Recent data suggest that hypoxia and its principal molecular signature HIF-1 (hypoxiainducing factor-1) may tune down inflammation by dictating anti-inflammatory programs. We tested the effects of hypoxia and HIF-1a on the homeostasis of naturally occurring regulatory T cells (Treg) and their transcriptional activator Foxp3. Hypoxia induced a timedependent increase in HIF-1a in mouse and human T cells. Hypoxia upregulated the expression of Foxp3 in Jurkat T cells, human and murine mononuclear cells. The effects of hypoxia on Foxp3 expression were HIF-1a-dependent as they were abolished upon transfection with short-interfering RNAs for HIF-1a and promoted by HIF-1a overexpression. Hypoxia increased the potency of Treg, as hypoxic CD4 1 CD25 1 lymphocytes were more effective than normoxic cells in suppressing the proliferation of CD4 1 CD25 À effectors. In vivo expression of HIF-1a achieved by hydrodynamic injection of the respective naked DNA similarly induced an increase in Foxp3 expression and an increase in the number of functionally active Foxp3 1 CD4 1 CD25 1 Treg. Thus, hypoxia dictates an antiinflammatory program by driving expression of HIF-1a that acts to increase the number and suppressive properties of naturally occurring CD4 1 CD25 1 Treg.Key words: Foxp3 Á HIF-1 Á Hypoxia Á Inflammation Á Regulatory T cells IntroductionUnder hypoxia, hypoxia-inducible factor-1 (HIF-1) plays a key role in controlling glycolysis, angiogenesis, erythropoiesis and cell survival [1]. HIF-1 constitutes an oxygen-dependent a-subunit and a constitutively expressed b-subunit that interact through mutual basic helix-loop-helix domains [2]. HIF-1a oxygen-dependent domain undergoes site-specific proline hydroxylation by prolyl hydroxylases, which allows subsequent ubiquitination mediated by the von Hippel-Lindau protein [3][4][5]. In the absence of molecular oxygen, HIF-a hydroxylation is abrogated, leading to its cellular accumulation. HIF subunits heterodimerize, and activate a wide range of target genes by binding to hypoxia response elements.T-lymphocytes that comprise a principal effector component of the cellular immune response are exposed to hypoxia in target microenvironments in which they are assumed to dictate inflammatory programs. Target sites include tumors and healthy organs that confront T cells with gradients of low oxygen tension. Recent literature suggests that blunted HIF-1a expression results in a net proinflammatory program evident by increased production inflammatory cytokines upon TCR engagement [6]. Similar results were obtained upon knocking out HIF-1 selectively in T cells [7]. Additionally, HIF-1a was reported to play an inhibitory role in the regulation of T-cell receptor signal transduction by controlling intracellular calcium balance [8]. Collectively, these observations suggest that HIF-1 drives a Th2 favored response by downregulated Th1 programs [9][10][11]. Naturally occurring CD4 1 CD25 1 regulatory T cells (Treg) comprise a relatively newly characterized population that has evolved to tune do...

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Background— Lymphocytes play an important role in the progression of atherosclerosis. Recently, hypoxia inducible factor-1 (HIF-1) was found to attenuate inflammation by regulating T cell activation and cytokine production. We studied the effects of overexpression of HIF-1α in ApoE knockout murine lymphocytes, on experimental atherosclerosis. Methods and Results— ApoE −/− mice were submitted to intravenous hydrodynamic injection of empty plasmid or HIF-1αP564A (HIF-1α mutated stabilized construct). Robust expression of HIF-1α was evident in spleen cells of recipient animals. Increased expression of IL-10 as well as decreased expression of IFN-γ was measured in splenocytes of HIF-1α–treated mice by RT-PCR. One week postinjection, antibody array analysis revealed a pattern consistent with a T helper 1 to T helper 2 shift. On sacrifice, assessment of aortic sinus lesions revealed a significant reduction in plaque size in HIF-1α injected mice. A reduced expression of IFN-γ was evident in CD4+ spleen-derived lymphocytes and aortas of HIF-1α–injected mice. Conclusions— HIF-1α expression in mouse lymphocytes is associated with a reduced IFN-γ expression and attenuation of experimental atherosclerosis.