Human mesenchymal stem cell-replicative senescence and oxidative stress are closely linked to aneuploidy.

In most clinical trials, human mesenchymal stem cells (hMSCs) are expanded in vitro before implantation. The genetic stability of human stem cells is critical for their clinical use. However, the relationship between stem-cell expansion and genetic stability is poorly understood. Here, we demonstrate that within the normal expansion period, hMSC cultures show a high percentage of aneuploid cells that progressively increases until senescence. Despite this accumulation, we show that in a heterogeneous culture the senescence-prone hMSC subpopulation has a lower proliferation potential and a higher incidence of aneuploidy than the non-senescent subpopulation. We further show that senescence is linked to a novel transcriptional signature that includes a set of genes implicated in ploidy control. Overexpression of the telomerase catalytic subunit (human telomerase reverse transcriptase, hTERT) inhibited senescence, markedly reducing the levels of aneuploidy and preventing the dysregulation of ploidy-controlling genes. hMSC-replicative senescence was accompanied by an increase in oxygen consumption rate (OCR) and oxidative stress, but in long-term cultures that overexpress hTERT, these parameters were maintained at basal levels, comparable to unmodified hMSCs at initial passages. We therefore propose that hTERT contributes to genetic stability through its classical telomere maintenance function and also by reducing the levels of oxidative stress, possibly, by controlling mitochondrial physiology. Finally, we propose that aneuploidy is a relevant factor in the induction of senescence and should be assessed in hMSCs before their clinical use.

Antioxidant effect of lemon verbena extracts in lymphocytes of university students performing aerobic training program.

Aerobic training is related to an increase in blood oxidation markers. The purpose of the present study was to investigate the antioxidant capacity of Lippia citriodora extracts (PLX(®) ) on plasma and blood cell oxidative status of university students beginning a 21 days aerobic training routine (3 days/week). Using a double-blind design, 15 male athletes (21 ± 2.1 years) were assigned to a group consuming 1.8 g/day of the plant extract (PLX(®) -group) or a placebo (PLB-group). Two blood extractions were performed at day 0 and 21, from which lymphocytes, erythrocytes and plasma were isolated. Several circulating parameters, antioxidant enzyme activities and oxidative stress markers were measured. The PLX(®) -group displayed an increased HDL-cholesterol, a modest decrease in erythrocyte number and an increased circulating urea. Activation of glutathione (GSH)-reductase was observed in erythrocytes and lymphocytes of PLX(®) -group, accompanied by lower levels of oxidative stress markers, such as malondialdehyde and protein carbonyls in plasma. The antioxidant action exerted by PLX(®) on GSH-reductase seems to be post-translational and mainly due to verbascoside, a phenylpropanoid that represents 10% (w/w) of extract content. In conclusion, PLX(®) shows antioxidant properties that could play an important role in modulating GSH-reductase activity in lymphocytes and erythrocytes and protecting plasma from exercise oxidative damage.

Culture of human mesenchymal stem cells at low oxygen tension improves growth and genetic stability by activating glycolysis.

Expansion of human stem cells before cell therapy is typically performed at 20% O(2). Growth in these pro-oxidative conditions can lead to oxidative stress and genetic instability. Here, we demonstrate that culture of human mesenchymal stem cells at lower, physiological O(2) concentrations significantly increases lifespan, limiting oxidative stress, DNA damage, telomere shortening and chromosomal aberrations. Our gene expression and bioenergetic data strongly suggest that growth at reduced oxygen tensions favors a natural metabolic state of increased glycolysis and reduced oxidative phosphorylation. We propose that this balance is disturbed at 20% O(2), resulting in abnormally increased levels of oxidative stress. These observations indicate that bioenergetic pathways are intertwined with the control of lifespan and decisively influence the genetic stability of human primary stem cells. We conclude that stem cells for human therapy should be grown under low oxygen conditions to increase biosafety.