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

A career in numbers: A citation network analysis of the work of RP Millar and his contribution to GnRH research

Here, we reflect on the long career in neuroendocrinology of a single, highly productive scientist ('Bob' Millar), by analysing his oeuvre of published papers through the lens of citation metrics. We use citation network analysis in a novel manner to identify the specific topics to which his papers have made a particular contribution, allowing us to compare the citations of his papers with those of contemporary papers on the same topic, rather than on the same broad field as generally used to normalise citations. It appears that citation rates are highest for topics on which Bob has published a relatively large number of papers that have become core to a tightly-knit community of authors that cite each other. This analysis shows that an author's impact depends on the existence of a receptive community that is alert to the potential utility of papers from that author, and which uses, amplifies, extends and qualifies the contents of their papers-activities that entail reciprocal citation between authors. The obvious conclusion is that a scientist's impact depends on the use that his or her contemporaries make of his or her contributions, rather than on the contributions in themselves.

Intracerebroventricular PROK2 infusion could increase the secretion of male reproductive hormones by stimulating the HPG axis

BACKGROUND

Prokineticin 2 (PROK2), an important neuropeptide that plays a key role in the neuronal migration of gonadotropin-releasing hormone (GnRH) in the hypothalamus, is known to have regulatory effects on the gonads. In the present study, the impact of intracerebroventricular (icv) PROK2 infusion on hypothalamic-pituitary-gonadal axis (HPG) hormones, testicular tissues, and sperm concentration was investigated.

METHODS AND RESULTS

Rats were randomly divided into four groups: control, sham, PROK2 1.5 and PROK2 4.5. Rats in the PROK2 1.5 and PROK2 4.5 groups were administered 1.5 nmol and 4.5 nmol PROK2 intracerebroventricularly for 7 days via an osmotic mini pump (1 µl/h), respectively. Rat blood serum follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone hormone levels were determined with the ELISA method in the blood samples after 7 days of infusion. GnRH mRNA expression was determined with the RT-PCR in hypothalamus tissues. analyze Sperm concentration was determined, and testicular tissue was examined histologically with the hematoxylin-eosin staining method. It was observed that GnRH mRNA expression increased in both PROK2 infusion groups. Serum FSH, LH and testosterone hormone levels also increased in these groups. Although sperm concentration increased in PROK2 infusion groups when compared to the control and sham, the differences were not statistically significant. Testicular tissue seminiferous epithelial thickness was higher in the PROK2 groups when compared to the control and sham groups.

CONCLUSION

The present study findings demonstrated that icv PROK2 infusion induced the HPG axis. It could be suggested that PROK2 could be a potential agent in the treatment of male infertility induced by endocrinological defects.

PROKR2 Mutations in Patients with Short Stature Who Have Isolated Growth Hormone Deficiency and Multiple Pituitary Hormone Deficiency

Objective

Recent reports have indicated the role of the prokineticin receptor 2 gene (PROKR2) in the etiology of pituitary hormone deficiencies, suggesting a potential role for the PROK2 pathway in pituitary development, in addition to its role in gonadotropin releasing hormone-expressing neuron development. Here, we present the clinical and molecular findings of four patients with PROKR2 mutations.

Methods

Next-generation targeted sequencing was used to screen 25 genes in 59 unrelated patients with multiple pituitary hormone deficiency (MPHD), isolated growth hormone (GH) deficiency, or idiopathic short stature.

Results

Two different, very rare PROKR2 missense alterations classified as pathogenic (NM_144773.4:c.518T>G; NP_658986.1:p. (Leu173Arg)) and likely pathogenic (NM_144773.4:c.254G>A; NP_658986.1:p.(Arg85His)) were identified in four patients in heterozygous form. Patient 1 and Patient 2 presented with short stature and were diagnosed as GH deficiency. Patient 3 and Patient 4 presented with central hypothyroidism and cryptorchidism and were diagnosed as MPHD. No other pathogenic alterations were detected in the remaining 24 genes related to short stature, MPHD, and hypogonadotropic hypogonadism. Segregation analysis revealed asymptomatic or mildly affected carriers in the families.

Conclusion

PROKR2 dominance should be kept in mind as a very rare cause of GH deficiency and MPHD. Expressional variation or lack of penetrance may imply oligogenic inheritance or other environmental modifiers in individuals who are heterozygous carriers.

Therapeutic Potential of Targeting Prokineticin Receptors in Diseases

The prokineticins (PKs) were discovered approximately 20 years ago as small peptides inducing gut contractility. Today, they are established as angiogenic, anorectic, and proinflammatory cytokines, chemokines, hormones, and neuropeptides involved in variety of physiologic and pathophysiological pathways. Their altered expression or mutations implicated in several diseases make them a potential biomarker. Their G-protein coupled receptors, PKR1 and PKR2, have divergent roles that can be therapeutic target for treatment of cardiovascular, metabolic, and neural diseases as well as pain and cancer. This article reviews and summarizes our current knowledge of PK family functions from development of heart and brain to regulation of homeostasis in health and diseases. Finally, the review summarizes the established roles of the endogenous peptides, synthetic peptides and the selective ligands of PKR1 and PKR2, and nonpeptide orthostatic and allosteric modulator of the receptors in preclinical disease models. The present review emphasizes the ambiguous aspects and gaps in our knowledge of functions of PKR ligands and elucidates future perspectives for PK research. SIGNIFICANCE STATEMENT: This review provides an in-depth view of the prokineticin family and PK receptors that can be active without their endogenous ligand and exhibits "constitutive" activity in diseases. Their non- peptide ligands display promising effects in several preclinical disease models. PKs can be the diagnostic biomarker of several diseases. A thorough understanding of the role of prokineticin family and their receptor types in health and diseases is critical to develop novel therapeutic strategies with safety concerns.

Inferring circadian gene regulatory relationships from gene expression data with a hybrid framework

BACKGROUND

The central biological clock governs numerous facets of mammalian physiology, including sleep, metabolism, and immune system regulation. Understanding gene regulatory relationships is crucial for unravelling the mechanisms that underlie various cellular biological processes. While it is possible to infer circadian gene regulatory relationships from time-series gene expression data, relying solely on correlation-based inference may not provide sufficient information about causation. Moreover, gene expression data often have high dimensions but a limited number of observations, posing challenges in their analysis.

METHODS

In this paper, we introduce a new hybrid framework, referred to as Circadian Gene Regulatory Framework (CGRF), to infer circadian gene regulatory relationships from gene expression data of rats. The framework addresses the challenges of high-dimensional data by combining the fuzzy C-means clustering algorithm with dynamic time warping distance. Through this approach, we efficiently identify the clusters of genes related to the target gene. To determine the significance of genes within a specific cluster, we employ the Wilcoxon signed-rank test. Subsequently, we use a dynamic vector autoregressive method to analyze the selected significant gene expression profiles and reveal directed causal regulatory relationships based on partial correlation.

CONCLUSION

The proposed CGRF framework offers a comprehensive and efficient solution for understanding circadian gene regulation. Circadian gene regulatory relationships are inferred from the gene expression data of rats based on the Aanat target gene. The results show that genes Pde10a, Atp7b, Prok2, Per1, Rhobtb3 and Dclk1 stand out, which have been known to be essential for the regulation of circadian activity. The potential relationships between genes Tspan15, Eprs, Eml5 and Fsbp with a circadian rhythm need further experimental research.

Sex differences in the coexpression of prokineticin receptor 2 and gonadal steroids receptors in mice

Loss-of-function mutations in prokineticin 2 (PROK2) and the cognate receptor prokineticin receptor 2 (PROKR2) genes have been implicated in reproductive deficits characteristic of Kallmann Syndrome (KS). Knock out of Prokr2 gene produces the KS-like phenotype in mice resulting in impaired migration of gonadotropin releasing hormone (GnRH) neurons, olfactory bulb dysgenesis, and infertility. Beyond a developmental role, pharmacological and genetic studies have implicated PROKR2 in the control of the estrous cycle in mice. However, PROKR2 is expressed in several reproductive control sites but the brain nuclei associated with reproductive control in adult mice have not been defined. We set out to determine if ProkR2 neurons in both male and female mouse brains directly sense changes in the gonadal steroids milieu. We focused on estrogen receptor α (ERα) and androgen receptor (AR) due to their well-described function in reproductive control via actions in the brain. We found that the ProkR2-Cre neurons in the posterior nucleus of the amygdala have the highest colocalization with ERα and AR in a sex-specific manner. Few colocalization was found in the lateral septum and in the bed nucleus of the stria terminalis, and virtually no colocalization was observed in the medial amygdala. Our findings indicate that the posterior nucleus of the amygdala is the main site where PROKR2 neurons may regulate aspects of the reproductive function and social behavior in adult mice.

