Induction of Apoptosis in Response to Anhydrobiotic Conditions in Mammalian Cells

Dry state preservation of nucleated cells: progress and challenges

Effective stabilization of nucleated cells for dry storage would be a transformative development in the field of cell-based biosensors and biotechnologic devices, as well as regenerative medicine and other areas in which stem cells have clinical utility. Ultimately, the tremendous promise of cell-based products will only be fully realized when stable long-term storage becomes available without the use of liquid nitrogen and bulky, energetically expensive freezers. Significant progress has been made over the last 10 years toward this goal, but obstacles still remain. Loading cells with the protective disaccharide trehalose has been achieved by several different techniques and has been shown to increase cell survival at low water contents. Likewise, the protective effect of heat shock proteins and other compounds have also been explored alone and in combination with trehalose. In some cases, the benefit of these molecules is seen not initially upon rehydration, but over time during cellular recovery. Other considerations, such as inhibiting apoptosis and utilizing isotonic buffer conditions have also provided stepwise increases in cell viability and function following drying and rehydration. In all these cases, however, a low level of residual water is required to achieve viability after rehydration. The most significant remaining challenge is to protect nucleated cells such that this residual water can be safely removed, thus allowing vitrification of intra- and extracellular trehalose and stable dry state storage at room temperature.

Inhibition of high glucose-induced erythrocyte phosphatidylserine exposure by leupeptin and disaccharides

High glucose can lead to serious phosphatidylserine exposure of erythrocytes which may influence the protective effect of glucose on lyophilization of erythrocytes. In this study, caspase activation has not occurred during phosphatidylserine exposure of erythrocytes. However, leupeptin can efficiently inhibit phosphatidylserine exposure of erythrocytes induced by high glucose. With increase of the leupeptin concentrations, the percentages of cells with exposed phosphatidylserine were decreased steadily. In addition, trehalose and sucrose can significantly inhibit phosphatidylserine exposure and cell shrinkage of erythrocytes induced by high glucose through increasing tolerance to osmotic shock. When the disaccharide concentrations were more than 100 mM, the percentages of cells with exposed phosphatidylserine were similar to those of control cells. Moreover, addition of disaccharides in the glucose buffer can result in high osmotic pressure which may facilitate uptake of glucose and disaccharides into erythrocytes and higher cellular glucose and disaccharide concentrations can provide more protection for lyophilized erythrocytes. Although disaccharides can increase the osmotolerance and decrease the phosphatidylserine exposure of erythrocytes exposed to high glucose, whether disaccharides can prevent phosphatidylserine exposure of lyophilized erythrocytes still needs further researches.

Desiccation Response of Mammalian Cells: Anhydrosignaling

Dehydration through evaporation, or air drying, is expected to have both similarities and differences to osmostress. Both stresses involve water loss, but the degree of dehydration will ultimately be more severe during desiccation. Despite the severity of desiccation stress, there are examples of organisms that can survive almost complete water loss, including resurrection plants and plant seeds, certain invertebrates among the nematodes, brine shrimps, tardigrades and bdelloid rotifers, and many microorganisms, including bakers' yeast. During desiccation, these organisms enter a state of suspended animation, a process known as anhydrobiosis ("life without water"). For other organisms, desiccation is lethal, but there is considerable interest in using what is known about anhydrobiosis to confer desiccation tolerance on sensitive cell types, such as mammalian cells. Success with this approach, which we have termed anhydrobiotic engineering, will require a more complete knowledge of the mechanisms of desiccation tolerance and the sensing and response of nontolerant organisms to extreme dehydration. With this goal in mind, we have attempted to characterize the response of human tissue culture cells to desiccation and to compare this response with osmotic upshift. This chapter describes some of the methods used to begin to uncover the response to evaporative water loss in human cell cultures.

Trehalose uptake through P2X7 purinergic channels provides dehydration protection

The tetra-anionic form of ATP (ATP4-) is known to induce monovalent and divalent ion fluxes in cells that express purinergic P2X7 receptors and with sustained application of ATP it has been shown that dyes as large as 831 Da can permeate the cell membrane. The current study explores the kinetics of loading alpha,alpha-trehalose (342 Da) into ATP stimulated J774.A1 cells, which are known to express the purinergic P2X7 receptor. Cells that were incubated at 37 degrees C in a 50 mM phosphate buffer (pH 7.0) containing 225 mM trehalose and 5 mM ATP, were shown to load trehalose linearly over time. Concentrations of approximately 50 mM were reached within 90 min of incubation. Cells incubated in the same solution at 4 degrees C loaded minimally, consistent with the inactivity of the receptor at low temperatures. However, extended incubation at 37 degrees C (>60 min) resulted in zero next-day survival, with adverse effects appearing even with incubation periods as short as 30 min. By using a two-step protocol with a short time period at 37 degrees C to allow pore formation, followed by an extended loading period on ice, cells could be loaded with up to 50 mM trehalose while maintaining good next day recovery (49 +/- 12% by Trypan blue exclusion, 56 +/- 20% by alamarBlue assay). Cells porated by this method and allowed an overnight recovery period exhibited improved dehydration tolerance suggesting a role for ATP poration in the anhydrous preservation of cells.