Metabolic Messengers: fibroblast growth factor 1

While fibroblast growth factor (FGF) 1 is expressed in multiple tissues, only adipose-derived and brain FGF1 have been implicated in the regulation of metabolism. Adipose FGF1 production is upregulated in response to dietary stress and is essential for adipose tissue plasticity in these conditions. Similarly, in the brain, FGF1 secretion into the ventricular space and the adjacent parenchyma is increased after a hypercaloric challenge induced by either feeding or glucose infusion. Potent anorexigenic properties have been ascribed to both peripheral and centrally injected FGF1. The ability of recombinant FGF1 and variants with reduced mitogenicity to lower glucose, suppress adipose lipolysis and promote insulin sensitization elevates their potential as candidates in the treatment of type 2 diabetes mellitus and associated comorbidities. Here, we provide an overview of the known metabolic functions of endogenous FGF1 and discuss its therapeutic potential, distinguishing between peripherally or centrally administered FGF1.

Localization of fibroblast growth factor 23 protein in the rat hypothalamus

Fibroblast growth factor 23 (FGF23) is an endocrine growth factor and known to play a pivotal role in phosphate homeostasis. Interestingly, several studies point towards a function of FGF23 in the hypothalamus. FGF23 classically activates the FGF receptor 1 in the presence of the co-receptor αKlotho, of both gene expression in the brain was previously established. However, studies on gene and protein expression of FGF23 in the brain are scarce and have been inconsistent. Therefore, our aim was to localise FGF23 gene and protein expression in the rat brain with focus on the hypothalamus. Also, we investigated the protein expression of αKlotho. Adult rat brains were used to localise and visualise FGF23 and αKlotho protein in the hypothalamus by immunofluorescence labelling. Furthermore, western blots were used for assessing hypothalamic FGF23 protein expression. FGF23 gene expression was investigated by qPCR in punches of the arcuate nucleus, lateral hypothalamus, paraventricular nucleus, choroid plexus, ventrolateral thalamic nucleus and the ventromedial hypothalamus. Immunoreactivity for FGF23 and αKlotho protein was found in the hypothalamus, third ventricle lining and the choroid plexus. Western blot analysis of the hypothalamus confirmed the presence of FGF23. Gene expression of FGF23 was not detected, suggesting that the observed FGF23 protein is not brain-derived. Several FGF receptors are known to be present in the brain. Therefore, we conclude that the machinery for FGF23 signal transduction is present in several brain areas, indeed suggesting a role for FGF23 in the brain.

FGF19 in the Hindbrain Lowers Blood Glucose and Alters Excitability of Vagal Motor Neurons in Hyperglycemic Mice

Fibroblast growth factor 19 (FGF19) is a protein hormone that produces antidiabetic effects when administered intracerebroventricularly in the forebrain. However, no studies have examined how FGF19 affects hindbrain neurons that participate directly in autonomic control of systemic glucose regulation. Within the dorsal hindbrain, parasympathetic motor neurons of the dorsal motor nucleus of the vagus (DMV) express fibroblast growth factor receptors and their activity regulates visceral homeostatic processes, including energy balance. This study tested the hypothesis that FGF19 acts in the hindbrain to alter DMV neuron excitability and lower blood glucose concentration. Fourth ventricle administration of FGF19 produced no effect on blood glucose concentration in control mice, but induced a significant, peripheral muscarinic receptor-dependent decrease in systemic hyperglycemia for up to 12 h in streptozotocin-treated mice, a model of type 1 diabetes. Patch-clamp recordings from DMV neurons in vitro revealed that FGF19 application altered synaptic and intrinsic membrane properties of DMV neurons, with the balance of FGF19 effects being significantly modified by a recent history of systemic hyperglycemia. These findings identify central parasympathetic circuitry as a novel target for FGF19 and suggest that FGF19 acting in the dorsal hindbrain can alter vagal output to produce its beneficial metabolic effects.

Genesis of the Master Circadian Pacemaker in Mice

The suprachiasmatic nucleus (SCN) of the hypothalamus is the central circadian clock of mammals. It is responsible for communicating temporal information to peripheral oscillators via humoral and endocrine signaling, ultimately controlling overt rhythms such as sleep-wake cycles, body temperature, and locomotor activity. Given the heterogeneity and complexity of the SCN, its genesis is tightly regulated by countless intrinsic and extrinsic factors. Here, we provide a brief overview of the development of the SCN, with special emphasis on the murine system.

Fibroblast Growth Factor 19 Increases the Excitability of Pre-Motor Glutamatergic Dorsal Vagal Complex Neurons From Hyperglycemic Mice

Intracerebroventricular administration of the protein hormone fibroblast growth factor 19 (FGF19) to the hindbrain produces potent antidiabetic effects in hyperglycemic mice that are likely mediated through a vagal parasympathetic mechanism. FGF19 increases the synaptic excitability of parasympathetic motor neurons in the dorsal motor nucleus of the vagus (DMV) from hyperglycemic, but not normoglycemic, mice but the source of this synaptic input is unknown. Neurons in the area postrema (AP) and nucleus tractus solitarius (NTS) express high levels of FGF receptors and exert glutamatergic control over the DMV. This study tested the hypothesis that FGF19 increases glutamate release in the DMV by increasing the activity of glutamatergic AP and NTS neurons in hyperglycemic mice. Glutamate photoactivation experiments confirmed that FGF19 increases synaptic glutamate release from AP and NTS neurons that connect to the DMV in hyperglycemic, but not normoglycemic mice. Contrary to expectations, FGF19 produced a mixed effect on intrinsic membrane properties in the NTS with a trend towards inhibition, suggesting that another mechanism was responsible for the observed effects on glutamate release in the DMV. Consistent with the hypothesis, FGF19 increased action potential-dependent glutamate release in the NTS in hyperglycemic mice only. Finally, glutamate photoactivation experiments confirmed that FGF19 increases the activity of glutamatergic AP neurons that project to the NTS in hyperglycemic mice. Together, these results support the hypothesis that FGF19 increases glutamate release from AP and NTS neurons that project to the DMV in hyperglycemic mice. FGF19 therefore modifies the local vago-vagal reflex circuitry at several points. Additionally, since the AP and NTS communicate with several other metabolic regulatory nuclei in the brain, FGF19 in the hindbrain may alter neuroendocrine and behavioral aspects of metabolism, in addition to changes in parasympathetic output.

Fibroblast Growth Factor 2-Mediated Regulation of Neuronal Exosome Release Depends on VAMP3/Cellubrevin in Hippocampal Neurons

Extracellular vesicles (EVs) are endogenous membrane-derived vesicles that shuttle bioactive molecules between glia and neurons, thereby promoting neuronal survival and plasticity in the central nervous system (CNS) and contributing to neurodegenerative conditions. Although EVs hold great potential as CNS theranostic nanocarriers, the specific molecular factors that regulate neuronal EV uptake and release are currently unknown. A combination of patch-clamp electrophysiology and pH-sensitive dye imaging is used to examine stimulus-evoked EV release in individual neurons in real time. Whereas spontaneous electrical activity and the application of a high-frequency stimulus induce a slow and prolonged fusion of multivesicular bodies (MVBs) with the plasma membrane (PM) in a subset of cells, the neurotrophic factor basic fibroblast growth factor (bFGF) greatly increases the rate of stimulus-evoked MVB-PM fusion events and, consequently, the abundance of EVs in the culture medium. Proteomic analysis of neuronal EVs demonstrates bFGF increases the abundance of the v-SNARE vesicle-associated membrane protein 3 (VAMP3, cellubrevin) on EVs. Conversely, knocking-down VAMP3 in cultured neurons attenuates the effect of bFGF on EV release. The results determine the temporal characteristics of MVB-PM fusion in hippocampal neurons and reveal a new function for bFGF signaling in controlling neuronal EV release.

