Gene transfer to the spinal cord neural scar with lentiviral vectors: predominant transgene expression in astrocytes but not in meningeal cells

Overexpression of GDNF in Spinal Cord Attenuates Morphine Analgesic Tolerance in Rats with Bone Cancer Pain

Bone cancer pain (BCP) is one of the typical and distressing symptoms in cancer patients. Morphine is a widely used analgesic drug for BCP; however, long-term morphine administration will lead to analgesic tolerance. Our previous study indicated that spinal glial cell line-derived neurotrophic factor (GDNF) exerts analgesic effects in rats with BCP. In this study, BCP was established by inoculated Walker 256 carcinoma cells into rat tibias, while morphine tolerance (MT) was induced by intrathecally injecting morphine twice daily from the 9th to 15th postoperative day (POD) in BCP rats. The BCP rats developed mechanical and thermal hyperalgesia on POD 5 and it lasted to POD 15. The analgesic effect of morphine was decreased after repeat administration. Western blots and immunochemistry tests showed that GDNF was gradually decreased in the spinal cord after the development of MT in rats with BCP, and GDNF was colocalized with the μ opioid receptor (MOR) in the superficial laminate of the spinal cords. The overexpression of GDNF by lentivirus significantly attenuated MT, and restored the expression of MOR in the spinal cord. In summary, our results suggest that the reduction of GDNF expression participated in the development of MT in rats with BCP and could be a promising therapeutic option for BCP.

The use of viral vectors to promote repair after spinal cord injury

Spinal cord injury (SCI) is a devastating event that can permanently disrupt multiple modalities. Unfortunately, the combination of the inhibitory environment at a central nervous system (CNS) injury site and the diminished intrinsic capacity of adult axons for growth results in the failure for robust axonal regeneration, limiting the ability for repair. Delivering genetic material that can either positively or negatively modulate gene expression has the potential to counter the obstacles that hinder axon growth within the spinal cord after injury. A popular gene therapy method is to deliver the genetic material using viral vectors. There are considerations when deciding on a viral vector approach for a particular application, including the type of vector, as well as serotypes, and promoters. In this review, we will discuss some of the aspects to consider when utilizing a viral vector approach to as a therapy for SCI. Additionally, we will discuss some recent applications of gene therapy to target extrinsic and/or intrinsic barriers to promote axon regeneration after SCI in preclinical models. While still in early stages, this approach has potential to treat those living with SCI.

Numerical characterization of regenerative axons growing along a spherical multifunctional scaffold after spinal cord injury

Spinal cord injury (SCI) followed by extensive cell loss, inflammation, and scarring, often permanently damages neurological function. Biomaterial scaffolds are promising but currently have limited applicability in SCI because after entering the scaffold, regenerating axons tend to become trapped and rarelyre-enter the host tissue, the reasons for which remain to be completely explored. Here, we propose a mathematical model and computer simulation for characterizing regenerative axons growing along a scaffold following SCI, and how their growth may be guided. The model assumed a solid, spherical, multifunctional, biomaterial scaffold, that would bridge the rostral and caudal stumps of a completely transected spinal cord in a rat model and would guide the rostral regenerative axons toward the caudal tissue. Other assumptions include the whole scaffold being coated with extracellular matrix components, and the caudal area being additionally seeded with chemoattractants. The chemical factors on and around the scaffold were formulated to several coupled variables, and the parameter values were derived fromexisting experimental data. Special attention was given to the effects of coating strength, seeding location, and seeding density, as well as the ramp slope of the scaffold, on axonal regeneration. In numerical simulations, a slimmer scaffold provided a small slope at the entry "on-ramp" area that improved the success rate of axonal regeneration. If success rates are high, an increased number of regenerative axons traverse through the narrow channels, causing congestion and lowering the growth rate. An increase in the number of severed axons (300-12000) did not significantly affect the growth rate, but it reduced the success rate of axonal regeneration. However, an increase in the seeding densities of the complexes on the whole scaffold, and that in the seeding densities of the chemoattractants on the caudal area, improved both the success and growth rates. However, an increase in the density of thecomplexes on the whole scaffold risks an over-eutrophic surface that harms axonal regeneration.Although theoretical predictions are yet to be validated directly by experiments, this theoretical tool can advance the treatment of SCI, and is also applicable to scaffolds with other architectures.

