Agnete Kirkeby

Direct conversion of human fibroblasts to dopaminergic neurons

Recent reports demonstrate that somatic mouse cells can be directly converted to other mature cell types by using combined expression of defined factors. Here we show that the same strategy can be applied to human embryonic and postnatal fibroblasts. By overexpression of the transcription factors Ascl1, Brn2, and Myt1l, human fibroblasts were efficiently converted to functional neurons. We also demonstrate that the converted neurons can be directed toward distinct functional neurotransmitter phenotypes when the appropriate transcriptional cues are provided together with the three conversion factors. By combining expression of the three conversion factors with expression of two genes involved in dopamine neuron generation, Lmx1a and FoxA2, we could direct the phenotype of the converted cells toward dopaminergic neurons. Such subtype-specific induced neurons derived from human somatic cells could be valuable for disease modeling and cell replacement therapy.

Generation of Regionally Specified Neural Progenitors and Functional Neurons from Human Embryonic Stem Cells under Defined Conditions.

To model human neural-cell-fate specification and to provide cells for regenerative therapies, we have developed a method to generate human neural progenitors and neurons from human embryonic stem cells, which recapitulates human fetal brain development. Through the addition of a small molecule that activates canonical WNT signaling, we induced rapid and efficient dose-dependent specification of regionally defined neural progenitors ranging from telencephalic forebrain to posterior hindbrain fates. Ten days after initiation of differentiation, the progenitors could be transplanted to the adult rat striatum, where they formed neuron-rich and tumor-free grafts with maintained regional specification. Cells patterned toward a ventral midbrain (VM) identity generated a high proportion of authentic dopaminergic neurons after transplantation. The dopamine neurons showed morphology, projection pattern, and protein expression identical to that of human fetal VM cells grafted in parallel. VM-patterned but not forebrain-patterned neurons released dopamine and reversed motor deficits in an animal model of Parkinsons disease.

Human ESC-Derived Dopamine Neurons Show Similar Preclinical Efficacy and Potency to Fetal Neurons when Grafted in a Rat Model of Parkinson’s Disease

Summary Considerable progress has been made in generating fully functional and transplantable dopamine neurons from human embryonic stem cells (hESCs). Before these cells can be used for cell replacement therapy in Parkinson’s disease (PD), it is important to verify their functional properties and efficacy in animal models. Here we provide a comprehensive preclinical assessment of hESC-derived midbrain dopamine neurons in a rat model of PD. We show long-term survival and functionality using clinically relevant MRI and PET imaging techniques and demonstrate efficacy in restoration of motor function with a potency comparable to that seen with human fetal dopamine neurons. Furthermore, we show that hESC-derived dopamine neurons can project sufficiently long distances for use in humans, fully regenerate midbrain-to-forebrain projections, and innervate correct target structures. This provides strong preclinical support for clinical translation of hESC-derived dopamine neurons using approaches similar to those established with fetal cells for the treatment of Parkinson’s disease.

Comparison of neuroprotective effects of erythropoietin (EPO) and carbamylerythropoietin (CEPO) against ischemia-like oxygen-glucose deprivation (OGD) and NMDA excitotoxicity in mouse hippocampal slice cultures

