Gene transfer of calbindin D28k cDNA via herpes simplex virus amplicon vector decreases cytoplasmic calcium ion response and enhances neuronal survival following glutamatergic challenge but not following cyanide

Sexually Dimorphic Formation of the Preoptic Area and the Bed Nucleus of the Stria Terminalis by Neuroestrogens

Testicular androgens during the perinatal period play an important role in the sexual differentiation of the brain of rodents. Testicular androgens transported into the brain act via androgen receptors or are the substrate of aromatase, which synthesizes neuroestrogens that act via estrogen receptors. The latter that occurs in the perinatal period significantly contributes to the sexual differentiation of the brain. The preoptic area (POA) and the bed nucleus of the stria terminalis (BNST) are sexually dimorphic brain regions that are involved in the regulation of sex-specific social behaviors and the reproductive neuroendocrine system. Here, we discuss how neuroestrogens of testicular origin act in the perinatal period to organize the sexually dimorphic structures of the POA and BNST. Accumulating data from rodent studies suggest that neuroestrogens induce the sex differences in glial and immune cells, which play an important role in the sexually dimorphic formation of the dendritic synapse patterning in the POA, and induce the sex differences in the cell number of specific neuronal cell groups in the POA and BNST, which may be established by controlling the number of cells dying by apoptosis or the phenotypic organization of living cells. Testicular androgens in the peripubertal period also contribute to the sexual differentiation of the POA and BNST, and thus their aromatization to estrogens may be unnecessary. Additionally, we discuss the notion that testicular androgens that do not aromatize to estrogens can also induce significant effects on the sexually dimorphic formation of the POA and BNST.

Protective effects of calbindin‑D28K on the UVB radiation‑induced apoptosis of human lens epithelial cells

Calbindin-D28K (Calb1) may protect human lens epithelial cells (HLECs) from apoptosis, which is a process resulting in individual cell death. The protective effects of Calb1 may be attributed to buffering high concentrations of Ca²⁺. The present study investigated the mechanisms through which Calb1 protects SRA01/04 cells (a human lens epithelial cell line) against apoptosis induced by ultraviolet B (UVB) exposure. Cells transfected with a lentivirus overexpressing Calb1 and control cells were treated with 40 µW/cm² irradiation for 15 min and then cultured for 24 h. The changes in intracellular Ca²⁺ were detected by colorimetry, and the protein expression levels of Bad, Bcl-2 and caspase-12 were measured by western blot analysis. The intracellular Ca²⁺ concentration of control HLECs increased significantly following UVB irradiation, whereas in Calb1-overexpressing cells, the Ca²⁺ levels remained steady. In the control cells, the expression of Bad and caspase-12 was upregulated, and that of Bcl-2 was down-regulated. Notably, during UVB radiation-induced apoptosis, the overexpression of Calb1 inhibited cell death, resulting in the decreased expression of Bad and caspase-12, and in the upregulated expression of Bcl-2. These results suggested that Calb1 inhibited the upregulation of genes involved in apoptosis. The siRNA-mediated knockdown of Calb1 resulted in increased rates of UVB radiation-induced apoptosis, the increased expression of Bad and caspase-12, and the decreased expression of Bcl-2, further demonstrating that Calb1 may mediate UVB radiation-mediated apoptosis by regulating Ca²⁺. On the whole, the findings of the present study indicate that UVB exposure can lead to an imbalance in the intracellular Ca²⁺ homeostasis in HLECs and that Calb1 protein exerts a negative effect on the expression of pro-apoptotic genes in HLECs. Calb1 may thus inhibit the UVB radiation-induced apoptosis of HLECs by regulating Ca²⁺.

Calcium-Binding Proteins as Determinants of Central Nervous System Neuronal Vulnerability to Disease

Neuronal subpopulations display differential vulnerabilities to disease, but the factors that determine their susceptibility are poorly understood. Toxic increases in intracellular calcium are a key factor in several neurodegenerative processes, with calcium-binding proteins providing an important first line of defense through their ability to buffer incoming calcium, allowing the neuron to quickly achieve homeostasis. Since neurons expressing different calcium-binding proteins have been reported to be differentially susceptible to degeneration, it can be hypothesized that rather than just serving as markers of different neuronal subpopulations, they might actually be a key determinant of survival. In this review, we will summarize some of the evidence that expression of the EF-hand calcium-binding proteins, calbindin, calretinin and parvalbumin, may influence the susceptibility of distinct neuronal subpopulations to disease processes.

Herpes simplex virus type 1-based amplicon vectors for fundamental research in neurosciences and gene therapy of neurological diseases

Somatic manipulation of the nervous system without the involvement of the germinal line appears as a powerful counterpart of the transgenic strategy. The use of viral vectors to produce specific, transient and localized knockout, knockdown, ectopic expression or overexpression of a gene, leads to the possibility of analyzing both in vitro and in vivo molecular basis of neural function. In this approach, viral particles engineered to carry transgenic sequences are delivered into discrete brain regions, to transduce cells that will express the transgenic products. Amplicons are replication-incompetent helper-dependent vectors derived from herpes simplex virus type 1 (HSV-1), with several advantages that potentiate their use in neurosciences: (1) minimal toxicity: amplicons do not encode any virus proteins, are neither toxic for the infected cells nor pathogenic for the inoculated animals and elicit low levels of adaptive immune responses; (2) extensive transgene capacity to carry up to 150-kb of foreign DNA; i.e., entire genes with regulatory sequences could be delivered; (3) widespread cellular tropism: amplicons can experimentally infect several cell types including glial cells, though naturally the virus infects mainly neurons and epithelial cells; (4) since the viral genome does not integrate into cellular chromosomes there is low probability to induce insertional mutagenesis. Recent investigations on gene transfer into the brain using these vectors, have focused on gene therapy of inherited genetic diseases affecting the nervous system, such as ataxias, or on neurodegenerative disorders using experimental models of Parkinson's or Alzheimer's disease. Another group of studies used amplicons to investigate complex neural functions such as neuroplasticity, anxiety, learning and memory. In this short review, we summarize recent data supporting the potential of HSV-1 based amplicon vector model for gene delivery and modulation of gene expression in primary cultures of neuronal cells and into the brain of living animals.