Perspective on innovative therapies for globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD), or Krabbe's disease, is a lysosomal storage disorder resulting from deficiency of the lysosomal hydrolase galactosylceramidase. The infantile forms are characterized by a unique relentless and aggressive progression with a wide range of neurological symptoms and complications. Here we review and discuss the basic concepts and the novel mechanisms identified as key contributors to the peculiar GLD pathology, highlighting their therapeutic implications. Then, we evaluate evidence from extensive experimental studies on GLD animal models that have highlighted fundamental requirements to obtain substantial therapeutic benefit, including early and timely intervention, high levels of enzymatic reconstitution, and global targeting of affected tissues. Continuous efforts in understanding GLD pathophysiology, the interplay between various therapies, and the mechanisms of disease correction upon intervention may allow advancing research with innovative approaches and prioritizing treatment strategies to develop more efficacious treatments. © 2016 Wiley Periodicals, Inc.

Vimentin Promotes Astrocyte Activation After Chronic Constriction Injury

Vimentin, among the family of the intermediate filament, plays as the organizer of some critical proteins involved in migration, attachment, and cell signaling. In this study, the role of vimentin in chronic constriction injury (CCI) was investigated. Western blot revealed increased protein level of vimentin following CCI, peaking at 7 days. Double immunofluorescent staining showed that vimentin was mostly co-localized with astrocytes, not with neurons or microglia. In vitro, sensory neuronal injury stimulated astrocytes to produce more pro-inflammation cytokines, p-ERK (phosphorylated extracellular signal-regulated protein kinase), and vimentin. However, vimentin knockdown by siRNA (small interfering RNA) reversed the upregulation of p-ERK and vimentin expression and reduced the release of pro-inflammatory cytokines. Overall, stimulated astrocytes might release pro-inflammatory cytokines to promote the development of neuropathic pain via vimentin/ERK signaling.

Destination Brain: the Past, Present, and Future of Therapeutic Gene Delivery

Neurological diseases and disorders (NDDs) present a significant societal burden and currently available drug- and biological-based therapeutic strategies have proven inadequate to alleviate it. Gene therapy is a suitable alternative to treat NDDs compared to conventional systems since it can be tailored to specifically alter select gene expression, reverse disease phenotype and restore normal function. The scope of gene therapy has broadened over the years with the advent of RNA interference and genome editing technologies. Consequently, encouraging results from central nervous system (CNS)-targeted gene delivery studies have led to their transition from preclinical to clinical trials. As we shift to an exciting gene therapy era, a retrospective of available literature on CNS-associated gene delivery is in order. This review is timely in this regard, since it analyzes key challenges and major findings from the last two decades and evaluates future prospects of brain gene delivery. We emphasize major areas consisting of physiological and pharmacological challenges in gene therapy, function-based selection of a ideal cellular target(s), available therapy modalities, and diversity of viral vectors and nanoparticles as vehicle systems. Further, we present plausible answers to key questions such as strategies to circumvent low blood-brain barrier permeability and most suitable CNS cell types for targeting. We compare and contrast pros and cons of the tested viral vectors in the context of delivery systems used in past and current clinical trials. Gene vector design challenges are also evaluated in the context of cell-specific promoters. Key challenges and findings reported for recent gene therapy clinical trials, assessing viral vectors and nanoparticles are discussed from the perspective of bench to bedside gene therapy translation. We conclude this review by tying together gene delivery challenges, available vehicle systems and comprehensive analyses of neuropathogenesis to outline future prospects of CNS-targeted gene therapies.

