ABSTRACT
UNLABELLED: Haploinsufficiency for the Notch ligand JAG1 in humans results in an autosomal-dominant, multisystem disorder known as Alagille syndrome, which is characterized by a congenital cholangiopathy of variable severity. Here, we show that on a C57BL/6 background, jagged1 heterozygous mice (Jag1(+/-) ) exhibit impaired intrahepatic bile duct (IHBD) development, decreased SOX9 expression, and thinning of the periportal vascular smooth muscle cell (VSMC) layer, which are apparent at embryonic day 18 and the first postnatal week. In contrast, mice double heterozygous for Jag1 and the glycosyltransferase, Poglut1 (Rumi), start showing a significant improvement in IHBD development and VSMC differentiation during the first week. At P30, Jag1(+/-) mice show widespread ductular reactions and ductopenia in liver and a mild, but statistically, significant bilirubinemia. In contrast, P30 Jag1/Rumi double-heterozygous mice show well-developed portal triads around most portal veins, with no elevation of serum bilirubin. Conditional deletion of Rumi in VSMCs results in progressive arborization of the IHBD tree, whereas deletion of Rumi in hepatoblasts frequently results in an increase in the number of hepatic arteries without affecting bile duct formation. Nevertheless, removing one copy of Rumi from either VSMCs or hepatoblasts is sufficient to partially suppress the Jag1(+/-) bile duct defects. Finally, all Rumi target sites of the human JAG1 are efficiently glucosylated, and loss of Rumi in VSMCs results in increased levels of full-length JAG1 and a shorter fragment of JAG1 without affecting Jag1 messenger RNA levels. CONCLUSIONS: On a C57BL/6 background, Jag1 haploinsufficiency results in bile duct paucity in mice. Removing one copy of Rumi suppresses the Jag1(+/-) bile duct phenotype, indicating that Rumi opposes JAG1 function in the liver.
Subject(s)
Bile Duct Diseases/congenital , Bile Duct Diseases/genetics , Calcium-Binding Proteins/genetics , Gene Deletion , Glucosyltransferases/genetics , Heterozygote , Intercellular Signaling Peptides and Proteins/genetics , Membrane Proteins/genetics , Animals , Humans , Jagged-1 Protein , Mice , Mice, Inbred C57BL , Serrate-Jagged ProteinsABSTRACT
RasGRP4 (Ras guanine nucleotide-releasing protein-4) is an intracellular, calcium-regulated guanine nucleotide exchange factor and diacylglycerol/phorbol ester receptor expressed in mast cells (MCs) and their progenitors. To study the function of this signaling protein in inflammatory disorders, a homologous recombination approach was used to create a RasGRP4-null C57BL/6 mouse line. The resulting transgenic animals had normal numbers of MCs in their tissues that histochemically and morphologically resembled those in WT C57BL/6 mice. MCs could also be generated from RasGRP4-null mice by culturing their bone marrow cells in IL-3-enriched conditioned medium. Despite these data, the levels of the transcripts that encode the proinflammatory cytokines IL-1ß and TNF-α were reduced in phorbol 12-myristate 13-acetate-treated MCs developed from RasGRP4-null mice. Although inflammation was not diminished in a Dermatophagoides farinae-dependent model of allergic airway disease, dextran sodium sulfate-induced colitis was significantly reduced in RasGRP4-null mice relative to similarly treated WT mice. Furthermore, experimental arthritis could not be induced in RasGRP4-null mice that had received K/BxN mouse serum. The latter findings raise the possibility that the pharmacologic inactivation of this intracellular signaling protein might be an effective treatment for arthritis or inflammatory bowel disease.
Subject(s)
Arthritis, Experimental/metabolism , Inflammatory Bowel Diseases/metabolism , Signal Transduction , ras Guanine Nucleotide Exchange Factors/metabolism , Animals , Antigens, Dermatophagoides/toxicity , Arthritis, Experimental/genetics , Arthritis, Experimental/pathology , Arthritis, Experimental/therapy , Asthma/chemically induced , Asthma/genetics , Asthma/metabolism , Asthma/pathology , Carcinogens/pharmacology , Cells, Cultured , Cytokines/genetics , Cytokines/metabolism , Cytokines/pharmacology , Inflammatory Bowel Diseases/genetics , Inflammatory Bowel Diseases/pathology , Inflammatory Bowel Diseases/therapy , Mice , Mice, Knockout , Tetradecanoylphorbol Acetate/pharmacology , ras Guanine Nucleotide Exchange Factors/geneticsABSTRACT
Although it has been shown that mast cell-deficient mice have diminished innate immune responses against bacteria, the most important immunoprotective factors secreted from activated mast cells have not been identified. Mouse mast cell protease 6 is a tetramer-forming tryptase. This serine protease is abundant in the secretory granules and is exocytosed upon bacterial challenge. Here we have described the generation of a mast cell protease-6-null mouse. Our discovery that mice lacking this neutral protease cannot efficiently clear Klebsiella pneumoniae from their peritoneal cavities reveals an essential role for this serine protease, and presumably its human ortholog, in innate immunity.
