Faculty Book
BARBARA GRIMPE, Ph.D.
Instructor, Neurological Surgery
Novel strategies for axon regeneration and stem cell differentiation
Research
Interests
POSTDOCTORAL ASSOCIATE POSITION AVAILABLE IMMEDIATELY. See position #034547 at http://careers.med.miami.edu
 My interest focuses on the extracellular matrix (ECM), one of the cell’s most important environmental components. It contains axon-growth promoting molecules (e.g. fibronectin) and one of the most powerful molecular families for neurite outgrowth and cell attachment, the laminins. Their expression and essential importance in the central nervous system (CNS) tissue as basement membrane independent proteins is accepted by some scientists and rejected by others. The differences in opinion are due to the difficulties of detecting laminins in CNS tissue based on their low expression rate. Further, the ECM contains axon-growth inhibitory families such as proteoglycans including chondroitin/dermatan sulfate-, heparin sulfate- and keratan sulfate proteoglycans. They play an important role by forming the glia scar, a combination of CNS and non-CNS cells that over time after injury form a rubber-like barrier and lead to reduced axon regeneration. However, their axon growth promoting function is still controversial. To investigate the role of laminins and proteoglycans in regeneration processes, I use a new technology, the DNA enzymes. These are small catalytic DNA molecules that are able to bind specifically to an mRNA of interest. For more detail please visit: Grimpe lab. Further strategies are imperative to support regeneration processes after injury in the CNS: 1) to make a substrate available on which regenerating axons can grow and 2) to replace the destroyed neurons with new ones. For both cases stem cells offer a great choice. Dependent on their environmental cues, they can differentiate into glia (astrocytes/oligodendrocyes) or neurons in CNS regions. Therefore, my focus is in the investigation of these environmental cues and how to initiate the demanded cell population. Using 80-90 % pure freshly isolated neuronal stem cells of E10-E12 mouse embryos, we microtransplant them into different areas of the injured or uninjured CNS to answer this question.
The Hippocampus:
In mammals, stem cell differentiation occurs every single day in two regions of the adult CNS. These regions are the subventricular zone/olfactory bulb and the hippocampus. In the latter, the newly differentiated neurons need to extend an axon along a particular route, the stratum lucidum and stratum pyramidal. In Grimpe et al., 2002, we showed that in juvenile (P4) organotypic hippocampal slice cultures, the granular neurons are able to regenerate their axons, that are called mossy fibers, after lesions were made close to their cell bodies. What makes the hippocampus and perhaps the subventricular zone/olfactory bulb such a special region for differentiation and regeneration processes in the CNS? The expression of laminin seems to be very critical especially during their regeneration process along the mossy fiber route. The laminin, which is made up of three chains, is found in the proximal part of the apical dendrite of the pyramidal neurons, the target cells for the mossy fiber synapses. By reducing the expression of one of the three chains, the g1-chain of laminin, with the use of a newly designed DNA enzyme, the mossy fibers were unable to regenerate. This shows that laminin is most likely directly or indirectly involved in the regeneration process of these mossy fibers.
The adult Spinal Cord:
In the last decade, proteoglycans have been identified as one of the major families of inhibitory molecules responsible for regeneration failure in the CNS and therefore also in the spinal cord. They are mainly involved in forming the glial scar after injury that represents a major mechanical, cellular and molecular inhibitory barrier for regenerating axons. Proteoglycans consist of two parts, 1) a protein core and 2) carbohydrates (sugar) chains. To reduce these carbohydrate chains, we targeted their initiating enzyme, the xylosyltransferase (XT), and were able to show that regenerating axons from nanoinjected adult dorsal root ganglion (DRG) cells can, indeed, bypass a lesion in the adult dorsal columns. However, in untreated animals the neurons were unable to pass the proteoglycan rich penumbra and lesion site (Grimpe and Silver, 2004).
Ries A, Goldberg JL, Grimpe B (2007) A novel biological function for CD44 in axon growth of retinal ganglion cells identified by a bioinformatics approach. Journal of Neurochemistry, in press.
Grimpe B, Pressman Y, Lupa MD, Horn KP, Bunge MB, Silver J (2005) The role of proteoglycans in Schwann cell/astrocyte interactions and in regeneration failure at PNS/CNS interfaces. Mol Cell Neurosci 28: 18-29.
Grimpe B. and Silver J. (2004) A novel DNA-enzyme reduces glycosaminoglycan chains in the glial scar and allows microtransplanted DRG axons to regenerate beyond lesions in the spinal cord, J. Neurosci., 24: 1393-1397.
Grimpe B., Dong S., Doller C., Temple K., Malouf A. and Silver J. (2002) The critical role of basement membrane-independent laminin g1 chain during axon regeneration in the CNS, J. Neurosci., 22: 3144-3160.
Grimpe B., Probst J.C. and Hager G. (1999) Suppression of nidogen-1 translation by antisense targeting affects the adhesive properties of cultured astrocytes, Glia, 28: 138-149.
Rauch U., Grimpe B., Kulbe G. Arnold-Ammer I., Beier D.R. and Fässler R. (1995) Structure and chromosomal localization of the mouse neurocan gene, Genomics, 28, 405-410.
Reviews:
Grimpe B (2004) Aspects of antisense oligonucleotide, ribozyme, DNA enzyme and RNAi design, Curr. Med. Chem.-Central Nervous System Agents, 4, 1-15.
Grimpe B. and Silver J. (2002) The extracellular matrix in axon regeneration, Prog. Brain Res. 137, 333-349.
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