. HPSE mRNA abundance also remained low in the CLs. The antiprogesterone, RU-486, elevated HPSE levels in GC culture, suggesting that progesterone secreted by CLs may inhibit HPSE. HPSE immunostaining was more abundant in GCs than thecae. In cultured GCs, LH induced a transient increase in HPSE mRNA 3-6 h after its addition, but not at 24 h. However, PTGS2 mRNA was clearly induced at this time. These findings suggest that: 1) HPSE may play a role in ovulation but much less so during CL development, and 2) GC-derived HSPE may be a novel member of the LH-induced extracellular matrix-degrading enzyme family and may contribute to follicular rupture.

Intact blood-perilymph barrier in the rat after impulse noise trauma

CONCLUSION

The permeability of the blood-labyrinth barrier for radioactive mannitol was unchanged after impulse noise trauma. The present findings are contradictory to the theory of an increased permeability in the blood-labyrinth barrier as a result of extensive noise exposure.

OBJECTIVE

Noise trauma is reported to cause multiple effects on the cochlea including mechanical and metabolic damage. The aim of the study was to observe the effects of impulse noise on cochlear homeostasis.

MATERIALS AND METHODS

A well-established rat model was used for evaluation of the early effects of impulse noise trauma on the integrity of the blood-perilymph barrier. To evaluate whether a blood-perilymph barrier disruption contributes to cochlear injury after impulse noise, the paracellular transport of radioactive mannitol into scala vestibuli perilymph (PLV) and electrolyte concentration in perilymph were estimated. Thirteen animals exposed to synthesized impulses of 160 dB SPL peak value, at a rate of 100 pulses, were designed as the study group and 15 rats not exposed to noise were designed as the control group. After mannitol infusion each ear of the animal in the study group was separately exposed to impulse noise and PLV samples were taken during 2 h post-infusion. In the control group, corresponding PLV samples were taken after mannitol injection.

RESULTS

At 2 h after mannitol infusion there was no difference in PLV mannitol concentration in the study group and control group (21.5%+/-2.2 and 20.5%+/-2.1, respectively). Impulse noise had no effect on the electrochemical composition of PLV.

Peripheral blood B lymphocytes derived from patients with idiopathic pulmonary arterial hypertension express a different RNA pattern compared with healthy controls: a cross sectional study

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and still incurable disease. Research of IPAH-pathogenesis is complicated by the lack of a direct access to the involved tissue, the human pulmonary vasculature. Various auto-antibodies have been described in the blood of patients with IPAH. The purpose of the present work was therefore to comparatively analyze peripheral blood B lymphocyte RNA expression characteristics in IPAH and healthy controls.

METHODS

Patients were diagnosed having IPAH according to WHO (mean pulmonary arterial pressure > or = 25 mmHg, pulmonary capillary occlusion pressure < or = 15 mmHg, absence of another explaining disease). Peripheral blood B-lymphocytes of patients and controls were immediately separated by density gradient centrifugation and magnetic beads for CD19. RNA was thereafter extracted and analyzed by the use of a high sensitivity gene chip (Affymetrix HG-U133-Plus2) able to analyze 47000 transcripts and variants of human genes. The array data were analyzed by two different softwares, and up-and down-regulations were defined as at least 1.3 fold with standard deviations smaller than fold-changes.

RESULTS

Highly purified B-cells of 5 patients with IPAH (mean pulmonary artery pressure 51 +/- 13 mmHg) and 5 controls were analyzed. Using the two different analyzing methods we found 225 respectively 128 transcripts which were up-regulated (1.3-30.7 fold) in IPAH compared with healthy controls. Combining both methods, there were 33 overlapping up-regulated transcripts and no down-regulated B-cell transcripts.

CONCLUSION

Patients with IPAH have a distinct RNA expression profile of their peripheral blood B-lymphocytes compared to healthy controls with some clearly up-regulated genes. Our finding suggests that in IPAH patients B cells are activated.

Biological function of prokineticins

Secreted peptides have been implicated in diverse physiological functions. Prokineticins are a pair of regulatory peptides that signal through two highly homologous G protein-coupled receptors. Prokineticins possess a unique structural motif of five disulfide bonds and conserved N-terminal stretches. Diverse biological functions, ranging from development to adult physiology, have been attributed to prokineticins. Herein we provide an overview of current knowledge of this interesting pair of regulatory peptides.

Bv8/Prokineticin proteins and their receptors

The Bv8/Prokineticins (PKs) are a new family of peptides identified in frog, fish, reptiles and mammals that signal through two highly homologous G-protein coupled receptors, PKR1 and PKR2. Bv8/PK proteins possess a unique structural motif comprising five disulfide bonds and a completely conserved N-terminal hexapeptide sequence that is essential for the peptide's biological activities. Over the past few years, several biological functions of Bv8/PK proteins have been elucidated. This review considers all the published data on the action and physiological role of this new biological system implicated in angiogenesis and neurogenesis, in reproduction and cancer and in regulating physiological functions that underly circadian rhythms, such as the sleep/wake cycle, hormone secretion and ingestive behaviors. The high expression level of human Bv8/PK2 in bone marrow, lymphoid organs and leukocytes suggested an involvement of these peptides in hematopoiesis and in inflammatory and immunomodulatory processes. Our review highlights the role of the Bv8/PK and their receptor system in setting the pain threshold under normal and pathological conditions.