X-linked GnRH deficiency: role of KAL-1 mutations in GnRH deficiency

Pathophysiology of Congenital Anomalies of the Kidney and Urinary Tract: A Comprehensive Review

Congenital anomalies of the kidney and urinary tract (CAKUT) represent a broad range of diseases with differing mechanisms, clinical presentations, and prognoses. With an estimated prevalence of between 4 and 60 per 10,000 births, CAKUT represents a sizable number of patients for pediatric and adult nephrologists as therapies have progressed, allowing longer life spans. Many CAKUT disorders are associated with genetic mutations, and with advances in genomic sequencing, these genes are being identified at an increasing rate. Understanding these mutations provides insight into these conditions' molecular mechanisms and pathophysiology. In this article, we discuss the epidemiology, presentation, and outcomes of CAKUT in addition to our current understanding of genetic and molecular mechanisms in these diseases.

Male hypogonadism: pathogenesis, diagnosis, and management

Organic male hypogonadism due to irreversible hypothalamic-pituitary-testicular (HPT) pathology is easily diagnosed and treated with testosterone-replacement therapy. However, controversy surrounds the global practice of prescribing testosterone to symptomatic men with low testosterone and non-gonadal factors reducing health status, such as obesity, type 2 diabetes, and ageing (ie, functional hypogonadism), but without identifiable HPT axis pathology. Health optimisation remains the gold-standard management strategy. Nevertheless, in the last decade large clinical trials and an individual patient data meta-analysis of smaller clinical trials confirmed that testosterone therapy induces modest, yet statistically significant, improvements in sexual function without increasing short-term to medium-term cardiovascular or prostate cancer risks in men with functional hypogonadism. Although testosterone improves bone mineral density and insulin sensitivity in these men, trials from the last decade suggest insufficient evidence to determine the safety and effectiveness of use of this hormone for the prevention of fractures or type 2 diabetes. This Review discusses the pathogenesis and diagnosis of male hypogonadism and appraises the evidence underpinning the management of this condition.

Long non-coding RNA MSTRG.5970.28 regulates proliferation and apoptosis of goose follicle granulosa cells via the miR-133a-3p/ANOS1 pathway

The development of follicles in the ovaries is a critical determinant of poultry egg production. There are existing studies on the follicular development patterns in poultry, but the specific regulatory mechanisms still need further study. In a previous study, we identified long non-coding RNA (lncRNA) MSTRG.5970.28, anosmin 1 (ANOS1), and its predicted target miR-133a-3p that may be associated with goose ovary development. However, the function of MSTRG.5970.28 in goose granulosa cells and its regulatory mechanisms affecting granulosa cell proliferation and apoptosis have not been reported. In the present study, MSTRG.5970.28 and miR-133a-3p overexpression and interference vectors were constructed. Combined with reverse-transcription real-time quantitative PCR (RT-qPCR), a dual luciferase activity assay, Cell Counting Kit-8 (CCK-8), and flow cytometric analysis, we investigated the role of the MSTRG.5970.28-miR-133a-3p-ANOS1 axis in goose follicular granulosa cells and the associated regulatory mechanisms. MSTRG.5970.28 was found to be localized in the cytoplasm and its expression was influenced by reproductive hormones. The targeting relationship among MSTRG.5970.28, ANOS1, and miR-133a-3p were verified by a dual luciferase activity assay. CCK-8 and apoptosis assays showed that MSTRG.5970.28 inhibited the proliferation and promoted apoptosis of goose granulosa cells. The regulatory role of miR-133a-3p on granulosa cell proliferation and apoptosis was opposite to MSTRG.5970.28. We found that the proliferative and apoptotic effects of granulosa cells caused by MSTRG.5970.28 overexpression were attenuated by miR-133a-3p. MSTRG.5970.28 functions as a competitive endogenous RNA that regulates ANOS1 expression by sponging miR-133a-3p and thus exerts regulatory functions in granulosa cells. In sum, the present study identified lncRNA MSTRG.5970.28 as associated with goose ovary development, which affects the expression of ANOS1 by targeting miR-133a-3p, thereby influencing the proliferation and apoptosis of goose granulosa cells.

