Receptors specific for the carboxyl-terminal region of parathyroid hormone on bone-derived cells: determinants of ligand binding and bioactivity

PTH comprises 84 amino acids of which the first 34 are sufficient for full activation of the classical PTH/PTHrP receptor, the type 1 PTH receptor. It is known that multiple carboxyl (C)-terminal fragments of PTH are present in the blood and that they comprise the majority of circulating PTH. C-PTH fragments, previously regarded as by-products of PTH metabolism, are directly secreted by the parathyroid glands or arise from the peripheral cleavage of the intact hormone. Compelling evidence now strongly suggests that these C-PTH fragments mediate biological effects via activation of a receptor that specifically recognizes the C-terminal portion of intact PTH, and this receptor is therefore named the carboxyl-terminal PTH receptor (CPTHR). We have previously reported that osteocytes abundantly express this novel receptor and that its activation is involved in cell survival and communication. Here we report the characterization of determinants of PTH that are required for high-affinity binding to the CPTHR. Using synthetic PTH peptides harboring alanine substitution or truncations, we showed the existence of discrete binding domains and critical residues within the intact hormone. We have furthermore identified eight amino acids within the PTH sequence that play key roles in optimizing the binding affinity of C-PTH fragments to CPTHRs. These include the tripeptide sequence Arg(25)-Lys(26)-Lys(27), the dibasic sequence Lys(53)-Lys(54), and three additional residues within the PTH (55-84) sequence, Asn(57), Lys(65), and Lys(72). Functional analysis of these residues demonstrated a strong correlation between binding affinity and biological effect and points to a potential role of CPTHR activation in regulating bone cell survival.

Helper virus-free HSV-1 vectors packaged both in the presence of VSV G protein and in the absence of HSV-1 glycoprotein B support gene transfer into neurons in the rat striatum

Herpes simplex virus (HSV-1) vectors have potential for gene transfer into quiescent cells, but the gene transfer process could be more efficient. In other vector systems, both the titers and the efficiency of gene transfer have been enhanced by pseudotyping the vector particles with vesicular stomatitis virus (VSV) G protein. In this report, we pseudotyped helper virus-free HSV-1 plasmid vectors with VSV G protein. Packaging was performed in the presence of both VSV G protein and a deletion in an essential HSV-1 glycoprotein, gB. The resulting vector stocks supported gene transfer into both fibroblast and neuronal cell lines. VSV G protein was required for gene transfer because preincubation of these vector stocks with antibodies directed against either VSV G protein or VSV reduced the titer to undetectable levels. Although the titers were lower than those obtained using the unmodified vector system, the titers were not increased by use of chimeric proteins that contain the extracellular domain of VSV G protein and the transmembrane and/or cytoplasmic domains of specific HSV-1 glycoproteins. Also, the titers were not increased by performing the packaging in the presence of deletions in multiple HSV-1 glycoproteins. Nonetheless, pHSVlac pseudotyped with VSV G protein supported gene transfer into striatal neurons in the rat brain. Thus, HSV-1 vectors pseudotyped with VSV G protein may be useful for specific gene transfer studies.

Enhanced auditory reversal learning by genetic activation of protein kinase C in small groups of rat hippocampal neurons

The hippocampus has a central role in specific types of learning, but there is only limited evidence identifying the requisite molecular changes in ensembles of hippocampal neurons. To investigate the role of protein kinase C (PKC) pathways in hippocampal mediated learning, a constitutively active, catalytic domain of rat PKC betaII was delivered into hippocampal dentate granule neurons using a Herpes Simplex Virus (HSV-1) vector. This PKC causes a long-lasting, activation-dependent increase in neurotransmitter release from cultured cells. Activation of PKC pathways in a small percentage (< or =0.26%) of dentate granule neurons was sufficient to enhance rat auditory discrimination reversal learning. The affected neurons altered hippocampal physiology as revealed by elevated NMDA receptor densities in specific hippocampal areas. Thus, these results directly suggest that activation of PKC pathways in a specific hippocampal area alters rat auditory discrimination reversal learning. Because each rat may contain a unique pattern of affected neurons, there appears to be considerable flexibility and/or redundancy in the groups of neurons that can modify learning.

Enhanced reporter gene expression in the rat brain from helper virus-free HSV-1 vectors packaged in the presence of specific mutated HSV-1 proteins that affect the virion

Herpes simplex virus (HSV-1) gene expression is hypothesized to shut off promoters in HSV-1 vectors, but in a helper virus-free HSV-1 vector system, a number of promoters support only short-term expression. Thus, recombinant gene expression remains short-term in the absence of approximately 99% of the HSV-1 genome. To resolve this paradox, we hypothesized that specific HSV-1 proteins that affect the virion can shut off recombinant gene expression. This study evaluated expression from HSV-1 vectors, containing neuronal-specific promoters, that were packaged in the presence of specific mutated HSV-1 proteins that affect the virion. The mutated HSV-1 proteins that were examined included two protein kinases (U(L)13 and U(S)3), the virion host shut-off factor (vhs), the transactivator of immediate early promoters (VP16), and a virion protein that affects RNA metabolism (U(S)11). Helper virus-free packaging could occur in the presence of each mutated protein alone or specific combinations of two or three mutated proteins. In BHK and PC12 cells, vectors packaged in the presence of each mutated protein increased ( approximately 2-fold) the level of expression per cell, and vectors packaged in the presence of specific combinations of mutated proteins supported larger (4-7-fold) increases. In the rat striatum, vectors packaged in the presence of a mutated U(S)3 displayed enhanced gene transfer (13-18-fold increases in the number of cells at 4 days), and vectors packaged in the presence of mutated U(L)13 or VP16 enhanced long-term expression (2 months). Vectors packaged in the presence of mutated vhs or U(S)11 displayed minimal changes in expression.

