The effect of basic fibroblast growth factor on glutamate-injured neuroarchitecture and arachidonic acid release in adult hippocampal neurons

FGFR Regulation of Dendrite Elaboration in Adult-born Granule Cells Depends on Intracellular Mediator and Proximity to the Soma

Fibroblast Growth Factor Receptors (FGFRs) play crucial roles in promoting dendrite growth and branching during development. In mice, three FGFR genes, Fgfr1, Fgfr2, and Fgfr3, remain expressed in the adult neurogenic niche of the hippocampal dentate gyrus. However, the function of FGFRs in the dendritic maturation of adult-born neurons remains largely unexplored. Here, using conditional alleles of Fgfr1, Fgfr2, and Fgfr3 as well as Fgfr1 alleles lacking binding sites for Phospholipase-Cγ (PLCγ) and FGF Receptor Substrate (FRS) proteins, we test the requirement for FGFRs in dendritogenesis of adult-born granule cells. We find that deleting all three receptors results in a small decrease in proximal dendrite elaboration. In contrast, specifically mutating Tyr766 in FGFR1 (a PLCγ binding site) in an Fgfr2;Fgfr3 deficient background results in a dramatic increase of overall dendrite elaboration, while blocking FGFR1-FRS signaling causes proximal dendrite deficits and, to a lesser extent than Tyr766 mutants, increases distal dendrite elaboration. These findings reveal unexpectedly complex roles for FGFRs and their intracellular mediators in regulating proximal and distal dendrite elaboration, with the most notable role in suppressing distal elaboration through the PLCγbinding site.

Characterizing the multiple roles of FGF-2 in SOD1G93A ALS mice in vivo and in vitro

We have previously shown that knockout of fibroblast growth factor-2 (FGF-2) and potential compensatory effects of other growth factors result in amelioration of disease symptoms in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). ALS is a rapidly progressive neurological disorder leading to degeneration of cortical, brain stem, and spinal motor neurons followed by subsequent denervation and muscle wasting. Mutations in the superoxide dismutase 1 (SOD1) gene are responsible for approximately 20% of familial ALS cases and SOD1 mutant mice still are among the models best mimicking clinical and neuropathological characteristics of ALS. The aim of the present study was a thorough characterization of FGF-2 and other growth factors and signaling effectors in vivo in the SOD1^G93A mouse model. We observed tissue-specific opposing gene regulation of FGF-2 and overall dysregulation of other growth factors, which in the gastrocnemius muscle was associated with reduced downstream extracellular-signal-regulated kinases (ERK) and protein kinase B (AKT) activation. To further investigate whether the effects of FGF-2 on motor neuron death are mediated by glial cells, astrocytes lacking FGF-2 were cocultured together with mutant SOD1 ^G93A motor neurons. FGF-2 had an impact on motor neuron maturation indicating that astrocytic FGF-2 affects motor neurons at a developmental stage. Moreover, neuronal gene expression patterns showed FGF-2- and SOD1 ^G93A -dependent changes in ciliary neurotrophic factor, glial-cell-line-derived neurotrophic factor, and ERK2, implying a potential involvement in ALS pathogenesis before the onset of clinical symptoms.

