The flavonoid rutin and its aglycone quercetin modulate the microglia inflammatory profile improving antiglioma activity

Microglia cells are the immune effector in the Central Nervous System (CNS). However, studies have showed that they contribute more to glioma progression than to its elimination. Rutin and its aglycone quercetin are flavonoids present in many fruits as well as plants and have been demonstrated to bear anti-inflammatory, antioxidant and antitumor properties also to human glioblastoma cell lines. Previous studies also demonstrated that rutin, isolated from the Brazilian plant Dimorphandra mollis Bent., presents immunomodulatory effect on astrocytes and microglia. In this study, we investigate the antitumor and immunomodulatory properties of rutin and its aglycone quercetin on the viability of glioma cells alone and under direct and indirect interaction with microglia. Flavonoid treatment of rat C6 glioma cells induced inhibition of proliferation and migration, and also induced microglia chemotaxis that was associated to the up regulation of tumor necrosis factor (TNF) and the down regulation of Interleukin 10 (IL-10) at protein and mRNA expression levels, regulation of mRNA expression for chemokines CCL2, CCL5 and CX3CL1, and Heparin Binding Growth Factor (HDGF), Insulin-like growth factor (IGF) and Glial cell-derived neurotrophic factor (GDNF) growth factors. Treatment of human U251 and TG1 glioblastoma cells with both flavonoids also modulated negatively the expression of mRNA for IL-6 and IL-10 and positively the expression of mRNA for TNF characterizing changes to the immune regulatory profile. Treatment of microglia and C6 cells either in co-cultures or during indirect interaction, via conditioned media from glioma cells treated with flavonoids or via conditioned media from microglia treated with flavonoids reduced proliferation and migration of glioma cells. It also directed microglia towards an inflammatory profile with increased expression of mRNA for IL-1β, IL-6, IL-18 and decreased expression of mRNA for nitric oxide synthase 2 (NOS2) and prostaglandin-endoperoxide synthase 2 (PTGS2), arginase and transforming growth factor beta (TGF-β), as well as Insulin-like growth factor (IGF). Treatment of U251 cells with flavonoids also reduced tumorigenesis when the cells were xenotransplanted in rat brains, and directed microglia and also astrocytes in the microenvironment of tumor cell implantation as well as in the brain parenchyma to a not favorable molecular inflammatory profile to the glioma growth, as observed in cultures. Together these results demonstrate that the flavonoid rutin and its aglycone quercetin present antiglioma effects related to the property of modulating the microglial inflammatory profile and may be considered for molecular and preclinical studies as adjuvant molecules for treatment of gliomas.

Hyperplasia-adenoma sequence in pituitary tumorigenesis related to aryl hydrocarbon receptor interacting protein gene mutation

Mutations of the aryl hydrocarbon receptor interacting protein (AIP) gene are associated with pituitary adenomas that usually occur as familial isolated pituitary adenomas (FIPA). Detailed pathological and tumor genetic data on AIP mutation-related pituitary adenomas are not sufficient. Non-identical twin females presented as adolescents to the emergency department with severe progressive headache caused by large pituitary macroadenomas require emergency neurosurgery; one patient had incipient pituitary apoplexy. Post-surgically, the patients were found to have silent somatotrope adenomas on pathological examination. Furthermore, the light microscopic, immunohistochemical, and electron microscopic studies demonstrated tumors of virtually identical characteristics. The adenomas were accompanied by multiple areas of pituitary hyperplasia, which stained positively for GH, indicating somatotrope hyperplasia. Genetic analyses of the FIPA kindred revealed a novel E216X mutation of the AIP gene, which was present in both the affected patients and the unaffected father. Molecular analysis of surgical specimens revealed loss of heterozygosity (LOH) in the adenoma but showed that LOH was not present in the hyperplastic pituitary tissue from either patient. AIP immunostaining confirmed normal staining in the hyperplastic tissue and decreased staining in the adenoma in the tumors from both patients. These results demonstrate that patients with AIP germline mutation can present with silent somatotrope pituitary adenomas. The finding of somatotrope hyperplasia unaccompanied by AIP LOH suggests that LOH at the AIP locus might be a late event in a potential progression from hyperplastic to adenomatous tissue.

The expression of PEA-15 (phosphoprotein enriched in astrocytes of 15 kDa) defines subpopulations of astrocytes and neurons throughout the adult mouse brain

Phosphoprotein enriched in astrocytes of 15 kDa (PEA-15) is an abundant phosphoprotein in primary cultures of mouse brain astrocytes. Its capability to interact with members of the apoptotic and mitogen activated protein (MAP) kinase cascades endows PEA-15 with anti-apoptotic and anti-proliferative properties. We analyzed the in vivo cellular sources of PEA-15 in the normal adult mouse brain using a novel polyclonal antibody. Immunohistochemical assays revealed numerous PEA-15-immunoreactive cells throughout the brain of wild-type adult mice while no immunoreactive signal was observed in the brain of PEA-15 -/- mice. Cell morphology and double immunofluorescent staining showed that both astrocytes and neurons could be cellular sources of PEA-15. Closer examination revealed that in a given area only part of the astrocytes expressed the protein. The hippocampus was the most striking example of this heterogeneity, a spatial segregation restricting PEA-15 positive astrocytes to the CA1 and CA3 regions. A PEA-15 immunoreactive signal was also observed in a few cells within the subventricular zone and the rostral migratory stream. In vivo analysis of an eventual PEA-15 regulation in astrocytes was performed using a model of astrogliosis occurring along motor neurons degeneration, the transgenic mouse expressing the mutant G93A human superoxyde-dismutase-1, a model of amyotrophic lateral sclerosis. We observed a marked up-regulation of PEA-15 in reactive astrocytes that had developed throughout the ventral horn of the lumbar spinal cord of the transgenic mice. The heterogeneous cellular expression of the protein and its increased expression in pathological situations, combined with the known properties of PEA-15, suggest that PEA-15 expression is associated with a particular metabolic status of cells challenged with potentially apoptotic and/or proliferative signals.

