Soluble factors released by human mesenchymal stem cells of fetal origin lead to cardiomyocyte protection through the inhibition of pro-apoptotic signaling

Background: Adult mesenchymal stem cells (MSC) repair infarcted hearts mainly through cytoprotective paracrine mechanisms. Recently, MSC of fetal origin have been isolated from human amniotic membrane (A-MSC) but it is unknown if A-MSC can mediate cytoprotection and which pathways are eventually involved.
Methods: A-MSC were isolated from human term placenta. Rat neonatal cardiomyocytes (H9c2) were exposed to 6 hours of hypoxia followed by 18 hours of reoxygenation in the presence of control medium (CTRL-M) or conditioned medium from A-MSC (A-MSC-CM). H9c2 viability was evaluated by MTS assay. Apoptosis was measured by TUNEL staining and by Caspase 3 activation (colorimetric assay and Western Blot). SAPK/JNK and p38 MAPK activation was analyzed by Western blotting. We used RT-PCR to evaluate pro- and anti-apoptotic genes in H9c2 cells and known cytoprotective factors in A-MSC.
Results: Compared with CTRL-M, A-MSC-CM remarkably increased viability of H9c2 by 45% (p<0.001) and significantly reduced the number of TUNEL positive nuclei by 91% (p<0.001). Furthermore, both colorimetric and Western Blot assay showed that A-MSC-CM prevented Caspase 3 cleavege (p= n.s. vs normoxia). The hypoxia/reoxygenation induced a marked activation of SAPK/JNK and p38 MAPK that was strongly limited by A-MSC-CM. Furthermore, the A-MSC-CM increased the expression of Bcl-2 and Stat3 and inhibited transcription of TNF-α and FasL compared with CTRL-M. Finally, we documented that A-MSC express cytoprotective factors such as PDGF-β , BMP2, EPO, IGF-1, FGF2 and VEGF.
Conclusions: We demonstrated that A-MSC express several cytoprotective factors and that A-MSC-CM remarkably protects cardiac myocytes against hypoxia/reoxygenation damage, through the inhibition of SAPK/JNK and p38 MAPK pro-apoptotic pathways. A-MSC-CM also mediates the over-expression of anti-apoptotic genes Bcl-2 and Stat3 and the downregulation of pro-apoptotic factors TNF-α and FasL. A-MSC theraphy may represent a novel and powerful approach for cardioprotection in ischemic heart disease.