Purinergic signaling pathways in endocrine system

Knockout mice with pituitary malformations help identify human cases of hypopituitarism

BACKGROUND

Congenital hypopituitarism (CH) and its associated syndromes, septo-optic dysplasia (SOD) and holoprosencephaly (HPE), are midline defects that cause significant morbidity for affected people. Variants in 67 genes are associated with CH, but a vast majority of CH cases lack a genetic diagnosis. Whole exome and whole genome sequencing of CH patients identifies sequence variants in genes known to cause CH, and in new candidate genes, but many of these are variants of uncertain significance (VUS).

METHODS

The International Mouse Phenotyping Consortium (IMPC) is an effort to establish gene function by knocking-out all genes in the mouse genome and generating corresponding phenotype data. We used mouse embryonic imaging data generated by the Deciphering Mechanisms of Developmental Disorders (DMDD) project to screen 209 embryonic lethal and sub-viable knockout mouse lines for pituitary malformations.

RESULTS

Of the 209 knockout mouse lines, we identified 51 that have embryonic pituitary malformations. These genes not only represent new candidates for CH, but also reveal new molecular pathways not previously associated with pituitary organogenesis. We used this list of candidate genes to mine whole exome sequencing data of a cohort of patients with CH, and we identified variants in two unrelated cases for two genes, MORC2 and SETD5, with CH and other syndromic features.

CONCLUSIONS

The screening and analysis of IMPC phenotyping data provide proof-of-principle that recessive lethal mouse mutants generated by the knockout mouse project are an excellent source of candidate genes for congenital hypopituitarism in children.

Enokitake Mushroom and Its Active Component, Adenosine, Which Restores Testosterone Production in Impaired and Fatigued Mouse Models

Several studies have reported the effects of the consumption of various mushroom species on the testes in animal experimental models. Mushrooms, including enokitake mushrooms (Flammulina velutipes), and vegetables contain adenosine may affect testosterone production. Here, we aimed to elucidate the effects of enokitake and its active component, adenosine, on testosterone production in primary cultures of testicular cells in vivo using mice models and in vitro. The administration of enokitake ethanolic extract increased testosterone production in the cisplatin-impaired mouse model. The direct effect of mushroom extracts on testicular cells was examined and liquid chromatography-mass spectrometry analysis confirmed that the mushroom- and vegetable-induced increase in testosterone production mainly involved adenosine. Additionally, the administration of enokitake extract or adenosine to wet floor fatigue model mice promoted testicular testosterone production and enhanced Leydig cell function through insulin-like peptide three level upregulation. Structurally related compounds, including cordycepin, showed lower bioactivity than adenosine. This study showed that the ingestion of adenosine-containing mushrooms and vegetables may effectively increase testicular testosterone production. We conclude that mushrooms with a relatively high adenosine content, such as enokitake, may be useful against aging and fatigue.

Purinergic signaling in thyroid disease

It is known that thyroid hormones play pivotal roles in a wide variety of pathological and physiological events. Thyroid diseases, mainly including hyperthyroidism, hypothyroidism, and thyroid cancer, are highly prevalent worldwide health problems and frequently associated with severe clinical manifestations. However, etiology of hyperthyroidism, hypothyroidism, and thyroid cancer is not fully understood. Purinergic signaling accounts for a complex network of receptors and extracellular enzymes responsible for the recognition and degradation of extracellular nucleotides and adenosine. It has been established that purinergic signaling modulates pathways in a wide range of physiopathological conditions including hypertension, diabetes, hepatic diseases, psychiatric and neurodegeneration, rheumatic immune diseases, and cancer. More recently, the purinergic system is found to exist in thyroid gland and play an important role in the pathophysiology of thyroid diseases. Therefore, throughout this review, we focus on elaborating the changes in purinergic receptors, extracellular enzymes, and extracellular nucleotides and adenosine in hyperthyroidism, hypothyroidism, and thyroid cancer. Profound understanding of the relationship between the purinergic signaling with thyroid diseases provides a promising research area for insights into the molecular basis of thyroid diseases and also develops new and exciting insights into the treatment of thyroid diseases, especially thyroid cancer.

