Novel galanin receptors in teleost fish: identification, expression and regulation by sex steroids

In fish, the onset of puberty, the transition from juvenile to sexually reproductive adult animals, is triggered by the activation of pituitary gonadotrophin secretion and its timing is influenced by external and internal factors that include the growth/adiposity status of the animal. Kisseptins have been implicated in the activation of puberty but peripheral signals coming from the immature gonad or associated to the metabolic/nutritional status are also thought to be involved. Additionally, there is evidence that the galaninergic system in the brain and testis of pre-pubertal male sea bass is a possible mediator involved in the translation of somatic signals leading to gonadal maturation. Here, the transcripts for four galanin receptors (GALR), named GALR1a, 1b, 2a and 2b, were isolated from European sea bass, Dicentrarchus labrax. Phylogenetic analysis confirmed the previously reported duplication of GALR1 in teleost fish, and unravelled the duplication of GALR2 in teleost fish and in some tetrapod species. Comparison with human showed that the key amino acids involved in ligand binding are present in the corresponding GALR1 and GALR2 orthologues. Transcripts for all four receptors are expressed in brain and testes of adult fish with GALR1a and GALR1b abundant in testes 15 and hardly detected in ovaries. In order to investigate whether GALR1 dimorphic expression was dependent on steroid context we evaluated the effect of 11-ketotestosterone and 17β-estradiol treatments on the receptor expression in brain and testes of pre-pubertal males. Interestingly, steroid treatments had no effect on the expression of GALRs in the brain while in the testes, GALR1a and GALR1b were significantly up regulated by 11KT. Altogether, these results support a role for the galaninergic system, in particular the GALR1 paralog in fish reproductive function

Mitogenic signaling by Gq/11-coupled receptors

By binding to their cognate GPCRs, many potent mitogens such as neuropeptides, angiotensin II or lysophosphatidic acid stimulate cell proliferation via engaging the ERK/MAPK cascade. As mentioned before, agonists stimulating Gq/11-coupled receptors activate PLCb isoforms thereby activating PKCs and elevating [Ca2+]i. These two second messengers represent key molecules for coupling Gq/11 proteins to the ERK/MAPK cascade. In this work, by means of GnRH in gonadotropic aT3-1 cells and galanin or bradykinin in SCLC cells, different aspects of Gq/11-dependent mitogenic signaling pathways were revealed. Our findings together with previous reports underline the notion that signaling pathways emanating from Gq/11-coupled receptors are tightly regulated in a cell- and receptor-specific manner

Development of therapeutics for the treatment of diabetic brain complications

Type-2 diabetes (T2D) is characterized by hyperglycemia and hyperlipidemia, resulting in impaired insulin production and insulin resistance in peripheral tissues. Several studies have demonstrated an association between diabetes and central nervous system complications such as stroke and Alzheimer’s disease. Due to the fact that T2D is one of the fastest growing chronic illnesses, there is an urgent need to improve our knowledge on the pathogenic mechanisms to why diabetes leads to brain complications as well as to identify novel drugable targets for therapeutic use. Project 1: studies I-II Pre-clinical studies have shown that adult neurogenesis is impaired in diabetic animal models. We hypothesized that diabetes leading to neurogenesis impairment plays a role in the development of neurological complications. If so, normalizing neurogenesis in diabetes/obesity could be therapeutically useful in counteracting neurological dysfunction. The aim of studies I-II was to establish an in vitro system where to study the effect of a diabetic milieu on adult neurogenesis. Furthermore, we determined the potential role of pituitary adenylate cyclase-activating polypeptide (PACAP) and galanin to protect adult neural stem cells (NSCs) from these diabetic-like conditions. Moreover, we determined whether apoptosis and the unfolded protein response (UPR) were induced by diabetic-like conditions and whether their regulation was involved in the PACAP/galanin-mediated protective effect. Finally, we studied the potential regulation of PACAP and galanin receptors in NSCs in response to diabetic-like conditions in vitro and ex vivo. The viability of NSCs isolated from the mouse brain subventricular zone (SVZ) was assessed in presence of a diabetic milieu, as mimicked by high palmitate and glucose, which characterize diabetic glucolipotoxicity. The results show that high palmitate and glucose impair NSC viability in correlation to increased apoptosis (Bcl-2, cleaved caspase-3) and UPR signaling (CHOP, BIP, XBP1, JNK phosphorylation). We also show that PACAP and galanin counteract glucolipotoxicity via PAC1 receptor and GalR3 activation, respectively. Furthermore, we also report that PACAP and galanin receptors are regulated by diabetes in NSCs in vitro and in the SVZ ex vivo. Project 2: study III T2D is a strong risk factor for stroke and no therapy based on neuroprotection is currently available. Exendin-4 (Ex-4) is a glucagon-like peptide-1 receptor (GLP-1R) agonist in clinical use for the treatment of T2D, which has also been shown to mediate neuroprotection against stroke pre-clinically. However, the applicability of a therapy based on Ex-4 has not been investigated in a pre-clinical setting with clinical relevance. The aim of this study was to determine the potential efficacy of Ex-4 against stroke in T2D rats by using a drug administration paradigm and a dose that mimics a diabetic patient on Ex-4 therapy. Moreover, we investigated inflammation and neurogenesis as potential cellular mechanisms at the basis of Ex-4 efficacy. T2D Goto-Kakizaki (GK) rats were treated peripherally for 4 weeks with daily clinical doses of Ex-4 (0.1, 1, 5 !g/kg body weight) before inducing stroke by transient middle cerebral artery occlusion. The Ex-4 treatment was continued for 2-4 weeks thereafter. The severity of ischemic damage was measured by evaluation of stroke volume and by stereological counting of neurons in the striatum and cortex. Evaluation of stroke-induced inflammation, stem cell proliferation and neurogenesis was also quantitatively assessed by immunohistochemistry. We show that peripheral administration of Ex-4 counteracts ischemic brain damage in T2D GK rats. The results also show that Ex-4 decreased microglia infiltration and increased stroke-induced neural stem cell proliferation and neuroblast formation, while stroke-induced neurogenesis was not affected by Ex-4 treatment. Together, our data in project 1 show that we have established an in vitro assay where to study the molecular mechanism on how diabetes impact adult neurogenesis. Furthermore, our results show that this assay has the potential to be developed into a screening platform for the identification of molecules that can regulate adult neurogenesis under diabetes. In project 2, we show neuroprotective efficacy against stroke by Ex-4 in a T2D rat model, by using a pre-clinical setting with clinical relevance. Ex-4 is an anti-diabetic drug in clinical use that has been reported to show limited side effects. Thus, at least in theory stroke patients should be able to easily receive this treatment, probably with minimal risks

