Growth and adipose differentiation of sheep preadipocyte fibroblasts in serum-free medium

Perspectives on scaling production of adipose tissue for food applications

With rising global demand for food proteins and significant environmental impact associated with conventional animal agriculture, it is important to develop sustainable alternatives to supplement existing meat production. Since fat is an important contributor to meat flavor, recapitulating this component in meat alternatives such as plant based and cell cultured meats is important. Here, we discuss the topic of cell cultured or tissue engineered fat, growing adipocytes in vitro that could imbue meat alternatives with the complex flavor and aromas of animal meat. We outline potential paths for the large scale production of in vitro cultured fat, including adipogenic precursors during cell proliferation, methods to adipogenically differentiate cells at scale, as well as strategies for converting differentiated adipocytes into 3D cultured fat tissues. We showcase the maturation of knowledge and technology behind cell sourcing and scaled proliferation, while also highlighting that adipogenic differentiation and 3D adipose tissue formation at scale need further research. We also provide some potential solutions for achieving adipose cell differentiation and tissue formation at scale based on contemporary research and the state of the field.

Identification of miRNA in Sheep Intramuscular Fat and the Role of miR-193a-5p in Proliferation and Differentiation of 3T3-L1

Intramuscular fat (IMF) is one of the most critical parameters affecting meat quality and mainly affected by genetic factors. MicroRNA as an important regulatory factor, which is still a lack of research in the development of sheep IMF deposition. We used RNA sequencing (RNA-seq) and cell-level validation to explore the role of miRNA in IMF deposition. As for this purpose, longissimus thoracis et lumborum (LTL) samples of 2 month-old (Mth-2) and 12 months-old (Mth-12) Aohan fine-wool sheep (AFWS) were used to identified miRNAs expression. We found 59 differentially expressed miRNAs (DE-miRNA) between these age groups and predicted their 1,796 target genes. KEGG functional enrichment analysis revealed eight pathways involved in lipid metabolism-related processes, including fatty acid elongation and the AMPK signaling pathway. A highly expressed DE-miRNA, miR-193a-5p, was found to serve a function in 3T3-L1 preadipocyte differentiation. Luciferase assay demonstrated that miR-193a-5p directly binds to the 3′-UTR region of ACAA2. By constructing mimics and inhibitor vector transfecting into 3T3-L1 cells to explore the effect of miR-193a-5p on cell proliferation and differentiation, we demonstrated that overexpression of miR-193a-5p inhibited 3T3-L1 preadipocyte proliferation, as evidenced by decreased mRNA and protein expression of CDK4 and CyclinB. CCK-8 assay showed that miR-193a-5p significantly inhibited cell proliferation. Similarly, the overexpression of miR-193a-5p inhibited 3T3-L1 preadipocyte differentiation and adipocyte-specific molecular markers’ expression, leading to a decrease in PPARγ and C/EBPα and ACAA2. Inhibition of miR-193a-5p had the opposite effects. Our study lists the miRNAs associated with intramuscular lipid deposition in sheep and their potential targets, striving to improve sheep meat quality.

Differentiation in vitro of omental and subcutaneous pre-adipocytes from Spanish Lacha and Rasa Aragonesa sheep

Factors responsible for breed- and depot-specific differences in the development of lipogenic enzymes, and hence lipogenic capacity of adipocytes, in sheep adipose tissue have been investigated using a serum-free cell culture system. Effects of insulin, tri-iodothyronine and exogenous lipid on the development in vitro of the lipogenic enzymes glycerol 3-phosphate dehydrogenase (G3PDH), fatty acid synthetase (FAS), NADP-malate dehydrogenase (ME), glucose 6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase (ICDH) in omental and subcutaneous pre-adipocytes from Lacha and Rasa Aragonesa lambs were investigated. Addition of insulin plus tri-iodothyronine caused pre-adipocyte differentiation, which was enhanced by addition of a lipid supplement. G3PDH activities achieved by differentiation of pre-adipocytes in vitro were similar to those found in vivo; furthermore after differentiation in vitro adipocytes from Rasa Aragonesa lambs had a greater G3PDH activity than adipocytes from Lacha lambs, as found in vivo. In contrast activities of FAS, G6PDH and ME achieved by differentiation in vitro were much greater than those found previously in vivo. While breed- and depot-specific changes in G6PDH observed after differentiation in vitro were similar to those observed in vivo, changes in FAS induced in vitro differed from those found during development in vivo. The study shows that pre-adipocytes from Rasa Aragonesa and Lacha lambs have intrinsic depot- and breed-specific differences in their ability to differentiate and express lipogenic enzymes. The combination of insulin, tri-iodothyronine and a lipid supplement appears to be sufficient to account for in vivo G3PDH activities but other factors are required to explain activities of FAS, G6PDH and ME found in vivo.

Engineered adipose tissue formation enhanced by basic fibroblast growth factor and a mechanically stable environment

Engineered adipose tissue can be used in plastic and reconstructive surgery to augment soft tissue lost due to mastectomy or lumpectomy. The three-dimensional space provided by a scaffold capable of withstanding in vivo compressive forces and neovascularization may promote engineered adipose tissue formation. The objective of this study was to determine whether voluminous adipose tissue can be engineered by combining a mechanically stable environment with basic fibroblast growth factor (bFGF). Mechanical support structures, fabricated from biodegradable synthetic polymers, were placed into subcutaneous pockets of athymic mice. Human preadipocytes, containing fibrin matrix, with (group 1) or without (group 2) bFGF were injected into the space created by the support structures. Additionally, human preadipocytes containing fibrin matrix, with (group 3) or without (group 4) bFGF, were injected into subcutaneous spaces without support structures. Six weeks after implantation, the original implant volume was approximately maintained in groups 1 and 2, whereas groups 3 and 4 showed significant implant shrinkage. Adipogenesis and angiogenesis were more extensive in the group 1 than any other group. The fraction of human nuclear antigen-positive adipocytes in the implant was highest in group 1. Mouse adipocyte-specific genes were also expressed in the implants, again at the highest levels in group 1. Implanted preadipocyte apoptosis was significantly reduced in the groups treated with bFGF (groups 1 and 3) as opposed to those without (groups 2 and 4). This study demonstrates that combining a mechanically stable environment with bFGF can promote voluminous adipose tissue regeneration. This adipogenesis was likely promoted by the mechanically stable three-dimensional space, enhanced neovascularization, implanted cell survival, and host adipogenic cell migration. The method described in this study could be useful to augment adipose tissue used in plastic and reconstructive surgery.

