B-cell metabolic reprogramming through Hexokinase-II

B-cell activation occurs via antigen binding to its membrane immunoglobulin along with T-cell help to initiate intracellular signaling cascades. B cell activation enhances glucose uptake, the phosphoinositide-3-kinase (PI3K) pathway, and glycolysis and oxidative phosphorylation in a balanced manner relative to resting B-cells. The enzyme Hexokinase (HK) is central to B cell activation as it catalyzes the first step of glucose metabolism by phosphorylating glucose to become glucose-6-phosphate, which then serves as an entry point for several metabolic pathways. Hexokinase-II (HKII) is one of four HK isoforms and is particularly interesting as the only isoform that can translocate between the cytoplasm and mitochondria. It is unknown if HKII, in comparison to the other isoforms, preferentially guides glucose-6-P down a particular metabolic pathway which may depend on the B-cell’s activation status and HKII’s cellular localization. B-cell activation through the T-cell dependent signals and the PI3K pathway reprograms resting B-cell metabolism by the modification of HKII expression and subcellular localization to meet the B-cell’s new activated metabolic program. B-cells with unusual HKII expression or subcellular localization may be a feature of B-cell metabolic dysregulation, such as that observed in Chronic Lymphocytic Leukemia (CLL). A novel intracellular staining and flow cytometry assay was developed to measure HKII expression levels across B-cell subsets throughout the body and a fluorescence microscopy based assay quantified HKII mitochondrial localization. A biological mechanism is presented herein, where B-cell activation dependent on the PI3K pathway significantly increased HKII expression and along with the presence of glucose enhanced HKII mitochondrial localization. CLL B-cells failed to increase HKII expression following in vitro B-cell activation and expressed significantly less HKII, which decreased with advanced clinical Rai stage, compared to control