Lipid metabolism, adipocyte depot physiology and utilization of meat animals as experimental models for metabolic research.

Meat animals are unique as experimental models for both lipid metabolism and adipocyte studies because of their direct economic value for animal production. This paper discusses the principles that regulate adipogenesis in major meat animals (beef cattle, dairy cattle, and pigs), the definition of adipose depot-specific regulation of lipid metabolism or adipogenesis, and introduces the potential value of these animals as models for metabolic research including mammary biology and the ontogeny of fatty livers.

Skeletal muscle stem cells from animals I. Basic cell biology.

Skeletal muscle stem cells from food-producing animals are of interest to agricultural life scientists seeking to develop a better understanding of the molecular regulation of lean tissue (skeletal muscle protein hypertrophy) and intramuscular fat (marbling) development. Enhanced understanding of muscle stem cell biology and function is essential for developing technologies and strategies to augment the metabolic efficiency and muscle hypertrophy of growing animals potentially leading to greater efficiency and reduced environmental impacts of animal production, while concomitantly improving product uniformity and consumer acceptance and enjoyment of muscle foods.

Allied industry approaches to alter intramuscular fat content and composition in beef animals.

Biochemical and biophysical research tools are used to define the developmental dynamics of numerous cell lineages from a variety of tissues relevant to meat quality. With respect to the adipose cell lineage, much of our present understanding of adipogenesis and lipid metabolism was initially determined through the use of these methods, even though the in vitro or molecular environments are far removed from the tissues of meat animals. This concise review focuses on recent cellular and molecular biology-related research with adipocytes, and how the research might be extended to the endpoint of altering red meat quality. Moreover, economic and policy impacts of such in animal production regimens is discussed. These issues are important, not only with respect to palatability, but also to offer enhanced health benefits to the consumer by altering content of bioactive components in adipocytes.

The Effect of Nutritional Supplements on Muscle-Derived Stem Cells in vitro.

Postnatal muscle stem cells, recognized as myogenic satellite cells, were isolated from sheep skeletal muscle and used in these experiments. Forty-one different metabolic compounds that are commonly found in commercially-available oral supplements were exposed to primary muscle stem cell cultures, in an effort to ascertain whether any one compound could alter satellite cell proliferation or differentiation (a first step towards elucidating the metabolomics or nutrigenomics of these stem cells). These compounds included energetic moieties, amino acid analogs, fatty acids and analogs including different forms of conjugated linoleic acid, minerals and mineral conjugates, insect hormones, caffeine, plant extracts, and extracts from over-the-counter supplements, and were obtained by key manufacturers in a form that would be commercially available. The compounds were sterilized and then exposed to myogenic satellite cell cultures at different levels (ranging from toxic to physiologic) to ascertain if there would be an effect. The results suggested that exposure of satellite cells to only a few compounds resulted in any measurable effect(s). Ten compounds elicited increases in proliferation, and four compounds promoted increases in differentiation. These results suggest avenues for the exploration of enhancing muscle stem cell activity of interest for muscle wasting disorders, sarcopenia of aging and physical performance.

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.

Progeny from dedifferentiated bovine adipocytes display protracted adipogenesis.

BACKGROUND: Progeny adipofibroblast cells, derived from mature bovine adipocytes, were used to determine their ability to redifferentiate into lipid-assimilating adipocytes. METHODS: Traditional cell biology methods were used, including the expression of adipogenic markers such as peroxisome proliferator-activated receptor gamma (PPARgamma). RESULTS: When exposed to medium supplemented with fetal bovine serum, but not horse serum, cells began to form structures reminiscent of foci. Horse serum-supplemented medium resulted in a slowed progression towards cell conversion to lipid-assimilating adipocytes. When analyzed, horse serum was found to contain more cortisol and insulin-like growth factor-1 as well as differing fatty acid ratios. Histological observations of the horse serum-treated cultures (alone), cultures treated with a traditional differentiation induction medium (dexamethasone, methylisobutylxanthine and insulin), treated with insulin with or without different lipid compounds, or treated with a PPARgamma agonist (rosiglitazone) resulted in the presence of intracellular vesicles, of which some contained lipid and some did not. Vesicles that did not stain for lipid did not possess glycogen or other types of storage moieties even though the cells expressed cellular markers thereby deeming them to be differentiated adipocytes (PPARgamma protein and mRNA were expressed by cells possessing vesicles as were hormone-sensitive lipase and lipoprotein lipase proteins). Non-lipid-filled intracellular vesicle walls possessed the structural protein perilipin. CONCLUSION: These results are supportive of the progeny adipofibroblasts representing a unique adipogenic model that displays protracted adipogenesis.

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.'

Oil red-O stains non-adipogenic cells: a precautionary note.

Bovine adipofibroblasts, 3T3-L1 cells, L-6 myogenic cells, and sheep satellite cells were allowed to proliferate for 48 h. Oil red-O (ORO) was dissolved in three different solvents isopropanol, propylene glycol and triethyl phosphate. At 48 h, the proliferative cultures were stained with the three stains. ORO stain prepared in both propylene glycol and triethyl phosphate resulted in bright red droplets appearing in all cultures, whereas ORO dissolved in isopropanol was not taken up by any of the cells. These data suggest that certain preparations of ORO may stain cells in non-adipogenic lineages as well as undifferentiated pre-adipocytes. Caution must be exercised when choosing solvents for ORO in differentiation studies using cells of the fat/adipose lineage.

Coulter counter use in the enumeration of muscle and fat stem cells.

Although the manual counting chamber (hemacytometer) is the gold standard for counting cells, this method is subject to great variability due to the 'human factor'. The automated cell counter (Coulter Counter) can enumerate cells in less time and with greater accuracy than the hemacytometer by removing many of the steps in which errors are made. While the Coulter Counter (and others of its type) has been used for many years in the cell culture field, there have been few studies to validate its use with specific cell types. We conducted several experiments in which we assessed the accuracy of the Coulter Counter over counts made with a hemacytometer as well as validated its use for the counting of satellite cells and preadipocytes.