Differential gene expression in glioblastoma defined by ADC histogram analysis: relationship to extracellular matrix molecules and survival

BACKGROUND AND PURPOSE

ADC histogram analysis can stratify outcomes in patients with GBM treated with bevacizumab. Therefore, we compared gene expression between high-versus-low ADC tumors to identify gene expression modules that could underlie this difference and impact patient prognosis.

MATERIALS AND METHODS

Up-front bevacizumab-treated patients (N = 38) with newly diagnosed glioblastoma were analyzed by using an ADC histogram approach based on enhancing tumor. Using microarrays, we compared gene expression in high-versus-low ADC tumors in patients subsequently treated with bevacizumab. Tissue sections from a subset of tumors were stained for collagen and collagen-binding proteins. Progression-free and overall survival was determined by using Cox proportional hazard ratios and the Kaplan-Meier method with the log rank test.

RESULTS

A total of 13 genes were expressed at 2-fold or greater levels in high- compared with low-ADC tumors at the P < .05 level. Of these, 6 encode for collagen or collagen-binding proteins. High gene expression for the collagen-binding protein decorin was associated with shorter survival (HR, 2.5; P = .03). The pattern and degree of collagen staining were highly variable in both high- and low-ADC tumors.

CONCLUSIONS

High-ADC GBMs show greater levels of ECM protein gene expression compared with low-ADC GBMs. It is unclear whether this translates to the accumulation of higher levels of the encoded proteins. However, because ECM molecules could contribute to a proinvasive phenotype, this relationship merits further investigation.

Relationship between tumor enhancement, edema, IDH1 mutational status, MGMT promoter methylation, and survival in glioblastoma

BACKGROUND AND PURPOSE

Both IDH1 mutation and MGMT promoter methylation are associated with longer survival. We investigated the ability of imaging correlates to serve as noninvasive biomarkers for these molecularly defined GBM subtypes.

MATERIALS AND METHODS

MR imaging from 202 patients with GBM was retrospectively assessed for nonenhancing tumor and edema among other imaging features. IDH1 mutational and MGMT promoter methylation status were determined by DNA sequencing and methylation-specific PCR, respectively. Overall survival was determined by using a multivariate Cox model and the Kaplan-Meier method with a log rank test. A logistic regression model followed by ROC analysis was used to classify the IDH1 mutation and methylation status by using imaging features.

RESULTS

MGMT promoter methylation and IDH1 mutation were associated with longer median survival. Edema levels stratified survival for methylated but not unmethylated tumors. Median survival for methylated tumors with little/no edema was 2476 days (95% CI, 795), compared with 586 days (95% CI, 507-654) for unmethylated tumors or tumors with edema. All IDH1 mutant tumors were nCET positive, and most (11/14, 79%) were located in the frontal lobe. Imaging features including larger tumor size and nCET could be used to determine IDH1 mutational status with 97.5% accuracy, but poorly predicted MGMT promoter methylation.

CONCLUSIONS

Imaging features are potentially predictive of IDH1 mutational status but were poorly correlated with MGMT promoter methylation. Edema stratifies survival in MGMT promoter methylated but not in unmethylated tumors; patients with methylated tumors with little or no edema have particularly long survival.

Impaired water maze learning performance without altered dopaminergic function in mice heterozygous for the GDNF mutation

Exogenous glial cell line-derived neurotrophic factor (GDNF) exhibits potent survival-promoting effects on dopaminergic neurons of the nigrostriatal pathway that is implicated in Parkinson's disease and also protects neurons in forebrain ischemia of animal models. However, a role for endogenous GDNF in brain function has not been established. Although mice homozygous for a targeted deletion of the GDNF gene have been generated, these mice die within hours of birth because of deficits in kidney morphogenesis, and, thus, the effect of the absence of GDNF on brain function could not be studied. Herein, we sought to determine whether adult mice, heterozygous for a GDNF mutation on two different genetic backgrounds, demonstrate alterations in the nigrostriatal dopaminergic system or in cognitive function. While both neurochemical and behavioural measures suggested that reduction of GDNF gene expression in the mutant mice does not alter the nigrostriatal dopaminergic system, it led to a significant and selective impairment of performance in the spatial version of the Morris water maze. A standard panel of blood chemistry tests and basic pathological analyses did not reveal alterations in the mutants that could account for the observed performance deficit. These results suggest that endogenous GDNF may not be critical for the development and functioning of the nigrostriatal dopaminergic system but it plays an important role in cognitive abilities.

Mammalian-cell-produced neurturin (NTN) is more potent than purified Escherichia coli-produced NTN

Neurturin (NTN) is a recently identified homologue of glial-cell-line-derived neurotrophic factor. Both factors promote the survival of dopaminergic (DA) neurons. We investigated the biological activity of mammalian-cell-produced NTN versus purified Escherichia coli-produced NTN. Baby hamster kidney cells were engineered to stably secrete mature human NTN. Mammalian-cell-derived NTN enhanced the activity of embryonic DA neurons in vitro, with greater potency (maximum effect achieved in the picogram range) than purified E. coli-produced NTN. Cell-based delivery of NTN (less than 10 ng/day) was also shown to be biologically active in vivo. These results suggest that mammalian-cell-derived NTN, synthesized de novo and delivered in small quantities to the parenchyma at the target site, may be as active as much larger quantities of purified, E. coli-produced NTN, delivered by other means.

The glial cell line-derived neurotrophic factor family receptor components are differentially regulated within sensory neurons after nerve injury

Glial cell line-derived neurotrophic factor (GDNF) has potent trophic effects on adult sensory neurons after nerve injury and is one of a family of proteins that includes neurturin, persephin, and artemin. Sensitivity to these factors is conferred by a receptor complex consisting of a ligand binding domain (GFRalpha1-GFRalpha4) and a signal transducing domain RET. We have investigated the normal expression of GDNF family receptor components within sensory neurons and the response to nerve injury. In normal rats, RET and GFRalpha1 were expressed in a subpopulation of both small- and large-diameter afferents projecting through the sciatic nerve [60 and 40% of FluoroGold (FG)-labeled cells, respectively]. GFRalpha2 and GFRalpha3 were both expressed principally within small-diameter DRG cells (30 and 40% of FG-labeled cells, respectively). Two weeks after sciatic axotomy, the expression of GFRalpha2 was markedly reduced (to 12% of sciatic afferents). In contrast, the proportion of sciatic afferents that expressed GFRalpha1 increased (to 66% of sciatic afferents) so that virtually all large-diameter afferents expressed this receptor component, and the expression of GFRalpha3 also increased (to 66% of sciatic afferents) so that almost all of the small-diameter afferents expressed this receptor component after axotomy. There was little change in RET expression. The changes in the proportions of DRG cells expressing different receptor components were mirrored by alterations in the total RNA levels within the DRG. The changes in GFRalpha1 and GFRalpha2 expression after axotomy could be largely reversed by treatment with GDNF.

