Physiological role of taurine – from organism to organelle

Abstract

Taurine is often referred to as a semi-essential amino acid as newborn mammals have a limited ability to synthesize taurine and have to rely on dietary supply. Taurine is not thought to be incorporated into proteins as no aminoacyl tRNA synthetase has yet been identified and is not oxidized in mammalian cells. However, taurine contributes significantly to the cellular pool of organic osmolytes and has accordingly been acknowledged for its role in cell volume restoration following osmotic perturbation. This review describes taurine homeostasis in cells and organelles with emphasis on taurine biophysics/membrane dynamics, regulation of transport proteins involved in active taurine uptake and passive taurine release as well as physiological processes, for example, development, lung function, mitochondrial function, antioxidative defence and apoptosis which seem to be affected by a shift in the expression of the taurine transporters and/or the cellular taurine content.

Taurocholic acid metabolism by gut microbes and colon cancer

“…Taurine is synthesized in hepatocytes from methionine and cysteine in adults, but is considered semi-essential due to the limited synthetic capacity of neonates, and declining biosynthetic capability with age and certain diseases. 21 The taurine content of various foods and food products are summarized in Table 1. Diets rich in taurine include those high in animal protein and seafood; while vegetarian diets, particularly vegan result in significantly lower levels of taurine measured in blood and urine.…”

Role of volume-regulated and calcium-activated anion channels in cell volume homeostasis, cancer and drug resistance

“…RVD reflects increase in the permeability to the dominant cellular cation K C , the anion Cl -and amino acids. 7,12,13 That cell swelling transiently activates electrogenic anion permeability was first described in Ehrlich ascites tumor cells (EATC) 10 and in lymphocytes. 14 Figure 1A illustrates Cl -efflux under isotonic, hypotonic and hypertonic conditions, and it has been determined that under isotonic conditions less than 5% represents conductive Cl -flux with the rest being electroneutral anion exchange (AE).…”

“…Taurine (b-amino ethane sulphonic acid), which accounts for approximately 0.1% of our total bodyweight, 83 is often used as a model to illustrate how cells modulate the cellular content of the organic osmolytes following cellular stress (osmotic challenge, hypoxia, ischemia). 13 It is emphasized that a shift in the cellular taurine content will not only affect cell volume but also have an impact on membrane dynamics, metabolism, antioxidative capacity as well as apoptotic progression and drug resistance (see e.g., 13 ). An extraordinarily high cellular to extracellular taurine concentration gradient (400:1) is reported in e.g.…”

“…EATC and the retina, 84,85 which reflects a low plasma membrane permeability to the zwitter-ionic taurine (high water solubility/low lipophilicity) and the presence of a Na C -dependent, high-affinity transporter TauT (SLC6A6) in the plasma membrane. 13 However, it has been demonstrated that following osmotic cell swelling in e.g., EATC 84 and NIH3T3 mouse fibroblasts 86,87 a net loss of taurine and hence restoration of cell volume are partly ensured by activation of a volume-sensitive leak pathway for organic osmolytes, designated VSOAC (volume sensitive organic anion channel) and a concomitant down-regulation of TauT. Using HeLa cells (Fig.…”

“…87 Swelling-induced activation of VSOAC has, in a variety of cell lines, been demonstrated to 74 involve sequential activation of a cell-specific phospholipase A 2 (PLA 2 ) and the 5-lipoxygenase (5-LO) and once activated, VSOAC activity can be modulated by (i) protein and phosphoinositide kinases/phosphatases, (ii) nucleotides/Ca 2C /calmodulin, as well as (iii) ROS generated by NADPH oxidases. 13,88,89 VRAC vs. VSOAC The molecular identity of VSOAC has been controversial and more than one channel has been demonstrated to be involved in release of organic osmolytes. 90 VRAC has been suggested as a VSOAC candidate 53,91 and as indicated below the discovery of LRRC8 family members as essential components of VSOAC and VRAC 2,4 nourishes this hypothesis.…”