The corridor task: Striatal lesion effects and graft-mediated recovery in a model of Huntington's disease

Recent approaches in regenerative medicine in the fight against neurodegenerative disease

Neurodegenerative diseases arise due to slow and gradual loss of structure and/or function of neurons and glial cells and cause different degrees of loss of cognition abilities and sensation. The little success in developing effective treatments imposes a high and regressive economic impact on society, patients and their families. In recent years, regenerative medicine has provided a great opportunity to research new innovative strategies with strong potential to treatleva these diseases. These effects are due to the ability of suitable cells and biomaterials to regenerate damaged nerves with differentiated cells, creating an appropriate environment for recovering or preserving existing healthy neurons and glial cells from destruction and damage. Ultimately, a better understanding and thus a further investigation of stem cell technology, tissue engineering, gene therapy, and exosomes allows progress towards practical and effective treatments for neurodegenerative diseases. Therefore, in this review, advances currently being developed in regenerative medicine using animal models and human clinical trials in neurological disorders are summarized.

Exploring the Central Mechanisms of Botulinum Toxin in Parkinson's Disease: A Systematic Review from Animal Models to Human Evidence

Botulinum toxin (BoNT) is an effective and safe therapy for the symptomatic treatment of several neurological disturbances. An important line of research has provided numerous pieces of evidence about the mechanisms of action of BoNT in the central nervous system, especially in the context of dystonia and spasticity. However, only a few studies focused on the possible central effects of BoNT in Parkinson's disease (PD). We performed a systematic review to describe and discuss the evidence from studies focused on possible central effects of BoNT in PD animal models and PD patients. To this aim, a literature search in PubMed and SCOPUS was performed in May 2023. The records were screened according to title and abstract by two independent reviewers and relevant articles were selected for full-text review. Most of the papers highlighted by our review report that the intrastriatal administration of BoNT, through local anticholinergic action and the remodulation of striatal compensatory mechanisms secondary to dopaminergic denervation, induces an improvement in motor and non-motor symptoms in the absence of neuronal loss in animal models of PD. In human subjects, the data are scarce: a single neurophysiological study in tremulous PD patients found that the change in tremor severity after peripheral BoNT administration was associated with improved sensory-motor integration and intracortical inhibition measures. Further clinical, neurophysiological, and neuroimaging studies are necessary to clarify the possible central effects of BoNT in PD.

Challenges in progressing cell therapies to the clinic for Huntington's disease: A review of the progress made with pluripotent stem cell derived medium spiny neurons

Huntington's disease (HD) is a hereditary, neurodegenerative disorder characterized by a triad of symptoms: motor, cognitive and psychiatric. HD is caused by a genetic mutation, expansion of the CAG repeat in the huntingtin gene, which results in loss of medium spiny neurons (MSNs) of the striatum. Cell replacement therapy (CRT) has emerged as a possible therapy for HD, aiming to replace those cells lost to the disease process and alleviate its symptoms. Initial pre-clinical studies used primary fetal striatal cells to provide proof-of-principal that CRT can bring about functional recovery on some behavioral tasks following transplantation into HD models. Alternative donor cell sources are required if CRT is to become a viable therapeutic option and human pluripotent stem cell (hPSC) sources, which have undergone differentiation toward the MSNs lost to the disease process, have proved to be strong candidates. The focus of this chapter is to review work conducted on the functional assessment of animals following transplantation of hPSC-derived MSNs. We discuss different ways that graft function has been assessed, and the results that have been achieved to date. In addition, this chapter presents and discusses challenges that remain in this field.

Concise Review: The Use of Stem Cells for Understanding and Treating Huntington's Disease

Two decades ago, researchers identified that a CAG expansion mutation in the huntingtin (HTT) gene was involved in the pathogenesis of Huntington's disease (HD). However, since the identification of the HTT gene, there has been no advance in the development of therapeutic strategies to prevent or reduce the progression of HD. With the recent advances in stem cell biology and human cell reprogramming technologies, several novel and exciting pathways have emerged allowing researchers to enhance their understanding of the pathogenesis of HD, to identify and screen potential drug targets, and to explore alternative donor cell sources for cell replacement therapy. This review will discuss the role of compensatory neurogenesis in the HD brain, the use of stem cell-based therapies for HD to replace or prevent cell loss, and the recent advance of cell reprogramming to model and/or treat HD. These new technologies, coupled with advances in genome editing herald a promising new era for HD research with the potential to identify a therapeutic strategy to alleviate this debilitating disorder. Stem Cells 2018;36:146-160.