Sulfatase-mediated manipulation of the astrocyte-Schwann cell interface

Schwann cell (SC) transplantation following spinal cord injury (SCI) may have therapeutic potential. Functional recovery is limited however, due to poor SC interactions with host astrocytes and the induction of astrogliosis. Olfactory ensheathing cells (OECs) are closely related to SCs, but intermix more readily with astrocytes in culture and induce less astrogliosis. We previously demonstrated that OECs express higher levels of sulfatases, enzymes that remove 6-O-sulfate groups from heparan sulphate proteoglycans, than SCs and that RNAi knockdown of sulfatase prevented OEC-astrocyte mixing in vitro. As human OECs are difficult to culture in large numbers we have genetically engineered SCs using lentiviral vectors to express sulfatase 1 and 2 (SC-S1S2) and assessed their ability to interact with astrocytes. We demonstrate that SC-S1S2s have increased integrin-dependent motility in the presence of astrocytes via modulation of NRG and FGF receptor-linked PI3K/AKT intracellular signaling and do not form boundaries with astrocytes in culture. SC-astrocyte mixing is dependent on local NRG concentration and we propose that sulfatase enzymes influence the bioavailability of NRG ligand and thus influence SC behavior. We further demonstrate that injection of sulfatase expressing SCs into spinal cord white matter results in less glial reactivity than control SC injections comparable to that of OEC injections. Our data indicate that sulfatase-mediated modification of the extracellular matrix can influence glial interactions with astrocytes, and that SCs engineered to express sulfatase may be more OEC-like in character. This approach may be beneficial for cell transplant-mediated spinal cord repair. GLIA 2016 GLIA 2017;65:19-33.

The role of the PI3K/Akt/mTOR pathway in glial scar formation following spinal cord injury

Several studies suggest that glial scars pose as physical and chemical barriers that limit neurite regeneration after spinal cord injury (SCI). Evidences suggest that the activation of the PI3K/Akt/mTOR signaling pathway is involved in glial scar formation. Therefore, inhibition of the PI3K/Akt/mTOR pathway may beneficially attenuate glial scar formation after SCI. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) negatively regulates the PI3K/Akt/mTOR pathway. Therefore, we hypothesized that the overexpression of PTEN in the spinal cord will have beneficial effects after SCI. In the present study, we intrathecally injected a recombinant adenovirus carrying the pten gene (Ad-PTEN) to cause overexpression of PTEN in rats with contusion injured spinal cords. The results suggest overexpression of PTEN in spinal cord attenuated glial scar formation and led to improved locomotor function after SCI. Overexpression of PTEN following SCI attenuated gliosis, affected chondroitin sulfate proteoglycan expression, and improved axon regeneration into the lesion site. Furthermore, we suggest that the activation of the PI3K/Akt/mTOR pathway in astrocytes at 3 days after SCI may be involved in glial scar formation. Because delayed treatment with Ad-PTEN enhanced motor function recovery more significantly than immediate treatment with Ad-PTEN after SCI, the results suggest that the best strategy to attenuate glial scar formation could be to introduce 3 days after SCI. This study's findings thus have positive implications for patients who are unable to receive immediate medical attention after SCI.

Gene delivery strategies to promote spinal cord repair

Gene therapies hold great promise for the treatment of many neurodegenerative disorders and traumatic injuries in the central nervous system. However, development of effective methods to deliver such therapies in a controlled manner to the spinal cord is a necessity for their translation to the clinic. Although essential progress has been made to improve efficiency of transgene delivery and reduce the immunogenicity of genetic vectors, there is still much work to be done to achieve clinical strategies capable of reversing neurodegeneration and mediating tissue regeneration. In particular, strategies to achieve localized, robust expression of therapeutic transgenes by target cell types, at controlled levels over defined time periods, will be necessary to fully regenerate functional spinal cord tissues. This review summarizes the progress over the last decade toward the development of effective gene therapies in the spinal cord, including identification of appropriate target genes, improvements to design of genetic vectors, advances in delivery methods, and strategies for delivery of multiple transgenes with synergistic actions. The potential of biomaterials to mediate gene delivery while simultaneously providing inductive scaffolding to facilitate tissue regeneration is also discussed.

