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PubMed2003

Increased expression of ceruloplasmin in the retina following photic injury.

PURPOSE: Oxidative stress plays a role in the photic injury model of retinal degeneration and in age-related macular degeneration. Our preliminary microarray analysis of retinal gene expression upon photic injury suggested increased expression of ceruloplasmin, a ferroxidase that could reduce retinal oxidative stress. Patients with acerul oplasminemia have retinal degeneration, indicating that ceruloplasmin is necessary for maintenance of retinal health. The purpose of this study was to determine whether retinal ceruloplasmin is upregulated following photo-oxidation, to localize ceruloplasmin protein, and to determine which ceruloplasmin isoform is present in the retina. METHODS: Balb/c mice were exposed to bright white light for seven hours. TUNEL labeling was used to detect photoreceptor apoptosis. At several intervals after the light injury, retinal ceruloplasmin was studied by quantitative PCR, immunohistochemistry, and western analysis. Expression of the secreted and expression of the membrane-anchored glycosyl phosphatidyl inositol (GPI) linked forms of ceruloplasmin were assesed in rat retina using primers specific for each form. Vitreous ceruloplasmin was detected by immunohistochemistry in Balb/c mouse eyes and by western analysis of aspirated vitreous from post-mortem human eyes. RESULTS: Retinal ceruloplasmin mRNA was upregulated eight-fold following photic injury. Ceruloplasmin protein was detected throughout normal retinas by immunohistochemistry, with a specific increase in Muller cell labeling following photic injury. Western analysis confirmed an increase in ceruloplasmin protein following photic injury and revealed eight-fold more ceruloplasmin protein in normal retina than in brain. The mRNAs for both the secreted and GPI linked forms of ceruloplasmin were detected by RT-PCR in the retina. Ceruloplasmin protein was detected by western analysis of normal human vitreous and was increased in mouse vitreous following photic injury. CONCLUSIONS: Ceruloplasmin, a retinal ferroxidase, is upregulated at the mRNA and protein levels upon light damage. The increased protein is primarily in Muller cells. Ceruloplasmin is considerably more abundant in retina than in brain. The retina expresses both the GPI-linked and secreted forms of ceruloplasmin, and since vitreous ceruloplasmin increases following photic injury, some of the retinal ceruloplasmin may be secreted into the vitreous. Ceruloplasmin may protect the retina from oxidative stress by decreasing the amount of ferrous iron available to produce reactive oxygen species.

Aged↗
PubMed1991

Induction of ceruloplasmin gene expression in rat lung during inflammation and hyperoxia.

To determine the effect of inflammation on extrahepatic ceruloplasmin gene expression we examined the ceruloplasmin mRNA content of adult rat tissues after endotoxin injection. Within 8 h of a dose of endotoxin ceruloplasmin mRNA content increased in the liver as expected and was also detectable in the lung. The effect of endotoxin was tissue specific because ceruloplasmin mRNA was not consistently detected in other extrahepatic tissues. The kinetics of ceruloplasmin mRNA accumulation in lung and liver tissue were similar with a maximum seven- to ninefold increase in ceruloplasmin mRNA content in each tissue within 24 h. The relative rate of ceruloplasmin gene transcription was increased in both tissues within 3 h of endotoxin, suggesting similar mechanisms of regulation of ceruloplasmin gene expression during inflammation. One cellular site of ceruloplasmin production in the inflamed lung was found to be the alveolar macrophage, which expressed the ceruloplasmin gene and synthesized ceruloplasmin protein in response to endotoxin in vitro. Because of these findings we also examined the effects of hyperoxia on ceruloplasmin gene expression. Exposure of adult rats to 95% O2 resulted in a five- to sixfold induction of ceruloplasmin mRNA in lung tissue within 46 h, and this response was time dependent, reaching maximum values at 86 h. Hyperoxic induction of ceruloplasmin mRNA was specific to the lung and not the result of systemic inflammation because hepatic ceruloplasmin mRNA content remained constant. These data indicate that the lung is a prominent site of ceruloplasmin gene expression during inflammation and hyperoxia and suggest that this protein may play a previously unappreciated role in pulmonary injury or repair.

Animals↗
PubMed1996

Role of endogenous ceruloplasmin in low density lipoprotein oxidation by human U937 monocytic cells.

Oxidation of lipids and lipoproteins by macrophages is an important event during atherogenesis. Activation of monocytic cells by zymosan and other agonists results in the release of multiple oxidant species and consequent oxidation of LDL. We now show evidence that ceruloplasmin, a copper-containing acute phase reactant, is secreted by zymosan-activated U937 monocytic cells, and that the protein has an important role in LDL oxidation by these cells. In one approach, ceruloplasmin has been shown to exhibit oxidant activity under the appropriate conditions. Exogenous addition of purified human ceruloplasmin stimulates U937 cell oxidation of LDL to nearly the same extent as activation by zymosan. In contrast to previous cell-free experiments (Ehrenwald, E., G.M. Chisom, and P.L. Fox. 1994. Intact human ceruloplasmin oxidatively modifies low density lipoprotein. J. Clin. Invest. 93:1493-1501.) in which ceruloplasmin by itself (in PBS) oxidizes LDL, under the conditions of the current experiments (in RPMI 1640 medium) ceruloplasmin only oxidizes LDL in the presence of cells; the mechanism by which cells overcome the inhibition by medium components has not been ascertained. As further evidence for a role of ceruloplasmin, activation of U937 cells with zymosan induces ceruloplasmin mRNA and ceruloplasmin protein synthesis after a 5-6 h lag that is consistent with that preceding LDL oxidation. Finally, neutralization by a highly specific polyclonal antibody to human ceruloplasmin inhibits LDL oxidation by at least 65%. Moreover, multiple antisense oligodeoxynucleotides targeted to different regions of the ceruloplasmin mRNA block LDL oxidation by up to 95%. The specific action of the antisense oligonucleotides has been verified by showing inhibition of ceruloplasmin synthesis and by the ability of exogenous ceruloplasmin to overcome the inhibition. In summary, these results are consistent with a mechanism in which cell-derived ceruloplasmin participates in oxidation of LDL by U937 monocytic cells. The data also show that cellular factors in addition to ceruloplasmin, possibly active oxygen species and/or lipoxygenases, are essential and act synergistically with ceruloplasmin to oxidize LDL.

