Immunoelectron microscopic localization of basic FGF in neuroglias and neurons of the trigeminal mesencephalic and motor nuclei

Trophic factors and central nervous system metastasis

To metastasize to the central nervous system (CNS) malignant cells must attach to brain microvessel endothelial cells, respond to brain endothelial cell-derived motility factors, respond to CNS-derived invasion factors and invade the blood-brain barrier (BBB), and finally, respond to CNS survival and growth factors. Trophic factors such as the neurotrophins play an important role in tumor cell invasion into the CNS and in the survival of small numbers of malignant cells under stress conditions. Trophic factors promote BBB invasion by enhancing the production of basement membrane-degrading enzymes in neurotrophin-responsive cells. The expression of certain neurotrophin receptors on brain-metastasic neuroendocrine cells occurs in relation to their invasive and survival properties. For example, CNS-metastatic melanoma cells respond to particular neurotrophins (nerve growth factor, neurotrophin-2) that can be secreted by normal cells within the CNS. In addition, a paracrine form of transferrin is important in CNS metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. CNS-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. Synthesis of paracrine factors and cytokines may influence the production of trophic factors by normal brain cells adjacent to tumor cells. Moreover, we found increased amounts of neurotrophins in brain tissue at the invasion front of human melanoma tumors in CNS biopsies. Thus the ability to form metastatic colonies in the CNS is dependent on tumor cell responses to trophic factors as well as autocrine and paracrine growth factors and probably other underdescribed factors.

A comprehensive analysis of the distribution of FGF-2 and FGFR1 in the rat brain

We have examined the cellular distribution of both FGF-2 and FGFR1 immunoreactivity and their mRNAs throughout the normal adult rat brain in order to reconcile numerous disparate findings in the published literature. The results confirm a widespread distribution of FGF-2 and FGFR1 in the rat brain, and different regions express distinct patterns of FGF-2 and FGFR1 mRNA and protein: neuronal and non-neuronal cells show different subcellular distributions that vary according to the area where they are located. The intensity of the staining and hybridization also varies according to the loci examined and the cell type involved. Astrocytes contain the highest levels of FGF-2 and FGFR1 mRNAs, and characteristically, possess high levels of immunoreactive FGF-2 within the nucleus. Amongst non-neuronal cells, oligodendrocytes do not synthesize or contain significant levels of FGF-2 immunoreactivity however, they do express FGFR1 mRNA. In these cells, immunoreactive FGFR1 is mainly associated with the myelin sheaths of neuronal fibers. In ventricular systems, ependymal cells synthesize and contain immunoreactive FGFR1. In contrast, only cells lining the lateral wall of the IIIrd ventricle express FGF-2 mRNA. Subependymal cells contain high levels of both FGF-2 and FGFR1 immunoreactivity. Neurons express low levels of FGF-2 mRNA and immunoreactive FGF-2 is localized predominantly to the perikaryon. However, selected populations of neurons, such as CA2 field of the hippocampus, show high levels of FGF-2 mRNA, in which the nucleus is strongly immunopositive. Similarly, high levels of FGFR1 mRNA are localized to select populations of neurons (e.g. amygdala). FGFR1 immunoreactivity is mainly associated with myelinated fiber tracts (e.g. striatum), and some neurons show immunoreactivity in the perikaryon (e.g. hippocampus), the nucleus (e.g. mesencephalic trigeminal nucleus), or in axonal projections (e.g. hypothalamus). Remarkably, in many of the areas studied, FGF-2 and FGFR1 mRNA and/or their translated protein do not co-localize in neurons (e.g. neo-cortices) or even in the same regions of the brain (e.g. substantia nigra). In other instances, mRNAs for both FGF-2 and FGFR1 colocalize (e.g. supraoptic nucleus). The brain, in contrast to peripheral tissues, contains high levels of FGF-2 and actively expresses its gene under normal physiological conditions. The highly specific anatomical distribution of immunoreactive FGF-2 in neuronal and non-neuronal brain cells, supports the notion that it plays a multifunctional role in the CNS under normal physiology. By correlating the localization and the synthesis of FGF-2 and one of its high affinity receptors, FGFR1, in the CNS, it should be possible to obtain a better understanding of the roles of FGF-2 in normal and pathological conditions.

