Kathleen M. Loomes

Endothelial expression of the Notch ligand Jagged1 is required for vascular smooth muscle development

The Notch ligand Jagged1 (Jag1) is essential for vascular remodeling and has been linked to congenital heart disease in humans, but its precise role in various cell types of the cardiovascular system has not been extensively investigated. We show that endothelial-specific deletion of Jag1 results in embryonic lethality and cardiovascular defects, recapitulating the Jag1 null phenotype. These embryos show striking deficits in vascular smooth muscle, whereas endothelial Notch activation and arterial-venous differentiation appear normal. Endothelial Jag1 mutant embryos are phenotypically distinct from embryos in which Notch signaling is inhibited in endothelium. Together, these results imply that the primary role of endothelial Jag1 is to potentiate the development of neighboring vascular smooth muscle.

Murine Jagged1/Notch signaling in the second heart field orchestrates Fgf8 expression and tissue-tissue interactions during outflow tract development

Notch signaling is vital for proper cardiovascular development and function in both humans and animal models. Indeed, mutations in either JAGGED or NOTCH cause congenital heart disease in humans and NOTCH mutations are associated with adult valvular disease. Notch typically functions to mediate developmental interactions between adjacent tissues. Here we show that either absence of the Notch ligand Jagged1 or inhibition of Notch signaling in second heart field tissues results in murine aortic arch artery and cardiac anomalies. In mid-gestation, these mutants displayed decreased Fgf8 and Bmp4 expression. Notch inhibition within the second heart field affected the development of neighboring tissues. For example, faulty migration of cardiac neural crest cells and defective endothelial-mesenchymal transition within the outflow tract endocardial cushions were observed. Furthermore, exogenous Fgf8 was sufficient to rescue the defect in endothelial-mesenchymal transition in explant assays of endocardial cushions following Notch inhibition within second heart field derivatives. These data support a model that relates second heart field, neural crest, and endocardial cushion development and suggests that perturbed Notch-Jagged signaling within second heart field progenitors accounts for some forms of congenital and adult cardiac disease.

NOTCH2 mutations in Alagille syndrome

Background Alagille syndrome (ALGS) is a dominant, multisystem disorder caused by mutations in the Jagged1 (JAG1) ligand in 94% of patients, and in the NOTCH2 receptor in <1%. There are only two NOTCH2 families reported to date. This study hypothesised that additional NOTCH2 mutations would be present in patients with clinical features of ALGS without a JAG1 mutation. Methods The study screened a cohort of JAG1-negative individuals with clinical features suggestive or diagnostic of ALGS for NOTCH2 mutations. Results Eight individuals with novel NOTCH2 mutations (six missense, one splicing, and one non-sense mutation) were identified. Three of these patients met classic criteria for ALGS and five patients only had a subset of features. The mutations were distributed across the extracellular (N=5) and intracellular domains (N=3) of the protein. Functional analysis of four missense, one nonsense, and one splicing mutation demonstrated decreased Notch signalling of these proteins. Subjects with NOTCH2 mutations demonstrated highly variable expressivity of the affected systems, as with JAG1 individuals. Liver involvement was universal in NOTCH2 probands and they had a similar prevalence of ophthalmologic and renal anomalies to JAG1 patients. There was a trend towards less cardiac involvement in the NOTCH2 group (60% vs 100% in JAG1). NOTCH2 (+) probands exhibited a significantly decreased penetrance of vertebral abnormalities (10%) and facial features (20%) when compared to the JAG1 (+) cohort. Conclusions This work confirms the importance of NOTCH2 as a second disease gene in ALGS and expands the repertoire of the NOTCH2 related disease phenotype.

Bile duct proliferation in liver‐specific Jag1 conditional knockout mice: Effects of gene dosage

The Notch signaling pathway is involved in determination of cell fate and control of cell proliferation in multiple organ systems. Jag1 encodes a ligand in the Notch pathway and has been identified as the disease‐causing gene for the developmental disorder Alagille syndrome. Evidence from the study of human disease and mouse models has implicated Jag1 as having an important role in the development of bile ducts. We have derived a conditional knockout allele (Jag1loxP) to study the role of Jag1 and Notch signaling in liver and bile duct development. We crossed Jag1loxP mice with a transgenic line carrying Cre recombinase under the control of the albumin promoter and α‐fetoprotein enhancer to ablate Jag1 in hepatoblasts. The liver‐specific Jag1 conditional knockout mice showed normal bile duct development. To further decrease Notch pathway function, we crossed the Jag1 conditional knockout mice with mice carrying the hypomorphic Notch2 allele, and bile duct anatomy remained normal. When Jag1 conditional mice were crossed with mice carrying the Jag1 null allele, the adult progeny exhibited striking bile duct proliferation. Conclusion: These results indicate that Notch signaling in the liver is sensitive to Jag1 gene dosage and suggest a role for the Notch pathway in postnatal growth and morphogenesis of bile ducts. (HEPATOLOGY 2007.)

