p53 regulates the proliferation, differentiation and spontaneous transformation of mesenchymal stem cells.

Mesenchymal stem cells (MSC) have been extensively studied and gained wide popularity due to their therapeutic potential. Spontaneous transformation of MSC, from both human and murine origin, has been reported in many studies. MSC transformation depends on the culture conditions, the origin of the cells and the time on culture; however, the precise biological characteristics involved in this process have not been fully defined yet. In this study, we investigated the role of p53 in the biology and transformation of murine bone marrow (BM)-derived MSC. We demonstrate that the MSC derived from p53KO mice showed an augmented proliferation rate, a shorter doubling time and also morphologic and phenotypic changes, as compared to MSC derived from wild-type animals. Furthermore, the MSC devoid of p53 had an increased number of cells able to generate colonies. In addition, not only proliferation but also MSC differentiation is controlled by p53 since its absence modifies the speed of the process. Moreover, genomic instability, changes in the expression of c-myc and anchorage independent growth were also observed in p53KO MSC. In addition, the absence of p53 implicates the spontaneous transformation of MSC in long-term cultures. Our results reveal that p53 plays a central role in the biology of MSC.

Detection of mouse endogenous type B astrocytes migrating towards brain lesions.

Neuroblasts represent the predominant migrating cell type in the adult mouse brain. There are, however, increasing evidences of migration of other neural precursors. This work aims at identifying in vivo endogenous early neural precursors, different from neuroblasts, able to migrate in response to brain injuries. The monoclonal antibody Nilo1, which unequivocally identifies type B astrocytes and embryonic radial glia, was coupled to magnetic glyconanoparticles (mGNPs). Here we show that Nilo1-mGNPs in combination with magnetic resonance imaging in living mice allowed the in vivo identification of endogenous type B astrocytes at their niche, as well as their migration to the lesion site in response to glioblastoma, demyelination, cryolesion or mechanical injuries. In addition, Nilo1(+) adult radial glia-like structures were identified at the lesion site a few hours after damage. For all damage models used, type B astrocyte migration was fast and orderly. Identification of Nilo1(+) cells surrounding an induced glioblastoma was also possible after intraperitoneal injection of the antibody. This opens up the possibility of an early identification of the initial damage site(s) after brain insults, by the migration of type B astrocytes.

Cu2+ binding triggers alphaBoPrP assembly into insoluble laminar polymers.

Cu(2+) binding is so far the best characterized property of the prion protein. This interaction has been mapped to the N-terminal domain of the prion protein where multiple His residues occur largely embedded within the repetitive PHGGGWGQ sequence known as octarepeats. When Cu(2+) interaction is studied using a solution of full-length bovine prion protein containing six octarepeats at protein concentrations above 25 microM, a drastic increase in solution turbidity is observed due to the formation of insoluble cation-protein complexes that appear as bidimensional polymer meshes. These bidimensional meshes consist of a single layer of protein molecules crosslinked by Cu(2+) cations. Polymer formation is a cooperative process that proceeds by nucleation of protein molecules with a Cu(2+) site occupancy of above 2. These results support the hypothesis that the N-terminal domain of prion protein is a ligand binding module that promotes crosslinked assembly, and suggest the existence of inter-repeat Cu(2+) sites.

Targeting neural stem cells with titanium dioxide nanoparticles coupled to specific monoclonal antibodies.