The Clinical and Genetic Characteristics in Children with Idiopathic Hypogonadotropin Hypogonadism

Background. Idiopathic hypogonadotropin hypogonadism (IHH) is caused by hypothalamic-pituitary-gonadal axis dysfunction. This is divided into Kallmann syndrome which has an impaired sense of smell and hypogonadotropin hypogonadism with normal olfactory (nIHH sense. Approximately 60% of patients are associated with Kallmann syndrome, whereas there are approximately 40% with hypogonadotropin hypogonadism (nIHH). This disease is associated with various variants in genes along with different phenotypic characteristics, and even those gene variations could also lead to the cancer formation in patients. So, current study has been designed to investigate and to better understand the characteristics of various IHH-associated genes and the correlation between IHH genes and phenotype. Methods. The cohort included 14 children with IHH (6 patients of KS and 8 patients of IHH), including 13 boys and 1 girl. Exclusion criteria are as follows: diagnosis of secondary hypogonadotropin hypogonadism due to tumor, trauma, drugs, or other systemic diseases. Clinical data and genetic results were analyzed. Results. Almost all male patients showed micropenis (12/13, 92.3%), and few of them had cryptorchidism (5/13, 41.7%). A total of 6 genes, CHD7, PROKR2, ANOS1, FGFR1, SEMA3A, and NDNF, were detected. CHD7 was the most common (11/17, 64.7%), and the main mutation type was missense mutation (14/16, 87.5%). Six reported variants and 10 new variants (5 genes, including entire ANSO1 duplicates) were found. Neonatal variation was detected in 3 patients with IHH. Eight patients inherited the variation from their father, while five patients inherited it from their mother. One patient had both FGFR1 and SEMA3A gene variants, while the other had two different CHD7 gene variants and entire ANSO1 repeats. According to ACMG criteria, 4 variants were pathogenic (P), 2 were possibly pathogenic (LP), and 8 had uncertain significance (US). In patients with P or LP (5/6, 83.3%), we found that extragonadal symptoms were more common. Conclusions. It was concluded that variations in the studied genes could lead to the IHH. Ten new variants have been reported which may lead to different symptoms of IHH. For CHD7 variants, the rare sequencing variants (RSVs) of P or LP showed commonly associated with CHARGE syndrome. Findings of the current study may help for the better diagnosis and treatment of IHH.

Genetics of congenital olfactory dysfunction: a systematic review of the literature

Olfaction, as one of our 5 senses, plays an important role in our daily lives. It is connected to proper nutrition, social interaction, and protection mechanisms. Disorders affecting this sense consequently also affect the patients' general quality of life. Because the underlying genetics of congenital olfactory disorders (COD) have not been thoroughly investigated yet, this systematic review aimed at providing information on genes that have previously been reported to be mutated in patients suffering from COD. This was achieved by systematically reviewing existing literature on 3 databases, namely PubMed, Ovid Medline, and ISI Web of Science. Genes and the type of disorder, that is, isolated and/or syndromic COD were included in this study, as were the patients' associated abnormal features, which were categorized according to the affected organ(-system). Our research yielded 82 candidate genes/chromosome loci for isolated and/or syndromic COD. Our results revealed that the majority of these are implicated in syndromic COD, a few accounted for syndromic and isolated COD, and the least underly isolated COD. Most commonly, structures of the central nervous system displayed abnormalities. This study is meant to assist clinicians in determining the type of COD and detecting potentially abnormal features in patients with confirmed genetic variations. Future research will hopefully expand this list and thereby further improve our understanding of COD.

Whole genome investigation of an atypical autism case identifies a novel ANOS1 mutation with subsequent diagnosis of Kallmann syndrome

We report an actionable secondary finding from whole-genome sequencing (WGS) of a 10-year-old boy with autism. WGS identified non-synonymous variants in several genes, including a nonsense mutation in the ANOS1 gene which is an X-linked cause of Kallmann syndrome. WGS can provide insights into complex genetic disorders such as autism, and actionable incidental findings can offer the potential for therapeutic interventions.

