Background: Proinflammatory cytokine interleukin-1beta (IL-1β) is expressed at high levels in the developing brain and declines to low constitutive levels in the adult. However, the pathophysiological function of IL-1β during brain development remains elusive. In this study, we investigated the role of IL-1β in neuronal migration.
Methods: The Boyden transwell assay was used to examine the effects of IL-1β on the migration of dissociated primary cortical neurons. To determine the role of IL-1β in neuron leading process pathfinding, we employed a growth cone turning assay. In utero electroporation combined with RNAi technology was used to examine the neuronal migration in vivo during brain development in Sprague-Dawley rats.
Results: IL-1β at concentrations ranging from 0.1 to 10 ng/mL in the lower chamber of a transwell induced a significant increase in the number of migrating neurons in a dose-dependent manner. When IL-1β was simultaneously put in both the upper and lower chambers to eliminate the gradient, no significant differences in cell migration were observed. IL-1 receptor antagonist IL-1RA dose-dependently blocked the attractive effect of IL-1β on neuronal migration. Microscopic gradients of IL-1β were created near the growth cones of isolated neurons by repetitive pulsatile application of picoliters of a IL-1β-containing solution with a micropipette. We found that growth cones exhibited a clear bias toward the source of IL-1β at the end of a one hour period in the IL-1β gradient. No significant difference was observed in the rate of neurite extension between IL-1β and controls. We electroporated specific siRNA constructs against IL-1R1 mRNA into cortical progenitors at embryonic day 16 and examined the position and distribution of transfected cells in the somatosensory cortex at postnatal day 5. We found that neurons transfected with IL-1R1-siRNA displayed a severe retardation in radial migration, with about 83% of total cells unable to arrive at the upper cortical layers.
Conclusions: Our study suggests an essential contribution of IL-1β to neuronal migration during brain development, which provides a basis to understand the physiological roles of IL-1β in the developing brain and could have significant implications for the prevention of some neurodevelopment disorders due to abnormal neuronal migration.