Combined VEGF and PDGF Treatment Reduces Secondary Degeneration after Spinal Cord Injury

Abstract

Trauma to the spinal cord creates an initial physical injury damaging neurons, glia and blood vessels, which then induces a prolonged inflammatory response leading to secondary degeneration of spinal cord tissue and further loss of neurons and glia surrounding the initial site of injury. Angiogenesis is a critical step in tissue repair but in the injured spinal cord angiogenesis fails; blood vessels formed initially, later regress. Stabilizing the angiogenic response is therefore a potential target to improve recovery after for spinal cord injury. Vascular Endothelial Growth Factor (VEGF) can initiate angiogenesis but cannot sustain blood vessel maturation. Platelet Derived Growth Factor (PDGF) can promote blood vessel stability and maturation. We therefore investigated a combined application of VEGF and PDGF as treatment for traumatic spinal cord injury, with the aim to reduce secondary degeneration by promotion of angiogenesis. Immediately after hemi-section of the spinal cord in the rat we delivered VEGF and PDGF and to the injury site. One and three months later the size of the lesion was significantly smaller in the treated group compared to controls and there was significantly reduced gliosis surrounding the lesion. There was no significant effect of the treatment on blood vessel density, although there was a significant reduction in the numbers of macrophages/microglia surrounding the lesion, and a shift in the distribution of morphological and immunological phenotypes of these inflammatory cells. VEGF and PDGF delivered singly exacerbated the secondary degeneration, increasing the size of the lesion cavity. These results demonstrate a novel therapeutic intervention for spinal cord injury and reveal an unanticipated synergy for these growth factors whereby they modulated inflammatory processes and create a microenvironment conducive to axon preservation/sprouting.