OR12-01 Blocking The Maladaptive Integrated Stress Response Increases Immunosuppressive PD-L1 In Pancreatic β-Cells

Disclosure: C. Muralidharan: None. F.H. huang: None. S.C. May: None. J. Enriquez: None. J.B. Nelson: None. E. Wang: None. A. Chakraborthy: None. K.T. Figatner: None. S.N. Navitskaya: None. S.A. Tersey: None. R.G. Mirmira: None. In type 1 diabetes (T1D), the immune system destroys the insulin-secreting β-cells. This autoimmune attack may be triggered by the β-cells themselves when they encounter viral infections or changes in gut microbiome or diet, years before clinical diagnosis of T1D. In response to these stressors, four kinases (PERK, PKR, GCN2, and HRI) activate the integrated stress response (ISR), which temporarily halts protein translation to promote cellular survival. However, if prolonged, the ISR can render β-cells dysfunctional. Therefore, we hypothesized that inhibiting the ISR under chronic inflammatory stress would suppress β-cell autoimmunity and reduce T1D risk. To test this, we pre-treated human islets with ISR inhibitors (ISRIB or a novel inhibitor of PERK, HC-PERKi) and then exposed them to proinflammatory cytokines (50 IU/mL IL-1β + 1000 IU/mL IFNγ) for 24h. As expected, cytokine treatment blocked protein translation, as revealed by polyribosomal profiling. Consistent with this, we saw reduced total protein synthesis (50% decrease) by puromycin incorporation assay. These effects were partially reversed by pretreating with ISR inhibitors. To determine if ISR inhibition delays or prevents diabetes development, we treated female pre-diabetic non-obese diabetic (NOD) mice with vehicle or HC-PERKi for four weeks (6-10 weeks of age). Compared to controls, NOD mice that received HC-PERKi showed a significant delay in diabetes development. Single cell RNA-sequencing analysis of the pancreatic islets revealed alterations in pathways involved in antigen processing and presentation in the β-cell clusters of HC-PERKi islets. Consistent with this observation, spatial proteomics analysis of the pancreatic β-cell area of HC-PERKi islets revealed a striking upregulation of programmed death-ligand 1 (PD-L1), an immune checkpoint regulator that suppresses adaptive T-cell immunity. Notably, there was no change in transcript levels of PD-L1, suggesting that PD-L1 levels are post-translationally regulated. Collectively, our studies show that inhibition of the ISR activates general protein synthesis, reduces immunogenicity via increased β-cell PD-L1 levels, and decreases T1D risk. Whereas the ISR is an adaptive response, our work emphasizes how the ISR coul