β₂-adrenergic agonists modulate TNF-α induced astrocytic inflammatory gene expression and brain inflammatory cell populations.
BACKGROUND
The NF-κB signaling pathway orchestrates many of the intricate aspects of neuroinflammation. Astrocytic β₂-adrenergic receptors have emerged as potential regulators in central nervous system inflammation and are potential targets for pharmacological modulation. The aim of this study was to elucidate the crosstalk between astrocytic β₂-adrenergic receptors and the TNF-α induced inflammatory gene program.


METHODS
Proinflammatory conditions were generated by the administration of TNF-α. Genes that are susceptible to astrocytic crosstalk between β₂-adrenergic receptors (stimulated by clenbuterol) and TNF-α were identified by qPCR-macroarray-based gene expression analysis in a human 1321 N1 astrocytoma cell line. Transcriptional patterns of the identified genes in vitro were validated by RT-PCR on the 1321 N1 cell line as well as on primary rat astrocytes. In vivo expression patterns were examined by intracerebroventricular administration of clenbuterol and/or TNF-α in rats. To examine the impact on the inflammatory cell content of the brain we performed extensive FACS analysis of rat brain immune cells after intracerebroventricular clenbuterol and/or TNF-α administration.


RESULTS
Parallel transcriptional patterns in vivo and in vitro confirmed the relevance of astrocytic β₂-adrenergic receptors as modulators of brain inflammatory responses. Importantly, we observed pronounced effects of β2-adrenergic receptor agonists and TNF-α on IL-6, CXCL2, CXCL3, VCAM1, and ICAM1 expression, suggesting a role in inflammatory brain cell homeostasis. Extensive FACS-analysis of inflammatory cell content in the brain demonstrated that clenbuterol/TNF-α co-administration skewed the T cell population towards a double negative phenotype and induced a shift in the myeloid brain cell population towards a neutrophilic predominance.


CONCLUSIONS
Our results show that astrocytic β₂-adrenergic receptors are potent regulators of astrocytic TNF-α-activated genes in vitro and in vivo, and ultimately modulate the molecular network involved in the homeostasis of inflammatory cells in the central nervous system. Astrocytic β₂-adrenergic receptors and their downstream signaling pathway may serve as potential targets to modulate neuroinflammatory responses.
Department of Neurology, University Hospital Brussels, Center for Neurosciences, Vrije Universiteit Brussel, Laarbeeklaan 101, 1090 Brussels, Belgium. laureysg@hotmail.com.
Guy
G
Laureys
Sarah
S
Gerlo
Anneleen
A
Spooren
Frauke
F
Demol
Jacques
J
De Keyser
Joeri L
JL
Aerts
D058666:Adrenergic beta-2 Receptor Agonists / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects*; D001254:Astrocytoma / Q000473:pathology; D001921:Brain / Q000166:cytology*; D002478:Cells, Cultured; D002976:Clenbuterol / Q000494:pharmacology*; D003546:Cysteine Endopeptidases; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D004660:Encephalitis / Q000473:pathology*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism
D058666:Adrenergic beta-2 Receptor Agonists; D016207:Cytokines; D004268:DNA-Binding Proteins; C090509:Icam1 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1; D018799:Intercellular Adhesion Molecule-1; D044767:Ubiquitin-Protein Ligases; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D003546:Cysteine Endopeptidases; C513261:Tnfaip3 protein, mouse; D002976:Clenbuterol