Differentially expressed proteins in rainbow trout adipocytes isolated from visceral and subcutaneous tissues

Gene expression profile during proliferation and differentiation of rainbow trout adipocyte precursor cells

BACKGROUND

Excessive accumulation of adipose tissue in cultured fish is an outstanding problem in aquaculture. To understand the development of adiposity, it is crucial to identify the genes which expression is associated with adipogenic differentiation. Therefore, the transcriptomic profile at different time points (days 3, 8, 15 and 21) along primary culture development of rainbow trout preadipocytes has been investigated using an Agilent trout oligo microarray.

RESULTS

Our analysis identified 4026 genes differentially expressed (fold-change >3) that were divided into two major clusters corresponding to the main phases observed during the preadipocyte culture: proliferation and differentiation. Proliferation cluster comprised 1028 genes up-regulated from days 3 to 8 of culture meanwhile the differentiation cluster was characterized by 2140 induced genes from days 15 to 21. Proliferation was characterized by enrichment in genes involved in basic cellular and metabolic processes (transcription, ribosome biogenesis, translation and protein folding), cellular remodelling and autophagy. In addition, the implication of the eicosanoid signalling pathway was highlighted during this phase. On the other hand, the terminal differentiation phase was enriched with genes involved in energy production, lipid and carbohydrate metabolism. Moreover, during this phase an enrichment in genes involved in the formation of the lipid droplets was evidenced as well as the activation of the thyroid-receptor/retinoic X receptor (TR/RXR) and the peroxisome proliferator activated receptors (PPARs) signalling pathways. The whole adipogenic process was driven by a coordinated activation of transcription factors and epigenetic modulators.

CONCLUSIONS

Overall, our study demonstrates the coordinated expression of functionally related genes during proliferation and differentiation of rainbow trout adipocyte cells. Furthermore, the information generated will allow future investigations of specific genes involved in particular stages of fish adipogenesis.

In vivo imaging and quantification of regional adiposity in zebrafish

Adipose tissues (ATs) are lipid-rich structures that supply and sequester energy-dense lipid in response to the energy status of an organism. As such, ATs provide an organism energetic insurance during periods of adverse physiological burden. ATs are deposited in diverse anatomical locations, and excessive accumulation of particular regional ATs modulates disease risk. Therefore, a model system that facilitates the visualization and quantification of regional adiposity holds significant biomedical promise. The zebrafish (Danio rerio) has emerged as a new model system for AT research in which the entire complement of regional ATs can be imaged and quantified in live individuals. Here we present detailed methods for labeling adipocytes in live zebrafish using fluorescent lipophilic dyes, and for identifying and quantifying regional zebrafish ATs.

In vivo analysis of white adipose tissue in zebrafish

White adipose tissue (WAT) is the major site of energy storage in bony vertebrates, and also serves central roles in the endocrine regulation of energy balance. The cellular and molecular mechanisms underlying WAT development and physiology are not well understood. This is due in part to difficulties associated with imaging adipose tissues in mammalian model systems, especially during early life stages. The zebrafish (Danio rerio) has recently emerged as a new model system for adipose tissue research, in which WAT can be imaged in a transparent living vertebrate at all life stages. Here we present detailed methods for labeling adipocytes in live zebrafish using fluorescent lipophilic dyes, and for in vivo microscopy of zebrafish WAT.

Proteomic analysis of bovine omental, subcutaneous and intramuscular preadipocytes during in vitro adipogenic differentiation

Given the substantial rise in obesity, depot-specific fat accumulation and its associated diseases like diabetes, it is important to understand the molecular basis of depot-specific adipocyte differentiation. Many studies have successfully exploited the adipocyte differentiation, but most of them were not related to depot-specificity, particularly using freshly isolated primary preadipocytes. Using 2-dimensional polyacrylamide gel electrophoresis coupled with sequencing mass spectrometry, we searched and compared the proteins differentially expressed in undifferentiated and differentiated preadipocytes from bovine omental, subcutaneous and intramuscular adipose depots. Our proteome mapping strategy to identify differentially expressed intracellular proteins during adipogenic conversion revealed 65 different proteins that were found to be common for the three depots. Further, we validated the differential expression for a subset of proteins by immunoblotting analyses. The results demonstrated that many structural proteins were down-regulated during differentiation of preadipocytes from all the depots. Most up-regulated proteins like Ubiquinol-cytochrome-c reductase complex core protein I (UQCRC1), ATP synthase D chain, Superoxide dismutase (SOD), Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Sulfotransferase 1A1 (SULT1A1), Carnitine O-palmitoyltransferase 2 (CPT2) and Heat-shock protein beta 1 (HSPB1) across the three depots were found to be associated with lipid metabolism and metabolic activity. Further, all the up-regulated proteins were found to have higher protein expression in omental than subcutaneous or intramuscular depots.