Treatment of pluripotential C3H 10T1/2 fibroblasts with bone morphogenetic protein-4 induces adipocyte commitment

The miR-23-27-24 cluster: an emerging target in NAFLD pathogenesis

The incidence of non-alcoholic fatty liver disease (NAFLD) is increasing globally, being the most widespread form of chronic liver disease in the west. NAFLD includes a variety of disease states, the mildest being non-alcoholic fatty liver that gradually progresses to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Small non-coding single-stranded microRNAs (miRNAs) regulate gene expression at the miRNA or translational level. Numerous miRNAs have been shown to promote NAFLD pathogenesis and progression through increasing lipid accumulation, oxidative stress, mitochondrial damage, and inflammation. The miR-23-27-24 clusters, composed of miR-23a-27a-24-2 and miR-23b-27b-24-1, have been implicated in various biological processes as well as many diseases. Herein, we review the current knowledge on miR-27, miR-24, and miR-23 in NAFLD pathogenesis and discuss their potential significance in NAFLD diagnosis and therapy.

SCARA5 plays a critical role in the commitment of mesenchymal stem cells to adipogenesis

Mesenchymal stem cells have the capacity to give rise to multiple cell types, such as adipocytes, osteoblasts, chondrocytes, and myocytes. However, the molecular events responsible for the lineage specification and differentiation of mesenchymal stem cells remain unclear. Using gene expression profile studies, we determined that Scavenger receptor class A, member 5 (SCARA5) is a novel mediator of adipocyte commitment. SCARA5 was expressed at a higher level in committed A33 preadipocyte cells compared to C3H10T1/2 pluripotent stem cells. Gain- and loss-of-function studies likewise revealed that SCARA5 acts as a mediator of adipocyte commitment and differentiation in both A33 and C3H10T1/2 cells. RNAi-mediated knockdown of SCARA5 in A33 cells markedly inhibited the adipogenic potential, whereas overexpression of SCARA5 enhanced adipocyte differentiation in C3H10T1/2 cells. We also demonstrated that the focal adhesion kinase (FAK) and ERK signaling pathways is associated with the SCARA5-mediated response, thereby modulating adipocyte lineage commitment and adipocyte differentiation. Additionally, glucocorticoids induced the expression of SCARA5 in differentiating adipocytes through glucocorticoids response elements (GRE) in the SCARA5 promoter. Taken together, our study demonstrates that SCARA5 is a positive regulator in adipocyte lineage commitment and early adipogenesis in mesenchymal stem cells.

Transcriptional Regulation of Adipogenesis

Adipocytes are the defining cell type of adipose tissue. Once considered a passive participant in energy storage, adipose tissue is now recognized as a dynamic organ that contributes to several important physiological processes, such as lipid metabolism, systemic energy homeostasis, and whole-body insulin sensitivity. Therefore, understanding the mechanisms involved in its development and function is of great importance. Adipocyte differentiation is a highly orchestrated process which can vary between different fat depots as well as between the sexes. While hormones, miRNAs, cytoskeletal proteins, and many other effectors can modulate adipocyte development, the best understood regulators of adipogenesis are the transcription factors that inhibit or promote this process. Ectopic expression and knockdown approaches in cultured cells have been widely used to understand the contribution of transcription factors to adipocyte development, providing a basis for more sophisticated in vivo strategies to examine adipogenesis. To date, over two dozen transcription factors have been shown to play important roles in adipocyte development. These transcription factors belong to several families with many different DNA-binding domains. While peroxisome proliferator-activated receptor gamma (PPARγ) is undoubtedly the most important transcriptional modulator of adipocyte development in all types of adipose tissue, members of the CCAAT/enhancer-binding protein, Krüppel-like transcription factor, signal transducer and activator of transcription, GATA, early B cell factor, and interferon-regulatory factor families also regulate adipogenesis. The importance of PPARγ activity is underscored by several covalent modifications that modulate its activity and its ability to modulate adipocyte development. This review will primarily focus on the transcriptional control of adipogenesis in white fat cells and on the mechanisms involved in this fine-tuned developmental process. © 2017 American Physiological Society. Compr Physiol 7:635-674, 2017.

