Feeder-independent continuous culture of the PICM-19 pig liver stem cell line

Finite cell lines of turkey sperm storage tubule cells: ultrastructure and protein analysis

Cell lines of turkey sperm storage tubule (SST) epithelial cells were established. Turkey SSTs were dissected from freshly obtained uterovaginal junction (UVJ) tissue and placed in explant culture on various substrates and media. Primary cultures of SST epithelium only survived and grew from SST explants that were cultured on inactivated Sandoz inbred strain, thioguanine- and ouabain-resistance (STO) mouse feeder-cell layers in 12% fetal bovine serum-supplemented Dulbecco's Modified Eagle Medium mixed 1:1 with F12 nutrient mixture. Three independent primary colonies gave rise to 3 finite cell lines, SST-1, -2, and -3, which were continuously cultured for 8 to 16 passages at 1:3 passage ratios over a period of 3 to 4 mo. The cells were passaged by pretreatment with Y27632 and dissociation with Accutase. The SST cells grew as tightly knit monolayers on top of the feeder cells at a slow rate (approximately 96 h doubling time) at a medium pH of approximately 6.9. Lipid vacuoles were visible by light microscopy in the cells particularly at the periphery of growth. Transmission electron microscopy revealed the cells to be a polarized epithelium with apical microvilli and to have lateral tight-junction-like unions and associated desmosomes. Numerous secretory vesicles filled the upper portion of the cells’ cytoplasm, and nuclei and other major organelles such as mitochondria, rough endoplasmic reticulum, and Golgi apparatus were distributed somewhat lower in the cytoplasm. The secretory vesicles resembled mucin secretory vesicles. Proteomic analysis by mass spectroscopy of the conditioned medium of the cells, and of the cells themselves, showed the cell lines did not secrete large amounts of any particular protein, and the analysis confirmed their epithelial character. In conclusion, the SST-derived cell lines resembled the mucus-secreting cells found in the epithelium lining the UVJ of the turkey's reproductive tract.

Materials for Neural Differentiation, Trans-Differentiation, and Modeling of Neurological Disease

Neuron regeneration from pluripotent stem cells (PSCs) differentiation or somatic cells trans-differentiation is a promising approach for cell replacement in neurodegenerative diseases and provides a powerful tool for investigating neural development, modeling neurological diseases, and uncovering the mechanisms that underlie diseases. Advancing the materials that are applied in neural differentiation and trans-differentiation promotes the safety, efficiency, and efficacy of neuron regeneration. In the neural differentiation process, matrix materials, either natural or synthetic, not only provide a structural and biochemical support for the monolayer or three-dimensional (3D) cultured cells but also assist in cell adhesion and cell-to-cell communication. They play important roles in directing the differentiation of PSCs into neural cells and modeling neurological diseases. For the trans-differentiation of neural cells, several materials have been used to make the conversion feasible for future therapy. Here, the most current applications of materials for neural differentiation for PSCs, neuronal trans-differentiation, and neurological disease modeling is summarized and discussed.

Magnetic cell labeling of primary and stem cell-derived pig hepatocytes for MRI-based cell tracking of hepatocyte transplantation

Pig hepatocytes are an important investigational tool for optimizing hepatocyte transplantation schemes in both allogeneic and xenogeneic transplant scenarios. MRI can be used to serially monitor the transplanted cells, but only if the hepatocytes can be labeled with a magnetic particle. In this work, we describe culture conditions for magnetic cell labeling of cells from two different pig hepatocyte cell sources; primary pig hepatocytes (ppHEP) and stem cell-derived hepatocytes (PICM-19FF). The magnetic particle is a micron-sized iron oxide particle (MPIO) that has been extensively studied for magnetic cell labeling for MRI-based cell tracking. ppHEP could endocytose MPIO with labeling percentages as high as 70%, achieving iron content as high as ~55 pg/cell, with >75% viability. PICM-19FF had labeling >97%, achieving iron content ~38 pg/cell, with viability >99%. Extensive morphological and functional assays indicated that magnetic cell labeling was benign to the cells. The results encourage the use of MRI-based cell tracking for the development and clinical use of hepatocyte transplantation methodologies. Further, these results generally highlight the importance of functional cell assays in the evaluation of contrast agent biocompatibility.

Gene expression profiling of MYC-driven tumor signatures in porcine liver stem cells by transcriptome sequencing

AIM: To identify the genes induced and regulated by the MYC protein in generating tumors from liver stem cells.

