Growing evidence from animal studies shows that adipose tissue-derived stem cells (ASCs) improve cardiac function of infarcted hearts. It is commonly accepted that therapeutic potential of ASCs may depend more on their paracrine effects than differentiation potential. The underlying mechanisms remain unclear. However, most data regarding paracrine factors were obtained from ASCs cultured in normoxic condition (20%). The present study investigated how in vivo physiological oxygen (4%) tension influenced the secretome of ASCs.
ASCs were isolated from three 8-week-old BALB/c mice. ASCs were confirmed by the expression of stem cell markers (CD44 and CD90) and their capacity to differentiate into adipocytes and osteocytes. ASCs at passage 5 were cultured in normoxic (20%) and lower oxygen (4%) incubators and conditioned for 24 h (3 cultures/group). The conditioned media (CM) from ASCs were subjected to trypsin digestion followed by analysis using automated nano-flow liquid chromatography tandem mass spectrometry. The collected LC/MS/MS data were searched against the rodent subset of the Uniprot database and the total proteomes were identified. The data were from 6 technical replicates.
A total of 28 proteins were identified and 7 proteins were unique to normoxic CM. Of the 21 common proteins detected in both normoxic and lower oxygen CM, 9 were extracellular matrix proteins. The abundance of 6 of these proteins (e.g., collagen I and laminin) differed noticeably between normoxic and lower oxygen CM. In addition, a greater amount of cytokine CXCL5 and matrix metalloproteinase (MMP)-2 was detected in lower oxygen CM than in normoxic CM while tissue inhibitor of metalloproteinase (TIMP)-1 was only detected in normoxic CM.
These results indicate that lower oxygen tension differentially regulates the secretome of ASCs. Extrapolating the results of this study to the in vivo setting, it would appear that injected ASCs may exert their anti-fibrotic and trophic effect by 1) directly regulating the balance of MMP/TIMP production and preventing collagen accumulation in ischemic hearts to decrease fibrosis, and 2) secreting trophic factors including CXCL5. These data suggest that proteomic analysis of CM is useful for elucidation of the paracrine effect of ASCs in vivo.
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