Abstract
Vascular disease is one of the most significant threats to the lives of patients suffering from diabetes, and chronic exposure of vascular endothelial cells to high glucose has been shown to significantly contribute to the process of endothelial cell dysfunction, one of the earliest events in diabetes-associated vascular disease. Nucleotide oligomerization domain (NOD)-like receptor pyrin domain-containing 3 (NLRP3) inflammasome plays a key role in initiating the inflammatory process by facilitating the production of interleukin-1β (IL-1β) and IL-18. ASC and caspase 1 are also implicated in NLRP3 inflammasome-mediated chronic inflammation. While under normal conditions, a balance exists between oxidants and antioxidants, exposure to high glucose significantly increases the production of ROS, which is enhanced by NOX4 expression. In the present study, we explored the role of orexin A, an endogenous peptide produced in the hypothalamus, in high glucose-induced activation of the NLRP3 inflammasome, oxidative stress, and expression of several key cytokines. Our findings demonstrate that orexin A exerts potent antioxidant effects in human aortic endothelial cells exposed to high glucose by inhibiting mitochondrial ROS and expression of NOX4 at both the mRNA and protein levels as revealed by MitoSOX staining, real-time PCR, and Western blot analysis. We also show that orexin A inhibits high glucose-induced expression of TxNIP, which is crucial to the activation of the NLRP3 inflammasome, as well as that of HMGB1. We confirmed via real-time PCR and Western blot analysis that orexin A suppressed the production of the inflammatory cytokines IL-1β and IL-18. Additionally, through SIRT1 knockdown siRNA experimentation, we confirmed that SIRT1 knockdown abolishes the effects of orexin A described above, thereby indicating a critical role of SIRT in the capacity of orexin A to ameliorate high glucose-induced oxidative stress and activation of NLRP3 inflammasome.