Botulinum Neurotoxin A Injected Ipsilaterally or Contralaterally into the Striatum in the Rat 6-OHDA Model of Unilateral Parkinson's Disease Differently Affects Behavior

Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders. The loss of dopaminergic neurons in the substantia nigra leads to a disinhibition of cholinergic interneurons in the striatum. Pharmacotherapeutical strategies of PD-related hypercholinism have numerous adverse side effects. We previously showed that ipsilateral intrastriatal injections of 1 ng in unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats inhibit apomorphine-induced rotation behavior significantly up to 6 months. In this study, we extended the behavioral testing of ipsilateral botulinum neurotoxin A (BoNT-A)-injection and additionally investigated the impact of intrastriatal BoNT-A-injections contralateral to the 6-OHDA-lesioned hemisphere on the basal ganglia circuity and motor functions. We hypothesized that the interhemispheric differences of acetylcholine (ACh) concentration seen in unilateral hemi-PD should be differentially and temporally influenced by the ipsilateral or contralateral injection of BoNT-A. Hemi-PD rats were injected with 1 ng BoNT-A or vehicle substance into either the ipsilateral or contralateral striatum 6 weeks after 6-OHDA-lesion and various behaviors were tested. In hemi-PD rats intrastriatal ipsilateral BoNT-A-injections significantly reduced apomorphine-induced rotations and increased amphetamine-induced rotations, but showed no significant improvement of forelimb usage and akinesia, lateralized sensorimotor integration and also no effect on spontaneous locomotor activity. However, intrastriatal BoNT-A-injections contralateral to the lesion led to a significant increase of the apomorphine-induced turning rate only 2 weeks after the treatment. The apomorphine-induced rotation rate decreases thereafter to a value below the initial rotation rate. Amphetamine-induced rotations were not significantly changed after BoNT-A-application in comparison to sham-treated animals. Forelimb usage was temporally improved by contralateral BoNT-A-injection at 2 weeks after BoNT-A. Akinesia and lateralized sensorimotor integration were also improved, but contralateral BoNT-A-injection had no significant effect on spontaneous locomotor activity. These long-ranging and different effects suggest that intrastriatally applied BoNT-A acts not only as an inhibitor of ACh release but also has long-lasting impact on transmitter expression and thereby on the basal ganglia circuitry. Evaluation of changes of transmitter receptors is subject of ongoing studies of our group.

Regenerative medicine in Huntington's disease: Strengths and weaknesses of preclinical studies

Huntington's disease (HD) is an inherited neurodegenerative disorder, characterized by impairment in motor, cognitive and psychiatric domains. Currently, there is no specific therapy to act on the onset or progression of HD. The marked neuronal death observed in HD is a main argument in favour of stem cells (SCs) transplantation as a promising therapeutic perspective to replace the population of lost neurons and restore the functionality of the damaged circuitry. The availability of rodent models of HD encourages the investigation of the restorative potential of SCs transplantation longitudinally. However, the results of preclinical studies on SCs therapy in HD are so far largely inconsistent; this hampers the individuation of the more appropriate model and precludes the comparative analysis of transplant efficacy on behavioural end points. Thus, this review will describe the state of the art of in vivo research on SCs therapy in HD, analysing in a translational perspective the strengths and weaknesses of animal studies investigating the therapeutic potential of cell transplantation on HD progression.

Donor age dependent graft development and recovery in a rat model of Huntington's disease: histological and behavioral analysis

Neural cell replacement therapy using fetal striatal cells has provided evidence of disease modification in clinical trials in Huntington's disease (HD) patients, although the results have been inconsistent. One of the contributing factors to the variable outcome could be the different capacity of transplanted cells derived from the primordial striatum to proliferate and maturate into striatal projection neurons. Based on the rodent lesion model of HD, the current study investigated how intrastriatal-striatal grafts from variable aged donors develop in vivo and how they influence functional recovery. Young adult female Sprague-Dawley rats were lesioned unilaterally in the dorso-striatum with quinolinic acid (0.12 M) and transplanted 14 days later with single cell suspension grafts equivalent of one whole ganglionic eminence (WGE) from donors of embryonic developmental age E13, E14, or E15; animals with or without striatal lesion served as controls. All animals were tested on the Cylinder and the Corridor tests, as well as on apomorphine-induced rotation at baseline, post-lesion/pre-grafting, and at 6 and 10 weeks post-grafting. A week prior to perfusion, a sub-group in each grafted group received fluorogold injections into the ipsilateral globus pallidus to study graft efferent projections. In summary, the data demonstrates that the age of the embryonic donor tissue has an impact on both the graft mediated functional recovery, and on the in vivo cellular composition of the striatal transplant. E13 tissue grafts gave the best overall outcome indicating that WGE from different donor ages have different potential to promote functional recovery. Understanding the stages and process in rodent striatal development could improve tissue selection in clinical trials of cell therapy in HD.