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.

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.

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.

New Biomarkers to Evaluate Hyperandrogenemic Women and Hypogonadal Men

Androgens can have variable effects on men and women. Women may be evaluated for androgen excess for several reasons. Typically, young premenopausal women present with clinical symptoms of hirsutism, alopecia, irregular menses, and/or infertility. The most common cause of these symptoms is polycystic ovary syndrome. After menopause, even though ovaries stop producing estrogen, they continue to produce androgen, and women can have new onset of hirsutism and alopecia. Laboratory evaluation involves measurement of the major ovarian and adrenal androgens. In women, age, phase of the menstrual cycle, menopausal status, obesity, metabolic health, and sex hormone-binding proteins significantly affect total-androgen levels and complicate interpretation. This review will summarize the clinically relevant evaluation of hyperandrogenemia at different life stages in women and highlight pitfalls associated with interpretation of commonly used hormone measurements. Hypogonadism in men is a clinical syndrome characterized by low testosterone and/or low sperm count. Symptoms of hypogonadism include decreased libido, erectile dysfunction, decreased vitality, decreased muscle mass, increased adiposity, depressed mood, osteopenia, and osteoporosis. Hypogonadism is a common disorder in aging men. Hypogonadism is observed rarely in young boys and adolescent men. Based on the defects in testes, hypothalamus, and/or pituitary glands, hypogonadism can be broadly classified as primary, secondary, and mixed hypogonadism. Diagnosis of hypogonadism in men is based on symptoms and laboratory measurement. Biomarkers in use/development for hypogonadism are classified as hormonal, Leydig and Sertoli cell function, semen, genetic/RNA, metabolic, microbiome, and muscle mass-related. These biomarkers are useful for diagnosis of hypogonadism, determination of the type of hypogonadism, identification of the underlying causes, and therapeutic assessment. Measurement of serum testosterone is usually the most important single diagnostic test for male hypogonadism. Patients with primary hypogonadism have low testosterone and increased luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Patients with secondary hypogonadism have low testosterone and low or inappropriately normal LH and FSH. This review provides an overview of hypogonadism in men and a detailed discussion of biomarkers currently in use and in development for diagnosis thereof.

ANOS1: a unified nomenclature for Kallmann syndrome 1 gene (KAL1) and anosmin-1

It is accepted that confusion regarding the description of genetic variants occurs when researchers do not use standard nomenclature. The Human Genome Organization Gene Nomenclature Committee contacted a panel of consultants, all working on the KAL1 gene, to propose an update of the nomenclature of the gene, as there was a convention in the literature of using the ‘KAL1’ symbol, when referring to the gene, but using the name ‘anosmin-1’ when referring to the protein. The new name, ANOS1, reflects protein name and is more transferrable across species.

Expanding the genetic spectrum of ANOS1 mutations in patients with congenital hypogonadotropic hypogonadism

STUDY QUESTION

What is the prevalence and functional consequence of ANOS1 (KAL1) mutations in a group of men with congenital hypogonadotropic hypogonadism (CHH)?

SUMMARY ANSWER

Three of forty-two (7.1%) patients presented ANOS1 mutations, including a novel splice site mutation leading to exon skipping and a novel contiguous gene deletion associated with ichthyosis.

WHAT IS KNOWN ALREADY

CHH is characterized by lack of pubertal development and infertility, due to deficient production, secretion or action of GnRH, and can be associated with anosmia/hyposmia (Kallmann syndrome, KS) or with a normal sense of smell (normosmic CHH). Mutations in the anosmin-1 (ANOS1) gene are responsible for the X-linked recessive form of KS.

