Vaspin Inhibits Apoptosis of Endothelial Cells as a Ligand for Cell-Surface GRP78/VDAC Complex

Rationale: Visceral adipose tissue-derived serine proteinase inhibitor (vaspin) is an adipokine identified from visceral adipose tissues of genetically obese rats. Objective: The role of vaspin in the diabetic vascular complications remains elusive and we investigated the effects of vaspin on the vascular function under diabetic milieu. Methods and Results: Adenovirus carrying full-length of vaspin gene (Vaspin-Ad) ameliorated intimal proliferation of balloon injured carotid arteries in diabetic Wistar rats. The expression of Ccl2, Pdgfb and Pdgfrb genes were significantly reduced by the treatment of Vaspin-Ad. In cuff injured femoral arteries, the intimal proliferation was ameliorated in vaspin transgenic (Vaspin Tg) mice. The application of recombinant vaspin and Vaspin-Ad promoted the proliferation and inhibited the apoptosis of human aortic endothelial cells (HAEC). Adenovirus expressing vaspin with calmodulin and streptavidin-binding peptides was applied to HAEC, subjected to tandem tag purification and LC-MS/MS, and we identified GRP78 (78 kDa glucose-regulated protein) as an interacting molecule. The complex formation of vaspin, GRP78 and VDAC (voltage-dependent anion channel) on plasma membrane was confirmed by the immunoprecipitation studies using aortae of Vaspin Tg mice. The binding assay using 125 I-vaspin in HAEC revealed high affinity binding (Kd=0.565×10 -9 M) by the treatment of 5 υM thapsigargin, which recruited GRP78 from ER to plasma membrane by inducing ER stress. In HAEC, vaspin induced phosphorylation of Akt, inhibited the kringle 5-induced Ca 2+ influx, and subsequent apoptosis. Conclusions: Vaspin is a novel ligand for cell-surface GRP78/VDAC complex in endothelial cells, promotes the proliferation, inhibits the apoptosis, and protects the vascular injuries in diabetes.