Early defect in the expression of mouse sperm DNAJ 1, a member of the DNAJ/heat shock protein 40 chaperone protein family, in the spinal cord of the wobbler mouse, a murine model of motoneuronal degeneration

Prevention of protein misfolding is ensured by chaperone proteins, including the heat shock proteins (HSP) of the DNAJ/HSP40 family. Detection of abnormal protein aggregates in various neurodegenerative diseases has led to the proposal that altered chaperone activity contributes to neurodegeneration. Msj-1, a DNAJ/HSP40 protein located around the spermatozoa acrosome, was recently found to be down-regulated in the testis of wobbler mutant mice. Wobbler is an unidentified recessive mutation which triggers progressive motoneuron degeneration with abnormal intracellular protein accumulations, and defective spermatozoa maturation. Here, we examined Msj-1 expression in the spinal cord of the mutants and their controls. Msj-1 transcripts were amplified by reverse transcription-polymerase chain reaction from mutant and wild-type spinal cord RNA. Sequencing of Msj-1 coding region revealed no change in the mutant. In contrast, decreased Msj-1 mRNA levels were observed in five to six-week-old wobbler mice spinal cord, when motoneuron degeneration is at its apex, as compared to controls. A similar decrease was observed in two-week-old wobbler spinal cord, when the number of motoneurons is still unaltered, indicating that the decreased mRNA content is intrinsic to the mutant and not simply related to the loss of cells expressing Msj-1. Assays of Msj-1 protein levels yielded similar results. Immunofluorescent labeling revealed numerous Msj-1-ir motoneurons in five-week-old control spinal cord while no signal was observed in age-matched wobbler. Our results show, therefore, that Msj-1 expression is down-regulated in both organs affected by the wobbler mutation, the CNS and the testis, and that this defect precedes the first histological signs of motoneuron degeneration. These results provide the first example of an association between transcriptional repression of a chaperone protein and a neurodegenerative process.

Two temporal stages of oligodendroglial response to excitotoxic lesion in the gray matter of the adult rat brain

Excitotoxic lesions in the gray matter induce profuse demyelination of passage and afferent fibers in areas of neuronal loss, independent of Wallerian degeneration. The time course of this phenomenon, which extends over weeks after the excitotoxin injection, suggests that demyelination is not related only to a direct effect of the toxin. In order to define mechanisms at work, a parallel study of myelin and oligodendrocytes was carried out following kainate injections into the adult rat thalamus. Within the 1st day postlesion, myelin alteration appeared throughout the area exhibiting neuronal loss, while the number of oligodendrocytes fell by 45%. No apoptotic oligodendrocytes were identified at that time. Over the following 2 days, there was no further loss of myelin and oligodendrocytes, but there was an increase in the number of oligodendrocytes displaying typical signs of apoptosis as revealed with TUNEL-end-labeled nuclei, Hoechst-labeled condensed chromatin bodies, or bax immunoreactivity. This resulted in a second, progressive loss of both myelin and oligodendrocytes leading to their almost complete disappearance 2 weeks postlesion. These results demonstrate two temporal stages of oligodendroglial cell death. The excitotoxin injection resulted in the rapid destruction of a first oligodendroglial population, most probably by necrosis. A second population died in a delayed manner from apoptosis. This second wave of death coincided with an activated microglia/macrophage invasion of the lesion, suggesting that delayed oligodendroglial death results from toxic microglia/macrophage effects. In addition, the longest surviving oligodendrocytes were located next to reactive astrocytes, suggesting the existence of trophic interactions between these two glial populations.

Transforming growth factor alpha: a promoter of motoneuron survival of potential biological relevance

Expression of transforming growth factor alpha (TGFalpha), a member of the epidermal growth factor (EGF) family, is a general response of adult murine motoneurons to genetic and experimental lesions, TGFalpha appearing as an inducer of astrogliosis in these situations. Here we address the possibility that TGFalpha expression is not specific to pathological situations but may participate to the embryonic development of motoneurons. mRNA of TGFalpha and its receptor, the EGF receptor (EGFR), were detected by ribonuclease protection assay in the ventral part of the cervical spinal cord from embryonic day 12 (E12) until adult ages. Reverse transcription-PCR amplification of their transcripts from immunopurified E15 motoneurons, associated with in situ double-immunohistological assays, identified embryonic motoneurons as cellular sources of the TGFalpha-EGFR couple. In vitro, TGFalpha promoted the survival of immunopurified E15 motoneurons in a dose-dependent manner, with a magnitude similar to BDNF neuroprotective effects at equivalent concentrations. In a transgenic mouse expressing a human TGFalpha transgene under the control of the metallothionein 1 promoter, axotomy of the facial nerve provoked significantly less degeneration in the relevant motor pool of 1-week-old mice than in wild-type animals. No protection was observed in neonates, when the transgene exhibits only weak expression levels in the brainstem. In conclusion, our results point to TGFalpha as a physiologically relevant candidate for a neurotrophic role on developing motoneurons. Its expression by the embryonic motoneurons, which also synthesize its receptor, suggests that this chemokine is endowed with the capability to promote motoneuron survival in an autocrine-paracrine manner.

Differential regulation of NGF receptors in primary sensory neurons by adjuvant-induced arthritis in the rat

In the adult brain, neurotrophins play a key role in adaptive processes linked to increased neuronal activity. A growing body of evidence suggests that chronic pain results from long-term plasticity of central pathways involved in nociception. We have investigated the involvement of nerve growth factor (NGF) in adaptive responses of primary sensory neurons during the course of a long-lasting inflammatory pain model. The amount and distribution of the NGF receptors p75(NTR) and TrkA were measured in the dorsal horn and dorsal root ganglia (DRG) of animals subjected to Freund's adjuvant-induced arthritis (AIA). We observed an increased immunoreactivity of both receptors in the central terminals of primary sensory neurons in the arthritic state. The increases were seen in the same population of afferent terminals in deep dorsal horn laminae. These changes paralleled the variations of clinical and behavioral parameters that characterize the course of the disease. They occurred in NGF-sensitive, but not GDNF-sensitive, nerve terminals. However, p75(NTR) and TrkA protein levels in the DRG (in the cell body of these neurons) showed different response patterns. An immediate rise of p75(NTR) was seen in parallel with the initial inflammation that developed after administration of Freund's adjuvant in hindpaws. In contrast, increases of the mature (gp140(trk)) form of TrkA occurred later and seemed to be linked to the development of the long-lasting inflammatory response. The changes in receptor expression were observed exclusively at lumbar levels, L3-L5, somatotopically appropriate for the inflammation. Together, these results implicate NGF in long-term mechanisms accompanying chronic inflammatory pain, via the up-regulation of its high affinity receptor, and offer additional evidence for differential processes underlying short- versus long-lasting inflammatory pain.

