Stroke is the third leading cause of morbidity and long-term disability. Due to cerebral artery occlusion, ischemic stroke causes a severe reduction in blood supply causing destruction of endothelial integrity and neuronal cell death. Indeed, patients with higher density of cerebral blood vessel show better recovery and survival after stroke. Many inflammatory chemokines support the development of vascular blood supply (angiogenesis) and progenitor cell migration to the site of injury. Particularly, the chemokine stromal derived factor (SDF1) acting via its receptor CXCR4 plays a central role in promoting angiogenesis and progenitor cell recruitment. However, SDF1 is often proteolytically cleaved and inactivated. This process may hinder neural (NPC) and endothelial progenitor cells (EPC) migration and angiogenesis necessary for brain injury repair. Thus preventing SDF1 inactivation is of clinical importance. Although the protease dipeptidyl peptidase 4 (DPPIV) is shown to cleave SDF1, its role in ischemic stroke is unknown. The goal of this proposal is to establish a ground work for evaluating the efficacy of the DPPIV inhibition in enhancing the activity of SDF1 for improved angiogenesis and brain injury repair. Our studies show a correlation between loss of DPPIV and increased levels of SDF1 resulting in increased migratory and angiogenic potential of neural crest stem cell derived neuroblastoma cells. We further observed significantly increased DPPIV expression in the post- ischemic brain. We hypothesize that following focal ischemia, DPPIV up regulation curtails SDF1 activity and thus hinders the migration of progenitor cells to the ischemic region and suppresses subsequent angiogenesis and neurogenesis. We further propose that genetic knockout or small molecule inhibitors of DPPIV increases post-ischemic SDF1 levels, which in turn enhances NPC and EPC migration and angiogenesis in ischemic brain. In this proposal, we will test the predicted inverse correlation between DPPIV expression and SDF1, and CXCR4 levels in mouse brain and serum following transient middle cerebral artery occlusion (MCAO) (Aim 1). We will examine whether genetic loss of DPPIV or small molecule inhibitor of DPPIV enhances EPC recruitment and angiogenesis in vivo ischemic brain and in an in vitro ischemic model of oxygen glucose deprivation. The luciferase expressing NPC/EPC will be transplanted into the contralateral striatum of the mice subjected to MCAO and migrating cells will be tracked using bioluminescence imaging (Aim 2). Importantly, DPPIV inhibitors are FDA approved anti-diabetic drugs that increase circulating EPCs in diabetic patients. Our studies if successful can be translated to pre-clinical and clinical studies for improved angiogenesis and neurogenesis. Results from these studies may provide strong foundation for better understanding of novel targets and mechanisms of brain injury repair and may also open up a new direction for stroke therapy.
Ischemic stroke causes death or long term disability presenting a unique challenge to patients and care givers. Stroke results in sudden decrease in blood flow and neural cell death. Restoring blood flow and neurogenesis is critical for stroke recovery. At present, there are limited therapeutic options to treat stroke patients. Our study represents an important first step in better understanding the novel molecular events that govern neurogenesis and angiogenesis (sprouting of new blood vessels) in the post-ischemic brain and establishes ground work for further testing the efficacy of small molecule inhibitors of DPPIV for improved brain injury repair after ischemic stroke that remains a major health problem in the world.
|Wesley, Umadevi V; Hatcher, James F; Dempsey, Robert J (2015) Sphingomyelin Synthase 1 Regulates Neuro-2a Cell Proliferation and Cell Cycle Progression Through Modulation of p27 Expression and Akt Signaling. Mol Neurobiol 51:1530-41|