dofetilide br Discussion Our previous studies showed that ta

Discussion Our previous studies showed that taurine had an effect of increasing the number of NPCs obtained from the SVZ of the adult mouse dofetilide (Hernandez-Benitez et al., 2012). An increase in the proliferation rate was suggested as the mechanism responsible for this effect of taurine because significantly higher numbers of BrdU+ cells were found in taurine-containing cultures than in control cultures. We hypothesized that rather than directly affecting the DNA replicative process, taurine increases the proportion of healthy cells or provided better conditions for cells to enter the proliferative phases of the cell cycle. The improvement of cell performance may result from a membrane-stabilization effect, a direct action on nuclear elements or an effect on cell adhesion/migration increasing cell proximity. The possibility of a rapid interaction that stabilizes the cell membrane appeared unlikely because we demonstrated in this study that the increase in the number of cells in the DNA replicative phase as a result of taurine requires a long time, and brief exposure was ineffective. This indicated that the action of taurine requires a certain amount of time, and its effect is not the result of a short-term interaction with cell membranes. The possibility that taurine increased cell contacts and aggregation during culture was also considered, based on evidence showing that the NPC proliferation rate increased in high-density cultures (Mori et al., 2006). The results from the cDNA microarray analysis showing changes in the expression of gene transcripts for molecules involved in cell–cell contacts would also favor this possibility. However, under our conditions, culturing cells at high-density did not increase or modify the effects of taurine. A direct interaction of taurine with nuclear elements was also excluded because it was demonstrated that taurine was not localized in the cell nucleus. The cDNA microarray analysis provided information about the gene transcripts of the components of signaling pathways involved in cell proliferation that were regulated in the taurine-containing cultures. The transcripts involved in the Wnt and Sonic hedgehog (Shh) pathways exhibited an increase between 1.5 and 4-fold in the taurine-containing cultures. The Wnt signaling pathway is a highly conserved pathway that plays an important role in brain development (Faigle and Song, 2013; Wei et al., 2012). The functional role of this pathway in NPCs derived from the hippocampus and SVZ has been demonstrated, in which Wnt promotes cell proliferation (Lie et al., 2005; Yu et al., 2006). The involvement of Shh in adult NPC proliferation is also well documented. Recent studies have shown that Shh overexpression in the adult hippocampus increases progenitor cell proliferation, whereas inhibition or conditional knock-out of elements of the Shh signaling pathway reduces this process (Lai et al., 2003; Machold et al., 2003). The activity of these two pathways might be regulated by taurine, as suggested by the DNA microarray analysis and corroborated by RT-PCR results, thus enhancing the proliferation of NPCs. However, taurine did not affect cell proliferation if present in cultures for only 1.5h, a time that is likely sufficient to activate directly these proliferation pathways. A direct effect on nuclear transcription was also excluded because taurine was confined to the cytosol. Evidence about a proliferative action of taurine is so far conflicting, with reported proliferative or antiproliferative effects in different cell types (Yoshimura et al., 2005; Jeon et al., 2007). Recent studies using microarray analyses provide some additional evidence about this subject. Previous microarray analyses about the regulation of gene expression induced by taurine have been developed in cells derived from heart, liver, skeletal muscle and kidney, and in cell lines HepG2 and Caco-2 cells (Park et al., 2006; Warskulat et al., 2006; Mortensen et al., 2010a, Mortensen et al., 2010b; Gondo et al., 2012; Liang et al., 2013; Han and Chesney, 2013). The present study contains the first analysis developed in brain cells. Some of these studies show regulation by taurine of genes related to proliferation, though different mechanisms are proposed. A microarray analysis in Caco-2 cells attributes the regulation of proliferation to the up regulation of molecules of MAPK signaling pathway (Gondo et al., 2012). In the embryonic kidney 293 cells this effect is attributed to the regulation of several genes involved in cell cycle such as CDK6 and CDC7 (Han and Chesney, 2013). The present study in NPCs showed an effect on the regulation of genes of the Shh and Wnt signaling pathways. Since all those studies were carried out in different cell types it cannot be concluded so far whether the differences found correspond to cell specific features.