The adipose tissue in farm animals: a proteomic approach.

Adipose tissue is not only a tissue where energy is stored but is also involved in regulating several body functions such as appetite and energy expenditure via its endocrine activity. Moreover, it thereby modulates complex processes like reproduction, inflammation and immune response. The products secreted from adipose tissue comprise hormones and cytokines that are collectively termed as adipocytokines or "adipokines"; the discovery and characterization of new proteins secreted by adipose tissue is still ongoing and their number is thus increasing. Adipokines act in both endocrine manner as well as locally, as autocrine or paracrine effectors. Proteomics has emerged as a valuable technique to characterize both cellular and secreted proteomes from adipose tissues, including those of main cellular fractions, i.e. the adipocytes or the stromal vascular fraction containing mainly adipocyte precursors and immune cells. The scientific interest in adipose tissue is largely based on the worldwide increasing prevalence of obesity in humans; in contrast, obesity is hardly an issue for farmed animals that are fed according to their well-defined needs. Adipose tissue is nevertheless of major importance in these animals, as the adipose percentage of the bodyweight is a major determinant for the efficiency of transferring nutrients from feed into food products and thus for the economic value from meat producing animals. In dairy animals, the importance of adipose tissue is based on its function as stromal structure for the mammary gland and on its role in participating in and regulating of energy metabolism and other functions. Moreover, as pig has recently become an important model organism to study human diseases, the knowledge of adipose tissue metabolism in pig is relevant for the study of obesity and metabolic disorders. We herein provide a general overview of adipose tissue functions and its importance in farm animals. This review will summarize recent achievements in farm animal adipose tissue proteomics, mainly in cattle and pigs, but also in poultry, i.e. chicken and in farmed fish. Proteomics advancement in adipocyte cell lines, have also been included.