Adrenalectomy reduces FGF-1 and FGF-2 gene expression in specific rat brain regions and differently affects their induction by seizures

Wwox deletion leads to reduced GABA-ergic inhibitory interneuron numbers and activation of microglia and astrocytes in mouse hippocampus

The association of WW domain-containing oxidoreductase WWOX gene loss of function with central nervous system (CNS) related pathologies is well documented. These include spinocerebellar ataxia, epilepsy and mental retardation (SCAR12, OMIM: 614322) and early infantile epileptic encephalopathy (EIEE28, OMIM: 616211) syndromes. However, there is complete lack of understanding of the pathophysiological mechanisms at play. In this study, using a Wwox knockout (Wwox KO) mouse model (2 weeks old, both sexes) and stereological studies we observe that Wwox deletion leads to a significant reduction in the number of hippocampal GABA-ergic (γ-aminobutyric acid) interneurons. Wwox KO mice displayed significantly reduced numbers of calcium-binding protein parvalbumin (PV) and neuropeptide Y (NPY) expressing interneurons in different subfields of the hippocampus in comparison to Wwox wild-type (WT) mice. We also detected decreased levels of Glutamic Acid Decarboxylase protein isoforms GAD65/67 expression in Wwox null hippocampi suggesting lower levels of GABA synthesis. In addition, Wwox deficiency was associated with signs of neuroinflammation such as evidence of activated microglia, astrogliosis, and overexpression of inflammatory cytokines Tnf-a and Il6. We also performed comparative transcriptome-wide expression analyses of neural stem cells grown as neurospheres from hippocampi of Wwox KO and WT mice thus identifying 283 genes significantly dysregulated in their expression. Functional annotation of transcriptome profiling differences identified 'neurological disease' and 'CNS development related functions' to be significantly enriched. Several epilepsy-related genes were found differentially expressed in Wwox KO neurospheres. This study provides the first genotype-phenotype observations as well as potential mechanistic clues associated with Wwox loss of function in the brain.

Implication of fibroblast growth factors in epileptogenesis-associated circuit rearrangements

The transformation of a normal brain in epileptic (epileptogenesis) is associated with extensive morpho-functional alterations, including cell death, axonal and dendritic plasticity, neurogenesis, and others. Neurotrophic factors (NTFs) appear to be very strongly implicated in these phenomena. In this review, we focus on the involvement of fibroblast growth factor (FGF) family members. Available data demonstrate that the FGFs are highly involved in the generation of the morpho-functional alterations in brain circuitries associated with epileptogenesis. For example, data on FGF2, the most studied member, suggest that it may be implicated both in seizure susceptibility and in seizure-induced plasticity, exerting different, and apparently contrasting effects: favoring acute seizures but reducing seizure-induced cell death. Even if many FGF members are still unexplored and very limited information is available on the FGF receptors, a complex and fascinating picture is emerging: multiple FGFs producing synergic or antagonistic effects one with another (and/or with other NTFs) on biological parameters that, in turn, facilitate or oppose transformation of the normal tissue in epileptic. In principle, identifying key elements in these phenomena may lead to effective therapies, but reaching this goal will require confronting a huge complexity. One first step could be to generate a "neurotrophicome" listing the FGFs (and all other NTFs) that are active during epileptogenesis. This should include identification of the extent to which each NTF is active (concentrations at the site of action); how it is active (local representation of receptor subtypes); when in the natural history of disease this occurs; how the NTF at hand will possibly interact with other NTFs. This is extraordinarily challenging, but holds the promise of a better understanding of epileptogenesis and, at large, of brain function.

Short-hairpin RNA silencing of endogenous fibroblast growth factor 2 in rat hippocampus increases anxiety behavior

BACKGROUND

The fibroblast growth factor system has been implicated in the pathophysiology of mood disorders in humans and in affective behavior in animal models. However, the studies have been either correlative or involved exogenous administration of fibroblast growth factor 2 (FGF2). None of them have directly linked endogenous FGF2 to changes in emotional responses. Therefore, we began a series of studies to knockdown FGF2 by RNA interference to examine the role of brain FGF2 in emotional responsiveness.