Changes in transcript and protein levels of calbindin D28k, calretinin and parvalbumin, and numbers of neuronal populations expressing these proteins in an ischemia model of rat retina

Excessive calcium is thought to be a critical step in various neurodegenerative processes including ischemia. Calbindin D28k (CB), calretinin (CR), and parvalbumin (PV), members of the EF-hand calcium-binding protein family, are thought to play a neuroprotective role in various pathologic conditions by serving as a buffer against excessive calcium. The expression of CB, PV and CR in the ischemic rat retina induced by increasing intraocular pressure was investigated at the transcript and protein levels, by means of the quantitative real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry. The transcript and protein levels of CB, which is strongly expressed in the horizontal cells in both normal and affected retinas, were not changed significantly and the number of CB-expressing horizontal cells remained unchanged throughout the experimental period 8 weeks after ischemia/reperfusion injury. At both the transcript and protein levels, however, CR, which is strongly expressed in several types of amacrine, ganglion, and displaced amacrine cells in both normal and affected retinas, was decreased. CR-expressing ganglion cell number was particularly decreased in ischemic retinas. Similar to the CR, PV transcript and protein levels, and PV-expressing AII amacrine cell number were decreased. Interestingly, in ischemic retinas PV was transiently expressed in putative cone bipolar cell types possibly those that connect with AII amacrine cells via gap junctions. These results suggest that these three calcium binding proteins may play different neuroprotective roles in ischemic insult by their ability to buffer calcium in the rat retina.

Parvalbumin-, calbindin-, and calretinin-immunoreactive hippocampal interneuron density in autism

BACKGROUND

There has been a long-standing interest in the possible role of the hippocampus in autism and both postmortem brain and neuroimaging studies have documented varying abnormalities in this limbic system structure.

AIMS

This study investigates the density of subsets of hippocampal interneurons, immunostained with the calcium binding proteins, calbindin (CB), calretinin (CR) and parvalbumin (PV) to determine whether specific subpopulations of interneurons are impacted in autism.

MATERIALS AND METHODS

Unbiased stereological techniques were used to quantify the neuronal density of these immunoreactive subpopulations of gamma-aminobutyric acid-ergic (GABAergic) interneurons analyzed in the CA and subicular fields in postmortem brain material obtained from five autistic and five age-, gender- and postmortem interval-matched control cases.

RESULTS

Results indicate a selective increase in the density of CB-immunoreactive interneurons in the dentate gyrus, an increase in CR-immunoreactive interneurons in area CA1, and an increase in PV-immunoreactive interneurons in areas CA1 and CA3 in the hippocampus of individuals with autism when compared with controls.

DISCUSSION/CONCLUSIONS

Although our sample size is small, these findings suggest that GABAergic interneurons may represent a vulnerable target in the brains of individuals with autism, potentially impacting upon their key role in learning and information processing. These preliminary findings further suggest the need for future more expanded studies in a larger number of postmortem brain samples from cases of autism and controls.

HSV-1 amplicon vectors: a promising and versatile tool for gene delivery

Amplicons are defective and non-integrative vectors derived from herpes simplex virus type 1. They carry no virus genes in the vector genome and are, therefore, not toxic to the infected cells or pathogenic for the transduced organisms, making these vectors safe. In addition, the large transgenic capacity of amplicons, which allow delivery of < or = 150 Kbp of foreign DNA, make these vectors one of the most powerful, interesting and versatile gene delivery platforms. Here, the authors present recent technological developments that have significantly improved and extended the use of amplicons, both in cultured cells and in living organisms. In addition, this review illustrates the many possible applications that are presently being developed with amplicons and discuss the many difficulties still pending to be solved in order to achieve stable and physiologically regulated transgenic expression.

Pretreatment with PTD-calbindin D 28k alleviates rat brain injury induced by ischemia and reperfusion

Calcium toxicity remains the central focus of ischemic brain injury. Calcium channel antagonists have been reported to be neuroprotective in ischemic animal models but have failed in clinical trials. Rather than block the calcium channels, calbindin proteins can buffer excessive intracellular Ca2+, and as a result, maintain the calcium homeostasis. In the present study, we investigated the effect of calbindin D 28k (CaBD) in ischemic brain using the novel technique protein transduction domain (PTD)-mediated protein transduction. We generated PTD-CaBD in Escherichia coli, tested its biologic activity in N-methyl-D-aspartate (NMDA)- and oxygen-glucose deprivation (OGD)-induced hippocampal injury models, and examined the protection of the fusion protein using a rat brain focal ischemia model. Infarct volume was determined using 2,3,5-triphenyl-tetrazolium chloride staining; neuronal injury was examined using terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) staining and cleaved caspase-3 assay. The results showed that the PTD-CaBD was efficiently delivered into Cos7 cells, hippocampal slice cells, and brain tissue. Pretreatment with PTD-CaBD decreased intracellular free calcium concentration and reduced cell death in NMDA- or OGD-exposed hippocampal slices (P<0.05). Intraperitoneal administration of PTD-CaBD before transient middle cerebral artery occlusion decreased brain infarct volume (280+/-47 versus 166+/-70 mm3, P<0.05), and improved neurologic outcomes compared with the control. Further studies showed that, compared with the control animals, PTD-CaBD decreased TUNEL (58%+/-7% versus 29%+/-3%, P<0.05)- and cleaved caspase-3 (62+/-4/field versus 31+/-6/field, P<0.05)-positive cells in the ischemic boundary zone. These results indicate that systemic administration of PTD-CaBD could attenuate ischemic brain injury, suggesting that PTD-mediated protein transduction might provide a promising and effective approach for the therapies of brain diseases, including cerebral ischemia.

