Nicolas Espagnolle

CD146 expression on mesenchymal stem cells is associated with their vascular smooth muscle commitment

Bone marrow mesenchymal stem cells (MSCs) are plastic adherent cells that can differentiate into various tissue lineages, including osteoblasts, adipocytes and chondrocytes. However, this progenitor property is not shared by all cells within the MSC population. In addition, MSCs vary in their proliferation capacity and expression of markers. Because of heterogeneity of CD146 expression in the MSC population, we compared CD146−/Low and CD146High cells under clonal conditions and after sorting of the non‐clonal cell population to determine whether this expression is associated with specific functions. CD146−/Low and CD146High bone marrow MSCs did not differ in colony‐forming unit‐fibroblast number, osteogenic, adipogenic and chondrogenic differentiation or in vitro haematopoietic‐supportive activity. However, CD146−/Low clones proliferated slightly but significantly faster than did CD146High clones. In addition, a strong expression of CD146 molecule was associated with a commitment to a vascular smooth muscle cell (VSMC) lineage characterized by a strong up‐regulation of calponin‐1 and SM22α expression and an ability to contract collagen matrix. Thus, within a bone marrow MSC population, certain subpopulations characterized by high expression of CD146, are committed towards a VSMC lineage.

Bioactivity and prognostic significance of growth differentiation factor GDF15 secreted by bone marrow mesenchymal stem cells in multiple myeloma

Overexpression of growth differentiation factor 15 (GDF15) by bone marrow mesenchymal stem cells occurs widely in patients with multiple myeloma, but the pathophysiologic effects of GDF15 in this setting remain undefined. GDF15 has been described in numerous solid tumors but never in hematologic malignancies. In this study, we report that GDF15 significantly increases survival of stroma-dependent multiple myeloma cells including primary multiple myeloma cells. In particular, GDF15 conferred resistance to melphalan, bortezomib, and to a lesser extent, lenalidomide in both stroma-dependent and stroma-independent multiple myeloma cells. Akt-dependent signaling was critical to mediate the effects of GDF15, whereas Src and extracellular signal-regulated kinase 1/2 signaling pathways were not involved. Given these results, we tested the clinical significance of plasma concentrations of GDF15 (pGDF15) in 131 patients with multiple myeloma and found that it correlated with disease prognosis. Specifically, patients with high levels of pGDF15 had lower probabilities of event-free and overall survival 30 months after diagnosis than patients with low pGDF15 levels. Our findings suggest that tumor microenvironment-derived GDF15 is a key survival and chemoprotective factor for multiple myeloma cells, which is pathophysiologically linked to both initial parameters of the disease as well as patient survival.

Pericyte-Like Progenitors Show High Immaturity and Engraftment Potential as Compared with Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) and pericyte progenitors (PPs) are both perivascular cells with similar multipotential properties regardless of tissue of origin. We compared the phenotype and function of the 2 cell types derived from the same bone-marrow samples but expanded in their respective media – pericyte conditions (endothelial cell growth medium 2 [EGM-2]) for PPs and standard medium (mesenchymal stem cell medium [MSM]) for MSCs. After 3 weeks of culture, whatever the expansion medium, all cells showed similar characteristics (MSC markers and adipo-osteo-chondroblastic differentiation potential), although neuronal potential was greater in EGM-2– than MSM-cultured cells. As compared with MSM-cultured MSCs, EGM-2–cultured PPs showed higher expression of the pericyte-specific antigen 3G5 than α-smooth muscle actin. In addition, EGM-2–cultured PPs showed an immature phenotype, with upregulation of stemness OCT4 and SOX2 proteins and downregulation of markers of osteoblastic, chondroblastic, adipocytic and vascular smooth muscle lineages. Despite having less effective in vitro immunosuppression capacities than standard MSCs, EGM-2–cultured PPs had higher engraftment potentials when combined with biomaterials heterotopically-transplanted in Nude mice. Furthermore, these engrafted cells generated more collagen matrix and were preferentially perivascular or lined trabeculae as compared with MSM-cultured MSCs. In conclusion, EGM-2–cultured PPs are highly immature cells with increased plasticity and engraftment potential.

Mechanically Isolated Stromal Vascular Fraction Provides a Valid and Useful Collagenase-Free Alternative Technique: A Comparative Study.

Background: The use of stromal vascular fraction and adipose-derived stromal cells in tissue regeneration is now being increasingly investigated, and studies have demonstrated that adipose-derived stromal cells present differentiation and immunomodulatory capacities. The development of a rapid, inexpensive, and enzyme-free technique to isolate adipose-derived stromal cell–enriched stromal vascular fraction is a major goal for stem cell therapy. Therefore, the authors compared innovative mechanical procedures to the gold standard technique, collagenase digestion. Methods: Stromal vascular fraction was prepared from 21 liposuctions using either enzymatic digestion or two different mechanical methods: high vortexing/centrifugation and dissociation by intersyringe processing. The effects of tissue processing on cell count, viability, proliferation, clonogenic enrichment, and the phenotypes of the different native cell were determined. Adipose-derived stromal cell phenotypes from the different protocols, and their differentiation and immunosuppressive potential, were compared. Results: Enzymatic digestion isolated more viable cells than dissociation by intersyringe processing and vortexing/centrifugation. The expansion rate and clonogenic enrichment were higher for stromal vascular fraction isolated with collagenase. The proportion of adipose-derived stromal cells was higher in stromal vascular fraction extracted with dissociation than with enzymatic digestion and vortexing/centrifugation (p < 0.01). Interestingly, all cultured adipose-derived stromal cells displayed similar differentiation and immunosuppressive capacities. Conclusions: Enzymatic digestion extracts more adipose-derived stromal cells, but intersyringe dissociation enables the rapid extraction of adipose-derived stromal cell–enriched stromal vascular fraction. Moreover, mechanical methods enable adipose-derived stromal cell isolation with stemness and immunosuppressive properties, similar to enzymatic digestion. Such mechanical procedures could allow easier and more rapid isolation of adipose-derived stromal cell–enriched stromal vascular fraction for practitioners. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.

T-cell antagonism by short half-life pMHC ligands can be mediated by an efficient trapping of T-cell polarization toward the APC.

T-cell activation results from productive T-cell receptor (TCR) engagement by a cognate peptide–MHC (pMHC) complex on the antigen presenting cell (APC) surface, a process leading to the polarization of the T-cell secretory machinery toward the APC interface. We have previously shown that the half-life of the TCR/pMHC interaction and the density of pMHC on the APC are two parameters determining T-cell activation. However, whether the half-life of the TCR/pMHC interaction can modulate the efficiency of T-cell secretory machinery polarization toward an APC still remains unclear. Here, by using altered peptide ligands conferring different half-lives to the TCR/pMHC interaction, we have tested how this parameter can control T-cell polarization. We observed that only TCR/pMHC interactions with intermediate half-lives can promote the assembly of synapses that lead to T-cell activation. Strikingly, intermediate half-life interactions can be competed out by short half-life interactions, which can efficiently promote T-cell polarization and antagonize T-cell activation that was induced by activating intermediate half-life interactions. However, short TCR/pMHC interactions fail at promoting phosphorylation of signaling molecules at the T-cell–APC contact interface, which are needed for T-cell activation. Our data suggest that although intermediate half-life pMHC ligands promote assembly of activating synapses, this process can be inhibited by short half-life antagonistic pMHC ligands, which promote the assembly of non activating synapses.