Mature Adipocyte-Derived Dedifferentiated Fat Cells Can Trans-Differentiate into Osteoblasts <i>In Vitro</i> and <i>In Vivo</i> only by All-Trans Retinoic Acid

Abstract

ABSTRACT. We investigated whether de-differentiated fat (DFAT) cells, a mature adipocyte-derived preadipocyte cell line, can be induced to trans-differentiate into osteoblasts in vitro and in vivo. All-trans retinoic acid (RA) induced expression of osteoblast-specific mRNAs encoding Cbfa1/Runx2, osterix, alkaline phosphatase, osteopontin, parathyroid hormone receptor, and osteocalcin in the DFAT cells, but did not induce the expression of adipocytespecific mRNAs encoding PPARγ2, C/EBPα, and GLUT4. Moreover, alkaline phosphatase activity was expressed in DFAT cells and the cells underwent mineralization of the bone matrix in vitro. Furthermore, when DFAT cells were transplanted subcutaneously into C57BL/6N mice in diffusion chambers, these cells formed ectopic osteoid tissue without any host cell-invasion of the chambers. These results indicate that DFAT cells derived from mature adipocytes can be converted into fully differentiated osteoblasts in vitro and in vivo using RA. DFAT cells provide a unique model for studying the lineage commitment of the adipocytes and osteoblasts derived from mesenchymal stem cells. Identification of the pathways that regulate these processes could lead to the development of new therapeutic strategies for control of unwarranted growth of bone and adipose tissue.

Dedifferentiated fat cells: an alternative source of adult multipotent cells from the adipose tissues

“…Following studies proved that DFAT cells can also be derived from the subcutaneous white adipose tissue (WAT) from various species, including human [17], rats [16], mouse [18] and cattle [8]. Because of the wide application of free-fat transfer and plastic liposuction [21][22], large amount of human DFAT cells can be derived by those convenient ways for autologous tissue engineering and reconstruction purposes.…”

“…According to the different studies [14, 16-17, 19, 23], in the following 2 to 3 weeks of uninterrupted culture, the fat drops within the adipocytes will gradually disappear and the cells shift into fibroblast-like morphology, reestablishing a strong proliferation ability as well. Distinct to the ASCs, DFAT cells derived from ceiling culture method were identified as a more homogenous cell group in most reports [16][17][18][19][23][24][25][26]. Although, this simple technique needs no complex procedures such as transfection or chemical induction, several key points should still be paid attention to.…”

“…PCR analysis showed that although DFAT cells had decreased level of LPL, leptin and glucose transporter 4 (GLUT4) compared with mature adipocytes, they still express key adipogenic markers including peroxisome proliferator-activated receptor gamma (PPARγ), CAAT/ enhancer-binding proteins (C/EBPα, C/EBPβ and C/EBPδ) and sterol regulatory element-binding protein-1c (SREBP1c) [14,[24][25]. In vitro, several recipes of adipogenic cultures were applied with different combination and dosage of induction chemicals such as dexamethasone, 3-isobutyl-1-methylxanthine and insulin transferring selenium X (ITS) [14][15]18]. Initial establishment of lipid droplets could found as early as 5-7 days of induction, while significant amount of lipid accumulation within cells could be observed after 2-3 weeks.…”

“…Therefore, the amount of dexamethasone in osteogenic induction is usually significantly lower than adipogenic induction. Osteogenic differentiation of DFAT cells could also be induced by all-trans retinoic acid, an analog of retinol which interacts with bone morphogenetic proteins (BMPs) to inhibit adipogenesis and enhance osteogenesis [18]. Chondrogenic induction could be facilitated with L-ascorbic acid-2-phosphate, proline, pyruvate, transforming growth factor β3 (TGF-β3) and ITS.…”

“…With this method and provided the fact that the mature adipocytes are the most abundant cell type in the adipose tissue, the DFAT cells which exhibit proliferation and multipotent capacity in vitro and in vivo have been regarded as an ideal source for adult postnatal pluripotent cells of much higher homogeneity than ASCs [14,[16][17][18][19]. In this review, by a briefing summary on the origin, identification and differentiation ability of DFAT cells, we're going to unveil the great application potentials of this unique cell kind in tissue engineering and regenerative medicine.…”