Increase in acid sphingomyelinase level in human retinal endothelial cells and CD34+ circulating angiogenic cells isolated from diabetic individuals is associated with dysfunctional retinal vasculature and vascular repair process in diabetes

Background Diabetic retinopathy is a microvascular disease that results from retinal vascular degeneration and defective repair due to diabetes-induced endothelial progenitor dysfunction. Objective Understanding key molecular factors involved in vascular degeneration and repair is paramount for developing effective diabetic retinopathy treatment strategies. We propose that diabetes-induced activation of acid sphingomyelinase (ASM) plays essential role in retinal endothelial and CD34 + circulating angiogenic cell (CAC) dysfunction in diabetes. Methods Human retinal endothelial cells (HRECs) isolated from control and diabetic donor tissue and human CD34 + CACs from control and diabetic patients were used in this study. ASM messenger RNA and protein expression were assessed by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. To evaluate the effect of diabetes-induced ASM on HRECs and CD34 + CACs function, tube formation, CAC incorporation into endothelial tubes, and diurnal release of CD34 + CACs in diabetic individuals were determined. Results ASM expression level was significantly increased in HRECs isolated from diabetic compared with control donor tissue, as well as CD34 + CACs and plasma of diabetic patients. A significant decrease in tube area was observed in HRECs from diabetic donors compared with control HRECs. The tube formation deficiency was associated with increased expression of ASM in diabetic HRECs. Moreover, diabetic CD34 + CACs with high ASM showed defective incorporation into endothelial tubes. Diurnal release of CD34 + CACs was disrupted with the rhythmicity lost in diabetic patients. Conclusion Collectively, these findings support that diabetes-induced ASM upregulation has a marked detrimental effect on both retinal endothelial cells and CACs.