Marzena Zdanowicz

Osteopontin is induced by hedgehog pathway activation and promotes fibrosis progression in nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a leading cause of cirrhosis. Recently, we showed that NASH‐related cirrhosis is associated with Hedgehog (Hh) pathway activation. The gene encoding osteopontin (OPN), a profibrogenic extracellular matrix protein and cytokine, is a direct transcriptional target of the Hh pathway. Thus, we hypothesize that Hh signaling induces OPN to promote liver fibrosis in NASH. Hepatic OPN expression and liver fibrosis were analyzed in wild‐type (WT) mice, Patched‐deficient (Ptc+/−) (overly active Hh signaling) mice, and OPN‐deficient mice before and after feeding methionine and choline–deficient (MCD) diets to induce NASH‐related fibrosis. Hepatic OPN was also quantified in human NASH and nondiseased livers. Hh signaling was manipulated in cultured liver cells to assess direct effects on OPN expression, and hepatic stellate cells (HSCs) were cultured in medium with different OPN activities to determine effects on HSC phenotype. When fed MCD diets, Ptc+/− mice expressed more OPN and developed worse liver fibrosis (P < 0.05) than WT mice, whereas OPN‐deficient mice exhibited reduced fibrosis (P < 0.05). In NASH patients, OPN was significantly up‐regulated and correlated with Hh pathway activity and fibrosis stage. During NASH, ductular cells strongly expressed OPN. In cultured HSCs, SAG (an Hh agonist) up‐regulated, whereas cyclopamine (an Hh antagonist) repressed OPN expression (P < 0.005). Cholangiocyte‐derived OPN and recombinant OPN promoted fibrogenic responses in HSCs (P < 0.05); neutralizing OPN with RNA aptamers attenuated this (P < 0.05). Conclusion: OPN is Hh‐regulated and directly promotes profibrogenic responses. OPN induction correlates with Hh pathway activity and fibrosis stage. Therefore, OPN inhibition may be beneficial in NASH (HEPATOLOGY 2011)

Role for Hedgehog signaling in hepatic stellate cell activation and viability

Hepatic stellate cells (HSC) have a complex phenotype that includes both neural and myofibroblastic features. The Hedgehog (Hh) pathway has been shown to direct the fate of neural and myofibroblastic cells during embryogenesis and during tissue remodeling in adults. Therefore, we hypothesized that Hh signaling may regulate the fate of HSC in adults. In this study, we find that freshly isolated stellate cells from adult Patched-lacZ transgenic mice exhibit β-galactosidase activity, indicating Hh pathway activity. Transcripts of Hh ligands, the Hh pathway receptor, and Hh-regulated transcription factors are expressed by stellate cells from mice, rats, and humans. Transfection experiments in a cell line using a Hh-inducible luciferase reporter demonstrate constitutive Hh pathway activity. Moreover, neutralizing antibodies to Hh increase apoptosis, while viability is restored by treatment with Hh ligand. In vitro treatment of primary stellate cells with cyclopamine (Cyc), a pharmacologic inhibitor of the Hh pathway, inhibits activation and slightly decreases cell survival, while a single injection of Cyc into healthy adult mice reduces activation of HSC by more than 50% without producing obvious liver damage. Our findings reveal a novel mechanism, namely the Hh pathway, that regulates the activation and viability of HSC.

HEDGEHOG SIGNALING IS CRITICAL FOR NORMAL LIVER REGENERATION AFTER PARTIAL HEPATECTOMY IN MICE

Distinct mechanisms are believed to regulate growth of the liver during fetal development and after injury in adults, because the former relies on progenitors and the latter generally involves replication of mature hepatocytes. However, chronic liver injury in adults increases production of Hedgehog (Hh) ligands, developmental morphogens that control progenitor cell fate and orchestrate various aspects of tissue construction during embryogenesis. This raises the possibility that similar Hh‐dependent mechanisms also might regulate adult liver regeneration. The current analysis of murine liver regeneration after 70% partial hepatectomy (PH), an established model of adult liver regeneration, demonstrated that PH induced production of Hh ligands and activated Hh signaling in liver cells. Treatment with a specific Hh signaling inhibitor interfered with several key components of normal liver regeneration, significantly inhibiting progenitor responses, matrix remodeling, proliferation of hepatocytes and ductular cells, and restoration of liver mass. These global inhibitory effects on liver regeneration dramatically reduced survival after PH. Conclusion: Mechanisms that mediate liver organogenesis, such as Hh pathway activation, are retained and promote reconstruction of adult livers after injury. Hepatology 2010

