New lines of GFP transgenic rats relevant for regenerative medicine and gene therapy

Synthesis and spectroscopic characterization of novel GFP chromophore analogues based on aminoimidazolone derivatives

In order to improve the fluorescence properties of the green fluorescent protein chromophore, p‑HOBDI ((5‑(4‑hydroxybenzylidene)‑2,3‑dimethyl‑3,5‑dihydro‑4H‑imidazol‑4‑one), sixteen dihydroimidazolone derivates were synthesized from thiohydantoin and arylaldehydes. The synthesis developed is an efficient, novel, one-pot procedure. The study provides a detailed description of the spectroscopic characteristics of the newly synthesized compounds, using p‑HOBDI as a reference. The new compounds all exhibited significantly stronger fluorescence than p‑HOBDI, up to 28 times higher quantum yields. An experimental and theoretical investigation of the relationship of the fluorescence properties with the molecular structure was also carried out. A good correlation was found between the emission wavenumber and the Hammett constant of the functional group, which suggests the intermolecular charge transfer (ICT) mechanism between the aromatic groups.

Potential Research Tool of Stem Cells from Human Exfoliated Deciduous Teeth: Lentiviral Bmi-1 Immortalization with EGFP Marker

Stem cells from human exfoliated deciduous teeth (SHED) are a favourable source for tissue engineering, for its great proliferative capacity and the ease of collection. However, the transplantation of stem cells and the study of stem cell-based tissue engineering require massive stem cells. After long-term expansion, stem cells face many challenges, including limited lifespan, senescence, and loss of stemness. Therefore, a cell line capable of overcoming those problems should be built. In this study, we generated a Bmi-1-immortalized SHED cell line with an enhanced green fluorescent protein (EGFP) marker (SHED-Bmi1-EGFP) using lentiviral transduction. We compared this cell line with the original SHED for cell morphology under a microscope. The expression of Bmi-1 was detected with Western blot. Replicative lifespan determination and colony-forming efficiency assessment were using to assay proliferation capability. Senescence-associated β-galactosidase assay was performed to assay the senescence level of cells. Moreover, multipotency, karyotype, and tumour formation in nude mice of SHED and SHED-Bmi1-EGFP were also tested. Our results confirmed that Bmi-1 immortalization did not affect the main features of SHED. SHED-Bmi1-EGFP could be passaged for a long time and stably expressed EGFP. SHED-Bmi1-EGFP at a late passage showed low activity of β-galactosidase and similar multilineage differentiation as SHED at an early passage. The immortalized cells had no potential tumourigenicity ability in vivo. Moreover, we provided some suggestions for potential applications of the immortalized SHED cell line with the EGFP marker. Thus, the immortalized cell line we built can be used as a functional tool in the lab for long-term studies of SHED and stem cell-based regeneration.

Improving Hepatocyte Engraftment Following Hepatocyte Transplantation Using Repeated Reversible Portal Vein Embolization in Rats

Hepatocyte transplantation (HT) has emerged as a promising alternative to orthotopic liver transplantation, yet liver preconditioning is needed to promote hepatocyte engraftment. A method of temporary occlusion of the portal flow called reversible portal vein embolization (RPVE) has been demonstrated to be an efficient method of liver preconditioning. By providing an additional regenerative stimulus, repeated reversible portal vein embolization (RRPVE) could further boost liver engraftment. The aim of this study was to determine the efficiency of liver engraftment of transplanted hepatocytes after RPVE and RRPVE in a rat model. Green fluorescent protein-expressing hepatocytes were isolated from transgenic rats and transplanted into 3 groups of syngeneic recipient rats. HT was associated with RPVE in group 1, with RRPVE in group 2, and with sham embolization in the sham group. Liver engraftment was assessed at day 28 after HT on liver samples after immunostaining. Procedures were well tolerated in all groups. RRPVE resulted in increased engraftment rate in total liver parenchyma compared with RPVE (3.4% ± 0.81% versus 1.4% ± 0.34%; P < 0.001). In conclusion, RRPVE successfully enhanced hepatocyte engraftment after HT and could be helpful in the frame of failure of HT due to low cell engraftment.

Genome Editing in Rats Using TALE Nucleases

The rat is an important animal model to understand gene function and model human diseases. Since recent years, the development of gene-specific nucleases has become important for generating new rat models of human diseases, to analyze the role of genes and to generate human antibodies. Transcription activator-like (TALE) nucleases efficiently create gene-specific knockout rats and lead to the possibility of gene targeting by homology-directed recombination (HDR) and generating knock-in rats. We describe a detailed protocol for generating knockout and knock-in rats via microinjection of TALE nucleases into fertilized eggs. This technology is an efficient, cost- and time-effective method for creating new rat models.

