Advances in stem cell and other therapies for Huntington's disease: An update.

Huntington's disease (HD) is a neurodegenerative disorder caused by an autosomal dominant mutation leading to an abnormal CAG repeat expansion. The result is the synthesis of a toxic misfolded protein, called the mutant huntingtin protein (mHTT). Most current treatments are palliative, but the latest research has expanded into multiple modalities, including stem cells, gene therapy, and even the use of 3D cell structures, called organoids. Stem cell research as a treatment for HD has included the use of various types of stem cells, such as mesenchymal stem cells, neural stem cells, embryonic stem cells, and even reprogrammed stem cells called induced pluripotent stem cells. The goal has been to develop stem cell transplant grafts that will replace the existing mutated neurons, as well as release existing trophic factors for neuronal support. Additionally, research in gene modification using CRISPR-Cas9, PRIME editing, and other forms of genetic modifications are continuing to evolve. Most recently, advancements in stem cell modeling have yielded 3D stem cell tissue models, called organoids. These organoids offer the unique opportunity to transplant a structured stem cell graft which, ideally, models normal human brain tissue more accurately. This manuscript summarizes the recent research in stem cells, genetic modifications, and organoids as a potential for treatment of HD.

Transplantation of mesenchymal stem cells genetically engineered to overexpress interleukin-10 promotes alternative inflammatory response in rat model of traumatic brain injury.

BACKGROUND: Traumatic brain injury (TBI) is a major cause for long-term disability, yet the treatments available that improve outcomes after TBI limited. Neuroinflammatory responses are key contributors to determining patient outcomes after TBI. Transplantation of mesenchymal stem cells (MSCs), which release trophic and pro-repair cytokines, represents an effective strategy to reduce inflammation after TBI. One such pro-repair cytokine is interleukin-10 (IL-10), which reduces pro-inflammatory markers and trigger alternative inflammatory markers, such as CD163. In this study, we tested the therapeutic effects of MSCs that were engineered to overexpress IL-10 when transplanted into rats following TBI in the medial frontal cortex. METHODS: Thirty-six hours following TBI, rats were transplanted with MSCs and then assessed for 3 weeks on a battery of behavioral tests that measured motor and cognitive abilities. Histological evaluation was then done to measure the activation of the inflammatory response. Additionally, immunomodulatory effects were evaluated by immunohistochemistry and Western blot analyses. RESULTS: A significant improvement in fine motor function was observed in rats that received transplants of MSCs engineered to overexpress IL-10 (MSCs + IL-10) or MSCs alone compared to TBI + vehicle-treated rats. Although tissue spared was unchanged, anti-inflammatory effects were revealed by a reduction in the number of glial fibrillary acidic protein cells and CD86 cells in both TBI + MSCs + IL-10 and TBI + MSC groups compared to TBI + vehicle rats. Microglial activation was significantly increased in the TBI + MSC group when compared to the sham + vehicle group. Western blot data suggested a reduction in tumor necrosis factor-alpha in the TBI + MSCs + IL-10 group compared to TBI + MSC group. Immunomodulatory effects were demonstrated by a shift from classical inflammation expression (CD86) to an alternative inflammation state (CD163) in both treatments with MSCs and MSCs + IL-10. Furthermore, co-labeling of both CD86 and CD163 was detected in the same cells, suggesting a temporal change in macrophage expression. CONCLUSIONS: Overall, our findings suggest that transplantation of MSCs that were engineered to overexpress IL-10 can improve functional outcomes by providing a beneficial perilesion environment. This improvement may be explained by the shifting of macrophage expression to a more pro-repair state, thereby providing a possible new therapy for treating TBI.

In vitro validation of effects of BDNF-expressing mesenchymal stem cells on neurodegeneration in primary cultured neurons of APP/PS1 mice.

Alzheimer's disease (AD), the most common type of dementia, is characterized by the presence of senile plaques, neurofibrillary tangles, and neuronal loss in defined regions of the brain including the hippocampus and cortex. Transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) offers a safe and potentially effective tool for treating neurodegenerative disorders. However, the therapeutic effects of BM-MSCs on AD pathology remain unclear and their mechanisms at cellular and molecular levels still need to be addressed. In this study, we developed a unique neuronal culture made from 5xFAD mouse, an APP/PS1 transgenic mouse model (FAD neurons) to investigate progressive neurodegeneration associated with AD pathology and efficacy of brain-derived neurotrophic factor expressing-MSCs (BDNF-MSCs). Analyses of the expression of brain-derived neurotrophic factor (BDNF), synaptic markers and survival/apoptotic signals indicate that pathological features of cultured neurons made from these mice accurately mimic AD pathology, suggesting that our protocol provided a valid in vitro model of AD. We also demonstrated amelioration of AD pathology by MSCs in vitro when these FAD neurons were co-cultured with MSCs, a paradigm that mimics the in vivo environment of post-transplantation of MSCs into damaged regions of brains. To overcome failed delivery of BDNF to the brain and to enhance MSCs releasing BDNF effect, we created BDNF-MSCs and found that MSCs protection was enhanced by BDNF-MSCs. This protection was abolished by BDNF-blocking peptides, suggesting that BDNF supply from BDNF-MSCs was enough to prevent AD pathology.