Neural repair with pluripotent stem cells

The nervous system is characterized by its complex network of highly specialized cells that enable us to perceive stimuli from the outside world and react accordingly. The computational integration enabled by these networks remains to be elucidated, but appropriate sensory input, processing, and motor control are certainly essential for survival. Consequently, loss of nervous tissue due to injury or disease represents a considerable biomedical challenge. Stem cell research offers the promise to provide cells for nervous system repair to replace lost and damaged neural tissue and alleviate disease. We provide a protocol-based chapter on fundamental principles and procedures of pluripotent stem cell (PSC) differentiation and neural transplantation. Rather than detailed methodological step-by-step descriptions of these procedures, we provide an overview and highlight the most critical aspects and key steps of PSC neural induction, subtype specification in different in vitro systems, as well as neural cell transplantation to the central nervous system. We conclude with a summary of suitable readout methods including in vitro phenotypic analysis, histology, and functional analysis in vivo.

Restoration of the striatal circuitry: from developmental aspects toward clinical applications

In the basal ganglia circuitry, the striatum is a highly complex structure coordinating motor and cognitive functions and it is severely affected in Huntington's disease (HD) patients. Transplantation of fetal ganglionic eminence (GE) derived precursor cells aims to restore neural circuitry in the degenerated striatum of HD patients. Pre-clinical transplantation in genetic and lesion HD animal models has increased our knowledge of graft vs. host interactions, and clinical studies have been shown to successfully reduce motor and cognitive effects caused by the disease. Investigating the molecular mechanisms of striatal neurogenesis is a key research target, since novel strategies aim on generating striatal neurons by differentiating embryonic stem cells or by reprogramming somatic cells as alternative cell source for neural transplantation.

Role of experience, training, and plasticity in the functional efficacy of striatal transplants

Cell-based treatments of neurodegenerative diseases have been tested clinically with partial success. In the context of Huntington's disease (HD), experimental studies show that the grafted embryonic striatal cells survive, integrate within the host brain, and reverse some functional deficits. Importantly, once transplanted, the grafted striatal neurons retain a significant level of cellular, morphological, and functional plasticity which allows the experimental modification of their character through the manipulation of environmental cues or learning protocols. Using embryonic striatal grafts in the rodent model of HD as the principal example, this chapter summarizes seminal experiments that demonstrate that environmental factors, training, and activity can tap into mechanisms that influence the development of the grafted cells and can change the profile of graft-mediated behavioral recovery. Although currently there is limited understanding of the biological rationale behind the recovery, we put forward experimental data indicating that striatal grafts can express experience-dependent physiological plasticity at the synaptic as well as at the systemic functional level.

Differential fate and functional outcome of lithium chloride primed adult neural progenitor cell transplants in a rat model of Huntington disease

INTRODUCTION

The ability to predetermine the fate of transplanted neural progenitor cells (NPCs) and specifically to direct their maturation has the potential to enhance the efficiency of cell-transplantation therapy for neurodegenerative disease. We previously demonstrated that transient exposure of subventricular zone (SVZ)-derived adult NPCs to lithium chloride during in vitro proliferation alters differential fate in vitro and increases the proportion of cells expressing neuronal markers while reducing glial progeny. To extend these findings, we examined whether in vitro priming of adult SVZ-derived NPCs with lithium chloride before transplantation into the quinolinic acid (QA) lesion rat model of Huntington disease altered in vivo neuronal differentiation and sensorimotor function compared with nonprimed NPC transplants.

METHODS

NPCs were isolated from the SVZ of the adult rat brain and cultured for 2 weeks. Four days before transplantation into the QA-lesioned rat striatum, the cells were labeled with BrdU and primed with lithium chloride. The rats underwent regular evaluation of forelimb use and sensorimotor neglect to establish functional effects of NPC transplantation. Twelve weeks after transplantation, the brains were analyzed with immunohistochemistry to compare the differential fate of primed and nonprimed NPCs.

RESULTS

We observed that in vitro priming of adult NPCs with lithium chloride reduced gliogenesis and enhanced the occurrence of DARPP-32-positive neurons when compared with nonprimed cells 12 weeks after transplantation into the QA-lesioned striatum. Lithium chloride priming also augmented the formation of efferent projections from newly formed neurons in the damaged host striatum to the globus pallidus. This was associated with acceleration of sensorimotor function recovery in rats receiving transplants of lithium chloride-primed adult NPCs compared with nonprimed transplants.

CONCLUSIONS

These initial findings indicate that in vitro priming of adult NPCs with lithium chloride may augment transplant efficiency and accelerate sensorimotor function outcome in vivo.