New Wistar Kyoto and spontaneously hypertensive rat transgenic models with ubiquitous expression of green fluorescent protein

The Wistar Kyoto (WKY) rat and the spontaneously hypertensive (SHR) rat inbred strains are well-established models for human crescentic glomerulonephritis (CRGN) and metabolic syndrome, respectively. Novel transgenic (Tg) strains add research opportunities and increase scientific value to well-established rat models. We have created two novel Tg strains using Sleeping Beauty transposon germline transgenesis, ubiquitously expressing green fluorescent protein (GFP) under the rat elongation factor 1 alpha (EF1a) promoter on the WKY and SHR genetic backgrounds. The Sleeping Beauty system functioned with high transgenesis efficiency; 75% of new rats born after embryo microinjections were transgene positive. By ligation-mediated PCR, we located the genome integration sites, confirming no exonic disruption and defining a single or low copy number of the transgenes in the new WKY-GFP and SHR-GFP Tg lines. We report GFP-bright expression in embryos, tissues and organs in both lines and show preliminaryin vitroandin vivoimaging data that demonstrate the utility of the new GFP-expressing lines for adoptive transfer, transplantation and fate mapping studies of CRGN, metabolic syndrome and other traits for which these strains have been extensively studied over the past four decades.

Regulatory B Cells with a Partial Defect in CD40 Signaling and Overexpressing Granzyme B Transfer Allograft Tolerance in Rodents

Emerging knowledge regarding B cells in organ transplantation has demonstrated that these cells can no longer be taken as mere generators of deleterious Abs but can also act as beneficial players. We previously demonstrated in a rat model of cardiac allograft tolerance induced by short-term immunosuppression an accumulation in the blood of B cells overexpressing inhibitory molecules, a phenotype also observed in the blood of patients that spontaneously develop graft tolerance. In this study, we demonstrated the presence in the spleen of regulatory B cells enriched in the CD24(int)CD38(+)CD27(+)IgD(-)IgM(+/low) subpopulation, which are able to transfer donor-specific tolerance via IL-10 and TGF-β1-dependent mechanisms and to suppress in vitro TNF-α secretion. Following anti-CD40 stimulation, IgD(-)IgM(+/low) B cells were blocked in their plasma cell differentiation pathway, maintained high expression of the inhibitory molecules CD23 and Bank1, and upregulated Granzyme B and Irf4, two molecules described as highly expressed by regulatory B cells. Interestingly, these B cells recognized specifically a dominant donor Ag, suggesting restricted specificity that could lead to a particular B cell response. Regulatory B cells were not required for induction of tolerance and appeared following Foxp3(+)CD4(+)CD25(+) regulatory T cells, suggesting cooperation with regulatory T cells for their expansion. Nevertheless, following transfer to new recipients, these B cells migrated to the allograft, kept their regulatory profile, and promoted local accumulation of Foxp3(+)CD4(+)CD25(+) regulatory T cells. Mechanisms of regulatory B cells and their cell therapy potential are important to decipher in experimental models to pave the way for future developments in the clinic.

Local control of the host immune response performed with mesenchymal stem cells: perspectives for functional intracerebral xenotransplantation

Foetal pig neuroblasts are interesting candidates as a cell source for transplantation, but xenotransplantation in the brain requires the development of adapted immunosuppressive treatments. As systemic administration of high doses of cyclosporine A has side effects and does not protect xenotransplants forever, we focused our work on local control of the host immune responses. We studied the advantage of cotransplanting syngenic mesenchymal stem cells (MSC) with porcine neuroblasts (pNb) in immunocompetent rat striata. Two groups of animals were transplanted, either with pNb alone or with both MSC and pNb. At day 63, no porcine neurons were detected in the striata that received only pNb, while four of six rats transplanted with both pNb and MSC exhibited healthy porcine neurons. Interestingly, 50% of the cotransplanted rats displayed healthy grafts with pNF70+ and TH+ neurons at 120 days post-transplantation. qPCR analyses revealed a general dwindling of pro- and anti-inflammatory cytokines in the striata that received the cotransplants. Motor recovery was also observed following the transplantation of pNb and MSC in a rat model of Parkinson's disease. Taken together, the present data indicate that the immunosuppressive properties of MSC are of great interest for the long-term survival of xenogeneic neurons in the brain.

