BackgroundDuring liver development, intrahepatic bile ducts are thought to arise by a unique asymmetric mode of cholangiocyte tubulogenesis characterized by a series of remodeling stages. Moreover, in liver diseases, cells lining the Canals of Hering can proliferate and generate new hepatic tissue. The aim of this study was to develop protocols for three-dimensional visualization of protein expression, hepatic portal structures and human hepatic cholangiocyte tubulogenesis.ResultsProtocols were developed to digitally visualize portal vessel branching and protein expression of hepatic cell lineage and extracellular matrix deposition markers in three dimensions. Samples from human prenatal livers ranging from 7 weeks + 2 days to 15½ weeks post conception as well as adult normal and acetaminophen intoxicated liver were used. The markers included cytokeratins (CK) 7 and 19, the epithelial cell adhesion molecule (EpCAM), hepatocyte paraffin 1 (HepPar1), sex determining region Y (SRY)-box 9 (SOX9), laminin, nestin, and aquaporin 1 (AQP1).Digital three-dimensional reconstructions using CK19 as a single marker protein disclosed a fine network of CK19 positive cells in the biliary tree in normal liver and in the extensive ductular reactions originating from intrahepatic bile ducts and branching into the parenchyma of the acetaminophen intoxicated liver. In the developing human liver, three-dimensional reconstructions using multiple marker proteins confirmed that the human intrahepatic biliary tree forms through several developmental stages involving an initial transition of primitive hepatocytes into cholangiocytes shaping the ductal plate followed by a process of maturation and remodeling where the intrahepatic biliary tree develops through an asymmetrical form of cholangiocyte tubulogenesis.ConclusionsThe developed protocols provide a novel and sophisticated three-dimensional visualization of vessels and protein expression in human liver during development and disease.
BackgroundTissue repair in the adult mammalian liver occurs in two distinct processes, referred to as the first and second tiers of defense. We undertook to characterize the changes in molecular constituents of the extracellular matrix when hepatic progenitor cells (HPCs) respond in a second tier of defense to liver injury.ResultsWe used transcriptional profiling on rat livers responding by a first tier (surgical removal of 70% of the liver mass (PHx protocol)) and a second tier (70% hepatectomy combined with exposure to 2-acetylaminofluorene (AAF/PHx protocol)) of defense to liver injury and compared the transcriptional signatures in untreated rat liver (control) with those from livers of day 1, day 5 and day 9 post hepatectomy in both protocols. Numerous transcripts encoding specific subunits of collagens, laminins, integrins, and various other extracellular matrix structural components were differentially up- or down-modulated (P < 0.01). The levels of a number of transcripts were significantly up-modulated, mainly in the second tier of defense (Agrn, Bgn, Fbn1, Col4a1, Col8a1, Col9a3, Lama5, Lamb1, Lamb2, Itga4, Igtb2, Itgb4, Itgb6, Nid2), and their signal intensities showed a strong or very strong correlation with Krt1-19, a well-established marker of a ductular/HPC reaction. Furthermore, a significant up-modulation and very strong correlation between the transcriptional profiles of Krt1-19 and St14 encoding matriptase, a component of a novel protease system, was found in the second tier of defense. Real-time PCR confirmed the modulation of St14 transcript levels and strong correlation to Krt-19 and also showed a significant up-modulation and strong correlation to Spint1 encoding HAI-1, a cognate inhibitor of matriptase. Immunodetection and three-dimensional reconstructions showed that laminin, Collagen1a1, agrin and nidogen1 surrounded bile ducts, proliferating cholangiocytes, and HPCs in ductular reactions regardless of the nature of defense. Similarly, matriptase and HAI-1 were expressed in cholangiocytes regardless of the tier of defense, but in the second tier of defense, a subpopulation of HPCs in ductular reactions co-expressed HAI-1 and the fetal hepatocyte marker Dlk1.ConclusionTranscriptional profiling and immunodetection, including three-dimensional reconstruction, generated a detailed overview of the extracellular matrix constituents expressed in a second tier of defense to liver injury.
Mitochondrial dysfunction has been demonstrated to result in premature aging due to its effects on stem cells. Nevertheless, a full understanding of the role of mitochondrial bioenergetics through differentiation is still lacking. Here we show the bioenergetics profile of human stem cells of embryonic origin differentiating along the hepatic lineage. Our study reveals especially the transition between hepatic specification and hepatic maturation as dependent on mitochondrial respiration and demonstrates that even though differentiating cells are primarily dependent on glycolysis until induction of hepatocyte maturation, oxidative phosphorylation is essential at all stages of differentiation.
Undifferentiated human embryonic stem cells are characterized by expression of specific cell markers like the transcription factors OCT4, SOX2, and NANOG, the stage-specific embryonic antigen SSEA4, and the tumor-related antigens TRA-1-60 and TRA-1-81 and by their ability to differentiate under proper conditions into cells of the three germ layers and later into derivatives of these germ layers. Recent studies suggest a certain micro-heterogeneity of the expression of hESC markers, which demonstrates that not all cells in a hESC colony of apparently undifferentiated cells express all the expected markers. We describe a technique allowing paraffin embedding an entire hESC colony (e.g., 150 microm thick) and prepare 2-microm thick serial sections. Different staining procedures applied to individual sections produce a 2D survey of the developing hESC colony. Furthermore, a new and useful visualization of this 2D-expression pattern can be created by developing a 3D-model of the culture, based on serial paraffin sections. Individual sections are stained using individual markers. Using 3D image processing software such as Mimics or 3D-Doctor, the actual 3D-rendering of an entire colony can be accomplished. An extended version of this technique even allows for a high-magnification 3D-reconstruction of an area of interest (AOI), e.g., the developing hepatic stem cells. These techniques allow both a 2D and a 3D visualization of hESC colonies and lead to new insights into and information about the interaction of stem cells.
Pluripotent human embryonic stem cells (hESCs) are characterized by two defining properties, self-renewal and differentiation. Self-renewing hESCs express transcription factors OCT4, SOX2, and NANOG, and surface markers SSEA-4 and TRA-1-60 and TRA-1-81 and their ability to differentiate into derivatives of the three germ layers show the differentiating potential. Studies suggest a certain microheterogeneity of the hESC colonies, in which not all cells in one colony of apparently undifferentiated cells express all the expected markers. We describe a technique to paraffin embed an entire hESC colony, and prepare 3-5 μm thick serial sections. Immunohistochemistry applied to individual sections produces a 2-dimensional survey of the developing hESC colony. Based on serial paraffin sections of the 2D-expression pattern, a new and useful 3D-visualization can be modeled. The actual 3D rendering of an entire colony is accomplished using 3D image processing software such as Mimics(®) or Amira(®). An extended version of this technique even allows for a high-magnification 3D-reconstruction of, e.g., hepatic stem cells in developing liver. These techniques combined allow for both a 2- and a 3-dimensional visualization of hESC colonies and stem cells in organs, which leads to new insights into and information about the interaction of stem cells with their surroundings.
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