Regional differences in porcine adipocytes isolated from skeletal muscle and adipose tissues as identified by a proteomic approach

The content and distribution of body lipids are of special interest for production efficiency and meat quality in the farm animal industry. Triglycerides represent the most variable fraction of tissue lipids, and are mainly stored in adipocytes. Although several studies have reported regional differences in the expression of genes and their products in adipocytes from various species, the characteristics of i.m. adipocytes remain poorly described. To evaluate adipocyte features according to muscle and other fat locations, adipocyte proteins were isolated from trapezius skeletal muscle, and intermuscular, s.c., or perirenal adipose tissues from 6 female pigs (80 d of age). Protein extracts were labeled and analyzed by 2-dimensional, fluorescent, differential gel electrophoresis. The comparisons revealed that 149 spots were always differentially expressed (P < 0.05, ratio exceeding vertical bar 2 vertical bar-fold difference) between i.m. adipocytes and the fat cells derived from the 3 other adipose locations. The proteins that were downregulated in i.m. fat cells belonged to various metabolic pathways, such as lipogenesis (cytosolic malate dehydrogenase and isocitrate dehydrogenase, P < 0.01), glycolysis (enolases and aldolase, P = 0.01), lipolysis (perilipin, P < 0.01), fatty acid oxidation (long-chain fatty-acyl CoA dehydrogenase, P < 0.01), and energy transfer (catalase, voltage-dependent anion channel 1, and electron-transfer flavoprotein, P < 0.05). In contrast, both prohibitin-1 and cell division cycle 42 homolog, with possible roles in cell growth, were upregulated (P < 0.05) in i.m. adipocytes compared with other fat cells. Fewer differences were observed when adipocytes isolated from s.c., perirenal, and intermuscular fat tissues were compared, with a maximum of 17 spots differing significantly in abundance between perirenal and s.c. adipose tissues. The findings that proteins involved in both anabolic and energy-yielding catabolic pathways are downregulated in i.m. adipocytes compared with s.c., visceral, or intermuscular adipocytes, suggest that the metabolic activity of i.m. adipocytes is low. Thus, triggering adipogenesis rather than cell metabolism per se might be a valuable strategy to control lipid deposition in pig skeletal muscles.