Sponge-mediated lentivirus delivery to acute and chronic spinal cord injuries

The environment within the spinal cord after injury, which changes in the progression from the acute to chronic stages, limits the extent of regeneration. The delivery of inductive factors to promote regeneration following spinal cord injury has been promising, yet, few strategies are versatile to allow delivery during acute or chronic injury that would facilitate screening of candidate therapies. This report investigates the intrathecal delivery of lentiviruses for long-term expression of regenerative factors. Lentivirus-filled sponges were inserted into the intrathecal space surrounding the spinal cord, with transgene expression observed within multiple cell types that persists for 12 weeks for both intact and injured spinal cord, without any apparent damage to the spinal cord tissue. Sponges loaded with lentivirus encoding for Sonic hedgehog (Shh) were investigated for acute (delivered at 0 weeks) and chronic (at 4 weeks) injuries, and for multiple locations relative to the injury. In an acute model, sponges placed directly above the injury increased oligodendrocyte and decreased astrocyte presence. Sponges placed caudal to the injury had reduced impact on oligodendrocytes and astrocytes in the injury. In a chronic model, sponges increased oligodendrocyte and decreased astrocyte presence. Furthermore, the effect of Shh was shown to be mediated in part by reduction of Bmp signaling, monitored with an Msx2-sensitive reporter vector. The implantation of lentivirus-loaded biomaterials intrathecally provides the opportunity to induce the expression of a factor at a specified time without entering the spinal cord, and has the potential to promote gene delivery within the spinal cord, which can influence the extent of regeneration.

Lentiviral-mediated silencing of glial fibrillary acidic protein and vimentin promotes anatomical plasticity and functional recovery after spinal cord injury

In spinal cord injury (SCI), absence of functional recovery and lack of spontaneous axonal regeneration are attributed, among other factors, to the formation of a glial scar that forms both physical and chemical barriers. The glial scar is composed mainly of reactive astrocytes that overexpress two intermediate filament proteins, glial fibrillary acidic protein (GFAP) and vimentin (VIM). To promote regeneration and sprouting of spared axons after spinal cord trauma and with the objective of translation to clinics, we designed an original in vivo gene transfer strategy to reduce glial scar formation after SCI, based on the RNA interference (RNAi)-mediated inhibition of GFAP and VIM. We first show that direct injection of lentiviral vectors expressing short hairpin RNA (shRNA) against GFAP and VIM in a mouse model of SCI allows efficient and specific targeting of astrocytes. We then demonstrate that the lentiviral-mediated and stable expression of shGFAP and shVIM leads to a strong reduction of astrogliosis, improves functional motor recovery, and promotes axonal regrowth and sprouting of spared axons. This study thus examplifies how the nonneuronal environment might be a major target within the lesioned central nervous system to promote axonal regeneration (and sprouting) and validates the use of lentiviral-mediated RNAi in SCI.

Developing a potentially immunologically inert tetracycline-regulatable viral vector for gene therapy in the peripheral nerve

Viral vector-mediated gene transfer of neurotrophic factors is an emerging and promising strategy to promote the regeneration of injured peripheral nerves. Unfortunately, the chronic exposure to neurotrophic factors results in local trapping of regenerating axons or other unwanted side effects. Therefore, tight control of therapeutic gene expression is required. The tetracycline/doxycycline-inducible system is considered to be one of the most promising systems for regulating heterologous gene expression. However, an immune response directed against the transactivator protein rtTA hampers further translational studies. Immunogenic proteins fused with the Gly-Ala repeat of the Epstein-Barr virus Nuclear Antigen-1 protein have been shown to successfully evade the immune system. In this article, we used this strategy to demonstrate that a chimeric transactivator, created by fusing the Gly-Ala repeat with rtTA and embedded in a lentiviral vector (i) retained its transactivator function in vitro, in muscle explants, and in vivo following injection into the rat peripheral nerve, (ii) exhibited a reduced leaky expression, and (iii) had an immune-evasive advantage over rtTA as shown in a novel bioassay for human antigen presentation. The current findings are an important step toward creating a clinically applicable potentially immune-evasive tetracycline-regulatable viral vector system.

