Regulation of FOXP3 Expression by c-Rel O-GlcNAcylation

The NF-kappaB protein c-Rel plays a critical role in controlling autoimmunity through regulating T cell function and T regulatory cell development. Type 1 diabetes is a T cell-mediated autoimmune disease associated with hyperglycemia and chronic inflammatory complications. Previously, we discovered that hyperglycemia induces hyper O-GlcNAcylation of c-Rel at serine residue 350 and enhances the transcription of c-Rel-dependent pro-autoimmune cytokines interleukin-2 (IL-2), interferon gamma (IFNG) and granulocyte macrophage colony-stimulating factor (GM-CSF). In contrast, our recent results show that c-Rel O-GlcNAcylation decreases forkhead boxP3 (FOXP3) expression in T cells. Chemically enhancing cellular O-GlcNAcylation decreases the DNA binding ability of c-Rel at the FOXP3 promoter as demonstrated both by oligonucleotide pulldown and chromatin immunoprecipitation assays. Moreover, mutation of serine 350 in c-Rel to alanine augments T cell receptor-induced FOXP3 expression. O-GlcNAcylation-dependent suppression of FOXP3 was also found in vivo in streptozotocin-induced diabetic mouse model. This study reveals a novel molecular mechanism that regulates hyperglycemia-dependent c-Rel function in autoimmune diabetes, with potential to develop novel therapeutics targeting c-Rel O-GlcNAcylation.

Platelet-derived TLT-1 is a prognostic indicator in ALI/ARDS and prevents tissue damage in the lungs in a mouse model

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) affect >200 000 individuals yearly with a 40% mortality rate. Although platelets are implicated in the progression of ALI/ARDS, their exact role remains undefined. Triggering receptor expressed in myeloid cells (TREM)-like transcript 1 (TLT-1) is found on platelets, binds fibrinogen, and mediates clot formation. We hypothesized that platelets use TLT-1 to manage the progression of ALI/ARDS. Here we retrospectively measure plasma levels of soluble TLT-1 (sTLT-1) from the ARDS Network clinical trial and show that patients whose sTLT-1 levels were >1200 pg/mL had nearly twice the mortality risk as those with <1200 pg/mL (P < .001). After correcting for confounding factors such as creatinine levels, Acute Physiology And Chronic Health Evaluation III scores, age, platelet counts, and ventilation volume, sTLT-1 remains significant, suggesting that sTLT-1 is an independent prognostic factor (P < .0001). These data point to a role for TLT-1 during the progression of ALI/ARDS. We use a murine lipopolysaccharide-induced ALI model and demonstrate increased alveolar bleeding, aberrant neutrophil transmigration and accumulation associated with decreased fibrinogen deposition, and increased pulmonary tissue damage in the absence of TLT-1. The loss of TLT-1 resulted in an increased proportion of platelet-neutrophil conjugates (43.73 ± 24.75% vs 8.92 ± 2.4% in wild-type mice), which correlated with increased neutrophil death. Infusion of sTLT-1 restores normal fibrinogen deposition and reduces pulmonary hemorrhage by 40% (P ≤ .001) and tissue damage by 25% (P ≤ .001) in vivo. Our findings suggest that TLT-1 uses fibrinogen to govern the transition between inflammation and hemostasis and facilitate controlled leukocyte transmigration during the progression of ARDS.