Base Sequence↗
PubMed1970

The role of ceruloplasmin in iron metabolism.

The importance of ceruloplasmin in iron metabolism was studied in swine made hypoceruloplasminemic by copper deprivation. When the plasma ceruloplasmin level fell below 1% of normal, cell-to-plasma iron flow became sufficiently impaired to cause hypoferremia, even though total body iron stores were normal. When ceruloplasmin was administered to such animals, plasma iron increased immediately and continued to rise at a rate proportional to the logarithm of the ceruloplasmin dose. The administration of inorganic copper induced increases in plasma iron only after ceruloplasmin appeared in the circulation. Thus, ceruloplasmin appeared to be essential to the normal movement of iron from cells to plasma. Studies designed to define the mechanism of action of ceruloplasmin were based on the in vitro observation that ceruloplasmin behaves as an enzyme (ferroxidase) that catalyzes oxidation of ferrous iron. Retention of injected ferrous iron in the plasma of ceruloplasmin-deficient swine was significantly less than that of ferric iron, reflecting impaired transferrin iron binding. Rat ceruloplasmin, which has little ferroxidase activity, was much less effective than porcine or human ceruloplasmin in inducing increases in plasma iron. These observations suggest that ceruloplasmin acts by virtue of its ferroxidase activity. Eight patients with Wilson's disease were evaluated in order to investigate iron metabolism in a disorder characterized by reduced ceruloplasmin levels. Evidence of iron deficiency was found in six of these, and in five of the six, plasma ceruloplasmin was less than 5% of normal. In comparison, the two patients without evidence of iron deficiency had ceruloplasmin levels of 11 and 18% of normal. It is suggested that iron deficiency tends to occur in those patients with Wilson's disease who have the severest degrees of hypoceruloplasminemia, possibly because of defective transfer of iron from intestinal mucosal cells to plasma.

Animals↗
PubMed1998

Evidence for a protein-protein complex during iron loading into ferritin by ceruloplasmin.

The formation of a protein-protein complex for the loading of iron into ferritin by ceruloplasmin was investigated. Ferritin stimulated the ferroxidase activity of ceruloplasmin unless the ferritin was fully loaded, in which case it inhibited the ferroxidase activity of ceruloplasmin. The apparent association constant for the interaction of ferritin and ceruloplasmin was 24 nM. Isothermal titration calorimetry indicated that the interaction of ceruloplasmin and ferritin was endothermic, driven by positive changes in entropy. The association constants for complex formation between ferritin and ceruloplasmin were 4.5 +/- 0.7 x 10(5) and 9.5 +/- 0.3 x 10(4) M-1 for the reduced and oxidized forms of ceruloplasmin, respectively. The oxidized form of ceruloplasmin was retained on an affinity column with ferritin immobilized as the ligand and remained bound to the column with mobile phases of increased hydrophobicity, but was eluted with increased ionic strength. The ability of ceruloplasmin to remain bound to the affinity resin was affected by the species from which ceruloplasmin was isolated. Gradient ultracentrifugation also provided evidence that the two proteins were associated, since ferritin promoted migration of ceruloplasmin through the gradient. Including ferrous iron in the gradient resulted in reduction of ceruloplasmin and increased the mobility of ceruloplasmin with ferritin. These data provide evidence that ferritin and ceruloplasmin form a protein-protein complex during iron loading into ferritin, which may limit redox cycling of iron in vivo.

Animals↗
PubMed2000

Milk ceruloplasmin and its expression by mammary gland and liver in pigs.

Concentrations of ceruloplasmin and copper in milk and blood plasma, the nature of milk ceruloplasmin, and the effects of lactation and gestation on these parameters, as well as the expression of ceruloplasmin mRNA by the mammary gland, were examined in pigs. As seen previously in humans, ceruloplasmin and copper concentrations in sow milk were much higher a few days after birth than 1 month later, averaging 26.5 and 6.6 mg ceruloplasmin/L (by immunoassay) and 1.67 and 0.34 mg total Cu/L, on days 3 and 33 postpartum, respectively. Values for ceruloplasmin oxidase activity (measured with p-phenylene diamine) were 7.8 and 1.3 nmol/min/L, respectively. Daily milk ceruloplasmin production went from 61 to 22 mg/day and daily copper output from 38 to 12 mg/day. In contrast, there was little or no variation in serum ceruloplasmin concentration during lactation or gestation, although total plasma copper was high at the end of gestation. Milk ceruloplasmin was of the same apparent size as serum ceruloplasmin, as determined by SDS-PAGE and immunoblotting, and ceruloplasmin mRNAs of liver and mammary gland were indistinguishable by Northern analysis and RT-PCR of the various exons. Expression of total RNA and ceruloplasmin mRNA, as detected in biopsies of mammary gland, increased markedly upon onset of lactation and then declined during the next month in conjunction with a drop in milk ceruloplasmin production. The results indicate that milk ceruloplasmin, while being the same protein as in plasma, is not derived from the plasma but is produced by the mammary gland.

Age Factors↗