Glucocorticoid Induced Leucine Zipper in Lipopolysaccharide Induced Neuroinflammation

Abstract

Glucocorticoids (GCs) are steroid hormones secreted as the end-product of the neuroendocrine stress cascade. Both absence and elevated GC mediate neurotoxic responses, suggesting that a narrow window ranging from physiological to slightly high GC mediate protective responses. The beneficial effects of GC are attributed to the transactivation of regulatory proteins and inhibition mediated by glucocorticoid receptor (GR) interactions with other co-factors. The glucocorticoid induced leucine zipper (GILZ) is a gene strongly upregulated by GC and mediates many of the anti-inflammatory and anti-proliferative effects of GC. Although GILZ is constitutively expressed in many tissues including the brain, the expression has been shown to occur with varying dynamics suggesting that the local milieu modulates its expression with consequent effects on cellular responses. Here we investigated the expression profile of GILZ in lipopolysaccharide (LPS) mediated neuroinflammation model of Alzheimer's disease (AD). Our data suggest that the GILZ expression is downregulated in neuroinflammation correlating inversely with the pro-inflammatory cytokines and innate immune responses.

Keywords: Alzheimer’s disease; cytokines; glucocorticoid induced leucine zipper; neuroinflammation; toll like receptor-4.

Figure 1

Immunohistochemistry of hippocampus of mouse induced neuroinflammation. Shows representative IHC section stained for Iba+ microglia (A,B), glial fibrillary acidic protein (GFAP)+ astrocytes (C,D), nuclear factor-kappa B (NF-κB) p65+ (E,F) and GLIZ+ cells (G,H) in the hippocampus of mouse subjected to lipopolysaccharide (LPS) induced neuroinflammation and vehicle treated mouse as indicated. Panel (I) shows the mean staining area of the 3,3′-diaminobenzidine (DAB)-positive cells depicting microglia, astrocytes, NF-κB p65 or GILZ+ cells in groups of mice induced neuroinflammation or vehicle treated mice (DG, dentate gyrus; CA 1, Cornu Ammonis 1; and CA 3, Cornu Ammonis 3; representing specific regions of the hippocampus). *p < 0.05 as compared with vehicle treated mice.

Figure 2

Effect of LPS induced neuroinflammation in the expression profiles of inflammatory markers and GILZ: groups of adult C57BL/6 mice were subjected to LPS induced neuroinflammation as described in the “Materials and Methods” section. Equal quantity of cDNA isolated from brain tissues were amplified for IL-1β, CD14, toll like receptor-4 (TLR-4), IL-12, CD4 and β-actin mRNA by quantitative real time polymerase chain reaction (PCR). (A) Gel electrophoresis of the PCR products β-actin IL-1β, CD14, TLR-4, GILZ, IL-12 and CD4. Panel (B) shows indicated inflammatory cytokines in the circulation as determined by enzyme linked immunosorbent assay (ELISA). (C–H) Relative mRNA quantitation of the indicated product with respect to that of housekeeping gene β-actin is shown. Data are average ± SD. * and ^@p < 0.05 with respect to the vehicle treated group or naïve group respectively. Panel (I,J) shows data from regression analysis for GILZ and TLR4 transcripts in mice administered saline (I) or LPS (J).