Erythropoietin production switches from fetal liver to adult kidney during development. GATA transcription factors 2 and 3 could be involved in modulating this switch, because they were shown to negatively regulate erythropoietin gene transcription through a promoter proximal GATA site. Herein, we analyzed the role of several GATA factors in the regulation of the erythropoietin gene in human liver and in hepatoma cells. Although GATA-3 expression in hepatocytes increases during human development, erythropoietin mRNA accumulation is unaltered in mutant mice lacking GATA-3. We found that GATA-2, -3, -4, and -6 are all expressed in human hepatocytes and that GATA-4 exhibits the most prominent Epo promoter binding activity in vitro and in vivo. Inhibition of GATA-4 expression by RNA interference leads to a dramatic reduction in Epo gene transcription in Hep3B cells. Moreover, GATA-4 expression is high and limited to hepatocytes in the fetal liver, whereas GATA-4 expression in the adult liver is low and restricted to epithelial cells surrounding the biliary ducts. Thus, GATA-4 is critical for transcription of the Epo gene in hepatocytes and may contribute to the switch in the site of Epo gene expression from the fetal liver to the adult kidney.

SummaryAging is associated with immune dysfunction, especially T‐cell defects, which result in increased susceptibility to various diseases. Previous studies showed that T cells from aged mice express multiple inhibitory receptors, providing evidence of the relationship between T‐cell exhaustion and T‐cell senescence. In this study, we showed that T‐cell immunoglobulin and immunoreceptor tyrosine‐based inhibitory motif (ITIM) domain (TIGIT), a novel co‐inhibitory receptor, was upregulated in CD8+ T cells of elderly adults. Aged TIGIT + CD8+ T cells expressed high levels of other inhibitory receptors including PD‐1 and exhibited features of exhaustion such as downregulation of the key costimulatory receptor CD28, representative intrinsic transcriptional regulation, low production of cytokines, and high susceptibility to apoptosis. Importantly, their functional defects associated with aging were reversed by TIGIT knockdown. CD226 downregulation on aged TIGIT + CD8+ T cells is likely involved in TIGIT‐mediated negative immune suppression. Collectively, our findings indicated that TIGIT acts as a critical immune regulator during aging, providing a strong rationale for targeting TIGIT to improve dysfunction related to immune system aging.

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. Thyroid hormone induces erythropoietin gene expression through augmented accumulation of hypoxiainducible factor-1. Am J Physiol Regul Integr Comp Physiol 287: R600 -R607, 2004. First published May 20, 2004 10.1152/ajpregu. 00115.2004.-Oxygen is of vital importance for the metabolism and function of all cells in the human body. Hypoxia, the reduction of oxygen supply, results in adaptationally appropriate alterations in gene expression through the activation of hypoxia-inducible factor 1 (HIF-1) to overcome any shortage of oxygen. Thyroid hormones are required for normal function of nearly all tissues, with major effects on oxygen consumption and metabolic rate. Thyroid hormones have been found to augment the oxygen capacity of the blood by increasing the production of erythropoietin (EPO) and to improve perfusion by vasodilation through the augmented expression of adrenomedullin (ADM). Because the hypoxic expression of both genes depends on HIF-1, we studied the influence of thyroid hormone on HIF-1 activation in the human hepatoma cell line HepG2 under normoxic and hypoxic conditions. We found that thyroid hormones increased HIF-1␣ protein accumulation by increasing HIF-1␣ protein synthesis rather than attenuating its proteasomal degradation. HIF-1␣ expression directly correlated with augmented HIF-1 DNA binding and transcriptional activity of luciferase reporter plasmids, whereas HIF-1␤ levels remained unaffected. Knocking down HIF-1␣ by short interfering RNA (siRNA) clearly demonstrated that thyroid hormoneinduced target gene expression required the presence of HIF-1. Although an increased association of the two known coactivators of HIF-1, p300 and SRC-1, was found, thyroid hormone did not affect the activity of the isolated COOH-terminal transactivating domain of HIF-1␣. Increased synthesis of HIF-1␣ may contribute to the adaptive response of increased oxygen demand under hyperthyroid conditions. hypoxic gene expression; oxygen sensing ERYTHROPOIETIN (EPO), a 30.4-kDa glycoprotein hormone, is the major physiological stimulator of red blood cell formation in mammals (18). The main EPO production sites are the kidney in adults and the liver in fetuses (6). EPO production is induced by hypoxia, a state when oxygen supply does not cover the demand of the tissue. EPO mRNA levels are induced 50-to 100-fold in vitro by physiologically relevant levels of hypoxia (9). In vivo under severe hypoxia, production of EPO can be increased up to 1,000-fold (18, 29).Oxygen-dependent EPO expression is regulated by hypoxiainducible factor 1 (HIF-1), a heterodimer of the O 2 -labile 120-kDa ␣-subunit, and the constitutive 91-to 94-kDa ␤-subunit (37). The cellular levels of HIF-1␣ are adjusted by the ubiquitin-proteasome-dependent degradation of HIF-1␣ under normoxic conditions, allowing to tightly couple the protein appearance to the ambient oxygen tension (31). At high PO 2 , HIF-1␣ is posttranslationally hydroxylated at proline residues 402 and 564 by O 2 -sensitive prolyl hydroxylases, termed PHD1, PHD2, and PHD3, which ...