Testicular adenosine acts as a pro-inflammatory molecule: role of testicular peritubular cells

Extracellular ATP has been described to be involved in inflammatory cytokine production by human testicular peritubular cells (HTPCs). The ectonucleotidases ENTPD1 and NT5E degrade ATP and have been reported in rodent testicular peritubular cells. We hypothesized that if a similar situation exists in human testis, ATP metabolites may contribute to cytokine production. Indeed, ENTPD1 and NT5E were found in situ and in vitro in HTPCs. Malachite green assays confirmed enzyme activities in HTPCs. Pharmacological inhibition of ENTPD1 (by POM-1) significantly reduced pro-inflammatory cytokines evoked by ATP treatment, suggesting that metabolites of ATP, including adenosine, are likely involved. We focused on adenosine and detected three of the four known adenosine receptors in HTPCs. One, A2B, was also found in situ in peritubular cells of human testicular sections. The A2B agonist BAY60-6583 significantly elevated levels of IL6 and CXCL8, a result also obtained with adenosine and its analogue NECA. Results of siRNA-mediated A2B down-regulation support a role of this receptor. In mouse peritubular cells, in contrast to HTPCs, all four of the known adenosine receptors were detected; when challenged with adenosine, cytokine expression levels significantly increased. Organotypic short-term testis cultures yielded comparable results and indicate an overall pro-inflammatory action of adenosine in the mouse testis. If transferable to the in vivo situation, our results may implicate that interference with the generation of ATP metabolites or interference with adenosine receptors could reduce inflammatory events in the testis. These novel insights may provide new avenues for treatment of sterile inflammation in male subfertility and infertility.

Update of P2X receptor properties and their pharmacology: IUPHAR Review 30

The known seven mammalian receptor subunits (P2X1–7) form cationic channels gated by ATP. Three subunits compose a receptor channel. Each subunit is a polypeptide consisting of two transmembrane regions (TM1 and TM2), intracellular N- and C-termini, and a bulky extracellular loop. Crystallization allowed the identification of the 3D structure and gating cycle of P2X receptors. The agonist-binding pocket is located at the intersection of two neighbouring subunits. In addition to the mammalian P2X receptors, their primitive ligand-gated counterparts with little structural similarity have also been cloned. Selective agonists for P2X receptor subtypes are not available, but medicinal chemistry supplied a range of subtype-selective antagonists, as well as positive and negative allosteric modulators. Knockout mice and selective antagonists helped to identify pathological functions due to defective P2X receptors, such as male infertility (P2X1), hearing loss (P2X2), pain/cough (P2X3), neuropathic pain (P2X4), inflammatory bone loss (P2X5), and faulty immune reactions (P2X7).

Effect of fluoride on endocrine tissues and their secretory functions -- review

The effects of fluoride on endocrine tissues has not been sufficiently explored to date. The current body of knowledge suggest significant effects of that mineral on reducing sex hormone levels, which may consequently impair fertility and disrupt puberty. The majority of studies confirm that sodium fluoride increases TSH levels and decreases the concentrations of T3 and T4 produced by the thyroid. Moreover, a correlation was observed between NaF and increased secretion of PTH by the parathyroid glands, without a significant impact on body calcium levels. Probably, fluoride may exert adverse effects on insulin levels, impairing pancreatic function and resulting in abnormal glucose tolerance. Observations also include decreased levels of cortisol secreted by the adrenal glands. In light of the few existing studies, the mechanism of fluoride toxicity on the endocrine system has been described.

Characterization of the N6-etheno-bridge method to assess extracellular metabolism of adenine nucleotides: detection of a possible role for purine nucleoside phosphorylase in adenosine metabolism

