Cellular and molecular mechanisms of the UCPs-dependent metabolic control and its patho-physiological relevance

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Uncoupling proteins (UCPs) are inner mitochondrial membrane proteins that mediate dissipation of the mitochondrial membrane potential as heat rather than ATP synthesis. To clarify the cellular and molecular mechanisms of the UCPs-dependent metabolic control, especially in relation with cellular ATP levels, we firstly investigated tissue uptake of 2-deoxyglucose (2-DG) in UCP1 -knockout (KO) mice in vivo. In wild-type (WT) mice, administration of norepinephrine (NE) accelerated the disappearance of plasma 2-DG and increased 2-DG uptake into brown adipose tissue (BAT) exclusively expressing UCP1 and heart without any rise of plasma insulin level. In UCP1-KO mice, the stimulatory effect of NE on 2-DG uptake into BAT, but not into heart, disappeared completely. Insulin administration increased 2-DG uptake into BAT and also heart similarly in WT and UCP1 -KO mice. NE also increased the ratio of AMP/ATP and the activity of AMP-activated protein kinase (AMPK) in BAT of WT, but not of UCP1-KO, mice. These results suggest that the sympathetically stimulated glucose utilization in BAT is due to the serial activation of UCP1 and AMPK. We next established mammalian cells expressing functional UCP1 in a mitochondrial fraction by using Stratagene's LacSwitch II Inducible Mammalian Expression System and Hep3B human hepatocellular carcinoma that dose not express any endogenous UCP isoforms. After developing respective cells expressing functional UCP2 and UCP3, they would be useful for the studies on the mechanisms of the UCP-dependent metabolic control in an isoform-specific manner.