Tanycyte-Like Cells Derived From Mouse Embryonic Stem Culture Show Hypothalamic Neural Stem/Progenitor Cell Functions

Tanycytes have recently been accepted as neural stem/progenitor cells in the postnatal hypothalamus. Persistent retina and anterior neural fold homeobox (Rax) expression is characteristic of tanycytes in contrast to its transient expression of whole hypothalamic precursors. In this study, we found that Rax+ residual cells in the maturation phase of hypothalamic differentiation in mouse embryonic stem cell (mESC) cultures had similar characteristics to ventral tanycytes. They expressed typical neural stem/progenitor cell markers, including Sox2, vimentin, and nestin, and differentiated into mature neurons and glial cells. Quantitative RT-PCR analysis showed that Rax+ residual cells expressed Fgf-10, Fgf-18, and Lhx2, which are expressed by ventral tanycytes. They highly expressed tanycyte-specific genes Dio2 and Gpr50 compared with Rax+ early hypothalamic progenitor cells. Therefore, Rax+ residual cells in the maturation phase of hypothalamic differentiation were considered to be more differentiated and similar to late progenitor cells and tanycytes. They self-renewed and formed neurospheres when cultured with exogenous FGF-2. Additionally, these Rax+ neurospheres differentiated into three neuronal lineages (neurons, astrocytes, and oligodendrocytes), including neuropeptide Y+ neuron, that are reported to be differentiated from ventral tanycytes toward the arcuate nuclei. Thus, Rax+ residual cells were multipotent neural stem/progenitor cells. Rax+ neurospheres were stably passaged and retained high Sox2 expression even after multiple passages. These results suggest the successful induction of Rax+ tanycyte-like cells from mESCs [induced tanycyte-like (iTan) cells]. These hypothalamic neural stem/progenitor cells may have potential in regenerative medicine and as a research tool.

Cross-Talk between Fibroblast Growth Factor Receptors and Other Cell Surface Proteins

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute signaling circuits that transmit signals across the plasma membrane, regulating pivotal cellular processes like differentiation, migration, proliferation, and apoptosis. The malfunction of FGFs/FGFRs signaling axis is observed in numerous developmental and metabolic disorders, and in various tumors. The large diversity of FGFs/FGFRs functions is attributed to a great complexity in the regulation of FGFs/FGFRs-dependent signaling cascades. The function of FGFRs is modulated at several levels, including gene expression, alternative splicing, posttranslational modifications, and protein trafficking. One of the emerging ways to adjust FGFRs activity is through formation of complexes with other integral proteins of the cell membrane. These proteins may act as coreceptors, modulating binding of FGFs to FGFRs and defining specificity of elicited cellular response. FGFRs may interact with other cell surface receptors, like G-protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs). The cross-talk between various receptors modulates the strength and specificity of intracellular signaling and cell fate. At the cell surface FGFRs can assemble into large complexes involving various cell adhesion molecules (CAMs). The interplay between FGFRs and CAMs affects cell–cell interaction and motility and is especially important for development of the central nervous system. This review summarizes current stage of knowledge about the regulation of FGFRs by the plasma membrane-embedded partner proteins and highlights the importance of FGFRs-containing membrane complexes in pathological conditions, including cancer.

The Hypothalamic Arcuate Nucleus-Median Eminence Is a Target for Sustained Diabetes Remission Induced by Fibroblast Growth Factor 1

In rodent models of type 2 diabetes (T2D), sustained remission of diabetic hyperglycemia can be induced by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1). To identify the brain areas responsible for this effect, we first used immunohistochemistry to map the hypothalamic distribution of phosphorylated extracellular signal-related kinase 1/2 (pERK1/2), a marker of mitogen-activated protein kinase-ERK signal transduction downstream of FGF receptor activation. Twenty minutes after icv FGF1 injection in adult male Wistar rats, pERK1/2 staining was detected primarily in two hypothalamic areas: the arcuate nucleus-median eminence (ARC-ME) and the paraventricular nucleus (PVN). To determine whether an action of FGF1 localized to either the ARC-ME or the PVN is capable of mimicking the sustained antidiabetic effect elicited by icv FGF1, we microinjected either saline vehicle or a low dose of FGF1 (0.3 µg/side) bilaterally into either the ARC-ME area or PVN of Zucker Diabetic Fatty rats, a model of T2D, and monitored daily food intake, body weight, and blood glucose levels over a 3-week period. Whereas bilateral intra-arcuate microinjection of saline vehicle was without effect, remission of hyperglycemia lasting >3 weeks was observed following bilateral microinjection of FGF1 into the ARC-ME. This antidiabetic effect cannot be attributed to leakage of FGF1 into cerebrospinal fluid and subsequent action on other brain areas, since icv injection of the same total dose was without effect. Combined with our finding that bilateral microinjection of the same dose of FGF1 into the PVN was without effect on glycemia or other parameters, we conclude that the ARC-ME area (but not the PVN) is a target for sustained remission of diabetic hyperglycemia induced by FGF1.

The central fibroblast growth factor receptor/beta klotho system: Comprehensive mapping in Mus musculus and comparisons to nonhuman primate and human samples using an automated in situ hybridization platform

Central activation of fibroblast growth factor (FGF) receptors regulates peripheral glucose homeostasis and reduces food intake in preclinical models of obesity and diabetes. The current work was undertaken to advance our understanding of the receptor expression, as sites of ligand action by FGF19, FGF21, and FGF1 in the mammalian brain remains unresolved. Recent advances in automated RNAscope in situ hybridization and droplet digital PCR (ddPCR) technology allowed us to interrogate central FGFR/beta klotho (Klb) system at the cellular level in the mouse, with relevant comparisons to nonhuman primate and human brain. FGFR1-3 gene expression was broadly distributed throughout the CNS in Mus musculus, with FGFR1 exhibiting the greatest heterogeneity. FGFR4 expression localized only in the medial habenula and subcommissural organ of mice. Likewise, Klb mRNA was restricted to the suprachiasmatic nucleus (SCh) and select midbrain and hindbrain nuclei. ddPCR in the rodent hypothalamus confirmed that, although expression levels are indeed low for Klb, there is nonetheless a bonafide subpopulation of Klb+ cells in the hypothalamus. In NHP and human midbrain and hindbrain, Klb + cells are quite rare, as is expression of FGFR4. Collectively, these data provide the most robust central map of the FGFR/Klb system to date and highlight central regions that may be of critical importance to assess central ligand effects with pharmacological dosing, such as the putative interactions between the endocrine FGFs and FGFR1/Klb, or FGF19 with FGFR4.

Tanycyte Gene Expression Dynamics in the Regulation of Energy Homeostasis

Animal survival relies on a constant balance between energy supply and energy expenditure, which is controlled by several neuroendocrine functions that integrate metabolic information and adapt the response of the organism to physiological demands. Polarized ependymoglial cells lining the floor of the third ventricle and sending a single process within metabolic hypothalamic parenchyma, tanycytes are henceforth described as key components of the hypothalamic neural network controlling energy balance. Their strategic position and peculiar properties convey them diverse physiological functions ranging from blood/brain traffic controllers, metabolic modulators, and neural stem/progenitor cells. At the molecular level, these functions rely on an accurate regulation of gene expression. Indeed, tanycytes are characterized by their own molecular signature which is mostly associated to their diverse physiological functions, and the detection of variations in nutrient/hormone levels leads to an adequate modulation of genetic profile in order to ensure energy homeostasis. The aim of this review is to summarize recent knowledge on the nutritional control of tanycyte gene expression.

