Transport of the pro-inflammatory chemokines CCL2 (MCP-1) and CCL5 (RANTES) across the intact mouse blood-brain barrier is inhibited by heparin and eprodisate and increased with systemic inflammation.

One important function of the vascular blood-brain barrier (BBB) is to facilitate neuroimmune communication. The BBB fulfills this function, in part, through its ability to transport cytokines and chemokines. CCL2 (MCP-1) and CCL5 (RANTES) are pro-inflammatory chemokines that mediate neuroimmune responses to acute insults, and aspects of brain injury and neurodegenerative diseases; however, a blood-to-brain transport system has not been evaluated for either chemokine in vivo. Therefore, we determined whether CCL2 and CCL5 in blood can cross the intact BBB and enter the brain. Using CD-1 mice, we found that 125 I-labeled CCL2 and CCL5 crossed the BBB, and entered the brain parenchyma. We next aimed to identify the mechanisms of 125 I-CCL2 and 125 I-CCL5 transport in an in-situ brain perfusion model. We found that both heparin and eprodisate inhibited brain uptake of 125 I-CCL2 and 125 I-CCL5 in situ, whereas antagonists of their receptors, CCR2 or CCR5 respectively, did not, suggesting that heparan sulfates at the endothelial surface mediate BBB transport. Finally, we showed that CCL2 and CCL5 transport across the BBB increased following a single injection of 0.3mg/kg lipopolysaccharide. These data demonstrate that CCL2 and CCL5 in the brain can derive, in part, from the circulation, especially during systemic inflammation. Further, binding to the BBB-associated heparan sulfate is a mechanism by which both chemokines can cross the intact BBB, highlighting a novel therapeutic target for treating neuroinflammation. Significance Statement Our work demonstrates that CCL2 and CCL5 can cross the intact BBB, and that transport is robustly increased during inflammation. These data suggest that circulating CCL2 and CCL5 can contribute to brain levels of each chemokine. We further show that the transport of both chemokines is inhibited by heparin and eprodisate, suggesting that CCL2/CCL5-heparan sulfate interactions could be therapeutically targeted to limit accumulation of these chemokines in the brain.