Basic fibroblast growth factor in the mature brain and its possible role in Alzheimer's disease

Ageing and the Autonomic Nervous System

The vertebrate nervous system is divided into central (CNS) and peripheral (PNS) components. In turn, the PNS is divided into the autonomic (ANS) and enteric (ENS) nervous systems. Ageing implicates time-related changes to anatomy and physiology in reducing organismal fitness. In the case of the CNS, there exists substantial experimental evidence of the effects of age on individual neuronal and glial function. Although many such changes have yet to be experimentally observed in the PNS, there is considerable evidence of the role of ageing in the decline of ANS function over time. As such, this chapter will argue that the ANS constitutes a paradigm for the physiological consequences of ageing, as well as for their clinical implications.

Autonomic dysfunction in older people

The autonomic nervous system comprises the sympathetic, parasympathetic and enteric nervous systems and plays an integral role in homeostasis. This includes cardiovascular and temperature control, glucose metabolism, gastrointestinal and reproductive function and increasing evidence to support its involvement in the inflammatory response to infection and cancer. Ageing is associated with autonomic dysfunction, and many clinical syndromes associated with older adults are due to inadequate autonomic responses to physiological stressors. The aim of this review is to explore the relationship between autonomic dysfunction and ageing illustrated with examples of maladaptive autonomic responses in a variety of different clinical syndromes including an exploration of autonomic cellular changes. Appropriate investigation and management strategies are outlined, recognizing the fine balance needed to improve symptoms without creating further medical complications.

A dyad symmetry element in the fibroblast growth factor-2 gene promoter with different levels of activity in astrocytoma and hepatocelluar carcinoma cell lines

Fibroblast growth factor-2 (FGF-2) gene expression is reported to be spatially and temporally regulated in the process of development, normal growth, and wound healing. We postulated that its constitutive expression in human malignant astrocytoma cells is due to loss of function of the regulatory mechanism of FGF-2 gene expression. Here, we report the characterization of a unique element in the FGF-2 gene promoter. We investigated the transcriptional regulation of the FGF-2 gene in a human malignant astrocytoma (U87MG) and a human hepatocellular carcinoma (HepG2) cell line. We found that a dyad symmetry element (DSE) in the FGF-2 gene promoter exhibited different promoter activities; in HepG2 cells it did, while in U87MG cells it did not, exhibit repressive activity. Examination of the relative promoter activities of the DSE in a thymidine kinase promoter revealed it exerted different activities, just as it did in the 2 cell lines studied. Gel shift assay demonstrated that 2 proteins bound to the DSE in nuclear extracts from HepG2 cells and that one protein was missing in nuclear extracts from U87MG cells. These results suggest that the DSE has a crucial role as a transcriptional regulatory element of FGF-2 gene expression.

Neuropathology and pathogenesis of diabetic autonomic neuropathy

Autonomic neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. A number of studies, which have shown correspondence between neuropathologic findings in experimental animals and human subjects, have demonstrated that axonal and dendritic pathology in sympathetic ganglia in the absence of significant neuron loss represents a neuropathologic hallmark of diabetic autonomic neuropathy. A recurring theme in sympathetic ganglia, as well as in the pot-ganglionic autonomic innervation of various end organs, is the involvement of distal portions of axons and nerve terminals by degenerative or dystrophic changes. In both animals and humans, there is a surprising selectivity of the diabetic process for subpopulations of autonomic ganglia, nerve terminals within sympathetic ganglia and end organs, from end organ to end organ, and between vascular and other targets within individual end organs. Although the involvement or autonomic axons in somatic nerves may reflect an ischemic pathogenesis, the selectivity of the diabetic process confounds simple global explanations of diabetic autonomic neuropathy as the result of diminished blood flow with resultant tissue hypoxia. A single unifying pathogenetic hypothesis has not yet emerged from clinical and experimental animal studies, and it is likely that diabetic autonomic neuropathy will be shown to have multiple causative mechanisms, which will interact to result in the variety of presentations of autonomic injury in diabetes. Some of these mechanisms will be shared with aging changes in the autonomic nervous system. The role of various neurotrophic substances and the polyol pathway in the pathogenesis and treatment of diabetic neuropathy likely represents a two-edged sword with both salutary and exacerbating effects. The basic neurobiologic process underlying the diabetes-induced development of neuroaxonal dystrophy, synaptic dysplasia, defective axonal regeneration, and alterations in neurotrophic substance may be mechanistically related.