Novel antiseizure drug mechanisms

The amount of new knowledge being generated regarding brain mechanisms in general, and epileptic mechanisms in particular, is enormous. Anticonvulsant drugs are ineffective in approximately a third of people with epilepsy. To our knowledge, strategies for preventing epilepsy after an initial insult are nonexistent. In this review, we briefly examine some recent novel concepts for preventing seizures, which might lead to enhanced anticonvulsant drug therapy. We start with some known seizure mechanisms that have yet to yield widely used anticonvulsant drugs, including potassium channels, chloride cotransporters, extracellular space constriction, gap junctions and magnesium. Pharmacoresistance is then discussed, focusing on the upregulation of drug-resistance proteins (a concept with significant therapeutic appeal) and the drug-target hypothesis. Two further areas that hold great promise for future therapeutics are sex hormones and inflammatory processes. The genetics of epilepsy are currently being elaborated, providing potential novel anticonvulsant targets. Prevention being better than a cure, we discuss epileptogenesis and its treatment. Given the astounding progress of neuroscience research, one hopes for many new therapeutics for our intractable epileptic patients.

Calbindin D-28 and microtubule-associated protein-2: their use as sensitive immunohistochemical markers of cerebellar neurotoxicity in a regulatory toxicity study

The aim of this study was to develop an immunohistochemical (IHC) method for calbindin D-28 (CB-28) and microtubule-associated protein-2 (MAP-2) and evaluate their expression as markers in the detection, characterisation and grading of unexpected cerebellar toxicity in the rat. High power examination of H&E-stained brain sections of treated rats 2 days following a single oral dose of a novel compound revealed irregular vacuolation of the molecular layer and Purkinje cell degeneration. Animals killed after 14 days recovery showed Purkinje cell degeneration but vacuolation of the molecular layer was absent. In control animals, CB-28 and MAP-2 expression was high in Purkinje cell dendrites and cell bodies in the molecular layer. In treated animals, low power examination revealed loss of CB-28 and MAP-2 expression in degenerating neurons arranged in parasagittal stripes within the vermis. This is the first description of successful use of these two markers in a regulatory toxicity study using FFPE brain. In particular, CB-28 provides a sensitive method for characterising CNS toxicity which can be detected at low power enabling easier detection, screening and grading of neurotoxicity.

Simultaneous glutamate and GABA(A) receptor agonist administration increases calbindin levels and prevents hippocampal damage induced by either agent alone in a model of perinatal brain injury

Perinatal brain injury is associated with the release of amino acids, principally glutamate and GABA, resulting in massive increases in intracellular calcium and eventual cell death. We have previously demonstrated that independent administration of kainic acid (KA), an AMPA/kainate receptor agonist, or muscimol, a GABA(A) receptor agonist, to newborn rats results in hippocampal damage [Hilton, G.D., Ndubuizu, A., and McCarthy, M.M., 2004. Neuroprotective effects of estradiol in newborn female rat hippocampus. Dev. Brain Res. 150, 191-198; Hilton, G. D., Nunez, J.L. and McCarthy, M.M., 2003. Sex differences in response to kainic acid and estradiol in the hippocampus of newborn rats. Neuroscience. 116, 383-391; Nunez, J.L. and McCarthy, M.M., 2003. Estradiol exacerbates hippocampal damage in a model of preterm infant brain injury. Endocrinology. 144, 2350-2359; Nunez, J.L., Alt, J.J. and McCarthy, M.M., 2003. A new model for prenatal brain damage. I. GABA(A) receptor activation induces cell death in developing rat hippocampus. Exp. Neurol. 181, 258-269]. We now report that KA or muscimol alone administered to immature hippocampal neurons in culture induces significant cell death as evidenced by TUNEL assay. Surprisingly, simultaneous administration of equimolar quantities of these two agonists blocks the effect of either one alone. Moreover, treatment of newborn pups results in less damage compared to either muscimol or KA alone. We further observed that immunoreactivity for the calcium-binding protein, calbindin D(28K), is increased in the brains of pups simultaneously administered KA and muscimol as compared to either alone.

Ketogenic diet increases calbindin-D28k in the hippocampi of male ICR mice with kainic acid seizures

The ketogenic diet (KD) increased the expression of calbindin-D(28k) (CB) in the interneurons of the hippocampus compared with the normal diet (ND)-fed mice. Also, 2 days after kainic acid (KA) administration, numerous CB-expressing astrocytes were found in the KD-fed mice compared with those of the ND-fed mice. These results suggest that the neuroprotective effect of the KD on the KA-induced toxicity may be, in part, mediated via an increased expression of CB.

Genetic and Cellular Therapies for Cerebral Infarction

Neurosurgeons, working as surgical scientists, can have a prominent role in developing and implementing genetic and cellular therapies for cerebral ischemia. The rapid emergence of both genetic and cellular therapies for neural regeneration warrants a careful analysis before implementation of human studies to understand the pitfalls and promises of this strategy. In this article, we review the topic of genetic and cellular therapy for stroke to provide a foundation for practicing neurosurgeons and clinical scientists who may become involved in this type of work. In Part 1, we review preclinical approaches with gene transfer, such as 1) improved energy delivery, 2) reduction of intracellular calcium availability, 3) abrogation of effects of reactive oxygen species, 4) reduction of proinflammatory cytokine signaling, 5) inhibition of apoptosis mediators, and 6) restorative gene therapy, that are paving the way to develop new strategies to treat cerebral infarction. In Part 2, we discuss the results of studies that address the possibility of using cellular therapies for stroke in animal models and in human trials by reviewing 1) the basics of stem cell biology, 2) exogenous and 3) and endogenous cell sources for therapy, and 4) clinical considerations in cell therapy applications. These emerging technologies based on the advancements made in recent years in the fields of genetics, therapeutic cloning, neuroscience, stem cell biology, and gene therapy provide significant potential for new therapies for stroke.

