KDM4 Regulates the Glycolysis of Hemocytes in the Immune Priming of Eriocheir sinensis

Immune priming confers a sustained, augmented response of innate immune cells to a secondary challenge, a process that is characteristically reliant on metabolic reprogramming. Recent evidence suggests that histone demethylases play essential roles in the immune priming, while its regulation role in the metabolic reprogramming remains largely unknown. In the present study, the concentration of glucose was significantly down-regulated in the hemocytes of crab <i>Eriocheir sinensis</i> after secondary stimulation with <i>Aeromonas hydrophila</i>, while the expression levels of phosphofructokinase (<i>Es</i>PFK) pyruvate kinase (<i>Es</i>PK), hexokinase-2 (<i>Es</i>HK-2) and Glucose-6-phosphate dehydrogenase (<i>Es</i>G-6-PD), along with the concentrations of lactate and the ratio of NAD⁺/NADH, were elevated. Additionally, the levels of H3K9me3 and its enrichment at the promoters of <i>Es</i>PFK and <i>Es</i>G-6-PD were significantly decreased at 7 days after <i>A. hydrophila</i> stimulation. The lysine Demethylase 4 homologue (<i>Es</i>KDM4) was observed to translocate into the nucleus of crab hemocytes after <i>A. hydrophila</i> stimulation, and its activity markedly increased after secondary stimulation with <i>A. hydrophila</i>. Following RNA interference of <i>Es</i>KDM4, there was a significant increase in H3K9me3 levels, and the enrichment of H3K9me3 at the <i>Es</i>PFK and <i>Es</i>G-6-PD promoters, as well as the concentration of glucose, in the hemocytes of crabs after secondary stimulation with <i>A. hydrophila</i>. Furthermore, mRNA transcripts of <i>Es</i>PFK and <i>Es</i>G-6-PD, as well as the concentration of lactate and ratio of NAD⁺/NADH, significantly decreased after secondary stimulation. These results suggested that <i>Es</i>KDM4 mediates the enrichment of H3K9me3 at the promoters of <i>Es</i>PFK and <i>Es</i>G-6-PD, thereby regulating glycolysis during the immune priming of crabs.