Funmei Yang

Regulation of Reticuloendothelial Iron Transporter MTP1 (Slc11a3) by Inflammation

Acute and chronic inflammation cause many changes in total body iron metabolism including the sequestration of iron in phagocytic cells of the reticuloendothelial system. This change in iron metabolism contributes to the development of the anemia of inflammation. MTP1, the duodenal enterocyte basolateral iron exporter, is also expressed in the cells of the reticuloendothelial system (RES) and is likely to be involved in iron recycling of these cells. In this study, we use a lipopolysaccharide model of the acute inflammation in the mouse and demonstrate that MTP1 expression in RES cells of the spleen, liver, and bone marrow is down-regulated by inflammation. The down-regulation of splenic expression of MTP1 by inflammation was also observed in a Leishmania donovani model of chronic infection. The response of MTP1 to lipopolysaccharide (LPS) requires signaling through the LPS receptor, Toll-like receptor 4 (TLR4). In mice lacking TLR4, MTP1 expression is not altered in response to LPS. In addition, mice lacking tumor necrosis factor-receptor 1a respond appropriately to LPS with down-regulation of MTP1, despite hyporesponsiveness to tumor necrosis factor-α signaling, suggesting that this cytokine may not be required for the LPS effect. We hypothesize that the iron sequestration in the RES system that accompanies inflammation is because of down-regulation of MTP1.

Extrahepatic expression of plasma protein genes during inflammation

The bodys protective responses to infection, wounding, trauma, and malignancy include the acute-phase reaction, which is modulated by various cytokines and their cellular receptors. During the acute-phase reaction, levels of specific proteins synthesized by the liver increase in the plasma. Little information is available about the extrahepatic synthesis of plasma proteins during the acute-phase reaction. The study described here analyzes the tissue-specific expression of genes encoding the plasma proteins albumin (ALB), α1,-antitrypsin (AAT), transferrin (TF), haptoglobin (HP), ceruloplasmin (CP), serum amyloid A (SAA), α1-acid glycoprotein (AGP) and α2-HS-glycoprotein (AHSG) during the acute-phase reaction in C57B1 mice. The acute-phase reaction was induced by intraperitoneal injections of bacterial lipopolysaccharide (LPS). During the acute-phase reaction, genes encoding CP, SAA, AGP, and HP demonstrate unique extrahepatic tissue specific patterns of expression in kidney, spleen, thymus, heart, brain, lung, testis, and epididymis. Different temporal patterns of HP gene expression also were observed in lung and thymus after induction by LPS. The function of extrahepatic synthesis of plasma proteins is not yet understood; however, a local provision of specific plasma proteins in mammalian tissues may offer the host a source of functionally important proteins during periods of stress.

Human α2-HS-glycoprotein/bovine fetuin homologue in mice: identification and developmental regulation of the gene

Human alpha 2-HS-glycoprotein (AHSG) is a plasma protein synthesized in liver and selectively concentrated in bone matrix. It has been reported to be involved in bone formation and resorption as well as immune responses. Recently, AHSG was found to be the species equivalent protein of fetuin, the major fetal serum protein in cattle and sheep. The function and regulation of AHSG/fetuin in different species are not understood. We have isolated a liver cDNA clone that encodes the human AHSG/bovine fetuin homologue in the mouse. The AHSG/fetuin gene may have a role in differentiation since it is expressed in mouse limb buds and brain only at certain stages during development. Mouse liver AHSG/fetuin mRNA was present at low level at 12 days gestation but its level increased during the late part of gestation and peaked between 1 to 3 months after birth. The regulation of mouse AHSG/fetuin synthesis during development was found to be significantly different from that of sheep and bovine fetuin. Compared to fetuin, which is reduced in adult to 1 to 2% of the fetal level, mouse AHSG synthesis subsides only 50% 4 months after birth.

Transferrin: evolution and genetic regulation of expression.

Publisher Summary Transferrin (TF) is a member of a conserved family of genes that have remained linked on the same chromosome for hundreds of millions of years. The TF gene is a member of a primitive family of genes which has remained chromosomally linked and structurally homologous. Each gene in the transferrin family encodes conserved sequences of the proteins that probably contribute to the iron-binding functions and contains conserved chromosomal DNA in the promoter regions that account for tissue-specific expression. The TF gene appears to be active in autocrine systems where a cell is stimulated by a factor which it synthesizes and to which it contains a receptor. This chapter concludes that analysis of TF gene expression in every possible cell type throughout development into the aging process offers a promising model for learning more about gene modulation.

α2-HS-glycoprotein: Expression in chondrocytes and augmentation of alkaline phosphatase and phospholipase A2 activity