SUN11602, a novel aniline compound, mimics the neuroprotective mechanisms of basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) offers some measure of protection against excitotoxic neuronal injuries by upregulating the expression of the calcium-binding protein calbindin-D28k (Calb). The newly synthesized small molecule 4-({4-[[(4-amino-2,3,5,6-tetramethylanilino)acetyl](methyl)amino]-1-piperidinyl}methyl)benzamide (SUN11602) mimics the neuroprotective effects of bFGF, and thus, we examined how SUN11602 exerts its actions on neurons in toxic conditions of glutamate. In primary cultures of rat cerebrocortical neurons, SUN11602 and bFGF prevented glutamate-induced neuronal death. This neuroprotection, which occurred in association with the augmented phosphorylation of the bFGF receptor-1 (FGFR-1) and the extracellular signal-regulated kinase-1/2 (ERK-1/2), was abolished by pretreatment with PD166866 (a FGFR-1 tyrosine kinase-specific inhibitor) and PD98059 (a mitogen-activated protein kinase [MAPK]/[ERK-1/2] kinase [MEK] inhibitor). In addition, SUN11602 and bFGF increased the levels of CALB1 gene expression in cerebrocortical neurons. Whether this neuroprotection was linked to Calb was investigated with primary cultures of cerebrocortical neurons from homozygous knockout (Calb(-/-)) and wild-type (WT) mice. In WT mice, SUN11602 and bFGF increased the levels of newly synthesized Calb in cerebrocortical neurons and suppressed the glutamate-induced rise in intracellular Ca(2+). This Ca(2+)-capturing ability of Calb allowed the neurons to survive severe toxic conditions of glutamate. In contrast, Calb levels remained unchanged in Calb(-/-) mice after exposure to SUN11602 or bFGF, and due to a loss of function of the gene, these neurons were no longer resistant to toxic conditions of glutamate. These findings indicated that SUN11602 activated a number of cellular molecules (FGFR-1, MEK/ERK intermediates, and Calb) and consequently contributed to intracellular Ca(2+) homeostasis as observed in the case of bFGF.

Depression and adipose and serum cholesteryl ester polyunsaturated fatty acids in the survivors of the seven countries study population of Crete

BACKGROUND

Studies have shown that depression relates to biomarkers of both short- and long-term polyunsaturated fatty acid (PUFA) intake. However, it is not known which of these two biomarkers has the closest relationship to depression.

OBJECTIVE

To examine the relationship of depression with both adipose tissue and serum cholesteryl ester PUFA and to assess the importance of each of these two biomarkers in relating to depression.

DESIGN

Cross-sectional study of healthy elderly men from the island of Crete.

SETTING

The Preventive Medicine and Nutrition Clinic, University of Crete, Greece.

SUBJECTS

A total of 150 males, aged 80-96 years. The subjects were survivors of the Greek Seven Countries Study group.

METHODS

Fatty acids were determined by gas chromatography in adipose tissue and serum cholesteryl esters. Information about depression was obtained through the use of the short form of the Geriatric Depression Scale (GDS-15).

RESULTS

Regression analysis showed that depression related positively to age and serum cholesteryl ester arachidonic/docosahexaenoic fatty acid ratio. The only significant unadjusted correlation between depression and serum cholesteryl ester and adipose fatty acids was with adipose alpha-linolenic acid (ALA) (r = -0.31, P < 0.01). Depressed males (GDS-15 > 5) had lower adipose ALA and sum n-3 fatty acids than non-depressed ones. There were no significant differences between depressed and non-depressed males in serum cholesteryl ester fatty acids. When adipose tissue ALA was included as one of the independent measures in the regression model, the observed positive relation between GDS-15 depression and cholesteryl ester arachidonic/docosahexaenoic ratio failed to persist. Instead, there was a negative relationship between GDS-15 depression and adipose tissue ALA.

CONCLUSIONS

It appears that the fatty acids of the adipose tissue are better predictors of depression than those of serum cholesteryl esters. This indicates that depression relates more strongly to long-term than to short-term fatty acid intake. The reason for this may be the reported slow rate of deposition of dietary PUFA to the brain.

Anti-fibroblast growth factor-2 antibodies attenuate mechanical allodynia in a rat model of neuropathic pain

Peripheral nerve injury leads to the activation of spinal cord astrocytes, which contribute to maintaining neuropathic (NP) pain behavior. Fibroblast growth factor-2 (FGF-2), a neurotrophic and gliogenic factor, is upregulated by spinal cord astrocytes in response to ligation of spinal nerves L5 and L6 (spinal nerve ligation [SpNL]). To evaluate the contribution of spinal astroglial FGF-2 to mechanical allodynia following SpNL, neutralizing antibodies to FGF-2 were injected intrathecally. Administration of 18 microg of anti-FGF-2 antibodies attenuated mechanical allodynia at day 21 after SpNL and reduced FGF-2 and glial acidic fibrillary protein mRNA expression and immunoreactivity in the L5 spinal cord segment of rats with SpNL. These results suggest that endogenous astroglial FGF-2 contributes to maintaining NP tactile allodynia associated with reactivity of spinal cord astrocytes and that inhibition of spinal FGF-2 ameliorates NP pain signs.

