Fig. 1

Effect of neural stem cells/progenitor cells and mesenchymal stem cell transplantation on Huntington’s disease etiology and progression. Huntington’s disease (HD) is caused by an expansion of (polyQ) repeats within the amino terminus of the huntingtin (HTT) protein, which promotes HTT aggregation and formation of intracellular inclusion bodies. These events lead to microglial activation, which correlates with striatal neuronal dysfunction and neuronal death as well as with reduced expression of striatal D1 and D2 receptors and of neurotrophic factors [136, 137]. In turn, striatal neuronal dysfunction correlates with cortex atrophy, motor deficits and cognitive deficits in HD patients. According to the most updated literature on HD, both neural stem cells (NSCs)/progenitor cells and mesenchymal stem cells (MSCs) improve motor coordination, behavior and memory. NSCs/progenitor cells and MSCs also seem to be able to reduce formation of HTT-ubiquitin aggregates. HD improvements occur as a result of NSC/progenitor cell and MSC transplantation through very similar mechanisms, such as immunomodulation, trophic properties, neurotrophic support and neuronal protection. These mechanisms are well known for MSCs and only marginally recognized for NSCs/progenitor cells [79, 94]. Until now, the great advantage of MSCs, in comparison with NSCs/progenitor cells, are their immunoprivileged properties, few or lack of ethical concerns regarding their origin, significant therapeutic quantities, non-teratogenicity (safety), as well as immunomodulation. Although in vivo differentiation of both cell types has been demonstrated, it is not clear if the number of differentiated cells is sufficient to justify all brain improvements found upon transplantation or whether changes are due to intrinsic cell regeneration. mHTT mutant huntingtin