Faculty Faculty 2008 Faculty 2009

Scott Whittemore, PhD

Spinal Cord Injury causes many changes at the molecular level that damage or destroy key components of the nervous system that carry signals to and from the brain – including neurons, axons and the myelin coating that protects the nervous system much like the insulation around an electrical cord, as well as the vascular infrastructure that carries oxygen to these tissues.

The Molecular Neurobiology Laboratory focuses on strategies to replace lost neurons, help axons regenerate, and regeneration of the myelin coating around damaged or regenerating axons. Using undifferentiated precursor cells, gene therapies, and transplanted neurons, the lab seeks to understand the development of these key components of the vascular and nervous system at the molecular and genetic level in order to protect them from damage and/or promote their regeneration.

The general research focus of my laboratory is to utilize molecular and cellular biological techniques to address repair in spinal cord injury (SCI). These studies are usually initiated in vitro and successful approaches then taken into whole animal experiments. When designing strategies to facilitate functional restoration in SCI, three issues need to be considered: 1) replacement of lost neurons, 2) remyelination of de-myelinated and/or regenerating axons, and 3) inducing axotomized descending motor and ascending sensory axons to regenerate. We are utilizing multiple strategies to examine all three issues.

Neuronal replacement requires transplantation of exogenous neurons, as CNS neurons do not regenerate. Similarly, injury-induced de-myelination is secondary to a loss of intrinsic oligodendrocytes. Our approach to re-myelination is to transplant oligodendrocyte precursors into the demyelinated area. We are using CNS-derived stem cells as a source for both neurons and oligodendrocytes. Ongoing experiments in vitro are using retroviral vectors to infect the undifferentiated precursor cells with transcription factors that direct either neuronal or oligodendrocytic differentiation. Additionally, we isolate neuronal-restricted and glial-restricted populations of precursor cells. These cells are then engrafted into specific SCI models that deplete functionally discrete populations of neurons or endogenous oligodendrocytes in specific ventral motor pathways. We utilize a battery of behavioral and electrophysiological analyses to both characterize the initial deficits and determine the degree to which functional recovery is observed.

Our attempts to engender axotomized supraspinal, propriospinal, and sensory axons to regenerate takes a two-fold approach. We again use undifferentiated stem cells and genetically engineer them to express specific neurotrophic factors and/or cell surface molecules that facilitate regeneration by providing trophic support or a permissive substrate for regeneration. In these studies, we induce the stem cells towards an astrocytic phenotype in vivo, as early differentiating astrocytes are permissive for axonal outgrowth. Concomitant with the engraftment of these cells into the injured spinal cord, we use adenoviral or lentiviral vectors to deliver specific neurotrophic molecules at specific times post-injury to the cell bodies in the brainstem and/or into the spinal cord caudal to the injury site. This should enhance the regenerative capacity of the axotomized neurons and coax the regenerating fibers to leave the graft and enter the distal cord, respectively. In the second approach, we are characterizing in the injured spinal cord and brain the expression of the eph family of receptor tyrosine kinases and their ligands the ephrins. These molecules mediate repulsive interactions between cells that express receptor and ligand. We hypothesize that the expression of ephs and ephrins in the injured spinal cord may contribute to the non-permissive environment for regeneration. We have devised a number of reagents that can block the function of these molecules and are examining their effects on regeneration of specific ascending and descending fiber populations.

We recognize that no single strategy will be by itself effective in eliciting optimal regeneration in SCI. Our ultimate goal is to combine those individual strategies of ours and our colleagues here in the Department of Neurological Surgery that are effective to design interventive approaches that will result in functionally significant improvements after SCI.