Molecular mechanisms underlying the glycation induced-impairment of antigen processing and presentation in diabetic (T2DM) patients and ob/ob mice

Abstract Patients with obesity, metabolic syndrome, or type-2 diabetes (T2D) often exhibit hyperglycemia and hyperlipidemia. A consequence of the dysmetabolism is non-enzymatic coupling of reactive sugars and lipids with proteins and DNA inducing glycation and glycoxidation. Biochemically, these modifications disrupt the cellular proteome by changing the protein chemical structure and inducing protein unfolding, cross-linking and aggregation. We investigated protein post-translational modifications (PTM) induced by glycation and glycoxidation in PBMC from non-diabetic, pre-diabetic and diabetic individuals as well as CD11c+ dendritic cells purified from mice fed a high-fat diet, obese (Ob/Ob) mice and relative controls. By employing label-free bottom-up proteomic and bioinformatics analysis we mapped several cellular pathways affected by the oxidative PTMs, including the antigen processing and presentation machinery. Functional assays of endosomal processing, using transthyretin and insulin as model antigens, determined how the oxidative PTMs interfered with antigen processing. Glycation and glycoxidation moieties on MHC II proteins were mapped at sites known to interact with peptides, with the peptide exchange factor DM, and with the TCR. In vitro glycation of human HLA-DR1 resulted in impaired interaction with the peptide exchange factor HLA-DM. In vivo and in vitro impaired immune response to a model antigen (I-Ea protein ) was also observed in Ob/Ob mice. Our results shed light on the biological implications of the role played by glycation and glycoxidation, as observed in T2D and metabolic syndrome, on the antigen processing machinery as well as its functional consequences for MHC II restricted immune responses.