Opposing effects of ethanol and nicotine on hippocampal calbindin-D28k expression

Long-term ethanol exposure produces multiple neuroadaptations that likely contribute to dysregulation of Ca(2+) balance and neurotoxicity during ethanol withdrawal. Conversely, nicotine exposure may reduce the neurotoxic consequences of Ca(2+) dysregulation, putatively through up-regulation of the Ca(2+)-buffering protein calbindin-D(28k). The current studies were designed to examine the extent to which 10-day ethanol exposure and withdrawal altered calbindin-D(28k) expression in rat hippocampus. Further, in these studies, we examined the ability of nicotine, through action at alpha(7)(*)-bearing nicotinic acetylcholine receptors (nAChRs), to antagonize the effects of ethanol exposure on calbindin-D(28k) expression. Organotypic cultures of rat hippocampus were exposed to ethanol (50-100 mM) for 10 days. Additional cultures were exposed to 500 nM (-)-nicotine with or without the addition of 50 mM ethanol, 100 nM methyllycaconitine (an alpha(7)*-bearing nAChR antagonist), or both. Prolonged exposure to ethanol (>/=50 mM) produced significant reductions of calbindin-D(28k) immunolabeling in all regions of the hippocampal formation, even at nontoxic concentrations of ethanol. Calbindin-D(28k) expression levels returned to near-control levels after 72 h of withdrawal from 10-day ethanol exposure. Extended (-)-nicotine exposure produced significant elevations in calbindin-D(28k) expression levels that were prevented by methyllycaconitine co-exposure. Co-exposure of cultures to (-)-nicotine with ethanol resulted in an attenuation of ethanol-induced reductions in calbindin-D(28k) expression levels. These findings support the suggestion that long-term ethanol exposure reduces the neuronal capacity to buffer accumulated Ca(2+) in a reversible manner, an effect that likely contributes to withdrawal-induced neurotoxicity. Further, long-term exposure to (-)-nicotine enhances calbindin-D(28k) expression in an alpha(7)* nAChR-dependent manner and antagonizes the effects of ethanol on calbindin-D(28k) expression.

Intracellular Ca2+ handling

Intracellular Ca2+ is regulated within three major compartments: the cytosol, the endoplasmic reticulum and mitochondria. This Chapter reviews the mechanisms involved in handling of Ca2+ within these compartments with reference to potential strategies for neuroprotection. In the cytosol, Ca2+ buffering has a major influence on Ca2+ signals. Cytosolic Ca(2+)-binding proteins such as CB28 participate in Ca2+ buffering and may have a role in resistance to neurotoxicity. In the endoplasmic reticulum, a number of proteins are involved in Ca2+ uptake, lumenal buffering or release, and these may be of value as potential targets for therapeutic intervention. Mitochondria are receiving increasing attention for their role in Ca2+ storage and signaling, and as key players in the processes leading to cell death following Ca2+ overload. An improved understanding of how Ca2+ is controlled within these intracellular compartments, and how these compartments interact, will be important for neuroprotective strategies.

Cytoprotective effects of calbindin-D(28k) against antimycin-A induced hypoxic injury in proximal tubular cells

Intracellular calcium plays an important role on the pathogenesis of hypoxia-induced cellular injury. Calbindin-D(28k), a cytosolic vitamin D-dependent calcium binding protein, can serve as a buffer to limit a surge in intracellular Ca2+ concentration ([Ca2+]i) induced by various stimulations. To evaluate the possible cytoprotective effect of calbindin-D(28k) against hypoxic injury in proximal tubular cells, a plasmid containing calbindin-D(28k) cDNA under the control of CMV immediate-early gene promoter was transfected into the murine proximal tubular epithelial (MCT) cells. The expression of calbindin-D(28k) in the transfected cells was verified with Northern blot analysis, Western blot analysis, and immunofluorescent staining. The non-transfected and transfected MCT cells were subjected to chemical hypoxia induced by antimycin A (10 microM) and glucose deprivation for 30-120 min. The transfection of calbindin-D(28k) reduced lactate dehydrogenase (LDH) release by 41%, 41%, 24%, and 24%, respectively, at 30, 60, 90 and 120 min after hypoxia when compared to the non-transfected cells (all p < 0.05). Cell viability after hypoxic injury was also significantly higher in transfected cells than non-transfected cells. Transfection with the plasmid without calbindin-D(28k) cDNA did not affect LDH release or cell viability after chemical hypoxic injury. [Ca+2]i was measured ratiometrically with fura-2 after exposure to chemical hypoxia. The rate of initial rise in [Ca2+]i and final [Ca+2]i at 30-120 min were significantly lowered in transfected cells. In conclusion, this study demonstrated that transfection of calbindin-D(28k) gene into MCT cells provide protective effects against chemical hypoxic injury probably through its buffering effects on [Ca+2]i.

Protective effect of parvalbumin on excitotoxic motor neuron death

The mechanism responsible for the selective vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS) is poorly understood. Several lines of evidence indicate that susceptibility of motor neurons to Ca(2+) overload induced by excitotoxic stimuli is involved. In this study, we investigated whether the high density of Ca(2+)-permeable AMPA receptors on motor neurons gives rise to higher Ca(2+) transients in motor neurons compared to dorsal horn neurons. Dorsal horn neurons were chosen as controls as these cells do not degenerate in ALS. In cultured spinal motor neurons, the rise of the cytosolic Ca(2+) concentration induced by kainic acid (KA) and mediated by the AMPA receptor was almost twice as high as in spinal neurons from the dorsal horn. Furthermore, we investigated whether increasing the motor neuron's cytosolic Ca(2+)-buffering capacity protects them from excitotoxic death. To obtain motor neurons with increased Ca(2+) buffering capacity, we generated transgenic mice overexpressing parvalbumin (PV). These mice have no apparent phenotype. PV overexpression was present in the central nervous system, kidney, thymus, and spleen. Motor neurons from these transgenic mice expressed PV in culture and were partially protected from KA-induced death as compared to those isolated from nontransgenic littermates. PV overexpression also attenuated KA-induced Ca(2+) transients, but not those induced by depolarization. We conclude that the high density of Ca(2+)-permeable AMPA receptors on the motor neuron's surface results in high Ca(2+) transients upon stimulation and that the low cytosolic Ca(2+)-buffering capacity of motor neurons may contribute to the selective vulnerability of these cells in ALS. Overexpression of a high-affinity Ca(2+) buffer such as PV protects the motor neuron from excitotoxicity and this protective effect depends upon the mode of Ca(2+) entry into the cell.