Differential control of lipogenesis and lipolysis during development of ovine preadipocytesin vitro

The stromovascular fraction of adipose tissue from sheep, like that of other species, contains preadipocytes which can be induced to differentiate in culture, providing a potentially useful system for studying adipocyte development. Differentiation of ruminant preadipocytes has only been partly characterized previously so we have investigated the factors regulating the development of lipogenesis and lipolysis in sheep cells. Insulin, rosiglitazone (a peroxisome proliferation activated receptor-γ agonist) and either dexamethasone or a lipid suplement are required during differentiation for maximum rates of lipogenesis, whereas all four components are required to achieve maximum rates of catecholamine-stimulated lipolysis. Tri-iodothyronine had no effect on the development of lipogenesis but resulted in a reduced rate of catecholamine-stimulated lipolysis. Lipogenesis and lipolysis also differed in that the rate of lipogenesis increased to a maximum at about 10 days of differentiation and then fell, whereas the rate of lipolysis reached a plateau at about 10 days. By contrast to catecholamine-stimulated lipolysis, there is little or no evidence for development of the adenosine-based antilipolytic system; this may be because response to adenosine develops very late during preadipocyte differentiation or additional, unidentified factors are required to induce this antilipolytic system. Lipogenesis in differentiated preadipocytes responded to both insulin and growth hormone. These studies show that the development of lipogenesis and lipolysis are under distinct control systems. Furthermore, while preadipocytes differentiatedin vitroshow many of the characteristics of adipocytes differentiatedin vivo, there are still significant differences.

In situ regeneration of adipose tissue in rat fat pad by combining a collagen scaffold with gelatin microspheres containing basic fibroblast growth factor

This study is an investigation to evaluate in situ adipose tissue regeneration in fat pads. Gelatin microspheres with different water contents were prepared for the controlled release of basic fibroblast growth factor (bFGF). After a collagen sponge scaffold was incorporated by the microspheres containing 0, 0.01, 0.1, 1, and 10 microg of bFGF with or without syngeneic rat preadipocytes (1 x 10(5) cells/site) into a defect of rat fat pad, adipogenesis at the implanted site of scaffold was evaluated histologically. in situ formation of adipose tissue accompanied with angiogenesis was observed in the scaffold implanted with the microspheres containing 1.0 microg of bFGF, although the extent was less at the lower and higher bFGF doses. The in situ formation induced by the microspheres containing bFGF was significantly higher than that induced by free bFGF of the same dose. Adipogenesis was enhanced with time after implantation up to 4 weeks and thereafter leveled off. Such in situ adipogenesis was reproducibly induced by implantation of collagen scaffold incorporating gelatin microspheres containing 1 microg of bFGF, whereas addition of rat syngeneic preadipocytes did not promote the adipogenesis. The degradation of microspheres and the consequent FGF release became faster with an increase in the water content of gelatin microspheres. Less in situ formation of adipose tissue was observed at the lower water content of microspheres, which showed longer-term bFGF release. We conclude that combination of scaffold collagen with an appropriate controlled release of bFGF was essential to achieve the in situ formation of adipose tissue even without preadipocytes.

Activated protein C stimulates proliferation, migration and wound closure, inhibits apoptosis and upregulates MMP-2 activity in cultured human keratinocytes

Activated protein C (APC) is a physiological serine protease that regulates blood clotting and inflammation. Keratinocytes are a major cell type of human skin and play a fundamental role in normal skin metabolism and cutaneous wound healing. In this study, we investigated the regulatory role of APC on the function of human primary cultured keratinocytes. In an in vitro wounding assay, APC accelerated wound closure which was due jointly to increased cell proliferation and migration. APC attenuated calcium-induced cell death via prevention of cell apoptosis, as indicated by a decrease in both active caspase-3 and morphologically apoptotic cells. APC dramatically enhanced the expression and activation of MMP-2 by keratinocytes, whilst having no effect on MMP-9. GM6001, a broad spectrum MMP inhibitor, abolished cell migration in a dose-dependent manner and delayed in vitro wound healing. APC also significantly increased the production of IL-6 and IL-8 and suppressed calcium- and LPS-stimulated NF-kappaB activity. These results demonstrate a central role for APC in promoting cell proliferation and migration, preventing apoptosis and increasing MMP-2 activity in cultured keratinocytes. This regulatory activity implicates APC as having potential to promote re-epithelialisation during wound healing.

Autologous human keratinocytes cultured on membranes composed of benzyl ester of hyaluronic acid for grafting in nonhealing diabetic foot lesions: a pilot study

Diabetic foot complications are the most common cause of nontraumatic lower extremity amputations in the industrialised world. Unsatisfactory healing requires advanced therapeutic strategies, such as the use of skin grafts, which may represent a helpful option for wound coverage. Alternatively, a method using autologous keratinocytes grown to thin sheet grafts is available. The purpose of this pilot study was to investigate the application of autologous human keratinocytes cultured on membranes composed of benzyl ester of hyaluronic acid (Laserskin autograft) to diabetic foot ulcers. We studied 14 patients with type 2 diabetes mellitus and a nonhealing diabetic foot lesion, defined as existing longer than 6 months or with no wound healing apparent for 12 weeks. Between 7 and 64 days after the transplantation (depending on the size of the ulceration), 11/14 of the lesions were completely healed. The transplantation of autologous keratinocytes may allow faster closure of diabetic foot lesions and subsequently reduce length of hospitalization. This method can easily be planned with regard to logistics and time, and furthermore, this therapy option can be carried out by the diabetologist.

Adipose tissue engineering based on human preadipocytes combined with gelatin microspheres containing basic fibroblast growth factor

Gelatin microspheres containing basic fibroblast growth factor (bFGF) were prepared for the controlled release of bFGF. Co-implantation with the gelatin microspheres enabled preadipocytes to induce adipose tissue formation at the implanted site. Preadipocytes isolated from human fat tissue were suspended with the gelatin microspheres containing bFGF and incorporated into a collagen sponge of cell scaffold. Following subcutaneous implantation of the collagen sponge incorporating human preadipocytes, and gelatin microspheres containing 1 microg of bFGF into the back of nude mice, adipose tissue was formed at the implanted site of collagen sponge within 6 weeks postoperatively although the extent depended on the number of preadipocytes transplanted and the bFGF dose. The formation of adipose tissue was significant compared with the implantation of collagen sponge incorporating human preadipocytes and 1 microg of free bFGF. The area of adipose tissue newly formed was increased with the number of preadipocytes transplanted until to 1.0 x 10(5) cells/site and thereafter leveled off. The maximum area was observed at the bFGF dose of 1 microg/site. The area was significantly smaller at the bFGF dose of 0.5 microg/site or larger than 1 microg/site. Immunohistochemical examination indicated that the adipose tissue newly formed was composed of human matured adipocytes. No adipogenesis was observed at the implanted site of collagen sponge incorporating either gelatin microspheres containing bFGF or human preadipocytes and the mixed gelatin microspheres containing bFGF and human preadipocytes. We conclude that combination of gelatin microspheres containing bFGF and preadipocytes with the collagen sponge is essential to achieve tissue engineering of fat tissue.