Crosstalk between receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCR) in the brain: Focus on heteroreceptor complexes and related functional neurotrophic effects

Neuronal events are regulated by the integration of several complex signaling networks in which G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) are considered key players of an intense bidirectional cross-communication in the cell, generating signaling mechanisms that, at the same time, connect and diversify the traditional signal transduction pathways activated by the single receptor. For this receptor-receptor crosstalk, the two classes of receptors form heteroreceptor complexes resulting in RTKs transactivation and in growth-promoting signals. In this review, we describe heteroreceptor complexes between GPCR and RTKs in the central nervous system (CNS) and their functional effects in controlling a variety of neuronal effects, ranging from development, proliferation, differentiation and migration, to survival, repair, synaptic transmission and plasticity. In this interaction, RTKs can also recruit components of the G protein signaling cascade, creating a bidirectional intricate interplay that provides complex control over multiple cellular events. These heteroreceptor complexes, by the integration of different signals, have recently attracted a growing interest as novel molecular target for depressive disorders. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'.

The role of fibroblast growth factor 2 in drug addiction

Fibroblast growth factor 2 (FGF2) is a member of the FGF-family, which consists of 22 members, with four known FGF receptors (five in humans). Over the last 30 years, FGF2 has been extensively studied for its role in cell proliferation, differentiation, growth, survival and angiogenesis during development, as well as for its role in adult neurogenesis and regenerative plasticity. Over the past decade, FGF2 has been implicated in learning and memory, as well as in several neuropsychiatric disorders, including anxiety, stress, depression and drug addiction. In this review, we present accumulating evidence indicating the involvement of FGF2 in neuroadaptations caused by drugs of abuse, namely, amphetamine, cocaine, nicotine and alcohol. Moreover, evidence suggests that FGF2 is a positive regulator of alcohol and drug-related behaviors. Thus, although additional studies are yet required, we suggest that reducing FGF2 activity may provide a novel therapeutic approach for substance use disorders.

Methylation changes and aberrant expression of FGFR3 in Lewy body disease neurons

Lewy body disease (LBD) is characterized by accumulation of aggregated α-synuclein in the central nervous system as eosinophilic cytoplasmic inclusions called Lewy bodies. According to their distribution pattern, it is classified into brainstem LBD, limbic LBD and diffuse neocortical LBD. It has been reported that α-synuclein affects various points in the MAPK cascade but its relationship with FGF receptors, which are the most upstream of the pathway, has not been previously investigated. We discovered that among the four FGFRs, FGFR3 showed neuronal upregulation in LBD brains histopathologically. Further examination using neuron-specific methylome analysis revealed that the gene body of FGFR3 was hypermethylated in LBD, suggesting its increased transcription. Altered methylation was not observed in the non-neuronal genome. Altered methylation status was associated with the severity of α-synuclein pathology.

Fibroblast growth factor 20 is protective towards dopaminergic neurons in vivo in a paracrine manner

Neuroprotective strategies are an unmet medical need for Parkinson's disease. Fibroblast growth factor 20 (FGF20) enhances survival of cultured dopaminergic neurons but little is known about its in vivo potential. We set out to examine whether manipulation of the FGF20 system affected nigrostriatal tract integrity in rats, to identify which fibroblast growth factor receptors (FGFRs) might reside on dopaminergic neurons and to discover the source of endogenous FGF20 in the substantia nigra (SN). Male Sprague Dawley rats were subject to a partial 6-OHDA lesion alongside treatment with exogenous FGF20 or an FGFR antagonist. Behavioural readouts and tyrosine-hydroxylase (TH) immunohistochemistry were used to evaluate nigrostriatal tract integrity. Fluorescent immunohistochemistry was used to examine FGFR subtype expression on TH-positive dopamine neurons and FGF20 cellular localisation within the SN. FGF20 (2.5 μg/day) significantly protected TH-positive cells in the SN and terminals in the striatum, while reducing the development of motor asymmetry at 5, 8 and 11 days post lesion. Conversely, the FGFR antagonist PD173074 (2 mg/kg) significantly worsened both the 6-OHDA lesion and resultant motor asymmetry. Within the SN, TH-positive cells expressed FGFR1, 3 and 4 while FGF20 co-localised with GFAP-positive astrocytes. In conclusion, FGF20 protects dopaminergic neurons in vivo, an action likely mediated through activation of FGFRs1, 3 or 4 found on these neurons. Given FGF20 is localised to astrocytes in the adult SN, endogenous FGF20 provides its protection of dopamine neurons through a paracrine action. Boosting the endogenous FGF20 production might offer potential as a future therapeutic strategy in Parkinson's disease.

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FGF20 infusion protects against a partial 6-OHDA nigrostriatal tract lesion in rats.

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Dopaminergic cells in the SNc express FGFR1, 3 and 4 upon which FGF20 can act.

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FGFR blockade exacerbates a partial 6-OHDA nigrostriatal tract lesion in rats.

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Endogenous FGF20 is expressed by astrocytes in the SN, not by dopaminergic neurons.

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Endogenous FGF20 most likely provides protection in a paracrine manner.

The expression of fgfr3 in the zebrafish head

Fibroblast growth factor (FGF) signaling is essential for many developmental processes and plays a pivotal role in skeletal homeostasis, regeneration and wound healing. FGF signals through one of five tyrosine kinase receptors: Fgfr1a, -1b, -2, -3, -4. To characterize the expression of zebrafish fgfr3 from the larval stage to adulthood, we used RNAscope in situ hybridization on paraffin sections of the zebrafish head. Our study revealed spatial and temporal distribution of fgfr3 transcript in chondrocytes of the head cartilages, osteoblasts involved in bone formation, ventricular zone of the brain, undifferentiated mesenchymal cells of the skin, and lens epithelium of the eye. In general, the expression pattern of zebrafish fgfr3 is similar to the expression observed in higher vertebrates.

Bile Acid Signaling Pathways from the Enterohepatic Circulation to the Central Nervous System

Bile acids are best known as detergents involved in the digestion of lipids. In addition, new data in the last decade have shown that bile acids also function as gut hormones capable of influencing metabolic processes via receptors such as FXR (farnesoid X receptor) and TGR5 (Takeda G protein-coupled receptor 5). These effects of bile acids are not restricted to the gastrointestinal tract, but can affect different tissues throughout the organism. It is still unclear whether these effects also involve signaling of bile acids to the central nervous system (CNS). Bile acid signaling to the CNS encompasses both direct and indirect pathways. Bile acids can act directly in the brain via central FXR and TGR5 signaling. In addition, there are two indirect pathways that involve intermediate agents released upon interaction with bile acids receptors in the gut. Activation of intestinal FXR and TGR5 receptors can result in the release of fibroblast growth factor 19 (FGF19) and glucagon-like peptide 1 (GLP-1), both capable of signaling to the CNS. We conclude that when plasma bile acids levels are high all three pathways may contribute in signal transmission to the CNS. However, under normal physiological circumstances, the indirect pathway involving GLP-1 may evoke the most substantial effect in the brain.

