The role of platelets and their microparticles in rehabilitation of ischemic brain tissue.

Stroke is a leading cause of mortality and chronic disability. Therapies aimed at reducing stroke related morbidity are currently limited. Therefore it is very important to develop effective treatments that will maximize rehabilitation after stroke. Current efforts in the field of cellular therapy focus on stem cell transplantations. This approach involves biological and ethical complications and therefore, the use of endogenous neural stem cells (eNSC) for repairing damage in various neurological disorders has been suggested. eNSCs reside in specialized vascular niches in defined regions, such as the subventricular zone (SVZ) of the lateral ventricle. These cells have an unlimited potential to create newborn cells. Interrelations between newborn neural and endothelial cells have an important role in eNSC survival, maturation, migration and differentiation and neurogenesis occurs in close spatio-temporal association with vessel growth in these niches. Previous studies have shown that application of external factors can boost long-term endogenous repair mechanisms in the cerebral cortex. Activated platelets and their microparticles contain a variety of growth and trophic factors essential to angiogenesis and neurogenesis and may therefore serve as novel therapeutic agents for brain injury. Specifically, factors from platelets and their microparticles may promote neurogenesis by stimulating eNSC proliferation, migration and differentiation, and by stimulating niche angiogenesis and the release of neurogenic signals from endothelial cells and astrocytes. In this review we will show that combined augmentation of angiogenesis, neurogenesis and neuroprotection using platelets and their microparticles is feasible and results in improved functional gain after stroke.