METHODS

We assessed the efficacy of short-hairpin RNA (shRNA) sequences targeted to FGF2 in COS7 cells transfected with a plasmid vector containing the full-length FGF2 sequence. We then sought to assess the effects of knocking down FGF2 gene expression in vivo on behavior. We microinjected a lentiviral vector containing either a shRNA targeting FGF2 or a nonsilencing sequence bilaterally into the dentate gyrus of the rat.

RESULTS

In a reporter assay system, three different shRNA sequences resulted in significant FGF2 knockdown in vitro. Five weeks following a single microinjection of one of those sequences in vivo, we observed a significant decrease in FGF2 gene expression by messenger RNA in situ hybridization in the hippocampus. The FGF2 knockdown increased the time spent in the closed arms of the elevated-plus maze, a test of anxiety behavior.

CONCLUSIONS

The FGF2 knockdown in the hippocampus resulted in an anxiogenic effect. Together with our findings of an inverse correlation between anxiety and FGF2 expression levels, these results implicate FGF2 in the genesis and expression of anxiety disorders.

Differential cellular FGF-2 upregulation in the rat facial nucleus following axotomy, functional electrical stimulation and corticosterone: a possible therapeutic target to Bell's palsy

BACKGROUND

The etiology of Bell's palsy can vary but anterograde axonal degeneration may delay spontaneous functional recovery leading the necessity of therapeutic interventions. Corticotherapy and/or complementary rehabilitation interventions have been employed. Thus the natural history of the disease reports to a neurotrophic resistance of adult facial motoneurons leading a favorable evolution however the related molecular mechanisms that might be therapeutically addressed in the resistant cases are not known. Fibroblast growth factor-2 (FGF-2) pathway signaling is a potential candidate for therapeutic development because its role on wound repair and autocrine/paracrine trophic mechanisms in the lesioned nervous system.

METHODS

Adult rats received unilateral facial nerve crush, transection with amputation of nerve branches, or sham operation. Other group of unlesioned rats received a daily functional electrical stimulation in the levator labii superioris muscle (1 mA, 30 Hz, square wave) or systemic corticosterone (10 mgkg-1). Animals were sacrificed seven days later.

RESULTS

Crush and transection lesions promoted no changes in the number of neurons but increased the neurofilament in the neuronal neuropil of axotomized facial nuclei. Axotomy also elevated the number of GFAP astrocytes (143% after crush; 277% after transection) and nuclear FGF-2 (57% after transection) in astrocytes (confirmed by two-color immunoperoxidase) in the ipsilateral facial nucleus. Image analysis reveled that a seven days functional electrical stimulation or corticosterone led to elevations of FGF-2 in the cytoplasm of neurons and in the nucleus of reactive astrocytes, respectively, without astrocytic reaction.

CONCLUSION

FGF-2 may exert paracrine/autocrine trophic actions in the facial nucleus and may be relevant as a therapeutic target to Bell's palsy.

Involvement of astroglial fibroblast growth factor-2 and microglia in the nigral 6-OHDA parkinsonism and a possible role of glucocorticoid hormone on the glial mediated local trophism and wound repair

