Glycine and other amino compounds prevent chromatin precipitation at physiological ionic strength

Water Homeostasis and Cell Volume Maintenance and Regulation

From early unicellular organisms that formed in salty water environments to complex organisms that live on land away from water, cells have had to protect a homeostatic internal environment favorable to the biochemical reactions necessary for life. In this chapter, we will outline what steps were necessary to conserve the water within our cells and how mechanisms have evolved to maintain and regulate our cellular and organismal volume. We will first examine whole body water homeostasis and the relationship between kidney function, regulation of blood pressure, and blood filtration in the process of producing urine. We will then discuss how the composition of the lipid-rich bilayer affects its permeability to water and salts, and how the cell uses this differential to drive physiological and biochemical cellular functions. The capacity to maintain cell volume is vital to epithelial transport, neurotransmission, cell cycle, apoptosis, and cell migration. Finally, we will wrap up the chapter by discussing in some detail specific channels, cotransporters, and exchangers that have evolved to facilitate the movement of cations and anions otherwise unable to cross the lipid-rich bilayer and that are involved in maintaining or regulating cell volume.

Taurine stimulates proliferation and promotes neurogenesis of mouse adult cultured neural stem/progenitor cells

This study reports an effect of taurine (1-10 mM) increasing markedly (120%) the number of neural precursor cells (NPCs) from adult mouse subventricular zone, cultured as neurospheres. This effect is one of the highest reported for adult neural precursor cells. Taurine-containing cultures showed 73-120% more cells than controls, after 24 and 96 h in culture, respectively. Taurine effect is due to enhanced proliferation as assessed by BrdU incorporation assays. In taurine cultures BrdU incorporation was markedly higher than controls from 1.5 to 48 h, with the maximal difference found at 1.5 h. This effect of taurine reproduced at every passage with the same window time. Taurine effects are not mimicked by glycine, alanine or GABA. Clonal efficiency values of 3.6% for taurine cultures and 1.3% for control cultures suggest a taurine influence on both, progenitor and stem cells. Upon differentiation, the proportion of neurons in control and taurine cultures was 3.1% (±0.5) and 10.2% (±0.8), respectively. These results are relevant for taurine implication in brain development as well as in adult neurogenesis. Possible mechanisms underlying taurine effects on cell proliferation are discussed.

Effect of compensatory organic osmolytes on resistance to freeze-drying of L929 cells and of their isolated chromatin

(1) Compensatory organic osmolytes are stabilizers of macromolecular structures. During acclimation to dehydration or high salinity, they accumulate in cells and effectively protect them against disruption that might otherwise result from increased inorganic ion concentrations. (2) Circular and electric dichroism, analysis of the kinetics of digestion by micrococcal nuclease, and UV spectra between 190 and 305 nm were used to investigate the resistance to dehydration upon freezing or freeze-drying that could confer such compounds to chromatin isolated from cultured L929 cells. Some work was also done on intact cells in vivo. (3) Sorbitol, sucrose, and trehalose appear to protect isolated chromatin very effectively; proline is less effective. (4) These compounds also effectively protect chromatin from the disrupting effects of NaCl. (5) Cells loaded and grown with sorbitol, sucrose, or proline can tolerate larger decreases in hydration than control cells. They cannot, however, tolerate complete dehydration.

"Compensatory" organic osmolytes in high osmolarity and dehydration stresses: history and perspectives

As stated in the conclusion, "life is a thing of macromolecular cohesion in salty water." This brief historical overview shows that "compensatory" organic osmolytes take an essential place in this cohesion. It reviews the major steps of the study of these compounds over more than 100 years, from the early beginnings of 1885 until now, showing some of its fascinating developments and ending on the idea that the most fascinating is still to come. This study can be taken as an example of the richness of the comparative approach.

