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Interleukin-1 receptors in mouse brain: characterization and neuronal localization
T Takao1, D E Tracey, W M Mitchell
1Neurobiology Laboratory, National Institute on Drug Abuse, Addiction Research Center, Baltimore, Maryland 21224.
Insights
Interleukin-1 (IL-1) receptors were identified in the mouse brain, primarily in the hippocampus. These receptors, localized to neurons, suggest a role for IL-1 in regulating central nervous system activity.
Area of Science:
- Neuroscience
- Immunology
- Endocrinology
Background:
- The cytokine interleukin-1 (IL-1) influences brain functions like fever, sleep, and neuroendocrine activity.
- Understanding IL-1's central nervous system targets is crucial for elucidating its physiological roles.
Purpose of the Study:
- To identify and characterize IL-1 receptors in the mouse brain.
- To investigate the distribution of IL-1 binding sites within the brain.
Main Methods:
- Used radiolabeled recombinant human interleukin-1 alpha ([125I]IL-1 alpha) for binding assays and autoradiography.
- Performed competition studies with various IL-1 analogs and other cytokines.
- Utilized quinolinic acid lesion studies to determine receptor localization on specific cell types.
Main Results:
- High-affinity IL-1 receptors were characterized in mouse hippocampus membranes.
- Autoradiography revealed highest IL-1 binding site densities in the hippocampus (dentate gyrus) and choroid plexus.
- Hippocampal IL-1 binding sites were localized to intrinsic neurons and unaffected by hypophysectomy.
Conclusions:
- The brain possesses IL-1 receptors with properties similar to those in immune and neuroendocrine tissues.
- These findings support a physiological role for IL-1 in regulating central nervous system functions.
Abstract:
The cytokine interleukin-1 (IL-1) has a variety of effects in brain, including induction of fever, alteration of slow wave sleep, and alteration of neuroendocrine activity. To examine the potential sites of action of IL-1 in brain, we used iodine-125-labeled recombinant human interleukin-1 [( 125I]IL-1) to identify and characterize IL-1 receptors in crude membrane preparations of mouse (C57BL/6) hippocampus and to study the distribution of IL-1-binding sites in brain using autoradiography. In preliminary homogenate binding and autoradiographic studies, [125I]IL-1 alpha showed significantly higher specific binding than [125I]IL-1 beta. Thus, [125I]IL-1 alpha was used in all subsequent assays. The binding of [125I]IL-1 alpha was linear over a broad range of membrane protein concentrations, saturable, reversible, and of high affinity, with an equilibrium dissociation constant value of 114 +/- 35 pM and a maximum number of binding sites of 2.5 +/- 0.4 fmol/mg protein. In competition studies, recombinant human IL-1 alpha, recombinant human IL-1 beta, and a weak IL-1 beta analog. IL-1 beta +, inhibited [125I]IL-1 alpha binding to mouse hippocampus in parallel with their relative bioactivities in the T-cell comitogenesis assay, with inhibitory binding affinity constants of 55 +/- 18, 76 +/- 20, and 2940 +/- 742 pM, respectively; rat/human CRF and human tumor necrosis factor showed no effect on [125I]IL-1 alpha binding. Autoradiographic localization studies revealed very low densities of [125I]IL-1 alpha-binding sites throughout the brain, with highest densities present in the molecular and granular layers of the dentate gyrus of the hippocampus and in the choroid plexus. Quinolinic acid lesion studies demonstrated that the [125I]IL-1 alpha-binding sites in the hippocampus were localized to intrinsic neurons. After hypophysectomy, homogenate binding and autoradiographic studies showed that there was no apparent change in the relative density of IL-1 receptors in the hippocampus. The identification of IL-1 receptors in brain with characteristics similar to IL-1 receptors in immune and neuroendocrine tissues provides further support for a physiological role for IL-1 to regulate central nervous system activity.