Abstract

BackgroundMammary cell cultures are convenient tools for in vitro studies of mammary gland biology. However, the heterogeneity of mammary cell types, e.g., glandular milk secretory epithelial or myoepithelial cells, often complicates the interpretation of cell-based data. The present study was undertaken to determine the relevance of bovine primary mammary epithelial cells isolated from American Holstein (bMECUS) or Swiss Holstein–Friesian (bMECCH) cows, and of primary bovine mammary alveolar epithelial cells stably transfected with simian virus-40 (SV-40) large T-antigen (MAC-T) for in vitro analyses. This was evaluated by testing their expression pattern of cytokeratin (CK) 7, 18, 19, vimentin, and α-smooth muscle actin (α-SMA).ResultsThe expression of the listed markers was assessed using real-time quantitative PCR, flow cytometry and immunofluorescence microscopy. Characteristic markers of the mesenchymal (vimentin), myoepithelial (α-SMA) and glandular secretory cells (CKs) showed differential expression among the studied cell cultures, partly depending on the analytical method used. The relative mRNA expression of vimentin, CK7 and CK19, respectively, was lower (P < 0.05) in immortalized than in primary mammary cell cultures. The stain index (based on flow cytometry) of CK7 and CK19 protein was lower (P < 0.05) in MAC-T than in bMECs, while the expression of α-SMA and CK18 showed an inverse pattern. Immunofluorescence microscopy analysis mostly confirmed the mRNA data, while partly disagreed with flow cytometry data (e.g., vimentin level in MAC-T). The differential expression of CK7 and CK19 allowed discriminating between immortal and primary mammary cultures.ConclusionsThe expression of the selected widely used cell type markers in primary and immortalized MEC cells did not allow a clear preference between these two cell models for in vitro analyses studying aspects of milk composition. All tested cell models exhibited to a variable degree epithelial and mesenchymal features. Thus, based on their characterization with widely used cell markers, none of these cultures represent an unequivocal alveolar mammary epithelial cell model. For choosing the appropriate in vitro model additional properties such as the expression profile of specific proteins of interest (e.g., transporter proteins) should equally be taken into account.

Highlights

  • Mammary cell cultures are convenient tools for in vitro studies of mammary gland biology

  • Primary mammary epithelial cells (MEC) isolated from mammary gland (MG) tissues [4, 7, 8] or prepared from milk [9], and bovine mammary cell lines obtained by transfection of mammary alveolar cells with simian virus-40 (SV40) large T-antigen such as (MAC-T) [10], HH2a [11] or BME-UV [12] are cell models that can be used for in vitro investigation of MG biology

  • Cell type marker mRNA expression Quantitative RT-PCR analysis of confluent MAC-T, bMECCH and bMECUS (Fig. 1a) revealed that the expression of reference genes did not vary among cell models

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Summary

Introduction

Mammary cell cultures are convenient tools for in vitro studies of mammary gland biology. The present study was undertaken to determine the relevance of bovine primary mammary epithelial cells isolated from American Holstein (bMECUS) or Swiss Holstein–Friesian (bMECCH) cows, and of primary bovine mammary alveolar epithelial cells stably transfected with simian virus-40 (SV-40) large T-antigen (MAC-T) for in vitro analyses. This was evaluated by testing their expression pattern of cytokeratin (CK) 7, 18, 19, vimentin, and α-smooth muscle actin (α-SMA). It appears important to evaluate the relevance of MAC-T and primary cells for in vitro studies on MG physiology by monitoring their expression level of marker antigens characteristic for different mammary cells e.g., luminal milk producing cells or mesenchymal cells

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