-Glial and stem cell expression of murine Fibroblast Growth Factor Receptor 1 in the embryonic and perinatal nervous system

BACKGROUND

Fibroblast growth factors (FGFs) and their receptors (FGFRs) are involved in the development and function of multiple organs and organ systems, including the central nervous system (CNS). FGF signaling via FGFR1, one of the three FGFRs expressed in the CNS, stimulates proliferation of stem cells during prenatal and postnatal neurogenesis and participates in regulating cell-type ratios in many developing regions of the brain. Anomalies in FGFR1 signaling have been implicated in certain neuropsychiatric disorders. Fgfr1 expression has been shown, via in situ hybridization, to vary spatially and temporally throughout embryonic and postnatal development of the brain. However, in situ hybridization lacks sufficient resolution to identify which cell-types directly participate in FGF signaling. Furthermore, because antibodies raised against FGFR1 commonly cross-react with other members of the FGFR family, immunocytochemistry is not alone sufficient to accurately document Fgfr1 expression. Here, we elucidate the identity of Fgfr1 expressing cells in both the embryonic and perinatal mouse brain.

METHODS

To do this, we utilized a tgFGFR1-EGFPGP338Gsat BAC line (tgFgfr1-EGFP+) obtained from the GENSAT project. The tgFgfr1-EGFP+ line expresses EGFP under the control of a Fgfr1 promoter, thereby causing cells endogenously expressing Fgfr1 to also present a positive GFP signal. Through simple immunostaining using GFP antibodies and cell-type specific antibodies, we were able to accurately determine the cell-type of Fgfr1 expressing cells.

RESULTS

This technique revealed Fgfr1 expression in proliferative zones containing BLBP+ radial glial stem cells, such as the cortical and hippocampal ventricular zones, and cerebellar anlage of E14.5 mice, in addition to DCX+ neuroblasts. Furthermore, our data reveal Fgfr1 expression in proliferative zones containing BLBP+ cells of the anterior midline, hippocampus, cortex, hypothalamus, and cerebellum of P0.5 mice, in addition to the early-formed GFAP+ astrocytes of the anterior midline.

DISCUSSION

Understanding when during development and where Fgfr1 is expressed is critical to improving our understanding of its function during neurodevelopment as well as in the mature CNS. This information may one day provide an avenue of discovery towards understanding the involvement of aberrant FGF signaling in neuropsychiatric disorders.

Quantitative assessment of fibroblast growth factor receptor 1 expression in neurons and glia

Background

Fibroblast growth factors (FGFs) and their receptors (FGFRs) have numerous functions in the developing and adult central nervous system (CNS). For example, the FGFR1 receptor is important for proliferation and fate specification of radial glial cells in the cortex and hippocampus, oligodendrocyte proliferation and regeneration, midline glia morphology and soma translocation, Bergmann glia morphology, and cerebellar morphogenesis. In addition, FGFR1 signaling in astrocytes is required for postnatal maturation of interneurons expressing parvalbumin (PV). FGFR1 is implicated in synapse formation in the hippocampus, and alterations in the expression of Fgfr1 and its ligand, Fgf2 accompany major depression. Understanding which cell types express Fgfr1 during development may elucidate its roles in normal development of the brain as well as illuminate possible causes of certain neuropsychiatric disorders.

Methods

Here, we used a BAC transgenic reporter line to trace Fgfr1 expression in the developing postnatal murine CNS. The specific transgenic line employed was created by the GENSAT project, tgFGFR1-EGFPGP338Gsat, and includes a gene encoding enhanced green fluorescent protein (EGFP) under the regulation of the Fgfr1 promoter, to trace Fgfr1 expression in the developing CNS. Unbiased stereological counts were performed for several cell types in the cortex and hippocampus.

Results

This model reveals that Fgfr1 is primarily expressed in glial cells, in both astrocytes and oligodendrocytes, along with some neurons. Dual labeling experiments indicate that the proportion of GFP+ (Fgfr1+) cells that are also GFAP+ increases from postnatal day 7 (P7) to 1 month, illuminating dynamic changes in Fgfr1 expression during postnatal development of the cortex. In postnatal neurogenic areas, GFP expression was also observed in SOX2, doublecortin (DCX), and brain lipid-binding protein (BLBP) expressing cells. Fgfr1 is also highly expressed in DCX positive cells of the dentate gyrus (DG), but not in the rostral migratory stream. Fgfr1 driven GFP was also observed in tanycytes and GFAP+ cells of the hypothalamus, as well as in Bergmann glia and astrocytes of the cerebellum.

Conclusions

The tgFGFR1-EGFPGP338Gsat mouse model expresses GFP that is congruent with known functions of FGFR1, including hippocampal development, glial cell development, and stem cell proliferation. Understanding which cell types express Fgfr1 may elucidate its role in neuropsychiatric disorders and brain development.

Existence of muscarinic acetylcholine receptor (mAChR) and fibroblast growth factor receptor (FGFR) heteroreceptor complexes and their enhancement of neurite outgrowth in neural hippocampal cultures

BACKGROUND

Recently, it was demonstrated that G-protein-coupled receptors (GPCRs) can transactivate tyrosine kinase receptors in absence of their ligands. In this work, driven by the observation that mAChRs and fibroblast growth factor receptors (FGFRs) share signalling pathways and regulation of brain functions, it was decided to explore whether mAChRs activation may transactivate FGFRs and, if so, to characterize the related trophic effects in cultured hippocampal neurons.

METHODS

Oxotremorine-M transactivation of FGFRs and related trophic effects were tested in primary hippocampal neurons. Western blotting and in situ proximity ligation assay (PLA) were used to detect FGFR phosphorylation (pFGFR) levels and M₁R-FGFR1 heteroreceptor complexes, respectively.

RESULTS

Oxotremorine-M, a non-selective mAChRs agonist, was able to transactivate FGFR and this transactivation was blocked by Src inhibitors. Oxotremorine-M treatment produced a significant increase in the primary neurite outgrowth that was blocked by pre-treatment with the pFGFR inhibitor SU5402 and Src inhibitors. This trophic effect was almost similar to that induced by fibroblast growth factor-2 (FGF-2). By using atropine as nonselective mAChRs or pirenzepine as selective antagonist for M₁ receptor (M₁R) we could show that mAChRs are involved in modulating the pFGFRs. Using PLA, M₁R-FGFR1 heteroreceptor complexes were identified in the hippocampus and cerebral cortex.

CONCLUSION

The current findings, by showing functional mAChR-FGFR interactions, will contribute to advance the understanding of the mechanisms involved in the actions of cholinergic drugs on neuronal plasticity.

GENERAL SIGNIFICANT

Data may help to develop novel therapeutic strategies not only for neurodegenerative diseases but also for depression-induced atrophy of hippocampal neurons.

Fibroblast Growth Factor 2 Modulates Hypothalamic Pituitary Axis Activity and Anxiety Behavior Through Glucocorticoid Receptors

BACKGROUND

Despite strong evidence linking fibroblast growth factor 2 (FGF2) with anxiety and depression in both rodents and humans, the molecular mechanisms linking FGF2 with anxiety are not understood.

METHODS

We compare 1) mice that lack a functional Fgf2 gene (Fgf2 knockout [KO]), 2) wild-type mice, and 3) Fgf2 KO with adult rescue by FGF2 administration on measures of anxiety, depression, and motor behavior, and further investigate the mechanisms of this behavior by cellular, molecular, and neuroendocrine studies.

RESULTS

We demonstrate that Fgf2 KO mice have increased anxiety, decreased hippocampal glucocorticoid receptor (GR) expression, and increased hypothalamic-pituitary-adrenal axis activity. FGF2 administration in adulthood was sufficient to rescue the entire phenotype. Blockade of GR in adult mice treated with FGF2 precluded the therapeutic effects of FGF2 on anxiety behavior, suggesting that GR is necessary for FGF2 to regulate anxiety behavior. The level of Egr-1/NGFI-A was decreased in Fgf2 KO mice and was reestablished with FGF2 treatment. By chromatin immunoprecipitation studies, we found decreased binding of EGR-1 to the GR promoter region in Fgf2 KO mice. Finally, we examined anxiety behavior in FGF receptor (FGFR) KO mice; however, FGFR1, FGFR2, and FGFR3 KO mice did not mimic the phenotype of Fgf2 KO mice, suggesting a role for other receptor subtypes (i.e., FGFR5).