A tyrosine hydroxylase-neurofilament chimeric promoter enhances long-term expression in rat forebrain neurons from helper virus-free HSV-1 vectors

Helper virus-free herpes simplex virus (HSV-1) plasmid vectors are attractive for neural gene transfer, but a promoter that supports neuronal-specific, long-term expression is required. Although expression from many promoters is unstable, a 6.8-kb, but not a 766-bp, fragment of the tyrosine hydroxylase (TH) promoter supports long-term expression. Thus, 5' upstream sequences in this promoter may enhance expression. In this study, we evaluated expression from vectors that contain 5' upstream sequences from this promoter (-0.5 to -6.8 kb) inserted at the 5' end of either a neurofilament heavy subunit (NF-H) promoter or the cytomegalovirus (CMV) immediate early promoter. The TH-NFH promoter supported expression for 6 months in the striatum, 2 months in the hippocampus, and for 1 month in both perirhinal and postrhinal cortex (the longest time points examined). Expression was targeted to neurons. The enhanced expression may require specific sequences in the TH promoter fragment because replacing this fragment with a similar sized fragment of bacteriophage lambda DNA did not enhance expression. The reverse orientation of the TH promoter fragment also enhanced expression. Insertion of insulators from the chicken beta-globin locus between the TH-NFHlac transcription unit and the vector backbone may support a modest additional enhancement in expression. Other eucaryotic sequences may also enhance expression; a S. cerevisiae (40-kb fragment)-NFH promoter enhanced expression. In contrast, the TH-CMV promoter did not enhance expression. Thus, the TH-NFH promoter may support some physiological studies that require long-term expression in forebrain neurons.

Modest increases in the titers of helper virus-free herpes simplex virus 1 (HSV-1) vectors by packaging in a cell line with inducible expression of HSV-1 VP16 or by treatment with N,N'-hexamethylene-bis-acetamide

A recently developed helper virus-free HSV-1 vector system has potential for both gene therapy and physiological studies, but relatively low vector titers have complicated use of this system. In this report, we explored improving the vector titers by isolating a Vero cell line that uses the tetracycline-regulated promoter system to induce HSV-1 VP16 at the beginning of the packaging procedure. We isolated the required cell line and demonstrated that it supports enhanced expression from a HSV-1 immediate early (IE) promoter. However, use of this cell line in helper virus-free vector packaging results in only a modest, approximately 2-fold increase in the vector titers. Additionally, treating the packaging cells with N,N'-hexamethylene-bis-acetamide (HMBA), which is known to induce HSV-1 IE promoters, also supports only modest increases in the vector titers. These results suggest that the lack of VP16 is not the rate limiting factor in the packaging procedure.

Fifty-one kilobase HSV-1 plasmid vector can be packaged using a helper virus-free system and supports expression in the rat brain

Herpes simplex virus type 1 (HSV-1) plasmid vectors have a number of attractive features for gene transfer into neurons. In particular, the large size of the HSV-1 genome suggests that HSV-1 vectors might be designed to accommodate large inserts. We now report the construction and characterization of a 51 kb HSV-1 plasmid vector. This vector was efficiently packaged into HSV-1 particles using a helper virus-free packaging system. The structure of the packaged vector DNA was verified by both Southern blot and PCR analyses. A vector stock was microinjected into the rat striatum, the rats were sacrificed at 4 days after gene transfer, and numerous X-gal positive striatal cells were observed. This 51 kb vector was constructed using general principles that may support the routine construction of large vectors. Potential applications of such HSV-1 vectors include characterizing large promoter fragments or genomic clones and co-expressing multiple genes.

Improved titers for helper virus-free herpes simplex virus type 1 plasmid vectors by optimization of the packaging protocol and addition of noninfectious herpes simplex virus-related particles (previral DNA replication enveloped particles) to the packaging procedure

A helper virus-free herpes simplex virus type 1 (HSV-1) plasmid vector system has potential for both gene therapy and physiological studies, but relatively low titers have complicated use of this system. In this article, the packaging efficiency was improved by optimizing the packaging protocol and by adding noninfectious HSV-1-related particles, i.e., previral DNA replication enveloped particles (PREPs), during the packaging procedure. PREPs contain many of the tegument proteins that are thought to enhance an HSV-1 infection. Use of both the optimized packaging protocol and the PREPs resulted in an approximately 50-fold increase in the titer, and five different HSV-1 vectors were packaged using this procedure. A purified vector stock (7.8x10(8) infectious vector particles/ml) was microinjected into the striatum, the rats were sacrificed 4 days after gene transfer, and the brains were found to contain an average of approximately 6740 X-Gal-positive striatal cells. This improved packaging procedure may augment use of this vector system.

Diverse stabilities of expression in the rat brain from different cellular promoters in a helper virus-free herpes simplex virus type 1 vector system

Many neural gene transfer studies require both long-term and cell type-specific expression. We have reported a helper virus-free HSV-1 plasmid vector system (Fraefel et al., 1996), and this system supports at least some long-term expression from herpesvirus immediate-early promoters. In this study, we constructed vectors that placed the lacZ reporter gene under the regulation of five different cellular promoters. Vector stocks were microinjected into the midbrain, striatum, or hippocampus; the rats were sacrificed at 4 days to 2 months after gene transfer; and the numbers of X-Gal-positive cells were determined. A 6.8-kb fragment of the rat tyrosine hydroxylase (TH) promoter supported relatively stable expression for up to 2 months and targeted expression to TH-immunoreactive neurons in the substantia nigra pars compacta. The other promoters that were examined were chosen with the goal of obtaining long-term, neuronal-specific expression. At 4 days after gene transfer, a 766-bp fragment of the TH promoter supported expression in cells with neuronal morphology in the midbrain and striatum, consistent with results in transgenic mice. However, expression was absent by 2 weeks. Similarly, at 4 days after gene transfer, a mouse neurofilament heavy subunit promoter supported expression in cells with neuronal morphology in the midbrain, striatum, and hippocampus, but expression was absent by 2 weeks. A rat neuron-specific enolase promoter supported only a low level of expression in cultured neuronal cells, and expression was not detected in the brain. A rat voltage-gated sodium channel promoter supported only a low level of expression in PC12 cells and expression could not be detected in cultured cortical cells. These results demonstrate that different promoters support a wide range of levels and stabilities of expression in this vector system, and the results suggest approaches to improving the stability of long-term expression.

