Multitract microtransplantation increases the yield of DARPP-32-positive embryonic striatal cells in a rodent model of Huntington's disease

Stem cell therapy for neurological disorders: A focus on aging

Age-related neurological disorders continue to pose a significant societal and economic burden. Aging is a complex phenomenon that affects many aspects of the human body. Specifically, aging can have detrimental effects on the progression of brain diseases and endogenous stem cells. Stem cell therapies possess promising potential to mitigate the neurological symptoms of such diseases. However, aging presents a major obstacle for maximum efficacy of these treatments. In this review, we discuss current preclinical and clinical literature to highlight the interactions between aging, stem cell therapy, and the progression of major neurological disease states such as Parkinson's disease, Huntington's disease, stroke, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis, and multiple system atrophy. We raise important questions to guide future research and advance novel treatment options.

An update on intracerebral stem cell grafts

INTRODUCTION

Primary neurological disorders are notoriously debilitating and deadly, and over the past four decades stem cell therapy has emerged as a promising treatment. Translation of stem cell therapies from the bench to the clinic requires a better understanding of delivery protocols, safety profile, and efficacy in each disease. Areas covered: In this review, benefits and risks of intracerebral stem cell transplantation are presented for consideration. Milestone discoveries in stem cell applications are reviewed to examine the efficacy and safety of intracerebral stem cell transplant therapy for disorders of the central nervous system and inform design of translatable protocols for clinically feasible stem cell-based treatments. Expert commentary: Intracerebral administration, compared to peripheral delivery, is more invasive and carries the risk of open brain surgery. However, direct cell implantation bypasses the blood-brain barrier and reduces the first-pass effect, effectively increasing the therapeutic cell deposition at its intended site of action. These benefits must be weighed with the risk of graft-versus-host immune response. Rigorous clinical trials are underway to assess the safety and efficacy of intracerebral transplants, and if successful will lead to widely available stem cell therapies for neurologic diseases in the coming years.

Ex vivo biomechanical characterization of syringe-needle ejections for intracerebral cell delivery

Intracerebral implantation of cell suspensions is finding its clinical translation with encouraging results in patients with stroke. However, the survival of cells in the brain remains poor. Although the biological potential of neural stem cells (NSCs) is widely documented, the biomechanical effects of delivering cells through a syringe-needle remain poorly understood. We here detailed the biomechanical forces (pressure, shear stress) that cells are exposed to during ejection through different sized needles (20G, 26G, 32G) and syringes (10, 50, 250 µL) at relevant flow rates (1, 5, 10 µL/min). A comparison of 3 vehicles, Phosphate Buffered Saline (PBS), Hypothermosol (HTS), and Pluronic, indicated that less viscous vehicles are favorable for suspension with a high cell volume fraction to minimize sedimentation. Higher suspension viscosity was associated with greater shear stress. Higher flow rates with viscous vehicle, such as HTS reduced viability by ~10% and also produced more apoptotic cells (28%). At 5 µL/min ejection using a 26G needle increased neuronal differentiation for PBS and HTS suspensions. These results reveal the biological impact of biomechanical forces in the cell delivery process. Appropriate engineering strategies can be considered to mitigate these effects to ensure the efficacious translation of this promising therapy.

Syringe needle skull penetration reduces brain injuries and secondary inflammation following intracerebral neural stem cell transplantation

Intracerebral neural stem cell (NSC) transplantation is beneficial for delivering stem cell grafts effectively, however, this approach may subsequently result in brain injury and secondary inflammation. To reduce the risk of promoting brain injury and secondary inflammation, two methods were compared in the present study. Murine skulls were penetrated using a drill on the left side and a syringe needle on the right. Mice were randomly divided into three groups (n=84/group): Group A, receiving NSCs in the left hemisphere and PBS in the right; group B, receiving NSCs in the right hemisphere and PBS in the left; and group C, receiving equal NSCs in both hemispheres. Murine brains were stained for morphological analysis and subsequent evaluation of infiltrated immune cells. ELISA was performed to detect neurotrophic and immunomodulatory factors in the brain. The findings indicated that brain injury and secondary inflammation in the left hemisphere were more severe than those in the right hemisphere, following NSC transplantation. In contrast to the left hemisphere, more neurotrophic factors but less pro-inflammatory cytokines were detected in the right hemisphere. In addition, increased levels of neurotrophic factors and interleukin (IL)-10 were observed in the NSC transplantation side when compared with the PBS-treated hemispheres, although lower levels of IL-6 and tumor necrosis factor-α were detected. In conclusion, the present study indicated that syringe needle skull penetration vs. drill penetration is an improved method that reduces the risk of brain injury and secondary inflammation following intracerebral NSC transplantation. Furthermore, NSCs have the potential to modulate inflammation secondary to brain injuries.

