Antimicrobial peptide rCRAMP induced glial cell activation through P2Y receptor signalling pathways

Antimicrobial peptides are part of the innate immune system of many organ systems, yet little is known about their expression and function in the brain. The antibacterial cathelicidin rCRAMP in rats (homologue of the human LL-37) not only exhibits potent bactericidal activities but also functions as a chemoattractant for immune cells. In this study, to further evaluate the role of rCRAMP in innate immunity of brain cells, we investigated the impact of rCRAMP on glial cell activation. To this end we analyzed the activation of rCRAMP-induced signalling by cytokine expression, Western blotting of certain signal transduction pathways and by cAMP level measurement in primary rat glial cells (astrocytes and microglia). We demonstrate (i) the induction of proinflammatory cytokine and neurotrophic factors and (ii) the activation of various signal transduction pathways by rCRAMP in glial cells. Moreover, (iii) we have been able to show that rCRAMP-induced IL-6 expression and ERK1/2 phosphorylation in glial cells were attenuated by the antagonists for purinergic receptor P2Y, whereas P2X and FPRL1 antagonists do not show any effects. Our results indicate for the first time that a newly identified P2Y11 receptor participates in rCRAMP-induced signal transduction. This study provides evidence that rCRAMP participates in brain immunity by stimulating cytokine production and glial cell activation, and aid in the protection of brain cells by inducing neurotrophic factors.