Kasper S. Wang

Molecular Mechanisms of Early Lung Specification and Branching Morphogenesis

The “hard wiring” encoded within the genome that determines the emergence of the laryngotracheal groove and subsequently early lung branching morphogenesis is mediated by finely regulated, interactive growth factor signaling mechanisms that determine the automaticity of branching, interbranch length, stereotypy of branching, left-right asymmetry, and finally gas diffusion surface area. The extracellular matrix is an important regulator as well as a target for growth factor signaling in lung branching morphogenesis and alveolarization. Coordination not only of epithelial but also endothelial branching morphogenesis determines bronchial branching and the eventual alveolar-capillary interface. Improved prospects for lung protection, repair, regeneration, and engineering will depend on more detailed understanding of these processes. Herein, we concisely review the functionally integrated morphogenetic signaling network comprising the critical bone morphogenetic protein, fibroblast growth factor, Sonic hedgehog, transforming growth factor-β, vascular endothelial growth factor, and Wnt signaling pathways that specify and drive early embryonic lung morphogenesis.

Fibroblast growth factor 10 is critical for liver growth during embryogenesis and controls hepatoblast survival via β‐catenin activation

Fibroblast growth factor (FGF) signaling and β‐catenin activation have been shown to be crucial for early embryonic liver development. This study determined the significance of FGF10‐mediated signaling in a murine embryonic liver progenitor cell population as well as its relation to β‐catenin activation. We observed that Fgf10−/− and Fgfr2b−/− mouse embryonic livers are smaller than wild‐type livers; Fgf10−/− livers exhibit diminished proliferation of hepatoblasts. A comparison of β‐galactosidase activity as a readout of Fgf10 expression in Fgf10+/LacZ mice and of β‐catenin activation in TOPGAL mice, demonstrated peak Fgf10 expression from E9 to E13.5 coinciding with peak β‐catenin activation. Flow cytometric isolation and marker gene expression analysis of LacZ+ cells from E13.5 Fgf10+/LacZ and TOPGAL livers, respectively, revealed that Fgf10 expression and β‐catenin signaling occur distinctly in stellate/myofibroblastic cells and hepatoblasts, respectively. Moreover, hepatoblasts express Fgfr2b, which strongly suggests they can respond to recombinant FGF10 produced by stellate cells. Fgfr2b−/−/TOPGAL+/+ embryonic livers displayed less β‐galactosidase activity than livers of Fgfr2b+/+/TOPGAL+/+ littermates. In addition, cultures of whole liver explants in Matrigel or cell in suspension from E12.5 TOPGAL+/+mice displayed a marked increase in β‐galactosidase activity and cell survival upon treatment with recombinant FGF10, indicating that FGFR (most likely FGFR2B) activation is upstream of β‐catenin signaling and promote hepatoblast survival. Conclusion: Embryonic stellate/myofibroblastic cells promote β‐catenin activation in and survival of hepatoblasts via FGF10‐mediated signaling. We suggest a role for stellate/myofibroblastic FGF10 within the liver stem cell niche in supporting the proliferating hepatoblast. (HEPATOLOGY 2007.)

The anatomic pattern of biliary atresia identified at time of kasai hepatoportoenterostomy and early postoperative clearance of jaundice are significant predictors of transplant-free survival

Objective:The goals of this study were to describe the clinical and anatomic features of infants undergoing Kasai portoenterostomy (KPE) for biliary atresia (BA) and to examine associations between these parameters and outcomes. Methods:Infants enrolled in the prospective Childhood Liver Disease Research and Education Network, who underwent KPE were studied. Patients enrolled in a blinded, interventional trial were excluded from survival analysis. Primary endpoints were successful surgical drainage (total bilirubin less than 2 mg/dL within the first 3 months), transplant-free survival (Kaplan-Meier), and time to transplant/death (Cox regression). Results:KPE was performed in 244 infants (54% female; mean age: 65 ± 29 days). Transplant-free survival was 53.7% and 46.7% at 1 and 2 years post-KPE. The risk of transplant/death was significantly lower in the 45.6% of patients who achieved successful bile drainage within 3 months post-KPE (HR: 0.08, P < 0.001). The risk of transplant/death was increased in patients with porta hepatis atresia (Ohi type II and III vs type I; HR: 2.03, P = 0.030), nonpatent common bile duct (Ohi subtype: b, c, and d vs a; HR: 4.31, P = 0.022), BA splenic malformation syndrome (HR: 1.92, P = 0.025), ascites > 20 mL (HR: = 1.90, P = 0.0230), nodular liver appearance compared to firm (HR: = 1.61, P = 0.008), and age at KPE ≥ 75 days (HR: 1.73, P < 0.002). Outcome was not associated with gestational age, gender, race, ethnicity, or extent of porta hepatis dissection. Conclusion:Anatomic pattern of BA, BASM, presence of ascites and nodular liver appearance at KPE, and early postoperative jaundice clearance are significant predictors of transplant-free survival.

