The emerging field of regenerative medicine will require a reliable source of stem cells in addition to biomaterial scaffolds and cytokine growth factors. Adipose tissue has proven to serve as an abundant, accessible and rich source of adult stem cells with multipotent properties suitable for tissue engineering and regenerative medical applications. There has been increased interest in Adipose-derived Stem Cells (ASCs) for tissue engineering applications. Here, methods for the isolation, expansion and differentiation of ASCs are presented and described in detail. While this article has focused on the isolation of ASCs from human adipose tissue, the procedure can be applied to adipose tissues from other species with minimal modifications.

The biologic characteristics of mesenchymal stem cells (MSCs) isolated from two distinct tissues, bone marrow and adipose tissue were evaluated in these studies. MSCs derived from human and non-human primate (rhesus monkey) tissue sources were compared. The data indicate that MSCs isolated from rhesus bone marrow (rBMSCs) and human adipose tissue (hASCs) had more similar biologic properties than MSCs of rhesus adipose tissue (rASCs) and human bone marrow MSCs (hBMSCs). Analyses of in vitro growth kinetics revealed shorter doubling time for rBMSCs and hASCs. rBMSCs and hASCs underwent significantly more population doublings than the other MSCs. MSCs from all sources showed a marked decrease in telomerase activity over extended culture; however, they maintained their mean telomere length. All of the MSCs expressed embryonic stem cell markers, Oct-4, Rex-1, and Sox-2 for at least 10 passages. Early populations of MSCs types showed similar multilineage differentiation capability. However, only the rBMSCs and hASCs retain greater differentiation efficiency at higher passages. Overall in vitro characterization of MSCs from these two species and tissue sources revealed a high level of common biologic properties. However, the results demonstrate clear biologic distinctions, as well.

Mesenchymal stem cells (MSC) derived from bone marrow stem cells (BMSC) and adipose tissue stem cells (ASC) of humans and rhesus macaques were evaluated for their cell cycle properties during protracted culture in vitro. Human ASCs (hASC) and rhesus BMSCs (rBMSC) underwent significantly more total population doublings than human BMSCs (hBMSC) and rhesus ASCs (rASC). The cell cycle profile of all MSCs was altered as cultures aged. hMSCs underwent an increase in the frequency of cells in the S phase at P20 and P30. However, rhesus MSCs from both sources developed a distinct polyploid population of cells at P20, which progressed to aneuploidy by P30. Karyotype analysis of MSCs revealed the development of tetraploid or aneuploid karyotypes in the rhesus cells at P20 or P30. Analysis of the transcriptome of the MSCs from early and late passages revealed significant alterations in the patterns of gene expression (8.8% of the genes were differentially expressed in hBMSCs versus hASCs, and 5.5% in rBMSCs versus rASCs). Gene expression changes were much less evident within the same cell type as aging occurred (0.7% in hMSCs and 0.9% in rMSC). Gene ontology analysis showed that functions involved in protein catabolism and regulation of pol II transcription were overrepresented in rASCs, whereas the regulation of IKB/nuclear factor-KB cascade were overrepresented in hBMSCs. Functional analysis of genes that were differentially expressed in rASCs and hBMSCs revealed that pathways involved in cell cycle, cell cycle checkpoints, protein-ubiquitination, and apoptosis were altered. [Cancer Res 2008;68(11):4229-38]