Cell transplantation in the damaged adult brain.

Parkinson's disease (PD) is the most common movement disorder in Europe, affecting more than two million people between 50 and 70 years of age. The current therapeutic approaches are of symptomatic nature and fail to halt the progressive neurodegenerative course of the disease. The development of innovative and complementary approaches to promote cellular repair may pave the way for disease-modifying therapies which may lead to less suffering for the patients and their families and finally to more cost-effective therapies. To date, cell replacement trials in PD aiming at replacing lost dopamine neurons were mainly focused on placing the transplanted cells within the target site, the striatum, and not within the lesioned site, the substantia nigra (SN). This was based on the misconception that the adult brain constitutes a non-permissive barrier not allowing the outgrowth of long distance axons originating from transplanted embryonic neurons. A growing body of evidence is challenging this concept and proposing instead to place the graft within its ontogenic site. This has been performed in several lesional animal models for various traumatic or neurodegenerative pathologies of the brain. For instance, transplanted neurons within the lesioned motor cortex were shown to be able to send distant and appropriate projections to target areas including the spinal cord. Similarly, in an animal model of PD, mesencephalic embryonic cells transplanted within the lesioned SN send massive projections to the striatum and, to a lesser extent, the frontal cortex and the nucleus accumbens. This has lead to the proposal that homotopic transplantation may be an alternative in cell-based therapies as transplanted neurons can integrate within the host brain, send projections to target areas, restore the damaged circuitry, increase neurotransmitter levels and ameliorate behavior. We will discuss also the potential of replacing embryonic neuronal cells by stem cell derived neurons as the use of embryonic cells is not without an ethical and logistical burden; in this line many have thrived to derive neurons from embryonic stem cells (ESC) in order to use them for cell transplantation. These studies are already yielding important information for future approaches in the field of cell therapies in PD but also in other neurodegenerative disorders where cell transplantation therapy may be considered. While the field of cell replacement therapies has been recently called into question with contrasting results in transplanted PD patients, these new sets of findings are raising new hopes and opening new avenues in this rejuvenated field.

Expression of ephrinA5 during development and potential involvement in the guidance of the mesostriatal pathway.

Identifying guidance cues that direct axon growth to their final connections during development is of crucial interest if we aim to repair circuits damaged in adulthood following neurodegenerative disorders or common traumatic injuries. In this work, we set out to determine the ephrinA5 guidance molecule involvement in the establishment of the mouse mesostriatal pathway during development. We showed, in vitro and in vivo, that a proportion of mesencephalic dopaminergic cells express the ephrinA5 receptor, EphA5. Moreover, we observed, using stripe assays, that ephrinA5 purified protein has a repulsive effect on most of the mesencephalic dopaminergic projections. In vivo, we detected rostro-caudal and ventro-dorsal ephrinA5 protein expression gradients in the vicinity of the dopaminergic axons in the ventral telencephalon and in the striatum, during the embryonic and early postnatal development. In addition, other EphA5 ligands were also detected in the mesostriatal pathway. Together, these expression patterns suggest that, ephrinAs and more specifically ephrinA5, may be actors in the guidance of dopaminergic projections. Further studies will focus on identifying the molecular specificity of these guidance cues, taking into account the mesencephalic dopaminergic heterogeneous neuronal population. This may help increase the integration of neuronal transplants in the mature lesioned brain or provide tools to re-establish mesostriatal circuits in vivo.

Association between integrin-dependent migration capacity of neural stem cells in vitro and anatomical repair following transplantation.

In previous transplantation studies using neural stem cell lines immortalized by the temperature-sensitive SV40 large T-antigen, we have shown that animals with experimental hippocampal lesions resulting from four vessel occlusion recover spatial memory functions more effectively when grafted with the MHP36 cell line than with the MHP15 cell line [Gray et al. (1999). Philos. Trans. R. Soc. London Biol. Sci. 354:1407-1421]. In the present study, we have investigated the cellular and molecular basis of these differences in repair capacity both in vivo and in vitro. Using the same model of hippocampal damage we have shown that following transplantation MHP36 cells migrate and align within the damaged CA1 of the ipsilateral hippocampus. MHP15 cells, in contrast, migrate in a more indiscriminate pattern that does not reflect the anatomy of the region. To analyze the migratory properties of these two cell lines in more detail, we performed migration assays at a nonpermissive temperature on the extracellular matrix substrates laminin, fibronectin, and vitronectin. These showed that MHP36 cells have a greater migration potential than the MHP15 cells. While the pattern of cell surface extracellular matrix receptors of the integrin family was identical in both cell lines, the different degrees of migration on vitronectin were both blocked by inhibitors of alphaV integrins. Differences in integrin signaling therefore contribute to the greater migration potential of the repairing MHP36 cell line.

Magnetic resonance imaging of transplanted oligodendrocyte precursors in the rat brain.

The lack of any markers for oligodendrocyte precursors that can be visualized within the intact CNS is a significant barrier to trials of transplantation of these cells which aim to enhance remyelination in multiple sclerosis. We have therefore asked whether dextran-coated superparamagnetic iron oxide (SPIO) can be used to label cells prior to transplantation and then visualized within the brain using MRI. We have shown that an oligodendrocyte precursor cell line CG-4 will take up dextran-coated SPIO particles in vitro. The label remains within the cells after transplantation into adult rat brain, as assessed by electron microscopy, and is visible by MRI as a reduction in signal intensity at the transplant site at both 1 and 7 days after surgery. We conclude that MRI detection of SPIO-labelled cells represents a promising and novel approach to the analysis of oligodendroglial cell behaviour following transplantation that has very significant advantages over currently available methods.

Differential UDP-galactose-4'-epimerase (GALE) enzymatic activity and mRNA expression in the rat mammary gland during lactation.

We have investigated the UDP-galactose-4'-epimerase (GALE) enzymatic activity and mRNA expression in the rat mammary gland during lactation. We report a dramatic increase in the GALE enzymatic activity correlated with an increase in the mRNA transcript expression. These results indicate a transcriptional regulation of the enzyme during lactation in the rat mammary gland. Our data are of double interest for further investigation: first, the mammary gland provides a suitable model for the characterisation of the transcriptional regulation elements of GALE which are still unknown in mammals; second, GALE expression could help to compensate UDP-galactose deficiency in classic galactosaemia.

Altered follicle stimulating hormone isoforms in female galactosaemia patients.

UNLABELLED: Many women affected with galactosaemia suffer from ovarian dysfunction and have elevated serum levels of follicle stimulating hormone (FSH). We have analysed FSH-glycoprotein isoforms from four galactosaemic and five healthy women. Besides the commonly found FSH species with a median isoelectric point (pI) of 4-5, the sera of the female galactosaemic patients contained qualitatively abnormal FSH isoforms with a pI close to neutral (6.4-7.0). The generally reduced galactosylation in patient samples was confirmed because sera of galactosaemic patients could incorporate 1.7 times more UDP-(14C)galactose than did healthy subjects. CONCLUSION: Our data indicate that the terminal disaccharides of FSH (a glycoprotein), galactose and sialic acid were partially deficient in three galactosaemic female patients with no galactose-1-phosphate uridyl transferase (GALT) activity in red cells. However, from a female patient with a residual GALT activity (a mild form of galactosaemia), no distinctive deficiency was observed. This again suggest an importance of GALT in retaining a correct FSH structure. Therefore the abundance of neutral FSH isoforms, which was described to have a higher binding affinity to its receptor and no capacity to activate cyclic adenosine mono-phosphate (cAMP), may cause a hormonal dysfunction in classical galactosaemia.