Long-term changes in calbindin D(28K) immunoreactivity in the rat hippocampus after cardiac arrest

Calbindin D(28K) (CB) expression was analyzed in the rat hippocampus following 10-min-cardiac arrest-induced ischemia within a year after reperfusion. In rats examined 3 days after ischemia, CB immunoreactivity disappeared completely from CA1 pyramidal neurons and from most CA2 pyramids. In the stratum granulosum of the dentate gyrus, mossy fibers, and hippocampal interneurons, CB immunoreactivity was preserved, although staining was somewhat paler than that in control rats. A similar pattern of CB immunoreactivity was found in rats sacrificed 14 days and 1 month after cardiac arrest. From the 14th postischemic day, neuronal loss in the stratum pyramidale of CA1 but not in that of CA2 became apparent. The reappearance of CB immunoreactivity in CA1 and CA2 pyramidal neurons was noticed 6 months after ischemia, and the pattern was identical to that observed in animals sacrificed 12 months after the ictus. The prolonged loss and delayed reappearance of CB immunoreactivity in the hippocampus demonstrate that ischemia may induce long-term disturbances of protein expression, which may in turn result in impairment of hippocampal functioning.

Gene therapy against neurological insults: sparing neurons versus sparing function

Increasing knowledge of neuron death mediators has led to gene therapy techniques for neuroprotection. Overexpression of numerous genes enhances survival after necrotic or neurodegenerative damage. Nonetheless, although encouraging, little is accomplished if a neuron is spared from death, but not from dysfunction. This article reviews neuroprotection experiments that include some measure of function, and synthesizes basic principles relating to its maintenance. Variations in gene delivery systems, including virus-type and latency between damage onset and vector delivery, probably impact the therapeutic outcome. Additionally, functional sparing might depend on factors related to insult severity, neuron type involved or the step in the death cascade that is targeted.

Gene therapy and the aging nervous system

In recent years, the first attempts have been made to apply gene transfer technology to protect neurons from death following neurological insults. There has been sufficient progress in this area that it becomes plausible to consider similar gene therapy approaches meant to delay aspects of aging of the nervous system. In this review, we briefly consider such progress and how it might be applied to the realm of the aging brain. Specifically, we consider: (a) the means of delivery of such therapeutic genes; (b) the choice of such genes; and (c) technical elaborations in gene delivery systems which can more tightly regulate the magnitude and duration of transgene protection.

Calbindin overexpression buffers hippocampal cultures from the energetic impairments caused by glutamate

A dramatic rise in free cytosolic calcium concentration is thought to be a central event in the pathogenesis of glutamate excitotoxicity in neurons. We have previously demonstrated that gene transfer of the calcium-binding protein calbindin D28k via a Herpes simplex amplicon vector decreases the rise in intracellular calcium and promotes cell survival following glutamatergic challenge. This study explores the effect of calbindin transgene expression on cellular metabolism following glutamate excitotoxicity. Because excitotoxic insults are often energetic in nature, and because calcium sequestering and extrusion place heavy energy demands on a cell, we hypothesized that calbindin overexpression may help preserve cellular energy levels during an insult. We overexpressed calbindin in primary hippocampal cultures, using a Herpes simplex amplicon vector system. We found that calbindin overexpression protected neurons from the decline in ATP levels, mitochondrial potential and metabolic rate following a glutamatergic insult. These results indicate that calbindin expression helps preserve cellular energy state following glutamate excitotoxicity. This illustrates the energetic load placed on neurons by increased free cytosolic calcium and may help explain the neuroprotective effects of calbindin.

Calretinin and calbindin D-28k delay the onset of cell death after excitotoxic stimulation in transfected P19 cells

In some neurological diseases, injury to neurones reflects an over-stimulation of their receptors for excitatory amino acids. This response may disturb the Ca(2+)-homeostasis and lead to a pronounced and sustained increase in the intracellular concentration of this ion. On the basis of data derived from correlative studies, calcium-binding proteins have been postulated to play a protective role in these pathologies. We tested, directly, the capacity of the three calcium-binding proteins calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) to buffer [Ca(2+)], and to protect cells against excitotoxic death. We used P19 murine embryonic carcinoma cells, which can be specifically induced (by retinoic acid) to transform into nerve-like ones. The differentiated cells express functional glutamate-receptors and are susceptible to excitotoxic shock. Undifferentiated P19-cells were stably transfected with the cDNA for CR, CB or PV, induced to differentiate, and then exposed to NMDA, a glutamate-receptor agonist. The survival rates of clones expressing CR, CB or PV were compared with those of untransfected P19-cells using the lactate-dehydrogenase assay. CR- and CB-expressing cells were protected from death during the first 2 h of exposure to NMDA. This protection was, however, transient, and did not suffice to rescue P19-cells after prolonged stimulation. Two of the three PV-transfected clones raised were vulnerable to NMDA-induced excitotoxicity; the third, which expressed the lowest level of PV, was protected to a similar degree as that found for the CR- and CB-transfected clones. Our results indicate that in the P19-cell model, CR and CB can help to delay the onset of cell death after excitotoxic stimulation.

Gene therapy for treatment of cerebral ischemia using defective herpes simplex viral vectors

Significant advances have been made over the past few years concerning the cellular and molecular events underlying neuron death. Recently, it is becoming increasingly clear that some of the genes induced during cerebral ischemia may actually serve to rescue the cell from death. However, the injured cell may not be capable of expressing protein at levels high enough to be protective. One of the most exciting arenas of such interventions is the use of viral vectors to deliver potentially neuroprotective genes at high levels. Neurotrophic herpes simplex viral strains are an obvious choice for gene therapy to the brain, and we have utilized bipromoter vectors that are capable of transferring various genes to neurons. Using this system in experimental models of stroke, cardiac arrest and excitotoxicity, we have found that it is possible to enhance neuron survival against such cerebral insults by over-expressing genes that target various facets of injury. These include energy restoration by the glucose transporter (GLUT-1), buffering calcium excess by calbindin, preventing protein malfolding or aggregation by stress proteins and inhibiting apoptotic death by BCL-2. We show that in some cases, gene therapy is also effective after the onset of injury, and also address whether successful gene therapy necessarily spares function. Although gene therapy is limited to the few hundred cells the vector is capable of transfecting, we consider the possibility of such gene therapy becoming relevant to clinical neurology in the future.

