Monocyte chemoattractant protein-1 (MCP-1) produced via NF-kappaB signaling pathway mediates migration of amoeboid microglia in the periventricular white matter in hypoxic neonatal rats

Monocyte chemoattractant protein-1 (MCP-1), a member of beta-chemokine subfamily, regulates the migration of microglia, monocytes, and lymphocytes to the inflammatory site in the central nervous system. We sought to determine if amoeboid microglial cells (AMC) produce MCP-1 that may be linked to migration of AMC in the corpus callosum periventricular white matter in hypoxic neonatal rats. A striking feature in 1-day-old rats subjected to hypoxia was a marked increase in cell numbers of AMC and immunoexpression of MCP-1 and its receptor (CCR(2)). By BrdU immunostaining, there was no significant change in the proliferation rate of AMC after hypoxic exposure when compared with the corresponding control rats. When injected intracerebrally into the corpus callosum of 7-day-old postnatal rats, MCP-1 induced the chemotactic migration of AMC to the injection site. In primary microglial cell culture subjected to hypoxia, there was a significant increase in MCP-1 release involving NF-kappaB signaling pathway. In in vitro chemotaxis assay, the medium derived from hypoxia-treated microglial cultures attracted more migratory microglial cells than that from the control microglial culture. The present results suggest that following a hypoxic insult, AMC in the neonatal rats increase MCP-1 production via NF-kappaB signaling pathway. This induces the migration and accumulation of AMC from the neighboring areas to the periventricular white matter (PWM). It is concluded that the preponderance and active migration of AMC, as well as them being the main cellular source of MCP-1, may offer an explanation for the PWM being susceptible to hypoxic damage in neonatal brain.