Glial restricted precursors and spinal cord repair

Baylor College Of Medicine, Houston TX

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Abstract

DESCRIPTION (provided by applicant): The primary focus of this research application is the development of an in vivo model of traumatic adult mammalian spinal cord injury with which to study the glial and matrix biology of spinal cord scar formation and characterize the ability of glial-restricted precursors (GRPs) and GRP-derived astrocytes (GDAs) to differentiate within forming glial scar tissue, suppress scar formation and provide an axon growth support bridge for axon regeneration. Preliminary data from our laboratory shows that spinal cord scar tissue is rich in a variety of axon growth inhibitory chondroitin sulfate proteoglycans (CSPGs), several of which are associated with astrocytes and adult glial progenitors that accumulate at sites of injury. Interestingly, although adult glial precursors can generate both astrocytes and oligodendrocytes in vitro, astrocytes are the predominant macroglia observed within spinal scar tissue. Experiments in aim 1 will therefore test the hypothesis that the environment of adult spinal scar tissue favors astrocytic differentiation, by transplanting a defined population of tripotent glial-restricted precursors (GRPs) directly into an acute stab injury of adult rat dorsal column white matter and quantifying the proportions of astrocytes and oligodendrocytes that these cells generate. As controls for the possible effects of scar tissue and axotomy on GRP differentiation, the macroglial differentiation of GRPs in the absence of glial scar tissue within intact white matter alone and in the presence of growing axons from adult neurons, will be investigated using an atraumatic micro-transplantation technique. Embryonic GRPs can be induced to differentiate into type-1 astrocytes or type-2 astrocytes in vitro. The generation of these two distinct astrocytic populations from GRPs in vitro permits an investigation of the impact of each of these distinct astrocytic cell types on scar formation and axon regeneration in vivo. Unlike adult astrocytes or type-2 astrocytes, type-1 astrocytes express low levels of CSPGs and transforming growth factor betas (TGFbetas) known to induce CSPG deposition in CNS scar tissue. In aim 2, quantitative western blot and confocal microscopy analysis will test the hypothesis that intra-lesion transplants of type-1 GDAs will suppress TGFbeta and CSPG levels within spinal cord scar tissue compared to type-2 GDAs or control lesions. Preliminary results show that type-1 GDAs are highly supportive of axon growth in vitro. Experiments in aim 3 will therefore test the hypothesis that intra-lesion transplanted type-1 GDAs will retain their axon growth supportive phenotype and promote axon regeneration across spinal cord injuries. Micro-transplantation and axon tracing techniques will be used to compare the ability of type-1 GDAs and type-2 GDAs grafted into injured spinal cord to support regeneration of adult sensory and corticospinal axons at acute to chronic time points post injury.