Zfp423 Promotes Adipogenic Differentiation of Bovine Stromal Vascular Cells

Intramuscular fat or marbling is critical for the palatability of beef. In mice, very recent studies show that adipocytes and fibroblasts share a common pool of progenitor cells, with Zinc finger protein 423 (Zfp423) as a key initiator of adipogenic differentiation. To evaluate the role of Zfp423 in intramuscular adipogenesis and marbling in beef cattle, we sampled beef muscle for separation of stromal vascular cells. These cells were immortalized with pCI neo-hEST2 and individual clones were selected by G418. A total of 288 clones (3×96 well plates) were isolated and induced to adipogenesis. The presence of adipocytes was assessed by Oil-Red-O staining. Three clones with high and low adipogenic potential respectively were selected for further analyses. In addition, fibro/adipogenic progenitor cells were selected using a surface marker, platelet derived growth factor receptor (PDGFR) α. The expression of Zfp423 was much higher (307.4±61.9%, P<0.05) in high adipogenic cells, while transforming growth factor (TGF)-β was higher (156.1±48.7%, P<0.05) in low adipogenic cells. Following adipogenic differentiation, the expression of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer binding protein α (C/EBPα) were much higher (239.4±84.1% and 310.7±138.4%, respectively, P<0.05) in high adipogenic cells. Over-expression of Zfp423 in stromal vascular cells and cloned low adipogenic cells dramatically increased their adipogenic differentiation, accompanied with the inhibition of TGF-β expression. Zfp423 knockdown by shRNA in high adipogenic cells largely prevented their adipogenic differentiation. The differential regulation of Zfp423 and TGF-β between low and high adipogenic cells is associated with the DNA methylation in their promoters. In conclusion, data show that Zfp423 is a critical regulator of adipogenesis in stromal vascular cells of bovine muscle, and Zfp423 may provide a molecular target for enhancing intramuscular adipogenesis and marbling in beef cattle.     

Hypoxia Promotes Osteogenesis but Suppresses Adipogenesis of Human Mesenchymal Stromal Cells in a Hypoxia-Inducible Factor-1 Dependent Manner

Background

Bone fracture initiates a series of cellular and molecular events including the expression of hypoxia-inducible factor (HIF)-1. HIF-1 is known to facilitate recruitment and differentiation of multipotent human mesenchymal stromal cells (hMSC). Therefore, we analyzed the impact of hypoxia and HIF-1 on the competitive differentiation potential of hMSCs towards adipogenic and osteogenic lineages.

Methodology/Principal Findings

Bone marrow derived primary hMSCs cultured for 2 weeks either under normoxic (app. 18% O₂) or hypoxic (less than 2% O₂) conditions were analyzed for the expression of MSC surface markers and for expression of the genes HIF1A, VEGFA, LDHA, PGK1, and GLUT1. Using conditioned medium, adipogenic or osteogenic differentiation as verified by Oil-Red-O or von-Kossa staining was induced in hMSCs under either normoxic or hypoxic conditions. The expression of HIF1A and VEGFA was measured by qPCR. A knockdown of HIF-1α by lentiviral transduction was performed, and the ability of the transduced hMSCs to differentiate into adipogenic and osteogenic lineages was analyzed. Hypoxia induced HIF-1α and HIF-1 target gene expression, but did not alter MSC phenotype or surface marker expression. Hypoxia (i) suppressed adipogenesis and associated HIF1A and PPARG gene expression in hMSCs and (ii) enhanced osteogenesis and associated HIF1A and RUNX2 gene expression. shRNA-mediated knockdown of HIF-1α enhanced adipogenesis under both normoxia and hypoxia, and suppressed hypoxia-induced osteogenesis.

Conclusions/Significance

Hypoxia promotes osteogenesis but suppresses adipogenesis of human MSCs in a competitive and HIF-1-dependent manner. We therefore conclude that the effects of hypoxia are crucial for effective bone healing, which may potentially lead to the development of novel therapeutic approaches.     

Coordinate Functional Regulation between Microsomal Prostaglandin E Synthase-1 (mPGES-1) and Peroxisome Proliferator-activated Receptor γ (PPARγ) in the Conversion of White-to-brown Adipocytes

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated nuclear receptor and a master regulator of adipogenesis. Microsomal prostaglandin E (PGE) synthase-1 (mPGES-1) is an inducible enzyme that couples with cyclooxygenase-2 for the biosynthesis of PGE₂. In this study we demonstrate the existence of a coordinate functional interaction between PPARγ and mPGES-1 in controlling the process of pre-adipocyte differentiation in white adipose tissue (WAT). Adipocyte-specific PPARγ knock-out mice carrying an aP2 promoter-driven Cre recombinase transgene showed a blunted response to the adipogenic effects of a high fat diet. Pre-adipocytes from these knock-out mice showed loss of PPARγ and were resistant to rosiglitazone-induced WAT differentiation. In parallel, WAT from these mice showed increased expression of uncoupling protein 1, a mitochondrial enzyme that dissipates chemical energy as heat. Adipose tissue from mice lacking PPARγ also showed mPGES-1 up-regulation and increased PGE₂ levels. In turn, PGE₂ suppressed PPARγ expression and blocked rosiglitazone-induced pre-adipocyte differentiation toward white adipocytes while directly elevating uncoupling protein 1 expression and pre-adipocyte differentiation into mature beige/brite adipocytes. Consistently, pharmacological mPGES-1 inhibition directed pre-adipocyte differentiation toward white adipocytes while suppressing differentiation into beige/brite adipocytes. This browning effect was reproduced in knockdown experiments using a siRNA directed against mPGES-1. The effects of PGE₂ on pre-adipocyte differentiation were not seen in mice lacking PPARγ in adipose tissue and were not mirrored by other eicosanoids (i.e. leukotriene B₄). Taken together, these findings identify PGE₂ as a key regulator of white-to-brown adipogenesis and suggest the existence of a coordinate regulation of adipogenesis between PPARγ and mPGES-1.     

