Insulin prevents pulmonary vascular leakage by inhibiting transglutaminase 2 in diabetic mice

Insulin is a central peptide hormone required for carbohydrate metabolism; however, its role in diabetes-associated pulmonary disease is unknown. Here, we investigated the preventative effect of insulin against hyperglycemia-induced pulmonary vascular leakage and its molecular mechanism of action in the lungs of diabetic mice. Vascular endothelial growth factor (VEGF) activated transglutaminase 2 (TGase2) by sequentially elevating intracellular Ca2+ and reactive oxygen species (ROS) levels in primary human pulmonary microvascular endothelial cells (HPMVECs). Insulin inhibited VEGF-induced TGase2 activation, but did not affect intracellular Ca2+ elevation and ROS generation. Insulin prevented VEGF-induced vascular leakage by inhibiting TGase2-mediated c-Src phosphorylation, disassembly of VE-cadherin and β-catenin, and stress fiber formation. Insulin replacement therapy prevented hyperglycemia-induced TGase2 activation, but not ROS generation, in the lungs of diabetic mice. Insulin also prevented vascular leakage and cancer metastasis in the diabetic lung. Notably, vascular leakage was not detectable in the lungs of TGase2-null (Tgm2−/−) diabetic mice. These findings demonstrate that insulin prevents hyperglycemia-induced pulmonary vascular leakage in diabetic mice by inhibiting VEGF-induced TGase2 activation rather than ROS generation.