NOTE: All patient samples were obtained with informed consent, and experimental protocols were reviewed and approved by Stanford University Institutional Review Board (Protocol #2188 and #9999).
1. Cell Isolation and Culture:
2. Staining
3. Fluorescence-activated Cell Sorting
NOTE: The following steps mandate previous knowledge in fluorescence-activated cell sorting (FACS) or the assistance of a skilled technician.
Using CD90 as a marker for cells with enhanced osteogenesis results in isolation of a highly-enriched populations of human ASCs (Figure 1A, 1B). ASCs were stained with Pacific Blue-conjugated anti-human CD45, FITC-conjugated anti-human CD105, and APC-conjugated anti-human CD90. After sorting, the level of purity was greater than 98%, as quantified by post-sort analysis.
Defining groups of cells based on transcriptional profiles allowed for prospective isolation of two novel subpopulations. To characterize the osteogenic potential of each promising subpopulation (CD90+ and CD105low), as well as that of the unsorted population in vitro, cells were cultured in osteogenic differentiation medium for 14 days, as previously described 6,8,9. Alkaline phosphatase staining (used for early detection of bone formation10) at Day 7 was significantly increased in the CD90+ population relative to other groups (Figure 2A). This was observed both grossly and after quantification (Figure 2A). Similarly, Alizarin Red staining (an assay used to detect extracellular matrix mineralization and a metric for end-terminal osteogenic differentiation9) at Day 14 showed that CD90+ ASCs were able to mineralize a significantly greater amount of extracellular matrix (Figure 2B). Isolated ASCs retain the ability to undergo osteogenic differentiation after sorting but may require a few days to recover. It is essential to perform all further experiments with low passage cells, as ASCs become senescent during propagation in culture.
Figure 1: (A) Gates for cell size and complexity were drawn to exclude cell debris and isolate a population of single cells for further analysis. (B) FACS analysis of single-sorted CD90 (left) and single-sorted CD105 (right) ASCs 36 hr after ASC harvest. Please click here to view a larger version of this figure.
Figure 2: (A) Alkaline phosphatase staining (top) and quantification (bottom) of ASCs after 7 days of culture in osteogenic differentiation medium. (B) Alizarin red staining (top) and quantification of staining (bottom) of ASCs after 14 days of culture in osteogenic differentiation medium. CD90+ ASCs and CD105low cells show increased alkaline phosphatase staining and extracellular matrix mineralization compared to unsorted cells (*p <0.05; two-tailed student’s t-test). Please click here to view a larger version of this figure.
Name of Reagent/Material | Company | Catalog Number | Comments |
Disposable 250 mL Conical Tubes | Corning (Thomas Scientific) | 2602A43 | |
Penicillin-Streptomycin (10,000 U/mL) | Gibco | 15140-122 | |
DMEM, high glucose, GlutaMAX Supplement | Gibco | 10566-016 | |
PBS, pH 7.4 | Gibco | 10010-023 | |
Betadine – Antiseptic Povidone/Iodine Solution | Purdue | PFC-67618015017 | |
Hank's Balanced Salt Solution, 1X | Cellgro | 21-023-CV | |
Fetal Bovine Serum, Certified, US Origin | Gibco | 16000-044 | |
Collagenase from Clostridium histolyticum | Sigma-Aldrich | C0130-5G | |
ACCUTASE Cell Detachment Solution | Stem Cell Technologies | 7920 | |
APC Mouse Anti-Human CD90 | BD Pharmingen | 559869 | |
FITC Mouse anti-Human CD105 (Endoglin) | BD Pharmingen | 561443 | |
Anti-Human CD45 eFluor 450 (Pacific Blue replacement) | eBioscience | 48-9459-41 | |
Anti-Human CD34 APC | eBioscience | 17-0349-41 | |
Anti-Human CD31 (PECAM-1) PE | eBioscience | 12-0319-41 | |
Streptavidin PE-Cyanine7 | eBioscience | 25-4317-82 | |
BD FACS Aria II instrument | BD Biosciences | ||
BD FACSDiva Software | BD Biosciences |
Bone marrow-derived mesenchymal stromal cells (BM-MSCs) are considered the gold standard for stem cell-based tissue engineering applications. However, the process by which they must be harvested can be associated with significant donor site morbidity. In contrast, adipose-derived stromal cells (ASCs) are more readily abundant and more easily harvested, making them an appealing alternative to BM-MSCs. Like BM-MSCs, ASCs can differentiate into osteogenic lineage cells and can be used in tissue engineering applications, such as seeding onto scaffolds for use in craniofacial skeletal defects. ASCs are obtained from the stromal vascular fraction (SVF) of digested adipose tissue, which is a heterogeneous mixture of ASCs, vascular endothelial and mural cells, smooth muscle cells, pericytes, fibroblasts, and circulating cells. Flow cytometric analysis has shown that the surface marker profile for ASCs is similar to that for BM-MSCs. Despite several published reports establishing markers for the ASC phenotype, there is still a lack of consensus over profiles identifying osteoprogenitor cells in this heterogeneous population. This protocol describes how to isolate and use a subpopulation of ASCs with enhanced osteogenic capacity to repair critical-sized calvarial defects.
Bone marrow-derived mesenchymal stromal cells (BM-MSCs) are considered the gold standard for stem cell-based tissue engineering applications. However, the process by which they must be harvested can be associated with significant donor site morbidity. In contrast, adipose-derived stromal cells (ASCs) are more readily abundant and more easily harvested, making them an appealing alternative to BM-MSCs. Like BM-MSCs, ASCs can differentiate into osteogenic lineage cells and can be used in tissue engineering applications, such as seeding onto scaffolds for use in craniofacial skeletal defects. ASCs are obtained from the stromal vascular fraction (SVF) of digested adipose tissue, which is a heterogeneous mixture of ASCs, vascular endothelial and mural cells, smooth muscle cells, pericytes, fibroblasts, and circulating cells. Flow cytometric analysis has shown that the surface marker profile for ASCs is similar to that for BM-MSCs. Despite several published reports establishing markers for the ASC phenotype, there is still a lack of consensus over profiles identifying osteoprogenitor cells in this heterogeneous population. This protocol describes how to isolate and use a subpopulation of ASCs with enhanced osteogenic capacity to repair critical-sized calvarial defects.
Bone marrow-derived mesenchymal stromal cells (BM-MSCs) are considered the gold standard for stem cell-based tissue engineering applications. However, the process by which they must be harvested can be associated with significant donor site morbidity. In contrast, adipose-derived stromal cells (ASCs) are more readily abundant and more easily harvested, making them an appealing alternative to BM-MSCs. Like BM-MSCs, ASCs can differentiate into osteogenic lineage cells and can be used in tissue engineering applications, such as seeding onto scaffolds for use in craniofacial skeletal defects. ASCs are obtained from the stromal vascular fraction (SVF) of digested adipose tissue, which is a heterogeneous mixture of ASCs, vascular endothelial and mural cells, smooth muscle cells, pericytes, fibroblasts, and circulating cells. Flow cytometric analysis has shown that the surface marker profile for ASCs is similar to that for BM-MSCs. Despite several published reports establishing markers for the ASC phenotype, there is still a lack of consensus over profiles identifying osteoprogenitor cells in this heterogeneous population. This protocol describes how to isolate and use a subpopulation of ASCs with enhanced osteogenic capacity to repair critical-sized calvarial defects.