An efficient in vivo recombination cloning procedure for modifying and combining HSV-1 cosmids

A helper virus-free herpes simplex virus type-1 (HSV-1) plasmid vector system developed recently may have applications in gene therapy and basic physiological studies. This system might be improved by mutating specific HSV-1 genes in the packaging system and by creating large vectors. An in vivo recombination cloning procedure is reported that supports the routine manipulation of relatively large DNAs such as the five cosmids that comprise this helper virus-free HSV-1 packaging system. In vivo recombination cloning is carried out by transforming overlapping DNA fragments into a specific RecA+ Escherichia coli, BJ5183. The cloning efficiency was improved by using a modified version of the Hanahan transformation procedure, and the background was lowered by either using vectors with different combinations of ends (5' overhangs, 3' overhangs, blunt ends) or by treating the vector with calf intestinal phosphatase. The range of usable overlap sizes is from 251 bp to 18 kb with 500 bp to 5 kb preferred. This procedure supports the routine construction and mutation of HSV-1 cosmids, by use of up to six different DNA fragments, and the construction of plasmids up to 65 kb in size. This procedure may also have applications to other vector systems and to studies on large viruses.

Genetic analysis of the role of protein kinase C signaling pathways in behaviors by direct gene transfer with HSV-1 vectors

A genetic intervention strategy is described to elucidate the specific biochemical pathways in identified types of neurons that underlie behavioral adaptations. This strategy contains three parts: A Herpes simplex virus (HSV-1) vector is used to obtain localized gene transfer, a cell type-specific promoter is used to target expression to a particular type of neuron, and a constitutively active signal transduction enzyme is expressed to alter neuronal physiology. To enable this approach, a constitutively active protein kinase C (PKC) was developed which causes a long-lasting, activation-dependent increase in neurotransmitter release from cultured sympathetic neurons. This genetic intervention strategy was tested using the nigrostriatal system: Microinjection of HSV-1 vectors that contain the tyrosine hydroxylase promoter targeted expression to dopaminergic nigrostriatal neurons. Expression of the constitutively active PKC in a small percentage of nigrostriatal neurons (approximately 0.1-2%) produced a long-term (> or = 1 month) change in apomorphine-induced rotational behavior, the amount of rotational behavior correlated with the number of affected nigrostriatal neurons, and D2-like dopamine receptor levels were elevated in the striatal regions innervated by the affected nigrostriatal neurons. The strengths and limitations of this genetic intervention strategy are discussed.

Modulation of rat rotational behavior by direct gene transfer of constitutively active protein kinase C into nigrostriatal neurons

The modulation of motor behavior by protein kinase C (PKC) signaling pathways in nigrostriatal neurons was examined by using a genetic intervention approach. Herpes simplex virus type 1 (HSV-1) vectors that encode a catalytic domain of rat PKCbetaII (PkcDelta) were developed. PkcDelta exhibited a constitutively active protein kinase activity with a substrate specificity similar to that of rat brain PKC. As demonstrated in cultured sympathetic neurons, PkcDelta caused a long-lasting, activation-dependent increase in neurotransmitter release. In the rat brain, microinjection of HSV-1 vectors that contain the tyrosine hydroxylase promoter targeted expression to dopaminergic nigrostriatal neurons. Expression of pkcDelta in a small percentage of nigrostriatal neurons (approximately 0.1-2%) was sufficient to produce a long-term (>/=1 month) change in apomorphine-induced rotational behavior. Nigrostriatal neurons were the only catecholaminergic neurons that contained PkcDelta, and the amount of rotational behavior was correlated with the number of affected nigrostriatal neurons. The change in apomorphine-induced rotational behavior was blocked by a dopamine receptor antagonist (fluphenazine). D2-like dopamine receptor density was increased in those regions of the striatum innervated by the affected nigrostriatal neurons. Therefore, this strategy enabled the demonstration that a PKC pathway or PKC pathways in nigrostriatal neurons modulate apomorphine-induced rotational behavior, and altered dopaminergic transmission from nigrostriatal neurons appears to be the affected neuronal physiology responsible for the change in rotational behavior.

An HSV-1 vector containing the rat tyrosine hydroxylase promoter enhances both long-term and cell type-specific expression in the midbrain

A defective herpes simplex virus type one (HSV-1) vector that contains a 6.8-kb fragment of the rat tyrosine hydroxylase promoter (pTHlac-7kb) was examined for its capability to target catecholaminergic cell type-specific expression in the CNS. Cell type-specific expression was assessed by comparison with a control vector (pHSVlac) that uses the HSV-1 immediate early 4/5 promoter to support expression in multiple cell types. In initial experiments comparing expression in catecholaminergic and noncatecholaminergic cell lines, pTHlac-7kb supported a seven- to 20-fold increase in reporter gene expression in catecholaminergic cell lines. Four days after stereotactic injection into the midbrain of adult rats, pTHlac-7kb supported a 10-fold targeting of beta-galactosidase expression to tyrosine hydroxylase-expressing neurons in the substantia nigra pars compacta compared with pHSVlac. Expression from pTHlac-7kb was stably maintained for 6 weeks with no significant changes in the pattern of expression. Long-term expression from pTHlac-7kb was confirmed by RNA and DNA analysis. In contrast, reporter gene expression in the midbrain from pHSVlac decreased approximately 30-fold between 4 days and 6 weeks after gene transfer. Thus, within the context of this HSV-1 vector system, the tyrosine hydroxylase promoter enhanced cell type-specific expression and contributed to stable, long-term expression of a recombinant gene product in neurons. The capability to target recombinant gene expression to catecholaminergic neurons in specific brain areas may be useful for studies on the roles of these neurons in brain physiology and behavior.

Helper virus-free herpes simplex virus-1 plasmid vectors for gene therapy of Parkinson's disease and other neurological disorders

Vectors based on herpes simplex virus type 1 (HSV-1) have potential for gene therapy of neurological disorders. HSV-1 plasmid vectors (amplicons) contain only approximately 1% of the 150-kb HSV-1 genome and have been packaged into virus particles by using a helper virus. We have demonstrated that HSV-1 plasmid vectors which express tyrosine hydroxylase can cause long-term biochemical and behavioral recovery in the 6-hydroxydopamine rat model of Parkinson's disease. Furthermore, we and others have used HSV-1 plasmid vectors which express a wide range of genes that affect neuronal physiology. Because of the pathogenicity of the HSV-1 helper virus, however, the use of this vector system has been limited to studies in animal models or primary cultures of neural cells. Thus, to increase the safety of HSV-1 plasmid vectors, we recently developed a helper virus-free packaging system that may facilitate studies on neuronal physiology and potential therapeutic applications.

