Intense Light-Mediated Circadian Cardioprotection via Transcriptional Reprogramming of the Endothelium.

Consistent daylight oscillations and abundant oxygen availability are fundamental to human health. Here, we investigate the intersection between light-sensing (Period 2 [PER2]) and oxygen-sensing (hypoxia-inducible factor [HIF1A]) pathways in cellular adaptation to myocardial ischemia. We demonstrate that intense light is cardioprotective via circadian PER2 amplitude enhancement, mimicking hypoxia-elicited adenosine- and HIF1A-metabolic adaptation to myocardial ischemia under normoxic conditions. Whole-genome array from intense light-exposed wild-type or Per2-/- mice and myocardial ischemia in endothelial-specific PER2-deficient mice uncover a critical role for intense light in maintaining endothelial barrier function via light-enhanced HIF1A transcription. A proteomics screen in human endothelia reveals a dominant role for PER2 in metabolic reprogramming to hypoxia via mitochondrial translocation, tricarboxylic acid (TCA) cycle enzyme activity regulation, and HIF1A transcriptional adaption to hypoxia. Translational investigation of intense light in human subjects identifies similar PER2 mechanisms, implicating the use of intense light for the treatment of cardiovascular disease.

Retinoic acid attenuates ileitis by restoring the balance between T-helper 17 and T regulatory cells.

BACKGROUND & AIMS: Retinoic acid (RA), produced by intestinal epithelial cells (IECs) and dendritic cells (DCs) promotes the induction of regulatory T cells (Tregs) and decreases the induction of T-helper (Th)17 cells. METHODS: We studied the roles of RA in mice that overproduce tumor necrosis factor (TNF) and develop chronic ileitis (TNF_ARE mice). We assessed the frequency and function of CD103+ DCs, Th17 cells, and Tregs by flow cytometry, and we measured expression of cytokines and retinaldehyde dehydrogenase (RALDH) enzymes in ileum samples, DCs, and IECs by real-time polymerase chain reaction. We quantified RA by electrochemical analysis and examined the effect of RA supplementation on TNF-induced ileitis using histologic, coculture, and suppression assays and flow cytometry. RESULTS: Numbers of CD103+ DCs decreased in the inflamed ilea of mice with chronic disease; RA synthetic machinery (RALDH1,2) was down-regulated. Nevertheless, the proportion of CD4+, CD25+, FoxP3+ Tregs increased, indicating an alternate source for RA. IECs responded to reduced levels of RA by up-regulating RALDH3 in vivo and in vitro. Net tissue levels of RA remained lower in TNF+ARE than wild-type mice, indicating that epithelial up-regulation of RALDH3 could not maintain adequate concentrations of RA, probably because of loss of IEC mass. RA supplementation significantly attenuated disease by increasing the number and function of CD103+ DCs and Tregs and reducing Th17 cells. CONCLUSIONS: Reduced levels of RA appear to induce IECs to up-regulate synthesis of RA. RA supplementation attenuates ileitis through its effects on CD103+ DCs, Tregs, and Th17 cells. RA supplementation might offer therapeutic benefit in Crohn's disease.

Identification of NR4A2 as a transcriptional activator of IL-8 expression in human inflammatory arthritis.

Expression of the orphan nuclear receptor NR4A2 is controlled by pro-inflammatory mediators, suggesting that NR4A2 may contribute to pathological processes in the inflammatory lesion. This study identifies the chemoattractant protein, interleukin 8 (IL-8/CXCL8), as a molecular target of NR4A2 in human inflammatory arthritis and examines the mechanism through which NR4A2 modulates IL-8 expression. In TNF-alpha-activated human synoviocyte cells, enhanced expression of IL-8 mRNA and protein correspond to temporal changes in NR4A2 transcription and nuclear distribution. Ectopic expression of NR4A2 leads to robust changes in endogenous IL-8 mRNA levels and co-treatment with TNF-alpha results in significant (p<0.001) secretion of IL-8 protein. Transcriptional effects of NR4A2 on the human IL-8 promoter are enhanced in the presence of TNF-alpha, suggesting molecular crosstalk between TNF-alpha signalling and NR4A2. A dominant negative IkappaB kinase antagonizes the combined effects of NR4A2 and TNF-alpha on IL-8 promoter activity. Co-expression of NR4A2 and the p65 subunit of NF-kappaB enhances IL-8 transcription and functional studies indicate that transactivation occurs independently of NR4A2 binding to DNA or heterodimerization with additional nuclear receptors. The IL-8 minimal promoter region is sufficient to support NR4A2 and NF-kappaB/p65 co-operative activity and NR4A2 can interact with NF-kappaB/p65 on a 39bp sequence within this region. In patients treated with methotrexate for active inflammatory arthritis, a reduction in NR4A2 synovial tissue levels correlate significantly (n=10, r=0.73, p=0.002) with changes in IL-8 expression. Collectively, these data delineate an important role for NR4A2 in modulating IL-8 expression and reveal novel transcriptional responses to TNF-alpha in human inflammatory joint disease.