The role of trophic factors and autocrine/paracrine growth factors in brain metastasis

The brain is a unique microenvironment enclosed by the skull, lacking lymphatic drainage and maintaining a highly regulated vascular transport barrier. To metastasize to the brain malignant tumor cells must attach to microvessel endothelial cells, respond to brain-derived invasion factors, invade the blood-brain barrier and respond to survival and growth factors. Trophic factors are important in brain invasion because they can act to stimulate this process. In responsive malignant cells trophic factors such as neurotrophins can promote invasion by enhancing the production of basement membrane-degradative enzymes (such as type IV collagenase/gelatinase and heparanase) capable of locally destroying the basement membrane and the blood-brain barrier. We examined human melanoma cell lines that exhibit varying abilities to form brain metastases. These melanoma lines express low-affinity neurotrophin receptor p75NTR in relation to their brain-metastatic potentials but the variants do not express trkA, the gene encoding a high affinity nerve growth factor (NGF) tyrosine kinase receptor p140trkA. Melanoma cells metastatic to brain also respond to paracrine factors made by brain cells. We have found that a paracrine form of transferrin is important in brain metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. Brain-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. We found that brain-metastatic melanoma cells synthesize transcripts for the following autocrine growth factors: TGF beta, bFGF, TGF alpha and IL-1 beta. Synthesis of these factors may influence the production of neurotrophins by adjacent brain cells, such as oligodendrocytes and astrocytes. Increased amounts of NGF were found in tumor-adjacent tissues at the invasion front of human melanoma tumors in brain biopsies. Trophic factors, autocrine growth factors, paracrine growth factors and other factors may determine whether metastatic cells can successfully invade, colonize and grow in the central nervous system.

Development of Purkinje cell bodies and processes with basic fibroblast growth factor-like immunoreactivity in the rat cerebellum

The development of basic fibroblast growth factor-like immunoreactivity was investigated in the nuclei, cell bodies and processes of Purkinje cells with attention to basic fibroblast growth factor-containing neuronal input to the deep cerebellar nuclei. Immunoblot analysis with the use of the antisera against basic fibroblast growth factor revealed that crude homogenate of the developing rat cerebellum exhibits a main band with the same molecular weight (18,000 mol. wt) as basic fibroblast growth factor in all the postnasal stages examined. Cerebellar cells were not labeled with the antisera during embryonic life. Under light microscopy, basic fibroblast growth factor-like immunoreactivity was detected initially in cortical cells located close to deep cerebellar fissures of the newborn rat but not in superficial cortical regions. It was difficult to determine whether or not they are Purkinje cells at the fusiform stage. On postnatal day 7, immunoreactive Purkinje cells were identified throughout the cerebellar cortex, and they expressed basic fibroblast growth factor-like immunoreactivity mainly in the apical cytoplasm and proximal dendrites. From postnatal day 14 to postnatal day 28, basic fibroblast growth factor-like immunoreactivity was noted not only throughout the cytoplasm of Purkinje cells but also in the nuclei of the immunopositive cells. Our statistical analysis showed that Purkinje cells with nuclear immunoreaction peaked on postnatal day 21. At these stages, nerve fibers immunoreactive for basic fibroblast growth factor were numerous in the cerebellar medulla and deep cerebellar nuclei. After postnatal day 42, Purkinje cells with intense immunoreactivity in the nuclei showed a marked decrease in number, and immunoreactive structures were distributed in the cerebellum in a fashion similar to that in adult rats. Electron microscopy demonstrated that immunoreactivity was located mainly in the apical cytoplasm of Purkinje cells on postnatal day 7 and throughout the cytoplasm and in the nuclear euchromatin from postnatal day 14 to postnatal day 28, as was expected from light-microscopic observations. Immunoreactivity, even though distributed diffusely in the cytoplasm, was absent from the lumen of endoplasmic reticulum and mitochondria. A small population of Purkinje cell axon terminals forming synapses with the soma and dendrites of deep cerebellar nucleus neurons began to express basic fibroblast growth factor on postnatal day 21. This is much later than the starting age for synaptogenesis between Purkinje cells and deep cerebellar nucleus neurons. The age-dependent changes in the localization of basic fibroblast growth factor within Purkinje cell nucleus, soma and processes suggest a complex transport system of this factor within Purkinje cells during postnatal development.