Pollen Typhae Total Flavone Inhibits Endoplasmic Reticulum Stress-Induced Apoptosis in Human Aortic-Vascular Smooth Muscle Cells through Down-Regulating PERK-eIF2α-ATF4-CHOP Pathway.

OBJECTIVE

To test the hypothesis that the inhibition of endoplasmic reticulum (ER) stress-induced apoptosis in oxidized low-density lipoproteins (ox-LDL)-induced human aortic-vascular smooth muscle cells (HA-VSMCs) was associated with suppression of the protein kinase RNA-like ER kinase (PERK)-eukaryotic translation initiation factor 2α (eIF2α)-activating transcription factor 4 (ATF4)-CCAAT/enhancer binding protein homologous protein (CHOP) signaling pathway by Pollen Typhae total flavone (PTF).

METHODS

Primary HA-VSMCs were cultured and identified. The cultured HA-VSMCs were randomized into 5 groups, including a normal control group, an ox-LDL group (70 μg/mL high ox-LDL), an HPTF group (70 μg/mL high ox-LDL+500 μg/mL PTF), an MPTF group (70 μg/mL high ox-LDL+250 μg/mL PTF), and a LPTF group (70 μg/mL high ox-LDL+100 μg/mL PTF) in the first part; and a normal control group, an ox-LDL group (70 μg/mL high ox-LDL), an MPTF group (70 μg/mL high ox-LDL+250 μg/mL PTF), a shRNA group (transducted with PERK shRNA lentiviral particles), a scramble shRNA group (transducted with control shRNA lentiviral particles), an MPTF+ox-LDL+shRNA group (250 μg/mL PTF+70 μg/mL high ox-LDL+PERK shRNA lentiviral particles) and an ox-LDL+shRNA group (70 μg/mL high ox-LDL+PERK shRNA lentiviral particles) in the second part. The protein expression levels of ER-associated apoptosis proteins were detected by Western blot, and their mRNA expression levels were detected by quantitative real-time reverse transcription-polymerase chain reaction. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was applied to test cell viability, and the level of apoptosis was monitored by flow cytometry.

RESULTS

The MTT assay and flow cytometry showed that the ox-LDL group had a significant increase in apoptosis, which was attenuated in PTF treatment groups and shRNA groups. Moreover, the ox-LDL group had increased protein and mRNA levels of binding immunoglobulin protein and ER-associated apoptosis proteins, such as PERK, eIF2α, ATF4 and CHOP, which were attenuated in PTF treatment groups and shRNA groups.

CONCLUSIONS

The apoptosis induced by ox-LDL had a strong relation to ER stress. The protective effect of PTF on ER stressinduced apoptosis was associated with inhibition of the PERK-eIF2α-ATF4-CHOP pathway, which might be a potential therapeutic strategy for enhancing the stability of atherosclerotic plaques.