Bone-marrow-derived mesenchymal stem cells attenuate cognitive deficits in an endothelin-1 rat model of stroke.

PURPOSE: Stroke is the third leading cause of death and permanent disability in the United States, often producing long-term cognitive impairments, which are not easily recapitulated in animal models. The goals of this study were to assess whether: (1) the endothelin-1 (ET-1) model of chronic stroke produced discernable cognitive deficits; (2) a spatial operant reversal task (SORT) would accurately measure memory deficits in this model; and (3) bone-marrow-derived mesenchymal stem cells (BMMSCs) could reduce any observed deficits. METHODS: Rats were given unilateral intracerebral injections of vehicle or ET-1, a stroke-inducing agent, near the middle cerebral artery. Seven days later, they were given intrastriatal injections of BMMSCs or vehicle, near the ischemic penumbra. The cognitive abilities of the rats were assessed on a novel SORT, which was designed to efficiently distinguish cognitive deficits from potential motoric confounds. RESULTS: Rats given ET-1 had significantly more cognitive errors at six weeks post-stroke on the SORT, and that these deficits were attenuated by BMMSC transplants. CONCLUSIONS: These findings indicate that: (1) the ET-1 model produces chronic cognitive deficits; (2) the SORT efficiently measures cognitive deficits that are not confounded by motoric impairment; and (3) BMMSCs may be a viable treatment for stroke-induced cognitive dysfunction.

Assessing the potential clinical utility of transplantations of neural and mesenchymal stem cells for treating neurodegenerative diseases.

Treatments for neurodegenerative diseases have little impact on the long-term patient health. However, cellular transplants of neuroblasts derived from the aborted embryonic brain tissue in animal models of neurodegenerative disorders and in patients have demonstrated survival and functionality in the brain. However, ethical and functional problems due to the use of this fetal tissue stopped most of the clinical trials. Therefore, new cell sources were needed, and scientists focused on neural (NSCs) and mesenchymal stem cells (MSCs). When transplanted in the brain of animals with Parkinson's or Huntington's disease, NSCs and MSCs were able to induce partial functional recovery by promoting neuroprotection and immunomodulation. MSCs are more readily accessible than NSCs due to sources such as the bone marrow. However, MSCs are not capable of differentiating into neurons in vivo where NSCs are. Thus, transplantation of NSCs and MSCs is interesting for brain regenerative medicine. In this chapter, we detail the methods for NSCs and MSCs isolation as well as the transplantation procedures used to treat rodent models of neurodegenerative damage.

NR2B selective NMDA receptor antagonist CP-101,606 prevents levodopa-induced motor response alterations in hemi-parkinsonian rats.

Sensitization of NMDA receptors containing the NR2B subunit has been increasingly associated with various forms of synaptic plasticity, including those implicated in the pathogenesis of extrapyramidal motor dysfunction. To determine whether activation of NR2B containing receptors contributes to the development and maintenance of levodopa-induced response changes in parkinsonian animals, we evaluated the effects of the selective NR2B antagonist CP-101,606 on these response alterations in unilateral 6-hydroxydopamine (6-OHDA) lesioned rats. Three weeks of twice-daily levodopa treatment decreased the duration of the rotational response to acute levodopa challenge. The response alteration was associated with an increase in GluR1 (S831) phosphorylation in medium spiny neurons of the dorsolateral striatum. Both the attenuated rotational response and augmented GluR1 phosphorylation were decreased by CP-101,606 treatment. These CP-101,606 effects were observed when the compound was administered either at the end of chronic levodopa treatment (ameliorative effect) or together with the twice-daily levodopa treatment for 3 weeks (preventive effect). Furthermore, concurrent administration of CP-101,606 with levodopa potentiated the ability of levodopa challenge to reverse the 6-OHDA lesion-induced contralateral forelimb movement deficit as measured in a drag test. These results suggest that activation of NR2B subunit containing NMDA receptors contributes to both the development and maintenance of levodopa-induced motor response alterations, through a mechanism that involves an increase in GluR1 phosphorylation in striatal spiny neurons.

