MEF2C negatively regulates plasmacytoid dendritic cell functions by modulating cholesterol homeostasis 2255238

Introduction Plasmacytoid dendritic cells (pDCs) are key innate immune cells specialized in producing type I interferons. Our prior research identified MEF2C as a novel transcription factor essential for pDC development, where Mef2c knockdown or knockout drastically reduced pDC frequency. Paradoxically, MEF2C deficiency also impaired pDC function, as evidenced by heightened expression of activation markers (e.g., CD86, MHC-II) and elevated cytokine secretion (e.g., IFN-α, IL-6, TNF-α, and IL-12) upon Toll-like receptor (TLR) stimulation. These opposing roles in pDC development and activation prompted us to elucidate the regulatory mechanisms underlying the immune modulatory activity of MEF2C on pDC effector functions. Methods Given the established link between immune cell activation and metabolic reprogramming, we investigated reactive oxygen species (ROS) production and transcriptomic changes in control and Mef2c-deficient pDCs stimulated with a TLR7 agonist R848. Activation markedly elevated ROS levels in both genotypes, indicating heightened oxidative stress. However, both cellular and mitochondrial ROS were heightened in the absence of Mef2c compared to the controls. We then perform a bulk RNA sequencing examination of both control and Mef2c-deficient pDCs. Results Bulk RNA sequencing revealed that genes encoding metabolic enzymes were differentially expressed in Mef2c-deficient pDCs, with significant enrichment in cholesterol homeostasis pathways. Inhibiting cholesterol synthesis with Simvastatin, a cholesterol synthesis inhibitor, curtailed activation marker expression in both genotypes, implicating excess cholesterol in hyperactivation via disrupted lipid rafts critical for TLR signaling. Conclusion Collectively, these findings uncover a novel role for MEF2C in restraining pDC activation by suppressing de novo cholesterol biosynthesis. Targeting this pathway holds therapeutic potential for modulating pDC responses in autoimmune and inflammatory diseases. Funding Source n/a Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)