STUDY DESIGN, SIZE, DURATION

This cross-sectional study included 42 unrelated men with CHH (20 with KS and 22 with normosmic CHH).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were screened for mutations in the ANOS1 gene by DNA sequencing. Identified mutations were further investigated by RT-PCR analysis and multiplex ligation-dependent probe amplification (MLPA) analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Hemizygous mutations were identified in three (7.1%) KS cases: a novel splice acceptor site mutation (c.542-1G>C), leading to skipping of exon 5 in the ANOS1 transcript in a patient with self-reported normosmia (but hyposmic upon testing); a recurrent nonsense mutation (c.571C>T, p.Arg191*); and a novel 4.8 Mb deletion involving ANOS1 and eight other genes (VCX3B, VCX2, PNPLA4, VCX, STS, HDHD1, VCX3A and NLGN4X) in KS associated with ichthyosis.

LIMITATIONS, REASONS FOR CAUTION

Objective olfactory testing was not performed in all cases of self-reported normosmia and this may have underestimated the olfactory deficits.

WIDER IMPLICATIONS OF THE FINDINGS

This study further expands the spectrum of known genetic defects associated with CHH and suggests that patients with self-reported normal olfactory function should not be excluded from ANOS1 genetic testing.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Portuguese Foundation for Science and Technology. The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Novel interstitial deletion in Xp22.3 in a typical X-linked recessive family with Kallmann syndrome

Kallmann syndrome (KS) is a clinically and genetically heterogeneous condition characterised by hypogonadotropic hypogonadism with anosmia or hyposmia. More than nineteen genes causing KS have been reported to date. KAL1, first identified to causing the X-linked form of KS, accounts for 10%-20% of KS patients. In this study, we designed a panel including 17 known genes causing KS for genetic diagnosis and research and report a typical and rare family of which three generations had been affected by KS. A novel CNV in Xp22.3 was identified through targeted next-sequencing technology and high-resolution microarray. The breakpoint (chrX:8536480 and chrX:8730416) was defined, and the size of deletion is about 0.24 Mb. The CNV including KAL1 and FAM9A had a negative effect on the expression of KAL1, resulting in decreased level of KAL1 mRNA in whole blood. In addition, the proband had significant improvement in testicular volumes and secondary sex characters except spermatogenesis after regular treatment, which indicates the CNV may have a negative effect on spermatogenesis. Our study expands the genotypic spectrum of KAL1 mutations associated with KS and provides a practical pipeline for genetic diagnosis or research.

Novel application of luciferase assay for the in vitro functional assessment of KAL1 variants in three females with septo-optic dysplasia (SOD)

KAL1 is implicated in 5% of Kallmann syndrome cases, a disorder which genotypically overlaps with septo-optic dysplasia (SOD). To date, a reporter-based assay to assess the functional consequences of KAL1 mutations is lacking. We aimed to develop a luciferase assay for novel application to functional assessment of rare KAL1 mutations detected in a screen of 422 patients with SOD. Quantitative analysis was performed using L6-myoblasts stably expressing FGFR1, transfected with a luciferase-reporter vector containing elements of the FGF-responsive osteocalcin promoter. The two variants assayed [p.K185N, p.P291T], were detected in three females with SOD (presenting with optic nerve hypoplasia, midline and pituitary defects). Our novel assay revealed significant decreases in transcriptional activity [p.K185N: 21% (p < 0.01); p.P291T: 40% (p < 0.001)]. Our luciferase-reporter assay, developed for assessment of KAL1 mutations, determined that two variants in females with hypopituitarism/SOD are loss-of-function; demonstrating that this assay is suitable for quantitative assessment of mutations in this gene.

Decreased expression of Kallmann syndrome 1 sequence gene (KAL1) contributes to oral squamous cell carcinoma progression and significantly correlates with poorly differentiated grade

BACKGROUND

Kallmann syndrome 1 sequence gene (KAL1) protein is an extracellular matrix associated protein which plays vital roles in neurons development and cell migration. However, its biological functions and clinical implications have yet not been revealed in oral carcinogenesis. The objective of the study was to evaluate the role of KAL1 in oral cancer and determine clinical significance of KAL1 in oral squamous cell carcinomas (OSCCs).