Time course of de novo adipogenesis in matrigel by gelatin microspheres incorporating basic fibroblast growth factor

Controlled release of basic fibroblast growth factor (bFGF) from gelatin microspheres achieved de novo adipogenesis at the implanted site of a basement membrane extract (Matrigel). Following subcutaneous co-implantation of Matrigel and gelatin microspheres incorporating 0.1 microg of bFGF into the back of mice, adipose tissue was formed at the implanted site after 4 weeks postoperatively although the extent increased with implantation time. Formation of adipose tissue was significantly faster than the co-implantation of Matrigel, and 0.1 microg of free bFGF while a larger volume of the adipose tissue formed was retained 15 weeks later. When measured in Matrigel co-implanted with the gelatin microspheres incorporating bFGF, the number of cells infiltrated into Matrigel increased to a significantly high extent compared with the bFGF co-implantation. Matrigel alone was much less effective in inducing formation of adipose tissue. We conclude that gelatin microspheres incorporating bFGF enable Matrigel to efficiently induce de novo adipogenesis at the implanted site in respect to the formation rate and volume of adipose tissue.

Differentiation of stromal-vascular cells isolated from canine adipose tissues in primary culture

A culture condition supporting adipocyte differentiation of stromal-vascular (S-V) cells isolated from canine adipose tissues was established. Morphological observation and determination of glycerol-3-phosphate dehydrogenase (GPDH) activity were used as the criteria for adipocyte differentiation. After reaching confluence, the cells were able to undergo terminal adipocyte differentiation by treatment with 100 microM indomethacin, 10 microg/ml insulin and 0.5 mM 1-methyl-3-isobutylxanthine (MIX) in medium supplemented with 5% fetal calf serum (FCS). In the absence of either indomethacin or insulin, the S-V cells did not undergo adipose conversion and GPDH activity was not increased, indicating that both indomethacin and insulin play essential roles in this culture system. The S-V cells from inguinal adipose tissues exhibited the greatest increase in GPDH activity among the four depots (inguinal > abdominal-subcutaneous > perirenal > omental). demonstrating that adipocyte differentiation was also intensely dependent on anatomic sites from which the S-V cells were derived. Interestingly, dimethylsulfoxide (DMSO) was found to accelerate adipocyte differentiation in combination with indomethacin and insulin. Under this condition, up to 90% of the cells displayed adipocyte phenotypes and the GPDH activity reached 1288 +/- 441 mU/mg protein. This culture system may be useful for investigating other adipogenic factors as well as anti-adipogenic factors involved in the regulation of canine adipose tissue development.

Engineering, expression, and renaturation of a collagen-targeted human bFGF fusion protein

Basic fibroblast growth factor (bFGF) is a potent in vitro mitogen for capillary endothelial cells, stimulates angiogenesis in vivo, and may participate in tissue repair. Basic FGF is found in abundance in tissues such as brain, kidney and cartilage. This study reports the expression, purification, and renaturation of a biologically active human basic fibroblast growth factor fusion protein (hbFGF-F1) from Escherichia coli. A prokaryotic expression vector was engineered to produce a tripartite fusion protein consisting of (i) a purification tag, (ii) a protease-sensitive linker/collagen-binding domain, and (iii) cDNA sequence encoding the active fragment of hbFGF. The expressed hbFGF-F1 and hbFGF-F2 (it contains a collagen-binding domain), located in inclusion bodies, were solubilized with 6 M guanidine-HCl and renatured using a glutathione redox system and protracted dialysis under various experimental conditions. The purification of the recombinant proteins was achieved by binding the His-tag of the fusion protein on a Ni-NTA metal chelate column. The biological activity of the recombinant growth factors was demonstrated by their ability to stimulate proliferation of human vein endothelial cells (HVEC), monitored by [3H]-thymidine incorporation, where commercial recombinant human bFGF (rhbFGF) served as a positive control. Purified rhbFGF-F1 and rhbFGF-F2 constructs exhibited proliferative activity comparable to commercial rhbFGF. Binding of the renatured hbFGF-F2 fusion protein to collagen was demonstrated by stable binding on a collagen-conjugated Sephadex-G15 column. The high affinity binding was also demonstrated by the binding of [3H]-collagen to the rhbFGF-F2 protein immobilized on a Ni-NTA column. The rhbFGF-F2 fusion protein bound to collagen coated surfaces with high affinity but exhibited comparatively lower biological activity than the fusion protein in solution, suggesting a potentially latent configuration. Taken together, these results demonstrate that biologically active rhbFGF fusion proteins can be recovered from transformed bacteria by oxidative refolding; thus, providing a means for its high-yield production, purification, and renaturation from microorganisms. Furthermore, we demonstrate that the auxiliary collagen-binding domain effectively targets the recombinant growth factor to type I collagen. The clinical effect of rhbFGF-F2 on wound healing is also studied in streptozotocin-induced diabetic rats and evaluated by histological examination comparing with rhbFGF-F1 and commercial bFGF effects. The highly beneficial effects of rhbFGF-F2 on wound healing is suggested to be due to its extremely potent angiogenesis and granulation tissue formation activities, leading to a rapid reepithelialization of the wound. Topical application of rhbFGF-F2 mixed with type I collagen is a more effective method in accelerating closure of full-thickness excisional skin-wound in diabetic rats when compared with the fusion protein alone or commercial hbFGF at the same doses. These studies advance the technology necessary to generate large quantities of targeted bFGF fusion proteins as well as to develop new strategies for specific biomedical applications.

