Tissue transglutaminase expression during neural differentiation of human mesenchymal stem cells

Herein, we assessed the expression of transglutaminase-2 (TG2) during in vitro neural differentiation of human Mesenchymal Stem Cells (hMSCs) induced by some Growth Factors (GFs). The amount and distribution of mRNAs for some transglutaminase (TGs) isoforms (TG1, TG2, TG3, TG5) were also evaluated. In addition, we tested some neural lineage markers (Glial Acid Fibrillary Protein, GFAP; Neurofilament Protein, NF; Nestin; β-Tubulin III). A progressive increase of all neural markers during GFs neural differentiation of hMSCs was found. A significant overexpression of TG1 and TG2 mRNA was observed in undifferentiated hMSCs. GFs-treatment induced a progressive decrease of TG1 mRNA during hMSCs differentiation. A significant down-regulation of TG2 mRNA in 2 days in vitro (DIV) GFs-treated cells was observed. TG2 mRNA progressively increased during GFs hMSCs differentiation, reaching after 6 DIV of GFs-treatment of similar values to those observed in undifferentiated cells. TG3 mRNA levels were express at very low only in undifferentiated hMSCs, whereas TG5 mRNA was undetectable in undifferentiated and differentiated hMSCs. Immunocytochemical and Western blot analysis showed an overexpression of TG2 in undifferentiated hMSCs. A dramatic reduction of the protein levels in 2 DIV GFs-treated cells was observed. Its expression levels progressively increased during the differentiation of hMSCs with GFs, reaching after 6 DIV of the treatment similar values to those observed in undifferentiated cells. Our findings demonstrate the presence of multiple TGs in hMSCs during neural differentiation in vitro induced by GFs, and suggest that TG2 may be part of the downstream events associated to neural differentiation.