Regulation of learning by EphA receptors: a protein targeting study

EphA family receptor tyrosine kinases and their ephrin-A ligands are involved in patterning axonal connections during brain development, but until now a role for these molecules in the mature brain had not been elucidated. Here, we show that both the EphA5 receptor and its ephrin-A ligands (2 and 5) are expressed in the adult mouse hippocampus, and the EphA5 protein is present in a phosphorylated form. Because there are no pharmacological agents available for EphA receptors, we designed recombinant immunoadhesins that specifically bind to the receptor binding site of the ephrin-A ligand (antagonist) or the ligand binding site of the EphA receptor (agonist) and thus target EphA function. We demonstrate that intrahippocampal infusion of an EphA antagonist immunoadhesin leads to impaired performance in two behavioral paradigms, T-maze spontaneous alternation and context-dependent fear conditioning, sensitive to hippocampal function, whereas activation of EphA by infusion of an agonist immunoadhesin results in enhanced performance on these tasks. Because the two behavioral tasks have different motivational, perceptual, and motor requirements, we infer the changes were not caused by these performance factors but rather to cognitive alterations. We also find bidirectional changes in gene expression and in electrophysiological measures of synaptic efficacy that correlate with the behavioral results. Thus, EphA receptors and their ligands are implicated as mediators of plasticity in the adult mammalian brain.

Protection and regeneration of nigral dopaminergic neurons by neurturin or GDNF in a partial lesion model of Parkinson's disease after administration into the striatum or the lateral ventricle

Both glial cell line-derived neurotrophic factor (GDNF) and its recently discovered congener, neurturin (NTN), have been shown to exert neuroprotective effects on lesioned nigral dopamine (DA) neurons when administered at the level of the substantia nigra. In the present study, we have explored the relative in vivo potency of these two neurotrophic factors using two alternative routes of administration, into the striatum or the lateral ventricle, which may be more relevant in a clinical setting. In rats subjected to an intrastriatal (IS) 6-hydroxydopamine (6-OHDA) lesion, GDNF and NTN were injected every third day for 3 weeks starting on the day after the 6-OHDA injection. GDNF provided almost complete (90-92%) protection of the lesioned nigral DA neurons after both IS and intracerebroventricular (ICV) administration. NTN, by contrast, was only partially effective after IS injection (72% sparing) and totally ineffective after ICV injection. Although the trophic factor injections protected the nigral neurons from lesion-induced cell death, the level of expression of the phenotypic marker, tyrosine hydroxylase (TH), was markedly reduced in the rescued cell bodies. The extent of 6-OHDA-induced DA denervation in the striatum was unaffected by both types of treatment; consistent with this observation, the high rate of amphetamine-induced turning seen in the lesioned control animals was unaltered by either GDNF or NTN treatment. In the GDNF-treated animals, and to a lesser extent also after IS NTN treatment, prominent axonal sprouting was observed within the globus pallidus, at the level where the lesioned nigrostriatal axons are known to end at the time of onset of the neurotrophic factor treatment. The results show that GDNF is highly effective as a neuroprotective and axon growth-stimulating agent in the IS 6-OHDA lesion model after both IS and ICV administration. The lower efficacy of NTN after IS, and particularly ICV, administration may be explained by the poor solubility and diffusion properties at neutral pH.

Protein targeting in the analysis of learning and memory: a potential alternative to gene targeting

Gene targeting using homologous recombination in embryonic stem (ES) cells offers unprecedented precision with which one may manipulate single genes and investigate the in vivo effects of defined mutations in the mouse. Geneticists argue that this technique abrogates the lack of highly specific pharmacological tools in the study of brain function and behavior. However, by now it has become clear that gene targeting has some limitations too. One problem is spatial and temporal specificity of the generated mutation, which may appear in multiple brain regions or even in other organs and may also be present throughout development, giving rise to complex, secondary phenotypical alterations. This may be a disadvantage in the functional analysis of a number of genes associated with learning and memory processes. For example, several proteins, including neurotrophins--cell-adhesion molecules--and protein kinases, that play a significant developmental role have recently been suggested to be also involved in neural and behavioral plasticity. Knocking out genes of such proteins may lead to developmental alterations or even embryonic lethality in the mouse, making it difficult to study their function in neural plasticity, learning, and memory. Therefore, alternative strategies to gene targeting may be needed. Here, we suggest a potentially useful in vivo strategy based on systemic application of immunoadhesins, genetically engineered fusion proteins possessing the Fc portion of the human IgG molecule and, for example, a binding domain of a receptor of interest. These proteins are stable in vivo and exhibit high binding specificity and affinity for the endogenous ligand of the receptor, but lack the ability to signal. Thus, if delivered to the brain, immunoadhesins may specifically block signalling of the receptor of interest. Using osmotic minipumps, the protein can be infused in a localized region of the brain for a specified period of time (days or weeks). Thus, the location and timing of delivery are controlled. Here, we present methodological details of this novel approach and argue that infusion of immunoadhesins will be useful for studying the role particular receptors play in behavioral and neural plasticity.

