The protein quality control system and Vms1 are involved in the cellular response to increased mitochondrial protein damage caused by advanced glycation endproducts

Question:

Advanced glycation endproducts (AGEs) result from the reaction of carbonyls with proteins, lipids and DNA. AGEs are known to be increased in patients with diabetes and seem to play a pivotal role in the development of late complications. Methylglyoxal (MG) is a highly reactive dicarbonyl that is formed non-enzymatically during glycolysis. It preferably binds to arginine residues, leading to the accumulation of hydroimidazolone (MG-H1). The cellular effects of MG-H1 are poorly understood. We questioned (i) which molecular pathways handle increased MG-H1 formation and (ii) where accumulates MG-H1 intracellularly.

Methods:

High throughput techniques in yeast were used to identify genes that are involved in MG-stress. These genes were further validated in mouse endothelial cells (MECs). In MECs, localization of MG-H1 formation (both endogenous and after MG-treatment) was analyzed using immunofluorescence (IF) and electron microscopy (EM).

Results:

In yeast, RNASeq analysis after MG-treatment revealed a strong induction of the protein quality control system including the inducible Hsp70 s. Accordingly, loss of Hsp70 and also Vms1 decreased MG-tolerance in yeast. To further validate these data in the mammalian system, MECs were treated with Hsp70 and Vms1 siRNA, which rendered the cells more vulnerable to MG. Using IF and EM in endothelial cells, we found that MG-H1 accumulates at the site of mitochondria under basal conditions and that mitochondrial MG-H1 accumulation is aggravated under MG-stress.

Conclusion:

Different components of the protein quality control are needed to handle AGE-induced proteotoxicity. Both, Hsp70 and Vms1, could play a central role in preserving mitochondrial function in diabetes.