Developments in intracerebral stem cell grafts

The field of stem cell therapy has emerged as a promising research area for brain repair. Optimizing the safety and efficacy of the therapy for clinical trials will require revisiting transplantation protocols. The cell delivery route stands as a key translational item that warrants careful consideration in facilitating the success of stem cell therapy in the clinic. Intracerebral administration, compared to peripheral route, requires an invasive procedure to directly implant stem cells into injured brain. Although invasive, intracerebral transplantation circumvents the prohibitive blood brain barrier in allowing grafted cells when delivered peripherally to penetrate the brain and reach the discreet damaged brain tissues. This review will highlight milestone discoveries in cell therapy for neurological disorders, with emphasis on intracerebral transplantation in relevant animal models and provide insights necessary to optimize the safety and efficacy of cell therapy for the treatment of Parkinson's disease, Huntington's disease, stroke and traumatic brain injury.

Two-step grafting significantly enhances the survival of foetal dopaminergic transplants and induces graft-derived vascularisation in a 6-OHDA model of Parkinson's disease

Following transplantation of foetal primary dopamine (DA)-rich tissue for neurorestaurative treatment of Parkinson's disease (PD), only 5-10% of the functionally relevant DAergic cells survive both in experimental models and in clinical studies. The current work tested how a two-step grafting protocol could have a positive impact on graft survival. DAergic tissue is divided in two portions and grafted in two separate sessions into the same target area within a defined time interval. We hypothesized that the first graft creates a "DAergic" microenvironment or "nest" similar to the perinatal substantia nigra that stimulates and protects the second graft. 6-OHDA-lesioned rats were sequentially transplanted with wild-type (GFP-, first graft) and transgenic (GFP+, second graft) DAergic cells in time interims of 2, 5 or 9days. Each group was further divided into two sub-groups receiving either 200k (low cell number groups: 2dL, 5dL, 9dL) or 400k cells (high cell number groups: 2dH, 5dH, 9dH) as first graft. During the second transplantation, all groups received the same amount of 200k GFP+ cells. Controls received either low or high cell numbers in one single session (standard protocol). Drug-induced rotations, at 2 and 6weeks after grafting, showed significant improvement compared to the baseline lesion levels without significant differences between the groups. Rats were sacrificed 8weeks after transplantation for post-mortem histological assessment. Both two-step groups with the time interval of 2days (2dL and 2dH) showed a significantly higher survival of DAergic cells compared to their respective standard control group (2dL, +137%; 2dH, +47%). Interposing longer intervals of 5 or 9days resulted in the loss of statistical significance, neutralising the beneficial two-step grafting effect. Furthermore, the transplants in the 2dL and 2dH groups had higher graft volume and DA-fibre-density values compared to all other two-step groups. They also showed intense growth of GFP+ vessels - completely absent in control grafts - in regions where the two grafts overlap, indicating second-graft derived angiogenesis. In summary, the study shows that two-step grafting with a 2days time interval significantly increases DAergic cell survival compared to the standard protocol. Furthermore, our results demonstrate, for the first time, a donor-derived neoangiogenesis, leading to a new understanding of graft survival and development in the field of cell-replacement therapies for neurodegenerative diseases.

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.

Brain repair in a unilateral rat model of Huntington's disease: new insights into impairment and restoration of forelimb movement patterns

