C-Peptide Prevents Hyperglycemia-Induced Endothelial Apoptosis Through Inhibition of Reactive Oxygen Species–Mediated Transglutaminase 2 Activation

Abstract

C-peptide is a bioactive peptide with a potentially protective role in diabetes complications; however, its molecular mechanism of protection against cardiovascular damage caused by hyperglycemia-induced apoptosis remains unclear. We investigated the protective mechanism of C-peptide against hyperglycemia-induced apoptosis using human umbilical vein endothelial cells and streptozotocin diabetic mice. High glucose (33 mmol/L) induced apoptotic cell death in endothelial cells via sequential elevation of intracellular Ca2+ and reactive oxygen species (ROS) as well as subsequent activation of transglutaminase 2 (TG2). C-peptide (1 nmol/L) prevented endothelial cell death by inhibiting protein kinase C– and NADPH oxidase–dependent intracellular ROS generation and by abolishing high glucose–induced TG2 activation, without affecting intracellular Ca2+ levels. Consistently, in the aorta of streptozotocin diabetic mice, hyperglycemia stimulated transamidating activity and endothelial cell apoptosis that was inhibited by C-peptide replacement therapy (35 pmol/min/kg) using osmotic pumps (control and diabetes, n = 8; diabetes + C-peptide, n = 7). In addition, C-peptide prevented hyperglycemia-induced activation of transamidation activity and apoptosis in the heart and renal cortex of streptozotocin diabetic mice. Thus, C-peptide protects endothelial cells from hyperglycemia-induced apoptotic cell death by inhibiting intracellular ROS-mediated activation of TG2. Furthermore, TG2 may be a promising avenue of therapeutic investigation to treat diabetic vasculopathies.

Essential Role of Transglutaminase 2 in Vascular Endothelial Growth Factor–Induced Vascular Leakage in the Retina of Diabetic Mice

“…In this study we elucidated the essential role of TGase2 in VEGFinduced vascular leakage in the retinas of diabetic mice. Additionally, we recently reported that TGase2 is involved in diabetic vasculopathy resulting from apoptosis in endothelial cells and in the aorta, heart, and kidneys of diabetic mice (28). Another study using streptozotocin-induced diabetic rats demonstrated that TGase inhibition ameliorates the progression of diabetic nephropathy (33), suggesting the possible role of TGase2 in this disease.…”

“…Transfection With Human TGase2-Specific siRNA HRECs were transfected with human TGase2-specific siRNA as described previously (28). Briefly, cells were transfected with various concentrations of human TGase2-siRNA or 100 nmol/L control siRNA (Dharmacon, Inc., Lafayette, CO) using siLentFect lipid reagent (Bio-Rad Laboratories, Hercules, CA) according to the manufacturer's instructions.…”

Glycemic Control in Simultaneous Islet-Kidney Versus Pancreas-Kidney Transplantation in Type 1 Diabetes: A Prospective 13-Year Follow-up

“…C-peptide levels remained stable during the first years after islet transplantation, with some decline after year 6. Sustained positive C-peptide response itself may be of importance regarding diabetesassociated complications, given the increasing evidence of the positive effects of C-peptide regarding vascular, renal, and nerve dysfunction (21)(22)(23).…”

Substance P Promotes Diabetic Corneal Epithelial Wound Healing Through Molecular Mechanisms Mediated via the Neurokinin-1 Receptor

“…However, hyperglycemia also directly impairs the cellular metabolism and causes abnormal changes of corneal epithelium, such as Akt-, epidermal growth factor receptor (EGFR)-, and Sirt1-mediated cell responses to environmental challenges (5)(6)(7). Moreover, excess oxidative stress, resulting from enhanced accumulation of reactive oxygen species (ROS) and impaired antioxidant capabilities in response to hyperglycemia, has been postulated as an important pathological mechanism, whereas the reduction of ROS attenuated the progression of various diabetes complications (8)(9)(10)(11)(12)(13), including in the cornea (5,14).…”