Jaime Chu

New school in liver development: Lessons from zebrafish†

There is significant overlap in the genes and pathways that control liver development and those that regulate liver regeneration, hepatic progenitor cell expansion, response to injury, and cancer. Additionally, defects in liver development may underlie some congenital and perinatal liver diseases. Thus, studying hepatogenesis is important for understanding not only how the liver forms, but also how it functions. Elegant work in mice has uncovered a host of transcription factors and signaling molecules that govern the early steps of hepatic specification; however, the inherent difficulty of studying embryogenesis in utero has driven developmental biologists to seek new systems. The rapidly developing vertebrate zebrafish is a favorite model for embryology. The power of forward genetic screens combined with live real‐time imaging of development in transparent zebrafish embryos has highlighted conserved processes essential for hepatogenesis and has uncovered some exciting new players. This review presents the advantages of zebrafish for studying liver development, underscoring how studies in zebrafish and mice complement each other. In addition to their value for studying development, zebrafish models of hepatic and biliary diseases are expanding, and using these small, inexpensive embryos for drug screening has become de rigueur. Zebrafish provide a shared platform for developmental biology and translational research, offering innovative methods for studying liver development and disease. The story of hepatogenesis has something for everyone. It involves transcriptional regulation, cell‐cell interaction, signaling pathways, control of cell proliferation and apoptosis, plus morphogenic processes that sculpt vasculature, parenchymal cells, and mesenchyme to form the multifaceted liver. Decades of research on liver development in mice and other vertebrates offer valuable lessons in how the multipotent endoderm is programmed to form a functional liver. Of equal importance are insights that have illuminated the mechanisms by which hepatic progenitors are activated in a damaged liver, how the adult liver regenerates, and, possibly, the basis for engineering liver cells in vitro for cell transplantation to sustain patients with liver failure. Moreover, processes that are key to liver development are often co‐opted during pathogenesis. Therefore, reviewing hepatogenesis is informative for both basic and translational researchers. In this review, we bring to light the many advantages offered by the tropical freshwater vertebrate zebrafish (Danio rerio) in studying hepatogenesis. By comparing zebrafish and mice, we highlight how work in each system complements the other and emphasize novel paradigms that have been uncovered using zebrafish. Finally, we highlight exciting efforts using zebrafish to model hepatobiliary diseases. (HEPATOLOGY 2009.)

UHRF1 phosphorylation by cyclin A2/cyclin-dependent kinase 2 is required for zebrafish embryogenesis.

Although UHRF1 is essential for many epigenetic marks, the mechanism that regulates UHRF1 is not understood. This study shows that a key component of the cell cycle machinery—cyclin-dependent kinase 2/cyclin A2—phosphorylates UHRF1 and that this phosphorylation is essential for early zebrafish development.

Psychosocial outcomes for children with nonalcoholic fatty liver disease over time and compared with obese controls.

Objectives: Children with nonalcoholic fatty liver disease (NAFLD) experience compromised quality of life (QOL) akin to those with other chronic disease. Our objectives were to examine the association between NAFLD and QOL as well as other psychosocial outcomes, to compare psychosocial outcomes to obese children without known NAFLD, and to determine whether present standard care for NAFLD results in weight loss and improvement in psychosocial outcomes longitudinally. Methods: Children with NAFLD between 8 and 18 years and obese control children without known NAFLD were consented to complete a brief psychosocial battery examining depression (Childrens Depression Inventory), QOL (Pediatric Quality of Life Inventory; PedsQL), and effect of weight on self-esteem (Body-Esteem Scale for Adolescents and Adults) at baseline; and additionally for the NAFLD group after at least 6 months. Results: A total of 48 children with NAFLD and 40 obese control children were enrolled. The PedsQL scores were not significantly different but the CDI total score and subscales of negative mood, ineffectiveness, and negative self-esteem as well as all of the 3 subscales of BESAA, appearance, attribution, and weight were worse in the NAFLD group compared with obese controls. The PedsQL scores also did not change after standard care in the 33 patients with NAFLD who completed the follow-up evaluations, but the CDI score differed between those whose body mass index improved or not. Conclusions: Children with NAFLD have higher levels of depression than obese controls. Outcomes did not improve with standard care. Larger longitudinal studies and appropriate interventions are required in this area.

