The Integrated Stress Response Promotes Macrophage Inflammation

Macrophages infiltrate islets early in the pathogenesis of Type 1 Diabetes (T1D), instigating islet inflammation and subsequent recognition by the adaptive immune system. A reanalysis of a publicly available single-cell RNA sequencing dataset from a pre-diabetic female non-obese diabetic (NOD) mouse revealed that the Integrated Stress Response (ISR), an evolutionarily conserved cellular pathway, is upregulated in macrophages during T1D progression. Triggered by environmental and pathological stressors, the ISR coordinates adaptive changes in gene expression to maintain cell functionality and survival and is identified as a candidate for targeted intervention. Following this, in vitro experiments on macrophage polarization and migration were conducted to evaluate changes resulting from ISR modulation. Results showed that ISR inhibition reduced the propensity of macrophages to polarize to a pro-inflammatory state without affecting anti-inflammatory polarization and reduced the migratory capabilities of pro-inflammatory macrophages. Observations from pre-diabetic female NOD mice administered ISRIB, a pharmacological ISR inhibitor, indicated a reduction in macrophage numbers within the islets, with increased PD-L1 expression on the macrophages. Overall design: Bone marrow-derived macrophages (BMDM) were isolated as described previously and cultured for 6 days in complete medium (RPMI containing 10% FBS, 10 mM HEPES, and 100 U/ml penicillin/ streptomycin) supplemented with 10 ng/ml M-CSF. On day 6, BMDM were pre-treated with vehicle or 50nM ISRIB for 1 h and then stimulated with 10 ng/ml LPS and 25 ng/mL IFN-? for M1-like polarization for 16 h in the presence of vehicle or ISRIB. RNA was isolated using RNAeasy Mini kit (Qiagen) and did RNA sequencing experiments.