Genetic variants of G-protein coupled receptors associated with pubertal disorders

Background

The human hypothalamic-pituitary-gonadal (HPG) axis is the regulatory center for pubertal development. This axis involves six G-protein coupled receptors (GPCRs) encoded by KISS1R, TACR3, PROKR2, GNRHR, LHCGR, and FSHR.

Methods

Previous studies have identified several rare variants of the six GPCR genes in patients with pubertal disorders. In vitro assays and animal studies have provided information on the function of wild-type and variant GPCRs.

Main Findings

Of the six GPCRs, those encoded by KISS1R and TACR3 are likely to reside at the top of the HPG axis. Several loss-of-function variants in the six genes were shown to cause late/absent puberty. In particular, variants in KISS1R, TACR3, PROKR2, and GNRHR lead to hypogonadotropic hypogonadism in autosomal dominant, recessive, and oligogenic manners. Furthermore, a few gain-of-function variants of KISS1R, PROKR2, and LHCGR have been implicated in precocious puberty. The human HPG axis may contain additional GPCRs.

Conclusion

The six GPCRs in the HPG axis govern pubertal development through fine-tuning of hormone secretion. Rare sequence variants in these genes jointly account for a certain percentage of genetic causes of pubertal disorders. Still, much remains to be clarified about the molecular network involving the six GPCRs.

Phenotypic and genotypic landscape of PROKR2 in neuroendocrine disorders

Prokineticin receptor 2 (PROKR2) encodes for a G-protein-coupled receptor that can bind PROK1 and PROK2. Mice lacking Prokr2 have been shown to present abnormal olfactory bulb formation as well as defects in GnRH neuron migration. Patients carrying mutations in PROKR2 typically present hypogonadotropic hypogonadism, anosmia/hyposmia or Kallmann Syndrome. More recently variants in PROKR2 have been linked to several other endocrine disorders. In particular, several patients with pituitary disorders have been reported, ranging from mild phenotypes, such as isolated growth hormone deficiency, to more severe ones, such as septo-optic dysplasia. Here we summarize the changing landscape of PROKR2-related disease, the variants reported to date, and discuss their origin, classification and functional assessment.

Hypogonadism in Males With Genetic Neurodevelopmental Syndromes

Genetic syndromes that affect the nervous system may also disrupt testicular function, and the mechanisms for these effects may be interrelated. Most often neurological signs and symptoms predominate and hypogonadism remains undetected and untreated, while in other cases, a thorough evaluation of a hypogonadal male reveals previously unrecognized ataxia, movement disorder, muscle weakness, tremor, or seizures, leading to a syndromic diagnosis. Androgen deficiency in patients with neurological diseases may aggravate muscle weakness and fatigue and predispose patients to osteoporosis and obesity. The purpose of this mini review is to provide a current understanding of the clinical, biochemical, histologic, and genetic features of syndromes in which male hypogonadism and neurological dysfunction may coexist and may be encountered by the clinical endocrinologist.

Prokineticin 2/PROK2 and Male Infertility

Male infertility represents about 50% of the causes of infertility in couples. The diagnosis process represents an important procedure for defining, when possible, the causes and approaching treatments (pharmacological, surgical) aimed at overcoming the problem. Several scientific studies have set out to discover early and indicative markers capable of providing information on the biological origin of infertility and increase current knowledge in the context of new potential therapeutic approaches. The prokineticin system (PROK) consists of the prokineticin 1 (PROK1) and prokineticin 2 (PROK2) proteins. Through the activation of two G-protein receptors (PROKR1 and PROKR2) regulate a wide range of biological functions, including gastrointestinal motility, circadian rhythm regulation, neurogenesis, angiogenesis, pain perception, and mood regulation. Several studies have highlighted the crucial role of the PROK system in the development and maturation of both male and female human reproductive organs. Particularly in men, the PROK system represents a new system useful to clarify some aspects of testicular pathophysiology and provide new potential hypotheses for therapeutic intervention. This narrative review aims to illustrate the state of the art regarding, in particular, the role of PROK2 in male infertility.

Biallelic PROKR2 variants and congenital hypogonadotropic hypogonadism: a case report and a literature review

Congenital hypogonadotropic hypogonadism (CHH) is a rare disorder that causes gonadotropin-releasing hormone (GnRH) deficiency and sexual immaturity. CHH may accompany an abnormal sense of smell (Kallmann syndrome, KS) or no such manifestation (normosmic-CHH). This unusual combination of manifestations is explained by the fact that GnRH neurons originate in the olfactory placode and migrate to the forebrain during embryogenesis. We describe the case of a 31-year-old man with normosmic-CHH, who also had obesity, type 2 diabetes and intellectual disability. He was noticed to have sexual immaturity (small testes with no pubic hair) at age 20 years, when diabetic ketoacidosis developed. Basal and GnRH-stimulated levels of LH (1.0→12.0 IU/L) and FSH (1.9→6.1 IU/L) were detectable but low. The results of the T&T olfactometer and the Alinamin test were definitely normal, with an anatomically normal olfactory system on MRI. Sequencing of 22 CHH-related genes was performed, and compound heterozygous PROKR2 variants were identified: one was a previously known loss-of-function variant (p.Trp178Ser) and the other was a nonsense variant (p.Trp212*). Through a literature review, we found 22 patients (including our patient) with CHH due to biallelic PROKR2 variants, which led us to recognize that most of the patients (86%) were diagnosed with KS. Clinical observations in this study indicate that, even though they have CHH, biallelic PROKR2 variant carriers may have a normal olfactory system as well as presumably normal migration of GnRH neurons. This suggests that the PROK2-PROKR2 pathway affects the function of GnRH neurons after their migration.

CgATP synthase β subunit involved in the regulation of haemocytes proliferation as a CgAstakine receptor in Crassostrea gigas

Astakine is considered as an endogenous cytokine-like factor of prokineticin homologue in invertebrate. Recently, an astakine homologue (CgAstakine) has been identified and characterized in oyster Crassostrea gigas. In the present study, a CgATP synthase β subunit was identified as the receptor of CgAstakine in C. gigas. There was an ATP-synt_ab_N domain and an AAA domain in the CgATP synthase β subunit protein. The mRNA transcripts of CgATP synthase β subunit were detected in all tested tissues, with the highest expression level in hepatopancreas and gills, which was 109.11-fold (p < 0.01) and 97.21-fold (p < 0.01) of that in labial palps, respectively. After rCgAstakine stimulation, the mRNA transcripts of CgATP synthase β subunit in agranulocytes and semi-granulocytes were significantly increased at 24 h (2.44-fold, and 9.01-fold of that in control group, p < 0.01), and those in granulocytes were significantly increased at 6 h (1.83-fold, p < 0.01), 12 h (1.92-fold, p < 0.01) and 24 h (3.47-fold, p < 0.01). The expression level of CgATP synthase β subunit protein in agranulocytes and granulocytes was also significantly increased after rCgAstakine stimulation, which was 1.64-fold (p < 0.05) and 1.85-fold (p < 0.05) of that in control group, respectively, while there were no significant changes in semi-granulocytes. The immunofluorescence assay showed that CgATP synthase β subunit positive signals were mainly located on the membrane of haemocytes. The number of haemocytes with EdU positive signals was significantly increased after rCgAstakine stimulation (2.04-fold of seawater group, p < 0.01), while significantly decreased after the RNA interference (RNAi) of CgATP synthase β subunit, which was 0.28-fold of that in NC group (p < 0.01). Bio-layer interferometry (BLI) assay confirmed in vitro interaction between rCgAstakine and rCgATP synthase β subunit. There results suggested that CgATP synthase β subunit acts as the receptor of CgAstakine and plays important roles in CgAstakine induced renewal of haemocytes in C. gigas.

Trafficking-defective mutant PROKR2 cycles between endoplasmic reticulum and Golgi to attenuate endoplasmic reticulum stress

The endoplasmic reticulum (ER) possesses a quality control system that prevents misfolded proteins from leaving the ER for routing to the ER-associated degradation pathway. Some misfolded proteins can escape the ER to reach the Golgi, where they are then retrieved from the Golgi back to the ER for degradation, but why this occurs needs to be clarified. Studying a mutant prokineticin receptor 2 identified in patients with hypogonadotropic hypogonadism as a model, we find that the post-ER retrieval system provides another layer of quality control and also lowers the load of misfolded proteins in the ER to reduce ER stress. Our findings reveal the importance of a post-ER quality control mechanism in contributing to cellular homeostasis.

