The role of taurine in cellular redox-homeostasis, muscle development and function - Studies in cultured cells and Atlantic salmon (Salmo salar)

Taurine is a non-proteinogenic ß-aminosulfonic acid. Important dietary sources of taurine are fish and seafood. Taurine interacts with ion channels, stabilizes membranes and regulates the cell volume. These actions confirm its high concentrations in excitable tissues like retina, neurons and muscles. Retinal degeneration, cardiomyopathy as well as skeletal muscle malfunction are evident in taurine deficient phenotypes. However, the underlying cellular and molecular mechanisms of taurine remain unclear. The aim of the present dissertation was to investigate the cytoprotective action of taurine with a special focus on cellular redox homeostasis. Furthermore, the role of taurine in myogenesis and mitochondrial biogenesis was studied. For this purpose, studies were conducted in vitro in cultured hepatocytes (HepG2) and myotubes (C2C12) and in vivo in liver and muscle tissue of Atlantic salmon (Salmo salar). Cell culture data revealed a significant reduction in lipid peroxidation after taurine incubation accompanied by a decrease in cellular glutathione (GSH). The mRNA expression of genes encoding GSH synthesis enzymes indicate a diminished GSH synthesis rate in response to taurine treatment. The relative heme oxygenase 1 (HMOX1) and catalase (CAT) mRNA levels were consistently downregulated in both cell lines following taurine supplementation. The decrease in lipid peroxidation along with a downregulation of anti-oxidative enzymes und GSH levels suggest a reduced need for anti-oxidative defence due to taurine.Myogenic markers were examined in C2C12 myotubes. Incubation with taurine enhanced the cellular myoglobin protein level, markers for mitochondrial biogenesis and several mitochondria-specific proteins, while cellular ATP level were unchanged. For the in vivo aquaculture studies, post-smolt salmon were randomly divided into four groups. The groups received four different diets with varying taurine concentrations and sources: 0FM (0 % fishmeal + 0 % taurine), 15FM (15 % fishmeal + 0 % taurine), 0FM+T (0 % fishmeal + 0.09 % taurine) and 0FM+TT (0 % fishmeal + 1 % taurine). The different experimental diets only had small effects on taurine metabolism and tissue concentrations. The amount of lipid peroxidation products, the GSH levels and the mRNA expression of several anti-oxidative enzymes were not affected by the dietary taurine. Overall, dietary taurine did not affect markers of myogenic differentiation or energy metabolism in vivo in muscle tissue of Atlantic salmon. In summary, the taurine-mediated effects observed in cultured cells in vitro could not be confirmed in Atlantic salmon in vivo. Because Atlantic salmon are relatively efficient taurine synthesizers, future studies should focus on animal models with a poor endogenous taurine synthesis capacity.