Abstract
Background: Fat is a tissue that not just stores energy and plays a protective role; it is also a vital endocrine organ that generates and integrates signals to influence metabolism. Meanwhile, the excessive accumulation of lipids in adipose tissue can lead to metabolic disturbance and diseases. To date, the complicated molecular mechanisms of bovine adipose tissue are still unknown. This study aimed to identify key genes and functionally enriched pathways in various adipose tissue types. Results: The RNAseq data of 264 samples were downloaded from Gene Expression Omnibus (GEO) and analyzed by weighted gene co-expression network analysis (WGCNA). We identified 19 modules that significantly associated with at least one adipose tissue type. The brown module from GSE39618 was most closely associated with intramuscular fat tissue, which contained 550 genes. These genes were significantly enriched in pathways that related to inflammation and disease, such as TNF signaling pathway, IL-17 signaling pathway, and NF-kappa B signaling pathway. The pink module (GSE39618) that contained 58 genes was most closely associated with omental fat tissue. The turquoise (GSE39618), blue (GSE116775), and yellow (GSE65125) module were most closely associated with subcutaneous fat tissue. Genes in these modules were significantly enriched in pathways related to fat metabolism, such as the PPAR signaling pathway, fatty acid metabolism and PI3K-Akt signaling pathway. At last, key genes for intramuscular fat (PTGS2 and IL6), omental fat (ARHGEF5 and WT1), and subcutaneous fat (KIT, QR6Q1, PKD2L1, etc.) were obtained and verified. In addition, it was found that IL10 and VCAM1 might be potential genes to distinguish adipose and muscle. Conclusion: The study applied WGCNA to generate a landscape of adipose tissue and provide a basis for identifying potential pathways and hub genes of different adipose tissue types.
Highlights
Adipose tissue exists within multiple anatomical positions where it plays a role in controlling energy expenditure and regulating many metabolic processes (Cinti, 2005; McGown et al, 2014)
Cluster analysis showed that samples of the same tissue type were classified into a group, indicating it was the main reason for the difference compared with gender type, breed, feed efficiency, etc. (Figure 1)
Network heatmap analysis revealed that genes within modules tend to have higher connectivity and these modules were independent of the others (Figure 2B, Supplementary Figures S1B, S2B)
Summary
Adipose tissue exists within multiple anatomical positions where it plays a role in controlling energy expenditure and regulating many metabolic processes (Cinti, 2005; McGown et al, 2014) It is usually considered as a major active endocrine organ that secretes adipokines, which can act locally or reach distant organs through the systemic circulation to exert a wide range of biological actions, including regulating food intake and body weight, insulin sensitivity, or inflammation (Smitka and Maresova, 2015). Lipids, such as triglycerides (TGs), excessively accumulated in internal adipose tissue can lead to metabolic disturbance and diseases (insulin resistance, fibrosis, dyslipidemia, and cancer) (Cinti, 2012). This study aimed to identify key genes and functionally enriched pathways in various adipose tissue types
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