A Novel Variant of Inpp5f Is Imprinted in Brain, and Its Expression Is Correlated with Differential Methylation of an Internal CpG Island

ABSTRACT Using a tissue-specific microarray screen in combination with chromosome anomalies in the mouse, we identified a novel imprinted gene, Inpp5f_v2 on mouse chromosome 7. Characterization of this gene reveals a 3.2-kb transcript that is paternally expressed in the brain. Inpp5f_v2 is a variant of the related 4.7-kb transcript, Inpp5f, an inositol phosphatase gene that is biallelically expressed in the mouse. Inpp5f_v2 uses an alternative transcriptional start site within an intron of Inpp5f and thus has a unique alternative first exon. Whereas other imprinted transcripts have a unique first exon located within intron 1 of a longer transcript variant (such as at the Gnas and WT1 loci), Inpp5f_v2 is the first example of which we are aware in which the alternative first exon of an imprinted gene is embedded in a downstream intron (intron 15) of a transcript variant. The CpG island associated with the nonimprinted Inpp5f gene is hypomethylated on both alleles, a finding consistent with biallelic expression, whereas the CpG island present 5′ of Inpp5f_v2 is differentially methylated on the maternal versus paternal alleles consistent with its imprinting status.

Jagged1 (JAG1) mutations in patients with tetralogy of Fallot or pulmonic stenosis.

Mutations in the Notch pathway ligand Jagged1 (JAG1) cause Alagille syndrome (AGS), as well as cardiac defects in seemingly nonsyndromic individuals. To estimate the frequency of JAG1 mutations in cases with right‐sided cardiac defects not otherwise diagnosed with AGS, we screened 94 cases with tetralogy of Fallot (TOF) and 50 with pulmonic stenosis/peripheral pulmonary stenosis (PS/PPS) or pulmonary valve atresia with intact ventricular septum (PA) for mutations. Sequence changes were identified in three TOF and three PS/PPS/PA patients, that were not present in 100 controls. We identified one frameshift and two missense mutations in the TOF cases, and one frameshift and two missense mutations in cases with PS/PPS/PA. The four missense mutations were assayed for their effect on protein localization, posttranslational modification, and ability to activate Notch signaling. The missense mutants displayed heterogeneous behavior in these assays, some with complete haploinsufficiency, suggesting that there are additional modifiers leading to organ specific features. We identified functionally significant mutations in 2% (2/94) of TOF patients and 4% (2/50) of PS/PPS/PA patients. Patients with right‐sided cardiac defects should be carefully screened for features of AGS or a family history of cardiac defects that might suggest the presence of a JAG1 mutation. Hum Mutat 31:594–601, 2010.

Notch1 and Jagged1 expression by the developing pulmonary vasculature

The molecular mechanisms of pulmonary vascular development are poorly understood. Cell‐specific developmental pathways are influenced by cell–cell signaling. Notch signaling molecules are highly conserved receptors active in many cell‐fate determination systems. Recent observations of Notch molecules and a Notch ligand, Jagged1, suggest their importance in vascular morphogenesis, and particularly pulmonary vascular development. We performed a systematic evaluation of Notch1/Jagged1 gene and protein expression in the developing mouse lung from embryonic day 11 until adulthood by using quantitative PCR, immunofluorescence, and electron microscopic analysis. mRNA transcripts for Notch1‐4 and Jagged1 increased progressively from early to later lung development, accompanied by a simultaneous rise in endothelial cell‐specific gene expression, a pattern not seen in other organs. Notch1 mRNA was identified on both epithelial and mesenchymal structures of the embryonic lung. Immunofluorescence staining revealed the progressive acquisition of Notch1 and Jagged1 proteins by the emerging endothelium. Notch1 and Jagged1 were seen initially on well‐formed, larger vessels within the embryonic lung bud and progressively on finer vascular networks. Each was also expressed on surrounding nonvascular structures. The localization of Notch1 and Jagged1 on endothelial cell surface membranes within the alveolar microvasculature was confirmed by immuno‐electron microscopy. These temporal and spatial patterns in Notch1/Jagged1 gene and protein expression suggest multiple potential paths of cell–cell signaling during lung development and vascular morphogenesis.