TTF-1, a homeodomain gene required for diencephalic morphogenesis, is postnatally expressed in the neuroendocrine brain in a developmentally regulated and cell-specific fashion

TTF-1 is a member of the Nkx family of homeodomain genes required for morphogenesis of the hypothalamus. Whether TTF-1, or other Nkx genes, contributes to regulating differentiated hypothalamic functions is not known. We now report that postnatal hypothalamic TTF-1 expression is developmentally regulated and associated with the neuroendocrine process of female sexual development. Lesions of the hypothalamus that cause sexual precocity transiently activate neuronal TTF-1 expression near the lesion site. In intact animals, hypothalamic TTF-1 mRNA content also increases transiently, preceding the initiation of puberty. Postnatal expression of the TTF-1 gene was limited to subsets of hypothalamic neurons, including LHRH neurons, which control sexual maturation, and preproenkephalinergic neurons of the lateroventromedial nucleus of the basal hypothalamus, which restrain sexual maturation and facilitate reproductive behavior. TTF-1 mRNA was also detected in astrocytes of the median eminence and ependymal/subependymal cells of the third ventricle, where it colocalized with erbB-2, a receptor involved in facilitating sexual development. TTF-1 binds to and transactivates the erbB-2 and LHRH promoters, but represses transcription of the preproenkephalin gene. The singular increase in hypothalamic TTF-1 gene expression that precedes the initiation of puberty, its highly specific pattern of cellular expression, and its transcriptional actions on genes directly involved in neuroendocrine reproductive regulation suggest that TTF-1 may represent one of the controlling factors that set in motion early events underlying the central activation of mammalian puberty.

What role(s) for TGFalpha in the central nervous system?

Transforming growth factor alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR or erbB1). Identified since 1985 in the central nervous system (CNS), its functions in this organ have started to be determined during the past decade although numerous questions remain unanswered. TGFalpha is widely distributed in the nervous system, both glial and neuronal cells contributing to its synthesis. Although astrocytes appear as its main targets, mediating in part TGFalpha effects on different neuronal populations, results from different studies have raised the possibility for a direct action of this growth factor on neurons. A large array of experimental data have thus pointed to TGFalpha as a multifunctional factor in the CNS. This review is an attempt to present, in a comprehensive manner, the very diverse works performed in vitro and in vivo which have provided evidences for (i) an intervention of TGFalpha in the control of developmental events such as neural progenitors proliferation/cell fate choice, neuronal survival/differentiation, and neuronal control of female puberty onset, (ii) its role as a potent regulator of astroglial metabolism including astrocytic reactivity, (iii) its neuroprotective potential, and (iv) its participation to neuropathological processes as exemplified by astroglial neoplasia. In addition, informations regarding the complex modes of TGFalpha action at the molecular level are provided, and its place within the large EGF family is precised with regard to the potential interactions and substitutions which may take place between TGFalpha and its kindred.

A role for transforming growth factor alpha as an inducer of astrogliosis

TGFalpha is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR). Synthesis of TGFalpha and EGFR in reactive astrocytes developing after CNS insults is associated with the differentiative and mitogenic effects of TGFalpha on cultured astrocytes. This suggests a role for TGFalpha in the development of astrogliosis. We evaluated this hypothesis using transgenic mice bearing the human TGFalpha cDNA under the control of the zinc-inducible metallothionein promoter. Expression levels of glial fibrillary acidic protein (GFAP) and vimentin and morphological features of astrocytes were used as indices of astroglial reactivity in adult transgenic versus wild-type mice provided with ZnCl2 in their water for 3 weeks. In the striatum, the hippocampus, and the cervical spinal cord, the three CNS areas monitored, transgenic mice displayed enhanced GFAP mRNA and protein levels and elevated vimentin protein levels. GFAP-immunoreactive astrocytes exhibited numerous thick processes and hypertrophied somata, which are characteristic aspects of reactive astrocytes. Their number increased additionally in the striatum and the spinal cord, but no astrocytic proliferation was observed using bromodeoxyuridine immunohistochemistry. Neither the morphology nor the number of microglial cells appeared modified. A twofold increase in phosphorylated EGFR was detected in the striatum and was associated with the immunohistochemical detection of numerous GFAP-positive astrocytes bearing the EGFR, suggesting a direct action of TGFalpha on astrocytes. Altogether, these results demonstrate that enhanced TGFalpha synthesis is sufficient to trigger astrogliosis throughout the CNS, whereas microglial metabolism is unaffected.

Regulation of growth factor gene expression in degenerating motoneurons of the murine mutant wobbler: a cellular patch-sampling/RT-PCR study

Motoneuronal degenerative diseases are characterized by their progressivity; once affected, the motoneurons remain in altered states during an intermediate phase of degeneration prior to their final disappearance. Whether this survival period coincides with active metabolic rearrangements in the affected neuron remains unknown. As a first step toward the elucidation of this question, we developed cDNA pooled samples obtained from degenerating and control motoneuron mRNA populations through cellular patch sampling and RT-PCR, using the murine wobbler mutant as a model of spinal atrophy. Hybridization of the cDNA pools to various markers of intact or degenerating motoneurons allowed us to verify the cellular specificity of the patch sampling and indicated conservation of the original mRNA population complexity. Exploration of transcriptional alterations of genes encoding growth factors thought to be involved in motoneuronal development revealed that gene expression of the neurotrophin BDNF was induced in affected motoneurons, while expression of neurotrophin-3 was present in both neuronal types. Likewise, expression of a member of the epidermal growth factor (EGF) family, the neuregulin transcript sensory motor neuron-derived factor, was detected in both control and degenerating motoneurons, while transforming growth factor alpha, the functional homolog of EGF, was present only in the affected motoneurons. Immunohistochemical detection of corresponding proteins corroborated these observations. These results demonstrate that, during the course of their degeneration, motoneurons can initiate expression of novel genes which lead to the production of molecules endowed with trophic and/or differentiative properties for the neurons themselves and their glial environment. They also validate the use of the developed cDNA pooled samples for further exploration of transcriptional alterations taking place in degenerating motoneurons.

