Often on the Stem Cellar we write about work that is in a clinical trial. But getting research to that stage takes years and years of dedicated work. Over the next few months we are going to profile some of the scientists we fund who are doing Discovery, or early stage research, to highlight the importance of this work in developing the treatments that could ultimately save lives.
This first profile is by Pat Olson, Ph.D., CIRM’s Vice President of Discovery & Translation
Most of us take our liver for granted. We don’t think about the fact that our liver carries out more than 500 functions in our bodies such as modifying and removing toxins, contributing to digestion and energy production, and making substances that help our blood to clot. Without a liver we probably wouldn’t live more than a few days.
Our liver typically functions well but certain toxins, viral infections, long-term excess alcohol consumption and metabolic diseases such as obesity and type 2 diabetes can have devastating effects on it. Under these conditions, functional liver cells, called hepatocytes, die and are replaced with cells called myofibroblasts. Myofibroblasts are cells that secrete excess collagen leading to fibrosis, a form of scarring, throughout the liver. Eventually, a liver transplant is required but the number of donor livers available for transplant is small and the number of persons needing a functional liver is large. Every year in the United States, around 6,000 patients receive a new liver and more than 35,000 patients die of liver disease.
Searching for options
Dr. Holger Willenbring, a physician scientist at UCSF, is one of the CIRM-funded researchers pursuing a stem cell/regenerative medicine approach to discover a treatment for patients with severe liver disease. There are significant challenges to treating liver disease including getting fully multi-functional hepatocytes and getting them to engraft and/or grow sufficiently to achieve adequate mass for necessary liver functions.
In previous CIRM–funded discovery research, Dr. Willenbring and his team showed that they could partially reprogram human fibroblasts (the most common cell found in connective tissue) and then turn them into immature hepatocytes. (see our Spotlight on Liver Disease video from 2012 featuring Dr. Willenbring.) These immature hepatocytes, when transplanted into an immune-deficient mouse model of human liver failure, were shown to mature over time into hepatocytes that were comparable to normal human hepatocytes both in their gene expression and their function.
This was an important finding in that it suggested that the liver environment in a living animal (in vivo), rather than in a test tube (in vitro) in the laboratory, is important for full multi-functional maturation of hepatocytes. The study also showed that these transplanted immature human hepatocytes could proliferate and improve the survival of this mouse model of chronic human liver disease. But, even though this model was designed to emphasizes the growth of functional human hepatocytes, the number of cells generated was not great enough to suggest that transplantation could be avoided
A new approach
Dr. Willenbring and his team are now taking the novel approach of direct reprogramming inside the mouse. With this approach, he seeks to avoid the challenge of low engraftment and proliferation of transplanted hepatocytes generated in the lab and transplanted. Instead, they aim to take advantage of the large number of myofibroblasts in the patient’s scarred liver by turning them directly into hepatocytes.
Recently, he and his team have shown proof-of principle that they can deliver genes to myofibroblasts and turn them into hepatocytes in a mouse. In addition these in vivo myofibroblasts-derived hepatocytes are multi-functional, and can multiply in number, and can even reverse fibrosis in a mouse with liver fibrosis.
From mice to men (women too)
Our latest round of funding for Dr. Willenbring has the goal of moving and extending these studies into human cells by improving the specificity and effectiveness of reprogramming of human myofibroblasts into hepatocytes inside the animal, rather than the lab.
He and his team will then conduct studies to test the therapeutic effectiveness and initial safety of this approach in preclinical models. The ultimate goal is to generate a potential therapy that could eventually provide hope for the 35,000 patients who die of liver disease each year in the US.