Expression analysis of bone morphogenetic protein 4 between fat and lean birds in adipose tissue and serum

The objectives of the present study were to characterize the tissue expression of chicken (Gallus gallus) bone morphogenetic protein 4 (BMP4) and compare differences in its expression in abdominal fat tissue and serum between fat and lean birds and to determine a potential relationship between the expression of BMP4 and abdominal fat tissue growth and development. The results showed that chicken BMP4 messenger RNA (mRNA) and protein were expressed in various tissues, and the expression levels of BMP4 transcript and protein were relatively higher in adipose tissues. In addition, the mRNA and protein expression levels of BMP4 in abdominal fat tissue of fat males were lower than those of lean males at 1, 2, 5, and 7 wk of age (P < 0.05). Furthermore, the serum BMP4 content of fat males was lower than that of lean males at 7 wk of age (P < 0.05). BMP4 mRNA expression levels were significantly higher in preadipocytes than those in mature adipocytes (P < 0.05), and the expression level decreased during differentiation in vitro (P < 0.05). These results suggested that chicken BMP4 might affect abdominal fat deposition through differences in its expression level. The results of this study will provide basic molecular information for studying the role of BMP4 in the regulation of adipogenesis in avian species.

Cells derived from murine induced pluripotent stem cells (iPSC) by treatment with members of TGF-beta family give rise to osteoblasts differentiation and form bone in vivo

Background

Induced pluripotent stem cells (iPSC) are generated by reprogramming somatic cells into embryonic like state (ESC) using defined factors. There is great interest in these cells because of their potential for application in regenerative medicine.

Results

iPSC reprogrammed from murine tail tip fibroblasts were exposed to retinoic acid alone (RA) or in combination with TGF-β1 and 3, basic fibroblast growth factor (bFGF) or bone morphogenetic protein 2 (BMP-2). The resulting cells expressed selected putative mesenchymal stem cells (MSCs) markers; differentiated toward osteoblasts and adipocytic cell lineages in vitro at varying degrees. TGF-beta1 and 3 derived-cells possessed higher potential to give rise to osteoblasts than bFGF or BMP-2 derived-cells while BMP-2 derived cells exhibited a higher potential to differentiate toward adipocytic lineage. TGF-β1 in combination with RA derived-cells seeded onto HA/TCP ceramics and implanted in mice deposited typical bone. Immunofluorescence staining for bone specific proteins in cell seeded scaffolds tissue sections confirmed differentiation of the cells into osteoblasts in vivo.

Conclusions

The results demonstrate that TGF-beta family of proteins could potentially be used to generate murine iPSC derived-cells with potential for osteoblasts differentiation and bone formation in vivo and thus for application in musculoskeletal tissue repair and regeneration.

Association of serum bone morphogenetic protein 4 levels with obesity and metabolic syndrome in non-diabetic individuals

Bone morphogenetic protein 4 (BMP-4) is involved in the earliest stages of adipocyte differentiation and is recognized as an adipogenic factor for white adipose tissue. The association of serum BMP-4 levels with anthropometric and metabolic parameters has not been previously studied. We aimed to explore the relationship of serum BMP-4 levels with obesity and metabolic syndrome. Serum BMP-4 levels were measured in 104 non-diabetic individuals from the Chungju Metabolic Disease Cohort Study. Anthropometric measurements and components of metabolic syndrome were assessed in all patients. Serum BMP-4 levels were significantly increased in individuals with obesity or metabolic syndrome. After adjusting for age and gender, serum BMP-4 levels were positively correlated with body mass index, waist circumference (WC), waist-to-hip ratio, fasting plasma insulin, homeostasis model assessment index, and triglycerides and were negatively correlated with high-density lipoprotein (HDL) cholesterol. Among these parameters, WC and HDL cholesterol were found to be independent contributing factors for serum BMP-4 levels. Serum BMP-4 levels were also significantly higher in subjects with positive diagnostic criteria for each component of metabolic syndrome. The area under the receiver operating characteristic curve for BMP-4 was 0.661 (P = 0.022, 95% CI = 0.528 to 0.794) and the cut-off value was 2.84 pg/mL. This is the first demonstration that serum BMP-4 levels are associated with adiposity, insulin resistance, and the presence of metabolic syndrome. Whether BMP-4 may be involved in the pathogenesis of obesity and metabolic syndrome deserves further investigation.