Transforming growth factor alpha expression as a response of murine motor neurons to axonal injury and mutation-induced degeneration

We previously showed that degenerating adult motor neurons of the murine mutant wobbler, a model of spinal muscular atrophy, express Transforming Growth Factor alpha (TGF alpha), a growth factor endowed with glio- and neurotrophic activities. Here, we evaluated whether TGF alpha expression is a general response of adult motor neurons to injury. Synthesis of its precursor (pro-TGF alpha) was investigated in another model of motoneuronal degeneration, the murine mutant muscle deficient, and in hypoglossal motor neurons following axonal crush and cut. In control conditions, motor neurons were devoid of pro-TGF alpha immunoreactivity. In the mutant lumbar spinal cord, pro-TGF alpha immunoreactive motor neurons appeared as soon as the disease developed and pro-TGF alpha expression persisted until the latest stages of degeneration. Motor neurons and astrocytes of the white matter weakly immunoreactive for the TGF alpha receptor were also present in both control and mutant lumbar spinal cords. Following hypoglossal nerve crush and cut, motoneuronal pro-TGF alpha expression was precocious and transient, visible at one day post-injury and lasting for only 3 days, during which time astrocyte-like cells immunoreactive for both TGF alpha and its receptor appeared within the injured nucleus. Enhanced TGF alpha mRNA levels following nerve crush showed that activation occurred at the transcriptional level. These results show that upregulation of TGF alpha is an early and common response of adult murine motor neurons to injury, regardless of its experimental or genetic origin.

Bcl-2 sensitivity differentiates two pathways for motoneuronal death in the wobbler mutant mouse

The molecular events leading to motoneuronal death are still poorly understood. In mammals, the bcl-2 proto-oncogene, which encodes a membrane-associated protein, has been shown to suppress both developmental motoneuronal death and experimental axotomy-induced motoneuronal death. We assessed a potential protective effect of Bcl-2 on pathological motoneuronal death processes in adult rodents. We took advantage of the murine mutant wobbler, which undergoes progressive degeneration of the spinal and brainstem motoneurons. A hybrid carrying both the wobbler mutation and the human bcl-2 transgene under the control of the neuron-specific enolase promoter was produced. Although Bcl-2 protected spinal and brainstem motoneurons from developmental death and the postnatal motoneurons of the facial nucleus from axotomy-induced death, the pathological motoneuronal death was not altered in the adult hybrid. These results demonstrate that Bcl-2 sensitivity distinguishes at least two different motoneuronal death pathways in the wobbler mutant. They support the hypothesis that experimental and pathological motoneuronal death are dependent on different cellular mechanisms.

Morphogenetic effect of kainate on adult hippocampal neurons associated with a prolonged expression of brain-derived neurotrophic factor

Intraperitoneal or intrahippocampal injections of kainate induce both hippocampal cell death and axonal remodeling of the dentate gyrus granular neurons. We report here that injection of kainate into the dorsal hippocampus of adult mice may also trigger a conspicuous and long-lasting global trophic response of granule cells. Morphological changes include somatic and dendritic growth and increased nuclear volume with ultrastructural features characteristic of neuronal development. The trophic response is correlated with a specific overexpression of brain-derived neurotrophic factor that is maintained for at least six months. This shows that plasticity in adult neurons can, in addition to axonal remodeling, extend to generalized cell growth. Our results further suggest that brain-derived neurotrophic factor could be involved in the activation and/or maintenance of this phenomenon.

Transforming growth factor alpha (TGF alpha) expression in degenerating motoneurons of the murine mutant wobbler: a neuronal signal for astrogliosis?

The enhanced expression of the trophic factor transforming growth factor alpha (TGF alpha) in reactive astrocytes following CNS injury suggests that TGF alpha has a role in the development of astrogliosis. We explored this hypothesis in the murine mutant wobbler, which presents a progressive motoneuronal degeneration associated with an astrogliosis. Evolution of astrogliosis, and expression of TGF alpha precursor (pro-TGF alpha) and of its receptor were examined over the course of the disease, using genetically diagnosed animals and immunocytochemical techniques. We report here that degenerating motoneurons of the cervical spinal cord and a subset of astrocytes express pro-TGF alpha, prior to the onset of astrogliosis, when the first clinical manifestations of the disease are observed at 4 weeks of age. TGF alpha expression appeared strongly correlated with motoneuronal degeneration. All pro-TGF alpha-immunoreactive neurons exhibited a degenerative morphology, and the number of pro-TGF alpha-immunoreactive neurons increased with the progression of the disease. At the glial level, we observed that astrogliosis was a transitory phenomenon in the wobbler mice, developing in coordination with the motoneuronal expression of pro-TGF alpha. Astrogliosis became evident in 6-week-old wobbler mice, when the number of pro-TGF alpha-immunoreactive motoneurons was maximal, and regressed in older mutant mice in correlation with the disappearance of pro-TGF alpha-immunoreactive motoneurons. Furthermore, TGF alpha/EGF receptor immunoreactivity was exclusively localized in a subset of reactive astrocytes, its expression following closely the course of the astrogliosis. These data show that TGF alpha synthesis by the affected motoneurons is an early event in the course of the wobbler disease, and suggest a role for TGF alpha as a neuronal inducer of astrocytic reactivity.