G protein–coupled receptors (GPCRs) play crucial roles in numerous physiological and pathological processes. Mutations in GPCRs that result in loss of function or alterations in signaling can lead to inherited or acquired diseases. Herein, studying prokineticin receptor 2 (PROKR2), we initially identify distinct interactomes for wild-type (WT) versus a mutant (P290S) PROKR2 that causes hypogonadotropic hypogonadism. We then find that both the WT and mutant PROKR2 are targeted for endoplasmic reticulum (ER)-associated degradation, but the mutant is degraded to a greater extent. Further analysis revealed that both forms can also leave the ER to reach the Golgi. However, whereas most of the WT is further transported to the cell surface, most of the mutant is retrieved to the ER. Thus, the post-ER itinerary plays an important role in distinguishing the ultimate fate of the WT versus the mutant. We have further discovered that this post-ER itinerary reduces ER stress induced by the mutant PROKR2. Moreover, we extend the core findings to another model GPCR. Our findings advance the understanding of disease pathogenesis induced by a mutation at a key residue that is conserved across many GPCRs and thus contributes to a fundamental understanding of the diverse mechanisms used by cellular quality control to accommodate misfolded proteins.

Genetic causes of central precocious puberty

Central precocious puberty (CPP) is a condition in which the hypothalamus–pituitary–gonadal system is activated earlier than the normal developmental stage. The etiology includes organic lesions in the brain; however, in the case of idiopathic diseases, environmental and/or genetic factors are involved in the development of CPP. A genetic abnormality in KISS1R, that encodes the kisspeptin receptor, was first reported in 2008 as a cause of idiopathic CPP. Furthermore, genetic alterations in KISS1, MKRN3, DLK1, and PROKR2 have been reported in idiopathic and/or familial CPP. Of these, MKRN3 has the highest frequency of pathological variants associated with CPP worldwide; but, abnormalities in MKRN3 are rare in patients in East Asia, including Japan. MKRN3 and DLK1 are maternal imprinting genes; thus, CPP develops when a pathological variant is inherited from the father. The mechanism of CPP due to defects in MKRN3 and DLK1 has not been completely clarified, but it is suggested that both may negatively control the progression of puberty. CPP due to such a single gene abnormality is extremely rare, but it is important to understand the mechanisms of puberty and reproduction. A further development in the genetics of CPP is expected in the future.

Genetic Etiology of Idiopathic Hypogonadotropic Hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) is a group of rare developmental disorders characterized by low gonadotropin levels in the face of low sex steroid hormone concentrations. IHH is practically divided into two major groups according to the olfactory function: normal sense of smell (normosmia) nIHH, and reduced sense of smell (hyposmia/anosmia) Kallmann syndrome (KS). Although mutations in more than 50 genes have been associated with IHH so far, only half of those cases were explained by gene mutations. Various combinations of deleterious variants in different genes as causes of IHH have been increasingly recognized (Oligogenic etiology). In addition to the complexity of inheritance patterns, the spontaneous or sex steroid-induced clinical recovery from IHH, which is seen in approximately 10–20% of cases, blurs further the phenotype/genotype relationship in IHH, and poses challenging steps in new IHH gene discovery. Beyond helping for clinical diagnostics, identification of the genetic mutations in the pathophysiology of IHH is hoped to shed light on the central governance of the hypothalamo-pituitary-gonadal axis through life stages. This review aims to summarize the genetic etiology of IHH and discuss the clinical and physiological ramifications of the gene mutations.

Serum Prokineticin-2 in Prepubertal and Adult Klinefelter Individuals

The prokineticin-2 (PROK2) is a small peptide belonging to the prokineticin family. In humans and rodents this chemokine is primarily involved in the control of central and peripheral reproductive processes. Klinefelter's syndrome (KS) is the first cause of male genetic infertility, due to an extra X chromosome, which may occur with a classical karyotype (47, XXY) or mosaic forms (46, XY/47, XXY). In affected subjects, pubertal maturation usually begins at an adequate chronological age, but when development is almost complete, they display a primary gonadal failure, with early spermatogenesis damage, and later onset of testosterone insufficiency. Thus, the main aim of the present study was to investigate the serum levels of PROK2 in prepubertal and adult KS patients, comparing them with healthy subjects. We showed for the first time the presence of PROK2 in the children serum but with significant changes in KS individuals. Indeed, compared to healthy subjects characterized by PROK2 serum elevation during the growth, KS individuals showed constant serum levels during the sexual maturation phase (higher during the prepubertal phase but lower during the adult age). In conclusion, these data indicate that in KS individuals PROK2 may be considered a biomarker for investigating the SK infertility process.

Oligogenic Inheritance Underlying Incomplete Penetrance of PROKR2 Mutations in Hypogonadotropic Hypogonadism

The role of the prokineticin 2 pathway in human reproduction, olfactory bulb morphogenesis, and gonadotropin-releasing hormone secretion is well established. Recent studies have highlighted the implication of di/oligogenic inheritance in this disorder. In the present study, we aimed to identify the genetic mechanisms that could explain incomplete penetrance in hypogonadotropic hypogonadism (HH). This study involved two unrelated Tunisian patients with HH, which was triggered by identifying a homozygous p.(Pro290Ser) mutation in the PROKR2 gene in a girl (HH1) with Kallmann syndrome (KS). The functional effect of this variant has previously been well demonstrated. Unexpectedly, her unaffected father (HH1P) and brother (HH1F) also carried this genetic variation at a homozygous state. In the second family, we identified a heterozygous p.(Lys205del) mutation in PROKR2, both in a male patient with normosmic idiopathic IHH (HH12) and his asymptomatic mother. Whole-exome sequencing in the three HH1 family members allowed the identification of additional variants in the prioritized genes. We then carried out digenic combination predictions using the oligogenic resource for variant analysis (ORVAL) software. For HH1, we found the highest number of disease-causing variant pairs. Notably, a CCDC141 variant (c.2803C > T) was involved in 18 pathogenic digenic combinations. The CCDC141 variant acts in an autosomal recessive inheritance mode, based on the digenic effect prediction data. For the second patient (HH12), prediction by ORVAL allowed the identification of an interesting pathogenic digenic combination between DUSP6 and SEMA7A genes, predicted as “dual molecular diagnosis.” The SEMA7A variant p.(Glu436Lys) is novel and predicted as a VUS by Varsome. Sanger validation revealed the absence of this variant in the healthy mother. We hypothesize that disease expression in HH12 could be induced by the digenic transmission of the SEMA7A and DUSP6 variants or a monogenic inheritance involving only the SEMA7A VUS if further functional assays allow its reclassification into pathogenic. Our findings confirm that homozygous loss-of-function genetic variations are insufficient to cause KS, and that oligogenism is most likely the main transmission mode involved in Congenital Hypogonadotropic Hypogonadism.

Genetics of hypogonadotropic Hypogonadism-Human and mouse genes, inheritance, oligogenicity, and genetic counseling

Hypogonadotropic hypogonadism, which may be normosmic (nHH) or anosmic/hyposmic, known as Kallmann syndrome (KS), is due to gonadotropin-releasing hormone deficiency, which results in absent puberty and infertility. Investigation of the genetic basis of nHH/KS over the past 35 years has yielded a substantial increase in our understanding, as variants in 44 genes in OMIM account for ~50% of cases. The first genes for KS (ANOS1) and nHH (GNRHR) were followed by the discovery that FGFR1 variants may cause either nHH or KS. Associated anomalies include midline facial defects, neurologic deficits, cardiac anomalies, and renal agenesis, among others. Mouse models for all but one gene (ANOS1) generally support findings in humans. About half of the known genes implicated in nHH/KS are inherited as autosomal dominant and half are autosomal recessive, whereas only 7% are X-linked recessive. Digenic and oligogenic inheritance has been reported in 2-20% of patients, most commonly with variants in genes that may result in either nHH or KS inherited in an autosomal dominant fashion. In vitro analyses have only been conducted for both gene variants in eight cases and for one gene variant in 20 cases. Rigorous confirmation that two gene variants in the same individual cause the nHH/KS phenotype is lacking for most. Clinical diagnosis is probably best accomplished by targeted next generation sequencing of the known candidate genes with confirmation by Sanger sequencing. Elucidation of the genetic basis of nHH/KS has resulted in an enhanced understanding of this disorder, as well as normal puberty, which makes genetic diagnosis clinically relevant.

