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

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.

Preadipocyte and adipose tissue differentiation in meat animals: influence of species and anatomical location

Early in porcine adipose tissue development, the stromal-vascular (SV) elements control and dictate the extent of adipogenesis in a depot-dependent manner. The vasculature and collagen matrix differentiate before overt adipocyte differentiation. In the fetal pig, subcutaneous (SQ) layer development is predictive of adipocyte development, as the outer, middle, and inner layers of dorsal SQ adipose tissue develop and maintain layered morphology throughout postnatal growth of SQ adipose tissue. Bovine and ovine fetuses contain brown adipose tissue but SQ white adipose tissue is poorly developed structurally. Fetal adipose tissue differentiation is associated with the precocious expression of several genes encoding secreted factors and key transcription factors like peroxisome proliferator activated receptor (PPAR)γ and CCAAT/-enhancer-binding protein. Identification of adipocyte-associated genes differentially expressed by age, depot, and species in vivo and in vitro has been achieved using single-gene analysis, microarrays, suppressive subtraction hybridization, and next-generation sequencing applications. Gene polymorphisms in PPARγ, cathepsins, and uncoupling protein 3 have been associated with back fat accumulation. Genome scans have mapped several quantitative trait loci (QTL) predictive of adipose tissue-deposition phenotypes in cattle and pigs.

Application of cell co-culture system to study fat and muscle cells

Animal cell culture is a highly complex process, in which cells are grown under specific conditions. The growth and development of these cells is a highly unnatural process in vitro condition. Cells are removed from animal tissues and artificially cultured in various culture vessels. Vitamins, minerals, and serum growth factors are supplied to maintain cell viability. Obtaining result homogeneity of in vitro and in vivo experiments is rare, because their structure and function are different. Living tissues have highly ordered complex architecture and are three-dimensional (3D) in structure. The interaction between adjacent cell types is quite distinct from the in vitro cell culture, which is usually two-dimensional (2D). Co-culture systems are studied to analyze the interactions between the two different cell types. The muscle and fat co-culture system is useful in addressing several questions related to muscle modeling, muscle degeneration, apoptosis, and muscle regeneration. Co-culture of C2C12 and 3T3-L1 cells could be a useful diagnostic tool to understand the muscle and fat formation in animals. Even though, co-culture systems have certain limitations, they provide a more realistic 3D view and information than the individual cell culture system. It is suggested that co-culture systems are useful in evaluating the intercellular communication and composition of two different cell types.

Clonal Mature Adipocyte Production of Proliferative-competent Daughter Cells Requires Lipid Export Prior to Cell Division

BACKGROUND AND OBJECTIVES

Numerous in vitro observations have been published to show that mature adipocytes may resume proliferation and begin to populate the adipofibroblast fraction or form other cell types.

METHODS AND RESULTS

In the present study, we evaluated clonal cultures of mature pig-derived adipocytes as they began to reestablish their ability to divide. The lipid contained within the cytoplasm was either moved to the apical ends of the cell, or large droplets were physically extruded from the cell. In the latter case, we ascertained that the cell lipid droplet was handled in a different manner to that by beef-derived adipocytes as described in other published studies.

CONCLUSIONS

Pig-derived adipocytes expel large amounts of lipid directly into the medium environment prior to becoming capable of cell division, rather than retaining all lipids like the beef cells. This difference in lipid handling and trafficking may be a novel mechanism in adipocyte resumption of proliferation.

Cell supermarket: adipose tissue as a source of stem cells

Adipose tissue is derived from numerous sources, and in recent years this tissue has been shown to provide numerous cells from what seemingly was a population of homogeneous adipocytes. Considering the types of cells that adipose tissue-derived cells may form, these cells may be useful in a variety of clinical and scientific applications. The focus of this paper is to reflect on this area of research and to provide a list of potential (future) research areas.

Cellular and molecular implications of mature adipocyte dedifferentiation

There is a voluminous amount of scientific literature dealing with the involvement of adipocytes in molecular regulation of carcass composition, obesity, metabolic syndrome, or diabetes. To form adipocytes (process termed adipogenesis) nearly all scientific papers refer to the use of preadipocytes, adipofibroblasts, stromal vascular cells or adipogenic cell lines, and their differentiation to form lipid-assimilating cells containing storage triacylglyceride. However, mature adipocytes, themselves, possess ability to undergo dedifferentiation, form proliferative-competent progeny cells (the exact plasticity is unknown) and reinitiate formation of cells capable of lipid metabolism and storage. The progeny cells would make a viable (and alternative) cell system for the evaluation of cell ability to reestablish lipid assimilation, ability to differentially express genes (as compared to other adipogenic cells), and to form other types of cells (multi-lineage potential). Understanding the dedifferentiation process itself and/or dedifferentiated fat cells could contribute to our knowledge of normal growth processes, or to disease function. Indeed, the ability of progeny cells to form other cell types could turn-out to be important for processes of tissue reconstruction/engineering and may have implications in clinical, biochemical or molecular processes.

