• The Role of Glycolysis and Oxidative Respiration in the Survival and Activation of B cells

      Saltis, Mark; Davidson, Wendy F. (2009)
      The activation of B cells in an immune response places significant metabolic demands on the cell for blast transformation, proliferation, and cytokine and antibody production. It is currently unclear how lymphocytes meet these bioenergetic demands, or conversely, how metabolism influences B cell activation. Evidence suggests that mitochondrial function is critical to the activation and survival of B cells in both resting and stimulated states. While the role of the mitochondria in the signaling of other cell types has been established, it is currently unclear how mitochondrial function and metabolism affect B cell signaling and activation. We have investigated the role of the glycolytic and oxidative pathways, metabolic pathways dependent on mitochondrial function, in events downstream of activation in B cells including cell survival, blast transformation, and proliferation, and determined the mechanisms of regulation of metabolism during different stages of activation. We observed two phases of glycolytic and oxidative activity in B cells stimulated with CpG at early and late stages of activation. We show that CpG-related signaling through the Akt and mTOR pathways are associated with increased metabolism early after activation, and that a more significant increase in metabolism occurs as cell cycle progression occurs that is dependent on activation downstream of cell cycle regulatory CDK proteins, and independent of Akt and mTOR pathways. We provide evidence that disruption of the oxidative pathway and mitochondrial function with rotenone induces rapid cell death. Disruption of glycolysis has indirect effect on oxidative activity and reduces cellular activation, raising the possibility that glycolytic inhibition may reduce availability of pyruvate to feed the citric acid cycle, or induce mitochondrial retrograde signaling resulting in indirect effects on cell activation and oxidative respiration. We observed evidence of increased metabolic activity in B cells from a mouse model of systemic autoimmunity, and a significant decrease in lymphoproliferative disease after glycolytic inhibition in vivo combined with a reduction in B cell subsets in autoimmune mice. In gld mice, a unique population of B cells with an activated phenotype is most significantly reduced, while transitional B cells are most affected B cell population in normal BALB/c mice. While interpretation of these data is complex, it suggests a significant role for glycolysis in the in vivo survival of B cells. In summary, utilization and regulation of energy pathways and mitochondrial function are complex processes that can have profound effects on B cell activation and survival, and that enhanced metabolic activity may play a significant role in the B cell immune response and autoimmunity.
    • μ-Crystallin: A Novel Protein Regulator of Mammalian Metabolism

      Kinney, Christian; Bloch, Robert J.; 0000-0002-9799-9097 (2021)
      Thyroid hormones control many aspects of physiology such as metabolism and thermogenesis. Because thyroid hormones control such crucial bodily functions, their levels in the body are tightly regulated. Hypo- and hyperthyroidism can result when the level of thyroid hormone is too low or too high, respectively, with potentially serious pathophysiological consequences. µ-Crystallin is an NADPH-regulated thyroid hormone binding protein. The protein is minimally expressed in the skeletal muscle of most people; however, some individuals express relatively high baseline levels of µ-crystallin. We generated a transgenic mouse, the Crym tg mouse, that expresses high levels of µ-crystallin in its skeletal muscle, in order to explore the consequences of expressing high levels, comparable to those seen in some humans. The Crym tg mouse expresses mouse µ-crystallin at levels 2.6-147.5-fold higher than control mice in their skeletal muscle. Consequently, intramuscular triiodothyronine (T3) levels are elevated ~190-fold in the tibialis anterior, while serum thyroxine levels are decreased by 1.2-fold. Crym tg mice have a decreased respiratory exchange ratio that corresponds to a 13.7% increase in fat utilization as an energy source. Female Crym tg mice gained weight faster on high fat or high simple carbohydrate diets. Gene ontology enrichment analysis of transcriptomic and proteomic data revealed alterations to the expression of genes associated with metabolism and fiber type, while the fiber sizes of Crym tg soleus muscle are significantly smaller than those of controls. Taken together, these results suggest that µ-crystallin may play a role in regulating metabolism, perhaps through the control of thyroid hormone in muscle. Thus, humans who naturally express higher levels of µ-crystallin in their skeletal muscle may have an altered metabolism, comparable to the Crym tg mice.