Regulation of hippocampal synaptic plasticity by the tyrosine kinase receptor, REK7/EphA5, and its ligand, AL-1/Ephrin-A5

The Eph-related tyrosine kinase receptor, REK7/EphA5, mediates the effects of AL-1/Ephrin-A5 and related ligands and is involved in the guidance of retinal, cortical, and hippocampal axons during development. The continued expression of REK7/EphA5 in the adult brain, in particular in areas associated with a high degree of synaptic plasticity such as the hippocampus, raises the question of its function in the mature nervous system. In this report we examined the role of REK7/EphA5 in synaptic remodeling by asking if agents that either block or activate REK7/EphA5 affect synaptic strength in hippocampal slices from adult mouse brain. We show that a REK7/EphA5 antagonist, soluble REK7/EphA5-IgG, impairs the induction of long-term potentiation (LTP) without affecting other synaptic parameters such as normal synaptic transmission or paired-pulse facilitation. In contrast, perfusion with AL-1/Ephrin-A5-IgG, an activator of REK7/EphA5, induces a sustained increase in normal synaptic transmission that partially mimics LTP. The sustained elevation of normal synaptic transmission could be attributable to a long-lasting binding of the AL-1/Ephrin-A5-IgG to the endogenous REK7/EphA5 receptor, as revealed by immunohistochemistry. Furthermore, maximal electrical induction of LTP occludes the potentiating effects of subsequent treatment with AL-1/Ephrin-A5-IgG. Taken together these results implicate REK7/EphA5 in the regulation of synaptic plasticity in the mature hippocampus and suggest that REK7/EphA5 activation is recruited in the LTP induced by tetanization.

Neurturin exerts potent actions on survival and function of midbrain dopaminergic neurons

Glial cell line-derived neurotrophic factor (GDNF) exhibits potent effects on survival and function of midbrain dopaminergic (DA) neurons in a variety of models. Although other growth factors expressed in the vicinity of developing DA neurons have been reported to support survival of DA neurons in vitro, to date none of these factors duplicate the potent and selective actions of GDNF in vivo. We report here that neurturin (NTN), a homolog of GDNF, is expressed in the nigrostriatal system, and that NTN exerts potent effects on survival and function of midbrain DA neurons. Our findings indicate that NTN mRNA is sequentially expressed in the ventral midbrain and striatum during development and that NTN exhibits survival-promoting actions on both developing and mature DA neurons. In vitro, NTN supports survival of embryonic DA neurons, and in vivo, direct injection of NTN into the substantia nigra protects mature DA neurons from cell death induced by 6-OHDA. Furthermore, administration of NTN into the striatum of intact adult animals induces behavioral and biochemical changes associated with functional upregulation of nigral DA neurons. The similarity in potency and efficacy of NTN and GDNF on DA neurons in several paradigms stands in contrast to the differential distribution of the receptor components GDNF Family Receptor alpha1 (GFRalpha1) and GFRalpha2 within the ventral mesencephalon. These results suggest that NTN is an endogenous trophic factor for midbrain DA neurons and point to the possibility that GDNF and NTN may exert redundant trophic influences on nigral DA neurons acting via a receptor complex that includes GFRalpha1.

Differential dependency of unmyelinated and A delta epidermal and upper dermal innervation on neurotrophins, trk receptors, and p75LNGFR

The impact of the nerve growth factor (NGF) family of neurotrophins and their receptors was examined on the cutaneous innervation in the mystacial pads of mice. Ten sets of unmyelinated and thinly myelinated sensory and autonomic innervation were evaluated that terminated in the epidermis, upper dermis, and upper part of the intervibrissal hair follicles. Mystacial pads were analyzed from newborn to 4-week-old mice that had homozygous functional deletions of the genes for NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), tyrosine kinase (trk) A, trkB, trkC, or p75. Mystacial pads were also analyzed in adult transgenic mice that had overproduction of NGF, BDNF, or NT-3 driven by a keratin promoter gene. The innervation was revealed by using immunofluorescence and immunocytochemistry with antibodies for protein gene product (PGP) 9.5, calcitonin gene-related product (CGRP), substance P (SP), galanin (GAL), neuropeptide Y (NPY), tyrosine hydroxylase (TH), and a neurofilament protein. The cumulative results indicated that NGF/trkA signaling plays a major role in the outgrowth and proliferation of sensory axons, whereas NT-3/ trkA signaling plays a major role in the formation of sensory endings. TrkC is also essential for the development of three sets of trkA-dependent sensory innervation that coexpress CGRP, SP, and GAL. Another set of sensory innervation that only coexpressed CGRP and SP was solely dependent upon NGF and trkA. Surprisingly, most sets of trkA-dependent sensory innervation are suppressed by trkB perhaps interacting with p75. BDNF and NT-4 appear to mediate this suppressing effect in the upper dermis and NT-4 in the epidermis. In contrast to sensory innervation, sympathetic innervation to the necks of intervibrissal hair follicles depends upon NGF/trkA signaling interacting with p75 for both the axon outgrowth and ending formation. Although NT-3/trkA signaling is essential for the full complement of sympathetic neurons, NT-3 is detrimental to the formation of sympathetic terminations to the necks of hair follicles. TrkB signaling mediated by BDNF but not NT-4 also suppresses these sympathetic terminations. One sparse set of innervation, perhaps parasympathetic, terminating at the necks of hair follicles is dependent solely upon NT-3 and trkC. Taken together, our results indicate that the innervation of the epidermis, upper dermis, and the upper portion of hair follicles is regulated by a competitive balance between promoting and suppressing effects of the various neurotrophins.

Csk and BatK show opposite temporal expression in the rat CNS: consistent with its late expression in development, BatK induces differentiation of PC12 cells

BatK is a second member of the Csk family of regulatory kinases that phosphorylate a key inhibitory tyrosine on Src family kinases, leading to down-regulation. To investigate the roles of BatK and Csk, both of which are expressed in the brain, we compared their temporal expression patterns during development of the central nervous system (CNS) in rats. BatK mRNA is undetectable at embryonic day 12 (E12), appears in the developing nervous system at approximately E15, and its expression progressively increases up to the time of birth, thereafter remaining high throughout the adult brain. In striking contrast, Csk is highly expressed throughout embryonic development and remains high in the CNS until birth. It is then dramatically down-regulated in the adult brain except in the olfactory bulb. BatK and Csk thus exhibit complementary temporal expression patterns. Since BatK expression correlates with late-stage development and terminal differentiation, we speculated that it might be involved in regulating neuronal differentiation. Using PC12 cells as a model system, we show that overexpression of BatK is sufficient to induce neurite outgrowth in the absence of nerve growth factor. Further, overexpression of BatK activates the mitogen-activated protein kinase cascade. We propose a model suggesting that, despite overlapping in vitro activities, BatK and Csk regulate different targets in vivo and have different functions during and after neuronal development, BatK being the dominant regulator of Src kinases in the fully differentiated adult brain.