Comparison of Clinical Characteristics and Spermatogenesis in CHH Patients Caused by PROKR2 and FGFR1 Mutations

A retrospective study was conducted to investigate the effect of gonadotropin or pulsatile gonadotropin-releasing hormone (GnRH) therapy on spermatogenesis in congenital hypogonadotropic hypogonadism (CHH) patients with PROKR2 (prokineticin receptor 2) or FGFR1 (fibroblast growth factor receptor 1) mutations. Clinical features, gonadotropin levels, testicular volume (TV), and sperm concentration in response to gonadotropin and pulsatile GnRH therapy were compared between groups with PROKR2 and FGFR1 mutations. Twelve patients with PROKR2 gene mutation and fourteen patients with FGFR1 gene mutation were included. The incidence of cryptorchidism in PROKR2 and FGFR1 groups was 16.7% and 50%, respectively (p = 0.110). The baseline TV in the PROKR2 group was larger than that in FGFR1 group (2.0 vs. 1.63, p = 0.047). The initial LH, FSH, and testosterone levels were similar between the two groups. Based on the analysis of achieving spermatogenesis using Kaplan-Meier and log-rank tests, the PROKR2 group demonstrated shorter period of seminal spermatozoa appearance than the FGFR1 group (χ² = 8.297, p = 0.004); the median duration of achieving spermatogenesis in the PROKR2 and FGFR1 groups was 9 and 16 months, respectively. The PROKR2 mutation group exhibited shorter required time to achieve different sperm concentration thresholds (5, 10, and 15 million/mL) than the FGFR1 mutation group (p = 0.012, 0.024, and 0.040). In conclusion, the PROKR2 group achieved spermatogenesis easily than the FGFR1 group, possibly due to the lower prevalence of cryptorchidism and larger baseline testicular volume in the PROKR2 group.

Molecular screening of PROKR2 gene in girls with idiopathic central precocious puberty

Background

Prokineticin receptor 2 (PROKR2) loss of function mutations have been described as cause of hypogonadotropic hypogonadism. In 2017, a first case of central precocious puberty (CPP) caused by PROKR2 heterozygous gain of function mutation was described in a 3.5 years-old girl. No other cases have been reported yet. This study performs a molecular screening in girls with early onset CPP (breast budding before 6 years of age) to identify possible alterations in PROKR2.

Methods

We analysed DNA of 31 girls with idiopathic CPP diagnosed via basal LH levels > 0.3 IU/L or peak-LH > 5 IU/L after stimulation, without any MKRN3 mutations. The Fisher exact test was used to compare polymorphism allele frequency to corresponding ones in genome aggregation database (gnomAD).

Results

No rare variants were identified. Five polymorphisms were found (rs6076809, rs8116897, rS3746684, rs3746682, rs3746683). All except one (i.e. rs3746682) had a minor allele frequency (MAF) similar to that reported in literature. rs3746682 presented a MAF higher than that described in the gnomAD (0.84 in our cohort vs 0.25 from gnomAD).

Conclusions

As for other G protein-coupled receptors (i.e. GPR54), mutations in PROKR2 do not seem to be a frequent cause of CPP in girls.

The wonderful and masterful G protein-coupled receptor (GPCR): A focus on signaling mechanisms and the neuroendocrine control of fertility

Human GnRH deficiency, both clinically and genetically, is a heterogeneous disorder comprising of congenital GnRH deficiency with anosmia (Kallmann syndrome), or with normal olfaction [normosmic idiopathic hypogonadotropic hypogonadism (IHH)], and adult-onset hypogonadotropic hypogonadism. Our understanding of the neural mechanisms underlying GnRH secretion and GnRH signaling continues to increase at a rapid rate and strikingly, the heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) continue to emerge as essential players in these processes. GPCRs were once viewed as binary on-off switches, where in the "on" state they are bound to their Gα protein, but now we understand that view is overly simplistic and does not adequately characterize GPCRs. Instead, GPCRs have emerged as masterful signaling molecules exploiting different physical conformational states of itself to elicit an array of downstream signaling events via their G proteins and the β-arrestins. The "one receptor-multiple signaling conformations" model is likely an evolved strategy that can be used to our advantage as researchers have shown that targeting specific receptor conformations via biased ligands is proving to be a powerful tool in the effective treatment of human diseases. Can biased ligands be used to selectively modulate signaling by GPCR regulators of the neuroendocrine axis in the treatment of IHH? As discussed in this review, the grand possibility exists. However, while we are still very far from developing these treatments, this exciting likelihood can happen through a much greater mechanistic understanding of how GPCRs signal within the cell.

Methane Ameliorates Lipopolysaccharide-Induced Acute Orchitis by Anti-inflammatory, Antioxidative, and Antiapoptotic Effects via Regulation of the PK2/PKR1 Pathway

Objective

The present study is aimed at investigating the anti-inflammatory, antioxidative, and antiapoptotic effects of methane on lipopolysaccharide- (LPS-) induced acute orchitis and its potential mechanisms.

Methods

Adult male rats were intraperitoneally (i.p.) injected with methane-rich saline (MS, 20 mL/kg) following LPS (5 mg/kg, i.p.). The survival rate was assessed every 12 h until 72 h after LPS induction, and surviving rats were sacrificed for further detection. The wet/dry (W/D) ratio was determined, and testicular damage was histologically assessed. Inflammatory cytokines in the testes and serum, including interleukin-1β (IL-1β), IL-6, IL-10, and tumor necrosis factor-α (TNF-α), were measured using ELISA and RT-qPCR. Oxidative stress was evaluated by the level of superoxide dismutase (SOD) and malondialdehyde (MDA). Testicular apoptosis was detected via TUNEL staining. The expression of prokineticin 2 (PK2)/prokineticin receptor 1 (PKR1) was also analyzed using RT-qPCR, western blotting, and immunohistochemistry.

Results

It was found that methane significantly prolonged rat survival, decreased the W/D ratio, alleviated LPS-induced histological changes, and reduced apoptotic cells in the testes. Additionally, methane suppressed and promoted the production of pro- and anti-inflammatory cytokines, respectively. Furthermore, methane significantly increased SOD levels, decreased MDA levels, and decreased testicular expression of PK2 and PKR1. Therefore, methane exerts therapeutic effects on acute orchitis and might be a new and convenient strategy for the treatment of inflammation-related testicular diseases.

Metformin Ameliorates Diabetic Cardiomyopathy by Activating the PK2/PKR Pathway

Diabetic cardiomyopathy (DCM) is a complication of diabetes that can cause damage to myocardial structure and function. Metformin (Met) is a widely used type 2 diabetes treatment drug that exerts cardioprotective effects through multiple pathways. Prokineticin 2 (PK2) is a small-molecule secreted protein that plays pivotal parts in cardiomyocyte survival and angiogenesis. However, the role of Met in regulating the PK2 signaling pathway in DCM remains unclear. This experiment explored the effects of Met on high glucose (HG)-induced injury through the PK2/PKR pathway in vivo and in vitro. Cardiomyocytes isolated from adult or AKT-knockout mice were treated with HG (33 mmol/L) and PK2 or AKT1/2 kinase inhibitor (AKT inhibitor). Heart contraction properties based on cell shortening were evaluated; these properties included the resting cell length, peak shortening (PS), maximum speed of shortening/relengthening (±dL/dt), time to 90% relengthening (TR₉₀), and time to peak shortening (TPS). Mice with streptozotocin-induced diabetes were treated with Met to evaluate cardiac function, myocardial structure, and the PK2/PKR and AKT/GSK3β pathways. Moreover, H9c2 cardiomyocytes were exposed to HG in the absence or presence of Met with or without the PK2 antagonist PKRA7 or the AKT inhibitor, and apoptotic proteins such as Bax and Bcl-2 and the PK2/PKR and AKT/GSK3β pathways were evaluated using western blot analysis. The prolongation of TR₉₀ and decreases in PS and ±dL/dt caused by HG were ameliorated by PK2 in cardiomyocytes, but the effects of PK2 were ameliorated or negated by the AKT inhibitor and in AKT-knockout mice. Diabetic mice showed metabolic abnormalities, aberrant myocardial enzyme levels, declines in myocardial systolic and diastolic function associated with myocardial fibrosis, and pronounced apoptosis, but these effects were greatly rescued by Met treatment. Moreover, PK2, PKR1, and PKR2 expression and p-AKT/AKT and p-GSK3β/GSK3β ratios were decreased in diabetic mice, and these decreases were attenuated by Met. Likewise, H9c2 cells exposed to HG showed reduced PK2/PKR expression and decreased p-AKT/AKT and p-GSK3β/GSK3β ratios, and these effects were nullified by Met. In addition, the effects of Met on cardiomyocytes exposed to HG were abolished after intervention with PKRA7 or the AKT inhibitor. These results suggest that Met can activate the PK2/PKR-mediated AKT/GSK3β pathway, thus improving cardiac function and alleviating apoptosis in DM mice.