Saccharides are reported to protect hepatocytes from acute liver injury through distinct mechanisms. To date, the protective role of galactose against acute liver injury induced by lipopolysaccharide (LPS) and D-galactosamine (D-GalN) has been attributed to competition with D-GalN. Here, we showed that in addition to its effects on LPS/D-GalN and tumor necrosis factor alpha (TNF-α)/D-GalN models, galactose improves hepatic injury in mice challenged with LPS alone or TNF-α/actinomycin D. Consistent with this result, galactose enhanced the viability of TNF-α-stimulated Chang Liver and Hu7.5 hepatic cell lines. Specifically, galactose prevented TNF-α-induced apoptosis of hepatocytes through promoting phosphorylation of nuclear factor kappa B (NF-κB) p65. Additionally, galactose enhanced expression of the anti-apoptotic genes, c-IAP1 and A20, and inhibited cleavage of caspase-8 and caspase-3. These findings collectively suggest that galactose prevents TNF-α-induced liver injury through activation of the NF-κB signaling pathway. Considering that monosaccharides protect against liver injury via distinct mechanisms, these compounds may represent a promising clinical approach to treat acute liver failure. Acute liver failure (ALF), defined as rapid onset of severe hepatic dysfunction with poor prognosis, is a serious problem in clinical practice. 1 A model of hepatic injury induced by lipopolysaccharide (LPS) and D-galactosamine (D-GalN) has been widely used to explore the mechanisms of ALF and screen for potential hepatoprotective drugs. 2 In this model, LPS triggers innate immune responses and induces TNF-α, which subsequently activates the pro-apoptotic caspase reaction directly or indirectly via mitogen-activated protein (MAP) kinases, including p38, JNK1/2 and ERK1/2, as well as an anti-apoptotic signal via the transcription factor nuclear factor kappa B (NF-κB). 3-5 D-GalN, which acts as a sensitizing agent, amplifies the toxicity of LPS and TNF-α to liver. 6 Since liver has a central role in human metabolism, ALF may cause metabolic defects and energy imbalance. 7 As the main source of energy, saccharides have an important role in maintaining hepatocyte survival and physiological processes.A recent study revealed that oral administration of glucose prevents endotoxin-and drug-induced liver failure by promoting secretion of IL-10 to repress liver inflammation in LPS/D-GalN and acetaminophen-treated mice. 8 Another monosaccharide, fructose, prevents TNF-α/ actinomycin D (ActD)-induced apoptosis of hepatocytes through inhibiting JNK signaling in a PKA-dependent manner. 9 Earlier studies have reported that galactose prevents LPS/DGalN-induced liver damage in mice. 10 A recent metabolic profiling study revealed a significant decrease in galactose in the plasma of LPS/D-GalN-treated mice. 7 For decades, the protective role of galactose has been attributed to competition with D-GalN. 11 However, recent evidence has challenged this notion. First, galactose and glucose share the same enzyme machinery for conversion to...