Differential dependency of cutaneous mechanoreceptors on neurotrophins, trk receptors, and P75 LNGFR

The impact of null mutations of the genes for the NGF family of neurotrophins and their receptors was examined among the wide variety of medium to large caliber myelinated mechanoreceptors which have a highly specific predictable organization in the mystacial pad of mice. Immunofluorescence with anti-protein gene product 9.5, anti-200-kDa neurofilament protein (RT97), and anti-calcitonin gene-related product was used to label innervation in mystacial pads from mice with homozygous null mutations for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), the three tyrosine kinase receptors (trkA, trkB, trkC), and the low-affinity nerve growth factor receptor p75. Specimens were sacrificed at birth and at 1, 2, and 4 weeks for each type of mutation as well as at 11 weeks and 1 year for p75 and trkC mutations, respectively. Our results demonstrate several major concepts about the role of neurotrophins in the development of cutaneous mechanoreceptors that are supplied by medium to large caliber myelinated afferents. First, each of the high-affinity tyrosine kinase receptors, trkA, trkB, and trkC, as well as the low-affinity p75 receptor has an impact on at least one type of mechanoreceptor. Second, consistent with the various affinities for particular trk receptors, the elimination of NGF, BDNF, and NT-3 has an impact comparable to or more complex than the absence of their most specific high-affinity receptors: trkA, trkB, and trkC, respectively. These complexities include potential NT-3 signaling through trkA and trkB to support some neuronal survival. Third, most types of afferents are dependent on a different combination of neurotrophins and receptors for their survival: reticular and transverse lanceolate afferents are dependent upon NT-3, NGF, and trkA; Ruffini afferents upon BDNF and trkB; longitudinal lanceolate afferents upon NGF, trkA, BDNF, and trkB; and Merkel afferents on NGF, trkA, NT-3, trkC, and p75. NT-4 has no obvious detrimental impact on the mechanoreceptor development in the presence of BDNF. Fourth, NT-4 and BDNF signaling through trkB may suppress Merkel innervation and NT-3 signaling through trkC may suppress Ruffini innervation. Finally, regardless of the neurotrophin/receptor dependency for afferent survival and neurite outgrowth, NT-3 has an impact on the formation of all the sensory endings. In the context of these findings, indications of competitive and suppressive interactions that appear to regulate the balance of innervation density among the various sets of innervation were evident.

Disruption of a single allele of the nerve growth factor gene results in atrophy of basal forebrain cholinergic neurons and memory deficits

Administration of nerve growth factor (NGF) to aged or lesioned animals has been shown to reverse the atrophy of basal forebrain cholinergic neurons and ameliorate behavioral deficits. To examine the importance of endogenous NGF in the survival of basal forebrain cholinergic cells and in spatial memory, mice bearing a disruption mutation in one allele of the NGF gene were studied. Heterozygous mutant mice (ngf+/-) have reduced levels of NGF mRNA and protein within the hippocampus and were found to display significant deficits in memory acquisition and retention in the Morris water maze. The behavioral deficits observed in NGF-deficient mice were accompanied by both shrinkage and loss of septal cells expressing cholinergic markers and by a decrease in cholinergic innervation of the hippocampus. Infusions of NGF into the lateral ventricle of adult ngf+/- mice abolished the deficits on the water maze task. Prolonged exposure to NGF may be required to induce cognitive effects, because reversal of the acquisition deficit was seen after long (5 weeks) but not short (3 d) infusion. Although NGF administration did not result in any improvement in the number of septal cells labeled for choline acetyltransferase, this treatment did effectively correct the deficits in both size of cholinergic neurons and density of cholinergic innervation of the hippocampus. These findings demonstrate the importance of endogenous NGF for survival and function of basal forebrain cholinergic neurons and reveal that partial depletion of this trophic factor is associated with measurable deficits in learning and memory.

Characterization of a multicomponent receptor for GDNF

Glial-cell-line-derived neurotrophic factor (GDNF) is a potent survival factor for central and peripheral neurons, and is essential for the development of kidneys and the enteric nervous system. Despite the potential clinical and physiological importance of GDNF, its mechanism of action is unknown. Here we show that physiological responses to GDNF require the presence of a novel glycosyl-phosphatidylinositol (GPI)-linked protein (designated GDNFR-alpha) that is expressed on GDNF-responsive cells and binds GDNF with a high affinity. We further demonstrate that GDNF promotes the formation of a physical complex between GDNFR-alpha and the orphan tyrosin kinase receptor Ret, thereby inducing its tyrosine phosphorylation. These findings support the hypothesis that GDNF uses a multi-subunit receptor system in which GDNFR-alpha and Ret function as the ligand-binding and signalling components, respectively.

Cardiotrophin-1, a cytokine present in embryonic muscle, supports long-term survival of spinal motoneurons

The muscle-derived factors required for survival of embryonic motoneurons are not clearly identified. Cardiotrophin-1 (CT-1), a cytokine related to ciliary neurotrophic factor (CNTF), is expressed at high levels in embryonic limb bud and is secreted by differentiated myotubes. In vitro, CT-1 kept 43% of purified E14 rat motoneurons alive for 2 weeks (EC50 = 20 pM). In vivo, CT-1 protected neonatal sciatic motoneurons against the effects of axotomy. CT-1 action on motoneurons was inhibited by phosphatidylinositol-specific phospholipase C (PIPLC), suggesting that CT-1 may act through a GPI-linked component. Since no binding of CT-1 to CNTFR alpha was detected, CT-1 may use a novel cytokine receptor alpha subunit. CT-1 may be important in normal motoneuron development and as a potential tool for slowing motoneuron degeneration in human diseases.

Expression of the trk family of neurotrophin receptors in developing and adult dorsal root ganglion neurons

Expression of trk receptors is a major determinant of neurotrophin responsiveness of sensory neurons. Although it has been apparent for some time that subpopulations of dorsal root and trigeminal ganglion neurons respond in vitro to each of the members of the neurotrophin family, the extent to which functionally distinct subclasses of sensory neurons are dependent on the actions of different neurotrophins for their development and function remains an active area of investigation. One step towards elucidating the role of various neurotrophins in development and function of sensory neurons has been to examine the distribution of trk receptors on sensory neurons. These studies have clearly revealed that members of the trk family are differentially expressed in functionally distinct populations of both developing and mature sensory neurons and, further, have provided evidence consistent with a shift in neurotrophin responsiveness during the development of sensory neurons.