Immunomodulatory effect of ginseng stem-leaf saponins and selenium on Harderian gland in immunization of chickens to Newcastle disease vaccine

Our previous study demonstrated that ginseng stem-leaf saponins (GSLS) in combination with selenium (GSLS-Se) have adjuvant effect on the live vaccine of Newcastle disease virus (NDV) and infectious bronchitis virus (IBV) in intraocular-and-intranasal immunization in chickens. The present study was to investigate the potential molecular mechanisms involved in the immunomodulation of GSLS-Se on the Harderian gland (HG). It was found that the window allowing animals susceptible to infections due to low antibody titers became smaller or even completely closed because of increased NDV-specific HI titers when NDV vaccine and GSLS-Se were coadministered for immunization at early life in chickens. In addition, NDV-specific sIgA and the numbers of IgG+, IgA+, IgM+ plasma cells were significantly more in GSLS-Se group than the control in the HGs. Transcriptome analysis of HGs identified 1184 differentially expressed genes (DEGs) between GSLS-Se treated and non-treated groups. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses identified 42 significantly enriched GO terms and 13 canonical immune pathways. These findings indicated that GSLS-Se might exert immunomodulatory effects through influencing the antioxidant regulation and modulating the activity of immune related enzymes. Besides, Toll-like receptor (TLR) signaling pathway and mitogen-activated protein kinase (MAPK) signaling pathway might be involved primarily in the immunomodulation. Therefore, enhanced antibody responses in GSLS-Se group may be attributed to the immunomodulatory effects of GSLS-Se on the immune-related gene profile expressed in the immunocompetent cells of the HGs.

Knocking-down of the Prokineticin receptor 2 affects reveals its complex role in the regulation of the hypothalamus-pituitary-gonadal axis in the zebrafish model

Prokineticin receptors (PROKR1 and PROKR2) are G protein-coupled receptors which control human central and peripheral reproductive processes. Importantly, allelic variants of PROKR2 in humans are associated with altered migration of GnRH neurons, resulting in congenital hypogonadotropic hypogonadism (CHH), a heterogeneous disease characterized by delayed/absent puberty and/or infertility. Although this association is established in humans, murine models failed to fully recapitulate the reproductive and olfactory phenotypes observed in patients harboring PROKR2 mutations. Here, taking advantage of zebrafish model we investigated the role of prokr1b (ortholog of human PROKR2) during early stages of GnRH neuronal migration. Real-Time PCR and whole mount in situ hybridization assays indicate that prokr1b spatial-temporal expression is consistent with gnrh3. Moreover, knockdown and knockout of prokr1b altered the correct development of GnRH3 fibers, a phenotype that is rescued by injection of prokr1b mRNA. These results suggest that prokr1b regulates the development of the GnRH3 system in zebrafish. Analysis of gonads development and mating experiments indicate that prokr1b is not required for fertility in zebrafish, although its loss determine changes also at the testis level. Altogether, our results support the thesis of a divergent evolution in the control of vertebrate reproduction and provide a useful in vivo model for deciphering the mechanisms underlying the effect of PROKR2 allelic variants on CHH.

Resistance Mechanisms to Anti-angiogenic Therapies in Cancer

Tumor growth and metastasis rely on tumor vascular network for the adequate supply of oxygen and nutrients. Tumor angiogenesis relies on a highly complex program of growth factor signaling, endothelial cell (EC) proliferation, extracellular matrix (ECM) remodeling, and stromal cell interactions. Numerous pro-angiogenic drivers have been identified, the most important of which is the vascular endothelial growth factor (VEGF). The importance of pro-angiogenic inducers in tumor growth, invasion and extravasation make them an excellent therapeutic target in several types of cancers. Hence, the number of anti-angiogenic agents developed for cancer treatment has risen over the past decade, with at least eighty drugs being investigated in preclinical studies and phase I-III clinical trials. To date, the most common approaches to the inhibition of the VEGF axis include the blockade of VEGF receptors (VEGFRs) or ligands by neutralizing antibodies, as well as the inhibition of receptor tyrosine kinase (RTK) enzymes. Despite promising preclinical results, anti-angiogenic monotherapies led only to mild clinical benefits. The minimal benefits could be secondary to primary or acquired resistance, through the activation of alternative mechanisms that sustain tumor vascularization and growth. Mechanisms of resistance are categorized into VEGF-dependent alterations, non-VEGF pathways and stromal cell interactions. Thus, complementary approaches such as the combination of these inhibitors with agents targeting alternative mechanisms of blood vessel formation are urgently needed. This review provides an updated overview on the pathophysiology of angiogenesis during tumor growth. It also sheds light on the different pro-angiogenic and anti-angiogenic agents that have been developed to date. Finally, it highlights the preclinical evidence for mechanisms of angiogenic resistance and suggests novel therapeutic approaches that might be exploited with the ultimate aim of overcoming resistance and improving clinical outcomes for patients with cancer.

Anosmin-1 activates vascular endothelial growth factor receptor and its related signaling pathway for olfactory bulb angiogenesis

Anosmin-1 is a secreted glycoprotein encoded by the ANOS1 gene, and its loss of function causes Kallmann syndrome (KS), which is characterized by anosmia and hypogonadism due to olfactory bulb (OB) dysfunction. However, the physiological function of anosmin-1 remains to be elucidated. In KS, disordered angiogenesis is observed in OB, resulting in its hypoplasia. In this study, we examined the involvement of anosmin-1 in angiogenic processes. Anosmin-1 was detected on the vessel-like structure in OB of chick embryos, and promoted the outgrowth of vascular sprouts as shown by assays of OB tissue culture. Cell migration, proliferation, and tube formation of endothelial cells were induced by treatment with anosmin-1 as well as vascular endothelial growth factor-A (VEGF-A), and further enhanced by treatment with both of them. We newly identified that anosmin-1 activated VEGF receptor-2 (VEGFR2) by binding directly to it, and its downstream signaling molecules, phospholipase Cγ1 (PLCγ1) and protein kinase C (PKC). These results suggest that anosmin-1 plays a key role in the angiogenesis of developing OB through the VEGFR2–PLCγ1–PKC axis by enhancing the VEGF function.

Dlx1/2 are Central and Essential Components in the Transcriptional Code for Generating Olfactory Bulb Interneurons

Generation of olfactory bulb (OB) interneurons requires neural stem/progenitor cell specification, proliferation, differentiation, and young interneuron migration and maturation. Here, we show that the homeobox transcription factors Dlx1/2 are central and essential components in the transcriptional code for generating OB interneurons. In Dlx1/2 constitutive null mutants, the differentiation of GSX2+ and ASCL1+ neural stem/progenitor cells in the dorsal lateral ganglionic eminence is blocked, resulting in a failure of OB interneuron generation. In Dlx1/2 conditional mutants (hGFAP-Cre; Dlx1/2F/- mice), GSX2+ and ASCL1+ neural stem/progenitor cells in the postnatal subventricular zone also fail to differentiate into OB interneurons. In contrast, overexpression of Dlx1&2 in embryonic mouse cortex led to ectopic production of OB-like interneurons that expressed Gad1, Sp8, Sp9, Arx, Pbx3, Etv1, Tshz1, and Prokr2. Pax6 mutants generate cortical ectopia with OB-like interneurons, but do not do so in compound Pax6; Dlx1/2 mutants. We propose that DLX1/2 promote OB interneuron development mainly through activating the expression of Sp8/9, which further promote Tshz1 and Prokr2 expression. Based on this study, in combination with earlier ones, we propose a transcriptional network for the process of OB interneuron development.

Transcription Factors Sp8 and Sp9 Coordinately Regulate Olfactory Bulb Interneuron Development

Neural stem cells in the postnatal telencephalic ventricular-subventricular zone (V-SVZ) generate new interneurons, which migrate tangentially through the rostral migratory stream (RMS) into the olfactory bulb (OB). The Sp8 and Sp9 transcription factors are expressed in neuroblasts, as well as in the immature and mature interneurons in the V-SVZ-RMS-OB system. Here we show that Sp8 and Sp9 coordinately regulate OB interneuron development: although Sp9 null mutants show no major OB interneuron defect, conditional deletion of both Sp8 and Sp9 resulted in a much more severe reduction of OB interneuron number than that observed in the Sp8 conditional mutant mice, due to defects in neuronal differentiation, tangential and radial migration, and increased cell death in the V-SVZ-RMS-OB system. RNA-Seq and RNA in situ hybridization reveal that, in Sp8/Sp9 double mutant mice, but not in Sp8 or Sp9 single mutant mice, newly born neuroblasts in the V-SVZ-RMS-OB system fail to express Prokr2 and Tshz1 expression, genes with known roles in promoting OB interneuron differentiation and migration, and that are involved in human Kallmann syndrome.

