Recent data suggest that stress-induced molecular pathways in the β cell may trigger the display of neoantigens that initiate autoimmunity in type 1 diabetes (T1D) . Polyamines (putrescine, spermidine, and spermine) are biogenic amines that participate in stress-induced mRNA translation, in part, through the posttranslational hypusine modification of eIF5A. Rate-limiting enzymes in this circuit include the ODC, which converts Arg to polyamines, and DHPS, which controls eIF5A hypusination. Previously, we showed that inhibition of ODC or DHPS in non-obese diabetic mice using either DFMO or GC7, respectively, resulted in preserved β-cell function, enhanced β-cell mass, and significantly reduced T1D incidence. DFMO treatment subjects with recent-onset T1D was suggestive of reductions in β cell stress. We hypothesized that polyamine depletion with DFMO reduces inflammatory stress in β cells and the consequent accumulation of unhypusinated eIF5A limits stress-related protein production. To test the hypothesis, we treated the human islets with proinflammatory cytokine (PIC) cocktail to mimic T1D in presence or absence of 5 mM DFMO. We observed induction of ER stress as shown by increased expression of unfolded protein response proteins within 24 h of PIC treatment. Treatment with DFMO reduced protein levels of IRE1α and downstream XBP1. Gene expression analysis showed significant downregulation of genes in the IRE1α pathway (CHOP, TNXIP, and XBP1s) . To clarify a mechanism underlying suppression of stress protein production by unhypusinated eIF5A, we treated HEK cells with DFMO or GC7, both of which enhanced the association of unhypusinated eIF5A with GCN2, an eIF2α kinase, suggesting a non-ER stress mediated mechanism of mRNA translational blockade. Collectively, these data suggest that inhibition of the polyamines-hypusine circuit suppresses ER stress via IRE1α signaling and enhances non-ER stress mediated suppression of mRNA translation.
A. Anderson: None. A. Kulkarni: None. R. G. Mirmira: None.