Hypoxia/hypercapnia-induced adaptation maintains functional capacity of cord blood stem and progenitor cells at 4°C.

We analyzed the effect of exposure to hypoxic/hypercapnic (HH) gas mixture (5% O2 /9% CO2 ) on the maintenance of functional cord blood CD34(+) hematopoietic stem and progenitor cells in severe hypothermia (4°C) employing the physiological and proteomic approaches. Ten-day exposure to HH maintained the Day 0 (D-0) level of hematopoietic stem cells as detected in vivo on the basis of hematopoietic repopulation of immunodeficient mice-short-term scid repopulating cells (SRC). Conversely, in the atmospheric air (20% O2 /0.05% CO2 ), usual condition used for cell storage at 4°C, stem cell activity was significantly decreased. Also, HH doubled the survival of CD34(+) cells and committed progenitors (CFCs) with respect to the atmospheric air (60% vs. 30%, respectively). Improved cell maintenance in HH was associated with higher proportion of aldehyde dehydrogenase (ALDH) positive cells. Cell-protective effects are associated with an improved maintenance of the plasma and mitochondrial membrane potential and with a conversion to the glycolytic energetic state. We also showed that HH decreased apoptosis, despite a sustained ROS production and a drop of ATP amount per viable cell. The proteomic study revealed that the global protein content was better preserved in HH. This analysis identified: (i) proteins sensitive or insensitive to hypothermia irrespective of the gas phase, and (ii) proteins related to the HH cell-protective effect. Among them are some protein families known to be implicated in the prolonged survival of hibernating animals in hypothermia. These findings suggest a way to optimize short-term cell conservation without freezing.