Target-deprived CNS neurons express the NGF gene while reactive glia around their axonal terminals contain low and high affinity NGF receptors

Reactive gliosis is part of the response of central nervous system to injury and neurodegeneration. Cellular components of the reactive gliosis have the capability to synthesize neurotrophic factors, and thus are capable of affecting the fate of neuronal populations in the injured tissue. In this study, we explored the putative involvement of reactive glia-derived neurotrophins in sustaining the axonal projections of target-deprived neurons. Neuronal targets of the dorsal column nuclei neurons were suppressed through excitotoxic lesion of the ventrobasal complex of the rat thalamus (VB). Despite the development of reactive gliosis, neither up-regulation of NGF, nor BDNF or NT3 mRNA could be detected by solution hybridization in the lesioned site at all times tested. In contrast, expression of the LNGFR gene increased progressively up to 90 days post-lesion. Immunocytochemical studies localized the LNGFR protein in a subset of small cells with ramified processes resembling microglia at 7 and 20 days post-lesion. At longer times, double immunolabelling studies revealed that a substantial part of LNGFR-immunoreactive cells filling the area of neuronal loss were neither microglial cells nor astrocytes although presence of LNGFR in a subset of microglial cells could not be excluded. Previous ultrastructural studies of the kainate-lesioned VB suggest that these LNGFR-immunoreactive cells correspond to oligodendrocytes and/or Schwann cells. At 2 months post-lesion, when LNGFR expression was maximal, increased levels of trkA mRNA were detected in the lesioned site. Immunocytochemical studies revealed the presence of numerous trkA-immunoreactive astrocytes. TrkB mRNA, encoding the full-length high-affinity receptor for BDNF, remained undetectable by non-isotopic in situ hybridization. In contrast to the lack of neurotrophin gene expression by glial components of the lesioned VB, dorsal column nuclei neurons contained NGF mRNA as revealed by in situ hybridization studies at 10 days--prior to enhanced LNGFR expression in the lesion--and 2 months post-lesion. In addition, the number and the staining intensity of NGF mRNA-positive neurons was increased in the target-deprived neurons, as compared with the contra-lateral nucleus projecting to intact targets. These results show that glial cells present in a reactive gliosis which develops in the kainic acid-lesioned thalamus, do not synthesize neurotrophins but instead produce high levels of both low- and high-affinity NGF receptors, LNGFR by Schwann cells/oligodendrocytes and possibly a subset of microglial cells, and trkA by reactive astrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of epidermal growth factor receptor changes in the hypothalamus during the onset of female puberty

Recent findings have led to the concept that transforming growth factor alpha (TGF alpha) contributes to the neuroendocrine regulation of female puberty by stimulating the release of luteinizing hormone-releasing hormone (LHRH), the neurohormone controlling sexual development. It was postulated that this effect is mediated by epidermal growth factor receptors (EGFR) and that EGFR may not be located on LHRH neurons, so that TGF alpha-induced LHRH release would require an intermediate cell-to-cell interaction, presumably of glial-neuronal nature. The present study was undertaken to characterize the presence of EGFR in rat hypothalamus and to determine if changes in EGFR gene expression and EGFR protein occur at the time of puberty. RNA blot hybridization demonstrated that the hypothalamus expresses all mRNA species known to encode EGFR. RNase protection assays revealed that alternative splicing of the EGFR primary mRNA transcript occurs in the hypothalamus and produces a predominant transcript encoding the full-length EGFR and a much less abundant, shorter mRNA encoding a truncated, and presumably secreted form of EGFR. EGFR-like immunoreactive material was found in several hypothalamic regions including the organum vasculosum of the lamina terminalis, supraoptic, suprachiasmatic, and paraventricular nuclei, ependymal cells lining the third ventricle, some astrocytes associated with blood vessels, astrocytes of the pial surface, and tanycytes and glial cells of the median eminence (ME). Low levels of EGFR mRNA were detected by hybridization histochemistry in cells of the same areas containing EGFR-like immunoreactivity. Double-immunohistochemistry revealed that even though LHRH neurons are in close proximity to EGFR-positive cells, they do not contain EGFR. In the ME, EGFR-immunonegative LHRH nerve terminals tightly coexist with EGFR-positive cells, presumably tanycytes and glial astrocytes. EGFR mRNA levels measured by quantitative reverse transcription-polymerase chain reaction assay (RT-PCR) in the ME-arcuate nucleus region at the time of puberty decreased in the morning of the first proestrus, i.e., preceding the first preovulatory surge of gonadotropins, and rebounded at the time of the surge. Functional EGFR protein levels, detected by the ability of the receptor to autophosphorylate in response to ligand or divalent antibody-induced activation, changed in a similar manner at the time of puberty. No such changes were observed in the cerebellum, a brain region irrelevant to neuroendocrine reproductive control. These results demonstrate the existence of EGF receptors in the prepubertal female rat hypothalamus and suggest that changes in EGFR gene expression and biologically active EGFR protein contributes to the neuroendocrine process underlying the first preovulatory surge of gonadotropins.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic lesions that induce female precocious puberty activate glial expression of the epidermal growth factor receptor gene: differential regulation of alternatively spliced transcripts

Injury of the nervous system triggers a complex series of repair mechanisms that include production of neurotrophic and mitogenic factors by cells neighboring the injured area. While trauma of most parts of the brain results in loss of function, lesions of certain regions of the female hypothalamus enhance the secretory activity of a group of specialized neurons that produce luteinizing hormone-releasing hormone (LHRH), the neuropeptide that controls sexual development. The increased output of LHRH causes sexual precocity by prematurely activating the neuroendocrine reproductive axis. Recent studies have implicated transforming growth factor alpha (TGF alpha) produced by reactive astrocytes in the process by which lesions hasten sexual maturation, and have suggested that the stimulatory actions of TGF alpha on LHRH neurons require the intermediacy of epidermal growth factor receptors (EGFRs). In the present study, we examined the changes in EGFR gene expression following lesions of the preoptic-anterior hypothalamic area (POA-AHA) of immature female rats, identified the cell types where EGFR synthesis increases, and assessed the biochemical activity of the newly formed EGFR protein. RNase protection assays demonstrated that the lesion significantly increased the levels of a predominant mRNA transcript encoding the full-length, membrane-spanning EGFR, but did not affect those of a much less abundant, alternatively spliced mRNA that encodes a truncated, presumably secreted form of EGFR. Following lesions, antibody-induced EGFR kinase activity increased twofold. Antibodies directed against a peptide sequence contained within the carboxy terminus of EGFR showed intense EGFR immunoreactivity in cells surrounding the lesion site; double immunohistochemistry identified these cells as astrocytes since EGFR immunoreactivity was colocalized with that of glial fibrillary acidic protein, an astrocytic marker. That these changes result from an increase in EGFR gene expression was indicated by the elevated levels of EGFR mRNA detected by in situ hybridization in cells of the same area. Although POA-AHA lesions did not result in appearance of EGFR in LHRH neurons themselves, EGFR-positive cells and processes were seen in close proximity to LHRH neurons and their nerve terminals, particularly in the area surrounding the lesion. Since TGF alpha gene expression is also increased in reactive astrocytes of POA-AHA lesions and blockade of EGFR prevented the advancing effect of the lesion on puberty (Junier et al., 1991b), the present results support the concept that, in lesioned animals, TGF alpha stimulates LHRH secretion indirectly via a paracrine mechanism that involves its interaction with EGFRs located on astroglial cells.

