In addition to the proliferative genes the microarray from N
In addition to the proliferative genes, the microarray from NPCs showed a significant regulation by taurine of certain types of GDC0199 cost and collagen genes. This result agrees with that by Warskulat et al. (2006) in cardiac cells. Also, the regulation exerted on a group of mitochondrial genes agrees with that by Mortensen et al. (2010b) in skeletal muscle and hepatic cells. A recent study of Liang et al. (2013) by a Gene Ontology analysis concludes that the genes modified by the presence of taurine in hepatic stellate cells are related to proliferation, oxidation and apoptosis functional clusters (Liang et al., 2013). These results are similar to the groups identified in the present study in NPCs. The cDNA microarray results for the taurine-containing cultures demonstrated the down regulation of pathways related to cell death mediated by the ubiquitin/proteosome (UBP) system. In particular, significant changes in the levels of gene transcripts for UBE1-3 were found in the microarray analysis. The UBP system is an essential regulator of apoptosis and plays a critical role in cell survival in cultures (Vucic et al., 2011; Canu et al., 2000). This system operates in brain stem cells, where it participates as a regulator of proliferation and apoptosis. Disturbance of the UBP system impairs proliferation and increases apoptosis in NPCs from the SVZ (An et al., 2006). The down regulation of gene transcripts of elements of this system in taurine-treated NPC cultures is consistent with the increase in the cell proliferation rate and the reduction in apoptosis and necrosis observed in these cultures compared to cultures without taurine. In our previous study (Hernandez-Benitez et al., 2012), cell viability evaluated using trypan blue was reported to be unchanged by taurine, whereas a small but significant increase in the number of viable cells was found in the present study by using a more precise quantification assay. A slight decrease in the number of apoptotic and necrotic cells in the taurine-containing cultures was also identified using this procedure. Taurine increased the fraction of the NPC population in the S phase of the cell cycle, which is the DNA synthesis phase, and conversely decreased the population in the G0/G1 phase. These effects of taurine occurred without affecting the length of the cell cycle. Altogether, these results suggest that the presence of taurine in cultures provides cells with better conditions for the transition between successive phases of the cell cycle. These results also confirmed our previous interpretation (Hernandez-Benitez et al., 2012), which attributed the increase in the number of cells in the taurine-containing cultures to enhanced cell proliferation. Mitochondrial functioning may be the site that is affected by taurine, which is a notion based on recent evidence relating taurine to the efficiency of mitochondrial function. Decreasing the taurine content in cells has been associated with deficits in function of the electron transport chain (Schaffer et al., 2014; Jong et al., 2012) due to less efficient biosynthesis of the respiratory chain complex subunits that are encoded by mitochondrial DNA. The site of taurine action has been identified as the post-transcriptional modification of the uracil ring in the bases located at the anticodon wobble positions of the mtRNAs for leucine, lysine, glutamate, and glutamine (Suzuki et al., 2002, 2011). The reaction of taurine with uridine bases of mtRNAs to form 5-taurinomethyluridines (tm5Us) improves the production of mitochondrial-encoded proteins related to the respiratory chain elements, consequently increasing the efficiency of the electron-transport chain and the synthesis of ATP. Furthermore, the delayed translation of mitochondrial gene-encoded proteins causes the accumulation of electron donors and superoxide anions, creating conditions of oxidative stress (Schaffer et al., 2009). The formation of taurine-conjugated mtRNAs facilitates an adequate energy balance and prevents oxidative stress by limiting the rate of superoxide production. Together, this represents an advantage for cells in the G1 phase of the cell cycle and their subsequent transition into later cell cycle phases. In the G1 and G2 phases, cells detect whether the internal and external environment is suitable for progression into the S phase and mitosis. In particular, the G1 phase length is sensitive to these environmental signals. If the extracellular or intracellular conditions are unfavorable, cells will delay their progress through G1. In contrast, if the conditions are favorable, cells become committed to DNA replication. These considerations are relevant to our results with NPCs and allow us to conclude that low levels of taurine and its consequences produce an unfavorable condition in control cultures that retains more cells in the G1 phase and decreases the cells in the S phase. In support of this notion, the microarray gene expression analysis of Mortensen et al. (2010a, 2010b) in cells from liver and skeletal muscle of newborn mice subjected to low protein maternal diet shows significant changes in mitochondrial genes, which are prevented by taurine. Even some mitochondrial genes are significantly up regulated by gestational taurine supplementation in the control offspring, suggesting taurine as an important factor in the control of mitochondrial gene expression (Mortensen et al., 2010b). The present results showed that several of the taurine up regulated genes (the main group according to their Z-score >2) were clustered in a pathway related with mitochondria function and in the same line were our results from the flow cytometry determinations about of the relative mitochondrial potential. Altogether, these results suggest a link between taurine effects and mitochondrial function.