Primary cell culture of suprachiasmatic nucleus

In mammals, the suprachiasmatic nucleus (SCN) contains a biological clock that drives circadian rhythms in vivo and in vitro. Primary dissociated neuronal culture is a useful research tool, which allows cell-by-cell morphological and physiological study of the SCN. A long-term primary dissociated SCN neuron culture is the prerequisite to understanding how neural activity and morphology interact in the SCN. The essential details of recent effective SCN culture methods are reviewed, including preparation of cells, medium and substrate, maintenance of cultures, and characterization of cultured SCN neurons. This technique is growing in importance, especially with the advent of multi-electrode array (MEA) recording.

Circadian rhythms in firing rate of individual suprachiasmatic nucleus neurons from adult and middle-aged mice

The suprachiasmatic nucleus contains a biological clock that drives circadian rhythms in vivo and in vitro. It has been suggested that the suprachiasmatic nucleus is a primary target of the aging process, because age-related changes in behavioral rhythms are mirrored in alterations in circadian pacemaker function. Using long-term, single-cell recording, we assessed the effect of age on firing-rate patterns of individual suprachiasmatic nucleus neurons of young adult (2-4 months) and middle-aged (9-11 months) C3H mice. Individual suprachiasmatic nucleus neurons from adult mice maintained in culture for at least one week exhibited robust circadian rhythms in spontaneous activity that were similar in the free-running period (23.7+/-0.3 h mean+/-S.E.M.) to recordings from neurons dispersed from neonatal tissue, and showed evidence of entrainment to prior light cycles by exhibiting peak activity, in vitro, approximately 4.0+/-0.3 h (mean+/-S.E.M.) after the time of expected light onset. Aging led to a decreased amplitude of impulse activity in dispersed suprachiasmatic nucleus neurons and increased variability in the circadian waveform. From these results we suggest that age-related deterioration in circadian clock function occurs at the level of individual cells, which may account for some of the age-related deficits observed in the expression of behavioral rhythmicity.

Involvement of the 5-lipoxygenase pathway in the neurotoxicity of the prion peptide PrP106-126

Transmissible spongiform encephalopathies are characterised by the transformation of the normal cellular prion protein (PrP(C)) into an abnormal isoform (PrP(TSE)). Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor antagonists can inhibit glutathione depletion and neurotoxicity induced by PrP(TSE) and a toxic prion protein peptide, PrP106-126, in vitro. NMDA receptor activation is known to increase intracellular accumulation of Ca(2+), resulting in up-regulation of arachidonic acid (AA) metabolism. This can stimulate the lipoxygenase pathways that may generate a number of potentially neurotoxic metabolites. Because of the putative relationship between AA breakdown and PrP106-126 neurotoxicity, we investigated AA metabolism in primary cerebellar granule neuron cultures treated with PrP106-126. Our studies revealed that PrP106-126 exposure for 30 min significantly up-regulated AA release from cerebellar granule neurons. PrP106-126 neurotoxicity was mediated through the 5-lipoxygenase (5-LOX) pathway, as shown by abrogation of neuronal death with the 5-LOX inhibitors quinacrine, nordihydroguaiaretic acid, and caffeic acid. These inhibitors also prevented PrP106-126-induced caspase 3 activation and annexin V binding, indicating a central role for the 5-LOX pathway in PrP106-126-mediated proapoptosis. Interestingly, inhibitors of the 12-lipoxygenase pathway had no effect on PrP106-126 neurotoxicity or proapoptosis. These studies clearly demonstrate that AA metabolism through the 5-LOX pathway is an important early event in PrP106-126 neurotoxicity and consequently may have a critical role in PrP(TSE)-mediated cell loss in vivo. If this is so, therapeutic intervention with 5-LOX inhibitors may prove beneficial in the treatment of prion disorders.

