Oxidized low-density lipoprotein induces matrix metalloproteinase-9 expression via a p42/p44 and JNK-dependent AP-1 pathway in brain astrocytes.
Upregulation of matrix metalloproteinases (MMPs), especially MMP-9, by oxidized low-density lipoprotein (oxLDL) is implicated in many inflammatory diseases including brain injury. However, the signaling mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes largely remain unknown. Here we report that oxLDL induces expression of proMMP-9 via a MAPK-dependent AP-1 activation in rat brain astrocyte (RBA)-1 cells. Results revealed by gelatin zymography, RT-PCR, and Western blotting analyses showed that oxLDL-induced proMMP-9 gene expression was mediated through Akt, JNK1/2, and p42/p44 MAPK phosphorylation in RBA-1 cells. These responses were attenuated by inhibitors of PI3K (LY294002), JNK (SP600125), and p42/p44 MAPK (PD98059), or transfection with dominant negative mutants and short hairpin RNA. Moreover, we demonstrated that AP-1 (i.e., c-Fos/c-Jun) is crucial for oxLDL-induced proMMP-9 expression which was attenuated by pretreatment with AP-1 inhibitor (curcumin). The regulation of MMP-9 gene transcription by AP-1 was confirmed by oxLDL-stimulated MMP-9 luciferase activity which was totally lost in cells transfected with the AP-1 binding site-mutated MMP-9 promoter construct (mt-AP1-MMP-9). These results suggested that oxLDL-induced proMMP-9 expression is mediated through PI3K/Akt, JNK1/2, and p42/p44 MAPK leading to AP-1 activation. Understanding the regulatory mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain injuries and diseases.
Wang
Hui-Hsin
HH
Department of Pharmacology, Chang Gung University, Tao-Yuan, Taiwan.
Hsieh
Hsi-Lung
HL
Wu
Cheng-Ying
CY
Sun
Chi-Chin
CC
Yang
Chuen-Mao
CM
D000818:Animals; D001253:Astrocytes / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D001921:Brain / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D004789:Enzyme Activation / Q000235:genetics; D004792:Enzyme Precursors / Q000096:biosynthesis* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D006801:Humans; D008077:Lipoproteins, LDL / Q000502:physiology*; D048670:MAP Kinase Kinase 4 / Q000502:physiology*; D020935:MAP Kinase Signaling System / Q000235:genetics; D020780:Matrix Metalloproteinase 9 / Q000096:biosynthesis* / Q000235:genetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology*; D010084:Oxidation-Reduction; D051381:Rats; D018808:Transcription Factor AP-1 / Q000378:metabolism*
D004792:Enzyme Precursors; D008077:Lipoproteins, LDL; D018808:Transcription Factor AP-1; C099252:oxidized low density lipoprotein; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048670:MAP Kinase Kinase 4; C120487:pro-matrix metalloproteinase 9; D020780:Matrix Metalloproteinase 9