Neurotrophin-3 reverses experimental cisplatin-induced peripheral sensory neuropathy

Cisplatin, a widely used chemotherapeutic agent, induces a sensory neuropathy with selective loss of vibration sense and proprioception. Here we demonstrate that neurotrophin-3 (NT-3), a member of the nerve growth factor family of neurotrophic factors, restored to normal levels the reduced H-reflex-related sensory nerve conduction velocity induced by cisplatin in rats. NT-3 treatment corrected an abnormal cytoplasmic distribution of neurofilament protein in large sensory neurons in dorsal root ganglia and the reduction in the numbers of myelinated fibers in sural nerves caused by cisplatin. The NT-3-dependent reversal of cisplatin neurotoxicity thus suggests the possible use of NT-3 in the treatment of peripheral sensory neuropathy.

Sensory and motor neuron-derived factor. A novel heregulin variant highly expressed in sensory and motor neurons

The heregulin family of polypeptides arise as splice variants from a single gene and share a conserved epidermal growth factor (EGF)-like domain thought to be the major determinant of their biological activities. We report here the cloning of a novel member of this family, termed sensory and motor neuron-derived factor or SMDF, which is highly expressed in sensory and motor neurons in human and rodent species. It contains a C-terminal beta-type EGF-like domain and an unique N-terminal sequence which lacks an Ig-like domain and is distinct from all known heregulin variants. Mammalian cell-expressed SMDF activates tyrosine phosphorylation of a 185-kDa protein in cell lines expressing p185erbB2, indicating that it is biologically active. Analyses of expression patterns suggest that, unlike other heregulin variants, SMDF is expressed mainly in the nervous system. In situ hybridization signals with the unique SMDF sequence probe and with a probe to the conserved EGF-like domain are comparable, suggesting that SMDF is the predominant isoform expressed in sensory and motor neurons. Expression of SMDF is maintained in both adult motor neurons and dorsal root ganglion neurons. These findings suggest that SMDF may mediate biological responses such as Schwann cell proliferation and acetylcholine receptor induction in the peripheral nervous system.

Truncated and catalytic isoforms of trkB are co-expressed in neurons of rat and mouse CNS

Localization of mRNA encoding trkB indicates that two truncated isoforms of trkB, T1trkB and T2trkB, are differentially distributed in the rodent nervous system, and that each of these transcripts is co-expressed with catalytic trkB (TK+trkB) in adult motor neurons. In contrast to the prominent expression of T1trkB by non-neuronal cells, T2trkB expression appeared to be restricted to neurons and demonstrated significant overlap with the pattern of TK+trkB distribution. In developing spinal cord ventral horn, an age-related increase in hybridization was observed for truncated isoforms. These findings suggest that truncated trkB may modulate neuronal responses to neurotrophins which act via trkB.

Human trks: molecular cloning, tissue distribution, and expression of extracellular domain immunoadhesins

Using molecular cloning techniques, human homologs of the known members of the trk family of neurotrophin receptors have been cloned and sequenced. Overall, there is a high degree of similarity between the human sequences and those from other mammals; however, there are differences in splicing patterns. There are two spliced forms of the extracellular domain of trkC in the human, a finding that has not been described in other species. In contrast, fewer spliced forms were detected of the intracellular domains of human trkB and trkC than has been described in other mammals. Northern analysis and in situ hybridization experiments indicate that the human trks are expressed in a similar pattern to that described in other mammals. Expression of the trk extracellular domains as fusion proteins with IgG heavy chain yields soluble molecules that mimic intact trks in their binding specificity and affinity. These soluble chimeras block the biological activity of their cognate neurotrophin(s) in vitro.

GDNF: a potent survival factor for motoneurons present in peripheral nerve and muscle

For survival, embryonic motoneurons in vertebrates depend on as yet undefined neurotrophic factors present in the limb bud. Members of the neurotrophin family are currently the best candidates for such neurotrophic factors, but inactivation of their receptor genes leads to only partial loss of motoneurons, which suggests that other factors are involved. Glial cell line-derived neurotrophic factor (GDNF), originally identified as a trophic factor specific for dopaminergic neurons, was found to be 75-fold more potent than the neurotrophins in supporting the survival of purified embryonic rat motoneurons in culture. GDNF messenger RNA was found in the immediate vicinity of motoneurons during the period of cell death in development. In vivo, GDNF rescues and prevents the atrophy of facial motoneurons that have been deprived of target-derived survival factors by axotomy. GDNF may therefore be a physiological trophic factor for spinal motoneurons. Its potency and specificity in vitro and in vivo also make it a good candidate for treatment of motoneuron disease.

TGF beta 2 and TGF beta 3 are potent survival factors for midbrain dopaminergic neurons

The vertebrate ventral midbrain contains 3-4 x 10(4) dopaminergic neurons that influence motor activity, emotional behavior, and cognition. Recently, glial cell line-derived neurotrophic factor (GDNF) was shown to be a potent survival factor for these dopaminergic neurons in culture. However, many midbrain dopaminergic neurons project to targets that do not express GDNF. We report here that transforming growth factors (TGFs) TGF beta 2 and TGF beta 3, which are distantly related to GDNF, also prevent the death of cultured rat embryonic midbrain dopaminergic neurons at picomolar concentrations. Furthermore, we find that TGF beta 2, TGF beta 3, and GDNF are expressed sequentially as local and target-derived trophic factors and that subpopulations of dopaminergic neurons projecting to distinct targets have access to only one of these factors. These findings are consistent with the idea that GDNF, TGF beta 2, and TGF beta 3 are physiological survival factors for developing midbrain dopaminergic neurons and may have applications as therapeutics for Parkinson's disease, a neurodegenerative disorder of dopaminergic neurons.