Bovine dedifferentiated adipose tissue (DFAT) cells: DFAT cell isolation

Dedifferentiated fat cells (DFAT cells) are derived from lipid-containing (mature) adipocytes, which possess the ability to symmetrically or asymmetrically proliferate, replicate, and redifferentiate/transdifferentiate. Robust cell isolation and downstream culture methods are needed to isolate large numbers of DFAT cells from any (one) adipose depot in order to establish population dynamics and regulation of the cells within and across laboratories. In order to establish more consistent/repeatable methodology here we report on two different methods to establish viable DFAT cell cultures: both traditional cell culture flasks and non-traditional (flat) cell culture plates were used for ceiling culture establishment. Adipocytes (maternal cells of the DFAT cells) were easier to remove from flat culture plates than flasks and the flat plates also allowed cloning rings to be utilized for cell/cell population isolation. While additional aspects of usage of flat-bottomed cell culture plates may yet need to be optimized by definition of optimum bio-coating to enhance cell attachment, utilization of flat plate approaches will allow more efficient study of the dedifferentiation process or the DFAT progeny cells. To extend our preliminary observations, dedifferentiation of Wagyu intramuscular fat (IMF)-derived mature adipocytes and redifferentiation ability of DFAT cells utilizing the aforementioned isolation protocols were examined in traditional basal media/differentiation induction media (DMI) containing adipogenic inducement reagents. In the absence of treatment approximately 10% isolated Wagyu IMF-mature adipocytes dedifferentiated spontaneously and 70% DFAT cells displayed protracted adipogenesis 12 d after confluence in vitro. Lipid-free intracellular vesicles in the cytoplasm (vesicles possessing an intact membrane but with no any observable or stainable lipid inside) were observed during redifferentiation. One to 30% DFAT cells redifferentiated into lipid-assimilating adipocytes in the DMI media, with distinct lipid-droplets in the cytoplasm and with no observable lipid-free vesicles inside. Moreover, a high confluence level promoted the redifferentiation efficiency of DFAT cells. Wagyu IMF dedifferentiated DFAT cells exhibited unique adipogenesis modes in vitro, revealing a useful cell model for studying adipogenesis and lipid metabolism.

Dedifferentiated adipocyte-derived progeny cells (DFAT cells): Potential stem cells of adipose tissue

Analyses of mature adipocytes have shown that they possess a reprogramming ability in vitro, which is associated with dedifferentiation. The subsequent dedifferentiated fat cells (DFAT cells) are multipotent and can differentiate into adipocytes and other cell types as well. Mature adipocytes can be easily obtained by biopsy, and the cloned progeny cells are homogeneous in vitro. Therefore, DFAT cells (a new type of stem cell) may provide an excellent source of cells for tissue regeneration, engineering and disease treatment. The dedifferentiation of mature adipocytes, the multipotent capacity of DFAT cells and comparisons and contrasts with mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPS) are discussed in this review.

Like pigs, and unlike other breeds of cattle examined, mature Angus-derived adipocytes may extrude lipid prior to proliferation in vitro

A large number of studies have shown that mature adipocytes are able to dedifferentiate in vitro into progeny cells, which possess proliferative capacity and mutilineage potential. Our present study confirms that mature adipocytes derived from Angus cattle also dedifferentiate into proliferative-competent progeny cells. However, this report is unlike any published for all other breeds of cattle we have worked with or that we have seen in published reports, in which mature adipocytes retain and distribute lipids into daughter cells symmetrically or asymmetrically. In the present work, we noted that Angus-derived mature adipocytes extruded a majority of their cellular lipid droplets prior to cell division. In this manner, these cells are processing lipid in a manner observed in mature adipocytes isolated from swine tissue. These results suggest that regulation of the mechanism(s) underlying lipid processing might be different between and within animal breeds. Lipid processing in beef-derived adipocytes during dedifferentiation may serve as a unique animal model for studying lipid metabolism during reverse adipogenesis.

Bovine mature adipocytes readily return to a proliferative state

The dynamics of human and animal adipogenesis has been defined using several traditional cell systems including stromal vascular cells and adipocyte-related cell lines. But a relatively new cell system using progeny cells stemming from the dedifferentiation of purified cultures of mature adipocytes may be used for studying the development and biology of adipocytes. In this research, we show that isolated (and purified) mature adipocytes derived from Wagyu cattle dedifferentiate into progeny cells, and that these spindle-shaped, proliferative-competent daughter cells possess ability to proliferate. We outline the optimum cell culture system and offer precautionary thoughts for effective mature adipocyte culture. Collectively, this represents a novel cell model which may provide new insights into cell development, physiology and use as a model for animal production/composition, tissue engineering and disease treatment.