A zebrafish model of congenital disorders of glycosylation with phosphomannose isomerase deficiency reveals an early opportunity for corrective mannose supplementation

SUMMARY Individuals with congenital disorders of glycosylation (CDG) have recessive mutations in genes required for protein N-glycosylation, resulting in multi-systemic disease. Despite the well-characterized biochemical consequences in these individuals, the underlying cellular defects that contribute to CDG are not well understood. Synthesis of the lipid-linked oligosaccharide (LLO), which serves as the sugar donor for the N-glycosylation of secretory proteins, requires conversion of fructose-6-phosphate to mannose-6-phosphate via the phosphomannose isomerase (MPI) enzyme. Individuals who are deficient in MPI present with bleeding, diarrhea, edema, gastrointestinal bleeding and liver fibrosis. MPI-CDG patients can be treated with oral mannose supplements, which is converted to mannose-6-phosphate through a minor complementary metabolic pathway, restoring protein glycosylation and ameliorating most symptoms, although liver disease continues to progress. Because Mpi deletion in mice causes early embryonic lethality and thus is difficult to study, we used zebrafish to establish a model of MPI-CDG. We used a morpholino to block mpi mRNA translation and established a concentration that consistently yielded 13% residual Mpi enzyme activity at 4 days post-fertilization (dpf), which is within the range of MPI activity detected in fibroblasts from MPI-CDG patients. Fluorophore-assisted carbohydrate electrophoresis detected decreased LLO and N-glycans in mpi morphants. These deficiencies resulted in 50% embryonic lethality by 4 dpf. Multi-systemic abnormalities, including small eyes, dysmorphic jaws, pericardial edema, a small liver and curled tails, occurred in 82% of the surviving larvae. Importantly, these phenotypes could be rescued with mannose supplementation. Thus, parallel processes in fish and humans contribute to the phenotypes caused by Mpi depletion. Interestingly, mannose was only effective if provided prior to 24 hpf. These data provide insight into treatment efficacy and the broader molecular and developmental abnormalities that contribute to disorders associated with defective protein glycosylation.

Zebrafish in Toxicology and Environmental Health

As manufacturing processes and development of new synthetic compounds increase to keep pace with the expanding global demand, environmental health, and the effects of toxicant exposure are emerging as critical public health concerns. Additionally, chemicals that naturally occur in the environment, such as metals, have profound effects on human and animal health. Many of these compounds are in the news: lead, arsenic, and endocrine disruptors such as bisphenol A have all been widely publicized as causing disease or damage to humans and wildlife in recent years. Despite the widespread appreciation that environmental toxins can be harmful, there is limited understanding of how many toxins cause disease. Zebrafish are at the forefront of toxicology research; this system has been widely used as a tool to detect toxins in water samples and to investigate the mechanisms of action of environmental toxins and their related diseases. The benefits of zebrafish for studying vertebrate development are equally useful for studying teratogens. Here, we review how zebrafish are being used both to detect the presence of some toxins as well as to identify how environmental exposures affect human health and disease. We focus on areas where zebrafish have been most effectively used in ecotoxicology and in environmental health, including investigation of exposures to endocrine disruptors, industrial waste byproducts, and arsenic.

trappc11 is required for protein glycosylation in zebrafish and humans

The trappc11 mutation in zebrafish causes a stressed UPR, leading to fatty liver disease. This phenotype is not due to a trafficking defect but instead results from N-glycosylation defects. Hypoglycosylation and lipid accumulation are also found in patient cells with knockdown or mutated TRAPPC11 genes, suggesting a common etiology with zebrafish.