Production of a recombinant human basic fibroblast growth factor with a collagen binding domain

Basic fibroblast growth factor (bFGF) is a potent in vitro mitogen for capillary endothelial cells, stimulates angiogenesis in vivo, and may participate in tissue repair. Basic FGF is found in abundance in tissues such as brain, kidney, and cartilage. This study reports the expression, purification, and renaturation of a biologically active human basic fibroblast growth factor fusion protein (hbFGF-F1) from Escherichia coli. A prokaryotic expression vector was engineered to produce a tripartite fusion protein consisting of a purification tag, a protease-sensitive linker and collagen binding domain, and a cDNA sequence encoding the active fragment of hbFGF. The expressed hbFGF-F1 and hbFGF-F2 (it contains the collagen binding domain), located in inclusion bodies, were solubilized with 6 M guanidine-HCl and renatured by a glutathione redox system and protracted dialysis under various experimental conditions. The purification of the recombinant proteins was achieved by binding the His-tag of the fusion protein on a nickel-nitrilotriacetic acid metal chelate column. The biological activity of the recombinant growth factor was demonstrated by its ability to stimulate proliferation of human vein endothelial cells, monitored by [3H]thymidine incorporation, where commercial recombinant human bFGF (rhbFGF) served as a positive control. Purified rhbFGF-F1 and rhbFGF-F2 constructs exhibited proliferative activity comparable to commercial rhbFGF. The high-affinity binding was demonstrated by the binding of [3H]collagen to the rhbFGF-F2 protein immobilized on a Ni-nitrilotriacetic acid column. The rhbFGF-F2 fusion protein bound to collagen-coated surfaces with high affinity. Taken together, these results demonstrate that biologically active rhbFGF fusion proteins can be recovered from transformed bacteria by oxidative refolding; thus, providing a means for their high-yield production, purification, and renaturation from microorganisms. Furthermore, we demonstrate that the auxiliary collagen binding domain effectively targets the recombinant growth factor to type I collagen. These studies advance the technology necessary to generate large quantities of targeted bFGF fusion proteins for specific biomedical applications.

Effects of gastric inhibitory polypeptide, somatostatin and epidermal growth factor on lipogenesis in ovine adipose explants

Feeding raises the plasma concentrations of a number of gut-related hormones that may, in turn, influence the metabolism of peripheral tissues. This study investigated the effects of gut-related hormones on lipogenesis in explants from three differing adipose depots in lambs (aged 4-9 months). Incorporation of [14C]-acetate into lipid was measured over a 2-h period, following 24 h pre-incubation in the presence of hormone combinations. In perirenal fat explants, gastric inhibitory polypeptide (GIP) in the concentration range 0.01-10 nM stimulated lipogenesis. Maximal effects were seen at 1 nM (an average increase of 64% over basal values). In contrast, in the presence of insulin (0.1 nM), a dose-dependent decrease in lipogenesis was seen with increasing GIP concentration (P < 0.001 for the insulin x GIP interaction). Epidermal growth factor (EGF) and somatostatin in the same concentration range each inhibited lipogenesis. both in the presence and the absence of insulin (P < 0.001 in each case). Subcutaneous (back) fat and intermuscular (popliteal) fat responded similarly to each other, but significantly differently from the perirenal depot (P < 0.001). Here GIP, somatostatin or EGF (each at 1 nM) all separately stimulated lipogenesis.

De novo formation of adipose tissue by controlled release of basic fibroblast growth factor

De novo adipogenesis at the implanted site of a basement membrane extract (Matrigel) was induced through controlled release of basic fibroblast growth factor (bFGF). bFGF was incorporated into biodegradable gelatin microspheres for its controlled release. When the mixture of Matrigel and bFGF-incorporated gelatin microspheres was implanted subcutaneously into the back of mice, a clearly visible fat pad was formed at the implanted site 6 weeks later. Histologic examination revealed that the de novo formation of adipose tissue accompanied with angiogenesis was observed in the implanted Matrigel at bFGF doses of 0.01, 0.1, and 1 microg/site, the lower and higher doses being less effective. The de novo formation induced by the bFGF-incorporated microspheres was significantly higher than that induced by free bFGF of the same dose. The mRNA of a lipogenesis marker protein, glycerophosphate dehydrogenase, was detected in the formed adipose tissues, biochemically indicating de novo adipogenesis. Free bFGF, the bFGF-incorporated gelatin microspheres, or Marigel alone and bFGF-free gelatin microspheres with or without Matrigel did not induce formation of adipose tissue. This de novo adipogenesis by mixture of Matrigel and the bFGF-incorporated gelatin microspheres will provide a new idea for tissue engineering of adipose tissue.

Characterization of recombinant human fibroblast growth factor (FGF)-10 reveals functional similarities with keratinocyte growth factor (FGF-7)

A newly identified member of the fibroblast growth factor (FGF) family, designated FGF-10, is expressed during development and preferentially in adult lung. The predicted FGF-10 protein is most related to keratinocyte growth factor (KGF, or FGF-7). The latter is unique among FGFs in that it binds and signals only through the FGF receptor (FGFR2b) isoform KGF receptor (KGFR) expressed specifically by epithelial cells. In order to examine the biological and biochemical properties of human FGF-10, we isolated the cDNA and expressed its encoded protein in bacteria. The recombinant protein (rFGF-10) was a potent mitogen for Balb/MK mouse epidermal keratinocytes with activity detectable at 0.1 nM and maximal at around 5 nM. Within this concentration range, FGF-10 did not stimulate DNA synthesis in NIH/3T3 mouse fibroblasts. rFGF-10 bound the KGFR with high affinity comparable to that of KGF, and did not bind detectably to either the FGFR1c (Flg) or FGFR2c (Bek) receptor isoforms. The mitogenic activity of FGF-10 could be distinguished from that of KGF by its different sensitivity to heparin and lack of neutralization by a KGF monoclonal antibody. These results indicate that FGF-10 and KGF have similar receptor binding properties and target cell specificities, but are differentially regulated by components of the extracellular matrix.

Regulators of adipocyte precursor cells

Lean and adipose tissue growth are two of the most important targets for manipulation in commercial livestock. Adipose tissue growth occurs by both hyperplasia and hypertrophy. The processes involved in adipocyte hypertrophy are relatively well understood but much less is known about adipocyte hyperplasia. The mature adipocyte has little capacity for cell division and the hyperplastic capacity of adipose tissue resides in a population of fibroblast-like adipocyte precursor cells. The origin of these cells and the processes involved in their commitment to the adipocyte lineage is not known. Growth factors, in particular the bone morphogenetic proteins (BMP), are likely to be involved in regulating commitment to the adipocyte lineage. In vitro studies have shown that once committed to the adipocyte lineage, the proliferation and differentiation of, adipocyte precursor cells is regulated by a number of different growth factors. A number of these growth factors are expressed in adipocyte precursor cells in vitro and may have an autocrine-paracrine role. Others, such as epidermal growth factor (EGF), are more likely to have an endocrine role. The precise role that each growth factor plays in regulating adipocyte development in vivo is poorly understood. The chick is a useful experimental system with which to study the precise function of growth factors in adipocyte development.