Rapid quantification of lipids in Acremonium chrysogenum using Oil red O

A method based on staining condition and volume of culture broth for the rapid estimation of the level of intracellular lipids in Acremonium chrysogenum using Oil red O was developed. Lipids in A. chrysogenum were strongly stained by the modified Oil red O after treatment for 10 min at 75°C. The results of the study indicated that the Oil red O staining method developed here is useful for the quantification of 0.1-5 mg ml(-1) of lipids in A. chrysogenum.

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.

Assessing a non-traditional view of adipogenesis: adipocyte dedifferentiation--mountains or molehills?

Based on our studies we propose the following hypothesis: mature, lipid-containing adipocytes possess the ability to undergo symmetrical or asymmetrical cell division, without losing lipid. While our research to discern the mechanism(s) involved in what we have termed 'dedifferentiation' of adipocytes is ongoing, we have identified several roadblocks to our work in this area. However, due to the newness of this research, we believe that none of these problems discounts the potential importance of our initial observations, or the excitement of contributing knowledge in the area. In this manuscript we address some of these problems and suggest possible solutions in an attempt to make 'molehills' out of 'mountains.'

Adult-derived stem cells and their potential for use in tissue repair and molecular medicine

This report reviews three categories of precursor cells present within adults. The first category of precursor cell, the epiblast-like stem cell, has the potential of forming cells from all three embryonic germ layer lineages, e.g., ectoderm, mesoderm, and endoderm. The second category of precursor cell, the germ layer lineage stem cell, consists of three separate cells. Each of the three cells is committed to form cells limited to a specific embryonic germ layer lineage. Thus the second category consists of germ layer lineage ectodermal stem cells, germ layer lineage mesodermal stem cells, and germ layer lineage endodermal stem cells. The third category of precursor cells, progenitor cells, contains a multitude of cells. These cells are committed to form specific cell and tissue types and are the immediate precursors to the differentiated cells and tissues of the adult. The three categories of precursor cells can be readily isolated from adult tissues. They can be distinguished from each other based on their size, growth in cell culture, expressed genes, cell surface markers, and potential for differentiation. This report also discusses new findings. These findings include the karyotypic analysis of germ layer lineage stem cells; the appearance of dopaminergic neurons after implantation of naive adult pluripotent stem cells into a 6-hydroxydopamine-lesioned Parkinson's model; and the use of adult stem cells as transport mechanisms for exogenous genetic material. We conclude by discussing the potential roles of adult-derived precursor cells as building blocks for tissue repair and as delivery vehicles for molecular medicine.

Isolation of two human fibroblastic cell populations with multiple but distinct potential of mesenchymal differentiation by ceiling culture of mature fat cells from subcutaneous adipose tissue

Adipose tissue is a source of adult multipotent stem cells that can differentiate along mesenchymal lineage. When mature fat cells obtained from human subcutaneous adipose tissue were maintained with attachment to the ceiling surface of culture flasks filled with medium, two fibroblastic cell populations appeared at the ceiling and the bottom surface. Both populations were positive to CD13, CD90, and CD105, moderately positive to CD9, CD166, and CD54, negative to CD31. CD34, CD66b, CD106, and CD117, exhibited potential of unlimited proliferation, and differentiated along mesenchymal lineage to produce adipocytes, osteoblasts, and chondrocytes. The population that appeared at the ceiling surface showed higher potential of adipogenic differentiation. These observations showed that the cells tightly attached to mature fat cells can generate two fibroblastic cell populations with multiple but distinct potential of differentiation. Since enough number of both populations for clinical transplantation can be easily obtained by maintaining fat cells from a small amount of subcutaneous adipose tissue, this method has an advantage in preparing autologous cells for patients needing repair of damaged tissues by reconstructive therapy.

Intercellular signaling between adipose tissue and muscle tissue

Adipose and muscle tissues undergo regulated growth and differentiation processes that are modulated by a wide range of factors. The interactions between myogenic cells and adipocytes play a significant role in growth and development, including the rate and extent of myogenesis, muscle growth, adipogenesis, lipogenesis/lipolysis, and in the utilization of energy substrates. Important hormones and growth factors involved in the regulation of these processes include glucocorticoids, insulin-like growth factors, various cytokines, insulin, and leptin. Interactions among these axes have important implications in their influence on relative fat and lean deposition and the efficiency of energy utilization in growth and development. As research progresses to better clarify the interactions among adipose tissue depots and muscle of different fiber types, pathways will become better understood, ultimately leading to the optimized management of fat and lean growth in domestic livestock species. This review will focus on elements of intercellular signaling, using data from cell culture studies to illustrate specific examples of signaling pathways between cells.

