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

In Vivo Engineering and Transplantation of Axially Vascularized and Epithelialized Flaps in Rats

The arteriovenous loop (AVL) model allows the in vivo engineering of axially vascularized flaps, the so-called AVL flaps. Although AVL flaps can be transplanted microsurgically to cover tissue defects, they lack an epithelial layer on the surface. Therefore, the objective of this study was to engineer axially vascularized AVL flaps with an accompanying epithelial layer for local defect reconstruction. In this study, AVLs were established in 20 male Lewis rats. Minimally invasive injection of keratinocytes onto the surface of the AVL flaps was performed on postoperative day (POD) 21. AVL flaps were explanted from 12 rats on POD 24 or POD 30, then the epithelium formed by the keratinocytes on the surface of the flaps was evaluated using immunofluorescence staining. In six other rats, the AVL flap was locally transposed to cover a critical defect in the rats' leg on POD 30 and explanted for analysis on POD 40. In two control rats, sodium chloride was applied instead of keratinocytes. These control flaps were also transplanted on POD 30 and explanted on POD 40. Our results revealed that 3 days after keratinocyte application, a loose single-layered epithelium was observed histologically on the AVL flaps surface, whereas after 9 days, a multilayered and structured epithelium had grown. The epithelium on the transplanted AVL flaps showed its physiological differentiation when being exposed to an air-liquid interface. Histologically, a layered epithelium identical to the rats' regular skin was formed. In the sodium chloride control group, no epithelium had been grown. This study clearly demonstrates that axially vascularized AVL flaps can be processed in the subcutaneous chamber by minimally invasive injection of keratinocytes. Thus, AVL flaps with an intact epithelial layer were engineered and could be successfully transplanted for local defect coverage in a small animal model.

Anodal Transcranial Direct Current Stimulation Enhances Survival and Integration of Dopaminergic Cell Transplants in a Rat Parkinson Model

Restorative therapy concepts, such as cell based therapies aim to restitute impaired neurotransmission in neurodegenerative diseases. New strategies to enhance grafted cell survival and integration are still needed to improve functional recovery. Anodal direct current stimulation (DCS) promotes neuronal activity and secretion of the trophic factor BDNF in the motor cortex. Transcranial DCS applied to the motor cortex transiently improves motor symptoms in Parkinson’s disease (PD) patients. In this proof-of-concept study, we combine cell based therapy and noninvasive neuromodulation to assess whether neurotrophic support via transcranial DCS would enhance the restitution of striatal neurotransmission by fetal dopaminergic transplants in a rat Parkinson model. Transcranial DCS was applied daily for 20 min on 14 consecutive days following striatal transplantation of fetal ventral mesencephalic (fVM) cells derived from transgenic rat embryos ubiquitously expressing GFP. Anodal but not cathodal transcranial DCS significantly enhanced graft survival and dopaminergic reinnervation of the surrounding striatal tissue relative to sham stimulation. Behavioral recovery was more pronounced following anodal transcranial DCS, and behavioral effects correlated with the degree of striatal innervation. Our results suggest anodal transcranial DCS may help advance cell-based restorative therapies in neurodegenerative diseases. In particular, such an assistive approach may be beneficial for the already established cell transplantation therapy in PD.

A Comparison of Exogenous Labels for the Histological Identification of Transplanted Neural Stem Cells

The interpretation of cell transplantation experiments is often dependent on the presence of an exogenous label for the identification of implanted cells. The exogenous labels Hoechst 33342, 5-bromo-2'-deoxyuridine (BrdU), PKH26, and Qtracker were compared for their labeling efficiency, cellular effects, and reliability to identify a human neural stem cell (hNSC) line implanted intracerebrally into the rat brain. Hoechst 33342 (2 mg/ml) exhibited a delayed cytotoxicity that killed all cells within 7 days. This label was hence not progressed to in vivo studies. PKH26 (5 μM), Qtracker (15 nM), and BrdU (0.2 μM) labeled 100% of the cell population at day 1, although BrdU labeling declined by day 7. BrdU and Qtracker exerted effects on proliferation and differentiation. PKH26 reduced viability and proliferation at day 1, but this normalized by day 7. In an in vitro coculture assay, all labels transferred to unlabeled cells. After transplantation, the reliability of exogenous labels was assessed against the gold standard of a human-specific nuclear antigen (HNA) antibody. BrdU, PKH26, and Qtracker resulted in a very small proportion (<2%) of false positives, but a significant amount of false negatives (∼30%), with little change between 1 and 7 days. Exogenous labels can therefore be reliable to identify transplanted cells without exerting major cellular effects, but validation is required. The interpretation of cell transplantation experiments should be presented in the context of the label's limitations.