Nasal Placode Development, GnRH Neuronal Migration and Kallmann Syndrome

The development of Gonadotropin releasing hormone-1 (GnRH) neurons is important for a functional reproduction system in vertebrates. Disruption of GnRH results in hypogonadism and if accompanied by anosmia is termed Kallmann Syndrome (KS). From their origin in the nasal placode, GnRH neurons migrate along the olfactory-derived vomeronasal axons to the nasal forebrain junction and then turn caudally into the developing forebrain. Although research on the origin of GnRH neurons, their migration and genes associated with KS has identified multiple factors that influence development of this system, several aspects still remain unclear. This review discusses development of the olfactory system, factors that regulate GnRH neuron formation and development of the olfactory system, migration of the GnRH neurons from the nose into the brain, and mutations in humans with KS that result from disruption of normal GnRH/olfactory systems development.

Modeling mutant/wild-type interactions to ascertain pathogenicity of PROKR2 missense variants in patients with isolated GnRH deficiency

A major challenge in human genetics is the validation of pathogenicity of heterozygous missense variants. This problem is well-illustrated by PROKR2 variants associated with Isolated GnRH Deficiency (IGD). Homozygous, loss of function variants in PROKR2 was initially implicated in autosomal recessive IGD; however, most IGD-associated PROKR2 variants are heterozygous. Moreover, while IGD patient cohorts are enriched for PROKR2 missense variants similar rare variants are also found in normal individuals. To elucidate the pathogenic mechanisms distinguishing IGD-associated PROKR2 variants from rare variants in controls, we assessed 59 variants using three approaches: (i) in silico prediction, (ii) traditional in vitro functional assays across three signaling pathways with mutant-alone transfections, and (iii) modified in vitro assays with mutant and wild-type expression constructs co-transfected to model in vivo heterozygosity. We found that neither in silico analyses nor traditional in vitro assessments of mutants transfected alone could distinguish IGD variants from control variants. However, in vitro co-transfections revealed that 15/34 IGD variants caused loss-of-function (LoF), including 3 novel dominant-negatives, while only 4/25 control variants caused LoF. Surprisingly, 19 IGD-associated variants were benign or exhibited LoF that could be rescued by WT co-transfection. Overall, variants that were LoF in ≥ 2 signaling assays under co-transfection conditions were more likely to be disease-associated than benign or 'rescuable' variants. Our findings suggest that in vitro modeling of WT/Mutant interactions increases the resolution for identifying causal variants, uncovers novel dominant negative mutations, and provides new insights into the pathogenic mechanisms underlying heterozygous PROKR2 variants.

PROKR2 mutations in idiopathic hypogonadotropic hypogonadism: selective disruption of the binding to a Gα-protein leads to biased signaling

Idiopathic hypogonadotropic hypogonadism (IHH) is a rare disorder caused by the deficient production, secretion, or action of gonadotropin-releasing hormone. Prokineticin (PROK) receptor 2 ( PROKR2), a causative gene for IHH, encodes a GPCR PROKR2. When PROKR2 binds to its ligands PROKs, it may activate several signaling pathways, including IP3/Ca²⁺, MAPK, and cAMP pathways. However, the mutational spectrum of PROKR2 in Chinese patients with IHH has not been established. In the present study, we found that up to 13.3% (18/135) of patients with IHH in China carried mutations in PROKR2. Most of the variants in this study were private; however, a PROKR2 (c.533G > C; p.W178S) mutation was identified in 10 independent patients, implying a possible founder mutation. Functional studies indicated that 6 novel PROKR2 mutations led to decreased signaling to various extents. Two IHH-associated mutations (L218P and R270H) disrupted Gαq-dependent signaling but maintained normal Gαs and ERK1/2 signaling. A glutathione S-transferase pull-down experiment demonstrated that R270H mutation disrupted the interaction of intracellular loop 3 of PROKR2 to Gαq protein but not Gαs protein. Our results indicated that selective disruption of the interaction with a specific Gα-protein might underlie the biased signaling for certain IHH-associated PROKR2 mutations.-Zhao, Y., Wu, J., Jia, H., Wang, X., Zheng, R., Jiang, F., Chen, D.-N., Chen, Z., Li, J.-D. PROKR2 mutations in idiopathic hypogonadotropic hypogonadism: selective disruption of the binding to a Gα-protein leads to biased signaling.

The Prokineticins: Neuromodulators and Mediators of Inflammation and Myeloid Cell-Dependent Angiogenesis

The mammalian prokineticins family comprises two conserved proteins, EG-VEGF/PROK1 and Bv8/PROK2, and their two highly related G protein-coupled receptors, PKR1 and PKR2. This signaling system has been linked to several important biological functions, including gastrointestinal tract motility, regulation of circadian rhythms, neurogenesis, angiogenesis and cancer progression, hematopoiesis, and nociception. Mutations in PKR2 or Bv8/PROK2 have been associated with Kallmann syndrome, a developmental disorder characterized by defective olfactory bulb neurogenesis, impaired development of gonadotropin-releasing hormone neurons, and infertility. Also, Bv8/PROK2 is strongly upregulated in neutrophils and other inflammatory cells in response to granulocyte-colony stimulating factor or other myeloid growth factors and functions as a pronociceptive mediator in inflamed tissues as well as a regulator of myeloid cell-dependent tumor angiogenesis. Bv8/PROK2 has been also implicated in neuropathic pain. Anti-Bv8/PROK2 antibodies or small molecule PKR inhibitors ameliorate pain arising from tissue injury and inhibit angiogenesis and inflammation associated with tumors or some autoimmune disorders.

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.

The hypothalamus-pituitary-gonad axis: Tales of mice and men

Reproduction is controlled by the hypothalamic-pituitary-gonadal (HPG) axis. Gonadotropin-releasing hormone (GnRH) neurons play a central role in this axis through production of GnRH, which binds to a membrane receptor on pituitary gonadotrophs and stimulates the biosynthesis and secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Multiple factors affect GnRH neuron migration, GnRH gene expression, GnRH pulse generator, GnRH secretion, GnRH receptor expression, and gonadotropin synthesis and release. Among them anosmin is involved in the guidance of the GnRH neuron migration, and a loss-of-function mutation in its gene leads to a failure of their migration from the olfactory placode to the hypothalamus, with consequent anosmic hypogonadotropic hypogonadism (Kallmann syndrome). There are also cases of hypogonadotropic hypogonadim with normal sense of smell, due to mutations of other genes. Another protein, kisspeptin plays a crucial role in the regulation of GnRH pulse generator and the pubertal development. GnRH is the main hypothalamic regulator of the release of gonadotropins. Finally, FSH and LH are the essential hormonal regulators of testicular functions, acting through their receptors in Sertoli and Leydig cells, respectively. The main features of the male HPG axis will be described in this review.

Resistance to Anti-Angiogenic Therapy in Cancer-Alterations to Anti-VEGF Pathway

Anti-angiogenic therapy is one of the promising strategies for many types of solid cancers. Bevacizumab (Avastin), a recombinant humanized monoclonal antibody of vascular endothelial growth factor (VEGF) A, was approved for the first time as an anti-angiogenic drug for the treatment of metastatic colorectal cancer (CRC) by the Food and Drug Administration (FDA) in 2004. In addition, the other VEGF pathway inhibitors including small molecule tyrosine kinase inhibitors (sunitinib, sorafenib, and pazopanib), a soluble VEGF decoy receptor (aflibercept), and a humanized monoclonal antibody of VEGF receptor 2 (VEGFR2) (ramucirumab) have been approved for cancer therapy. Although many types of VEGF pathway inhibitors can improve survival in most cancer patients, some patients have little or no beneficial effect from them. The primary or acquired resistance towards many oncological drugs, including anti-VEGF inhibitors, is a common problem in cancer treatment. This review summarizes the proposed alternative mechanisms of angiogenesis other than the VEGF pathway. These mechanisms are involved in the development of resistance to anti-VEGF therapies in cancer patients.

Effects of prokineticin 2 on testicular inflammation in rats

PROBLEM

Prokineticin 2 (PK2), a pro-inflammatory peptide, is highly expressed in primary spermatocytes. However, systematic research on PK2 and testicular inflammation is lacking to date.

METHOD OF STUDY

An experimental autoimmune orchitis (EAO) model was established to detect the expression of PK2 and its receptor (prokineticin receptor 1, PKR1) 50 and 80 days after immunization. PK2 siRNA sequence was injected into the rat rete testis to downregulate the expression of PK2. PK2 was over-expressed in the testis by injecting PK2 protein through the rat rete testis at different concentrations. Testicular morphology and expression of inducible nitric oxide synthase (iNOS) were detected after the intervention.