Gene therapy for treatment of cerebral ischemia using defective herpes simplex viral vectors

Significant advances have been made over the past few years concerning the cellular and molecular events underlying neuron death. Recently, it is becoming increasingly clear that some of genes induced during cerebral ischemia may actually serve to rescue the cell from death. However, the injured cell may not be capable of expressing protein at high enough levels to be protective. One of the most exciting arenas of such interventions is the use of viral vectors to deliver potentially neuroprotective genes at high levels. Neurotropic herpes simplex viral (HSV) strains are an obvious choice for gene therapy to the brain, and we have used bipromoter vectors that are capable of transferring various genes to neurons. Using this system in experimental models of stroke, cardiac arrest, and excitotoxicity, we have found that it is possible to enhance neuron survival against such cerebral insults by overexpressing genes that target various facets of injury. These include energy restoration by the glucose transporter (GLUT-1), buffering calcium excess by calbindin, preventing protein malfolding or aggregation by stress proteins and inhibiting apoptotic death by BCL-2. We show that in some cases, gene therapy is also effective after the onset of injury, and also address whether successful gene therapy necessarily spares function. Although gene therapy is limited to the few hundred cells the vector is capable of transfecting, we consider the possibility of such gene therapy becoming relevant to clinical neurology in the future.

Gene therapy effectiveness differs for neuronal survival and behavioral performance

If neuronal gene therapy is to be clinically useful, it is necessary to demonstrate neuroprotection when the gene is introduced after insult. We now report equivalent neuronal protection if calbindin D(28K) gene transfer via herpes simplex virus amplicon vector occurs immediately, 30 min, or 1 h after an excitotoxic insult, but not after a 4 h delay. Behavioral performance was evaluated for immediate and 1 h delay groups using a hippocampal-dependent task. Despite equivalent magnitude and pattern of sparing of neurons with the immediate and 1 h delay approaches, the delay animals took a significantly longer time after insult to return to normal performance.

Calcium buffering and protection from excitotoxic cell death by exogenous calbindin-D28k in HEK 293 cells

Calbindin-D28k (CaBP) is a calcium-binding protein found in specific neuronal populations in the mammalian brain that, as a result of its proposed calcium-buffering action, may protect neurons against potentially harmful increases in intracellular calcium. We have stably transfected HEK 293 cells with recombinant human CaBP in order to determine the influence of this protein upon transient increases in intracellular ionic calcium concentration ([Ca(2+)](i)) induced either by transient transfection of the NR1 and NR2A subunits of the N-methyl-D-aspartate (NMDA) receptor and brief exposure to glutamate, photolysis of the caged calcium compound NP-EGTA, or exposure to the Ca(2+)]-ionophore 4-Br-A23187. The presence of CaBP did not significantly reduce the peak [Ca(2+)](i)stimulated by glutamate activation of NMDA receptors but significantly prolonged the recovery to baseline values. Flash photolysis of NP-EGTA in control cells resulted in an almost instantaneous increase in [Ca(2+)](i)followed by a bi-exponential recovery to baseline values. In cells stably expressing CaBP, the peak [Ca(2+)](i)levels were not statistically different from the controls, however, there was a significant prolongation of the initial portion of the slow recovery phase. In cells exposed to 4-Br-A23187, the presence of CaBP significantly reduced the rate of rise of [Ca(2+)](i), reduced the peak response, slowed the rate of recovery, and reduced the depolarization of mitochondria. In studies of delayed, Ca(2+)]-dependent cell death, CaBP transfected cells exhibited enhanced survival 24h after a 1-h exposure to 200 microM NMDA. However, necrotic cell death observed after the first 6h was not prevented by the presence of CaBP. These results provide direct evidence for a Ca(2+)-buffering effect of CaBP which serves to limit Ca(2+)entry and the depolarization of mitochondria, thereby protecting cells from death mediated most likely by apoptosis.

Gene therapy for amyotrophic lateral sclerosis and other motor neuron diseases

There are several incurable diseases of motor neuron degeneration, including amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, hereditary spastic hemiplegia, spinal muscular atrophy, and bulbospinal atrophy. Advances in gene transfer techniques coupled with new insights into molecular pathology have opened promising avenues for gene therapy aimed at halting disease progression. Nonviral preparations and recombinant adenoviruses, adeno-associated viruses, herpesviruses, and lentiviruses may ultimately transduce sufficient numbers of cerebral, brainstem, and spinal cord neurons for therapeutic applications. This could be accomplished by direct injection, transduction of lower motor neurons via retrograde transport after intramuscular injection, or cell-based therapies. Studies using transgenic mice expressing mutant superoxide dismutase 1 (SOD1), a model for one form of ALS, established that several proteins were neuroprotective, including calbindin, bcl-2, and growth factors. These same molecules promoted neuronal survival in other injury models, suggesting general applicability to all forms of ALS. Potentially correctable genetic lesions have also been identified for hereditary spastic hemiplegia, bulbospinal atrophy, and spinal muscular atrophy. Finally, it may be possible to repopulate lost corticospinal and lower motor neurons by transplanting stem cells or stimulating native progenitor populations. The challenge ahead is to translate these basic science breakthroughs into workable clinical practice.

Sparing of neuronal function postseizure with gene therapy

Numerous studies have demonstrated that gene therapy interventions can protect neurons from death after neurological insults. In nearly all such studies, however, "protection" consists of reduced neurotoxicity, with no demonstrated preservation of neuronal function. We used a herpes simplex virus-1 system to overexpress either the Glut-1 glucose transporter (GT) (to buffer energetics), or the apoptosis inhibitor Bcl-2. Both decreased hippocampal neuron loss to similar extents during excitotoxic insults in vitro and in vivo. However, the mediating mechanisms and consequences of the two interventions differed. GT overexpression attenuated early, energy-dependent facets of cell death, blocking oxygen radical accumulation. Bcl-2 expression, in contrast, blocked components of death downstream from the energetic and oxidative facets. Most importantly, GT- but not Bcl-2-mediated protection preserved hippocampal function as assessed spatial maze performance. Thus, gene therapeutic sparing of neurons from insult-induced death does not necessarily translate into sparing of function.

