In the liver, bile ducts are distributed in a network of tubes that deliver bile from the liver to the intestines. In biliary tract disease, bile transport disorders can lead to toxic cholestasis, liver damage, and permanent scarring (cirrhosis) in the liver, which can only be treated by liver transplantation. In fact, biliary tract disease (cholangiopathic disease) is the leading cause of liver transplantation in children (70%), accounting for one-third of the cause of adult liver transplantation.
Although the impact of such diseases is enormous, our understanding of the pathogenesis of biliary diseases is still very limited. On the one hand, due to the lack of effective experimental models, on the other hand, it is very difficult to culture bile duct cells (biliary epithelial cells) in vitro. In addition, current treatments are limited, lacking specific drugs, and lacking the normal cells and tissues needed to reconstruct or replace the bile ducts. My research focus is on solving these problems.
Specifically, my research goal was to develop a system suitable for in vitro growth of human bile duct epithelial cells; to construct an in vitro model of cholangiocarcinoma using these cells; and to use this in vitro model to screen, test, and discover new biliary disease treatments. I also tried to construct bioengineered bile ducts using healthy biliary cells and demonstrated in animal models that they could be used for surgical reconstruction or replacement of the biliary tract.
Cultured human bile duct epithelial cells
The culture of human bile duct epithelial cells faces two major obstacles: the acquisition of bile duct tissue by surgery and the loss of function during primary culture of bile duct epithelial cells. In order to solve the problem of tissue acquisition, I designed a set of procedures for obtaining bile duct epithelial cells from human induced pluripotent stem cells (hIPSC), and hIPSC can be conveniently obtained from patient skin samples.
In order to preserve the function and characteristics of human bile duct epithelial cells in vitro, I used three-dimensional culture to grow cells into organoids, which showed a cystic or tubular structure with a central cavity (1, 2). The structure of the organoids that gradually develop around the lumen resembles the natural biliary tract. This hIPSC-derived bile duct epithelial cells function better and grow faster. This method also enables the first large-scale culture of human primary bile duct epithelial cells using a resected bile duct or gallbladder (3).
In order to prove that this type of organ platform has both the culture advantage and the normal bile duct epithelial cell function, I compared the physiological and functional comparison between hIPSC-derived biliary epithelial cells or primary cultures and human biliary cells. The experimental results show that the bile duct epithelial cells obtained by organ-like culture are similar to the human bile duct cells derived from the body, and are the most accurate in vitro bile duct epithelial cell platform.
Construction of an in vitro model of biliary disease
I hypothesized that biliary epithelial cells from patients with biliary tract disease can reproduce the key features of these diseases when cultured in vitro. This hypothesis was validated by the use of biliary epithelial cells in patients with Alagille syndrome (AGS), polycystic liver disease (PLD), and cystic fibrosis (CF). Without exception, the phenotype of each of these diseases was reproducible in the experiment (AGS, lack of lumen; PLD, cyst formation; CF, organosomal lumen chloride defect), providing the first in vitro disease for the above diseases Biliary model (1).
Drug screening
Subsequently, I used the constructed disease model to screen known drugs (octreotide) and new drug compounds. The results showed that an experimental drug (VX809) originally used to treat cystic fibrosis in the lungs can also be used to prevent hepatic cysticity. Fibrosis (1). This finding is extremely important because the VX809 has entered Phase 2 clinical trials and is expected to test hepatic cystic fibrosis soon. This result is the first successful application of in vitro screening for biliary disease drugs.
Bioengineering bile duct construction and transplantation
In some cases, such as bile duct atresia, it is also the primary cause of liver transplantation in children. The common exit of the biliary system (the common bile duct) is missing. The only treatment is surgery. At this point, the use of bioengineered bile ducts can be an alternative to liver transplantation.
To achieve this goal, I developed a method for constructing bioengineered bile ducts and bile duct tissue using normal bile duct epithelial cells (3). This bioengineered organ retains the structural, structural properties, markers and functions of human bile ducts (alkaline phosphatase and gamma-glutamyltransferase activity).
This bioengineered bile duct was transplanted into immunodeficient mice and successfully replaced the original bile duct. In addition, mice undergoing artificial bile duct transplantation have normal liver function and prolonged survival. As far as I know, this is the first application of organ engineering in the biliary system, and the first report on the use of organs to construct bioengineered organs.
in conclusion
The range of tools developed in this study has unique transformational applications in the field of biliary diseases. I have confirmed that the bile duct epithelial cell-like organ system constructs the first in vitro biliary disease model. These models can deepen our understanding of the mechanisms underlying the disease and allow for technology transfer to benefit multiple research groups working in the field. In addition, the system has established the first platform for screening for biliary disease drugs, and I have verified in principle that the system demonstrates potential for new drug development in the field of biliary diseases where liver transplantation is the only treatment.
Finally, by constructing the engineering bile duct, I have verified in principle that regenerative medicine can be used as a treatment for biliary tract diseases, and promotes the development of organ regeneration by developing techniques suitable for the regeneration of various organs and tissues.
references
1. F. Sampaziotis et al ., Nat. Biotech 33 , 845 (2015).
2.F. Sampaziotis et al., Nat. Protocols 12 , 814 (2017).
3.F. Sampaziotis et al., Nat. Med. 23 , 954 (2017).
This article is translated by Sartorius. To read the original English text, please click: http://science.sciencemag.org/content/359/6380/1113.2.full
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