Identification and characterization of Batk, a predominantly brain-specific non-receptor protein tyrosine kinase related to Csk

A novel cDNA, brain-associated tyrosine kinase (Batk), was isolated from a rat hippocampal library and appears to encode a new member of the Csk subfamily of non-receptor protein tyrosine kinases, with 52% overall amino acid identity to rat Csk. Batk resembles kinases of the Src family in that it contains a Src homology 2 (SH2) domain and an SH3 domain, followed by a tyrosine kinase domain. Analysis of incompletely spliced Batk cDNAs suggests that the genomic structure of Batk is similar to that of Csk with identical exon/intron boundaries. Batk also shows significant homology (86% overall amino acid identity) to the recently described human megakaryocyte-specific Matk. Although Batk is 41 amino acids shorter than Matk, Southern blot analysis suggests that Batk might be a rat homolog of Matk. Batk is predominantly expressed in the brain, with lower expression in the spleen and undetectable expression in other tissues. In situ hybridization and Northern blot analysis show that Batk is widely distributed throughout the adult brain, being primarily expressed in neurons, including those of the hippocampus and cortex. In contrast, embryos appear to have markedly decreased expression levels. Analysis of postnatal day 1 brain suggests that Batk may be upregulated at birth throughout the brain except in the cerebellum. In view of its homology to Csk, a negative regulator of Src family tyrosine kinases, and its generalized expression in the adult brain, we suggest that Batk may function as a brain-specific regulator of kinases involved in the development and maintenance of the nervous system.

Expression and coexpression of Trk receptors in subpopulations of adult primary sensory neurons projecting to identified peripheral targets

To determine whether neurotrophins act on functionally distinct populations of adult sensory neurons, the distributions of mRNAs for TrkA and tyrosine kinase-containing isoforms of TrkB and TrkC were determined in rat DRG neurons projecting to different peripheral targets. Whereas trkA was expressed by a very high percentage of visceral afferents, trkC was expressed frequently only in muscle afferents. Among cutaneous afferents, the size distributions for trkA- and trkC-positive cells showed little overlap. The percentages and size distributions of cells labeled for the trks argue strongly that almost all trkB-expressing cells must also express trkA or trkC. These results indicate that NGF and NT-3 act on functionally distinct populations of adult sensory neurons and suggest that a sizeable number of small DRG neurons may not respond to neurotrophins via a known Trk in the adult rat.

Developmental expression of binding sites and messenger ribonucleic acid for vascular endothelial growth factor suggests a role for this protein in vasculogenesis and angiogenesis

Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen and angiogenic inducer produced by a variety of cell lines and tissues. As a soluble protein that exhibits a unique target cell specificity for vascular endothelial cells, VEGF has the potential to play an important role in the development of the vascular system. To better understand the role of VEGF in the processes of vasculogenesis and embryonic angiogenesis, patterns of mRNA expression and [125I]VEGF-binding sites were examined in sections of rat embryos and surrounding tissues during the early stages of development. In situ hybridization revealed the most intense hybridization of VEGF mRNA in the giant trophoblast cells and the mesometrium of early postimplantation specimens. In contrast, only low levels of expression were detected in the embryo until later in embryonic development. Possible embryonic targets for this secreted protein, as identified by displaceable [125I] VEGF binding, were found in association with the early egg sac at E8 and evident in hemangioblasts (blood islands) within the yolk sac at E8-E11. In addition, at all stages, binding was observed along the lumina of blood vessels, of both maternal and embryonic origin. These results provide evidence to support the hypothesis that VEGF plays an important role in the normal development of the embryo and supporting tissues. In the presence of ubiquitous and persistent high affinity binding sites on vascular endothelial cells and precursors, the growth of the vascular system may be regulated in early development by regional expression of VEGF by trophoblast and maternally derived cells, and later on by cells within the embryo as they develop their differentiated phenotype.

Inhibition of vascular endothelial growth factor-induced angiogenesis suppresses tumour growth in vivo

The development of new blood vessels (angiogenesis) is required for many physiological processes including embryogenesis, wound healing and corpus luteum formation. Blood vessel neoformation is also important in the pathogenesis of many disorders, particularly rapid growth and metastasis of solid tumours. There are several potential mediators of tumour angiogenesis, including basic and acidic fibroblast growth factors, tumour necrosis factor-alpha and transforming factors-alpha and -beta. But it is unclear whether any of these agents actually mediates angiogenesis and tumour growth in vivo. Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen and an angiogenesis inducer released by a variety of tumour cells and expressed in human tumours in situ. To test whether VEGF may be a tumour angiogenesis factor in vivo, we injected human rhabdomyosarcoma, glioblastoma multiforme or leiomyosarcoma cell lines into nude mice. We report here that treatment with a monoclonal antibody specific for VEGF inhibited the growth of the tumours, but had no effect on the growth rate of the tumour cells in vitro. The density of vessels was decreased in the antibody-treated tumours. These findings demonstrate that inhibition of the action of an angiogenic factor spontaneously produced by tumour cells may suppress tumour growth in vivo.

Expression of vascular endothelial growth factor does not promote transformation but confers a growth advantage in vivo to Chinese hamster ovary cells

Vascular endothelial growth factor (VEGF) is a mitogen with a specificity for endothelial cells in vitro and an angiogenic inducer in vivo. We tested the hypothesis that VEGF may confer on expressing cells a growth advantage in vivo. Dihydrofolatereductase--Chinese hamster ovary cells were transfected with expression vectors which direct the constitutive synthesis of VEGF. Neither the expression nor the exogenous administration of VEGF stimulated anchorage-dependent or anchorage-independent growth of Chinese hamster ovary cells in vitro. However, VEGF-expressing clones, unlike control cells, demonstrated an ability to proliferate in nude mice. Histologic examination revealed that the proliferative lesions were compact, well vascularized, and nonedematous. Ultrastructural analysis revealed that capillaries within the lesions were of the continuous type. These findings indicate that the expression of VEGF may confer on cells the ability to grow in vivo in the absence of transformation by purely paracrine mechanisms. Since VEGF is a widely distributed protein, this property may have relevance for a variety of physiological and pathological proliferative processes.