Using Gene Expression Arrays to Elucidate Transcriptional Profiles Underlying Prolactin Function

Prolactin is an ancient hormone, with different functions in many species. The binding of prolactin to its receptor, a member of the cytokine receptor superfamily, results in the activation of different intracellular signaling pathways, such as JAK2/STAT5, MAP kinase, and PI3K/AKT. How prolactin elicits so many different biological responses remains unclear. Recently, microarray technology has been applied to identify prolactin target genes in different systems. Here, we attempt to summarize and compare the available data. Our comparison of the genes reported to be transcriptionally regulated by prolactin indicates that there are few genes in common between the different tissues. Among the organs studied, mammary and prostate glands displayed the largest number of overlaps in putative prolactin target genes. Some of the candidates have been implicated in tumorigenesis. The relevance and validation of microarray data, as well as comparison of the results obtained by different groups, will be discusse

Gene expression profiling en association with prion-related lesions in the medulla oblongata of symptomatic natural scrapie animals.

The pathogenesis of natural scrapie and other prion diseases remains unclear. Examining transcriptome variations in infected versus control animals may highlight new genes potentially involved in some of the molecular mechanisms of prion-induced pathology. The aim of this work was to identify disease-associated alterations in the gene expression profiles of the caudal medulla oblongata (MO) in sheep presenting the symptomatic phase of natural scrapie. The gene expression patterns in the MO from 7 sheep that had been naturally infected with scrapie were compared with 6 controls using a Central Veterinary Institute (CVI) custom designed 4×44K microarray. The microarray consisted of a probe set on the previously sequenced ovine tissue library by CVI and was supplemented with all of the Ovis aries transcripts that are currently publicly available. Over 350 probe sets displayed greater than 2-fold changes in expression. We identified 148 genes from these probes, many of which encode proteins that are involved in the immune response, ion transport, cell adhesion, and transcription. Our results confirm previously published gene expression changes that were observed in murine models with induced scrapie. Moreover, we have identified new genes that exhibit differential expression in scrapie and could be involved in prion neuropathology. Finally, we have investigated the relationship between gene expression profiles and the appearance of the main scrapie-related lesions, including prion protein deposition, gliosis and spongiosis. In this context, the potential impacts of these gene expression changes in the MO on scrapie development are discussed

Afferent Neuronal Control of Type-I Gonadotropin Releasing Hormone Neurons in the Human.

