Objective. Vascular abnormalities represent the main component of the pathobiology of systemic sclerosis (SSc), progressing from structural derangements of the microcirculation with abortive neoangiogenesis to final vessel loss. Since circulating endothelial progenitor cells (EPCs) are important in the vascular repair process, we undertook this study to examine their numbers in the peripheral blood (PB) of SSc patients and to evaluate whether their status is related to impaired quantitative and/or qualitative aspects of the bone marrow (BM) microenvironment.Methods. Circulating EPCs from 62 SSc patients were evaluated by flow cytometry and characterized as CD45 negative and CD133 positive. BM EPCs, identified as CD133 positive, were isolated from 14 SSc patients and grown to induce endothelial differentiation. In addition, progenitor numbers and functional properties of hematopoietic and stromal compartments were analyzed by various assays.Results. We found that EPCs were detectable in the PB of patients with SSc, and their number was significantly increased in patients with early-stage disease but not in those with late-stage disease. All of the examined BM samples contained reduced numbers of EPCs and stromal cells, both of which were functionally impaired. Both endothelial and stromal progenitors expressed vascular endothelial growth factor receptor, indicating that BM is strongly induced to differentiate into the endothelial lineage; furthermore, only BM EPCs from patients with early disease led to endothelial differentiation in vitro.Conclusion. This study provides the first demonstration that in SSc, there is a complex impairment in the BM microenvironment involving both the endothelial and mesenchymal stem cell compartments and that this impairment might play a role in defective vasculogenesis in scleroderma.

Stem cells hold great promise in tissue engineering for repairing tissues damaged by disease or injury. Mesenchymal stem cells (MSCs) are multipotent cells able to proliferate and differentiate into multiple mesodermal tissues such as bone, cartilage, muscle, tendon, and fat. We have previously reported that the low-affi nity nerve growth factor receptor (L-NGFR or CD271) defi nes a subset of cells with high proliferative, clonogenic, and multipotential differentiation ability in adult bone marrow (BM). It has been recently shown that adipose tissue is an alternative source of adult multipotent stem cells and human adipose-derived stem cells, selected by plastic adherence (PA hASCs), have been extensively characterized for their functional potentials in vitro. In this study, immunoselected L-NGFR + and CD34 + subpopulations have been analyzed and compared with the PA hASCs. Phenotypic profi le of freshly purifi ed subpopulations showed an enrichment in the expression of some stem cell markers; indeed, a great percentage of L-NGFR + cells co-expressed CD34 and CD117 antigens, whereas the endothelial-committed progenitor markers KDR and P1H12 were mainly expressed on CD34 + cells. Differently from PA hASCs, the immunoseparated fractions showed high increments in cell proliferation, and the fi broblast colony-forming activity (CFU-F) was maintained throughout the time of culture. Furthermore, the immunoselected populations showed a greater differentiative potential toward adipocytes, osteoblasts, and chondrocytelike cells, compared to PA hASCs. Our data suggest that both CD34+ and L-NGFR + hASCs can be considered alternative candidates for tissue engineering and regenerative medicine applications. IntroductionI n the recent years, the emerging fi eld of cell-based therapies for repair and regeneration of damaged tissues has been focusing on the identifi cation of the ideal source of stem cells, which combines the ability of multipotential differentiation and the accessibility in large amounts under a minimally invasive procedure, not complicated by immunological rejection concerns and ethical controversies.Adult mesenchymal stem cells (MSCs) are a population of multipotent cells able to proliferate and differentiate into multiple mesodermal tissues. MSCs have been initially identifi ed in bone marrow (BM) [ 1 ], but have been subsequently isolated from many other tissues [ 2-10 ]. Among them, human MSCs derived from adipose tissue (hASCs) show stem cell key features such as the ability to form fi broblast-like colonies (CFU-F), the expression of several common cell surface antigens, the capacity of extensive proliferation, and the potential to differentiate in vitro and in vivo into multiple lineages of mesodermal origin, and also to transdifferentiate into neurogenic and hepatic lineages [ 4 , 11-21 ]. Similarly to BM-derived MSCs (BM MSCs), hASCs are able to suppress immunoreactivity, suggesting a possible overcoming of histocompatibility limitations in allogeneic transplantation [ 22 , 23 ]; furthermore, they ar...

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