Promotion of survival and differentiation of neural stem cells with fibrin and growth factor cocktails after severe spinal cord injury

Neural stem cells (NSCs) can self-renew and differentiate into neurons and glia. Transplanted NSCs can replace lost neurons and glia after spinal cord injury (SCI), and can form functional relays to re-connect spinal cord segments above and below a lesion. Previous studies grafting neural stem cells have been limited by incomplete graft survival within the spinal cord lesion cavity. Further, tracking of graft cell survival, differentiation, and process extension had not been optimized. Finally, in previous studies, cultured rat NSCs were typically reported to differentiate into glia when grafted to the injured spinal cord, rather than neurons, unless fate was driven to a specific cell type. To address these issues, we developed new methods to improve the survival, integration and differentiation of NSCs to sites of even severe SCI. NSCs were freshly isolated from embryonic day 14 spinal cord (E14) from a stable transgenic Fischer 344 rat line expressing green fluorescent protein (GFP) and were embedded into a fibrin matrix containing growth factors; this formulation aimed to retain grafted cells in the lesion cavity and support cell survival. NSCs in the fibrin/growth factor cocktail were implanted two weeks after thoracic level-3 (T3) complete spinal cord transections, thereby avoiding peak periods of inflammation. Resulting grafts completely filled the lesion cavity and differentiated into both neurons, which extended axons into the host spinal cord over remarkably long distances, and glia. Grafts of cultured human NSCs expressing GFP resulted in similar findings. Thus, methods are defined for improving neural stem cell grafting, survival and analysis of in vivo findings.

Embryo development, fetal growth and postnatal phenotype of eGFP lambs generated by lentiviral transgenesis

Lentiviral technology has been recently proposed to generate transgenic farm animals more efficiently and easier than traditional techniques. The objective was to evaluate several parameters of lambs obtained by lentiviral transgenesis in comparison with non-transgenic counterparts. In vitro produced embryos were microinjected (TG group) at two-cell stage with a lentiviral construct containing enhanced green fluorescent protein (eGFP) gene, while embryos produced by in vitro fertilization (IVF group) or intrauterine insemination (IUI group) were not microinjected. Microinjection technique efficiently generated eight-cell transgenic embryos (97.4%; 114/117). Development rate on day 5 after fertilization was similar for TG (39.3%, 46/117) and IVF embryos (39.6%, 44/111). Pregnancy rate was detected in 50.0% (6/12) of recipient ewes with TG embryos, in 46.7% (7/15) with IVF embryos, and in 65.0% (13/20) of IUI ewes (P = NS). Nine lambs were born in TG group, six lambs in IVF group, and 16 lambs in IUI group. All TG lambs (9/9) were GFP positive to real-time PCR and eight (88.9%) showed a strong and evident GFP expression in mucosae, eyes and keratin tissues. Fetal growth monitored every 15 day by ultrasonography did not show significant differences. Transgenic lambs neither differ in morphometric variables in comparison with non transgenic IVF lambs within 3 months after birth. Transmission of the transgene to the progeny was observed in green fluorescent embryos produced by IVF using semen from the TG founder lambs. In conclusion, this study demonstrates the high efficiency of lentiviral technology to produce transgenic sheep, with no clinic differences in comparison with non transgenic lambs.

Development and characterization of a new inbred transgenic rat strain expressing DsRed monomeric fluorescent protein

The inbred rat is a suitable model for studying human disease and because of its larger size is more amenable to complex surgical manipulation than the mouse. While the rodent fulfills many of the criteria for transplantation research, an important requirement is the ability to mark and track donors cells and assess organ viability. However, tracking ability is limited by the availability of transgenic (Tg) rats that express suitable luminescent or fluorescent proteins. Red fluorescent protein cloned from Discosoma coral (DsRed) has several advantages over other fluorescent proteins, including in vivo detection in the whole animal and ex vivo visualization in organs as there is no interference with autofluorescence. We generated and characterized a novel inbred Tg Lewis rat strain expressing DsRed monomeric (DsRed mono) fluorescent protein under the control of a ubiquitously expressed ROSA26 promoter. DsRed mono Tg rats ubiquitously expressed the marker gene as detected by RT-PCR but the protein was expressed at varying levels in different organs. Conventional skin grafting experiments showed acceptance of DsRed monomeric Tg rat skin on wild-type rats for more than 30 days. Cardiac transplantation of DsRed monomeric Tg rat hearts into wild-type recipients further showed graft acceptance and long-term organ viability (>6 months). The DsRed monomeric Tg rat provides marked cells and/or organs that can be followed for long periods without immune rejection and therefore is a suitable model to investigate cell tracking and organ transplantation.

Gene targeting in rats using transcription activator-like effector nucleases

The rat is a model of choice to understanding gene function and modeling human diseases. Since recent years, successful engineering technologies using gene-specific nucleases have been developed to gene edit the genome of different species, including the rat. This development has become important for the creation of new rat animals models of human diseases, analyze the role of genes and express recombinant proteins. Transcription activator-like (TALE) nucleases are designed nucleases consist of a DNA binding domain fused to a nuclease domain capable of cleaving the targeted DNA. We describe a detailed protocol for generating knockout rats via microinjection of TALE nucleases into fertilized eggs. This technology is an efficient, cost- and time-effective method for creating new rat models.