Helper virus-free transfer of herpes simplex virus type 1 plasmid vectors into neural cells

Herpes simplex virus type 1 (HSV-1) plasmid vectors have promise for genetic intervention in the brain, but several problems caused by the helper virus have compromised their utility. To develop a helper virus-free packaging system for these vectors, the DNA cleavage/packaging signals were deleted from a set of cosmids that represents the HSV-1 genome. Following cotransfection into cells, this modified cosmid set supported replication and packaging of vector DNA. However, in the absence of the DNA cleavage/packaging signals, the HSV-1 genome was not packaged, and consequently vector stocks were free of detectable helper virus. In the absence of helper virus, the vectors efficiently infected rat neural cells in culture or in the brain with minimal cytopathic effects. beta-galactosidase-positive cells were observed for at least 1 month in vivo, and vector DNA persisted for this period. This system may facilitate studies on neuronal physiology and potential therapeutic applications.

Expression of the calcium-binding protein, parvalbumin, in cultured cortical neurons using a HSV-1 vector system enhances NMDA neurotoxicity

Calcium-binding proteins (CaBPs) are a family of proteins having a unique distribution in the brain and are thought to be important in buffering intracellular calcium. Glutamate neurotoxicity is a process by which the over-activation of glutamate receptors can cause the influx of excessive extracellular calcium and neuronal cell death. It has been proposed that neurons containing CaBP may be more resistant to glutamate neurotoxicity due to their increased ability to buffer calcium. Using a herpes simplex virus-1 (HSV-1) vector system we packaged the CaBP gene, parvalbumin, or the marker gene, beta-galactosidase (beta-gal), correctly in viron particles, which were found upon infection to express mRNA specific to these vectors. PC12 and neocortical cultures showed strong immunohistochemical staining for either beta-gal or parv. The cortical cultures stained positively for endogenous glutamate decarboxylase, a marker for GABAergic neurons, but not for endogenous parvalbumin, indicating that parvalbumin was being expressed ectopically from the HSV-1 vector. Interestingly, the expression of parvalbumin increased cortical culture's susceptibility to N-methyl-D-aspartate-induced neurotoxicity. This increase in neurotoxicity was not due to the wild-type virus or the helper virus which accompanies the packaging of these vectors. We speculate that the ectopic expression of parvalbumin in cortical cultures may be increasing glutamate release which in turn increases cell death.

A method to codetect introduced genes and their products in gene therapy protocols

To monitor the presence of introduced genes and the distribution of the encoded proteins in host tissues after gene transfer, we combined fluorescence in situ hybridization (FISH) and immunohistochemistry in two separate gene therapy paradigms. In brain tissue sections from animals injected with pHSVlac vector, we localized nuclei containing vector DNA both in cells expressing and not expressing beta-galactosidase (beta-gal). This suggests that the efficiency of gene transfer is affected not only by gene delivery, but also by cellular controls on gene expression. In a second paradigm, following myoblast transplantation, we detected donor nuclei in the muscle of a patient with Duchenne's muscular dystrophy. The donor nuclei were either surrounded by host nuclei or apparently fused in the patient's muscle fiber producing dystrophin. The combined FISH and immunohistochemistry assay offers greater sensitivity and more information than currently used polymerase chain reaction and protein detection methods.

Long-term persistence of defective HSV-1 vectors in the rat brain is demonstrated by reactivation of vector gene expression

Wild-type HSV-1 is known to persist indefinitely in neurons in the latent state; however, defective HSV-1 vectors, or amplicons, contain only approximately 1% of the HSV-1 genome and persistence of these HSV-1 vectors has not been studied even semiquantitatively in the adult rat brain. Defective HSV-1 vectors contain both an HSV-1 origin of replication and a packaging site, and in the presence of helper virus can undergo DNA replication and packaging into HSV-1 particles. Our prototype defective HSV-1 vector, pHSVlac, uses the HSV-1 immediate-early (IE) promoter to regulate expression of the Escherichia coli lacZ gene. Using cultured neuronal cells, we have previously shown that expression from pHSVlac can be augmented by superinfection with a helper virus. In this study, pHSVlac was delivered into the adult rat striatum or hippocampus, and 2-3 months after gene transfer we utilized superinfection with several replication-incompetent HSV-1 mutants to reactivate expression from pHSVlac in approximately 30% of the number of cells observed at 4 days after gene transfer. Thus, HSV-1 plasmid vectors can persist for at least 2-3 months in at least approximately 30% of the cells which are initially infected.

Generation of high-titer defective HSV-1 vectors using an IE 2 deletion mutant and quantitative study of expression in cultured cortical cells

Vectors based on herpes simplex virus type 1 (HSV-1) show promise for gene transfer into mammalian cells because of their wide host range, efficient infection and ability to deliver genes to nondividing cells. Defective HSV-1 vectors, or amplicons, are plasmid vectors which are unable to propagate on their own but contain specific HSV-1 sequences that, in the presence of helper virus, support DNA replication and subsequent packaging into virus particles. We compared three replication-incompetent HSV-1 mutants (KOS strain 5dl1.2, strain 17 D30EBA, KOS strain d120) as the helper virus for packaging the prototype defective HSV-1 vector, pHSVlac, which uses the HSV-1 immediate-early (1E) 4/5 promoter to regulate expression of the Escherichia coli lacZ gene. Use of 5dl1.2, which contains a deletion in the IE 2 gene, consistently produced virus stocks that contained a high level of vector, undetectable levels of wild-type HSV-1 and a ratio of vector to helper greater than 1. Virus stocks prepared using 5dl1.2 were superior to those prepared using helper viruses that harbor a deletion in the IE 3 gene, either D30EBA or dl20, and supported more efficient gene transfer than possible with previously published procedures. Lactate dehydrogenase efflux assays in rat cortical cultures showed that 5dl1.2 was no more cytotoxic than either D30EBA or dl20, despite the expression of more viral genes. Rat cortical cultures infected with pHSVlac packaged with either 5dl1.2 or D30EBA were used to quantify the stability of vector expression. Our results show a decrease in the number of cells with detectable levels of beta-galactosidase to 30% of peak levels after one week, irrespective of the helper virus used. However, simultaneous superinfection with 5dl1.2, but not with either D30EBA or dl20, produced a transient increase in the number of cells expressing beta-galactosidase. Superinfection with 5dl1.2 at 9 days after gene transfer increased the number of cells expressing detectable beta-galactosidase back to peak levels, most probably because of reactivation of the IE 4/5 promoter in pHSVlac. These results thus provide the first quantitative demonstration of long-term persistence of defective HSV-1 vectors in neurons.