Hypertonic-hyperoncotic saline differentially affects healthy and glutamate-injured primary rat hippocampal neurons and cerebral astrocytes

Hypertonic-hyperoncotic saline solutions (HHS) have been used for small-volume resuscitation and to treat intracranial hypertension and cerebral edema in neurocritical care. Little is known on the response of brain cells to direct exposure in HHS, which may occur in blood-brain barrier disruption. We studied the effects of HHS on healthy and glutamate-injured brain cells in vitro. To model a hypertonic-hyperoncotic environment, rat hippocampal neurons and cerebral astrocytes were exposed to hypertonic saline and hydroxyethyl starch (HES) added to medium for 15 minutes (final osmolarity: 350 mOsm/L in the neuronal, 373 mOsm/L in the glial medium; 2.5 mg/mL HES in both media). To simulate excitotoxicity, cells were exposed to 100 microM glutamate for 8 minutes before exposure to HHS. Cell viability was analyzed by morphology and vital dye staining; intracellular water space (WS) and glucose use were measured by scintillation spectrometry using 3-O-methyl[14C]-D-glucose and [3H]2-deoxy-D-glucose ([3H]2-DG). After 24 hours, exposure to HHS added to medium caused a 30% reduction in viability of healthy neurons (P < .05), but did not exacerbate the glutamate-induced 50% decrease in neuronal survival. One hundred percent astrocyte viability remained unchanged. The WS of astrocytes and surviving neurons was negligibly altered. Exposure to HHS added to medium caused a 35% reduction in [3H]2-DG in healthy and glutamate-injured neurons (P < .05), but did not affect [3H]2-DG in astrocytes. Our data show that HHS may potentially injure hippocampal neurons. Preserved WS values imply that live cells maintained volume regulation capabilities, indicating a lack of dehydration 24 hours after exposure to HHS. Impaired glucose use predisposes neurons to disturbed metabolism, which may influence neuronal outcome after brain injury.

S(+)-ketamine up-regulates neuronal regeneration associated proteins following glutamate injury in cultured rat hippocampal neurons

In previous studies, racemic ketamine improved neurological outcome after experimental brain injury and S(+)-ketamine demonstrated neuroprotective effects in neurons after damage in vitro. We compared the expression of regeneration-associated proteins in rat hippocampal neurons after glutamate injury and treatment with S(+)-ketamine versus racemic ketamine. Following an 8 minute exposure to 100 microM glutamate, neurons were maintained untreated or in the presence of S(+)-ketamine or racemic ketamine (10(-4) M, 10(-5) M, 10(-6) M) for one week. Growth-associated protein-43 (GAP-43) and synaptosomal-associated protein-25 (SNAP-25) was analyzed by Western Blotting, the mitochondrial transmembrane potential (MTP) by fluorescence imaging, and [3H]2-deoxy-D-glucose ([3H]2-DG) uptake by scintillation spectrometry. Seven days after exposure, GAP-43 decreased to 15% and SNAP-25 to 30% in the glutamate-injured, untreated neurons. The MTP declined to 50% and [3H]2-DG to 30%. Both S(+)-ketamine and racemic ketamine at 10(-4) M and 10(-5) M minimized the decline in MTP, almost maintaining it at control value. Additionally, S(+)-ketamine and racemic ketamine decreased the reduction in [3H]2-DG. S(+)-ketamine at 10(-4) M and 10(-5) M and racemic ketamine at 10(-4) M reduced the decline in SNAP-25 to 60% of controls (P < .05). However, S(+)-ketamine at 10(-4) M and 10(-5) M only reversed the decrease in GAP-43 to 50% and 40% of controls, respectively (P < .05). We conclude that the synthesis of a growth-associated protein related to plasticity and repair in the adult nervous system is increased by S(+)-ketamine but is not increased by racemic ketamine.

