Tetramethylpyrazine attenuates chronic intermittent hypoxia-exacerbated diabetic atherosclerosis: a mechanistic study of the IRE1α-XBP1 signaling pathway

Objective: A complex relationship exists between obstructive sleep apnea syndrome and diabetes mellitus (DM). Chronic intermittent hypoxia (CIH), which is a core pathological feature of obstructive sleep apnea syndrome, may play an important role in the onset and development of DM-related atherosclerosis (DM-AS). This study aimed to investigate the mechanism of action of tetramethylpyrazine (TMP) in CIH-associated DM-AS. Methods: In vivo , a DM-AS mouse model was established by intraperitoneal injection of streptozotocin combined with a high-fat diet. They were exposed to CIH or normoxic conditions for 8 weeks and received different doses of TMP, rosuvastatin, toyocamycin, and purified water. Glycolipid metabolism, inflammation levels, degree of aortic AS, and expression levels of endoplasmic reticulum stress (ERS) and autophagy proteins were examined in mice. In vitro , human umbilical vein endothelial cells (HUVECs) were treated with high glucose and fat in combination with insulin to establish an insulin-resistant cell model (HUVEC-IR). After pretreatment with 4μ8C (IRE1 inhibitor) and different doses of TMP, intermittent hypoxic intervention was performed. Changes in cell morphology, proliferative activity, glucose consumption, and ability to migrate were observed, and the expression levels of ERS and autophagy proteins were detected. Results: In vivo experiments showed that CIH significantly increased blood glucose levels and Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) ( P < 0.001 or P < 0.05), low-density lipoprotein cholesterol (LDL-C) content ( P < 0.001), and the levels of three inflammatory factors interleukin-1 beta (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α) in the mice ( P < 0.001) compared with those of the mice with DM alone; moreover, the aortic atherosclerotic (AS) plaque area in CIH mice was significantly enlarged ( P < 0.001). Western blotting results showed that the expressions of aortic IRE1α, XBP1s, Beclin1, and LC3A proteins were significantly increased in CIH mice compared with DM mice ( P < 0.05). After treatment with different doses of TMP, rosuvastatin calcium, and toyocamycin, serum inflammation and lipid levels and plaque area were significantly reduced in mice ( P < 0.001 and P < 0.001, respectively). The expression levels of aortic XBP1s, Beclin1, and LC3A were reduced in TMP- and toyocamycin-treated mice ( P < 0.05). In the in vitro experiments, compared with normoxic cells, the cells treated with intermittent hypoxia (IH) showed a significant decrease in cell migration distance ( P < 0.05), a significant increase in apoptosis rate ( P < 0.001), a substantial increase in proliferation inhibition rate ( P < 0.001), a significant increase in the levels of XBP1s and LC3A proteins ( P < 0.05), and an increase in the number of autophagic vesicles/lysosomes, as observed under transmission electron microscopy. After treatment with different doses of TMP and 4μ8C, cell morphology was significantly restored, apoptosis rate significantly reduced ( P < 0.001), and XBP1s, Beclin1, and LC3A expressions significantly inhibited ( P < 0.05). Conclusion: CIH promoted the onset of DM-AS, whereas TMP attenuated ERS and excessive autophagy by modulating the IRE1α-XBP1 signaling pathway and inhibiting XBP1 splicing, thereby ameliorating DM-AS exacerbated by CIH.