Downregulated expression of the secreted glycoprotein follistatin-like 1 (Fstl1) is a robust hallmark of preadipocyte to adipocyte conversion

Obesity is a public health crisis in the United States. Targeting preadipocyte to adipocyte conversion may be an effective approach to regulate adipose mass. Using differential screening we identified Fstl1, a secreted glycoprotein with roles in immunomodulation, cell growth, cardioprotection, and vascularization, as a "preadipokine". Fstl1 is highly expressed in 3T3-L1 preadipocytes and dramatically downregulated early in their differentiation to adipocytes. Northern blot analysis of murine tissues reveals white adipose tissue (WAT), lung and heart as primary sites of Fstl1 transcript expression. In WAT, Fstl1 transcript is restricted to the preadipocyte-containing stromal-vascular cell population. Time course studies in multiple adipogenesis models reveal downregulation of Fstl1 is a hallmark of white and brown adipocyte conversion. By Western blot, we show culture media of 3T3-L1 preadipocytes contains high levels of Fstl1 protein that rapidly decline in adipocyte conversion. Moreover, we observe a correlation between preadipocyte phenotype and Fstl1 expression in that TNFalpha-mediated de-differentiation of 3T3-L1 adipocytes is accompanied by re-expression of Fstl1 transcript and protein. Treatment of 3T3-L1 preadipocytes with a panel of 18 hormones and other agents revealed the demethylating agent 5-aza-cytidine decreases Fstl1 transcript and protein levels by approximately 90%. Furthermore, of 10 additional preadipocyte-expressed genes analyzed we find Pref-1, Col1A1, Sca-1/Ly6a, Lox and Thbs2, are also downregulated by 5-aza-cytidine. Using luciferase reporter constructs containing 791 or 3922 bp of the Fstl1 5' flanking region, we determine negative transcriptional regulation by Kruppel-like factor 15. Together, our data suggest downregulation of Fstl1 expression may be an important feature of preadipocyte to adipocyte conversion.

Emerging role of bone morphogenetic proteins in adipogenesis and energy metabolism

Bone morphogenetic proteins (BMPs) regulate many processes in embryonic development as well as in the maintenance of normal tissue function later in adult life. However, the role of this family of proteins in formation of adipose tissue has been underappreciated in the field of developmental biology. With the growing epidemic of obesity, improved knowledge of adipocyte development and function is urgently needed. Recently, there have been significant advances in understanding the role of different members of the BMP superfamily in control of adipocyte differentiation and systemic energy homeostasis. This review summarizes recent progress in understanding how BMPs specify adipose cell fate in stem/progenitor cells and their potential role in energy metabolism. We propose that BMPs provide instructive signals for adipose cell fate determination and regulate adipocyte function. These findings have opened up exciting opportunities for developing new therapeutic approaches for the treatment of obesity and its many associated metabolic disorders.