Combination of engineered Schwann cell grafts to secrete neurotrophin and chondroitinase promotes axonal regeneration and locomotion after spinal cord injury

Transplantation of Schwann cells (SCs) is a promising therapeutic strategy for spinal cord repair. SCs introduced into lesions support axon regeneration, but because these axons do not exit the transplant, additional approaches with SCs are needed. Here, we transplanted SCs genetically modified to secrete a bifunctional neurotrophin (D15A) and chondroitinase ABC (ChABC) into a subacute contusion injury in rats. We examined the effects of these modifications on graft volume, SC number, degradation of chondroitin sulfate proteoglycans (CSPGs), astrogliosis, SC myelination of axons, propriospinal and supraspinal axon numbers, locomotor outcome (BBB scoring, CatWalk gait analysis), and mechanical and thermal sensitivity on the hind paws. D15A secreted from transplanted SCs increased graft volume and SC number and myelinated axon number. SCs secreting ChABC significantly decreased CSPGs, led to some egress of SCs from the graft, and increased propriospinal and 5-HT-positive axons in the graft. SCs secreting both D15A and ChABC yielded the best responses: (1) the largest number of SC myelinated axons, (2) more propriospinal axons in the graft and host tissue around and caudal to it, (3) more corticospinal axons closer to the graft and around and caudal to it, (4) more brainstem neurons projecting caudal to the transplant, (5) increased 5-HT-positive axons in the graft and caudal to it, (6) significant improvement in aspects of locomotion, and (7) improvement in mechanical and thermal allodynia. This is the first evidence that the combination of SC transplants engineered to secrete neurotrophin and chondroitinase further improves axonal regeneration and locomotor and sensory function.

Intrathecal administration of IGF-I by AAVrh10 improves sensory and motor deficits in a mouse model of diabetic neuropathy

Different adeno-associated virus (AAV) serotypes efficiently transduce neurons from central and peripheral nervous systems through various administration routes. Direct administration of the vectors to the cerebrospinal fluid (CSF) could be an efficient and safe strategy. Here, we show that lumbar puncture of a nonhuman AAV leads to wide and stable distribution of the vector along the spinal cord in adult mice. AAVrh10 efficiently and specifically infects neurons, both in dorsal root ganglia (60% total sensory neurons) and in the spinal cord (up to one-third of α-motor neurons). As a proof of concept, we demonstrate the efficacy of AAVrh10 in a mouse model of diabetic neuropathy, in which intrathecal delivery of the vector coding for insulin-like growth factor (IGF-I) favored the release of the therapeutic protein into the CSF through its expression by sensory and motor neurons. IGF-I-treated diabetic animals showed increased vascular endothelial growth factor expression, activation of Akt/PI3K pathway, and stimulated nerve regeneration and myelination in injured limbs. Moreover, we achieved restoration of nerve conduction velocities in both sensory and motor nerves by AAVrh10, whereas we reached only sensory nerve improvement with AAV1. Our results indicate that intrathecal injection of AAVrh10 is a promising tool to design gene therapy approaches for sensorimotor diseases.

A multilevel screening strategy defines a molecular fingerprint of proregenerative olfactory ensheathing cells and identifies SCARB2, a protein that improves regenerative sprouting of injured sensory spinal axons

Olfactory ensheathing cells (OECs) have neuro-restorative properties in animal models for spinal cord injury, stroke, and amyotrophic lateral sclerosis. Here we used a multistep screening approach to discover genes specifically contributing to the regeneration-promoting properties of OECs. Microarray screening of the injured olfactory pathway and of cultured OECs identified 102 genes that were subsequently functionally characterized in cocultures of OECs and primary dorsal root ganglion (DRG) neurons. Selective siRNA-mediated knockdown of 16 genes in OECs (ADAMTS1, BM385941, FZD1, GFRA1, LEPRE1, NCAM1, NID2, NRP1, MSLN, RND1, S100A9, SCARB2, SERPINI1, SERPINF1, TGFB2, and VAV1) significantly reduced outgrowth of cocultured DRG neurons, indicating that endogenous expression of these genes in OECs supports neurite extension of DRG neurons. In a gain-of-function screen for 18 genes, six (CX3CL1, FZD1, LEPRE1, S100A9, SCARB2, and SERPINI1) enhanced and one (TIMP2) inhibited neurite growth. The most potent hit in both the loss- and gain-of-function screens was SCARB2, a protein that promotes cholesterol secretion. Transplants of fibroblasts that were genetically modified to overexpress SCARB2 significantly increased the number of regenerating DRG axons that grew toward the center of a spinal cord lesion in rats. We conclude that expression of SCARB2 enhances regenerative sprouting and that SCARB2 contributes to OEC-mediated neuronal repair.

