Basic Biology IV
Alagille syndrome (ALGS) is caused by mutations in the so-called Notch pathway. The defects seen in ALGS patients, including abnormal bile ducts in the liver, and the known role of Notch in stem cells suggest that ALGS arises from defective interactions between different cell types, including liver progenitors, during development. However, this idea has not been directly tested, in part because of the inherent difficulty of studying human development. A major recent scientific advance has been the possibility to generate and culture induced pluripotent stem cells (iPS cells). iPS cells can propagate indefinitely in culture and be induced to generate all the mature cell types in the body, including liver cells. Compared to embryonic stem cells, which comes from early embryos, iPS cells are generated from a small number of any mature cell type by expression of reprogramming factors. We propose here to generate iPS cells from ALGS patients, starting from small numbers of skin cells from these patients. We will use these cells to investigate the molecular and cellular basis of the liver defects observed in ALGS. These experiments include the development of assays to recapitulate human liver development in culture. We hope that these experiments will allow us to better understand the basis of ALGS and the role of Notch in stem cells. A better understanding of liver development may also help identify novel regenerative strategies for patients with a wide range of liver diseases.
Statement of Benefit to California:
Alagille syndrome (ALGS) is a rare disease (1 in ~70,000 births – less than 10 new cases in California every year) but the signaling pathway that is mutated in ALGS patients, the Notch pathway, is important for many developmental processes and its alteration contributes to the development of many diseases, including cancer, hereditary stroke, and multiple sclerosis. In addition, liver disease affects a wide range of patients, including from alcohol abuse, viral infection, or genetic defects. Irreversible liver dysfunction, such as what is found in some ALGS patients, requires liver transplantation. Strikingly, ~3,500 people are on the waiting list for a liver in California. While the number of people waiting for a liver transplant increases every year, the supply of available donor organs does not. This leads to longer waiting times, sicker patients, and decreased transplant success. Our work on the role cell-cell interactions and Notch signaling in liver development may ultimately identify novel ways to regenerate liver tissue and benefit these patients. Thus, our experiments focusing on the role of Notch signaling in liver development may benefit a large number of patients in California beyond ALGS patients.
This project proposes to investigate the role of Notch signaling in liver development in the context of Alagille syndrome (ALGS), a rare autosomal dominant disorder most often caused by mutations in the Notch pathway. The defects seen in ALGS patients suggest that ALGS arises from defective interactions between different cell types, including liver progenitors, during development. The PI proposes to focus on defects in the development of bile ducts in the liver of ALGS patients, which they hypothesize, arise from abnormal Notch signaling in liver progenitors during development. To investigate the cellular and molecular mechanisms by which decreased Notch signaling results in liver disease in ALGS, the PI proposes 2 aims: The first aim will be to generate induced pluripotent stem (iPS) cell lines from ALGS patients, as well as isogenic gene corrected cell lines from each ALGS iPS cell line, followed by examination of Notch signaling in each of the generated line. The second specific aim examines the cellular and molecular basis of ALGS development in the liver by differentiating both ALGS and gene-corrected cell lines into hepatocytes and cholangiocytes (bile duct cells). The PI will also utilize tissue-engineering approaches to develop 3-D hepatic cultures that may more closely mimic human liver development. Significance and Innovation - Although reviewers agreed that it would be interesting to study to role of Notch signaling in liver development and function, they were discouraged by the lack of sufficient details and were not convinced that the proposal would lead to a greater mechanistic understanding or novel therapeutic approaches. - Reviewers generally believed that the choice of ALGS to model liver development is not well defined and expressed further concerns that the mixed patterns of organ dysfunction associated with this syndrome make it extremely difficult to understand liver development. - Some reviewers were unclear of the focus of this proposal, Notch signaling, liver development or ALGS pathology, and considered this a weakness. Feasibility and Experimental Design - The preliminary data for differentiation of iPS cells to specific hepatic lineages was poor. - The research plan lacked appropriate functional readouts for the differentiation of mature, functional hepatocytes or cholangiocytes, the latter cell type being critical to their disease choice for study. - Experimental design and alternative approaches were viewed as superficial and lacking sufficient experimental details. - Some reviewers were not convinced of the rationale for the 3-D hepatic cultures and argued that this system is too complex for an effective in vitro study. Principal Investigator (PI) and Research Team - Reviewers generally agreed that the PI is an excellent researcher, but were concerned with the lack of expertise and sufficient publication on the differentiation of iPS cells to hepatic lineages and overall understanding on hepatic and cholangiocyte biology. Responsiveness to the RFA - The proposed research was viewed as responsive to the RFA.
- James Ellis