Regulation of Interleukin -6 Gene Expression in the Brain of Aged Mice

Abstract

The occurrence of certain neurodegenerative diseases increases with age. Because over expression of inflammatory cytokines in the brain may establish a state that is permissive to the onset of neurodegenerative diseases, in the present thesis study the effect of aging on the expression of inflammatory cytokine, interleukin-6 (IL-6), was determined. Competitive RT-PCR and ELISA assay showed that IL-6 mRNA and protein concentration were higher in aged brain compared to adult and neonate brain. To begin identifying the cell type responsible for increased IL-6 in the CNS, glial cells were cultured from brains of neonate, adult, and aged mice. Flow cytometric analysis revealed that increased IL-6 production in glia from aged mice is a result of an increase in reactive microglia, which spontaneously secret copious amount of IL-6. To determine the molecular basis responsible for increased IL-6 gene expression in the aged brain, the binding of transcription factors to the major response elements on the IL-6 promoter was evaluated in brains of 1-, 3-, and 24-month old mice by gel mobility shift assay. Whereas NFkappaB activity was increased in aged brain, NF-IL-6, MRE and AP-1 were either unaffected by aging or decreased. Inhibition of increased NFkappaB activity both in vivo and in vitro decrease IL-6 mRNA expression and protein level. These results suggest that increased NFkappaB activity in aged brain contributes to the elevated levels of IL-6. An anti-inflammatory cytokine IL-10 inhibits NFkappaB activity and expression of IL-6. The coronal brain sections and glia from aged mice secreted more IL-6 and less IL-10 than brain sections and glia from adults. Recombinant murine IL-10 decreased NFkappaB DNA binding activity, and therefore, reduced both constitutive and inducible IL-6 mRNA and protein levels in glia from aged mice. However, in glia from adult mice, supplemental IL-10 only decreased inducible, but not constitutive NFkappaB activity, IL-6 mRNA, and IL-6 protein. These data suggest that IL-10 constrains IL-6 gene expression in the adult brain, but in the aged brain it decreases and thus enables a cascade of intracellular events that increase the expression of the IL-6 gene.