Gene therapies that enhance hippocampal neuron survival after an excitotoxic insult are not equivalent in their ability to maintain synaptic transmission

Research shows that overexpression of cytoprotective genes can spare neurons from necrotic death, but few studies have addressed the functional status of surviving neurons. Overexpression of a brain glucose transporter, Glut-1, or the anti-apoptotic protein, Bcl-2, in rats decreases the size of hippocampal lesions produced by kainic acid (KA) treatment. In animals in which KA-induced lesions are reduced to similar extents by Glut-1 or Bcl-2 overexpression, spatial learning is spared by Glut-1, but not Bcl-2. We postulated that Glut-1 and Bcl-2 act differently to protect hippocampal function and investigated the effects of vector overexpression on synaptic physiology after KA treatment. Three days after KA and vector delivery to the dentate gyrus, mossy fiber-CA3 (MF-CA3) population excitatory postsynaptic potentials (EPSPs) were recorded in vitro. In addition to producing a lesion in area CA3, KA treatment reduced baseline MF-CA3 synaptic strength, posttetanic potentiation (PTP), and long-term potentiation (LTP). A similar reduction in the KA-induced lesion was produced by overexpression of Glut-1 or Bcl-2. Glut-1, but not Bcl-2, attenuated the impairments in synaptic strength and PTP. Overexpression of Glut-1 or Bcl-2 preserved LTP after KA treatment. Results indicate greater protection of MF-CA3 synaptic transmission with overexpression of Glut-1 compared to Bcl-2 and suggest that not all neuroprotective gene therapy techniques are equivalent in their ability to spare function.

Cloning and expression of secretagogin, a novel neuroendocrine- and pancreatic islet of Langerhans-specific Ca2+-binding protein

We have cloned a novel pancreatic beta cell and neuroendocrine cell-specific calcium-binding protein termed secretagogin. The cDNA obtained by immunoscreening a human pancreatic cDNA library using the recently described murine monoclonal antibody D24 contains an open reading frame of 828 base pairs. This codes for a cytoplasmic protein with six putative EF finger hand calcium-binding motifs. The gene could be localized to chromosome 6 by alignment with GenBank genomic sequence data. Northern blot analysis demonstrated abundant expression of this protein in the pancreas and to a lesser extent in the thyroid, adrenal medulla, and cortex. In addition it was expressed in scant quantity in the gastrointestinal tract (stomach, small intestine, and colon). Thyroid tissue expression of secretagogin was restricted to C-cells. Using a sandwich capture enzyme-linked immunosorbent assay with a detection limit of 6.5 pg/ml, considerable amounts of constitutively secreted protein could be measured in tissue culture supernatants of stably transfected RIN-5F and dog insulinoma (INS-H1) cell clones; however, in stably transfected Jurkat cells, the protein was only secreted upon CD3 stimulation. Functional analysis of transfected cell lines expressing secretagogin revealed an influence on calcium flux and cell proliferation. In RIN-5F cells, the antiproliferative effect is possibly due to secretagogin-triggered down-regulation of substance P transcription.

Neuroprotective potential of a viral vector system induced by a neurological insult

Gene transfer into neurons via viral vectors for protection against acute necrotic insults has generated considerable interest. Most studies have used constitutive vector systems, limiting the ability to control transgene expression in a dose-dependent, time-dependent, or reversible manner. We have constructed defective herpes simplex virus vectors designed to be induced by necrotic neurological insults themselves. Such vectors contain a synthetic glucocorticoid-responsive promoter, taking advantage of the almost uniquely high levels of glucocorticoids-adrenal stress steroids-secreted in response to such insults. We observed dose-responsive and steroid-specific induction by endogenous and synthetic glucocorticoids in hippocampal cultures. Induction was likely to be rapid enough to allow transgenic manipulation of relatively early steps in the cascade of necrotic neuron death. The protective potential of such a vector was tested by inclusion of a neuroprotective transgene (the Glut-1 glucose transporter). Induction of this vector by glucocorticoids decreased glutamatergic excitotoxicity in culture. Finally, both exogenous glucocorticoids and excitotoxic seizures induced reporter gene expression driven from a glucocorticoid-responsive herpes simplex virus vector in the hippocampus in vivo.

Herpes simplex viral and amplicon vector-mediated gene transfer into glia and neurons in organotypic spinal cord and dorsal root ganglion cultures

The progression of neurodegenerative diseases and secondary consequences of spinal cord injury may be diminished by introducing transgenes to glia, spinal neurons, and/or sensory neurons. Organotypic cultures of spinal cord slices and dorsal root ganglia proved to be an excellent system in which to compare the relative neurotropism of a replication-defective recombinant herpes simplex virus and herpes virus-derived amplicon vectors. Hundreds of beta-galactosidase-expressing cells, transduced by the viral vectors, were observed in spinal cord slices 3 and 8 days postinfection. Immunostaining to identify the infected cell type indicated that oligodendrocytes were permissive for viral vector transduction of beta-galactosidase in the spinal cord slice, whereas neurons were not. Heparan sulfate proteoglycan, the initial receptor for herpes contact with cells, was highly expressed in the white matter of the spinal cord slice, but was negligible in the gray matter. In contrast to the spinal cord, many fewer cells were infected in the dorsal root ganglia (DRG) by these vectors, but a majority of infected cells were identified as sensory neurons. Heparan sulfate proteoglycan expression was abundant in the sensory fibers emanating from the DRG and also surrounded each neuron within the ganglion. Our results demonstrate HSV-induced transgene expression that is amenable to ex vivo assessment of its physiological impact.