The goal of this study was to determine the validity of using N6-etheno-bridged adenine nucleotides to evaluate ecto-nucleotidase activity. We observed that the metabolism of N6-etheno-ATP versus ATP was quantitatively similar when incubated with recombinant CD39, ENTPD2, ENTPD3, or ENPP-1, and the quantitative metabolism of N6-etheno-AMP versus AMP was similar when incubated with recombinant CD73. This suggests that ecto-nucleotidases process N6-etheno-bridged adenine nucleotides similarly to endogenous adenine nucleotides. Four cell types rapidly (t1/2, 0.21 to 0.66 h) metabolized N6-etheno-ATP. Applied N6-etheno-ATP was recovered in the medium as N6-etheno-ADP, N6-etheno-AMP, N6-etheno-adenosine, and surprisingly N6-etheno-adenine; intracellular N6-etheno compounds were undetectable. This suggests minimal cellular uptake, intracellular metabolism, or deamination of these compounds. N6-etheno-ATP, N6-etheno-ADP, N6-etheno-AMP, N6-etheno-adenosine, and N6-etheno-adenine had little affinity for recombinant A1, A2A, or A2B receptors, for a subset of P2X receptors (3H-α,β-methylene-ATP binding to rat bladder membranes), or for a subset of P2Y receptors (35S-ATP-αS binding to rat brain membranes), suggesting minimal pharmacological activity. N6-etheno-adenosine was partially converted to N6-etheno-adenine in four different cell types; this was blocked by purine nucleoside phosphorylase (PNPase) inhibition. Intravenous N6-etheno-ATP was quickly metabolized, with N6-etheno-adenine being the main product in naïve rats, but not in rats pretreated with a PNPase inhibitor. PNPase inhibition reduced the urinary excretion of endogenous adenine and attenuated the conversion of exogenous adenosine to adenine in the renal cortex. The N6-etheno-bridge method is a valid technique to assess extracellular metabolism of adenine nucleotides by ecto-nucleotidases. Also, rats express an enzyme with PNPase-like activity that metabolizes N6-etheno-adenosine to N6-etheno-adenine.

Update of P2Y receptor pharmacology: IUPHAR Review 27

Eight G protein-coupled P2Y receptor subtypes respond to extracellular adenine and uracil mononucleotides and dinucleotides. P2Y receptors belong to the δ group of rhodopsin-like GPCRs and contain two structurally distinct subfamilies: P2Y₁ , P2Y₂ , P2Y₄ , P2Y₆ , and P2Y₁₁ (principally G_q protein-coupled P2Y₁ -like) and P2Y_12-14 (principally G_i protein-coupled P2Y₁₂ -like) receptors. Brain P2Y receptors occur in neurons, glial cells, and vasculature. Endothelial P2Y₁ , P2Y₂ , P2Y₄ , and P2Y₆ receptors induce vasodilation, while smooth muscle P2Y₂ , P2Y₄ , and P2Y₆ receptor activation leads to vasoconstriction. Pancreatic P2Y₁ and P2Y₆ receptors stimulate while P2Y₁₃ receptors inhibits insulin secretion. Antagonists of P2Y₁₂ receptors, and potentially P2Y₁ receptors, are anti-thrombotic agents, and a P2Y₂ /P2Y₄ receptor agonist treats dry eye syndrome in Asia. P2Y receptor agonists are generally pro-inflammatory, and antagonists may eventually treat inflammatory conditions. This article reviews recent developments in P2Y receptor pharmacology (using synthetic agonists and antagonists), structure and biophysical properties (using X-ray crystallography, mutagenesis and modelling), physiological and pathophysiological roles, and present and potentially future therapeutic targeting.

Role of Mast Cell-Derived Adenosine in Cancer

Accumulating evidence has highlighted the accumulation of mast cells (MCs) in tumors. However, their impact on tumor development remained controversial. Indeed, cumulative data indicate an enigmatic role for MCs in cancer, whereby depending on the circumstances, which still need to be resolved, MCs function to promote or restrict tumor growth. By responding to multiple stimuli MCs release multiple inflammatory mediators, that contribute to the resolution of infection and resistance to envenomation, but also have the potency to promote or inhibit malignancy. Thus, MCs seem to possess the power to define tumor projections. Given this remarkable plasticity of MC responsiveness, there is an urgent need of understanding how MCs are activated in the tumor microenvironment (TME). We have recently reported on the direct activation of MCs upon contact with cancer cells by a mechanism involving an autocrine formation of adenosine and signaling by the A3 adenosine receptor. Here we summarized the evidence on the role of adenosine signaling in cancer, in MC mediated inflammation and in the MC-cancer crosstalk.

