Fatty acid-binding protein 1 increases steer fat deposition by facilitating the synthesis and secretion of triacylglycerol in liver

Abstract

Castration is an important means of improving the beef quality via increasing fat deposition. However, little is known about the molecular mechanism underlying the fat deposition after castration. Here, the intramuscular fat (IMF) content of the steer group was shown to be much higher than the bull group. To understand transcriptional changes in the genes involved in fat deposition following castration, differential expression patterns of mRNAs in liver tissue were investigated in steers and bulls using RNA sequencing. In total, we obtained 58,282,367-54,918,002 uniquely mapped reads, which covered 90.13% of the currently annotated transcripts; 5,864 novel transcripts and optimized 9,088 known genes were determined. These results indicated that castration could change the expression patterns of mRNAs in liver tissue, and 282 differentially expressed genes (DEGs) were detected between steers and bulls. KEGG pathway analysis showed that the DEGs were mostly enriched in PPAR signaling pathway, steroid biosynthesis, steroid hormone biosynthesis, and biosynthesis of fatty acids. Furthermore, eight DEGs were corroborated via quantitative real-time PCR and we found that FABP1 gene knockdown in bovine hepatocytes prominently reduced intracellular triacylglycerol (TAG) synthesis and very low density lipoprotein (VLDL) secretion in culture medium. In summary, these results indicate that FABP1 may promote fat deposition by promoting the production and secretion of TAG and VLDL in steer liver.

Fig 1. The differential expression of bovine mRNAs between BL and SL tissues.

Note: Each point in the figure represents a mRNA. Red points represent up-expressed mRNAs; blue points represent equally-expressed mRNAs; green points represent down-expressed mRNAs. BL = bull liver; SL = steer liver; n = 3 replicates per group.

Fig 2. Different expression levels of eight mRNAs in BL and SL.

The values are presented as means ± S.E.M. Statistically significant differences are indicated: **P < 0.01. BL = bull liver; SL = steer liver.

Fig 3. KEGG pathway analysis of the differentially expressed genes between BL and SL.

BL = bull liver; SL = steer liver.

Fig 4

(A) Relative mRNA expression levels of FABP1 in bovine hepatocytes. Cells were collected after 48 hours of transfection with control or FABP1 siRNA. (B) The content of cellular TAG changed by FABP1 silencing in bovine hepatocytes.(C) The content of extracellular VLDL changed by FABP1 silencing in bovine hepatocytes. The values are presented as means ± S.E.M. Statistically significant differences are indicated: *P < 0.05, **P < 0.01. The experiments were done in three biological replicates and two technical replicates.