Expression of genes controlling fat deposition in two genetically diverse beef cattle breeds fed high or low silage diets

Abstract

Background: Both genetic background and finishing system can alter fat deposition, thus indicating their influence on adipogenic and lipogenic factors. However, the molecular mechanisms underlying fat deposition and fatty acid composition in beef cattle are not fully understood. This study aimed to assess the effect of breed and dietary silage level on the expression patterns of key genes controlling lipid metabolism in subcutaneous adipose tissue (SAT) and longissimus lumborum (LL) muscle of cattle. To that purpose, forty bulls from two genetically diverse Portuguese bovine breeds with distinct maturity rates, Alentejana and Barrosã, were selected and fed either low (30% maize silage/70% concentrate) or high silage (70% maize silage/30% concentrate) diets.

Results: The results suggested that enhanced deposition of fatty acids in the SAT from Barrosã bulls, when compared to Alentejana, could be due to higher expression levels of lipogenesis (SCD and LPL) and β-oxidation (CRAT) related genes. Our results also indicated that SREBF1 expression in the SAT is increased by feeding the low silage diet. Together, these results point out to a higher lipid turnover in the SAT of Barrosã bulls when compared to Alentejana. In turn, lipid deposition in the LL muscle is related to the expression of adipogenic (PPARG and FABP4) and lipogenic (ACACA and SCD) genes. The positive correlation between ACACA expression levels and total lipids, as well trans fatty acids, points to ACACA as a major player in intramuscular deposition in ruminants. Moreover, results reinforce the role of FABP4 in intramuscular fat development and the SAT as the major site for lipid metabolism in ruminants.

Conclusions: Overall, the results showed that SAT and LL muscle fatty acid composition are mostly dependent on the genetic background. In addition, dietary silage level impacted on muscle lipid metabolism to a greater extent than on that of SAT, as evaluated by gene expression levels of adipogenic and lipogenic factors. Moreover, the response to diet composition evaluated through mRNA levels and fatty acid composition showed interesting differences between Alentejana and Barrosã bulls. These findings provide evidence that the genetic background should be taken into account while devising diet-based strategies to manipulate fatty acid composition of beef cattle tissues.

Figure 1

Relative expression levels of nine genes in the subcutaneous adipose tissue of Alentejana and Barrosã bulls fed high or low silage diets. Each value was normalized to RPLP0 expression. Al-HS: Alentejana bulls fed the high silage diet; Al-LS: Alentejana bulls fed the low silage diet; Ba-HS: Barrosã bulls fed the high silage diet; Ba-LS: Barrosã bulls fed the low silage diet. Error bars indicate standard error. FABP4 relative expression levels were adjusted for SAT total lipids content. ^†Tendencies were considered for 0.05 < P < 0.10. ^a,b,c Least square means with different superscripts differ at least P < 0.05.

Figure 2

Relative expression levels of nine genes in the longissimus lumborum muscle of Alentejana and Barrosã fed high or low silage diets. Each value was normalized to PPIB expression. Al-HS: Alentejana bulls fed the high silage diet; Al-LS: Alentejana bulls fed the low silage diet; Ba-HS: Barrosã bulls fed the high silage diet; Ba-LS: Barrosã bulls fed the low silage diet. ACACA and PPARG relative expression levels were adjusted for total lipids content. CRAT relative expression levels were adjusted for breed × diet × total lipids content. FABP4 relative expression levels were adjusted for diet × total lipids content. SCD relative expression levels were adjusted to breed × total lipids content. Error bars indicate standard error. ^†Tendencies were considered for 0.05 < P < 0.10. ^a,b,c Least square means with different superscripts differ at least P < 0.05.

Figure 3

Loading plot of the first and second principal components (PC) of the pooled data (A) and component’s score vectors (B) for longissimus lumborum muscle and subcutaneous adipose tissue from Alentejana and Barrosã bulls fed high or low silage diets. TL: total lipids; SAT: subcutaneous adipose tissue; Al-HS: Alentejana bulls fed the high silage diet; Al-LS: Alentejana bulls fed the low silage diet; Ba-HS: Barrosã bulls fed the high silage diet; Ba-LS: Barrosã bulls fed the low silage diet.