Liver transplantation for children with biliary atresia in the pediatric end‐stage liver disease era: The role of insurance status

Socioeconomic status influences health outcomes, although its impact on liver transplantation (LT) in children with biliary atresia (BA) is unknown. We hypothesized that governmental insurance [public insurance (PU)], rather than private insurance (PR), would be associated with poorer outcomes for children with BA. Children with BA who underwent first isolated LT between January 2003 and June 2011 were identified from United Network for Organ Sharing Standard Transplant Analysis and Research files. We identified 757 patients with PR and 761 patients with PU. The race/ethnicity distribution was significantly different between the groups (65% white, 12% black, and 10% Hispanic in the PR group and 33% white, 26% black, and 29% Hispanic in the PU group, P < 0.01). Wait‐list mortality was higher for the PU group versus the PR group [46/1654 (2.7%) versus 29/1895 (1.5%), P < 0.01]. PR patients were older than PU patients at transplant (2.4 ± 4.5 versus 1.5 ± 3.0 years, P < 0.01). The donor types differed between the groups: 165 children (21.8%) in the PR group received living donor grafts, whereas 79 children (10.4%) in the PU group did (P < 0.01). The 1‐ and 5‐year posttransplant patient survival rates were greater for the PR group versus the PU group (98.0% versus 94.1% at 1 year, P < 0.01; 97.8% versus 92.2% at 5 years, P < 0.01). Cox proportional hazards models revealed that the insurance type (PU), the donor type (deceased), and life support were significant risk factors for death. A separate analysis of deceased donor LT revealed that the PU group still had significantly worse patient and graft survival. In conclusion, PU coverage is an independent risk factor for significantly increased wait‐list and posttransplant mortality in children with BA. Further studies are needed to unearth the reasons for these important differences in outcomes. Liver Transpl 19:543–550, 2013.

Liver Transplantation for Biliary Atresia: Is There a Difference in Outcome for Infants?

Objectives: Liver transplantation (LT) in children with biliary atresia (BA) is often performed because of poor bile drainage, complications of biliary cirrhosis, or recurrent cholangitis. Poor bile drainage after a Kasai hepatoportoenterostomy is the primary driver for LT in infancy. The aim of the present study was to compare the clinical characteristics and outcome of first isolated liver transplantation for infants with BA who underwent transplant before 2 years of age (transplanted at infancy [TAI]) with children transplanted later in life (age 2–<18 years = transplanted at childhood [TAC]). Methods: Children with BA who underwent LT between 2002 and 2012 were identified from the United Network for Organ Sharing Standard Transplant Analysis and Research data set files. Results: A total of 1818 children underwent first isolated liver transplantation for BA (TAI 1408 [77.4%]; TAC 410 [22.6%]). One and 5-year patient survival of the TAI and TAC patients was 95.2%, 93.8%, and 97.8 %, 97.1%, respectively (P < 0.01 for both periods). One and 5-year graft survival of the TAI and TAC patients was 87.6%, 84.6 % and 93.2%, 90.7%, respectively (P < 0.01 for both periods). Removal from the waitlist for disease progression or death was significantly higher for TAI compared with TAC (120 patients [6.3%] vs 21 [3.7%], P = 0.02). Cold ischemic time was found to be the prognostic factor for death after LT in TAI, whereas being on life support was a poor prognostic factor in TAC by multivariate risk factor analysis. Conclusions: The vast majority of transplants for BA occur in children <2 years of age. Younger patients with BA had significantly higher waitlist and posttransplant mortality. Given the consistently poorer outcomes, there is an urgent need to find methods to improve bile drainage after the Kasai hepatoportoenterostomy.

Partial internal biliary diversion for Alagille syndrome: case report and review of the literature

This is a case report of the first patient with Alagille syndrome (AGS) to undergo a partial internal biliary diversion (PIBD) for the treatment of symptoms refractory to medical therapy. Alagille syndrome is a hereditary disease resulting in chronic cholestasis and hypercholesterolemia that can lead to severe and intractable pruritus and disfiguring and debilitating xanthomas. PIBD has proven to be an effective treatment option for other causes of cholestatic liver disease. This report reviews the immediate and 2-year follow-up of a patient after this surgical procedure. The results suggest that PIBD has potential to provide relief of intractable symptoms and improve the quality of life in patients with AGS while avoiding an external stoma. It does not, however, appear to prevent the progression of liver disease. Long-term follow-up is still needed.

Epstein-Barr virus-associated smooth muscle tumors in children following solid organ transplantation: a review.

EBV‐SMT are a rare entity following organ transplantation. Given the rarity of the tumor, there is no standard approach to diagnosis and treatment. A literature search identified 28 reported cases of EBV‐SMT in addition to our own experience with one case. The aim of this review is to summarize the existing data regarding pathogenesis, diagnosis, and treatment.