Fgfr3 expression by astrocytes and their precursors: evidence that astrocytes and oligodendrocytes originate in distinct neuroepithelial domains

The postnatal central nervous system (CNS) contains many scattered cells that express fibroblast growth factor receptor 3 transcripts (Fgfr3). They first appear in the ventricular zone (VZ) of the embryonic spinal cord in mid-gestation and then distribute into both grey and white matter - suggesting that they are glial cells, not neurones. The Fgfr3(+) cells are interspersed with but distinct from platelet-derived growth factor receptor alpha (Pdgfra)-positive oligodendrocyte progenitors. This fits with the observation that Fgfr3 expression is preferentially excluded from the pMN domain of the ventral VZ where Pdgfra(+) oligodendrocyte progenitors--and motoneurones--originate. Many glial fibrillary acidic protein (Gfap)- positive astrocytes co-express Fgfr3 in vitro and in vivo. Fgfr3(+) cells within and outside the VZ also express the astroglial marker glutamine synthetase (Glns). We conclude that (1) Fgfr3 marks astrocytes and their neuroepithelial precursors in the developing CNS and (2) astrocytes and oligodendrocytes originate in complementary domains of the VZ. Production of astrocytes from cultured neuroepithelial cells is hedgehog independent, whereas oligodendrocyte development requires hedgehog signalling, adding further support to the idea that astrocytes and oligodendrocytes can develop independently. In addition, we found that mice with a targeted deletion in the Fgfr3 locus strongly upregulate Gfap in grey matter (protoplasmic) astrocytes, implying that signalling through Fgfr3 normally represses Gfap expression in vivo.

Effect of NGF and neurotrophin-3 treatment on experimental diabetic autonomic neuropathy

Peripheral neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. Deficiencies of neurotrophic substances (e.g. NGE NT-3, and IGF-I) have been proposed as pathogenetic mechanisms in the development of distal symmetrical sensory diabetic polyneuropathy, and salutary effects of exogenous NGF administration have been reported in animal models. In comparison, relatively little is known concerning the effect of NGF on experimental diabetic sympathetic autonomic neuropathy. We have developed an experimental animal model of diabetic autonomic neuropathy characterized by the regular occurrence of pathologically distinctive dystrophic axons in prevertebral sympathetic ganglia and ileal mesenteric nerves of rats with chronic streptozotocin (STZ)-induced diabetes. Treatment of STZ-diabetic rats for 2-3 months with pharmacologic doses of NGF or NT-3, neurotrophic substances with known effects on the adult sympathetic nervous system, did not normalize established neuroaxonal dystrophy (NAD) in diabetic rats in the prevertebral superior mesenteric ganglia (SMG) and ileal mesenteric nerves as had pancreatic islet transplantation and IGF-I in earlier experiments. NGF treatment of control animals actually increased the frequency of NAD in the SMG. New data suggests that, in adult sympathetic ganglia. NGF may contribute to the pathogenesis of NAD rather than its amelioration, perhaps as the result of inducing intraganglionic axonal sprouts in which dystrophic changes are superimposed. NT-3 administration did not alter the frequency of NAD in diabetic animals, although it resulted in a significant decrease in NAD in control SMG. Although deficiencies of neurotrophic substances may represent the underlying pathogenesis of a variety of experimental neuropathies, delivery of excessive levels of selected substances may produce untoward effects.

