Seeds in the liver

Fine-scale visualizing the hierarchical structure of mouse biliary tree with fluorescence microscopy method

The liver is a vital organ and the hepatic lobule serves as the most basic structural and functional unit which is mainly assembled with parenchymal cells including hepatocytes and biliary epithelial cells. The continuous tubular arrangement of biliary cells which constitutes the biliary tracts is critical for liver function, however, the biliary tracts are often disrupted in many liver diseases such as cirrhosis and some congenital disorders. Visualization of the biliary tracts in fine-scale and three-dimension will help to understanding the structure basis of these liver diseases. In the present study, we established several biliary tract injury mouse models by diet feeding, surgery or genetic modification. The cytoplasm and nuclei of the parenchymal cells were marked by active uptake of fluorescent dyes Rhodamine B (red) and Hoechst (blue), respectively. After the removal of liver en bloc, the biliary tracts were retrogradely perfused with green fluorescent dye, fluorescein isothiocyanate (FITC). The liver was then observed under confocal microscopy. The fine-scale and three-dimensional (3D) structure of the whole biliary tree, particularly the network of the end-terminal bile canaliculi and neighboring hepatocytes were clearly visualized. The biliary tracts displayed clear distinct characteristics in normal liver and diseased liver models. Taken together, we have developed a simple and repeatable imaging method to visualize the fine-scale and hierarchical architecture of the biliary tracts spreading in the mouse liver.

Differentiation of Cells Isolated from Afterbirth Tissues into Hepatocyte-Like Cells and Their Potential Clinical Application in Liver Regeneration

Toxic, viral and surgical injuries can pose medical indications for liver transplantation. The number of patients waiting for a liver transplant still increases, but the number of organ donors is insufficient. Hepatocyte transplantation was suggested as a promising alternative to liver transplantation, however, this method has some significant limitations. Currently, afterbirth tissues seem to be an interesting source of cells for the regenerative medicine, because of their unique biological and immunological properties. It has been proven in experimental animal models, that the native stem cells, and to a greater extent, hepatocyte-like cells derived from them and transplanted, can accelerate regenerative processes and restore organ functioning. The effective protocol for obtaining functional mature hepatocytes in vitro is still not defined, but some studies resulted in obtaining functionally active hepatocyte-like cells. In this review, we focused on human stem cells isolated from placenta and umbilical cord, as potent precursors of hepatocyte-like cells for regenerative medicine. We summarized the results of preclinical and clinical studies dealing with the introduction of epithelial and mesenchymal stem cells of the afterbirth origin to the liver failure therapy. It was concluded that the use of native afterbirth epithelial and mesenchymal cells in the treatment of liver failure could support liver function and regeneration. This effect would be enhanced by the use of hepatocyte-like cells obtained from placental and/or umbilical stem cells.

Dicer1 facilitates liver regeneration in a manner dependent on the inhibitory effect of miR-21 on Pten and Rhob expression

AIMS

Tamoxifen-induced liver-specific Dicer1 deletion (iDicer1^-/-) in mature mice may provide clues demonstrating the genuine effects of acute loss of Dicer1 and miRNAs in the liver regeneration process.

MAIN METHODS

In this study, mice with tamoxifen-induced Dicer1 deletion through the Cre/LoxP system were constructed and then underwent classic 70% partial hepatectomy or CCl4-induced liver injury. To rescue the inhibitory effect of Dicer1 ablation on liver regeneration, miR-21 agomir was injected into the tail vein of iDicer1^-/- mice.

KEY FINDINGS

Unlike constitutive embryonic deletion of Dicer1, tamoxifen-induced Dicer1 deletion did not result in severe liver injury or lesions, providing an ideal model for investigating acute loss of Dicer1 and miRNAs in liver regeneration. Dicer1 deletion led to impaired liver regeneration through the inhibitory effect of miR-21 on PTEN and Rhob expression.

SIGNIFICANCE

In our previous study, we found that embryonic loss of Dicer1 impairs hepatocyte survival and leads to chronic inflammation and progenitor cell activation, while the role of Dicer1 in liver regeneration remains largely unknown. We clearly identified the promotion effect of Dicer1 on liver regeneration by increasing miR-21 expression, which inhibits the expression of two negative cell proliferation regulators, Pten and Rhob.