Fibroblast growth factor modulates HIV coreceptor CXCR4 expression by neural cells. HNRC Group

Recent studies suggest that the chemokine receptor CXCR4 may be involved in mediating the neurodegenerative process in the brains of patients with acquired immunodeficiency disease (AIDS). In this context, we hypothesize that neurotrophic factors, such as fibroblast growth factor (FGF), might protect against human immunodeficiency virus (HIV)-mediated neurotoxicity via regulating the expression of CXCR4 in neural cells. For this purpose, levels of CXCR4 were determined in neuronal and glial cell lines after FGF1 and 2 treatment. In addition, levels of CXCR4 immunoreactivity were associated with levels of FGF1 immunoreactivity in the brains of HIV-positive patients. These studies showed that neuronal CXCR4 levels decreased in a dose-dependent manner after exposure to FGF. Conversely, glial CXCR4 was increased in a dose-dependent manner after FGF2 treatment. These effects were dependent on the FGF receptor tyrosine kinase signaling pathway, because FGF-induced effects on CXCR4 were blocked by the tyrosine kinase inhibitor, 5'-deoxy-5'methylthioadenosine, or by anti-FGF receptor antibody. Stromal cell-derived factor-1, the ligand for CXCR4, and HIV gp120 neurotoxicity was attenuated by FGF1 in a dose-dependent manner in vitro, further supporting physiological relevance. In the brains of AIDS patients, the levels of neural CXCR4 immunoreactivity were inversely associated with FGF levels. Taken together, these results support the possibility that the neuroactive effects of FGF in HIV encephalitis might be mediated through regulation of the expression of CXCR4.

Sequential pharmacotherapy with magnesium chloride and basic fibroblast growth factor after fluid percussion brain injury results in less neuromotor efficacy than that achieved with magnesium alone

Combinational pharmacotherapy with individually efficacious agents is a potential strategy for the treatment of traumatic central nervous system (CNS) injury. Basic fibroblast growth factor (bFGF) has been shown to be neuroprotective against excitotoxic, ischemic, and traumatic injury to the CNS, while acute posttraumatic treatment with magnesium (Mg2+) has been shown to decrease the motor and cognitive deficits following experimental brain injury. In this study, bFGF and Mg2+ were evaluated separately and in combination to assess their potential additive effects on posttraumatic neurological recovery and histological cell loss (lesion volume). Twenty minutes after fluid percussion (FP) brain injury of moderate severity (2.2-2.4 atm), anesthetized rats received a 15-min intravenous infusion of either 125 mumol of MgCl2 or vehicle, followed 5 min later by a 24-h constant intravenous infusion of either bFGF (16 micrograms/h) or vehicle. Injured animals had a significant motor deficit when compared to sham (uninjured) animals at both 48 h and 7 days postinjury. At 48 h postinjury, there were no significant differences among injured animals when compared by treatment. By 7 days postinjury, injured animals treated with MgCl2 alone displayed significantly improved motor function when compared to brain-injured, vehicle-treated animals (p < 0.05). Animals treated with either bFGF alone or a combination of MgCl2 and bFGF displayed no significant neurological improvement relative to vehicle-treated injured animals at 7 days. No effect of any drug treatment of combination was observed on the extent of the postinjury lesion volume in the injured cortex. These results suggest that caution must be exercised when combining "cocktails" of potentially neuroprotective compounds in the setting of traumatic brain injury.