Regulated release and polarized localization of brain-derived neurotrophic factor in hippocampal neurons

The site and regulation of neurotrophic factor release from neurons is poorly understood. We used a combination of model cell lines and primary culture systems to study the polarity of BDNF sorting and the regulation of its release from hippocampal neurons. Transfection and expression of a human BDNF cDNA in a mouse pituitary cell line, AtT20, resulted in the colocalization of BDNF with the secretory granule marker, chromogranin A. Furthermore, stimulation of these cells with 56 mM KCl or with 5 mM 8-bromo-cAMP increased the release of BDNF approximately 10-to 15-fold within 30 min. To study BDNF release from primary cultures of hippocampal neurons, cells were infected with a defective Herpes Simplex Viral (HSV) vector expressing human BDNF. Depolarizing conditions increased the release of BDNF 5-fold from these cells, further verifying that secretion is regulated. Immunocytochemical analysis using highly specific antibodies determined that endogenous BDNF was predominantly localized to the somatodentritic domain of hippocampal neurons. These findings support the view that BDNF functions as a target-derived signal for afferents to hippocampal pyramidal cells and that it may serve as a regulator of hippocampal plasticity.

A herpes simplex virus-1 vector containing the rat tyrosine hydroxylase promoter directs cell type-specific expression of beta-galactosidase in cultured rat peripheral neurons

A defective herpes simplex virus-1 (HSV-1) vector system was used to study cell type-specific expression of the tyrosine hydroxylase (TH) gene. HSV-1 particles containing 663 bp (pTHlac 663), 278 bp (pTHlac 278), or 181 bp (pTHlac 181) of the rat TH promoter driving E. coli LacZ were used to infect superior cervical ganglia (SCG: TH-expressing tissue) and dorsal root ganglia (DRG:non-TH-expressing tissue) cultures. One day after infection, expression of beta-galactosidase was visualized by X-gal cytochemistry. Following viral transduction with pTHlac 663 at a multiplicity of infection of 0.2, 14.4% of the SCG neurons were X-gal positive whereas only about 0.9% of DRG neurons were X-gal positive. Infection with either pTHlac278 or 181 resulted in 3-fold more X-gal-positive DRG neurons. These results suggest that (i) the defective HSV-1 vector system may be useful in defining regulatory promoter motifs; (ii) 663 bp of the rat TH promoter contains sufficient information for cell type-specific expression in peripheral nervous system neurons; and (iii) sequences between -278 and -663 contain an element(s) that represses gene expression in non-catecholamingeric neurons.

Long-term expression in sensory neurons in tissue culture from herpes simplex virus type 1 (HSV-1) promoters in an HSV-1-derived vector

Amplicons, defective herpes simplex virus type 1 (HSV-1) vectors, were constructed to use four HSV-1 promoters, from the immediate-early (IE) 1 IE 3, IE 4/5, and late glycoprotein C (gC) genes, to regulate expression of the Escherichia coli lacZ gene, encoding beta-galactosidase, and packaged into infectious particles. Infection of sensory neurons in vitro with amplicons containing the IE 1, IE 3, or IE 4/5 promoter resulted in stable long-term expression of beta-galactosidase from 2 to 10 weeks after gene transfer. The number of neurons expressing beta-galactosidase was not changed by treatments previously shown to produce reactivation of latent HSV-1. In addition, the latency-associated transcript was detected in many of the same neurons that expressed beta-galactosidase, indicating that the viral IE promoters in the amplicons can function in the same neurons that harbor latent virus. Delivery of beta-galactosidase protein directly into neurons by microinjection indicated that the half-life for histochemical detection of beta-galactosidase was between 24 and 48 h, suggesting that the persistence of beta-galactosidase histochemical staining cannot be explained by the stability of the reporter protein alone. In contrast to the IE promoters, the gC promoter of the late gene class did not support long-term expression of beta-galactosidase; instead, beta-galactosidase was detected in only a few neurons per culture at 2 weeks after infection, and superinfection with wild-type HSV-1 did not increase the level of expression from the gC promoter. These results suggest that the HSV-1 IE promoters in the amplicons are not subject to the promoter inactivation that occurs with many types of virus vectors and that the IE promoters in the context of the amplicon avoid the promoter inactivation observed from the same promoters in the HSV-1 genome during latency.

An HSV-1 vector expressing tyrosine hydroxylase causes production and release of L-dopa from cultured rat striatal cells

In this report we demonstrate that a defective herpes simplex virus type one (HSV-1) vector can express enzymatically active tyrosine hydroxylase in cultured striatal cells that are thereby converted into L-DOPA-producing cells. A human tyrosine hydroxylase cDNA (form II) was inserted into an HSV-1 vector (pHSVth) and packaged into virus particles using an HSV-1 strain 17 mutant in the immediate early 3 gene (either ts K or D30EBA) as helper virus. Cultured fibroblasts were infected with pHSVth and 1 day later tyrosine hydroxylase immunoreactivity and tyrosine hydroxylase enzyme activity were observed. The tyrosine hydroxylase enzyme activity directed the production of L-DOPA. pHSVth infection of striatal cells in dissociated cell culture resulted in expression of tyrosine hydroxylase RNA and tyrosine hydroxylase immunoreactivity. Release of L-DOPA and low levels of dopamine were observed from cells in pHSVth-infected striatal cultures. Expression of tyrosine hydroxylase and release of catecholamines were maintained for at least 1 week after infection.

Long-term behavioral recovery in parkinsonian rats by an HSV vector expressing tyrosine hydroxylase

One therapeutic approach to treating Parkinson's disease is to convert endogenous striatal cells into levo-3,4-dihydroxyphenylalanine (L-dopa)-producing cells. A defective herpes simplex virus type 1 vector expressing human tyrosine hydroxylase was delivered into the partially denervated striatum of 6-hydroxydopamine-lesioned rats, used as a model of Parkinson's disease. Efficient behavioral and biochemical recovery was maintained for 1 year after gene transfer. Biochemical recovery included increases in both striatal tyrosine hydroxylase enzyme activity and in extracellular dopamine concentrations. Persistence of human tyrosine hydroxylase was revealed by expression of RNA and immunoreactivity.

