PKA regulates HMGB1 through activation of IGFBP-3 and SIRT1 in human retinal endothelial cells cultured in high glucose

Objective and DesignInflammation is a key component of a number of diseases, including diabetic retinopathy. We investigated the cellular pathway by which protein kinase A (PKA) inhibited high mobility group box 1 (HMGB1).MethodsPrimary human retinal endothelial cells (REC) were grown in normal glucose (5mM) or high glucose (25mM). Cells in high glucose were treated with exchange protein for cAMP 1 (Epac1) and IGFBP-3 siRNA. Additional cells in high glucose were treated with forskolin, a PKA agonist, and Epac1 siRNA. Some cells were treated with a plasmid for insulin-like growth factor binding protein 3 (IGFBP-3) that does not bind IGF-1. Finally, some REC received Ex527, a sirtuin 1 (SIRT1) antagonist, prior to forskolin treatment. Protein analyses were done for HMGB1, Epac1, IGFBP-3, SIRT1, and PKA.ResultsPKA inhibited cytoplasmic HMGB1, independent of Epac1 actions. PKA activated IGFBP-3 and SIRT1 to inhibit cytoplasmic HMGB1. High glucose inhibited SIRT1 levels and increased cytoplasmic HMGB1 in REC.ConclusionsPKA requires active IGFBP-3 and SIRT1 to inhibit HMGB1 inflammatory actions in the retina vasculature. Activation of these pathways may offer new targets for therapy development.