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Kai Schönig

Publications and source records attributed to Kai Schönig.

6 recordsLinked to original sources
PubMed2006

Tissue-specific expression of ferritin H regulates cellular iron homoeostasis in vivo.

Ferritin is a ubiquitously distributed iron-binding protein. Cell culture studies have demonstrated that ferritin plays a role in maintenance of iron homoeostasis and in the protection against cytokine- and oxidant-induced stress. To test whether FerH (ferritin H) can regulate tissue iron homoeostasis in vivo, we prepared transgenic mice that conditionally express FerH and EGFP (enhanced green fluorescent protein) from a bicistronic tetracycline-inducible promoter. Two transgenic models were explored. In the first, the FerH and EGFP transgenes were controlled by the tTA(CMV) (Tet-OFF) (where tTA and CMV are tet transactivator protein and cytomegalovirus respectively). In skeletal muscle of mice bearing the FerH/EGFP and tTA(CMV) transgenes, FerH expression was increased 6.0+/-1.1-fold (mean+/-S.D.) compared with controls. In the second model, the FerH/EGFP transgenes were controlled by an optimized Tet-ON transactivator, rtTA2(S)-S2(LAP) (where rtTA is reverse tTA and LAP is liver activator protein), resulting in expression predominantly in the kidney and liver. In mice expressing these transgenes, doxycycline induced FerH in the kidney by 14.2+/-4.8-fold (mean+/-S.D.). Notably, increases in ferritin in overexpressers versus control littermates were accompanied by an elevation of IRP (iron regulatory protein) activity of 2.3+/-0.9-fold (mean+/-S.D.), concurrent with a 4.5+/-2.1-fold (mean+/-S.D.) increase in transferrin receptor, indicating that overexpression of FerH is sufficient to elicit a phenotype of iron depletion. These results demonstrate that FerH not only responds to changes in tissue iron (its classic role), but can actively regulate overall tissue iron balance.

Animals↗
PubMed2005

Chronic hepcidin induction causes hyposideremia and alters the pattern of cellular iron accumulation in hemochromatotic mice.

We report the generation of a tetracycline-regulated (Tet ON) transgenic mouse model for acute and chronic expression of the iron regulatory peptide hepcidin in the liver. We demonstrate that short-term and long-term tetracycline-dependent activation of hepcidin in adult mice leads to hypoferremia and iron-limited erythropoiesis, respectively. This clearly establishes the key role of hepcidin in regulating the extracellular iron concentration. We previously demonstrated that, when expressed early in fetal development, constitutive transgenic hepcidin expression prevented iron accumulation in an Hfe-/- mouse model of hemochromatosis. We now explore the effect of chronic hepcidin expression in adult Hfe-/- mice that have already developed liver iron overload. We demonstrate that induction of chronic hepcidin expression in 2-month-old Hfe-/- mice alters their pattern of cellular iron accumulation, leading to increased iron in tissue macrophages and duodenal cells but less iron in hepatocytes. These hepcidin-induced changes in the pattern of cellular iron accumulation are associated with decreased expression of the iron exporter ferroportin in macrophages but no detectable alteration of ferroportin expression in the hepatocytes. We speculate that this change in iron homeostasis could offer a therapeutic advantage by protecting against damage to parenchymal cells.

Animals↗
PubMed2003

Conditional tetracycline-regulated expression of TGF-beta1 in liver of transgenic mice leads to reversible intermediary fibrosis.

