The Proteinase-activated receptor 1 in mesenchymal stem cellProteinase-activated receptor 1 in mesenchymal stem cells : importance for the progression of hepatocellular carcinoma

Mesenchymal stem cells (MSCs) provide a valuable resource for the treatment of diseased tissues like chronic wounds or especially liver cirrhosis. However, inflammation- and coagulation-affected tissues produce proteinases that activate proteinase-activated receptors (PARs), which are insufficiently characterized in MSCs. In this context, we characterized the four subtypes of the PAR family in adipose tissue-derived (AT-MSCs. Using expression analysis and Ca2+ mobilization arrays, our results pointed out that PAR1 was the predominating PAR subtype in AT MSCs. We showed that PAR1 activation reduced the migration rate of AT-MSCs and played a crucial role in the upregulation of expression and secretion of interleukins 6 and 8. Our data suggests a major dependence of the PAR1-elicited elevation on the intracellular free Ca2+ level and the Ca2+-dependent protein kinase C for AT-MSC’s cytokine production and secretion. In order to assess the biologic relevance of a potential interaction of MSCs and aberrant hepatocytes during cellular therapy of diseased liver tissue we subcutaneously co-injected AT-MSCs and cells from the HCC cell line Hep3B into immunocompromised mice. Hep3B cells and AT-MSCs together caused a strong formation of tumors with typical histologic HCC characteristics, while Hep3B cells alone only occasionally caused tumors of significantly smaller size and AT-MSCs alone caused no tumors. Using green fluorescent protein (GFP)-labeled AT MSCs, we were not able to detect GFP in the formed Hep3B tumors, suggesting promoting effects of AT-MSCs on Hep3B cells during initial tumor formation. The application of a shRNA-mediated stable knockdown of PAR1 in AT-MSCs had no significant impact on the observed tumor formation. Therefore, the potentially PAR1-triggered signaling in AT-MSCs did not seem to have an influence on the experimental tumor formation.Hence, we show that PAR1 has an important impact for AT-MSC’s biology and microenvironment.