Aiming to characterize the use of biomaterials in cancer therapy, we took advantage of the n-type semiconductor properties, which upon irradiation excite their electrons into the conduction band to induce photoelectrochemical reactions generating oxygen reactive species (ROS). Indeed, photoactivated TiO(2) nanoparticles have been shown to kill in vitro either bacteria or tumor cells in culture following UV irradiation, as a consequence of the ROS levels generated; the killing was highly effective although devoid of specificity. In this report, we have directed the TiO(2) nanoparticles to particular targets by coupling them to the monoclonal antibody (mAb) Nilo1, recognizing a surface antigen in neural stem cells within a cell culture, to explore the possibility of making this process specific. TiO(2) nanoparticles generated with particular rutile/anatase ratios were coupled to Nilo1 antibody and the complexes formed were highly stable. The coupled antibody retained the ability to identify neural stem cells and upon UV irradiation, the TiO(2) nanoparticles were activated, inducing the selective photokilling of the antibody-targeted cells. Thus, these data indicate that antibody-TiO(2) complexes could be used to specifically remove target cell subpopulations, as demonstrated with neural stem cells. The possible applications in cancer therapy are discussed.

Live imaging of mouse endogenous neural progenitors migrating in response to an induced tumor.

Adult neurogenesis is restricted to specific brain regions. Although involved in the continuous supply of interneurons for the olfactory function, the role of neural precursors in brain damage-repair remains an open question. Aiming to in vivo identify endogenous neural precursor cells migrating towards a brain damage site, the monoclonal antibody Nilo2 recognizing cell surface antigens on neuroblasts, was coupled to magnetic glyconanoparticles (mGNPs). The Nilo2-mGNP complexes allowed, by magnetic resonance imaging in living animals, the in vivo identification of endogenous neural precursors at their niche, as well as their migration to a lesion site (induced brain tumor), which was fast (within hours) and orderly. Interestingly, the rapid migration of neuroblasts towards a damage site is a characteristic that might be exploited to precisely localize early damage events in neurodegenerative diseases. In addition, it might facilitate the study of regenerative mechanisms through the activation of endogenous neural cell precursors. A similar approach, combining magnetic glyconanoparticles linked to appropriate antibodies could be applied to flag other small cell subpopulations within the organism, track their migration, localize stem cell niches, cancer stem cells or even track metastatic cells.

Mesenchymal stem cells: biological properties and clinical applications.

IMPORTANCE OF THE FIELD: In the last decade, knowledge of mesenchymal stem cells (MSCs) has evolved rapidly; their immunomodulatory properties and paracrine interactions with specific cell types in damaged tissues and promising results in some clinical applications have made these cells an attractive option for the treatment of certain diseases. AREAS COVERED IN THIS REVIEW: We present some relevant methodological issues and biological properties of MSCs, as well as clinical applications of MSC therapies with particular emphasis in the treatment of graft versus host disease (GVHD), complex perianal fistula and refractory metastatic neuroblastoma. Other topical aspects relevant to the application of cellular therapies such as biosafety studies and cellular production of MSCs are also discussed in this review. WHAT THE READER WILL GAIN: The growing optimism regarding MSCs research is based on the promising results obtained in in vitro and in vivo studies. The rapid translational research with MSCs necessitated standardization of methodology and terminology and greater focus on other aspects such as biosafety and cellular production, especially for clinical use of MSCs. TAKE HOME MESSAGE: Much has been learned about the biology and applications of MSCs and much remains to be learned.

Biosynthesis of prion protein nucleocytoplasmic isoforms by alternative initiation of translation.

The cellular prion protein PrP(C) is synthesized as a family of four distinct forms. Of these, (Cyt)PrP is a minor member that segregates outside of the secretory route and can generate cytotoxic forms. Using signal sequence mutants, we found that (Cyt)PrP is translated from a downstream AUG (coding for Met-8 in human PrP or Met-15 in Syrian hamster PrP). Shortening of the signal sequence dictated the spillage of this isoform into the cytosol, from where it accessed the nucleus or formed insoluble cytosolic aggregates if the proteasome is inhibited. The PrP isoform isolated from the nuclear fractions of cell and brain homogenates was partially SUMO-1-conjugated. Expression of HaPrP(M15) in cells caused an antiproliferative phenotype due to a cell cycle arrest at the G(0)/G(1) phase. The identification of this PrP isoform and its properties provides novel insight into PrP(C) physiological and pathological functions.