Methylglyoxal induces advanced glycation end product (AGEs) formation and dysfunction of PDGF receptor‐β: implications for diabetic atherosclerosis

PURPOSE

Low molecular weight carbonyl compounds, such as the alpha-ketoaldehydes methylglyoxal (MGO) and glyoxal (GO), are formed under hyperglycemic conditions and behave as advanced glycation end product (AGE) precursors. They form adducts on proteins, thereby inducing cellular dysfunctions involved in chronic complications of diabetes.

METHODS AND MAIN FINDINGS

Nontoxic concentrations of GO or MGO altered the PDGF-induced PDGFRbeta-phosphorylation, ERK1/2-activation, and nuclear translocation, and the subsequent proliferation of mesenchymal cells (smooth muscle cells and skin fibroblasts). This resulted mainly from inhibition of the intrinsic tyrosine kinase of PDGFRbeta and in part from altered PDGF-BB binding to PDGFRbeta. Concomitantly, the formation of AGE adducts (N(epsilon)carboxymethyl-lysine and N(epsilon)carboxyethyl-lysine) was observed on immunoprecipitated PDGFRbeta. Arginine and aminoguanidine, used as carbonyl scavengers, reversed the inhibitory effect and the formation of AGE adducts on PDGFRbeta. AGE-PDGFRbeta adducts were also detected by anti-AGE antibodies in PDGFRbeta immunopurified from aortas of diabetic (streptozotocin-treated) compared to nondiabetic apolipoprotein E-null mice. Mass spectrometry analysis of aortas demonstrated increased AGE formation in diabetic specimens.

CONCLUSIONS

These data indicate that MGO and GO induce desensitization of PDGFRbeta that helps to reduce mesenchymal cell proliferation.

Chlamydia pneumoniae alters mildly oxidized low-density lipoprotein-induced cell death in human endothelial cells, leading to necrosis rather than apoptosis

BACKGROUND

Atherosclerosis is characterized by oxidative stress that induces lipid and protein oxidation in the vascular wall. Oxidized low-density lipoproteins (oxLDLs) are present in lesions, and one of their actions is to induce apoptosis or necrosis in vascular cells. A role for Chlamydia pneumoniae in atherosclerosis has been proposed, but the mechanisms involved remain largely unknown.

METHODS

The in vitro effect of C. pneumoniae infection on apoptosis induced by mildly oxidized LDLs (moxLDLs) in human endothelial cells was studied.

RESULTS

Infection inhibited apoptosis, as was demonstrated by a decrease in such apoptotic features as cytochrome c release, caspase activity, 89-kilodalton poly(ADP-ribose) polymerase (PARP) fragment formation, nuclear condensation and fragmentation, and DNA fragmentation. However, the inhibition of apoptosis did not favor cell survival, because infection promoted cell death with necrotic features, as was illustrated by an increase in lactate dehydrogenase release, an enhancement of necrotic cellular morphological characteristics, and generation of low-molecular-mass PARP fragments. The increase in occurrence of necrosis-like cell death was correlated with a strong increase in intracellular reactive oxygen species (ROS) concentration. Vitamin E inhibited ROS production and promoted cell survival, underscoring the involvement of ROS in cell death induced by the combination of C. pneumoniae and moxLDLs.

CONCLUSION

C. pneumoniae infection enhances the inflammatory action of oxLDLs in the vascular wall, leading to cell necrosis rather than apoptosis.

Proliferation and wound healing of vascular cells trigger the generation of extracellular reactive oxygen species and LDL oxidation

Cell proliferation of vascular cells is a key feature in vascular biology, wound healing, and pathophysiological processes such as atherosclerosis and restenosis. In atherosclerotic intima, cell proliferation colocalizes with oxidized LDL that indicate a local oxidative stress. This study aims to investigate whether cell proliferation is causally related with extracellular ROS generation and subsequent LDL oxidation. Sparse proliferating endothelial and smooth muscle cells generate higher levels of extracellular ROS (O2*- and H2O2) and LDL oxidation than confluent contact-inhibited cells. During wound healing of confluent cell layer, cell proliferation associated with healing also induced enhanced extracellular ROS generation and LDL oxidation. Proliferation-associated extracellular ROS generation is mediated through mitogenic signaling pathways, involving ERK1/2 and PKC, but is independent of de novo DNA synthesis, gene expression and protein synthesis. Data obtained with inhibitors of oxidases suggest that proliferation-associated extracellular ROS are not generated by a single ROS-generating system and are not essential for cell proliferation. In conclusion, our data show that proliferating vascular cells (in sparse culture or during wound healing) generate high levels of extracellular ROS and LDL oxidation through regulation of ROS-generating systems by mitogenic signaling. This constitutes a link between proliferative events and oxidative stress/LDL oxidation in atherosclerotic lesions and restenosis.