Hepatic Tissue Engineering
The liver has over 500 functions, including protein, carbohydrate, and lipid metabolism; detoxification of endogenous and exogenous compounds; production of bile for digestion; and secretion of many serum proteins (i.e. albumin, coagulation factors). Each year, over 40,000 people die due to liver failure in the US alone, with over 2 million deaths estimated worldwide. Orthotopic liver transplantation is the only proven therapy for liver failure; however, there is a severe shortage of donor organs. Cell-based therapies have been proposed as an alternative to whole organ transplantation, as a temporary bridge to transplantation, and/or an adjunct to traditional therapies during liver regeneration. The three main approaches that have been proposed are: transplantation of isolated hepatocytes, implantable tissue-engineered constructs, and perfusion of blood through an extracorporeal bioartifical liver device containing parenchymal liver cells called hepatocytes. Despite significant investigations into each of these areas, progress has been stymied due to the propensity for isolated hepatocytes to rapidly lose viability and key liver-specific functions upon isolation from the native microenvironment of the liver.
Figure 1: Engineering liver tissue for therapeutic, scientific, and screening applications. Our approach is to study the role of the cellular microenvironment in modulating hepatocyte function. We translate our findings into strategies for tissue fabrication- miniature tissue arrays & large, multilayer tissues.
Our lab is developing novel engineering methodologies to understand how microenvironmental signals around liver cells (hepatocytes and the neighboring non-parenchymal cells of the liver) affect their fate and function. With a better understanding of such signals, we are engineering robust models of animal and human livers for both in vitro (i.e. drug screening [Khetani, Nature Biotechnology]) and in vivo applications. We utilize microfabrication tools borrowed from the semiconductor industry to control and study the role of cell-cell interactions in liver constructs[(Bhatia, FASEB 99 Review; Khetani, Hepatology; Hui, PNAS ; Hui, JoVE ]; novel extracellular matrix microarrays to study the role of matrix combinations on liver functions [Flaim, Nature Methods ]; bioreactors to expose hepatocytes to gradients of soluble stimuli [Allen, Biotech and Bioeng]; and photopolymerizable hydrogels yo probe the role of the 3D context and deliver tissues to the body [Liu, Biomedical Microdevices; Liu, FASEB; Albrecht, Nature Methods] . Finally, the sourcing of hepatic cells is problematic due to the limited growth of primary hepatocytes in vitro. We are therefore studying both progenitor and stem cell sources of hepatic cells to understand the cues that drive differentiation along different hepatic lineages [Underhill, Current Opinion in Chemical Biology ; Underhill/Chen, Biomaterials ]. Collectively, these studies provide a systematic approach to hepatic tissue engineering. Our long-term goals are to translate the application of these tissues to prevent liver disease via elimination of harmful drugs from the pharmaceutical pipeline and develop cell-based therapies for patients who remain vulnerable to liver disease.
The liver has over 500 functions, including protein, carbohydrate, and lipid metabolism; detoxification of endogenous and exogenous compounds; production of bile for digestion; and secretion of many serum proteins (i.e. albumin, coagulation factors). Each year, over 40,000 people die due to liver failure in the US alone, with over 2 million deaths estimated worldwide. Orthotopic liver transplantation is the only proven therapy for liver failure; however, there is a severe shortage of donor organs. Cell-based therapies have been proposed as an alternative to whole organ transplantation, as a temporary bridge to transplantation, and/or an adjunct to traditional therapies during liver regeneration. The three main approaches that have been proposed are: transplantation of isolated hepatocytes, implantable tissue-engineered constructs, and perfusion of blood through an extracorporeal bioartifical liver device containing parenchymal liver cells called hepatocytes. Despite significant investigations into each of these areas, progress has been stymied due to the propensity for isolated hepatocytes to rapidly lose viability and key liver-specific functions upon isolation from the native microenvironment of the liver.
Figure 1: Engineering liver tissue for therapeutic, scientific, and screening applications. Our approach is to study the role of the cellular microenvironment in modulating hepatocyte function. We translate our findings into strategies for tissue fabrication- miniature tissue arrays & large, multilayer tissues.
Our lab is developing novel engineering methodologies to understand how microenvironmental signals around liver cells (hepatocytes and the neighboring non-parenchymal cells of the liver) affect their fate and function. With a better understanding of such signals, we are engineering robust models of animal and human livers for both in vitro (i.e. drug screening [Khetani, Nature Biotechnology]) and in vivo applications. We utilize microfabrication tools borrowed from the semiconductor industry to control and study the role of cell-cell interactions in liver constructs[(Bhatia, FASEB 99 Review; Khetani, Hepatology; Hui, PNAS ; Hui, JoVE ]; novel extracellular matrix microarrays to study the role of matrix combinations on liver functions [Flaim, Nature Methods ]; bioreactors to expose hepatocytes to gradients of soluble stimuli [Allen, Biotech and Bioeng]; and photopolymerizable hydrogels yo probe the role of the 3D context and deliver tissues to the body [Liu, Biomedical Microdevices; Liu, FASEB; Albrecht, Nature Methods] . Finally, the sourcing of hepatic cells is problematic due to the limited growth of primary hepatocytes in vitro. We are therefore studying both progenitor and stem cell sources of hepatic cells to understand the cues that drive differentiation along different hepatic lineages [Underhill, Current Opinion in Chemical Biology ; Underhill/Chen, Biomaterials ]. Collectively, these studies provide a systematic approach to hepatic tissue engineering. Our long-term goals are to translate the application of these tissues to prevent liver disease via elimination of harmful drugs from the pharmaceutical pipeline and develop cell-based therapies for patients who remain vulnerable to liver disease.