A NOVEL ROLE FOR CARDIAC NEURAL CREST IN HEART DEVELOPMENT

Ablation of premigratory cardiac neural crest results in defective development of the cardiac outflow tract. The purpose of the present study was to correlate the earliest functional and morphological changes in heart development after cardiac neural crest ablation. Within 24 hours after neural crest ablation, the external morphology of the hearts showed straight outflow limbs, tighter heart loops, and variable dilations. Incorporation of bromodeoxyuridine in myocytes, an indication of proliferation, was doubled after cardiac neural crest ablation. The myocardial calcium transients, which are a measure of excitation-contraction coupling, were depressed by 50% in both the inflow and outflow portions of the looped heart tube. The myocardial transients could be rescued by replacing the cardiac neural crest. The cardiac jelly produced by the myocardium was distributed in an uneven, rather than uniform, pattern. An extreme variability in external morphology could be attributed to the uneven distribution of cardiac jelly. In the absence of cardiac neural crest, the myocardium was characterized by somewhat disorganized myofibrils that may be a result of abnormally elevated proliferation. In contrast, endocardial development appeared normal, as evidenced by normal expression of fibrillin-2 protein (JB3 antigen) and normal formation of cushion mesenchyme and trabeculae. The signs of abnormal myocardial development coincident with normal endocardium suggest that the presence of cardiac neural crest cells is necessary for normal differentiation and function of the myocardium during early heart development. These results indicate a novel role for neural crest cells in myocardial maturation.

Fetal alcohol exposure impairs hedgehog cholesterol modification and signaling

Consumption of alcohol by pregnant women can cause fetal alcohol spectrum defects (FASD), a congenital disease, which is characterized by an array of developmental defects that include neurological, craniofacial, cardiac, and limb malformations, as well as generalized growth retardation. FASD remains a significant clinical challenge and an important social problem. Although there has been great progress in delineating the mechanisms contributing to alcohol-induced birth defects, gaps in our knowledge still remain; for instance, why does alcohol preferentially induce a spectrum of defects in specific organs and why is the spectrum of defects reproducible and predictable. In this study, we show that exposure of zebrafish embryos to low levels of alcohol during gastrulation blocks covalent modification of Sonic hedgehog by cholesterol. This leads to impaired Hh signal transduction and results in a dose-dependent spectrum of permanent developmental defects that closely resemble FASD. Furthermore, supplementing alcohol-exposed embryos with cholesterol rescues the loss of Shh signal transduction, and prevents embryos from developing FASD-like morphologic defects. Overall, we have shown that a simple post-translational modification defect in a key morphogen may contribute to an environmentally induced complex congenital syndrome. This insight into FASD pathogenesis may suggest novel strategies for preventing these common congenital defects.

Hedgehog pathway activation parallels histologic severity of injury and fibrosis in human nonalcoholic fatty liver disease

The Hedgehog (HH)‐signaling pathway mediates several processes that are deregulated in patients with metabolic syndrome (e.g., fat mass regulation, vascular/endothelial remodeling, liver injury and repair, and carcinogenesis). The severity of nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome generally correlate. Therefore, we hypothesized that the level of HH‐pathway activation would increase in parallel with the severity of liver damage in NAFLD. To assess potential correlations between known histologic and clinical predictors of advanced liver disease and HH‐pathway activation, immunohistochemistry was performed on liver biopsies from a large, well‐characterized cohort of NAFLD patients (n = 90) enrolled in the Nonalcoholic Steatohepatitis Clinical Research Network (NASH CRN) Database 1 study. Increased HH activity (evidenced by accumulation of HH‐ligand–producing cells and HH‐responsive target cells) strongly correlated with portal inflammation, ballooning, and fibrosis stage (each P < 0.0001), supporting a relationship between HH‐pathway activation and liver damage. Pathway activity also correlated significantly with markers of liver repair, including numbers of hepatic progenitors and myofibroblastic cells (both P < 0.03). In addition, various clinical parameters that have been linked to histologically advanced NAFLD, including increased patient age (P < 0.005), body mass index (P < 0.002), waist circumference (P < 0.0007), homeostatic model assessment of insulin resistance (P < 0.0001), and hypertension (P < 0.02), correlated with hepatic HH activity. Conclusion: In NAFLD patients, the level of hepatic HH‐pathway activity is highly correlated with the severity of liver damage and with metabolic syndrome parameters that are known to be predictive of advanced liver disease. Hence, deregulation of the HH‐signaling network may contribute to the pathogenesis and sequelae of liver damage that develops with metabolic syndrome. (HEPATOLOGY 2012;55:1711–1721)

Cardiac neural crest in zebrafish embryos contributes to myocardial cell lineage and early heart function

Myocardial dysfunction is evident within hours after ablation of the cardiac neural crest in chick embryos, suggesting a role for neural crest in myocardial maturation that is separate from its role in outflow septation. This role could be conserved in an animal that does not have a divided systemic and pulmonary circulation, such as zebrafish. To test this hypothesis, we used cell marking to identify the axial level of neural crest that migrates to the heart in zebrafish embryos. Unlike the chick and mouse, the zebrafish cardiac neural crest does not originate from the axial level of the somites. The region of neural crest cranial to somite 1 was found to contribute cells to the heart. Cells from the cardiac neural crest migrated to the myocardial wall of the heart tube, where some of them expressed a myocardial phenotype. Laser ablation of the cardiac premigratory neural crest at the three‐ to four‐somite stage resulted in loss of the neural crest cells migrating to the heart as shown by the absence of AP2‐ and HNK1‐expressing cells and failure of the heart tube to undergo looping. Myocardial function was assessed 24 hr after the cardiac neural crest ablation in a subpopulation of embryos with normal heart rate. Decreased stroke volume, ejection fraction, and cardiac output were observed, indicating a more severe functional deficit in cardiac neural crest‐ablated zebrafish embryos compared with neural crest–ablated chick embryos. These results suggest a new role for cardiac neural crest cells in vertebrate cardiac development and are the first report of a myocardial cell lineage for neural crest derivatives. Developmental Dynamics 226:000–000, 2003.

