Description of Research Expertise

Research Interests
- TGF-ß receptor biology
- Hepatic stellate cell function in liver fibrosis
- The role of mechanical factors and ECM proteins in myofibroblast differentiation in fibrosis
– Characterization of myofibroblast precursor populations in liver fibrosis, including the role of EMT
– The role of liver stiffness in fibrosis and cirrhosis

Key words: Hepatic stellate cells, TGF-ß receptors, liver fibrosis, betaglycan, TGF-ß, portal fibroblasts, epithelial to mesenchymal transition, biliary atresia, liver mechanics

Description of Research
My research focuses on two broad but overlapping areas: basic TGF-β receptor function and signaling, and the mechanism of hepatic fibrosis. We have two major ongoing projects:

1) The mechanism of hepatic fibrosis: Liver fibrosis results from the deposition of excess, abnormal extracellular matrix by myofibroblasts derived from non-fibrogenic cells that undergo “activation” in the context of chronic liver injury. We are investigating the mechanism of fibrosis in three ways: a) by studying the mechanical and soluble factors that influence activation of known myofibroblast precursor populations; b) by identifying new fibrogenic cell populations and new means of studying previously identified cells; and c) by applying the results of our experiments with isolated cells to whole animal models.

We are studying the mechanical and soluble factors that influence activation of two known myofibroblast precursor populations, hepatic stellate cells (HSC) and portal fibroblasts (PF). HSC have for many years been regarded as the most important myofibroblast precursor population and have been studied extensively in a cell culture model of activation. PF have only recently been identified and isolated but are now appreciated to be as important in some liver diseases as HSC. We have successfully developed and characterized an in vitro activation assay for PF. We have used a novel cell culture system to study the role of mechanical and chemical factors in activation of both PF and HSC and have demonstrated for the first time that activation of both PF and HSC is determined by matrix stiffness. Additionally, we have shown that PF absolutely require TGF-β for activation, while HSC require TGF-β, signaling specifically via the downstream mediator Smad3, only in late stages of activation. We have proposed different models of in vitro activation for each cell type.

Projects in the lab also focus on the identification of new fibrogenic cells in fibrosis. We have determined that, in the pediatric disease biliary atresia and in any liver disease with marked bile duct proliferation, significant numbers of biliary epithelial cells undergo an epithelial to mesenchymal transition (EMT), becoming fibrogenic myofibroblasts. This is the first demonstration of EMT in human liver disease and provides new insight into the mechanisms underlying the rapid fibrosis of biliary atresia. Current work is focused on studying an in vitro culture system for EMT of biliary epithelial cells and determining the mechanical and soluble factors that mediate EMT.

We are also applying our findings about the role of mechanical stiffness in liver myofibroblast activation to whole animal models. We have demonstrated in rat models of fibrosis that increased liver stiffness precedes matrix deposition and that fibrosis and liver stiffness are not linearly related. Current work is focused on determining the cause of early increases in liver stiffness, in particular the role of collagen cross-linking enzymes, the relevance of in vivo liver stiffness to myofibroblast activation, the role of early matrix synthesis, and the role of TGF-β in the mechanical changes of the liver in fibrosis. We are also interested in the role of mechanical changes in driving the architectural changes of late fibrosis and cirrhosis.

2) Betaglycan as a modulator of TGF-β signaling: The proteoglycan TGF-β receptor betaglycan is a modulator of TGF-β signaling. We have previously demonstrated that betaglycan has cell-type specific effects on TGF-β signaling and on complex formation between the two TGF-β serine/threonine kinase receptors. We have recently observed that the isolated cytoplasmic domain of betaglycan is a common form of the receptor, potentially the result of a γ-secretase-mediated cleavage, and may have a significant role in TGF-β signaling. Ongoing work is focused on determining the mechanism whereby betaglycan mediates receptor/receptor interactions and on determining the function of the different domains of betaglycan. These experiments are performed in a hepatoma model system but are also applicable to our study of TGF-β signaling in fibrosis.

Summary: Overall, my goal is to develop a unified and comprehensive model of liver fibrosis that incorporates multiple cell types, soluble and secreted factors, and local and regional mechanical factors. It is clear that TGF-β is one of the most important soluble factors in the liver and that it plays a significant role in mediating mechanical changes in the liver; thus, we also focus in detail on new mechanisms of TGF-β signaling that are particularly relevant to fibrosis.

Rotation Projects
There are several; please speak with Dr. Wells.

Lab personnel:
Cheyne Blair - Grad Student
Andy Chu, MD - Fellow
Jia-Ji Hui, MD - Research Specialist
Abby Olsen - Grad Student
Jessica Wen, MD - Fellow
Miho Kikuchi, MD - Postdoctoral Researcher

Description of Clinical Expertise

Dr. Wells attends on the Gastroenterology and Hepatology inpatient consult service at the Philadelphia VAMC, caring for patients with a variety of GI and liver disorders including GI bleeding, pancreatitis, inflammatory bowel disease, GI cancers, and chronic and acute liver disease. Additionally, she has a weekly endoscopy session, carrying out screening and therapeutic upper and lower endoscopies. Her clinical practice is limited to the VAMC.