BMP signaling pathway is required for commitment of C3H10T1/2 pluripotent stem cells to the adipocyte lineage

Obesity is accompanied by an increase in both adipocyte number and size. The increase in adipocyte number is the result of recruitment to the adipocyte lineage of pluripotent stem cells present in the vascular stroma of adipose tissue. These pluripotent cells have the potential to undergo commitment and then differentiate into adipocytes, as well as myocytes, osteocytes, and chondrocytes. In this article, we show that both bone morphogenetic protein (BMP)2 and BMP4 can induce commitment of C3H10T1/2 pluripotent stem cells into adipocytes. After treatment of C3H10T1/2 stem cells with these BMPs during proliferation followed by exposure to differentiation inducers at growth arrest, nearly all cells enter the adipose development pathway, express specific adipocyte markers, and acquire the adipocyte phenotype. Overexpression of constitutively active BMP receptor (CA)-BMPr1A or CA-BMPr1B induces commitment in the absence of BMP2/4, whereas overexpression of a dominant-negative receptor dominant-negative-BMPr1A suppresses commitment induced by BMP. Also, knockdown of the expression of Smad4 (coregulator in the BMP/Smad signaling pathway) with RNAi disrupts commitment by the BMPs. However, knockdown of expression of p38 MAPK (an intermediary in the BMP/MAPK signaling pathway) with RNAi had little effect on BMP-induced commitment. Together, these findings indicate that the BMP/Smad signaling pathway has a dominant role in adipocyte lineage determination. Proteomic analysis identified lysyl oxidase (LOX), a bona fide downstream target gene of the BMP signaling pathway. Expression of LOX is induced by BMP2/4 during adipocyte lineage commitment, and knockdown of its expression disrupts the commitment process.

Flexible and dynamic organization of bone marrow stromal compartment

The bone marrow mesenchymal compartment contains putative stem/progenitors of skeletal tissue components such as bone, cartilage, haematopoiesis-supporting stroma and adipocytes. Previously appreciated as vital to the support of haematopoiesis, these cells have also been recently recognized as having significant immunomodulatory properties with implications for allogeneic haematopoietic cell transplantation. Despite having been studied for more than three decades and currently being used in different clinical settings, their biology remains elusive. The aim of this review is to critically analyse the field of mesenchymal stem/progenitor cell biology, in respect of their relationship with other mesenchymal cell-types. Several issues concerning lineage commitment and inter-conversion potential between different mesenchymal cell-types are reviewed.

Heparin-binding epidermal growth factor-like growth factor inhibits adipocyte differentiation at commitment and early induction stages

Adipocytokines, bioactive molecules secreted from adipose tissues, play important roles in physiology, development, and disease. Recently, heparin-binding epidermal growth factor-like growth factor (HB-EGF) was identified as an adipocytokine whose expression correlates with obesity. However, the biological role of fat-secreted HB-EGF is still unclear. In this study, we investigated the effects of HB-EGF on the adipocyte differentiation of C3H10T1/2 pluripotent mesenchymal cells. Upon adipogenic conversion of C3H10T1/2 cells, HB-EGF displayed dynamic changes in expression where an initial decrease was followed by increased levels of expression at later stages. HB-EGF treatment during adipogenic induction inhibited lipid accumulation and decreased the expression of adipocyte molecular markers (fatty acid-binding protein, peroxisome proliferator-activated receptor gamma, and CAAT enhancer-binding protein alpha) and lipogenic genes (glucose transporter, fatty acid synthetase, and lipoprotein lipase). Therefore, HB-EGF has an inhibitory effect on adipocyte differentiation. Administration of HB-EGF at various intervals during adipocyte differentiation revealed that HB-EGF acts during the early stages of adipocyte differentiation, but not at the later stages of differentiation. Furthermore, HB-EGF was able to block the commitment of pluripotent mesenchymal cells to the adipocyte lineage triggered by bone morphogenic protein 4 treatment. These data suggest that HB-EGF acts as a negative regulator of adipogenesis by inhibiting the commitment and early differentiation of the adipose lineage. The inhibitory role of HB-EGF on adipocyte differentiation of pluripotent mesenchymal cells sheds light on potential mechanisms that control adipose tissue homeostasis.