We have observed in previous studies that 6-hydroxydopamine (6-OHDA)-induced lesions in the nigrostriatal dopamine (DA) system promote increases of the astroglial basic fibroblast growth factor (FGF-2, bFGF) synthesis in the ascending DA pathways, event that could be modified by adrenosteroid hormones. Here, we first evaluated the changes of microglial reactivity in relation to the FGF-2-mediated trophic responses in the lesioned nigrostriatal DA system. 6-OHDA was injected into the left side of the rat substantia nigra. The OX42 immunohistochemistry combined with stereology showed the time course of the microglial activation. The OX42 immunoreactivity (IR) was already increased in the pars compacta of the substantia nigra (SNc) and ventral tegmental area (VTA) 2 h after the 6-OHDA injection, peaked on day 7, and remained increased on the 14th day time-interval. In the neostriatum, OX42 immunoreactive (ir) microglial profiles increased at 24 h, peaked at 72 h, was still increased at 7 days but not 14 days after the 6-OHDA injection. Two-colour immunofluorescence analysis of the tyrosine hydroxylase (TH) and OX42 IRs revealed the presence of small patches of TH IR within the activated microglia. A decreased FGF-2 IR was seen in the cytoplasm of DA neurons of the SNc and VTA as soon as 2 h after 6-OHDA injection. The majority of the DA FGF-2 ir cells of these regions had disappeared 72 h after neurotoxin. The astroglial FGF-2 IR increased in the SNc and VTA, which peaked on day 7. Two-colour immunofluorescence and immunoperoxidase analyses of the FGF-2 and OX42 IRs revealed no FGF-2 IR within the reactive or resting microglia. Second, we have evaluated in a series of biochemical experiments whether adrenocortical manipulation can interfere with the nigral lesion and the state of local astroglial reaction, looking at the TH and GFAP levels respectively. Rats were adrenalectomized (ADX) and received a nigral 6-OHDA stereotaxical injection 2 days later and sacrificed up to 3 weeks after the DA lesion. Western blot analysis showed time-dependent decrease and elevation of TH and GFAP levels, respectively, in the lesioned versus contralateral midbrain sides, events potentiated by ADX and worsened by corticosterone replacement. ADX decreased the levels of FGF-2 protein (23 kDa isoform) in the lesioned side of the ventral midbrain compared contralaterally. The results indicate that reactive astroglia, but not reactive microglia, showed an increased FGF-2 IR in the process of DA cell degeneration induced by 6-OHDA. However, interactions between these glial cells may be relevant to the mechanisms which trigger the increased astroglial FGF-2 synthesis and thus may be related to the trophic state of DA neurons and the repair processes following DA lesion. The findings also gave further evidence that adrenocortical hormones may regulate astroglial-mediated trophic mechanisms and wound repair events in the lesioned DA system that may be relevant to the progression of Parkinson's disease.

Stress and cocaine interact to modulate basic fibroblast growth factor (FGF-2) expression in rat brain

RATIONALE

Our laboratory has previously demonstrated that the expression of basic fibroblast growth factor (FGF-2), a protein involved in survival and maintenance of several cell phenotypes as well as in synaptic plasticity, is modulated by stress (Molteni et al., Brain Res Rev 37:249-258, 2001; Fumagalli et al., Neurobiol Dis 20:731-737, 2005) and cocaine (Fumagalli et al., J Neurochem 96:996-1004, 2006).

OBJECTIVES

Since it is widely recognized that stress influences drug seeking, we decided to investigate whether stress, acute or repeated, could influence the changes in FGF-2 gene expression brought about by cocaine.

RESULTS

Our data demonstrate that stress and cocaine interact to produce significant changes on FGF-2 expression in rat prefrontal cortex and striatum. In prefrontal cortex, our experiments demonstrated that a single exposure to stress potentiated cocaine-induced FGF-2 elevation, whereas prolonged stress prevented the modulation of the trophic factor in response to cocaine. In striatum, the magnitude of cocaine-induced FGF-2 response is enhanced by repeated stress, whereas no interaction was observed when acute stress and single exposure to cocaine were combined.

CONCLUSIONS

Our findings demonstrate that stress interacts with cocaine to alter the pattern of FGF-2 expression in a way that depends on whether stress is acute or chronic and in a regionally selective fashion. These results identify a potential molecular target through which stress alters cellular sensitivity to cocaine and might prove useful in understanding the mechanisms underlying brain vulnerability to stress.

Stress-induced glucocorticoids suppress the antisense molecular regulation of FGF-2 expression

