C/EBPβ regulates multiple IL-1β-induced human astrocyte inflammatory genes

Background: CCAAT enhancer-binding protein (C/EBP)beta regulates gene expression in multiple organ systems and cell types, including astrocytes in the central nervous system (CNS). Inflammatory stimuli, interleukin (IL)-1 beta, tumor necrosis factor-alpha, human immunodeficiency virus (HIV)-1 and lipopolysaccharide induce astrocyte C/EBP beta expression. C/EBP beta is detectable in brains of Alzheimer's disease (AD), Parkinson's disease (PD) and HIV-1-associated dementia (HAD) patients, yet little is known about how C/EBP beta contributes to astrocyte gene regulation during neuroinflammation. Methods: The expression of 92 human inflammation genes was compared between IL-1 beta-treated primary human astrocytes and astrocytes transfected with C/EBP beta-specific small interfering (si)RNA prior to IL-1 beta treatment for 12 h. Transcripts altered by > two-fold compared to control were subjected to one-way analysis of variance and Newman-Keuls post-test for multiple comparisons. Expression of two genes, cyclooxygenase-2 (COX-2) and bradykinin receptor B2 (BDKRB2) was further confirmed in additional human astrocyte donors. Astrocytes were treated with mitogen-activated protein kinase-selective inhibitors, then with IL-1 beta for 12 or 24 h followed by COX-2 and BDKRB2, expression analyses. Results: IL-1 beta altered expression of 29 of 92 human inflammation genes by at least two-fold in primary human astrocytes in 12 h. C/EBP beta knockdown affected expression of 17 out of 29 IL-1 beta-regulated genes by > 25%. Two genes relevant to neuroinflammation, COX-2 and BDKRB2, were robustly decreased and increased, respectively, in response to C/EBP beta knockdown, and expression was confirmed in two additional donors. COX-2 and BDKRB2 mRNA remained altered in siRNA-transfected astrocytes at 12, 24 or 72 h. Inhibiting p38 kinase (p38K) activation blocked IL-1 beta-induced astrocyte COX-2 mRNA and protein expression, but not IL-1 beta-induced astrocyte BDKRB2 expression. Inhibiting extracellularregulated kinase (ERK)1/2 activation blocked IL-1 beta-induced BDKRB2 mRNA expression while increasing COX-2 expression. Conclusion: These data support an essential role for IL-1 beta in the CNS and identify new C/EBP beta functions in astrocytes. Additionally, this work suggests p38K and ERK1/2 pathways may regulate gene expression in a complementary manner to fine tune the IL-1 beta-mediated astrocyte inflammatory response. Delineating a role for C/EBP beta and other involved transcription factors in human astrocyte inflammatory response may lead to effective therapies for AD, PD, HAD and other neurological disorders.