Effect of streptozotocin-induced diabetes on NGF, P75(NTR) and TrkA content of prevertebral and paravertebral rat sympathetic ganglia

Diabetic autonomic neuropathy results in significant morbidity and mortality. Both diabetic humans and experimental animals show neuroaxonal dystrophy of autonomic nerve terminals, particularly in the prevertebral superior mesenteric ganglia (SMG) and celiac ganglia (CG) which innervate the hyperplastic/hypertrophic diabetic small intestine. Previously, investigators suggested that disturbances in ganglionic nerve growth factor (NGF) content or transport might play a pathogenetic role in diabetic autonomic pathology. To test this hypothesis, we measured NGF content and NGF receptor expression, p75(NTR) (low affinity neurotrophin receptor) and trkA (high affinity NGF receptor), in control and diabetic rat SMG, CG and superior cervical ganglia (SCG). Surprisingly, rather than a decrease, we observed an approximate doubling of NGF content in the diabetic SMG and CG, a result which reflects increased NGF content in the hyperplastic diabetic alimentary tract. No change in NGF content was detected in the diabetic SCG which is relatively spared in experimental diabetic autonomic neuropathy. NGF receptor expression was not consistently altered in any of the autonomic ganglia. These observations suggest that increased NGF content in sympathetic ganglia innervating the diabetic alimentary tract coupled with intact receptor expression may produce aberrant axonal sprouting and neuroaxonal dystrophy.

Repression of human fibroblast growth factor 2 by a novel transcription factor

Here we describe the cloning of the regulator of fibroblast growth factor 2 (FGF-2) transcription (RFT) using a yeast one-hybrid screening with a defined motif in FGF-2 promoter as a target sequence. Overexpression of human RFT (RFT-A) reduces FGF-2 RNA and protein levels in both normal and tumor cell lines. Its splice variants, RFT-A' and RFT-B, have deletions in the putative DNA binding domain and fail to bind FGF-2 promoter and repress FGF-2 gene expression. The ratios of RFT isoforms differ between normal and tumor cells, with the splice variants dominating in tumor cells. Overexpression of RFT-A induces glioma cell death. Our data suggest that regulation of FGF-2 by RFT is important for cellular functions and may be impaired in certain tumors.

Distribution of fibroblast growth factor receptor-1 (FGFR-1) and FGFR-3 in the hippocampus of patients with Alzheimer's disease

To learn about the localization of fibroblast growth factor (FGF) ligands in normal and pathologic brains, fibroblast growth factor receptor-1 (FGFR-1; Flg) and FGFR-3 immunoreactivities were examined in the hippocampus of patients with Alzheimer's disease and age-matched controls. Flg immunoreactivity was found in practically all neurons of the hippocampus and dentate gyrus in control and Alzheimer's disease cases. In patients with Alzheimer's disease, Flg immunoreactivity was present in tangle-bearing and non-tangle-bearing neurons, as well as in neurons with granulovacuolar degeneration, but not in ghost tangles. Aberrant neurites of senile plaques were negative. FGFR-3 immunoreactivity was found in reactive glial cells, most of them astrocytes, including those in the vicinity of senile plaques.

bFGF and FGFR-3 immunoreactivity in the rat brain following systemic kainic acid administration at convulsant doses: localization of bFGF and FGFR-3 in reactive astrocytes, and FGFR-3 in reactive microglia

Strong bFGF immunoreactivity was observed in reactive astrocytes, as shown by double-labeling immunohistochemistry of bFGF and GFAP, from days 7 up to 30 (last time point examined) following kainic acid (KA) injection at convulsant doses in the adult rat. bFGF was not found in OX-42-positive reactive microglia. A few reactive glia co-localized FGFR-3 and GFAP, whereas the majority of cells expressing FGFR-3 were OX-42-immunoreactive. This was further supported by the observation that only approximately 10% of reactive glia co-localized bFGF and FGFR-3. These results show that reactive astrocytes are a major source of bFGF during the subacute stages of tissue damage following KA injection and that reactive astrocytes and, most particularly, reactive microglia are putative targets of bFGF through FGFR-3.

beta-Amyloid converts an acute phase injury response to chronic injury responses

As the brain ages, amyloid deposits accumulate and, as these deposits condense into a beta-sheet conformation, they contribute to the organization of cellular responses and maintain a chronic level of stimulation and injury. Furthermore, accompanying reactions can lead to the production of additional beta-amyloid, the build up of additional fibrillar beta-amyloid, and prolongation of the response. As it accumulates, beta-amyloid appears to develop properties that drive many signal transduction processes in the classic injury cascade and also activate complement, which results in an amplified beta-amyloid AD cascade. In this way several mechanisms, although apparently independent, proceed in parallel, reinforce each other, and perpetuate pathology and structural damage to the brain. Specifically, we suggest that via the activation of complement, initiation, and perpetuation of other cascades, and its own direct toxic actions, beta-amyloid converts an acute response to injury into a chronic damaging inflammatory reaction thereby contributing to neuronal dysfunction and degeneration.

