Fractalkine is a unique member of the CX3C chemokine family by unfolding its potential through the chemokine (C-X3-C motif) receptor 1 (CX3CR1) with dual function acting both as an adhesion molecule and a soluble chemokine. The regulation of this chemokine is still not clear. Therefore, we were interested in the regulation of fractalkine and of CX3CR1 in experimental sepsis. In addition, we investigated the role of NF-κB for the regulation of fractalkine and of CX3CR1.
Using a mouse model of cecal ligation and puncture (CLP)-induced sepsis, we found elevated fractalkine mRNA levels in the heart, lung, kidney, and liver, as well as increased plasma levels 24 and 48 h after CLP, respectively. In parallel, CLP resulted in a significant downregulation of CX3CR1 mRNA receptor expression in all investigated murine tissues. Septic mice that were pretreated with the selective NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) were found to have a decreased liberation of proinflammtory cytokines such as TNF-α, IL-1β, IL-6, or IFN-γ. Further PDTC pretreatment attenuated CLP-induced downregulation of CX3CR1 mRNA as well as CLP-induced upregulation of fractalkine mRNA expression in the heart, lung, kidney, liver, and the increase in fractalkine plasma levels of septic mice. In addition, CLP-induced downregulation of renal CX3CR1 protein expression was inhibited by PDTC-pretreatment.
Taken together, our data indicate a CLP-induced inverse regulation of the expression between the relating ligand and the receptor with an upregulation of fractalkine and downregulation of CX3CR1, which seems to be mediated by the transcripting factor NF-κB likely via reduced liberation of proinflammtory cytokines in the whole murine organism.