Determining a clinically relevant strategy for bone tissue engineering: an "all-in-one" study in nude mice

Purpose

Autologous bone grafting (BG) remains the standard reconstruction strategy for large craniofacial defects. Calcium phosphate (CaP) biomaterials, such as biphasic calcium phosphate (BCP), do not yield consistent results when used alone and must then be combined with cells through bone tissue engineering (BTE). In this context, total bone marrow (TBM) and bone marrow-derived mesenchymal stem cells (MSC) are the primary sources of cellular material used with biomaterials. However, several other BTE strategies exist, including the use of growth factors, various scaffolds, and MSC isolated from different tissues. Thus, clinicians might be unsure as to which method offers patients the most benefit. For this reason, the aim of this study was to compare eight clinically relevant BTE methods in an “all-in-one” study.

Methods

We used a transgenic rat strain expressing green fluorescent protein (GFP), from which BG, TBM, and MSC were harvested. Progenitor cells were then mixed with CaP materials and implanted subcutaneously into nude mice. After eight weeks, bone formation was evaluated by histology and scanning electron microscopy, and GFP-expressing cells were tracked with photon fluorescence microscopy.

Results/Conclusions

Bone formation was observed in only four groups. These included CaP materials mixed with BG or TBM, in which abundant de novo bone was formed, and BCP mixed with committed cells grown in two- and three-dimensions, which yielded limited bone formation. Fluorescence microscopy revealed that only the TBM and BG groups were positive for GFP expressing-cells, suggesting that these donor cells were still present in the host and contributed to the formation of bone. Since the TBM-based procedure does not require bone harvest or cell culture techniques, but provides abundant de novo bone formation, we recommend consideration of this strategy for clinical applications.

Low titer lentiviral transgenesis in rodents with simian immundeficiency virus vector

Efficient production of transgenic animals using low-titer lentiviral constructs remains challenging. Here we demonstrate that microinjection of simian immundeficiency virus-derived lentiviral constructs can produce transgenic mice and rats with high efficiency even when using low-titer virus preparations.

Mesenchymal stem cell therapy prevents interstitial fibrosis and tubular atrophy in a rat kidney allograft model

In solid organ transplantation, mesenchymal stem cell (MSC) therapy is strongly emerging among other cell therapies due to the positive results obtained in vitro and in vivo as an immunomodulatory agent and their potential regenerative role. We aimed at testing whether a single dose of MSCs, injected at 11 weeks after kidney transplantation for the prevention of chronic mechanisms, enhanced regeneration and provided protection against the inflammatory and fibrotic processes that finally lead to the characteristic features of chronic allograft nephropathy (CAN). Either bone marrow mononuclear cells (BMCs) injection or no-therapy (NT) were used as control treatments. A rat kidney transplantation model of CAN with 2.5 h of cold ischemia was used, and functional, histological, and molecular parameters were assessed at 12 and 24 weeks after transplantation. MSC and BMC cell therapy preserves renal function at 24 weeks and abrogates proteinuria, which is typical of this model (NT24w: 68.9 ± 26.5 mg/24 h, MSC24w: 16.6 ± 2.3 mg/24 h, BMC24w: 24.1 ± 5.3 mg/24 h, P<0.03). Only MSC-treated animals showed a reduction in interstitial fibrosis and tubular atrophy (NT24w: 2.3 ± 0.29, MSC24w: 0.4 ± 0.2, P<0.03), less T cells (NT: 39.6 ± 9.5, MSC: 8.1 ± 0.9, P<0.03) and macrophages (NT: 20.9 ± 4.7, MSC: 5.9 ± 1.7, P<0.05) infiltrating the parenchyma and lowered expression of inflammatory cytokines while increasing the expression of anti-inflammatory factors. MSCs appear to serve as a protection from injury development rather than regenerate the damaged tissue, as no differences were observed in Ki67 expression, and kidney injury molecule-1, Clusterin, NGAL, and hepatocyte growth factor expression were only up-regulated in nontreated animals. Considering the results, a single delayed MSC injection is effective for the long-term protection of kidney allografts.

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.

Dynamic lineage analysis of embryonic morphogenesis using transgenic quail and 4D multispectral imaging

We describe the development of transgenic quail that express various fluorescent proteins in targeted manners and their use as a model system that integrates advanced imaging approaches with conventional and emerging molecular genetics technologies. We also review the progression and complications of past fate mapping techniques that led us to generate transgenic quail, which permit dynamic imaging of amniote embryogenesis with unprecedented subcellular resolution.