Psychological stress can upregulate basic fibroblast growth factor (FGF-2) expression. Because glucocorticoids can also upregulate FGF-2 expression, the present studies investigated whether stress-induced glucocorticoids mediate the effects of stress on FGF-2. FGF-2 is regulated by an FGF-2 antisense (AS) molecular mechanism and so the present experiments also, for the first time, assessed the effects of stress on FGF-2-AS mRNA, as well as the mediating role of glucocorticoids. The effects of either escapable shock (ES) or yoked-inescapable tail shock (IS) on FGF-2 and FGF-2-AS were determined. To test whether glucocorticoids mediate the effect of stress on FGF-2 and FGF-2-AS, animals were pretreated with temporary corticosterone (CORT) synthesis inhibitors and exposed to IS. To test whether glucocorticoids are sufficient to modulate FGF-2 and FGF-2-AS mRNA, animals were injected with CORT and mRNA measured. ES and IS similarly downregulated FGF-2-AS mRNA at 0 h post-stress and upregulated FGF-2 mRNA 2 h post-stress. Inhibition of CORT synthesis abrogated the effect of IS on both FGF-2-AS and FGF-2 mRNA. Exogenous CORT mimicked the effects of ES and IS on FGF-2, but not FGF-2-AS mRNA. The present study demonstrates that glucocorticoids mediate the effects of stress on FGF-2 and FGF-2-AS.

Differential effects of reproductive and hormonal state on basic fibroblast growth factor and glial fibrillary acid protein immunoreactivity in the hypothalamus and cingulate cortex of female rats

Morphological changes in astrocytes occur in a number of brain regions including the hypothalamus and hippocampal regions as a function of hormonal and reproductive state. Because basic fibroblast growth factor has been shown to play an important role in morphological changes in astrocytes, we investigated whether basic fibroblast growth factor immunoreactivity would also be influenced by reproductive state and circulating gonadal steroids. To do this we compared astrocytic basic fibroblast growth factor and glial fibrillary acid protein immunoreactivity in hypothalamic nuclei and the cingulate cortex, area 2 among groups of cycling, late pregnant and lactating rats as well as in ovariectomized and ovariectomized hormone-replaced females. Significant differences in both basic fibroblast growth factor and glial fibrillary acid protein immunoreactivity were observed across groups in the supraoptic nucleus, parvocellular paraventricular nucleus, medial preoptic area of the hypothalamus and cingulate cortex 2. The pattern of change in basic fibroblast growth factor and glial fibrillary acid protein immunoreactivity varied across regions both in direction and magnitude. For example, although in the supraoptic nucleus ovariectomized rats had lower levels of basic fibroblast growth factor-ir than cycling females, this pattern was reversed within cingulate cortex. Overall the results of this study suggest that reproductive and hormonal states are associated with robust changes in basic fibroblast growth factor and glial fibrillary acid protein immunoreactivity in a number of brain areas but that the changes observed vary in magnitude as well as direction from one brain region to another.

The effects of corticosterone and dehydroepiandrosterone on neurotrophic factor mRNA expression in primary hippocampal and astrocyte cultures

The effects of corticosterone (CORT) and dehydroepiandrosterone (DHEA) on the expression of growth factor mRNA in either primary hippocampal cultures or astrocyte-enriched cultures from E18 CD rats was studied. In mixed primary cultures, 1 microM CORT up-regulated basic fibroblast growth factor (bFGF; FGF2) after 6 h of exposure, but down-regulated nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) were unchanged. A 100 microM NMDA alone decreased NT-3, increased BDNF, but had no effect on NGF or FGF2. Concurrently administered CORT had no additional effect on either NGF, BDNF or NT-3, but up-regulated FGF2. In astrocytic cultures, 1 microM CORT increased FGF2 and NT-3, but decreased BDNF and NGF. A dose-response study confirmed these results. DHEA (100 nM) up-regulated NGF after 3 h, but not at other time points (6, 12, 24, 48 h). It had no effect on the other growth factors in mixed primary cultures. In astrocytic cultures, there was no effect of DHEA. Adding DHEA or its sulphate (up to 1 microM) to CORT did not alter the latter's action on growth factor mRNA expression. These results show that CORT has a selective action on growth factor expression, which was greater in astrocytic than in mixed cultures, that CORT amplifies or moderates activity-induced expression following NMDA, but that DHEA does not influence the effects of CORT on growth factor mRNA expression under these conditions.

