Felicity S. Newell

Characterization of the transcriptional and functional effects of fibroblast growth factor-1 on human preadipocyte differentiation

We recently established that fibroblast growth factor (FGF)‐1 promotes adipogenesis of primary human preadipocytes (phPA). In the current report, we have characterized the adipogenic effects of FGF‐1 in phPA and also in a human PA strain derived from an individual with Simpson‐Golabi‐Behmel syndrome (SGBS PA), which exhibit an intrinsic capacity to differentiate with high efficiency. In further studies, we compared these models with the well‐characterized murine 3T3‐L1 preadipocyte cell line (3T3‐L1 PA). FGF‐1 up‐regulated the adipogenic program in phPA, with increased expression of peroxisome proliferator‐activated receptor‐γ in confluent PA prior to induction of differentiation and increased expression of adipocyte markers during differentiation. Moreover, phPA differentiated in the presence of FGF‐1 were more insulin responsive and secreted increased levels of adiponectin. FGF‐1 treatment of SGBS PA further enhanced differentiation. For the most part, the adipogenic program in phPA paralleled that observed in 3T3‐L1 PA; however, we found no evidence of mitotic clonal expansion in the phPA. Finally, we investigated a role for extracellular regulated kinase 1/2 (ERK 1/2) in adipogenesis of phPA. FGF‐1 induced robust phosphorylation of ERK1/2 in early differentiation and inhibition of ERK1/2 activity significantly reduced phPA differentiation. These data suggest that FGF‐1 treated phPA represent a valuable in vitro model for the study of adipogenesis and insulin action and indicate that ERK1/2 activation is necessary for human adipogenesis in the absence of mitotic clonal expansion.—Newell, F. S., Su, H., Tornqvist, H., Whitehead, J. P., Prins, J. B., Hutley, L. J. Characterization of the transcriptional and functional effects of fibroblast growth factor‐1 on human preadipocyte differentiation FASEB J. 20, E2133–E2145 (2006)

Identification of BMP and Activin Membrane-Bound Inhibitor (BAMBI) as a Potent Negative Regulator of Adipogenesis and Modulator of Autocrine/Paracrine Adipogenic Factors

Adipose tissue dysfunction underpins the association of obesity with type 2 diabetes. Adipogenesis is required for the maintenance of adipose tissue function. It involves the commitment and subsequent differentiation of preadipocytes and is coordinated by autocrine, paracrine, and endocrine factors. We previously reported that fibroblast growth factor-1 (FGF-1) primes primary human preadipocytes and Simpson Golabi Behmel syndrome (SGBS) preadipocytes and increases adipogenesis through a cascade involving extracellular signal–related kinase 1/2 (ERK1/2). Here, we aimed to use the FGF-1 system to identify novel adipogenic regulators. Expression profiling revealed bone morphogenetic protein (BMP) and activin membrane-bound inhibitor (BAMBI) as a putative FGF-1 effector. BAMBI is a transmembrane protein and modulator of paracrine factors that regulate adipogenesis, including transforming growth factor (TGF) superfamily members (TGF-β and BMP) and Wnt. Functional investigations established BAMBI as a negative regulator of adipogenesis and modulator of the anti- and proadipogenic effects of Wnt3a, TGF-β1, and BMP-4. Further studies showed that BAMBI expression levels are decreased in a mouse model of diet-induced obesity. Collectively, these findings establish BAMBI as a novel, negative regulator of adipogenesis that can act as a nexus to integrate multiple paracrine signals to coordinate adipogenesis. Alterations in BAMBI may play a role in the (patho)physiology of obesity, and manipulation of BAMBI may present a novel therapeutic approach to improve adipose tissue function.

A putative role for endogenous FGF-2 in FGF-1 mediated differentiation of human preadipocytes

The defining characteristic of obesity is increased adipose tissue (AT) mass following chronic positive energy supply. AT mass is determined by adipocyte number and size, which reflect proliferation and differentiation of preadipocytes and hypertrophy of pre-existing adipocytes. The molecular pathways governing AT expansion are incompletely defined. We previously reported that FGF-1 primes proliferating primary human preadipocytes (phPA), thereby increasing adipogenesis. Here we examined whether FGF-1s adipogenic actions were due to modulation of other FGFs. Treatment of phPA with FGF-1 reduced FGF-2 mRNA/protein by 80%. To examine a putative functional role we performed siRNA knockdown studies. Following FGF-2 knockdown preadipocyte proliferation was decreased and expression of adipogenic genes (PPARγ, G3PDH and adiponectin) was increased at day 1 of differentiation. These results suggest that changes in endogenous FGF-2 levels contribute to FGF-1s early adipogenic effects and highlight the complexity of the paracrine interplay between FGFs within human AT.

Inhibition of inosine monophosphate dehydrogenase reduces adipogenesis and diet-induced obesity.

We previously described a putative role for inosine monophosphate dehydrogenase (IMPDH), a rate-limiting enzyme in de novo guanine nucleotide biosynthesis, in lipid accumulation. Here we present data which demonstrate that IMPDH activity is required for differentiation of preadipocytes into mature, lipid-laden adipocytes and maintenance of adipose tissue mass. In 3T3-L1 preadipocytes inhibition of IMPDH with mycophenolic acid (MPA) reduced intracellular GTP levels by 60% (p<0.05) and blocked adipogenesis (p<0.05). Co-treatment with guanosine, a substrate in the salvage pathway of nucleotide biosynthesis, restored GTP levels and adipogenesis demonstrating the specificity of these effects. Treatment of diet-induced obese mice with mycophenolate mofetil (MMF), the prodrug of MPA, for 28 days did not affect food intake or lean body mass but reduced body fat content (by 36%, p=0.002) and adipocyte size (p=0.03) and number. These data suggest that inhibition of IMPDH may represent a novel strategy to reduce adipose tissue mass.