Rapid and stable gene expression in hippocampal slice cultures from a defective HSV-1 vector

Stable transfer of genetic information into neurons is a powerful strategy to elucidate specific mechanisms of neurophysiology and to develop therapies for neurological disorders. To evaluate the optimal parameters for efficient gene delivery of defective herpes simplex virus type one (HSV-1) vectors into a specific brain region, an HSV-1 vector expressing E. coli beta-galactosidase was used to infect organotypic cultures of hippocampal slices. beta-Galactosidase was expressed as early as 2 h after infection in a dose-dependent manner as measured on immunoblots, and reached a maximum level after approximately 35 h. Expression of the RNA and the antigen was still evident after the longest time sampled (11-12 days), whereas no beta-galactosidase was ever detected in cultured slices infected with a control virus lacking the reporter gene. Hippocampal cells expressing the reporter gene outlined the contour of the neuronal cell body layers in fields CA3 and dentate gyrus; such correspondence was less evident in field CA1. Anatomical, morphological, and immunohistochemical criteria also confirmed that the majority of these infected cells were neurons. beta-Galactosidase was also detected in the somata and processes of infected interneurons. Tests for synaptic pathology associated with virus infection showed no changes in pre- and postsynaptic markers.

Effect of exogenous nerve growth factor on neurotoxicity of and neuronal gene delivery by a herpes simplex amplicon vector in the rat brain

We have previously shown that local destruction of neural tissue by wild-type herpes simplex virus type 1 (HSV-1) is attenuated by intracerebral infusion of nerve growth factor (NGF). To investigate the effect of NGF on the extent of neurolysis and efficacy of neuronal gene transfer mediated by an HSV-1 amplicon vector system in vivo, rats were stereotaxically injected in the striatum with an amplicon preparation, pHSVlac. This amplicon contains the Escherichia coli lacZ gene under the transcriptional control of the HSV-1 immediate early 4/5 promoter and is packaged by an HSV-1 helper virus carrying a deletion in the immediate early 3 gene. Vector injection was followed by continuous intracerebral infusion of NGF-beta (total dose 5 micrograms) or vehicle solution over 7 days. Animals were sacrificed at the end of the 7-day infusion period for histological analysis of the brains. A distinct zone of inflammation and necrosis surrounded the injection site in all vector-inoculated animals. The volume of striatal tissue destruction was significantly smaller in NGF-treated animals (1.27 +/- 0.19 mm3; mean +/- SEM) than in the vehicle-treated controls (2.16 +/- 0.37 mm3; P < 0.05 by t-test). Immunohistochemical staining for HSV and beta-galactosidase (beta-Gal) in vehicle-treated animals revealed that many striatal cells harbored HSV antigens (3,678 +/- 636), but only a small number expressed the reporter gene at 7 days post-injection (294 +/- 60). NGF infusion did not significantly affect the number of HSV-immunoreactive cells (4,224 +/- 618), or the number of cells expressing beta-Gal (330 +/- 72) at this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Transfer of the nerve growth factor gene into cell lines and cultured neurons using a defective herpes simplex virus vector. Transfer of the NGF gene into cells by a HSV-1 vector

Nerve growth factor (NGF) can be expressed in cells by gene transfer using a defective Herpes Simplex virus type 1 (HSV-1) vector. In this report, the defective HSV-1 vector, pHSVngf, is used to infect established cell lines and cultured neurons. Infection of cell lines with pHSVngf results in gene transcription, correct RNA processing, and production of biologically active NGF. Infection of the PC12 neuronal cell line results in the production of biologically active NGF and infection of NGF-dependent neonatal sympathetic neurons in primary culture with pHSVngf leads to neuronal survival in the absence of exogenously-added NGF. NGF expressed by pHSVngf-infected cells does not appear to work through an autocrine intracellular pathway since NGF antibody added to culture media of infected cells could block NGF action. Infection with pHSVngf of cholinergic striatal or septal neurons in dissociated cell culture resulted in an increase in choline acetyltransferase activity. These studies demonstrate the efficacy of defective HSV-1 vectors for delivery and expression of neurotrophin genes in cultured neural cells.

Long-term increases in neurotransmitter release from neuronal cells expressing a constitutively active adenylate cyclase from a herpes simplex virus type 1 vector

Signal-transduction pathways mediate a wide range of short-term changes in the physiology of neuronal systems from invertebrates to mammals. However, examples of long-term changes in neuronal physiology mediated by these pathways have been limited to invertebrate systems. In this report, long-term changes in the physiology of mammalian neurons were studied by using genetic intervention to cause a long-lasting activation of the cAMP pathway. The catalytic domain of yeast adenylate cyclase (cyr), encoding a constitutive enzyme activity, was expressed in neuronal cells infected with a defective herpes simplex virus vector (pHSVcyr). In PC-12 cells infected with pHSVcyr, increases were seen in cAMP levels, protein kinase A activity, protein phosphorylation, phosphorylation of the tyrosine hydroxylase protein kinase A site (Ser40), and catecholamine release. Infection of sympathetic neurons with pHSVcyr increased cAMP levels, protein phosphorylation, and catecholamine release. Yeast adenylate cyclase immunoreactivity and elevated cAMP levels were localized to the cell bodies of sympathetic neurons. The increase in neurotransmitter release was both Ca(2+)- and activity-dependent and persisted for at least 1 week after infection of the sympathetic neurons, suggesting that sustained physiological activation of the cAMP pathway may mediate long-term changes in the neuronal physiology of mammalian systems.

HSV-1 vector-mediated gene transfer of the human nerve growth factor receptor p75hNGFR defines high-affinity NGF binding

A series of recombinant herpes simplex virus (HSV-1) vectors have been constructed that encode either the full-length cDNA of the human p75 NGF receptor (p75hNGFR) or truncated forms of the receptor. Infection of cultured fibroblast cells with viral stocks results in abundant expression of all three cDNAs, as detected by affinity cross-linking, immunoblot analysis, and equilibrium binding. Furthermore, viral infection of primary neuronal cultures gives easily detectable p75 expression by immunofluorescence and affinity cross-linking. When p75 was introduced by viral infection into fibroblast cells expressing the trk proto-oncogene, a new binding site was created, consistent with high-affinity NGF binding. This site is not created by the coexpression of truncated forms of p75 that lack either the extracellular ligand binding domain or the cytoplasmic domain of the receptor, suggesting that both of these regions of the receptor are required for the formation of the high-affinity NGF binding site. Hence, these HSV-1 vectors give rise to appropriate NGF receptor binding after viral infection. The application of these HSV-1 constructs to primary neuronal culture and in vivo models of p75NGFR function is discussed.