Effects of compensatory solutes on DNA and chromatin structural organization in solution

We investigated the effect of glycine and other osmotic effectors on DNA and chromatin precipitation by mono-, di- and multivalent cations and histone H1. The addition of these compounds drastically reduces the precipitation effects with an efficiency in the order taurine > glycine > proline and sorbitol > inositol > betaine. Aminocarboxylic acids with increasing distance between the charged C- and N-terminal groups displayed enhanced efficiency in the protection effect against DNA precipitation. We interpreted these observations on the basis of Manning's counterion condensation theory, taking into account the increase in dielectric constant upon osmotic effector addition. 23Na-NMR was used to evidence sodium counterions release as a result of this increase in dielectric constant.

23Na NMR study of the effect of organic osmolytes on DNA counterion atmosphere

The effect of different organic osmolytes on the DNA counterion condensation layer has been investigated by 23Na NMR relaxation measurements. The zwitterionic compounds glycine, beta-alanine, 4-aminobutyric acid, and 6-aminocaproic acid have shown an increasing capacity to decrease the amount of sodium ions in the vicinity of the macromolecule. The experimental data have been correlated with the dielectric constant increase in their corresponding solutions and have been compared with the prediction of counterion condensation theory. Polyols (sorbitol and mannitol) did not display the same effect. These compounds largely increase the relaxation rate of sodium ions in the proximity of DNA, unlike the zwitterionic compounds. This probably results from a perturbation of the water dynamic around the macromolecule, of the primary or secondary hydration shell of the sodium nuclei involved, or both.

Dielectric constant and ionic strength effects on DNA precipitation

We have investigated the effect of different zwitterionic compounds on DNA precipitation induced by spermine4+. Glycine, beta-alanine, 4-aminobutyric acid, and 6-aminocaproic acid have shown an increasing capacity to attenuate DNA precipitation. This protection effect has been correlated with the dielectric constant increase of their corresponding solutions. Calculations based on these experimental data and counter-ion condensation theory have confirmed the importance of this parameter for DNA-ion interactions and precipitation mechanisms. We have also observed a resolubilization of DNA in the presence of 6-aminocaproic acid at high spermine4+ concentration and in the presence of glycine at high spermidine3+ concentration. This could be explained by an increase of screening effect with polyamine concentration.

Tolerance to osmotic shocks in rats kidney cortex and medulla

Kidney medulla cells of mammals have to cope with large changes in environmental osmolarity, a challenge most other mammalian cells never have to experience. In these last cells, application of osmotic shocks induces dramatic modifications in chromatin organization. The present paper reports on the changes of medulla cell chromatin in situ, in rat kidney slices submitted to osmotic challenges and in vitro, on preparations of extracted chromatin submitted to changes in environmental ion concentrations. Our results show that the chromatin of kidney medulla cells: (1) does not behave differently from the other mammalian chromatins when submitted in situ or in vitro to osmotic challenges; (2) presents in vitro physico-chemical characteristics similar to those of the other mammalian chromatins; and (3) is protected in vitro, as the other mammalian chromatins, from the disrupting effects of increases in inorganic ion concentrations by different compensatory organic solutes. The ability of kidney medulla cells to adapt to large increases in osmolarity could thus be related to a rapid control of the level of such compounds rather than to some rather specific, intrinsic molecular adaptations of macromolecules.

Effect of high osmolarity acclimation on tolerance to hyperosmotic shocks in L929 cultured cells

Application of abrupt, large hyperosmotic shocks induces in L929 cultured cells changes similar to those previously described in other cell types, notably a hypercondensation of the nuclear chromatin. This paper shows that; 1) this phenomenon is concomitant with a complete disappearance of deoxyribonucleic acid, as visualized by immunogold labelling, from the nucleoplasmic spaces; 2) acclimation to high osmolarities (600 mOsm) by addition to the culture medium of NaCl, sorbitol or proline protects the cells from these effects, which appear to be largely attenuated-acclimated cells also survive much better to the osmotic shock than do control cells and; 3) the best protection seems to be provided by sorbitol and NaCl. Proline acclimation is less effective. These effects are discussed in terms of increased tolerance to NaCl load induced at the level of different macromolecules by so-called 'compensatory' organic compounds.