Creatine reduces 3-nitropropionic-acid-induced cognitive and motor abnormalities in rats.

This study assessed whether creatine could attenuate 3-nitropropionic acid (3NP)-induced neuropathological and behavioral abnormalities that are analogous to those observed in Huntington's disease (HD). Rats were fed diets containing either 1% creatine or normal rat chow for 2 weeks prior to the onset of 3NP administration, and for the duration of the study. 3NP was administered systemically in gradually increasing concentrations over an 8-week testing period. Results show that creatine can attenuate 3NP-induced striatal lesions, striatal atrophy, ventricular enlargement, cognitive deficits, and motor abnormalities on a balance beam task. Collectively, these findings indicate that creatine provides significant protection against 3NP-induced behavioral and neuropathological abnormalities and may have therapeutic potential for HD.

Quinolinic acid released from polymeric brain implants causes behavioral and neuroanatomical alterations in a rodent model of Huntington's disease.

Quinolinic acid (QA) is an N-methyl-d-aspartate agonist that has been shown to produce neurotoxic effects that mimic certain neurodegenerative diseases when administered to laboratory animals. Intrastriatal injections of QA in rats have been used extensively to produce some of the neuropathological and behavioral deficits that are analogous to Huntington's disease (HD). However, acute intrastriatal injections of QA produce symptoms that are not analogous to the progressive nature of HD. Thus far, models using chronic administration of QA that produce HD-like behavioral and neuroanatomical changes have necessitated the use of a relatively bulky and fragile microdialytic pump apparatus. The present study tested an alternative way of chronically administering QA. Specifically, this study tested whether gradual release of QA from ethylene vinylacetate (EVA) polymers could produce symptoms analogous to HD. Rats received either no implants or bilateral intrastriatal implants of polymers with or without QA. Subsequent tests for spontaneous motor activity (SMA), grip strength, balance, and learning ability in a radial-arm-water-maze task revealed QA-induced impairments in balance and learning ability, but did not affect grip strength or SMA. Histological analysis revealed QA-induced enlargement of lateral ventricles, striatal atrophy, and striatal neuronal loss, with relative sparing of NADPH-diaphorase-positive neurons. These results suggest that QA released from polymers can produce behavioral and neuropathological profiles analogous to early stages of HD and that EVA polymers offer a useful means of chronically delivering QA in rodent models of neurodegeneration.

Comparison of intrastriatal injections of quinolinic acid and 3-nitropropionic acid for use in animal models of Huntington's disease.

1. The present study compared the effects of acute intrastriatal administration of quinolinic acid (QA) and 3-nitropropionic acid (3-NP), two neurotoxins used in animal models of Huntington's disease (HD), on the following behavioral and histological measures: (1) open field activity levels; (2) performance on balance beam and grip strength tasks; (3) acquisition of a radial-arm-water-maze (RAWM) task; (4) size of striatum and lateral ventricles; (5) amount of cytochrome oxidase (CYO) labeling; and (6) counts of Nissl-stained neurons and NADPH-diaphorase-labeled neurons in the striatum. 2. Rats were given bilateral intrastriatal injections of either 200 nmol QA, 750 nmol 3-NP, or phosphate buffered saline (PBS) two weeks prior to behavioral testing and four weeks prior to histological processing. 3. The behavioral results indicated that both QA and 3-NP injections caused an increase in activity levels at two weeks postlesion, but only the QA rats showed hyperactivity at four weeks postlesion. Both QA and 3-NP rats showed significant impairment in the balance beam task, but only 3-NP rats differed significantly on the grip-strength task. Both toxins caused learning impairments in the RAWM task, with 3-NP rats being more severely impaired. 4. The neuroanatomical results indicated that both QA and 3-NP produced significant striatal atrophy and ventricular dilation, as well as a reduction in CYO staining and loss of Nissl-stained neurons, but only the 3-NP lesions created necrotic cavities in the striatum. However, the QA treatments resulted in significant loss of NADPH-diaphorase neurons in regions peripheral to the site of injection. 5. In general, these results suggest that QA treatments produce milder behavioral and neuroanatomical effects that mimic some of the earlier symptoms of HD, while 3-NP produced more severe effects which mimic both the later symptoms and the juvenile onset of HD.

