Selective Neuronal and Brain Regional Expession of IL-2 in IL2P 8-GFP Transgenic Mice: Relation to Sensorimotor Gating

Abstract

Brain-derived interleukin-2 (IL-2) has been implicated in diseases processes that arise during CNS development (e.g., autism) to neurodegenerative alterations involving neuroinflammation (e.g., Alzheimer's disease). Progress has been limited, however, because the vast majority of current knowledge of IL-2's actions on brain function and behavior is based on the use exogenously administered IL-2 to make inferences about the function of the endogenous cytokine. Thus, to identify the cell-type(s) and regional circuitry that express brain-derived IL-2, we used B6.Cg-Tg/ IL2-EGFP17Evr (IL2p8-GFP) transgenic mice, which express green fluorescent protein (GFP) in peripheral immune cells known to produce IL-2. We found that the IL2-GFP transgene was localized almost exclusively to NeuN-positive cells, indicating that the IL-2 is produced primarily by neurons. The IL2-GFP transgene was expressed in discrete nuclei throughout the rostral-caudal extent of the brain and brainstem, with the highest levels found in the cingulate, dorsal endopiriform nucleus, lateral septum, nucleus of the solitary tract, magnocellular/gigantocellular reticular formation, red nucleus, entorhinal cortex, mammilary bodies, cerebellar fastigial nucleus, and posterior interposed nucleus. Having identified IL-2 gene expression in brain regions associated with the regulation of sensorimotor gating (e.g., lateral septum, dorsal endopiriform nucleus, entorhinal cortex, striatum), we compared prepulse inhibition (PPI) of the acoustic startle response in congenic mice bred in our lab that have selective loss of the IL-2 gene in the brain versus the peripheral immune system, to test the hypothesis that brain-derived IL-2 plays a role in modulating PPI. We found that congenic mice devoid of IL-2 gene expression in both the brain and the peripheral immune system, exhibited a modest alteration of PPI. These finding suggest that IL2p8-GFP transgenic mice may be a useful tool to elucidate further the role of brain-derived IL-2 in normal CNS function and disease.

Keywords: Congenic mice; Interleukin-2; Prepulse inhibition; Sensorimotor gating.

Figure 1

Photomicrographs of IHC stained GFP-positive cells in the septum (A and B; most GFP+ cells are in the lateral septum, with fewer in the medial septum), and the spleen (C) in IL2p8-GFP mice. Panel D illustrates that the reactivity of primary antibody was quenched in the spleen with 5 μg/ml free recombinant GFP protein prior to use in staining protocol.

Figure 2

Representative photomicrographs showing expression of GFP+ cells in the septum (top: most GFP+ cells in the lateral septum and some in the medial septum) and red nucleus (bottom). Arrows label cells positive for GFP (left), the pan-neuronal cell marker NeuN (center), the co-localization of both markers (right).

Figure 3

In the septum, most of the GFP-positive cells were found in the lateral septum, and some in the medial septum (left). GFP-positive cells were also found in fastigial nucleus and the interposed nucleus of the cerebellum (right). 10X magnification is shown here

Figure 4

Comparison of acoustic startle reactivity in WT (n=23), IL2-KO (n=25), WT/SCID (n=22) and IL2 KO/SCID mice (n=28). Data are expressed as the mean ± S.E.M. of each subject group. *p < .05: at 80 db WT is different from WT/SCID and IL2-KO/SCID; at 90 db WT and IL2-KO are different than WT/SCID and IL2-KO/SCID; at 100 db WT is different than WT/SCID; at 110 and 120 db WT/SCID are different than WT and IL2-KO/SCID.

Figure 5

Comparison of prepulse inhibition (PPI) in WT (n=23), IL2-KO (n=25), WT/SCID (n=22) and IL2-KO/SCID mice (n=28). Data are expressed as the mean ± S.E.M. of each subject group. *p < .05, IL2-KO/SCID is different from all other subject groups.