Herpesviruses: expression of genes in postmitotic brain cells

Gene transfer into neural cells in the adult mammalian brain using vectors derived from the herpes simplex virus HSV-1 has great promise both for elucidating neuronal physiology and brain mechanisms, and for gene therapy of neurological diseases. Two kinds of HSV-1 vectors are being explored: first, defective HSV-1 vectors are small plasmids containing essential HSV-1 cis-acting functions that use HSV-1 mutants as helper virus for packaging; and second, vectors that contain a recombinant gene inserted into the HSV-1 genome. Recently, several genes that alter neuronal physiology have been expressed from defective HSV-1 vectors, both in cultured neurons and in vivo.

Expression of nerve growth factor in vivo from a defective herpes simplex virus 1 vector prevents effects of axotomy on sympathetic ganglia

Sympathetic neurons in the superior cervical ganglion (SCG) of adult rats depend on target-derived nerve growth factor (NGF) for maintenance of tyrosine hydroxylase (TH) levels and the noradrenergic neurotransmitter system. Axotomy of a SCG results in NGF deprivation, causing a decline in TH activity; continuous local application of NGF can prevent this decline in TH activity. We now report that injection of a defective herpes simplex virus 1 vector that expresses NGF (pHSVngf) into a SCG can prevent the decline in TH activity that follows axotomy. SCG of adult rats were injected with either pHSVngf virus or pNFlac virus, which expresses Escherichia coli beta-galactosidase. Analysis of RNA from pHSVngf-infected SCG indicated that the NGF gene was efficiently transcribed and processed. Furthermore, 4 days after pHSVngf injection animals underwent axotomy of the virus-injected SCG. After another 10 days, animals were sacrificed and both the injected-axotomized and contralateral control ganglia were assayed for TH activity. Axotomy of SCG injected with pNFlac virus produced a 50% decline in TH activity relative to control ganglia (P = 0.02). In contrast, SCG injected with pHSVngf virus did not show a decline in TH activity following axotomy; instead, these ganglia manifested an 18% increase in TH levels relative to control ganglia. These data demonstrate that herpes simplex virus 1 vectors can be used to modify neuronal physiology in vivo; specifically, expression of a critical gene product by neural cells that do not normally produce it has potential applications for gene therapy.

Molecular analysis of neuronal physiology by gene transfer into neurons with herpes simplex virus vectors

A genetic analysis of mammalian neuronal physiology might now be possible due to the development of defective herpes simplex virus vectors, which allow gene transfer directly into mature neurons, in culture or in the adult brain. Genetically altered proteins that play critical roles in neuronal physiology, including those responsible for the generation of action potentials, synthesis and release of neurotransmitters, and signal transduction enzymes, can now be stably expressed in neurons. The effect of such altered proteins on neuronal physiology can therefore be examined, using the tools of modern neuroscience. Genetic manipulation is biochemically specific and stable, and can be targeted both to a particular cell type and to a particular subregion of the cell to yield insights into the molecular basis for specific brain functions.

Molecular analysis of the function of the neuronal growth-associated protein GAP-43 by genetic intervention

GAP-43 is a presynaptic membrane phosphoprotein that has been implicated in both the development and the modulation of neural connections. The availability of cDNA clones for GAP-43 makes it possible to examine with greater precision its role in neuronal outgrowth and physiology. We used Northern blots and in situ hybridization with GAP-43 antisense RNA probes to show that GAP-43 is expressed selectively in associative regions of the adult brain. Immunocytochemical analyses showed alterations in the pattern of GAP-43 expression in the hippocampus during reactive synaptogenesis following lesions of the perforant pathway. Genetic intervention methodology was used to analyze the molecular nature of GAP-43 involvement in synaptic plasticity. GAP-43-transfected PC12 cells displayed an enhanced response to nerve growth factor, suggesting that GAP-43 may be directly involved in neurite extension and in the modulation of the neuronal response to extrinsic trophic factors. Studies of PC12 cell transfectants, in which the synthesis of GAP-43 was blocked by expression of GAP-43 antisense RNA, showed that evoked dopamine release was significantly attenuated in these cells. The use of gene transfer into neurons with the HSV-1 vector is presented as a method of analyzing the interaction of GAP-43 with signal transduction systems during neurotransmitter release.

Influence of the helper virus on expression of beta-galactosidase from a defective HSV-1 vector, pHSVlac

Defective herpes simplex virus type 1 (HSV-1) vectors can deliver genes into both mitotic and postmitotic cells, including neurons and these vectors, therefore, have great potential use. pHSVlac, the prototype HSV-1 vector, expresses the E. coli Lac Z gene from the HSV-1 immediate early 4/5 promoter. pHSVlac can stably express beta-galactosidase in a range of mammalian cell lines and in neurons from throughout the nervous system, both in culture and in the adult rat brain. Thus, HSV-1 vectors may be useful for studying HSV-1 latency, neuronal physiology, and performing gene therapy for neurological conditions. A virus stock of pHSVlac consists of identical HSV-1 particles containing either pHSVlac DNA or the HSV-1 helper virus DNA. Thus, a cell can be infected with the pHSVlac virus, the helper virus, or both; consequently, it is important to determine if the helper virus influences the behavior of pHSVlac. The effect of the helper virus on expression of beta-galactosidase from pHSVlac was investigated: it was demonstrated first, that pHSVlac can be efficiently packaged into HSV-1 virus particles using each of five HSV-1 temperature sensitive (ts) mutants as helper virus. Second, pHSVlac grown with each of the five HSV-1 ts mutants expressed high levels of beta-galactosidase. Third, pHSVlac grown with HSV-1 strain 17 ts K as helper virus expresses the same amount of beta-galactosidase in the absence or presence of ts K. Thus, pHSVlac can efficiently express a gene independent of the HSV-1 helper virus.

