Mice with targeted disruption of the fatty acid transport protein 4 (Fatp 4, Slc27a4) gene show features of lethal restrictive dermopathy.

The fatty acid transport protein family is a group of evolutionarily conserved proteins that are involved in the cellular uptake and metabolism of long and very long chain fatty acids. However, little is known about their respective physiological roles. To analyze the functional significance of fatty acid transport protein 4 (Fatp4, Slc27a4), we generated mice with a targeted disruption of the Fatp4 gene. Fatp4-null mice displayed features of a neonatally lethal restrictive dermopathy. Their skin was characterized by hyperproliferative hyperkeratosis with a disturbed epidermal barrier, a flat dermal-epidermal junction, a reduced number of pilo-sebaceous structures, and a compact dermis. The rigid skin consistency resulted in an altered body shape with facial dysmorphia, generalized joint flexion contractures, and impaired movement including suckling and breathing deficiencies. Lipid analysis demonstrated a disturbed fatty acid composition of epidermal ceramides, in particular a decrease in the C26:0 and C26:0-OH fatty acid substitutes. These findings reveal a previously unknown, essential function of Fatp4 in the formation of the epidermal barrier.

Model Based Targeting of IL-6-Induced Inflammatory Responses in Cultured Primary Hepatocytes to Improve Application of the JAK Inhibitor Ruxolitinib.

IL-6 is a central mediator of the immediate induction of hepatic acute phase proteins (APP) in the liver during infection and after injury, but increased IL-6 activity has been associated with multiple pathological conditions. In hepatocytes, IL-6 activates JAK1-STAT3 signaling that induces the negative feedback regulator SOCS3 and expression of APPs. While different inhibitors of IL-6-induced JAK1-STAT3-signaling have been developed, understanding their precise impact on signaling dynamics requires a systems biology approach. Here we present a mathematical model of IL-6-induced JAK1-STAT3 signaling that quantitatively links physiological IL-6 concentrations to the dynamics of IL-6-induced signal transduction and expression of target genes in hepatocytes. The mathematical model consists of coupled ordinary differential equations (ODE) and the model parameters were estimated by a maximum likelihood approach, whereas identifiability of the dynamic model parameters was ensured by the Profile Likelihood. Using model simulations coupled with experimental validation we could optimize the long-term impact of the JAK-inhibitor Ruxolitinib, a therapeutic compound that is quickly metabolized. Model-predicted doses and timing of treatments helps to improve the reduction of inflammatory APP gene expression in primary mouse hepatocytes close to levels observed during regenerative conditions. The concept of improved efficacy of the inhibitor through multiple treatments at optimized time intervals was confirmed in primary human hepatocytes. Thus, combining quantitative data generation with mathematical modeling suggests that repetitive treatment with Ruxolitinib is required to effectively target excessive inflammatory responses without exceeding doses recommended by the clinical guidelines.

Novel Endothelial Cell-Specific AQP1 Knockout Mice Confirm the Crucial Role of Endothelial AQP1 in Ultrafiltration during Peritoneal Dialysis.

The water channel aquaporin-1 (AQP1) mediates about 50% ultrafiltration during a 2-hour hypertonic dwell in global AQP1 knockout (AQP1-/-) mice. Although AQP1 is widely expressed in various cell types including mesothelial cells, the ultrafiltration has been assumed to be mediated via endothelial AQP1 of the peritoneum. The partial embryonic lethality and reduced body weight in AQP1-/- mice may reflect potential confounding phenotypic effects evoked by ubiquitous AQP1 deletion, which may interfere with functional analysis of endothelial AQP1. Using a Cre/loxP approach, we generated and characterised endothelial cell- and time-specific AQP1 knockout (AQP1fl/fl; Cdh5-Cre+) mice. Compared to controls, AQP1fl/fl; Cdh5-Cre+ mice showed no difference in an initial clinical and biological analysis at baseline, including body weight and survival. During a 1-hour 3.86% mini-peritoneal equilibration test (mini-PET), AQP1fl/fl; Cdh5-Cre+ mice exhibited strongly decreased indices for AQP1-related transcellular water transport (43.0% in net ultrafiltration, 93.0% in sodium sieving and 57.9% in free water transport) compared to controls. The transport rates for small solutes of urea and glucose were not significantly altered. Our data provide the first direct experimental evidence for the functional relevance of endothelial AQP1 to the fluid transport in peritoneal dialysis and thereby further validate essential predictions of the three-pore model of peritoneal transport.

Iron overload in adult Hfe-deficient mice independent of changes in the steady-state expression of the duodenal iron transporters DMT1 and Ireg1/ferroportin.