The three sorCS genes are differentially expressed and regulated by synaptic activity

We have isolated the murine sorCS3 gene, a new member of the family of receptors containing a Vps10p-domain. Receptors of this family facilitate rapid endocytosis and are thought to be involved in intracellular sorting. SorCS3 and the highly homologous sorCS1 and sorCS2 genes were expressed in a combinatorial, mostly non-overlapping pattern in both the developing and mature central nervous system. During development, distribution and abundancy of their transcripts was regulated. Moreover, their expression was differentially influenced by neuronal activity in the hippocampus of adult mice. Although kainic acid-induced seizures had no effect on sorCS2 mRNA levels, they dramatically increased the expression of sorCS1 and sorCS3. The activity-dependent induction of sorCS1 expression required de novo protein synthesis, whereas that of sorCS3 did not. Our results imply that the three sorCS genes have diverse, but partly overlapping functions in the developing and mature central nervous system.

Gene expression changes in single dentate granule neurons after adrenalectomy of rats

Removal of corticosterone by adrenalectomy induces apoptosis 3 days later, in some, but not all, rat dentate granule cells. We hypothesized that individual dentate cells trigger specific gene expression profiles that partly determine their apoptosis susceptibility. RNA was collected from physiologically characterized granule cells at 2 or 3 days after adrenalectomy or sham operation, and linearly amplified. The amplified RNA was hybridized to cDNA clones of: (1) candidate genes earlier identified after adrenalectomy in whole hippocampi with SAGE; and (2) genes encoding growth factors and their receptors. We observed that based on the entire expression profile, cells relatively resistant to apoptosis 3 days after adrenalectomy clustered together with one-third of cells 2 days after adrenalectomy. Within the group of ADX cells, a limited number of transcript ratios were found to correlate-positively or negatively-with a known risk factor for apoptosis, calcium influx. The overall analysis of physiological properties and multiple gene expression in single cells can narrow down the number of critical genes involved in apoptosis identified with large scale gene screening methods and allows a first impression of their role as being a potential risk factor or neuroprotective.

Modulation of fibroblast growth factor-2 by stress and corticosteroids: from developmental events to adult brain plasticity

Neurotrophic factors are a heterogeneous group of peptides that play important roles on brain function at different development stages. Basic fibroblast growth factor (FGF-2), one of these molecules, is highly expressed in developing and adult brain. Its expression can be regulated under different experimental situations and this may be relevant for cellular vulnerability and brain plasticity. Stress and glucocorticoid hormones produce short- and long-term effects on brain function, which can involve the regulation of specific neurotrophic factors within selected brain structures. Treatments with corticosterone or dexamethasone up-regulate FGF-2 expression in different rat brain regions as well as in cultured astroglial cells. A similar elevation of FGF-2 biosynthesis is also observed in several brain regions following an acute restraint stress. This response is rapid and transient and, as FGF-2 is neuroprotective, may represent a defense mechanism through which the brain may limit the deleterious effect of stress over time. Moreover exposure to corticosterone during late stage of embryonic life (E18-E20) produces a significant reduction of FGF-2 mRNA levels in the adult hippocampus of male rats as well as changes in its acute modulation in response to stress or corticosterone. These data suggest that stress-related events taking place during brain maturation can modulate the expression of FGF-2 within selected brain regions thus contributing to permanent structural and functional alterations leading to an increased vulnerability to challenging life events.

Kainate-induced genes in the hippocampus: lessons from expression patterns

Kainate, the analog of the excitatory amino acid L-glutamate, upon binding to non-NMDA glutamate receptors, causes depolarization of neurons followed by severe status epilepticus, neurodegeneration, plasticity and gliosis. These events are best observed in hippocampus, the limbic structure implicated in learning and long-term memory formation. Neurons in all hippocampal structures undergo hyper-activation, however, whereas the cells in the CA subfields degenerate within 2--3 days following the application of kainate, the granule cells of the dentate gyrus are resistant to any form of neurodegeneration and even initiate new synaptic contacts. These physiological and histological changes are modulated by short-term and long-term alterations in gene expression. Perhaps close examination of the changing spatio-temporal patterns of mRNAs of various genes may help in generating a clearer picture of the molecular events leading to complex cognitive functions.