CONCLUSIONS

These data suggest that FGF2 levels are critically related to anxiety behavior and hypothalamic-pituitary-adrenal axis activity, likely through modulation of hippocampal glucocorticoid receptor expression, an effect that is likely receptor mediated, albeit not by FGFR1, FGFR2, and FGFR3.

FGFR1-5-HT1A Heteroreceptor Complexes: Implications for Understanding and Treating Major Depression

The serotonin and neurotrophic factor hypotheses of depression are well known. The discovery of brain fibroblast growth factor receptor 1 (FGFR1)-5 hydroxytryptamine receptor 1A (5-HT1A) heteroreceptor complexes, and their enhancement of neuroplasticity, offers an integration of these hypotheses at the molecular level. They were first described in the hippocampus and later in midbrain 5-HT neurons, where these heterocomplexes are enriched in 5-HT1A autoreceptors. Combined FGF2 and 5-HT1A agonist treatment increased the formation of these heterocomplexes and the facilitatory allosteric receptor-receptor interactions within them led to the enhancement of FGFR1 signaling and was associated with the development of antidepressant effects. We discuss these findings with regard to a theory of motifs critically involved in these interactions and suggest that these complexes represent novel targets for antidepressants.

Hypothalamic tanycytes-masters and servants of metabolic, neuroendocrine, and neurogenic functions

There is a resurgent interest in tanycytes, a radial glial-like cell population occupying the floor and ventro-lateral walls of the third ventricle (3V). Tanycytes reside in close proximity to hypothalamic neuronal nuclei that regulate appetite and energy expenditure, with a subset sending projections into these nuclei. Moreover, tanycytes are exposed to 3V cerebrospinal fluid and have privileged access to plasma metabolites and hormones, through fenestrated capillaries. Indeed, some tanycytes act as conduits for trafficking of these molecules into the brain parenchyma. Tanycytes can also act as neural stem/progenitor cells, supplying the postnatal and adult hypothalamus with new neurons. Collectively, these findings suggest that tanycytes regulate and integrate important trophic and metabolic processes and possibly endow functional malleability to neuronal circuits of the hypothalamus. Hence, manipulation of tanycyte biology could provide a valuable tool for modulating hypothalamic functions such as energy uptake and expenditure in order to tackle prevalent eating disorders such as obesity and anorexia.

Evidence for the existence of FGFR1-5-HT1A heteroreceptor complexes in the midbrain raphe 5-HT system

The ascending midbrain 5-HT neurons known to contain 5-HT1A autoreceptors may be dysregulated in depression due to a reduced trophic support. With in situ proximity ligation assay (PLA) and supported by co-location of the FGFR1 and 5-HT1A immunoreactivities in midbrain raphe 5-HT cells, evidence for the existence of FGFR1-5-HT1A heteroreceptor complexes were obtained in the dorsal and median raphe nuclei of the Sprague-Dawley rat. Their existence in the rat medullary raphe RN33B cell cultures was also established. After combined FGF-2 and 8-OH-DPAT treatment, a marked and significant increase in PLA positive clusters was found in the RN33B cells. Similar results were reached upon coactivation by agonists in HEK293T cells using the Fluorescent Resonance Energy Transfer (FRET) technique resulting in increased FRETmax and reduced FRET50 values. The heteroreceptor complex formation was dependent on TMV of the 5-HT1A receptor since it was blocked by incubation with TMV but not with TMII. Taken together, the 5-HT1A autoreceptors by being recruited into a FGFR1-5-HT1A heteroreceptor complex in the midbrain raphe 5-HT nerve cells may develop a novel function, namely a trophic role in many midbrain 5-HT neuron systems originating from the dorsal and medianus raphe nuclei.

Anatomical, molecular and pathological consideration of the circumventricular organs

BACKGROUND AND PURPOSE

Circumventricular organs (CVOs) are a diverse group of specialised structures characterized by peculiar vascular and position around the third and fourth ventricles of the brain. In humans, these organs are present during the fetal period and some become vestigial after birth. Some, such as the pineal gland (PG), subcommissural organ (SCO) and organum vasculosum of the lamina terminalis (OVLT), which are located around the third ventricle, might be the site of origin of periventricular tumours. In contrast to humans, CVOs are present in the adult rat and can be dissected by laser capture microdissection (LCM).

METHODS

In this study, we used LCM and microarrays to analyse the transcriptomes of three CVOs, the SCO, the subfornical organ (SFO) and the PG and the third ventricle ependyma of the adult rat, in order to better characterise these organs at the molecular level. Furthermore, an immunohistochemical study of Claudin-3 (CLDN3), a membrane protein involved in forming cellular tight junctions, was performed at the level of the SCO.

RESULTS

This study highlighted some potentially new or already described specific markers of these structures as Erbb2 and Col11a1 in ependyma, Epcam and CLDN3 in the SCO, Ren1 and Slc22a3 in the SFO and Tph, Anat and Asmt in the PG. Moreover, we found that CLDN3 expression was restricted to the apical pole of ependymocytes in the SCO.

Fibroblast growth factor-21 enhances mitochondrial functions and increases the activity of PGC-1α in human dopaminergic neurons via Sirtuin-1

Mitochondrial dysfunctions accompany several neurodegenerative disorders and contribute to disease pathogenesis among others in Parkinson’s disease (PD). Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a major regulator of mitochondrial functions and biogenesis, and was suggested as a therapeutic target in PD. PGC-1α is regulated by both transcriptional and posttranslational events involving also the action of growth factors. Fibroblast growth factor-21 (FGF21) is a regulator of glucose and fatty acid metabolism in the body but little is known about its action in the brain. We show here that FGF21 increased the levels and activity of PGC-1α and elevated mitochondrial antioxidants in human dopaminergic cells in culture. The activation of PGC-1α by FGF21 occurred via the NAD⁺-dependent deacetylase Sirtuin-1 (SIRT1) subsequent to an increase in the enzyme, nicotinamide phosphoribosyltransferase (Nampt). FGF21 also enhanced mitochondrial respiratory capacity in human dopaminergic neurons as shown in real-time analyses of living cells. FGF21 is present in the brain including midbrain and is expressed by glial cells in culture. These results show that FGF21 activates PGC-1α and increases mitochondrial efficacy in human dopaminergic neurons suggesting that FGF21 could potentially play a role in dopaminergic neuron viability and in PD.

Expression and purification of biologically active human FGF2 containing the b'a' domains of human PDI in Escherichia coli

Among the members of the fibroblast growth factor (FGF) family that affect the growth, differentiation, migration, and survival of many cell types, FGF2 is the most abundant in the central nervous system. Because of its wound healing effects, FGF2 has potential as a therapeutic agent. The protein is also added to the culture media to maintain stem cells. Expression and purification procedures for FGF2 that are highly efficient and low cost have been intensively investigated for the past two decades. Our current study focuses on the purification of FGF2 fused with b'a' domains of human protein disulfide isomerase to elevate overexpression, solubility, and stability with a simplified experimental procedure using only ion exchange chromatography, as well as on the confirmation of the biological activity of FGF2 on fibroblast Balb/c 3T3 cells and hippocampal neural cells.