Transforming growth factor-alpha gene expression in the hypothalamus is developmentally regulated and linked to sexual maturation

Hypothalamic injury causes female sexual precocity by activating luteinizing hormone-releasing hormone (LHRH) neurons, which control sexual development. Transforming growth factor-alpha (TGF-alpha) has been implicated in this process, but its involvement in normal sexual maturation is unknown. The present study addresses this issue. TGF-alpha mRNA and protein were found mostly in astroglia, in regions of the hypothalamus concerned with LHRH control. Hypothalamic TGF-alpha mRNA levels increased at times when secretion of pituitary gonadotropins--an LHRH-dependent event--was elevated, particularly at the time of puberty. Gonadal steroids involved in the control of LHRH secretion increased TGF-alpha mRNA levels. Blockade of TGF-alpha action in the median eminence, a site of glial-LHRH nerve terminal association, delayed puberty. These results suggest that TGF-alpha of glial origin is a component of the developmental program by which the brain controls mammalian sexual maturation.

Effect of hypothalamic lesions that induce precocious puberty on the morphological and functional maturation of the luteinizing hormone-releasing hormone neuronal system

Recent evidence has implicated the transforming growth factor-alpha (TGF alpha)/epidermal growth factor receptor (EGFR) system in the mechanism by which hypothalamic lesions accelerate female sexual development. Since acquisition and maintenance of reproductive functions depend on the secretory activity of LHRH neurons, the present studies were undertaken to characterize some of the cellular and molecular events that underlie lesion-induced activation of the LHRH neuronal network. Bilateral electrolytic lesions of the posterior portion of the preoptic region and anterior hypothalamic area (POA-AHA) in 22-day-old rats resulted in vaginal opening and ovulation within 7 days. Morphological maturation of LHRH neurons was assessed by the relative frequency of irregular and smooth neurons (the former being the predominant type in adult animals). Within 20 h after the lesion, there was a significant decrease in the proportion of LHRH neurons with spiny irregular contours, indicating reversal to a more immature morphological type. This change was followed by accelerated spine reformation, so that at the time of precocious proestrus, the incidence of irregular LHRH neurons was similar in lesioned and age-matched control rats. A striking increase in c-fos mRNA levels occurred within 1 h after the lesion in the area neighboring the site of injury, reflecting the immediate cell response to trauma. Immunohistochemical localization of the c-fos protein, used to estimate changes in cellular activity at the single cell level, demonstrated c-fos induction in unidentified cells near the lesion and astrocytes, but not in LHRH neurons 20 h after injury. In contrast, a selective increase in c-fos expression was observed in LHRH neurons during the initiation of precocious puberty 5-7 days later at the time of the first proestrus. An increase in plasma LH associated with a drop in LHRH content in the median eminence and an increase in pro-LHRH precursor in the POA-AHA, with no changes in LHRH mRNA, was found to antedate the first preovulatory surge of gonadotropins in lesioned rats. Assessment of the changes in PC2 mRNA, which encodes a novel dibasic endoprotease presumptively involved in tissue-specific processing of a class of prohormones that includes pro-LHRH, showed that the content of PC2 mRNA in the AHA-POA increases during normal puberty, but not in lesioned animals, thus providing a potential explanation for the divergent changes in pro-LHRH and mature decapeptide found in lesioned rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurotrophic factors and female sexual development

The concept is proposed that polypeptide neurotrophic factors contribute to the developmental regulation of ovarian and hypothalamic function in mammals. Nerve growth factor (NGF) and neurotrophin-3, two members of the neurotrophin family, have been identified in the rat ovary and one of its receptors has been localized to the innervation and thecal cells of developing follicles. Although NGF supports the sympathetic innervation of the gland, the extent to which follicles are innervated appears to be defined by the differential expression of NGF receptors in the theca of developing follicles. The presence of NGF receptors in steroid-producing cells suggests a direct involvement of neurotrophins in the regulation of gonadal endocrine function. Evidence is beginning to emerge suggesting that development of the reproductive hypothalamus is affected by insulin-like growth factor 1 secreted by peripheral tissues, and transforming growth factor alpha (TGF alpha) produced locally. In the rat hypothalamus, TGF alpha appears to be synthesized in both neurons and glial cells. In glial cells it may interact with epidermal growth factor (EGF) receptors to further enhance TGF alpha synthesis and to, perhaps, stimulate eicosanoid formation. In turn, one of these eicosanoids, prostaglandin E2, may act on luteinizing hormone-releasing hormone (LHRH) neurons to stimulate the release of LHRH in a genomic-independent manner. This provides the basis for the notion that during development LHRH secretion is regulated by a dual mechanism, one that involves transsynaptic effects exerted by neurotransmitters, the other that requires a glial-neuronal interaction and that may predominantly regulate release of the neuropeptide. An increased expression of the TGF alpha and EGF receptor genes in reactive astrocytes is postulated to contribute to the process by which hypothalamic injury causes sexual precocity. Morphological maturation of the reproductive hypothalamus is thought to occur during sexual development. The process is accelerated by estradiol, which exerts its neurotrophic effects by enhancing the expression of genes encoding cytoskeletal proteins involved in neuronal development and regeneration. It is suggested that acquisition of functional competence by both the ovaries and the reproductive hypothalamus requires the participation of specific, but not similar, neurotrophic factors. The relevance of these concepts to the process of sexual development in other species, particularly primates, remains to be defined.