BMP-4 treatment of C3H10T1/2 stem cells blocks expression of MMP-3 and MMP-13

Microarray gene expression profiling was used to identify bone morphogenetic protein-4 (BMP-4) responsive factors involved in late stages of adipocyte commitment in C3H10T1/2 cells. The analysis revealed that the matrix metalloproteinase-3 (MMP-3) gene decreased 100-fold after BMP-4 treatment, and expression of MMP-13 decreased 19.5-fold. Uncommitted C3H10T1/2 cells exhibit dramatic up-regulation of MMP-3 and MMP-13 genes as cells become confluent. Real-time RT-PCR demonstrated that BMP-4 blocks expression of both transcripts. Likewise, a stable committed preadipocyte line derived from C3H10T1/2 cells did not express MMP-3 or MMP-13 at confluence, despite never receiving BMP-4. Active forms of both proteins were detected in media from confluent C3H10T1/2 cells but not in BMP-4 treated cells. Addition of BMP-4 to confluent C3H10T1/2 cells repressed the expression of both genes but did not induce adipocyte differentiation. The findings indicate that BMP-4-induced down-regulation of MMP-3 and MMP-13 is associated with commitment, but is insufficient to induce adipogenesis.

Adipose development: from stem cell to adipocyte

Cell culture models have been developed to study commitment and subsequent differentiation of preadipocytes into adipocytes. Bone morphogenetic protein 4 commits mesenchymal stem cells to the adipose lineage. Other factors, including Wnt signaling, cell density, and cell shape, play a role in lineage commitment. Following commitment to the adipose lineage, growth-arrested preadipocytes can differentiate to adipocytes by treatment with insulin-like growth factor 1, glucocorticoid and an agent that increases cAMP level. This process is characterized by a rapid and transient increase in CCAAT/enhancer binding protein (C/EBP) beta and synchronous re-entry into the cell cycle. Acquisition of DNA-binding by C/EBPbeta occurs after the transcription factor becomes phosphorylated. The cells enter a growth-arrested state and begin terminal differentiation. C/EBPalpha, peroxisome proliferator-activated receptor gamma, and adipocyte determination, and differentiation-dependent factor 1 coordinate the expression of genes that create and maintain the adipocyte phenotype.

Adipogenesis: forces that tip the scales

The balance of contradictory signals experienced by preadipocytes influences whether these cells undergo adipogenesis. In addition to the endocrine system, these signals originate from the preadipocytes themselves or operate as part of a feedback loop involving mature adipocytes. The factors that regulate adipogenesis either promote or block the cascade of transcription factors that coordinate the differentiation process. Some of the positive factors reviewed include insulin-like growth factor I, macrophage colony-stimulating factor, fatty acids, prostaglandins and glucocorticoids, and negative factors reviewed include Wnt, transforming growth factor beta, inflammatory cytokines and prostaglandin F(2alpha). Tipping the scales towards or away from adipogenesis has profound implications for human health. In this review, we describe recent contributions to the field and will focus on factors that probably play a role in vivo.

The biology of white adipocyte proliferation

Expanded adipose tissue mass increases the risk for many clinical conditions including diabetes, hypertension, coronary atherosclerotic heart disease, and some forms of cancer. Therefore, it is imperative that we understand the mechanisms by which fat pads expand. The enlargement of fat cells during the development of obesity has been previously hypothesized to be a triggering factor for the proliferation of new fat cells. There is now a preponderance of evidence that adipose tissue is a source of growth factors such as IGF-I, IGF binding proteins, TNF alpha, angiotensin II, and MCSF that are capable of stimulating proliferation. The relative importance of these autocrine/paracrine factors in the normal control of preadipocyte proliferation is unknown. In addition, the proliferative response of preadipocytes to the paracrine milieu is undoubtedly modulated by neural inputs to fat tissue and/or serum factors. Together, these multiple regulatory controls orchestrate overall and region-specific adipose tissue cellularity responses associated with the development of hyperplastic obesity. Both in vivo and in vitro studies are needed to understand the complex, interacting physiological mechanisms by which growth of this important organ is regulated.