Apert syndrome with fused thalami

Apert syndrome (Acrocephalosyndactyly type I; AS) is a rare but well-known autosomal dominant disorder characterized by craniosynostosis, midface hypoplasia, bony/cutaneous syndactyly of fingers and toes as well as a variety of associated congenital anomalies involving the brain, heart, limbs and other organ systems. We report the case of a fetus with molecularly confirmed Apert syndrome and additional fusion of the thalamic nuclei. Various central nervous system anomalies, have been reported in patients with AS. However, as far as we know cases of fused thalami in Apert syndrome have never been reported so far.

Fasciculation and guidance of spinal motor axons in the absence of FGFR2 signaling

During development, fibroblast growth factors (FGF) are essential for early patterning events along the anterior-posterior axis, conferring positional identity to spinal motor neurons by activation of different Hox codes. In the periphery, signaling through one of four fibroblast growth factor receptors supports the development of the skeleton, as well as induction and maintenance of extremities. In previous studies, FGF receptor 2 (FGFR2) was found to interact with axon bound molecules involved in axon fasciculation and extension, thus rendering this receptor an interesting candidate for the promotion of proper peripheral innervation. However, while the involvement of FGFR2 in limb bud induction has been extensively studied, its role during axon elongation and formation of distinct nervous projections has not been addressed so far. We show here that motor neurons in the spinal cord express FGFR2 and other family members during the establishment of motor connections to the forelimb and axial musculature. Employing a conditional genetic approach to selectively ablate FGFR2 from motor neurons we found that the patterning of motor columns and the expression patterns of other FGF receptors and Sema3A in the motor columns of mutant embryos are not altered. In the absence of FGFR2 signaling, pathfinding of motor axons is intact, and also fasciculation, distal advancement of motor nerves and gross morphology and positioning of axonal projections are not altered. Our findings therefore show that FGFR2 is not required cell-autonomously in motor neurons during the formation of initial motor projections towards limb and axial musculature.

Molecular characterization of circumventricular organs and third ventricle ependyma in the rat: potential markers for periventricular tumors

Circumventricular organs (CVOs) are specialized ventricular structures around the third and fourth ventricles of the brain. In humans, these structures are present during the fetal period and some become vestigial after birth. Some of these organs, such as the pineal gland (PG), subcommissural organ (SCO), and organum vasculosum of the lamina terminalis, might be the sites of origin of periventricular tumors, notably pineal parenchymal tumors, papillary tumor of the pineal region and chordoid glioma. In contrast to the situation in humans, CVOs are present in the adult rat and can be dissected by laser capture microdissection (LCM). In this study, we used LCM and microarrays to analyze the transcriptomes of three CVOs, the SCO, the subfornical organ (SFO), and the PG and the third ventricle ependyma in the adult rat, in order to better characterize these organs at the molecular level. Several genes were expressed only, or mainly, in one of these structures, for example, Erbb2 and Col11a1 in the ependyma, Epcam and Claudin-3 (CLDN3) in the SCO, Ren1 and Slc22a3 in the SFO and Tph, Aanat and Asmt in the PG. The expression of these genes in periventricular tumors should be examined as evidence for a possible origin from the CVOs. Furthermore, we performed an immunohistochemical study of CLDN3, a membrane protein involved in forming cellular tight junctions and found that CLDN3 expression was restricted to the apical pole of ependymocytes in the SCO. This microarray study provides new evidence regarding the possible origin of some rare periventricular tumors.

Facilitation of AMPA receptor synaptic delivery as a molecular mechanism for cognitive enhancement

Cell adhesion molecules and downstream growth factor-dependent signaling are critical for brain development and synaptic plasticity, and they have been linked to cognitive function in adult animals. We have previously developed a mimetic peptide (FGL) from the neural cell adhesion molecule (NCAM) that enhances spatial learning and memory in rats. We have now investigated the cellular and molecular basis of this cognitive enhancement, using biochemical, morphological, electrophysiological, and behavioral analyses. We have found that FGL triggers a long-lasting enhancement of synaptic transmission in hippocampal CA1 neurons. This effect is mediated by a facilitated synaptic delivery of AMPA receptors, which is accompanied by enhanced NMDA receptor-dependent long-term potentiation (LTP). Both LTP and cognitive enhancement are mediated by an initial PKC activation, which is followed by persistent CaMKII activation. These results provide a mechanistic link between facilitation of AMPA receptor synaptic delivery and improved hippocampal-dependent learning, induced by a pharmacological cognitive enhancer.

Cell-autonomous FGF signaling regulates anteroposterior patterning and neuronal differentiation in the mesodiencephalic dopaminergic progenitor domain

The structure and projection patterns of adult mesodiencephalic dopaminergic (DA) neurons are one of the best characterized systems in the vertebrate brain. However, the early organization and development of these nuclei remain poorly understood. The induction of midbrain DA neurons requires sonic hedgehog (Shh) from the floor plate and fibroblast growth factor 8 (FGF8) from the isthmic organizer, but the way in which FGF8 regulates DA neuron development is unclear. We show that, during early embryogenesis, mesodiencephalic neurons consist of two distinct populations: a diencephalic domain, which is probably independent of isthmic FGFs; and a midbrain domain, which is dependent on FGFs. Within these domains, DA progenitors and precursors use partly different genetic programs. Furthermore, the diencephalic DA domain forms a distinct cell population, which also contains non-DA Pou4f1(+) cells. FGF signaling operates in proliferative midbrain DA progenitors, but is absent in postmitotic DA precursors. The loss of FGFR1/2-mediated signaling results in a maturation failure of the midbrain DA neurons and altered patterning of the midbrain floor. In FGFR mutants, the DA domain adopts characteristics that are typical for embryonic diencephalon, including the presence of Pou4f1(+) cells among TH(+) cells, and downregulation of genes typical of midbrain DA precursors. Finally, analyses of chimeric embryos indicate that FGF signaling regulates the development of the ventral midbrain cell autonomously.

Fibroblast growth factor receptor 1- 5-hydroxytryptamine 1A heteroreceptor complexes and their enhancement of hippocampal plasticity

BACKGROUND

The hippocampus and its 5-hydroxytryptamine transmission plays an important role in depression related to its involvement in limbic circuit plasticity.

METHODS

The analysis was made with bioluminescence resonance energy transfer, co-immunoprecipitation, in situ proximity ligation assay, binding assay, in cell western and the forced swim test.

RESULTS

Using bioluminescence resonance energy transfer analysis, fibroblast growth factor receptor 1 (FGFR1)-5-hydroxytryptamine 1A (5-HT1A) receptor complexes have been demonstrated and their specificity and agonist modulation characterized. Their presence based on co-immunoprecipitation and proximity ligation assay has also been indicated in hippocampal cultures and rat dorsal hippocampal formation showing a neuronal location. In vitro assays on extracellular signal-regulated kinases 1 and 2 phosphorylation have shown synergistic increases in signaling on coactivation with fibroblast growth factor 2 (FGF2) and a 5-HT1A agonist, and dependent on the heteroreceptor interface. In vitro and in vivo studies also revealed a 5-HT1A agonist induced phosphorylation of FGFR1 and extracellular signal-regulated kinase 1/2 in rat hippocampus without changing FGF2 levels. Co-activation of the heteroreceptor also resulted in synergistic increases in extensions of PC12 cells and neurite densities and protrusions in primary hippocampal cultures dependent on the receptor interface. The combined acute and repeated intracerebroventricular treatment with FGF2 and 8-OH-DPAT was found to produce evidence of highly significant antidepressant actions in the forced swim test.

CONCLUSIONS

The findings indicate that neurotrophic and antidepressant effects of 5-HT in brain may, in part, be mediated by activation of the 5-HT1A receptor protomer in the hippocampal FGFR1-5-HT1A receptor complex enhancing the FGFR1 signaling.

