Three-dimensional spheroids of dedifferentiated fat cells enhance bone regeneration.

INTRODUCTION: Mesenchymal stromal/stem cells (MSCs) are multipotent, self-renewing cells that are extensively used in tissue engineering. Dedifferentiated fat (DFAT) cells are derived from adipose tissues and are similar to MSCs. Three-dimensional (3D) spheroid cultures comprising MSCs mimic the biological microenvironment more accurately than two-dimensional cultures; however, it remains unclear whether DFAT cells in 3D spheroids possess high osteogenerative ability. Furthermore, it is unclear whether DFAT cells from 3D spheroids transplanted into calvarial bone defects are as effective as those from two-dimensional (2D) monolayers in promoting bone regeneration. METHODS: We compared the in vitro osteogenic potential of rat DFAT cells cultured under osteogenic conditions in 3D spheroids with that in 2D monolayers. Furthermore, to elucidate the ability of 3D spheroid DFAT cells to promote bone healing, we examined the in vivo osteogenic potential of transplanting DFAT cells from 3D spheroids or 2D monolayers into a rat calvarial defect model. RESULTS: Osteoblast differentiation stimulated by bone morphogenetic protein-2 (BMP-2) or osteogenesis-inducing medium upregulated osteogenesis-related molecules in 3D spheroid DFAT cells compared with 2D monolayer DFAT cells. BMP-2 activated phosphorylation in the canonical Smad 1/5 pathways in 3D spheroid DFAT cells but phosphorylated ERK1/2 and Smad2 in 2D monolayer DFAT cells. Regardless of osteogenic stimulation, the transplantation of 3D DFAT spheroid cells into rat calvarial defects promoted new bone formation at a greater extent than that of 2D DFAT cells. CONCLUSIONS: Compared with 2D DFAT cells, 3D DFAT spheroid cells promote osteoblast differentiation and new bone formation via canonical Smad 1/5 signaling pathways. These results indicate that transplantation of DFAT cells from 3D spheroids, but not 2D monolayers, accelerates bone healing.

Enhancement of jaw bone regeneration via ERK1/2 activation using dedifferentiated fat cells.

BACKGROUND AIMS: Mesenchymal stem/stromal cells (MSCs) are multipotent and self-renewing cells that are extensively used in tissue engineering. Adipose tissues are known to be the source of two types of MSCs; namely, adipose tissue-derived MSCs (ASCs) and dedifferentiated fat (DFAT) cells. Although ASCs are sometimes transplanted for clinical cytotherapy, the effects of DFAT cell transplantation on mandibular bone healing remain unclear. METHODS: The authors assessed whether DFAT cells have osteogenerative potential compared with ASCs in rats in vitro. In addition, to elucidate the ability of DFAT cells to regenerate the jaw bone, the authors examined the effects of DFAT cells on new bone formation in a mandibular defect model in (i) 30-week-old rats and (ii) ovariectomy-induced osteoporotic rats in vivo. RESULTS: Osteoblast differentiation with bone morphogenetic protein 2 (BMP-2) or osteogenesis-induced medium upregulated the osteogenesis-related molecules in DFAT cells compared with those in ASCs. BMP-2 activated the phosphorylation signaling pathways of ERK1/2 and Smad2 in DFAT cells, but minor Smad1/5/9 activation was noted in ASCs. The transplantation of DFAT cells into normal or ovariectomy-induced osteoporotic rats with mandibular defects promoted new bone formation compared with that seen with ASCs. CONCLUSIONS: DFAT cells promoted osteoblast differentiation and new bone formation through ERK1/2 and Smad2 signaling pathways in vitro. The transplantation of DFAT cells promoted new mandibular bone formation in vivo compared with that seen with ASCs. These results suggest that transplantation of ERK1/2-activated DFAT cells shorten the mandibular bone healing process in cytotherapy.

Three-dimensional spheroids of mesenchymal stem/stromal cells promote osteogenesis by activating stemness and Wnt/ß-catenin.

Mesenchymal stem/stromal cells (MSCs) are multipotent and self-renewal cells that are widely used in regenerative medicine. The culture of three-dimensional (3D) spheroid MSCs more accurately mimics the biological microenvironment. However, it is unclear which key molecules are responsible for the cell fate control of MSCs during 3D spheroid formation and their impact on the functional characteristics of these stem cells. Furthermore, it remains unclear what effects 3D spheroid MSC transplantation has on new bone formation compared with that of 2D monolayer MSCs. We assessed whether the osteogenerative potential of 3D spheroid MSCs is greater than that of 2D monolayer MSCs in vitro. In addition, to elucidate the ability of 3D spheroid MSCs to regenerate bone, we examined the effects of transplanting wild-type (WT) or knockout (KO) spheroid MSCs on new bone formation in mice calvarial defect model in vitro. The 3D spheroid MSC culture dramatically upregulated into stemness markers compared with the 2D monolayer MSC culture. In contrast, BMP-2 significantly increased the osteogenesis-related molecules in the 3D spheroid MSCs but, in turn, downregulated the stemness markers. BMP-2 activated Smad1/5 together with Wnt/ß-catenin in 3D spheroid MSCs. Transplantation of these MSCs into aged mice with calvarial defects promoted new bone formation compared with that of 2D monolayer MSCs. In contrast, transplantation of 3D or 2D ß-catenin knockout MSCs induced little new bone formation. The 3D spheroid MSC culture had higher stemness compared with the 2D monolayer MSC culture. The culture of 3D spheroid MSCs rapidly promoted osteoblastogenesis and bone formation through synergistic activation of the Wnt/ß-catenin pathway in vitro. The transformation of 3D spheroid, but not 2D monolayer, MSCs promoted new bone regeneration in vivo. These results indicate that transplantation of 3D spheroid MSCs in regeneration therapy contributes to a shorter regenerative healing process, including new bone formation.