Noninvasive Bioluminescence Imaging of Olfactory Ensheathing Glia and Schwann Cells following Transplantation into the Lesioned Rat Spinal Cord

In this study, we assess the feasibility of bioluminescence imaging to monitor the survival of Schwann cells (SCs) and olfactory ensheathing glia cells (OECs) after implantation in the lesioned spinal cord of adult rats. To this end, purified SCs and OECs were genetically modified with lentiviral vectors encoding luciferase-2 and GFP and implanted in the lesioned dorsal column. The bioluminescent signal was monitored for over 3 months, and at 7 and 98 days postsurgery, the signal was compared to standard histological analysis of GFP expression in the spinal cords. The temporal profile of the bioluminescent signal showed three distinct phases for both cell types. (I) A relatively stable signal in the first week. (II) A progressive decline in signal strength in the second and third week. (III) After the third week, the average bioluminescent signal stabilized for both cell types. Interestingly, in the first week, the peak of the bioluminescent signal after luciferin injection was delayed when compared to later time points. Similar to in vitro, our data indicated a linear relationship between the in vivo bioluminescent signal and the GFP signal of the SCs and OECs in the spinal cords when the results of both the 7 and 98 day time points are combined. This is the first report of the use of in vivo bioluminescence to monitor cell survival in the lesioned rat spinal cord. Bioluminescence could be a potentially powerful, non-invasive strategy to examine the efficacy of treatments that aim to improve the survival of proregenerative cells transplanted in the injured rat spinal cord.

Early regenerative effects of NGF-transduced Schwann cells in peripheral nerve repair

Peripheral nerve injury leads to a rapid and robust increase in the synthesis of neurotrophins which guide and support regenerating axons. To further optimize neurotrophin supply at the earliest stages of regeneration, we over-expressed NGF in Schwann cells (SCs) by transducing these cells with a lentiviral vector encoding NGF (NGF-SCs). Transplantation of NGF-SCs in a rat sciatic nerve transection/repair model led to significant increase of NGF levels 2weeks after injury and correspondingly to substantial improvement in axonal regeneration. Numbers of NF200, ChAT and CGRP-positive axon profiles, as well as the gastrocnemius muscle weights, were significantly higher in the NGF-Schwann cell group compared to the animals that received control SCs transduced with a lentiviral vector encoding GFP (GFP-SCs). Comparison with other models of NGF application signifies the important role of this neurotrophin during the early stages of regeneration, and supports the importance of developing combined gene and cell therapy for peripheral nerve repair.

Lentiviral vectors carrying enhancer elements of Hb9 promoter drive selective transgene expression in mouse spinal cord motor neurons

Recombinant lentiviral vectors (rLVs) have emerged as versatile tools for gene delivery applications due to a number of favorable features, such as the possibility to maintain long-term transgene expression, the flexibility in the design of the expression cassettes and recent improvements in their biosafety profile. Since rLVs are able to infect multiple cell types including post-mitotic cells such as neurons and skeletal muscle cells, several studies have been exploring their application for the study and cure of neurodegenerative diseases. In particular, the introduction of rLVs carrying cell-type specific promoters could restrict the transgene expression either to neuronal or glial cells, thus helping to better dissect in vivo the role played by these cell populations in several neurodegenerative processes. In this study we developed rLVs carrying motor neuron specific regulatory sequences derived from the promoter of homeobox gene Hb9, and demonstrated that these constructs can represent a suitable platform for selective gene-targeting of murine spinal cord motor neurons, in vivo. This tool could be instrumental in the dissection of the molecular mechanisms involved in the selective degeneration of motor neurons occurring in Motor Neuron Diseases.

