Calmodulin kinase II-dependent transactivation of PDGF receptors mediates astrocytic MMP-9 expression and cell motility induced by lipoteichoic acid

Background: Lipoteichoic acid (LTA) is a component of Gram-positive bacterial cell walls, which has been found to be elevated in cerebrospinal fluid of patients suffering from meningitis. Moreover, matrix metalloproteinases (MMPs), MMP-9 especially, have been observed in patients with brain inflammatory diseases and may contribute to brain disease pathology. However, the molecular mechanisms underlying LTA-induced MMP-9 expression in brain astrocytes remain unclear. Objective: The goal of this study was to examine whether LTA-induced cell migration is mediated by calcium/calmodulin (CaM)/CaM kinase II (CaMKII)-dependent transactivation of the PDGFR pathway in rat brain astrocytes (RBA-1 cells). Methods: Expression and activity of MMP-9 induced by LTA was evaluated by zymographic, western blotting, and RT-PCR analyses. MMP-9 regulatory signaling pathways were investigated by treatment with pharmacological inhibitors or using dominant negative mutants or short hairpin RNA (shRNA) transfection, and chromatin immunoprecipitation (ChIP)-PCR and promoter activity reporter assays. Finally, we determined the cell functional changes by cell migration assay. Results: The data show that c-Jun/AP-1 mediates LTA-induced MMP-9 expression in RBA-1 cells. Next, we demonstrated that LTA induces MMP-9 expression via a calcium/CaM/CaMKII-dependent transactivation of PDGFR pathway. Transactivation of PDGFR led to activation of PI3K/Akt and JNK1/2 and then activated c-Jun/AP-1 signaling. Activated-c-Jun bound to the AP-1-binding site of the MMP-9 promoter, and thereby turned on transcription of MMP-9. Eventually, up-regulation of MMP-9 by LTA enhanced cell migration of astrocytes. Conclusions: These results demonstrate that in RBA-1 cells, activation of c-Jun/AP-1 by a CaMKII-dependent PI3K/Akt-JNK activation mediated through transactivation of PDGFR is essential for up-regulation of MMP-9 and cell migration induced by LTA. Understanding the regulatory mechanisms underlying LTA-induced MMP-9 expression and functional changes in astrocytes may provide a new therapeutic strategy for Gram-positive bacterial infections in brain disorders.