p16(INK4a) deficiency promotes IL-4-induced polarization and inhibits proinflammatory signaling in macrophages
ABSTRACT The CDKN2A locus, which contains the tumor suppressor gene p16(INK4a), is associated with an increased risk of age-related inflammatory diseases, such as cardiovascular disease and type 2 diabetes, in which macrophages play a crucial role. Monocytes can polarize toward classically (CAMϕ) or alternatively (AAMϕ) activated macrophages. However, the molecular mechanisms underlying the acquisition of these phenotypes are not well defined. Here, we show that p16(INK4a) deficiency (p16(-/-)) modulates the macrophage phenotype. Transcriptome analysis revealed that p16(-/-) BM-derived macrophages (BMDMs) exhibit a phenotype resembling IL-4-induced macrophage polarization. In line with this observation, p16(-/-) BMDMs displayed a decreased response to classically polarizing IFNγ and LPS and an increased sensitivity to alternative polarization by IL-4. Furthermore, mice transplanted with p16(-/-) BM displayed higher hepatic AAMϕ marker expression levels on Schistosoma mansoni infection, an in vivo model of AAMϕ phenotype skewing. Surprisingly, p16(-/-) BMDMs did not display increased IL-4-induced STAT6 signaling, but decreased IFNγ-induced STAT1 and lipopolysaccharide (LPS)-induced IKKα,β phosphorylation. This decrease correlated with decreased JAK2 phosphorylation and with higher levels of inhibitory acetylation of STAT1 and IKKα,β. These findings identify p16(INK4a) as a modulator of macrophage activation and polarization via the JAK2-STAT1 pathway with possible roles in inflammatory diseases.
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ABSTRACT: A genomic region near the CDKN2A locus, encoding p16(INK4a), has been associated to type 2 diabetes and atherosclerotic vascular disease, conditions in which inflammation plays an important role. Recently, we found that deficiency of p16(INK4a) results in decreased inflammatory signaling in murine macrophages and that p16(INK4a) influences the phenotype of human adipose tissue macrophages. Therefore, we investigated the influence of immune cell p16(INK4a) on glucose tolerance and atherosclerosis in mice. Bone marrow p16(INK4a)-deficiency in C57Bl6 mice did not influence high fat diet-induced obesity nor plasma glucose and lipid levels. Glucose tolerance tests showed no alterations in high fat diet-induced glucose intolerance. While bone marrow p16(INK4a)-deficiency did not affect the gene expression profile of adipose tissue, hepatic expression of the alternative markers Chi3l3, Mgl2 and IL10 was increased and the induction of pro-inflammatory Nos2 was restrained on the high fat diet. Bone marrow p16(INK4a)-deficiency in low density lipoprotein receptor-deficient mice did not affect western diet-induced atherosclerotic plaque size or morphology. In line, plasma lipid levels remained unaffected and p16(INK4a)-deficient macrophages displayed equal cholesterol uptake and efflux compared to wild type macrophages. Bone marrow p16(INK4a)-deficiency does not affect plasma lipids, obesity, glucose tolerance or atherosclerosis in mice.PLoS ONE 03/2012; 7(3):e32440. DOI:10.1371/journal.pone.0032440 · 3.53 Impact Factor
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ABSTRACT: Signal transducer and activator of transcription 1 (STAT1) is important for innate and adaptive immunity. Histone deacetylase inhibitors (HDACi) antagonize unbalanced immune functions causing chronic inflammation and cancer. Phosphorylation and acetylation regulate STAT1 and different IFNs induce phosphorylated STAT1 homo-/heterodimers, e.g. IFNα activates several STATs whereas IFNγ only induces phosphorylated STAT1 homodimers. In transformed cells HDACi trigger STAT1 acetylation linked to dephosphorylation by the phosphatase TCP45. It is unclear whether acetylation differentially affects STAT1 activated by IFNα or IFNγ, and if cellular responses to both cytokines depend on a phosphatase-dependent inactivation of acetylated STAT1. Here, we report that HDACi counteract IFN-induced phosphorylation of a critical tyrosine residue in the STAT1 C-terminus in primary cells and hematopoietic cells. STAT1 mutants mimicking a functionally inactive DNA binding domain (DBD) reveal that the number of acetylation-mimicking sites in STAT1 determines whether STAT1 is recruited to response elements after stimulation with IFNγ. Furthermore, we show that IFNα-induced STAT1 heterodimers carrying STAT1 molecules mimicking acetylation bind cognate DNA and provide innate anti-viral immunity. IFNγ-induced acetylated STAT1 homodimers are though inactive, suggesting that heterodimerization and complex formation can rescue STAT1 lacking a functional DBD. Apparently, the type of cytokine determines how acetylation affects the nuclear entry and DNA binding of STAT1. Our data contribute to a better understanding of STAT1 regulation by acetylation.Cellular Signalling 03/2012; 24(7):1453-60. DOI:10.1016/j.cellsig.2012.02.018 · 4.47 Impact Factor
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ABSTRACT: Oxidative stress is believed to play a key role in cardiovascular disorders. Thioredoxin (Trx) is an oxidative stress-limiting protein with anti-inflammatory and antiapoptotic properties. Here, we analyzed whether Trx-1 might exert atheroprotective effects by promoting macrophage differentiation into the M2 anti-inflammatory phenotype. Trx-1 at 1 μg/mL induced downregulation of p16(INK4a) and significantly promoted the polarization of anti-inflammatory M2 macrophages in macrophages exposed to interleukin (IL)-4 at 15 ng/mL or IL-4/IL-13 (10 ng/mL each) in vitro, as evidenced by the expression of the CD206 and IL-10 markers. In addition, Trx-1 induced downregulation of nuclear translocation of activator protein-1 and Ref-1, and significantly reduced the lipopolysaccharide-induced differentiation of inflammatory M1 macrophages, as indicated by the decreased expression of the M1 cytokines, tumor necrosis factor-α and monocyte chemoattractant protein-1. Consistently, Trx-1 administered to hyperlipoproteinemic ApoE2.Ki mice at 30 μg/30 g body weight challenged either with lipopolysaccharide at 30 μg/30 g body weight or with IL-4 at 500 ng/30 g body weight significantly induced the M2 phenotype while inhibiting differentiation of macrophages into the M1 phenotype in liver and thymus. ApoE2.Ki mice challenged once weekly with lipopolysaccharide for 5 weeks developed severe atherosclerotic lesions enriched with macrophages expressing predominantly M1 over M2 markers. In contrast, however, daily injections of Trx-1 shifted the phenotype pattern of lesional macrophages in these animals to predominantly M2 over M1, and the aortic lesion area was significantly reduced (from 100%±18% to 62.8%±9.8%; n=8; P<0.01). Consistently, Trx-1 colocalized with M2 but not with M1 macrophage markers in human atherosclerotic vessel specimens. The ability of Trx-1 to promote differentiation of macrophages into an alternative, anti-inflammatory phenotype may explain its protective effects in cardiovascular diseases. These data provide novel insight into the link between oxidative stress and cardiovascular diseases.Arteriosclerosis Thrombosis and Vascular Biology 04/2012; 32(6):1445-52. DOI:10.1161/ATVBAHA.112.249334 · 5.53 Impact Factor