ABSTRACT
The purpose of this study was to investigate whether activating transcription factor 6 (ATF6), a sensor to endoplasmic reticulum stress (ERS), would mediate advanced glycated albumin (AGE-alb)-induced macrophage apoptosis and to elucidate the possible molecular mechanisms. RAW264.7 macrophages were cultured in vitro and treated with AGE-alb (2, 4 and 6 g/L), normal control albumin or tunicamycin (TM, 4 mg/L) for 24 h. ATF6 small interfering RNA (siRNA) was transfected to RAW264.7 cells by Lipofectamine 2000. Cell viability and apoptosis were determined by MTT method and Annexin V-FITC/propidium iodide apoptosis detection kit, respectively. The activities of lactate dehydrogenase (LDH) in medium and caspase-3 in cells were measured by corresponding detection kits. ATF6 nuclear translocation was detected by Western blot and immunofluorescence cytochemistry. Protein and mRNA levels of C/EBP homologous protein (CHOP, a key-signaling component of ERS-induced apoptosis) were detected by Western blot and real-time fluorescence quantitative PCR, respectively. The results showed that similar to TM, AGE-alb increased the expression of CHOP at both the protein and mRNA levels in a concentration dependent manner. ATF6, as a factor that positively regulates CHOP expression, was activated by AGE-alb in a concentration dependent manner. siRNA-mediated knockdown of ATF6 significantly inhibited AGE-alb-induced macrophage injury, as indicated by the increased cell viability and the decreased LDH release, apoptosis and caspase-3 activation. Additionally, ATF6 siRNA attenuated AGE-alb-induced CHOP upregulation at both the protein and mRNA levels. These results suggest that ATF6 and its downstream molecule CHOP are involved in AGE-alb-induced macrophage apoptosis.
ABSTRACT
AIM:To investigate the inhibitory effect of allicin on apoptosis and caspase-12 activation of macro-phage-derived foam cells,and to elucidate the underlying molecular mechanisms. METHODS:RAW264.7 macrophages were pretreated with allicin (12.5,25 and 50 mg/L) or 4-phenylbutyric acid(PBA,4 mmol/L) for 1 h and then treated with oxidized low-density lipoprotein(ox-LDL,100 mg/L) or tunicamycin(TM,4 mg/L) for 24 h. The cell viability and apoptosis were examined by MTT assay and flow cytometry with Annexin V-FITC/PI staining,respectively. The activities of caspase-3 in the cells and lactic dehydrogenase (LDH) in the medium were measured. The protein levels of caspase-12 were determined by Western blot. The intracellular lipid accumulation was measured with oil red O staining and the content of intracellular total cholesterol was determined by enzymatic colorimetry. RESULTS:Similar to the endoplasmic reticulum stress (ERS) inhibitor PBA, allicin inhibited ox-LDL-induced injury of RAW264.7 macrophages in a concentration-de-pendent manner,as determined by the increased cell viability and the decreased LDH leakage,apoptosis and caspase-3 ac-tivity. The decrease in cell viability and increases in LDH leakage and apoptosis induced by TM (an ERS inducer) were also suppressed by allicin. Moreover, similar to PBA, allicin remarkably inhibited ox-LDL- or TM-induced activation of caspase-12. Furthermore, allicin remarkably attenuated ox-LDL-induced lipid accumulation in the RAW264.7 cells and foam cells formation in a concentration-dependent manner. CONCLUSION:Allicin may inhibit macrophage-derived foam cell apoptosis induced by ox-LDL,and the mechanism is partially related to suppressing the activation of caspase-12.