JNK/ERK/FAK mediate promigratory actions of basic fibroblast growth factor in astrocytes via CCL2 and COX2

While the role of cytokines in causing pro- and anti-inflammatory cascades in the brain and that of chemokines in promoting chemotaxis is well recognized, the immunomodulatory actions of neurotrophins released during brain injury remains largely undetermined. This knowledge gap affects basic fibroblast growth factor (FGF2), which in the brain is mainly produced by astrocytes and characteristically upregulated in reactive astrocytes. The goal of this study was to characterize the inflammatory actions of FGF2 in astrocytes using primary cultures. We report that FGF2 induced the upregulation of monocyte chemoattractant protein (CCL2) and cyclo-oxygenase type 2 (COX2), and the inhibition of lipopolysaccharide-elicited ICAM1 upregulation. The effects of FGF2 were: (i) dependent on gene transcription as revealed by the concomitant regulation of CCL2 or ICAM1 mRNAs; (ii) mediated by the FGF2 receptor type 2; (iii) dependent on ERK, JNK and FAK, and (iv) NF-κB-independent. FGF2 also caused accelerated wound closure dependent on CCL2, COX2, ERK, JNK and FAK in a scratch assay. We conclude that the signaling network triggered by FGF2 in astrocytes converged into accelerating directed motion. It follows that astrocyte migration to injury sites may be a key factor in the repair mechanisms orchestrated by FGF2.

A peptide mimetic targeting trans-homophilic NCAM binding sites promotes spatial learning and neural plasticity in the hippocampus

The key roles played by the neural cell adhesion molecule (NCAM) in plasticity and cognition underscore this membrane protein as a relevant target to develop cognitive-enhancing drugs. However, NCAM is a structurally and functionally complex molecule with multiple domains engaged in a variety of actions, which raise the question as to which NCAM fragment should be targeted. Synthetic NCAM mimetic peptides that mimic NCAM sequences relevant to specific interactions allow identification of the most promising targets within NCAM. Recently, a decapeptide ligand of NCAM—plannexin, which mimics a homophilic trans-binding site in Ig2 and binds to Ig3—was developed as a tool for studying NCAM's trans-interactions. In this study, we investigated plannexin's ability to affect neural plasticity and memory formation. We found that plannexin facilitates neurite outgrowth in primary hippocampal neuronal cultures and improves spatial learning in rats, both under basal conditions and under conditions involving a deficit in a key plasticity-promoting posttranslational modification of NCAM, its polysialylation. We also found that plannexin enhances excitatory synaptic transmission in hippocampal area CA1, where it also increases the number of mushroom spines and the synaptic expression of the AMPAR subunits GluA1 and GluA2. Altogether, these findings provide compelling evidence that plannexin is an important facilitator of synaptic functional, structural and molecular plasticity in the hippocampal CA1 region, highlighting the fragment in NCAM's Ig3 module where plannexin binds as a novel target for the development of cognition-enhancing drugs.

Expression and Functions of Fibroblast Growth Factor 2 (FGF-2) in Hippocampal Formation

Among the 23 members of the fibroblast growth factor (FGF) family, FGF-2 is the most abundant one in the central nervous system. Its impact on neural cells has been profoundly investigated by in vitro and in vivo studies as well as by gene knockout analyses during the past 2 decades. Key functions of FGF-2 in the nervous system include roles in neurogenesis, promotion of axonal growth, differentiation in development, and maintenance and plasticity in adulthood. From a clinical perspective, its prominent role for the maintenance of lesioned neurons (e.g., ischemia and following transection of fiber tracts) is of particular relevance. In the unlesioned brain, FGF-2 is involved in synaptic plasticity and processes attributed to learning and memory. The focus of this review is on the expression of FGF-2 and its receptors in the hippocampal formation and the physiological and pathophysiological roles of FGF-2 in this region during development and adulthood.

The FGF-2/FGFRs neurotrophic system promotes neurogenesis in the adult brain

Neurogenesis occurs in two regions of the adult brain, namely, the subventricular zone (SVZ) throughout the wall of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus (DG) in hippocampal formation. Adult neurogenesis requires several neurotrophic factors to sustain and regulate the proliferation and differentiation of the adult stem cell population. In the present review, we examine the cellular and functional aspects of a trophic system mediated by fibroblast growth factor-2 (FGF-2) and its receptors (FGFRs) related to neurogenesis in the SVZ and SGZ of the adult rat brain. In the SVZ, FGF-2 is expressed in GFAP-positive cells of SVZ but is not present in proliferating precursor cells, which instead express FGFR-1 and FGFR-2, but not FGFR-3 mRNA, although expressed in the SVZ, and FGFR-4. Therefore, it seems that in the SVZ FGF-2 may be released by GFAP-positive cells, different from the precursor cell lineage, and via volume transmission it reaches the proliferating precursor cells. FGFR-1 mRNA is also expressed in the SGZ and is localized in BrdU-labeled precursor cells, whereas FGFR-2 and FGFR-3 mRNA, although expressed in the SGZ, are not located within proliferating precursor cells. An aged-related decline of proliferating precursor cells in the SVZ and DG of old rats has been well documented, and there is the suggestion that in part it could be the consequence of alterations in growth factor expression levels. Thus, the old precursors may respond to growth factors, suggesting that during aging the basic components for neuronal precursor cell proliferation are retained and the capacity to increase neurogenesis after appropriate stimulation is still preserved. In conclusion, the trophic system mediated by FGF-2 and its receptors contributes to create an important micro-environmental niche that promotes neurogenesis in the adult and aged brain.

Fibroblast growth factor-2 and its receptor expression in proliferating precursor cells of the subventricular zone in the adult rat brain

Several findings have suggested the existence in the subventricular zone (SVZ) from sagittal sections of adult rat brain of a trophic mechanism, mediated by fibroblast growth factor-2 (FGF-2) and its multiple high-affinity FGF receptors (FGFRs), regulating neurogenesis mainly by controlling precursor cell proliferation. However, no clear data are available on the expression of FGF-2 and FGFRs in proliferating precursor cells of the SVZ. To address these questions we examined FGF-2 mRNA and its FGFR mRNA expression in proliferating precursor cells of the SVZ by using a double labeling procedure, combining in situ hybridization for FGF-2 and its FGFR mRNA with immunohistochemistry for bromodeoxyuridine (BrdU), a marker for proliferating cells. The results showed that FGFR1 and FGFR2 mRNAs were expressed in BrdU-labeled proliferating precursor cells, whereas FGFR3 and FGF-2 mRNAs were not, suggesting that in the SVZ the proliferating precursor cells express FGFR1 or FGFR2 and they may respond to FGF-2 released by non-proliferating cells. The FGFR4 mRNA was not found expressed in the SVZ. In the future, by identifying the cell types expressing FGFRs, it will be possible to gain insight into the functional activity of FGF2 within the SVZ.

Nicotine-induced fibroblast growth factor-2 restores the age-related decline of precursor cell proliferation in the subventricular zone of rat brain

Precursor cell proliferation is present in the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus of the hippocampus of adult rat and persists during aging although at reduced levels. Previous studies have shown that acute intermittent nicotine treatment significantly increases fibroblast growth factor-2 (FGF-2) expression in several brain regions of aged rats. The aim of the present investigation was to test the hypothesis that nicotine-induced expression of FGF-2 may restore the age-related decline of precursor cell proliferation. It was first demonstrated that nicotine treatment increases both mRNA and protein FGF-2 in the SVZ of aged male rats (18 months old). The effect of nicotine on precursor cell proliferation in the SVZ was studied by i.p. injection of 5-bromo-2'-deoxyuridine (BrdU) 40 mg/kg to label dividing cells. The nicotine treatment was found to significantly enhance precursor cell proliferation in the SVZ. This increase was sufficiently large to restore the age-related decline of proliferating precursor cells observed in aged rats to that found in young adult rats (3 months old). FGF-2 was expressed in GFAP-positive cells and may act via its receptor FGFR1 that was found expressed in nestin-positive cells of the SVZ. The data obtained demonstrated that the age-related decline of precursor cell proliferation may be counteracted by activating a trophic mechanism mediated by FGF-2.