Based on the tetracycline-regulated gene expression system, a double-transgenic mouse model for liver fibrosis was established in which the expression of transforming growth factor beta1 (TGF-beta1) can be regulated deliberately by addition or removal of doxycycline hydrochloride to the drinking water. TGF-beta1 plasma levels in induced double-transgenic mice reached values ranging from 250 to 1,200 ng/mL, being 10 to 30 times above the normal plasma levels. By applying a cyclic induction-deinduction protocol, deleterious effects of the high plasma TGF-beta1 levels were overcome. By using this protocol, liver fibrosis occurred within a few cycles and progressed further to an intermediary fibrosis when cyclic induction was continued. On histochemical staining, a marked perisinusoidal deposition of extracellular matrix was detected accompanied by the activation of hepatic stellate cells as shown by alpha-smooth muscle actin (alpha-SMA) expression. Apoptosis of hepatocytes was prominent in TGF-beta1 high producers, leading to a decreasing number of TGF-beta1-expressing cells with time. No compensatory proliferation of hepatocytes could be detected. In advanced stages, fibrogenesis could be stopped by switching off TGF-beta1 production and reversal of fibrosis could be shown by (immuno)histochemistry within 6 to 21 days. Determination of messenger RNA (mRNA) levels of procollagen I and III, laminin (B1), matrix metalloproteinase (MMP)-2, -9, and -13, and tissue inhibitor of matrix metalloproteinase (TIMP)-1 and -2 by real-time reverse-transcription polymerase chain reaction (RT-PCR) provided insight into some mechanistic details of the fibrogenic process and its reversal. In conclusion, this model will enable the analysis of fibrogenesis at progressive stages and help in elucidating the cellular changes during development and regression of liver fibrosis caused by elevated TGF-beta1 expression.

Animals↗
PubMed2003

Use of the tetracycline system for inducible protein synthesis in the kidney.

The great advantage of the tetracycline-inducible system lies in its ability to address a large variety of biological questions in a time-dependent and tissue-specific manner. This study describes a transgenic mouse line, rTA(LAP)-1, which produces the reverse tetracycline transactivator under control of the liver activator protein (LAP) promoter. Two reporter lines with luciferase and LacZ reporter genes were used to demonstrate predominant expression in the kidney and liver when doxycycline was added to the drinking water. In the kidney, transgene expression was found primarily in cortical proximal tubules. No luciferase and beta-galactosidase activity was detected in mice without doxycycline in the drinking water, which attests to the tight control of this system. One of the advantages of the tet system lies in its reversibility, and indeed, a virtually complete remission of transgene activity in both the kidney and liver was observed when doxycycline was withdrawn. Also examined was transactivator activity during development by exposing the mothers producing the reverse transactivator to doxycycline before mating. Transgene activity was detected in newborn kidneys and liver, indicating that sufficient amounts of doxycycline had crossed the placental barrier. During nephron development, the LAP promoter appeared to be only active in the more mature proximal tubules. Finally, the rTA(LAP)-1 line was used to inducibly express the human PKD2 cDNA in proximal tubules of transgenic mice, but no cystic changes were detected, even after 6 mo of induction.

Alkaline Phosphatase↗
PubMed2002

Stringent doxycycline dependent control of CRE recombinase in vivo.

The strategy of modulating gene activities in vivo via CRE/loxP recombination would greatly profit from subjecting the recombination event to an independent and stringent temporal control. Here, we describe a transgenic mouse line, LC-1, where the expression of the cre and luciferase gene is tightly controlled by the Tet system. Using the R26R mouse line as indicator for CRE activity, and mouse lines expressing tetracycline controlled transactivators (tTA/rtTA) in various tissues, we show that; (i) in the non-induced state CRE recombinase is tightly controlled throughout the development and adulthood of an animal; (ii) upon induction, efficient recombination occurs in the adult animal in all tissues where tTA/rtTA is present, including hepatocytes, kidney cells, neurons and T lymphocytes; and (iii) no position effect appears to be caused by the LC-1 locus. Moreover, using the novel rTA(LAP)-1 mouse line, we show that in hepatocytes, complete deletion of the loxP-flanked insert in R26R animals is achieved less than 48 h after induction. Thus, the LC-1 mouse appears suitable for exploiting two rapidly increasing collections of mouse lines of which one provides tTA/rtTA in specific cell types/tissues, and the other a variety of loxP-flanked genes.

Animals↗