A novel and atypical NF-KB pro-inflammatory program regulated by a CamKII-proteasome axis is involved in the early activation of Muller glia by high glucose

background diabetic retinopathy (DR) is a microvascular complication of diabetes with a heavy impact on the quality of life of subjects and with a dramatic burden for health and economic systems on a global scale. although the pathogenesis of DR is largely unknown, several preclinical data have pointed out to a main role of muller glia (MG), a cell type which spans across the retina layers providing nourishment and support for retina ganglion cells (RGCs), in sensing hyper-glycemia and in acquiring a pro-inflammatory polarization in response to this insult. results by using a validated experimental model of DR in vitro, rMC1 cells challenged with high glucose, we uncovered the induction of an early (within minutes) and atypical nuclear Factor-kB (NF-kB) signalling pathway regulated by a calcium-dependent calmodulin kinase II (CamKII)-proteasome axis. phosphorylation of proteasome subunit Rpt6 (at serine 120) by camKII stimulated the accelerated turnover of IkB alpha (i.e., the natural inhibitor of p65-50 transcription factor), regardless of the phosphorylation at serine 32 which labels canonical NF-kB signalling. this event allowed the p65-p50 heterodimer to migrate into the nucleus and to induce transcription of IL-8, Il-1 beta and MCP-1. pharmacological inhibition of camKII as well as proteasome inhibition stopped this pro-inflammatory program, whereas introduction of a Rpt6 phospho-dead mutant (Rpt6-S120A) stimulated a paradoxical effect on NF-kB probably through the activation of a compensatory mechanism which may involve phosphorylation of 20S alpha 4 subunit. conclusions cthis study introduces a novel pathway of MG activation by high glucose and casts some light on the biological relevance of proteasome post-translational modifications in modulating pathways regulated through targeted proteolysis.