Because of huge interest in using adipose-derived cells as “therapies”, it is important to know what is a cellular composition of this tissue. You may frequently hear a statement about fat tissue as a “richest source of stem cells” in our body. What kind of stem cells exist in adipose tissue? Can we define them?
We can roughly break down fat tissue on mature adipocytes, blood and everything else. The latter frequently called “stromal vascular fraction” (SVF). SVF is enriched for multiple progenitor cell populations and stem cells. SVF was isolated for the first time by Rodbell in 1964 using proteolytic enzymes and centrifugation. The “multipotent potential” of stem cells from human fat-derived SVF-like population was characterized by Zuk in 2001. Zuk called these cells “PLA cells”, because of starting material – processed lipoaspirates.
In the last decade there were a lot of confusions about nomenclature of stem cells, derived from adipose tissue. Some professionals called SVF as “stem cells”, but some use this term only for the cells, propagated in culture. Until now, you can find a multiple terms for adipose tissue-derived stem cells, used as synonyms in literature. For example:
- adipose-derived adult stem (ADAS) cells;
- adipose-derived adult stromal cells;
- adipose-derived stromal cells (ADSC);
- adipose stromal cells (ASC);
- adipose mesenchymal stem cells (AdMSC);
- processed lipoaspirate (PLA) cells;
- adipose-derived stromal/stem cells (ASCs);
International Federation for Adipose Therapeutics and Science (IFATS) has a leading role in establishing nomenclature and standards for using adipose-derived cells in medicine. About 6 years ago, IFATS recommended to use a term “adipose-derived stem cells” (ASCs) “ to identify the isolated, plastic-adherent, multipotent cell population“. However, IFATS later statement does not recommend to use term “stem cells”, but use “adipose tissue-derived stromal cells (ASCs)” instead to characterize culture-propagated cells. Therefore, despite IFATS recommendation, there is no clarity in literature on using term “stem cells” for adipose-derived cells, propagated in culture:
Recognizing the validity of the term “stem cell” may be questioned; it is accepted that some investigators will use the acronym to mean “adipose-derived stromal cells.”
Unlike cultured adipose stromal cells, the consensus on using of term “stem cells” to describe SVF, has been reached. Taking in account of high heterogeneity, the term “stem cells” should not be applied to SVF cells, freshly isolated from adipose tissue. The difference between SVF and ASCs is significant! Unlike SVF, ACSs relatively homogenous, plastic adherent population and serially passaged in culture.
Since, cultured SVF cells remarkably similar to bone marrow-derived mesenchymal stromal cells (MSC), the most professionals consider ASCs as an equivalent of MSC. However, other stem cell populations were described in adipose tissue, such as pericytes (considered as equivalent of MSC by some researchers), supra-adventitial adipose stromal cells and hematopoietic stem cells.
Stromal Vascular Fraction (SVF) – freshly isolated heterogeneous cell fraction, isolated from native adipose tissue or liposuction aspirates.
Adipose-derived stem cells = adipose-derived stromal cells (ASCs) = adipose-derived MSC – homogeneous, plastic adherent cell population, derived from SVF and propagated in culture.
This post is a part of series Breaking Down Fat. In this series we will talk about identification, characterization and clinical processing of potentially therapeutic cell populations from adipose tissue. We started this series in response to the growing trend of wide (mostly uncontrolled) clinical use adipose-derived cells and some controversies/ misconceptions in the field.If you would like to contribute to this series or become a sponsor, please contact us!