Vascular endothelial growth factor messenger ribonucleic acid expression in the primate ovary

We studied the distribution of messenger RNA (mRNA) that encodes for vascular endothelial growth factor (VEGF) within the primate ovary by in situ hybridization and Northern analysis to determine if the presence of mRNA for this angiogenic factor is associated with structures within the ovary in which angiogenesis is thought to play a role in development and/or function. In situ hybridization to sections of cynomolgus ovaries with a 35S-labeled antisense RNA probe revealed specific tissue localization within the follicle as well as the corpus luteum, but not stromal tissue. Intense expression of mRNA for VEGF during the late follicular phase was confined to the maturing follicle which, we presume, was destined for ovulation. Hybridization within the corpus luteum exhibited a punctate pattern suggesting that there may be specific cells within the corpus luteum that express mRNA for VEGF. The expression of mRNA for VEGF during the early and late luteal phase of the menstrual cycle was studied by Northern analysis. Messenger RNAs were detectable at approximately 3.7 and 5.0 kb positions in corpora lutea collected during the early luteal phase of the menstrual cycle (days 3-5 postovulation). No hybridization signals were observed with RNA prepared from regressing corpora lutea (1-2 days following the onset of menses). The gonadotropic regulation of the expression of mRNA for VEGF in the corpus luteum was studied by treating monkeys with a potent GnRH antagonist during the midluteal phase of the menstrual cycle. Administration of the antagonist for 1 or 2 days did not alter the expression of mRNA for VEGF in comparison to corresponding controls. However, a 3-day treatment regimen brought about a significant reduction in the levels of mRNA for VEGF (P less than 0.01). These studies demonstrate a development-related expression of mRNA for VEGF in the ovary during the menstrual cycle and are consistent with the hypothesis that VEGF may play important roles in follicle selection and corpus luteum function in primates.

BDNF mRNA is decreased in the hippocampus of individuals with Alzheimer's disease

In recent years, nerve growth factor (NGF) has gained attention as a potential therapeutic agent for Alzheimer's disease (AD). To study the expression of NGF and its homologs, brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3), postmortem samples of hippocampus from AD and control donors were examined by in situ hybridization. Hybridization signal for BDNF, but not NGF or NT-3, was decreased in samples of hippocampus from donors with AD. Decreased transcript abundance of BDNF mRNA in hippocampi of individuals with AD was verified by an RNAase protection assay. These results suggest the possibility that decreased expression of BDNF may contribute to the progression of cell death in AD.

Molecular cloning and expression of a novel adhesion molecule, SC1

SC1, an integral membrane glycoprotein of 100 kd, is uniquely and transiently expressed on spinal cord motoneurons early in development and appears in peripheral neurons and several other tissues during development. SC1 has been purified by immunoaffinity techniques, and SC1 cDNA clones have been obtained by screening an E4 chick embryo phage expression library with a rabbit polyclonal antibody produced against purified SC1. The deduced protein sequence of 588 amino acids consists of a signal peptide, five immunoglobulin-like domains, a transmembrane region, and a short cytoplasmic tail. The sequence is most similar to MUC18, reported as a tumor progression marker in human melanoma. Transfection of SC1 cDNA into mammalian cells leads to cell surface expression of SC1 antigen and a subsequent increase in cell-cell adhesion. SC1 molecules bind to each other via a homophilic adhesion mechanism, independently of calcium or magnesium ions. SC1 may have a role in lateral motor column formation or neurite growth or fasciculation.

Autoradiographic localization of relaxin binding sites in rat brain

Relaxin is a member of the insulin family of polypeptide hormones and exerts its best understood actions in the mammalian reproductive system. Using a biologically active 32P-labeled human relaxin, we have previously shown by in vitro autoradiography specific relaxin binding sites in rat uterus, cervix, and brain tissues. Using the same approach, we describe here a detailed localization of human relaxin binding sites in the rat brain. Displaceable relaxin binding sites are distributed in discrete regions of the olfactory system, neocortex, hypothalamus, hippocampus, thalamus, amygdala, midbrain, and medulla of the male and female rat brain. Characterization of the relaxin binding sites in the subfornical organ and neocortex reveals a single class of high-affinity sites (Kd = 1.4 nM) in both regions. The binding of relaxin to two of the circumventricular organs (subfornical organ and organum vasculosum of the lamina terminalis) and the neurosecretory magnocellular hypothalamic nuclei (i.e., paraventricular and supraoptic nuclei) provides the anatomical and biochemical basis for emerging physiological evidence suggesting a central role for relaxin in the control of blood pressure and hormone release. We conclude that specific, high-affinity relaxin binding sites are present in discrete regions of the rat brain and that the distribution of some of these sites may be consistent with a role for relaxin in control of vascular volume and blood pressure.

Widespread expression of BDNF but not NT3 by target areas of basal forebrain cholinergic neurons

Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) are homologs of the well-known neurotrophic factor nerve growth factor. The three members of this family display distinct patterns of target specificity. To examine the distribution in brain of messenger RNA for these molecules, in situ hybridization was performed. Cells hybridizing intensely to antisense BDNF probe were located throughout the major targets of the rat basal forebrain cholinergic system, that is, the hippocampus, amygdala, and neocortex. Strongly hybridizing cells were also observed in structures associated with the olfactory system. The distribution of NT3 mRNA in forebrain was much more limited. Within the hippocampus, labeled cells were restricted to CA2, the most medial portion of CA1, and the dentate gyrus. In human hippocampus, cells expressing BDNF mRNA are distributed in a fashion similar to that observed in the rat. These findings point to both basal forebrain cholinergic cells and olfactory pathways as potential central targets for BDNF.

Vascular endothelial growth factor is expressed in rat corpus luteum

In the course of the development of the ovarian follicle and differentiation of granulosa cells into corpus luteum (CL), extensive changes in the microvasculature of these structures take place. This suggests the local release of angiogenic factors. In the present work we examined whether a newly described secreted vascular endothelial growth factor (VEGF) is expressed in normal rat ovary by in situ hybridization. Our results demonstrate the expression of VEGF in the CL but not in mural granulosa cells, suggesting a temporal relation between VEGF expression and growth of capillary vessels. The hybridization pattern in the CL was consistent with localization of VEGF message to luteal cells. Expression of VEGF was detected also in cumulus oophorus cells. These findings suggest that VEGF is involved in the process of CL angiogenesis.

Spider toxins selectively block calcium currents in Drosophila

Toxins from spider venom, originally purified for their ability to block synaptic transmission in Drosophila, are potent and specific blockers of Ca2+ currents measured in cultured embryonic Drosophila neurons using the whole-cell, patch-clamp technique. Differential actions of toxins from two species of spiders indicate that different types of Drosophila neuronal Ca2+ currents can be pharmacologically distinguished. Hololena toxin preferentially blocks a non-inactivating component of the current, whereas Plectreurys toxin blocks both inactivating and non-inactivating components. These results suggest that block of a non-inactivating Ca2+ current is sufficient to block neurotransmitter release at Drosophila neuromuscular junction.

