Figure 5.

HIF-1α and HIF-2α acts antagonistically in terms of NO production by inducing iNOS and arginase1 expression. (A) Hypothesized model of NO production under low or high concentration of IFNγ. Under low IFNγ condition, HIF-2α is present and induces arginase1 expression, resulting in the suppression of NO production. Under high IFNγ condition, HIF-2α is diminished and iNOS uses L-arginine for the production of NO. (B) Network diagram for a mathematical model of L-arginine metabolism through iNOS and arginase1 (values for the rate constants k1–k26 are listed in Table 1). HIF-1α and HIF-2α act antagonistically in terms of NO production in macrophages. (C) Heat maps of computational simulation results of iNOS, arginase1, and NO levels in response to altered rates of HIF-1α and HIF-2α transcription under IFNγ stimulation revealed that both L-arginine concentration and the balance of HIF-1α/HIF-2α could affect NO secretion from macrophages. Arrows indicate the responses to different doses of IFNγ. (D) Nitrite productions from TEPMs were measured in supernatant of cultured macrophages using Griess reaction systems. TEPMs were incubated in hypoxia (1%) for 12 h, and were treated with IFNγ under normoxia for 36 h. HIF-2α KO TEPMs produced higher NO than wild type in low–middle concentration of IFNγ under an excess amount of L-arginine (1140 mM). Nitrite production was decreased in HIF-1α KO TEPMs. Production of nitrite was strikingly increased in HIF-2α KO TEPMs under physiological concentration of L-arginine (228 mM) (n = 6). (E) Measurement of plasma nitrite and nitrate levels 6 h or 24 h after LPS 1 mg/kg i.p. of HIF-1α^flox/flox; LysM^+/− (HIF-1α KO) or HIF-2α^flox/flox; LysM^+/− (HIF-2α KO) mice. NO level was decreased in 6 h after LPS in HIF-1α KO; however, NO level was increased at 24 h in HIF-2α KO mice (n = 8).