In addition to its well-known hematopoietic effects, erythropoietin (EPO) also has neuroprotective properties. However, hematopoietic side effects are unwanted for neuroprotection, underlining the need for EPO-like compounds with selective neuroprotective actions. One such compound, devoid of hematopoietic bioactivity, is the chemically modified, EPO-derivative carbamylerythropoietin (CEPO). For comparison of the neuroprotective effects of CEPO and EPO, we subjected organotypic hippocampal slice cultures to oxygen-glucose deprivation (OGD) or N-methyl-d-aspartate (NMDA) excitotoxicity. Hippocampal slice cultures were pretreated for 24 h with 100 IU/ml EPO (=26 nM) or 26 nM CEPO before OGD or NMDA lesioning. Exposure to EPO and CEPO continued during OGD and for the next 24 h until histology, as well as during the 24 h exposure to NMDA. Neuronal cell death was quantified by cellular uptake of propidium iodide (PI), recorded before the start of OGD and NMDA exposure and 24 h after. In cultures exposed to OGD or NMDA, CEPO reduced PI uptake by 49+/-3 or 35+/-8%, respectively, compared to lesion-only controls. EPO reduced PI uptake by 33+/-5 and 15+/-8%, respectively, in the OGD and NMDA exposed cultures. To elucidate a possible mechanism involved in EPO and CEPO neuroprotection against OGD, the integrity of alpha-II-spectrin cytoskeletal protein was studied. Both EPO and CEPO significantly reduced formation of spectrin cleavage products in the OGD model. We conclude that CEPO is at least as efficient neuroprotectant as EPO when excitotoxicity is modeled in mouse hippocampal slice cultures.

Functional and immunochemical characterisation of different antibodies against the erythropoietin receptor

Since it was discovered that the hematopoietic hormone erythropoetin (EPO) exerts neuroprotective effects in the CNS, many studies on the EPO receptor (EPOR) function and localisation in the CNS have been performed. For this purpose, commercially available anti-EPOR antibodies have often been applied. As the literature data on these antibodies show inconsistencies, we here systematically compared six frequently used, commercially available EPOR antibodies for different applications. Five of the antibodies appeared to specifically recognize recombinant rat and human EPOR in HEK293 cells by Western blotting, but the same antibodies yielded different and inconsistent results when human UT-7 cells or rat brain tissue were applied. Immunocytochemical staining of EPOR-transfected HEK cells only produced consistent results with three of the six antibodies. All antibodies stained neurons in rat brain sections, but with large differences in the staining pattern and only the C-20 EPOR antibody was found to label astrocytes. Since EPOR antibodies have been applied in several studies as EPOR antagonists, we further tested the antibodies for their capacity to functionally block the EPO-EPOR interaction in a cellular signalling system with STAT-5 phosphorylation as readout. Here, only the MAB307 antibody showed a partial effect at concentrations of 5-50 microg/ml.

High-dose erythropoietin alters platelet reactivity and bleeding time in rodents in contrast to the neuroprotective variant carbamyl-erythropoietin (CEPO)

The haematopoietic hormone erythropoietin (EPO) has neuroprotective properties and is currently being explored for treatment of stroke and other neurological disorders. Short-term, high-dose treatment with EPO seems to improve neurological function of stroke patients but may be associated with increased thrombotic risk, whereas alternative non-erythropoietic neuroprotective derivatives of EPO, such as carbamylated EPO (CEPO), may be devoid of such side-effects. We investigated the effects of short-term, high-dose treatment with EPO and CEPO on platelet function and haemostasis in healthy mice and rats. Animals received three daily doses of EPO or CEPO (50 microg/kg), and blood was compared with respect to alterations in haematology and platelet reactivity. In rats, treatment with EPO increased the haematocrit to >50% and the mean platelet volume by 37%, while CEPO had no effect on these parameters. Platelets from EPO-treated rats showed an increased sensitivity to thrombin receptor agonist peptides and elevated plasma levels of soluble P-selectin (sP-selectin) were found in treated mice. Further indicators of platelet hyperreactivity in EPO, but not CEPO-treated animals, were significantly increased aggregatory responses to collagen in whole blood and platelet-rich plasma (PRP). The increased platelet reactivity was paralleled by a decreased bleeding time after tail transection in rats. Samples from EPO-treated rats showed an attenuated response to ADP in whole blood aggregometry and thrombelastography (TEG) platelet mapping but not in apyrase-treated PRP, suggesting involvement of ADP receptor desensitization. These findings suggest that while EPO affects various aspects of platelet function, CEPO is devoid of such effects.