Adipogenesis: usefulness of in vitro and in vivo experimental models

The use of experimental models is the foundation of experimental biology, so it is important to know how much the models can tell us about actual animals. Inconsistent or contradictory results from in vitro models are often associated with the perception that a particular model or results are somehow wrong and therefore cannot tell us anything important about how an animal works. In fact, in vitro conditions do not create new biology. Differences between in vitro and in vivo behavior can only result from the actual cellular repertoire, which provides a powerful tool to uncover new information. Adipose tissue research provides a useful context for examining this issue because the regulation of adipose growth and metabolism has important economic implications for livestock production. Examples are discussed in which either excess skepticism or narrow interpretation of results slowed progress toward our current understanding of adipose biology. Similarly, contemporary examples using genomics are used to suggest that large inconsistencies are still apparent with in vitro methods. Careful consideration of these inconsistencies may provide new insights.

Adult stem cells

Development of a multicellular organism is accomplished through a series of events that are preprogrammed in the genome. These events encompass cellular proliferation, lineage commitment, lineage progression, lineage expression, cellular inhibition, and regulated apoptosis. The sequential progression of cells through these events results in the formation of the differentiated cells, tissues, and organs that constitute an individual. Although most cells progress through this sequence during development, a few cells leave the developmental continuum to become reserve precursor cells. The reserve precursor cells are involved in the continual maintenance and repair of the tissues and organs throughout the life span of the individual. Until recently it was generally assumed that the precursor cells in postnatal individuals were limited to lineage-committed progenitor cells specific for various tissues. However, studies by Young, his colleagues, and others have demonstrated the presence of two categories of precursor cells that reside within the organs and tissues of postnatal animals. These two categories of precursor cells are lineage-committed (multipotent, tripotent, bipotent, and unipotent) progenitor cells and lineage-uncommitted pluripotent (epiblastic-like, ectodermal, mesodermal, and endodermal) stem cells. These reserve precursor cells provide for the continual maintenance and repair of the organism after birth.

Existence of reserve quiescent stem cells in adults, from amphibians to humans

Several theories have been proposed to explain the phenomenon of tissue restoration in amphibians and higher order animals. These theories include dedifferentiation of damaged tissues, transdifferentiation of lineage-committed stem cells, and activation of quiescent stem cells. Young and colleagues demonstrated that connective tissues throughout the body contain multiple populations of quiescent lineage-committed progenitor stem cells and lineage-uncommitted pluripotent stem cells. Subsequent cloning and cell sorting studies identified quiescent lineage-uncommitted pluripotent mesenchymal stem cells, capable of forming any mesodermal cell type, and pluripotent epiblastic-like stem cells, capable of forming any somatic cell type. Based on their studies, they propose at least 11 categories of quiescent reserve stem cells resident within postnatal animals, including humans. These categories are pluripotent epiblastic-like stem cells, pluripotent ectodermal stem cells, pluripotent epidermal stem cells, pluripotent neuronal stem cells, pluripotent neural crest stem cells, pluripotent mesenchymal (mesodermal) stem cells, pluripotent endodermal stem cells, multipotent progenitor stem cells, tripotent progenitor stem cells, bipotent progenitor stem cells, and unipotent progenitor stem cells. Thus, activation of quiescent reserve stem cells, i.e., lineage-committed progenitor stem cells and lineage-uncommitted pluripotent stem cells, resident within the connective tissues could provide for the continual maintenance and repair of the postnatal organism after birth.

Clonogenic analysis reveals reserve stem cells in postnatal mammals: I. Pluripotent mesenchymal stem cells

Clonal populations of lineage-uncommitted pluripotent mesenchymal stem cells have been identified in prenatal avians and rodents. These cells reside in the connective tissue matrices of many organs and tissues. They demonstrate extended capabilities for self-renewal and the ability to differentiate into multiple separate tissues within the mesodermal germ line. This study was designed to determine whether such cells are present in the connective tissues of postnatal mammals. This report describes a cell clone derived by isolation from postnatal rat connective tissues, cryopreservation, extended propagation, and serial dilution clonogenic analysis. In the undifferentiated state, this clone demonstrates a high nuclear-to-cytoplasmic ratio and extended capacity for self-renewal. Subsequent morphological, histochemical, and immunochemical analysis after the induction of differentiation revealed phenotypic markers characteristic of multiple cell types of mesodermal origin, such as skeletal muscle, smooth muscle, fat cells, cartilage, and bone. These results indicate that this clone consists of pluripotent mesenchymal stem cells. This report demonstrates that clonal populations of reserve stem cells are present in mammals after birth. Potential roles for such cells in the maintenance, repair, and regeneration of mesodermal tissues are discussed.