A system, using neural cell lines, to characterize HSV-1 vectors containing genes which affect neuronal physiology, or neuronal promoters

Among the potential uses of defective herpes simplex virus (HSV-1) vectors are to study neuronal physiology, neuronal gene regulation, and to perform gene therapy of neuronal diseases. The prototype HSV-1 vector, pHSVlac, stably expresses Escherichia coli beta-galactosidase from the HSV-1 immediate early (IE) 4/5 promoter in cultured rat peripheral and CNS neurons, and in neurons in the adult rat brain. The LacZ gene and the IE 4/5 promoter in pHSVlac can be replaced with genes which affect neuronal physiology or cellular promoters, respectively. A system is required to characterize these HSV-1 vectors; cultured neurons, a mixture of different kinds of neurons and glia, cannot be used. In contrast, neural cell lines represent a homogenous population of neural cells available in virtually unlimited quantities. A system, using neural cell lines, to characterize HSV-1 vectors carrying other genes or promoters is now reported: First, 4 assays are described to detect HSV-1 vector DNA, RNA transcribed from the vector, and to quantitate beta-galactosidase expression. Second, 8 cell lines derived from rodents, primates, and humans were infected with pHSVlac virus and shown to express beta-galactosidase. The cell lines tested included adrenergic and cholinergic mouse neuroblastoma cells, rat pheochromocytoma cells, rodent pituicytes, and human neuroblastoma cells. Infection of these cell lines should prove useful for characterizing HSV-1 vectors with molecular and biochemical assays. Third, differentiated rat pheochromocytoma and mouse neuroblastoma cells, which resemble neurons, were infected with pHSVlac virus and shown to stably express beta-galactosidase. Infection of these cells should be useful for determining the effect of various HSV-1 vectors on neuronal physiology. Thus, HSV-1 vectors containing various genes or promoters can be characterized using the system described in this study.

An efficient deletion mutant packaging system for defective herpes simplex virus vectors: potential applications to human gene therapy and neuronal physiology

We have previously described a defective herpes simplex virus (HSV-1) vector system that permits the introduction of virtually any gene into nonmitotic cells. pHSVlac, the prototype vector, stably expresses Escherichia coli beta-galactosidase from a constitutive promoter in many human cell lines, in cultured rat neurons from throughout the nervous system, and in cells in the adult rat brain. HSV-1 vectors expressing other genes may prove useful for studying neuronal physiology or performing human gene therapy for neurological diseases, such as Parkinson disease or brain tumors. A HSV-1 temperature-sensitive (ts) mutant, ts K, has been used as helper virus; ts mutants revert to wild type. In contrast, HSV-1 deletion mutants essentially cannot revert to wild type; therefore, use of a deletion mutant as helper virus might permit human gene therapy with HSV-1 vectors. We now report an efficient packaging system for HSV-1 vectors using a deletion mutant, D30EBA, as helper virus; virus is grown on the complementing cell line M64A. pHSVlac virus prepared using the deletion mutant packaging system stably expresses beta-galactosidase in cultured rat sympathetic neurons and glia. Both D30EBA and ts K contain a mutation in the IE3 gene of HSV-1 strain 17 and have the same phenotype; therefore, changing the helper virus from ts K to D30EBA does not alter the host range or other properties of the HSV-1 vector system.

Infection of cultured central nervous system neurons with a defective herpes simplex virus 1 vector results in stable expression of Escherichia coli beta-galactosidase

We have developed a defective herpes simplex virus (HSV) vector system that permits the introduction of virtually any gene into mammalian central nervous system neurons. The prototype vector, pHSVlac, contains a transcription unit that places the Escherichia coli lacZ gene under the control of the HSV-1 immediate early 4/5 promoter. pHSVlac was propagated using the HSV-1 temperature-sensitive mutant ts K as helper virus. Infection of rat neurons in primary culture derived from various regions throughout the central nervous system, including spinal cord, cerebellum, thalamus, basal ganglia, hippocampus, occipital cortex, temporal cortex, and frontal cortex, resulted in stable expression of high levels of beta-galactosidase for at least 2 weeks, without cell damage. Since other genes can be expressed from pHSVlac, HSV-1 vectors may prove useful for delivery of genes into central nervous system neurons for studies on nervous system physiology or to perform gene therapy for neurological conditions.

Expression of the E. coli Lac Z gene from a defective HSV-1 vector in various human normal, cancer-prone and tumor cells

Introducing foreign genetic material into human cells is essential for the elucidation of the function of various human genes and has potential use in the treatment of human diseases by gene therapy. In this study we demonstrate that a defective herpes simplex virus type 1 vector, pHSVlac, can effectively transfer and express the Escherichia coli Lac Z gene in a variety of exponential and quiescent human cells. The human cells tested included representative cells derived from cancer-prone patients that presumably have various DNA repair deficiencies.

A defective HSV-1 vector expresses Escherichia coli beta-galactosidase in cultured peripheral neurons

A defective herpes simplex virus 1 (HSV-1) vector, pHSVlac, has been developed that contains a transcription unit that places the Escherichia coli lacZ gene under the control of the HSV-1 immediate early 4/5 promoter. The vector pHSVlac was propagated with the HSV-1 temperature-sensitive mutant ts K as helper virus. Infection of neurons from rat superior cervical ganglia and dorsal root ganglia in primary culture resulted in stable expression of high levels of beta-galactosidase without cell death. These HSV-1 vectors should be useful for introducing genes into postmitotic cells, such as neurons, in vitro and in vivo.

A defective HSV-1 vector expresses Escherichia coli beta-galactosidase in cultured peripheral neurons

A defective herpes simplex virus 1 (HSV-1) vector, pHSVlac, has been developed that contains a transcription unit that places the Escherichia coli lacZ gene under the control of the HSV-1 immediate early 4/5 promoter. The vector pHSVlac was propagated with the HSV-1 temperature-sensitive mutant ts K as helper virus. Infection of neurons from rat superior cervical ganglia and dorsal root ganglia in primary culture resulted in stable expression of high levels of beta-galactosidase without cell death. These HSV-1 vectors should be useful for introducing genes into postmitotic cells, such as neurons, in vitro and in vivo.

A UGA termination suppression tRNATrp active in rabbit reticulocytes

A tRNATrp was purified from rabbit reticulocytes which suppresses the UGA termination codon of beta-haemoglobin mRNA. Evidence is presented that the beta-haemoglobin readthrough protein is found in reticulocyte translations and intact cells. Some natural readthrough proteins perform essential functions; they are synthesised through suppression of UGA or UAG but not UAA termination codons.