Expression of genes involved in adipogenesis and lipid metabolism in subcutaneous adipose tissue and longissimus muscle in low-marbled Pirenaica beef cattle

The ability to accumulate intramuscular fat (IMF) is a highly variable characteristic in beef cattle. In breeds with a low tendency to accumulate IMF, this can lead to compromised meat quality because of the contribution of fat to such organoleptic attributes as juiciness and taste. This study considered adiposity and gene expression of some of the main markers involved in adipogenesis and lipid metabolism in the subcutaneous (SC) adipose tissue (AT) and the longissimus thoracis muscle (LM) and investigated differences in adipogenic regulation between the tissues during growth and fattening under different conditions. Pirenaica beef cattle were chosen for the study due to the breed's low tendency to accumulate IMF and the breed's regional importance. The young Pirenaica bulls used (n=16) were allocated to four groups and slaughtered at 6, 12 and 18 months. From 12 months onwards the bulls slaughtered at 18 months were fed diets having different energy densities. Backfat thickness increased from 6 to 12 months (P < 0.05) but then was unchanged, while other fattening parameters such as percentage chemical fat and marbling did not vary. The adipose cell size distribution displayed a bimodal distribution for SC adipocytes and a unimodal distribution for IMF cells, suggestive of tissue-specific hyperplasia. Gene expression of peroxisome proliferator-activated receptor gamma (PPARG), CCAAT/enhancer-binding protein (CEBPA), sterol regulatory element-binding transcription factor 1 (SREBF1), wingless-type MMTV integration site family 10B (WNT10B), fatty acid-binding protein 4 (FABP4), acetyl Co-A carboxylase alpha , lipoprotein lipase and fatty acid synthase (FASN) were determined by real-time quantitative PCR. Expression did not differ between the experimental groups within the tissues but did differ between the tissues: PPARG, FABP4 and FASN were upregulated in the SC AT, while CEBPA, WNT10B and SREBF1 were upregulated in the LM. Although age and diet energy density did not have a significant effect on increasing the amount of IMF, these factors could have influenced adipocyte development in this tissue differently than in the SC AT. This was evidenced by the different size distributions of the cells in the two tissues, and the differing expression patterns of certain markers in the SC AT and the LM, which may indicate a differential role of PPARG and WNT10B in triggering adipocyte proliferation and fat accumulation capacity.