A primary concern in stem cell biology is that observations made in vitro may be an artifact of the in vitro culture environment. In vitro derived stem cells can be implanted into the environment from which they are derived so that their response to physiological conditions may be observed. Several important cellular characteristics need to be examined following the cell's reintroduction to the in vivo environment, including the potential for differentiation, proliferative ability, and life span. Studying implanted stem cells will assist in determining the potential for stem cell use in clinical therapies and provide further understanding of the role adult stem cells have in the adult body. Currently, the scientific literature is lacking a detailed description of the cellular response of adipose-derived stem cells (ADSCs) reintroduced to their exact tissue of origin. Thus, the aim of this study was to evaluate porcine ADSC growth in vivo and to analyze cell differentiation in vivo following injection of undifferentiated ADSCs into subcutaneous fat. Subcutaneous adipose tissue was isolated from the back fat of male pigs (11 months of age) and digested with 0.075% collagenase at 37�C for 90 min. The digested tissue was centrifuged at 200g for 10 min to obtain a cell pellet. The pellet was re-suspended with DMEM and the ADSCs were plated onto 75 cm2 flasks (5000-10 000 cells per cm2) and cultured in DMEM supplemented with 10% fetal bovine serum (FBS) and 1% gentamicin. Passage 3 ADSCs were labeled with fluorescent dye (PKH26; Sigma, St. Louis, MO, USA) and sorted by flow cytometry. After sorting, positive cells were washed and re-suspended in culture medium. For transplantation, 100 �L of cell suspension in DMEM containing one of four cell concentrations (0 (control); 30 000; 300 000; and 900 000 cells) were placed in a 1-mL syringe and injected into the subcutaneous back fat of recipient pigs (n = 2). Each pig had previously been tattooed with 12 13 � 13 squares to mark injection sites. The treatments were replicated three times within each animal. Two and three weeks after transplantation, animals were euthanized, the back fat containing the transplantation site was harvested, and the cells were disaggregated as described above. The buoyant adipocytes and pelleted ADSCs cells were then analyzed by flow cytometry. The results indicated that there were dose- and time-dependent increases in labeled ADSCs and labeled adipocytes in the fat samples with increasing cell number (from 0 to 300 000 cells). There was, however, a decrease in labeled ADSCs at the 900 000-cell dose, which is likely due to excess cells being transplanted or an immune reaction. Both of these aspects are currently being evaluated. In conclusion, undifferentiated ADSCs from swine can be isolated from and returned to the subcutaneous adipose layer and differentiate into mature adipocytes.
This work was supported by the Council for Food and Agricultural Research (C-FAR) Sentinel Program, University of Illinois.
Autologous decellularized extracellular matrix protects against H2O2-induced senescence and aging in adipose-derived stem cells and stimulates proliferation in vitro