The cardioprotective paracrine effects exerted by human mesenchymal stem cells are negatively influenced by donor age

Background: Mesenchymal stem cells (MSC) repair infarcted hearts mainly through the release of cytoprotective factors. We compared fetal MSC (F-MSC) with adult MSC from young and elderly patients to establish if donor age influences their cardioprotective paracrine properties.
Methods: F-MSC were isolated from human placenta while adult MSC were isolated from bone marrow samples of young (yBM-MSC; age < 65 years) or old (oBM-MSC; age > 65 ) donors. Rat neonatal cardiomyocytes (H9c2) were exposed to hypoxia/reoxygenation (6/18 hours) in the presence of control medium (CTRL-M) or conditioned medium from F-MSC (F-CM), yBM-MSC (Y-CM) or oBM-MSC (O-CM). H9c2 viability was evaluated by MTS assay. Apoptosis was measured by TUNEL staining and by Caspase 3 activation (colorimetric assay and Western Blot). We used RT-PCR to verify the expression of known cytoprotective factors.
Results: The hypoxia/reoxygenation protocol reduced H9c2 viability by 55% compared with basal condition (p<0.001). F-CM and Y-CM increased cell viability by 45% and 33% (p<0.017), respectively; O-CM had no significant effect on H9c2 viability (p=n.s. vs CTRL-M). Compared with CTRL-M and O-CM, F-CM significantly reduced the number of TUNEL positive nuclei by 91% (p<0.001) and 89% (p<0.001), respectively. The Y-CM also reduced H9c2 apoptotic nuclei (- 67,5% vs CTRL-M, p<0.01; - 64% vs O-CM, p<0.01). In contrast, O-CM did not prevent H9c2 apoptotic death (-11% vs CTRL-M, p=n.s.). Both colorimetric assay and Western Blot analysis showed that Caspase-3 activation was prevented by F-CM and Y-CM but not by O-CM. F-MSC expressed PDGF-β, BMP2, EPO, FGF2 and VEGF at significantly higher level compared with oBM-MSC (p<0.05); VEGF, FGF2 and HGF transcripts were significantly higher in yBM-MSC than in oBM-MSC (p<0.05).
Conclusions: MSC can mediate cardiomyocyte protection through the release of soluble anti-apoptotic factors. However, we documented that donor age negatively influences the paracrine cytoprotective properties of adult MSC.