RESULTS

Results showed that PK2 and PKR1 were upregulated in EAO at 50 days and downregulated at 80 days. PK2 over-expression contributed to the apoptosis of spermatogenic epithelial cells and increased infiltration of the inflammatory cells, whereas PK2 under-expression showed no change. Furthermore, iNOS expression was increased significantly when PK2 was over-expressed.

CONCLUSION

This finding demonstrated that the PK2/PKR1 signals may have an essential role in the regulation of testicular inflammation through iNOS. PK2 interference may represent a novel and promising therapeutic strategy for the clinical management of orchitis.

GENETICS IN ENDOCRINOLOGY: Genetic counseling for congenital hypogonadotropic hypogonadism and Kallmann syndrome: new challenges in the era of oligogenism and next-generation sequencing

Congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS) are rare, related diseases that prevent normal pubertal development and cause infertility in affected men and women. However, the infertility carries a good prognosis as increasing numbers of patients with CHH/KS are now able to have children through medically assisted procreation. These are genetic diseases that can be transmitted to patients' offspring. Importantly, patients and their families should be informed of this risk and given genetic counseling. CHH and KS are phenotypically and genetically heterogeneous diseases in which the risk of transmission largely depends on the gene(s) responsible(s). Inheritance may be classically Mendelian yet more complex; oligogenic modes of transmission have also been described. The prevalence of oligogenicity has risen dramatically since the advent of massively parallel next-generation sequencing (NGS) in which tens, hundreds or thousands of genes are sequenced at the same time. NGS is medically and economically more efficient and more rapid than traditional Sanger sequencing and is increasingly being used in medical practice. Thus, it seems plausible that oligogenic forms of CHH/KS will be increasingly identified making genetic counseling even more complex. In this context, the main challenge will be to differentiate true oligogenism from situations when several rare variants that do not have a clear phenotypic effect are identified by chance. This review aims to summarize the genetics of CHH/KS and to discuss the challenges of oligogenic transmission and also its role in incomplete penetrance and variable expressivity in a perspective of genetic counseling.

Sexually dimorphic distribution of Prokr2 neurons revealed by the Prokr2-Cre mouse model

Prokineticin receptor 2 (PROKR2) is predominantly expressed in the mammalian central nervous system. Loss-of-function mutations of PROKR2 in humans are associated with Kallmann syndrome due to the disruption of gonadotropin releasing hormone neuronal migration and deficient olfactory bulb morphogenesis. PROKR2 has been also implicated in the neuroendocrine control of GnRH neurons post-migration and other physiological systems. However, the brain circuitry and mechanisms associated with these actions have been difficult to investigate mainly due to the widespread distribution of Prokr2-expressing cells, and the lack of animal models and molecular tools. Here, we describe the generation, validation and characterization of a new mouse model that expresses Cre recombinase driven by the Prokr2 promoter, using CRISPR-Cas9 technology. Cre expression was visualized using reporter genes, tdTomato and GFP, in males and females. Expression of Cre-induced reporter genes was found in brain sites previously described to express Prokr2, e.g., the paraventricular and the suprachiasmatic nuclei, and the area postrema. The Prokr2-Cre mouse model was further validated by colocalization of Cre-induced GFP and Prokr2 mRNA. No disruption of Prokr2 expression, GnRH neuronal migration or fertility was observed. Comparative analysis of Prokr2-Cre expression in male and female brains revealed a sexually dimorphic distribution confirmed by in situ hybridization. In females, higher Cre activity was found in the medial preoptic area, ventromedial nucleus of the hypothalamus, arcuate nucleus, medial amygdala and lateral parabrachial nucleus. In males, Cre was higher in the amygdalo-hippocampal area. The sexually dimorphic pattern of Prokr2 expression indicates differential roles in reproductive function and, potentially, in other physiological systems.

Paradoxical gain-of-function mutant of the G-protein-coupled receptor PROKR2 promotes early puberty

The human genome encodes ~750 G‐protein‐coupled receptors (GPCRs), including prokineticin receptor 2 (PROKR2) involved in the regulation of sexual maturation. Previously reported pathogenic gain‐of‐function mutations of GPCR genes invariably encoded aberrant receptors with excessive signal transduction activity. Although in vitro assays demonstrated that an artificially created inactive mutant of PROKR2 exerted paradoxical gain‐of‐function effects when co‐transfected with wild‐type proteins, such a phenomenon has not been observed in vivo. Here, we report a heterozygous frameshift mutation of PROKR2 identified in a 3.5‐year‐old girl with central precocious puberty. The mutant mRNA escaped nonsense‐mediated decay and generated a GPCR lacking two transmembrane domains and the carboxyl‐terminal tail. The mutant protein had no in vitro signal transduction activity; however, cells co‐expressing the mutant and wild‐type PROKR2 exhibited markedly exaggerated ligand‐induced Ca²⁺ responses. The results indicate that certain inactive PROKR2 mutants can cause early puberty by enhancing the functional property of coexisting wild‐type proteins. Considering the structural similarity among GPCRs, this paradoxical gain‐of‐function mechanism may underlie various human disorders.

Involvement of Prokineticin 2 and Prokineticin Receptor 1 in Lipopolysaccharide-Induced Testitis in Rats

Prokineticin 2, a newly discovered proinflammatory peptide, has been amply evidenced to be involved in the occurrence and progress of local and systematical inflammation. Although the presence of Prokineticn 2 in mammal testis has been documented clearly, research targeting the involvement of prokineticin 2 in testicular pathology, especially testitis, is rather scarce. Employing a lipopolysaccharide-induced testitis rat model, we for the first time demonstrated the expression and upregulation of prokineticin 2 in orchitis at several levels. Our effort also addressed the differential expression patterns of prokineticin 2 and interleukin-1β, a key inflammation indicator, during testitis suggesting Prokineticn 2 serves more than a proinflammatory factor in the context of testitis. Given one of the cognate receptors of prokineticin 2, prokineticin receptor 1 (PKR1) was also significantly upregulated in orchitis as discussed in the current study, it is very likely that PK2/PKR1 signaling contribute to the development of inflammation-related testicular diseases.

Prokineticin-2 upregulation during neuronal injury mediates a compensatory protective response against dopaminergic neuronal degeneration

Prokineticin-2 (PK2), a recently discovered secreted protein, regulates important physiological functions including olfactory biogenesis and circadian rhythms in the CNS. Interestingly, although PK2 expression is low in the nigral system, its receptors are constitutively expressed on nigrostriatal neurons. Herein, we demonstrate that PK2 expression is highly induced in nigral dopaminergic neurons during early stages of degeneration in multiple models of Parkinson's disease (PD), including PK2 reporter mice and MitoPark mice. Functional studies demonstrate that PK2 promotes mitochondrial biogenesis and activates ERK and Akt survival signalling pathways, thereby driving neuroprotection. Importantly, PK2 overexpression is protective whereas PK2 receptor antagonism exacerbates dopaminergic degeneration in experimental PD. Furthermore, PK2 expression increased in surviving nigral dopaminergic neurons from PD brains, indicating that PK2 upregulation is clinically relevant to human PD. Collectively, our results identify a paradigm for compensatory neuroprotective PK2 signalling in nigral dopaminergic neurons that could have important therapeutic implications for PD.

Prokineticin-2 (PK2) is a secreted protein involved in a number of physiological functions. Here, the authors find that PK2 expression increases in surviving DA neurons from Parkinson's disease patients, and show it protects against dopaminergic degeneration in PD mouse models.

Gene Expression Changes Underlying Idiopathic Central Hypogonadism in Cryptorchidism with Defective Mini-Puberty

The whole genome RNA profiling of testicular biopsies by DNA strand-specific RNA sequencing was examined to determine a potential causative role of isolated congenital cryptorchidism in azoospermia and/or infertility in the context of our previously published GeneChip data. Cryptorchid patients, aged 7 months to 5 years and otherwise healthy, were enrolled in this prospective study. During surgery, testicular tissue biopsies were obtained for histological examination and RNA sequencing. Fifteen patients were selected based on the histological results and were divided into 2 groups. Seven were classified as belonging to the high infertility risk (HIR) and 8 to the low infertility risk (LIR) group. Cryptorchid boys in the HIR group lacked transformation of gonocytes into Ad spermatogonia due to impaired mini-puberty. This group of patients will be infertile despite successful surgery. The new important finding was a decreased PROK2, CHD7, FGFR1, and SPRY4 gene expression in the HIR group. Furthermore, identification of multiple differences in gene expression between HIR and LIR groups underscores the importance of an intact hypothalamic-pituitary-gonadal axis for fertility development. Our RNA profiling data strongly support the theory that in the HIR group of cryptorchid boys insufficient PROK2/CHD7/FGFR1/SPRY4 gene expression induces deficient LH secretion, resulting in impaired mini-puberty and infertility. We therefore recommend hormonal treatment for this cohort of cryptorchid boys with defective mini-puberty following a seemingly successful orchidopexy.