METHODS: In this study, we have used an immortal porcine liver stem cell line, PICM-19, to study the role of c-MYC in hepatocarcinogenesis. PICM-19 cells were converted into cancer cells (PICM-19-CSCs) by overexpressing human MYC. To identify MYC-driven differential gene expression, transcriptome sequencing was carried out by RNA sequencing, and genes identified by this method were validated using real-time PCR. In vivo tumorigenicity studies were then conducted by injecting PICM-19-CSCs into the flanks of immunodeficient mice.

RESULTS: Our results showed that MYC-overexpressing PICM-19 stem cells formed tumors in immunodeficient mice demonstrating that a single oncogene was sufficient to convert them into cancer cells (PICM-19-CSCs). By using comparative bioinformatics analyses, we have determined that > 1000 genes were differentially expressed between PICM-19 and PICM-19-CSCs. Gene ontology analysis further showed that the MYC-induced, altered gene expression was primarily associated with various cellular processes, such as metabolism, cell adhesion, growth and proliferation, cell cycle, inflammation and tumorigenesis. Interestingly, six genes expressed by PICM-19 cells (CDO1, C22orf39, DKK2, ENPEP, GPX6, SRPX2) were completely silenced after MYC-induction in PICM-19-CSCs, suggesting that the absence of these genes may be critical for inducing tumorigenesis.

CONCLUSION: MYC-driven genes may serve as promising candidates for the development of hepatocellular carcinoma therapeutics that would not have deleterious effects on other cell types in the liver.

Proteome array identification of bioactive soluble proteins/peptides in Matrigel: relevance to stem cell responses

Matrigel and similar commercial products are extracts of the Engelbreth-Holm-Swarm sarcoma that provide a basement-membrane-like attachment substrate or gel that is used to grow cells on or in, respectively. To ascertain further what proteins may be present in Matrigel, besides its major basement-membrane constituents, an analysis of the expressed liquid of gelled Matrigel was performed using proteome array technology. Among the growth factors/cytokines assayed, high positive detection was found for IGFBP1, IGFBP3, LIF, platelet factor 4, PlGF-2, and VEGF; moderate reactivity was found for cyr61, IGFBP2, IGFBP6, IL-1ra, and NOV; and low, but detectable, responses occurred for aFGF, IL-13, IL-23, M-CSF, and VEGF-B. Among the chemokines assayed, high positive detection was found for MIG and serpin E1; moderate reactivity was found for IP-10, MCP-1, and MCP-5, and low, but detectable, responses occurred for CXCL16, I-TAC, and MIP-1α. Among the other biologically active proteins assayed, high positive detection was found for adiponectin, C5a, endocan, lipocalin-2, sICAM-1, MMP-3, and TIMP-1; moderate reactivity was found for C-reactive protein, coagulation factor III, endoglin, endostatin/collagen XVIII, endothelin-1, ICAM-1, MMP-9, osteopontin, pentraxin-3, and RANTES; and low, but detectable, responses occurred for fetuin A, MMP-8, pentraxin-2, RBP4, resistin, and TIMP-4. The study found several growth factors, chemokines, and biologically active proteins not previously identified in Matrigel, and this may have significance to the interpretations of observed cellular responses when cells are grown on or in Matrigel.

A feeder-cell independent subpopulation of the PICM-19 pig liver stem cell line capable of long-term growth and extensive expansion

A method for the feeder-independent culture of PICM-19 pig liver stem cell line was recently devised, but the cell line's growth was finite and the cells essentially ceased dividing after approximately 20 passages over a 1 year culture period. Here we report the isolation, continuous culture, and initial characterization of a spontaneously arising feeder-independent PICM-19 subpopulation, PICM-19FF, that maintained replication rate and hepatocyte functions over an extended culture period. PICM-19FF cells grew to 90-98 % confluency after each passage at 2 week intervals, and the cells maintained a high cell density after 2 years and 48 passages in culture (average of 2.6 × 10(6) cells/T25 flask or 1 × 10(5) cells/cm(2)). Morphologically, the PICM-FF cells closely resembled the finite feeder-independent PICM-19 cultures previously reported, and, as before, no spontaneous formation of 3D multicellular ductules occurred in the cells' monolayer. Their bipotent stem cell nature was therefore not evident. Over extensive passage, cytochrome P450 (EROD) activity was maintained, although urea production was reduced on a per mg protein basis at later passages. Two other attributes of fetal hepatocytes, γ-glutamyl transpeptidase activity and serum-protein secretion, were also shown to be maintained by the PICM-19FF cells. The PICM-19FF cells therefore appear to have indefinite growth potential as a feeder-independent cell line and this should enhance the experimental usefulness of the cell line, in general, and may also improve its application to toxicological/pharmacological assays and artificial liver devices.