Huntington's disease (HD) produces severe neurodegeneration in the striatum leading to disabling motor impairments, including the loss of control of skilled reaching movements. Fetal GABAergic transplants can physically replace the lost striatal cells but with only partial success in functional recovery. Here, we aimed to determine the extent and quality of the repair produced by fetal cell transplantation through an in-depth analysis of reaching behavior in the quinolinic acid-lesioned rat model of HD. Control, quinolinic acid-lesioned plus sham graft, and quinolinic acid-lesioned plus graft groups of rats were assessed in skilled reaching performance prior to and following lesion surgery and 3 months following injection of 400,000 fetal whole ganglionic eminence-derived cells into the striatum. This was compared to their performance in two more rudimentary tests of motor function (the adjusting step and vibrissae-evoked hand-placing tests). Grafted rats demonstrated a significant improvement in reaching success rate (graft +59%, shamTX +3%). Importantly, the quality of reaching behavior, including all components of the movement, was fully restored with no identifiable differences in the normal behavior shown by control rats. Postmortem immunohistochemical examination verified the survival of large intrastriatal grafts, and Fluoro-Gold tracing indicated appropriate outgrowth to the globus pallidus. Our study illustrates for the first time the detailed analysis of qualitative improvement of motor function following brain repair in a rat model of HD. The results demonstrate significant improvements not only in gross movements but also in the skilled motor patterns lost during HD. Fetal GABAergic cell transplantation showed a demonstrable ability to restore motor function to near normal levels, such that there were few differences from intact control animals, an effect not observed in standard tests of motor function.

[18F]desmethoxyfallypride as a novel PET radiotracer for quantitative in vivo dopamine D2/D3 receptor imaging in rat models of neurodegenerative diseases

INTRODUCTION

[(18)F]desmethoxyfallypride ([(18)F]DMFP) is a promising tracer for longitudinal assessment of striatal dopamine D2/D3-receptor (D2R) availability by positron emission tomography (PET) in small animal models. We explored the feasibility of [(18)F]DMFP-PET to image D2R availability in rat models of Huntington's (HD) and Parkinson's disease (PD).

METHODS

Animals received either unilateral intrastriatal quinolinic acid lesions or medial forebrain bundle injections of 6-OHDA to produce the loss of striatal projection neurones or deplete the striatal dopamine, corresponding to established animal models for HD and PD, respectively. Three weeks after lesioning, PET scans were acquired on a microPET Focus 120 system following the tail vein injection of [(18)F]DMFP.

RESULTS

[(18)F]DMFP-PET clearly visualized lesion induced decreases and increases of D2R availability. In vivo estimates of D2R binding and changes thereof gained by pharmacokinetic analyses correlated significantly with D2R density and its change provided by in vitro [(3)H]raclopride-autoradiography.

CONCLUSIONS

In conclusion, [(18)F]DMFP-PET is a suitable method for in vivo D2R-assessment in preclinical research, e.g for monitoring cell-based therapies.

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.

The Lewis GFP transgenic rat strain is a useful cell donor for neural transplantation

Stem cell transplantation is a promising therapeutic approach in neurodegenerative diseases. Studying graft survival and development has important implications for the further development of experimental and clinical transplantation protocols. Cellular elements in neural transplants are sometimes difficult to identify. The existing labeling methods cannot reliably provide stably labeled cells that can be detected in long-term experiments. Transgenic (tg) Lewis rats ubiquitously expressing green fluorescent protein (GFP) provide an ideal donor source. The aim of this project was to investigate the potential of GFP-tg Lewis rats to serve as donor tissue for neural stem cell transplantation. Ventral mesencephalon (VM) GFP-tg E14.5-derived cells were compared to wild-type (wt) in vitro and in vivo. Firstly, cells from GFP and non-GFP VM tissue were compared with regard to their proliferation and response towards 6-OHDA-toxicity in culture. Secondly, 6-OHDA-lesioned hemiparkinsonian Sprague-Dawley/Crl:CD(SD) rats received intrastriatal grafts derived from VM of E14.5 GFP-tg rats. Due to the fact that donor and recipient belong to two different rat strains, we focused on graft survival in correlation with immunosuppression and graft GFP and tyrosine hydroxylase (TH) expression. In summary, in vitro tg cells exhibited 98% GFP expression and did not differ from wt cells in any of the measured parameters. In vivo, all experimental groups showed a significant compensation in rotation behavior after transplantation. Furthermore, there was no difference on rotation behavior or graft morphology and survival pattern as well as GFP expression between immunosuppressed and nonimmunosuppressed animals. The GFP-positive population of the graft was composed of 13.3% GFAP-positive, 56.1% NeuN-positive, and 1.9% TH-positive cells. Analysis of graft subpopulations manifested that 70.6% of GFAP-positive, 86.9% of NeuN-positive, and 80.1% of TH-positive cells coexpressed GFP. In conclusion, our data show that the Lewis GFP-tg rats serve as an excellent cell source for studying primary neural precursor cells in the transplantation paradigm.