Effects of pro-inflammatory cytokines on in vitro measures of gene expression, protein expression, and process extension in primary hippocampal neurons

Abstract

A bi-directional relationship exists between the immune system and the central nervous system. A number of in vivo studies have reported that immune stimulation through administration of endotoxin or pro-inflammatory cytokines can lead to cognitive deficits in a variety of paradigms. However, despite a large body of work characterizing the behavioral effects of immune stimulation, the cellular mechanisms that underlie this global cognitive impairment remain unclear. The present study utilized primary hippocampal cell culture to examine the effect of pro-inflammatory cytokines on process extension and expression of relevant proteins. Specifically, we hypothesized that administration of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), or tumor necrosis factor-alpha (TNF-alpha) would lead to morphological alterations (as evidenced by decreased process length, process number, and density of processes), and decreased protein and gene expression of GAP-43 and synapsin-I, two proteins important in synapse formation and process extension. Furthermore, in addition to replicating the prior findings of Neumann et al (2002) with regard to TNF-alpha, our goal was to extend this line of investigation to IL-1beta and IL-6. The observed results were generally inconsistent to our original hypotheses. Rather than decreasing expression, exposure to TNF-alpha led to significantly increased expression of synapsin-I mRNA, and exposure to IL-1beta, IL-6, and TNF-alpha led to significant increases in expression of synapsin-I protein. However, pro-inflammatory cytokine treatment did not significantly impact gene or protein expression of GAP-43. Further, these changes in synapsin-I, though correlated, did not significantly impact cellular morphology, in terms of process number, length, and density. The present study is the first to investigate the effects of IL-1beta or IL-6 on primary hippocampal neurons.