The role of cytokines and growth factors in seizures and their sequelae

Although the neuropathological changes caused by severe or repeated seizures have been well characterized, many questions about the molecular mechanisms involved remain unanswered. Neuronal cell death, reactive gliosis, enhanced neurogenesis, and axonal sprouting are four of the best-studied sequelae of seizures. In vitro, each of these pathological processes can be substantially influenced by soluble protein factors, including neurotrophins, cytokines, and growth factors. Furthermore, many of these proteins and their receptors are expressed in the adult brain and are up-regulated in response to neuronal activity and injury. We review the evidence that these intercellular signaling proteins regulate seizure activity as well as subsequent pathology in vivo. As nerve growth factor and brain derived neurotrophic factor are the best-studied proteins of this class, we begin by discussing the evidence linking these neurotrophins to epilepsy and seizure. More than a dozen additional cytokines, growth factors, and neurotrophins that have been examined in the context of epilepsy models are then considered. We discuss the effect of seizure on expression of cytokines and growth factors, and explore the regulation of seizure development and aftermath by exogenous application or antagonist perturbation of these proteins. The experimental evidence supports a role for these factors in each aspect of seizure and pathology, and suggests potential targets for future therapeutics.

Adrenal steroid regulation of neurotrophic factor expression in the rat hippocampus

Adrenal steroids and neurotrophic factors are important modulators of neuronal plasticity, function, and survival in the rat hippocampus. Adrenal steroids act through two receptor subtypes, the glucocorticoid receptor (GR) and the mineralocorticoid receptor, and activation of each receptor subtype has distinct biochemical and physiological consequences. Adrenal steroids may exert their effects on neuronal structure and function through the regulation of expression of neurotrophic and growth-associated factors. We have examined adrenal steroid regulation of the neurotrophins brain-derived neurotrophic factor, neurotrophin-3, and basic fibroblast growth factor, as well as the growth associated protein GAP-43, through activation of GR or mineralocorticoid receptor with selective agonists. Our findings indicated that in CA2 pyramidal cells, adrenalectomy resulted in decreases in the levels of basic fibroblast growth factor and neurotrophin-3 messenger RNA, which were prevented by activation of mineralocorticoid but not glucocorticoid receptors. Adrenalectomy-induced increases in GAP-43 and brain-derived neurotrophic factor messenger RNA levels could be blocked by activation of glucocorticoid receptors in CA1, but not in CA3, pyramidal cells. Thus the extent to which adrenal steroids regulate hippocampal neurotrophic and growth-associated factors, appears to be dependent both on the adrenal steroid receptor subtype activated and on the hippocampal subregion examined.

Differential regulation of FGF-2 and FGFR-1 in rat cortical astrocytes by dexamethasone and isoproterenol

We have used rat cortical astrocytes in culture to investigate the signaling pathways involved in the regulation of fibroblast growth factor-2 (FGF-2) and one of its high affinity receptor FGF receptor-1 (FGFR-1). These cells represent a source of different neurotrophic factors and play important roles in physiological and pathological conditions of the central nervous system. FGF-2 mRNA levels are increased by stimulation of beta-adrenergic receptors or exposure to glucocorticoid hormones and these effects are additive to each other. The regulation of FGFR-1, highly expressed in cultured astroglial cells, appears to be different. Isoproterenol produced an elevation of FGFR-1 mRNA levels, whereas dexamethasone decreased its expression alone or in the presence of isoproterenol, suggesting that the glucocorticoid pathway may predominate over the cAMP-induced up-regulation of the receptor. FGF-2 over-expression may produce different cellular responses depending on the concomitant regulation of its receptor and the cell phenotype where these changes do occur. These mechanisms can contribute to adaptive changes taking place in the CNS in different physiological and pathological situations.

Adrenalectomy-induced neuronal degeneration

The binding of glucocorticoids to CNS receptors results in the modulation of many processes, ranging from neurotransmission to cell birth and death. It is of no surprise, therefore, that the removal of these steroids following adrenalectomy disrupts a variety of physiological functions throughout the brain. It is the aim of this review to briefly describe the findings of research examining some of these glucocorticoid-mediated CNS effects; however, as many of these areas have been reviewed extensively by others, this review will focus on the recently described phenomenon, adrenalectomy-induced hippocampal cell death.