METHODS

The expression pattern of KAL1 was examined in a testing cohort including OSCCs (n = 42) and paired adjacent tissues (PATs) (n = 14) by real-time PCR. The result was further validated in a validating cohort of OSCCs (n = 32). Correlation between clinicopathological parameters and KAL1 mRNA levels was analyzed by Kruskal-Wallis test. In vitro, the effects of KAL1 ablation through siRNA-mediated knockdown on the proliferation of OSCC cells were determined by CCK-8, BrdU, and colonies formation assays, respectively. In addition, cell cycle distribution was further evaluated by cytometry.

RESULTS

We observed that remarkably decreased expression of KAL1 mRNA in two independent cohorts (P = 0.0002 and P = 0.033, respectively). Furthermore, downregulated KAL1 mRNA was significantly associated with worse pathological grade (P = 0.013 and P = 0.035, respectively). Upon KAL1 silencing, the proliferation and colonies formation potentials of OSCC cells were notably promoted by accelerating G1 to M phase transition.

CONCLUSION

These data indicated that KAL1 plays a potential suppressive role on OSCC initiation and progression, and KAL1 gene may serve as an adjuvant biomarker for the identification of pathological grade.

Exogenous kisspeptin administration as a probe of GnRH neuronal function in patients with idiopathic hypogonadotropic hypogonadism

CONTEXT

Idiopathic hypogonadotropic hypogonadism (IHH) results from defective synthesis, secretion, or action of GnRH. Kisspeptin is a potent stimulus for GnRH secretion.

OBJECTIVE

We probed the functional capacity of the GnRH neuronal network in patients with IHH.

PARTICIPANTS

Eleven subjects with congenital IHH (9 men and 2 women) and one male subject who underwent reversal of IHH were studied. Six of the twelve subjects had an identified genetic cause of their IHH: KAL1 (n = 1), FGFR1 (n = 3), PROKR2 (n = 1), GNRHR (n = 1).

INTERVENTION

Subjects underwent q10 min blood sampling to measure GnRH-induced LH secretion at baseline and in response to intravenous boluses of kisspeptin (0.24 nmol/kg) and GnRH (75 ng/kg) both pre- and post-six days of treatment with exogenous GnRH (25 ng/kg sc every 2 h).

RESULTS

All subjects with abiding IHH failed to demonstrate a GnRH-induced LH response to exogenous kisspeptin. In contrast, the subject who achieved reversal of his hypogonadotropism demonstrated a robust response to kisspeptin.

CONCLUSIONS

The functional capacity of the GnRH neuronal network in IHH patients is impaired, as evidenced by their inability to respond to the same dose of kisspeptin that effects a robust GnRH-induced LH response in healthy men and luteal-phase women. This impairment is observed across a range of genotypes, suggesting that it reflects a fundamental property of GnRH neuronal networks that have not been properly engaged during pubertal development. In contrast, a patient who had experienced reversal of his hypogonadotropism responded to exogenous kisspeptin.

ERK1/2 signaling is essential for the chemoattraction exerted by human FGF2 and human anosmin-1 on newborn rat and mouse OPCs via FGFR1

Signaling through fibroblast growth factor receptors (FGFRs) is essential for many cellular processes including proliferation and migration, as well as differentiation events such as myelination. Anosmin-1 is an extracellular matrix (ECM) glycoprotein that interacts with the fibroblast growth factor receptor 1 (FGFR1) to exert its biological actions through this receptor, although the intracellular pathways underlying anosmin-1 signaling remain largely unknown. This protein is defective in the X-linked form of Kallmann syndrome (KS) and has a prominent role in the migration of neuronal and oligodendroglial precursors. We have shown that anosmin-1 exerts a chemotactic effect via FGFR1 on neuronal precursors from the subventricular zone (SVZ) and the essential role of the ERK1/2 signaling. We report here the positive chemotactic effect of FGF2 and anosmin-1 on rat and mouse postnatal OPCs via FGFR1. The same effect was observed with the truncated N-terminal region of anosmin-1 (A1Nt). The introduction in anosmin-1 of the missense mutation F517L found in patients suffering from KS annulled the chemotactic activity; however, the mutant form carrying the disease-causing mutation E514K also found in KS patients, behaved as the wild-type protein. The chemoattraction exhibited by FGF2 and anosmin-1 on OPCs was blocked by the mitogen-activated protein kinase (MAPK) inhibitor U0126, suggesting that the activation of the ERK1/2 MAPK signaling pathway following interaction with the FGFR1 is necessary for FGF2 and anosmin-1 to exert their chemotactic effect. In fact, both proteins were able to induce the phosphorylation of the ERK1/2 kinases after the activation of the FGFR1 receptor.