Predictive Markers Guide Differentiation to Improve Graft Outcome in Clinical Translation of hESC-Based Therapy for Parkinson’s Disease

Summary Stem cell treatments for neurodegenerative diseases are expected to reach clinical trials soon. Most of the approaches currently under development involve transplantation of immature progenitors that subsequently undergo phenotypic and functional maturation in vivo, and predicting the long-term graft outcome already at the progenitor stage remains a challenge. Here, we took an unbiased approach to identify predictive markers expressed in dopamine neuron progenitors that correlate with graft outcome in an animal model of Parkinson’s disease through gene expression analysis of >30 batches of grafted human embryonic stem cell (hESC)-derived progenitors. We found that many of the commonly used markers did not accurately predict in vivo subtype-specific maturation. Instead, we identified a specific set of markers associated with the caudal midbrain that correlate with high dopaminergic yield after transplantation in vivo. Using these markers, we developed a good manufacturing practice (GMP) differentiation protocol for highly efficient and reproducible production of transplantable dopamine progenitors from hESCs.

Tracking differentiating neural progenitors in pluripotent cultures using microRNA-regulated lentiviral vectors

In this study, we have used a microRNA-regulated lentiviral reporter system to visualize and segregate differentiating neuronal cells in pluripotent cultures. Efficient suppression of transgene expression, specifically in undifferentiated pluripotent cells, was achieved by using a lentiviral vector expressing a fluorescent reporter gene regulated by microRNA-292. Using this strategy, it was possible to track progeny from murine ES, human ES cells, and induced pluripotent stem cells as they differentiated toward the neural lineage. In addition, this strategy was successfully used to FACS purify neuronal progenitors for molecular analysis and transplantation. FACS enrichment reduced tumor formation and increased survival of ES cell–derived neuronal progenitors after transplantation. The properties and versatility of the microRNA-regulated vectors allows broad use of these vectors in stem cell applications.

Therapeutic window for nonerythropoietic carbamylated-erythropoietin to improve motor function following multiple infarct ischemic strokes in New Zealand white rabbits

Carbamylated erythropoietin (CEPO) is a novel neuroprotective agent that does not bind to the classical erythropoietin receptor or affect hematocrit. Since CEPO has not been systematically studied in a fully blinded and randomized manner in an embolic stroke model, we determined if CEPO would be useful to attenuate clinical deficits associated with multiple infarct ischemia using the rabbit small clot embolic stroke model (RSCEM). Rabbits were embolized and treated with vehicle or CEPO within 6 h of embolization and behavioral analysis was conducted 48 h after embolization. Using quantal analysis, we determined the quantity of blood clot (mg) in brain that produce neurologic dysfunction in 50% of the rabbits (P(50)), with intervention considered beneficial if it increased the P(50) compared to controls. CEPO administered between 5 min and 3 h after embolization significantly (p<0.05) improved behavioral function and increased the P(50) value by 55-216%. However, CEPO administration did not improve behavior when administered 6 h following embolization. In conclusion, in the RSCEM, CEPO had a therapeutic window of at least 3 h, where it effectively improved clinical rating scores and motor function. Our results suggest that CEPO may be useful to treat acute ischemic stroke and supports the study of CEPO in stroke patients.

Monosynaptic Tracing using Modified Rabies Virus Reveals Early and Extensive Circuit Integration of Human Embryonic Stem Cell-Derived Neurons.

Summary Human embryonic stem cell (hESC)-derived dopamine neurons are currently moving toward clinical use for Parkinson’s disease (PD). However, the timing and extent at which stem cell-derived neurons functionally integrate into existing host neural circuitry after transplantation remain largely unknown. In this study, we use modified rabies virus to trace afferent and efferent connectivity of transplanted hESC-derived neurons in a rat model of PD and report that grafted human neurons integrate into the host neural circuitry in an unexpectedly rapid and extensive manner. The pattern of connectivity resembled that of local endogenous neurons, while ectopic connections were not detected. Revealing circuit integration of human dopamine neurons substantiates their potential use in clinical trials. Additionally, our data present rabies-based tracing as a valuable and widely applicable tool for analyzing graft connectivity that can easily be adapted to analyze connectivity of a variety of different neuronal sources and subtypes in different disease models.