Understanding the regulation of the human menstrual cycle represents an important ultimate challenge of reproductive neuroendocrine research. However, direct translation of information from laboratory animal experiments to the human is often complicated by strikingly different and unique reproductive strategies and central regulatory mechanisms that can be present in even closely related animal species. In all mammals studied so far, type-I gonadotropin releasing hormone (GnRH) synthesizing neurons form the final common output way from the hypothalamus in the neuroendocrine control of the adenohypophysis. Under various physiological and pathological conditions, hormonal and metabolic signals either regulate GnRH neurons directly or act on upstream neuronal circuitries to influence the pattern of pulsatile GnRH secretion into the hypophysial portal circulation. Neuronal afferents to GnRH cells convey important metabolic-, stress-, sex steroid-, lactational-, and circadian signals to the reproductive axis, among other effects. This article gives an overview of the available neuroanatomical literature that described the afferent regulation of human GnRH neurons by peptidergic, monoaminergic, and amino acidergic neuronal systems. Recent studies of human genetics provided evidence that central peptidergic signaling by kisspeptins and neurokinin B (NKB) play particularly important roles in puberty onset and later, in the sex steroid-dependent feedback regulation of GnRH neurons. This review article places special emphasis on the topographic distribution, sexual dimorphism, aging-dependent neuroanatomical changes, and plastic connectivity to GnRH neurons of the critically important human hypothalamic kisspeptin and NKB systems

Duplicated membrane estrogen receptors in the European sea bass (Dicentrarchus labrax): Phylogeny, expression and regulation throughout the reproductive cycle

The numerous estrogen functions reported across vertebrates have been classically explained by their binding to specific transcription factors, the nuclear estrogen receptors (ERs). Rapid non-genomic estrogenic responses have also been recently identified in vertebrates including fish, which can be mediated by membrane receptors such as the G protein-coupled estrogen receptor (Gper). In this study, two genes for Gper, namely gpera and gperb, were identified in the genome of a teleost fish, the European sea bass. Phylogenetic analysis indicated they were most likely retained after the 3R teleost-specific whole genome duplication and raises questions about their function in male and female sea bass. Gpera expression was mainly restricted to brain and pituitary in both sexes while gperb had a widespread tissue distribution with higher expression levels in gill filaments, kidney and head kidney. Both receptors were detected in the hypothalamus and pituitary of both sexes and significant changes in gpers expression were observed throughout the annual reproductive season. In female pituitaries, gpera showed an overall increase in expression throughout the reproductive season while gperb levels remained constant. In the hypothalamus, gpera had a higher expression during vitellogenesis and decreased in fish entering the ovary maturation and ovulation stage, while gperb expression increased at the final atresia stage. In males, gpers expression was constant in the hypothalamus and pituitary throughout the reproductive cycle apart from the mid- to late testicular development stage transition when a significant up-regulation of gpera occurred in the pituitary. The differential sex, seasonal and subtype-specific expression patterns detected for the two novel gper genes in sea bass suggests they may have acquired different and/or complementary roles in mediating estrogens actions in fish, namely on the neuroendocrine control of reproduction.info:eu-repo/semantics/publishedVersio

The generation of knock-in mice expressing fluorescently tagged galanin receptors 1 and 2

The neuropeptide galanin has diverse roles in the central and peripheral nervous systems, by activating the G protein-coupled receptors Gal(1), Gal(2) and the less studied Gal(3) (GalR1–3 gene products). There is a wealth of data on expression of Gal(1–3) at the mRNA level, but not at the protein level due to the lack of specificity of currently available antibodies. Here we report the generation of knock-in mice expressing Gal(1) or Gal(2) receptor fluorescently tagged at the C-terminus with, respectively, mCherry or hrGFP (humanized Renilla green fluorescent protein). In dorsal root ganglia (DRG) neurons expressing the highest levels of Gal(1)-mCherry, localization to the somatic cell membrane was detected by live-cell fluorescence and immunohistochemistry, and that fluorescence decreased upon addition of galanin. In spinal cord, abundant Gal(1)-mCherry immunoreactive processes were detected in the superficial layers of the dorsal horn, and highly expressing intrinsic neurons of the lamina III/IV border showed both somatic cell membrane localization and outward transport of receptor from the cell body, detected as puncta within cell processes. In brain, high levels of Gal(1)-mCherry immunofluorescence were detected within thalamus, hypothalamus and amygdala, with a high density of nerve endings in the external zone of the median eminence, and regions with lesser immunoreactivity included the dorsal raphe nucleus. Gal(2)-hrGFP mRNA was detected in DRG, but live-cell fluorescence was at the limits of detection, drawing attention to both the much lower mRNA expression than to Gal(1) in mice and the previously unrecognized potential for translational control by upstream open reading frames (uORFs)

Using the CRISPR/Cas9 system to understand neuropeptide biology and regulation

Funding was provided by a Wellcome Trust ISSF starting grant (105625/Z/14/Z), Medical Research Scotland (PhD-719-2013), GW Pharmaceuticals (PhD-719-2013 - S.5242.001) and the BBSRC (BB/J012343/1).Peer reviewedPublisher PD