Long-Term Adult Feline Liver Organoid Cultures for Disease Modeling of Hepatic Steatosis

Abstract

Hepatic steatosis is a highly prevalent liver disease, yet research is hampered by the lack of tractable cellular and animal models. Steatosis also occurs in cats, where it can cause severe hepatic failure. Previous studies demonstrate the potential of liver organoids for modeling genetic diseases. To examine the possibility of using organoids to model steatosis, we established a long-term feline liver organoid culture with adult liver stem cell characteristics and differentiation potential toward hepatocyte-like cells. Next, organoids from mouse, human, dog, and cat liver were provided with fatty acids. Lipid accumulation was observed in all organoids and interestingly, feline liver organoids accumulated more lipid droplets than human organoids. Finally, we demonstrate effects of interference with β-oxidation on lipid accumulation in feline liver organoids. In conclusion, feline liver organoids can be successfully cultured and display a predisposition for lipid accumulation, making them an interesting model in hepatic steatosis research.

Keywords: adult liver stem cells; disease modeling; feline hepatic lipidosis; feline liver organoids; hepatic steatosis; species differences.

Figure 1

Establishment of an Organoid Culture from Feline Liver Samples (A) Fresh and snap-frozen liver samples (wedge biopsies of 5 mm³) could be used with equal success rate to establish an organoid culture. It was also possible to start a feline liver organoid culture from a fine-needle aspirate (aspirate visible in the conus of the needle). (B) Representative phase-contrast images of duct isolation and organoid culture. After enzymatic digestion of feline liver samples, biliary duct fragments (arrow) were observed (scale bar represents 50 μm). Ducts were cultured in Matrigel and defined medium. After approximately 3 days in culture (d3), spherical structures appeared that rapidly grew out to large organoids within 6 days (d6) (scale bars represent 100 μm). (C) Representative phase-contrast image of an undigested fine-needle aspirate (FNA) plated straight into Matrigel. After 5 days, organoids emerged from the remnant liver tissue fragments. Scale bar represents 100 μm. (D) Representative phase-contrast images of feline liver organoids in early, medium, and late passages (p1, p12, and p25). Morphology remained similar during long-term culture. Scale bars represent 100 μm. See also Figure S1.

Figure 2

Characterization of Feline Liver Organoids (A) Representative cytological and immunofluorescent images of feline liver organoids. H&E staining showed that organoids consisted of single-layered cubical epithelium. They stained positive for epithelial marker E-cadherin (green) and were highly proliferative in culture as shown by EdU staining (green, marks S phase of the cell cycle). DAPI (blue) was used as nuclear counterstain. (B) Gene expression analysis of feline liver organoids (n = 4 donors) in different passages (p2, p8, p14) and normal cat liver. Relative gene expression (expr.) is shown of adult stem cell, progenitor/biliary, and early and mature hepatocyte markers. (C) Representative images of immunocyto-/histochemical stainings of feline liver organoids and normal cat liver. Organoids stained positive for progenitor/biliary markers K19, HNF1β, and BMI1. They stained negative for hepatocyte marker HepPar-1, but for albumin and ZO1 small clusters of cells within single organoids stained positive (indicated by arrowheads and arrows, respectively). (D) Karyotyping of feline liver organoids. A representative metaphase spread is shown of a cell with a normal chromosome number (n = 38). Chromosome counts were compared between low- and high-passage number cultures (p3–p7 versus p16–p23, n = 4 donors per category) and plotted as percentage of cells with a normal chromosome number (n = 38), one gain (n = 39), one loss (n = 37), or two or more losses (n ≤ 36).

Figure 3

Differentiation of Feline Liver Organoids toward Hepatocyte-like Cells (A) Relative gene expression of feline liver organoids cultured in expansion medium (EM) and differentiation medium (DM) (n = 4 donors). ^∗p < 0.05, Mann-Whitney U test. (B) Representative images of immunocytochemical stainings for K19, BMI1, and ZO1 and PAS staining (indicating glycogen accumulation) of feline liver organoids cultured in EM and DM. (C) Growth curve derived from an Alamar blue assay of feline liver organoids cultured in EM and DM for 7 days (n = 4 donors). Proliferation is presented as percentage relative to measurement at day 0. Error bars indicate SD. (D) Hepatocyte function tests of feline liver organoids cultured in EM and DM (n = 4 donors). Aspartate aminotransferase (AST) levels, albumin secretion in the medium, and CYP450 activity were corrected for cell input with Alamar blue. ^∗p < 0.05, Mann-Whitney U test.

Figure 4

Liver Organoids for Disease Modeling of Hepatic Steatosis (A) Lipid accumulation in liver organoids from mouse, human, dog, and cat (n = 4 donors per species). Intracellular lipids were stained with LD540 and fluorescence was quantified using flow cytometry (see also Figure S2). Data are presented as a dot plot and indicate the increase in LD540 median fluorescence intensity after free fatty acid (FFA) treatment compared with control treatment with BSA. ^∗p < 0.05, Mann-Whitney U test. (B) Representative immunofluorescent images of LD540 staining of mouse, human, dog, and cat liver organoids after control treatment (BSA) and FFA treatment. Intracellular lipid droplets stain green, nuclei are counterstained with DAPI (blue). (C) Heatmap representing the transcriptional analysis of human and cat liver organoids treated with FFA compared with control treatment (BSA). Red indicates decreased gene expression, black unchanged gene expression, and green increased gene expression. See also Figure S3. (D) Lipid accumulation in feline liver organoids treated with control (BSA), FFA, FFA plus etomoxir, and FFA plus L-carnitine. Intracellular lipid accumulation (left) was quantified with flow cytometry and plotted as LD540 median fluorescence intensity for each individual donor (cats 1, 2, 3, 4; ^∗p < 0.05, Wilcoxon signed-rank test). Cellular viability after treatment (right) was measured using a trypan blue assay (^∗p < 0.05, Wilcoxon signed-rank test). (E) Representative phase-contrast images of feline liver organoids treated with control (BSA), FFA, FFA plus etomoxir, and FFA plus L-carnitine.