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

Abstract

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 γ (PPARG), CCAAT/enhancer-binding protein α (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 α, 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.

Adiposity and adipogenic gene expression in four different muscles in beef cattle

“…Regarding WNT10B , it was previously found that its expression was upregulated in the Longissimus muscle in Pirenaica young bulls compared to the SAT [6]. Other authors observed that the expression of WNT10B was high in stromal vascular cells (which contains predominantly preadipocytes) and undetectable in mice primary adipocytes, which is consistent with the role of WNT10B in maintaining the preadipocytes in an undifferentiated state [61].…”

“…Adipocytes were extracted from the four muscles and the SAT following the technique described by Robdell [29] slightly modified to extract intramuscular adipocytes [6, 30]. As indicated, the samples were transported to the laboratory in the Tyrode solution at 39°C within 20 min after slaughter.…”

“…This is the case of Pirenaica breed for example, which is widely used in northern Spain and is highly appreciated for its value as a genetic resource and its contribution to the maintenance of local beef production systems [6]. Different approaches have been considered with the objective of increasing Pirenaica IMF content, as extending the fattening period from 12 months of age (the usual endpoint) to 18 and increasing the feed energy density, but neither seem to have a significant effect on the amount of IMF in the longissimus muscle as shown in a previous and independent study [6]. Then, deepening the knowledge of IMF accretion mechanisms would be important to find appropriate strategies to increase the value of the meat produced in these systems.…”

Correction for adipocyte size and number in the analysis of differences in gene expression in fat tissues

“…Adipocyte populations of each tissue were simulated assuming bimodality for adipocyte size distribution for SCF and unimodality for IMF, based on previous results (Abad ıa, Mendizabal, & Alfonso, 2008;Alfonso, Mourot, Insausti, Mendizabal, & Arana, 2005;Soret et al, 2016). Five different experiments were simulated, two for SCF and three for IMF assuming that the treatment affected the cellularity in size and number of adipocytes ( Figure 2).…”

“…Summary of assumptions considered (fat percentage and adipocyte size distribution) to simulate the designs recreating the subcutaneous adipose (SCF) and the intramuscular fat (IMF) tissues, to evaluate type I error (false positives) and type II error (false negatives) Values from the outer subcutaneous backfat layer of sows (Abad ıa et al, 2008).Values from the longissimus intramuscular fat in beef cattle(Soret et al, 2016).…”