Stimulation of interleukin-6 secretion and gene transcription in primary astrocytes by adenosine

During cerebral ischemia, the expression of interleukin-6 (IL-6), which has neuroprotective properties increases. To understand the underlying mechanism, the regulation of IL-6 expression by neurotransmitters that accumulate during cerebral ischemia was investigated Adenosine stimulated IL- 6 secretion in primary astrocytes four- to 10-fold. The effect was concentration dependent, the EC₅₀ being ≃8 μM. Although the nonselective analogue 2-chloroadenosine (2CA) increased IL-6 secretion to a similar extent, the A₁-selective agonist N⁶-cyclopentyladenosine or the A(2a) agonist CGS-21680 had only a marginal effect on IL-6 secretion. IL-6 secretion stimulated bY 2CA (10 μM) was inhibited by the nonselective adenosine antagonist 8-(p-sulfophenyl) theophylline, whereas the A₁- selective antagonist 8-cyclopentyl-1,3-dipropylxanthine or the A(2a)- selective antagonist 8-(3-chlorostyryl) caffeine had no effect, to a concentration of 0.1 μM. Transcription of the IL-6 gene was investigated by transfecting primary astrocytes with a reporter fusion gene containing the human IL-6 promoter (-179/+12). 2CA stimulated IL-6 gene transcription 2.5- fold. Mutations of the binding site for NF-κB or NF-IL6 abrogated the response to 2CA. Thus, an increase of extracellular adenosine during focal cerebral ischemia may stimulate IL-6 expression via A(2b) receptors. The induction of IL-6 expression appears to involve a transcriptional effect that depends on NF-κB and NF-IL6.