Purinergic implication in amyotrophic lateral sclerosis-from pathological mechanisms to therapeutic perspectives

Amyotrophic lateral sclerosis (ALS) is a clinically heterogeneous disorder characterized by degeneration of upper motor neurons in the brainstem and lower motor neurons in the spinal cord. Multiple mechanisms of motor neuron injury have been implicated, including more than 20 different genetic factors. The pathogenesis of ALS consists of two stages: an early neuroprotective stage and a later neurotoxic. During early phases of disease progression, the immune system through glial and T cell activities provides anti-inflammatory factors that sustain motor neuron viability. As the disease progresses and motor neuron injury accelerates, a rapidly succeeding neurotoxic phase develops. A well-orchestrated purine-mediated dialog among motor neurons, surrounding glia and immune cells control the beneficial and detrimental activities occurring in the nervous system. In general, low adenosine triphosphate (ATP) concentrations protect cells against excitotoxic stimuli through purinergic P2X4 receptor, whereas high concentrations of ATP trigger toxic P2X7 receptor activation. Finally, adenosine is also involved in ALS progression since A2A receptor antagonists prevent motor neuron death. Given the complex cellular cross-talk occurring in ALS and the recognized function of extracellular nucleotides and adenosine in neuroglia communication, the comprehensive understanding of purinome dynamics might provide new research perspectives to decipher ALS and help to design more efficient and targeted drugs. This review will focus on the purinergic players involved in ALS etiology and disease progression and current therapeutic strategies to enhance neuroprotection and suppress neurotoxicity.

Interactions of Pannexin1 channels with purinergic and NMDA receptor channels

Pannexins are a three-member family of vertebrate plasma membrane spanning molecules that have homology to the invertebrate gap junction forming proteins, the innexins. However, pannexins do not form gap junctions but operate as plasma membrane channels. The best-characterized member of these proteins, Pannexin1 (Panx1) was suggested to be functionally associated with purinergic P2X and N-methyl-D-aspartate (NMDA) receptor channels. Activation of these receptor channels by their endogenous ligands leads to cross-activation of Panx1 channels. This in turn potentiates P2X and NMDA receptor channel signaling. Two potentiation concepts have been suggested: enhancement of the current responses and/or sustained receptor channel activation by ATP released through Panx1 pore and adenosine generated by ectonucleotidase-dependent dephosphorylation of ATP. Here we summarize the current knowledge and hypotheses about interactions of Panx1 channels with P2X and NMDA receptor channels. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Molecular Mechanisms and Signaling Pathways Involved in the Nutritional Support of Spermatogenesis by Sertoli Cells

Sertoli cells play a central role in spermatogenesis. They maintain the blood-testis barrier, an essential feature of seminiferous tubules which creates the proper environment for the occurrence of the spermatogenesis. However, this confinement renders germ cells almost exclusively dependent on Sertoli cells' nursing function and support. Throughout spermatogenesis, differentiating sperm cells become more specialized, and their biochemical machinery is insufficient to meet their metabolic demands. Although the needs are not the same at all differentiation stages, Sertoli cells are able to satisfy their needs. In order to maintain the seminiferous tubule energetic homeostasis, Sertoli cells react in response to several metabolic stimuli, through signaling cascades. The AMP-activated kinase, sensitive to the global energetic status; the hypoxia-inducible factors, sensitive to oxygen concentration; and the peroxisome proliferator-activated receptors, sensitive to fatty acid availability, are pathways already described in Sertoli cells. These cells' metabolism also reflects the whole-body metabolic dynamics. Metabolic diseases, including obesity and type II diabetes mellitus, induce changes that, both directly and indirectly, affect Sertoli cell function and, ultimately, (dys)function in male reproductive health. Insulin resistance, increased estrogen synthesis, vascular disease, and pubic fat accumulation are examples of metabolic-related conditions that affect male fertility potential. On the other hand, malnutrition can also induce negative effects on male sexual function. In this chapter, we review the molecular mechanisms associated with the nutritional state and male sexual (dys)function and the central role played by the Sertoli cells.

Antipurinergic therapy for autism-An in-depth review

Are the symptoms of autism caused by a treatable metabolic syndrome that traces to the abnormal persistence of a normal, alternative functional state of mitochondria? A small clinical trial published in 2017 suggests this is possible. Based on a new unifying theory of pathogenesis for autism called the cell danger response (CDR) hypothesis, this study of 10 boys, ages 5-14years, showed that all 5 boys who received antipurinergic therapy (APT) with a single intravenous dose of suramin experienced improvements in all the core symptoms of autism that lasted for 5-8weeks. Language, social interaction, restricted interests, and repetitive movements all improved. Two children who were non-verbal spoke their first sentences. None of these improvements were observed in the placebo group. Larger and longer studies are needed to confirm this promising discovery. This review introduces the concept of M2 (anti-inflammatory) and M1 (pro-inflammatory) mitochondria that are polarized along a functional continuum according to cell stress. The pathophysiology of the CDR, the complementary functions of M1 and M2 mitochondria, relevant gene-environment interactions, and the metabolic underpinnings of behavior are discussed as foundation stones for understanding the improvements in ASD behaviors produced by antipurinergic therapy in this small clinical trial.