Effects of Rho Kinase Inhibitors on Grafts of Dopaminergic Cell Precursors in a Rat Model of Parkinson's Disease

In models of Parkinson's disease (PD), Rho kinase (ROCK) inhibitors have antiapoptotic and axon-stabilizing effects on damaged neurons, decrease the neuroinflammatory response, and protect against dopaminergic neuron death and axonal retraction. ROCK inhibitors have also shown protective effects against apoptosis induced by handling and dissociation of several types of stem cells. However, the effect of ROCK inhibitors on dopaminergic cell grafts has not been investigated. In the present study, treatment of dopaminergic cell suspension with ROCK inhibitors yielded significant decreases in the number of surviving dopaminergic neurons, in the density of graft-derived dopaminergic fibers, and in graft vascularization. Dopaminergic neuron death also markedly increased in primary mesencephalic cultures when the cell suspension was treated with ROCK inhibitors before plating, which suggests that decreased angiogenesis is not the only factor leading to cell death in grafts. Interestingly, treatment of the host 6-hydroxydopamine-lesioned rats with ROCK inhibitors induced a slight, nonsignificant increase in the number of surviving neurons, as well as marked increases in the density of graft-derived dopaminergic fibers and the size of the striatal reinnervated area. The study findings discourage treatment of cell suspensions before grafting. However, treatment of the host induces a marked increase in graft-derived striatal reinnervation. Because ROCK inhibitors have also exerted neuroprotective effects in several models of PD, treatment of the host with ROCK inhibitors, currently used against vascular diseases in clinical practice, before and after grafting may be a useful adjuvant to cell therapy in PD.

SIGNIFICANCE

Cell-replacement therapy is one promising therapy for Parkinson's disease (PD). However, many questions must be addressed before widespread application. Rho kinase (ROCK) inhibitors have been used in a variety of applications associated with stem cell research and may be an excellent strategy for improving survival of grafted neurons and graft-derived dopaminergic innervation. The present results discourage the treatment of suspensions of dopaminergic precursors with ROCK inhibitors in the pregrafting period. However, treatment of the host (patients with PD) with ROCK inhibitors, currently used against vascular diseases, may be a useful adjuvant to cell therapy in PD.

Cyclosporin promotes neurorestoration and cell replacement therapy in pre-clinical models of Parkinson's disease

BACKGROUND

The early clinical trials using fetal ventral mesencephalic (VM) allografts in Parkinson's disease (PD) patients have shown efficacy (albeit not in all cases) and have paved the way for further development of cell replacement therapy strategies in PD. The preclinical work that led to these clinical trials used allografts of fetal VM tissue placed into 6-OHDA lesioned rats, while the patients received similar allografts under cover of immunosuppression in an α-synuclein disease state. Thus developing models that more faithfully replicate the clinical scenario would be a useful tool for the translation of such cell-based therapies to the clinic.

RESULTS

Here, we show that while providing functional recovery, transplantation of fetal dopamine neurons into the AAV-α-synuclein rat model of PD resulted in smaller-sized grafts as compared to similar grafts placed into the 6-OHDA-lesioned striatum. Additionally, we found that cyclosporin treatment was able to promote the survival of the transplanted cells in this allografted state and surprisingly also provided therapeutic benefit in sham-operated animals. We demonstrated that delayed cyclosporin treatment afforded neurorestoration in three complementary models of PD including the Thy1-α-synuclein transgenic mouse, a novel AAV-α-synuclein mouse model, and the MPTP mouse model. We then explored the mechanisms for this benefit of cyclosporin and found it was mediated by both cell-autonomous mechanisms and non-cell autonomous mechanisms.

CONCLUSION

This study provides compelling evidence in favor for the use of immunosuppression in all grafted PD patients receiving cell replacement therapy, regardless of the immunological mismatch between donor and host cells, and also suggests that cyclosporine treatment itself may act as a disease-modifying therapy in all PD patients.

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.

Bioimaging of Transgenic Rats Established at Jichi Medical University: Applications in Transplantation Research

Research in the life sciences has been greatly advanced by the ability to directly visualize cells, tissues, and organs. Preclinical studies often involve many small and large animal experiments and, frequently, cell and organ transplantations. The rat is an excellent animal model for the development of transplantation and surgical techniques because of its small size and ability to breed in small spaces. Ten years ago, we established color-imaging transgenic rats and methods for the direct visualization of their tissues. Since then, our transgenic rats have been used throughout the various fields that are concerned with cell transplantation therapy. In this minireview, we summarize results from some of the groups that have used our transgenic rats at the bench level and in cell transplantation research.

In Vivo Bioimaging Rats for Translational Research in Cell and Tissue Transplantation

The rat is an excellent cell transplantation model. In accordance with the innovative development of in vivo bioimaging technology, over the last decade we have been developing an engineered rat system based on transgenic technology and have been demonstrating the usefulness of the system with genetically encoded imaging probes such as fluorescent and luminescent proteins. In cooperation with the Japan Society for Organ Preservation and Medical Biology (President: Professor T. Asano), we have also been using luciferase-Tg rats for research into organ preservation and cell transplantation. In this minireview, we introduce the results obtained recently by using these powerful experimental tools during international collaboration in cell transplantation research.