Identification of UACA, EXOSC9, and ΤΜX2 in bovine periosteal cells by mass spectrometry and immunohistochemistry.

Inspection of patient-derived cells used in transplantation is non-invasive. Therefore, proteomics analysis using supernatants of cells cultured before transplantation is informative. In order to investigate the cell niche of bovine periosteal cells, supernatants of these cultured cells were subjected to 2-D electrophoresis followed by mass spectrometry, which identified type 1 collagen and the C-terminus of type 3 collagen. Only the C-terminal peptide from type 3 collagen was found in supernatants. It is known that type 3 collagen may be expressed intra- or extra-cellularly. Paraffin sections of the cultured cells were next examined by immunohistochemistry, which revealed that type 3 collagen regions besides the C-terminal peptide were present around the bovine periosteal cells but were not found in supernatants. Full-length type 3 collagen was closely associated with the cells, and only the C-terminal peptide was detectable in culture supernatants. Mass spectrometry analysis of partial peptide data combined with immunohistochemistry also indicated that uveal autoantigen with coiled coil domains and ankyrin repeats (UACA), exosome complex component RRP45 (EXOSC9), and thioredoxin-related transmembrane protein 2 (TMX2) were expressed in bovine periosteal cells. Results of this study indicate that analysis of culture supernatants before cell transplantation can provide useful biomarkers indicating the niche of cells used for transplantation.