Lentiviral vectors express chondroitinase ABC in cortical projections and promote sprouting of injured corticospinal axons

Several diseases and injuries of the central nervous system could potentially be treated by delivery of an enzyme, which might most effectively be achieved by gene therapy. In particular, the bacterial enzyme chondroitinase ABC is beneficial in animal models of spinal cord injury. We have adapted the chondroitinase gene so that it can direct secretion of active chondroitinase from mammalian cells, and inserted it into lentiviral vectors. When injected into adult rat brain, these vectors lead to extensive secretion of chondroitinase, both locally and from long-distance axon projections, with activity persisting for more than 4 weeks. In animals which received a simultaneous lesion of the corticospinal tract, the vector reduced axonal die-back and promoted sprouting and short-range regeneration of corticospinal axons. The same beneficial effects on damaged corticospinal axons were observed in animals which received the chondroitinase lentiviral vector directly into the vicinity of a spinal cord lesion.

The influence of epileptic neuropathology and prior peripheral immunity on CNS transduction by rAAV2 and rAAV5

Adeno-associated virus (AAV) provides a promising platform for clinical treatment of neurological disorders owing to its established efficacy and lack of apparent pathogenicity. To use viral vectors in treating neurological disease, however, transduction must occur under neuropathological conditions. Previous studies in rodents have shown that AAV5 more efficiently transduces cells in the hippocampus and piriform cortex than AAV2. Using the kainic acid (KA) model of temporal lobe epilepsy and AAV2 and 5 carrying a hybrid chicken β-actin promoter driving green fluorescent protein (GFP), we found that limbic seizure activity caused substantial neuropathology and resulted in a significant reduction in subsequent AAV5 transduction. Nonetheless, this reduced transduction still was greater than AAV2 transduction in control rats. Although KA seizures compromise blood-brain barrier function, potentially increasing exposure of target tissue to circulating neutralizing antibodies, we observed no interaction between KA seizure-induced damage and immunization status on AAV transduction. Finally, while we confirmed the near total neuronal-specific transgene expression for both serotypes in control rats, AAV5-GFP expression was increasingly localized to astrocytes in seizure-damaged areas. Thus, the pathological milieu of the injured brain can reduce transduction efficacy and alter viral tropism- both relevant concerns when considering viral vector gene therapy for neurological disorders.

Lentiviral vector-mediated knockdown of the NG2 [corrected] proteoglycan or expression of neurotrophin-3 promotes neurite outgrowth in a cell culture model of the glial scar

BACKGROUND

Following spinal cord injury, a highly inhibitory environment for axonal regeneration develops. One of the main sources of this inhibition is the glial scar that is formed after injury by reactive astrocytes. The inhibitory environment is mainly a result of chondroitin sulphate proteoglycans (CSPGs). NG2, [corrected] one of the main inhibitory CSPGs, is up-regulated following spinal cord injury.

METHODS

Small interfering RNA (siRNA) was designed to target NG2 and this short hairpin RNA (shRNA) was cloned into a lentiviral vector (LV). The neurotrophic factor neurotrophin-3 (NT-3) promotes the growth and survival of developing neurites and has also been shown to aid regeneration. NT-3 was also cloned into a LV. In vitro assessment of these vectors using a coculture system of dorsal root ganglia (DRG) neurones and Neu7 astrocytes was carried out. The Neu7 cell line is a rat astrocyte cell line that overexpresses NG2, thereby mimicking the inhibitory environment following spinal cord injury.

RESULTS AND DISCUSSION

These experiments show that both the knockdown of NG2 via shRNA and over-expression of NT-3 can significantly increase neurite growth, although a combination of both vectors did not confer any additional benefit over the vectors used individually. These LVs show promising potential for growth and survival of neurites in injured central nervous system tissue (CNS).