Chronic administration of quinolinic acid in the rat striatum causes spatial learning deficits in a radial arm water maze task.

Chronic intrastriatal administration of quinolinic acid (QA) in the rat produces a pattern of neurodegeneration similar to that seen in Huntington's disease (HD). Although these changes have been related to transient motor abnormalities, the effects of chronic QA administration on cognitive abilities have not been assessed. The present study investigated whether the striatal deterioration observed during chronic QA administration produces cognitive impairments in this animal model of HD by testing the effects of chronic administration of QA on spatial learning ability of rats in a radial arm water maze (RAWM) task. Rats were given bilateral implantation of a chronic dialysis probe apparatus which delivered either vehicle or QA (20 mM) into the striatum. Beginning 1 day after implantation, the rats were tested daily for 3 weeks in the RAWM. Nocturnal activity levels were also assessed at 1-, 3-, 5-, 7-, 14-, and 21-days following probe implantation. Results of behavioral testing indicated that chronic exposure to QA causes spatial learning deficits in the RAWM task with only a transient increase in activity levels. Collectively, these results suggest that chronic striatal exposure to QA mimics some aspects of the cognitive deficits observed in HD.

Small drug sample fabrication of controlled release polymers using the microextrusion method.

Ethylene vinylacetate polymer (EVA) has been used for many years to fabricate controlled-release polymeric implant devices with which drugs of high or low molecular weight compounds could be delivered with zero-order kinetics. However, because the known fabrication methods such as solvent evaporation, casting and possible shrinkage are not sufficiently controllable we have now developed the microextrusion method with which even small amount of clinically important and expensive drugs can be incorporated into EVA with high reproducibility. We show here that devices produced by the microextrusion method allows for a controlled delivery of several neurotoxic and neurotherapeutic compounds such as alpha-methyl-p-tyrosine, diazepam, quinolinic acid, and phencyclidine. Each substance is slowly released from the polymer, as evidenced by spectrophotometric data, for up to 120 days at daily rates varying from 18.4 microg of phencyclidine to 97.6 microg/day of diazepam. Thus, microextrusion is a valuable method for fabricating controlled-release polymers in which small amounts of scarce drugs can be incorporated. Another advantage of the current procedure is that polymers can be fabricated with very little amount of solvent.

Medial septal lesions in rats produce permanent deficits for strategy selection in a spatial memory task.

Rats with medial septal (MS) lesions have been shown to consistently use a stereotypic response strategy rather than a nonstereotypic spatial learning strategy when solving a radial maze task. The present study examined the long-term effects of MS lesions on spatial memory performance to determine whether MS lesions permanently impair rats from using a nonstereotypic strategy. Male rats, initially trained on a radial maze, were given either MS or sham surgeries and were subsequently retested on the maze. Consistent with previous studies, all rats with MS lesions used a stereotypic strategy during the postoperative retest. However, when placed through a series of retraining phases that required the rat to use a nonstereotypic strategy to solve the task, none of the MS rats could solve the task. These results indicate that lesions of the medial septum produce permanent spatial memory deficits that cannot be restored through extensive behavioral training.

Comparison of GM1 ganglioside, AGF2, and D-amphetamine as treatments for spatial reversal and place learning deficits following lesions of the neostriatum.

These experiments tested the effectiveness of parenterally administered gangliosides and amphetamine as treatments for spatial learning deficits caused by bilateral lesions of the neostriatum. In Expt. 1, rats were tested postsurgically for 30 days on a shock-avoidance, spatial reversal task. Treatments of gangliosides (GM1 at 30 mg/kg, and AGF2 at 20 mg/kg and 30 mg/kg) and D-amphetamine (2 mg/kg) significantly decreased lesion-induced learning deficits on this task, while treatments of 10 mg/kg AGF2 and the combination of GM1 (30 mg/kg) and D-amphetamine (2 mg/kg) were ineffective. In Expt. 2, rats were given bilateral neostriatal lesions and treated with GM1 (30 mg/kg), AGF2 (20 mg/kg) or D-amphetamine (2 mg/kg) and tested postsurgically for 5 days on a place learning task in the Morris water maze. Only the GM1-treated rats showed a reduction in lesion-induced place learning deficits on this task. Since in both experiments, cell counts near the area of the lesion revealed no differences among any of the brain-damaged groups, it was suggested that the treatments exert their behavioral effects by biochemically activating spared neurons, independent of any ultimate effects they may have on neuronal survival.

Hippocampal choline acetyltransferase activity correlates with spatial learning in aged rats.