Neurorehabilitation with neural transplantation

Cell replacement therapy has been tested clinically in Parkinson's disease (PD) and Huntington's disease (HD), epilepsy, spinal cord injury, and stroke. The clinical outcomes have been variable, perhaps partly because of the differing levels of preclinical, basic experimental evidence that was available prior to the trials. The most promising results have been seen in PD trials, with encouraging ones in HD. A common feature of most trials is that they have concentrated on the biological and technical aspects of transplantation without presupposing that the outcomes might be influenced by events after the surgery. The growing evidence of plasticity demonstrated by the brain and grafts in response to environmental and training stimuli such as rehabilitation interventions has been mostly neglected throughout the clinical application of cell therapy. This review suggests that a different approach may be required to maximize recovery: postoperative experiences, including rehabilitation with explicit behavioral retraining, could have marked direct as well as positive secondary effects on the integration and function of grafted cells in the host neural system. The knowledge gained about brain plasticity following brain damage needs to be linked with what we know about promoting intrinsic recovery processes and how this can boost neurobiological and surgical strategies for repair at the clinical level. With proof of principle now established, a rich area for innovative research with profound therapeutic application is open for investigation.

BDNF regulation under GFAP promoter provides engineered astrocytes as a new approach for long-term protection in Huntington's disease

Brain-derived neurotrophic factor (BDNF) is the main candidate for neuroprotective therapeutic strategies for Huntington's disease. However, the administration system and the control over the dosage are still important problems to be solved. Here we generated transgenic mice overexpressing BDNF under the promoter of the glial fibrillary acidic protein (GFAP) (pGFAP-BDNF mice). These mice are viable and have a normal phenotype. However, intrastriatal administration of quinolinate increased the number of reactive astrocytes and enhanced the release of BDNF in pGFAP-BDNF mice compared with wild-type mice. Coincidentally, pGFAP-BDNF mice are more resistant to quinolinate than wild-type mice, suggesting a protective effect of astrocyte-derived BDNF. To verify this, we next cultured astrocytes from pGFAP-BDNF and wild-type mice for grafting. Wild-type and pGFAP-BDNF-derived astrocytes behave similarly in nonlesioned mice. However, pGFAP-BDNF-derived astrocytes showed higher levels of BDNF and larger neuroprotective effects than the wild-type ones when quinolinate was injected 30 days after grafting. Interestingly, mice grafted with pGFAP-BDNF astrocytes showed important and sustained behavioral improvements over time after quinolinate administration as compared with mice grafted with wild-type astrocytes. These findings show that astrocytes engineered to release BDNF can constitute a therapeutic approach for Huntington's disease.

Striatal transplantation in a rodent model of multiple system atrophy: effects on L-Dopa response

Progressive degeneration of striatal projection neurons is thought to account for the loss of L-Dopa response observed in the majority of patients with the parkinsonian variant of multiple system atrophy (MSA-P). Here we have investigated the effects of E14 embryonic striatal allografts on dopaminergic responsiveness in the unilateral double-lesion rat model of MSA-P by using tests of complex motor behavior. Both sham and graft animals showed an increase in apomorphine-induced rotations as well as an improvement in cylinder test performance following surgical intervention. In contrast, L-Dopa responsiveness of stepping behavior was improved only in grafted animals. The restoration of apomorphine-induced rotation correlated with the P-zone volume of grafts. Our findings indicate that transplantation of embryonic striatal grafts might, at least to some extent, restore responsiveness to L-Dopa in tasks of complex motor behavior. Therefore, striatal transplantation should be further defined preclinically as a possible therapeutic option for patients with MSA-P and a failing L-Dopa response.

Ketamine anaesthesia interferes with the quinolinic acid-induced lesion in a rat model of Huntington's disease

Ketamine, a non-competitive N-methyl-D-aspartate (NMDA) antagonist, is a commonly used injectable anaesthetic agent. In the present study, ketamine- and isoflurane-induced anaesthesias were tested to identify the influence of different anaesthesia methods in conjunction with the unilateral quinolinic acid-induced excitotoxic lesion rat model of Huntington's disease (HD). Quinolinic acid, a glutamate analogue, exerts its excitotoxic effect via the NMDA receptor, the principle target of ketamine as well, rendering the choice of anaesthesia an important pharmacokinetic issue. Twenty Sprague-Dawley females were lesioned using quinolinic acid: one group was anaesthetised with ketamine and the other with isoflurane. The injection coordinates and the dosage of quinolinic acid were identical. Two weeks post-lesion, the animals were tested on apomorphine-induced rotation test, followed by perfusion, immunohistochemical and volumetric analysis. The isoflurane, compared with the ketamine, anaesthetised animals showed greater ipsilateral rotation behaviour, larger striatal lesions and significant differences in other measurements reflecting the extent of the lesion. The data demonstrates that the use of ketamine anaesthesia in the excitotoxic model of HD can severely compromise the development of the lesion.