Immunohistochemical analyses of fibroblast growth factor receptor-1 in the human substantia nigra. Comparison between normal and Parkinson's disease cases

The use of neurotrophic growth factors as a means of preventing loss of the dopaminergic (DA) neurons in the substantia nigra (SN) is becoming an accepted treatment strategy for Parkinson's disease (PD). In earlier studies, we showed that there was a selective loss of basic fibroblast growth factor (bFGF) immunoreactivity in DA neurons of the SN in PD suggesting that a deficiency of bFGF might contribute to cell death. As a preliminary step to assessing the potential for using bFGF or its analogs as therapeutic agents, the expression of fibroblast growth factor receptor-1 (FGFR-1) in the SN of normal and PD cases was investigated immunohistochemically. FGFR-1 immunoreactivity could be detected in DA neurons of the SN in young and old neurologically normal cases with an apparent decline with age. FGFR-1 immunoreactivity was also detected in many of the residual SN neurons in most of the idiopathic PD cases. These results indicate that FGFR-1 immunoreactivity, and possibly FGF binding activity, is retained in DA neurons in PD.

Structural alterations and changes in cytoskeletal proteins and proteoglycans after focal cortical ischemia

In order to study structural alterations which occur after a defined unilateral cortical infarct, the hindlimb region of the rat cortex was photochemically lesioned. The infarcts caused edema restricted to the perilesional cortex which affected allocortical and isocortical areas differently. Postlesional changes in cytoskeletal marker proteins such as microtubule-associated protein 2, non-phosphorylated (SMI32) and phosphorylated (SMI35, SMI31 and 200,000 mol. wt) neurofilaments and 146,000 mol. wt glycoprotein Py as well as changes in proteoglycans visualized with Wisteria floribunda lectin binding (WFA) were studied at various time points and related to glial scar formation. The results obtained by the combination of these markers revealed six distinct regions in which transient, epitope-specific changes occurred: the core, demarcation zone, rim, perilesional cortex, ipsilateral thalamus and contralateral homotopic cortical area. Within the core immunoreactivity for microtubule-associated protein 2 and SMI32 decreased and the cellular components showed structural disintegration 4 h post lesion, but partial recovery of somatodendritic staining was seen after 24 h. Microtubule-associated protein 2 and SMI32 persisted up to days 7 and 5 respectively in the core, whereas the number of glial fibrillary acidic protein- and WFA-positive cells decreased between days 7 and 14. The demarcation zone showed a dramatic loss of immunoreactivity for all epitopes 4 h post lesion which was not followed by a phase of recovery. In the inner region of the demarcation zone there was an invasion and accumulation of non-neuronal WFA-positive cells which formed a tight capsule around the core. Neuronal immunoreactivities for microtubule-associated protein 2, SMI31 and Py as well as astrocytic glial fibrillary acidic protein increased strongly within an approximately 0.4-1.0 mm-wide rim region directly bordering the demarcation zone. Py immunoreactivity increased significantly in the perilesional cortex, whereas glial fibrillary acidic protein-positive astrocytes became transiently more numerous in the entire lesioned hemisphere including strongly enhanced immunoreactivity in the thalamus by days 5-7 post lesion. Glial fibrillary acidic protein immunoreactivity increased in the corpus callosum and the homotopic cortical area of the unlesioned hemisphere by days 5-7. In this homotopic area additional changes in SMI31 immunoreactivity occurred. Our results showed that a cortical infarct is not only a locally restricted lesion, but leads to a variety of cytoskeletal and other structural changes in widely-distributed functionally-related areas of the brain.

Effects of growth factors and estrogen on the development of septal cholinergic neurons from the rat

Cholinergic neurons of the septum are preferentially subject to degeneration in Alzheimer's disease. There is evidence that nerve growth factor, basic fibroblast growth factor, insulin-like growth factors, and estrogen all have effects on survival of this specific population of neurons at risk. We used a bilaminar culturing method to grow embryonic septal neurons from the rat in the presence of a separate glial plane but in the absence of serum. These neurons were treated with a number of factors, and neurite development of cholinergic neurons was assessed. Basic fibroblast growth factor and estrogen altered the number of primary neurites, number of secondary neurites, and mean total neurite lengths, while none of the other factors affected these end points. This would suggest a mechanism for the effects of these factors on memory.