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.

Extrahepatic Anomalies in Infants With Biliary Atresia: Results of a Large Prospective North American Multicenter Study

The etiology of biliary atresia (BA) is unknown. Given that patterns of anomalies might provide etiopathogenetic clues, we used data from the North American Childhood Liver Disease Research and Education Network to analyze patterns of anomalies in infants with BA. In all, 289 infants who were enrolled in the prospective database prior to surgery at any of 15 participating centers were evaluated. Group 1 was nonsyndromic, isolated BA (without major malformations) (n = 242, 84%), Group 2 was BA and at least one malformation considered major as defined by the National Birth Defects Prevention Study but without laterality defects (n = 17, 6%). Group 3 was syndromic, with laterality defects (n = 30, 10%). In the population as a whole, anomalies (either major or minor) were most prevalent in the cardiovascular (16%) and gastrointestinal (14%) systems. Group 3 patients accounted for the majority of subjects with cardiac, gastrointestinal, and splenic anomalies. Group 2 subjects also frequently displayed cardiovascular (71%) and gastrointestinal (24%) anomalies; interestingly, this group had genitourinary anomalies more frequently (47%) compared to Group 3 subjects (10%). Conclusion: This study identified a group of BA (Group 2) that differed from the classical syndromic and nonsyndromic groups and that was defined by multiple malformations without laterality defects. Careful phenotyping of the patterns of anomalies may be critical to the interpretation of both genetic and environmental risk factors associated with BA, allowing new insight into pathogenesis and/or outcome. (Hepatology 2013;58:1724–1731)

Expansion of hepatic tumor progenitor cells in Pten-null mice requires liver injury and is reversed by loss of AKT2.

BACKGROUND & AIMS The tumor suppressor PTEN inhibits AKT2 signaling; both are aberrantly expressed in liver tumors. We investigated how PTEN and AKT2 regulate liver carcinogenesis. Loss of PTEN leads to spontaneous development of liver tumors from progenitor cells. We investigated how the loss of PTEN activates liver progenitor cells and induces tumorigenesis. METHODS We studied mice with liver-specific disruptions in Pten and the combination of Pten and Akt2 to investigate mechanisms of liver carcinogenesis. RESULTS PTEN loss leads to hepatic injury and establishes selective pressure for tumor-initiating cells (TICs), which proliferate to form mixed-lineage tumors. The Pten-null mice had increasing levels of hepatic injury before proliferation of hepatic progenitors. Attenuation of hepatic injury by deletion of Akt2 reduced progenitor cell proliferation and delayed tumor development. In Pten/Akt2-null mice given 3,5-diethoxycarbonyl-1,4 dihydrocollidine (DDC), we found that the primary effect of AKT2 loss was attenuation of hepatic injury and not inhibition of progenitor-cell proliferation in response to injury. CONCLUSIONS Liver carcinogenesis in Pten-null mice requires not only the transformation of TICs but selection pressure from hepatic injury and cell death, which activates TICs. Further research is required to elucidate the mechanism for hepatic injury and its relationship with TIC activation.

WNT5A Knock-Out Mouse As A New Model of Anorectal Malformation

BACKGROUND Anorectal malformations (ARM) represent a variety of congenital disorders that involve abnormal termination of the anorectum. Mutations in Shh signaling and Fgf10 produce a variety of ARM phenotypes. Wnt signaling has been shown to be crucial during gastrointestinal development. We therefore hypothesized that Wnt5a may play a role in anorectal development. METHODS Wild type (WT), Wnt5a(+/-) and Wnt5a(-/-) embryos were harvested from timed pregnant mice from E15.5 to E18.5, and analyzed for anorectal phenotype. Tissues were processed for whole-mount in situ hybridization and histology. RESULTS Wnt5a is expressed in the embryonic WT colon and rectum. Wnt5a(-/-) mutants exhibit multiple deformities including anorectal malformation. A fistula between the urinary and intestinal tracts can be identified as early as E15.5. By E18.5, the majority of the Wnt5a(-/-) mutants display a blind-ending pouch of the distal gut. CONCLUSIONS The expression pattern of Wnt5a and the ARM phenotype seen in Wnt5a(-/-) mutants demonstrate the critical role of Wnt5a during anorectal development. This study establishes a new model of ARM involving the Wnt5a pathway.