Abstract The α 2 -HS-glycoprotein is a plasma protein synthesized in liver and enriched in bone. The concentration of α 2 -HS-glycoprotein dynamically changes in various physiological conditions and is highest in bone during growth, suggesting that it is involved in regulation of endochondral ossification. Northern blot analysis demonstrated that mRNA transcripts from growth zone and resting zone costochondral chondrocyte cultures hybridized with α 2 -HS-glycoprotein cDNA. However, a difference of mRNA transcript size was observed, with chondrocyte mRNA transcripts being 2.2 kb, while mRNA isolated from liver was 1.6 kb. Presence of α 2 -HS-glycoprotein in cartilage cells was found by immuno-histochemical staining of human fetal epiphyses using anti-human α 2 -HS-glycoprotein antibody. To understand the role of α 2 -HS-glycoprotein in cartilage growth, the effects of exogenous α 2 -HS-glycoprotein were correlated with alkaline phosphatase (ALPase) and phospholipase A 2 (PA 2 ) activity in the chondrocyte cultures. Alkaline phosphatase specific activity was stimulated by α 2 -HS-glycoprotein at concentrations between 0.25 and 1.25μ/mL in the growth zone and resting zone cultures 2.7 and 2.0-fold, respectively. Matrix vesicle PA 2 activity was increased only in the growth zone chondrocyte cultures. These results suggested that α 2 -HS-glycoprotein may contribute to the regulation of the expression of the chondrocyte phenotype. Steady state mRNA levels of ALPase were analyzed in chondrocytes after additions of α 2 -HS-glycoprotein. The ALPase mRNA levels remained stationary during the stimulation of enzymatic activity, indicating that the effect of α 2 -HS-glycoprotein upon alkaline phosphatase activity is not at the transcriptional level.

Iron homeostasis in the lung

Iron is essential for many aspects of cellular function. However, it also can generate oxygen-based free radicals that result in injury to biological molecules. For this reason, iron acquisition and distribution are tightly regulated. Constant exposure to the atmosphere results in significant exposure of the lungs to catalytically active iron. The lungs have a mechanism for detoxification to prevent associated generation of oxidative stress. Those same proteins that participate in iron uptake in the gut are also employed in the lung, to transport iron intracellularly and sequester it in an inactive form within ferritin. The release of metal is expedited (as transferrin and ferritin) from lung tissue to the respiratory lining fluid for clearance by the mucocilliary pathway or to the reticuloendothelial system for long-term storage. This pathway is likely to be the major method for the control of oxidative stress presented to the respiratory tract.

TISSUE SPECIFIC EXPRESSION OF MOUSE TRANSFERRIN DURING DEVELOPMENT AND AGING

Transferrin (TF) is a major plasma protein that binds ferric iron and transports it to all target tissues of the body. This study is the first step to identify the tissue specific expression of the transferrin gene in mice during development, into maturity and throughout the aging process. The transferrin gene expresses mainly in mouse liver, the cerebral hemispheres and cerebellum. In mouse, transferrin is expressed in peritoneal macrophages and in mouse macrophage cell line MO59. At 19 days of gestation, transferrin mRNA is detected in the fetal lung, heart, stomach and kidney. TF mRNA levels increase in liver throughout gestation with maximum expression occurring at 19 days. Transferrin mRNA was detected in placentas of pregnant mice, with levels progressively increasing throughout the term of pregnancy. The levels of liver TF mRNA in mouse vary in a cyclic manner during the development increasing with the aging processes. Because of the dynamic nature of tissue requirements for transferrin during homeostasis the TF gene serves as a promising system for analyzing tissue-specific regulation in vivo during development and aging. Results from this study designate periods in the life-span of the mouse where regulatory mechanisms interacting with the TF gene appear to dynamically alter its expression.

Resistance of hypotransferrinemic mice to hyperoxia-induced lung injury

Oxidative stress plays a central role in the pathogenesis of acute and chronic pulmonary diseases. Safe sequestration of iron, which participates in the formation of the hydroxyl radical, is crucial in the lungs defense. We used a mouse line defective in the major iron transport protein transferrin to investigate the effect of aberrant iron metabolism on the lungs defense against oxidative injury. The tolerance to hyperoxic lung injury was greater in the hypotransferrinemic than in wild-type mice as documented by histopathology and biochemical indexes for lung damage. There was no increase in the levels of intracellular antioxidants, inflammatory cytokines, and heme oxygenase-1 in the hypotransferrinemic mouse lung compared with those in wild-type mice. However, there were elevated expressions of ferritin and lactoferrin in the lung of hypotransferrinemic mice, especially in the alveolar macrophages. Our results suggest that pulmonary lactoferrin and ferritin protect animals against oxidative stress, most likely via their capacity to sequester iron, and that alveolar macrophages are the key participants in iron detoxification in the lower respiratory tract.

Localization of the haptoglobin α and β genes (HPA and HPB) to human chromosome 16q22 by in situ hybridization

Human haptoglobin (Hp) is a protein that binds free hemoglobin and circulates in plasma of vertebrates as a tetrachain (αβ)2 structure. This study maps HPA and H

Mapping and conservation of the group-specific component gene in mouse

The group-specific component (GC), also known as the vitamin D-binding protein, transports vitamin D and its metabolites in plasma to target tissues throughout the body. The GC gene shares an evolutionary origin with genes encoding albumin (ALB) and alpha-fetoprotein (AFP). All three genes are descendants of an evolutionary ancestor that arose from an intragenic triplication. As a result, each gene is composed of three homologous domains. The study described here characterizes and compares mouse GC to the corresponding nucleotide and amino acid sequences of GC from human and rat. The deduced amino acid sequence of mouse GC was 78% identical to human and 91% identical to rat GC. The results suggest that, unlike the corresponding sequences in the ALB and AFP genes, chromosomal sequences encoding the first domain and the leader sequence of the GC gene have specifically been conserved throughout vertebrate evolution. Protection of domain I during evolution may correlate with an important functional aspect of its sequence. The mouse GC gene was mapped to chromosome 5, where the ALB and AFP genes are also located, demonstrating conservation of the three genes in vertebrate species.