Dose-response comparison of recombinant human nerve growth factor and recombinant human basic fibroblast growth factor in the fimbria fornix model of acute cholinergic degeneration

Both nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) have been proposed for the treatment of Alzheimer's disease. This study describes a comparative, dose-response analysis of recombinant human (rh)NGF and rhbFGF in a rat unilateral fimbria-fornix model of acute cholinergic neuronal degeneration. Doses for rhNGF were 0.6, 6, 60, 600 and 1,800 ng/rat/day and for rhbFGF were 600, 1,800, 3,000 and 6,000 ng/rat/day, delivered for 4 weeks. The number of surviving septal cholinergic neurons was evaluated using ChAT immunohistochemistry. In control animals, the number of ChAT-positive neurons remaining on the lesioned side was between 22 and 18% compared to the non-lesioned side. Infusion with either neurotrophic factor increased the number of ChAT-positive neurons on the lesioned side in a dose-dependent manner. The maximal response to rhbFGF peaked at 3,000 ng/rat/day with a cell savings of 47%. However, there was evidence of neuropathological changes associated with rhbFGF. In contrast, rhNGF produced a maximal response with an infusion of 600 ng rhNGF/rat/day and a cell savings of 70% and no evidence of neuropathology, indicating that rhNGF was better tolerated and more efficacious than rhbFGF.

Insulin-like growth factor-1 mRNA is increased in deafferented hippocampus: spatiotemporal correspondence of a trophic event with axon sprouting

Deafferentation is known to induce axonal sprouting in adult brain, but the signals that direct this response are not understood. To evaluate the possible roles of insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF) in central axonal sprouting, the present study used in situ hybridization to evaluate IGF-1 and bFGF mRNA expression in entorhinal deafferented rat hippocampus. Alternate tissue sections were processed for Fink-Heimer impregnation of axonal degeneration, Bandeiraea simplicifolia (BS-1) labeling of microglia, and glial fibrillary acidic protein immunocytochemistry. In control hippocampus, IGF-1 mRNA was localized to a few neurons, with no labeled cells in the dentate gyrus molecular layer; bFGF cRNA hybridization was diffuse in dendritic fields but was dense in CA2 stratum pyramidale. Both mRNA species were increased by deafferentation. The distribution of elevated IGF-1 mRNA corresponded precisely to fields of axonal degeneration and was greatest in the dentate gyrus outer molecular layer and stratum lacunosum moleculare. In these fields, IGF-1 mRNA was elevated by 2 days, reached maximal levels at 4 days, and declined by 10 days postlesion. Double labeling revealed that the majority of IGF-1 cRNA-labeled cells were microglia. In deafferented hippocampus, bFGF mRNA was broadly increased across fields both containing and lacking axonal degeneration. In the dentate, bFGF mRNA levels peaked at 5 days postlesion and remained elevated through 14 days. These results demonstrate that reactive microglia within deafferented hippocampal laminae express IGF-1 mRNA just prior to and during the period of reactive axonal growth and suggest that IGF-1 plays a role in directing the sprouting of spared afferents into these fields.

Fibroblast growth factors: activities and significance of non-neurotrophin neurotrophic growth factors

Although first characterized by virtue of their ability to stimulate endothelial cell proliferation in vitro and angiogenesis in vivo, the fibroblast growth factors are now also well recognized for their neurotrophic activities. Understanding the physiological significance of these multifunctional, virtually ubiquitous and pluripotential molecules, however, remains enigmatic. Recent advances describing their molecular, biochemical and biological characteristics has led to a better understanding of their role in the central nervous system.