Advanced glycation endproducts alter functions and promote apoptosis in endothelial progenitor cells through receptor for advanced glycation endproducts mediate overpression of cell oxidant stress

Abstract

Endothelial progenitor cells (EPCs) play an important role in preventing atherosclerosis. The factors that regulate the function of EPCs are not completely clear. Increased formation of advanced glycation endproducts (AGEs) is generally regarded as one of the main mechanisms responsible for vascular damage in patients with diabetes and atherosclerosis. AGEs lead to the generation of reactive oxygen species (ROS) and part of the regenerative capacity of EPCs seems to be due to their low baseline ROS levels and reduced sensitivity to ROS-induced cell apoptosis. Therefore, we tested the hypothesis that AGEs can alter functions and promote apoptosis in EPCs through overpress cell oxidant stress. EPCs, isolated from bone marrow, were cultured in the absence or presence of AGEs (50, 100, and 200 microg/ml). A modified Boyden's chamber was used to assess the migration of EPCs and the number of recultured EPCs was counted to measure the adhesiveness function. MTT assay was used to determine the proliferation function. ROS were analyzed using the ROS assay kit. A spectrophotometer was used to assess superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) activity, and PCR was used to test mRNA expression of SOD and GSH-PX. SiRNA was used to block receptor for advanced glycation endproducts (RAGEs) expression. Apoptosis was evaluated by Annexin V immunostaining and TUNEL staining. Co-culturing with AGEs increases ROS production, decreases anti-oxidant defenses, overpresses oxidant stress, inhibits the proliferation, migration, and adhesion of EPCs, and induces EPCs apoptosis. In addition, these effects were attenuated during block RAGE protein expression by siRNA. AGEs may serve to impair EPCs functions through RAGE-mediate oxidant stress, and promote EPCs sensitivity toward oxidative-stress-mediated apoptosis, which indicates a new pathophysiological mechanism of disturbed vascular adaptation in atherosclerosis and suggests that lower levels of AGEs might improve the success of progenitor cell therapy.

Progenitor Cell Dysfunctions Underlie Some Diabetic Complications

“…Predominantly, changes in ROS and hypoxia from neighboring cells in the presence of excessive glucose alter juxtacrine and paracrine signaling to the stem cells. 77,78 Moreover, diabetes causes an influx of inflammatory cells and stimulates adipocyte production, altering the stem cell microenvironment. 79 These molecular changes are addressed in this section.…”

Critical Role of the Nitric Oxide/Reactive Oxygen Species Balance in Endothelial Progenitor Dysfunction

“…In line, Wu et al identified HO-1 as a potent stimulus for increasing circulating EPC numbers; however the underlining mechanisms remain unclear (129). An increase in advanced glycylation endproducts (AGEs) or oxidized LDLs can impair endothelial and EPC function by increasing ROS levels (15,101,102). However, this effect could be blocked by siRNA against the receptor for advanced glycation endproducts (RAGE) or blockade of the oxLDL receptor LOX-1 (94,101).…”

“…However, this effect could be blocked by siRNA against the receptor for advanced glycation endproducts (RAGE) or blockade of the oxLDL receptor LOX-1 (94,101). RAGE is also regulated by C-reactive protein (CRP), which is considered as a proatherosclerotic protein, resulting in impaired EPC function (15). Accordingly, AGE treatment leads to a downregulation of eNOS and Bcl-2 expression, as well as an elevation in cyclooxygenase-2, Bax, NF-kappaB, and caspase-3 in a MAPK (ERK=P38=JNK)-dependant manner (83).…”

Anti-apoptotic effect of hyperglycemia can allow survival of potentially autoreactive T cells

“…Glucose also upregulates the expression of the receptor for advanced glycation end products (RAGE) and the RAGE pathway is known to promote apoptosis. 29,30 Like glucose transporters, RAGE expression was comparable in control and NF-kB p65 knockout thymocytes (Supplementary Figure 4). Thus, it appears that it is a lack of survival factors in the knockout cells that lead to their apoptosis and not a lack of glucose transporters or RAGE.…”