PK2/PKR1 Signaling Regulates Bladder Function and Sensation in Rats with Cyclophosphamide-Induced Cystitis

Prokineticin 2 (PK2) is a novel chemokine-like peptide with multiple proinflammatory and nociception-related activities. This study aimed to explore the potential role of PK2 in modulating bladder activity and sensation in rats with cyclophosphamide- (CYP-) induced cystitis. Changes of PK2 and prokineticin receptors (PKRs) in normal and inflamed urinary bladders were determined at several time points (4 h, 48 h, and 8 d) after CYP treatment. Combining a nonselective antagonist of prokineticin receptors (PKRA), we further evaluated the regulatory role of PK2 in modulating bladder function and visceral pain sensation via conscious cystometry and pain behavioral scoring. PK2 and prokineticin receptor 1 (PKR1), but not prokineticin receptor 2, were detected in normal and upregulated in CYP-treated rat bladders at several levels. Immunohistochemistry staining localized PKR1 primarily in the urothelium. Blocking PKRs with PKRA showed no effect on micturition reflex activity and bladder sensation in control rats while it increased the voiding volume, prolonged voiding interval, and ameliorated visceral hyperalgesia in rats suffering from CYP-induced cystitis. In conclusion, PK2/PKR1 signaling pathway contributes to the modulation of inflammation-mediated voiding dysfunction and spontaneous visceral pain. Local blockade of PKRs may represent a novel and promising therapeutic strategy for the clinical management of inflammation-related bladder diseases.

Expert consensus document: European Consensus Statement on congenital hypogonadotropic hypogonadism--pathogenesis, diagnosis and treatment

Congenital hypogonadotropic hypogonadism (CHH) is a rare disorder caused by the deficient production, secretion or action of gonadotropin-releasing hormone (GnRH), which is the master hormone regulating the reproductive axis. CHH is clinically and genetically heterogeneous, with >25 different causal genes identified to date. Clinically, the disorder is characterized by an absence of puberty and infertility. The association of CHH with a defective sense of smell (anosmia or hyposmia), which is found in ∼50% of patients with CHH is termed Kallmann syndrome and results from incomplete embryonic migration of GnRH-synthesizing neurons. CHH can be challenging to diagnose, particularly when attempting to differentiate it from constitutional delay of puberty. A timely diagnosis and treatment to induce puberty can be beneficial for sexual, bone and metabolic health, and might help minimize some of the psychological effects of CHH. In most cases, fertility can be induced using specialized treatment regimens and several predictors of outcome have been identified. Patients typically require lifelong treatment, yet ∼10-20% of patients exhibit a spontaneous recovery of reproductive function. This Consensus Statement summarizes approaches for the diagnosis and treatment of CHH and discusses important unanswered questions in the field.

Novel FGFR1 and KISS1R Mutations in Chinese Kallmann Syndrome Males with Cleft Lip/Palate

Kallmann syndrome (KS) is characterized by isolated hypogonadotropic hypogonadism (IHH) with anosmia and is sometimes associated with cleft lip/palate (CLP). In order to describe the clinical features, genetic etiology, and treatment outcome of KS males with CLP, we performed genetic screening for 15 known causal IHH genes (KAL1, FGFR1, NELF, FGF8, CHD7, WDR11, SEMA3A, KISS1R, KISS1, PROKR2, PROK2, TAC3, TACR3, GNRH1, and GNRHR) in four KS with CLP patients and six IHH patients without CLP. Two novel heterozygous missense mutations in FGFR1, (NM_001174066): c.776G>A (p.G259E) and (NM_001174066): c.358C>T (p.R120C), were identified in a 23-year-old KS male with cleft lip and an 18-year-old KS patient with cleft lip and palate, dental agenesis, and high arched palate, respectively. These two mutations were not presented in their healthy parents and 200 normal controls. One novel heterozygous missense mutation in KISS1R, (NM_032551): c.587C>A (p.P196H), was identified in an 18-year-old KS male with cleft lip and dental agenesis who developed sperm after being treated with gonadotropin. This mutation was also presented in his healthy father and grandfather. These results have implications for the diagnosis, genetic counseling, and treatment of KS and CLP males with mutations in FGFR1 gene.

Mutation analyses in pedigrees and sporadic cases of ethnic Han Chinese Kallmann syndrome patients

Kallmann syndrome, a form of idiopathic hypogonadotropic hypogonadism, is characterized by developmental abnormalities of the reproductive system and abnormal olfaction. Despite association of certain genes with idiopathic hypogonadotropic hypogonadism, the genetic inheritance and expression are complex and incompletely known. In the present study, seven Kallmann syndrome pedigrees in an ethnic Han Chinese population were screened for genetic mutations. The exons and intron-exon boundaries of 19 idiopathic hypogonadotropic hypogonadism (idiopathic hypogonadotropic hypogonadism)-related genes in seven Chinese Kallmann syndrome pedigrees were sequenced. Detected mutations were also tested in 70 sporadic Kallmann syndrome cases and 200 Chinese healthy controls. In pedigrees 1, 2, and 7, the secondary sex characteristics were poorly developed and the patients' sense of smell was severely or completely lost. We detected a genetic mutation in five of the seven pedigrees: homozygous KAL1 p.R191ter (pedigree 1); homozygous KAL1 p.C13ter (pedigree 2; a novel mutation); heterozygous FGFR1 p.R250W (pedigree 3); and homozygous PROKR2 p.Y113H (pedigrees 4 and 5). No genetic change of the assayed genes was detected in pedigrees 6 and 7. Among the 70 sporadic cases, we detected one homozygous and one heterozygous PROKR2 p.Y113H mutation. This mutation was also detected heterozygously in 2/200 normal controls and its pathogenicity is likely questionable. The genetics and genotype-phenotype relationships in Kallmann syndrome are complicated. Classical monogenic inheritance does not explain the full range of genetic inheritance of Kallmann syndrome patients. Because of stochastic nature of genetic mutations, exome analyses of Kallmann syndrome patients may provide novel insights.

Discovery and cardioprotective effects of the first non-Peptide agonists of the G protein-coupled prokineticin receptor-1

Prokineticins are angiogenic hormones that activate two G protein-coupled receptors: PKR1 and PKR2. PKR1 has emerged as a critical mediator of cardiovascular homeostasis and cardioprotection. Identification of non-peptide PKR1 agonists that contribute to myocardial repair and collateral vessel growth hold promises for treatment of heart diseases. Through a combination of in silico studies, medicinal chemistry, and pharmacological profiling approaches, we designed, synthesized, and characterized the first PKR1 agonists, demonstrating their cardioprotective activity against myocardial infarction (MI) in mice. Based on high throughput docking protocol, 250,000 compounds were computationally screened for putative PKR1 agonistic activity, using a homology model, and 10 virtual hits were pharmacologically evaluated. One hit internalizes PKR1, increases calcium release and activates ERK and Akt kinases. Among the 30 derivatives of the hit compound, the most potent derivative, IS20, was confirmed for its selectivity and specificity through genetic gain- and loss-of-function of PKR1. Importantly, IS20 prevented cardiac lesion formation and improved cardiac function after MI in mice, promoting proliferation of cardiac progenitor cells and neovasculogenesis. The preclinical investigation of the first PKR1 agonists provides a novel approach to promote cardiac neovasculogenesis after MI.

Combined pituitary hormone deficiency with unique pituitary dysplasia and morning glory syndrome related to a heterozygous PROKR2 mutation

Recent reports have indicated the role of the prokineticin receptor 2 gene (PROKR2) in the etiology of congenital hypopituitarism, including septo-optic dysplasia and Kallmann syndrome. In the present study, using next-generation targeted sequencing, we identified a novel heterozygous PROKR2 variant (c.742C>T; p.R248W) in a female patient who had combined pituitary hormone deficiency (CPHD), morning glory syndrome and a severely malformed pituitary gland. No other mutation was present in 27 genes related to hypogonadotropic hypogonadism, pituitary hormone deficiency and optic nerve malformation. The substituted amino acid was located on the third intracellular loop of the PROKR2 protein, which is a G protein-coupled receptor. Computational analyses with two programs (SIFT and PolyPhen-2) showed that the substitution was deleterious to PROKR2 function. The p.R248W mutation was transmitted from the patient’s mother, who had a slightly delayed menarche. Collectively, we provide further genetic evidence linking heterozygous PROKR2 mutations and the development of CPHD.