Invertebrate models of kallmann syndrome: molecular pathogenesis and new disease genes

Kallmann Syndrome is a heritable disorder characterized by congenital anosmia, hypogonadotropic hypogonadism and, less frequently, by other symptoms. The X-linked form of this syndrome is caused by mutations affecting the KAL1 gene that codes for the extracellular protein anosmin-1. Investigation of KAL1 function in mice has been hampered by the fact that the murine ortholog has not been identified. Thus studies performed in other animal models have contributed significantly to an understanding of the function of KAL1. In this review, the main results obtained using the two invertebrate models, the nematode worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster, are illustrated and the contribution provided by them to the elucidation of the molecular pathogenesis of Kallmann Syndrome is discussed in detail. Structure-function dissection studies performed in these two animal models have shown how the different domains of anosmin-1 carry out specific functions, also suggesting a novel intramolecular regulation mechanism among the different domains of the protein. The model that emerges is one in which anosmin-1 plays different roles in different tissues, interacting with different components of the extracellular matrix. We also describe how the genetic approach in C. elegans has allowed the discovery of the genes involved in KAL1-heparan sulfate proteoglycans interactions and the identification of HS6ST1 as a new disease gene.

Transforming growth factor-β regulates the expression of anosmin (KAL-1) in human retinal pigment epithelial cells

In a microarray analysis of human retinal pigment epithelial cells (HRPE) treated with TGF-β, in addition to the alteration of a number of known Extracellular matrix (ECM)-related genes regulated by TGF-β, we found a significant increase in the expression of Kallmann Syndrome (KAL)-1 gene, that codes for the protein anosmin-1. Enhanced expression of KAL-1 by TGF-β was validated by real-time PCR analysis. In in vitro experiments, TGF-β receptor inhibitor abolished TGF-β-induced expression of KAL-1. Immunofluorescence staining showed increased presence of anosmin-1 in TGF-β treated HRPE cells, with distinct localization at the intercellular junctions. Treatment of HRPE cells with TGF-β enhanced secretion of anosmin-1 and the release of anosmin-1 was further augmented by heparin sulfate. Enhanced secretion of anosmin-1 in the presence of TGF-β and heparin was also observed in other ocular cells such as corneal epithelial and corneal fibroblast cultures. The role of anosmin-1, a protein with adhesion functions, in retinal structure, function and pathology has not been known and remains to be investigated.

The cysteine-rich region and the whey acidic protein domain are essential for anosmin-1 biological functions

The protein anosmin-1, coded by the KAL1 gene responsible for the X-linked form of Kallmann syndrome (KS), exerts its biological effects mainly through the interaction with and signal modulation of fibroblast growth factor receptor 1 (FGFR1). We have previously shown the interaction of the third fibronectin-like type 3 (FnIII) domain and the N-terminal region of anosmin-1 with FGFR1. Here, we demonstrate that missense mutations reported in patients with KS, C172R and N267K did not alter or substantially reduce, respectively, the binding to FGFR1. These substitutions annulled the chemoattraction of the full-length protein over subventricular zone (SVZ) neuronal precursors (NPs), but they did not annul it in the N-terminal-truncated protein (A1Nt). We also show that although not essential for binding to FGFR1, the cysteine-rich (CR) region is necessary for anosmin-1 function and that FnIII.3 cannot substitute for FnIII.1 function. Truncated proteins recapitulating nonsense mutations found in KS patients did not show the chemotropic effect on SVZ NPs, suggesting that the presence behind FnIII.1 of any part of anosmin-1 produces an unstable protein incapable of action. We also identify the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway as necessary for the chemotropic effect exerted by FGF2 and anosmin-1 on rat SVZ NPs.