Characterization of hepatic stellate cells, portal fibroblasts, and mesothelial cells in normal and fibrotic livers

BACKGROUND & AIMS Contribution of hepatic stellate cells (HSCs), portal fibroblasts (PFs), and mesothelial cells (MCs) to myofibroblasts is not fully understood due to insufficient availability of markers and isolation methods. The present study aimed to isolate these cells, characterize their phenotypes, and examine their contribution to myofibroblasts in liver fibrosis. METHODS Liver fibrosis was induced in Collagen1a1-green fluorescent protein (Col1a1(GFP)) mice by bile duct ligation (BDL), 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet, or CCl4 injections. Combining vitamin A (VitA) lipid autofluorescence and expression of GFP and glycoprotein M6a (GPM6A), we separated HSCs, PFs, and MCs from normal and fibrotic livers by fluorescence-activated cell sorting (FACS). RESULTS Normal Col1a1(GFP) livers broadly expressed GFP in HSCs, PFs, and MCs. Isolated VitA+ HSCs expressed reelin, whereas VitA-GFP+GPM6A- PFs expressed ectonucleoside triphosphate diphosphohydrolase-2 and elastin. VitA-GFP+GPM6A+ MCs expressed keratin 19, mesothelin, and uroplakin 1b. Transforming growth factor (TGF)-β1 treatment induced the transformation of HSCs, PFs, and MCs into myofibroblasts in culture. TGF-β1 suppressed cyclin D1 mRNA expression in PFs but not in HSCs and MCs. In biliary fibrosis, PFs adjacent to the bile duct expressed α-smooth muscle actin. FACS analysis revealed that HSCs are the major source of GFP+ myofibroblasts in the injured Col1a1(GFP) mice after DDC or CCl4 treatment. Although PFs partly contributed to GFP+ myofibroblasts in the BDL model, HSCs were still dominant source of myofibroblasts. CONCLUSION HSCs, PFs, and MCs have distinct phenotypes, and PFs partly contribute to myofibroblasts in the portal triad in biliary fibrosis.

Mesodermal mesenchymal cells give rise to myofibroblasts, but not epithelial cells, in mouse liver injury

Hepatic stellate cells (HSCs) and portal fibroblasts (PFs) are believed to be the major source of myofibroblasts that participate in fibrogenesis by way of synthesis of proinflammatory cytokines and extracellular matrices. Previous lineage tracing studies using MesP1Cre and Rosa26lacZflox mice demonstrated that MesP1+ mesoderm gives rise to mesothelial cells (MCs), which differentiate into HSCs and PFs during liver development. In contrast, several in vivo and in vitro studies reported that HSCs can differentiate into other cell types, including hepatocytes, cholangiocytes, and progenitor cell types known as oval cells, thereby acting as stem cells in the liver. To test whether HSCs give rise to epithelial cells in adult liver, we determined the hepatic lineages of HSCs and PFs using MesP1Cre and Rosa26mTmGflox mice. Genetic cell lineage tracing revealed that the MesP1+ mesoderm gives rise to MCs, HSCs, and PFs, but not to hepatocytes or cholangiocytes, in the adult liver. Upon carbon tetrachloride injection or bile duct ligation surgery‐mediated liver injury, mesodermal mesenchymal cells, including HSCs and PFs, differentiate into myofibroblasts but not into hepatocytes or cholangiocytes. Furthermore, differentiation of the mesodermal mesenchymal cells into oval cells was not observed. These results indicate that HSCs are not sufficiently multipotent to produce hepatocytes, cholangiocytes, or oval cells by way of mesenchymal‐epithelial transition in vivo. Conclusion: Cell lineage tracing demonstrated that mesodermal mesenchymal cells including HSCs are the major source of myofibroblasts but do not differentiate into epithelial cell types such as hepatocytes, cholangiocytes, and oval cells. (Hepatology 2014;60:311–322)

Contemporary management of lipoblastoma

PURPOSE Lipoblastoma is a rare, benign, adipose tissue tumor. We report the largest single institution experience managing these uncommon neoplasms. METHODS We retrospectively reviewed 32 cases of lipoblastoma entered in the pathology database at our institution between January 1991 and August 2005. We conducted a comprehensive literature review of lipoblastoma and summarized the results of the largest series published. RESULTS Most patients presented with an enlarging, palpable, firm, nontender, mobile mass. The male-to-female ratio was 1.9:1. The anatomical distribution was trunk (n = 12), extremity (n = 12), groin (n = 5), and neck (n = 3). Average age at resection was 2.8 years (range, 2.6 months to 12 years). Thirty-one cases were completely excised, although 1 patient underwent staged partial excision to preserve nerve function. Chromosomal analysis performed in selected patients revealed characteristic aberrations in chromosome 8. Complications included keloid formation (n = 3), wound infection/dehiscence (n = 2), wound seroma (n = 1), and transient brachial plexus neurapraxia (n = 1). Average follow-up was 7.4 months (range, 1 day to 6.5 years); 2 patients were lost to follow-up. There were no recurrences. CONCLUSIONS A staged approach with meticulous sparing of the neurovascular bundle provides excellent functional outcome for patients with large tumors. Nonmutilating surgical excision is the treatment of choice.