Abstract
Although therapeutic use of stem cells (SCs) is already available in some tissues (cornea, blood, and skin), in most organs we are far from reaching the translational goal of regenerative medicine. In the nervous system, due to intrinsic features which make it refractory to regeneration/repair, it is very hard to obtain functionally integrated regenerative outcomes, even starting from its own SCs (the neural stem cells; NSCs). Besides NSCs, mesenchymal stem cells (MSCs) have also been proposed for therapeutic purposes in neurological diseases. Yet, direct (regenerative) and indirect (bystander) effects are often confused, as are MSCs and bone marrow-derived (stromal, osteogenic) stem cells (BMSCs), whose plasticity is actually overestimated (i.e., trans-differentiation along non-mesodermal lineages, including neural fates). In order to better understand failure in the “regenerative” use of SCs for neurological disorders, it could be helpful to understand how NSCs and BMSCs have adapted to their respective organ niches. In this perspective, here the adult osteogenic and neurogenic niches are considered and compared within their in vivo environment.
Highlights
Stem cells (SCs) are considered “functional states” rather than “cell types” with a specific morphology and function, these being features more typical of mature cells (Morrison and Spradling, 2008)
In vitro research on SC biology has been characterized by repeated breakthroughs, resulting in the perception that SCs can cure many diseases
Despite a lack of reliable evidence, statements in the media and even scientific papers have emphasized the use of “mesenchymal” stem cells (MSCs) such as those residing in the bone marrow (BM) stroma, as a source of trans-differentiating elements capable of colonizing different organs to replace lost cells
Summary
Stem cells (SCs) are considered “functional states” rather than “cell types” with a specific morphology and function, these being features more typical of mature cells (Morrison and Spradling, 2008). Despite a lack of reliable evidence, statements in the media and even scientific papers have emphasized the use of “mesenchymal” stem cells (MSCs) such as those residing in the bone marrow (BM) stroma, as a source of trans-differentiating elements capable of colonizing different organs (including the brain) to replace lost cells On these bases, MSCs have often been presented as elements which could overcome the strict rules regulating the SC niche/tissue relationships, even if most of their regenerative outcomes have not been confirmed by subsequent studies, since “MSCs commonly defined by in vitro functions have entered clinical application despite little definition of their function in residence” (Park et al, 2012). This review outlines the state-of-the-art regarding the inherent specificity of osteogenic and neurogenic niches through a detailed comparison of the microenvironment housing stromal (osteogenic) and NSCs, as well as their outcome in physiological and regenerative conditions
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