Abstract
The stromal-vascular fraction (SVF) of adipose tissue is a rich source of multipotent stem cells. We and others have described three major populations of stem/progenitor cells in this fraction, all closely associated with small blood vessels: endothelial progenitor cells (EPC, CD45-/CD31+/CD34+), pericytes (CD45-/CD31-/CD146+), and supra-adventitial adipose stromal cells (SA-ASC, CD45-/CD31-/CD146-/CD34+). EPC are luminal, pericytes are adventitial, and SA-ASC surround the vessel like a sheath. The multipotency of the pericytes and SA-ASC compartments is strikingly similar to that of CD45-/CD34-/CD73+/CD105+/CD90+ bone marrow-derived mesenchymal stem cells (BM-MSC). Here, we determine the extent to which this mesenchymal pattern is expressed on the three adipose stem/progenitor populations. Eight independent adipose tissue samples were analyzed in a single tube (CD105-FITC/CD73-PE/CD146-PETXR/CD14-PECY5/CD33-PECY5/CD235A-PECY5/CD31-PECY7/CD90-APC/CD34-A700/CD45-APCCY7/DAPI). Adipose EPC were highly proliferative with (14.3 ± 2.8)% (mean ± SEM) having >2N DNA. About half (53.1 ± 7.6)% coexpressed CD73 and CD105, and (71.9 ± 7.4)% expressed CD90. Pericytes were less proliferative [(8.2 ± 3.4)% >2N DNA)] with a smaller proportion [(29.6 ± 6.9)% CD73+/CD105+, (60.5 ± 10.2)% CD90+] expressing mesenchymal associated markers. However, the CD34+ subset of CD146+ pericytes were both highly proliferative [(15.1 ± 3.6)% with >2N DNA] and of uniform mesenchymal phenotype [(93.3 ± 3.7)% CD73+/CD105+, (97.8 ± 0.7)% CD90+], suggesting transit amplifying progenitor cells. SA-ASC were the least proliferative [(3.7 ± 0.8)%>2N DNA] but were also highly mesenchymal in phenotype [(94.4 ± 3.2)% CD73+/CD105+, (95.5 ± 1.2)% CD90+]. These data imply a progenitor/progeny relationship between pericytes and SA-ASC, the most mesenchymal of SVF cells. Despite phenotypic and functional similarities to BM-MSC, SA-ASC are distinguished by CD34 expression.