Transforming growth factor alpha contributes to the mechanism by which hypothalamic injury induces precocious puberty

It has long been known that lesions of the hypothalamus lead to female sexual precocity. While an increased production of luteinizing hormone-releasing hormone (LHRH), the neurohormone that controls sexual development, appears to mediate the advancement of puberty induced by these lesions, little is known about the mechanism(s) by which hypothalamic injury activates LHRH secretion. Since brain lesions result in accumulation of neurotrophic/mitogenic activities in the injured area, we tested the hypothesis that transforming growth factor alpha (TGF-alpha), a mitogenic polypeptide recently shown to stimulate LHRH release, is produced in response to hypothalamic injury and mediates the effect of the lesion on puberty. Radiofrequency lesions of the preoptic area-anterior hypothalamic area (POA-AHA) of 22-day-old female rats resulted in precocious puberty within 7 days after the operation. RNA blot hybridization revealed that lesion-induced puberty was preceded by an increase in TGF-alpha mRNA levels in the POA-AHA. Epidermal growth factor (EGF) mRNA was undetectable in both intact and lesioned hypothalami. TGF-alpha mRNA levels, quantitated by RNase protection assays, were 3.5-fold greater in lesioned animals approaching puberty than in age-matched controls. Immunohistochemical studies, utilizing single- and double-staining procedures, demonstrated the presence of TGF-alpha precursor-like immunoreactivity in reactive astrocytes surrounding the lesion site. Hybridization histochemistry showed increased TGF-alpha mRNA expression in cells of the same area, further implicating reactive astrocytes as a site of TGF-alpha synthesis. The actions of TGF-alpha are mediated by its interaction with EGF receptors. Continuous infusion of RG-50864, an inhibitor of EGF receptor kinase activity, at the site of injury prevented the advancement of puberty induced by the lesion. These results suggest that TGF-alpha acting via EGF-like receptors contributes to the acceleration of puberty induced by anterior hypothalamic lesions. They also indicate that activation of TGF-alpha gene expression in glial cells is a component of the hypothalamic response to injury.

A competitive receptor binding assay for platelet-activating factor (PAF): quantification of PAF in rat brain

A radioreceptor assay (RRA) was developed using rabbit platelet membrane preparations to quantify platelet-activating factor (PAF) and lyso-PAF, the deacylated derivative of PAF, in a variety of tissues and biological fluids. We examined PAF and lyso-PAF levels in different rat brain areas with regard to the many proven and postulated actions of PAF in brain functions. Human saliva was selected to check the validity of this RRA. The samples were extracted with methanol/chloroform/water and purified by high-performance liquid chromatography on a 5-microns Nucleosil Si column (overall recovery: 78%). Sample extracts were acetylated before chromatography to assay lyso-PAF. PAF itself was assayed in non-aceylated samples. A competitive binding assay was performed using aliquots of platelet membrane preparation and tritiated PAF. The minimum detectable amount of PAF was 144 pg per tube and the receptor was highly specific for PAF. In human saliva, we confirm the presence of PAF and lyso-PAF within the range expected. Moreover there was a good correlation between the RRA and the aggregation assay (r = 0.976). A defined cocktail of protease inhibitors allowed storage of platelet membrane preparations for at least 3 months at -20 degrees C with no change in binding properties. In the brain we observed the prevalent presence of lyso-PAF and large variations in PAF and lyso-PAF concentrations between the different brain areas analyzed. PAF was undetectable in the hypothalamus but the lyso-PAF concentration was 2.5 micrograms/g wet tissue. The PAF concentration in the cortex varied from 0 to 16 ng/g wet tissue while that of lyso-PAF was 0.7 micrograms/g wet tissue. Moreover the amount of lyso-PAF varied between the different brain areas analyzed. The hippocampus contained the highest amount (7 micrograms/g wet tissue), and relatively high levels were found in the hypothalamus, medulla oblongata and corpus striatum. The cerebellum and cortex contained the lowest levels of lyso-PAF. These findings show that PAF is present in the central nervous system mainly in its inactive form, lyso-PAF, and suggest that its effects as a modulator of brain function may be dependent on deacetylation, rather than synthesis.

Intracerebroventricular injection of platelet-activating factor induces secretion of adrenocorticotropin, beta-endorphin and corticosterone in conscious rats: a possible link between the immune and nervous systems

To investigate whether platelet-activating factor (PAF) exerts an indirect action on immune cells by altering the secretion of hypothalamic-pituitary-adrenal (HPA) axis products, the effects of intracerebroventricular (i.c.v.) PAF on adrenocorticotropic hormone (ACTH), beta-endorphin and corticosterone blood levels were examined in adult male rats. Hormones were radioimmunoassayed on blood samples from conscious or ether-anesthetized rats after i.c.v. injection of PAF or vehicle into the left lateral ventricle. PAF induced significant increases in these stress-related hormones under both, basal and ether-induced stress conditions. The analysis of the time course response to PAF of hormone release into the blood of unrestrained rats revealed that: i.c.v. injection of 5.4 nmol PAF resulted in rapid increases in ACTH and beta-endorphin, at the latest within 15 min after the onset of injection. The maximal response of both hormones was reached within 45 min after the onset of injection and was followed by an elevation of plasma corticosterone. Hormone release is related to the PAF dose infused, the lowest effective PAF concentration was 1 nmol. The stimulatory effect of PAF on ACTH and beta-endorphin secretion was strongly decreased in rats previously treated with purified anti-rat corticotropin-releasing factor (CRF) antibody. These results, associated with the in vitro demonstration that PAF increases CRF release from incubated rat median eminence, strongly support the hypothesis that the stimulatory action of PAF on the secretion of HPA axis products is mediated at least partly, by stimulating hypothalamic CRF release.(ABSTRACT TRUNCATED AT 250 WORDS)

