Hepatic Lipoprotein Metabolism: Current and Future In Vitro Cell-Based Systems

Abstract

Changes in hepatic lipoprotein metabolism are responsible for the majority of metabolic dysfunction-associated disorders, including familial hypercholesterolemia (FH), metabolic syndrome (MetS), metabolic dysfunction-associated fatty liver disease (MAFLD), and age-related diseases such as atherosclerosis, a major health burden in modern society. This review aims to advance the understanding of state-of-the-art mechanistic concepts in lipoprotein metabolism, with a particular focus on lipoprotein uptake and secretion and their dysregulation in disease, and to provide a comprehensive overview of experimental models used to study these processes. Human lipoprotein research faces several challenges. First, significant differences in lipoprotein metabolism between humans and other species hinder the reliability of non-human model systems. Additionally, ethical constraints often limit studies on human lipoprotein metabolism using tracers. Lastly, while 2D hepatocyte cell culture systems are widely used, they are commonly of cancerous origins, limiting their physiological relevance and necessitating the use of more physiologically representative models. In this review, we will elaborate on key findings in lipoprotein metabolism, as well as limitations and challenges of currently available study tools, highlighting mechanistic insights throughout discussion of these models. These include human tracer studies, animal studies, 2D tissue culture-based systems derived from cancerous tissue as well as from induced pluripotent stem cells (iPSCs)/embryonic stem cells (ESCs). Finally, we will discuss precision-cut liver slices, liver-on-a-chip models, and, particularly, improved 3D models: (i) spheroids generated from either hepatoma cancer cell lines or primary human hepatocytes and (ii) organoids generated from liver tissues or iPSCs/ESCs. In the last section, we will explore future perspectives on liver-in-a-dish models in studying mechanisms of liver diseases, treatment options, and their applicability in precision medicine approaches. By comparing traditional and advanced models, this review will highlight the future directions of lipoprotein metabolism research, with a focus on the growing potential of 3D liver organoid models.

Keywords: human; iPSCs/ESCs; lipoproteins; liver; metabolism; organoids; tissue culture.

Figure 1

Comparison of model systems with regard to hepatic lipoprotein metabolism.

Figure 2

Cell-type composition of the human liver and of pluripotent stem cell-derived liver organoids generated by the current state-of-the-art technology. The human liver consists of several cell types, including hepatocytes, biliary epithelial cells/cholangiocytes forming the bile ducts, stellate cells, Kupffer cells, and liver sinusoidal endothelial cells. Each of these cell types possesses unique functions that cooperatively regulate the hepatic function. Hepatocytes make up the majority of the liver volume and perform many of the functions ascribed to the hepatic metabolism. Pluripotent stem cell-derived liver organoids contain all the major cell types of liver tissue, as demonstrated by several groups. These may be used to study lipoprotein metabolism extrinsically by adding fluorescently labeled lipoprotein particles (upper right) or intrinsically by analysis of endogenously produced lipoproteins (lower right). All figures were created with BioRender.com.