Zebrafish: an important tool for liver disease research

Abstract

As the incidence of hepatobiliary diseases increases, we must improve our understanding of the molecular, cellular, and physiological factors that contribute to the pathogenesis of liver disease. Animal models help us identify disease mechanisms that might be targeted therapeutically. Zebrafish (Danio rerio) have traditionally been used to study embryonic development but are also important to the study of liver disease. Zebrafish embryos develop rapidly; all of their digestive organs are mature in larvae by 5 days of age. At this stage, they can develop hepatobiliary diseases caused by developmental defects or toxin- or ethanol-induced injury and manifest premalignant changes within weeks. Zebrafish are similar to humans in hepatic cellular composition, function, signaling, and response to injury as well as the cellular processes that mediate liver diseases. Genes are highly conserved between humans and zebrafish, making them a useful system to study the basic mechanisms of liver disease. We can perform genetic screens to identify novel genes involved in specific disease processes and chemical screens to identify pathways and compounds that act on specific processes. We review how studies of zebrafish have advanced our understanding of inherited and acquired liver diseases as well as liver cancer and regeneration.

Keywords: Development; Liver Cancer; Regeneration; Technology; Toxicology.

Figure 1

Timeline of hepatology advances in zebrafish research. Major milestones or historic events in human liver pathology are indicated in yellow, and corresponding milestones in zebrafish research are indicated in green. The timeline indicates years B.C. and A.D.

Figure 2

Comparative anatomy of human and zebrafish livers. (A) Live zebrafish at 6, 28, 72, and 120 hours postfertilization show that a large number of synchronously developing larvae can be easily cultured. Cellular anatomy and architecture of the liver in (B) zebrafish and (C) humans. (B, inset) A histological section of adult zebrafish liver stained with H&E.

Figure 3

Fluorescent zebrafish with live markers of liver cells. Images of live transgenic zebrafish on 5 dpf with fluorescent proteins expressed in (A) hepatocytes (fabp10), (B) biliary cells (Tp1), (C) endothelial cells (flk1), and (D) stellate cells (hand2). The image of Tg(hand2:GFP) larvae was provided by C. Yin.

Figure 4

Cell signaling and lipid metabolism insights into FLD from studies in zebrafish. Research using zebrafish has identified several factors that cause fatty liver, as indicated by the red arrows. The pathways illustrated in this figure are described in the text. Hbv, hepatitis B X antigen; TAA, thioacetamide; trappc11, trafficking protein particle complex 11.

Figure 5

Progressive hepatocyte response to ethanol in zebrafish. Zebrafish exposed to ethanol show signs of liver toxicity as well as gross morphological and behavioral changes that increase over time. The progression of steatosis is illustrated by the yellow droplets in the cytoplasm, and the activation of stellate cells at advanced stages of toxicity is illustrated in blue.

Figure 6

Comparative histology of HCC and the diagnostic criteria for liver cancer in zebrafish. H&E-stained sections from (A) normal human liver and (B) 20 dpf normal zebrafish liver are compared with sections from HCC in both species. (C) Criteria for diagnosing HCC in zebrafish.