Growth and Development Symposium: Development, characterization, and use of a porcine epiblast-derived liver stem cell line: ARS-PICM-19

Totipotent embryonic stem cell lines have not been established from ungulates; however, we have developed a somatic stem cell line from the in vitro culture of pig epiblast cells. The cell line, ARS-PICM-19, was isolated via colony cloning and was found to spontaneously differentiate into hepatic parenchymal epithelial cell types, namely hepatocytes and bile duct cells. Hepatocytes form as monolayers and bile duct cells as 3-dimensional bile ductules. Transmission electron microscopy revealed that the ductules were composed of radially arranged, monociliated cells with their cilia projecting into the lumen of the ductule whereas hepatocytes were arranged in monolayers with lateral canalicular structures containing numerous microvilli and connected by tight junctions and desmosomes. Extensive Golgi and rough endoplasmic reticulum networks were also present, indicative of active protein synthesis. Analysis of conditioned medium by 2-dimensional electrophoresis and mass spectrometry indicated a spectrum of serum-protein secretion by the hepatocytes. The PICM-19 cell line maintains a range of inducible cytochrome P450 activities and, most notably, is the only nontransformed cell line that synthesizes urea in response to ammonia challenge. The PICM-19 cell line has been used for several biomedical- and agricultural-related purposes, such as the in vitro replication of hepatitis E virus, a zoonotic virus of pigs, and a spaceflight experiment to evaluate somatic stem cell differentiation and liver cell function in microgravity. The cell line was also evaluated as a platform for toxicity testing and has been used in a commercial artificial liver rescue device bioreactor. A PICM-19 subclone, PICM-19H, which only differentiates into hepatocytes, was isolated and methods are currently under development to grow PICM-19 cells without feeder cells. Feeder-cell-independent growth will facilitate the study of mesenchymal-parenchymal interactions that influence the divergent differentiation of the PICM-19 cells, enhance our ability to genetically modify the cells, and provide a better model system to investigate porcine hepatic metabolism.

Culture of porcine hepatocytes or bile duct epithelial cells by inductive serum-free media

A serum-free, feeder cell-dependent, selective culture system for the long-term culture of porcine hepatocytes or cholangiocytes was developed. Liver cells were isolated from 1-wk-old pigs or young adult pigs (25 and 63 kg live weight) and were placed in primary culture on feeder cell layers of mitotically blocked mouse fibroblasts. In serum-free medium containing 1% DMSO and 1 μM dexamethasone, confluent monolayers of hepatocytes formed and could be maintained for several wk. Light and electron microscopic analysis showed hepatocytes with in vivo-like morphology, and many hepatocytes were sandwiched between the feeder cells. When isolated liver cells were cultured in medium without dexamethasone but with 0.5% DMSO, monolayers of cholangioctyes formed that subsequently self-organized into networks of multicellular ductal structures, and whose cells had monocilia projecting into the lumen of the duct. Gamma-glutamyl transpeptidase (GGT) was expressed by the cholangiocytes at their apical membranes, i.e., at the inner surface of the ducts. Cellular GGT activity increased concomitantly with the development of ductal structures. Cytochrome P-450 was determined in microsomes following addition of metyrapone to the cultures. In vivo-like levels of P-450s were found in hepatocyte monolayers while levels of P-450 were markedly reduced in cholangiocyte monolayers. Serum protein secretion in conditioned media was analyzed by Western blot and indicated that albumin, transferrin, and haptoglobin levels were maintained in hepatocytes while albumin and haptoglobin declined over time in cholangiocytes. Quantitative RT-PCR analysis showed that serum protein mRNA levels were significantly elevated in the hepatocytes monolayers in comparison to the bile ductule-containing monolayers. Further, mRNAs specific to cholangiocyte differentiation and function were significantly elevated in bile ductule monolayers in comparison to hepatocyte monolayers. The results demonstrate an in vitro model for the study of either porcine hepatocytes or cholangiocytes with in vivo-like morphology and function.