Myocardial volume and organization are changed by failure of addition of secondary heart field myocardium to the cardiac outflow tract

Cardiac neural crest ablation results in primary myocardial dysfunction and failure of the secondary heart field to add the definitive myocardium to the cardiac outflow tract. The current study was undertaken to understand the changes in myocardial characteristics in the heart tube, including volume, proliferation, and cell size when the myocardium from the secondary heart field fails to be added to the primary heart tube. We used magnetic resonance and confocal microscopy to determine that the volume of myocardium in the looped heart was dramatically reduced and the compact layer of myocardium was thinner after neural crest ablation, especially in the outflow tract and ventricular regions. Proliferation measured by 5‐bromo‐2′‐deoxyuridine incorporation was elevated at only one stage during looping, cell death was normal and myocardial cell size was increased. Taken together, these results indicate that there are fewer myocytes in the heart. By incubation day 8 when the heart would have normally completed septation, the anterior (ventral) wall of the right ventricle and right ventricular outflow tract was significantly thinner in the neural crest‐ablated embryos than normal, but the thickness of the compact myocardium was normal in all other regions of the heart. The decreased volume and number of myocardial cells in the heart tube after neural crest ablation most likely reflects the amount of myocardium added by the secondary heart field. Development Dynamics 228:152–160, 2003.

Approaching Cardiac Development in Three Dimensions by Magnetic Resonance Microscopy

Cardiac neural crest (CNC) ablation in embryonic chicks leads to conotruncal anomalies of the heart as a result of altered cardiac looping. Altered looping results from failure of the myocardium from the secondary heart field to be added to the outflow tract. Various imaging techniques have been applied to visualize embryonic heart development. However, morphological abnormalities frequently cannot clearly be identified or appreciated in 2 dimensions, particularly those involving misorientation of cardiovascular structures and changes of myocardial volume. We present here 3-dimensional (3D) reconstructions of the embryonic chick heart at looping stages in sham-operated and CNC-ablated embryos acquired by magnetic resonance microscopy (MRM) using a new dual-contrast method for specimen preparation that combines perfusion fixation and immersion in fixative with a macro-molecular gadolinium-based contrast agent. In contrast to previous techniques, this method provides imaging not only of the cardiac chambers and vessel lumens but also of internal and external cardiac structures, such as the ventricular wall, myocardial trabeculations, cardiac jelly, and endocardial cushions. Furthermore, it allows morphovolumetric analysis of hearts at different stages. There is an excellent correlation between images obtained from MRM and those obtained by routine …

Analysis of Cx43α1 Promoter Function in the Developing Zebrafish Embryo

The Cx43α1 gap junctions play an important role in cardiovascular development. Studies using transgenic mouse models have indicated that this involves an essential role for Cx43α1 in modulating neural crest cell motility. We previously showed that a 6.8 kb mouse genomic sequence containing the promoter and upstream regulatory sequences of the Cx43α1 gene can drive lacZ reporter gene expression in all neural crest cell lineages in the mouse embryo. To obtain further insights into the sequence motifs and regulatory pathways involved in targeting Cx43 or 1 gene expression in neural crest cells, we assayed the activity of the mouse Cx43α 1 promoter in evolutionarily distantly related zebrafish embryos. For these studies, the 6.8kb Cx43α 1 genomic sequence and various deletion derivatives were used to generate GFP or lacZ expression vectors. The transcriptional activities of these constructs were analyzed in vivo after microinjection into one- or two- cell stage zebrafish embryos. These studies indicated that the mouse Cx43α 1 promoter can drive lacZ expression in neural crest cells in the zebrafish embryos. Analysis by whole mount in situ hybridization showed that the endogenous zebrafish Cx43α 1 gene is expressed maternally and zygotically, and expression is observed in regions where neural crest cells are found. To further elucidate the developmental regulation of Cx43α 1 gene expression, we screened a zebrafish BAC library and identified a clone containing the entire zebrafish Cx43α 1 gene and flanking upstream and downstream sequences. The upstream Cx43α1 promoter sequences from zebrafish, mouse, and human were analyzed for evolutionarily conserved DNA motifs. Overall these studies suggest that the sequence motifs and transcriptional regulation involved in the targeting Cx43α1 expression to neural crest cells are evolutionarily conserved in zebrafish and mouse embryos.