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. 2011 Sep 16;286(37):32002-10.
doi: 10.1074/jbc.M111.253344. Epub 2011 Jul 21.

VSports在线直播 - Taurine biosynthesis by neurons and astrocytes

Affiliations

Taurine biosynthesis by neurons and astrocytes

Victor Vitvitsky et al. J Biol Chem. .

Abstract

The physiological roles of taurine, a product of cysteine degradation and one of the most abundant amino acids in the body, remain elusive. Taurine deficiency leads to heart dysfunction, brain development abnormalities, retinal degradation, and other pathologies. The taurine synthetic pathway is proposed to be incomplete in astrocytes and neurons, and metabolic cooperation between these cell types is reportedly needed to complete the pathway. In this study, we analyzed taurine synthesis capability as reported by incorporation of radioactivity from [(35)S]cysteine into taurine, in primary murine astrocytes and neurons, and in several transformed cell lines (human (SH-SY5Y) and murine (N1E-115) neuroblastoma, human astrocytoma (U-87 MG and 1321 N1), and rat glioma (C6)). Extensive incorporation of radioactivity from [(35)S]cysteine into taurine was observed in rat glioma cells as well as in primary mouse astrocytes and neurons, establishing the presence of an intact taurine synthesis pathway in these cells VSports手机版. Interestingly, exposure of cells to cysteine or cysteamine resulted in elevated intracellular hypotaurine without a corresponding increase in taurine levels, suggesting that oxidation of hypotaurine limits taurine synthesis in cells. Consistent with its role as an organic osmolyte, taurine synthesis was stimulated under hypertonic conditions in neurons. .

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"V体育ios版" Figures

FIGURE 1.
FIGURE 1.
Schematic showing pathways for hypotaurine and taurine synthesis in mammals.
FIGURE 2.
FIGURE 2.
Elevation of intracellular hypotaurine does not affect taurine levels in human astrocytoma (U-87MG) (A) or human neuroblastoma (SH-SY5Y) (B) cells. Cells were incubated for 24 h with the indicated concentrations of cysteamine or cystamine in the medium, and intracellular taurine and hypotaurine concentrations were determined as described under “Experimental Procedures.” Symbols in A represent the mean ± S.D. of two independent samples.
FIGURE 3.
FIGURE 3.
Time-dependent changes in intracellular taurine and hypotaurine concentrations in human astrocytoma (U-87MG) (A) and human neuroblastoma (SH-SY5Y) (B) cells, incubated with 200 μm extracellular cysteamine. The data represent the mean ± S.D. n = 4 and 6 for U-87MG and SH-SY5Y cells, respectively.
FIGURE 4.
FIGURE 4.
Incorporation of [35S] from cysteine to taurine and hypotaurine in different cell types. Cells were incubated with 2 μCi/ml of [35S]cysteine in the medium for 10 h, and incorporation of radioactivity into the taurine and hypotaurine pools was determined as described under “Experimental Procedures.” Data are the mean ± S.D. n = 2 for U-87MG, 1321 N1, SH-SY5Y, and N1E-115 cell lines and n = 11, 4, and 6 for the C6 cell line, neurons, and astrocytes, respectively. CPM, counts per minute.
FIGURE 5.
FIGURE 5.
Time-dependent changes in concentrations of sulfur metabolites (A), incorporation of radioactivity into sulfur metabolites (B), and incorporation of radioactivity into proteins (C) in C6 rat glioma cells following incubation with [35S]-cysteine. Symbols represent the mean ± S.D. of two separate samples. Representative data from four independent experiments are shown. CPM, counts per minute.
FIGURE 6.
FIGURE 6.
Time-dependent changes in sulfur metabolite concentrations (A), incorporation of radioactivity into sulfur metabolites (B), and incorporation of radioactivity into proteins (C) in primary mouse astrocytes following incubation with [35S]cysteine. Symbols represent the mean ± S.D. of two separate samples. Representative data from four independent experiments are shown. CPM, counts per minute.
FIGURE 7.
FIGURE 7.
Time-dependent changes in sulfur metabolite concentrations (A), incorporation of radioactivity into sulfur metabolites (B), and incorporation of radioactivity into proteins (C) in primary mouse neurons following incubation with [35S]cysteine. Representative data from three independent experiments are shown. CPM, counts per minute.
FIGURE 8.
FIGURE 8.
Relative concentrations of sulfur metabolites (A) and incorporation of radioactivity into protein and metabolite pools (B) after 10 h of incubation with [35S]cysteine. Metabolite concentrations and radioactivity were normalized per gm of cell protein. The data summarize results from multiple repeats of experiments shown in Figs. 5–7 and represent the mean ± S.D. n = 8, 8, and 3 for rat glioma cells, astrocytes, and neurons, respectively.
FIGURE 9.
FIGURE 9.
Incubation with exogenous cysteamine elicits an increase in intracellular hypotaurine but not taurine in cells capable of taurine synthesis. Cells were incubated for 48 h in the presence of 200 μm of cysteamine, and the intracellular hypotaurine (A) and taurine (B) concentrations were measured as described under “Experimental Procedures.” The concentrations are represented as percentage of untreated controls. Data are the mean ± S.D. n = 6 and 3 for astrocytes and neurons, respectively.
FIGURE 10.
FIGURE 10.
Intracellular concentrations of taurine in the human astrocytoma cell line (U-87MG) and in primary murine astrocytes cultured in media containing untreated or dialyzed FBS as described under “Experimental Procedures.” Data are the mean ± S.D. n = 6 and 18 for U-87MG and astrocytes, respectively.
FIGURE 11.
FIGURE 11.
Hypertonic conditions increase intracellular taurine concentrations. A, human astrocytoma cells (U-87MG) were incubated for 48 h in normal (300 mosmol) or hypertonic (400 mosmol) medium. Data are the mean ± S.D. n = 8. B, primary mouse astrocytes were incubated for 48 h in normal (300 mosmol) or hypertonic (400 mosmol) medium, supplemented with [35S]cysteine. Data are the mean ± S.D. n = 4. C, primary mouse neurons were incubated for 48 h in normal (300 mosmol) or hypertonic (400 mosmol) medium supplemented with [35S]cysteine. [Tau]in, [Tau]ex, and Tau RA indicate taurine concentration in cells, in the medium, and radioactivity associated with the intracellular taurine pool, respectively. Data represent the mean ± S.D. n = of five to seven independent experiments.

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