Epoxygenase products of arachidonic acid are endogenous constituents of the hypothalamus involved in D2 receptor-mediated, dopamine-induced release of somatostatin

The epoxyeicosatrienoic acids (EETs) were discovered as products of a cyclooxygenase/lipoxygenase-independent, cytochrome P-450 catalyzed metabolism of arachidonic acid (AA) termed the "epoxygenase" pathway. The rat hypothalamus is able to synthesize EETs from exogenous AA, and 5,6-EET has been found to release the neuropeptide somatostatin (SRIF) from hypothalamic nerve terminals of the median eminence (ME). In the present study, hypothalami from male rats were examined for the presence of endogenous EETs, using chemical, chromatographic, and mass spectral analysis procedures. The samples were initially separated in a C18 Sepralyte column, fractionated on TLC plates, and purified by reverse phase HPLC. Thereafter, they were esterified (pentafluorobenzyl esters) and subjected to negative ion chemical ionization/gas chromatography (GC)/mass spectral (MS) analysis. The GC retention time and the MS fragmentation patterns revealed the presence of a mixture of 8,9-, 11,12- and 14,15-EETs; instability of 5,6-EET during the isolation protocol precluded its identification. Total hypothalamic EET concentration was estimated to be 120 ng/g wet tissue. The 8,9-regiosomer released SRIF from ME nerve terminals with an ED50 of 5 x 10(-12) M; Dopamine (DA) and the D2 receptor agonist PPHT, but not the D1 receptor agonist SKF-38393, induced SRIF release from the ME. This effect was blocked by clotrimazole and ketoconazole, two inhibitors of microsomal cytochrome P-450 function and AA epoxygenase in particular. In contrast, the inhibitors failed to affect the increase in SRIF release induced by 8,9-EET. These results indicate that: 1) in addition to cyclooxygenase and lipoxygenase products, epoxygenase metabolites of AA are endogenous compounds of the hypothalamus, and 2) EETs may mediate the increase in SRIF release from hypothalamic neurons induced by the interaction of DA with D2 receptors.

Contribution of arachidonate metabolites to basal and thyrotropin releasing-hormone-stimulated release of prolactin from purified lactotrophs in primary culture

Among the different biochemical pathways which have been suggested to play a role in the control of prolactin (Prl) release from anterior pituitaries, arachidonate and its metabolites have been proposed to be involved in the process of Prl release. In this study we investigated the contribution of arachidonate metabolites to both basal and TRH-stimulated Prl release from perifused lactotrophs in culture (derived from pituitary glands of lactating female rats), which exhibit a high sustained release of Prl in absence of inhibitory input. Inhibition of the general oxidative metabolism of arachidonate by 10(-5) M ETYA or of the arachidonate lipoxygenase metabolism by 10(-5) M NDGA decreased basal Prl release to 45 +/- 10% (n = 3) and 36 +/- 4% (n = 6) of the control release, respectively. Indomethacin, an inhibitor of the cyclooxygenase pathway, was without effect. Of the lipoxygenase metabolites tested at 10(-6) M only 15-HPETE and 15-HETE induced Prl release. 15-HETE elicited prolactin release in a concentration dependent manner with a maximal effect at 10(-6) M (10.72 +/- 3 ng/ml vs control 5.1 +/- 0.8 ng/ml, n = 3). The quantity of Prl release induced by TRH was markedly decreased in the presence of NDGA. However, the fraction of Prl release elicited by TRH, calculated as a percentage of the amount of Prl released prior to TRH application, was similar under control conditions, and in the presence of NDGA. In contrast, inhibition of the protein kinases A and G by H8 (10(-5) M) failed to alter basal Prl release but inhibited the effect of TRH by 58 +/- 6% (n = 3). These data suggest that in absence of inhibitory inputs the high sustained release of Prl observed in cultures of lactotrophs derived from lactating female rats depends on the availability of lipoxygenase metabolites, and that the blockade of lipoxygenase reduces the absolute amount of Prl released by TRH without suppressing the ability of TRH to stimulate Prl release.

Inhibitory effect of platelet-activating factor (PAF) on luteinizing hormone-releasing hormone and somatostatin release from rat median eminence in vitro correlated with the characterization of specific PAF receptor sites in rat hypothalamus

Platelet-activating factor (PAF) exhibits a wide range of biological activities, including the stimulation of secretory processes in various cell types. However, little is known regarding its possible influence on the release of brain neuropeptides. In the present study we have examined the effect of PAF on the release of three hypothalamic releasing hormones in adult male rats, and have characterized the presence of specific PAF binding sites in rat hypothalamic membranes. PAF decreased LHRH and somatostatin (SRIF) release from the median eminence with a maximal inhibition at 10(-14) M for both neuropeptides, whereas GRF release was not significantly altered. Moreover, PAF strongly counteracted the Ca2+ ionophore A 23187-stimulated release of LHRH and SRIF from median eminence and medial basal hypothalamus (greater than 50% inhibition). These results suggest an involvement of Ca2+ dependent events in PAF action. This inhibitory effect was specifically exerted at a hypothalamic site because PAF failed to depress LH and GH release from the anterior pituitary. A specific, reversible and saturable binding of [3H]PAF to membrane preparations of rat hypothalamus was demonstrated and two classes of binding sites were characterized. The affinity (KD) of each binding class was 2.14 +/- 0.32 nM and 61.63 +/- 16.4 nM, respectively, and the corresponding maximal number of each binding class was 25.41 +/- 3.2 fmol/mg protein and 146.2 +/- 47.5 fmol/mg protein. In the same conditions no specific binding was observed using rat pituitary membranes. The specificity of PAF analogs for these binding sites was well correlated to their relative effectiveness in altering LHRH and SRIF release (order of potency: L-652,731, kadsurenone greater than BN 52021 greater than Lyso-PAF). These data suggest that the binding sites identified in the hypothalamus have the characteristics expected of a specific PAF receptor and that PAF effect on neuropeptides release is a receptor-mediated process.