br Materials and methods br Results br
Materials and methods
Discussion Several studies have demonstrated the benefits of bone-marrow cell transplantation in different models of procollagen c proteinase ischemia, as well as in other brain injuries (de Vasconcelos Dos Santos et al., 2010; Qu et al., 2008; Zaverucha-do-Valle et al., 2011). In our study, we used a model of global ischemia to investigate the responses of the adult neurogenic niche to cell therapy with BMMCs. Cell therapies have been proposed as an attempt to increase NSC proliferation, differentiation, and/or cell survival, and consequently functional improvement after ischemic lesions in the adult brain. Bone marrow-derived stem cells have been used in these models, and several reports have shown that, despite the small number of transplanted cells that reach the lesion area, this therapy results in functional benefits in the treated animals (Borlongan et al., 2004; Ohtaki et al., 2008; Vasconcelos-Dos-Santos et al., 2012). The BMMC fraction includes both hematopoietic and mesenchymal stem cells, several progenitors, and differentiated bone-marrow cells. Both BMMCs and mesenchymal cells have been used in a model of focal ischemia in adult rats, with similar beneficial functional effects (de Vasconcelos Dos Santos et al., 2010). However, in a clinical setting, the BMMC fraction might be safer than MSCs, since these cells are obtained after several passages. For these reasons, in this study we investigated the mechanisms of action of BMMCs. Several mechanisms have been suggested to explain the functional benefits after bone-marrow cell therapy, and among these, it has been suggested that these cells could modulate the NSCs in order to increase endogenous regeneration after injury. In this study, we assessed the presence of RGLCs in different groups: sham, sham+BMMC treatment, BCCL, and BCCL+BMMC. During development, radial glia cells play an important role as NSCs and as a migration guide for the newly born neurons (Malatesta et al., 2003; Noctor et al., 2001; Parnavelas and Nadarajah, 2001). In the adult, RGLCs also seem to play a role as NSCs in the two main neurogenic regions, the SVZ and the SGL (Mirzadeh et al., 2008; Shapiro et al., 2005). The presence of RGLCs was investigated using vimentin, as previously described by our group (Gubert et al., 2009). Vimentin is an intermediate filament protein expressed in glial cells, especially radial glia cells during development, and it is highly expressed in the RGLCs in the adult. In control animals, we observed vimentin-positive cells around the LV, staining the ependymal layer and RGLC processes extending from the walls of the LV, as previously described (Gubert et al., 2009). In the current study, we observed an increase in the number of RGLCs on the third day after BCCL in animals that did or did not receive the BMMC transplant. However, this increase persisted until 21days after injury only in the animals that received the transplant. In 2007, Zhang and co-workers demonstrated that ependymal cells proliferate and transform into RGLCs 1–2days after a stroke. Seven days after injury, fewer RGLCs were observed (Zhang et al., 2007). These findings concord with our observation that after BCCL, the number of RGLCs increased temporarily. However, in animals that received BMMC treatment, we observed more radial cells for a longer period (at least until 21days). This suggests that BCCL and BMMCs stimulate the cells in the lateral wall differently. BCCL could be stimulating the transitory transformation of ependymal cells, and BMMCs could be stimulating the proliferation of RGLCs in the SVZ. In accordance with this hypothesis, we observed an increase in cell proliferation in the SVZ 7days after BCCL only in the animals that received the transplant. Importantly, the number of RGLCs progressively increased in the sham animals that received the BMMC transplant. This result also supports the idea that two different stimuli can cause an increase in the number of RGLCs, since we observed this event even in uninjured animals.