Lutropin-choriogonadotropin receptor: an unusual member of the G protein-coupled receptor family

A complementary DNA (cDNA) for the rat luteal lutropin-choriogonadotropin receptor (LH-CG-R) was isolated with the use of a DNA probe generated in a polymerase chain reaction with oligonucleotide primers based on peptide sequences of purified receptor protein. As would be predicted from the cDNA sequence, the LH-CG-R consists of a 26-residue signal peptide, a 341-residue extracellular domain displaying an internal repeat structure characteristic of members of the leucine-rich glycoprotein (LRG) family, and a 333-residue region containing seven transmembrane segments. This membrane-spanning region displays sequence similarity with all members of the G protein-coupled receptor family. Hence, the LH-CG-R gene may have evolved by recombination of LRG and G protein-coupled receptor genes. Cells engineered to express LH-CG-R cDNA bind human choriogonadotropin with high affinity and show an increase in cyclic adenosine monophosphate when exposed to hormone. As revealed by RNA blot analysis and in situ hybridization, the 4.4-kilobase cognate messenger RNA is prominently localized in the rat ovary.

Identification and purification of an irreversible presynaptic neurotoxin from the venom of the spider Hololena curta

A search for potent toxins that inhibit neuronal calcium channels in Drosophila melanogaster has resulted in the identification of a presynaptic neurotoxin from the venom of the hunting spider Hololena curta. Using Drosophila neuromuscular junction as an assay, presynaptic inhibitory activity was purified using gel filtration and reverse-phase HPLC. Data from gel electrophoresis indicate that the toxin is composed of two different subunits of Mr 7000 and 9000. At nanomolar concentrations the toxin produced a complete and long-lasting inhibition of synaptic transmission at the Drosophila larval neuromuscular junction without affecting the amplitudes of the spontaneously occurring miniature junction potentials. The block of transmission produced by the toxin was observed even during the direct depolarization of the motor nerve terminal. These physiological results indicate that the terminal is the site of action for the toxin. Indirect evidence using abnormally excitable Drosophila mutants suggests that the toxin is inhibiting transmitter release by altering the electrical properties of the nerve terminal rather than by interfering with nonelectrical events that may occur subsequent to calcium influx. All of the actions of the Hololena toxin can be explained by a specific and direct effect on presynaptic calcium channels in Drosophila motor neurons.

A deletion truncating the gonadotropin-releasing hormone gene is responsible for hypogonadism in the hpg mouse

Hereditary hypogonadism in the hypogonadal (hpg) mouse is caused by a deletional mutation of at least 33.5 kilobases encompassing the distal half of the gene for the common biosynthetic precursor of gonadotropin-releasing hormone (GnRH) and GnRH-associated peptide (GAP). The partially deleted gene is transcriptionally active as revealed by in situ hybridization histochemistry of hpg hypothalamic tissue sections, but immunocytochemical analysis failed to show the presence of antigen corresponding to any part of the precursor protein.

Immunocytochemical localization in rat brain of a prolactin release-inhibiting sequence of gonadotropin-releasing hormone prohormone

The structure of a precursor protein for gonadotropin-releasing hormone (GnRH) of relative molecular mass 10,000 has recently been deduced from cloned complementary DNA sequences derived from human placental messenger RNA. The 56-amino-acid peptide representing residues 14-69 of this prohormone exhibits potent inhibition of prolactin secretion. To investigate whether the same prohormone is synthesized in mammalian brain and describe the anatomical distribution of the prolactin-inhibiting region of this molecule, we have generated antiserum to a synthetic peptide containing residues 40-53 of the human placental precursor. We report here that a substance recognized by this antibody is present in GnRH-containing neurones of the rat brain and appears to coexist with GnRH in secretory granules of nerve terminals in the median eminence. These results indicate homology between hypothalamic and placental prohormones for GnRH and are consistent with the suggestion elsewhere in this issue that a prolactin-inhibiting factor (PIF) is generated from this prohormone and cosecreted with GnRH by nerve terminals in the median eminence.

A phase II study on the postsurgical management of Stage II malignant melanoma with a Newcastle disease virus oncolysate

A Newcastle disease virus lysate of malignant melanoma cells was examined for its possible value in delaying the progression of malignant melanoma with palpable regional node disease (Stage II) to disseminated melanoma (Stage III). This Phase II study was carried out in a group of 32 patients following therapeutic lymphadenectomy. The patients were not prospectively randomized. In each patient, the viral oncolysate was administered subcutaneously at regular intervals over 3 years. The cumulated progressions to disseminated disease at 1, 2 and 3 years were 6%, 8% and 12% of the study group, respectively. These experienced losses were considerably lower than in the control group and in similar control groups described by other investigators. The results suggest that an oncolysate prepared with Newcastle disease virus is a helpful adjunct to surgery in the management of Stage II malignant melanoma.

Ultrastructural localization of LH-RH-immunoreactive synapses in the hamster accessory olfactory bulb

Electron microscopic immunocytochemistry was used to localize luteinizing hormone-releasing (LH-RH) immunoreactivity within the male golden hamster accessory olfactory bulb. Two LH-RH-immunoreactive fiber populations were identified in the accessory olfactory bulb. A superficial system of immunoreactive axons was localized to the vomeronasal nerve and glomerular layers, and a periventricular system appeared in granule cell and periventricular layers. LH-RH-immunoreactive varicosities were observed to contain large reactive vesicles (80-120 nm) as well as a variable degree of cytoplasmic reaction product. Additionally, small vesicles with unreactive lumens and mitochondria were often present. Intravaricose segments of immunoreactive fibers invariably displayed fewer reactive vesicles than did varicosities. Within both glomerular and periventricular layers, some LH-RH-immunoreactive varicosities were observed to form asymmetric contacts characterized by prominent postjunctional densities. In the glomerular layer, these junctions could be identified as synaptic by several features. The presence of LH-RH-immunoreactivity in presynaptic elements supports a neuromodulatory role for LH-RH. As the accessory olfactory system is critically involved in the initiation of mating behavior of the male golden hamster, LH-RH-immunoreactive synapses in the accessory olfactory bulb may function to regulate reproductive behavior.