Proliferation and differentiation of progeny of ovine unilocular fat cells (adipofibroblasts)

The responsiveness of progency of sheep-derived unilocular fat cells (adipofibroblasts) to dexamethasone, insulin, insulinlike growth factor I (IGF-I), growth hormone (GH), and basic fibroblst growth factor (FGF) was determined in a clonal culture system. Primary cultures of mature adipocytes were obtained from intermuscular adipose tissue (semimembranosus/semitendinosus seam depot) of sheep by ceiling culture techniques. Following degeneration of unilocular fat droplets and re-establishment of fibroblasticlike adipofibroblasts, all adipofibroblasts adhering to upper flask surfaces were collected and isolated away from fibroblasts (which had no multilocular vesicles) by Percoll gradient centrifugation. Progeny derived from a single adipofibroblast were isolated and tested for the ability to proliferate, differentiate, and accumulate lipids. Stock cultures of adipofibroblasts reached confluence in 5 d and were induced to differentiate from 7 to 9 d with dexamethasone-methyl isobutylxanthine-insulin (DMI). Incubation with insulin, IGF-I, GH, or FGF prior to confluence followed by induction with DMI produced no direct (priming) effect on subsequent differentiation. When substituted individually in place of DMI during the 2 d differentiation/induction period, all factors induced differentiation of cultured adipofibroblasts as determined by lipogenesis (P < .05) and lipoprotein lipase activity (P < .05). Thus, isolated adipofibroblasts from sheep muscle may be induced by hormones and growth factors to display mature adipocyte morphology in cell culture. Further definition of the adipofibroblast culture system may aid in the identification of mechanisms regulating adipocyte development in sheep skeletal muscle, as well as in the study of intercommunication between fat and muscle cells.

Two hierarchies of FGF-2 signaling in heparin: mitogenic stimulation and high-affinity binding/receptor transphosphorylation

FGF-2 activates multiple signaling pathways by a cell surface signaling complex assembled with FGF, its receptor tyrosine kinase, and heparan sulfate proteoglycan. Heparan sulfate binds to a site on the receptor and at least one site on the growth factor. Several models propose an important role for heparan sulfate not only in facilitating FGF-2 binding to its receptor tyrosine kinase but also in promoting signaling via formation of receptor dimers. Such dimers are capable of transphosphorylation of the cytoplasmic domain of the receptor, leading to the generation of phosphotyrosines that are important initiators of intracellular signaling pathways. To explore the participation of heparan sulfates in the formation of a signaling complex that activates these pathways, the binding and activity of FGF-2 on Swiss 3T3 fibroblasts and F32 lymphoid cells is examined with either native or modified forms of heparin. As shown previously, fibroblasts treated with chlorate, which inhibits the sulfation of heparan sulfate and its subsequent binding to FGF-2, display a dramatically reduced response to picomolar concentrations of FGF-2, but binding to receptors and a mitogenic response is restored by heparin. However, the restoration of high-affinity binding is seen only at an optimal concentration of heparin. Excess heparin competes for binding sites within the signaling complex such that high-affinity binding and receptor transphosphorylation are reduced. Despite this, mitogenic signaling is not diminished. A similar result is observed using heparin fragments that promote mitogenesis but not high-affinity binding. These results suggest that the high-affinity signaling complex that is necessary for stable receptor transphosphorylation differs from the signaling complex sufficient for triggering mitogenesis. We speculate that heparan sulfate in vivo participates in two hierarchies of receptor activation. In one, heparan sulfate participates in FGF-2 binding to its receptor tyrosine kinase and activation of mitogenic signaling, perhaps through monomeric receptors or the transient formation of receptor dimers. In the second hierarchy, heparan sulfate participates in the stabilization of a signaling complex that is likely to be comprised of receptor multimers that carry out effective receptor transphosphorylation. A further description of this mechanism may lead to an understanding of how heparan sulfate or its homologues can regulate specific signaling pathways within the cell.

Antagonistic effects of different members of the fibroblast and platelet-derived growth factor families on adipose conversion and NADPH-dependent H2O2 generation in 3T3 L1-cells

3T3 L1-cells, which undergo adipose conversion in vitro, possess a stimulus-sensitive H2O2-generating system in their plasma membrane, and its properties are virtually identical with those of the insulin-sensitive human fat-cell oxidase [Krieger-Brauer and Kather (1992) J. Clin. Invest. 89, 1006-1013]. Insulin and insulin-like growth factor I were found to be active stimulators of NADPH-dependent H2O2 generation. Surprisingly, the acidic (a) and basic (b) isoforms of fibroblast growth factor (FGF) as well as the AA and BB homodimers of platelet-derived growth factor (PDGF) had antagonistic effects on NADPH-dependent H2O2 generation in plasma membranes which were parallelled by corresponding changes in H2O2 accumulation in intact cells. bFGF and PDGF BB (which inhibit NADPH-dependent H2O2 generation) prevented the adipose conversion of 3T3 L1-preadipocytes, and this effect could be reversed by exogenously supplied H2O2. Conversely, aFGF and PDGF AA, which stimulated H2O2 generation, accelerated adipocyte conversion in the presence of insulin and were adipogenic in themselves. Consistently, expression of the adipocyte phenotype induced by insulin, dexamethasone and isobutylmethylxanthine was enhanced in the presence of exogenous hypoxanthine/xanthine oxidase, whereas antioxidants, such as N-acetylcysteine or ascorbate, suppressed the process of differentiation. It is concluded that the H2O2 produced in response to hormones and cytokines may contribute to the development and maintenance of the differentiated state.

Effects of epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) on human adipocyte development and function

We investigated the effects of epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) on the differentiation of human adipocyte precursor cells and some metabolic aspects of newly formed fat cells kept in primary culture. Exposure of stromal cells from human adipose tissue to EGF (0.01-100 ng mL-1) resulted in a dose- and time-dependent decrease in the number of developing fat cells and the activity of glycerol-3-phosphate dehydrogenase (GPDH), a marker of adipose differentiation. Continuous presence of EGF completely blocked lipid accumulation with a ED50 in the range of 0.2 ng mL-1. This inhibitory action of EGF was associated with a potent stimulation of cell proliferation, up to 8-fold compared with cultures in the absence of EGF. PDGF (0.1-50 ng mL-1) and FGF (0.1-100 ng mL-1) provoked a less marked suppression of GPDH activities which was significant at concentrations of 10 ng mL-1 and higher. A 12 day exposure to EGF of differentiated cells was followed by a suppression of GPDH and, again, a significant increase in cell number. Concomitantly, a distinct loss of cellular lipids was observed in the newly formed adipocytes. This effect could be partly explained by a stimulation of lipolysis, since EGF caused an increase of glycerol in the culture medium. Addition of PDGF or FGF to newly developed fat cells had no effect on lipolysis but, at higher concentrations, also decreased GPDH activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of adipose differentiation

Adipose differentiation is a multistep process with the following sequence: adipoblasts --> preadipocytes --> adipocytes. Adipogenic agents are only involved in the terminal differentiation of preadipocytes to adipocytes by means of circulating hormones (growth hormone, glucocorticoids, or triiodothyronine) and locally produced hormones (prostacyclin). Fatty acids also behave as hormones and act as transcriptional regulators of lipid-related genes. Once differentiated, adipocytes become secretory cells able to synthetize and release an impressive number of peptide and nonpeptide compounds, suggesting a potential link between excess of adipose tissue mass and various physiopathphysiologic consequences.