P2 purinergic receptor antagonists disrupt maternal behavior in lactating rats

The involvement of purinergic signaling in several brain functions has been recognized, but the modulation on maternal behavior by the purinergic system is not established, even though there are functional interactions between the purinergic and oxytocinergic systems. Therefore, the aim of our study was to investigate whether central administration of P2 receptor antagonists affected the maternal behavior of lactating rats and c-Fos immunoreactivity in the forebrain. On day 7 of lactation, female rats were treated with vehicle (5μL; i.c.v.), suramin (9.4-75.0μg/5μL; i.c.v.) or PPADS (9.4-75.0μg/5μL; i.c.v.) 30min before the experiment began. The maternal behavior was evaluated during the 30min following suramin or PPADS administration. In addition, c-Fos-positive nuclei were counted in the medial preoptic area (MPOA) and in the bed nucleus of the stria terminalis (BNST), and neurons that were double-labeled for c-Fos/OT were counted in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus of lactating rats. The results show that P2 receptor antagonists decreased maternal care and decreased neuronal activation in the MPOA and BNST and activation of oxytocinergic neurons in hypothalamic nuclei. Our results indicate that the purinergic system modulates maternal behavior and neuronal activation induced by suckling during lactation.

Functional expression of P2 purinoceptors in a primary neuroglial cell culture of the rat arcuate nucleus

The arcuate nucleus (ARC) plays an important role in the hypothalamic control of energy homeostasis. Expression of various purinoceptor subtypes in the rat ARC and physiological studies suggest a modulatory function of P2 receptors within the neuroglial ARC circuitry. A differentiated mixed neuronal and glial microculture was therefore established from postnatal rat ARC, revealing neuronal expression of ARC-specific transmitters involved in food intake regulation (neuropeptide Y (NPY), proopiomelanocortin (POMC), tyrosine hydroxylase (TH)). Some NPYergic neurons cosynthesized TH, while POMC and TH expression proved to be mutually exclusive. Stimulation with the general purinoceptor agonists 2-methylthioadenosine-5'triphosphate (2-MeSATP) and ATP but not the P2X1/P2X3 receptor subtype agonist α,β-methyleneadenosine-5'triphosphate (α,β-meATP) induced intracellular calcium signals in ARC neurons and astrocytes. Some 5-10% each of 2-MeSATP responsive neurons expressed POMC, NYP or TH. Supporting the calcium imaging data, radioligand binding studies to hypothalamic membranes showed high affinity for 2-MeSATP, ATP but not α,β-meATP to displace [α-(35)S]deoxyadenosine-5'thiotriphosphate ([(35)S]dATPαS) from P2 receptors. Repetitive superfusion with equimolar 2-MeSATP allowed categorization of ARC cells into groups with a high or low (LDD) degree of purinoceptor desensitization, the latter allowing further receptor characterization. Calcium imaging experiments performed at 37°C vs. room temperature showed further reduction of desensitization. Agonist-mediated intracellular calcium signals were suppressed in all LDD neurons but only 25% of astrocytes in the absence of extracellular calcium, suggestive of metabotropic P2Y receptor expression in the majority of ARC astrocytes. The highly P2Y1-selective receptor agonists MRS2365 and 2-methylthioadenosine-5'diphosphate (2-MeSADP) activated 75-85% of all 2-MeSATP-responsive ARC astrocytes. Taking into consideration the high potency to dose-dependently stimulate ARC cells of the LDD group, the high affinity for rat P2X(1-3) and low affinity for rat P2X4, P2X7 and P2Y receptor subtypes except P2Y1 and P2Y13, the agonist 2-MeSATP primarily acted upon P2X2 and P2Y1 purinoceptors to trigger intracellular calcium signaling in ARC neurons and astrocytes.