Human adipose tissue contains erythroid progenitors expressing fetal hemoglobin

Abstract

AIM: To investigate the origin of hematopoietic progenitors contained in the stromal vascular fraction (SVF) of human adipose tissue.

METHODS: Tissue samples obtained from lipectomies were subjected to enzymatic digestion with collagenase to obtain a single-cell suspension. The centrifuged cell pellet, termed SVF, was separated immunomagnetically into CD45⁺ and CD45^- cells and cultured in serum-free medium containing hematopoietic cytokines. The freshly isolated and cultured cells were evaluated to determine their ability to form hematopoietic colony-forming units in clonogenic assays and for the expression of certain hematopoietic transcription factors by reverse transcription-polymerase chain reaction; the gene expression level was compared to that in CD34⁺ hematopoietic progenitor cells from cord blood (CB) and adult peripheral blood (PB). To characterize erythroid progenitors, burst-forming units-erythroid (BFU-E) were developed in a semisolid medium under different culture conditions, and the hemoglobin composition and globin gene expression in the erythroid colonies were determined.

RESULTS: The transcription factors SCL/TAL1, RUNX1, RUNX2 and GATA2 were expressed in both the CD45⁺ and CD45^- SVF populations; however, in contrast to our observations in the CD34⁺ cells from CB and adult PB, GATA1 was not detected. Nevertheless, GATA1 could be detected in the SVF cells after seven days in culture, whereas its expression was upregulated in the CB CD34⁺ cells. The analysis of BFU-E-derived colonies revealed that virtually all erythroid cells produced by SVF cells expressed fetal hemoglobin, and the γ-globin mRNA levels ranged between those obtained in the adult- and neonatal-derived erythroid cells. Moreover, the SVF-derived erythroid cells synthesized similar levels of α- and β-globin mRNA, whereas the α-globin transcript levels were consistently higher those of β-globin in the cells derived from CB or PB CD34⁺ cells. Furthermore, although the cellular distribution of hemoglobin in the erythroid cells derived from the CD34⁺ cells obtained from hematopoietic tissues was dependent on the presence or absence of serum in the culture medium, this did not affect the SVF-derived erythroid cells.

CONCLUSION: Our results demonstrate that hematopoietic progenitors in SVF have molecular and functional features that differ from those exhibited by circulating progenitors, suggesting the possibility of a different origin.

Keywords: Hemoglobin; Adipose tissue; Stromal vascular fraction; Erythroid cells; Hematopoietic progenitors

Core tip: Stromal vascular fraction (SVF) from human adipose tissue contains mesodermal precursors with the ability to form mixed hematoendothelial colonies and hematopoietic colony-forming units, though this occurs at an extremely low frequency. It is well known that hematopoietic progenitors residing in the bone marrow are released into the circulation and enter peripheral tissues; therefore, the most plausible explanation for this hematopoietic activity is that these cells are actually circulating hematopoietic progenitors. However, it is also possible that they may originate from the adipose tissue itself. To address this hypothesis, we compared the expression levels of the most relevant hematopoietic transcription factors in cells isolated from SVF with their expression levels in CD34⁺ cells isolated from adult peripheral blood and cord blood. Moreover, because the composition of hemoglobin in erythroid cells varies depending on the origin of the hematopoietic progenitors and their ontogenic stage, burst-forming units-erythroid were developed in culture, and the hemoglobin composition and globin gene expression in erythroid colonies were determined. Our results provide evidence that erythroid progenitors contained in SVF exhibit features that differ from those of circulating progenitors. These findings should encourage further research on stem cells and the microenvironment of human adipose tissue.