Molecular events in adipocyte development

Adipocyte hyperplasia occurs by the proliferation and differentiation of adipocyte precursor cells or preadipocytes. Although the process of commitment to the adipocyte lineage is poorly understood, a great deal of information has accumulated about the processes and regulatory mechanisms involved in preadipocyte differentiation. The differentiation of preadipocytes is known to be characterized by increased transcription of a number of specific genes. AP-1 and C/EBP binding sites within these genes have been identified as important regulatory sequences. In addition, a specific enhancer sequence has been shown to confer adipose tissue specificity. This article will review the changes in gene transcription that occur during preadipocyte differentiation and how these are regulated. The potential role of autocrine/paracrine acting factors in the proliferation and differentiation of the preadipocyte is also discussed.

Effect of serum on differentiation of porcine adipose stromal-vascular cells in primary culture

1. Serum-containing media without additional hormones failed to support the differentiation of porcine SV cells while hormone-supplemented serum-free medium (ITTC) stimulated differentiation as indicated by higher GPDH specific activity. 2. All sera tested stimulated proliferation and inhibited porcine SV cell differentiation to some degree; fetal calf and rat sera were more inhibitory than calf and pig sera. 3. Morphologically, in serum-free medium porcine SV cells developed into individual adipocytes while in all serum-containing media they formed fat cell clusters. 4. Insulin and hydrocortisone in serum-free medium were important factors in SV cell differentiation while transferrin, T3, and fibroblast growth factor (FGF) were less important.

Immunohistochemical localization of basic fibroblast growth factor in cultured rat astrocytes and oligodendrocytes

The distribution of basic fibroblast growth factor in cultured astrocytes and oligodendrocytes was examined using immunocytochemistry. The results demonstrate a localization of basic fibroblast growth factor immunoreactivity predominantly in astrocyte nuclei at all stages of differentiation. Cytoplasmic and process staining was best detected during early stages of differentiation, under normal growth conditions or as a result of treatment with dibutyryl cyclic adenosine monophosphate. Astrocytes at all stages of differentiation bound antibody-complexed bFGF, suggesting the presence of cell-associated low affinity binding sites for the growth factor. Our studies also show the presence of immunoreactivity for basic fibroblast growth factor in process-bearing oligodendrocytes. These results suggest a role for endogenous basic fibroblast growth factor in astrocyte and oligodendrocyte growth and function.

Size distribution of adipocytes and variation in adipocyte number in lines of mice selected for high or low body fat

1. Adipocyte size and number were measured in epididymal fat pads from lines of mice selected for high or low body fat. 2. Epididymal fat pad weight at 10 weeks of age was 4-fold greater in the high fat than the low fat mice, accompanied by a 7-fold greater adipocyte volume but there was no difference in adipocyte number. Smaller differences in fatness and cell volume were observed at younger ages. 3. The high fat mice showed one or two populations of cells up to 5 weeks of age and at 7 weeks 3 days and 10 weeks showed two or more populations. In contrast, the low fat animals at all ages showed either one or two populations. 4. These findings imply that greater lipogenesis and cell filling, not cell proliferation, is the primary mechanism of increased fatness in these selected lines of mice.

Multiple growth factor mRNAs are expressed in chicken adipocyte precursor cells

We have examined the expression of growth factor genes in primary cultures of chicken adipocyte precursors. RNA was extracted from proliferating and differentiated cells, reversed transcribed and amplified by PCR using gene specific primers. The identity of the PCR products was confirmed by restriction mapping. We show, for the first time, constitutive expression of TGF-beta 2, TGF-beta 3, TGF-beta 4 and bFGF genes in chicken adipocyte precursors. We also detect GH-independent, but differentiation-dependent IGF-I gene expression. The synthesis and action of these growth factors supports the hypothesis that they act as autocrine and/or paracrine regulators of adipocyte precursor cell proliferation and differentiation.

FDC-P1 myeloid cells engineered to express fibroblast growth factor receptor 1 proliferate and differentiate in the presence of fibroblast growth factor and heparin

Full-length murine fibroblast growth factor (FGF) receptor 1 (FGFR-1L) cDNA was introduced into the FDC-P1 mouse myeloid progenitor cell line, which lacks FGF receptors and depends on interleukin 3 (IL-3) or granulocyte/macrophage colony-stimulating factor (GM-CSF) for its proliferation and survival. The expression of the FGFR-1L gene in FDC-P1 cells allowed these cells to grow in the presence of FGF and heparin. The resulting cell line, designated FD FGFR-1L.A, exhibited a more mature myeloid phenotype than did the parental FD FGFR-1L cells or uninfected FDC-P1 cells. They formed mainly dispersed colonies in soft-agar cultures when grown in the presence of FGF and heparin, suggestive of myeloid differentiation. The cells can be switched between growth on FGF/heparin and IL-3. Northern blot analysis and cytochemical staining demonstrated that FD FGFR-1L.A cells expressed myeloperoxidase mRNA and protein, biochemical markers specifically expressed during differentiation from the promyelocytic to the granulocytic stages, whereas the parental FD FGFR-1L cells and FDC-P1 cells failed to express this marker. These results indicate that the expression of FGFR-1L by FDC-P1 cells transmitted signals for growth in the presence of FGF and heparin and generated an additional signal for early myeloid differentiation but failed to commit FD FGFR-1L.A cells to terminal differentiation. This in vitro culture system can be used for molecular analysis of the regulation of cellular growth and differentiation mediated by the FGFs and their receptors.

Differentiation of A31T6 proadipocytes to adipocytes: a flow cytometric analysis

A flow cytometric assay has been developed which provides precise, quantitative information on the accumulation of cytoplasmic triglycerides in individual A31T6 proadipocytes as they differentiate into adipocytes. The opportunity to measure multiple optical parameters on a cell-by-cell basis has enabled us to monitor phenotypic aspects of differentiation with a greater level of sensitivity than was previously possible. Using the fluorescent hydrophobic probe, Nile red, we have found that as a cell proceeds along the differentiation pathway, the gold fluorescence signal from the cell increases, reflecting the accumulation of cytoplasmic lipid droplets. The value of the ratio of gold to red fluorescence defines a cell as being differentiated or undifferentiated. The greater resolution afforded by this cytometric method over more conventional approaches has allowed us to determine (1) the presence of an undifferentiated population of cells whose existence is not detected by conventional phase microscopy, (2) that insulin is not required to drive differentiation in this system, though the rate of differentiation is increased when the cells are exposed to insulin in combination with dexamethasone, (3) that exposure to a combination of insulin and dexamethasone results in a lower accumulation of lipid in a cell than does exposure to either agent alone, and (4) that A31T6 cells show the same response to differentiation-promoting agents whether applied at the time of plating or at confluence.