Age-related cognitive deficits in both humans and experimental animals appear to relate to dysfunction of basal forebrain cholinergic neuron systems. The present study assessed spatial learning performance in a water maze task as a function of choline acetyltransferase and high-affinity choline uptake specific activity (the two phenotypic markers for cholinergic neurons) in frontal cortex, hippocampus and striatum of aged male Fischer-344 rats. We observed that increased hippocampal choline acetyltransferase activity was related to better performance on the water maze task, and that, of the individual measures, hippocampal choline acetyltransferase activity was the best predictor of behavioral performance in the spatial learning task.

Reduction of anterograde degeneration in brain damaged rats by GM1-gangliosides.

After receiving a nigrostriatal hemitransection in the left hemisphere and an electrolytic caudate nucleus (CN) lesion in the right hemisphere, rats were given intraperitoneal injections of saline or GM1-gangliosides. Significantly smaller areas of terminal degeneration were seen in the substantia nigra pars reticulata (SNr) ipsilateral to the caudate lesion of animals treated with GM1. No statistical differences were seen in the number of degenerating terminals in the CN and SNr on the side with the hemitransection. Exogenous GM1 may thus be effective in preventing anterograde degeneration following brain injury.

GM1 gangliosides stimulate neuronal reorganization and reduce rotational asymmetry after hemitransections of the nigro-striatal pathway.

The effects of monosialoganglioside (GM1) injections on neuronal reorganization and behavioral recovery were studied in rats with unilateral transections of the nigro-striatal pathway. In Experiment 1, animals were treated daily with injections of saline or GM1 for not more than 14 days. At 2 days after surgery, GM1-treated animals exhibited less amphetamine-induced rotational asymmetry than did saline treated counterparts. This difference was still apparent at day 12, but vanished at postoperative day 39. Apomorphine-induced rotational asymmetry was equal in both groups at day 15, but by day 42, asymmetries increased in saline controls while remaining unchanged in GM1-treated animals. Rats were killed at either post-operative days 3, 15, or 45 after having received injections of horseradish peroxidase (HRP) into the denervated caudate nucleus. The number of neurons labelled by retrograde HRP-transport were counted in the ipsilateral substantia nigra pars compacta (iSNc), ipsilateral ventral tegmental area (iVTA), frontal cortex, and in the contralateral substantia nigra pars compacta (cSNc). Anterograde transport was also examined in the ipsilateral substantia nigra pars reticulata (iSNr). A significant loss of retrograde labelling in iSNc and iVTA was observed for both groups at post-operative day 3. At day 15, however, GM1-treated animals showed more labelling in these structures as well as in the cSNc. At 45 days after surgery comparable labelling was seen in both lesion groups. The total area of anterograde HRP-labelling in the iSNr significantly increased over time, with no differences between treatment groups. In Experiment 2, rats given the same hemitransections as in Experiment 1, were treated with daily injections of saline or GM1 for 14 days, and then received unilateral injections of 6-hydroxydopamine into the iSNc and iVTA. Nine days later, brain tissue was stained for examination of anterograde degeneration. Significantly more degenerating axons and terminals were found in the caudate nucleus of GM1-terminals were found in the caudate nucleus of GM1-treated rats than in saline-treated controls. We propose that the early reduction of behavioral deficits may be related to a ganglioside-induced reduction of secondary degeneration or edema. The effect of gangliosides on later behavioral recovery is to accelerate neuronal reorganization. This reorganization probably involves terminal proliferation of ascending, intact striatal afferents spared by the hemitransection.

Gangliosides minimize behavioral deficits and enhance structural repair after brain injury.

Injections of GM1-gangliosides (30 mg/kg, i.p.) in adult rats were shown to reduce behavioral deficits after brain lesions. This was observed (1) after bilateral electrolytic lesions of the caudate nucleus in a learning task involving negative reinforcement; (2) following aspiration lesions of the mediofrontal cortex in a learning task involving positive reinforcement; and (3) when rotational behavior was assessed after amphetamine or apomorphine injections in animals with partial hemitransections of the nigro-striato-nigral fibers. A detailed anatomical analysis of the latter study, using a retrograde tract-tracing dye wheat germ agglutinin-horseradish peroxidase (WGA-HRP), provided evidence for ganglioside-stimulated, neuronal reorganization of connections to the caudate nucleus. Our findings support the notion that gangliosides reduce behavioral deficits following brain injury by preventing secondary neuronal degeneration and/or enhancing structural reorganization of remaining afferents, rather than by influencing denervation supersensitivity.