Anti-inflammatory effect by lentiviral-mediated overexpression of IL-10 or IL-1 receptor antagonist in rat glial cells and macrophages

Neuroinflammation, as defined by activation of local glial cells and production of various inflammatory mediators, is an important feature of many neurological disorders. Expression of pro-inflammatory mediators produced by glial cells in the central nervous system (CNS) is considered to contribute to the neuropathology observed in those diseases. To diminish the production or action of pro-inflammatory mediators, we have used lentiviral (LV) vector-mediated encoding rat interleukin-10 (rIL-10) or rat interleukin-1 receptor antagonist (rIL-1ra) to direct the local, long-term expression of these anti-inflammatory cytokines in the CNS. We have shown that cultured macrophages or astroglia transduced with LV-rIL-10 or LV-rIL-1ra produced far less tumor necrosis factor (TNF)alpha or IL-6, respectively in response to pro-inflammatory stimuli. Moreover, intracerebroventricular (i.c.v.) administration of LV-rIL-10 or LV-rIL-1ra resulted in transduction of glial cells and macrophages and, subsequently reduced TNFalpha, IL-6 and inducible nitric oxide synthase (iNOS) expression in various brain regions induced by inflammatory stimuli, whereas peripheral expression of these mediators remained unaffected. In addition, expression levels of the anti-inflammatory cytokines IL-4 and transforming growth factor-beta were not altered in either brain or pituitary gland. Furthermore, i.c.v. administration of LV-rIL-10 or LV-rIL-1ra given during the remission phase of chronic-relapsing experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis, improved the clinical outcome of the relapse phase. Thus, local application of LV vectors expressing anti-inflammatory cytokines could be of therapeutic interest to counteract pro-inflammatory processes in the brain without interfering with the peripheral production of inflammatory mediators.

Comparison of AAV serotypes for gene delivery to dorsal root ganglion neurons

For many experiments in the study of the peripheral nervous system, it would be useful to genetically manipulate primary sensory neurons. We have compared vectors based on adeno-associated virus (AAV) serotypes 1, 2, 3, 4, 5, 6, and 8, and lentivirus (LV), all expressing green fluorescent protein (GFP), for efficiency of transduction of sensory neurons, expression level, cellular tropism, and persistence of transgene expression following direct injection into the dorsal root ganglia (DRG), using histological quantification and qPCR. Two weeks after injection, AAV1, AAV5, and AAV6 had transduced the most neurons. The time course of GFP expression from these three vectors was studied from 1 to 12 weeks after injection. AAV5 was the most effective serotype overall, followed by AAV1. Both these serotypes showed increasing neuronal transduction rates at later time points, with some injections of AAV5 yielding over 90% of DRG neurons GFP(+) at 12 weeks. AAV6 performed well initially, but transduction rates declined dramatically between 4 and 12 weeks. AAV1 and AAV5 both transduced large-diameter neurons, IB4(+) neurons, and CGRP(+) neurons. In conclusion, AAV5 is a highly effective gene therapy vector for primary sensory neurons following direct injection into the DRG.

Lentiviral vectors for gene transfer into the spinal cord glial cells

Activated glial cells in the dorsal spinal cord participate in the development and maintenance of pain after peripheral nerve injury. Our understanding of mechanisms involved in functional changes of spinal glia remains incomplete. Excepting drugs that completely disrupt glial function, pharmacological studies fail to target glia and to modify locally its function to really discriminate the function of neuronal versus glial cells in chronic pain. Lentivirus-derived vectors fulfill several criteria that make them potentially interesting for this preferential targeting of glial cells in the spinal cord. We showed that in vivo single microdelivery of vesicular stomatitis virus G pseudotyped lentiviral vectors into the rat dorsal spinal cord led to a highly preferential expression of transgenes in astrocytes and microglial cells. This local and glia-targeted intervention allowed, for instance, the blockade of intracellular nuclear factor kappaB signaling pathway leading then to downregulation of the enhanced expression of several markers related to inflammation and pain, and, finally, to prolonged antihyperalgesic and antiallodynic effects. Targeted modulation of the expression of gene of interest in glial cells, closely restricted to a particular region of the spinal cord, may thus represent an interesting approach to refine the understanding of mechanisms by which spinal glial cells participate in pain processing.