Enhanced production and dendritic growth of new dentate granule cells in the middle-aged hippocampus following intracerebroventricular FGF-2 infusions

Declined production and diminished dendritic growth of new dentate granule cells in the middle-aged and aged hippocampus are correlated with diminished concentration of fibroblast growth factor-2 (FGF-2). This study examined whether increased FGF-2 concentration in the milieu boosts both production and dendritic growth of new dentate granule cells in the middle-aged hippocampus. The FGF-2 or vehicle was infused into the posterior lateral ventricle of middle-aged Fischer (F)344 rats for 2 weeks using osmotic minipumps. New cells born during the first 12 days of infusions were labeled via daily intraperitoneal injections of 5'-bromodeoxyuridine (BrdU) and analysed at 10 days after the last BrdU injection. Measurement of BrdU(+) cells revealed a considerably enhanced number of new cells in the subgranular zone (SGZ) and granule cell layer (GCL) of the dentate gyrus (DG) ipsilateral to FGF-2 infusions. Characterization of beta-III tubulin(+) neurons among newly born cells suggested an increased addition of new neurons to the SGZ/GCL ipsilateral to FGF-2 infusions. Quantification of DG neurogenesis at 8 days post-infusions via doublecortin (DCX) immunostaining also revealed the presence of an enhanced DG neurogenesis ipsilateral to FGF-2 infusions. Furthermore, DCX(+) neurons in FGF-2-infused rats exhibited enhanced dendritic growth compared with their counterparts in vehicle-infused rats. Thus, subchronic infusion of FGF-2 is efficacious for stimulating an enhanced DG neurogenesis from neural stem/progenitor cells in the middle-aged hippocampus. As dentate neurogenesis is important for hippocampal-dependent learning and memory and DG long-term potentiation, strategies that maintain increased FGF-2 concentration during ageing may be beneficial for thwarting some of the age-related cognitive impairments.

Fibroblast growth factor receptor-1 is required for long-term potentiation, memory consolidation, and neurogenesis

BACKGROUND

Although substantial evidence supports the view that adult neurogenesis is involved in learning and memory, how newly generated neurons contribute to the cognitive process remains unknown. Fibroblast growth factor 2 (FGF-2) is known to stimulate the proliferation of neuronal progenitor cells (NPCs) in adult brain. Using conditional knockout mice that lack brain expression of FGFR1, a major receptor for FGF-2, we have investigated the role of adult neurogenesis in hippocampal synaptic plasticity and learning and memory.

METHODS

The Fgfr1 conditional knockout mice were generated by crossing the Fgfr1-null line, the Fgfr1-flox line, and the Nestin-Cre transgenic mice. Bromodeoxyuridine (BrdU) labeling, slice electrophysiology, and Morris Water Maze experiments were performed with the Fgfr1 conditional mutant mice.

RESULTS

Bromodeoxyuridine labeling experiments demonstrate that FGFR1 is required for the proliferation of NPCs as well as generation of new neurons in the adult dentate gyrus (DG). Moreover, deficits in neurogenesis in Fgfr1 mutant mice are accompanied by a severe impairment of long-term potentiation (LTP) at the medial perforant path (MPP)-granule neuron synapses in the hippocampal dentate. Moreover, the Fgfr1 mutant mice exhibit significant deficits in memory consolidation but not spatial learning.

CONCLUSIONS

Our study suggests a critical role of FGFR1 in adult neurogenesis in vivo, provides a potential link between proliferative neurogenesis and dentate LTP, and raises the possibility that adult neurogenesis might contribute to memory consolidation.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrain with few synapses, and where deficits in serotonergic function appeared to play a major role in depression. We propose that serotonin reuptake inhibitors may produce antidepressant effects through increasing serotonergic neurotrophism in serotonin nerve cells and their targets by transactivation of receptor tyrosine kinases (RTK), involving direct or indirect receptor/RTK interactions. Early chemical neuroanatomical work on the monoamine neurons, involving primitive nervous systems and analysis of peptide neurons, indicated the existence of alternative modes of communication apart from synaptic transmission. In 1986, Agnati and Fuxe introduced the theory of two main types of intercellular communication in the brain: wiring and volume transmission (WT and VT). Synchronization of phasic activity in the monoamine cell clusters through electrotonic coupling and synaptic transmission (WT) enables optimal VT of monoamines in the target regions. Experimental work suggests an integration of WT and VT signals via receptor-receptor interactions, and a new theory of receptor-connexin interactions in electrical and mixed synapses is introduced. Consequently, a new model of brain function must be built, in which communication includes both WT and VT and receptor-receptor interactions in the integration of signals. This will lead to the unified execution of information handling and trophism for optimal brain function and survival.

Achondroplasia

Achondroplasia is the most common form of short limb dwarfism in human beings, affecting more than 250,000 individuals worldwide. More than 95% of patients have the same point mutation in the gene for fibroblast growth factor receptor 3 (FGFR3) and more than 80% of these are new mutations. The mutation, which causes gain of FGFR3 function, affects many tissues, most strikingly the cartilaginous growth plate in the growing skeleton, leading to a variety of manifestations and complications. The biology of FGFR3 and the molecular and cellular consequences of the achondroplasia mutation are being elucidated, providing a more complete understanding of the disorder and a basis for future treatments targeted directly at relevant pathogenetic pathways. Furthermore, the natural history of the condition, which has been well delineated in childhood and adolescence, is being defined more fully in adults with achondroplasia; most of the serious complications can be modified favourably or prevented by anticipation and early treatment. Possible future treatments include chemical inhibition of receptor signalling, antibody blockade of receptor activation, and alteration of pathways that modulate the downstream propagation of FGFR3 signals.

The physiological and pharmacological role of basic fibroblast growth factor in the dopaminergic nigrostriatal system

Basic fibroblast growth factor (FGF-2) is a physiological relevant neurotrophic factor in the nigrostriatal system and hence a promising candidate for the establishment of alternative therapeutic strategies in Parkinson's disease. FGF-2 and its high-affinity receptors (FGFR) display an expression in the developing, postnatal, and adult substantia nigra (SN) and in the striatum. Exogenous application promoted survival, neurite outgrowth and protection from neurotoxin-induced death of dopaminergic (DA) neurons both in vitro and in vivo. In animal models of Parkinson's disease, co-transplantation of fetal DA cells with FGF-2 expressing cells increased survival and functional integration of the grafted DA neurons resulting in improved behavioral performance. Analyzing the physiological function of the endogenous FGF-2 system during development and after neurotoxin-induced lesion revealed for the DA neurons of the SNpc a dependence on FGFR3 signaling during development. In addition, in the absence of FGF-2 an increased number of DA neurons was found, whereas enhanced levels of FGF-2 resulted in a reduced DA cell density. Following neurotoxin-induced lesion of DA neurons, FGF-2-deleted mice displayed a higher extent of DA neuron death whereas in FGF-2 overexpressing mice more DA neurons were protected. According to the data, FGF-2 seems to promote DA neuron survival via FGFR3 during development, whereas absence of this ligand could be compensated by other members of the FGF family. In contrast, in the adult organism, FGF-2 cannot be compensated by other factors under lesion conditions suggesting a central role for this molecule in the nigrostriatal system.