Concentration-dependent modulation of basic fibroblast growth factor action on multiplication and locomotion of human teratocarcinoma cells

A human teratoma cell line (Tera 2) was grown in serum-free medium, and the population multiplication was stimulated by the addition of 1-10 ng basic fibroblast growth factor (bFGF)/ml. The bFGF-effect was abrogated by the addition of protamine sulphate. When high concentrations of bFGF were added, a preferential effect on cell locomotion was observed. 100 ng bFGF/ml stimulated cell movement but only exerted a marginal effect on cell multiplication. These observed exogenous requirements for multiplication and locomotion were complemented by the expression of bFGF receptors. Scatchard analysis of binding data suggests the existence of a high-affinity and a low-affinity class of receptors.

The primary culture of mouse adipocyte precursor cells in defined medium

1. A defined medium supporting the proliferation and differentiation of adipocyte precursors isolated from inguinal fat pads of 8-12-day-old mice was developed. 2. It consists of a 1:1 mixture of DME and WAJC404A media supplemented with insulin (10 micrograms/ml), transferrin (10 micrograms/ml), fibroblast growth factor (10 ng/ml) and high density lipoproteins (HDL) (90 micrograms protein/ml). 3. DME-F12 medium (1:1 mixture) used as a nutrient mixture in the defined medium of rat and human adipocyte precursors was inadequate for cultivating mouse adipocyte precursors. 4. HDL had a definite beneficial effect on both preadipocyte growth and differentiation. 5. Differentiation was enhanced by addition of dexamethasone (10(-9) M) but could be almost completely inhibited by transforming growth factor beta 1 (TGF-beta 1). 6. TGF-beta 1 was shown to be effective only when present in the early stages of differentiation.

Endothelin-1 inhibits adipogenic differentiation of 3T3-L1 preadipocytes

The effect of endothelin (ET)-1 on the adipogenic differentiation of 3T3-L1 preadipocytes was examined. Cellular morphology and lipoprotein lipase activity were used as differentiation markers. ET-1 inhibited the hormone-induced adipogenic differentiation of 3T3-L1 preadipocytes morphologically and biochemically in a dose-dependent manner. These findings promote ET-1 as a potent inhibitor of adipogenic differentiation, playing an important role in cellular differentiation of preadipocytes and making it a significant regulator of lipid metabolism.

Differentiation of ovine brown adipocyte precursor cells in a chemically defined serum-free medium. Importance of glucocorticoids and age of animals

The rapid apparent conversion of brown adipose tissue into white adipose tissue in newborn offspring of large mammals, such as sheep and cattle is not explained at the cellular level. To study the differentiation of lamb brown adipocyte, a genomic fragment corresponding to the uncoupling protein was cloned from an ovine DNA library. Stromal vascular fibroblasts isolated from the perirenal adipose tissue of newborn lambs completely differentiated into brown adipocytes expressing the uncoupling protein gene, in a chemically defined serum-free medium. Dexamethasone was necessary for the expression of the uncoupling protein gene. When stromal vascular fibroblasts were isolated from 3-week-old lambs, the glucocorticoid analog still promoted in vitro differentiation of adipocytes. However those adipocytes were unable to express uncoupling mRNA and could be considered as white adipocytes. The data indicate that dexamethasone is necessary but not sufficient clone for the complete differentiation of brown adipocytes, and that the preadipocytes are committed to differentiation into brown or white adipocytes before culture.

The expression of lipoprotein lipase activity and mRNA in mesenchymal rat heart cell cultures is modulated by bFGF

The effect of basic fibroblast growth factor (FGF) on lipoprotein lipase (LPL) production was studied in mesenchymal rat heart cell cultures. Addition of FGF to culture medium containing 20% serum resulted in a 3-fold increase in LPL activity. The minimal effective dose of FGF was 10 ng/ml and the increase occurred after exposure for 48 h. Addition of FGF was effective during the first week in culture, when enzyme activity was increasing, but not after 11 days when the cultures were superconfluent and the enzyme activity was high. Addition of FGF to serum-poor medium was able to replace serum required to sustain LPL activity. In FGF-treated cultures, more LPL activity was present in the functional pool, but not in the medium, than in the controls. The increase in enzymic activity was accompanied by an increase in enzyme mass and in LPL mRNA.

Effects of transforming growth factor beta 1 and basic fibroblast growth factor on lipoprotein lipase activity in primary cultures of chicken (Gallus domesticus) adipocyte precursors

1. The effect of TGF-beta and bFGF on lipoprotein lipase activity in chicken adipocyte precursors was investigated. 2. Lipoprotein lipase activity was reduced by up to 80% by incubation with TGF-beta whereas bFGF had no effect. 3. Contrary to that found with the 3T3-L1 preadipocyte cell line it was not necessary for TGF-beta to be present prior to the start of differentiation in order to be effective. 4. Incubation of adipocyte precursors with actinomycin D abolished the effect of TGF-beta suggesting that synthesis of a protein effector is required. 5. These results indicate differences in responsiveness to TGF-beta and bFGF between primary chicken adipocyte precursors and some preadipocyte cell lines.

Autocrine regulation of cell growth and transformation by basic fibroblast growth factor

Basic FGF (bFGF) and acidic FGF (aFGF) are multipotential factors that stimulate and support proliferation, migration and differentiation. Both bFGF and aFGF are non-secreted growth factors consistent with the lack of a signal peptide. However, bFGF and aFGF are deposited in extracellular matrix (ECM) suggesting that an alternative mechanism for FGF release exists. Four oncogenes, int-2, hst/K-fgf, FGF-5 and FGF-6 have been isolated that are highly homologous to aFGF and bFGF. Unlike bFGF and aFGF, they possess signal peptides and are secreted. These oncogenes transform cells and induce tumors, ostensibly via an autocrine mechanism. The involvement of bFGF and aFGF in autocrine transformation has been clarified by studies using FGF cDNA transfection. NIH-3T3 cells transfected with native bFGF cDNA and expressing 20 to 100 times as much bFGF as parental 3T3 cells acquire an enhanced proliferation rate and higher saturation density. NIH cells transfected with a construct in which bFGF cDNA is altered by addition of a signal peptide, undergo autocrine transformation and exhibit morphological and biochemical alterations characteristic of highly transformed cells. Injection of cells expressing native bFGF even at levels 100 times greater than parental 3T3 cells fails to induce tumors or lung metastasis in syngeneic mice. Signal peptide bFGF-transected cells on the other hand, acquire a high tumorigenic and metastatic potential with tumor incidence and numbers comparable to those induced by ras transformed cells. Acquisition of a signal peptide converts bFGF into a transforming protein analogous to FGF-related oncogenes which naturally have signal peptide sequences.