Increased tolerance to large hyperosmotic shocks and compensatory solutes in mammalian cultured cells

L929 and MDCK cells acclimated to sorbitol, proline or taurine media can tolerate a NaCl load that they would be unable to stand when cultured in normal conditions. The protecting effect is observed only at high concentrations, between 100 and 300 mM. In that range, the effect is increasing with increasing concentration. The presence of the compound is not necessary, in the extracellular medium, to induce tolerance. These results are discussed in the framework of the theory considering preferential interactions of proteins with solvent components to explain the protecting effect of such compounds.

Osmotic effectors and DNA structure: effect of glycine on precipitation of DNA by multivalent cations

We have investigated the effect of glycine (an organic osmolyte) on DNA precipitation induced by spermine4+, spermidine3+ and Tb3+ addition, using circular dichroism (CD), UV spectroscopy (UV), and electric linear dichroism (ELD) techniques. DNA precipitation by the three compounds is perturbed by glycine: more spermine4+, spermidine3+ and Tb3+ must be added to obtain the same extent of precipitation as compared to the behaviour in absence of this organic osmolyte. It seems that glycine has a general effect on the DNA environment. Calculations based on experimental results and Manning's counterion condensation theory show that glycine could modify the electrostatic environment of DNA as a consequence of a change in dielectric constant.

Effect of organic effectors on chromatin solubility, DNA-histone H1 interactions, DNA and histone H1 structures

We have extended our previous investigations on the effect of organic osmolytes (glycine, proline, taurine, mannitol, sorbitol and trimethylammonium oxide (TMAO)) on chromatin solubility, to the study of their influence on DNA stability and DNA-histone interactions. Our aim was to understand the molecular origin of the protection effects observed. To this end, we determined the amount of histone H1 required to precipitate DNA or H1-depleted chromatin, at various salt concentrations, in the presence of the above mentioned organic compounds. We found a shift of the H1/DNA ratio required to reach 50% precipitation, towards higher values. Taurine was the most efficient compound followed by mannitol and glycine, then sorbitol and proline. On the contrary, TMAO favoured the precipitation process. We attempted to interpret these results on the basis of Manning's counterion condensation theory. Changes in histone H1 structure folding and in DNA melting temperature Tm were also analyzed. Glycine, taurine, sorbitol and TMAO increased the degree of secondary structure folding of the protein while mannitol and sorbitol had no effect. Taurine, glycine and proline decreased the Tm of DNA, TMAO largely destabilized DNA, but mannitol and sorbitol had no effect. Measurements of NaCl activity in the presence of organic osmolytes did not reveal sufficiently large changes to account for their protection effect against chromatin precipitation. The osmotic coefficient j of the organic effectors solutions increased in the order: taurine < glycine < sorbitol < mannitol < proline << TMAO. For the two latter compounds, the j values increased above 1 at high concentration. We consider that the organic compounds investigated may be classified into three categories: (i) class I (zwitterionic compounds: glycine, proline, taurine) would produce sodium ions release from the DNA surface; (ii) class II (the very polar molecule TMAO) would increase sodium counterions condensation on DNA together with histone H1 folding; (iii) class III compounds (mannitol and sorbitol) would possibly produce a modification of NaCl activity but no definite explanation could be found for the complex behavior of these compounds.

Organic osmotic effectors and chromatin structure

Organic amino compounds (taurine, glycine) and polyols (mannitol, sorbitol) are used as osmotic effectors by most animal cells, particularly by some marine invertebrates, but also to a limit extent by mammalian cells. Using physico-chemical techniques (circular dichroism, thermal denaturation, solubility, electrophoresis and electric linear dichroism), we demonstrated that some of these effectors prevent chromatin aggregation, without histone release. The influence of glycine on chromatin aggregation, dissociation and reconstitution was thoroughly investigated. Glycine at 2 M concentration does not in itself induce chromatin dissociation; it does hinder salt-induced histone dissociation from chromatin (especially at 1.2 M NaCl) but does not impede chromatin reconstitution. Several hypothesis may be put forward to explain the action of these effectors: (i) a modulation of histone conformation; (ii) a modification of fractional DNA charge, either directly by the zwitterions (glycine, taurine) or indirectly by alteration of cations counterions hydration. The physiological relevance of our experiments is also discussed.