Use of Corticosteroids After Hepatoportoenterostomy for Bile Drainage in Infants With Biliary Atresia: The START Randomized Clinical Trial

IMPORTANCE Biliary atresia is the most common cause of end-stage liver disease in children. Controversy exists as to whether use of steroids after hepatoportoenterostomy improves clinical outcome. OBJECTIVE To determine whether the addition of high-dose corticosteroids after hepatoportoenterostomy is superior to surgery alone in improving biliary drainage and survival with the native liver. DESIGN, SETTING, AND PATIENTS The multicenter, double-blind Steroids in Biliary Atresia Randomized Trial (START) was conducted in 140 infants (mean age, 2.3 months) between September 2005 and February 2011 in the United States; follow-up ended in January 2013. INTERVENTIONS Participants were randomized to receive intravenous methylprednisolone (4 mg/kg/d for 2 weeks) and oral prednisolone (2 mg/kg/d for 2 weeks) followed by a tapering protocol for 9 weeks (n = 70) or placebo (n = 70) initiated within 72 hours of hepatoportoenterostomy. MAIN OUTCOMES AND MEASURES The primary end point (powered to detect a 25% absolute treatment difference) was the percentage of participants with a serum total bilirubin level of less than 1.5 mg/dL with his/her native liver at 6 months posthepatoportoenterostomy. Secondary outcomes included survival with native liver at 24 months of age and serious adverse events. RESULTS The proportion of participants with improved bile drainage was not statistically significantly improved by steroids at 6 months posthepatoportoenterostomy (58.6% [41/70] of steroids group vs 48.6% [34/70] of placebo group; adjusted relative risk, 1.14 [95% CI, 0.83 to 1.57]; P = .43). The adjusted absolute risk difference was 8.7% (95% CI, -10.4% to 27.7%). Transplant-free survival was 58.7% in the steroids group vs 59.4% in the placebo group (adjusted hazard ratio, 1.0 [95% CI, 0.6 to 1.8]; P = .99) at 24 months of age. The percentage of participants with serious adverse events was 81.4% [57/70] of the steroids group and 80.0% [56/70] of the placebo group (P > .99); however, participants receiving steroids had an earlier time of onset of their first serious adverse event by 30 days posthepatoportoenterostomy (37.2% [95% CI, 26.9% to 50.0%] of steroids group vs 19.0% [95% CI, 11.5% to 30.4%] of placebo group; P = .008). CONCLUSIONS AND RELEVANCE Among infants with biliary atresia who have undergone hepatoportoenterostomy, high-dose steroid therapy following surgery did not result in statistically significant treatment differences in bile drainage at 6 months, although a small clinical benefit could not be excluded. Steroid treatment was associated with earlier onset of serious adverse events in children with biliary atresia. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00294684.

Evaluation of iron overload by single voxel MRS measurement of liver T2

To overcome the difficulty of poor signal‐to‐noise ratio of magnetic resonance imaging (MRI) in evaluating heavy iron overload by using a single voxel magnetic resonance spectroscopy (MRS) technique.

Bile duct proliferation in Jag1/fringe heterozygous mice identifies candidate modifiers of the Alagille syndrome hepatic phenotype.

Alagille syndrome (AGS) is a heterogeneous developmental disorder associated with bile duct paucity and various organ anomalies. The syndrome is caused by mutations in JAG1, which encodes a ligand in the Notch signaling pathway, in the majority of cases and mutations in the NOTCH2 receptor gene in less than 1% of patients. Although a wide array of JAG1 mutations have been identified in the AGS population, these mutational variants have not accounted for the wide phenotypic variability observed in patients with this syndrome. The Fringe genes encode glycosyltransferases, which modify Notch and alter ligand‐receptor affinity. In this study, we analyzed double heterozygous mouse models to examine the Fringe genes as potential modifiers of the Notch‐mediated hepatic phenotype observed in AGS. We generated mice that were haploinsufficient for both Jag1 and one of three paralogous Fringe genes: Lunatic (Lfng), Radical (Rfng), and Manic (Mfng). Adult Jag1+/−Lfng+/− and Jag1+/−Rfng+/− mouse livers exhibited widespread bile duct proliferation beginning at 5 weeks of age and persisting up to 1 year. The Jag1+/−Mfng+/− livers showed a subtle, yet significant increase in bile duct numbers and bile duct to portal tract ratios. These abnormalities were not observed in the newborn period. Despite the portal tract expansion by bile ducts, fibrosis was not increased and epithelial to mesenchymal transition was not shown in the affected portal tracts. Conclusion: Mice heterozygous for mutations in Jag1 and the Fringe genes display striking bile duct proliferation, which is not apparent at birth. These findings suggest that the Fringe genes may regulate postnatal bile duct growth and remodeling, and serve as candidate modifiers of the hepatic phenotype in AGS. (HEPATOLOGY 2008;48:1989–1997.)