Diverse forms of a receptor for acidic and basic fibroblast growth factors

We recently reported the isolation of a chicken cDNA clone encoding a basic fibroblast growth factor (FGF) receptor that has three immunoglobulinlike domains in the extracellular region. We have now identified four unique human cDNA clones encoding previously unknown FGF receptor variants which contain only two immunoglobulinlike domains. Two of the human clones encode membrane-spanning receptors, and two encode putative secreted forms. Both the three- and two-immunoglobulinlike-domain forms mediate biological responsiveness to acidic and basic FGF. Thus, the first immunoglobulinlike domain of the three-domain form may have a function other than binding of acidic and basic FGF.

Diverse forms of a receptor for acidic and basic fibroblast growth factors

We recently reported the isolation of a chicken cDNA clone encoding a basic fibroblast growth factor (FGF) receptor that has three immunoglobulinlike domains in the extracellular region. We have now identified four unique human cDNA clones encoding previously unknown FGF receptor variants which contain only two immunoglobulinlike domains. Two of the human clones encode membrane-spanning receptors, and two encode putative secreted forms. Both the three- and two-immunoglobulinlike-domain forms mediate biological responsiveness to acidic and basic FGF. Thus, the first immunoglobulinlike domain of the three-domain form may have a function other than binding of acidic and basic FGF.

Promoting effect of glucocorticoids on the differentiation of human adipocyte precursor cells cultured in a chemically defined medium

Stromal-vascular cells obtained from adult human subcutaneous adipose tissue were cultured in a chemically defined serum-free medium. In the presence of 0.2 nM triiodothyronine and 0.5 microM insulin, up to 25% of the cells were able to undergo terminal adipose differentiation within 18 d, as assessed by lipid accumulation and the expression of lipoprotein lipase (LPL) and glycerol-3-phosphate dehydrogenase (GPDH) activities. Addition of cortisol resulted in a potent dose-dependent stimulation of the adipose differentiation process. Cortisol could be replaced by dexamethasone and partly by aldosterone, but not by sex steroids. The proportion of differentiated cells was dependent upon the age of the donor; when isolated from young adults, up to 70% of the stromal-vascular cells expressed the adipocyte phenotype as compared with 5-10% when the cells were isolated from the oldest subjects. An inverse relationship was observed between the age of the 27 normal-weight donors and the extent of GPDH expression after maintenance of the cells for 18 d in chemically defined medium supplemented with insulin, triiodothyronine, and cortisol (r = -0.787, P less than 0.001). It is concluded that adult human adipose tissue still contains precursor cells that are able to undergo adipose differentiation in vitro. This improved culture system may offer the opportunity to characterize other adipogenic factors as well as antiadipogenic factors involved in the control of adipose tissue growth.

Differentiation of rabbit adipocyte precursor cells in a serum-free medium

A serum-free, hormone-supplemented medium containing insulin, transferrin, and triiodothyronine (ITT medium), able to support differentiation of rat adipose precursor cells, has been used to study the regulation of the development of adipocytes in the rabbit. Adipose conversion was assessed by the appearance of glycerol-3-phosphate dehydrogenase activity. Stromal-vascular cells from rabbit perirenal adipose tissue differentiated to a very low extent or not at all in ITT medium. Supplementation of ITT medium with growth hormone or fibroblast growth factor did not increase the proportion of differentiated cells. In contrast, rabbit stromal-vascular cells were able to differentiate in ITT medium supplemented with glucocorticoids (dexamethasone, corticosterone) whereas sex steroids (beta-estradiol, testosterone, progesterone) did not affect the differentiation process. In the presence of both dexamethasone and insulin, 20 to 50% of rabbit stromal-vascular cells differentiated into adipocytes within 2 wk of culture. The stimulatory actions of dexamethasone or insulin were dose-dependent. Insulin-like growth Factor-I (IGF-I), did not replace insulin under our culture conditions and had only a slight effect when added along with dexamethasone (100 nM) and insulin (1.7 nM). The results suggest that glucocorticoids, in association with insulin, may play an important role in the development of adipocytes from rabbit precursor cells.

The fibroblast growth factor family: structural and biological properties

This article summarizes the structural and biological properties of the family of fibroblast growth factors (FGF). Basic FGF (bFGF) and acidic FGF (aFGF) are the best characterized members of this family. bFGF and aFGF are potent modulators of cell proliferation, motility and differentiation. They are also potent angiogenesis factors in vivo. Some of the important biological characteristics of bFGF and aFGF discussed in the review include the affinity of bFGF and aFGF for heparin, their lack of secretion in culture and their association with extracellular matrix. Recently, several oncogenes, 40-50% homologous in sequence to bFGF and aFGF have been identified. These include int-2, hst, K-fgf and FGF-5. The structural and biological properties of these FGF-related oncogenes are also discussed.

Adipose tissue development: the role of precursor cells and adipogenic factors. Part I: Adipose tissue development and the role of precursor cells

Obesity is regarded as a heterogeneous syndrome, which may appear in different forms. Various causes have been found to contribute to its pathogenesis. During recent years investigations of adipose tissue cellularity and its dynamic changes have gained growing interest. An important progress was the discovery of adipose tissue precursor cells. These cells have not yet been precisely identified by morphological and biochemical methods in intact tissue. However, due to methodological developments such precursor cells can be cultured both as primary cultures and as established cell lines. These culture systems have proven to be valuable models for the study of the processes involved in the formation of new fat cells.

Evidence that fibroblast growth factor promotes lens fibre differentiation

Lens epithelial cells from newborn rats undergo changes characteristic of fibre differentiation when cultured with rat neural retina or with a soluble mitogenic factor present in calf retina-conditioned medium. Mitogens have been isolated from retina in other laboratories, but have not previously been shown to promote fibre differentiation in mammalian lens. We prepared eye-derived growth factors I and II and alpha- and beta-retina-derived growth factors from bovine retinas. These factors all promoted lens fibre differentiation in our culture system, as assessed by morphological changes and the appearance of fibre cell-specific crystallins. There is now strong evidence that these retina-derived factors are identical to the acidic and basic forms of fibroblast growth factor (FGF), which is present in a variety of tissues. We found that acidic and basic FGF from rat brain also promoted lens fibre differentiation, suggesting that FGF is the factor from the retina responsible for inducing lens fibre differentiation.