Introduction: Intra-arterial transplantation of neural progenitor cells (NPCs) to treat ischemic stroke requires efficient mechanisms for cellular migration, guided by CCL2 and other chemokines. Here we examine the sufficiency of CCL2 to enhance such homing following intracarotid NPC delivery in non-stroked mice.
Methods: Non-stroked FVB mice received stereotactic injections of CCL2 to the striatum. 24 hours later, 500,000 NPCs expressing green fluorescent protein (GFP) and luciferase were injected into the ipsilateral common carotid artery with the external carotid artery ligated. Bioluminescence imaging (BLI) was performed immediately and 24 hours post-transplant to characterize in vivo cell distribution. Brains were then sectioned for immunohistochemical detection of GFP, ionized calcium binding adaptor molecule-1 (Iba-1), and glial fibrillary acidic protein (GFAP), the latter two to examine inflammatory effects of the injection process with or without CCL2. Additional mice received stereotactic injections of biotinylated CCL2; IHC was then performed with a streptavidin-conjugated fluorophore to examine intraparenchymal CCL2 distribution.
Results: Post-transplant BLI showed no significant difference in signal intensity or retention of NPCs transplanted after intraparenchymal CCL2 versus saline (p = 0.47, n = 5). There was a trend toward significance of greater average brain/body BLI signal ratio in the CCL2 group (27.3% vs. 22.5%). IHC also showed Iba-1 and GFAP specifically along the needle track, with greater expression in CCL2 recipients. Although biotinylated CCL2 was detectable immediately post-transplant, it was not 1 day later.
Conclusions: Although necessary, CCL2 is likely insufficient to increase NPC recruitment following intra-arterial delivery in non-stroked mice. While in vitro migration data suggest some role from direct signaling, contributions from inflammation and blood-brain barrier compromise that accompany intraparenchymal injection and, to a greater degree, stroke appear to be important in allowing intravascularly-delivered cells access to the brain compartment. They may then migrate along chemokine gradients to reach sites of therapeutic potential.
Patient Care: These and other findings will contribute to progress being made on incorporating neural-stem-cell-based therapies for stroke and neurodegenerative disorders into the surgeon's armamentarium. Specifically, utilizing an intravascular approach may allow for more effective and less invasive delivery of neural stem cells to injured brain tissue, likely improving outcomes and decreasing complications from cell transplantation. This would be particularly relevant following catheter-directed thrombolysis for acute ischemic/embolic stroke.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the importance of CCL2 and the post-stroke/post-injection inflammatory response in directing the transendothelial migration of intravascularly delivered neural progenitor cells.
2) Discuss, in small groups, how to use these and other methods to identify additional key mediators of effective neural progenitor cell delivery to ischemic brain regions and select for or upregulate these factors when evaluating NPC-based therapies.
3) Identify an effective treatment for ischemic brain injury using catheter-based delivery of a CCR2-enriched neural progenitor cell population, likely after thrombolysis with intra-arterial tPA.