Effects of the immunological niche on adult stem cell biology.

PATRÍCIA MATHIEU, ANA PAULA PIANTANIDA, DANIELA BATTISTA, MARIANA GRACIARENA AND FERNANDO PITOSSI.

Buenos Aires, Argentina

Simposio; International Symposium on Stem Cell Research; 2009

The neurogenic niche is composed by a variety of signals that include molecules from the immune system. Immune cytokines are known to be involved in the proliferation, differentiation and survival of endogenous and transplanted adult neural stem cells (NSC). The general objective of our work was to assess the effects of immune signals on the biology of endogenous NSC and after NSC transplantation. In particular, we studied NSC proliferation and differentiation in an altered neurogenic niche by adrenal gland removal (ADX). ADX increased adult neurogenesis and activated microglial cells till stage 3. In addition, transforming growth factor beta (TGF-b) expression was increased 10-fold in ADX animals and co-localized with activated microglia. Furthermore, blockade of TGF-b  biological activity diminished neurogenesis in vivo. Moreover, TGF-b ƒnƒnwas able to increase neuronal differentiation (bIII tubulin expression) in NSC primary hippocampal and subventricular zone (SVZ) cultures. TGF-b effects were mediated by Smad 2/3 activation. Surprisingly, in SVZ cultures, the percentage of bIII tubulin-positive cells increased from 31.55% to 70.38% after 2 and 6 weeks in the untreated culture, respectively. In addition, 40.73% and 57.90% of cells were Nestin-positive at 2 weeks and 6 weeks in culture, respectively. The fraction of GFAP+ cells remained relatively constant over a 6 week-period (3%). The addition of TGF-b to the NSC culture produced an additional increased in bIII-expression. Finally, undifferentiated NSC were transplanted into the rat striatum and survival, differentiation and the host inflammatory response were determined 1, 3 and 6 weeks after grafting. 6 weeks after transplantation of untreated NSC, 31% of the transplanted cells survived and inflammation was only evident in the grafted area. The percentage of GFAP-positive grafted cells increased at 6 weeks post-transplantation, while Nestin-positive cells declined over time. Only 15.78% of transplanted cells were NeuN-positive at 6 weeks post-grafting. These data show that TGF-b, an anti-inflammatory cytokine, possess pro-neurogenic effects in vivo and in vitro. In addition, bIII expression increases with time in cultured NSC from the SVZ. Our results also indicate that without any further stimulus, grafted NSC in the striatum diverted to glial differentiation.