Cytomegalovirus cell tropism, replication, and gene transfer in brain

Cytomegalovirus (CMV) infects a majority of adult humans. During early development and in the immunocompromised adult, CMV causes neurological deficits. We used recombinant murine cytomegalovirus (mCMV) expressing either green fluorescent protein (GFP) or beta-galactosidase under control of human elongation factor 1 promoter or CMV immediate early-1 promoter as reporter genes for infected brain cells. In vivo and in vitro studies revealed that neurons and glial cells supported strong reporter gene expression after CMV exposure. Brain cultures selectively enriched in either glia or neurons supported viral replication, leading to process degeneration and cell death within 2 d of viral exposure. In addition, endothelial cells, tanycytes, radial glia, ependymal cells, microglia, and cells from the meninges and choroid were infected. Although mCMV showed no absolute brain cell preference, relative cell preferences were detected. Radial glia cells play an important role in guiding migrating neurons; these were viral targets in the developing brain, suggesting that cortical problems including microgyria that are a consequence of CMV may be caused by compromised radial glia. Although CMV is a species-specific virus, recombinant mCMV entered and expressed reporter genes in both rat and human brain cells, suggesting that mCMV might serve as a vector for gene transfer into brain cells of non-murine species. GFP expression was sufficiently strong that long axons, dendrites, and their associated spines were readily detected in both living and fixed tissue, indicating that mCMV reporter gene constructs may be useful for labeling neurons and their pathways.

Calretinin and calbindin-D28k in dopaminergic neurons of the rat midbrain: a triple-labeling immunohistochemical study

We used triple-labeling immunohistochemistry in rat midbrain sections to identify dopaminergic neurons that contain either one or both of the calcium-binding proteins, calretinin (CR) and calbindin-D28k (CB). Midbrain dopaminergic neurons were immunohistochemically labeled for tyrosine hydroxylase (TH), CR, and CB. In the substantia nigra pars compacta (SNC), TH+/CR+/CB+ cells were clustered in two regions: the dorsal tier of the rostral SNC and the medial part of the intermediate SNC. The ventral tier of the rostral SNC mainly comprised both TH+/CR+/CB- and TH+/CR-/CB- cells. The lateral part of the intermediate SNC and the caudal SNC primarily consisted of TH+/CR-/CB- cells. Throughout the extent of the SNC, approximately half of the TH+ neurons were stained for neither CR nor CB, while the remaining TH+ populations were labeled for CR and/or CB. Throughout the ventral tegmental area, TH+/CR+/CB+ cells, TH+/CR+/CB- cells, TH+/CR-/CB+ cells, and TH+/CR-/CB- cells were found generally scattered, though the TH+/CR-/CB- cells were dominant in number. In the substantia nigra pars lateralis, interfascicular nucleus, and caudal linear nucleus, more than half of the TH+ cells were stained for both CR and CB. In the retrorubral field, two-thirds of the TH+ neurons contained neither protein. The present findings suggest that the SNC can be divided into subcompartments based on the distribution of dopaminergic neurons that contain calcium-binding proteins. Furthermore, because CR and CB likely contribute to calcium homeostasis by buffering intracellular calcium concentrations, midbrain dopaminergic neurons containing one or both of these calcium-binding proteins may have a higher calcium-buffering capacity than those lacking the two proteins.

Delivery of herpes simplex virus amplicon-based vectors to the dentate gyrus does not alter hippocampal synaptic transmission in vivo

Herpes simplex virus type-1 (HSV) amplicon vectors containing neuroprotective genes can alter cell physiology and enhance survival following various insults. However, to date, little is known about effects of viral infection itself (independent of the gene delivered) on neuronal physiology. Electrically-evoked synaptic responses are routinely recorded to measure functional alterations in the nervous system and were used here to assess the potential capability of HSV vectors to disrupt physiology of the hippocampus (a forebrain structure involved in learning that is highly susceptible to necrotic insult, making it a frequent target in gene therapy research). Population excitatory post-synaptic potentials (EPSPs) were recorded in the dentate gyrus (DG) and in area CA3 in vivo 72 h after infusion of an HSV vector expressing a reporter gene (lacZ) or vehicle into the DG. Evoked perforant path (PP-DG) or mossy fiber (MF-CA3) EPSPs slope values measured across input/output (I/O) curves were not altered by infection. Paired-pulse facilitation at either recording site was also unaffected. X-gal-positive granule cells surrounded the recording electrode (PP-DG recording) and stimulating electrode tracts (MF-CA3 recording) in animals that received vector, suggesting that we had measured function, at least in part, in infected neurons. Because of the negative electrophysiological result, we sought to deliver a gene with an HSV amplicon which would affect the measured endpoints, as a positive control. Delivery of calbindin D28kpotentiated PP-DG synaptic strength, indicating that our recording system could detect alterations due to vector expression. Thus, the data indicate that HSV vectors are benign, in regard to effects on synaptic function, and support the use of these vectors as a safe method to deliver selected genes to the central nervous system.

Calbindin D28K gene transfer via herpes simplex virus amplicon vector decreases hippocampal damage in vivo following neurotoxic insults

Increases in cytoplasmic Ca2+ concentration ([Ca2+]i) can lead to neuron death. Preventing a rise in [Ca2+]i by removing Ca2+ from the extracellular space or by adding Ca2+ chelators to the cytosol of target cells ameliorates the neurotoxicity associated with [Ca2+]i increases. Another potential route of decreasing the neurotoxic impact of Ca2+ is to overexpress one of the large number of constitutive calcium-binding proteins. Previous studies in this laboratory demonstrated that overexpression of the gene for the calcium-binding protein calbindin D28K, via herpes simplex virus (HSV) amplicon vector, increases the survival of hippocampal neurons in vitro following energetic or excitotoxic insults but not following application of sodium cyanide. We now report that in vivo hippocampal infection with the calbindin D28K HSV vector increases neuronal survival in the dentate gyrus after application of the antimetabolite 3-acetylpyridine and increases transsynaptic neuronal survival in area CA3 following kainic acid neurotoxicity. The protective effects of infection with the calbindin D28K vector in an intact brain may prove to be beneficial during changes in Ca2+ homeostasis caused by neurological trauma associated with aging and certain neurological diseases.