Posttranslational modification of islet autoantigens in type 1 diabetes

Abstract

Abstract Autoimmune diseases are typically initiated by self-proteins, either native proteins or those with posttranslational modifications (PTMs), that break immune tolerance and lead to tissue pathology. Inflammation and oxidative stress amplifies various PTMs such as glutathionylation, nitrosylation and carbonylation, although these pathways are not clearly understood in the genesis of type 1 diabetes (T1D). By various proteomic analyses, including two-dimensional gel electrophoresis and mass spectroscopy, we identified more than a dozen carbonyl modified islet proteins bound by autoantibodies in non-obese diabetic (NOD) mice and in human T1D. In particular, we identified the beta subunit of prolyl-4-hydroxylase (P4Hb) as a carbonylated autoantigen in both human and murine T1D. P4Hb is a conserved protein catalyst known to be critical for proinsulin folding and trafficking in insulin biosynthesis. Of interest, we detected circulating autoantibodies against P4Hb in prediabetic NOD mice, before the onset of hyperglycemia and anti-insulin autoimmunity. Similarly, autoantibodies arise in early onset human T1D prior to anti-insulin autoimmunity. Finally, we demonstrate that carbonyl modified P4Hb is elevated in human pancreatic islets stressed with inflammatory cytokines (INF-γ, IL-1β and TNF-α). These studies provide mechanistic insight into the pathways of creating autoantigens and define a linked set of autoimmune responses (P4Hb and insulin) in the development of T1D.