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J Biol Chem. 2005 May 13;280(19):19062-9. Epub 2005 Mar 9.

Persistent nuclear factor-kappa B activation in Ucp2-/- mice leads to enhanced nitric oxide and inflammatory cytokine production.

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Division of Biological Sciences, Endocrine Biology Program, CIIT Centers for Health Research, Research Triangle Park, North Carolina 27709-2137, USA.


One of the phenotypes of mice with targeted disruption of the uncoupling protein-2 gene (Ucp2-/-) is greater macrophage phagocytic activity and free radical production, resulting in a striking resistance to infectious microorganisms. In this study, the molecular mechanisms of this enhanced immune response were investigated. We found that levels of nitric oxide measured in either plasma or isolated macrophages from Ucp2-/- mice are significantly elevated in response to bacterial lipopolysaccharide challenge compared with similarly treated Ucp2+/+ mice. Likewise, expression of inducible nitric-oxide synthase and inflammatory cytokines is higher in Ucp2-/- mice in vivo and in vitro. Key steps in the activation cascade of nuclear factor (NF)-kappa B, including I kappa B kinase and nuclear translocation of NF-kappa B subunits, are all remarkably enhanced in Ucp2-/- mice, most notably even under basal conditions. The elevated basal activity of I kappa B kinase in macrophages from Ucp2-/- mice can be blocked by cell-permeable inhibitors of superoxide and hydrogen peroxide generation, but not by a specific inhibitor for inducible nitric-oxide synthase. Isolated mitochondria from Ucp2-/- cells produced more superoxide/hydrogen peroxide. We conclude that mitochrondrially derived reactive oxygen from Ucp2-/- cells constitutively activates NF-kappa B, resulting in a "primed" state to both potentiate and amplify the inflammatory response upon subsequent stimulation.

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