Interleukin 1 type 1 receptor restore: A genetic mouse model for studying interleukin 1 receptor-mediated effects in specific cell types

Interleukin-1 (IL-1) mediates diverse neurophysiological and neuropathological effects in the CNS through type IIL-1 receptor (IL-1R1). However, identification of IL-1R1-expressing cell types and cell-type-specific functions of IL-1R1 remains challenging. In this study, we created a novel genetic mouse model in which IL-1R1 gene expression is disrupted by an intronic insertion of a loxP flanked disruptive sequence that can be deleted by Cre recombinase, resulting in restored IL-1R1 gene expression under its endogenous promoters. A second mutation was introduced at stop codon of the IL-1R1 gene to allow tracking of the restored IL-1R1 protein by a 3HA tag and IL-1R1 mRNA by tdTomato fluorescence. These animals were designated as IL-1R1^r/r and exhibited an IL-1R1 knock-out phenotype. We used IL-1R1 globally restored mice (IL-1R1 ^GR/GR) as an IL-1R1 reporter and observed concordant labeling of IL-1R1 mRNA and protein in brain endothelial cells. Two cell-type-specific IL-1R1 restore lines were generated: Tie2Cre-IL-1R1^r/r and LysMCre-IL-1R1^r/r. Brain endothelial COX-2 expression, CNS leukocyte infiltration, and global microglia activation induced by intracerebroventricular injection of IL-1 ¡5 were not observed in IL-1R1 r/rorLysMCre-IL-1R1^r/r mice, but were restored in Tie2Cre-IL-1R1^r/r mice. These results reveal IL-1R1 expression in endothelial cells alone is sufficient to mediate these central IL-1-induced responses. In addition, ex vivo IL-1β stimulation increased IL-1β expression in bone marrow cells in wild-type, Tie2Cre-IL-1R1^r/r, and LysMCre-IL-1R1^r/r, but not IL-1R1^r/r mice. These results demonstrate this IL-1R1 restore model is a valuable tool for studying cell-type-specific functions of IL-1R1.