Longissimus dorsi muscle label-free quantitative proteomic reveals biological mechanisms associated with intramuscular fat deposition.

The pathways involved in intramuscular fat (IMF) deposition in Longissimus dorsi muscle were investigated using an integrated transcriptome-assisted label-free quantitative proteomic approach by High Definition Mass Spectrometry. We quantified 1582 proteins, of which 164 were differentially abundant proteins (DAPs, p < 0.05) between animals with high (H) and low (L) genomic estimated breeding values (GEBV) for IMF content. Ingenuity pathway analysis (IPA) revealed that these DAPs were mainly involved in glycolysis metabolism, actin cytoskeleton signaling, cell-cell adherens junction and pathways for MAPK and insulin. A comparative study between transcriptomic (mRNA) and proteomic data showed 17 differentially expressed genes corresponding to DAPs, of which three genes/proteins did not agree on the direction of the fold change between groups. Moreover, we investigated microRNAs data to explain these differences in fold change direction, being able to unravel two of the three unexpected mRNA/protein relationships. Results demonstrated that changes in protein/mRNA levels of sarcomere organization, intracellular signal transduction and regulation of actin cytoskeleton, are involved in IMF deposition. These findings provide a deeper understanding of the highly complex regulatory mechanisms involved in IMF deposition in cattle and indicate target pathways for future studies. SIGNIFICANCE: Intramuscular fat is the amount of fat deposited inside muscle and plays an important role in human health and meat quality attributes, influencing energy metabolism of skeletal muscle, as well as, tenderness, flavor, and juiciness of beef. We performed for the first time the utilization of integrated transcriptome-assisted label-free quantitative proteomic approach using High Definition Mass Spectrometry for characterization of the changes in the proteomic profile of the Longissimus dorsi muscle associated with intramuscular fat deposition in cattle. Furthermore, we compared the muscle proteome with the muscle transcriptome (mRNA and microRNAs), obtained by RNA-sequencing, to better understand the relationship between expression of mRNAs and proteins and to unravel essential biological mechanisms involved in bovine skeletal muscle IMF deposition.