Up-regulated miR-145 Expression Inhibits Porcine Preadipocytes Differentiation by Targeting IRS1

Generally, most miRNAs that were up-regulated during differentiation promoted adipogenesis, but our research indicated that up-regulation of miR-145 in porcine preadipocytes did not promote but inhibit adipogenesis. In this study, miR-145 was significantly up-regulated during porcine dedifferentiated fat (DFAT) cells differentiation. In miR-145 overexpressed DFAT cells, adipogenesis was inhibited and triglycerides accumulation was decreased after hormone stimulation (P<0.05). Furthermore, up-regulation of miR-145 expression repressed induction of mRNA levels of adipogenic markers, such as CCAAT/enhancer-binding protein α (C/EBPα), and peroxisome proliferator-activated receptor γ2 (PPARγ2). These effects caused by miR-145 overexpression were mediated by Insulin receptor substrate 1 (IRS1) as a mechanism. These data suggested that induced miR-145 expression during differentiation could inhibit adipogenesis by targeting IRS1, and miR-145 may be novel agent for adipose tissue engineering.     

BMP-2 promotes osteogenic differentiation of mesenchymal stem cells by enhancing mitochondrial activity

Objectives:Mesenchymal stem cells (MSCs) have become seed cells and basic elements for bone regeneration and bone tissue engineering. The aim of the present study was to investigate the roles and mechanisms of bone morphogenetic protein 2 (BMP-2) on osteogenic differentiation of MSCs.Methods:Primary MSCs were isolated from the femur and tibia bone of rats and then transfected with BMP-2 and PGC-1α adenovirus vectors. Alkaline phosphatase (ALP) activity and alizarin red staining were used to measure osteogenic differentiation of MSCs. Real-time PCR and western blot assays were performed to assess osteogenic differentiation-related proteins levels. The activities of mitochondrial respiratory chain complexes I and II and mitochondrial fluorescence intensity were used to explore mitochondria status during osteogenic differentiation of MSCs.Results:We found that the ability of BMP-2 overexpressed (OE) group osteogenic differentiation was significantly improved, compared with the negative control (NC) group. The results also indicated that BMP-2 can promote the activity of mitochondria. We further used the gain- and loss-of-function approaches to demonstrate that BMP-2 promotes mitochondrial activity by up-regulating PGC-1α to promote osteogenic differentiation of MSCs.Conclusions:These results explored the important role of BMP-2 in the osteoblast differentiation of MSCs from a new perspective, providing a theoretical and experimental basis for bone defect and repair.     

Ultraviolet A Regulates Adipogenic Differentiation of Human Adipose Tissue-derived Mesenchymal Stem Cells via Up-regulation of Kruppel-like Factor 2

Adipocyte dysfunction is strongly associated with the development of obesity, which is a major risk factor for many disorders, including diabetes, hypertension, and heart disease. This study shows that ultraviolet A (UVA) inhibits adipogenic differentiation of human adipose tissue-derived mesenchymal stem cells and its action mechanisms. The mRNA levels of peroxidase proliferator-activated receptor (PPAR) γ and CCAAT/enhancer-binding protein α (C/EBPα), but not CCAAT/enhancer-binding protein ((C/EBP) β and δ, were reduced by UVA. Moreover, the mRNA levels of PPAR γ target genes (lipoprotein lipase (LPL), CD36, adipocyte protein (aP2), and liver X receptor α (LXR)) were down-regulated by UVA. Additionally, attempts to elucidate a possible mechanism underlying the UVA-mediated effects revealed that UVA induced migration inhibitory factor (MIF) gene expression, and this was mediated through activation of AP-1 (especially JNK and p42/44 MAPK) and nuclear factor-κB. In addition, reduced adipogenesis by UVA was recovered upon the treatment with anti-MIF antibodies. AMP-activated protein kinase phosphorylation and up-regulation of Kruppel-like factor 2 (KLF2) were induced by UVA. Taken together, these findings suggest that the inhibition of adipogenic differentiation of human adipose tissue-derived mesenchymal stem cells by UVA occurs primarily through the reduced expression of PPAR γ, which is mediated by up-regulation of KLF2 via the activation of MIF-AMP-activated protein kinase signaling.