Abstract 258: Palmitate Regulates Diabetic Macrophage Inflammation via the Epigenetic Enzyme JMJD3

Macrophage (Mϕ) plasticity, allowing for transition of Mϕs from an inflammatory to a reparative phenotype, is critical for normal wound healing. In pathologic conditions, such as type 2 diabetes (T2D), wounds fail to heal due to impaired resolution of inflammation. The mechanism(s) responsible for the persistent inflammatory phenotype in T2D wounds are unclear. Prior studies have shown that the Toll-like receptor (TLR) 4 pathway regulates Mϕ-mediated inflammation in tissues. Growing evidence indicates that TLR4 is a versatile receptor binding a spectrum of ligands including non-microbial ligands such as saturated fatty acids (SFAs). Given the excess SFAs in T2D, the purpose of this study was to examine the role of the SFA palmitate on TLR4 signaling and Mϕ phenotype in diabetic wound healing. We have previously shown that Mϕs isolated from wounds in a murine model of glucose intolerance (diet-induced obesity; DIO) maintained on a 60% high fat diet (HFD) for 12-18 weeks, display increased levels of inflammatory cytokines (IL-1β, IL-12, and TNFα) at both a gene expression and protein level. In the current study, we found that blood monocytes and wound Mϕs from DIO mice display increased TLR4 receptors compared to control blood and wounds. To determine if altered metabolites in the diabetic environment impact Mϕ phenotype, bone marrow derived macrophages (BMDMs) were incubated in serum isolated from DIO or control mice. BMDMs incubated with DIO serum displayed a hyperinflammatory response following LPS stimulation. Further, stimulation with the metabolite palmitate produced significantly increased IL-1β expression in DIO BMDMs compared to controls suggesting that DIO BMDMs are programmed toward an inflammatory response. To determine the mechanism, we examined several epigenetic enzymes known to affect Mϕ polarization and found that palmitate stimulated expression of JMJD3, a histone demethylase, which increases inflammatory gene expression. In conclusion, these studies suggest that the diabetic milieu, specifically increased levels of the SFA palmitate, induces expression of the epigenetic enzyme, JMJD3, in Mϕs and this regulates inflammatory gene expression and cell function.