Integrated Transcriptomic and Metabolomic Analysis of the Mechanism of Intramuscular Fat Differences in Wandong Cattle

This study aimed to collaboratively investigate the mechanism of variations in intramuscular fat (IMF) content in Wandong cattle using transcriptomics and metabolomics techniques. Longissimus dorsi (LD) muscle samples were collected from thirteen free-range Wandong cattle in Fengyang County, Anhui Province, China. From this initial cohort, eight animals closely matched in age and body weight were selected. Based on IMF content measured by Soxhlet extraction, these eight cattle were divided into two groups: the high-IMF (HF, n = 4) and low-IMF (LF, n = 4) groups. Subsequent analyses were performed on integrated datasets comprising the transcriptome, metabolome, and fatty acid profile. The results revealed a significant increase in IMF in the HF group compared to the LF group (<i>p</i> < 0.05). Specifically, α-linolenic acid (C18:3n3) and γ-linolenic acid (C18:3n6) were significantly more abundant in the LF group compared to the HF group (<i>p</i> < 0.05), whereas oleic acid (C18:1n9c) and cis-9-palmitoleic acid (C16:1) predominated in the HF group. However, saturated fatty acids (SFAs), such as myristic acid (C14:0), palmitic acid (C16:0), stearic acid (C18:0), and Margaric acid (C17:0), did not show significant differences (<i>p</i> > 0.05). A total of 9164 differentially expressed genes (DEGs) were identified via transcriptome analysis, with 2202 genes upregulated and 6962 genes downregulated in the HF group compared to the LF group. The expression profiles exhibited a distinct pattern, characterized by the upregulation of genes such as FABP1, SREBF1, and LIPE, while genes including SCD, PPARGC1A, and LEP were downregulated. GO enrichment analysis demonstrated that the majority of DEGs were predominantly abundant across 25 distinct functional categories distributed across the three primary ontologies. KEGG pathway analysis further identified 341 significantly enriched signaling pathways in the HF group (<i>p</i> < 0.05), predominantly involving metabolic pathways, FoxO, AMPK, and PPAR signaling pathways. Untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics analysis revealed 404 differential accumulated metabolites (DAMs), with 187 in positive ion mode and 217 in negative ion mode (<i>p</i> < 0.05). These DAMs were notably enriched in pathways such as glycerophospholipid metabolism, terpene and steroid biosynthesis, fatty acid degradation, and fatty acid metabolism. Notably, C16:1, C18:1n9c, arachidonic acid (peroxide free) (C20:4n6), oleoyl-L-carnitine, and linoleoyl-carnitine were identified as key players in lipid metabolism. Integrating transcriptomics with metabolomics data unveiled significant associations between DAMs linked to lipid metabolism and DEGs. Specifically, C18:1n9c exhibited a positive correlation with LPIN3, while C16:1 showed negative associations with PPAP2B, PPAP2A, CDS2, HADHA, LPL, HSD17B12, ELOVL5, ACSL1, and ACOX1, and positive correlations with PLA2G15, CDIPT, AGPSBG1, and GPD1. In summary, the variation in IMF content in Wandong cattle is co-regulated by key genes (SREBF1, ACSL1, SCD) via the AMPK, PPAR, and FoxO signaling pathways, coupled with alterations in specific fatty acid metabolites such as C18:1n9c, C16:1, and C20:4n6. These findings provide critical molecular insights for the genetic selection and breeding of Wandong cattle, which are renowned for their superior meat quality.