Absence of tight junction formation in an allogeneic graft cell line used for developing an engineered artificial salivary gland

An essential structural feature of fluid-secreting epithelial tissues is the presence of tight junctions. To develop a tissue-engineered organ capable of fluid secretion, the cellular component must establish these structures. As part of efforts to create an engineered artificial salivary gland, we have examined the ability of a candidate allogeneic graft cell line, HSG, to produce several key tight junction proteins, as well as to exhibit functional activities consistent with effective tight junction strand formation. In contrast to results obtained with a control kidney cell line, MDCK-II, HSG cells were unable to synthesize four important tight junction-associated proteins: ZO-1, occludin, claudin-1, and claudin-2. In addition, unlike MDCK-II cells, HSG cell monolayers could not restrict paracellular permeability. HSG cells were, thus, unable to generate significant transepithelial electrical resistance or serve as an effective barrier to osmotically imposed fluid movement. Furthermore, these two functional activities could not be reconstituted via the stable transfection of HSG cells with cDNAs encoding either claudin-1 or claudin-2. We conclude that because of their inability to form tight junctions, HSG cells are unsuitable for use as an allogeneic graft cell in an artificial salivary fluid secretory device. These studies also emphasize the importance of graft cell selection in artificial organ development, as certain required characteristics may be difficult to reengineer.