Patients suffering from hereditary hemochromatosis (HH) show progressive iron overload as a consequence of increased duodenal iron absorption. It has been hypothesized that mutations in the HH gene HFE cause misprogramming of the duodenal enterocytes towards a paradoxical iron-deficient state, resulting in increased iron transporter expression. Previous reports concerning gene expression levels of the duodenal iron transporters DMT1 and IREG1 in HH patients and animal models are controversial, however, and in many cases only mRNA expression levels were investigated. To analyze the duodenal expression of DMT1, Ireg1, Dcytb, and hephaestin and the association with iron overload in adult Hfe(-/-) mice, an Hfe(-/-) mouse line was generated. Duodenal DMT1 and Ireg1 protein levels, duodenal DMT1, Ireg1, Dcytb, hephaestin, and TfR1 mRNA levels, and hepatic hepcidin mRNA levels were quantified and the correlation to liver iron contents was calculated. We report that duodenal DMT1 and Ireg1 mRNA levels and DMT1 and Ireg1 protein levels remained unaffected by the Hfe deletion. Furthermore, duodenal hephaestin and TfR1 mRNA expression and hepatic hepcidin mRNA expression remained unaltered, while the duodenal mRNA expression of the brush border ferric reductase Dcytb was significantly increased in Hfe(-/-) mice. We found no correlation between the expression level of any of the analyzed transcripts and the liver iron content. In conclusion, the lack of correlation between DMT1 and Ireg1 protein expression and the liver iron content suggests that elevated duodenal iron transporter expression is not required for high liver iron overload. Hfe(-/-) mice do not necessarily display features of iron deficiency in the duodenum, indicated by an increase in mRNA and protein levels of DMT1 and Ireg1. Rather, the duodenal ferric reductase Dcytb may act as a possible mediator of iron overload in Hfe deficiency.

Aloxe3 knockout mice reveal a function of epidermal lipoxygenase-3 as hepoxilin synthase and its pivotal role in barrier formation.

Loss-of-function mutations in the lipoxygenase (LOX) genes ALOX12B and ALOXE3 are the second most common cause of autosomal recessive congenital ichthyosis. The encoded proteins, 12R-LOX and epidermal LOX-3 (eLOX-3), act in sequence to convert fatty acid substrates via R-hydroperoxides to specific epoxyalcohol derivatives and have been proposed to operate in the same metabolic pathway during epidermal barrier formation. Here, we show that eLOX-3 deficiency in mice results in early postnatal death, associated with similar but somewhat less severe barrier defects and morphological changes than reported earlier for the 12R-LOX-knockout mice. Skin lipid analysis demonstrated that the severity of barrier failure is related to the loss of covalently bound ceramides in both 12R-LOX- and eLOX-3-null mice, confirming a proposed functional linkage of the LOX pathway to ceramide processing and formation of the corneocyte lipid envelope. Furthermore, analysis of free oxygenated fatty acid metabolites revealed strongly reduced levels of hepoxilin metabolites in eLOX-3-deficient epidermis, indicating an additional function of eLOX-3 in mammalian skin as a hepoxilin synthase linked to the 12S-LOX pathway.

Germ line transmission and expression of an RNAi cassette in mice generated by a lentiviral vector system.

We have used a lentiviral delivery system (LentiLox3.7) to generate transgenic mice harbouring RNA interference (RNAi) against the hepatocyte nuclear factor 4 gamma (HNF4gamma). HNF4gamma is a nuclear receptor with unknown function. Our analyses performed on founder (F(0)) and first generation (F(1)) mice revealed mosaicism in F(0) founders and a low efficiency of transgenesis (6%) in F(1) mice. These data, together with the observation of multiple silenced transgenes, do not favour the use of LentiLox3.7 lentivirus for transgenesis. Despite the low efficiency of transgenesis, we achieved a tissue-dependent knockdown of HNF4gamma expression in some mice.

Multiple epigenetic maintenance factors implicated by the loss of Mll2 in mouse development.

Epigenesis is the process whereby the daughters of a dividing cell retain a chromatin state determined before cell division. The best-studied cases involve the inheritance of heterochromatic chromosomal domains, and little is known about specific gene regulation by epigenetic mechanisms. Recent evidence shows that epigenesis pivots on methylation of nucleosomes at histone 3 lysines 4, 9 or 27. Bioinformatics indicates that mammals have several enzymes for each of these methylations, including at least six histone 3 lysine 4 methyltransferases. To look for evidence of gene-specific epigenetic regulation in mammalian development, we examined one of these six, Mll2, using a multipurpose allele in the mouse to ascertain the loss-of-function phenotype. Loss of Mll2 slowed growth, increased apoptosis and retarded development, leading to embryonic failure before E11.5. Using chimera experiments, we demonstrated that Mll2 is cell-autonomously required. Evidence for gene-specific regulation was also observed. Although Mox1 and Hoxb1 expression patterns were correctly established, they were not maintained in the absence of Mll2, whereas Wnt1 and Otx2 were. The Mll2 loss-of-function phenotype is different from that of its sister gene Mll, and they regulate different Hox complex genes during ES cell differentiation. Therefore, these two closely related epigenetic factors play different roles in development and maintain distinct gene expression patterns. This suggests that other epigenetic factors also regulate particular patterns and that development entails networks of epigenetic specificities.

A reliable lacZ expression reporter cassette for multipurpose, knockout-first alleles.

Alteration of the mouse genome through homologous recombination in embryonic stem (ES) cells is the most accurate and versatile way to dissect gene function in a vertebrate model. Most often, a selectable marker is used to create a knockout allele by replacing an essential part of the gene. However, knockout strategies are limited because the mutation is present constitutively. Conditional approaches based on the Cre-loxP site-specific recombination (SSR) system address this limitation; however, it requires that all parts of the targeted gene remain in ES cells. Here we report success with a "knockout-first" strategy that ablates gene function by insertion of RNA processing signals without deletion of any of the target gene. Incorporation of site-specific recombination target sites creates a multipurpose allele for both knockout and conditional applications.