Modeling Nonalcoholic Fatty Liver Disease in the Dish Using Human-Specific Platforms: Strategies and Limitations

Abstract

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease affecting multiple cell types of the human liver. The high prevalence of NAFLD and the lack of approved therapies increase the demand for reliable models for the preclinical discovery of drug targets. In the last decade, multiple proof-of-principle studies have demonstrated human-specific NAFLD modeling in the dish. These systems have included technologies based on human induced pluripotent stem cell derivatives, liver tissue section cultures, intrahepatic cholangiocyte organoids, and liver-on-a-chip. These platforms differ in functional maturity, multicellularity, scalability, and spatial organization. Identifying an appropriate model for a specific NAFLD-related research question is challenging. Therefore, we review different platforms for their strengths and limitations in modeling NAFLD. To define the fidelity of the current human in vitro NAFLD models in depth, we define disease hallmarks within the NAFLD spectrum that range from steatosis to severe fibroinflammatory tissue injury. We discuss how the most common methods are efficacious in modeling genetic contributions and aspects of the early NAFLD-related tissue response. We also highlight the shortcoming of current models to recapitulate the complexity of inter-organ crosstalk and the chronic process of liver fibrosis-to-cirrhosis that usually takes decades in patients. Importantly, we provide methodological overviews and discuss implementation hurdles (eg, reproducibility or costs) to help choose the most appropriate NAFLD model for the individual research focus: hepatocyte injury, ductular reaction, cellular crosstalk, or other applications. In sum, we highlight current strategies and deficiencies to model NAFLD in the dish and propose a framework for the next generation of human-specific investigations. Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease affecting multiple cell types of the human liver. The high prevalence of NAFLD and the lack of approved therapies increase the demand for reliable models for the preclinical discovery of drug targets. In the last decade, multiple proof-of-principle studies have demonstrated human-specific NAFLD modeling in the dish. These systems have included technologies based on human induced pluripotent stem cell derivatives, liver tissue section cultures, intrahepatic cholangiocyte organoids, and liver-on-a-chip. These platforms differ in functional maturity, multicellularity, scalability, and spatial organization. Identifying an appropriate model for a specific NAFLD-related research question is challenging. Therefore, we review different platforms for their strengths and limitations in modeling NAFLD. To define the fidelity of the current human in vitro NAFLD models in depth, we define disease hallmarks within the NAFLD spectrum that range from steatosis to severe fibroinflammatory tissue injury. We discuss how the most common methods are efficacious in modeling genetic contributions and aspects of the early NAFLD-related tissue response. We also highlight the shortcoming of current models to recapitulate the complexity of inter-organ crosstalk and the chronic process of liver fibrosis-to-cirrhosis that usually takes decades in patients. Importantly, we provide methodological overviews and discuss implementation hurdles (eg, reproducibility or costs) to help choose the most appropriate NAFLD model for the individual research focus: hepatocyte injury, ductular reaction, cellular crosstalk, or other applications. In sum, we highlight current strategies and deficiencies to model NAFLD in the dish and propose a framework for the next generation of human-specific investigations. SummaryThis review article presents the latest research on nonalcoholic fatty liver disease (NAFLD) in vitro modeling. Benefits and limitations of using human induced pluripotent stem cell-derived approaches, primary organoids, liver-on-a-chip, and precision-cut liver sections are discussed to help researchers choose the most appropriate model. This review article presents the latest research on nonalcoholic fatty liver disease (NAFLD) in vitro modeling. Benefits and limitations of using human induced pluripotent stem cell-derived approaches, primary organoids, liver-on-a-chip, and precision-cut liver sections are discussed to help researchers choose the most appropriate model. Up to one-fourth of the global population presents with some degree of nonalcoholic fatty liver disease (NAFLD). Furthermore, the incidence is expected to rise in the coming years primarily because of Western life habits.1Karlsen T.H. Sheron N. Zelber-Sagi S. et al.The EASL-Lancet Liver Commission: protecting the next generation of Europeans against liver disease complications and premature mortality.Lancet. 2022; 399: 61-116Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar NAFLD can range from hepatocellular steatosis to chronic fibroinflammatory liver injury and cirrhosis with liver failure at end stages. Although some pathomechanisms, especially in early NAFLD development, are well-understood, there is currently no approved treatment for patients. For this reason, there is an urgent need to implement methods that reliably model human NAFLD for therapeutic target discovery or candidate drug testing. In recent years, a debate has emerged on the translational utility of NAFLD animal models. Despite the rationale for preclinical studies in vivo, significant inter-species differences have led to a vast collection of lost-in-translation cases such that therapeutic candidates validated in animals did not effectively ameliorate NAFLD in clinical trials. Here, we review the state of advanced in vitro models that allow a better understanding of human NAFLD. We focus on different human-specific modeling strategies, their promises, and progress, and finally emphasize their limitations. In our assessment, we analyze the different human platforms through a lens of how effectively they model the clinical hallmarks of the NAFLD spectrum. Chronic substrate excess induces NAFLD, characterized by subcellular lipid accumulation in hepatocytes (steatosis). NAFLD may progress to nonalcoholic steatohepatitis (NASH) and a fibroinflammatory tissue response. Persistent steatosis triggers a lipotoxic cell response, progressively leading to a surge in oxidative stress, endoplasmic reticulum stress, and compromised mitochondrial function. Consequently, hepatocytes may undergo cell death and release damage-associated patterns and alarmins found in the liver and systemic circulation.2Lambrecht J. Tacke F. Controversies and opportunities in the use of inflammatory markers for diagnosis or risk prediction in fatty liver disease.Front Immunol. 2020; 11634409Google Scholar This cascade of events activates liver resident macrophages (ie, Kupffer cells [KCs]) and liver sinusoidal endothelial cells (LSECs) to secrete a wide range of chemokines to recruit circulating myeloid and lymphoid immune cells.3Nasiri-Ansari N. Androutsakos T. Flessa C.M. et al.Endothelial cell dysfunction and nonalcoholic fatty liver disease (NAFLD): a concise review.Cells. 2022; : 11PubMed Google Scholar, 4Wallace S.J. Tacke F. Schwabe R.F. et al.Understanding the cellular interactome of non-alcoholic fatty liver disease.JHEP Rep. 2022; 4100524PubMed Google Scholar, 5Peiseler M. Schwabe R. Hampe J. et al.Immune mechanisms linking metabolic injury to inflammation and fibrosis in fatty liver disease: novel insights into cellular communication 2022; Full Text Full Text PDF PubMed Scopus Google Scholar, J. et and cellular of the in the of liver Scholar The inflammatory triggers the of cells into for the injury for genetic can the risk for NAFLD and Importantly, NAFLD usually decades in patients. the of the we focus on in vitro models mechanisms in the liver. 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