Abstract P379: Inhibition Of O-glcnac Transferase Ogt Activates P38 Signaling In Neonatal Rat Cardiomyocytes

Abstract

The mitogen activated protein kinase (MAPK) p38 is important in cardiac hypertrophic responses and p38 inhibition has been tested as a potential therapeutic approach to heart failure. p38 is tightly regulated by upstream kinases and phosphatases. While p38 inhibitors suppress cardiac hypertrophy in vitro and in animal models, the partial efficacy of p38 inhibitors in clinical trials for heart failure illustrates the need for a deeper understanding of p38-regulatory mechanisms. O -linked N-Acetylglucosamine ( O -GlcNAc) on Ser/Thr residues is a ubiquitous intracellular modification ( O -GlcNAcylation) that participates in intracellular signaling, often occurring in counterpoint to phosphorylation. O -GlcNAcylation is catalyzed by O -GlcNAc Transferase (OGT) and removed by O -GlcNAc-Ase (OGA). Given the crucial regulation of p38 activity by phosphorylation, we hypothesized that O -GlcNAcylation regulates p38 phosphorylation during basal and hypertrophic cardiomyocyte signaling. Treating neonatal rat ventricular myocytes (NRVM) with OSMI-1 (inhibitor of OGT) significantly decreased O -GlcNAcylation (0.48 ± 0.02, P <0.001 vs. vehicle), whereas treatment with Thiamet-G (inhibitor of OGA) significantly increased O -GlcNAcylation (3.0-fold increase ± 0.35, P <0.05 vs. vehicle). OSMI1 treatment induced the phosphorylation of p38 at its activation site (3.9-fold increase ± 0.46, P <0.001 vs. vehicle) and promoted the phosphorylation of the downstream target, heat shock protein Hsp27 (8-fold increase ± 1.3, P <0.0001 vs. vehicle) and transcription factor Creb (3.3-fold increase ± 0.12, P <0.001 vs. vehicle). OSMI-1 had an additive effect in inducing p38 and Creb phosphorylation following hypertrophic stimulation by phenylephrine (3.1-fold and 1.4-fold increase vs. phenylephrine respectively, P <0.05). Treatment with the p38 inhibitor SB202190 abolished the phosphorylation of Hsp27 and Creb that was induced by OSMI-1. Canonical upstream activators of p38 include the MAP3Ks, TAK1 and ASK1. However, we found that treatment with ASK1 or TAK1 inhibitors (GS-444217 and Takinib, respectively) either alone, or in combination, did not negate the phosphorylation of p38 by OSMI-1. We conclude that regulation of p38 by OGT activity could occur at a level downstream of canonical MAP3Ks or through non-canonical pathways.